JPS6152800B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved manufacturing method for producing a blanket for a printing press that can exhibit excellent printability, and in particular a compressible blanket having a compressible layer made of a rubber-like elastic material mixed with hollow microspheres. It is. In order to improve the printability defects caused by the lack of compressibility in conventional printing blankets based on rubber-like elastic materials, a porous compressible layer was introduced into the structure. For example, in the technology disclosed in Japanese Patent Publication No. 37-13110 and Japanese Patent Publication No. 38-7761, the compressible layer is formed by impregnating an elastomer material into an entangled fiber material. Because the cells are formed, each cell communicates with each other, and the partition walls of each cell chamber are necessarily extremely thin and have low pressure resistance.
Since the compressible layer in the technology disclosed in Publication No. 47-18243 is formed by foaming rubber with a foaming agent, uniform bubbles may be formed due to variations in the amount of foaming agent, vulcanization temperature, pressure, etc. All of them have not been able to satisfy the desired printability due to insufficient pressure resistance and local variations such as difficulty in forming chambers. In order to overcome the shortcomings of the prior art and form a multicellular compressible layer with uniform microbubble chambers, a rubber-like material containing numerous elastic hollow microspheres made of thermoplastic plastic or the like is used. A technique for constructing a compressible layer using an elastic material has been proposed by an invention disclosed in Japanese Patent Publication No. 7371/1983. The blanket for a printing press according to the above invention is composed of a surface printing layer made of a rubber-like elastic material, at least one fiber-reinforced layer, and a compressible layer made of a rubber elastic material mixed with countless elastic hollow microspheres. However, in the actual manufacturing process of the blanket, the compressible layer meets the requirements for crush prevention, dimensional stability, and conventional spreading of the hollow microspheres embedded therein. From the viewpoint of requirements, etc., prior to lamination with the remaining structural members such as the surface printing layer, a long sheet is formed in advance into a mold with a required thickness, wound on a vulcanization drum, and then vulcanized. It is vulcanized and molded by heating under pressure in a sulfur can. By the way, the variation in the thickness of the compressible layer formed by vulcanization becomes larger than that before vulcanization,
This is a major cause of local variations in pressure resistance in finished products and, ultimately, variations in printability. The reason for the increase in the thickness variation of the compressible layer during the vulcanization process is not only due to the volatilization of the solvent in the rubber composition that is the constituent material, but also due to the increase in the thickness variation of the compressible layer being wound around the vulcanization drum. Since the temperature rise in the middle part is slower than that in the inner part and the outer part, the vulcanization rate in this part is delayed, and the hollow microspheres mixed in this part are melted and crushed. It turned out to be due to. The inventors of the present invention have studied methods to eliminate such drawbacks, and have found that before winding up the compressible layer formed in the form of a long sheet onto a vulcanization drum, the long sheet is incompletely cured in advance. We came up with the idea of curing (semi-vulcanizing) the material, winding it up on the drum, and completing the vulcanization in the usual way, and conducted an experiment to semi-vulcanize it using a heat vulcanization method that uses conventional general-purpose infrared rays. However, when such heat vulcanization is used, it is difficult to achieve a constant semi-vulcanized state due to the influence of the temperature of the rubber itself, temperature conditions such as room temperature, and variations in heat transfer coefficients, etc. Since the hollow microspheres embedded in the rubber elastic body are made of thermoplastic plastic, uneven heating may cause some of the microspheres to expand excessively or be melted and crushed. It turns out that this leads to new undesirable results. The present inventors therefore conducted repeated experiments on a method of achieving the desired semi-vulcanized state of the compressible layer using an electron beam irradiation method that can cause a crosslinking reaction between rubber molecules without increasing heat. As a result, we have completed the present invention. The method for producing a printing press blanket according to the present invention includes a surface printing layer made of a rubber-like elastic material, at least one fiber-reinforced layer, and a compressible material made of a rubber-like elastic material mixed with countless elastic hollow microspheres. In the production of a compressible blanket consisting of a layer, the compressible layer is formed into a long sheet mold of a desired thickness from an unvulcanized rubber-like elastic material mixed with a countless number of elastic hollow microspheres, and the long sheet is is exposed to electron beam irradiation of about 9 megarad or less to be incompletely vulcanized, then wound onto a vulcanizing drum, heated and pressurized in a conventional manner to complete vulcanization, and then the surface printed layer The final product is completed by laminating the remaining required layers, etc., and vulcanizing each layer. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for manufacturing a printing press blanket according to the present invention will be described below with reference to the accompanying drawings. The compressible blanket manufactured by the method of the present invention illustrated in FIG. A fiber-reinforced layer 2 consisting of a fiber reinforced layer 2 (which may be made of polyvinyl chloride/vinylidene chloride copolymer) and a rubber-like elastic material in which a large number of hollow microspheres (diameter 0.12 mm or less) of thermoplastic plastic such as vinyl chloride/vinylidene chloride copolymer are uniformly dispersed. a compressible layer 3 consisting of a material (e.g. NBR)
and two fiber reinforcing layers 5 and 6 laminated with a rubber-like elastic layer 4 in between. According to the method of the present invention, the compressible layer 3 of the compressible blanket is first made as follows. That is, a paste-like nitrile-butadiene copolymer rubber composition in which countless hollow microspheres are mixed is spread on a fiber reinforcing layer 5 with a number of turns of 10 mm on a rotary endless belt conveyor using a known spreading device. The long sheet of unvulcanized rubber elastic material backed with a fiber reinforcing layer is passed through a drying chamber to volatilize the solvent in the rubber composition, and then The long sheet is conveyed on a rotating endless belt conveyor in an electron beam irradiation device, exposed to electron beam irradiation, completely vulcanized (semi-vulcanized), wound on a vulcanization drum, and constantly exposed to electron beam irradiation. Vulcanization is completed in a vulcanization can using the method. The appropriate dose of electron beam for semi-vulcanization of the compressible layer was selected as follows based on experimental results. That is, irradiation doses of 3 mega rad, 6 mega rad, and 9 mega rad were applied to several types of sample sheets consisting of an unvulcanized rubber-like elastic material mixed with countless hollow microspheres and backed by a fiber reinforcing layer. After pre-semi-vulcanization by irradiation with rad electron beam, final vulcanization was completed at 120℃ for 150 minutes, and each sample was
The change in thickness was measured. The results are shown in Table 1.

