JPS63280788A - Composition for gasket - Google Patents

Abstract

PURPOSE:To obtain the titled composition, containing graphitized carbon fibers, having acidic functional groups and prepared by a vapor growth method and having improved airtightness, heat, oil, antifreeze, chemical, solvent resistance, etc., and excellent mechanical strength, dispersibility and joining properties. CONSTITUTION:The aimed composition containing normally >=0.1wt.% (optimally 2-98wt.%) graphitized fibers, having preferably <=6.86 (optimally 6.78-6.72) lattice constant in structural analysis by X-ray diffractometry, obtained by a method for heat-treating carbon fibers prepared by a vapor growth method at >=1,500 deg.C (optimally at 2,100-3,000 deg.C) and oxidizing the heat-treated fibers with an oxidizing agent, etc., and having 3-500mu equiv/g (especially preferably 15-350mu equiv/g) acidic functional groups. Furthermore, the above-mentioned fibers preferably have fine fiber diameter and >=10 (optimally >=100) ratio of the fiber length/fiber diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a composition for gaskets having excellent temperament and heat resistance.

Conventionally, there are gaskets of various types, but the present invention is a gasket that requires particularly heat resistance, such as an EVA gasket, which is sandwiched between the upper surface of an engine's cylinder block and the lower surface of the cylinder head to maintain airtightness between both surfaces. A composition suitable for use as a constituent material of gaskets used in high-temperature parts, such as cylinder head gaskets for gaskets, or gaskets that maintain airtightness in the exhaust manifold part of engines, such as gaskets made of metal plates. It is applied by laminating it on both sides of the core material.

(Prior art) Conventionally, for example, cylinder head gaskets were made by laminating a composition made by mixing asbestos into a small amount of rubber as a binder on both sides of a metal plate core material. . However, since the asbestos used here has the risk of causing injury to the human body, it has become necessary to use other materials instead.

(Problems to be Solved by the Invention) For this reason, materials to replace asbestos have been extensively studied.

For example, attempts have been made to use carbon fibers made by carbonizing organic fibers or carbon fibers made by carbonizing pitch after spinning. However, this method has poor sealing properties and is difficult to put into practical use.

For this reason, a method using granular expanded graphite has been proposed. However, this method is not only expensive, but also
It had poor oil resistance and antifreeze resistance, and a decrease in sealing performance during use due to this was observed, and improvements were needed.

In this way, the gasket performance is well-balanced,
There is an urgent need to develop a composition with excellent performance.

(Means for Solving the Problems) The present inventors have been conducting basic research on the development of vapor-grown carbon fiber as a new carbon material and the characteristics and reactivity of this material. Furthermore, as we conducted various practical tests focusing on the unique morphology and chemical and thermal stability of this single fiber, we found that the structure, shape, and cohesiveness of this fiber work specifically, and that it is difficult to interact with other substances. It was discovered that it has excellent sealing properties depending on the state of dispersion, and as a result of further study, the present invention was arrived at.

That is, in the present invention, the acidic functional group is
This is a gasket composition containing a graphitized material of vapor-grown carbon fiber having the following properties.

In the present invention, the graphitized material of vapor grown carbon fiber is
It is a graphitic material obtained by heat-treating a fibrous carbonaceous material such as a hydrocarbon in the presence of a catalyst and growing it in a vapor phase. It is a graphitic material in various forms such as fibrous and crushed or cut forms, and when the graphitized material of vapor grown carbon fiber referred to in the present invention is observed with an electron microscope, it can be seen that the core part and , surrounding this, it has a unique shape consisting of a tree-ring-like carbon layer. , which has undergone processing such as crushing, cutting, etc.

The graphitized material of vapor grown carbon fiber as used in the present invention preferably has a diameter of 5 μm or less, generally 0.01 to 4 μm.
, especially 0.01 to 2 μm, more preferably 0.01 to 2 μm
The fiber length is 0.5 μm, and the length of the fiber is not particularly limited. In general, it is 5000 μm or less, but it may be even shorter, such as 1000 μm, 100 μm, or 10 μm. You can also use objects.

In the present invention, the graphitized product of vapor grown carbon fiber has a high carbon purity, generally 98.5% or more, 99% or more, most preferably 99.5% or more.

In addition, the graphitized material of the vapor grown carbon fiber in the present invention is a highly graphitic substance, and furthermore, among them, in the structural analysis by xm analysis, the lattice constant is in the range of 6.88 or less, Preferably 6.86 or less, particularly preferably in the range 6.80 to 6.70, most preferably
It is in the range of 6.78 to 6.72.

In the present invention, the vapor grown carbon fiber graphitized material is also characterized in that it has acidic functional groups of 3 to 500 μeq/g, and the amount of acidic functional groups is preferably 8 to 450 μeq/g.
g s is particularly in the range of 15 to 350 μeq/g. If the amount of the acidic functional group is within this range, it not only provides excellent workability but also good dispersibility at the stage of mixing with the binder and other components such as inorganic powder and other fibers during the preparation of the gasket composition. Furthermore, gasket performance is also improved.

