JPS63280787A - Composition for gasket - Google Patents

Abstract

PURPOSE:To obtain the titled composition, containing 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.%) fibers, having preferably 7.1-6.88 (optimally 7.06-6.89) lattice con stant in structural analysis by X-ray diffractometry, obtained by oxidizing carbon fibers, consisting of a readily graphitizable carbonaceous substance, etc., and prepared by a vapor growth method with an oxidizing agent, such as oxidizing gas, e.g. oxygen, or nitric acid and having 3-500mu equiv/g (espe cially 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 (Industrial Application Field) The present invention relates to a gasket composition with excellent airtightness and heat resistance.

Conventionally, there are various types of gaskets, but the present invention is a gasket that requires particularly heat resistance, such as a gasket that 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. This composition is suitable for use as a constituent material of gaskets used in high-temperature parts, such as cylinder head gaskets to maintain airtightness in engine exhaust manifold parts, and gaskets used in high-temperature parts. It is applied by laminating it on both sides of a board 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, various materials to replace asbestos are being studied.

For example, attempts have been made to use carbon fibers made by carbonizing organic fibers, or carbon fibers made by spinning pitch and then spinning it back. 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 has poor oil resistance and antifreeze resistance, which results in a decrease in sealing performance during use, which requires improvement.

As described above, there is an urgent need to develop a composition that can replace the gasket assembly using asbestos.

(Means for solving the problem) 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 anti-spreading properties of this material. Furthermore, as we conducted various practicality tests focusing on the unique morphology and chemical and thermal stability of this fiber, we found that due to the shape, agglomeration state, and dispersion state of this fiber, They discovered that it has excellent sealing properties, and as a result of further study, they arrived at the present invention.

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

In the present invention, vapor-grown carbon fiber refers to a fibrous carbonaceous material that is produced by heating a carbon source such as a hydrocarbon in the presence of a catalyst and growing it in a vapor phase, and which is pulverized or cut. It is a carbonaceous material in the form of a smooth, smooth carbonaceous material, or a carbonaceous material obtained by heat treatment of these materials.When observed with an electron microscope, the vapor grown carbon fiber referred to in the present invention shows a core part and a carbonaceous material that is heat-treated. Surrounding the fibers are uniquely shaped fibers made of annual ring-shaped carbon layers, which have been subjected to processes such as crushing, crushing, and cutting.

The 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 9.
01-2 Am, more preferably 0.01-1 μm,
Most preferably, it is 0.01 to 0.5 μm, and the length of the fiber is not particularly limited. Generally, the length is 5000 μm or less, but it may be even shorter, such as 1000 μm or 100 μm.
The diameter may be 1 or 10 μm, and fibrous materials obtained by crushing, cutting, or pulverizing these into shorter lengths, or granular or irregularly shaped materials may also be used.

The vapor grown carbon fiber referred to in the present invention has a high carbon purity, generally K, 97.5% or more, particularly 98% or more, most preferably 98.5% or more.

Further, in the present invention, the vapor-grown carbon fiber is an easily graphitizable carbonaceous material or a highly graphitizable carbonaceous material, and an easily graphitizable carbonaceous material is particularly preferable. In structural analysis by line analysis, the lattice constant is particularly preferably in the range of 7.1 to 6.88, and most preferably in the range of 7.06S6.89.

In the present invention, the gasket composition containing vapor-grown carbon fibers is a composition in which the above-mentioned vapor-grown carbon fibers are present as a constituent component of the gasket, and the gasket composition contains the vapor-grown carbon fibers in the composition. The amount of carbon fiber is not particularly limited. It is generally present in an amount of at least 0.1% by weight of the solid components of the composition, preferably at least 0.2%, particularly from 0.4% to 99.9% by weight. The composition is most preferably 2% by weight or more and 98% by weight or less.

In the present invention, the vapor grown carbon fiber has 3 acidic functional groups.
The amount of acidic functional groups is preferably in the range from 8 to 450 μeq/g, particularly from 15 to 350 μeq/'g. When the amount of acidic functional groups is within this range, not only is workability extremely excellent at the stage of mixing with the binder and other components such as machine powder and other fibers when creating the gasket composition, but also the dispersibility is good. Furthermore, gasket performance is also improved.

The most common method for producing vapor grown carbon fibers having acidic functional groups in the present invention is to oxidize vapor grown carbon fibers with an oxidizing gas such as oxygen or an oxidizing agent such as nitric acid. In place of the oxidation method, a plasma method, a graft method, etc. may also be used.

In the present invention, a gasket composition containing a vapor grown carbon fiber having an acidic functional group is a composition in which the above vapor grown carbon fiber is present as a constituent component of the gasket composition. There is no particular limit to the amount of vapor grown carbon fiber inside. Generally, 0 among the solid components of the composition
．． 1% or more by weight, preferably 0.2% or more, especially 0.4% to 99.9% by weight, most preferably 2% or more 98% by weight.
% by weight or less.

In the present invention, the effect of the vapor grown carbon fiber is to improve the airtightness, heat resistance, oil resistance, antifreeze resistance, chemical resistance, and solvent resistance of the gasket composition, as well as to improve the acidic functional group. By having this, 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 vapor-grown carbon fibers be used in an extremely fine state and in the form of fibers, since the effects are remarkable. At this time, not only the diameter of the fiber is small, but also the ratio of fiber length/fiber diameter is
The number 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 vapor grown carbon fibers having acidic functional groups, but the gasket composition also includes a binder, Fibers other than vapor grown carbon fibers, fillers, other chemicals, additives, etc. 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, Acryminitril butadiene rubber, chloro-o7'rene rubber, fluororubber, 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 essential in order to bind the vapor grown carbon fibers referred to in the present invention, and also to bind fibers other than the vapor grown carbon fibers, fillers, etc. that are used as necessary. However, if used in excess, the heat resistance and phasing properties of the gasket will decrease, so the amount used should be determined in balance with the bonding effect. Generally, the amount is preferably from 0.5 to 10,000 parts by weight, particularly preferably from 1 to 1,000 parts by weight, and most preferably from 2 to 500 parts by weight, based on 100 parts by weight of vapor grown carbon fiber.

