JPH05279571A - Silicone rubber composition excellent in mold release property - Google Patents

Abstract

PURPOSE:To obtain a curable silicone rubber composition capable of forming a matrix greatly improved in the persistence of releasability by incorporating a specified compound generally used as the curing catalyst for a condensation- curing composition. CONSTITUTION:This composition contains a diorganopolysiloxane (A) having at least two alkenyl groups in the molecule and a viscosity at 25 deg.C of 1,000-100,000cp, an organohydrogenpolysiloxane (B) having at least two SiH groups in the molecule in an amount sufficient to provide a molar ratio of the SiH groups to the alkenyl groups of component A of (0.4 to 4.0):1, a fine silica powder (C) having a specific surface of at least 50m<2>/g in an amount of at most 50 pts.wt. based on 100 pts.wt. component A, a platinum group metal catalyst (D), and at least one compound (E) selected from an organotin compound, an organotitanium compound and an imidazole compound in an amount of 0.01-2 pts.wt. based on 100 pts.wt. component A. The incorporation of component E can give the objective composition capable of forming a matrix remarkably improved in the persistence of releasability even from, e.g. a urethane resin with excellent physical properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition having excellent releasability, which is effectively used as a reversal mother die for molding.

[0002]

2. Description of the Related Art It is a known technique to use a silicone rubber mold as an inversion mother mold, and to fill it with a resin and cast it to produce a replica. Recently,
Such a duplicated product, that is, a resin molded product, has come to be actually used as a part of automobile parts and home appliance parts. For this reason, the characteristics of the casting resin have come to be emphasized, and the mechanical characteristics and the like thereof are remarkably improved. On the other hand, such an improvement in the properties of the casting resin impairs the durability of the silicone rubber mother die, and the number of duplicates obtained from one mother die is currently significantly reduced. Therefore, it is desired to improve the mold release durability of the silicone rubber mother die.

[0003]

Conventionally, as means for improving the mold release durability of a silicone rubber mother die, as a filler of the silicone rubber composition constituting the mother die,
It has been practiced to use a hydrophobized reinforcing silica or a hydrophilic or hydrophobic silica treated with a silazane compound. Although a master mold formed from a silicone rubber composition using such a filler can be confirmed to have an improvement in mold release durability, it has a high physical property urethane resin, which is currently the mainstream of casting resins. Does not yet exhibit satisfactory release durability.

Therefore, an object of the present invention is to provide a silicone rubber composition capable of forming a mother die having excellent mold release durability even for a urethane resin having high physical properties.

[0005]

According to the present invention, (A) a diorganopolysiloxane having at least two alkenyl groups in one molecule and having a viscosity of 1,000 to 100,000 cP at 25 ° C., (B) An organohydrogenpolysiloxane having at least two SiH groups in one molecule, wherein the SiH groups are
An amount of 0.4 to 4.0 times the molar amount of the alkenyl group in the component (A), (C) a fine powder silica having a specific surface area of 50 m ² / g or more, 50 parts by weight per 100 parts by weight of the component (A). Below the section,
(D) at least one selected from a catalytic amount of a platinum group metal-based catalyst, (E) an organotin compound, an organotitanium compound and an imidazole compound, and 0.01 to 100 parts by weight of the (A) component.
Provided is a silicone rubber composition containing 2 parts by weight and having excellent releasability.

That is, an important feature of the present invention is that an addition-curing type silicone rubber composition is blended with an organotin compound, an organotitanium compound or an imidazole compound which is widely used as a curing catalyst in a condensation-curing type composition. Therefore, by using at least one of these, it becomes possible to form a mother die having remarkably improved mold release durability even for a high physical property urethane resin or the like.

Component (A) The organopolysiloxane of component (A), which is the main component in the composition of the present invention, has at least two alkenyl groups in one molecule in order to form a cured product by an addition curing reaction. It is necessary to have. Also, the viscosity at 25 ℃ is 1,0
It is also necessary to be in the range of 100 to 100,000 cP, and when the viscosity is out of this range, workability is deteriorated and physical properties of the obtained cured product are impaired.

