JPH0688281B2 - Method for producing a single molded silicone body comprising a high hardness surface layer portion and a low hardness inner layer portion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a method for producing a silicone one-piece molded product comprising a surface layer having a high hardness and an inner layer having a low hardness.

[Prior Art] Conventionally, a silicone one-piece molded body composed of a high hardness surface layer portion and a low hardness inner layer portion has been known as a cushioning member or a protective coating member. Method of impregnating a quality member with room temperature-curable silicone rubber to prepare an uncured or semi-cured gel-like molded body, immersing the molded body in a curing agent for the silicone rubber, and completely curing the surface layer portion ( Japanese Patent Publication No. 59-30932), a molded product having a gel-like silicone cured product formed on a metal surface is prepared, and then the surface of this molded product is coated with a silicon atom-bonded hydrogen atom-containing organopolysiloxane. A method of curing (see JP-A-58-163652) is known.

[Problems to be Solved by the Invention] However, it is difficult to obtain a molded product with high dimensional accuracy by these methods, and it is very difficult to form a uniform and smooth cured coating layer on the surface of the molded product. Further, these methods require a step of forming a gel-like molded body and a step of treating the surface thereof with a curing agent or a cross-linking agent and heat-curing, resulting in complicated production steps and low productivity. there were.

The inventors of the present invention have completed the present invention as a result of extensive studies to eliminate such problems.

It is an object of the present invention to provide a method for producing a silicone molded product having a high hardness surface layer portion having a uniform and smooth hard coating layer on the surface and a low hardness inner layer portion.

[Means for Solving Problems and Its Action] The above-mentioned object is to coat an inner surface of a molding die with an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and then apply the molding die. It is achieved by injecting a liquid silicone rubber composition into the interior and heating and curing the organopolysiloxane and the liquid silicone rubber composition to obtain a silicone one-piece molded product having a high hardness surface layer portion and a low hardness inner layer portion. .

Explaining this, a molding die means a mold used for molding a liquid silicone rubber composition, a silicone rubber mold,
It is not particularly limited as long as it is a synthetic resin type such as polyester or nylon, and can be obtained as a molded article by inflowing and curing the liquid silicone rubber composition.

The organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, which is applied to the inner surface of these molds, is brought into contact with the liquid silicone rubber composition at the time of molding to be cured, and the surface layer of the obtained silicone molded product. It is a component that functions to form a hard coating layer on the part. This organopolysiloxane must have at least two, and preferably three or more, silicon atom-bonded hydrogen atoms in one molecule. There is no particular limitation on the molecular structure of this component,
It may be linear or linear, including branched, or cyclic, but when it is necessary to form a hard and tough coating layer on the surface of the silicone molded product, a branched organopolysiloxane such as (CH ₃₎ consists of ₂ HSiO _^1/2 units and SiO _^4/2 units, copolymers composed of co consisting ^{_{(CH 3) 2 SiO 1/}} 2 units and ^{_{(CH 3) 2 HSiO 1/}} 2 units and SiO _^4/2 units Polymers are preferably used.
Specific examples of such components include, for example, methylhydrogenpolysiloxane having trimethylsiloxy groups blocked at both ends, dimethylsiloxane-methylhydrogenpolysiloxane copolymer having trimethylsiloxy groups blocked at both ends,
Methylhydrogensiloxane copolymer, dimethylsiloxane - - dimethylsiloxane both ends endcapped with dimethyl hydrogen siloxy group methylhydrogensiloxane cyclic copolymers, consisting of ^{_{(CH 3) 2 HSiO 1/}} 2 units and SiO _^4/2 units ^{_{copolymer, (CH 3) 3 SiO 1}} /2 units, copolymers thereof consisting of ^{_{(CH 3) 2 HSiO 1/}} 2 units and SiO _^4/2 units.

As a method of applying the organopolysiloxane to the inner surface of the molding die, there are spray coating, brush coating, sponge coating and the like, and any method may be used in the present invention. Further, the coating amount of the organopolysiloxane is not particularly limited as long as the coating film is continuously molded on the inner surface of the molding die.

