JP3360698B2 - Blanket for offset printing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing blanket used in an offset printing machine, and more particularly, to a blanket for offset printing which enhances the durability of the uppermost layer of a surface layer and has high printing durability when swollen. It is about.

[0002]

2. Description of the Related Art In offset printing, an image is transferred from a printing plate to a blanket once, and the image transferred to the blanket is printed on paper. Plates conventionally used for offset printing have low durability, and so-called “printing plate”
Sometimes occurred. The printing plate is generated because the printing plate and the blanket come into contact with each other at the time of printing and the printing plate is worn. For this reason, at least the uppermost layer of the surface layer of the blanket which comes into contact with the printing plate has been required to have low abrasion resistance. However, in recent years, the durability of a printing plate has been dramatically improved due to improvements in plate materials and plate making techniques.

On the other hand, the conventional blanket cleaning method is as follows.
The blanket surface was manually wiped with a cleaning agent in a waste cloth to remove ink, paper powder, and the like. Such hand-wiping cleaning is a dangerous and time-consuming operation, and has to be performed under bad conditions such as odor and stains of the cleaning agent. In order to improve the washing operation under such bad conditions, automatic blanket washing machines have recently been used to save labor in the printing operation. As one of automatic blanket washing machines, for example, a cleaning liquid is sprayed and moistened on a cleaning cloth (nonwoven fabric), the wet cleaning cloth (nonwoven fabric) is pressed against a blanket of the blanket cylinder, and then the blanket cylinder is rotated. Rub off ink and paper powder.

As described above, in the method of rubbing while pressing the blanket surface, a high load is applied to the blanket surface. Therefore, if the pressing force on the surface of the blanket becomes excessive, or if the cleaning conditions are inappropriate such as the amount of the cleaning liquid supplied to the cleaning cloth (nonwoven fabric) is insufficient, the surface of the blanket is worn in a short time. Become. In addition, the load on the blanket has increased with the speeding up of the printing press, and the frequency of replacement due to wear of the blanket has also increased. Therefore, as the printing durability of the printing plate has been improved, there is now a demand for a highly durable blanket having enhanced rubber strength, particularly abrasion resistance, for forming the surface layer of the blanket. As a method of improving rubber strength, a method of filling a large amount of a reinforcing filler such as hydrated silica, a method of adding a large amount of hydrated silica, and a method of adding a coupling such as a silane coupling agent are known. .

[0005]

However, in order to greatly improve the rubber strength by adding a coupling, it is necessary to fill a large amount of a reinforcing filler. Increasing the filling amount of the reinforcing filler also increases the hardness of the rubber. When the hardness of the rubber in the surface layer of the blanket increases, so-called "image fatness" occurs. That is, a phenomenon occurs in which the image transferred from the blanket to the sheet becomes larger than the image on the original printing plate, and the gradation of printing is significantly impaired. From these facts, it is considered that the hardness of the rubber material used for the surface layer of the blanket is preferably about 50 according to a JIS A hardness meter. However, the conventional method of filling a large amount of the reinforcing filler cannot be applied to the rubber material of the surface layer of the blanket because the hardness cannot be suppressed. Therefore, it is required to increase the strength of the rubber without increasing the hardness of the rubber.

The invention described in Japanese Patent Application Laid-Open No. 5-85080 discloses a method in which an oil-resistant rubber and a polysulfide rubber are mixed with a surface layer for the purpose of improving the paper discharge property of a blanket, that is, the ease of separation of the paper from the blanket. It is proposed to form with a blend that has been prepared. And in order to achieve the above purpose,
The mixing amount of the polysulfide rubber with respect to the oil-resistant rubber is appropriately from 99/1 to 60/40, more preferably from 95/5 to 85/15 by weight of the oil-resistant rubber / polysulfide rubber (paragraph). No. 0011).