Such an organopolysiloxane can be obtained, for example, by the following average composition formula (1): R ¹ _a R ² _b R ³ _c SiO _{(4-abc) / 2} (1) [wherein R ¹ , R ² and R ^{3 are} Are the same or different and each is a substituted or unsubstituted monovalent hydrocarbon group, a, b and c are numbers of 0 or more, and 1.9 ≦ a +
It is a number that satisfies b + c ≦ 2.4]. Here, as the monovalent hydrocarbon group, a methyl group, an ethyl group, a propyl group, an alkyl group such as a butyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group, an alkenyl group such as an isopropenyl group, A phenyl group, an aryl group such as a xylyl group, a benzyl group, an aralkyl group such as a phenylethyl group, and a group in which all or part of the hydrogen atoms of these groups are substituted with a halogen atom, for example, a chloromethyl group, 3, Examples thereof include a 3,3-trifluoropropyl group, and two or more alkenyl groups are averaged in one molecule. This organopolysiloxane may be linear or branched containing RSiO _3/2 units (R is the monovalent hydrocarbon group) or SiO ₂ units. The alkenyl group may be bonded to either the terminal of the molecule or in the middle of the molecular chain, and a vinyl group is preferable as the alkenyl group. The monovalent hydrocarbon group other than the alkenyl group may be any group exemplified above, but is generally preferably a methyl group, and is particularly required to have solvent resistance. In such a case, a 3,3,3-trifluoropropyl group is desirable.

In the present invention, suitable specific examples of the organopolysiloxane used as the component (A) include, but are not limited to, the following.

[Chemical 1]

[Chemical 2]

[Chemical 3]

[Chemical 4] [In the formula, R'is the monovalent hydrocarbon group other than the alkenyl group, and n and m are positive numbers such that the viscosity falls within the range described above.]

The above-mentioned organopolysiloxane can be produced by a known method. For example, organocyclopolysiloxane and a compound having an R ₃ SiO _1/2 unit are equilibrated in the presence of an alkali or acid catalyst. It can be produced by reacting.

The organohydrogenpolysiloxane of the component (B) (B) is
It acts as a cross-linking agent, and it is necessary to have at least two SiH groups in one molecule. That is,
The SiH group and the alkenyl group in the organopolysiloxane of the component (A) undergo an addition reaction to form a cured product that is a rubber elastic body.

As the organohydrogenpolysiloxane, those used in conventional addition-curable silicone rubber compositions can be used. For example, the molecular structure thereof is not particularly limited and may be linear or cyclic. It may have any structure such as a branched structure. As the substituent bonded to a silicon atom other than a hydrogen atom, the same groups as those exemplified for the organopolysiloxane of the component (A) can be mentioned. The viscosity of this organohydrogenpolysiloxane at 25 ° C is generally
It is preferably in the range of 5 to 500 cP.

This organohydrogenpolysiloxane can also be produced by a method known per se,
For example, octamethylcyclotetrasiloxane and / or tetramethylcyclotetrasiloxane and a compound containing (CH ₃ ) ₃ SiO _1/2 units and H (CH ₃ ) ₂ SiO _1/2 units, which can serve as terminal groups, are mixed with sulfuric acid, In the presence of a catalyst such as trifluoromethanesulfonic acid or methanesulfonic acid,
It can be produced by equilibrating at a temperature of 10 ° C to 40 ° C.

In the present invention, in the organohydrogenpolysiloxane, the SiH group is 0.4 to 4.0 mole times, especially 0.8 to 2. times the alkenyl group in the component (A).
It is used in an amount such that it is 0 molar times. If the amount of the SiH groups is less than the above range, the obtained cured product will have too low a crosslink density and the properties such as heat resistance will deteriorate. If the amount of SiH groups is larger than the above range, a problem of foaming due to a dehydrogenation reaction may occur during curing, and the heat resistance of the cured product may be adversely affected.

