US3420167A - Screen printing machine with driven screen - Google Patents

Description

7, 1969 J. B. VAN DER WINDEN 3,420,167

SCREEN PRINTING MACHINE WITH DRIVEN SCREEN Filed Jan. 10, 1967 Sheet Of 5 FIG. I

INVENTOR. JOHANNES B. VAN DER WINDEN ATTORNEYS.

1969 J. B. VAN DER WINDEN 3,420,167

SCREEN PRINTING MACHINE WITH DRIVEN SCREEN Filed Janv 10, 1967 Sheet 2 of 5 mmvrox ATTORNEYS.

JOHANNES B. VAN DER WINDEN B. VAN DER WINDEN 3,420,167

SCREEN PRINTING MACHINE WITH DRIVEN SCREEN Filed Jan. 10, 1967 Jan. 7, 1969 Sheet INVENTOR. JOHANNES B. VAN DER WINDEN ATTORNEYS.

United States Patent 3,420,167 SCREEN PRINTING MACHINE WITH DRIVEN SCREEN Johannes Bernardus Van der Winden, Anistelveen, Netherlands, assignors to Gebr. Stork & Co.s Apparatenfabriek N.V., Amsterdam, Netherlands Continuation-impart of application Ser. No. 395,656, Sept. 11, 1964. This application Jan. 10, 1967, Ser. No. 608,268 US. Cl. 101116 4 Claims Int. Cl. B411 13/04 ABSTRACT OF THE DISCLOSURE The speed at which the material being printed upon travels and the speed of the printing screen are slightly different, the speed of the screen being somewhat slower. The internal drag of the squeegee on the screen is thereby counteracted by the external drag on the screen exerted by the material being printed upon. The net torsional loading on the screen is therefor minimized to lengthen screen life.

This application is a continuation-in-part of application Ser. No. 395,656, filed Sept. 11, 1964 and now abandoned.

In a screen printing machine, the stationary squeegee engaging the inner surface of the rotating cylindrical screen exerts a frictional drag tending to twist the screen and thereby ultimately lead to its destruction. According to the present invention, the screen is positively driven at a tangential speed related to but slightly less than the linear speed of the belt or carrier which supports the material being printed :upon.

The difference between these two speeds is sufficiently small as to insignificantly affect the quality of the printing but at the same time opposes the internal drag on the screen due to the squeegee. As a result, the twisting of the screen is minimized, thereby materially prolonging screen life.

Moreover, it has been found that if the driving roll of the material transporting belt is dimensioned so that its diameter is at least 300 times the thickness of the belt, the naturally occurring linear speed fluctuations of the belt will never be great enough to affect the speed difference between the material and the screen so as to either reduce this speed difference to zero or increase it sutficiently to adversely affect the quality of printing.

Specifically, it has been found that if the tangential speed v of the screen is equal to 0.995 V, where V is the tangential speed of the driven roll or drum for a material transporting belt of thickness t and wherein the diameter of the drum is at least about 3001, then the tangential speed v of the screen will always be about 0.2% less than the linear speed of the material transported by the belt. This condition of speed differential (about 0.2%) will be sufficient to materially prolong the life of the screen while being insufiicient to detectably afi'ect the quality of printing.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together, with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the several figures and in which:

FIG. 1 is a diagrammatic side view of the entire machine;

3,420,167 Patented Jan. 7, 1969 FIG. 2 shows on an enlarged scale a detail from the lefthand part of FIG. 1; and

FIG. 3 shows a partial section, along the line HIIII in FIG. 2 of a bearing device with a screen and driving elements.

As can be seen in FIG. 1, the screen printing machine consists of a frame 1, on which is provided an endless belt 2, which is adapted to travel in a continuous path between a driving roll or drum 3 and an idler drum 4. In the operative path 5 this belt 2 forms a surface for supporting the material 6 to be printed upon, which is unrolled from a supply roll not shown in the drawing. On the frame 1 a driving motor 7 is present, which transmits the driving force via a connecting rod 8 to the drum 3. Above the path 5 are provided a number of bearing devices 9 for cylindrical screens 10 (see FIG. 2). The screens 10 enclose conventional stationary squeegee members 5 which, as will be understood by those skilled in the art, engage the inner surfaces of the screens during the printing operation. The material 6 to be printed upon is delivered on the side of the machine to the left in FIG. 1, to an apparatus, not illustrated, for the further treatment of this material. On the underside of the path traversed by the belt 2 a device 11 for washing the belt, a tension device 12, and a device 13 for applying an adhesive layer on the belt 2 are present, so that after passing round the idler 4 said belt can support the material 6 to be printed upon and grip it temporarily. After the material 6 has been released at the end of the machine shown to the left in FIG. 1, the remnants of adhesive are removed from the belt 2 by means of the washing device 11.

