JP2006218752A - Printing blanket - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To povide a printing blanket, in which both the inking properties of ink or crushing of ink and sheet separating properties are reconciled. <P>SOLUTION: The surface rubber layer of the printing blanket is made of a rubber composition, which includes acrylonitrile-budadiene rubber, a vulcanizer and zinc carbonate, preferably no zinc oxide, under the condition that the compounding amount of the zinc carbonate is 1-10 pts.wt. to 100 pts.wt. of the rubber component including acrylonitrile-butadiene rubber, resulting in suppressing the increase of hardness under the condition that the loss tangent (tanδ) of the surface rubber layer contributing to sheet separation is kept smaller and consequently both the excellent sheet separating properties and the excellent inking properties of the ink can be reconciled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a blanket used for offset printing, and more particularly to a printing blanket suitable for high-speed offset printing on paper media.

In recent years, high-speed printing with a blanket cylinder rotation speed of about 1000 revolutions per minute has become the mainstream for printing on paper by offset printing. For this reason, in the design of a printing blanket, the surface rubber layer that is in direct contact with the printing paper has a tendency to place importance on its hardness, ink inking property, paper separation and the like.
In recent printing, (i) surface rubber is used for the purpose of improving the crushing of the ink, that is, preventing the occurrence of minute areas (so-called blanks) where the ink is not transferred on the printing paper. On the other hand, the surface rubber layer has a tendency to set the degree of swelling of the layer by the solvent of the ink, while (ii) the surface rubber layer from the viewpoint of facilitating separation of the printing paper from the surface of the printing blanket. The loss tangent (tan δ) obtained by solid viscoelasticity measurement tends to be set small.

Generally, rubber having high oil resistance such as acrylonitrile-butadiene rubber (NBR) is used for the surface rubber layer of the blanket. Moreover, as a rubber composition used for forming the surface rubber layer, generally, a rubber having high oil resistance such as NBR, a vulcanizing agent (crosslinking agent), zinc oxide as a vulcanization auxiliary, a vulcanization accelerator, What mix | blended fillers, such as carbon black, is used (refer patent documents 1-3).
JP 2003-1964 A JP 2003-341251 A JP 2000-313180 A

However, when the degree of swelling of the surface rubber layer is set large as in (i) above, the inking property and crushing of the ink are good, and the hardness of the surface rubber layer tends to be small. However, the loss tangent (tan δ) of the surface rubber layer is increased, and the paper releasability is reduced.
On the other hand, as a method for reducing the loss tangent (tan δ) of the surface rubber layer, for example, in the rubber composition for forming the surface rubber layer, there is a method of increasing the compounding amount of the vulcanization accelerator and the zinc oxide. However, when the blending amount of the vulcanization accelerator is increased, the loss tangent (tan δ) of the surface rubber layer is decreased, but the hardness is increased and the ink setting property is decreased. Further, a large amount of the vulcanization accelerator may cause so-called bloom, which gradually oozes on the surface of the printing blanket. Further, by increasing the blending amount of zinc oxide, the loss tangent (tan δ) becomes a value suitable for practical use. Specifically, the loss tangent (tan δ) at a temperature of 23 ° C. and a frequency of 10 Hz becomes 0.10 or less. If it is going to set, it will be necessary to mix | blend zinc oxide in the ratio of 7 weight part or more with respect to 100 weight part of rubber components, such as NBR. For this reason, the hardness of a surface rubber layer becomes large, and the malfunction that the ink setting property falls will be caused.

That is, as described in (ii) above, when the loss tangent (tan δ) of the surface rubber layer is set small, it is easy to separate the paper, but the hardness of the surface rubber layer is increased or the ink is hardened. Inconveniences such as deterioration and occurrence of omission occur.
Accordingly, an object of the present invention is to provide a printing blanket that achieves both ink fillability, ink crushing, and paper separation.

