JPH09296865A - Cylinder head gasket - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a cylinder head gasket having excellent seal durability obtained by a simple manufacturing process that does not include a primer treatment process. A cylinder head gasket obtained by screen-printing an addition reaction-curable liquid silicone composition into a thin film on a surface of a gasket substrate not subjected to primer treatment, and curing and adhering the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder head gasket of an engine used in various fields such as a gasoline engine for automobiles or a diesel engine.

[0002]

2. Description of the Related Art Conventionally, as a cylinder head gasket for an engine, there has been known a gasket in which a liquid silicone composition is applied to a gasket substrate and then cured. By the way, since a normal liquid silicone rubber is originally poor in adhesiveness, it is necessary to pre-treat the surface of the gasket substrate in advance in order to favorably adhere the cured product of the composition to the gasket substrate. However, when a substrate that has been subjected to a primer treatment is used, the adhesiveness of the cured product immediately after curing is improved, but the adhesive durability, in particular, the adhesive durability when immersed in engine oil or a cooling liquid, becomes poor. There are drawbacks. Therefore, there is a drawback in that the period during which the sealing performance of the cylinder head gasket can be maintained is short. Further, since the primer to be used usually contains an organic solvent, there is a concern that it may adversely affect the working environment.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cylinder head gasket having excellent seal durability obtained by a simple manufacturing process which does not include a primer treatment process.

[0004]

By adopting screen printing, a thin film can be formed uniformly on the gasket substrate, so that the sealing performance of the gasket substrate can be maintained. Since it is difficult to form a uniform thin film by simple coating, the sealing performance cannot be maintained.

The present invention is a cylinder head gasket obtained by screen-printing an addition reaction-curable liquid silicone composition in a thin film on the surface of a gasket substrate which has not been treated with a primer, and curing and adhering the same.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

Gasket Substrate As the gasket substrate used in the present invention, a known gasket substrate can be used. For example, metal aramid fiber gasket substrate for gasoline engine, metal graphite gasket substrate, metal gasket substrate, carbon for diesel engine. Examples include a system-based gasket substrate (for example, a carbon-based compression material laminated on a mild steel plate) and a semi-metallic gasket substrate.

Addition Reaction-Curable Liquid Silicone Composition The cylinder head gasket of the present invention uses an addition reaction-curable liquid silicone composition as the liquid silicone composition. The composition includes (A) one molecule Diorganopolysiloxane containing at least two alkenyl groups therein, (B) Organohydrogenpolysiloxane containing at least three hydrogen atoms bonded to silicon atoms in one molecule, (C) Platinum group metal catalyst And (D) containing fine powder silica having a specific surface area of 50 m ² / g or more is preferable.

(A) Alkenyl group-containing diorganopolicy
Roxane The alkenyl group-containing diorganopolysiloxane used in the above composition has the following average compositional formula: R _a SiO _{(4-a) / 2} (wherein R is an unsubstituted or substituted monovalent hydrocarbon group,
a is 1.9 to 2.4, preferably 1.95 to 2.2)

## STR1 ## which contains at least two alkenyl groups in one molecule. In this diorganopolysiloxane, the main chain portion is usually basically composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ),
Both ends of the molecular chain are triorganosiloxy groups (R ₃ SiO
_Although it is a straight chain which is blocked with _1/2 ), it may be a branched chain which contains RSiO _3/2 units or SiO _4/2 units in a part of the molecular structure. It may be a cyclic body composed of repeating organosiloxane units (R ₂ SiO _2/2 ). From the viewpoint of physical properties such as mechanical strength of the cured product, linear diorganopolysiloxane is preferable. Even if the alkenyl group is present only at both ends of the molecular chain,
Alternatively, it may be present at both ends of the molecular chain and in the middle of the molecular chain, or may be present at one end of the molecular chain and in the middle of the molecular chain, or may be present only in the middle of the molecular chain.

Examples of the unsubstituted or substituted monovalent hydrocarbon group for R include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group and hexyl group. Group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group and other alkyl groups; cyclopentyl group, cyclohexyl group,
A cycloalkyl group such as a cycloheptyl group; a phenyl group,
Aryl groups such as tolyl group, xylyl group, naphthyl group, biphenylyl group; aralkyl groups such as benzyl group, phenylethyl group, phenylpropyl group, methylbenzyl group; vinyl group, allyl group, propenyl group, isopropenyl group,
Alkenyl groups such as butenyl group, hexenyl group, cyclohexenyl group; and some or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms such as fluorine, chlorine and bromine, cyano groups, etc. Groups, for example, chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,
Examples thereof include those having 1 to 12 carbon atoms, preferably about 1 to 8 carbon atoms, such as 3,4,4,5,5,6,6,6-nonafluorohexyl group.

