WO1993022069A1

WO1993022069A1 - Method and apparatus for deposition of insoluble monolayers and complex langmuir films on continuous substrate webs

Info

Publication number: WO1993022069A1
Application number: PCT/US1993/004061
Authority: WO
Inventors: Alan D. Pendley
Original assignee: Pendley Alan D
Priority date: 1992-04-30
Filing date: 1993-04-30
Publication date: 1993-11-11
Also published as: AU4224893A

Abstract

A system for continuous generation of Langmuir and Langmuir-Blodgett film includes a troughing slider bed conveyor (2a) with an endless belt (2h); an element (2m) for delivering a subphase liquid to the liquid-extruding orifice (2e) at a rate proportional to the speed of the conveyor (2a), such that the desired depth of liquid is maintained without flow relative to the troughing belt (2h); an element (2n) delivers Langmuir-film forming liquids and suspensions to the surface of said subphase liquid at a rate proportional to the speed of the conveyor (2a), so as to maintain predetermined film thickness; and an element (2a) for transferring said film to a solid substrate.

Description

DESCRIPTION

METHOD AND APPARATUS FOR DEPOSITION OF INSOLUBLE MONOLAYERS AND COMPLEX LANGMUIR FILMS ON CONTINUOUS SUBSTRATE WEBS

* Background of the Invention

The invention relates to the continuous generation of Langmuir films and to their transfer onto continuous or discrete substrates. The invention has applicability to the production of objects and webs bearing decorative, multicolored marbled patterns, as well as to the deposition of non-decorative insoluble monolayers on substrates such as Langmuir-Blodgett films.

Traditional marbling has its roots in a Japanese printing process developed over 1000 years ago called suminagashi. A small, pointed paint-brush, full of sumi ink suspended in pine resin, is_. touched to the surface of still, pure water contained within a tray. The pine resin acts as a hydrophobic agent and spreads out into a Langmuir film, taking the ink pigments along for the ride. In the same spot another paint brush containing only pine resin is subsequently touched. By alternating between the two brushes, concentric rings are formed. By gently blowing on the surface of the water, air turbulence swirls the floating pigments into unique patterns. The pattern is transferred onto a sheet of moisture-absorbent paper which is laid on the surface of the water, lifted off, and placed on a flat surface to dry.

Some time in the thirteenth century or so this process was introduced to Europe, where it evolved into the process known as marbling. Marbling is distinct from suminagashi in several ways. Where suminagashi uses pure water, marbling uses a water solution thickened with a vegetable polymer called carragheen. It has the effect of damping turbulence and increasing v scosity, but has very little effect on the high surface tension of water. The shear thinning properties of carragheen solutions make possible the combed patterns which became traditional in Europe. Another difference between suminagashi and marbling is the surfactant used to cause the pigments to spread on the liquid surface. Rather than using pine resin, European marblers use an extract from the gall of an ox. By varying the amount of ox gall in the various pigment suspensions, one can control the spreading pressure of each color. Those colors laid down first are pushed aside when subsequent colors use more ox gall.

To increase the adhesion of pigments or dyes to the paper or object being marbled, it is •i first saturated with a solution of alum sulfate and dried. When the substrate comes into contact

J with the suspended pigment film the coating of alum acts as a reaction insolublizer, which t ^' reacts with the surfactant in the film to create a stable yet fragile insoluble coating on the substrate. The dried, microscopic, salt crystals allow the transfer of more pigment than would < otherwise be possible. The alum-surfactant reaction also keeps the colors from smearing as the paper is lifted off the carragheen bath and rinsed of the residual layer of carragheen solution in a tray of water. The finished pieces are then hung to dry or dried on a flat surface. The surface of tray of water. The finished pieces are then hung to dry or dried on a flat surface. The surface of the carragheen bath must be cleaned by scraping a tightly fitting boom across the liquid surface before a new pattern can be created.

Traditional marbling has developed numerous distinctive patterns. These patterns are created by following a particular sequence of color dispensation and dragging tools, such as ( combs, forks, and other objects, through' the carragheen. Patterns such as peacock, thistle, non- pareil, feather comb, French curl, Spanish wave, and tiger's eye are all distinct, traditional pat¬ terns which can be produced by following a specific processing recipe. Use of the traditional marbling tray has limited artisans to manually producing relatively small printed objects, each of which is unique.

A more complete understanding of marbling may be attained by reference to Suminagashi -^'- The Japanese Art of Marbling. Chambers, Thames & Hudson, Ltd. (1991), and to Marbling on Fabric. Cohen et al. Interweave Press (1990)

Marbling is but one class of so-called Langmuir films. These are films that are formed at the interface of a liquid and a gas by adding small quantities of molecules which have both phobic or repelling and philic or attractive properties relative to the majority liquid (the subphase). These molecule are thus referred to as amphiphilic and typically one end of the molecule is phobic while the other end is philic to the subphase. These molecules will spontaneously migrate to the surface, forming a thin layer, and the portion of the molecule most phobic to the sub-phase will orient itself toward the gas. Adding amphiphilic solutions in droplets onto the subphase surface is the most effective method for forming a molecular monolayer as the drops spread outward until they are a single molecular layer in thickness. However, many systems require that the film forming molecules first be dissolved in a solvent.

If the surface layer is subsequently compressed by reducing the area of the film, and if the time is given for the solvent to evaporate, a highly ordered insoluble monolayer will form which is structurally similar to a liquid crystal. Compression is achieved by sweeping a boom across the liquid surface until the molecules in the film, while still in a monolayer, must align themselves like sardines in a can. This monolayer may then be transferred onto a solid substrate by dipping the substrate, either vertically or horizontally, thus creating a so-called Langmuir- Blodgett (LB) film. The method and rate of film transfer has a marked effect on the molecular orientation of these films, as does the number of film layers which are stacked one upon the other.

The technique for transferring compressed insoluble monolayers onto solid substrates was pioneered by Katherine Blodgett. Hence the term "Langmuir-Blodgett film." The term

"Langmuir film" refers to the more general case which includes monolayers, multilayers, ves- icles and suspended particles in a film at the liquid-gas interface not yet transferred to a solid substrate.

A more complete understanding of Langmuir and Langmuir-Blodgett films may be at¬ tained by reference to Langmuir-Blodgett Films. Ed: Roberts, G., Plenum Press (1990). - J -

The prior art provides mechanized methods for generating decorative marbled patterns by using a stationary, inclined trough in which the sub phase liquid flows. Such methods, as disclosed for example in U.S. Patent No. 2,140,498, suffer the inability to rapidly generate marble pattern coated webs without significant pattern distortion.

The prior art also discloses, in Albrecht et al, U.S. Patent No. 4,722,856, a method for continuous generation of LB films. This relies on a stationary trough with upper and lower chambers connected by a narrow passage. As the subphase flows from the upper chamber, the monolayer is compressed in the narrow passage whence it flows into the lower chamber. The monolayer film is transferred to the substrate by dipping it (the substrate) into the lower chamber according to a conventional vertical or horizontal method.

Other methods of continuous fabrication of LB films are described in Langmuir- Blodgett Films, supra, in sections 3.7.1 and 7.1.3.

In view of the foregoing, an object of this invention is to provide improved methods and apparatus for the continuous generation and transfer of Langmuir films onto continuous and discrete substrates.

Another object is to provide improved methods and apparatus for creating decorative, e.g., marbled, films and for transferring them to sheets, webs, and the surface of three dimen¬ sional objects.

One other object is to provide improved methods and apparatus for distributing insoluble precipitates, ceramic particles, metal whiskers and other particulate, engineering materials into textured patterns within a Langmuir film and for transferring them to sheets and webs.

Still another object is to provide improved methods and apparatus for deposition of non- decorative, insoluble, monolayer films on continuous and discrete substrates.

Yet another object is to provide such foregoing methods and apparatus which can rapidly produce and transfer such films to sheets and webs without distortion or with deliberately induced and controlled distortion.

Summary of the Invention

The foregoing and other objects are attained by the invention which provides, in one as¬ pect, improved methods and apparatus for generating complex Langmuir films on a continuous basis and for transferring them onto continuous or non-continuous substrates.

These methods and apparatus utilize a heretofore unknown "Langmuir" trough, formed by guiding an endless conveyor belt over a railed slider bed. The outer surface of the conveyor belt is covered with rubber or flourocarbon, such as TeflonT , which is tightly stretched over the conveyor bed by extending the tail pulley bearing frame. This causes the belt to "dish," that is, to flatten in the middle and bend upward at the sides along the rails.

As successive sections of the belt are pulled onto the "tail" of the slider bed, its rails force the belt to dish upward and. thereby, form fluid-containing sides. As those sections leave the bed downstream, i.e.. at the "head," they are flattened.

Subphase liquid is pumped from a reservoir tank to a weir at the conveyor's tail end. The weir allows any entrained bubbles to rise to the surface and be trapped there until they burst. It fits perfectly into the troughing portion of the conveyor to form a liquid-tight seal with the conveyor belt. Because it contacts the belt immediately downstream from the point at which the edges of the belt are folly bent upward, the weir forms a stationary end of the moving Langmuir trough.

The sub phase liquid is distributed in an even sheet across the conveyor through a narrow slit at the bottom of the weir. The size of the slit is adjustable to match the flow of the sub phase liquid to the speed of the conveyor, thereby minimizing turbulence. By pumping the liquid at a carefully controlled rate, which is proportional to the speed of the conveyor, the desired depth of liquid is extruded into the moving conveyor trough. And, slightly downstream from its point of extrusion, the sub phase liquid becomes still relative to the belt.

Dispensing valves are suspended slightly above the moving subphase. At the point of subphase quiescence, these valves dispense drops of liquid. In the case of decorative pattern generation, the liquid constitutes pigments suspended in water, with a binder and a surfactant, that is, paint or ink. Alternatively some dyes may be used. In the case of LB film formation, the liquid constitutes an insoluble, monolayer-forming material dissolved in a solvent.

Downstream from the initial color dispensers are stationary and motorized combs sus¬ pended above the moving bath. These combs are lowered into the subphase and moved to gen¬ erate desired patterns in the monolayer. This movement can be controlled by computer, e.g., in accord with stored programs for each pattern, or they can be controlled manually, e.g., by an artisan.

Once the desired film pattern is formed, it is transferred to the substrate, which can be a discrete object or a continuous web coated, for example, with alum sulfate. The object or web is dipped into the liquid or contacted with its liquid surface at a speed and direction substantially the same as that of the moving Langmuir trough. Discrete objects which have a significant third dimension require a greater troughing depth than do flat objects or continuous webs.

In addition to the aspects discussed above, the invention provides, in other aspects, methods and apparatus for generating continuous compressed Langmuir films. These methods and apparatus are similar to those described above, however, they additionally employ mechanisms for compressing the continuously generated monolayers.

A first such compression mechanism employs a series of metered micro valves positioned along the length of the conveyor at both extreme edges of the subphase. The first of these valves are positioned just downstream from the point where the dispensed monolayer material has fully spread. The valves dispense a non-evaporative surfactant solution along the length of the conveyor, so that the spreading pressure of the dispensed surfactant compresses the monolaver. A second such compression mechanism uses a system of moving side walls similar to the constant-perimeter Langmuir trough. The flourocarbon tape converges very gradually, thus providing a slow rate of compression while moving in the same direction and at a proportional linear speed as the conveyed liquid, thus minimizing distortions within the film near the tape.

These and other aspects of the invention are evident in the description which follows and in the attached drawings.

