JPS6148439B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a compressed layer of a printing blanket, particularly a compressible blanket. Printing blankets used in high speed offset printing have been provided with compressed layers of elastomeric polymers. Firstly, the compressed layer described above uniformly absorbs the bulge that occurs on the compressed surface of the blanket during printing pressure, thereby reducing deformation of the blanket surface and making it possible to obtain a clear image. Secondly, because of this compression layer, when the printing paper is folded and sent, or when two or more sheets are sent in piles, the compression layer compresses the printing paper cylinder. It can absorb and relieve the forces (other than printing pressure) applied to the blanket surface, and therefore the plate cylinder,
The lifetime of the blanket surface layer can be significantly improved.
Thirdly, when tailoring the torso, for ordinary blankets, the thickness must be adjusted very precisely, but by providing a compressed layer, even if the body is tailored slightly over the standard torso design, it will still be sharp. This method has the advantage that it is possible to obtain accurate printing, and that the cylinder can be tailored regardless of the skill level of the operator. It is known to manufacture such compressed layers from foam. For example, a foaming agent is blended into synthetic rubber and heated and foamed during vulcanization of the rubber to form a compressed layer with countless closed cells, or a method of curing as disclosed in JP-A No. 48-97609. There is a method in which fine latex spongy rubber particles are dispersed in an elastic substrate to form a large number of non-interconnected cells (closed cells) in the substrate. Furthermore, a method (Japanese Patent Publication No. 7371/1983) is also known in which hollow microspheres are dispersed in an elastomer to form closed cells. However, printing blankets with compressed layers as described above do not fully achieve the effect of providing a compressed layer. That is, the compressed layer cannot sufficiently and uniformly absorb the bulge that occurs on the compressed surface of the blanket during printing pressure, making it difficult to obtain a sufficiently clear image. Furthermore, since the plate cylinder rotates at high speed during printing,
Compression of the blanket is performed at an extremely high speed, and it is necessary to relieve compression strain with a response speed proportional to this compression speed, but the above-mentioned known example has the disadvantage that this response speed is slow. This is basically due to the fact that the compressed layer of the above-mentioned known blanket is a closed cell foam. This is because in a closed cell system, the pores are independent, so there is no place for the air within the cells to escape due to compressive deformation, and the deformation due to compressive stress cannot be fully absorbed, and in addition, the relaxation rate of compressive strain is This is because it will be late. On the other hand, in the case of open cells, since the cells communicate with each other, air can circulate freely and can freely buffer against large compressive deformations, and the relaxation rate of compressive strain can also be reduced. It is possible to obtain clear printing, and it is also possible to improve the durability of the plate cylinder and blanket. As described above, it is desirable that the compressed layer of a printing blanket be made of a foam with a high open cell ratio, but as mentioned above, closed cell foams are mainly used because they have a high open cell ratio. Furthermore, it is extremely difficult to manufacture a foam having micropores, which is an essential factor for obtaining halftone dot reproducibility in printed matter. For example, in a rubber foam foamed with an organic blowing agent, it is difficult to provide uniform micropores of 100 μm or less, and the open cell ratio is extremely low at 50% or less. Figure 2 is a 75x micrograph of a foam produced by this method, and as is clear from the figure, the bubbles are non-uniform, ranging from large to small, and the open cell ratio is low. Furthermore, according to the method of mixing hollow microspheres into elastomer (Japanese Patent Publication No. 7371/1989), it is easy to adjust the size of the bubbles because the microspheres are mixed in in advance, but the microspheres mixed in are individual. Since it is an independent sphere, the bubbles are 100% closed cells. In addition, in the method of dispersing fine particles of cured latex spongy rubber in a substrate to form a compressed layer (Japanese Patent Application Laid-Open No. 1976-97609), it is possible to produce a foam with small bubbles; It takes a lot of work to do this, and it also has the disadvantage that it gets mixed into the rubber glue and clogs the doctor knife during sizing, resulting in poor production efficiency.In addition, the open cell rate is not 100%, so it is difficult to compress. The performance as a layer is also not sufficient. The object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for producing a foam having 100% open cells and micropores of 100 μm or less. Therefore, the method for producing the compressed layer of the printing blanket according to the present invention is to use a polymer in a solvent at a polymer concentration of 2 to 70%.