[0007] However, only by mixing a polysulfide rubber with a conventionally used synthetic rubber such as an acrylonitrile butadiene rubber copolymer, chloroprene rubber or polyurethane rubber exemplified as an oil-resistant rubber, the paper discharging property is improved. Although it is possible to do so, it cannot meet the demand for a highly durable blanket with enhanced rubber strength, particularly abrasion resistance, forming the surface layer portion. That is, there is a problem that the wear resistance of the swollen blanket cannot be improved by using the automatic washing machine.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. To solve the above-mentioned problems, the present invention uses an automatic washing machine for pressing a wet cleaning cloth (non-woven fabric) against a blanket to scrape ink or paper powder. It is an object of the present invention to provide a highly durable offset printing blanket which is sufficiently resistant to swelling and has enhanced abrasion resistance when swollen.

[0009]

The inventors of the present invention have made various studies to solve the above-mentioned problems. As a result, the present inventor found that polysulfide rubber was replaced with acrylonitrile-butadiene-isoprene copolymer rubber to improve abrasion resistance. Was found to be effective to mix. Accordingly, the present invention provides a printing blanket comprising a support layer made of one or a plurality of woven fabrics and a surface layer laminated thereon, wherein at least the uppermost layer of the surface layer is made of acrylonitrile butadiene-isoprene. A binary blend of a copolymer rubber and a polysulfide rubber, or a ternary blend of an acrylonitrile butadiene-isoprene copolymer rubber, a polysulfide rubber and another rubber, wherein the polysulfide rubber is one of the polymer components. Are mixed at a ratio of 5 to 40% by weight.

[0010] When the acrylonitrile-butadiene-isoprene copolymer rubber (hereinafter, simply referred to as NBIR) is formed from a ternary blend of a polysulfide rubber and another rubber, the other rubber is made of acrylonitrile-butadiene copolymer. Rubber (hereinafter simply referred to as NBR) can be used. In this case, it is preferable to mix NBIR at a ratio of 40% by weight or more of the polymer component in the uppermost layer.

The polysulfide rubber is obtained by reacting an organic dihalide compound with an inorganic alkali polysulfide. The polysulfide rubbers currently used include Thiokol FA and Thiokol ST. Thiokol FA is composed of ethylene dichloride and bis-2-chloroethylformal 5
It is a 0:50 disulfide polymer and is represented by the following chemical formula 1.

[0012]

Embedded image

Thiokol ST is a polysulfide polymer of bis-2-chloroethylformal and 2% of trichloropropane, and has a sulfuration degree of 2.25 and a sulfur content of 37%.

The mixing ratio of the polysulfide rubber in the polymer component is 5 to 40% by weight. 5% by weight of polysulfide rubber
This is because the abrasion resistance at the time of swelling cannot be improved even if the amount is less than or equal to or more than 40% by weight. Also, NBI
In the case of a ternary blend in which R and polysulfide rubber are blended with another third rubber, the mixing ratio of NBIR is preferably 40% by weight or more of the polymer component. If the content is 40% by weight or less, the wear resistance characteristics of NBIR cannot be utilized. One or more kinds of commonly used vulcanizing agents, vulcanization accelerators, reinforcing agents, antioxidants and the like can be added to the rubber compounding.

[0015]

The NBIR acts to increase the strength without increasing the hardness of the rubber itself, and the polysulfide rubber acts to improve the abrasion resistance during swelling.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described.
First, the blanket to be used is, like the compressible blanket made of a regular abrasive, coated with a rubber composition on a support layer formed by laminating a plurality of cotton cloths and dried to form a surface layer. Is provided. Then, only the rubber composition in the surface layer was changed. The composition of the surface layer is as shown in Tables 1 and 2. Table 1 shows the case where the mixing ratio of NBIR and polysulfide rubber was changed as the rubber composition, and Table 2 shows the case where NBR was blended as the third rubber.