In the present invention, the method for producing a graphitized vapor-grown carbon fiber having an acidic functional group includes heat-treating the vapor-grown carbon fiber at a high temperature, and then treating the graphitized vapor-grown carbon fiber with oxygen or The most common method is oxidation using an oxidizing agent such as nitric acid, and other methods such as a plasma method and a graft method may also be used instead of the oxidation method.

The heat treatment temperature is 1000°C or higher, preferably 1700°C or higher, particularly 2000°C or higher, and the most preferable range is 2100 to 300°C.

In the present invention, a gasket composition containing a graphitized vapor-grown carbon fiber having an acidic functional group is a composition in which the graphitized vapor-grown carbon fiber described above is present as a constituent component of the gasket composition. There is no particular restriction on the amount of graphitized material of the vapor grown carbon fiber in the composition. Generally, it is present in an amount of 0.1% or more by weight of the solid components of the composition, preferably 0.2% or more, and 0.43[fi
% to 99.9% by weight of the composition, most preferably from 2% to 98% by weight.

In the present invention, the effects of graphitized vapor grown carbon fibers include improvements in gasket composition airtightness, heat resistance, oil resistance, antifreeze resistance, chemical resistance, solvent resistance, etc. By having an acidic functional group, it has excellent dispersion and bonding with the binder used in the composition, and also has the effect of improving the mechanical strength of the composition, and these are combined to appear as a synergistic effect. .

In order to maximize such effects, it is preferable that the graphitized material of the vapor-grown carbon fiber is used in an extremely fine state and in the form of fibers, since the effects are remarkable. In this case, not only the diameter of the fibers is small, but also the ratio of fiber length/fiber diameter is 5 or more, preferably 10 or more, particularly 20 or more, and most preferably 80 or more.

As described above, the gasket composition of the present invention is characterized by containing graphitized vapor-grown carbon fibers having acidic functional groups, but the gasket composition may also contain other substances. Fibers other than binders, vapor-grown carbon fiber graphitized materials, fillers, and their additives and additives can be selected and used as necessary.

In particular, a binder is a necessary component for the present composition, and organic resins and rubbers are used as such binders, and rubbers are particularly preferably used, such as acrylic rubber, styrene-butadiene rubber, Acrylonitrile butadiene rubber, chloroprene rubber, fluorine rubber, shrimp chlorohydrin rubber, chlorosulfonated polyethylene rubber, chlorinated polyethylene rubber, ethylene propylene rubber.

Examples include synthetic rubbers such as ethylene propylene diene rubber and silicone rubber, and natural rubber.

The binder is used to bind the graphitized material of the vapor grown carbon fiber referred to in the present invention, and also binds fibers, fillers, etc. other than the graphitized material of the vapor grown carbon fiber, which are used as necessary. However, if used in excess, it will reduce the heat resistance and stress relaxation properties of the gasket.
The amount should be determined in balance with the binding effect. In general, it is preferably 0.5 to 10,000 parts by weight, particularly 1 to 1 to 100 parts by weight of graphitized material of vapor grown carbon fiber.
000 parts by weight is preferred, and most preferably in the range of 2 to SOO parts by weight.

Various organic and inorganic fibers can be used as the fibers other than the graphitized material of the vapor grown carbon fiber, but fibers with excellent heat resistance are preferable, such as various ceramic fibers, quartz glass fibers, Rock wool, stainless fiber.

Carbon fiber, alumina fiber, alumina silicate fiber, other inorganic fibrous substances such as asbestos, kynor fiber, aramid fiber.

Organic fibers such as polyimide fibers can also be used, but they may cause a decrease in heat resistance, airtightness, chemical resistance, etc. Therefore, it is recommended to reduce the amount used as much as possible within the purpose of using these fibers, or to avoid using them. You need to consider not doing so.

In addition, various fillers, chemicals, and additives that have been conventionally used in gasket compositions can be used. For example, fillers such as clay, Merck, calcium hydroxide, barium sulfate, vulcanizing agents, vulcanization aids, vulcanization accelerators, antioxidants, metal damage inhibitors, colorants, surfactants, and other agents. additives, etc. If these are used in excessive amounts, there is a risk of deteriorating the gasket's properties, so it is necessary to appropriately control the amount depending on the purpose of use.

(Example) The present invention will be explained below with reference to Examples.

Example 1 Vapor-grown carbon fibers with a diameter of 0.05 to 0.1 μm (trisacetylacetonate iron and benzene were introduced into a heating space of 1'400°C and synthesized in a floating state) were grown at 2400°C.
The carbon content was 99.9% and the lattice constant was 6.74.
A graphitized product was obtained. This was oxidized with a gas containing 0.5% oxygen to obtain a vapor-grown carbon fiber graphitized material with an acidic functional group content of 65 μe q/g. Microscopic observation shows that the fiber length is essentially 5.
A graphitized product of vapor grown carbon fiber with a size of 0 μm or more was obtained. 100 parts by weight of this and 15.0 parts by weight of acrylic butadiene rubber.
3 parts by weight, rubber compounding agent 3.8 parts by weight, Merck 10.8 parts by weight
A composition was prepared by mixing 5.9 parts by weight of clay with toluene.