In order to achieve the above object, the present invention provides:
(1) A printing blanket having a surface rubber layer, wherein the surface rubber layer contains acrylonitrile-butadiene rubber, a vulcanizing agent and zinc carbonate, and the compounding amount of the zinc carbonate is the acrylonitrile-butadiene rubber. A blanket for printing, characterized in that it is formed using 1 to 10 parts by weight of a rubber composition with respect to 100 parts by weight of a rubber component containing
(2) The printing blanket according to (1), wherein the rubber composition does not contain zinc oxide,
(3) The loss tangent (tan δ) obtained by measuring the solid viscoelasticity of the surface rubber layer is 0.10 or less at a temperature of 23 ° C. and a frequency of 10 Hz, (1) or (2) Printing blanket, as described in
(4) The printing blanket according to any one of (1) to (3), wherein the surface rubber layer has an international rubber hardness (IRHD) of 40 to 64,
Is to provide.

  According to the printing blanket of the present invention, it is possible to suppress an increase in hardness in a state where the loss tangent (tan δ) of the surface rubber layer contributing to paper separation is kept small, excellent paper separation properties, and excellent Ink fillability can be made compatible.

The printing blanket of the present invention comprises a surface rubber layer, and the rubber composition used for forming the surface rubber layer contains acrylonitrile-butadiene rubber, a vulcanizing agent and zinc carbonate, and the zinc carbonate The blending amount is 1 to 10 parts by weight with respect to 100 parts by weight of the rubber component containing the acrylonitrile-butadiene rubber.
The surface rubber layer is obtained by blending a rubber component mainly composed of acrylonitrile-butadiene rubber (NBR), a vulcanizing agent and zinc carbonate, and, if necessary, a vulcanization accelerator, a filler, a reinforcing agent and the like. The rubber composition is formed.

As the rubber component, in addition to NBR, for example, chloroprene rubber (CR), polyurethane rubber (U), a mixture thereof, a mixture of the above exemplified rubber and polysulfide rubber, and the like may be included. The rubber component is preferably only NBR.
NBR is not particularly limited. In the present invention, various known NBRs such as very high nitrile type and high nitrile type NBR having a large amount of bonded acrylonitrile, low nitrile type and medium nitrile type NBR having a small amount of bonded acrylonitrile are known. NBR can be used. Among them, in the present invention, from the viewpoint of oil resistance of the surface rubber layer, a medium to high nitrile type (with a bound acrylonitrile amount of 31% or more and less than 36%) or a high nitrile type (a bound acrylonitrile amount of 36% or more, It is more preferable to use less than 43%).

Examples of the vulcanizing agent include sulfur; organic sulfur-containing compounds such as N, N′-dithiobismorpholine; and organic peroxides such as benzoyl peroxide and dicumyl peroxide. Of these, sulfur and organic sulfur-containing compounds are preferable.
Although the compounding quantity of a vulcanizing agent is not specifically limited, Usually, it is 0.5-2 weight part with respect to 100 weight part of rubber components.

The compounding quantity of zinc carbonate is 1-10 weight part with respect to 100 weight part of rubber components, Preferably, it is 3-7 weight part.
When the blending amount of zinc carbonate is less than 1 part by weight with respect to 100 parts by weight of the rubber component, the loss tangent (tan δ) of the surface rubber layer is reduced and the paper blanket of the printing blanket is improved. No effect can be obtained. On the contrary, if the blending amount of zinc carbonate exceeds 10 parts by weight with respect to 100 parts by weight of the rubber component, the hardness of the surface rubber layer increases, leading to a decrease in ink inking property and occurrence of omission. Such a problem occurs.

  In the present invention, zinc oxide may be blended together with zinc carbonate for the purpose of reducing the loss tangent (tan δ) of the surface rubber layer. However, since zinc oxide is less effective in reducing the loss tangent (tan δ) of the surface rubber layer than zinc carbonate, its amount is large for the purpose of reducing the loss tangent (tan δ) of the surface rubber layer. There is a risk that the hardness of the surface rubber layer will increase. Therefore, zinc oxide is preferably blended in a proportion of 3 parts by weight or less with respect to 100 parts by weight of the rubber component, and more preferably not blended at all.