Component (C) The finely divided silica of component (C) acts as a reinforcing material. That is, the composition of the present invention is particularly used as a molding material, and the cured product is used as a mother mold to mold various shapes. Therefore, the cured product may form a matrix having an inverse taper shape, and in such a case, strength characteristics such as tear strength are particularly required. In the composition of the present invention, by using fine powder silica as a reinforcing material, it becomes possible to form a cured product satisfying such strength characteristics.

Such fine powder silica has a specific surface area (BET
Method) is 50 m ² / g or more, and if the specific surface area is less than 50 m ² / g, satisfactory strength characteristics cannot be imparted.

In the present invention, as such finely divided silica, dry silica such as fumed silica or synthetic silica such as wet silica is used, provided that the specific surface area is within the above range. Commercially available products of dry silica include Aerosil 130, 200, 30 manufactured by Nippon Aerosil Co., Ltd.
0, Cabosil MS-5, MS-7 made by Cabot, made by Tokuyama Soda
Rheorosil QS-102, QS-103, Nippon Silica Nipsil L
There are P, etc., as commercial products of wet silica, Aerosil R-812, R-812S, R-972, R-974 made by Degussa, Rheorosil MT-10 made by Tokuyama Soda, Nipsil made by Nihon Silica. SS
There are series etc. Since these silicas have a large amount of silanol groups on the surface, they can also be used as so-called treated silicas which have been surface-treated with, for example, halogenated silanes, alkoxysilanes, various silazane compounds and the like.

Further, the compounding amount of this fine powder silica is as described above.
The amount is 50 parts by weight or less per 100 parts by weight of the component (A) organopolysiloxane, and is appropriately compounded so as to obtain appropriate strength within such a range. If the amount is more than 50 parts by weight, the workability of the composition will be impaired.

Component (D) The platinum group metal-based catalyst of component (D) comprises the alkenyl group and Si.
It is used for accelerating the addition curing reaction with the H group, and includes platinum-based, palladium-based, and rhodium-based ones, and particularly platinum-based ones such as platinum black, chloroplatinic acid, and chloroplatinic acid. Alcohol-modified platinic acid, chloroplatinic acid and olefins, aldehydes, vinyl siloxanes,
A complex with acetylene alcohol or the like is preferably used. The amount of the component (D) used may be a so-called catalytic amount, and specifically, it is used in an amount of 0.1 to 10,000 ppm, particularly 1 to 1,000 ppm in terms of platinum group metal based on the organopolysiloxane of the component (A). It

Component (E) Component (E) is at least one selected from organic tin compounds, organic titanium compounds and imidazole compounds,
These act as a releasing property improver. By blending this component, the cured product obtained by curing the composition of the present invention exhibits remarkably excellent mold release durability.

Examples of such organotin compounds include those used as curing agents for general condensation-curable silicone rubber compositions, and examples thereof include dibutyltin dilaurate, dibutyltin dibenzyl maleate and dibutyltin dioctoate. , Tin dioctylate, di-n-butyldimethoxytin, bisethylmaleyldibutyltin oxide, dibutyltin benzyl maleate, tetrabutylbis (ethylmalate) ditin oxide, dibutyltin bis (isooctylphthalate), dibutyltin bis ( 3-Methyl-3-methoxybutylmalate), dioctyltin bis (benzylmalate), dioctyltin dilaurate and the like can be mentioned.

Examples of the organic titanium compound include tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate dimer, tetra (2-ethylhexyl) titanate, diethoxytitanium acetylacetonate, titanium diacetylacetonate, titanium octylglycate, titanium. Lactate ethyl ester, titanium triethanolaminate, and titanic acid esters such as partial hydrolysis-condensation products thereof, titanium partially alkoxylated chelate compounds, titanium chelate compounds, and other silicic acid esters of titanium and their chelate products. be able to.