Powdered crystals and/or cellulose with an average length of 300 μm or less are added to the polymer solution in an amount of 30% or less to the polymer solution, and the basic composition is coated on a base fabric and can be dissolved in the solvent. in,
and does not dissolve in the polymer. 50℃～100℃
It is characterized by being immersed in a gelling solution, dried, and optionally vulcanized. According to the present invention, it is possible to easily produce a compressed foam layer having micropores of 100 μm or less with a 100% open cell ratio,
The printing blanket provided with the compressed layer produced according to the present invention can evenly and reliably absorb the swelling of the blanket surface caused by printing pressure, making it possible to obtain clear images. In addition, the compression strain relaxation speed during high-speed printing becomes faster, which not only makes it possible to obtain clear printing, but also has the advantage of improving the durability of the plate cylinder or blanket. The present invention will be explained in more detail. The polymer used in the present invention is a general rubber, a thermoplastic resin, or a compound containing this rubber or this thermoplastic resin as a main component. It is preferable to use one that has strong resistance to the solvent used.
For example, it may be one or more of butadiene/acrylonitrile copolymer, polyvinyl chloride, and chloroprene rubber, or a compound containing one or more of these copolymers, polyvinyl chloride, and chloroprene rubber as a main component. This compound is made by adding a vulcanizing agent such as sulfur to the main component, such as rubber.
Adding vulcanization accelerators, reinforcing agents such as carbon black, anti-aging agents and processing aids such as stearic acid,
It may be kneaded. Next, as the solvent for dissolving this polymer, any solvent may be used as long as it can be dissolved in the gelling liquid. That is, since the gelling liquid gels the polymer solution by mutually diffusing with the solvent, the solvent must mutually diffuse with the gelling liquid, which has a stronger affinity than the polymer. . Therefore, this solvent varies depending on the type of gelling solution, but is generally one or a mixed solvent of two or more of N,N'-dimethylformamide, diethylformamide, dimethylacetamide, dimethyl sulfoxide, etc. be able to. The polymer is dissolved in this solvent, and the polymer concentration at this time is 2 to 70%. If it is outside this range, it will be difficult to apply glue and work efficiency will be reduced. By adjusting the polymer concentration, the density of the foam can be changed from a high-density open cell to a low-density open cell. For example, if the polymer concentration is 30%, a foam with a specific gravity of 0.35-0.40 can be obtained, and if it is 60%, a foam with a specific gravity of 0.65-0.75 can be obtained. This is because, as will be described later, the pores are formed by the mutual diffusion of the solvent and the gelling solution, and therefore the density can be changed depending on the polymer concentration. In the method according to the invention, powder crystals and/or cellulose having an average length of less than 300 μm are then added to the polymer solution. This is added in order to prevent coarsening of pores and non-uniformity of dimensions caused by various factors during manufacturing operations when manufacturing a compressed layer for printing. For example, when coating a polymer solution on a base fabric, air is drawn in and
When extracting the solvent, it is necessary to create coarse pores of 100 μm or more in the center of the foam when extracting the solvent. This prevents the pores from becoming coarse and non-uniform due to insufficient control during manufacturing, and facilitates manufacturing operations. Such powder crystals or cellulose may include one or a mixture of two or more of silica, calcium carbonate powder, wood pulp, and synthetic fiber floc, but they do not achieve the above purpose. Basically, it can be anything. The amount of crystals and/or fibers added varies depending on the cohesive force caused by the polymer (including rubber and compounding agents) in the polymer solution, but is generally 30% or less based on the polymer solution. If it exceeds 30%, the stability of pore size and uniformity is improved, but the produced compressed layer becomes too hard and is not suitable as a printing blanket compressed layer. The average length of this powder crystal and/or cellulose is 300 μm or less. This is because if the diameter exceeds 300 μm, coarse pores exceeding 100 μm will be produced depending on the length. A preferable average length of the crystals and cellulose is determined by the composition of the polymer (ie, cohesive force). For example, 50 parts of carbon black (reinforcing filler) is added to butadiene-acrylonitrile copolymer (Hiker 1042; manufactured by Zeon Corporation).
In the case of polymers containing MT-Carbon Black, the diameter is 45μm or less, SRF-Carbon Black is 90μm or less, and HAF-Carbon Black is less than 45μm.