The liquid silicone rubber composition used in the present invention is a liquid or paste-like composition at room temperature, which contains a liquid organopolysiloxane having a reactive group, a crosslinking agent and / or a curing catalyst as a main component, and is left at room temperature. It cures to a rubber-like elastic body when heated or heated, and may be a sag type or a non-sag type. Examples of the curing mechanism include an addition reaction type, a radical reaction curing type using an organic peroxide, and a condensation reaction type, but the addition reaction type is preferable from the viewpoint of high curing speed and excellent curing uniformity.
Particularly preferable in the present invention as such an addition reaction type liquid silicone rubber composition is (A) an organopolysiloxane having at least two lower alkenyl groups in one molecule, and (B) at least two organopolysiloxanes in one molecule. Organopolysiloxane having silicon atom-bonded hydrogen atoms The molar ratio of the total amount of silicon atom-bonded hydrogen atoms in this component to the total amount of all lower alkenyl groups in component (A) is (0.
1: 1) to (1: 1), (C) Platinum catalyst 0.1 to 1000 parts by weight of platinum metal per 1 million parts by weight of the total amount of components (A) to (B). It is a liquid silicone rubber composition.

Explaining this, the component (A) is the main component of the organopolysiloxane that gives the silicone rubber, and is the component that undergoes an addition reaction with the component (B) by the catalytic action of the component (C) and cures. The component (A) is required to have at least two lower alkenyl groups bonded to a silicon atom in one molecule. When the number of the lower alkenyl groups is less than 2, a network structure is not formed, which is preferable. A cured product cannot be obtained.
Examples of such lower alkenyl group include vinyl group, allyl group,
A propenyl group is exemplified. The lower alkenyl group may be present anywhere in the molecule, but is preferably present at least at the terminal of the molecule. Further, the molecular structure of this component may be linear, branched linear, cyclic or network, but is preferably linear with or without slight branching. . The molecular weight of this component is not particularly limited, and includes from low viscosity liquid to very high raw rubber, but is not particularly limited, but it is preferable that the viscosity at 25 ° C. is 100 centipoise or more for the cured product to become a rubber-like elastic body. . Examples of such a methyl vinyl organopolysiloxane include vinyl polysiloxane, a copolymer of methyl vinyl siloxane and dimethyl siloxane, dimethyl polysiloxane having both ends dimethyl vinyl siloxy group blocked, and dimethyl siloxane-methyl having both ends dimethyl vinyl siloxy group blocked. Phenyl siloxane copolymer, dimethyl siloxane with both ends dimethyl vinyl siloxane group blocked-Diphenyl siloxane-methyl vinyl siloxane copolymer, dimethyl siloxane with both ends trimethyl siloxy group blocked-
Methylvinylsiloxane copolymer, dimethylsiloxane-methylphenylsiloxane-methylvinylsiloxane copolymer with both ends trimethylsiloxy group blocked, methyl (3,3,3-trifluoropropyl) polysiloxane with both ends methylvinylsiloxy group blocked , Dimethylsiloxane-methyl (3,3,3-
Trifluoropropyl) siloxane copolymer, CH ₂ = CH (CH
_{3) 2} and SiO _^1/2 units (CH ₃₎ polysiloxane consisting ₃ SiO _^1/2 units and SiO _^4/2 units is illustrated. In the present invention, the above organopolysiloxane may be used in combination.

The component (B) used in the present invention is a cross-linking agent of the component (A), and the silicon atom-bonded hydrogen atom in the component is a lower alkenyl group in the component (A) due to the catalytic action of the component (C). It undergoes an addition reaction with and cures. This (B) component is 1
It is necessary to have at least two silicon atom-bonded hydrogen atoms in the molecule in order to function as a crosslinking agent.

The molecular structure of this component is not particularly limited, and may be linear,
It may be linear, including branched, or cyclic. The molecular weight of this component is also not particularly limited, but in order to improve the compatibility with the component (A), the viscosity at 25 ° C is preferably 1 to 50,000 centipoise.

