JP2000043442A - Compressible rubber blanket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to make cells of microballoons even in a final product requiring neither special processes nor complicated facilities. SOLUTION: This compressible rubber blanket includes at least two reinforcing layer. A compression layer 2, which is made of an oil-resistant rubber compound formed on the first reinforcing layer 1a containing microballoons made of a copolymer of a methacrylonitrile and an acrylonitrile having a thermal deformation temperature of 120 deg.C or higher and a pressure resistance of 40 kg/cm2 and turned into microballoons substantially having the diameter of 60 μm by being heated and foamed in advance, a second reinforcing layer 1b pasted to the compression layer 2 and a surface rubber layer 4 formed further on the second reinforcing layer 1b are equipped. The compression layer 2 and the surface rubber layer 4 are integrally formed through one vulcanization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a compressible rubber blanket.

[0002]

2. Description of the Related Art Conventionally, as a compressible rubber blanket, for example, New Developments in Offset Blanket has been used.
s. Prof. Print. , Vol. twenty two. No. 6, Nov. / D
ec. 1978, pp. 2-7 (prior art 1) are known.
This compressible rubber blanket is available from N.I. G. FIG. Chamerlain
According to this, it was developed to improve smash resistance, and functionally, when it rotates in contact with the plate cylinder or impression cylinder of a printing press, compression in the vertical direction occurs, States that no uplift occurs. There are four methods of forming the compressed layer of the compressible rubber blanket: (1) a method using impregnated paper, (2) a salt elution method, (3) a foaming agent method, and (4) a microballoon method.

Japanese Patent Publication No. 52-7371 (GB 132)
7758) (Prior Art 2) discloses that cells which are substantially completely closed, that is, closed cells, are formed by mixing microballoons exhibiting elasticity and / or crushing property against pressure in an elastic polymer. A method is disclosed. The publication discloses that glass, phenolic resin, carbon or a thermoplastic material, particularly a copolymer of acrylonitrile and vinylidene chloride, is suitable as the microballoon. The publication also discloses that the blanket is made by vulcanizing at 140 ° C. for 90 minutes.

Japanese Patent Publication No. Sho 61-52800 (prior art 3) discloses the use of a copolymer of acrylonitrile and vinylidene chloride. As an improvement method, an unvulcanized compressible rubber sheet is irradiated with an electron beam of about 9 Mrad or less, incompletely vulcanized to fix microballoons, then wound around a drum, pressurized and heated. There has been proposed a two-step vulcanization method in which vulcanization is performed.

US Pat. No. 4,770,928 (Prior Art 4) discloses a compression layer intermediate obtained by mixing a microballoon made of a copolymer of acrylonitrile and vinylidene chloride in an elastomer material at a temperature at which the microballoon does not melt, that is, About 110F (43 ° C)-170F (77 ° C)
To secure the microballoons within the elastomeric material for 1 to 12 hours. In the case of the above publication, in order to vulcanize at a low temperature, it is an essential condition to use dithiocarbamate which is a special super-vulcanization accelerator. Further, in the above-mentioned publication, the main vulcanization is carried out at 132 ° C. after a cloth and a surface rubber layer are further applied to the vulcanized compression layer intermediate.
It is characterized in that it is performed at a temperature of 160 ° C. to obtain a final product, that is, in two steps.

[0006]

However, the above-described prior art has the following problems.

(A) Prior art 1: The blanket according to the above methods (1) and (2) has a structure in which pores are continuous. For this reason, the dampening solution or the cleaning agent used during printing penetrates into the compressed layer of the blanket, and the portion becomes thick and over-pressurized, causing printing troubles such as tearing and thickening of dots on printed matter.

[0008] The production of the compressed layer by the method (3) is as follows.
This is a method in which an organic foaming agent is mixed into an unvulcanized rubber compound to form a sheet, and the sheet is heated to a predetermined temperature to vulcanize and foam (sponge) the rubber. The disadvantage of this method is that the vulcanization and foaming of the rubber proceed simultaneously by heating, causing a variation in the size of the cells, which results in a variable blanket compressibility. In addition, when wound around a drum and heated to effect vulcanization and foaming, a difference in winding pressure occurs between the lower winding and the upper winding. In particular, since the lower winding portion has a high pressure, foaming hardly occurs and sufficient compressibility is hardly obtained. On the other hand, since the upper winding portion does not receive sufficient pressure, the growth of bubbles occurs quickly, so that coarse bubbles are formed.
Compressibility is too large and printing pressure is insufficient when mounted on a printing press for printing.

(B) Prior art 2: During the process of being wound on a vulcanizing drum and heating and vulcanizing, the microballoons are melted and broken, causing a variation in the thickness of the compressed layer, and a large variation in printability. Cause.