Brief Description of the Drawings

A more complete understanding of the invention may be attained by reference to the drawings, in which:

Figure 1 depicts an overview of a preferred system for deposition of insoluble monolay¬ ers and multi-layers on continuous substrate webs according to the invention;

Figure 2 depicts views of a preferred Langmuir trough in a system according to the invention;

Figure 3 depicts view of a preferred apparatus for transverse combing of Langmuir films on the subphase liquid in a system according to the invention;

Figure 4 depicts views of a preferred apparatus for bi-directional parallel combing of Langmuir films on the subphase liquid in a system according to the invention;

Figure 5 depicts views of a preferred apparatus for creating controlled density distortions of Langmuirs films during deposition on continuous substrate webs in a system according to the invention;

Figure 6 depicts views of a preferred apparatus for continuous removal of rinse solution from a continuous web in a system according to the invention;

Figure 7 depicts a preferred Langmuir conveyor trough using a non-recirculating con¬ veyor belt in, a system according to the invention;

Figure 8 depicts views of a preferred apparatus for continuous compression of insoluble monolayers on a subphase liquid in a system according to the invention;

Figure 9 depicts views of a preferred apparatus for electrostatic distortion of ionic Langmuir films on the subphase liquid in a system according to the invention; and

Figure 10 depicts views of a preferred apparatus for the continuous removal of film residue, after transfer of films to the substrate web, from the subphase in a system according to the invention.

Detailed Description of the Illustrated Embodiment

Figure 1 depicts an overview of the system for the deposition of insoluble monolayers and multi-layers on continuous substrate webs according to the invention. The substrate path begins at the web unwind roll (Detail 1.a). The web is unwound from the unwind roll by the use of motor-driven nip rolls (Detail 1.b). The web then passes over the first idler roll for web path control (Detail 1.o) and into the insolubilizer coater station (Detail 1.c). After being coated with the insolubilizer. the web is pulled through the first vented dryer (Detail 1.d). Once dried, the web passes over two more idler rolls (Detail 1.o) and begins the coating web loop (Detail 1.e). During this loop, the web passes around the driven coater roll assembly (Detail 1.f, elaborated in Figure 5). Here, the substrate web is brought into contact with the film, which has been prepared within the Langmuir Conveyor trough (Detail 1.m, elaborated in Figure 2).

Figure 2 depicts a preferred Langmuir trough used to practice the invention. The trough is formed by modifying a conventional slider bed conveyor with progressively inclined ramps or rails, placed along the sides, which guide the edges of the belt upward to form a trough.

The outer surface of the endless conveyor belt (Detail 2.h) is covered with rubber or flourocarbon, such as Teflon™, which is tightly stretched over the conveyor bed by extending the tail pulley bearing frame (Detail 2.b). This causes the belt to be flat in the middle with its sides bent upward. As the belt moves forward at a constant speed, the sides of the trough are continuously formed at the tail end of the conveyor, and continuously flattened at the head end.

The sub phase liquid is pumped from a reservoir tank (Detail 1m) at the head of the con¬ veyor to a weir at the conveyor's tail end (Detail 1.e). The weir allows any entrained bubbles to rise to the surface and be trapped there until they burst. It is designed to fit perfectly into the troughing portion of the conveyor, and form a liquid-tight seal with the conveyor belt. Hence, it must contact the belt immediately downstream from the point at which the edges of the belt are fully bent upward. Thus, the weir forms one stationary end of the moving Langmuir trough.

The sub phase liquid is distributed in an even sheet across the conveyor through a narrow slit at the bottom of the weir. The size of the slit should be adjustable to match the flow of the sub phase liquid to the speed of the conveyor, thereby minimizing turbulence. However, it is also desirable to adjust the weir slit to maintain a liquid level slightly higher in the weir than the trough in order to trap bubbles. This will vary depending on the viscosity of the sub phase liquid and the need to trap bubbles.

By pumping the liquid at a carefully controlled rate, which is proportional to the speed of the conveyor, the desired depth of liquid is extruded into the moving conveyor trough, (typically less than 2 cm deep). A few seconds after extrusion, the subphase liquid becomes still relative to the belt. For all it knows, it is sitting in a still Langmuir trough or marbling tray. The distance required for the liquid subphase to quiesce depends on the speed of the conveyor and the properties of the liquid. A carragheen solution 2 cm deep or less will quiesce rapidly, so only a few centimeters at most are required at belt speeds less than 10 cm/sec. Pure water, however, requires more time to quiesce, and hence a longer length of conveyor even if it is running at less than 1 cm/sec. Alternatively, a few millimeters of a pure water subphase are sufficient to form an LB film and reduce the time for the water to quiesce. (When using a low viscosity subphase, minimizing its depth will markedly reduce the time required for the liquid to settle provided the liquid depth is equal to or less than the boundary layer between the belt and the liquid.) At the far end of the conveyor, the surface of the subphase is cleaned of any residue not transferred to the substrate by a device called the suction scraper (Detail 2.f, elaborated in Figure 10). A carragheen solution 2 cm deep will exhibit flow relative to the belt about 4 cm before the suction scraper at a conveyor speed of 10 cm/sec while the web is not in contact with the liquid surface. The region of the conveyor trough between the onset of subphase quiescence and the resuption subphase flow relative to the belt is referred herein as the Zone of Quiescence, (Detail 2.s). All Langmuir film dispensing, film transformation, and transfer to a solid substrate occurs within the Zone of Quiescence. While the web is in contact with the Langmuir film a boundary layer is established between the web and the liquid extending toward the belt. Conversely, a boundary layer extends upwards from the belt toward the web. If the viscosity of the subphase is high (comparable to an aqueous carragheen solution) and the subphase depth is low (in the carragheen solution case less than 2 cm), then the two boundary layers meet and prevent flow of the liquid relative to the belt. However, continuous suminigashi requires the more difficult case of 6 cm or more of pure water. To prevent subphase flow in this case a wide toothed baffle is used after the suction scraper such that lamellar flow of water through the baffle teeth balances the flow of water into the Langmuir conveyor trough while maintaining the required depth (Detail 10 c). In this case the point of substrate transfer must be sufficiently upstream from the suction scraper/baffle to remain in the Zone of Quiescence.

A variety of dispensing valves (Figure 2.n) are suspended slightly above the moving subphase. At the point of subphase quiescence, the machine dispenses drops of liquid by having the computer which controls the process open and close the valves in a manner conventional in the art in particular accord with the teachings herein. In the case of LB film formation, the liquid would most likely be an insoluble monolayer forming material dissolved in a solvent, such as stearic acid dissolved in chloroform. In the case of pattern generation, the liquid would be pigments suspended in water with a binder and a surfactant. (Non aqueous paints, inks or dyes may also be used but with less environmental advantage.) As in traditional marbling, the final pattern is determined by the order in which the colors are dispensed, the relative amounts and properties of surfactant solution added to each color, and subsequent combing techniques.

A blunt hypodermic needle is connected to the valve by a small tube, and may be moved back and forth across the width of the conveyor under computer control to allow a single outlet to cover the entire width of the pattern being formed. The opening and closing of the valves and the manner in which the needles are moved back and forth are important process parameters for determining the final pattern.

While the complex nature of marbling makes reproducible dispensing difficult, the basic statistical distribution of color can be reproduced. Accurately controlled combing motions, on the other hand, can be highly reproducible.

Downstream from the initial color dispensers, several stationary and motorized combs (Figure 2.p, a few exemplary motorized combs are elaborated in figures 3 and 4) are attatched to the modular tooling plates (Detail 2.g) and suspended above the moving bath. They are optionally lowered into the subphase under computer control depending on the desired pattern. Each pattern is determined by both its color dispensing and its subsequent transformations. This is referred to herein as "Continuous Dynamic Pattern Generation."

The color patterns and combs can be controlled using conventional numerical control techniques, preferrably, using a computer file that stores parameters required to control the process to consistently generate each pattern. The total range of possible patterns is thus governed by the variety of color solutions, the variety of surfactant concentrations, the number and variety of dispensing orifices, and the control of their motion, and the number and variety of pattern transformers. Because pattern transformers act sequentially on the Langmuir film, the number of distinct patterns increases geometrically as the number of pattern transformers increases linearly. Ultimately, the range of different patterns is limited by the amount of space available to mount pattern transformers, such as combs and electrostatic surfaces. Therefore, the number of possible patterns any one machine can generate is limited by the length of the conveyor. Each distinct effect created by a given film transformer may be multiplied by the distinct effects of all the other film transformers. A machine with a dozen or so programmable film transformers, each with between twenty and fifty significantly different effects will be capable of generating millions of patterns. The many patterns may also be multiplied by the variety in which the colors may be dispensed leading to a nearly uncountable number of possible patterns.

Some patterns are too complex or spontaneous to be performed by a programmable mechanism. Accordingly an artisan-operator can manually manipulate the illustrated appartus to modify the machine-generated pattern or generate the entire pattern manually using the conveyor trough. A preferred embodiment permitting such manipulation includes an open section of trough to give the artisan access. In this manual or semi-manual mode, the pattern can be transferred onto sheets of paper by hand, or the continuous mechanism can be employed.

After color dispensing, many patterns require that the color domains be distributed into transverse streaks by combing. Figure 3 depicts a preferred apparatus for transverse combing of Langmuir films on the subphase liquid in a system according to the invention.

With further attention to the pattern process, the illustrated apparatus permits high speed combing of viscous liquids into a parallel combed pattern known by the marbling nomenclature as nonpareil. Figure 4 depicts a preferred apparatus for bi-directional parallel combing of Langmuir films on the subphase liquid in a system according to the invention. This is performed by a motor-driven rotary comb with thin discs (Detail 4.j) impaled on a rotating shaft (Detail 4.i). The inner diameter of the discs is just able to clear the rotating shaft diameter such that in the normal case, the discs are flat and mounted perpendicular to the rotating shaft. To maintain this perpendicular alignment and to regulate the spaces between the combing discs, spacers with the same inner diameter and a smaller outer diameter are assembled onto the shaft between the combing thin discs and the entire assebly is compressed by nut which are tighed on a short section of thread on each end of the shaft.

When combing is desired, the disc comb mechanism is lowered into the sub phase such that the discs are partially submerged to an equal extent, but the spacers remain above the film level. In the case of a stationary trough filled with a shallow viscous liquid, the rotary comb may be translated along the length of the trough or tray such that the rotating shaft remains parallel to the film surface and the shaft is perpendicular to the direction of motion. The rate and direction of rotation may be controlled to account for the speed of its translation.

In the case of a viscous liquid flowing in a stationary trough or a continuous troughing conveyor filled with a shallow viscous liquid, the rotary comb is not translated, but may be low¬ ered into use when desired and rotates in a direction and speed which is proportional to the speed of the conveyed liquid.

When used to comb Langmuir films, the discs need not penetrate far below the sub phase surface. In this way, a rotary disc comb of almost any diameter can be brought into tangential contact with a floating thin film.

The choice of dies materials should minimize the adhesion of the liquids to the combing discs. Plastics such as polypropalene, flourocarbons of the Teflon™ class, and nylon are suit¬ able. Glass, brass, and other materials with non-stick coatings applied to their surfaces may also be used. The rate of shearing is thus controlled by the rotational speed and the wettability of the disc.

The primary advantage of a rotating comb is that the maximum possible speed of comb¬ ing for fine combs is much greater than for conventional tootheti combs. There are two reasons for the increased production capacity. As conventional combs become progressively finer, the teeth must be made thinner to allow space for the fluid to flow. A very fine conventional comb when translated through a viscous liquid will cause the liquid to build up behind it unless it is moved very slowly.

A rotary comb can be made with discs which are less than 0.1 mm thick provided the outer diameter of the supporting spacers are approximately half the outer diameter of the comb¬ ing disc. Moreover, the geometry of a disc comb provides maximum strength to the combing disc in the direction in which it meets the viscous liquid. The dimension in which it is thinnest does not require strength. By controlling the rate of rotation proportional to the linear speed of the liquid (relative to the disc comb) a very fine rotary comb can produce a nonpareil combing pattern at high speeds without liquid building up behind it.

