GB2106836A - Preprinted master sheets and continuous process for producing same - Google Patents

Abstract

Master sheets having image-to- image registry of material printed on both sides of such masters and produced by a continuous printing process. An offset, letterpress, gravure, of flexographic printing process 12 is used to print images on one side of a continuous web 11. On the opposite side of the web reverse images are printed in registry with the images on the first side of the web using a rotary screen press 22 and a fluid hot melt or solvent-based ink. After printing, the web is cut into individual masters which are then stacked or collated and assembled into booklets. The masters can be used for spirit duplicating processes or iron on transfers. The first-side printing may be omitted. The web preferably enters a rotary screen printer horizontally, and leaves it inclined upwardly at an angle of 0.5 DEG to 6.0 DEG to the horizontal before being cut. Protective material 36 may be applied to the master image. <IMAGE>

Description

SPECIFICATION Preprinted master sheets and continuous process for producing same This invention relates to preprinted master sheets and a method for making masters for example for spirit duplication system and iron on transfers, and, more particularly, to a method for printing a continuous web on one side using a standard printing press and on the other side with a hot melt ink or solvent-based ink using a rotary screen press.

Spirit duplicating is a widely used process and is especially attractive because of its low per copy and equipment costs and because no special training is required to operate or service the equipment. It is a tool frequently used by teachers and instructors for producing copies of tests and instructional materials. Typically, a master or master copy is made which is in turn used to produce plural copies as required.

Generally, a spirit duplicating master includes a substrate, usually paper, carring an ink mirror image of the material to be duplicated. The ink, such as for example a hot melt ink, on the master contains a spirit or alcohol soluble dye which when pressed into momentary printing contact with a sheet of paper which has been previously wetted with a spirit or alcohol solution transfers dye from the master to the sheet. With each copy made, some of the ink from the master is used. In order to have a relatively long copy run life and to print legible copies, the master must have a relatively thick and uniform ink image thereon, and the image must have sharply defined edges.

Initially, the masters were individually made from a transfer sheet having a surface coating of a spirit duplicating material. Using a typewriter, for example, some of the material on the transfer sheet was transferred to a sheet overlying the transfer sheet by striking the overlay sheet and causing the ink to be crash printed on the overlay sheet.

It is also known to preprint spirit masters with an appropriate ink composition. One reason for doing so is so that the teacher can use such preprinted masters to make copies for students on a given subject without having to compose the assignment itself. That is, images (text, math problems, etc.) are reverse printed with spirit duplicating ink directly onto the back side of a sheet to form a master, rather than being made by a transfer technique at the time of teacher test preparation. Other uses of the preprinted masters include the hobby craft and areas where the masters are used to produce images on wood, ceramic, fabric, leather, etc. and in the amusement area for producing images in colouring books, as games, etc.

Such preprinted spirit duplicating masters may also have images printed in the normal manner on the front surface of the master in substantial registry with the reverse printed images on the back side.

The front surface printing provides the user with a visible, easily read portrayal of the reverse printed images.

With preprinted duplicating masters, however, the ink often bleeds through the paper to the front surface giving a "halo" effect to the image on the front surface. This is particularly objectionable in the preprinted master field since such masters are mass printed months or even years in advance of use, and thus, must be stored for long periods of time. The longer the period of storage, with changes in humidity and temperature taking place during this time, the more change of a "halo" occurring. Under some circumstances the "halo", if severe enough, renders the sheet aesthetically undesirable and even unacceptable because the printing on the front side of the sheet is obscured and rendered unreadable by the "halo".

At present, one solution to the "halo" effect is to utilize non-bleeding ink compositions such as those taught by Panken, U.S. Patent No. 3,962,526 and 4,005,237 and optionally to treat the paper with an oleophobic material to resist bleeding. Another solution to the "halo" effect is to obtain as close registry as possible between the printing on the front surface and the spirit duplicating ink reverse printed on the back side in a discontinuous printing process.

Offset-silk screened sheets have been prepared on a batch basis. In a batch process each of the printing steps on a given "batch" of individual sheets is handled by different operators: an offset printing operator, a silk screen printing operator, a cutter, an assembly step, etc. This can lead to material waste and lost personnel time.

Also of interest in that regard is Guthrie, U.S.

Patent No. 3,336,864, which discloses a silk screen printing device which allows a first image to be printed on the surface which will support the paper being silk screened. The paper is then placed over the ink impression on the surface. The screen is then placed over the upper suface of the paper and ink is again applied and the subsequent pressure applies inkto both sides in correct registry. This is, of course, a batch process.

Additionally, there still are often severe registry problems with such batch processes. Since the printed sheets may be thin and/or transparent, the inks, to the extent they are to be the reverse of the printing on the front side, will show through and will appear out of focus with the figures and printing on the front surface if they are not in precise registry.

