JPH0778213B2 - Joint sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of heat resistance and steam resistance of a non-asbestos joint sheet (hereinafter abbreviated as NA joint sheet) used as a gasket base material.

[0002]

2. Description of the Related Art Conventionally, asbestos joint sheets have been widely used as joint sheets, and by utilizing the excellent heat resistance and chemical resistance of asbestos fibers, gaskets for transportation pipes and equipment such as water, oil, air and water vapor can be used. It has been stamped. However, asbestos fiber is a natural mineral, and it is difficult to obtain it due to the depletion of resources, the rising cost of mining and transportation,
In addition, health problems caused by asbestos fibers have become a social problem, and the use of asbestos has been regulated worldwide. Because of these, recently, asbestos fibers are not used at all, and joint sheets (called asbestos-free joint sheets or non-asbestos joint sheets) that use inorganic fibers and / or organic fibers other than asbestos are used. It started to come.

In the first place, a general method for producing a joint sheet is to first add a fiber material, a filler, and a rubber chemical to a rubber swollen with a solvent (or a powder rubber or latex with a solvent added), a Henschel mixer, or the like. Kneading thoroughly to prepare a composition for forming a joint sheet, and then applying this composition to a hot roll (150 ° C) and a cold roll (20 ° C)
It has been manufactured by putting it between a pair of rolls consisting of and, evaporating and vulcanizing the solvent while laminating it on the hot roll side, and finally peeling off the laminated sheet. Depending on the product, in order to complete the vulcanization, the obtained sheet-shaped material may be subjected to secondary vulcanization in an autoclave or the like. As constituent materials, in addition to the above, small amounts of additives such as coupling agents, softening agents, plasticizers, water swelling agents, oil swelling agents, etc. are blended according to the application, and pigments are blended from the viewpoint of storage and identification. There are many things that have been done.

The fiber material used for the NA joint sheet is roughly classified into organic fiber and inorganic fiber (other than asbestos fiber). Since the organic fiber is relatively flexible and the SP value (solubility parameter) is similar to that of the rubber material, the organic fiber is liable to be entangled, bonded or joined with the rubber material or the filler, and has a high reinforcing effect. In particular, aramid pulp made by fibrillating aramid fibers (trade name, Kevlar pulp) has a larger surface area than chopped ones because the fibers are branched like asbestos fibers, and entanglement with rubber materials and fillers is extremely high. The properties such as tensile strength and flow resistance are improved, but there is a defect that heat resistance, especially steam resistance is significantly inferior to that of asbestos fiber. On the other hand, inorganic fibers are more rigid than organic fibers and have a SP value different from that of a rubber material that is a binder. Therefore, entanglement or joining with rubber materials or fillers
Although the binding property is poor and the reinforcing effect cannot be expected so much, the resilience and stress relaxation resistance are good due to the rigidity of the inorganic fiber, and the heat resistance and steam resistance are also better than those of the organic fiber. In consideration of this, NA joint sheets are often used in combination with these organic and inorganic fiber materials according to the intended use, and although some performance has approached that of asbestos joint sheets. However, the present situation is that tensile strength, heat resistance, and steam resistance are significantly inferior to those of asbestos joint sheets.

Further, as a difference between the asbestos joint sheet and the NA joint sheet, attention must be paid to the mixing ratio of the fiber material to the solid content of the joint sheet, in addition to the use of asbestos fiber. In asbestos joint sheets, asbestos fibers are often used in a proportion of 60% by weight or more, whereas in NA joint sheets, as the amount of fibers increases, sheeting on a calender roll tends to become difficult. The amount is often less than 50% by weight. The amount of reduced fiber is compensated by the filler, and the filler mixing ratio of the asbestos joint sheet is 3 to 40% by weight, while that of the NA joint sheet is in the range of 50 to 80% by weight. This is also N
A joint sheet is the cause of poor tensile strength, heat resistance, and steam resistance.

[0006]

That is, the conventional NA
In the joint sheet, when the organic fiber having a reinforcing effect is used under a high heat condition / steam atmosphere, it is significantly deteriorated together with the rubber material, and the product life is remarkably reduced as compared with the asbestos joint sheet. Also, heat resistance
Even when used in combination with inorganic fibers having high water vapor resistance, its reinforcing effect is significantly lower than that of organic fibers, and since the compounding amount cannot be increased as much as asbestos fibers in terms of manufacturability, reinforcing performance does not increase, It is considerably lower than that of the asbestos joint sheet. In addition, when used under high heat conditions and steam atmosphere, the deterioration of the inorganic fiber itself is small, but due to the deterioration of the rubber material, the combined effect of the inorganic fiber cannot be fully exerted, and as a result, compared to the asbestos joint sheet, NA There is a problem that the product life of the joint sheet is considerably reduced.

