US 3235772 A
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E. GURIN 3,235,772 ER'S BLANKET IN COMBINATION AL ROLLER Feb. 15, 1966 ANTI-STATIC PRINT WITH GROUNDED MET Filed Aug. 8. 1961 FIGZ FIGI
CYLINDER ELASTOMER CYLINDER HIGH STRENGTH WOVEN FABRIC ELECTRICALLY CONDUCTING METAL BASE FIGZI) ELASTOMER LAYER CYLINDER MULTIPLE LAYERS HIGH STRENGTH WOVEN FABRIC HIGH STRENGTH WOVEN FABRIC 1 IIIIIII/I,
ELASTOMER LAYER CONDUCTIVE ELASTOMER LAYER CONDUCTIVE HIGH STRENGTH WOVEN MULTIPLE LAYERS HIGH FABRIC WITH METAL STRENGTH WOVEN FABRIC WIRE INSERTS WITH METAL WIRE INSERTS ELASTOMER LAYER INVENTOR PER EMANUEL GURIN A ORNEY CYLINDER ELASTOMER LAYER MULTIPLE LAYERS HIGH STRENGTH WOVEN FABRIC United States Patent O ice 3,235,772 ANTI-STATIC PRINTERS BLANKET IN COMBINA- TION WITH GROUNDED METAL RGLLER Emanuel Gurin, P.O. Box 10142, Caparra Heights, Puerto Rico Filed Aug. 8, 1961, Ser. No. 130,123 4 Claims. (Cl. 317-2) This invention relates to a novel printing blanket which is especially adapted by Virtue of its new composition and construction to eliminate static electricity build-up of particles of lint, dust and debris in the air and on the printing roller of the printing machine in non-air-conditioned or non-dusty-free rooms in which the printing machine is used and thereby provides printing of better quality.
It is well known that friction builds up electrostatic charges particularly on the paper web during normal printing operations and many devices have been suggested in the prior art to eliminate the build-up of charge which interferes with the paper feeding and printing operation. These prior art devices have all been based upon the conception that since the electrostatic charge build-up is on the paper, it is necessary to provide a means to drain the charge from the paper to some conductive part of the paper feeding machine such as the metal frame. An example of this type of device suggested in the prior art is the conductive tympan sheet proposed in United States patent, No. 2,295,134 granted to Smith. After the paper has been printed with ink, the charge is drained in Smiths device.
In contrast to this concept of draining the charge after printing, the present novel printing blanket is based upon a new modification of the structure of the printing blanket used to deposit the inked image on to the paper whereby electrostatic charges caused by friction of moving parts of dissimilar materials is drained during the printing transfer of liquid ink to the receiving sheet. This blanket itself effectively drains the electrical charges from the paper and from other parts of the printing apparatus. As a result, the objectionable build-up of lint, dust and debris which occurs on the blanket itself as a result of static electrification is eliminated. The printing blanket being modified in a new way to become electrostatically conductive drains any electrical charge build-up directly to the underlying metal cylinder used for mounting the blanket.
This static pick-up of lint causes build-up of finely divided debris on the blanket itself, first in the nonprinting surface area of the blanket during use since the blanket itself becomes electrically charged in use due to the inherent electrical solid state characteristics of the elastomer material and underlying plies of which the blanket is constructed. The greatest amount of dirt, lint and dust comes from the paper itself in that it is picked up by the surface of the blanket in the non-printing areas. This debris builds up during printing and crowds around the edges of the printing areas to work its way into the printing ink dots on the blanket to a degree such as to clog these ink dot areas with debris impurity and thereby impair the quality of printing.
Heretofore, it was not appreciated that finely dispersed airborne dust, lint and debris as build-up on conventional printing blankets first on the non-printing areas of the coventional printing blanket and then about the edges of the printing areas on the blanket could be eliminated by modification of the blanket itself. The fact that dirt, lint or dust appeared on the blanket was merely evidence that the blanket needed to be cleaned or perhaps that the ink had become contaminated or perhaps that the ink did not print well from the particular synthetic rubber or elastomer formula used in vulcanizing the blanket. Since the operator had little or no special knowledge of the characteristics of the rubber or elastomer formula and even less 3,235,772 Patented Feb. 15, 1966 knowledge of the properties of the new inks used, he merely stopped production, cleaned the blanket and started over again. This results in increased costs and inferior printing quality.