As the imidazole compound, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2
-Undecyl imidazole, 2-heptadecyl imidazole, 2-phenyl imidazole, 2-phenyl-4-
Methyl imidazole, 1-benzyl-2-methyl imidazole, 2-ethyl imidazole, 2-isopropyl imidazole, 2-phenyl-4-benzyl imidazole, 2-phenyl-4,5-dihydroxymethyl imidazole, 2-phenyl-4-methyl Examples include -5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 4,4'-methylene-bis (2-ethyl-5-methylimidazole) and the like.

These may be used alone or in combination of two or more, and the compounding amount is the above.
0.01 to 2 parts by weight, especially 0.05 to 100 parts by weight of component (A)
The amount is 1.0 part by weight. If the amount is less than 0.01 parts by weight, the desired releasability improving effect will not be exhibited, and if it is used in an amount greater than 2 parts by weight, the curability of the composition will decrease and the rubber properties of the resulting cured product will be reduced. And so on.

Other compounding agents In addition to the above-mentioned respective components, known compounding agents may be added to the composition of the present invention within a range that does not impair the object of the present invention of improving the release durability. You can For example, in order to adjust the curing time, as a control agent, vinyl-containing low molecular weight organopolysiloxane such as vinylcyclotetrasiloxane, triallyl isocyanurate, alkyl maleate, acetylene alcohols and silane or siloxane modified products thereof, Hydroperoxide, tetramethylethylenediamine, benzotriazole and the like can be used alone or in combination of two or more kinds.

When transparency is required, it is basically composed of SiO ₂ units and R ₃ SiO _1/2 units (R is a monovalent hydrocarbon group described above), and at least one unit is present in the molecule. A silicone oil-soluble silicone resin having an alkenyl group can be used in combination with the finely divided silica as the component (B). Further, in some cases, it is possible to substitute the fine powder silica. In particular, this silicone oil-soluble silicone resin includes the R ₃ SiO _1/2 unit and Si
The ratio with O ₂ units (where R is selected from methyl group, phenyl group and vinyl group) is in the range of 0.6 to 1.5, and the vinyl group content in 100 g of the resin is 0.01 to 0.20.
Those having a molar range of about 3 to 20 SiO ₂ units in one molecule are suitable for the addition of solubility or strength imparting to the component (A). Generally, the amount of the silicone oil-soluble silicone resin used is the amount of the component (A) 1
A suitable range is 5 to 100 parts by weight per 00 parts by weight.

In addition, inorganic pigments such as cobalt blue; coloring agents such as organic dyes; heat resistance and flame retardancy improving agents such as cerium oxide, zinc carbonate, manganese carbonate, red iron oxide, titanium oxide and carbon black; It is possible.

Silicone Rubber Composition The curable silicone rubber composition of the present invention is easily prepared by uniformly mixing the above components. This rubber composition is easily cured under a temperature condition of, for example, about 0 to 150 ° C. to form a cured product of a rubber elastic body. As is clear from the examples described later, this cured product is remarkably excellent in mold release durability, and is effectively used as a mold material of various shapes as a molding material. In addition, when a replica is manufactured by casting a resin using a mother mold formed from a cured product of the silicone rubber composition of the present invention, a mold release agent such as silicone oil or fluorine oil is applied to the mold. By doing so, the releasability can be further improved.

[0029]

EXAMPLE As the base component organopolysiloxane, dimethylpolysiloxane having both ends of the molecular chain blocked with vinyldimethylsilyl groups and a viscosity (25 ° C.) of about 5,000 cP is used. As the organohydrogenpolysiloxane of the cross-linking agent, the following average formula,

[Chemical 5] Use the one that has. As fine powder silica, BE
Finely powdered silica having a T specific surface area of about 200 m ² / g (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.) is used.

