US2217366A - Silk screen printing apparatus - Google Patents

Description

0."s,194o." HJHICK'S- 2,217,366A

SILK SCREEN PRINTING APPARATUS l y Filed Aug. 4, 1959A v `2 sheets-sneer 1 oct. s, 1940. H, J. kma@ 2,217,366

SILK SCREEN PRINTING APPARATUS Filed Aug. 4, 19:59 2' sheets-sheer 2 2a v x 7 Patented Oct. 8, 1940 UNITED STATES PATENT OFFICE SILK SCREEN PRINTING APPARATUS Harry J. Hicks, Lynchburg, Va., assignorv to Precision Finishing Machine Corporation,Lynch burg, Va., a. corporation of Virginia Application August 4, 1939, Serial No. 288,437

s claims. (Crm1- 122)r 'I'his invention pertains to printing machines of the type for so-called screen or web printing.

Especially is the invention concerned with coop\ printing machine and thus to enhance the veiii- 's erating means to maintain accurate alignment 5 and constant tensioning on the fine screen that is used in this type of printing.

Screen printing applies ink through a ne mesh web such as silk in contact with a surface to be printed. A stencil against the web outlines suit- 0 able characters to be printed. Ink' applied with a squeegee fills the stencil openings. In modern practice the stencil with the screen inthe form of an endless web is carried around suitable rolll ers. The moving web and stencil contact a sheet to be printed carried on a travelling conveyor.

The meshes of the web must remain taut and in alignment so as not to distort the printing nor to transmitrso much ink as to blur. Moreover, this requirement must be met throughout a rela-v tively long period of usefulness despite relatively high speed operations. v

Heretofore the printingr screen has been shortv lived. A silk web should be as taut substantially as a drum head. Tension to effect requisite tautness has tended to separate the meshes. TheV tendency of the meshes to` separate is accentuated in travel around thev rolls not only because previous tensioning means along Ythe edge of the screen have imposed too severe strains, but also because change in the linear rate of travel aroundV the periphery ofthe rolls imposes added stressy on the tensioning means and thus on the fabric of the screen. Travelling metal bands have beenY used to tension the screen laterally, but hereto--r fore have tended either to release the fabric or else to break the bands. If the bands are of sufciently heavy material'to lremain tight, they tend to bind around the rolls and thus to impede travel of the screen.

4i) If the lateralI tensioning means of the screen i be of relatively thick material, a problem arising at the periphery of the rolls is that rthe inner surface and the outer surface of the thick material must travel at different linear speeds. The 45 outer surface moving on the greater arc increases its speed while the inner surface on the smaller arc decreases its speed. Thus the outer surface tends to stretch While the inner surfacetends to material to be printed;

A purpose of this invention is to provide means to hold a printing screen under'substantially con stant tension throughout during its travel' in the ciency and the period of usefulness of the screen. 5 A specific purpose is to provide lateral tensioning means for the printing screen that shall remain constantly and accurately spaced so as to maintain constant lateral tensioning, but alsofto im pose no added longitudinal strains at the periph-r 10 ery .of the rolls over which the screen travels. A further purpose is tov provide tensioning-means of extreme simplicity so that the screen may be v applied or may be released quickly. Anvobject alsol of this inventionl is to provide simple means 16 to adjust the tensioned screen vertically. These and other objects will be apparent'in the follow# Y ing illustrative description of this invention, prelsented in conjunction with .the accompanyingA drawings and pointed out morebroadly' inthe 20 appended claims. Y A

In the drawings: v Figure 1 presents in side elevation an assemblage lof printing rolls carrying a' printingscreen and stencil in conjunction with a conveyor for Figure 2 presents an enlargedivertical section of the roll and screen assembly according to this4 invention viewed from opposite to Figure 1; Figure 3 shows a vertical cross-section through therollsand screen assemblage of Figure 1; Figure 4 shows a detailed section across a screen and stencilwith suitable tensioning means,

, taken along the line 4--4 of Figure 2;

Figure 5 .presents an exploded perspective view 35 of means to secure the ends of a printing screen f are accomplished by providing a series of lateral tensioningvmeans to travel around the rolls of a 40 printing machine on what is known as theipitch linof the tensioning means. vThis'is an arcuate Y path Where the change in linear travel or in 1ongitudinal tension deviates scarcely at all from that at intermediate positions of travel between the rolls. In the `preferred embodimentof this invention illustrated in the drawings accurate spacing` is maintained between opposite edges of the screen at positions intermediate the several rolls. sioned laterally between tentering hooks carried by chains that run in guides between the rolls and also in grooves at the ends of the rolls in such manner as to maintain' accurate lateral spacing throughout and also to move the tentering hooks 55 As illustrated, the printing screen istenthe inner face in the form of a ilat plate. Thus,Y