It is only recently that air pollution studies have indicated the degree and kind of contamination which might cause impairment of printing quality. However, for most uses of blankets in ordinary printing a completely dust and debris-free atmosphere is too costly. It is the dirt which comes from the paper used in printing and not from the atmosphere or the air around the machine which is eliminated by creating a nonstatic blanket assembly so that there is effectively eliminated the particular factor of attraction of the dirt and the lint to the blanket surface which causes poor printing quality.
The present invention thus provides a solution to this problem in printing quality specifically directed to eliminate build-up of finely divided debris on the blanket during normal printing operations. In the case of the conductive blanket of the invention, there will generally be required the use of paper underneath the blanket to bring it up to the proper printing pressure and height. Since untreated paper itself is a non-conductor, the paper must be treated to make it also static conducting.
Thus, it is a principal feature of the novel conductive blanket of the present invention that both the elastomeric ink-bearing surface of the blanket and the reinforcing backing layer are each conductive and that the backing layer is mounted on a conductive metal mounting cylinder or roller whereby electrostatic charges are drained directly through the metal mounting roller.
It has been found that the use of the new conductive blanket construction eliminates pickup of lint and dust on the printing roller and is successful when used in non air-conditioned rooms to provide superior printing quality and avoiding the clogging observed in runs with conventional printing blankets.
To achieve complete conduction throughout the entire cross-section certain special and unique conductive materials are added to the elastomer layer and the reinforcing backing layers as well as the paper packing.
In a preferred embodiment, each of the elements of the printing blanket is modified, e.g., the elastomer layer of uniform thickness and smooth surface vulcanized to the base, the dimensionally stable flexible reinforcing, the reinforcing plies in a multi-ply structure and the adhesive layers. Each embodies a special conductive pigment or filler material having an electrical conductivity which corresponds to a resistance of less than ohm-centimeters.
The elastomer ink-bearing layer is provided with sufficient conductive pigment such as the conductive carbon blacks, particularly Shawinigan Black or acetylene black. Also there may be included conductive metal and metal compound such as silver oxide, tin oxide, silver sulfide, cadmium oxide, indium oxide, chromium oxide, or borides as nickel boride or chromium boride, or carbides as nickel carbide or iron carbide, and compounds such as alkaline earth manganites. The conductive metals may be silver, copper, nickel, iron, platinum, palladium and electrically conducting iron and iron alloys, nickel and nickel alloys in finely divided flakes, spheres or fragments.
The conductive pigment or filler is used in an amount sufiicient to make the elastomer conducting. In the case of conductive carbon black, which is the preferred pigment, from about 40 to about parts of Shawinigan Black or acetylene black may be incorporated into the elastomer and surprisingly, the ink resisting qualities, surface printing qualities and mechanical properties of the ink receiving layer are not impaired. The printing performance of the blanket is equal to that of high quality conventional blankets.
When using finely divided metal pigments such as silver,
copper, nickel or iron, a much smaller amount is used in the elastomer top layer of the blanket; amounts of from about 4 to about 12% are suificient. Since carbon black is a desirable constituent of the elastomer, it can be used alone or it can be used in combination with finely divided metal pigments. These pigments are preferably used in the finest particle size commercially available con sistent with high purity and quality for conduction. A suitable particle size range is about 200-400 mesh when used in the top elastomer layer.
When the conductive metal oxide is used, the amount 7 for good conduction is similar to that used with the metal pigments. The particle size is also the same. In the top layer, it is preferred to use the metal oxide in addition to conductive carbon. Amounts of only 2-3% of such oxides as silver oxide or tin oxide are suflicient to enhance conduction and lower the specific resistance, particularly when formulated with acetylene black in amounts of 50-75 parts per 100 parts of elastomer and vulcanized to the backing layer.
The backing layer which reinforces the blanket must also be selected or modified physically and chemically to make it conductive. Conductive flexible woven metal, preferably in square weave, to make it resistant to stretching may be made of such fine denier (6.5 denier for example) metal wire as iron, copper, nickel and conductive alloys of these. Also a uniformly thin flexible metal sheet of iron, steel, nickel or copper may be used as the backing for contacting the metal face of the printing roller. With woven textile fabric made from cotton, polyethylene terephthalate, polymeric formaldehyde or trioxane polymer, cellulose acetate, saponified cellulose acetate, high tenacity rayon, etc., the woven fabric must be modified to make it electrically conductive and for this purpose, there may be incorporated from about 2 to about 14% of the conductive metal, metal oxide or carbon fillers and pigments which are described above. It is preferred to use amounts sufficient to provide desired conductivity and not to add excessive amounts of these fillers or pigments.
