JPH08906B2 - Manufacturing method of joint sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

This invention relates to a non-asbestos joint sheet (hereinafter referred to as NA) used as a base material for gaskets.
(Abbreviated as a joint sheet).

[0002]

2. Description of the Related Art Conventionally, asbestos joint sheets have been punched out as gaskets for transportation pipes and equipment for water, oil, air, water vapor, etc. by utilizing the excellent heat resistance and chemical resistance of asbestos fibers. . However, asbestos fibers have become difficult to obtain due to depletion of resources and soaring prices, and health disorders have become a social problem, and the use of asbestos tends to be regulated. Due to these factors, NA joint sheets that do not use asbestos fibers at all have been used recently.

In the conventional method for producing a NA joint sheet, first, a fiber material, a filler, a rubber chemical, and a rubber swollen with a solvent (or powder rubber or latex with a solvent added) are sufficiently kneaded with a Henschel mixer or the like. (This is called kneading material), then hot roll (about 150 ℃)
It is put between a pair of rolls consisting of a cold roll and a cold roll (about 20 ° C), the solvent is evaporated and vulcanized while laminating the kneading material on the hot roll side, and finally the laminated sheet-like material is peeled off. Has been manufactured. Depending on the product, in order to complete the vulcanization, the sheet-like material may be subjected to secondary vulcanization in an autoclave or the like. In addition to the above-mentioned constituent materials depending on the application, a small amount of additives such as a coupling agent, a softening agent, a plasticizer, a water swelling agent, and an oil swelling agent are added, and a pigment is added from the viewpoint of storage and identification. There are also things.

The fiber materials used for the NA joint sheet are roughly organic fibers and inorganic fibers (other than asbestos).
It is divided into Since the organic fiber is flexible and the SP value (solubility parameter) is similar to that of the rubber, the organic fiber is likely to be entangled or bonded with the rubber or the filler and has a high reinforcing effect. In particular, fibrillated aramid fiber (trade name, Kevlar pulp) has a larger surface area than the chipped one because it is branched like asbestos fiber, and the entanglement with rubber and filler is very developed and the tensile strength is increased. It is
Properties such as flow resistance are improved, but heat resistance, especially steam resistance, is significantly inferior to that of asbestos fibers.

On the other hand, the inorganic fiber is not only rigid but also S
Since the P value is far from that of rubber, the entanglement with the rubber and the filler and the bondability are poor, and the reinforcing effect cannot be expected so much,
Due to its rigidity, the resilience and stress relaxation resistance are good,
It has better heat resistance and steam resistance than organic fibers.

In view of the above, NA joint sheets are often used in combination with organic and inorganic fiber materials depending on the purpose of use, and in some performances, NA joint sheet is at the level of asbestos joint sheets. Although approaching, the present situation is still inferior to the asbestos joint sheet in terms of tensile strength, heat resistance, and steam resistance.

Another difference between the asbestos joint sheet and the NA joint sheet other than the characteristics is the manufacturability in the roll process. That is, since the asbestos fibers are branched, they are easily entangled with the rubber and the filler and are easily laminated on the heat roll side. On the other hand, in the NA joint sheet, even the aramid pulp has a small degree of branching, so that the heat roll side is Difficult to laminate, much less difficult if rigid inorganic fibers are blended. This is related to the problem that the defective rate of the product is large and the required amount of fiber cannot be put in due to the limited composition. This also causes the NA joint sheet to be inferior to the asbestos joint sheet in tensile strength, heat resistance, and steam resistance.

Further, due to recent process rationalization and improvement of the work environment, powder rubber and latex are mixed with a solvent instead of the conventional process of masticating solid rubber and then swelling it by immersing it in a solvent. In many cases, a step of directly charging into a mixer and kneading is adopted, but in this case, if the swelling is not performed uniformly, a lump of rubber is generated, which adversely affects the productivity. Especially in the case of latex, the water content in the kneading material interferes with the adhesion between the fiber and the rubber, and there is a problem that the tensile strength of the sheet is reduced.

[0009]

SUMMARY OF THE INVENTION In summary, the conventional N
In the A joint sheet, the reinforcing organic fiber deteriorates when used under high heat conditions and steam atmosphere,
The life is significantly reduced compared to asbestos joint sheets.
In addition, even if an inorganic fiber with high heat resistance and water vapor resistance is used together, its reinforcing effect is low, and since the compounding amount cannot be increased in terms of manufacturability, asbestos joint sheet can be used for heat resistance and water vapor resistance. It is considerably lower than the above. In addition, when latex is used, there is a problem that the tensile strength of the sheet is small, the swelling tends to be nonuniform, and the productivity is poor.

An object of the present invention is to improve the tensile strength, heat resistance and steam resistance of the latex by using N, which has good manufacturability.
It is to provide a method for manufacturing an A joint sheet.