[Table] From the above table, it can be seen that there is almost no difference in the thickness of each sample after drying, but the thickness after vulcanization of the samples that were not exposed to the electron beam irradiation according to the present invention is as follows. The thickness decreased by about 0.1 mm on average, whereas the sample based on the method of the present invention, which was partially vulcanized by electron beam irradiation and finally fully vulcanized, The amount of thickness reduction during vulcanization was extremely small, approximately 0.03 mm to 0.01 mm, and there was almost no variation in thickness among the samples. This was because the hollow microspheres were hardly destroyed during the vulcanization process. Show that. However, in samples that were irradiated with electron beams at a dose of 9 megarad, some of them were observed to have slightly increased thickness (about 0.02 mm) after irradiation, and depending on the dose, some of the hollow microspheres expanded in diameter. It is estimated that it is possible. The effect of improving the amount of decrease in the thickness of the compressible layer due to electron beam irradiation, in other words, the effect of preventing the hollow microspheres from expanding in diameter or melting and breaking during vulcanization is also shown graphically in FIG. On the other hand, the effect of improving compressive stress by the method of the present invention, in which the compressible layer is semi-vulcanized by electron beam irradiation, was evaluated in the third section.
As shown in the figure. In the same figure, for example, when comparing the compressive stress of each sample at 35% compression (that is, when the compressible layer is compressed to 35% of its original thickness by the rolling pressure of the printing cylinder), which is the practical range, While that of the sample that was not exposed to electron beam irradiation (the sample that was not once semi-vulcanized) was about 9.3 Kgf, that of the sample according to the method of the present invention was 7.3 to 7.9 Kgf, which was about 15% smaller. This is because the decrease in thickness during vulcanization became smaller, so that the embedded hollow microspheres were less likely to be damaged. From the above experimental results, the dose of electron beam for pre-semi-vulcanization of the compressible layer according to the present invention is 9 M
less than rad, preferably 1 merad to 6 merad
A range of was selected. The compressible layer 3 that has been vulcanized and molded as described above is then covered with a fiber reinforced layer 6 on which the rubbery elastic material layer 4 is spread, on the lower surface thereof, and a rubbery elastic material layer 6 on the upper surface of the compressible layer 3. The expanded fiber reinforcement layer 2 and the surface printing layer 1 are laminated and vulcanized by heat and pressure in a heating can in a conventional manner to complete a compressible blanket having a total thickness of about 1.9 mm. As explained in detail above, the method for manufacturing a blanket for a printing press according to the present invention, in particular, when forming the compressible layer of the blanket, the compressible layer is incompletely vulcanized (semi-vulcanized) by electron beam irradiation in advance. The above is wound up on a vulcanizing drum in the usual manner and completely cured in a vulcanizing can, so that the compressible layer is heated for vulcanization as in the conventional manufacturing method. Due to temperature variations, etc., some of the hollow microspheres embedded inside the microspheres may be destroyed or the diameter may expand excessively. This completely eliminates the disadvantage of not being able to fully utilize the advantages of introducing a compressible layer that is equipped with small bubble chambers and can contribute to excellent printability, and exhibits excellent printability. This makes it possible to produce moist, compressible blankets.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a blanket for a printing press manufactured by the method of the present invention, FIG. 2 is a graph showing the effect of preventing the thickness reduction of the compressible layer of the blanket according to the present invention, and FIG. 3 is a graph showing the effect of improving the compressive stress of the elastic layer. 1... Surface printing layer, 2... Fiber reinforcement layer, 3...
Compressible layer, 4... rubber-like elastic layer, 5, 6... fiber reinforced layer.

Claims (1)

[Claims] 1. In the production of a compressible blanket comprising a surface printing layer made of a rubber-like elastic material, at least one fiber-reinforced layer, and a compressible layer made of a rubber-like elastic material mixed with countless elastic hollow microspheres, the above-mentioned The compressible layer is formed from an unvulcanized rubber-like elastic material mixed with countless elastic hollow microspheres into a long sheet of the desired thickness, and this long sheet is exposed to electron beam irradiation of approximately 9 megarad or less. After completing the vulcanization process, it is wound up on a vulcanization drum, and vulcanization is completed by applying heat and pressure in a conventional manner.Then, it is laminated with the remaining required layers such as the surface printing layer, and each of these layers is A method of manufacturing a blanket for a printing press, characterized by completing the final product by vulcanizing the blanket.