Adhesive which is used to bond and vulcanize the backing to the intermediate plies and to the surface layer is also modified in the same manner and in the same proportions to make it conductive. Generally, the adhesive is an inert volatile hydrocarbon, ketone or ester solvent solution of the same elastomer material used to form the top layer. In this connection, the lastomer of the top layer may consist of rubber, butadiene-acryloniflrile polymer, butadlieneastyrene polymer, isobutylene-isoprene polymer, polysulfide rubber, polyvinyl chloride containing at least 90% vinyl chloride and the remainder polyvinyl acetate, chlorotrifluorethylene polymer, tetrafluorethylene polymers, perfiuoralkyl acrylate polymers, polyisoprene, polybutadiene or polyurethanes.
The elastomer may compose 50% or more of the finished composition of the top layer and contains the usual accelerators, anti-oxidants, reinforcing pigments, fillers, softeners, plasticizers, activators, and of course, a vulcanizing agent such as sulfur.
Anti-static organic materials can be incorporated into the formulation without materially affecting the properties of the rubber. In the rubber between the layers of fabric there may be used conducting acetylene black or carbon black.
As anti-oxidants there may be utilized such materials as phenyl-a-naphthylamine, or others known in the art. As softeners there may be used tricresyl phosphate, paraflin, dibntyl phthalate, etc. As accelerator, there may be used N-cyclohexyl-Zbenzothiazyl-sulfonamide, mercaptobenzothiazole, tetramethylthiuramidsulfide, etc.
The reinforcing other pigments or fillers may include any of the various grades of non-conducting carbon black, whit-ing, clays or the like. The composition should also preferably'contain zinc oxide as an activator for the accelerator and stearic acid as a plasticizer and aid in vulcanizing. In order to render the composition spreadable, there is incorporated with the solid materials a suitable solvent, preferably a hydrocarbon such as toluol, in the proportion of one .part of the solid ingredients to two parts of toluol or in somewhat greater proportions.
The conventional printers blanket in the case of a three-ply blanket has a thickness of from .062 to .066 inch, and from .072 to .076 in the case of a fouraply blanket. In the event a packing blanket is used it must also be modified to make it conductive. The packing blanket is of a thickness so that the composite dimension of both the covering printing blanket and the backing blanket are equal to the thickness of the conventional blanket. Also, depending on the particular undercut of the printing cylinder, there may be used an appropriate conductive packing blanket with the conductive printing blanket of the invention when it is made in conventional three and four ply thicknesses.
Thus, it is within the contemplation of the invention to make the anti-static printing blanket and combinations of the anti-static printing blanket and conductive packing blanket in the thickness of the conventional three-ply and four-ply blankets as well as to make thinner blankets of anti-static construction in combination with a conductive packing blanket.
The total thickness of a thinner covering blanket may be between .020 and .040 inch and preferably approximately .030 inch.
The ink-receiving layer preferably has a thickness of between .015 and .025 inch, preferably approximately .020, and is composed of the natural or synthetic rubber of the types known in the art.
When a woven back-ing is used the fabric layer of the blanket may be formed of a high tenacity rayon yarn, as for example, Fortisan rayon, a cellulose acetate yarn of high tenacity which is square woven so as to prevent any stretch and this backing is treated with a conductive filler material.
Details of the preferred embodiments of the invention will be seen from the consideration of the foregoing examples, reference being made to the accompanying drawing, forming a part of this specification, in which:
FIG. 1 is a cross-sectional view of a single ply printing blanket embodying the invention, in which a thin elas tomer layer is coated and vulcanized upon a flexible electrically conducting metal base, the blanket being mounted on a cylinder;
FIG. 2 is a cross-sectional view of another blanket embodying the invention in which a conductive elastomer layer of determined thickness is supported by an underlayer of conductive elastomer and this assembly backed by strong flexible woven fabric treated to make it conductive;
FIG. 2a is a cross-sectional view of fabric backed blanket similar to FIG. 2 but omitting the conductive elastomer underlayer;
FIG. 2b is a cross-sectional view similar to FIG. 2a but showing a multi-ply conductive structure;
FIG. 3 is a cross-sectional view of an embodiment of the electrostatically conductive printing blanket in which a high strength woven fabric reinforcing layer filled with conductive short pieces of metal wire constitutes the base and there in inter-positioned a conductive layer of conductive elastomer below the flexible top conductive layer;
FIG. 3a is a cross-sectional view of a modification of the blanket of FIG. 3 showing a multi-ply structure; and
FIG. 4 is a cross sectional view of a preferred embodiment comprising multi-ply woven fabric reinforcing layers and supported on a conductive paper layer.