1 Sand screen along the pitch line of the chains.

under the lower rolls 2 and 3 by driven wheels 6 and 1 in synchronism with the rolls. l

1 The triangular frame l carries an endless; screen 8 on the inner side of Ywhich are suitable stencil elements 9. 'I'his stencil also maybe in the Vform of an endless web. It is secured byY conventional means to the screen 8.sovas to move in synchronism therewith. The screen is carried around the frame over the rolls 2, 3 and 4. At

Vthe bottombetween rolls `2 and 3, the screen 8 is lmoved substantially'in contact with the conveyor 5.- The conveyor 5 carries material to be printed in concurrent travel with the screenand stencil so that printing occurs over this horizontal course. Within the frame I are maintained suitable adjuncts toprinting, such as a source of ink supply I0 and a squeegee plate' I I whichrides upon theinner surface of the stencil l 9l so asto distributeink evenly. *l Y Figure-3, a vertical section across the frame' YI, shows .upper `roller `4 and lowerrear roll 2 carryingrollerchains I3 and I4 with tentering hooks LI2 forlaterally tensioning the printing screen k8'. .These tentering hooks are carried b; chains I3 and I4 at each side ofthe screen V8. To propel the chains I3 and I4, sprocket rims are secured at the .outer endsof each roll. Fon? example, on "upper drum 4 is fastened gear wheel VI5 to engage the chain I 3'and at theotherend ofthe drum 4 is secured-the vgear wheel IGto engage the chain I4. Atthebottmy similar sprocket wheels are placed on the rolls 2 and^3 likewise; to Yengage ,thef respective-chains 'I3 andu. Y

i Means are included under `this -invention to? channel 20.

maintain the sprocket chains I3 and I4'in'vcon1f stant, accurate, spaced relation to eachother.

For thisl purposegguide walls are fixed 'between the'threerolls 2, 3 and 4. Thus at the Vbottom 'ofl' the frame between` rolls2 and 3 is secured a pair ofopposedguide channels I1 and I8 while alongtheaupper sidesof the "triangular printing 'frame I arelsecured similar' pairs of guidel channels between the'vwheels 2`and 4 and 3 andY 4. fThe sprocket chain links bear against the inner wall of the channels. This isV shown,for example, in Figure 4 where chain link vI3 rides in channel .I91fand .sprocketY link I4 isvshown in A ,The chain links may be of standard construction except that=preferably theroller pins conventional with such chains are extended from for example, the link I3 bearsv the-extended plate 2I'and link I4 bears an opposed plate 22. Each lateral plate bears` a tentering hook I2 and each is positioned betweenthe topV and the bottom of the chain sothe' hook l2 is effective a1; the pitchl line of the chain. Thus as the chains and hooksfor the screen travel around each roll,V they maintain the'same lineal speedand preserve an even longitudinal tension on the screen. Y I

' other.

At 4the end of eachl rolll means are provided to permit lower portions of the chain links and tentering hooks to travel somewhat below the level of the roll surface. For example, as shown in VIlligure 3, the end of each'roll is depressed or grooved'so that the lower portion of hook I2 travels. below the surface of the roll. Hook I2 may abut the end of the roll or may be spaced somewhat therefrom. A further improvement is vprovided to prevent sagging'of the chain or of the hook at the rolls. This is accomplished by adjusting the height of the grooved outer ends of the rolls to act as support for the inner Iside of the tensioning chains I3 and I4.

Intermediate the rolls are guide walls I9 and 20, shown in Figure 4, -which maintain the driven chains I3 and I4 constantly spaced from each .This is conveniently accomplished by channel members secured to the printing frame in which channelsy the chains I3 and-I4 fit. To prevent sagging of rthe sintering hooks I2 and of the screen 8, the inner side of the chain is supported by the inner guide walls I9 and 20.

Further serving to maintain suitable tension on the screen 8 are plates adapted to it between the lateral tensioning chains I3 and I4., To

these plates are fastened rends of screen 8.

shown in Figure 5, ends of the screen 8 are se# cured between a pair of these plates 28 and 23. Conveniently the lower plate 29 may be slotted so that'the ends of the lscreen 3 may be brought up therethrough.Y Upon these aresecured the upper plate 28, for example bysuitableQscrews.