(C) Prior art 3: Microballoons composed of a copolymer of acrylonitrile and vinylidene chloride melt and break at ordinary vulcanization temperatures, so that an unvulcanized rubber sheet is about 5 megarads. The microballoon is fixed by incomplete vulcanization by irradiation with the following electron beam. Thereafter, it is a two-step method of winding around a drum and vulcanizing again. Therefore, the method is uneconomical in two steps and requires expensive and dangerous special equipment.

(E) Prior art 4: Microballoons composed of a copolymer of acrylonitrile and vinylidene chloride are:
Since the material is melted at a normal vulcanization temperature of 120 to 150 ° C., the production method is divided into two steps. Therefore, the process is complicated and the cost is increased. Also,
In this technique, a rubber is vulcanized and fixed at a temperature at which the microballoons do not melt using dithiocarbamate, a super-vulcanization accelerator, which means that the rubber paste mixed with the microballoons is improper even at room temperature. Means stable. That is, there is a danger that premature vulcanization occurs during production and storage of the rubber paste.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compressible blanket in which cells can be constituted by microballoons even in a final product without requiring a special process or complicated equipment. And

[0013]

SUMMARY OF THE INVENTION The present invention is a compressible rubber blanket including at least two reinforcing layers,
A microballoon of a copolymer of methacrylonitrile and acrylonitrile having a heat distortion temperature of 120 ° C. or more and a pressure resistance of 40 Kg / cm ² is previously heated and expanded in the oil-resistant rubber compound formed on the first reinforcing layer. A compression layer having a diameter of substantially 60 μm, a second reinforcement layer bonded to the compression layer, and a surface rubber layer formed on the second reinforcement layer. The compression rubber blanket is formed by integrating the compression layer and the surface rubber layer by a single vulcanization.

In the present invention, the amount of microballoons to be added to the oil-resistant rubber to be the compression layer varies depending on the type of printing machine and the printed matter, but is preferably 5 to 40 parts by weight per 100 parts by weight of the oil-resistant rubber. Is 10 to 30 parts by weight. Here, the amount of the mixed microballoon affects the performance of the completed blanket, particularly the compressibility. That is, when the amount is small, the porosity is small and the compressibility is small. Conversely, compressibility increases as the amount increases.

In the present invention, the diameter of the microballoon is preferably 30 to 100 μm. Here, the diameter of the microballoon also affects the compressibility of the blanket. In other words, if it is too fine, the thickness of the wall forming the cell becomes thick, and the compressibility becomes insufficient. Conversely, if it is too large, the wall thickness will be thin and the compressibility will be excessive (too soft)
Becomes

In the present invention, the material for forming the microballoon is most preferably a copolymer of methacrylonitrile and acrylonitrile. The present inventors conducted the following comparative test in selecting this material. That is, first, microballoons composed of three kinds of materials of (a) a copolymer of vinylidene chloride and acrylonitrile, (b) a copolymer of methyl methacrylate and acrylonitrile, and (c) a copolymer of methacrylonitrile and acrylonitrile are prepared. did. These materials all contain isobutane or isopentane as an expanding agent. Next, these three types of microballoons were
° C, 90 ° C, 100 ° C, 110 ° C, 120 ° C, 130
After leaving for 1 hour in an oven whose temperature was controlled at 140 ° C., 140 ° C., 150 ° C., and 160 ° C., it was observed under a microscope to see whether the micro balloon was melted, broken or abnormal. As a result, data as shown in the following “Table 1” was obtained.

[0017]

[Table 1]

According to the above Table 1, in the case of the microballoon made of the material (a) and the material (b), the microballoon is stable up to 100 ° C. It is clear that at temperatures higher than this, it was completely melted and broken. This means that the vulcanization temperature of rubber, which is commonly used, is 120 to
When vulcanized at 150 ° C, the microballoons melt,
It means destroying. On the other hand, it has been found that the microballoon made of the material (c) has extremely high stability to heat and can sufficiently withstand the vulcanization temperature generally used.

The microballoon made of the material (a) has a heat deformation temperature of 100 ° C. or less. For this purpose, it is necessary to once cure at a temperature lower than the heat deformation temperature to fix the microballoon in the rubber. Then, a surface rubber layer or the like is formed again, and vulcanization is performed at a higher temperature.
However, when vulcanization is performed at a high temperature, the microballoons are melted, and eventually the microballoons do not remain in the cell. Therefore, the cells of the compression layer using the material (a) or the material (b) are ultimately formed by a rubber film.

On the other hand, a compressible rubber blanket using a compression layer containing microballoons made of the material (c) has a high thermal deformation temperature of the microballoons and does not melt at the vulcanization temperature of the rubber. In the product as well, the cells will be formed by microballoons.