It is preferable to use one with an average length of 150 μm or less. (This is because the pores become coarse.) This polymer solution is coated on a base fabric, and this base fabric can be made of, for example, cotton, polyester, nylon, or the like. This base fabric is basically not limited in the present invention, and the method of coating is not similarly limited. For example, as a coating method, a doctor knife, a roll coater, etc. may be used. Next, the base fabric coated with this polymer solution is immersed in a gelling solution. The gelling liquid must be insoluble in the polymer and soluble in the solvent. As mentioned above, this is to selectively elute the solvent from this polymer solution, and therefore, rather than the affinity between the solvent and the polymer,
It is a liquid that has a high affinity between the solvent and the gelling liquid. As long as it is such, the type of gelling liquid is basically not limited in the present invention. For example, the liquid may be one or a mixture of two or more of water, monools such as methanol and ethanol, and polyols such as glycerin and ethylene glycol. The temperature of this gelling liquid is 50 to 100°C. The purpose of heating the gelling liquid in this manner is to remove the solvent as quickly as possible, shorten the semi-gel state, and generate fine pores. in this case,
When the gelling solution is at room temperature, the semi-gel state continues for a long time, and the pores gradually become larger while coagulating and destroying. If the temperature of the gelling solution is lower than 50℃, the result will be the same as simply immersing it in the gelling solution at room temperature, and the temperature of 200μ
This results in a mixture of pores ranging from large pores of m or more to minute pores of 20 μm or less. Moreover, if the temperature is 100° C. or higher, the pores become too fine, resulting in a drawback that it becomes unusable. Preferably the temperature is 60°C or higher. This is because fine pores are formed quickly and reliably. In the present invention, as described above, the solvent and the gelling liquid are mutually diffused to form a gel. That is, since the affinity between the gelling liquid and the solvent is greater than the affinity between the polymer and the solvent, the polymer is in an undissolved state rather than a dissolved state, and the polymers coagulate and aggregate together. At this time, spaces are created in areas other than the agglomerated and aggregated polymer parts. This becomes a micropore,
The micropores generated in this way are the result of mutual diffusion of the polymer solvent and gelling liquid, so
This results in 100% continuous micropores. After being immersed in the gelling solution in this way, e.g.
Dry for 20 minutes or more in a hot air dryer at 100-160℃.
Vulcanize at the same time. In the case of a thermoplastic elastomer, vulcanization is not necessary, so it may be dried for about 30 minutes at a temperature of 150° C. or lower, for example. Of course, the drying time, drying temperature, and drying method are not limited in the present invention. It can be determined functionally by considering the type of polymer solution, etc. Examples of the present invention will be described below. Example 1 Composition A Group butadiene/acrylonitrile copolymer
70 parts by weight (Hiker 1041; manufactured by Zeon Corporation) Polyvinyl chloride (degree of polymerization 1100) 30 〃 Zinc white 3.5 〃 Stearic acid 1.0 〃 Carbon black (MT) 60 〃 Anti-aging agent 1.0 〃 Plasticizer (DOP) 5 〃 Total 170.5〃 Group B Sulfur 1.5〃 Vulcanization accelerator 3.0〃 Total 4.5〃 Group C Fiber flock (average length 30μm) 6〃 Knead the compounding ingredients of Group A with a roll, add N,N'-dimethylformamide to a polymer concentration of 45 %, a solution with a viscosity of 500 poise was obtained. After adding the fiber flock (group C) and stirring thoroughly, the vulcanizing agent of group B and the like are added. This composition was applied to a thickness of 0.38 mm at a rate of 70 strokes/inch.