A typical example of such an alkenyl group-containing diorganopolysiloxane is, for example, the following general formula (1):

[0013]

Embedded image (In the formula, R ¹ is independently an unsubstituted or substituted monovalent hydrocarbon group having no aliphatic unsaturated bond, X is an alkenyl group, n is an integer of 0 or more, and m is an integer of 0 or more. , Preferably an integer satisfying 10 ≦ n + m ≦ 10,000, more preferably 50 ≦ n + m ≦ 2,000, and 0 ≦ m /
A diorganopolysiloxane represented by the formula (n + m) ≦ 0.2, which is represented by the following general formula (2):

[0014]

Embedded image (In the formula, R ¹ and X are the same as above, r is an integer of 0 or more, s is an integer of 2 or more, preferably 10 ≦ r + s
An integer satisfying ≦ 5000, more preferably 50 ≦ r + s ≦ 20
And an integer satisfying 0 <s / (r + s) ≦ 0.2) and the like.

In the formula, the unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic unsaturated bond as R ^{1 is the same as} the unsubstituted or substituted monovalent hydrocarbon group exemplified as the above R ( However, alkenyl groups are excluded), typical ones have 1 to 10 carbon atoms, and particularly typical ones have 1 to 6 carbon atoms, preferably methyl group, ethyl group , A propyl group, a chloromethyl group, a bromoethyl group, a 3,3,3-trifluoropropyl group, a cyanoethyl group and the like, an unsubstituted or substituted alkyl group having 1 to 3 carbon atoms; a phenyl group, a chlorophenyl group, a fluorophenyl group An unsubstituted or substituted phenyl group such as; a xylyl group.

In the formula, the alkenyl group represented by X is, for example, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a hexenyl group, a cyclohexenyl group or the like and usually having about 2 to 8 carbon atoms. Among them, lower alkenyl groups such as vinyl group and allyl group are preferable.

The alkenyl group-containing diorganopolysiloxane is 100 to 100,000 at room temperature (eg 25 ° C.).
Those having a viscosity of about cP are preferable. This alkenyl group-containing diorganopolysiloxane can be obtained by a known method, and a specific production method is, for example, equilibration of organocyclopolysiloxane and hexaorganodisiloxane in the presence of an alkali catalyst or an acid catalyst. The method of carrying out a chemical reaction can be mentioned.

(B) Organohydrogen polysiloxy
The organohydrogenpolysiloxane used in the composition described above is a component (crosslinking agent) that undergoes a crosslinking reaction with the component (A), and also acts as an adhesive component to the gasket substrate. The organohydrogenpolysiloxane as the component (B) contains at least three hydrogen atoms (that is, SiH groups) bonded to silicon atoms in one molecule, and may be linear, branched, cyclic, or Any resinous material having a three-dimensional network structure may be used. As a typical example of such an organohydrogenpolysiloxane, for example, the following average composition formula (4): H _i (R ² ) _j SiO _{(4-ij) / 2} (4) (wherein R ² is independent Is an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic unsaturated bond, wherein i and j are 0
<I <2, 0.8 ≦ j ≦ 2 and 0.8 <i + j ≦ 3, preferably 0.3 ≦ i ≦ 1, 1.5 ≦ j ≦ 2 and 1.
8 is a number satisfying 8 ≦ i + j ≦ 2.7).

In the formula, examples of the unsubstituted or substituted monovalent hydrocarbon group which does not contain an aliphatic unsaturated bond represented by R ² include the same ones exemplified as R ^{1 in the} general formula (1). Typical examples are those having 1 to 10 carbon atoms, particularly 1 to 7 carbon atoms, preferably a lower alkyl group having 1 to 3 carbon atoms such as a methyl group, a phenyl group, 3, 3
, 3-trifluoropropyl group. Examples of such organohydrogenpolysiloxanes include, for example, 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethyltetracyclosiloxane, 1,3,5,7, Siloxane oligomers such as 8-pentamethylpentacyclosiloxane; methylhydrogenpolysiloxane blocked with trimethylsiloxy groups at both ends of molecular chain, dimethylsiloxane / methylhydrogensiloxane copolymer blocked with trimethylsiloxy groups at both ends of molecular chain, silanol at both ends of molecular chain Group-blocked methyl hydrogen polysiloxane, molecular chain terminal silanol group-blocked dimethylsiloxane / methyl hydrogen siloxane copolymer, molecular chain terminal dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, molecular chain terminal dimethylhydrogensiloxy group-blocked Methyl hydrogen Polysiloxane with both molecular chain terminals blocked with dimethylhydrogensiloxy groups dimethylsiloxane-methylhydrogensiloxane copolymers; (R ^{₂₎ 2}
(H) consists of SiO _1/2 units and SiO _4/2 units, optionally with (R ² ) ₃ SiO _1/2 units, (R ² ) ₂ SiO _2/2 units, R ² HSiO _2/2 units, HSiO _3/2 units or (R
² ) Silicone resins capable of containing SiO _3/2 units (wherein R ² is the same as described above) and the like, and further the following formula:

[0020]

Embedded image [Where p is an integer of 0 or more, q is an integer of 3 or more, t is an integer of 1 or more, and p + q; 3 to 200, p + t; 1 to 200
] Etc. are mentioned.

The organohydrogenpolysiloxane as the component (B) can be obtained by a known method. Specific examples of the production method include cyclic polysiloxanes such as octamethylcyclotetrasiloxane and tetramethylcyclotetrasiloxane. And hexamethyldisiloxane or 1,1-dihydro-1,1,3 for sealing the ends
A method of equilibrating 3-tetramethyldisiloxane in the presence of a catalyst such as sulfuric acid, trifluoromethanesulfonic acid or methanesulfonic acid at a temperature of about -10 to + 40 ° C can be mentioned.

The amount of the component (B) used is such that the hydrogen bonded to the silicon atom in the organohydrogenpolysiloxane of the component (B) is based on 1 mol of the alkenyl group in the alkenyl group-containing diorganopolysiloxane of the component (A). The amount of the atom (that is, SiH group) is usually 1.0 to 10 mol, preferably 3.0 to 8.0 mol. If the amount used is too small, the adhesion between the gasket substrate and the cured composition may deteriorate. On the contrary, if the amount is too large, the composition may foam during curing due to the dehydrogenation reaction, and the heat resistance of the cured composition may deteriorate.

(C) Platinum Group Metal-Based Catalyst The platinum group metal-based catalyst used in the above composition is the addition reaction of the alkenyl group of the component (A) with the hydrogen atom bonded to the silicon atom of the component (B). Examples of the catalyst for accelerating the reaction include well-known catalysts used in the hydrosilylation reaction. Specific examples thereof include, for example, platinum (including platinum black), platinum group metal simple substances such as rhodium and palladium; H ₂ PtCl ₄ · nH ₂ O, H ₂ PtCl ₆ ·.
nH ₂ O, NaHPtCl ₆ · nH ₂ O, KHPtCl
₆・ nH ₂ O, Na ₂ PtCl ₆・ nH ₂ O, K ₂ Pt
Cl ₄ · nH ₂ O, PtCl ₄ · nH ₂ O, PtC
l ₂ , Na ₂ HPtCl ₄ .nH ₂ O (however, in the formula, n
Is an integer of 0 to 6, preferably 0 or 6), such as platinum chloride, chloroplatinic acid and chloroplatinate; alcohol-modified chloroplatinic acid (see US Pat. No. 3,220,972). A complex of chloroplatinic acid and an olefin (US Pat. No. 3,159,601, US Pat.
59,662 and 3,775,452); platinum group metal such as platinum black or palladium supported on a carrier such as alumina, silica or carbon; rhodium-olefin complex; chlorotris (Triphenylphosphine) rhodium (Wilkinson's catalyst); Platinum chloride, chloroplatinic acid or chloroplatinate and a vinyl group-containing siloxane, particularly a complex of vinyl group-containing cyclic siloxane, and the like.

The amount of the component (C) to be used can be appropriately increased or decreased according to the desired curing rate, but it is usually 0.1 to 1,000 p in terms of the weight of the platinum group metal relative to the component (A).
pm, especially about 1 to 200 ppm.