An object of the present invention is to provide an NA joint sheet having improved heat resistance and steam resistance.

[0008]

The present invention has been made in view of the above-mentioned conventional problems. It is possible to increase the heat resistance of the joint sheet by about 30 ° C by using ethylene propylene rubber (EPR), which has excellent heat resistance and water vapor resistance, as the type of rubber used as the binder of the NA joint sheet. . However, when using EPR alone, the tensile strength of the joint sheet
We focused on the problems of oil resistance, flow resistance, and stress relaxation resistance. Therefore, the present inventors considered blending other rubbers having large tensile strength and oil resistance, and performed various experiments by changing the types and amounts of all rubbers,
NBR was most suitable for improving the tensile strength and oil resistance. However, rubber with low polarity such as EPR and NB
With diene rubber having high polarity such as R, S between rubbers
Since the P values are different, the compatibility is poor, and the vulcanization of the NBR is too advanced during vulcanization, and the EPR is unvulcanized, resulting in partial vulcanization.

The mechanism of this partial vulcanization will be further explained.
In the vulcanization of a blend system such as BR and EPR, even if the vulcanizing agent / vulcanization accelerator is uniformly dispersed in both rubbers at the beginning, NBR will be vulcanized when vulcanization proceeds. Since the vulcanization is fast, the vulcanizing agent / vulcanization accelerator is consumed first, but the EPR does not progress vulcanization and the concentrations of the vulcanizing agent / vulcanization accelerator in both rubbers are significantly different. Then, the vulcanizing agent / vulcanization accelerator remaining in the EPR easily migrates into the NBR, and the NBR is further vulcanized, whereas
The EPR ends unvulcanized.

When such partial vulcanization occurs, the rubber is blended to improve the properties, but the properties are not improved because the addition rule is not satisfied. There is also a case where the performance is lower than that.
Figure 2 shows the tensile strength of the NBR / EPR blend system.
Fig. 3 shows the deformation rate (flow) of the sample in the horizontal direction with respect to the surface pressure of 5 ton (broken line in the figure is an ideal straight line where the addition rule is satisfied). In the NBR blending range of 25 to 50% by weight, the tensile strength in FIG. 2 is hardly improved, and the deformation rate (flow) in FIG. 3 is rather large (the flow resistance is deteriorated).

Therefore, as a result of the examination of the type of NBR and the experiment of changing the ratio, the inventors of the present invention have shown that, instead of NBR, a highly saturated nitrile rubber obtained by hydrogenating a part of carbon-carbon double bonds of NBR ( The above problem could be solved by blending NEM) with EPR. Compared to NBR, NEM has fewer double bonds that contribute to vulcanization, so it has superior tensile strength, oil resistance, flow resistance, and heat resistance.
In addition to being able to remarkably improve the properties even in a smaller amount than in, the double bond contributing to vulcanization is less than in NBR, so that vulcanization becomes slow and the difference in vulcanization rate from EPR is It turned out to be smaller.

That is, the joint sheet of the present invention is
Ethylene propylene rubber and highly saturated nitrile rubber are used together to form the binder main component, and ethylene propylene rubber is 60% by weight to the total amount of the binder.
90% by weight, characterized in that the highly saturated nitrile rubber is 10% by weight to 40% by weight with respect to the total amount of the binder.

The inventors of the present invention further studied this, and as a result, by using a sulfenamide type and a dithiocarbamate type as a vulcanization accelerator in combination,
It was discovered that there was almost no partial vulcanization between EPR and NEM. A vulcanization curve showing this is shown in FIG. In FIG. 1, the EPR + NEM-based curve uses a sulfenamide-based + dithiocarbamate-based vulcanization accelerator, and the EPR + NEM-based curve uses a thiazole-based + thiuram-based vulcanization accelerator, but EPR + NEM
The vulcanization degree of the system is NBR more than that of the EPR + NEM system
It is close to the system and almost no vulcanization occurs.

This mechanism is because the sulfenamide type + dithiocarbamate type vulcanization accelerator is relatively easy to dissolve in EPR and is difficult to dissolve in NEM. Therefore, vulcanization itself is slightly faster in NEM than in EPR. Although the concentration of the vulcanization accelerator progresses as it progresses, it is considered that the migration does not easily occur even if the concentration gradient of the vulcanization accelerator occurs. It is also preferable to crosslink with only a peroxide.