The amount of this component added is such that the molar ratio of the total amount of silicon atom-bonded hydrogen atoms in this component to the total amount of all lower alkenyl groups in component (A) is (0.1: 1) to (1: 1). Is preferable, and an amount of (0.4: 1) to (0.6: 1) is particularly preferable.
When the molar ratio is less than (0.1: 1), the crosslink density is too small and the curing is insufficient, and when it is more than (1.0: 1), the crosslink density is too high, and a hard coating layer is formed on the surface of the silicone molding. It is difficult to form. When organopolysiloxanes containing a large amount of alkenyl groups are added separately for reinforcement, it is preferable to add the present component containing silicon atom-bonded hydrogen atoms commensurate with the alkenyl groups.

Specific examples of this component include methyl hydrogen polysiloxane having trimethylsiloxy groups blocked at both ends, dimethylsiloxane-methylhydrogen polysiloxane copolymer having trimethylsiloxy groups blocked at both ends, and dimethylhydrogensiloxy group blocked at both ends. dimethylsiloxane - methylhydrogensiloxane copolymer, dimethylsiloxane - methylhydrogensiloxane cyclic copolymers, (CH _{3) 2} consisting of HSiO _^1/2 units and SiO _^4/2 units, copolymers composed, (CH _{3) 3} SiO ^{_{1/2 units, (CH 3) 2 HSiO 1}} /2 units and SiO ⁴ /
_{An example} is a copolymer composed of ₂ units.

Component (C) is a catalyst for addition-reacting a hydrogen atom bonded to a silicon atom and an alkenyl group, and specific examples thereof include chloroplatinic acid, a solution of the chloroplatinic acid dissolved in an alcohol or a ketone, and a solution thereof. Examples thereof include complex compounds of chloroplatinic acid and olefins, complex compounds of chloroplatinic acid and alkenylsiloxanes, complex compounds of chloroplatinic acid and diketones, platinum black and platinum supported on a carrier.

This component is added in a total amount of (A) and (B) components of 10
The amount of platinum-based metal is set to 0.1 to 1000 parts by weight with respect to 0,000 parts by weight, because the crosslinking reaction does not proceed sufficiently at 0.1 parts by weight or less and it is uneconomical at 1000 parts by weight or more.
When normally used, the amount of platinum metal added is preferably about 1 to 100 parts by weight.

The liquid silicone rubber composition used in the present invention may be mixed with a filler in order to adjust the fluidity and improve the mechanical strength of the molded product. As such a filler,
Reinforcing fillers such as precipitated silica, fumed silica, pyrogenic silica, fumed titanium oxide, ground quartz, diatomaceous earth, asbestos, aluminosilicates, iron oxides, zinc oxides,
Non-reinforcing fillers such as calcium carbonate are exemplified, and may be surface-treated as they are or with an organic silicon compound such as hexamethylsilazane, trimethylchlorosilane, and polymethylsiloxane. Further, to the organopolysiloxane composition used in the present invention, as an additive for suppressing the curing reaction, an acetylene compound, hydrazines, triazoles, phosphines, mercaptans, etc. may be added in a trace amount or in a small amount, There is no problem as long as the object of the present invention is not impaired. Other pigments if necessary,
You may mix | blend a heat-resistant agent, a flame retardant, a plasticizer, or organopolysiloxane which has one alkenyl group in 1 molecule for low modulus.

Next, as a preferred liquid silicone rubber composition, there is a radical reaction curable liquid silicone rubber composition with an organic peroxide, which comprises a vinyl group-containing diorganopolysiloxane which is liquid at room temperature and a catalytic amount of an organic peroxide as a main component. If necessary, an inorganic filler such as fumed silica, precipitated silica, a heat-resistant agent, or a pigment is added. It is preferable to select an organic peroxide having a decomposition temperature in the range of + 25 ° C to + 100 ° C.

The cured form of the one-body silicone molded product composed of the high-hardness surface layer portion and the low-hardness inner layer portion thus produced will be described. The high-hardness surface layer portion has a crosslinking density relatively to that of the inner layer portion. It is composed of a high-hardness silicone cured product, and its hardness value is not particularly limited, but when the present invention is used as a vibration isolating member or a cushioning member, the hardness may be 40 or more in a JIS rubber hardness meter. preferable.

The thickness of this layer varies depending on the curing temperature condition of the liquid silicone rubber, but is usually 1000 μm or less.

