JP6789091B2 - Silicone rubber composition for molding - Google Patents

Description

The present invention relates to a silicone rubber composition for molding, and more specifically, a silicone rubber that is cured into a rubber shape and is used for molding that requires a high degree of releasability, such as molding of a prototype model, that is, prototype molding. Regarding the composition.

Conventionally, silicone rubber has been widely used in various fields by taking advantage of its excellent heat resistance, cold resistance, and electrical characteristics. In particular, it has been used as a molding material because of its good releasability. The molding material is a manufacturing of a replica made of resin or the like by contacting the entire surface or a part of the surface of the prototype (hereinafter, also referred to as a mother mold) with a method such as casting or coating and curing the material. An uncured material for obtaining a mold to be used for.

In recent years, in the fields of electronic devices, office machines, home appliances, automobile parts, etc., in the molding of prototype models used for product development and product sample creation, that is, prototype molding, it has excellent workability, cost and required time. Since it is effective for improvement, an addition reaction curing type liquid silicone rubber is attracting attention. Further, the addition reaction curing type silicone rubber has preferable molding characteristics as a molding material, such as no reaction by-products and an extremely small shrinkage rate at the time of curing.

However, as the mechanical properties of the urethane resin and epoxy resin used for prototype molding are improved, the mold releasability (hereinafter, also referred to as demoldability) of the molded product (replica product) from the cured silicone rubber mold becomes higher. There is a tendency to get worse.

In order to solve such a problem, a non-reactive silicone oil that does not participate in the cross-linking reaction is blended in the addition reaction curable silicone rubber composition, and the non-reactive oil is bleeded on the surface of the cured product. A method for obtaining demoldability has been proposed (see, for example, Patent Document 1). Further, a silicone rubber composition containing fuming silica surface-treated with silazane having a vinyl group has been proposed (see, for example, Patent Document 2). Further, by blending titanium oxide having an average particle size of 0.1 to 10 μm as a part of the filler in the silicone rubber composition, the duplicated product is not soiled and excellent in mechanical strength and releasability. A technique for obtaining a silicone rubber mold is disclosed (see, for example, Patent Document 3). Further, a composition having improved releasability by blending a vinyl polymer having a low degree of polymerization and a liquid polyorganohydrogensiloxane having a specific structure in an addition reaction curable silicone rubber composition is disclosed. (See, for example, Patent Document 4).

However, all of the silicone rubber compositions described in Patent Documents 1 to 4 have strong adhesion to molded products such as urethane resin and epoxy resin, which are duplicates of the cured silicone rubber mold, and are silicone rubber. The demolding property, which is the releasability of the duplicated product from the mold, was not sufficiently good. Then, if the duplicated product is forcibly peeled off from the silicone rubber mold, there is a problem that the mold is destroyed.

Further, the composition disclosed in Patent Document 3 has a problem that it is difficult to observe the state of the replica inside because the obtained silicone rubber mold is colored with titanium oxide.

Further, as a measure for the work surface of prototype molding, an external mold release agent is frequently applied to the silicone rubber mold. However, this method not only complicates the work, but also causes the release agent to migrate to the surface of the obtained replica, which requires cleaning with an organic solvent when painting or plating the replica. , There was a risk of deterioration of the working environment and pollution. Further, when used for molding a resin that requires transparency, the transfer of the release agent to the resin may impair the transparency of the duplicated product.

JP-A-58-225152 JP-A-2002-194219 Japanese Unexamined Patent Publication No. 7-033985 Japanese Patent Application Laid-Open No. 2502714

The present invention has been made to solve these problems, and has excellent releasability of replicas, and in particular, molding of transparent resins and molding of replicas such as prototypes that require a high degree of releasability. It is an object of the present invention to provide a silicone composition suitable for release.

The silicone rubber composition for molding of the present invention
(A) 100 parts by mass of polyorganosiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule and having a viscosity at 23 ° C. of 1,000 to 200,000 mPa · s.
Formula (B): A monofunctional siloxane unit represented by R ¹ ₃ SiO _1/2 (in the formula, R ¹ is an alkenyl group or a substituted or unsubstituted alkyl group, respectively), and the formula: 0.5 to 10 parts by mass of polyorganosiloxane having a tetrafunctional siloxane unit represented by SiO _4/2 and having 3 or more alkenyl groups contained in the monofunctional siloxane unit in one molecule.
(C) 1 to 50 parts by mass of aerosol silica
(D) 1,3-Divinyl-1,1,3,3-tetramethyldisilazane 0.05 to 1.0 part by mass,
Formula (E): A monofunctional siloxane unit represented by R ² ₂ HSiO _1/2 (in the formula, R ² is an independently substituted or unsubstituted alkyl group), and formula: SiO _{4 /. The} polyorganohydrogensiloxane having a tetrafunctional siloxane unit represented by ₂ and having a hydrogen atom bonded to a silicon atom in an amount of 0.5 to 1.2% by mass based on the whole component is described in (A). ) The hydrogen atom in the component is 0.5 to 5.0 with respect to a total of 1 mol of the alkenyl group in the component, the alkenyl group in the component (B), and the alkenyl group in the component (D). It is characterized by containing an amount of molars and (F) a catalytic amount of a platinum-based compound.

