US 3418864 A
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Description (OCR text may contain errors)
Dec. 31, 1968 w. C. Ross 3,418,864
PRNTING BLANKET AND METHOD 0F MAKING THE SAME Filed Jan. .'51, 1964 FIG.|
United States Patent C) 3,418,864 PRINTING BLANKET AND METHOD F MAKING THE SAME William Campbell Ross, Winchester, Mass., assignor to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut Continuation-impart of application Ser. No. 280,872, May 16, 1963. This application Jan. 31, 1964, Ser. No. 341,547
9 Claims. (Cl. 74-232) ABSTRACT 0F THE DISCLOSURE This is a continuation-in-part of application Ser. No. 280,872, filed May 16, 1963, now abandoned.
This invention relates to printing blankets and especially to -blankets adapted for use on screen print machines.
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. lf the variation in an entire traverse of the loop at any point exceeds 40 thousandths (0.040) of an inch, interior printing will occur. If the amount of stretch as the blanket advances through one repeat pattern is greater than or less than the stretch in the preceding step, the pattern will not lit This is serious, for t in the textile printing sense means that each color, as it is successively applied, has been placed in the exact position required by the design. When t 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.
So far as I am aware, no blanket presently maintains a suiciently high degree of dimensional stability. Consequently, in screen printing machinery, various mechanical expedients have been used to stop each individual repeat of the blanket as exactly the right position under the various colored screens. Nonetheless, variable stretching still remains a problem despite these expedients, and whenever the blanket stretches o-r recovers from stretch in a non-uniform manner as it advances around the loop, poor fit results.
The present invention produces a blanket in which movement of the working surface is inconsiderable and makes it possible to operate a screen printing machine with blanket lengths of 100 yards without mechanical correcting devices. The operating speed can be 800 yards per hour or more, yet at this speed the blanket maintains the necessary tolerance of no greater than 15 thousandths (0.015) of an inch at any point in the whole blanket run.
The process of screen printing is essentially a stencil operation and so differs materially `from the engraved roller rotary textile printing process. Screen print blankets do not have to withstand the enormous compressional load which, in roller printing, is imposed by the color rolls. Their working surfaces do not have to withstand the compressional wave which travels along the blanket, and, in contrast to a roller press textile print blanket, they do not have to transmit any significant amount of power, for in roller type textile printing, much of the auxiliary 3,418,864 Patented Dec. 31, 1968 equipment, particularly the blanket washer, is driven by the blanket itself. In short, the only demands on a screen printing blanket are that it shall remain tight, at, have substantially no tracking error, and be strong enough to move itself, without variable stretch.
In view of the very successful constructions of textile print -blankets used in engraved roller printing and the phenomenal service life which they deliver under vastly more drastic conditions, it `would be expected that blankets made in the manner found satisfactory for this type of textile printing could be used on screen printing machinery. Su-rprisingly, this is not the case.
Although these blankets give absolutely clean, sharp, and brilliant patterns on textile printing presses, the color outlines do not fit accurately when such blankets are used on screen printing machinery. Careful measurements have disclosed that in screen printing service, such blankets change lengths minutely as the blanket progresses through successive repeat pattern steps.
A construction which is common in power transmission belts was then tried. A continuous, longitudinal winding of cord located in essentially the median plane of the blanket was tried. But although cords in such a position are placed where the compressional and extension forces acting on the cords as the blanket passes over the pulleys are both at minimum values, and where the cords as the limiting members should control the length of the blanket, such blankets were unsatisfactory. They exhibited dimensional change greater than that which good screen printing permits.
After considerable experimentation, it was determined that the critical plane where dimension control must be exerted on a screen print blanket was neither the median plane nor the working surface but a plane which lay as near as possible to the plane of the cylinder ply. This nding is all the more remarkable when it is remembered that the cloth in screen printing is cemented to a working surface which is remote from the cords, and that it is the movement of the cloth together with the movement of that working surface which destroys the sharpness and clarity of the print.
Nonetheless, it Iwas found that the critical position where linear displacement must be prevented is at and adjacent to the surface which is in contact with the drive roll. In printing machines, the blanket is either pushed or pulled as it moves ahead, step by step.
The general solution to this problem was achieved by adopting the construction which is illustrated in FIGURE 2, and assembling the blanket in the manner which follows.