As fibers other than vapor grown carbon fibers, various organic and inorganic fibers can be used, but fibers with excellent heat resistance are preferred, such as various ceramic fibers, quartz glass fibers, rock fibers, etc. Wool, stainless fiber, carbon am.

Alumina fiber, alumina silicate fiber,
Other inorganic fibrous materials such as asbestos, organic fibers such as kynor fibers, aramid fibers, and polyimide fibers can also be used, but they may cause a decrease in heat resistance, airtightness, chemical resistance, etc., so do not use these fibers. It is necessary to consider reducing the amount used or not using it as much as possible within the purpose.

In addition, various fillers, chemicals, and additives that have been conventionally used in gasket compositions can be used. For example, fillers such as clay, talc, 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 degrading the various properties of the gasket, so it is necessary to properly control the tray depending on the purpose of use.

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

Example 1 Vapor-grown carbon fiber with a diameter of 0.05 to 0.1 μm (trisacetylacetonate iron and benzene were introduced into a heating space at 1400°C and synthesized in a floating state, carbon content of 99% or more, lattice constant 7.02) was oxidized with a gas containing 0.7% oxygen to obtain a vapor grown carbon fiber with an amount of acidic functional groups of 88 μeq/g. By microscopic observation, a vapor grown carbon fiber having a fiber length of substantially 50 μm or more was obtained, and this 1001 portion and
A composition was prepared by kneading 13.3 parts by weight of acrylic butadiene rubber, 33 parts by weight of a rubber compounding agent, 10.8 parts by weight of Merck, and 5.9 M parts of clay with toluene.

A gasket was produced to evaluate this composition. In other words, the above composition was rubbed on both sides of an iron plate with hooks, the toluene was removed, and the composition was heated in a heating furnace at 150°C for 30 minutes to perform vulcanization, resulting in a thickness of 1.25J11.
I got a gasket for this.

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.

Compressibility and recovery rate of this gasket at room temperature according to ASTM F104 Type 1 test method.

Stress relaxation resistance, heat resistance, water sealing properties, oil resistance, and antifreeze resistance were measured to evaluate its practicality as a gasket. 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: strain relief rate is 20% or less, compression ratio after heating is 50% or more of the compression ratio before heating, water resistance is 5 atm or more, and oil resistance is 20% or less. The compression rate after immersion was 2 times or less and the recovery rate was 25% or more, and the antifreeze resistance was determined when the compression rate was 1.8 times or less and the recovery rate was 30% or more.

Example 2 A vapor-grown carbon fiber (carbon content of 99% or more, lattice constant of 6.98) having a fiber diameter of 0.05 to 0.2μ was slightly crushed and observed with an electron microscope to determine that it was substantially long. A vapor grown carbon fiber having a length of 20 km or more and good dispersibility was obtained. This was oxidized with a gas containing 0.5% oxygen, and the amount of acidic functional groups was 58%.
A vapor grown carbon fiber of μeq/g was obtained, and a gasket composition was prepared using the same in the same manner as in Example 1. Furthermore, the practical performance of the gasket was evaluated, and good results satisfying the evaluation criteria were obtained.

Example 3 In Example 1, 80 parts by weight of vapor grown carbon fiber and asbestos 2 were used instead of 100 parts by weight of vapor grown carbon fiber.
A gasket composition was prepared in the same manner as in Example 1 using 0 parts by weight, and a practical performance test was conducted as a gasket. Good results satisfying the practicality evaluation criteria were obtained.

Example 4 Rock wool 2 instead of asbestos in Actual M Example 3
A gasket composition was prepared in the same manner as in Example 1 using 0 parts by weight, and a practical performance evaluation test was conducted as a gasket, and satisfactory results were 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 practical performance evaluation test as a gasket was conducted, and satisfactory results were obtained.

Example 6 In Example 5, acrylic rubber was used instead of acrylic butadiene rubber. A gasket composition was obtained in the same manner as in Example 1. This composition was tested for practicality 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 rubber latex in an aqueous dispersion system without using toluene. Example 1 for this composition
A gasket was made using the same procedure as above.

The obtained gasket showed good performance satisfying the evaluation criteria in the same practicality evaluation test as in Example 1.

For comparison, a similar test was conducted on a vapor-grown carbon fiber graphitized material without introducing acidic functional groups, but it was difficult to disperse in water and required a long time, resulting in problems in workability.

Comparative Example 1 In the test of Example 1, pitch-based carbon fiber (diameter 14 μm, length 6 ta) was used instead of vapor grown carbon fiber.
Similar tests were conducted for preparing a composition and evaluating it as a gasket.

However, in this case, it was difficult to form a gasket, and its water sealing properties, oil resistance, and antifreeze resistance were poor, and it was not practical.

Comparative Example 2 In Example 2, a gasket was obtained by conducting the same test by reducing the amount of pitch-based carbon fiber in Comparative Example 1 instead of using 80 parts of vapor-grown carbon fiber and 20 parts by weight of asbestos. . 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 Aspes in place of 100 parts by weight of the vapor grown carbon fiber. However, among the performances as a gasket, water sealing properties were somewhat insufficient.

(Efficacy Table 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 composition has good workability when making a gasket, and the mechanical strength of the composition is also good, making it extremely useful industrially.

Patented wheat flour Asahi Kasei Industries, Ltd.

Claims (1)

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