Printing offset blanket

Abstract: A printing offset blanket is provided comprising a supporting layer, which may have a porous compressive layer, and a surface printing layer provided on the supporting layer, the surface printing layer being formed of a rubber composition comprising 100 parts by weight of a rubber material, 1 to 10 parts by weight of a zinc oxide and 5 to 15 parts by weight of an inorganic filler other than zinc oxide or reinforcer.

Description: This invention relates to a printing offset blanket. More particularly, it relates to a printing offset blanket having a surface printing layer, which is superior in printability at the time of high-speed printing, particularly paper discharging properties. Offset blankets to be used for gravure offset printing are normally formed by providing a surface printing layer on a supporting layer which may have a porous compressive layer in the interior thereof, and the surface printing layer is composed of a layer of a rubber having an elastic modulus and an oil resistance, such as acrylonitrile-butadiene rubber (NBR). However, when high-speed printing is conducted using a normal offset blanket, an adhesion arises between a paper as a material to be printed and the offset blanket, thereby causing a problem that the paper curls and tears. The similar problem arises at the time of printing on a paper having a smooth surface, such as coat paper. Furthermore, when a normal offset blanket is used for a web offset printing press, such a problem arises that a paper is caught with the offset blanket to cause misregistering, or tearing and scumming of the paper, i.e. so-called delamination arises. These problems are caused on the ground that the offset blanket is not rapidly separated from the paper, i.e. so-called paper discharging properties are inferior. Since such a problem deteriorates a printing precision and a productivity, considerably, it has hitherto been requested to improve the paper discharging properties of the offset blanket. As the method of improving the paper discharging properties of the offset blanket, for example, there is suggested a method of making the surface of the surface printing layer rough or a method of increasing a hardness of the surface printing layer. However, according to the former method, the shape of a dot to be formed on the offset blanket becomes inferior, which results in deterioration of a reproducibility of the spot. In addition, according to the latter method, an applicability of ink at the solid portion having a 100 % dot surface, i.e. a so-called solid applicability, becomes inferior. That is, there is a problem that the printing precision is deteriorated in both methods. There is also suggested a method of coating the surface of the surface printing layer with polyvinyl chloride, polyvinyl acetate, silicone rubber, etc. This method causes a problem that the number of steps is increased in the production process of the offset blanket. Furthermore, there is suggested a method of modifying the surface of the surface printing layer by irradiating ultraviolet ray on the surface of the surface printing layer (Japanese Laid-Open Patent Publication No. 51-37706) or subjecting to a chlorination treatment (Japanese Laid-Open Patent Publication No. 47-51729). However, both methods cause a problem that the number of steps is increased in the production process of the offset blanket and a working atmosphere becomes inferior. On the other hand, a problem that a paper powder is liable to separate from the surface of the paper by contacting with the offset blanket is caused by the fact that the paper discharging properties of the offset blanket is inferior, as described above. Such a paper powder is accumulated on the surface printing layer of the offset blanket by the long-term printing, thereby causing inclusion of the paper powder into ink. As a result, such a printing failure that white spots are formed at the printed portion arises. Since an opportunity to use a regenerated paper having an inferior paper quality has recently been increasing according to energy saving, recycling, etc., the above problem becomes serious. Furthermore, the surface of the blanket must be frequently washed so as to prevent the printing failure due to inclusion of the paper powder and, therefore, it becomes a problem that a printing operation becomes complicated due to the addition of a washing step. GB-A-848156 discloses an offset printing element and more particularly offset printing rollers and offset printing blankets. Said offset printing element having non-glazing characteristics during use comprises a surface layer of a butadiene-acrylic nitrile copolymer having incorporated therewith a minor proportion of nickel dibutyl dithiocarbamate. A typical