Another important advantage is the ability to create nonpareil patterns in either direction by controlling the speed and direction of the combs' rotations. Viscous shear thinning is the phenomenon which makes possible the nonpareil pattern, hence the direction of the pattern is determined by the direction of shearing at the point of contact between the discs and the liquid, rather than the direction of translation of the liquid relative to the comb. By using two such combs with a complimentary spacing, one tuned for forward nonpareil and the other offset by one half disc and tuned for backward nonpareil, the result is the pattern known as the "feather", which is also the precursor to the traditional pattern known as "thistle". Hence the use of one or two offset disc combs provides a means for the continuous generation of nonpareil in either direction, and the feather pattern. In conjunction with a motorized peacock comb, the patterns peacock and thistle can be continuously generated at higher speeds than would be possible with a static comb. Peacock in particular is a pattern in high demand.

After all dispensing and transforming has occurred and the desired pattern has been reached, it is time to transfer the pattern to the substrate. This can be a discrete object or a con¬ tinuous web of paper, fabric, or any solid surface coated with alum sulfate, or other reaction in- solublizer. Discrete objects must be dipped onto the surface of the moving bath in such a way as to minimize speed differences between the object and the conveyed film. Decorative films are best transferred by touching them to the surface of the substrate using the horizontal dipping technique, although vertical dipping is possible while using deep Langmuir conveyor troughs. For example, decorating three dimensional objects with marbled patterns can be achieved with programmably varied patterns at highly productive rates provided the trough is deeper the the immersion depth of the object.

LB films deposited onto discrete substrates can be dipped vertically or horizontally fol¬ lowing the method of Blodgett while providing a mechanism for the substrate to match the speed and direction of the conveyor prior to dipping. The conveyor must be very long if the belt speed is rapid relative to the dipping rate. Nevertheless, this provides a new strategy for high volume production of LB-films on discrete substrates without violating the necessarily slow dipping rates required by some LB-film systems..

Continuous webs must move at the same constant speed as the subphase liquid to avoid any pattern distortion. If pattern distortions are desired, the speed of the web can be varied at the point of contact with the floating pattern. Paper, for example. Is unwound from a roll and threaded through a series of idler rolls which guide the paper to one or more coater rolls.

Figure 5 depicts a preferred apparatus for creating controlled density distortions of Langmuir film during deposition on continuous substrate webs in a system according to the in¬ vention. The film coater roll (Detail 5.f) is an idler roll (non-driven) positioned just above the moving pattern, downstream from all the dispensing and transformation stations, but still within the Zone of Quiescence. The web is looped straight down, around the coater roll and back up again, with the alum coated side facing the surface of the moving pattern. To transfer the pattern onto the web, the coater roll is lowered until it is just slightly below the liquid surface. As the web moves forward at the same rate as the conveyor, a distortion-free transfer of the pattern occurs.

The reason for guiding the web in a path that provides for a long downward loop (Detail 1.e) is to allow the coater roll to slide horizontally several centimeters in a back and forth man- ner, driven by a computer-controlled linear actuator (Detail 5.b). This creates controllable vari¬ ations in the speed of the web relative to the floating Langmuir film without substantially changing the length of the web's path or tension.

This results in a pattern distortion known by the traditional marbling term "Spanish wave." In the continuous mode I call it "California wave." This method of horizontally moving the coater roll is more easily controlled than speeding up and slowing down the entire web. Moreover, the two ends of the coater roll can be displaced independently so that one side experiences an increase and the other side a decrease in relative speed, or they can act in concert as well. This more accurately reproduces the effect of the traditional Spanish wave.

The coated web then moves straight up, around an idler roll, and through a gently sloping rinse chamber (Detail l.g), a blow-off chamber (Detail l.h), and a vented dryer (Detail 1.i), after which it is rolled up at a rewind station (Detail 1.1). While the coating on the web will not run or smear, it is a fragile film until dried. Rinsing is accomplished by using an array of gentle spray nozzles which move a large volume of low velocity water over the web. Provided this rinse water is filtered properly, it can be recirculated.

Between the rinsing station and drying chamber, the web rolls through a blow-off cham¬ ber (Detail 1.h elaborated in Figure 6). Figure 6 depicts a preferred apparatus for continuous re¬ moval of rinse solution from a continous web in a system according to the invention. An air knife (Detail 6.c,e.g., a large pipe with a narrow slit along the length which can direct a volume of air into a fast moving sheet) blows any excess water from the web at a glancing angle. When carefully adjusted, the water will be removed, but the still fragile film will be unharmed.

The tension of the web is governed by a variable slip clutch in the rewind station (Detail 1.1) which is coupled to tension sensors (Detail 1.k) on one of the idler rolls. The speed of the web is controlled by driven nip rolls or S-wrap rolls (Detail 1.b) just downstream from the un¬ wind station (Detail 1.a). The path of the web must not allow the film coated side to contact any surface until it has been rinsed and dried.

Downstream from the film transfer point, is the suction-scraper device (Detail 2.f, elabo¬ rated in figure 10). Figure 10 depicts a preferred apparatus for the continuous removal of film residue, after transfer of films to the substrate web, from the subphase. A rigid rubber or flouro¬ carbon boom (Detail lO.a) is lowered across the width of the conveyor trough until it is just be¬ low the subphase surface. This apparatus skims off any residual Langmuir film while forming a liquid tight seal with the conveyor belt. As the residual film backs up behind the scraper boom, the fluid level rises to the point that suction tubes (Detail lO.b) carry it away to a filtration and storage station. The vast majority of the subphase liquid passes beneath the scraper boom. As the conveyor belt rolls over the head pulley, the remaining liquid subphase is carried with it.

A belt wiper (Detail 2.d) contacts the belt at the head pulley (Detail 2.c) at approximately a 45 degree angle, contacting the belt before it turns under the pulley. The belt wiper is a rubber sheet adhesively bonded to an adjustable wiper frame which can be rigidly locked into place. The rubber sheet extends from the conveyor belt to a point below the • reservoir liquid level. The liquid is plowed off of the conveyor and glides down this rubber sheet into the reservoir tank (Detail 2.m) in a smooth continuous film without inducing entrained bubbles. The liquid level in the reservoir tank is kept constant by a float valve connected to a fresh source of subphase hquid. This is required to replenish the subphase liquid lost to the rinse subsystem and suction scraper tubes.

The subphase liquid in the reservoir tank must be deep enough to allow any bubbles which may occasionally form to rise to the surface rather than be caught in the inlet port of the pump (located near the bottom of the tank).

To generate continuous compressed Langmuir films the process is the same with one important detail: the primary film transformer is a mechanism for compressing the film. One way in which stationary Langmuir troughs compress the monolayer is by sweeping a moving boom across the surface. To measure the structural transitions within the film, a Wilhelmy plate monitors the surface tension. The rate at which the film can be compressed is characteristic of each LB film system. Some films require very slow rates of compression.

Most research currently conducted on LB films uses pure water for the subphase. To use pure water in this process, it is advantageous to operate with a subphase no more than 2 or 3 mm deep for reasons of turbulence, as previously discussed. The additional constraint of compressing monolayers slowly while operating the continuous process at high speeds has led to the following solutions.

The first technique employs a series of carefully metered microvalves positioned along the length of the conveyor at both extreme edges of the subphase. These valves begin just downstream from where the dispensed monolayer material has folly spread. A non-evaporative surfactant solution is slowly dispensed in a continuous stream from valves along each side of the conveyor until the monolayer domain is compressed by the spreading pressure of the dispensed surfactant domains on either side.

At high speeds, a Wilhelmy plate is not practical for monitoring the compression of the monolayer. In this case, the flow rates of the surfactant and monolayer solutions may be extrapolated from studies conducted in a stationary Langmuir trough. Ordinarily, the use of surfactants is anathema to any Langmuir system because of the extreme difficulty in cleaning the trough to an acceptable and reproducable level of purity. Consequently, using this compression method, the subphase cannot be recirculated, and the belts must be aggressively cleaned with jets of forced water, air, and/or hot dichromic acid. Figure 7 depicts a preferred Langmuir conveyor trough using a non-recirculating conveyor belt in a system according to the invention. If extraordinary purity is required the belt itself may be a clean, smooth, flexible web such as a thermoplastic film, which is taughtly stretched over the top surface of the Langmuir conveyor bed and passed only once through the process, afterwhich it is wound up and recycled for other products.

Figure 8 depicts a preferred apparatus for continuous compression of insoluble monolayers on a subphase liquid a a system according to the invention. This second method for film compression uses a system of moving side walls similar to the constant-perimeter Langmuir trough. The Teflon tape (Detail 8.f) converges very gradually, thus providing a slow rate of compression. The advantage over the first technique is the ability to use a deeper subphase and avoid the contamination of surfactants. In this method, re-use of the subphase liquid can be practical for those systems which are tolerant of minute contamination from monolayer materials not transferred to the substrate. The conventional method of suctioning the subphase surface after substrate deposition is used, employing the suction scraper. The speed of the tape is regulated by photosensor which monitors registration marks on the tape itself. The tape speed is adjusted such that the vector componant of the tape speed which is parallel to the motion of the conveyor belt is equal to the conveyor speed. The vector componant of the tape while is orthoganal to the conveyor speed is equal to one half the rate of compression because both tape converge at the same angle. Thus a very long Langmuir conveyor trough with driven tape barriers which converge at a low angle may provide for rapid ^' rates of film formation while maintaining slow rates of compression. The long conveyor also provides the time required for any necessary solvent evaporation.

Stationary Langmuir troughs have the advantage of being easily isolated from mechanical vibrations. By careful choice of materials and the use of active damping transducers, much can be done to minimize vibrations for a Langmuir conveyor trough. Langmuir films vary in their sensitivity to vibrations. Minute concentrations of polysacharrides in the aqueous subphase does much to diminish vibration sensitivity. Those films which are more tolerant of vibrations are good candidates for use with the moving Langmuir conveyor trough.

Langmuir conveyor troughs which use a recirculating viscous subphase must be wiped in a manner which does not produce entrained air bubbles. However, contacting belt wipers are an additional source of vibration. Use of a more viscous or turbulance damping subphase improves vibration tolerance, and in the case of continuous marbling, the necessary belt wiper poses no serious vibration problem. For LB film systems which use a pure water subphase, the belt is best wiped by an airknife and suction hood or not wiped at all.

The primary source of vibration is the conveyor drive motor (Detail 2.k) and its linkages (Detail 2.j). By mounting this motor on a separate pedestal (Detail 2.i) which is isolated from the conveyor base, the noise source is largely eliminated. In terms of linkages, flexible timing belts are preferable to chains, and flexible driveshafts are better still.

The second major source of vibration is the rubbing action of the belt (Detail 2.h) over the conveyor frame (Detail 2.a). Polished granite is an excellent material for use as a troughing conveyor bed for its stiffness, inherent vibration damping properties and its smooth surface. Actively damped optical tables can also be used for a troughing conveyor bed, although the transducers must handle higher amplitudes and lower frequencies than an ordinary optical table. The base of the conveyor pedestal is isolated from vibrations conducted from the floor, and is also isolated from the main conveyor. With continued reference to Figure 1. a still better understanding of the structure and op¬ eration of an apparatus for depostion of insoluble monolayers on continuous substrate webs may be attained be reference to the sections which follow. A. The Conveyor Trough Tdetail 1.m. elaborated in figure 2)

The conveyor should be constructed in a manner and from materials which minimize and absorb vibrations caused by the drive motor (Detail 2.k), the drive linkage (Detail 2.j), the sliding of the belt (Detail 2.h) over the slider bed, and the belt wiper (Detail 2.d). Vibrations are detrimental to the formation of compressed LB films, but are less troublesome for continuous marbling. A.1. Slider Bed Dimensions

The length of the conveyor is determined by the following factors: the speed of the process; the depth of the subphase; the compression rate of any monolayer film; the rheological properties of the subphase; and the physical dimension of any film transformers. For example, if a pure water subphase is used for LB film generation and the process is moving rapidly, several meters must be allotted for film compression.