(D) Finely divided silica The finely divided silica used in the above composition has a specific surface area (BE
Measured value by T method. Hereinafter the same) is 50 m ² / g or more, preferably about 100 to 500 m ² / g. Examples of such finely divided silica include hydrophilic silica obtained by high-temperature hydrolysis of silicon tetrachloride in an oxyhydrogen flame, and hydrophobic silica obtained by surface-treating the hydrophilic silica with chlorosilane or silazane. Is mentioned. Commercially available products of this finely divided silica include, for example, Aerosil 130 (trade name of Nippon Aerosil Co., Ltd.), Aerosil 200 (same as above), Ae.
rosil 300 (same as above), Cabosil MS-5 (trade name of Cabot), Cabosil MS-7 (same as above), Rheorosil QS-102 (trade name of Tokuyama Soda), Rheorosil QS-103 (same as above), Nipsil
LP (trade name of Nihon Silica Co., Ltd.) [The above are hydrophilic silica]; Aerosi R-812 (trade name of Degussa Co.), Aerosi
R-812S (same as above), Aerosi R-972 (same as above), Aerosi R-9
74 (same as above), Rheorosil MT-10 (product name of Tokuyama Soda Co., Ltd.), Nipsil SS series (product name of Nippon Silica Co., Ltd.)
[The above are hydrophobic silica] and the like.

The amount of the component (D) used is usually 5 to 100 parts by weight of the diorganopolysiloxane of the component (A).
It is 50 parts by weight, preferably 10 to 30 parts by weight. If the amount used is too small, it may not be possible to impart sufficient strength to the cured product. On the contrary, when the amount is too large, the viscosity of the composition becomes high, which may make screen printing on the gasket substrate difficult.

Other Components In addition to the components (A) to (D), the above-mentioned composition contains, for example, vinyl group-containing organopolysiloxane such as vinylcyclotetrasiloxane; triallyl isocyanurate;
A reaction control agent such as alkyl maleate; acetylene alcohols and silane-modified products thereof or siloxane-modified products; hydroperoxide; benzotriazole can be used. These may be used alone or in combination of two or more.

The above-mentioned composition also includes non-reinforcing fillers such as quartz powder, diatomaceous earth and calcium carbonate; inorganic pigments such as cobalt blue and colorants such as organic dyes; cerium oxide, zinc carbonate and manganese carbonate. , Red iron oxide, titanium oxide,
A heat resistance or flame retardancy improver such as carbon black can be added.

Cylinder Head Gasket The cylinder head gasket of the present invention is obtained by screen-printing an addition reaction-curable liquid silicone composition on the surface of the above-mentioned gasket substrate without subjecting it to primer treatment, from the viewpoint of sealing property as a gasket. Usually 1-100 μm,
It is preferably cured to form a uniform thin film having a thickness of about 5 to 80 μm, more preferably about 20 to 70 μm, and adhered onto a substrate.

In the present application, screen printing broadly and generally means the case where a mesh material is a metal mesh such as stainless steel or a plastic mesh such as polyester fiber, and includes silk screen printing. Silk screen printing means a case where a plastic mesh such as polyester fiber is used as the mesh material. By adopting screen printing, a uniform thin film can be applied and the sealing performance of the gasket substrate can be maintained. It is difficult to form a uniform thin film and maintain the sealing performance by the usual coating method.

As a method of screen printing, a known method can be used. For example, the addition reaction curable liquid silicone composition is placed on a mesh tray (for example, a stainless sill screen) on which a shape to be printed is made. An example is a method in which an appropriate amount of the composition is placed on the gasket substrate and the composition is passed through a mesh using a squeegee and extruded onto the surface of the substrate.

The curing temperature of the composition thus printed is preferably 100 to 200 ° C. By curing the composition within this temperature range, the adhesion between the gasket substrate and the cured product becomes good. If the curing temperature is too low, it takes a long time to cure and the adhesiveness may deteriorate. On the contrary, if it is too high, the printed composition may foam.

[0033]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 Dimethylpolysiloxane with both ends of the molecular chain blocked with dimethylvinylsilyl groups (viscosity at 25 ° C .: 10,000 c
P) 80 parts by weight, 20 parts by weight of fumed silica having a specific surface area of 300 cm ² / g, 8 parts by weight of hexamethyldisilazane, and 1 part by weight of water were stirred and mixed for 1 hour at room temperature using a kneader. Then, the mixture was heated to 150 ° C. and stirred for 2 hours while maintaining this temperature. Then, after the temperature of the mixture was cooled to room temperature, the mixture was dimethylpolysiloxane (viscosity at 25 ° C .: 10,000 cP) at both ends of the molecular chain blocked with dimethylvinylsilyl groups as described above.
Weight part, the following formula (5):

[0035]