The above difference appears as a difference in pressure resistance. Actually, two types of compressible blankets were made using the microballoon made of the material (a) and the microballoon made of the material (c), and a printing test was performed to compare the pressure resistance. That is, the printing pressure is set to 0.1 mm and the thickness is set to 0.05
Paper having a width of 1 cm and a thickness of 0.25 mm was adhered to a printing paper having a thickness of 0.2 mm, and printing was performed by partially providing an overpressure portion.

As a result, a dent was formed at the location of the overpressure, and the ink density at that portion was reduced. After that, the normal thickness of 0.
Printing was continued on 05 mm paper, and it was examined at which sheet the density returned to normal. As a result, the blanket produced by the microballoon made of the material (a) had a normal ink density on the 20th printing. In contrast, the blanket made by the microballoon made of the material (c) returned to the normal ink density on the fifth sheet. That is, it was found that the blanket according to the present invention had excellent cell restorability. This is probably because the walls of the microballoons did not melt due to vulcanization but remained.

Next, the pressure resistance of the microballoon will be described.

In general, in offset printing, the blanket is compressed by 0.1 mm to 0.15 mm with respect to the original thickness of the blanket, and rotates at high speed in contact with the plate cylinder and the impression cylinder. Here, the stress when compressing a blanket having a thickness of 1.9 mm by 0.1 mm with Tensilon (a compression tester manufactured by Orientec) is generally 3 to 5 kg / cm ² . Also,
The stress at the time of 0.15 mm compression is 5 to 10 kg / cm
² . These stresses vary depending on the type of blanket. By the way, the blanket sometimes breaks during printing and wraps around the blanket cylinder, resulting in a very high pressure. In such a case, probably 40 kg / cm ²
To a certain degree of stress. In such a case, a balloon having no pressure resistance, such as a glass balloon, is easily broken, and even the rubber surrounding the balloon is broken. In such a glass balloon having inferior pressure resistance, when an excessive pressure is applied, a permanent dent is generated in that portion and the portion is not restored, and the printed matter becomes uneven and defective.

To manufacture a blanket, sulfur, a vulcanization accelerator, a reinforcing agent, a softening agent, a processing aid and the like are sufficiently mixed with a rubber having ink resistance by a kneading roll or the like, and then a good solvent for the rubber is used. Must be dissolved. The micro balloon is mixed with the rubber paste and coated on the woven fabric with a spreader (sizing machine). The most common rubbers having ink resistance include, for example, NBR (acrylonitrile butadiene rubber) and chloroprene rubber. Common solvents for these rubbers include, for example, M.P. E. FIG. K
(Methyl ethyl ketone). Therefore, the microballoons forming the compressed layer must withstand this solvent. Therefore, the above materials (a), (b) and (c) are E. FIG. When immersed in K for 4 hours, it was dissolved except for the material (c). This means that the microballoons are dissolved in the rubber paste and no bubbles are formed. Therefore, it was found that only the microballoon made of the material (c) can form pores.

As described above, as a result of verifying the requirements for producing a compressible blanket and the performance as a compressible blanket, only the compressible blanket having a compressible layer made of the above-mentioned material (c) with microballoons satisfies the following requirements. found.

(1) Solvent resistance of microballoons for stably forming bubbles (2) Thermal deformation temperature with respect to vulcanizing temperature of blanket (3) Pressure resistance during printing Next, production of compressible blanket The method will be described. FIG. 1 shows a schematic sectional view of a compressible rubber blanket.

(1) First, the compression layer 2 is placed on the first cotton cloth 1a.
Is applied and bonded to the second cotton cloth 1b. When the compression layer 2 is a salt elution method, a fixed amount of crushed salt is put in the rubber compound.

(2) Then, the rubber is vulcanized by heating in a vulcanizer at 120 ° C. to 150 ° C. for about 4 hours.

(3) Thereafter, the salt is immersed in hot water to elute the salt and dried.

(4) Next, the first bonding rubber 3a is used to attach to the third cotton cloth 1c.

(5) Next, the second bonding rubber 3b is used to bond the fourth cotton cloth 1d.

(6) Next, the surface rubber layer 4 is coated via the third bonding rubber 3c.

(7) Finally, the blanket material thus formed is wrapped around a drum, wrapped around a drum, introduced into a vulcanizer, and heated again at 120 to 150 ° C. to complete vulcanization.

[0035]

According to the present invention, microballoons composed of a copolymer of methacrylonitrile and acrylonitrile are not melted and broken at a usual vulcanization temperature of 120 to 150 ° C. After forming a blanket integrally, the formation of the compression layer and the vulcanization of the surface rubber layer can be performed in a single vulcanization step at a normal vulcanization temperature. Therefore, deterioration of the cotton fabric due to heat can be prevented.