Generally, the lack of precision of registry comes about because each sheet must be handled individually be different operators and by different pieces of printing equipment in the different printing steps.

It would be more desirable to continuously print an ink, particularly a spirit duplicating ink, onto the back side of a sheet in registry with the printing on the front surface. But traditional continuous printing processes are inadequate for that purpose. Twosided continuous printing, such as shown in Florin Leclerco, U.S. Patent No. 530,831, does not involve registry and cannot be used with spirit duplicating inks. Ordinary relief printing processes, such as conventional letterpress and flexographic printing, do not apply sufficient ink for preprinted spirit duplicating masters. The ink squeeze out tends to result in a bead at the periphery of image elements but a low level of ink within character strokes. A continuous process for printing spirit duplicating masters is disclosed by Dadowski, U.S. Patent No.

4,152,986 which utilizes a raised relief printing area formed by the exposure through a half-screen of a photosensitive printing plate. However, this process also suffers from the inability to produce a uniform ink image of sufficient thickness and sharpness.

Typical intaglio printing processes, such as rotogravure, are not economically feasible for short run copy production.

Accordingly, the need exists in the art for a continuous, economical method of printing inks to a uniform thickness and sharpness onto master sheets that will yield the number of copies desired, and yet will overcome the problem of registry with printed images on the opposite side of the paper.

The present invention meets that need by providing a method for printing one side of a continuous web by offset, letterpress, gravure, orflexographic means and the other side by means of a rotary screen press. The method of the invention is fast, efficient, and economical because of a larger quantity of master sheets can be made at a higher rate of speed and with fewer personnel than can be achieved by a "batch basis" printing process.

Moreover, by making masters by the process of the present invention, the problem of registration of the printing on respective sides of the web, a frequent problem in printing such masters, is overcome.

In accordance with the process of the present invention, a continuous web of material, such as paper or fabric, to be printed is passed to a first printing station where a desired pattern, design, printing, or image is printed using either an offset, letterpress, gravure, or flexog raphic printing process. Optionally, more than one printing station can be utilized to print different portions of the desired pattern, design, or printing orto print using different coloured inks. The printing on the first side of the web can take place eitherfrom above or below. If the web is first printed from above, then the web must be inverted (such as by use of conventional turn bars) prior to printing on the opposite side. In either event, the second side to be silk screen printed is, thus, positioned so that it faces upwardly.

The web is then passed to a second printing station where the opposite side of the web is printed in reverse image using one or more rotary screen presses. In the rotary screen press, the web is passed between a pair of rolls. The upper roll is a hollow cylindrical screen on which the reverse image to be printed has been prepared. The ink, such as a fluid hot melt material or a solvent-based ink, is supplied to the interior of the upper roll and is squeezed out through the screen in controlled amounts to form the printed image of desired thickness on the web. In a preferred embodiment, the lower roll on the rotary screen press is magnetized and controls the presure exerted by a magnetic squeegee blade or roll-rod inside the upper roll which forces the ink through the screen.

After the web is printed in this manner, it may then be cut into individual sheets or masters. Additionally and alternatively to the cutting of the continuous web into individual sheets, processing steps which can be performed to or with the web include rolling up the continuous web, spraying the rotary screen printed sides of the sheets with a protective material, putting the printed sheets in envelopes, interleaving or joining additional sheet material, binding the sheet with protective sheets to form a set, etc. The additional sheet material can be a protective sheet, such as tissue paper, wax paper, silicone impregnated paper, glassine, plastic sheet material, or the like, or could be any othertype of coated paper.

When a spirit duplicating ink is screened onto the reverse side of the web, it may be desirable to place a protective sheet over it by stapling, gluing, embossing, adhesive bonding or the like. In such cases, it may be desirable to perforate the printed sheet so that it may readily be torn or separated from the protected sheet. The masters in this form may then be collated into a booklet.

Because the web is continually gripped and is in a state of tension as it passes through the continuous web printing process and apparatus of the present invention, the registration of the two images printed on the two sides of the web is achieved primarily by controlling the speed of the web and the timing of the printing steps. The reverse image on the rotary screen is positioned using a pin registration system on the end ring of the screen to align accurately that image with the image printed from the previous station. Thus, once the speeds of the printing steps are set in timed sequence, the images printed on the web should be in registry.This registry may be further maintained by conventional web perfecting techniques such as use of web guides and automatic registration check means which sense marks printed on the web at the first printing station and then adjust the timing of the second printing sequence accordingly.

The method of the invention provides a fast, efficient, and economical method and apparatus for producing improved preprinted masters by printing one side of a continuous web with an offset, letterpress, gravure, or flexographic print and the reverse side with a screened ink from a rotary screen press in image-to-image registry with the printing on the first side of the web.