Further, when zinc oxide is blended together with zinc carbonate, the total amount of zinc carbonate and zinc oxide is preferably 10 parts by weight or less, more preferably 7 parts by weight with respect to 100 parts by weight of the rubber component. It is as follows.
Examples of the vulcanization accelerator include tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD), tetrakis (2-ethylhexyl) thiuram disulfide, tetramethylthiuram monosulfide (TMTM), Thiurams such as dipentamethylene thiuram tetrasulfide (TPTT); 2-mercaptobenzothiazole (MBT), dibenzothiazyl disulfide (MBTS), zinc salt of 2-mercaptobenzothiazole (ZnMBT), cyclohexyl of 2-mercaptobenzothiazole Thiazoles such as amine salts (CMBT), 2- (N, N′-diethylthiocarbamoylthio) benzothiazole, 2- (4-morpholinodithio) benzothiazole Class: pentamethylenedithiocarbamate piperidine salt (PPDC), pipecolyldithiocarbamate pipecoline salt (PMPDC), dimethyldithiocarbamate zinc (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc dibutyldithiocarbamate (ZnBDC), N-ethyl -Zinc N-phenyldithiocarbamate (ZnEPDC), zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate (NaEDC), sodium dibutyldithiocarbamate (NaBDC), dimethyldithiocarbamate (CuMDC), dimethyl Dithiocarbamates such as ferric dithiocarbamate (FeMDC) and tellurium diethyldithiocarbamate; Sil-2-benzothiazolylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (BBS), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS) N, Sulfenamides such as N′-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS); thioureas such as trimethylthiourea (TMU) and N, N′-diethylthiourea (DEU); 1,3-diphenyl Guanidines such as guanidine (DPG), di-o-tolylguanidine (DOTG), 1-o-tolylbiguanide (OTBG); organic vulcanization accelerators such as hexamethylenetetramine and n-butyraldehyde aniline, slaked lime, Inorganic vulcanization accelerators such as magnesium oxide, titanium oxide, and resurge (PbO) Advancement agents. These may be used alone or in combination of two or more. Of the vulcanization accelerators exemplified above, thiurams and thiazoles are preferable.

  The blending amount of the vulcanization accelerator is not particularly limited, but from the viewpoint of preventing the so-called bloom phenomenon from gradually oozing out on the surface of the surface rubber layer, for example, the blending amount of thiurams is It is preferable to set the amount of thiazole to be 2.5 parts by weight or less with respect to 100 parts by weight of the rubber component so that it is 3 parts by weight or less with respect to 100 parts by weight of the rubber component.

In general, the total amount of the vulcanization accelerator is preferably 1 to 5.5 parts by weight, more preferably 2 to 4.5 parts by weight as the total amount.
Examples of the filler include inorganic fillers such as calcium carbonate, clay, barium sulfate, diatomaceous earth, mica, asbestos, and graphite; organic fillers such as recycled rubber, powder rubber, asphalt, styrene resin, and glue. It is done.

Examples of the reinforcing agent include inorganic reinforcing agents such as carbon black, silica-based or silicate-based white carbon, surface-treated precipitated calcium carbonate, magnesium carbonate, talc, and clay; coumarone indene resin, phenol resin, high Examples thereof include organic reinforcing agents such as styrene resin (styrene-butadiene copolymer having a high styrene content).
The blending amount of the filler and the reinforcing agent is not particularly limited as long as the loss tangent (tan δ) and hardness of the surface rubber layer do not become excessively large. The strength and the rubber composition required for the surface rubber layer are not limited. What is necessary is just to set suitably according to a bulk.