A gasket was produced to evaluate this composition. That is, the above composition was rubbed on both sides of an iron plate with hooks, then toluene was removed, and this was heated in a heating furnace at 150°C for 30 minutes to perform vulcanization, thereby obtaining a gasket with a thickness of 1.25 m. Ta.

At this time, the vapor grown carbon fiber graphitized material having an acidic functional group was well dispersed with the rubber component, rubber compounding agent, and inorganic powder, and a good gasket with excellent workability was produced.

For this gasket, the compressibility, recovery rate, stress relaxation rate, heat resistance, water sealing property, oil resistance, and antifreeze resistance at room temperature were measured according to the ASTM F104 type 1 test method.
The practicality as a gasket was evaluated. As a result, it was found that the gasket made from the composition of this example had excellent performance and was practical.

The evaluation criteria for practicality are as follows: stress relaxation rate is 20% or less, compression rate after heating is 50% or more of the compression rate before heating, water sealability is 5 atm or more, and oil resistance is determined by compression after immersion in oil. The compression ratio was set to be 2 times or less and the recovery rate was 25% or more, and the antifreeze resistance was set to 1.8 times or less and a recovery rate of 30% or more.

Example 2 A vapor-grown carbon fiber having a fiber diameter of 0.05 to 0.2 μm was heat-treated at 2500°C to obtain a graphitized material with a lattice constant of 6.73 and a carbon content of 99.9%. Crush,
Observation with an electron microscope revealed a graphitized vapor grown carbon fiber having a length of substantially 20/am or more and good dispersibility.

This was oxidized with a gas containing 1% oxygen, and the amount of acidic functional groups was 8
A graphitized material of vapor grown carbon fiber having a carbon fiber density of 3 μeq/g was obtained, a gasket composition was made using this in the same manner as in Example 1, and further, the practical performance as a gasket was evaluated and good results satisfying the evaluation criteria were obtained. Obtained.

Example 5 In Example 3, 10 parts by weight of asbestos and 10 parts by weight of expanded graphite powder were used instead of 20 parts by weight of asbestos,
A gasket composition was prepared in the same manner as in Example 1, and a test to evaluate its practicality as an iK gasket was conducted, and satisfactory results were obtained.

Example 6 In Example 5, a gasket composition was obtained in the same manner as in Example 1 except that acrylic rubber was used instead of acrylic butadiene rubber. This composition was subjected to a practical evaluation test as a gasket using the same method as in Example 1, and satisfactory results were obtained.

Example 7 In Example 1, a gasket composition was obtained by mixing and dispersing acrylic butadiene and rubber latex in an aqueous dispersion system without using toluene. A gasket was produced using this composition using the same procedure as in Example 1.

The obtained gasket showed good performance satisfying the evaluation criteria in the same practicality evaluation test as in Example 1.For comparison, the same was true for a vapor-grown carbon fiber graphitized material without introducing acidic functional groups. A test was conducted, but it required a long time to disperse it in water, which caused problems in workability.

Comparative Example 1 In the test of Example 1, pitch-based carbon #R1tkC with a diameter of 14 μm was used instead of the graphitized material of the vapor grown carbon fiber.
A similar test was attempted for preparing a composition and evaluating it as a gasket using the length s am ).

However, in this case, it is difficult to form a gasket, and the water sealing properties, heat resistance, and antifreeze resistance are poor.
Practicality was not recognized.

Comparative Example 2 In Example 2, graphitized vapor grown carbon fiber 80
A similar test was conducted using 25 parts by weight of pitch-based carbon fiber and 75 parts by weight of asbestos of Comparative Example 1 in place of the 201 parts by weight of asbestos g and 201 parts by weight, and reducing the amount of pitch-based carbon fiber to obtain a gasket. However, this gasket had insufficient water sealing properties, oil resistance, and antifreeze resistance, making it less practical.

Comparative Example 3 In the test of Example 1, a similar test was attempted using 100 parts by weight of asbestos instead of 100 parts by weight of the graphitized material of the vapor grown carbon fiber. However, among the performances as a gasket, water sealing properties were somewhat insufficient.

(Effects of the Invention) The gasket composition of the present invention has excellent airtightness, heat resistance, oil resistance, antifreeze resistance, chemical resistance, solvent resistance, etc. The workability during production is good, and the mechanical strength of the composition is also good, making it extremely useful industrially.

Claims (1)

[Claims] Gasket composition containing graphitized vapor grown carbon fiber having 3 to 500 μeq/g of acidic functional groups