In the following description, the "alkenyl group bonded to a silicon atom" may be simply referred to as an "alkenyl group". Further, the "hydrogen atom bonded to the silicon atom" may be simply referred to as a "hydrogen atom" or a "Si—H group".

According to the silicone rubber composition for molding of the present invention, a silicone rubber mold having hardness suitable for drawing out a resin replica and having excellent mold releasability can be obtained. This silicone rubber mold also has excellent mold releasability with respect to urethane resin and epoxy resin for prototype molding with improved mechanical properties and the like. Therefore, the silicone rubber composition for molding of the present invention is suitable for molding a replica that requires a high degree of releasability, such as prototype molding. Furthermore, since it is not necessary to apply an external mold release agent at the time of molding, and it is not necessary to add a non-reactive silicone oil or the like to improve the mold release property, transparency and surface smoothness are required. It is also suitable for molding resin replicas.

A method for producing a silicone rubber mold in an example of the present invention is shown, (a) is a vertical sectional view, and (b) is a top view. It is a vertical cross-sectional view which shows the molding method of the replica using the silicone rubber mold in the evaluation of the demoldability of the Example of this invention.

Hereinafter, embodiments of the present invention will be described.
The silicone rubber composition for molding according to the embodiment of the present invention
(A) 100 parts by mass of polyorganosiloxane having two or more alkenyl groups in one molecule and having a viscosity at 23 ° C. of 1,000 to 200,000 mPa · s.
(B) Formula: It has a monofunctional siloxane unit represented by R ¹ ₃ SiO _1/2 and a tetrafunctional siloxane unit represented by the formula: SiO _4/2 , and is included in the monofunctional siloxane unit. 0.5 to 10 parts by mass of polyorganosiloxane having 3 or more alkenyl groups in one molecule.
(C) 1 to 50 parts by mass of aerosol silica
(D) 1,3-Divinyl-1,1,3,3-tetramethyldisilazane 0.05 to 1.0 part by mass,
(E) Formula: It has a monofunctional siloxane unit represented by R ² ₂ HSiO _1/2 and a tetrafunctional siloxane unit represented by the formula: SiO _4/2 , and has a hydrogen atom content of 0. A hydrogen atom in this component is added to 5 to 1.2% by mass of polyorganohydrogensiloxane with respect to a total of 1 mol of the alkenyl group of the component (A), the component (B) and the component (D). Contains an amount of 0.5 to 5.0 mol, and (F) a catalytic amount of a platinum-based compound.
The polyorganosiloxane of the component (B) and the polyorganohydrogensiloxane of the component (E) both contain a tetrafunctional siloxane unit and have a structure having a branched chain or a three-dimensional network structure. In the present invention, a polyorganosiloxane "having a branched chain structure or a three-dimensional network structure" is referred to as a "resin-like" polyorganosiloxane.
Hereinafter, each component contained in the silicone rubber composition for molding of the embodiment will be described.

<(A) Polyorganosiloxane containing an alkenyl group>
The component (A) is a polyorganosiloxane having two or more alkenyl groups in one molecule, and is a base component of the silicone rubber composition for molding of the present invention. If the viscosity of the component (A) is too low, the rubber elasticity after curing becomes poor, and if it is too high, the workability is lowered. Therefore, the viscosity at 23 ° C. (hereinafter, simply referred to as “viscosity”) is 1,000. The range is ~ 200,000 mPa · s. The viscosity of the component (A) is more preferably in the range of 5,000 to 20,000 mPa · s.

The molecular structure of the component (A) is preferably linear, that is, the main chain basically consists of repeating diorganosiloxane units, and both ends of the molecular chain are sealed with a triorganosyloxy group. A structure having a partially branched chain may be used.

Examples of the alkenyl group bonded to the silicon atom in the component (A) include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, and a heptenyl group, which have 2 to 7 carbon atoms, more preferably 2 to 4 carbon atoms. Can be mentioned. A vinyl group is particularly preferable. The alkenyl group may be bonded to a silicon atom at either the terminal end or the intermediate portion of the molecular chain, or may be bonded to both the silicon atom at the terminal end and the intermediate portion of the molecular chain, but is linear. A structure in which one alkenyl group is bonded to each of the silicon atoms at both ends of the molecular chain is preferable.

In the component (A), examples of the organic group other than the alkenyl group bonded to the silicon atom include an unsubstituted or substituted monovalent hydrocarbon group. The unsubstituted monovalent hydrocarbon group includes an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group and a dodecyl group; a phenyl group, a trill group, Aryl groups such as xsilyl groups; aralkyl groups such as 2-phenylethyl groups, 2-phenylpropyl groups and the like are exemplified. The substituted monovalent hydrocarbon group includes an alkyl halide group such as a chloromethyl group, a 3-chloropropyl group, a 3,3,3-trifluoropropyl group, and a cyanoalkyl group such as a 3-cyanopropyl group. The group and the like can be mentioned. A methyl group is preferable as the organic group other than the alkenyl group in the component (A) because the synthesis is easy.