A base ply of duck is coated on one side with a vulcanizable rubber compound. This forms the base or cylinder ply of the blanket. Two pulleys are arranged so that the cylinder ply, when stretched over them, forms a loop. The ends of the fabric are then spliced together. Subsequently power is applied to `one of the pulley shafts and the ply is tensioned in small successive increments until the tension of the fabric is about 10- pounds per transverse inch. The running-in of the ply is continued under tension until no slack develops and the ply maintains an exact length. The time of run-in is variable, depending on the tightness of weave of the canvas. Thereafter, an essentially non-stretchable cord which previously has been coated with a rubber compound is laid on the rubber-covered surface of the cylinder ply with tension maintained on the ply. A continuous length of this cord is helically wound from the center to the margin. To eliminate pucker or stretch, two windings are simultaneously wound from the center outwards-one extending to the left and the other extending to the right hand margins of the ply. The tension of the cylinder ply with attached cords is then increased to generally between about 20 to 40 pounds and preferably about 25 pounds. Thereafter a ply of duck, coated on both sides with a vulcanizable rubber compound is laid over the cords and is spliced at a point remote 4from the splice in the cylinder ply. A further (third) ply of duck, coated with a vulcanizable rubber compound is then laid on the cordcovering layer and is spliced at a point remote from the two underlying splices. Ordinarily, the top surface of this third ply is coated with a heavy coat of a solventresistant rubber compound which, when press-curing is complete, forms the working surface of the blanket. The entire assembly or sandwich is then press-cured under quite heavy pressures in a heated vulcanizing press. As the blanket cures and the rubber flows, the cords become totally embedded in rubber compound. The covering plies of duck are entirely embedded and the top or working surface of the blanket becomes a smooth, unbroken rubber sheet.
Occasionally, when certain proprietary cloth cements or glue are to be used, it is desired that fabric shall be exposed on the top working surface. Accordingly, the top rubber coating can be omitted.
The run-in of the coated cylinder ply under tension and before the assembly of the blanket is commenced appears to be a necessary step. If that step is omitted, minor dimensional changes in the blanket will occur. lt also appears to be necessary to maintain the pull or tension under which the cords are wound on the cylinder ply at some unchanging value, which should be uniform throughout the entire winding operation. However, the tensioning of the cords should be held to a minimum, and preferably less than two pounds per cord.
Generally, to prevent the stretching of one margin of the blanket more than the other, and to minimize any tracking error-in the resulting blanket, it is preferred that the cord winding, superposed on the cylinder ply, be two opposed helices starting from the center and running outwardly to each margin. There are certain canvas constructions which are so tight that stretching one margin more than the other as the cord is wound on the ply does not occur. If the cylinder ply is of such canvas construction, the cord may then be wound uninterruptedly from one selvage to the other.
In the drawings:
FIG. l is a perspective view of a portion of the blanket 10.
FIG. 2 is an exploded sectional view.
Referring to FIG. 2, the cylinder ply, 12, carries a rubber coating, 13 (which later forms part of the rubber embedment of the cords). The helices, 14, of rubbercoated cords are wound on top of rubber coating, 13. The covering ply, 15, carries a rubber coating on each face. The lower coating, 16, later forms the top half of the cord embedment. The upper coating, 17, later unites with the lower coating, 18, of the canvas ply, 19. The top surface of ply, 19, carries a rubber coating, 21, which later becomes the working surface.
The number of plies is not critical. Another or even more intermediate plies may be added if required. Ply, 19, can be omitted, provided ply, 15, is dense and very tightly woven. Usually, however, its presence is an advantage.
It is, of course, to be understood that after the blanket has been exposed to vulcanizing heat and pressure in the vulcanizing press, the rubber layers are indistinguishable and f-orm a solid rubber mass in which all of the fibrous elements, whether cords or fabric, are embedded. In the curing operation, the rubber flows. It thoroughly interpenetrates all of the space between the strands of the textile, and in many places penetrates deeply into the interber spaces of the textile strands themselves. The cords are completely embedded in the rubber which has flowed around them. The surface of the blanket, which is cured against a polished sheet, is smooth and free of any Cil surface imperfection. The cords, save for the surrounding rubber, take up a position which is immediately adjacent to the cylinder ply.