If a pure water subphase is used for suminagashi at any speed, several meters must be allotted for the subphase to quiesce before depositing pigment solutions. Whereas if the process is moving at less than 10 cm/sec. and the subphase is a carragheen solution less than 2 cm deep, only 10 cm are required for the subphase to quiesce.

While continuous marbling requires little conveyor length for the subphase to quiesce, length must be allotted for the various pattern transformers (Detail 2.p, elaborated in figures 3,4, and 9). As the process is operated at higher speeds, it may be necessary o allot conveyor length for greater spaces between these transformers. One must also allow space for the coater roll (Detail 1.f and Detail 2.q, elaborated in Figure 5) or dipping mechanisms and the post-coat film scraper (Detail 2.f, elaborated in Figure 10).

Because the slider bed must guide the endless conveyor belt into a trough, length must be allotted to smoothly guide the belt edge upward and lay it flat again before contacting the driven head pulley (Detail 2.c). Only the Zone of Quiescence within the troughed portion is useful for production purposes. As the speed of the process increases grteatly, longer distances are required to curl up and lay down the sides of the belt.

Some dependency also exists between the width and length of the conveyor. As the conveyor design is widened, some film transformers must consume more of the conveyor's length to compensate for the additional time required to traverse the larger width. This is especially true of the transversely mounted rotary belt comb (Figure 3), described in detail below. A.2. Endless Belt Dimensions

This process may use two styles of endless, flexible belt (Detail 2.h). One is a multi-ply flat belt with two grooves scϊved into the back of the belt which leave the surface layers intact. These grooves improve the flexibility of the belt to form a trough while most of the multi-ply belt is unaffected and provides good traction and wear material for driving and tracking the belt. The distance between the centers of these grooves is equal to the flat portion of the slider bed. The distance from each groove to the nearest edge should be equal and is determined by the an¬ ticipated subphase depth and the troughing angle (35 degrees works well). Ample belt width should be allotted to provide for at least twice the desired subphase depth to avoid overflows while tuning the process. These belts are widely available commercially and are inexpensive.

The second style of belt is one which is not flat but has troughing sidwalls built into it. This specially molded belt must be flexible enough to pass over the end pulleys and resiliant enough to regain and maintain its shape over the flat portion of the conveyor. When using this style of belting, the troughing conveyor is replace with a simple slider bed conveyor. This ap¬ proach is most appropriate when the subphase is expected to be as shallow as 1 cm or less. The primary advantage is a more simple conveyor design. Because all conveyor belts experience some back and forth tracking, this approach works best when an air knife is used to wipe the belt, rather than a contacting rubber sheet. The choice of an air knife is most appropriate when the subphase does not foam easily, such as pure water, or when the subphase is not recirculated. A.3. Head and Tail Pulleys (Details 2.c and b)

Both the head (Detail 2.c) and tail pulleys(Detail 2.b) should be slightly below the flat portion of the slider bed to stretch the belt flat over the conveyor frame. For steady belt tracking on a troughing conveyor of this type it is best to fix the bearings of the drive or head pulley in a manner which is perpendicular to the conveyor frame. The tail pulley (Detail 2.b) is mounted on telescoping adjustable bearing frames. The extent of the required telescoping adjustment is determined by the depth of the conveyor trough.

The belt (Detail 2.h) must be put on from the side while the tail pulley (Detail 2.b) is re¬ tracted to the minimum extension. Once mounted, the belt is fully tightened and adjusted for tracking. The diameter of the head(Detail 2.c) and tail (Detail 2.b) pulleys is a function of con¬ veyor width and can be determined by industry standard engineering tables. To aid in belt tracking, the drive and tail pulleys should be crowned in the industry standard manner, however, the centering effect of the conveyor trough allows for slightly less crowning than a slider bed conveyor would use. This will reduce the effect of stretching and bowing of the belt center over time. A.4. Drive Motor. Linkage and Controls (Details 2.k andf ^' )

The power required to drive a Langmuir conveyor trough must match the resistance of deforming the belt into the trough and the drag of any physically contacting belt wiper (Detail 2.d) ans well as the suction scraper and extrusion weir. The energy required to convey the sub- phase is negligible by comparison for most designs. As the width of the conveyor increases so does the pulley diameter and hence the rotary speed of the drive pulley decreases. The required gear reduction to find an appropriate speed enables the use of fractional horsepower motors for conveyors which are less than three meters long and one meter wide. Conventional conveyors are usually designed with the drive motor mounted somewhere on the conveyor frame or base. For Langmuir conveyor troughs, the need to minimize vibration calls for mounting the drive motor on a separate, vibration isolated base (Detail 2.i), especially when the machine is used for the continuous production of insoluble monolayers. For continous marbling one can mount the drive motor on the same base provided a low vibration gearbox is used and vibration damping motor mounts are employed.

Flexible, low stretch timing belts are better drive linkages than chain and sprockets be¬ cause of their lower transmission and generation of vibrations. N-belts are not appropriate be¬ cause the speed of the system must be carefully controlled.

Another drive linkage option which is useful for systems requiring better vibration isola¬ tion than timing belts are capable of is the flexible coaxial shaft. These are most cost efffective for smaller, lower power designs, however they can be scaled up if required. In this configura¬ tion the drive motor and gearbox are mounted on a separate vibration damped base from that which isolates the conveyor. The flexible shaft which connects them is encased in a low friction shroud which in turn is encased in a vibration damping material such as commercially available PNC alloys.

The speed of the conveyor must be carefully controlled at a constant rate so that the speed of the subphase pump (Detail 2.1) and the mechanism which moves the substrate to be coated can be driven at a proportional rate.

In the past, belts and pulleys, chains and sprockets or gears would be used to synchronize these three subsystems. While that remains a valid option, today one can realize better design flexiblity by electronically controlling variable speed motors with some form of feedback sensor such as a tachometer- Microprocessor equipped motor drives are affordable which can establish one drive as a master and the other drives must follow at a preset ratio.

This flexibility is crucial for process development as one scales up a process in phases. In production, its utility is found in the ease with which one can compensate for the wear of parts in one subsystem and retune the process to the appropriate speed ratios. The master drive must follow a signal from the master process controlling computer, sense the actual speed and automatically adjust for any variances. By employing intelligent electronic motor drives, a master process control computer (not shown) need not be burdened by the slaved motor drives. A.5. Belt Wiper ( et il ^

When using a viscous subphase, the belt wiper should be designed to minimize entrained bubbles while removing the subphase from the conveyor belt and guiding it to a reservoir tank. The angle of contact with the belt is a function of the conveyor speed, the rheological properties of the subphase liquid, and the surface interaction between the wiper material and the subphase liquid. Therefore, it is important to use an adjustable frame which can be raised and lowered, pivoted to change the contact angle with the belt, and a sliding adjustment to compensate for the wear of the wiper material. By adhesively bonding a rubber sheet to a slide adjustable plate which in turn is locked into the pivoting frame, a ramp is established which extends below the reservoir liquid surface. Conventional belt wipers use a frame on both sides of a slotted rubber sheet. Bubbles are readily formed as the liquid splashes over the upper half of the wiper frame.

When non-viscous subphases are employed, a combination of an air-knife and suction hood provide a push-pull air transport mechanism for blasting the belt free of the subphase. The suction hood provides for a channelled path for the condensed liquid and any airosol spray which the air knife may generate. Conventional stainless steel mesh mist condensers may be used in the suction path to eliminate most of the spray. A.6. Drip Trav (Detail 2.

A drip tray is mounted beneath the conveyor at an incline to allow any residual liquid on the belt which falls to be channelled into the reservoir tank or a disposal catch basin. A.7. Tooling Plates (Detail 2.g)

Along the entire length of the conveyor, on either side of the belt, a pair of identical, modular, fixturing plates provides variable attachment points for the conveyor tooling. They are a regularly spaced array of holes drilled and tapped into identical slabs of material which are parallel and run the length of the conveyor. B. Conveyor Tooling

The conveyor has two types of tooling: that which is fixed and that which is intended to be repositioned when needed. The fixed tooling consists of the extrusion weir (Detail 2.e), the actuated coater roll (Detail l.f and 2.q, elaborated in Figure 5) and the suction scraper (Detail 2.f, elaborated in Figure 10). The removable tooling consists of the dispensing manifold (Detail 2.n) and all the film transformers (Detail 2.p, elaborated in Figures 3, 4, and 9). The film transformers can be raised or lowered into the subphase liquid, for example, under computer control. The sequence in which they occur has a deterministic effect on the eventual pattern. Size and cost may limit the possibility of having many redundant film transformers to provide for every possible sequential combination of these different devices. Therefore, it is useful to be able to easily mount them or remove them from the multitude of positions provided by the flexible tooling plates (Detail 2.g) on either side of the Langmuir conveyor trough. B.l . Subphase Extrusion Weir (Detail 2.e

The subphase liquid is pumped from the subphase reservoir (Detail 2.m) into the sub- phase extrusion weir from which it flows or is extruded into the Langmuir conveyor trough. The purpose of the weir is to 1) allow the subphase liquid to spread across the width of the conveyor trough 2) allow the subphase liquid to dissipate any turbulance which may have been intoduced by pumping 3) form a liquid tight seal with the troughed portion of the conveyor belt and thereby establish one stationary side of the Langmuir conveyor trough.. B.2. Dispensing Manifolds (Detail 2.ή) and Motion Control

When the clean subphase liquid has reached quiescence within the trough, it is like a clean slate, ready for a variety of speading liquids or liquid suspensions to be dispensed upon it. Therefore the size and placement of the drops as well as the number and type of valve required will vary depending on the film being formed and the variety of liquids used to form it. B.2.a. Pressurized Solenoid Valves

One of the least expensive and most easily controlled dispensing strategies calls for the use of pressurized vessles for each liquid with the outlet tube connected to a solenoid valve. These valves may be easily turned on or off by the control system which takes into account the rate of flow of the Hquid and the speed of the conveyor. B.2.b. Ultra-Sonic Atomization Valves

A useful technique for dispensing a fine mist of liquids or liquid born suspensions is an ultra-sonic atomization valve. The advantage of these valves over gas propelled atomizers is that the drops fall onto the subphase surface under gravity alone, rather than creating an aerosol mist which could easily be inhaled. A shroud is required to create a turbulance free air space between the ulta-sonic atomizer and the subphase surface. B.2.c. X and X-Y translation stages

To avoid the expense of covering the entire width of the conveyor with an independently controlled dispensing valve for each liquid required for a given film, dispensing orifices can be moved at a sufficiently high speed to cover the entire width of the film. A variety of single and double axis linear actuators and stages may be used for this purpose. However, the ability to achive a statistically reproducible result will depend on the reproducible accuracy of these actuators and the ability of the control system to command them. B.2.d. Automated Concentric Dispensing and Suminagashi

To continuously generate suminagashi patterns with the Langmuir conveyor trough re¬ quires a troughing depth of approximately 6 or more cm, a conveyor length of 3m or more and a conveyor speed which is sufficiently slow to alow the water to quiesce and still have time to generate the pattern. Faster process speeds will require a longer conveyor, but eventually the shear between the film surface and the atmosphere will disrupt the film. A speed of 1 cm/sec is appropriate for continuous generation of suminigashi in a Langmuir conveyor trough.