composition comprises 100 parts by weight of an acrylicnitrile-butadiene copolymer (35% acrylicnitrile content), 30 parts by weight of a soft factice, 2 parts by weight of sulfur, 1 part by weight of an accelerator (benzothiazol disulphide), 1 part by weight of an antioxidant (phenylbetanaphthylamine), 5 parts by weight of zinc oxide, 25 parts by weight of a plasticizer (mineral oil) and 6 parts by weight of nickel dibutyl dithiocarbamate. FR-A-2.173.211 discloses a printing offset blanket comprising a supporting layer and a printing layer comprising 100 parts by weight of an acrylonitrile-butadiene copolymer, small amounts of zinc oxide, carbon black and an accelerator. It is a main object of this invention to provide a printing offset blanket wherein paper discharging properties are improved without causing deterioration of printing quality, increase in steps of making the offset blanket, etc. It is another object to provide a printing offset blanket wherein retention of paper powder, solid applicability and durability are improved. In order to accomplish these objects, the printing offset blanket of this invention comprises a supporting layer, which may have a porous compressive layer, and a surface printing layer provided on the supporting layer, the surface printing layer being formed of a rubber composition comprising 100 parts by weight of a rubber material, 1 to 10 parts by weight of a zinc oxide and 5 to 15 parts by weight of an inorganic filler other than zinc oxide or reinforcer. The inorganic filler or reinforcer is added in the rubber material for the purpose of maintaining a mechanical strength and extending. However, it has been found that the inorganic filler or reinforcer other than zinc oxide may be added in an amount which is reduced in comparison with a conventional case in order to improve the paper discharging properties, to prevent the paper powder from accumulating and to improve the solid applicability and durability. The zinc oxide is the filler or reinforcer which also serve as a vulcanization accelerator. Other objects and advantages of this invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawing. Fig. 1 is a sectional view illustrating one embodiment of the printing offset blanket in this invention. The printing offset blanket of this invention is, as shown in Fig. 1, composed of a supporting layer 2, which may have a porous compressive layer 5, and a surface printing layer 3 provided on the supporting layer 2. A rubber layer forming the surface printing layer 3 is prepared by blending various additives in a rubber material, and molding the mixture, followed by vulcanizing. Examples of the rubber material include synthetic rubbers such as acrylonitrile-butadiene rubber (NBR), hydrogenated NBR, chloroprene rubber (CR), polyurethane rubber, acrylic rubber, etc., or a mixture of at least two sorts of these synthetic rubbers, or a mixture of at least one sort of these synthetic rubbers and a polysulfide rubber. Among the above rubber materials, NBR is suitably used in this invention, because of it's elastic modulus and high oil resistance. Furthermore, examples of the additive include vulcanizing agents, vulcanization accelerators, auxiliary vulcanization accelerators, fillers, reinforcers, softeners, plasticizers, antioxidants, etc. As a vulcanizing agent, for example, there can be used organic peroxides, as well as sulfur, organic sulfurcontaining compound, etc. Examples of the organic sulfur-containing compound include tetramethylthiuram disulfide, N,N-dithiobismorpholine, etc. Furthermore, examples of the organic peroxide include benzoyl peroxide, etc. The amount of the vulcanizing agent to be added is normally 0.3 to 4 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the rubber material. Examples of the vulcanization accelerator include inorganic accelerators such as calcium hydroxide, magnesia (MgO), litharge (PbO), etc. and organic accelerators such as thiurams (e.g. tetramethylthiuram disulfide, tetraethylthiuram disulfide, etc.), dithiocarbamates (e.g. zinc dibutyldithiocarbamate, zinc diethyldithiocarbamate, etc.), thiazoles (e.g. 2-mercaptobenzothiazole, N-dicyclohexyl-2-benzothiazole sulfenamide, etc.), thioureas (e.g. trimethylthiourea, N,N'-diethylthiourea, etc.). Examples of the auxiliary vulcanization accelerator include metallic oxides such as zinc oxide, etc.; fatty acids such as stearic acid, oleic acid, cottonseed fatty acid, etc.; and vulcanization accelerators which have hitherto been known. Examples of the reinforcer or filler include zinc oxide, calcium carbonate, silica, magnesium carbonate, magnesium silicate, barium sulfate, clay, carbon black, etc. Examples of the softener include fatty acid (e.g. stearic acid, lauric acid, -etc.), cottonseed oil, tall oil, asphalt