Embedded image Methylhydrogenpolysiloxane represented by (viscosity at room temperature: 10 cP) 6.6 parts by weight (that is, the molar ratio of the SiH group in the methylhydrogenpolysiloxane to the vinyl group in the above-mentioned dimethylpolysiloxane; 6.0 mo
l / mol), vinyl group bonded to silicon atom [CH ₂ ＝ CH-SiO
-] 5 parts by weight of vinylmethylpolysiloxane (viscosity at room temperature: 1,000 cP) 4 parts by weight, acetylene alcohol 0.1 parts by weight to extend the curing time at room temperature, and platinum vinylsiloxane complex 50 ppm [above [In terms of platinum weight relative to the total amount (100 parts by weight) of dimethylpolysiloxane blocked at both molecular chain ends with dimethylvinylsilyl groups] and mixed until uniform to give an addition reaction curable silicone composition. Prepared.

Next, 100 g of this addition reaction-curable silicone composition was screen-printed on a carbon-based gasket substrate not treated with a primer in a uniform thin film of about 80 μm. Then, the substrate printed in this way
The composition was cured by heating at 50 ° C./30 minutes to prepare a cylinder head gasket. The cured product was firmly adhered to the gasket substrate. Next, the obtained cylinder head gasket was used as a commercial vehicle engine coolant [LLC
(Long Life Coolant) solution] for 30 days. As a result, the cured product was firmly adhered to the gasket substrate even after the immersion.

Comparative Example 1 As in Example 1, except that a carbon-based gasket substrate surface-treated with a titanium coupling-based primer was used instead of the carbon-based gasket substrate not treated with a primer. A cylinder head gasket was produced in the same manner. The cured product was firmly adhered to the gasket substrate. Next, the obtained cylinder head gasket was immersed in a commercially available automotive coolant as in Example 1. As a result, the cured product was easily separated from the gasket substrate.

Comparative Example 2 The same as Example 1 except that a carbon gasket substrate surface-treated with an acrylic primer was used instead of the carbon gasket substrate not treated with the primer. To produce a cylinder head gasket. The cured product was firmly adhered to the gasket substrate. Next, the obtained cylinder head gasket was immersed in a commercially available automotive coolant as in Example 1. As a result, the cured product was easily separated from the gasket substrate.

Example 2 In Example 1, 15 parts by weight of fumed silica having a specific surface area of 200 cm ² / g was used in place of 20 parts by weight of fumed silica having a specific surface area of 300 cm ² / g. Instead of 6.6 parts by weight of methyl hydrogen polysiloxane represented,
The following formula:

[0040]

Embedded image 1.1 parts by weight of methylhydrogenpolysiloxane (viscosity at room temperature: 10 cP) (that is, molar ratio of SiH group in methylhydrogenpolysiloxane to vinyl group in dimethylpolysiloxane; 3.0 mol / mo
An addition reaction-curable silicone composition was prepared in the same manner as in Example 1 except that l) was used. Then, in Example 1, the addition reaction-curable silicone composition prepared in this example was applied to a non-primed metal graphite gasket substrate in place of the non-primed carbon gasket substrate to form a uniform coating of about 50 μm. A cylinder head gasket was produced in the same manner as in Example 1 except that screen printing was performed on a thin film. The cured product was firmly adhered to the gasket substrate. Next, the obtained cylinder head gasket was immersed in a commercially available automobile engine oil for 30 days. As a result, the cured product was firmly adhered to the gasket substrate even after the immersion.

Comparative Example 3 An example except that a metal graphite gasket substrate surface-treated with a silane coupling primer was used in place of the metal graphite gasket substrate not treated with the primer in Example 2. A cylinder head gasket was produced in the same manner as in 2. The cured product was firmly adhered to the gasket substrate. Next, the obtained cylinder head gasket was immersed in a commercially available engine oil in the same manner as in Example 1. As a result, the cured product was easily separated from the gasket substrate.

[0042]

The cylinder head gasket of the present invention is
Sealing due to excellent adhesion durability of the cured product of addition reaction curable liquid silicone composition (addition reaction curable silicone rubber) to the gasket substrate, especially when immersed in cooling liquid or engine oil. Excellent durability performance. In addition, since it can be manufactured by a simple manufacturing process that does not include a primer treatment process, the working environment is not adversely affected by the organic solvent contained in the primer, and the manufacturing process can be simplified.

Claims (1)

[Claims] 1. A cylinder head gasket obtained by screen-printing an addition reaction-curable liquid silicone composition on a surface of a gasket substrate which has not been treated with a primer, and curing and adhering the same.