Thus, strengtheningmeansand fastening means4 and vconstant tensioning means are comprised in this pair of plates 28and 29.r

vIt is desirable'to adjust'thetensioned screen vertically and evenly in some simple manner. For example, thismay be desirable toaccommodatev diierent thicknessesjof stock to beprinted. v To this end the frame I islsupported at each corner upon jackscrews 23 and 24. Eachscrew is pro-` vided with a sprocket wheel for a llexible drive element, for example chain' 25. to engage the sprocket-wheels and encircle the entire frame and ance of even tensioning A I and contact over the en-- tire printing screen. f

In use, 'printing stock is fed to the printing ,K55

frame I'upon the travelling 'conveyor 5. vConveyor 5 and the screen rolls are driven in syn-vv chronism by suitable means of conventional na-v ture. Suitable stencils are fastened Voutside lthe continuous screen sof as to travel aroundthe rolls with the screen. The screen `is adjusted ver- Y tically to the stock to beprintedg 'The tension on the screen is adjusted suitably byvertical adjustment ofthe apex roll. VThis adjustment both laterally land 'longitudinally is maintained throughout a considerable period of usefulness of the screen by theconstant lateral tension and longitudinal tension that is imposed both between the rolls and at the rolls.,`As the screen with its attached stencil moves along the bottom of the frame a supply of inkis furnished to the stencil and distributed evenly thereover by a squeegee blade that presses upon the face of the stencil.-

move each gjackscrew insynchronism with the 455 others. Simple means to rotate this chain 25 and thus to adjust the frame vertically is providedin Y the 'sprocket wheel 2B maintained to; engagethe.

Surplus ink may be carried toupper portions of the frame but will be caught by suitable launders the entire course of travel of the printing screen is exceedingly effective to maintain clear printing and a long period of usefulness of the screen.

In this description the word ink is intended to be representative of paint or other desired media. The term screen printing" is intended to represent broadly a method of imprinting or transposing a desired design upon stock. Reference to silk is intended to include also other textiles or rubber, orother fibres or porous material This application is a. continuation-impart of my copending application Serial No. 264,819, iiled March 29, 1939.

In accordance with the patent statutes the principles of this invention have been illustrated by a preferred embodiment thereof, but it will now be apparent to those skilled in the art that modications and alterations may be practiced within the scope of the appended claims.

What I claim is:

1. In a screen printing machine comprising a continuous screen trained around rolls with means to engage the edges of the screen with driven elements along each side of the screen and guiding means at the ends of each roll to maintain constant lateral spacing between the driven lateral elements and of the screen in passage around each roll, an improvement to maintain screen alignment comprising rigid guide walls extending between each roll and positioned between the driven elements to maintain constant lateral spacing between the driven lateral elements and of the screen at positions between each roll.

2. In a screen printing machine comprising a continuous cloth screen trained around rolls, an improvement to maintain screen alignment comprising a chain along each side of the screen, tentering hooks extending from the chains to engage the edges of the screen for lateral tensioning, sprocket wheels to drive each chain, guiding means at the end of each roll to maintain constant lateral spacing between the chains andofthe screen in passage around each roll, the

tentering hooks being mounted on the chains at the pitchline of the chains, and rigid walls extending between each roll and positioned between 5 the chains to maintain constant lateral spacing between the chains and of the screen at positions between each roll.

' 3. In a screen printing machine comprising a continuous cloth screen trained around rolls, an improvement to maintain screen alignment comprising sprocket wheels at the ends of each roll, a chain at each side of the rolls engaged by the sprocket wheels, tentering hooks extending from the inner sides of each chain at the pitch line of the chains to secure the screen, a groove at each of the rolls for travel of the chains and screen around the rolls, and guide walls for the hooks extending betweenA each roll to maintain constant lateral tensioning of the screen at positions between each roll.

4. In a screen printing machine comprising a continuous cloth screen trained aroundl rolls, an improvement to maintain screen alignment comprising sprocket wheels at the ends' of each roll, a chain at each side of the rolls engaged by the sprocket wheels, tentering hooks extending from the inner sides of each chain at the pitch line of the chains 'to secure the. screen, and guide walls for the hooks extending between each roll to maintain constant lateral tensioning of the screen at positions between each roll, there be,

4improvement to maintain screen alignment comprising driven chains at the sides of the screen, sprocket wheels at the ends of the rolls for driving the chains and guide walls spaced apart intermediate the rolls for spacing the chains, and plates fitting between the chains to engage ends of the screen to maintain lateral and longitudinal tension on the screen.

6. A screen printing machine comprising a triangular i'rame, rolls mounted'in the frame for support of a continuous screen, guide elements mounted on the rolls to maintain constant lateral and longitudinal tension on the screen in passage over the rolls and spaced guide walls mounted on the frame between the rolls to maintain constant lateral tension at positions intermecorners of the :frame and a flexible drive element encircling the frame and engaging the lifting screws to provide uniform vertical adjustment w of the frame and oi the printing screen.

HARRY J. HICKS.

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