  In addition to the components exemplified above, vulcanization accelerators such as stearic acid, oleic acid, and cottonseed fatty acid are optionally added; for example, aromatic organic acids such as salicylic acid, phthalic anhydride, and benzoic acid. Vulcanization retarders such as nitroso compounds such as N-nitrosodiphenylamine, N-nitroso-2,2,4-trimethyl-1,2-dihydroquinone, N-nitrosophenyl-β-naphthylamine; Imidazoles such as imidazole, amines such as phenyl-α-naphthylamine, N, N′-di-β-naphthyl-p-phenylenediamine, N-phenyl-N′-isopropyl-p-phenylenediamine, di-tert- Anti-aging agents such as butyl-p-cresol, phenols such as styrenated phenol; Acids, lauric acid and other fatty acids, cottonseed oil, tall oil, asphalt material, paraffin wax and other softeners such as vegetable oils, mineral oils and synthetic oils; for example, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate You may mix | blend plasticizers, such as.

What is necessary is just to set the compounding quantity about said other compounding component suitably in the range by which the loss tangent (tan-delta) and hardness of a surface rubber layer do not become large too much.
For the surface rubber layer, the loss tangent (tan δ) obtained by the solid viscoelastic properties is set to be 0.10 or less at a temperature of 23 ° C. and a frequency of 10 Hz.
When the loss tangent (tan δ) of the surface rubber layer at a temperature of 23 ° C. and a frequency of 10 Hz exceeds 0.10, the paper blanket of the printing blanket is deteriorated, which may cause problems such as thicker halftone dots and doubles. There is.

  The loss tangent (tan δ) of the surface rubber layer at 23 ° C. and 10 Hz is preferably a smaller value in the above range, and the lower limit thereof is not particularly limited, but is usually about 0.05. In order to set the loss tangent (tan δ) of the surface rubber layer at 23 ° C. and 10 Hz to less than 0.05, it is usually necessary to reduce the amount of the reinforcing agent or the like as much as possible. May cause problems.

  In the present invention, the condition of the temperature of 23 ° C. and the frequency of 10 Hz is selected for the measurement of the loss tangent (tan δ) for the following reason. Various types of offset printing machines in which a printing blanket is installed on a blanket cylinder and used at a rotational speed of the blanket cylinder from about 100 revolutions / minute to about 1200 revolutions / minute are known. Here, when the number of rotations of the blanket cylinder is converted into a frequency of deformation applied to the printing blanket, the frequency is approximately 1.7 to 20 Hz. Therefore, in the present invention, as the test frequency for evaluating the viscoelastic properties of the printing blanket, 10 Hz, which is a substantially intermediate value in the above range, is selected, and the test temperature is set to 23 ° C. (Tan δ) was measured.

Hardness of the surface rubber layer has a JIS _{K 6253 -1997} (vulcanized rubber and thermoplastic hardness test method of the rubber) to define international rubber hardness of (IRHD), is set to be 40 to 64.
When the international rubber hardness (IRHD) of the surface rubber layer exceeds 64, there is a possibility that ink inking property may be lowered, and particularly when printing on low-quality printing paper having a large surface roughness. In this case, there is a risk that it may easily cause omission. Conversely, when the international rubber hardness (IRHD) is less than 40, the degree of deformation of the surface rubber layer becomes too large when using a printing blanket, which may lead to thickening of halftone dots, doubles and the like.

The international rubber hardness (IRHD) of the surface rubber layer is preferably 50-60 within the above range.
The printing blanket of the present invention is not particularly limited except that it has a surface rubber layer. For example, the printing blanket may have a support formed by laminating a plurality of base fabric layers (reinforcing layers). Further, it may be a surface rubber layer alone or a so-called solid type printing blanket having a surface rubber layer and the support, and a compressible layer made of a porous elastic member inside the support. It may be a so-called air type printing blanket.