substance, paraffin wax, etc. Examples of the plasticizer include dioctyl adipate, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, etc. Examples of the antioxidant include imidazoles such as 2-mercaptobenzimidazole, etc.; amines such as phenyl-α-nephthylamine, N,N'-di-β-naphthyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, etc.; phenols such as di-t-butyl-p-cresol, styrenated phenol, etc. The supporting layer 2 is prepared by laminating a plurality of supporting bases 4a , 4b and 4c , which are impregnated with a rubber cement, and at least one compressive layer 5, which is optionally provided. The supporting bases 4a , 4b and 4c are woven fabrics of cotton, polyester, layon, etc. Examples of the rubber cement to be impregnated include acrylonitrile-butadiene rubber, chloroprene, etc. The rubber cement contains a predetermined amount of a vulcanizing agent, a vulcanization accelerator and, if necessary, a thickener. The rubber cement is coated on the above woven fabric using a blade coating method. Then, the above rubber material for forming the surface printing layer is applied on the surface of the supporting layer 2 through a primer layer (not shown), followed by drying to form a surface printing layer 3. Thereafter, the resulting laminate is vulcanized by heating at a predetermined temperature under a predetermined pressure to obtain an offset blanket 1 having a compressive layer 5 in the supporting layer 2 . The compressive layer 5 is formed as follows. That is, a rubber cement in which a water-soluble powder such as sodium chloride is dissolved is applied on at least one middle supporting substrate and, after drying and vulcanizing, the substrate was dipped in hot water at 60 to 100 °C for 6 to 10 hours and the water-soluble powder is eluted and dried. The offset blanket 1 thus obtained is used after adhering on the peripheral surface of a transfer cylinder, directly or through a lining material. The surface printing layer in this embodiment is formed of a rubber composition comprising 100 parts by weight of a rubber material, 10 to 1 parts by weight of a zinc oxide and 5 to 15 parts by weight of an inorganic filler or reinforcer other than zinc oxide. When the amount of the inorganic filler or reinforcer other than zinc oxide to be added exceeds 15 parts by weight, the paper discharging properties become inferior and, at the same time, the paper powder is liable to be accumulated. The amount of the inorganic filler or reinforcer to be added is preferably 5 to 10 parts by weight. Even if the amount of the inorganic filler or reinforcer to be added is within this range, the smaller the total amount to be added, the better. Examples of the inorganic reinforcer or filler other than zinc oxide include calcium carbonate, silica, magnesium carbonate, magnesium silicate, barium sulfate, clay, carbon black, etc., as described above. The zinc oxide is surely added in the rubber as the auxiliary vulcanization accelerator, or filler or reinforcer. However, when the amount to be added exceeds the amount required as the auxiliary vulcanization accelerator, the paper discharging properties are likely to be deteriorated and, at the same time, the paper powder is likely to be accumulated. Accordingly, in this invention, it is preferred that the amount of the zinc oxide to be added is small. The amount of the zinc oxide to be added is 10 to 1 parts by weight, preferably 7 to 1 parts by weight, for 100 parts by weight of the rubber. As the rubber material in the rubber composition, there can be any one which was described above. Furthermore, as the additive other than the filler and reinforcer (e.g. vulcanizing agents, vulcanization accelerators, auxiliary vulcanization accelerators, softeners, plasticizers, antioxidants, etc.), there can also be used any one which was described above. The offset blanket in this embodiment can be produced according to the same manner as that described above. The following Examples and Comparative Example further illustrate this invention in detail but are not to be construed to limit the scope thereof. Examples 1 to 4 and Comparative Example 1 (a) Preparation of supporting layer A cotton fabric was used as the supporting substrate. After impregnating with NBR so that the film thickness may become 0.08 mm, four supporting substrates were laminated to each other. Among them, a rubber material obtained by impregnating one supporting substrate which is present at the middle position is prepared according to a leaching method using sodium chloride as the water-soluble powder. (b) Preparation of surface printing layer The components shown in Table 1 were mixed in the proportion shown in the same table, and the mixture was dissolved in a toluene-methyl ethyl ketone mixed solvent to