[0036]

Embodiments of the present invention will be described below.

Example 1 First, a medium-high nitrile rubber (N
(BR) 100 parts by weight of sulfur, a vulcanization accelerator, an antioxidant, a reinforcing agent, and a plasticizer were mixed and dissolved in methyl ethyl ketone to obtain a rubber paste. Next, a micro balloon of a copolymer of methacrylonitrile and acrylonitrile (trade name: Expancel 091DE, Nobel
(Industry) is added to prepare 20 parts by weight of rubber paste. Here, the microballoon is heated in advance,
What was expanded to a diameter of about m was used. Further, the vulcanization accelerator is described in D.I. Very common ones such as M (dibenzothiazole. Disulfide) and M (2-mercaptobenzothiazole) were used. The rubber paste forms a compressed layer having a large cushioning property containing a large number of microballoons by vulcanization. Next, the rubber paste is coated on the first cotton cloth 1a having a thickness of about 0.4 mm to a thickness of 0.35 mm. Then, the second cotton cloth 1b is attached. Thereafter, the third cotton cloth 1c and the fourth cotton cloth 1d are bonded to each other via the bonding rubbers 3a and 3b. Lastly, the adhesive rubber 3c is applied on the second cotton cloth 1b in contact with the rubber layer to be the compression layer, and then the nitrile rubber compound is laminated as a surface rubber layer 4 in a sheet form. The overall thickness is
It is about 2.1 mm.

The unvulcanized compressible rubber blanket prepared in this manner is wound around a metal drum, and 1
It is placed inside a double can into which steam at 50 ° C. has been introduced, and heated for 6 hours to complete vulcanization. After cooling, the surface rubber layer is polished with 240 mesh sandpaper to a thickness of 1.9 mm.

According to Example 1 described above, the microballoon 11 made of a copolymer of methacrylonitrile and acrylonitrile is not melted or broken at the usual vulcanization temperature of 120 to 150 ° C. After mixing the micro-balloon 11 into a blanket and forming a blanket integrally, the vulcanization temperature (i.e., 120-150)
C) in one vulcanization step to form the compression layer 2 and the surface rubber layer 4
Vulcanization, etc. can be performed. Therefore, deterioration of the cotton fabric due to heat can be prevented.

In fact, when the cross section of the blanket thus produced is observed with a microscope, it can be seen that the compressed layer 2 has a void 13 surrounded by the wall 12 of the micro balloon 11 as shown in FIG. confirmed. Incidentally, 14 in the figure is a rubber layer.

Example 2 In Example 1, a medium-high nitrile rubber (NBR, acrylonitrile content: 33%) was used as the oil-resistant synthetic rubber. In Example 2, high nitrile was used instead. Rubber (NBR, trade name Nipol 1031, manufactured by Zeon Corporation, acrylonitrile amount 41%)
To produce a compressible rubber blanket in the same manner as in Example 1. Since the high nitrile rubber has high oil resistance and solvent resistance, it does not dissolve in toluene when preparing a rubber paste, and does not become a rubber paste unless it is a strong solvent such as methyl ethyl ketone (MEK). The advantage of using the high nitrile rubber is that it has a high resistance to a cleaning agent used for washing out ink when the ink is attached to a printing machine and used for printing.

When the compressible rubber blanket according to Example 2 was used in an offset rotary press, no intrusion of the cleaning agent into the compressed layer was observed, and the blanket could be used for a long period of 6 months. On the other hand, the life of the conventional blanket was about one month.

[0043]

As described above in detail, according to the present invention, it is possible to provide a compressible rubber blanket in which cells can be constituted by microballoons even in a final product without requiring special steps or complicated equipment.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a compressible rubber blanket according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged view of a compression layer constituting the compressible rubber blanket of FIG.

[Explanation of symbols]

1a, 1b, 1c, 1d: cotton cloth, 2: compression layer, 3a, 3
b ... adhesive rubber, 4 ... surface rubber layer.

Claims (1)

[Claims] 1. A compressible rubber blanket comprising at least two reinforcing layers, wherein the oil-resistant rubber compound formed on the first reinforcing layer has a heat deformation temperature of 120 ° C. or more and 40 kg / cm. ^A compressed layer formed by pre-heating and expanding a microballoon of a copolymer of methacrylonitrile and acrylonitrile having a pressure resistance of ² to have a diameter of substantially 60 μm, and a second reinforcement bonded to the compressed layer And a surface rubber layer formed on the second reinforcing layer, wherein the compression layer and the surface rubber layer are integrated and formed by a single vulcanization.