The surface rubber layer can be prepared by dissolving and dispersing in a solvent such as toluene or methyl ethyl ketone to form a rubber paste, and then blade coating the substrate or the support to a predetermined thickness. .
The support is not particularly limited, and various known supports can be used. Specifically, for example, a base cloth such as cotton cloth impregnated with rubber paste and a plurality of the obtained base cloth layers are laminated, or a resin film is used. The rubber paste impregnated into the base fabric is not particularly limited. For example, it is preferable to use a rubber paste containing the same rubber component as the rubber composition for forming the surface rubber layer in consideration of adhesion to the surface rubber layer. .

  The compressible layer is not particularly limited, and various known compressible layers can be used.

EXAMPLES Next, although this invention is demonstrated based on an Example, this invention is not limited by the following Example.
<Manufacture of printing blankets>
In the following Examples and Comparative Examples, various components used to form a printing blanket are as follows.
-Medium-high nitrile NBR: Acrylonitrile-butadiene rubber, medium-high nitrile type (bonded acrylonitrile amount 33.0%), trade name "Nipol DN3350" manufactured by Nippon Zeon Co., Ltd.
Medium nitrile NBR: acrylonitrile-butadiene rubber, medium nitrile type (bound acrylonitrile amount 28.0%), Mooney viscosity ML _{1 + 4} (100 ° C.) = 50, trade name “Nipol DN2850” manufactured by Nippon Zeon Co., Ltd.
-Silica: Tosoh Silica Co., Ltd. trade name "Nipsil RS-150"
Silane coupling agent: Degussa's trade name “Si-69”
-Plasticizer: Dioctyl phthalate-Zinc carbonate: Made by Sakai Chemical Co., Ltd.-Zinc oxide: Made by Mitsui Kinzoku Co., Ltd.-Anti-aging agent (A): 2,6-di-tert-butyl-4-methylphenol, large Product name “NOCRACK 200” manufactured by Uchinoseki Chemical Co., Ltd.
Anti-aging agent (B): 2,2-methylenebis (4-methyl-6-tert-butylphenol), trade name “NOCRACK NS-6” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Thiuram vulcanization accelerator: Tetraethylthiuram disulfide (TETD), trade name “Noxeller TET” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Thiazole-based vulcanization accelerator: dibenzothiazyl disulfide (MBTS), trade name “Noxeller DM” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Sulfenamide vulcanization accelerator: N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), trade name “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur powder: manufactured by Tsurumi Chemical Co., Ltd. ・ Hollow microspheres: unexpanded hollow microspheres (thermal expansion microcapsules) whose shell is a copolymer of acrylonitrile and methyl methacrylate, shell wall softening point (Td) 120 ° C, trade name “F50D” manufactured by Matsumoto Yushi Seiyaku Co., Ltd.
(Reference Example 1)
Carbon black (GPF) 50 parts by weight, powdered sulfur 2 parts by weight, sulfenamide vulcanization accelerator 1.5 parts by weight, thiuram vulcanization accelerator 0.6 parts by weight with respect to 100 parts by weight of medium nitrile NBR 1 part by weight of stearic acid, 5 parts by weight of zinc oxide and 1 part by weight of anti-aging agent (B) were blended and kneaded in a kneader (manufactured by Moriyama Co., Ltd., 3 L capacity), then dissolved in toluene and rubber Glue was obtained. Next, hollow microspheres were blended and dispersed in the obtained rubber paste, and then this rubber paste was applied onto a cotton cloth having a width of 1 m and a length of 1 m and dried to obtain a thickness of 0.3 mm. An unvulcanized rubber layer (a precursor of the compressible layer) was formed. The blending amount of the hollow microspheres is a ratio M / the ratio of the volume M of the hollow microspheres to the volume R of the medium nitrile NBR, assuming that the average particle diameter when the hollow microspheres are expanded is 50 μm. R was set to be 1 (so that the volume of the hollow microsphere and the medium nitrile NBR was the same).