Figure lisa schematic illustration of the continuous process of the invention; and Figure 2 is an elevational view of the apparatus for performing the process of the invention.

The present invention will be described wih respecs to a system for printing spirit duplicating masters although it will be apparent to those skilled in the art that the process of the present invention may be modified somewhat to produce imaging on other substrates such as cloth or to produce iron on transfers or pressure transferable masters for arts and crafts applications.

Referring to Figure 1, a roll 10 of a continuous web material 11, such as paper, is fed continuously past a first printing station 12 where the first side of web 11 is printed with a desired pattern or image. Printing station 12 may utilize either an offest, letterpress, gravure, or flexographic printing process. Optionally, more than one printing station can be utilized to print different portions of the desired patterns or images or to print such patterns or images in different colours. The printing may take place either from above or below the web. In an alternative embodiment of the invention, a blank plate may be utilized at the first printing station so that the first side of the web is not printed.

However, if the upper side of the web is printed, it must be inverted prior to the next printing station. To accomplish this, web 11 is inverted by a web inverter means 14. Web inverter means 14 consists of a turn bar 16 at a 45 angle to the direction of web travel, a guide roller 18 normal to the direction of web travel, and a turn bar 20 which is at a 45O angle to the direction of web travel and a 90O angle to turn bar 16.

After passing through web inverter means 14, the unprinted side of web 11 is exposed upwardly.

Alternatively, if at the initial printing station the images or patterns were printed onto the underside of web 11, the need for web inverter means 14 is eliminated.

The web is then passed to a second printing station 22 where the opposite side of web 11 is printed in reverse image using one or more rotary screen presses. In the rotary screen press, web 11 is passed over guide roll 24 and fed through the nip between upper screen roll 26 and lower magnetized roll 28. Upper roll 26 is a hollow cylindrical metal screen having a high mesh count and a high open area such as 185 Penta screen, available from Stork Brabant BV, Boxmeer, Netherlands or a 140 Topaz screen, available from Nickel Mesh Co. Greer, South Carolina. Other mesh screens are also useful in the practice of the present invention. Such screens include regular screens above 80 mesh count up to 255 Penta or Topaz screen. A preferred screen for use in the practice of the present invention is a 140 Topaz screen.A reverse image 30 is put on the screen of roll 26 by standard screen preparation techniques, which basically are: coating the screen with a photopolymerizable emulsion, exposing the emulsion through a positive mask of the image, washing away the unexposed portion of the emulsion and any excess emulsion, and then drying the emulsion coated screen.

In a preferred embodiment of the invention, a Model MW-RS rotary screen press, available from Johannes Zimmer of Klagenfurt, Austria us used.

This press is described in more detail in U.S. Patent Nos. 3,942,438; 3,919,973; 3,921,520; 3,949,667 and 3,949,666. In that press, a magnetic doctor blade or roller rod is positioned inside upper screen roll 26 and applies the pressure on the ink inside the screen to force it through the screen openings. Lower magnetized roll 28 controls the amount of pressure applied by the doctor blade or roll rod. However, other rotary presses can also be used in the practice of the present invention. Such presses are available from Precision Products Co., Hawthorne, New Jersey, Buser Co., of Switzerland, and Reggiani Co., of Italy.

To print the reverse image, generai types of spirit duplicating inks may be used. Typically, a fluid hot melt ink is supplied to the interior of the screen on roll 26 and then is squezzed out through the openings in the screen onto the web. The hot melt ink will include a visible dye such as Crystal Violet, a wax such as a carnauba, spermacetti, or candelilla wax, a wetting agent such as lecithin, and one or more oils such as mineral oil orcastoroil.Alterna- timely, solvent-based inks may also be utilized. The spirit duplicating masters can be printed on almost all types of paper including coated and uncoated and trea.ted and untreated papers.

If a hot melt ink is used, the press is modified somewhat to provide for a heated ink supply reservoir. Heated air is supplied to the interior of the screen at a temperature (which may range from ambient to 800 F, and is preferably around 550 F for the preferred hot melt spirit duplicating ink) sufficlient to maintain the ink fluid during printing. Such air may be supplied to the opposite end of the screen from the ink supply inlet.

Image-to-image registry between the two printed sides of the web is achieved by use of a pin registration system at the second printing station as well as conventional web perfecting techniques such as web guides. Moreover, the repeat lengths of the print rolls in printing stations 12 and 22 can be sized so that they have the same lengths and the image portion on the rotary screen can be located at a prdetermined initial position using the pin registration system. Because the process of the present invention provides for continuous controlled web movement, image registry is much more readily achieved than with prior batch-type printing operations.

Roll speeds through the process may be set at up to approximately 650 web feet per minute, and are preferably around 200 ft./min. Roller pressures for both printing stations 12 and 22 are conventional for the respective type of printing operations involved, and may, as is also conventional be varied according to web speed ink temperature, image thickness desired, etc.