On the other hand, the low-hardness inner layer portion is composed of a silicone cured product having a low cross-linking density and a low hardness relative to the surface layer portion, and the value of the hardness is 10 in a JIS rubber hardness tester.
The following is preferable.

As a method for injecting the liquid silicone rubber composition into the molding die and heating and curing it, compression molding, transfer molding, or injection molding, which are usually used for molding liquid silicone rubber compositions, can be used. .

If the heat-curing temperature of the liquid silicone rubber composition, that is, the molding temperature is too low, the curing speed of the liquid silicone rubber composition is lowered and the productivity is lowered, and conversely, if the molding temperature is too high, the obtained silicone rubber molding is obtained. Usually 50 to 22 because the body adheres to the inner surface of the mold and tends to be difficult to demold.
It is in the range of 0 ° C, preferably in the range of 50 to 170 ° C.

EXAMPLES Next, the present invention will be described with reference to examples. In the examples, "parts" means "parts by weight" and the viscosity is a value at 25 ° C.

Example 1 100 parts of dimethylpolysiloxane with a viscosity of 2000 centipoise (both vinyl group content 0.23% by weight) in which both ends of the molecular chain were blocked with dimethylvinylsiloxy groups, 25 parts of dry silica having a specific surface area of 200 m ² / g, both molecular chains Methylhydrogenpolysiloxane with a viscosity of 10 centipoise blocked at the ends with trimethylsiloxy groups (content of hydrogen atoms bonded to silicon atoms is 0.
(9% by weight) 0.5 part, and mixed, 500 at a shear rate of 10 sec ^-1
A mixture having a viscosity of 0 poise was obtained. Next, 0.1 part of an isopropyl alcohol solution of chloroplatinic acid (platinum content: 3% by weight) was added to the mixture and mixed to obtain a liquid silicone rubber composition.

On the other hand, a metal mold having an inner surface plated with chrome was prepared, and methyl hydrogen polysiloxane (containing silicon atom-bonded hydrogen atoms: 1.0% by weight) was uniformly applied to the inner surface to a thickness of 0.2 g / m ² . Next, the liquid silicone rubber composition obtained above was poured into the inside of the cavity, and was heated and cured at 150 ° C. for 10 minutes. After cooling, the silicone molded product was taken out and the inside was cut with a knife to measure the hardness of each part.The hardness of the surface layer was 50 degrees, and the hardness of the inner layer was 10 degrees.
The hard coating layer in the surface layer had a thickness of 0.5 mm.

Example 2 100 parts of dimethylpolysiloxane having a viscosity of 2000 centipoise (vinyl group content 0.23% by weight) in which both ends of the molecular chain are blocked with dimethylvinylsiloxy groups, 20 parts of dry silica having a specific surface area of 200 m ² / g, and both ends are Add 0.4 parts of methylhydrogenpolysiloxane blocked with trimethylsiloxy group (content of hydrogen atom bonded to silicon atom 1.0% by weight) and 0.1 part of chloroplatinic acid solution in isopropyl alcohol (content of platinum 3% by weight) And mixed to obtain a liquid silicone rubber composition. Next, the same methylhydrogenpolysiloxane as described above (amount of silicon atom-bonded hydrogen atoms of 1.0%) was applied by spraying to the inner surface of the injection molding die. Next, this mold was heated to 120 ° C., and then the liquid silicone rubber composition obtained above was injected into the mold to obtain a molded silicone rubber body. This molded product had a hardness of 38 degrees in the surface layer and a hardness of 3 degrees in the inner layer, and was a one-body silicone molded product composed of a surface layer of high hardness and an inner layer of low hardness.

Example 3 100 parts by weight of dimethylvinylsiloxane having a viscosity of 2000 centipoise (both vinyl group content 0.23% by weight) in which both ends of the molecular chain were blocked with dimethylvinylsiloxy group, carbon black [Denka Black manufactured by Denki Kagaku KK] 10 parts , 0.3 parts of methylhydrogenpolysiloxane with a viscosity of 10 centipoise (both silicon atom-bonded hydrogen atom content: 0.8% by weight) with both ends of the molecular chain blocked with trimethylsiloxy groups was added and mixed at a shear rate of 10 sec ^-1 . A mixture having a viscosity of 800 poise was obtained. Next, 0.1 part of an isopropyl alcohol solution of chloroplatinic acid (platinum content: 3% by weight) was added to this mixture and mixed to obtain a liquid silicone rubber composition.