Further, the obtained unvulcanized rubber layer was heated for 30 minutes under the conditions of a vulcanization pressure (Pv) of 3 kPa and a vulcanization temperature (Tv) of 140 ° C., while foaming the hollow microspheres, A compressible layer was formed by vulcanization.
Next, 40 parts by weight of silica, 5 parts by weight of plasticizer, 5 parts by weight of zinc oxide, 0.2 parts by weight of thiuram vulcanization accelerator, 0.2 parts by weight of thiazole vulcanization accelerator, and 100 parts by weight of medium / high nitrile NBR. Part by weight and 1.5 parts by weight of powdered sulfur were blended and kneaded by a kneader (manufactured by Moriyama Co., Ltd., internal volume 3 L), and then dissolved in toluene to obtain a rubber paste for forming a support.

  Further, the obtained rubber paste for forming a support is impregnated into a cotton cloth to form a base cloth, and the obtained three base cloths and the above compressible layer are laminated to form a support (base cloth lamination). Body). In this support, a compressible layer is arranged on one surface of one base fabric (herein, simply referred to as “single layer”), and two base fabrics are overlapped (here, simply “laminated”). A body ”) is formed so as to be opposed to the single-layer body with the compressible layer interposed therebetween.

Example 1
25 parts by weight of silica, 2.5 parts by weight of silane coupling agent, 20 parts by weight of plasticizer, 1 part by weight of zinc carbonate, 1 part by weight of stearic acid, 5 parts by weight of pigment, anti-aging agent for 100 parts by weight of medium-high nitrile NBR (A) 2 parts by weight, 3.5 parts by weight of a vulcanization accelerator (total amount of TETD and MBTS) and 1 part by weight of powdered sulfur were blended and kneaded with a kneader (manufactured by Moriyama Co., Ltd., internal volume 3 L). did. Next, the obtained rubber composition for forming the surface rubber layer was dissolved in toluene to obtain a rubber paste for forming the surface rubber layer.

  Next, after the rubber paste for forming the surface rubber layer is glued to one surface of the support obtained in Reference Example 1 (specifically, the other surface of the single layer body in the support) And press vulcanized at 160 ° C. Further, after vulcanization, the surface rubber layer was polished to obtain a printing blanket. The surface roughness of the surface rubber layer was adjusted so that the 10-point average roughness Rz was about 6 μm after polishing.

(Examples 2 to 6 and Comparative Examples 1 and 2)
In the rubber composition for forming the surface rubber layer, the blending amount of zinc carbonate is 0.5 parts by weight (Comparative Example 1), 3 parts by weight (Example 2), 5 parts by weight with respect to 100 parts by weight of the medium-high nitrile NBR. (Example 3) A blanket for printing was obtained in the same manner as in Example 1 except that the amount was 10 parts by weight (Example 4) or 15 parts by weight (Comparative Example 2).

(Comparative Example 3)
Example 1 except that in the rubber composition for forming the surface rubber layer, zinc oxide was blended instead of zinc carbonate, and the blending amount of zinc oxide was 5 parts by weight with respect to 100 parts by weight of the medium-high nitrile NBR. In the same manner as above, a printing blanket was obtained.
(Comparative Examples 4 to 8)
In the rubber composition for forming the surface rubber layer, the blending amount of zinc oxide is 7 parts by weight (Comparative Example 4), 10 parts by weight (Comparative Example 5), 15 parts by weight (comparative) with respect to 100 parts by weight of the medium-high nitrile NBR. A blanket for printing was obtained in the same manner as in Example 1 except that Example 6), 20 parts by weight (Comparative Example 7) and 25 parts by weight (Comparative Example 8) were used.