Example l A base ply of No. l2 duck was coated on one side with yapproximately "710 of a pound per square yard of vul-canizable neoprene rubber compound (Neoprene Type WRT, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.). Two pulleys were then set up so that when this cylinder ply was stretched over them, the loop which was formed was 40 yards long. The fabric was then spliced. Subsequently, power was applied to one of the pulley shafts, and the loop was tensioned in small successive increments until the tension of the fabric Was l0 pounds per transverse inch. Run-in was continued until, under a tension of 10 pounds per transverse inch, no slack developed, and the ply maintained an exact length. Thereafter, two 6-ply, 2.70 denier cords of saponified acetate rayon (Fortisan), which previously had been coated with a vulcanizable neoprene rubber cornpound (Neoprene Type WRT), were wound on the entire loop of the cylinder ply while the cylinder ply was still under tension. The cord winding was started at the ply center, and each cord was run outwardly from the center to the selvage as a continuous helix, one helix running in a right-hand direction, the other running lefthanded. The pitch of the cord was such as to maintain a uniform spacing between the cords of 1/8 of an inch. During the entire winding, the tension applied to the cord was maintained at a uniform value. Thereafter, a ply of No. 12 duck, coated on its under side with 5%@ of a pound per square yar-d of a vulcanizable neoprene compound (Neoprene Type WRT) and having its upper side coated with i710 of a pound per square yard of a second neoprene compound (Neoprene Latex Type 571, E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.) was laid over the cords and spliced at a point remote from the splice in the cylinder ply. A third ply of duck, coated with 2/10 of a pound of neoprene compound (neoprene latex type 571) on its under side and having its top surface coated with sufficient butadiene-acrylonitrile rubber (Hycar 1051, high acrylonitrile, B. F. Goodrich Company, Cleveland, Ohio) to produce a surface 0.015 of an inch thick was laid over the cord covering layer and spliced at a position remote from the two underlying splices. The whole blanket was then passed through a vulcanizing press, with a polished metal sheet interposed between the top platen and the top surface coat of rubber. The blanket was vulcanized at 310 F. under a 500 pounds per square inch pressure.
Example Il A smaller test blanket was constructed in the same manner as that used for construction 'of the blanket of Example I. Samples one inch wide by 18 inches long, some of which contained a fabric splice and others containing no splice, were placed in a tensile test apparatus, so arranged that the tension load could be varied at a given instant and thus simulate the load change in stopping and in starting a screen print machine. The deviations in stretch were carefully measured in a series of such pulls exerted on eaoh of the samples. At equilibrium conditions, both the spliced and the unspliced sections of the blanket of Example II showed essentially no deviation in stretch.
As a counter-example, samples one inch wide and 18 inches long were lcut from a blanket now commercially employed. These samples were tested in the same machine and in the same manner. In the commercial blanket, the deviation in extension of the spliced sample, when compared to the deviation in extension of an unspliced sample when undergoing a load of 10 pounds per inch width to pounds per inch Width, was 0.025 in. (25 mils). In going from 50 pounds per inch Width to 100 pounds per inch width, an additional deviation in extension of 0.017 in. (17 mils) occurred.
The large blanket of Example I was placed on an Ichinose automatic screen printing machine. Extremely diflicult patterns were selected from a number which previous experience had shown could not be run on the machine because of mis-registration. Various repeat lengths and speeds were evaluated in printing runs which totaled 100,000 yards. No repeat pattern deviation was found in any run which varied from the above-mentioned i0.015 in limits.
In contrast, when similar runs were made on the same textile material carried on a commercial blanket on the same machine, deviations in register of 3h@ of an inch resulted.
Particularly useful as cords in the present invention are glass cords. The low stretch of the glass cord permits the construction of a blanket having less loverall stretch and 100 percent elastic recovery and, therefore, greater repea accuracy than blankets with, for example, rayon cords. Since glass cords have more strength per unit diameter than other substantially nonstretchable cords, glass cords of smaller diameter can be used which exhibit considerably less tendency to show through the surface of the top ply of the finished blanket after curing and which still will provide the necessary strength and dimensional control.
Since the glass cords laid on the cemented cylinder ply may crimp in passing around the circumference of the end rolls during the construction of the blanket, it may be desirable to apply a greater degree of tensioning to the carcass during the assembly of the blanket and during the cure than is applied to a blanket of nonglass cords. The degree of tension maintained during the application of the top plys and the cure is a variable depending upon the diameter of the cord and the diameter of the end roll. In a preferred embodiment 20 to 40 pounds per transverse inch is applied and more preferably, about 25 pounds.