On the other hand, a press-molding die (cavity 12 × 30φmm) was prepared, and 5 g of a 10% toluene solution of methylhydrogenpolysiloxane (hydrogen atom content 1.0 wt%) was prepared on the inner surface of this die.
The liquid silicone rubber composition obtained above was poured into the inside of this cavity after being spray-coated so as to have a size of m ² , and was cured by heating at 150 ° C. for 5 minutes. The obtained cured product is
The inside of the gel was a molded silicone single body having a hard coating layer on the surface. Also, when the electrical characteristics of this molded product were measured, the resistance value was 500 Ω, and
The resistance value when compressed by% was 250Ω.

Example 4 100 parts by weight of a dimethylpolysiloxane having a viscosity of 10,000 centipoises (vinyl group content 0.12% by weight) in which both ends of a molecular chain are blocked with dimethylvinylsiloxy groups, a specific surface area of 200 m ² / g
30 parts of dry silica, 0.1 part of isopropyl alcohol solution of chloroplatinic acid (platinum content 3% by weight) and 0.08 part of dibutyl phthalate solution of dicumyl peroxide (peroxide content 40%) are added and mixed, and the shear rate 10 sec
A liquid silicone rubber composition having a viscosity of 13,000 poise was obtained at ^-1 . The liquid silicone rubber composition was previously coated with methylhydrogenpolysiloxane (the same as the methylhydrogenpolysiloxane used in Example 1).
Fill the mold for press molding coated with 5 g / m ² and leave it at 170 ° C for 10
Heated and cured for a minute. The obtained molded product was a molded product having a surface-hardened coating layer and an inner layer portion being a low hardness gel-like silicone cured product. When the physical properties of this molded product were measured, the hardness was 5 (JIS A) and the impact resilience was 10%.

Example 5 Example methylhydrogenpolysiloxane (silicon-bonded hydrogen atom content of 1.0 wt%) in 1 become instead of 0.5 parts of Me ₂ HSiO _^1/2 units and SiO ₂ units, silicon-bonded hydrogen atoms A silicone molding was obtained in the same manner as in Example 1 except that 0.5 part of 1.2% methylhydrogenpolysiloxane was applied to the mold. The hardness of the surface layer portion of the obtained silicone one-body molded body was 55 degrees, and the hardness of the inner layer portion was 10 degrees.

EFFECTS OF THE INVENTION In the present invention, at least 2 in one molecule on the inner surface of the molding die.
Since the organopolysiloxane having silicon atom-bonded hydrogen atoms is applied and then the liquid silicone rubber composition is flown into the molding die, the organopolysiloxane and the liquid silicone rubber composition are heated and cured. Thus, it is possible to obtain a silicone one-body molded article having a high hardness surface layer portion and a low hardness inner layer portion having a uniform and smooth hard coating layer on the surface.

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Claims (2)

[Claims] 1. An inner surface of a molding die is coated with an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and then a liquid silicone rubber composition is flown into the inside of the molding die. Then, the above-mentioned organopolysiloxane and the liquid silicone rubber composition are cured by heating, and a method for producing a silicone one-body molded article comprising a high hardness surface layer portion and a low hardness inner layer portion. 2. A liquid silicone rubber composition comprising (A) an organopolysiloxane having at least two lower alkenyl groups in one molecule, and (B) an organopolysiloxane having at least two silicon atom-bonded hydrogen atoms in one molecule. Polysiloxane The molar ratio of the total amount of silicon atom-bonded hydrogen atoms in this component to the total amount of all lower alkenyl groups in component (A) is (0.
1: 1) to (1: 1), 0.1 to 1000 parts by weight of platinum metal based on 1 million parts by weight of (C) platinum-based catalyst (A) to (B) in total. The manufacturing method according to claim 1, which is a product.