Furthermore, as a result of studying the blend ratio of EPR and NEM, it was found that if the ratio of NEM was 10% or more, E
It does not contribute to the improvement of tensile strength, flow resistance, and oil resistance, which is insufficient for PR, and the NEM ratio is close to 50%. When molding the joint sheet described above, it is extremely laminated on the heat roll. It has been found that it becomes difficult and the properties of the obtained sheet also deteriorate. This is because NEM is less likely to swell in the solvent, so that the viscosity of the joint sheet molding composition is reduced and the adhesion of the material to the hot roll side is deteriorated.

Further, when the above-mentioned sulfenamide type + dithiocarbamate type is not used, vulcanization is often insufficient only on the roll at the time of production, but even in such a case, it is then autoclaved. By performing secondary vulcanization, almost complete vulcanization can be reached, in which case creep resistance is improved.

[0017]

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

Example 1 A predetermined amount of a rubber material thinned to 0.1 mm by a rubber masticating roll was weighed, swollen in 300 parts by weight of toluene, and a fiber material / filler having the composition shown in Table 1 was added. In a Henschel mixer (rotation speed 1000 RPM) with rubber chemicals
Kneaded for 30 minutes. The joint sheet-forming composition thus obtained was applied to a hot roll (150 ° C) and a cold roll (20
(° C) pressure vulcanization molding with calender rolls and thickness
A 1.5 mm joint sheet was obtained.

The joint sheets of Examples 2 to 6 and Comparative Examples 1 to 4 were prepared with the formulations shown in Table 1 and Table 2 in the same manner as in Example 1. In particular, in Example 5,
The joint sheet obtained by the above method was subjected to secondary vulcanization at 120 ° C. for 2 hours in an autoclave, and in Example 6, peroxide vulcanization was performed using an organic peroxide as a rubber chemical in the above method. Is going. In addition, Table 1 and Table
In the symbol 2 of vulcanization accelerator, MSA is N-oxydiene
Ethylene-2-benzothiazylsulfenamide, Z
nDMDC is zinc dimethyldithiocarbamate, MB
T is 2-mercaptobenzothiazole and TMTD is
Represents tramethylthiuram disulfide.

[0020]

[Table 1]

[0021]

[Table 2]

Next, Table 3 and Table 4 show main physical property values of the respective Examples and Comparative Examples thus obtained. The tensile strength, compression rate, restoration rate, stress relaxation rate, and oil resistance of the joint sheet were measured according to JIS-R3453.
The flow resistance was evaluated by the horizontal deformation rate of the sample when a surface pressure of 5 tons was applied, and the heat resistance was judged by the reduction rate of tensile elongation after heating for 8 hours in a 200 ° C gear oven. .

[0023]

[Table 3]

[0024]

[Table 4]

[0025]

As can be seen from Tables 3 and 4, Examples 1 to 6 have higher tensile strength / stress relaxation rate, flow resistance / oil resistance than Comparative Example 1 using only EPR. It is remarkably improved, and it can be seen that the heat resistance is clearly better than that of Comparative Example 3 using NBR alone. Further, as shown in Comparative Example 2, when the amount of NEM is too large, the performance tends to be deteriorated as a whole. Further, as shown in Comparative Example 4, it can be seen that the blend of EPR and NBR markedly deteriorates the flow resistance due to partial vulcanization.

It is also understood that the secondary vulcanization is effective for improving the tensile strength and the stress relaxation rate, and the peroxide vulcanization also has a good stress relaxation rate.

As described above, the joint sheet obtained by the present invention has excellent heat resistance and water vapor resistance.
The performance of PR is synergistically exhibited by the combined use of NEM, and the heat resistance and steam resistance, which were the drawbacks of the conventional NA joint sheet, are greatly improved, and at the same time, other properties are equal to or higher than those of the conventional one. It can be seen that it has performance comparable to that of an asbestos joint sheet.

[Brief description of drawings]

FIG. 1 is a vulcanization time-vulcanization degree graph for explaining the operation of the present invention.

[FIG. 2] N in rubber for explaining problems of related art
It is a graph of BR amount-tensile strength.

[FIG. 3] N in rubber for explaining problems of related art
It is a graph of BR amount-deformation rate (flow).

Claims (2)

[Claims] 1. An ethylene propylene rubber and a highly saturated nitrile rubber are used together to form a binder main component, and the ethylene propylene rubber is in a ratio of 60% by weight to 90% by weight with respect to the total amount of the binder, and is highly saturated. A joint sheet characterized in that the nitrile rubber is contained in an amount of 10% by weight to 40% by weight based on the total amount of the binder. 2. The joint sheet according to claim 1, which is vulcanized by adding a sulfenamide vulcanization accelerator and a dithiocarbamate vulcanization accelerator.