Concentric rings are the primary design motif of suminagashi and are also appropriate for marbling and other heterogeneous Langmuir films. To produce a heterogeneous film with concentric rings a series of various liquids must be dropped one upon the other with a time interval inbetween. In this continuous process, the time interval is effectively a distance interval. Hence, by placing several different liquid dispensing needles in approximately a straight line in the longitudinal direction of motion, the control system can be pre-programmed to momentarily open each valve as the spreading disc passes below it.

This line of dispensing needles can also be programmed to move across the width of the conveyor, thus allowing the set of valves to cover more area. By alternating between two or more pigment-surfactant solutions and pigment free surfactant solutions, the primary dispensing strategy of sumingashi can be achieved. Aesthetically suminigashi is a free form, non determi- nistic process. Therefore the programming of the concentric ring dispensors are best done with an element of statistical variation.

Following concentric ring dispensing, programmable air jets may be used to distort the floating rings. As was previously described for marbling, the Langmuir conveyor trough can be used as a productivity enhancing tool for the artisan to manually dispense and/or transform the suminigashi film. The substrate need not necessarily use a reaction insolublizer such as alum if the density of pigment is not high and the substrate is very moisture absorbant.

Because suminagashi requires the combination of subphase depth and low viscosity, the head end of the trough must be bounded by a suction scraper baffle which extends to near the bottom of the trough allowing for a slow rate of subphase flow equivalent to the flow entering from the subphase dispensing weir. The design of the Langmuir conveyor trough is meant to increase film formation speeds while preventing any flow of the subphase relative to the belt. The combination of increased subphase depth and low subphase viscosity requires a region of non-turbulant flow beneath the suction scraper. It is best to locate the substrate transfer several inches upstream of the suction scraper to avoid any distortion effects caused by this flow region. In general, when the combination of subphase depth and viscosity lead to a region of flow at the head end of the conveyor, the suction scrapper baffle should be adjusted lower. B.3. Z-Axis Control Manifold

Each film transformer must be optionally used or not. When not in use it must be pow¬ ered down and/or lifted out of the subphase liquid. Because most such devices span the con¬ veyor transversely, they must be mounted on a pair of lifting devices which are mounted to the flexible tooling plates (Detail 2.g and 5.j). Pneumatic or hydraulic cylinders (Details 3 and 4.d), which are plumbed together, are preferrably controlled by computer by actuating 4-way double solenoid valves.

A pair of locking electromagnetic solenoid plungers is another option. For safety, the first option is more desirable because the rate of motion can be more carefully adjusted using inexpensive flow controllers which also prevents shock damage to the devices being lifted. In addition, the use of 4-way double solenoids will leave the devices in place in case of a power failure or loss of computer signal. Some of these devices involve sharp corners which might cause injury to an operator if they were to unexpectedly move during a system failure, hence the preferrence for the double solenoid, fluid powered approach. B.4. Electro-Mechanical Film Transformers

Mechanical interaction with the film or the subphase liquid can produce useful transfor¬ mations in film density and distribution. This is true of a broad class of Langmuir films. The devices described below are a small subset of the possible electromechanical devices for trans¬ forming the continuous Langmuir film within the Langmuir conveyor trough. B.4.a. Film compressors

Langmuir-Blodgett films routinely require that the film be compressed to achieve the desired molecular orientation and packing density. The rate of compression which a given film- subphase system will tollerate varies widely.

Figure 8 depicts a preferred apparatus for continuous compression of insoluble monolayers on a subphase liquid in a system according to the invention. Use of a viscous sub- phase in the Langmuir conveyor trough, such as polysacharride colloids, helps damp turbulance and allows for more than one centimeters of subphase depth. With such a clearance between the film and the bottom of the trough (the belt) converging moving sidewalls (Detail 8.f) may be used over a long distance. Povided the conveyor is long and the convergence is gradual relative to the conveyor speed, slow rates of compression can be achieved at rapid conveyor speeds.

Many L-B film systems require ultrapure water for the subphase. To achieve quiecence over an economically viable distance, the depth of the pure water subphase is limited to 2mm. In this case, the above technique may still be used, albeit with more exacting dimensional control. However, another useful approach is the use of incrementally dispensed dilute surfactant solutions which compress the film with slow spreading pressure. A steady stream of surfactant solution dispensed from clean stainless steel needles on either side of the uncompressed film domain forms a gradually compressed region inbetween the needles. Several such pairs of surfactant compressor needles may be used in line to control the desired rate of compression which may not always be linear.

It is not practical to reuse the subphase in this case and the belt must be agressively cleaned. Air knives, pure water jets, hot dichromic acid dips and UV lasers are needed to thor¬ oughly clean the belt when operated at high speeds. B.4.b. Transverse Motorized Combs (Figures 3 and 4)

1. Belt Combs (Figure 31

The transverse motorized belt comb employs a pair of motor driven timing belt pulleys (Details 3.g and f) suspended just above the film surface. Combing tines are attached to the outer portion of the belt at a variety of spacings. By varying the speed and direction of this belt comb, the film is combed from side to side at high speeds relative to the conveyor speed or at very slow speeds, mostly in the longitudinal direction.

2. Rigid Combs

Rigid combs of one or more rows of tines and a variety of spacing may be driven back and forth, for example, by a computer controlled linear actuator. Continuous generation of the traditional marbling patterns of peacock and thistle depend on this single axis, transversely actuated rigid comb. By electronically controlling this linear actuator the number of intermediate and final patterns possible is multiplied by the number of distinct wave forms the actuator can respond to. B.4.c. Stationary Rigid Combs

Stationary rigid combs of various spacings, row numbers and tine dimensions may be lowered into place to create variations on the non-pareil pattern when using a viscous subphase. As the spacings between tines becomes smaller, a point is reached at which the cross sectional area availble for the subphase to flow through is so diminished that the subphase backs up be¬ hind the comb. This effect limits the rate of production of very fine non-pareil combed patterns. B.4.d. Rotary Disc Combs (Figure 4)

Rotary disc combs are thin shim washers (Detail 4.j) arranged on a motorized shaft (Detail 4.i) with smaller spacers (Detail 4.k) in between. The larger shim washers touch the liq¬ uid surface tangentially. They are so thin that they present little resistance to the conveyed sub- phase. In addition, the speed and direction of the rotary disc comb can be varied to produce the nonpareil pattern in either direction and with varying amounts of boundary layer adhesion de¬ pending on rotational velocity and the wettability of the shim washer material. TeflonTM and nylon work well with aqueous polysacharride subphases.

Two rotary disc combs set one half space apart can produce the feather and fine feather patterns on a continuous basis. The fine feather pattern is the precursor to the thistle pattern. A fine nonpareil pattern is the precursor to the peacock pattern. Because of the above mentioned productivity limitations of fine static combs, the use of one or more rotary disc combs is crucial to the productivity of producing the peacock and thistle patterns: two of the most widely sought traditional patterns in the marketplace. B.4.e. X-Y-Z-Theta Combs

Multi-axis robotic actuators which can move combs in and out of the subphase (z axis) as well as provide smooth in plane curves and rotations enable continuous generation of the French curl, birds wing, and other complex patterns. B.4.f. Air Jets

Air jets which cause the film to move without driving the film material into the subphase are an effective pattern transformer. The jets can be controlled, for example, by computer via solenoid valves, proportional gas valves, and electronic motion control devices. These are especially effective for continuous marbling and continuous suminigashi. B.4.g. Translatable Coater Roll (Detail l .f and 2.q. elaborated in Figure 5)

The film coater roll must be raised and lowered under command of the control system such that it is raised away from the Langmuir film whenever the continuous web stops moving. Conversely, it should be lowered into place whenever the web is moving and a film is ready for deposition. Fluid power actuators (Detail 5.c) on either end of the coater roll shaft are an effec¬ tive means to this end. They can also be easily tied together with other cylinders which move web dryers into position and fluid powered cluthes which engage or disengage the web drive motor with a soft start and stop. To act as a film transformer, the coater roll is moved back and forth in a reciprocating fashion, driven, for example, by a computer controlled linear actuator (Detail 5.b). Provided the web path follows a downward loop (Detail l.e) around the coater roll which is long relative to the reciprocating displacement distance, the overall path length of the web is barely affected by motion in the film plane. Hence, web tension problems are unlikely to arise, such as web breaks or rewind problems. At the same time, the linear speed of the web throughout the process does not change and remains identical to the speed of the Langmuir conveyor trough.

The purpose of controlled, horizontal dispacements of the coater roll during the coating process is to create wave distortion in the density of film applied to the web. This replicates the traditional pattern known as "Spanish wave." Two independently driven actuators at either end of the coater roll provide the most acurate Spanish wave distortions. B.5. Electro Static Film Transformers

Surfactants, or surface active agents, are chemicals which alter the surface tension of a condensed phase interface. In aqueous systems they are non-ionic, cationic, or anionic. The two charged varieties are always locally balanced in their charge by an ion of opposite charge. Non-ionic and anionic surfactants are most suitable for use in marbling and continuous marbling. By placing a charged surface in the gas above the Langmuir film, any surfactant of opposite charge will move in response to the electro-static potential. The variables to consider are the distance of the charged surface from the film, the distribution of charge on the surface or similarly, the shape of the surface, the magnitude of the electrical potential between the charged surface and the subphase, and the length of time any part of the film is in close proximity to the charged surface. The distorting effects of charged surfaces near a Langmuir film with charged surfactants vary as follows: o surfactant mobility increases as the distance between the charged surface and the film decreases, with opposite electrical polarity attracting and like charges repelling. The ef¬ fect of distance is nonlinear and follows the inverse square law. o the most effective charge level to induce planar transport of a given ionic surfactant is characteristic of that particular surfactant-film system. o planar transport of charged surfactants in a Langmuir film increases with time at any charge level with diminishing rates over time. o planar transport of charged surfactants in a Langmuir film is a dynamical system with final transport results dependent on the charge and distance history of the charged sur¬ face.

These four concepts should be considered in the design and control of the below men¬ tioned electrostatic film transformers. B.5.a. Stationary' Charged Plates and Combs

Combs and plates of various shapes and dimensions may be mounted above the Langmuir film surface and lowered into place just above the film when needed. The electrical potential between these stationary devices and the subphase may be varied by using a high volt- age power supply which responds with variable voltage to a control signal from the master con¬ trol computer, which coordinates the overall process. By coordinating the fluctuations in volatage with the speed of the continuous process, different film transformations will result. B.5.b. Motorized Charged Plates and Combs

These are a class of electrostatic film transformers identical to the above stationary de¬ vices with the exception that they may be moved in the plane parallel to the film as well as up and down. These are analogous to the motorized combs. B.5.C. Rotating Charged Roller with Textured Surface (Electronic Embossing. Figure 9)

A rotating charged roller (Detail 9.e) with a textured surface (Detail 9.h) which may be lowered close to the Langmuir film such that this cylinder is parallel to the coater roll and rotates at a rate proportional to the speed of the conveyor produces film distortion which is similar and analogous to mechanical embossing. The texture effect will repeat with each revolution of the charged, textured roller. If the voltage at the surface is approximately one million volts per square meter and the initial distribution of ionic surfactants is nearly uniform, the the effect will be very reproducible. However, if the roll voltage is programmed to fluctuate and or the distribution of ionic molecules in the Langmuir film is initially uneven and random, then the effects will be more chaotic. B.5.d. Scrolling Charged Array

An additional degree of programmable control compared with the above rotating cylinder is the scrolling charged array. An array of independently charged pins is mounted close above the Langmuir film. A charge intensity map is generated with computer graphics and mapped from the data which is represented in graphics to the charged array. By smoothly scrolling the graphics and synchonized pin array at the same speed as the conveyor, the result is a computer controlled electrostatically embossed film transformation which can be repeated at any interval or can be non-repeating. The economic advantage is the ability to rapidly change embossing effects without the need to amortize the cost of each embossing roll. The primary limitation is the resolution of the charged pin array. B.6. Electro Optical Film Transformers

B.6.a. Photo-Sensitive Film Exposure for Polymerization. Photosensitive Pigments.and Photo- modified Surfactants.