prepare a coating solution for surface printing layer. Then, this coating solution was applied on the surface of the above supporting layer, followed by drying to prepare a surface printing layer having a thickness of 0.30 mm. (c) Vulcanization and molding The surface printing layer was dried, molding with heating at a temperature of 150 °C under a pressure of 1 kg/cm 2 , and then polished so that a ten-point average roughness (Rz, JIS B 0601-1982) of the surface of the surface printing layer may be 3 to 6 µ m to obtain an offset blanket. In Table 1, DOP is dioctyl phthalate. DOP was added at an amount corresponding to the total amount of the filler and reinforcer other than zinc oxide in order to adjust the hardness. As a vulcanization accelerator, tetraethylthiuram disulfide was used. (Printing test) In order to evaluate the paper discharging properties, the retention of paper powder and the printing characteristics of the offset blanket obtained in Examples 1 to 4 and Comparative Example 1, the printing test was conducted. The test was conducted by winding the resulting offset blanket (thickness: 1.90 mm) on a transfer cylinder of an offset press (model 560, manufactured by Ryobi Co., Ltd.) and printing on a coat paper ("Yutoriro Coat 110kg", manufactured by Daio Seishi Co., Ltd.). As ink for printing, "Mark V New" manufactured by Toyo Ink Co., Ltd. was used, and a printing speed was 10,000 pieces/hour. The results of the printing test are shown in Table 2. In Table 2, the respective characteristics were evaluated according to the following formula. (a) Paper discharging properties (delamination) Ten coat papers printed in solid printing were laminated to measure a height (h, unit: mm) of the part where the paper is curled. The lower the height of the curling is, the smaller the frequency of delamination, which shows good paper discharging properties. o ○: 0 ≦ h < 3 ○: 3 ≦ h < 5 Δ: 5 ≦ h < 7 X: h ≧ 7 (b) Solid applicability The density distribution of the solid printing portion was examined by the image analysis to determine a standard deviation (n) thereof. The smaller the standard deviation is, the better the solid applicability. o ○: n ≦ 7 ○: 7 < n ≦ 9 Δ: 9 ≦ n < 11 x: n ≧ 11 (c) Retention of paper powder After 100,000 pieces were printed, paper powder adhered on the surface of the offset blanket was visually evaluated according to the following criteria. o ○ : The amount of the paper powder is extremely small. ○: The paper powder is scarcely adhered. Δ: The paper powder is accumulated in the vicinity of the edge part. x: The paper powder is accumulated on the whole surface. (c) Durability After 5,000,000 pieces was printed by using a web offset printing press, the surface of the offset blanket was visually evaluated according to the following criteria. ○: Cut and wear not observed. Δ: Little cut and wear were observed. x: A large amount of cut and wear were observed. PAPER DISCHARGING PROPERTIES SOLID APPLICABILITY RETENTION OF PAPER POWDER DURABILITY EX. 1 ○∼o ○ ○∼o ○ o ○ o ○ EX. 2 ○ ○ ○∼o ○ o ○ EX. 3 ○ ○ ○∼o ○ o ○ EX. 4 o ○ ○ ○∼o ○ o ○ COMP. EX. 1 × × ×∼Δ × As apparent from the results shown in Table 2, the smaller the total amount of the filler and reinforcer other than zinc oxide is, the better the paper discharging properties, retention of paper powder, solid applicability and durability are. Furthermore, the smaller the amount of the filler and reinforcer other than zinc oxide is, the more the mechanical strength of the surface printing layer is liable to be deteriorated. The reason why the durability is improved nevertheless is that it becomes difficult to cause slip between the surface printing layer and paper, which results in a remarkable decrease in wear.

Claims: A printing offset blanket comprising a supporting layer, which may have a porous compressive layer, and a surface printing layer provided on the supporting layer, the surface printing layer being formed of a rubber composition comprising 100 parts by weight of a rubber material, 1 to 10 parts by weight of a zinc oxide and 5 to 15 parts by weight of an inorganic filler other than zinc oxide or reinforcer. A printing offset blanket according to claim 1, wherein the inorganic filler or the reinforcer is added at an amount of 5 to 10 parts by weight for 100 parts by weight of the rubber material. A printing offset blanket according to claim 1 or 2, wherein the inorganic filler or reinforcer is selected from the group consisting of calcium carbonate, silica, magnesium carbonate, magnesium silicate, barium sulfate, clay and carbon black.

Inventors: FUSHIHARA KAZUHISA, MATSUKI TAKETO, TOMONO SEIJI, FUSHIHARA, KAZUHISA, MATSUKI, TAKETO, TOMONO, SEIJI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1995
Main classification: B41N10
IPC codes: B41N10