[0011]

As a result of intensive studies, the present inventors have found that when NBR latex is used as a binder for NA joint sheets, there is a large difference in properties and manufacturability depending on the constitution of the latex rubber. discovered. That is, it was found that the use of rubber particles having a low low molecular weight content as the rubber particles contained in the latex improves the productivity of the sheet and also increases the tensile strength of the sheet. It was also found that, of the mixed emulsifiers used for polymerization, the amount of the anionic emulsifier was about 70% by weight.

The manufacturing method of the joint sheet of the present invention is as follows.
As the rubber, a latex having an ethylenically unsaturated nitrile component content such as acrylonitrile of 20 to 45% by weight polymerized in the presence of a mixed emulsifier of 60 to 80% by weight of an anionic emulsifier, in a molecular weight distribution Molecular weight 5
If less than 000 is 20% by weight or less, the average rubber particle size is 100 to 150 nm, and the gel insoluble matter in toluene is
It is characterized by using 10 to 30% by weight.

Another method for producing a joint sheet according to the present invention is to use, as the rubber, a latex having an ethylenically unsaturated nitrile component content such as acrylonitrile of 20 to 45% by weight and having a molecular weight of 50,000 or less in a molecular weight distribution. 20% by weight or less and an average rubber particle size of 130
It is characterized in that it has a gel insoluble content of 30 to 80% by weight with respect to toluene and is about 200 nm.

It is assumed that the productivity is improved by this method for the following reason.

Generally, rubber having a large molecular weight is difficult to swell. The fast swelling low molecular weight rubber surrounds the unswollen rubber particles and leaves them in the kneaded material as a mass. Such a rubber block hinders evaporation of the solvent and the like at the time of production to generate bubble defects, and on the contrary, since the binder rubber content uniformly dispersed in the kneading material is small, lamination on the heat roll side is difficult. It gets harder. When the low molecular weight component of 50,000 or less is reduced from the conventional 50% by weight or less to 20% by weight or less, the swelling uniformity can be secured.

Further, the viscosity of rubber having a large molecular weight is high,
Due to the large shearing force during kneading, the rubber is well dispersed and uniform. At the same time, the viscosity of the kneaded material becomes high, and the kneaded material is easily laminated on the hot roll side, and the green strength of the sheet during production is increased. From these facts, the manufacturability is considerably improved.

As a result of many experiments based on such an idea, when the anionic emulsifier was polymerized with 80 to 60% by weight of the mixed emulsifier, the average rubber particle diameter was 100 to 150.
N and gel insoluble matter in toluene of 10 to 30% by weight
BR latex (in the case of latex, it is difficult to measure / define by molecular weight distribution, and can be defined by particle size and gel insoluble matter), the average rubber particle size is 13 when the emulsifier is not limited.
By using the NBR latex having a gel insoluble content of 30 to 80% by weight with respect to toluene of 0 to 200 nm, an NA joint sheet having good manufacturability can be obtained. In the conventional latex, the gel insoluble content in toluene was less than 10% by weight.

The molecular weight distribution in the present invention is measured by JI
According to S-K6392 "Testing method for NBR latex", a latex coagulation product is obtained, the coagulation product is dissolved in tetrahydrofuran, and soluble components are analyzed by GPC. Acrylonitrile content is measured according to JIS
-By K 6392. The average rubber particle diameter is measured by a light scattering method. Gel insoluble content is measured by cutting the latex film created by casting into fine pieces, placing it in a wire mesh basket of 80 mesh, and immersing it in toluene for 48 hours,
The weight of the insoluble matter remaining in the wire mesh is calculated, and the weight% with respect to the film weight is calculated.

Further, the tensile strength of the joint sheet is considerably increased as the molecular weight of the rubber is increased,
The sealability was also improved by better dispersion of the material. Furthermore, the heat resistance and steam resistance could be improved by improving the manufacturability and by increasing the blending amount of the inorganic fibers.

Next, it was discovered that the mechanical stability of the latex also greatly affects the manufacturability of the NA joint sheet.

Regarding the mechanical stability of latex, there is the idea that the worse the latex is, the more easily it swells in the solvent and the more suitable it is as the rubber of the joint sheet.
It was discovered that when mechanical stability is poor, the latex agglomerates and becomes difficult to swell when mixed with a solvent in a Henschel mixer. It was found that setting the Marron stability of the NBR latex to 0.50% or less eliminates bubble defects, facilitates lamination on the hot roll side, and improves manufacturability.

The measurement of the Marlon stability referred to herein is based on JI
The mechanical stability of S-K 6392 was measured under a load of 10 kg for 10 minutes.
It is obtained under the condition of 100 mesh.

In addition to the above conditions of an average particle size of 130 nm or more and a gel insoluble content in toluene of 30 to 80% by weight or more, setting the Marlon stability to 0.50% or less makes the swelling rate of the rubber in toluene significantly optimized. To help
Tensile strength, heat resistance, steam resistance, and manufacturability are further improved.