Example III A base ply of No. 12 duck was coated on one side with approximately A0 of a pound per square yard of vulcanizable butadiene-acrylonitrile rubber compound (Hycar 1051, high acrylonitrile, B. F. Goodrich Company, Cleveland, Ohio). Two pulleys approximately inches in diameter were then set up so that when this cylinder ply was stretched over them, the loop which was formed was 24 yards long. The fabric was then spliced. Subsequently power was applied to one of the pulley shafts, and the loop was tensioned in small successive increments until the tension on the fabric was 10 pounds per transverse inch. Run-in was continued until, under a tension of 10 pounds per transverse inch, no slack developed and the ply maintained an exact length.
Thereafter, with tension maintained on the ply, two 3-ply glass yarns (Owens-Corning-E.C.G. 1501/3) which previously had been coated with a vulcanizable butadiene-acylonitrile rubber compound (Hycar 1051) havling 20 percent solids and a coating pickup of 2.67 wet pounds per thousand yards of cord were wound on the entire loop of the cylinder ply. The cord winding was started at the ply center, and each cord was run outwardly from the center to the selvage as a continuous helix` one helix running in a right-hand direction and the other running left-handed. The pitch of the cords was such as to maintain auniform lay of 12 cords per transverse inch. Each of the cords was maintained under a tension during the Winding of approximately 1 pound, and this tension was maintained at a uniform value throughout the entire winding operation. The wound loop, or carcass, was then removed from the winding frame and taken to a lay-up and vulcanizing assembly station. Two rolls approximately 10 inches in diameter were arranged in a similar set-up to those used in the run-in and cord-winding operation. In this case, however, the rolls were so arranged in front and behind the vulcanizing press that the loop passed through the press. The axle of one of the rolls was then jacked backwards until the tension applied to the carcass between the lrolls was 25 pounds per transverse inch. A ply of No. 12 duck coated on its under side with V10 of a pound per square yard of a vulcanizable butadiene-acrylonitrile rubber compound (Hycar 1051) and having its upper side coated with 2/10 lbs. per square yard of a second butadiene-acrylonitrile rubber compound (Hycar 1042, med-high acrylonitrile, B. F. Goodrich Company, Cleveland, Ohio) was laid over the cords and spliced at a point remote from the splice in the cylinder ply. A third ply of duck, coated with 2A@ of a pound of butadiene-acrylonitrile rubber compound (Hycar 1042) on its under side, and having its top surface coated with sufficient butadiene-acrylonitrile rubber compound (Hycar 1051) to produce a surface of 0.015 of an inch thick, was laid over the intermediate ply and spliced at a position remote from the two underlying splices. Maintaining the tension of 25 pounds per transverse inch, the whole blanket was then passed through the vulcanizing press which had a polished stainless steel sheet interposed between the top platen and the top surface coat of rubber and the bottom platen and the bottom surface coat of rubber. The blanket was vulcanized at 310 F. under a pressure of 500 pounds per square inch. This blanket, when completed, was installed on a Stork Automatic Screen Printing machine and tested for accuracy in repeat steps in the following manner:
After the blanket was properly installed and tensioned, a coating of color was applied to the blanket surface and a hairline was drawn transverse to the blanket at the far end. The blanket was then rotated until the hairline appeared at the head end of the machine, and a matching hairline index attached to a xed portion `of the machine was set in position. Thereafter, the blanket was run through a successi-on of step-and-repeat operations, hairlines being drawn on the blanket at the head end of each repeat. Deviation between each repeat and the xed index marks was read as the blanket progressed through several entire step-and-repeat cycles. In no instance did the deviation exceed i0.015 in. per blanket revolution.
The use of the blanket of this invention on screen printing machines, particularly those which use a simple endroll drive such as the Ichinose and the Stork machines, eliminates the need of mechanical stops, steel belt reinforcements, or other more complicated beltadvancing equipment. The only mechanical stop equipment required is that used to control the movement of the drive roll. On such machines using only `roll stop control, color registration is remarkably Well sustained from repeat to repeat throughout the Whole piece of goods.
The rubber compounds which were employed `are those conventionally used in textile print blanket manufacture, and considerable variability in the choice of suitable compounds exists. Thus, it is possible to use compounds which lie within the production experience or compounding preference of an experienced textile blanket manufacturer. The rubber-coated plies may be cold pressed to ensure the adhesion of the rubber to the adjacent layer or the rubber-compound may be `of the pressure-sensitive type to obviate such cold pressing.
