CA1131497A - Transverse stiffened screen printing blanket - Google Patents

Abstract

Abstract A method of printing is disclosed. In this method material to be pripted is affixed to a continuous belt printing blanket, and the printing blanket is stabilized by providing transverse bend resistance on both sides of the printing blanket neutral plane and spaced from the neutral plane while retaining relative ease of bending in the direction of the loop of the con-tinuous belt.

Description

Background of the Invention This invention relates to a printing method which uses a continu-ous belt printing blanket. The application is a division of applicant's Canadian Application Serial No. 320,072, filed on January 22, 1979, and all-owed on October 6, 1981.
Printing blankets used on screen print machinery are very large, and are enormously heavy. Frequently they are some 100 inches wide, and 100 yards long. Such blankets are formed in a closed loop. The material which is to be screen printed is glued to the blanket, and as each color step is imprinted on the goods, the blanket is advanced through one "repeat pattern".
As a consequence, the entire blanket must start, move, and stop with an extraordinary degree of exactitude. If the variation in an entire traverse of the loop at any point exceeds 4 thousandths (0.004) of an inch, inferior printing will occur. If the amount of displacment as the blanket advances through one repeat pattern is greater than, or less than, in the preceding step, the pattern will not "fit".
This is serious, for "fit" in the textile printing sense means that each color, as it is successively applied, has been placed in the exact posi-tion required by the design. When fit is poor, some color margins overlap, the printed design on the finished goods appears "mushy", and sometimes unpleasant color mixing results. Poor fit results in severe economic loss, for the printed goods can then only be sold at sacrifice prices.
The blanket is generally engaged over and extends between two opp-osed rolls for the screen printing operation. One of the rolls is driven and drives the blanket through frictional engagement. The other roll is an idler roll. There are other commonly used methods of driving the hlanket such as through the use of side clamps. The blanket is frequently guided by ,~

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being engaged on its sides by opposing collar guides mounted on idler rolls.
Even more abusive guides are sometimes used which do not rotate with the pass-ing of the blanket but scrape against the blanket's edges. It is necessary for the blanket to have a high degree of cross machine direction stiffness for these guides to work, a belt that is limp transversely will tend to buckle or bend during use when in contact with these guides and consequently will not align or track properly. Another reason requiring a blanket to have high transverse stiffness is the provision of sufficient stiffness to prevent the blanket's bending in the cross machine direction due to the contracting forces caused by the shrinkage of the fabric being printed when the fabric goes from dry to wet to dry during various printing stages.
So far as I am aware, transverse stiffness against transverse col-lapse, folding or distortion of printing blankets has in the past been achiev-ed by providing thickness in the blanket. This thickness has many obvious disadvantages such as increasing the blanket's weight, depending on materials chosen increasing the blanket's cost and causing creping (wrinkling) in the material glued on the blanket if the blanket goes around a roll without first havlng the material removed.
As pointed out in said Canadian Application Serial No. 320,072~ trans-verse stiffness against transverse collapse, folding or distortion has been pro-vided in an expeditious way providing many improvements and also providing an enhanced ability to have good transverse stiffness in thinner blankets. Even in thicker blankets the blanket performance and life would in many instances be significantly lmproved by use of the present invention.
Summary of the Invention The present invention in its broadest aspect may be defined as a method of printing comprising affixing material to be printed to a continu-, -, .~ , ..
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Best Mode . .
In the drawings:
Figure 1 is a side elevation schematic view of a blanket which may be used in practising the method of the present invention.
Figure 2 is an enlarged schematic cut away sectional view of the blanket of Figure l.
Referring to Figure 1 a screen printing blanket 11 may be engaged over the cylinders or rolls 13 and 14 for operation in the manner well known in the screen printing industry. One of rolls 13 and 14 is usually powered to drive the blanket 11 through frictional engagement with the blanket ll.
Referring to Figure 2 it may be seen that the cylinder ply 12 of blanket ll contains transverse rods 15 joined into a woven cloth by fibers 16~ The fibers or threads 16 extend in a perpendicular direction to the rods and curve over and under the rods to form the textile. Ply 12 is a trans-verse stiffening ply because it contains the transverse stiffening rods 15.
A rubber coating 17 is present on outer face 18 of the cylinder ply, and serves as an adhesive layer. A layer l9 of inelastic cord 20 is laid over the rubber coating 17. This cord ply 19 is the longitudinal load bearing ply that provides the primary strength against longitudinal stretching. It has a high modulus of elasticity. A rubber coating 21 is present over the cord ply 19. Rubber coating 21 also serves as an adhesive layer.
A second transverse stiffening ply 22, containing transverse rods 15A joined into a woven cloth by threads 16A, overlies the rubber layer 21.

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~' ' A working surface of rubber 23 overlies the second transverse stiffening ply 22 The composite structure consisting of layers 12, 17, 19 21, 22 and 23 is pressed and vulcanized into a unitary structure. Layers 17, 19 and 21 form an intermediate layer that separates the transverse stiffening plies 12 and 22.
The transverse rods may be of any material that is relatively stiff.
Multifilament yarns impregnated with stiff resins such as phenolics or mela-mine and formed in~o monofilament-like structures and cured can be used.
~owever, preferred rods are stiff plastic monofilament fibers. Glass, nylon, polypropylene and steel monofilaments may be used in some applications. ~low-ever, by far the preferred rods, the only ones that are known to give out-standing results and provide economy in manufacture, are stiff polyester fibers and preferably polyethylene terephthalate monofilament fibers. Pre-ferably the monofilaments have diameters of about 2 to about 35 mils more preferably about 5 to about 15 mils.
The- above described blanket is especially useful in practising the method of the invention. This novel method of screen printing involves affixing the material to be printed to a printing blanket such as the one described above. Thereafter the blanket is moved through its normal steps and indicia is applied as desired. After completion of the printing proced-ure, including any adjunct procedure, the printed material is removed from the blanket.
The present invention includes a printing method which comprises positioning material to be printed on a continuous belt prin~ing blanket and stabilizing the printing blanket by providing transverse bend resistance in two separate planes of the printing blanket separated by a rubber layer.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of printing comprising affixing material to be printed to a continuous belt printing blanket, and stabilizing the printing blanket by providing transverse bend resistance on both sides of the printing blanket neutral plane and spaced from the neutral plane while retaining relative ease of bending in the direction of the loop of the continuous belt.

2. The method of Claim 1 wherein said transverse bend resistance is provided by at least two separated layers in the printing blanket, each of which is comprised of a plurality of transversely extending rods.

3. The method of Claim 2 wherein said rods are substantially straight monofilament plastic fibers woven into a textile with the fibers extending in the longitudinal direction curving over and under to form the textile.

4. A method of printing comprising positioning material to be printed on a continuous belt printing blanket and stabilizing the printing blanket by providing transverse bend resistance in two separate planes of the print-ing blanket separated by a rubber layer.