The following examples illustrate specific embodiments of conductive blankets made in accordance with the invention and shown in FIGS. l-3a herein. For these examples the general method of manufacture comprises the steps of formulating the elastomer layer identified as 10, 11, 11a, 12 or 13 in FIGS. 1-3a by following conventional formulating procedures except that a critical amount of conductive filler is embodied in the elastomer formula. Also a conductive base is selected such as the metal base in FIG. 1, the conductive filler impregnated woven fabric base of FIG. 2 or 2:1 and the multi-ply reinforced base structures of FIGS. 3 and 3a.
FIG. 3 illustrates use of an intermediate conductive adhesive layer 40 between the conductive elastomer layer 12 and the conductive woven fabric base. FIG. 3a illustrates the use of multiple plies of conductive high strength Woven fabrics as the base support of the conductive elastomer layer 13. In the embodiment illustrated in FIG. 3a the thickness may vary within the limits of conventional printers blanket.
It is preferred for reasons of economy to use the cheaper carbon pigment or metal pigments or oxides and it is to be noted that the pigment or filler must be conductive at room temperature.
In all of the embodiments of the invention shown in FIGS. 1-3, including 2a and 3a, the blanket is designated by reference characters 10, 11, 12 and 13 and comprises a single top layer 1 consisting of smooth, dimensionally stable vulcanized elastomer which is provided with sufficient conductive pigment.
The printing blanket consists of a layer ll of conductive elastomer as defined above which is used as the printing surface and the immediate supporting conductive structure is in the form of a harder flexible support.
Example 1 illustrates the formation of the ink-receiving layer.
EXAMPLE 1 An essential ingredient of the ink-receiving layer is electrostatically conducting carbon and following are formulae illustrating the composition of this layer:
Formula A Parts by weight Smoked sheet rubber 100 Graphite Acetylene black 85 Zinc oxide 5 Stearic acid 4 Sulfur 3 Paraifin wax 3 Benzothiazyl disulfide 1 Formula B Parts by weight Elastomer based on polymers of chloroprene 100 Light magnesium oxide 4 Zinc oxide 6 Soy bean oil 10 Mineral oil 10 Stearic acid b. Parafiin /2 Graphite (powdered) 15 Acetylene black 85 To the foregoing solid constituents for each part of solid there was added one part of toluol.
The mixture was then suitably milled and then coated onto the conductive fabric (as prepared in Example 2 below) in a conventional manner to form a smooth coating of .020 inch in thickness. It was then vulcanized at 290 F. for approximately two hours. The resultant single-ply printers blanket was mounted upon a cylinder of an offset printing press.
EXAMPLE 2 The following illustrates the preparation of conductive woven fabric used in accordance with the invention.
High strength cellulose acetate woven rayon fabric backing, this rayon fabric being available under the Celanese Corporation of America trademark Fortisan, is impregnated with a binder of the following formula:
6 Formula C Weight percent Stearic acid coated silver flake 25-35 Methyl cellulose binder 2-40 Water 60 Formula D Parts by weight Silver oxide 50 Gum arabic 2 Polyvinyl alcohol 2 Ethyl alcohol 3 Water 43 (Each conductive when dry) The high strength cellulose acetate fabric is the fabric which is employed with the binder of Formula C and this fabric is impregnated in the same manner with composition of Formula D as with Formula C above.
EXAMPLE 3 This example illustrates a preferred formulation and construction of conductive printing blanket in combination with anti-static and conducting paper blanket.