The word rubber has been used in a generic sense and implies no chemical significance whatever. It signifies only long-chain, vulcanizable polymeric substances of whatever chemical origin which possess the requisite physical properties of exibility, resilience, :or resistance to the colors and solvents used in the screen printing process.
Although this blanket has been designed specifically for solving problems arising in the screen printing industry, the usefulness of such a blanket is not confined to screen printing machinery. Presses exist in which the work is carried by a blanket linearly under a rotating printing surface. Other presses exist where the printing surface is attached to the blanket itself land passes under a cylinder which carries the sheet to be printed. On both such presses, these blankets will find utility and maintain page dimensions in a superior manner.
What is claimed is:
1. The process of manufacturing a blanket suitable for use on `a screen printing machine which consists of coating one side of a length of textile with a rubber compound, looping the textile length lover pulleys, splicing its ends together to form an endless loop to form thereby a cylinder ply, running in the yply by vapplying power to a pulley to rotate the said ply, meanwhile applying tension to the ply in incremental amounts until the applied tension reaches about 10 pounds per inch of width, continuing the running-in until no slack develops further and the ply maintains a constant length, thereafter, while maintaining the said tension, superposng a layer of essentially non-stretchable rubber-coated cord on said coated ply by winding said cord in a helix about said ply while maintaining the tension applied to the cord at a value not exceeding 2 pounds, covering the cord layer with at least a second named rubber-coated textile ply while the said cord-covered structure is maintained under tension and then vulcanizing the Aassembly between suitably finished platens under heat and pressure to produce thereby a consolidated, unitary blanket structure, having a smooth working surface.
2. The process of claim 1 wherein a third-named ply of fabric having both surfaces coated with rubber compound is superposed on the said second-named coated ply and the blanket is thereafter cured under heat and pressure to produce a unitary blanket structure.
3. The process of claim 1 wherein `a third-named ply of fabric, coated on its lower side only with a rubber compound, is superposed on the said second-named ply, and the blanket thereafter is cured under heat and pressure to produce a unitary blanket having a working surface comprising exposed fabric.
4. The process of claim 1 wherein Cords are simultaneously wound on said ply as two helices, each begin ning adjacent the center line of said ply and extending outwardly respectively to the rightand left-hand margins of said ply.
5. The process of claim 1 wherein the said cords consist of glass, and the said cords are helically wound over the said cylinder ply while subject to a tension of approximately one pound.
6. The process of claim 5 wherein, subsequent to the application of said glass cord winding, the cord-covered cylinder ply is stretched between rollers at a tension of between 20 and 40 pounds per transverse inch.
7. The process of claim 6 wherein the said tension is maintained at 25 pounds per transverse inch.
8. A blanket adapted for use 4on roll drive screen printing machinery and capable of maintaining the deviation of repeat pattern register to within 1.015 inch per blanket revolution which consists of a rubber-coated cylinder ply rendered dimensionally stable by running-in and stretching under a tension of about 10 pounds per transverse inch, a helix of rubber-coated cord wound about the exposed surface of said cylinder ply at a cord tension not in excess of 2 pounds and extending across the said surface, and at least a second coated ply covering said helical layer of cords, the said blanket having been cured under heat and pressure to produce a unitary blanket structure presenting a smooth working surface.
9. A blanket as claimed in claim 8 wherein the helix of rubber-covered cord is composed of glass cord wound on said cylinder ply under tension applied to the cord not exceeding l pound, the said cords being free of crimping within the blanket structure when passing around the blanket driving rolls.
References Cited UNITED STATES PATENTS 228,186 1/1880 Gandy 156-229 X 1,096,896 5/1914 Ellis 161-400 X 1,412,309 4/1922 Lambert 156-172 X 2,386,761 10/ 1945 Wetherbee. 2,489,791 1 1/ 1949 Liles et al. 2,547,220 4/1951 Merrill. 2,630,603 3/1953 Freedlander et al. 156-137 X 3,122,934- 3/1964 Fike. 2,653,886 9/ 1953 Gentle.
ROBERT F. BURNETT, Primary Examiner.
I) W. POWELL, Assistant Examiner.
U.S. C1. X.R.