As can be seen in FIGS. 2 and 3, each bearing device 9 for a screen 10 is coupled with a driving gear. For this purpose both parts of the bearing device 9 comprise sleeves 14 and 15 respectively, both of which are provided with exterior teeth 17. Via freely rotatable gear wheels 18 and 19 respectively the sleeves 14, 15 engage with gear wheels 20 and 21 respectively, which are mounted on a shaft 22. This shaft is connected via a worm gearing 23 with a stub axle 24.

As can be seen in FIG. 2, the stub axles 24, the number of which is equal to that of the bearing devices 9 mounted in the machine, are in line with each other, with a small gap in between, which is bridged by a sleeve 25 between every two adjacent stub axles 24. These sleeves 25 couple the stub axles 24 in the direction of rotation, but permit some axial movement. At the lefthand end of the machine is illustrated in FIG. 2 the last stub axle 24 is coupled via a sleeve 25 with a shaft 26, which forms the connection with a driving gear train 27.

This driving gear train is formed by a freely rotatable gear wheel 28 mounted on the shaft 26, which gear wheel permanently meshes with a gear wheel 29 on an intermediate shaft 30. Said gear wheel 29 meshes with a gear wheel 31 (only partly visible in FIG. 2), which is mounted on a shaft 42 and is freely rotatable. The gear wheel 31 meshes with a gear wheel 32, which is rigidly mounted on a shaft 33, which is connected via a conventional universal joint 34 with the connecting rod 8, and thus with the motor 7. The gear wheel 28 can be connected with the shaft 26 via an element 35 rigidly mounted on said shaft and a hydraulically operated clutch 36. This situation is shown in FIG. 2, the screens 10 thus being driven from the motor 7 and the gear wheels 32, 31, 29, and 28. The transmission ratio thus created is adapted to a particular diameter of the screen, this also in dependence upon the production rate aimed at.

To enable the use of screens 'having a smaller diameter, in the driving gear 27 an intermediate step is included, which is formed by a gear wheel 37 mounted on the intermediate shaft 30, which gear wheel meshes with a gear wheel 38 forming one unit with the element 35 rigidly mounted on the shaft 26. Via a hydraulically operated clutch 39 the gear wheels 29 and 37 can be connected with each other. In that case first the clutch 36 should be released. In the latter case the screens are driven from the motor 7 via the gear wheels 32, 31, 37, and 38.

A feature of this invention consists, inter alia, in that the speed of rotation of the screens is synchronous with the travelling speed of the supporting surface formed by the belt-2, in such a way that in the contact zone between screen and surface the speed of the screen will always be slightly lower than the speed of the supporting surface. The belt 2 is driven by the drum 3, which is provided with a worm wheel 40 shown diagrammatically in FIG. 2. This worm wheel 40 meshes with a worm 41 on the shaft 42, on which the above-mentioned freely rotatable gear wheel 31 is mounted. Rigidly mounted on the shaft 42 is a coupling element 43, which forms part of a clutch 44, which can be operated hydraulically and which can bring about a connection between the shaft 42 and the gear Wheel 31 via the element 43.

The transmission ratio between the elements 32, 31, 41, and 40 to the drum 3 is such, relative to the transmission ratio to the screens 10 (via the gear wheels 32, 31, 29, and 28 on the one hand), that the above-mentioned variation of speed occurs in the zone of contact between the screen and the material 6 to be printed upon.

Two problems appear to present themselves in connection with the endless belt 2, both of which are connected with the elasticity of the belt and both of which may cause fluctuations in the surface speed of the belt even though the speed of the driving drum 3 is constant. In the first place the thickness of such a belt is not uniform throughout its length, and this thickness as Well as the elasticity may show fluctuations in the order of magnitude of 1%. A more important factor, however, is that variations of elasticity tend to occur in different directions inside the belt. This has the consequence that the position of the neutral line, i.e. the imaginary line running in the longitudinal direction of the belt the length of which line does not change when the belt curves around the driving and idler drums, fluctuates considerably and will sometimes be closer to and sometimes further away from the lower surface of the belt, i.e. the surface passing round the driving drum. It has been found that these fluctuations may be in the order of magnitude of 10 per cent of the thickness of the belt.

The two above-mentioned differences of the belt are responsible for the fact that as deviating parts of the belt pass around the driving drum (which rotates with a constant speed) a temporary change, i.e. a retardation or an acceleration, occurs in the upper surface of the belt, i.e. the surface on which the material to be printed upon is supported. These temporary changes of speed are not followed by the screens, since the latter have a driving gear coupled with the driving drum of the belt.

If these fluctuations in linear speed of the belt are large as compared to the difference in tangential speed of the screen and the linear speed of the belt, such fluctuations may act detrimentally on the system.

The difference between the tangential speed v of the screen and the linear speed V of the material with which the screen is in contact should be about 0.2% V. This speed differential will minimize twisting of the screen and will not significantly affect the printing quality.