The elastomer formulation of the printing blanket uses the preferred proportions of 4095 parts of conductive carbon black per 100 parts of natural or synthetic rubber as shown in Example 1. If there is used more than 100 parts of carbon black total, e.g., conductive carbon black which is derived by the burning of acetylene, has a particle diameter of 43 millimicrons and a surface area of 7.3 acres per pound and is available in the trade under the grade name of Shawinigan Black, and non-conducting black as may be used for reinforcing the elastomer layer the result will be unsatisfactory because the elastomer layer will be too hard for producing high quality printing and will represent a hard type of formulation which will not be acceptable to the printing industry. Thus, the total carbon of Formula A derived from conductive graphite 15 parts and acetylene black 50 parts is 65 parts per 100 parts of smoked sheet rubber which is satisfactory as regards softness and pliability. Likewise, the total carbon of Formula B derived from powdered graphite, 15 parts, and acetylene black, 75 parts, is parts which also provides satisfactory softness and pliability for the elastomer layer for a commercially acceptable printing blanket of high quality.
Within these limitations of ratio of carbon black to rubber, e.g., not more than parts of total carbon black per 100 parts of rubber the anti-static characteristics may be further improved in accordance with this example by incorporating an effective amount of a surface-active cationic long-chain organic compound or surface active long-chain non-ionic organic compound.
Suitable non-ionic long-chain organic compounds which may be used are polyoxyethylene sorbitan monolaurate, polyethylene glycol oleate and highly oxyethylated nonyl phenols. The polyethylene glycol (polyoxyethylene) radical has a molecular weight of about 400 which indicates a chain length of about 8l0 (C H O) units. The oleate and laurate radicals are typical of fatty acid radicals which may be used. These mono-esters are readily compatible with the rubber formulations and are available commercially as non-ionic emulsifying agents and dispersants. As many as 90 units of ethylene oxide have been incorporated into these non-ionic agents, but generally from about 5 to about 60 units in the highly oxyethylated polyhydric mono-esters and nonyl phenols pro vide satisfactory anti-static properties.
Amounts of about 0.3 to 20% of the non-ionic agents "are effective to enhance the anti-static properties of the elastomer layer.
Examples of surface active cationic materials which may be employed as substitutes for the non-ionic antistatic agents include the quaternary ammonium halides, "the alkyl imidazoline hydroacetates, the alkyl betaines and the fatty acid polyamine condensates. Each of these are commercially available. To illustrate, cetyl dimethyl benzyl ammonium is available commercially and di-isobutyl phenoxy ethoxyethyl dimethyl benzyl ammonium chloride monohydrate is available commercially.
The molecular weight of these quaternary ammonium compounds is generally about 400 or higher.
Fatty acid amine condensates which may be used include condensation products of such polyamines as triethylene tetramine, diethylene triamine and tetraethylene pentamine or mixtures of these with such fatty acids or fatty acid glycerides as stearic acid or oleic acid or glycerides of these acids. The products of condensation are determined by the number of molecules of acid reacting with amine, the major or principal product being of the type as in distearoyl ethylene diamine for example, e.g., two molecules of fatty acid or glyceride per single molecule of amine and the condensation carried to completion by removing water of reaction under high temperature, preferably with a hydrocarbon solvent such as toluene or xylene, and then under vacuum.
Alkyl imidazoline hydroacetate are similar in method of preparation to the polyamine fatty acid condensates but instead of being largely straight chain in structure, these materials contain the imidazoline ring which is formed by heating polyethylene, polyamine and fatty acid to higher temperatures under conditions which eliminate more water of reaction. A typical example of suitable imidazoline compound is heptadecyl N-amino ethyl imidazoline dehydroacetate prepared from diethylene amine triamine and stearic acid which is thereafter neutralized with acetic acid. The mono and diacetylated derivatives prepared by reacting this compound with one or two moles of acetic anhydride may also be used.
Another specific example of cationic agent used for enhancing or imparting anti-static activity to the printing and supporting elements are the alkyl betaines which contain a carboxyl group as the anion group but which also have a positively charged quaternary ammonium group in the molecule to neutralize the carboxyl anion group and are thereby cationic in action although the groupings are capable of acting in both anionic and cationic capacities as ampholytes. A typical alkyl betaine usable as an anti-static agent has the formula in which R is a long-chain alkyl such as dodecyl, stearyl or oleyl and Me is the methyl group. These alkyl betaines are well known, are available commercially and can be prepared from condensing a fatty amino ether with chloroacetic acid.