Comparative Example 1 800 g of the above-mentioned dimethylpolysiloxane 200 g of the above-mentioned finely divided silica was put into a kneader, 80 g of hexamethylsilazane and 10 g of water were added with thorough stirring, and mixing was carried out for 1 hour without heating. .. After that, the temperature was raised to 150 ° C., mixing was further performed for 2 hours, and after the mixing was completed, the temperature was lowered to room temperature. To 500 g of this mixture, 25 g of the organohydrogenpolysiloxane described above and 100 ppm of octyl alcohol chloroplatinate complex (in terms of platinum) were added, well stirred, and then defoamed under vacuum,
A silicone rubber composition was prepared. This composition (viscosity at 25 ° C. is shown in Table 1) is cured at 60 ° C. for 2 hours to obtain JIS K
A sheet was prepared according to 6301 and its physical properties were measured. Similarly, a concave mother die is molded, and urethane resin (3075 manufactured by H & K Co., Ltd.) is cast into the concave portion, and the temperature is 60 ° C x 1
The urethane resin was cured over time, and a mold was taken. This molding was continuously performed, and the surface glossiness of the urethane resin molded product was measured every time. The results are shown in Table 1.

Example 1 0.1 part by weight of dibutyltin dilaurate (dimethylpolysiloxane) was added to the silicone rubber composition obtained in Comparative Example 1.
A silicone rubber composition was prepared by adding it (per 100 parts by weight) (its viscosity at 25 ° C. is shown in Table 1). Thereafter, the physical properties of the cured product and the surface gloss of the urethane resin molded product after each molding were measured in the same manner as in Comparative Example 1 except that the curing conditions were changed to 100 ° C. × 2 hours. The results are shown in Table 1.

Example 2 A silicone rubber composition was prepared in the same manner as in Example 1 except that 0.1 part by weight of tin dioctoate was used instead of 0.1 part by weight of dibutyltin dilaurate.
In the same manner as above, the physical properties of the cured product were measured, and the surface glossiness of the urethane resin molded product was measured for each molding. The results are shown in Table 1.

Example 3 Example 1 except that 0.1 part by weight of tetrabutyl titanate was used instead of 0.1 part by weight of dibutyltin dilaurate.
A silicone rubber composition was prepared in exactly the same manner as above, and in the same manner as in Example 1, the physical properties of the cured product were measured, and the surface glossiness of the urethane resin molded product was measured for each molding. The results are shown in Table 1.

Example 4 A silicone rubber composition was prepared in exactly the same manner as in Example 1 except that 0.1 part by weight of 2-phenylimidazole was used instead of 0.1 part by weight of dibutyltin dilaurate.
In the same manner as in Example 1, the physical properties of the cured product were measured, and the surface gloss of the urethane resin molded product was measured after each molding. The results are shown in Table 1.

[0035]

[Table 1]

[0036]

EFFECTS OF THE INVENTION According to the present invention, a curable silicone rubber composition capable of forming a mother mold having remarkably improved mold release durability is obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location C08L 83/05 LRP 8319-4J (72) Inventor Mitsuaki Igarashi 1 Otomijin, Osamu-gun, Usui-gun, Gunma Prefecture Address 10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory

Claims (2)

[Claims] 1. (A) A diorganopolysiloxane having at least two alkenyl groups in one molecule and having a viscosity of 1,000 to 100,000 cP at 25 ° C., (B) At least two SiH groups in one molecule. An organohydrogenpolysiloxane having a hydrogen atom, wherein the SiH group is the above (A)
0.4 to 4.0 mol times the amount of alkenyl groups in the component, (C) a fine powder silica having a specific surface area of 50 m ² / g or more,
(A) 50 parts by weight or less per 100 parts by weight, (D) a catalytic amount of a platinum group metal-based catalyst, (E) at least one selected from organotin compounds, organotitanium compounds and imidazole compounds; Ingredient 1
A silicone rubber composition containing 0.01 to 2 parts by weight per 00 parts by weight and having excellent releasability. 2. A cured product obtained by curing the composition according to claim 1.