Another method of transforming Langmuir films continuously is with light, visible and otherwise. UV polimerization is an important transformation step which has long been used for batch production of some Langmuir film systems. On a continuous basis the below mentioned exposure strategies provide additional utlilty.

When photo-sensitive insoluble particles, such as silver halides or other photographic film chemicals, are incorporated into the continuous Langmuir film during the dispensing proc¬ ess, then exposure to the appropriate electromagnetic frequencies using the below mentioned exposure stategies will result in a new method for continuous image generation. These electro- optical film transformations can be the final transformation before transferring the film to the substrate. They may also be followed by other film distorting transformations which will result in modifications in the image exposed once the film has been developed.

These photo-sensitive chemicals may also be incorporated into Langmuir films without light exposure until after they are transferred to the substrate. One may, for example, dispense photo-sensitive salts of differing light sensitivity and comb them into a marbled pattern using the programmable motorized combs mounted on a Langmuir conveyor trough. Once these films are transferred to photographic film or print paper, any image with which a photographer may expose them would have a structured marbled pattern within the exposed image.

In any case, the process must be conducted in darkness to avoid premature exposure of these photosensitive chemicals. In particular, the use of infared dryers should be avoided be¬ cause they also emit other frequencies of light.

Some surfactant systems are also light sensitive and can be chemically cleaved or cross linked upon photo-exposure. For example, a broad class of molecules known as spiropyrans exhibit photochomism. The molecules are stuctured in two orthoganal halves linked together by a commom tetrahedral sp3 carbon atom. One half, the benzopyran part is the common structure to all spiropyran compounds. The other part is the H heterocyclic structure and is variable. UV light in the 320-380 nm range will cleave the carbon-oxygen bond leading to colored isomers called "open form", as opposed to the "closed form" which is colorless. By careful selection of the H heterocylic structure, the spiropyrans molecule can initiate spreading within a Langmuir film upon cleavage with UV light. In addition to this light induced spreading, the photochromic effects of all spiropyrans molecules active within a Langmuir film may be used as another process variant in Continuous Dynamic Pattern Generation. The above discussion and additional insight into photochromic molecules may be found in Photochromism. Durr et al, Elsevier Press, 1990, page 314.

Some specific examples of spiropyrans which exhibit the above described spreading ef¬ fect are report by Eiji Ando, et al, of the Matsushita Electric Industrial Co. in the journal Langmuir, 1990, 6, 1451-1454. There, it is stated *'[w]e observe that the PMC forms of SP12, SP16, and SP18 showed better spreading behavior compared with the SP forms when the spiropyrens were spread on the subphase. It is suggested that the hydophobicity of the alkyl chain balances the hyrophilicity of ther zwitterionic chromophore in a molecule under UN irra¬ diation for SP12, SP16. and SP18."

As a method of Langmuir film transformation, the effect is locallized spreading after ex¬ posure if the effect of exposure is to increase the spreading pressure of the exposed surfactant or other spreading molecules. Conversely, films may be locally photo-exposed to eliminate the ef¬ fective spreading pressure of other surfactants. With the loss of spreading pressure in the ex¬ posed regions, the unexposed area expands until a new balance is reached within the film. These two methods of modifying Langmuir films provide another multipying effect to the number of structured patterns that a programmable Langmuir conveyor trough may produce. B.ό.a.l . Exposure Strategies

The below-mentioned exposure strategies used for the above-mentioned photosensitive systems are intended for photo enlargement, photo reduction, and direct image exposure. B.6.a.l.a. Strobed Projected Light Mask

A light, containing photo-modifying frequencies that transform the molecular structure of the surfactant in the Langmuir film is projected in a strobing manner through an image mask over a portion of the film. That portion is isolated from the other portions of the film by a shroud which extends to just above the film surface. The transformation of the surfactant can either enhance or inhibit the strength of said surfactant. By repeating the strobe pulses at differ¬ ent intervals relative to the conveyor speed, a variety of repeating film transformation effects re¬ sult. The intensity and frequency of the pulses as well as the image mask are characteristic variables of any continuous Langmuir film generation system. B.6.a.l .b. Coordinated Moving Film Exposure

This exposure strategy uses the same method as above with the exception that the film mask is a continuous film which is moved past the exposing radiation source at a rate coordi¬ nated with and proportional to the speed of the conveyor. The illumination can be strobed to expose image frames or a thin slit beam can project across a smoothly moving film. B.6.a.1.c. Strobed LCD Projection

A progammable image mask can be formed from a projecting liquid crystal display. By strobing the light source behind the array at a rate proportional to the conveyor speed while changing the image in the LCD mask at a rate coordinated with the strobe, a wide variety of electro-optical film transformations can result depending largely on the distribution of photo¬ sensitive chemicals in the Langmuir film at the point of exposure. B.ό.a.l.d. Coordinated Scrolling LCD Projection

By smoothly scrolling the LCD mask at a rate proportional to the speed of the continuous Langmuir film generation process, smooth, continuous electro optical film transformations result which depend on the image being scrolled, the distribution of photo¬ sensitive chemicals in the exposed portion of the Langmuir film, and the intensity of the illuminating source. A thin slit apeture which projects in the transverse direction of the Langmuir film is best used with a scrolling programmable mask which scolls in the longitudinal direction of Langmuir film movement. B.ό.a.l .e. Programmably Scanned Laser Spot

A laser beam can be scanned across the surface of the Langmuir film to induce the above mentioned electro optical film transformations. The relevant process variables which may be varied by the control system in coordination with the speed of the process are 1 ) the laser frequency 2) the power intensity 3) the pulse rate 4) the pulse duration 5) the spatial beam deflection in the plane of the film 6) the focus of the beam. C. Dispensing Subsystem

To programmatically generate heterogeneous Langmuir films, one needs a plurality of dispensing reservoirs to contain the many Langmuir film forming liquids and suspensions. These liquids must be delivered at the desired place and rate. To achieve programmable flexi¬ bility in this task to^" a degree compatible with the above mention programmable film transform¬ ers requires a programmable liquid dispensing and routing subsystem. Cl. Dispensing Vessels

The dispensing vessels should not chemically react with their, contents. If the contents are photo-sensitive they should serve as an effective filter to the exposing frequencies of hght. If the contents are not photo-sensitive, the vessels should provide sufficient translucence to discern the liquid level. Pressurized vessels are a cost effective means for dispensing such liquids, so the ability to maintain a pressure of approximately 10 psi or more is desired. C.2. Agitation and Fluid Mixing

Some suspensions will selltle and must be constantly agitated by a propeller, magnetic stirring bar or shaker table. Whatever method used it is best to avoid the introduction of air bubble into the agitated system. The dispensing vessle should be able to withstand the effects of whatever agitation system is used especially If it is pressurized.

Because the concentration of surfactant in the dispensed fluids is a critical process vari¬ able it is critical to be able to measure and control this concentration. Otherwise, interesting films can be produced but they can not be accurately reproduced at another time with a new batch of fluids. Minimally, a ring tensiometer should be used to measure the surface tension of each fluid dispensed on a standard area of the intended subphase. While more expensive by an order of magnitude, a Wilhelmy plate is an equal amount more accurate.

One may then pre-mix each concentration of surfactant within a liquid to bring the total spreading pressure of the mixure to the desired level. On a consistant basis this is best achieved by a recipe which will consistantly- bring the mixture to a point just above the desired surface tension as measured on the subphase liquid. One may then add drops of dilute surfactant to bring the mixture down to the desired level which is confirmed by direct measurement.

Another approach is to programmatically mix the desired surfactant concentration. For each distict liquid being used, mix two batches in separate vessles, one with minimal surface tension (maximum spreading pressure) and the other with no added surfactant, (minimal spread¬ ing preasure). The two fluids are then pump or pressurized such that a tube leading from each vessle meets in a three way mixing valve.

Downstream from this programmably controlled mixing valve, the outlet tube is con¬ nected to a programmabley controlled solenoid valve for on/off dispensing into streams or drops. Accurate liquid mixing valves which blend to liquids proportionally in respons to a programmable signal tend to be expensive. Nevertheless, this approach provides another dimension of programmable control to the generation of heterogeneous Langmuir films by providing a continuous range of spreading pressures for each fluid used. 3. Fluid Patch Manifold

Because the sequential transformation of Langmuir films in a continuous process can be flexibly controlled by computer without interrupting the process, it is important to design for a similar level of flexibility in dispensing a plurality of film forming liquids. One low cost ap¬ proach is to mannually patch the required dispensing vessel to the required dispensing valve. A second approach is a programmable liquid patching and routing system which can automatically change the liquids going to a particular valve. A third method is to plumb the dispensing needles of many liquid circuits to a manifold which is rapidly translated back and forth above the film surface in the transverse direction of subphase transport. A combination of the three approaches can best balance the cost and benefits of the three aproaches. a. Manual Liquid Patch Panel

A manual liquid patch pannel employs connector fittings with built in shut-off valves. By pannel mounting an array of connectors with automatic shut-off valves, one portion of the array is plumbed to the pressurised dispensing vessels and the other portion is plumbed to the dispensing solenoid valves. The appropriate connection is made by manually patching a tube with compatible shut-off connectors between the source connector and the connector leading to the dispensing valve. This manual liquid patch pannel is analogous to the manual electrical patch pannels which telephone operators once used. It is also important to be able to clear and flush each liquid line before patching a new liquid. To this end, the tube which pressurises each dispensing vessle is plumbed to a three way valve which can switch from a pressure source to a vaccuum source. The circuit which connects the control system to each dispensing valve may is also wired with a display light or LED and a manual switch.

To flush a line the dispensing vessle is switch to the vacuum source and the manual switch opens the dispensing valve. The liquid remaining in the line is litterally sucked back into the vessle. This approach is useful to avoid purging the lines into the process but is not advisable if the liquids being dispensed are for high purity LB films. The valves are turned off and the vessle is repressurised. Also present on this manual patch pannel is a three way valve which connects each pressurized vessel and a pressurized source of distilled water or other solvent. The output of this three way valve flows to the pannel mounted connector. Having suctioned the liquid circuit is is then flushed with water by switchin a three way valve to dispense water or solvent through the tube. Flushing commences once the dispensing valve is switched open again. b. Programmable Liquid Patch Panel

The functional mechanisms of the above described manual patch pannel can be auto¬ mated. The three way valves can be three way solenoid valves which are switched in sequence to accomplish the flushing operation. The patching can be automated using a network of three way solenoid valves which connects each possible source to a manifold which drains into each possible dispensing valve. This has the added optional benefit of mixing liquids by routing more than one source to one dispensing valve. Alternatively, a motorized, many position valve may be used to substitute for the network of solenoid valves, c. Rapidly Translated Dispensing Array

Another approach calls for mounting a dispensing needle from each liquid circuit in a closely packed arrangement and moving this array of needles rapidly back and forth in the transverse direction of subphase transport. Provided the control system is fed information on the position of the array, it can then coordinate the opening and closing of the dispensing valves so that the intended liquid reaches the intended place in the film. This approach is similar to a multi-colored Inkjet printer, however, precise registration need not be used. D. Subphase Circulation Subsystem

Langmuir film systems which require ultra-pure water or other subphase liquids and clean room conditions should not recirculate the subphase. For continuous marbling, recircula- tion is practical and desirable to reuse the subphase liquid.