In Comparative Example 8, it was impossible to form the surface rubber layer because the vulcanization rate in the rubber composition for forming the surface rubber layer was too high.
<Physical property evaluation of printing blanket>
(Hardness of surface rubber layer)
Each surface printed layer was cut out from the printing blanket obtained in the above Examples and Comparative Examples to prepare a sample having a thickness of 0.2 mm. Then, for this sample, based on the provisions of JIS _{K 6253 -1,997,} using Wallace (H.W.Wallace) manufactured by a hardness meter "H5B type" International Rubber Hardness of (IRHD) was measured.

(Measurement of loss tangent (tan δ))
Loss tangent (tan δ) at a temperature of 23 ° C. and a frequency of 10 Hz using a viscoelastic spectrometer (FT-Rheospectra “DVE-V4”) manufactured by Rheology Co., Ltd. for a sample similar to that used for the measurement of hardness. Was measured.
<Evaluation of printability>
(Releasability from paper)
The printing blankets obtained in the above examples and comparative examples were respectively installed on the blanket cylinder of an offset printing machine (model number “RYOBI 520”) manufactured by Ryobi Co., Ltd., and offset rotary printing was performed. Recycled paper was used as the printing paper, and solid printing was performed at a blanket cylinder rotation speed of 150 revolutions per minute.

After solid printing was performed on 100 sheets of recycled paper, the curl amount (mm) of the recycled paper was measured to evaluate paper separation. Paper separation was evaluated as AA (very good) when the curl amount was less than 15 mm, A (good) when it was 15 mm or more and less than 20 mm, and B (bad) when it was 20 mm or more.
(Ink fillability)
In the same manner as the evaluation of the paper separation property, after performing solid printing on 100 sheets of recycled paper, the area of the portion where white spots (elementary omission) occurred in the solid portion after printing was measured. Next, the area ratio of the white areas in the total area of the solid part is calculated, and when the area ratio is less than 1.5%, AA (very good), 1.5% or more, less than 2.0% A (good) when it was, and B (bad) when it was 2.0% or more.

  The evaluation results of the above physical properties and printability are shown in Table 1 and Table 2 together with the blending amounts of zinc carbonate and zinc oxide (blending amount with respect to 100 parts by weight of NBR) in the rubber composition for forming the surface rubber layer.

  As shown in Table 1 and Table 2, the amount of zinc carbonate in the rubber composition for forming the surface rubber layer is set in the range of 1 to 10 parts by weight with respect to 100 parts by weight of NBR, and the hardness of the surface rubber layer ( IRHD) is 20 to 64, and the tan δ (23 ° C., 10 Hz) of the surface rubber layer is adjusted to be 0.10 or less. Paper releasability and ink fillability were compatible.

  In Comparative Example 1 in which the tan δ (23 ° C., 10 Hz) of the surface rubber layer could not be sufficiently reduced because the blending amount of zinc carbonate was too small, the ink removability was good, but the paper releasability Decreased. On the other hand, since the blending amount of zinc carbonate was too large, in Comparative Example 2 in which the hardness (IRHD) of the surface rubber layer exceeded 60, although the paper separability was good, the ink inking property was lowered.

Further, in Comparative Examples 3 to 8 in which zinc oxide was blended instead of zinc carbonate, it was not possible to achieve both paper separation and ink fillability.
The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

Claims (4)

A printing blanket having a surface rubber layer,
The surface rubber layer contains acrylonitrile-butadiene rubber, a vulcanizing agent and zinc carbonate, and the blending amount of the zinc carbonate is 1 to 10 weights with respect to 100 parts by weight of the rubber component containing the acrylonitrile-butadiene rubber. A blanket for printing, which is formed using a rubber composition as a part.   The printing blanket according to claim 1, wherein the rubber composition does not contain zinc oxide.   The printing blanket according to claim 1 or 2, wherein a loss tangent (tan δ) obtained by solid viscoelasticity measurement of the surface rubber layer is 0.10 or less at a temperature of 23 ° C and a frequency of 10 Hz. .   The printing blanket according to any one of claims 1 to 3, wherein the hardness of the surface rubber layer is 40 to 64 in terms of international rubber hardness (IRHD).