A doctor knife was used to coat a 0.37 mm thick cotton cloth. This was immersed in hot water at 80°C, pulled out after 40 minutes, and sent directly to a drying room at 140°C to dry. A micrograph of this compressed layer is shown in FIG. 1st
The figure is a 75x micrograph of a compressed layer according to the method of the invention. For comparison, FIG. 2 shows a 75x micrograph of a compressed layer produced using a conventional organic blowing agent. As is clear from these photographs, the compressed layer manufactured by the method of the present invention mostly consists of micropores of 25 μm or less and has an open cell ratio of 100%, whereas the compressed layer manufactured by the conventional method has micropores of 100 μm or less. Compared to the above-mentioned large-sized ones, the small-sized ones are more uneven and have a lower open cell rate. Next, from the above composition, fiber flock (group C)
A compressed layer was similarly produced using the composition except for. A micrograph of this compressed layer is shown in FIG. As is clear from FIG. 3, when Group C is not included, most of the parts have micropores of 25 μm or less with an open cell ratio of 100%, but it can be seen that coarse pores exceeding 100 μm occur. As mentioned above, this is caused by variations in the temperature of the gelling liquid during solvent extraction when coating the composition with a doctor knife (when air is drawn in) to produce a thick foam layer. However, according to the present invention, such coarse pores will not be mixed in even if the manufacturing process is not strictly controlled. Example 2 A compressed layer according to the invention manufactured with a composition according to the table below, a compressed layer manufactured using an organic blowing agent, and a compressed layer manufactured by incorporating hollow microspheres into an elastomer (Tokuko Showa) A compressive stress-strain curve test was conducted using a blanket manufactured using the same method (No. 52-7371). The results are shown in FIG.

[Table] As is clear from FIG. 4, the blanket of the present invention (curves C ₁ , C ₂ , C ₃ , C ₄ ) is different from the conventional blanket having a compressed layer in which micro hollow spheres are mixed in an elastomer (curve A ) showed a significantly better stress-strain curve than the blanket made with organic blowing agent (curve B). When printing tests were carried out using these blankets, the dot reproducibility was excellent and the durability was 2 to 3 times higher than that of the blankets with compressed layers manufactured using the hollow microspheres. This is thought to be because the strain rate is much larger for the same compressive force compared to conventional blankets (curves A and B), so the compressed layer can sufficiently cope with the deformation load.

[Brief explanation of the drawing]

FIG. 1 is a 75x micrograph of a printing blanket compressed layer according to an embodiment of the present invention, and FIG. 2 is a 75x micrograph of a conventional compressed layer using an organic blowing agent. FIG. 3 is a 75x micrograph of a compressed layer prepared from the composition used in the present invention without the fiber flock. FIG. 4 is a stress-strain graph of a printing blanket with a compressed layer produced by the method according to the invention and a conventional printing blanket with a compressed layer. A...Stress-strain curve of a printing blanket having a compressed layer manufactured by mixing micro hollow spheres in an elastomer. B... Stress of a printing blanket with a compressed layer manufactured using an organic blowing agent
Distortion rate curve. C ₁ , C ₂ , C ₃ , C ₄ ... Stress-strain rate curves of printing blankets with compressed layers produced by the method according to the invention.

Claims (1)

[Claims] 1. Polymer in a solvent with a polymer concentration of 2 to 70%
(wt%, same hereinafter) Add powder crystals and/or cellulose having an average length of 300 μm or less to the polymer solution in an amount of 30% or less to the polymer solution, and then apply the composition on the base fabric. coated,
Soluble in the solvent but not in the polymer, immersed in a gelatinizing solution at 50 to 100°C and dried;
1. A method for producing a compressed layer of a printing blanket, which is optionally vulcanized. 2. A method for producing a compressed layer of a printing blanket according to claim 1, wherein the polymer is a rubber or a thermoplastic resin. 3. A method for producing a compressed layer of a printing blanket according to claim 2, characterized in that the polymer is resistant to printing inks and/or solvents used during ink changes. 4. The polymer is a compound whose main component is one or more of butadiene/acrylonitrile copolymer, polyvinyl chloride, and chloroprene rubber, or one or more of butadiene/acrylonitrile copolymer, polyvinyl chloride, and chloroprene rubber. A method for manufacturing a compressed layer of a printing blanket according to claim 3. 5. Any one of claims 1 to 4, wherein the solvent is one or a mixture of two or more selected from N,N'-dimethylformamide, diethylformamide, dimethylformamide, and dimethyl sulfoxide. A method of manufacturing a compressed layer of a printing blanket. 6. The printing according to any one of claims 1 to 5, wherein the powder crystal and/or cellulose is one or a mixture of two or more of silica, calcium carbonate, wood pulp, and synthetic fiber flock. Method for manufacturing compressed layers for blankets. 7. The printing blanket according to claim 1, wherein the gelling liquid is one or a mixture of two or more selected from the group consisting of water, monools, and polyols. Method of manufacturing compressed layer. 8. The method for producing a compressed layer of a printing blanket according to claim 7, wherein the gelling liquid is hot water.