The amount of cationic agent, above exemplified, which is added to the elastomer formula as an anti-static agent to enhance conduction of static electricity is between about 0.2 up to about 2.0% by weight of the total ingredients, the cationic or non-ionic agent being used in the form of a volatile solvent solution, e.g., alcohol, acetone, Xylol or mixed solvents so that the material is uniformly distributed in the formula prior to the vulcanizing step.
In the same manner as set forth in the preceding paragraph for incorporation of surface active agent into the elastomer layer, the solvent solution of the surface active agent may be added to the adhesive rubber ply used for vulcanizing the fabric backing layer to the top elastomer l aer- In ibi manner, the concentration of surface active agent may be between 0.22.0% of the total solids in the adhesive layer.
In most cases from about 0.2 to about 1.2% of surface active agent may be present in the rubber of the top printing surface without having any adverse effect on the printing qualities of the rubber material and without detracting from the adhesion due to its incorporation in the adhesive layer to the base reinforcing fabric after the printing blanket assembly is vulcanized in the normal commercial manner.
In contrast to the requirement for use of volatile solvent solutions of surface active agents in adding these to the rubber formulation, an aqueous bath of the surface active agent in appropriate concentration, e.g., about 1-10% of active ingredient in H O may be employed to incorporate the agent into the reinforcing textile backing. Immersion, impregnation 0r spraying is sufilcient to introduce the desired amount of surface active agent into the square weave strong textile reinforcing backing after which the textile is dried at elevated temperatures e.g., from -180 C. to set the surface active agent. In this manner amounts of about 0.2-2% of anti-static surface active material are dispersed throughout the fibrous backmg.
The independent paper packing blanket must also be made conductive to static electricity and it is a feature of this example illustrating a preferred embodiment of the invention that the electrostatic conductive material, e.g., the surface active agent of either the cationic type or of the non-ionic type be uniformly incorporated throughout the packing blanket by a thorough going impregnation. Impregnation is effected by dipping or spraying with 210% aqueous solution of the surface active agent and thereafter drying the backing to set the conductive agent which imparts electrical static conductivity throughout the entire backing and through to the top surface of the blanket.
It can therefore be seen that this example of this application follows the general assembly of two or three ply square weave reinforced packing blanket construction, each element of which has been made electrically conductive with surface active agent and an independent paper blanket, also treated with surface active agent to make it electrically conductive whereby electrostatic charges on the paper and blanket are drained through the blanket to the metal of the mounting roller, the rubber adhesive and rubber formulation for the top surface layer being modified with conductive carbon black, but giving a vulcanized formulation which matches the physical properties of the conventional blanket assembly.
It should be borne in mind that the present concept of a completely electrically conductive blanket is completely different than the concept of a conductive belt made of rubber which has been used heretofore, for example, Baldwin, U.S. Patent No. 1,401,303, since the present blanket bears ink which is needed to transfer an image to a sheet being printed. In the Baldwin patent, the purpose of having a conductive belt is to eliminate electrostatic concentration of charges on the surface of a rubber belt used in cooperation with a paper web sent through drying apparatus, the purpose being to eliminate the electrostatic attraction of the paper to the rubber belt. The belt thus is designed to leave the paper untouched while the blanket is designed to alter the surface paper permanently. There is no relationship between the concept of the present printing problem using the blanket of this invention in offset printing to the problem of drying in Baldwin, Patent No. 1,401,303.
While the invention has been particularly shown and described with'reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inven tion.
What is claimed is:
1. In combination, an anti-static printing blanket of at least three plies and a thickness of between ,062 and .076", a metal roller upon which said blanket is mounted and a ground electrically connected with said roller to drain the static electricity which accumulates in the blanket and to eleminate the pickup of lint and dust from the air during printing, said blanket consisting essentially of a top layer of butadiene acrylonitrile vulcanized copolymer containing from 40 to 95 parts of conductive carbon black per 100 parts of copolymer and finely divided conductive metal selected from the group consisting of silver, copper, nickel, iron, platinum and palladium in an amount of from 4 to 12 percent by weight of the copolymer to provide electrical resistance of less than 80 ohm-centimeters, and alternating plies of woven fabric and of the same electrically conductive elastomer as in the top layer, said alternating plies of woven fabric, elastomer and top layer all being vulcanized to make up a single assembly consisting of at least three plies and not more than four plies, said woven fabric consisting of high strength cellulose acetate fibers and being irnpregnated with silver flake in an amount of 5 percent by weight on a dry fabric basis.