[0017]

[Table 1]

[0018]

[Table 2]

The blanket sheet produced from the compounded rubber shown in Tables 1 and 2 was wound around a drum to form a sheet.
It was placed in a dry heat vulcanizer at 5 ° C. for 10 hours and vulcanized. And
The abrasion resistance of the blanket vulcanized under the above conditions was evaluated as follows. The abrasion tester is ASTM D16
30 NBS abrasion tester. That is, as shown in FIG. 3, in the abrasion tester, a cleaning cloth (nonwoven fabric) 11 is wound around an iron drum 10 having a diameter of 150 mm, and the sample holder 13 is attached so that the surface layer of the blanket 15 contacts the cleaning cloth 11. Before installing the blanket 15, the cleaning agent “Mineral Spirits A” manufactured by Nippon Oil Co., Ltd.
25 m immersed and swelled in a condition of 50 ° C. × 72 hours
An m-square one was used. The sample holder 13 is a support 1
6, which is rotatably supported by a shaft 6, and a weight 17 is attached to the tip to press the blanket against the iron drum 10. The weight 17 was designed to apply a load of 4 N to the blanket 15.

As the cleaning cloth 11, a cleaning cloth manufactured by Nippon Baldwin Co., Ltd. is used.
5,000 rpm. The blanket 15
The wear of the blanket was caused by the rotation of the iron drum 10, and the wear amount was measured with a dial gauge 19. A
STM D1630 specifies that a load of 22 N is applied. However, when this load is applied, the cleaning cloth is cut off from the seam when the cleaning cloth 11 is wound around the iron drum 10. The load was 4N.

The results of the abrasion test by the above method are shown in Tables 3 and 4, and FIGS. 1 and 2. Table 3 and FIG. 1 show the amount of wear of the blanket according to the composition shown in Table 1.

[0022]

[Table 3]

Table 4 and FIG. 2 show the amount of wear of the blanket according to the composition shown in Table 2.

[0024]

[Table 4]

From the above results, it can be seen that the rubber composition blended with NBIR and polysulfide rubber has excellent abrasion resistance during swelling. That is, in the case of a binary blend of NBIR and polysulfide rubber, as shown in Table 3 and FIG.
When the polysulfide rubber is mixed at a ratio of 5 to 40% by weight, an improvement in wear resistance is observed. Further, in the case of a ternary blend in which NBR is blended as the other third rubber, as shown in Table 4 and FIG. 2, the effect is obtained when NBIR is mixed in a proportion of 40% by weight or more of the polymer component. There is.

[0026]

As described in detail above, at least the uppermost layer of the surface layer of the blanket is a binary blend of NBIR and polysulfide rubber, or a triple blend of NBIR, polysulfide rubber and other rubber. Made from the original blend, it withstands the use of an automatic washing machine that rubs ink and paper powder by pressing a wet cleaning cloth (non-woven fabric) against a blanket, and has enhanced durability when swelling. A high blanket for offset printing can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of an abrasion test on the uppermost layer on the surface with different mixing ratios of NBIR and polysulfide rubber.

FIG. 2 is a graph showing the results of a wear test of the uppermost layer on the surface when NBR is mixed as the third rubber.

FIG. 3 is an explanatory front view of the abrasion tester.

[Explanation of symbols]

 Reference Signs List 10 iron drum 11 cleaning cloth 13 sample holder 15 sample blanket 17 weight 19 dial gauge

Claims (2)

(57) [Claims] 1. A printing blanket comprising a support layer made of one or a plurality of woven fabrics and a surface layer laminated thereon, wherein at least the uppermost layer of the surface layer is made of acrylonitrile butadiene-isoprene. Formed from a binary blend of a polymerized rubber and a polysulfide rubber, or a ternary blend of an acrylonitrile butadiene-isoprene copolymer rubber, a polysulfide rubber and another rubber, and among the polymer components in the uppermost layer, A blanket for offset printing, wherein a polysulfide rubber is mixed at a ratio of 5 to 40% by weight. 2. The method according to claim 1, wherein the other rubber is an acrylonitrile-butadiene copolymer rubber, and the acrylonitrile-butadiene-isoprene copolymer rubber is mixed in a proportion of 40% by weight or more of the polymer component in the uppermost layer. The blanket for offset printing according to claim 1.