Once web 11 has been printed it exits the rotary screen press atan angle inclined slightly upwardly from the horizontal, preferably from 0.5% to 6.0%, for satisfactory printing results. A roll 31, positioned immediately following the exit of the web from between rolls 28 and 30, provides the slight upward inclination which results in a heavier laydown of ink onto the web and improves image quality.

The web then may be cut up into individual sheets rolled up for later processing, or may be further processed as shown in Figure 1. Adhesive appiicator 34 may be used to apply adhesive dots 32 in order to adhere a protective sheet 36 to the web. The protective sheet can be fed from a continuous roll 38.

Alternatively, protective sheet 36 will be selfadhered to web 11. At station 40 the joined webs may be perforated and/or trimmed. Roller 42 can be used to cut or separate longitudinally the continuous webs and may perforate also, if desired. Rollers 44a and b will longitudinally trim the webs. Cutter 46 will divide the webs laterally.

The preferred continuous web printing apparatus for performing the process of this invention is shown in Figure 2. As shown in Figure 2, web 11 is fed from roll 10 by web feeding means 50. This could be, for example, a Schriber Model H-500 roll stand made by Schriber Division of Harris Corporation, a D-G 175 roll stand of Didde-Glasser, Inc., or any other equivalent means. Web 11 is then conveyed via roller 52 to a first printing station 12. First printing station 12 could be, for example, a Schriber Model H-500 offset unit, a D-G 175 offset unit, or other offset printer.

Web 11, having a first side printed, is inverted at web inverter means 14 which has been described with reference to Figure 1. After web 11 is inverted by web inverted means 14, it passes through and is printed by the rotary screen press at second printing station 22. The ink utilized may be a hot melt material which is solid at room temperature but which becomes fluid when heated. As described with reference to Figure 1, above, the fluid hot melt ink is forced through upper screen roll 26 and is printed onto web 11. As the web leaves printing station 22, the hot melt ink images cool and solidify.

Having been printed, the completed sheet can then have other operations performed on and with it as described previously. For example, adhesive applicator 34 can be used to apply adhesive dots to one surface on the sheet, protective sheet material can be supplied from a roll 38, and the continuous web can be cut into individual sheets by cutting means at station 40 and with cutter 46. Drive rolls 48 and 50 control the speed of the web. All of these operations may be performed by a Schriber Model H-500 or D-G 175 sheeter delivery unit having a glue pump, web delivery, shear knife, and perforator. The individual sheets are then stacked on stacker table 52 for later assembly, such as into a booklet of preprinted spirit duplicating masters, if desired.

Claims (10)

1. A method forthe continuous production of pre-printed master sheets comprising the steps of: a) feeding a continuous web of material having first and second sides to be printed from a roll of the web, b) passing the web through a first printing station and printing images on the first side of the web during continuous web movement, c) with the second side of said web facing upwardly, passing the web through a second printing station and printing the reverse images of the images from step b) on the second side of the web in registry with the images on the first side of the web during continuous web movement using a rotary screen press having a screen roll in which an ink is supplied to the interior of the screen roll and is forced outwardly through the screen roll to form the reverse images, and d) cutting the continuous web into individual master sheets having images printed on the first side and reverse images printed on the second side in exact image-to-image registry with those images on the first side.

2. A method as claimed in claim 1 including the step of covering the first web with a second web of material and adhering the webs to each other prior to the cutting step.

3. A method as claimed in claim 1 or claim 2 in which the first side of the web is printed by an offset printing process.

4. A method as claimed in any one of the preceding claims in which the ink is a hot melt ink or a solvent-based ink.

5. A method as claimed in any one of the preceding claims in which the interior of the screen roll is heated.

6. A method as claimed in any one of the preceding claims in which the web is maintained at an angle of from 0.5 to 6.0 upwardly from the horizontal between steps c) and d).

7. A method for the continuous production of pre-printed master sheets comprising the steps of: a) feeding a continuous web of material having first and second sides from a roll of the web, b) passing the web generally horizontally through a printing station and printing a reverse image on the upper side of the web during continuous movement using a rotary screen press having a screen roll in which an ink is supplied to the interior of the screen roll and is forced outwardly through the screen roll to form the reverse image, c) maintaining the web at an angle of between from 0.5 to 6.0 upwardly from the horizontal immediately succeeding step b), and d) cutting the continuous web into individual master sheets.

8. A method as claimed in claim 7 wherein the ink is a hot melt ink.

9. A method as claimed in claim 1 substantially as herein before described with reference to and as illustrated in the accompanying drawings.

10. A preprinted master sheet whenever prepared by a method as claimed in any one of the preceding claims.