1. . Reservoir Tank (Detail 2.m)

The subphase reservoir tank should be located at the head end of the Langmuir conveyor trough below the under side of the belt. This placement allows the tank to receive drainage from the drip tray (Detail 2.r) beneath the belt as well as the belt wiper (Detail 2.d). The top of the tank is best kept covered with a minimal opening to allow the belt scraped to descend beneath the tank liquid level. The inside surface of the tank should be phobic to the intended subphase but should not leach solvents, monomers or chemically react with the subphase or small quantities of the film foimϊng liquid.

2. Subphase Pump (Detail 2.1)

The subphase pump is connected to the reservoir tank (Detail 2.m) on the inlet side with a suction hose. The pump should not cause cavitation or bubbles to form in the subphase liquid, nor is pulsation desireable. A flexible impeller pump is appropriate for polysacharride solutions. Positive displacement pumps are also suitable but are more expensive. The pump should be driven by a variable speed motor or connected through mechanical linkages to the conveyor motor. The outlet of the subphase pump is connected to the subphase weir (Detail 2.e).

3. Subphase Weir (Detail 2.e)

The subphase weir is designed to distribute the subphase in a uniform layer across the transverse dimension of the Langmuir conveyor trough while forming a liquid tight seal between the weir and the troughing conveyor belt. For some subphase materials, it is also designed as a bubble trap and may also be equiped with a surface skimmer. The exit oriface of the weir should be adjustable in the vertical dimension if more than one subphase or process speed is anticipated.

4. Subphase Skimmer and Disposal System (Detail 2.f, elaborated in Figure 10)

The subphase skimmer is used for systems which recirculate the subphase and for im¬ proving the waste disposal of all systems with subphase depth greater than 3mm. It consists of a scraper boom (Detail lO.a) constructed of a flexible rubber or flourocarbon strip mounted on a ridgid surface (Detail lO.d). It functions like a ploughing squeegee. As film material builds up in front of the scraper, it rises to a level which contacts several suction tubes (Detail lO.b) at regular intervals across the width of the machine. The level of the suction tubes should be such that they would not suction the subphase if the scraper were not present, while being as close as possible to the film surface. E. Web Path Control

1. Unwind Station (Detail La)

The unwind station for continuous webs of substrate material includes a mechanical or pneumatic roll chuck, a stand which mounts the roll parallel to all other rolls in the process, and a tension brake for maintaining adequate tension in the zone between the unwind roll and the speed control rolls.

2. Drive Rolls (Speed Control rolls, Detail 1.b)

This process has two primary tension zones: the one between the unwind stand and the drive rolls and the one between the drive rolls and the rewind stand. The rewind stand pulls the web through the process. The drive rolls pull the web from the unwind stand and release it to the rewind stand. Hence the speed of the web is controlled by the speed of the drive rolls. The driven roll should be rigid and the opposing roll should be slightly compliant, for example a high durometer rubber coating a metal roll. Roll diameters are determined by the roll width. As the roll width increases so must the roll diameter to prevent flexing of the rolls. One way to hold the rolls together with an appropriate force is to use fluid controled cylinders to press the compiant roll against the ridgid roll. An adjustable stop mechanism should be provided to adjust the gap between the rolls in the unthreaded state to enable webs of various thicknesses to be driven without crushing them.

S-wrap rolls are also an option although they are sometimes less accurate than driven nip-rolls.

The drive motor is a variable speed motor and is driven at a speed proportional to the speed of the conveyor. Ususally, the linear film speed and the web speed are identical.

3. Guide Rolls (Detail l.o)

Undriven idler rolls are used throughout the process to guide the web from one process¬ ing step to another.

4. Coater Roll (Detail 1.f and 2.q, elaborated in Figure 5)

The coater roll is an idler roll (Detail 5.g) mounted on a translatable stage (Detail 5.e) which moves in the film plane, along the axis of the conveyor's motion, under computer control of a linear actuator (Detail 5.b). The roll may also be moved into tangential contact with the film by any linear actuator which brings both ends of the roll out of contact with the film when the web stops. One low cost method for achieving this is to connect pneumatic cylinders (Detail 5.c) which control the up and down motion of the coater roll together with a pneumatically actuated clutch placed between the drive roll motor and its speed reduction gear box.

5. Low Friction Slider Plate/Water Baffle

The rinse chamber (Detail l.g) is composed of two parts: an upper shroud with an array of gentle fan-jets, and a lower catch tray which diverts the rinse water to gutters on either side of the web. The catch tray must slope to one side or the other or be shaped like an inverted "V". In either case the web must not contact it. The downward sloping angle of the web must be gentle enough to prevent a high velocity boundary layer of rinse water from disturbing the deposited Langmuir film. A problem thus arrises at the end of the drip tray. Water must not be allowed to fall onto the under-side of the web as it loops back over the blow-off roll. One solution which allows for a gently sloping rinse chamber is to have the web contact a low friction slider plate which overhangs the blow-off roll. This plate catches any water which might have dripped onto the back side of the web and diverts it either backward toward the catch tray or forward over the front of the blow-off roll (Detail 6,b) and into the blow-off chamber (Detail 1.h, elaborated in Figure 6).

6. Blow Off Roll (Detail 6.b)

The blow-off roll is an idler roll which is used as a blow-off surface for the air-knife (Detail 6.c) to remove the excess water from the rinsed web prior to drying. The blow-off chamber is a duct which wraps around the blow-off roll to create a high velocity air stream directed upward from the airknife and continuing into a filtered suction duct (Detail 6.a.3) at the top of the blow-off chamber. The low pressure created by the suction hood allows the web to enter and exit the blow-off chamber as it wraps around the blow-off roll without being splashed by water spray generated by the air-knife. The diameter of the blow off roll should be approximately 10cm or more.

7. Drying Chamber (Detail 1.i)

Immediately following the blow-off chamber the web passes through a drying chamber. The method of drying can be hot-air, infared, an ultrasonic hot air-knife or any other industry standard method. Some highly reflective coatings such as those with a significant gold content are not well dried by infared heaters. Similarly, photo-sensitive webs are best dried by hot air to avoid the visible spectrum associated with infared dryers. The water vapor produced by the drying process must be carried away in a suction duct to avoid condensation and dripping onto the web near the dryer.

8. Optional Chiller Roll

At higher speeds the web may not have sufficient time following the dryer to cool before the coated surface contacts the first idler roll following the coating process. This can lead to a fragile coating being damaged by the idler roll. It is common in conventional printing to use a chilled idler roll following the heater as a solution to this problem. The chilled roll is especially appropriate for this process when the coating contains thermoplastic particles or when the web speed is high and the distance between the dryer and the first contacting idler is too small to provide ambient air cooling. 8. Guided Rewind Station (Detail 1.1)

A conventional guided rewind stand with a sensed tension control clutch is used to pull the web through the process at speeds governed by the web drive rolls.

F. Insolublizer Coating Subsystem (Detail 1.c)

The deposition of LB films onto a substrate requires careful surface preparation of the substrate. The preparation recipe depends on the film and substrate. Techniques for substrate preparation are generally known, as illustrated for example by Langmuir-Blodgett Films. Ed: Roberts, G., Plenum Press (1990), the teachings of which are incorporated herein by reference.

In connection with a system according to the invention, preparation is preferably done to the substrate prior to coating or may be incorporated into this process as an integral step up¬ stream from the coating step. Similarly, for continuous marbling the surface to be coated is first coated with a reaction insolublizer which binds the film onto the substrate in a chemical reaction resulting in a thin, transparent, insoluble layer. Non-toxic, inexpensive and effective, alum sulfate is the reaction insolublizer of choice for continuous marbling and marbling in general. However, any other reaction insolublizer appropriate to traditional batch marbling is also appropriate for continuous Langmuir coating of marbled films. Again, the coating of the reaction insolublizer can be done separately before film deposition or it can be performed inline.

1. Coater Boat

The liquid bearing the reaction insolublizer is kept at a constant level and continuously replenished in a coater boat into which a coater roll is partially submerged. The coating can be applied via a nip roll coater, a kiss coater, or submersion coating.

2. Dryer (Detail l.d)

The solvent bearing the reaction insolublizer must be evaporated prior to film reaction coating. Water is the solvent for alum sulfate and has clear environmental advantages over hy- docarbon solvents. However, hydocarbon solvent born coatings may also be used. If so, care must be taken to treat the evaporated gasses before release into the air. The heat output of this dryer depends on the web speed, the absorbancy of the web, and the thickness of the applied coating. In any case, the web must be dried prior to reaction coating.

G. Rinse Subsystem

Some subphase liquids can be completely evaporated while others contain molecules which modify the rheological properties of the liquid. The latter variety must be gently rinsed from the web surface prior to drying. 1. Rinse Chamber (Detail 2.g)

The rinse chamber consists of three parts: the removable top cover, the spray manifold, and the lower catch tray. The top cover is designed to seal with the lower catch tray to form a rinsing tunnel through which the coated web passes with the coated side facing up. The spray manifold is suspended to the removable top cover with the array of spray nozzles oriented to gently spread a large volume of water evenly over the web surface without erroding the still fragile coating. Fan-jets under low pressure ( 20 psi ) work particularly well especially when gently pulsated. The top cover should be hinged on one side to allow access to the chamber for threading the machine. Pneumatic cylinders are one useful way to pivot the top cover while threading the web path. The lower catch tray can be sloped to one side or symmetrically sloped in the middle like a peaked roof. In either case the entire chamber must gentley slope in the di¬ rection of the blow off chamber to allow a slow gravity flow of rinse water to continuously drain the catch tray and the web surface into the blow-off chamber.

2. Water Circulation System

The rinse water can be in a closed loop which is filtered. It consists of a holding reser¬ voir, a pump with protective float switch, a filter, and plumbing to connect it to the spray mani¬ fold- The drain from the blow-off chamber feeds into the rinse water reservoir. Some viscosity modifiers in the subphase can be continuously broken down in the closed loop rinse system by using digestive en-gαnes- Another technique is to passing the rinse water through a UV sterili¬ zation system which causes some viscosity modifiers to cross-link and precipitate out of solu¬ tion. The precipitates are then trapped in the filtration system.

3. Blow-Off Chamber (Detail 1.h, elaborated in Figure 6)

The purpose of the blow-off chamber is to use a carefully directed high volume air stream to mechanically remove as much rinse water from the web as possible without damaging the coating or filling the surrounding air with water mist. An air-knife (Detail 6.c) within the chamber is aimed at an idler roll (Detail 6.b) which guides the web with the^' wet, coated side exposed. A duct (Detail 6.a.l), which closely follows the contours of the idler roll, guides the air stream into an upper chamber which is vented with a suction hood (Detail 6.a.3). In the top of the suction hood is a mist elimination filter which coalesces most of the air mist. The condensed mist drips down into guide rails(Detail 6.i) which shunt the water away from the web toward drain scuppers (Detail 6.j) leading back to the lower chamber (Detail 6.a.2). The lower chamber serves as a catch basin for the condensed mist and the flow from the rinse chamber. The lower chamber is plumbed at the bottom to a drain pipe (Detail 6.g) leading to the rinse system reservoir. H. Drying Subsystem (Detail 1.i)

After passing through the blow-off chamber, the web is no longer dripping wet. but the coated side requires an energy input for drying. Infared. hot air, and hot air with ultrasonic boundary layer disruptors are commercially available techniques for web drying. Given the relatively slow web speeds. Infared dryers are easily controlled for variable output Hot air is preferred if the coating is light sensitive. The process control computer should be programmed to vary the dryer output to proportionally match the web speed given a factor for the water satu¬ ration of the coating and substrate. I. Coordinated Motor Controls of Conveyor. Web. and Subphase Pump The process control computer is preferably programmed in a manner conventional in the art to maintain a constant velocity for the Langmuir conveyor trough. All other proportionally controlled elements are driven at speeds related to the conveyor speed.