It has been found that if the diameter of the driving roll 3 is at least about 300 times the nominal thickness of the belt 2, fluctuations in the surface or linear speed of the belt 2 (and consequently of the material being printed upon) as discussed above will not materially affect the speed differential of 0.2%. Of course, with an ideal belt or with one more closely approximating the ideal than those presently available, linear speed fluctuations of the belt would disappear or at least be of no consequence. However, for belts normally encountered in practice, fluctuations in surface speed such as those discussed will occur and it is therefor preferred to employ the mentioned relation between driving drum diameter and belt thickness.

Using a driving drum 3 having a diameter of at least 300 times the belt thickness will require that the difference between the tangential speed V of the driving drum 3 and the tangential speed v of the screen 10 be about 0.5% V, with V V. With this condition prevailing, the tangential speed of the screen will be about 0.2% less than the linear speed of the material 6, due to relative slippage or creep between the belt and driving drum.

Further details of this screen printing machine and the manner in which the machine is driven form the subject matter of my copending patent applications 395,764, 395,878, 395,879 and 395,880, all filed Sept. 11, 1964 the last three now being patents numbered 3,304,860, 3,313- 232 and 3,291,044 respectively. This invention here concerned consists in the positive drive of the screens, as contrasted with the conventional complete or partial taking along of the screens owing to friction, and in the particular speed with which the screens are driven relative to the traveling speed of the material to be printed upon, which rests on the belt. According to the invention, care is taken that the variation or difference in speed between speed in which the screen is driven relative to the travelling speed of the material to be printed upon is very small. Preferably, such variation or difference in speed is in the order of 0.2% so that the material is always travelling at a slightly higher rate than the screen. In this way, the material being printed upon will exert a unidirectional frictional force upon the screens at all times and this frictional force will oppose the frictional force imposed upon the screens by the squeegees therein.

As a result, the torsional loading of a screen as imposed thereon by the squeegee is in part opposed by the torsional loading imposed upon the screen by the material with which it is in contact so that a net torsional loading on the screen always is less than that imposed by the squeegee alone. If the material being printed upon were to be travelling slower than the screen, a torsional loading would be imparted to the screen which is additive to the torsional loading imposed thereon by the squeegee blade.

To asure that the material being printed upon will exert a unidirectional frictional force on the screen regardless of the fluctuations in speed of the material which may occur naturally, it is preferred that the driving roll be of a diameter at least about 300 times the belt thickness.

In any event, it is important that the relative speeds between the screen and the material being printed upon is such that the material being printed upon always travels at a slightly greater speed than does the screen, regardless of fluctuations in speed of the material being printed upon, wherein such difference is insuflicient to significantly distort the pattern being printed upon the material as compared to the pattern on the screen itself.

That which is claimed is:

1. A screen printing machine comprising, in combination,

a frame a drive pulley and an idler pulley rotatably mounted on said frame in horizontally spaced relation,

an endless belt trained about said pulleys and presenting an upper flight for supporting and carrying along material to be printed upon,

drive means for rotating said drive pulley,

a cylindrical screen rotatably mounted on said frame and extending transversely of said upper flight of the belt and having a predetermined pattern for engaging and printing upon the material carried along by the belt,

said drive means also being connected to said screen for rotating same, the circumferential speed of said screen being less than the circumferential speed of said drive pulley by an amount suificient to continuously maintain the circumferential speed of said screen less than the linear speed of the material with which it is in contact and as carried along by said belt, but insuflicient to significantly distort the pattern printed upon the material with respect to said predetermined pattern of the screen.

2. The machine according to claim 1 wherein the diameter of said drive pulley is at least 300 times the thickness of said belt and the circumferential speed of said screen is about 0.5% less than the circumferential speed of said drive pulley.

3. The machine according to claim 1 wherein a squeegee blade is engaged against the inner surface of said screen, the circumferential speed of said screen being such that the material contacting the screen and carried along by the belt continually opposes the torsional loading imposed by the squeegee blade upon the screen regardless of fluctuations in the linear speed of said belt which may be occasioned by variations in the thickness and elasticity of said belt.

4. A screen printing machine comprising, in combination,

a frame, a drive pulley and an idler pulley rotatably mounted on said frame in horizontally spaced relation, an endless belt trained about said pulleys and presenting an upper flight for supporting and carrying along material to be printed upon,

above and transversely of said upper flight of the belt for engaging the material carried along thereby,

a squeegee blade contacting the inner surface of said screen,

said drive means also being connected to said screen for rotating same, the rotational speeds of said drive pulley and said screen and their diameters being such as to provide a circumferential speed for said screen which is about 0.5% less than the circumferential speed of said drive pulley, and said drive pulley having a diameter at least about 300 times the thickness of said belt whereby the material contacting the screen and carried along by said belt continually opposes the torsional loading imposed by the squeegee blade upon the screen regardless of fluctuations in the linear speed of said upper flight which may be occasioned by variations in the thickness and elasticity of said belt.

References Cited UNITED STATES PATENTS 2,375,237 5/1945 Morgan et a1. 101-114 2,511,511 6/1950 Murphy 101-120 3,170,396 2/1965 Augerinos 101269 WILLIAM B. PENN, Primary Examiner.

F. A. WINANS, Assistant Examiner.

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