2. In combination, an anti-static printing blanket of at least three plies and not more than four plies and a thickness of between about .062" and about .076", a metal roller upon which said blanket is mounted and a ground electrically connected With said roller to drain the static electricity which accumulates in the blanket and to eliminate the pickup of lint and dust from the air during printing, said blanket consisting essentially of a top layer of vulcanized chloroprene polymer containing from 40 to 95 parts of conductive carbon black per 100 parts of polymer and finely divided conductive metal selected from the group consisting of silver, copper, nickel, iron, platinum and palladium in an amount of from 4 to 12 percent by weight of the polymer to provide electrical resistance of less than 80 ohm-centimeters, and alternating plies of woven fabric and of the same electrically conductive elastomer as in the top layer, said alternating plies of Woven fabric, elastomer and top layer all being vulcanized to make up a single assembly consisting of at least three plies and not more than four plies, said woven fabric consisting of high strength cellulose acetate fibers and being impregnated with silver flake in an amount of 5 percent by weight on a dry fabric basis.
3. In combination, an anti-static printing blanket of at least one ply, a one ply blanket having a thickness of between about .020" and about .040, a conductive paper supporting layer between the blanket and the metal mounting roller for the blanket, a metal roller upon which said blanket is mounted and a ground electrically connected with said roller to drain the static electricity which accumulates in the blanket and to eliminate the pickup of lint and dust from the air during printing, said multiple ply blanket consisting essentially of a top layer of butadiene acrylonitrile vulcanized copolymer containing from 40 to 95 parts of conductive carbon black per 100 parts of copolymer and finely divided conductive metal selected from the group consisting of silver, copper, nickel, iron, platinum and palladium in an amount of from 4 to 12 percent by weight of the copolymer to provide electrical resistance of less than ohm-centimeters, and alternating plies of woven fabric and of the same electrically conductive elastomer as in the top layer, said alternating plies of woven fabric, elastomer and top layer all being vulcanized to make up a single assembly which together with said paper has a thickness of about .076", said woven fabric consisting of high strength cellulose acetate fibers impregnated with silver flake in an amount of 5 percent by weight on a dry fabric basis, said conductive paper supporting layer being impregnated with a wetting agent selected from the group consisting of nonionic wetting agents and cationic wetting agents.
4. In combination, an anti-static printing blanket of at least one ply, a one ply blanket having a thickness of between about .020 .and about .040", a conductive paper supporting layer between the blanket and the metal mounting roller for the blanket, a metal roller upon which said blanket is mounted and a ground electrically connected with said roller to drain the static electricity which accumulates in the blanket and to eliminate the pickup of lint and dust from the air during printing, said multiple ply blanket consisting essentially of a top layer of butadiene acrylonitrile vulcanized copolymer containing from 40 to parts of conductive carbon black per parts of copolymer and finely divided conductive metal selected from the group consisting of silver, copper, nickel, iron, platinum and palladium in an amount of from 4 to 12 percent by Weight of the copolymer to provide electrical resistance of less than 80 ohmcentimeters, and alternating plies of woven fabric and of the same electrically conductive elastomer as in the top layer, said alternating plies of woven fabric, elastomer and top layer all vulcanized to make up a single assembly which together with said paper has thickness of about .076, said woven fabric consisting of high strength cellulose acetate fibers and being impregnated with silver flake in an amount of 5 percent by weight on a dry fabric basis, said conductive paper supporting layer being formed of rubberized paper containing conductive carbon black in an amount of from 50 parts up to about 95 parts of carbon black per 100 parts of rubber used to impregnate said paper.
References Cited by the Examiner UNITED STATES PATENTS 1,211,706 l/1917 Hoerbelt 161-401 1,782,712 11/1930 Chapman 317-2 2,266,578 12/1941 Wheldon et al. 317-2 2,295,134 9/1942 Smith 154-545 2,441,945 5/1948 Frolich et a1 154-521 2,489,791 11/1949 Liles et al. 161-93 2,714,075 7/1955 Watson et al. 1l7-138.8 3,045,595 7/1962 Gurin 154-545 XR 3,060,853 10/1962 Remer 101-426 3,063,884 1l/1962 Glover et al. 161-96 EARL M. BERGERT, Primary Examiner JACOB STEINBERG, ALEXANDER WYMAN,