1. Mechanical Linkages

Timing belts which link the conveyor drive motor to the web drive rolls and subphase pump are one method to maintain the correct proportional control.

2. Electronic Motion Control

A more flexible system employs micro-processor controlled motor drives capable of re¬ sponding to a speed signal from the process control computer or from other motor drives. In particular it is some time advantageous to run the web speed faster or slower than the conveyor. Mechanical linkages are less flexibly controlled for this requirement. J. Control System - The Process Control Comptuer

The primary control elements of the process control computer are the on/off dispensing valves, the conveyor motor speed, the pump motor speed, the web drive motor speed, the heater output, and the variable speed and variable position elements of the film transformers, as well as the actuators which lift and lower pattern transformers into and out of useful range of the floating film. Optical and electrical pattern transformers may also be controlled by this computer. If the motor drives are intelligent and accept an external speed signal, they should be connected together with the conveyor motor drive serving as the master drive which accepts its signal from the process control computer.

The process control computer preferrably stores and plays back recipe files of parameters which determine each pattern and the amount to be produced. More preferably, the system provides the flexibly to permit the creation of new pattern parameter files and to automatically switch from one to the other when the preceding batch has been completed.

The progammability of the pattern transformers coordinated with the control of the overall process coupled with a computer based control system for scheduling and generating the type and length of each pattern is among the features that distinguish this system as a uniquly flexible manufacturing system for the high speed generation of distortion free marbled patterns and other Langmuir films which are transferred to a solid substrate.

The process control computer can be a special purpose hardware device but, preferably, is a general purpose digital data processor programmed, using conventional numerical control techniques (with software packages such as the L/T Control from Laboratory Technologies, Inc., Wilmington, MA), to control the operation of the aforementioned system components to provide the operationality and functions described above. 1. External Input/Output Circuits

All dispensing valve solenoids and film transformer solenoid actuated pneumatic circuits should be switched from the process control computer using programmable, optically- isolated dry contact switches connecting each circuit to an appropriately rated external power supply. Other control circuits are for sending analog signals or serial line data to the appropriate actuator. The process control computer must be equiped with a sufficient number of such channels which are addressable from the software system to accomodate the total number of devices under analog and digital control. Standard field wiring connects the devices to the control system's wiring termination pannels. 2. Power Supplies

Several AC and DC electric power supplies must be available for switching power to the total mix of devices under control. Careful purchasing of the devices can minimize the number of different power supplies required to only a few.

Listing of Components Shown in Application Drawings

Figure 1 a. Web unwind station with tesion brake to control tension between unwind station (1.) and drive rolls (2.) b. Drive rolls, motor driven of the nip roll or S-wrap roll variety c. Coater station for inline coating of reation insolublizer most ofter potassium aluminum sulfate in an aqueous solution d. Dryer for reation insolublizer coating station vented by blower ducts to transport steam or other vapor for safe handling e. Coating web loop for optional actuator driven coating density distortion known as "California Wave" f. Driven coater roll assembly descibed in detail in Figure 4 g. Two piece rinse chamber consisting of upper shroud with rinse nozzle array and lower catch tray with side gutters. The hinged upper chamber pivots away to provide access to the web path for threading the machine. Water is the preferred solvent but others are possible depending on the subphase. h. Rinse solvent blow-off chamber depicted in detail in

Figure 6 i. Web dryer for drying rinse solvent dispensed in (7.) j. Bowed roll for eliminating wrinkles which may be induced during web drying, k. Tension sensor for controlling tension clutch which drives rewind stand 1. Web rewind stand with tension feedback clutch and edge guide, m. Langmuir conveyor trough depicted in detail in Figure 1. n. Web handling frame o. Idler rolls for web path control

Fi ure 2 a. Langmuir conveyor trough frame ^• b. Tail pulley c. Head pulley d. Belt wiper e. Extrusion weir f. Suction scraper g. Modular tooling plates h. Endless conveyor belt i. Vibration isolation base j. Drive linkage k. Drive gearmotor

1. Subphase pump m. Subphase reservoir n. Dispensing valves for film forming liquids

0. Linear actuator for dispensing orifices p. Film transformers q. Actuated web transfer mechanism r. Troughing take-up ramps s. Constant inclination troughing ramps or rails t. Troughing let-down ramps u. Drip tray

Fi ure 3 a. Transverse support bar b. Suspended component support bar c. Gear motor support bar d. Z-axis lift cylinders e. Gear motor with electrical connection to motor controller not shown. f. Shaft bearings g. Idler pulley shaft h. Driven pulley shaft i. Shaft coupling between gear motor and driven pulley shaft j. Driven timing belt pulley k. Idler Timing belt pulley

1. Timing belt with attached combing tines on outside m. Fine thread connecting rods for adjustable spacing between support bars.

Figure 4 a. Transverse support bar b. Suspended component support bar c. Gear motor support bar d. Z-axis lift cylinders e. Gear motor with electrical connection to motor controller not shown. f. Shaft bearings g. Timing belt pulleys h. Timing belt i. Rotary shaft j. Combing discs k. Disc spacers

1. Shaft assebly compression nuts m. Adjustable fine thread connecting rods between 1. and 2.

Figure 5 a. Parallel linear bearing slides with tapped holes for tooling attachment b. Linear actuator with position feedback sensor for computer control of actuator position. c. Z-Axis cylinders for lowering coater roll into contact with Langmuir film d. Pivoting rod eye for connecting Z-Axis cylinders with dead shaft idler coater roll e. Main support tooling plate drilled for fastening to slides, coupling to linear actuator, and mounting of Z-Axis cylinders f. Coater roll shaft with shaft collars g. Coater roll with internal bearings h. Coupler plate connecting main support tooling plate (5.) with linear actuator (2.) i. Flexible coupling connecting linear actuator (2.) with

(S.) j. Modular fixturing plates running parallel along the

Langmuir conveyor trough

Figure 6 a. Rinse solvent blow-off chamber shroud divided into

1) Lower chamber which serves as a solvent reservoir and contains ducting for air-knife blow-off of the web against the blow-off roll (2.)

2) Middle chamber which ducts the air upward and ducts the rinse solvent downward to the lower chamber (a)

3) Upper chamber which ducts the mist saturated air through a mist coalescing filter and provides an attachment point for the suction blower duct. b. Blow-off roll, an idker roll of 10cm or more diameter c. Air-knife d. Air-knife supply duct. e. Mounting plate and access port for air-knife f. Air-knife stand-offs for X-Axis adjustment g. Solvent return drain h. Blow-off duct i. Dϊverters to shunt coalesced solvent to drain skuppers

(8.) j. Drain skuppers to provide solvent drain from middle chamber into lower chamber while preventing significant air flow via this opening k. Access port in side of Blow-off chamber shroud

Figure 7 a. Single use conveyor belt unwind stand b. Idler guide rolls c. Langmuir conveyor trough tail pulley d. Langmuir conveyor trough e. Langmuir conveyor trough head pulley f. Single use conveyor belt rewind stand g. Single use subphase reservoir, unused h. Single use subphase reservoir, used i. Zone of quiescence j. Weir k. Air-Knife

1. Suction hood

Figure 8 a. Transverse support bar for converging side wall drive assembly b. Shaft bearings and collars c. Drive gear-motors d. Drive rolls e. Idler rolls f. Flourocarbon tape loop with registration marks g. Registration sensor for accurate speed control h. Cross section of tape and rollers illustrating guided _\ contour i. Transvers support bar for converging side wall idler assembly, slotted for adjustable conver- gance angle

Figure 9 a. Support frame b. Electrical insulators c. V+ conduction strip d. V+ tinsel brushes e. Electronic embossing roll, electrically coducting relief surface or an insulated cyllinder f. Insulating roll shaft g. Drive motor h. Roll surface i. Air gap j. Langmuir film k. Subphase liquid

1. Conveyor belt m. Grounded conveyor bed (Vo)

Figure 10 a. Flexible, flouro-carbon. scraper boom b. Suction tubes c. Wide-toothed baffle d. Rigid surface for mounting flexible scraper boom e. Suction manifold

Summary

The foregoing describes improved methods and apparatus for depositing insoluble monolayers and complex Langmuir films on continuous substrate webs. Those skilled in the art will appreciate that the illustrated embodiment is exemplary and that forther embodiments, in¬ corporating modifications thereto, fall within the scope of the invention of which I claim:

Claims

1. An apparatus for the continuous generation of Langmuir and Langmuir-Blodgett films comprising '

A. a troughing slider bed conveyor with an endless belt,

B. means for delivering a subphase liquid to the liquid-extruding orifice at a rate proportional to the speed of the conveyor, such that the desired depth of liquid is maintained without flow relative to the troughing belt,

C means for delivering Langmuir-film forming liquids and suspensions to the sur¬ face of said subphase liquid at a rate proportional to the speed of the conveyor, so as to maintain predetermined film thickness, and

D. transfer means for transferring said film to a solid substrate.

2. An apparatus according to claim 1, comprising film modification means disposed above said Langmuir film-coated surface, at a point downstream from said delivery of that film, for modifying a structure of that film.

3. An apparatus according to claim 2, wherein said film modification means includes means for modifying a structure of that film to create a decorative effect.

4. An apparatus according to claim 2, wherein said film modification means includes means for modifying a structure of that film to create a compressed Langmuir film structures, including, but not limited to, an insoluble monolayers, bilayer, vesicles.

5. An apparatus according to claim 1 , wherein said transfer means includes means for transferring said film to a solid substrate by dipping the substrate in said fluid while moving the substrate in substantially the same direction and speed as the conveyor belt.

6. An apparatus according to claim 5, comprising transfer means for dipping said moving substrate in fluid in at least one of a horizontal and vertical direction.

7. An apparatus according to claim 1 , wherein said substrate comprises any of discrete ob¬ ject or a continuous web.

8. An apparatus according to claim 6, wherein said continuous web is coated with a reaction insolublizer which reacts with surfactants or other constituents of the Langmuir film to form an insoluble binder

9. An apparatus according to claim 8, wherein said reaction insolublizer is potassium alu¬ minum sulfate. ammonium aluminum sulfate, or aluminum sulfate.

10. A method for continuous generation of Langmuir and Langmuir-Blodgett films comprising

A. delivering a subphase liquid into a troughing slider bed conveyor with an endless belt such that a desired depth of liquid is maintained without flow relative to the troughing belt,

B. delivering a Langmuir-film forming composition to the surface of said subphase liquid at a rate proportional to the speed of the conveyor, so as to maintain predetermined film thickness, and

SUBSTITUTE SHEET C transferring said film to a solid substrate, and D . removing said substrate from said fluid for fixation of a film pattern left thereon.

11. A method according to claim 10, comprising modifying a pattern of said Langmuir film at a point downstream from its delivery onto said surface of said subphase liquid.

12. A method according to claim 10, wherein said modifying step includes modifying a structure of said film to create at least one of a decorative effect, such as marbling, a compressed Langmuir film structures, such as insoluble monolayers, bilayer, vesicles, and other complex Langmuir film structures.

13. A method according to claim 10, wherein said transferring step comprises dipping said substrate into said fluid while moving the substrate in substantially the same direction and speed as the conveyor belt.

14. A method according to claim 13, comprising dipping said moving substrate in fluid in at least one of a horizontal and vertical direction.

15. A method according to claim 14, comprising selecting said substrate to be any of a dis¬ crete object and a continuous web.

16. A method according to claim 15, comprising coating said web with a reaction insolub¬ lizer which reacts with surfactants or other constituents of the Langmuir film to form an insol¬ uble binder.

17. A method according to claim 16, comprising coating said web with potassium aluminum sulfate, ammonium aluminum sulfate or aluminum sulfate.

SUBSTIT