The latex in the present invention is easily dispersed in a solvent. By mixing the solvent and the latex, the conventional latex is in a separated state, but the latex in the present invention gives a creamy mixture. Therefore, in the method for manufacturing the joint sheet of the present invention,
First, the latex and the solvent are mixed for 2 to 3 minutes to form a cream, and then fibers and the like can be mixed, resulting in extremely good kneading properties. On the other hand, conventional latex is separated by mixing with solvent, so latex, solvent, fiber,
It was necessary to mix the other components at the same time, and there were insufficient shearing force during mixing, mechanical instability, latex agglomeration, and insufficient swelling speed, but these can be significantly improved by the present invention.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 With a molecular weight of 50,000 or less of 20% by weight or less, an acrylonitrile content of 28% by weight, and an anionic emulsifier / nonionic emulsifier ratio of 70/30, the content of the mixed emulsifier was 1.5% by weight based on the copolymer. NBR rubber latex # 1 having an average particle size of 120 nm, a gel insoluble content of 20% by weight in toluene and a Marlon stability of 0.70% as shown in Table 1.
100 parts by weight and 600 parts by weight of toluene at a rotation speed of 1000 R
After kneading with a PM Henschel mixer for 10 minutes, add the fiber materials, fillers, and rubber chemicals in the amounts shown in Table 2 and then add
Kneaded for 20 minutes. Add this kneading material to a heat roll (150 ℃),
Pressure vulcanization molding was performed using a cold roll (20 ° C.) calender roll to obtain a joint sheet having a thickness of 1.5 mm.

Examples 2 to 4 and Comparative Examples 1 to 4 Each joint sheet was manufactured in the same manner as in Example 1 according to the constitution of the NBR latex shown in Table 1 and the formulations shown in Tables 2 and 3.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

Next, Tables 4 and 5 show the manufacturability and physical property values of each example and each comparative example. The tensile strength, compression rate, restoration rate and stress relaxation rate of the joint sheet are JIS
-Measured according to R3453. Also, the sealing property is
It was evaluated by the gas leakage amount of time multiplied by the nitrogen gas 7kgf / cm ² to tighten 300kgf / cm ^2. Heat resistance was evaluated by the reduction rate of tensile elongation after heating in a 200 ° C gear oven for 8 hours.

[0032]

[Table 4]

[0033]

[Table 5] * 1: △: defective plate making, ×: impossible plate making

[0034]

As can be seen from Tables 4 and 5, Examples 1 to 4 are remarkably improved in manufacturability as compared with Comparative Examples 1 to 4. In particular, Comparative Examples 2 and 4 having a large amount of glass fibers could not be plate-formed by a roll, but Examples 2 and 4 having the same glass fiber amount could be plate-formed. Also, in terms of physical properties, Examples 1 and 3 are Comparative Examples 1 and 3.
It is possible to manufacture joint sheets having good tensile strength, stress relaxation rate, and sealability as compared with those of Example 1, and good stress relaxation rate and heat resistance, which could not be manufactured conventionally, as in Examples 2 and 4. It was

As described above, the NA joint sheet obtained by the present invention has a greatly improved manufacturability by changing the constitution of NBR latex, and has a composition which cannot be manufactured by the conventional method. Since it has become possible to manufacture joint sheets, it has become possible to obtain joint sheets with good characteristics such as stress relaxation rate and heat resistance. In addition, the tensile strength of the joint sheet is better than that of conventional products.

Claims (2)

[Claims] 1. When producing a joint sheet having a composition consisting of organic fibers, inorganic fibers other than asbestos, inorganic filler, rubber and rubber chemicals, the rubber is 20 to 45% by weight of ethylenically unsaturated nitrile monomer. And the presence of a mixed emulsifier consisting of 80 to 60% by weight of a monomer mixture consisting of 80 to 55% by weight of a monomer having a functional group copolymerizable therewith and 80 to 60% by weight of an anionic emulsifier and 20 to 40% of a nonionic emulsifier. A latex of a copolymer obtained by polymerizing below, wherein the latex contains 5 to 12% by weight of an emulsifier with respect to the copolymer,
The average particle diameter is 100 to 150 nm, the toluene insoluble content of the copolymer is 10 to 30% by weight, and the ratio of the polymer having a molecular weight of 50,000 or less in the tetrahydrofuran soluble content of the copolymer is 20. A method for producing a joint sheet, characterized in that the content is less than or equal to% by weight. 2. When producing a joint sheet having a composition consisting of organic fibers, inorganic fibers other than asbestos, inorganic filler, rubber and rubber chemicals, the rubber is 20 to 45% by weight of ethylenically unsaturated nitrile monomer. And a copolymer latex obtained by polymerizing a monomer mixture comprising 80 to 55% by weight of a monomer having a functional group capable of being copolymerized therewith, having an average particle diameter of 130 to 200. nm, wherein the toluene insoluble content of the copolymer is 30 to 80% by weight, and the ratio of the polymer having a molecular weight of 50,000 or less in the tetrahydrofuran soluble content of the copolymer is 20% by weight or less. Manufacturing method of joint sheet.