Specific examples of the component (A) include dimethylpolysiloxane with both ends of the molecular chain dimethylvinylsiloxy group blockage, dimethylvinylsiloxy group blockage at both ends of the molecular chain dimethylsiloxane / diphenylsiloxane copolymer, and dimethylvinylsiloxy group blockade at both ends of the molecular chain. Methylvinylpolysiloxane, dimethylvinylsiloxy group-blocking at both ends of the molecular chain dimethylsiloxane / methylvinylsiloxane copolymer, dimethylvinylsiloxy group-blocking at both ends of the molecular chain dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxane copolymer, both molecular chains Terminal trimethylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane copolymer, molecular chain double-ended trimethylsiloxy group-blocked methylvinylpolysiloxane, molecular chain double-ended trimethylsiloxy group-blocked dimethylsiloxane / methylvinylsiloxane / methylphenylsiloxane copolymer, Examples thereof include dimethylpolysiloxane, which blocks trivinylsiloxy groups at both ends of the molecular chain.
These polymers or copolymers can be used alone or in combination of two or more.

<(B) Resin-like polyorganosiloxane containing an alkenyl group>
Component (B), ^wherein: a 1 tetrafunctional siloxane units represented by _R 1 _{3 SiO 1/2, wherein:} tetrafunctional siloxane unit represented by _{SiO 4/2} (. Hereinafter referred to Q units) and It is a resin-like polyorganosiloxane having 3 or more alkenyl groups contained in the monofunctional siloxane unit in one molecule. The component (B) works to improve the strength of the silicone rubber after curing and prevent the silicone rubber mold from being destroyed during demolding. (B) resin-like polyorganosiloxane as the component is preferably comprised of said monofunctional type siloxane units and Q units, in addition to these units, the formula: represented by R ¹ ₂ SiO _2/2 It can contain a bifunctional siloxane unit.

In the formulas representing the monofunctional siloxane unit and the bifunctional siloxane unit, R ¹ is an alkenyl group or a substituted or unsubstituted alkyl group, respectively. Among the plurality of R ¹ that are present in one molecule, an alkenyl group of at least three included in one functional type siloxane units. Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group and the like. Vinyl groups are preferred. Examples of the unsubstituted alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and the like. Examples of the substituted alkyl group include a halogen-substituted alkyl group such as a chloromethyl group, a 3-chloropropyl group, a 3,3,3-trifluoropropyl group, and a cyanoalkyl group such as a 3-cyanopropyl group. As the substituted or unsubstituted alkyl group, a methyl group is preferable.
As the resin-like polyorganosiloxane containing the alkenyl group which is the component (B), one type may be used alone, or two or more types may be used in combination.

The resin-like polyorganosiloxane as the component (B) preferably has a weight average molecular weight (Mw) of 1,000 to 10,000. The weight average molecular weight (Mw) is a value measured by gel permeation chromatography (GPC) using toluene as a solvent and converted into polystyrene. (B) When the Mw of the resin-like polyorganosiloxane is less than 1,000, a cured product having good mechanical properties such as strength cannot be stably obtained. On the other hand, when Mw exceeds 10,000, the viscosity of the composition becomes high and the workability deteriorates. (B) A more preferable range of Mw of the resin-like polyorganosiloxane is 2,000 to 7,000.

The blending amount of the component (B) is 0.5 to 10 parts by mass, preferably 1 to 5 parts by mass with respect to 100 parts by mass of the component (A). If the blending amount of the component (B) is less than 0.5 parts by mass, the effect of improving the strength of the silicone rubber after curing cannot be sufficiently obtained. Further, if the blending amount of the component (B) exceeds 10 parts by mass, the cured product becomes a gel, and a mold capable of molding and removing the resin replica cannot be obtained.

<(C) Aerosol silica and (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane>
The fumigant silica, which is the component (C), is a silica powder produced by a dry method and is also called fumed silica. The fumes silica preferably has a specific surface area (hereinafter referred to as BET specific surface area) of 180 to 500 m ² / g by the BET method. When an aerosol silica having a BET specific surface area in the above range is used, the cured product can be provided with excellent mechanical properties and transparency. The fumes silica may be used alone or in combination of two or more.

The fumes silica (D) whose surface has been treated with (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane is contained in the composition.

(C) Hydroxy silica has hydroxyl groups on its surface when it is not surface-treated. (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane reacts with the active hydrogen of the hydroxyl group on the surface of (C) aerosol silica, and as a result, (C) the surface of the aerosol silica. It is considered that a vinyldimethylsiloxy group is attached to the. Then, by substituting the hydroxyl group on the surface of (C) aerosolic silica with a vinyldimethylsilyl group in this way, the components (A) and (B) and (C) fumigant silica are more familiar with each other. Sufficient hardness and mechanical properties can be imparted to the cured product. Therefore, the releasability (demoldability) when molding a replica such as an epoxy resin by using a silicone rubber mold obtained by curing the composition of the embodiment is improved.
It should be noted that such an excellent effect is specifically obtained by blending (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane (C) aerosol silica whose surface is treated. However, it cannot be obtained by blending an aerosol silica surface-treated with another surface treatment agent used for hydrophobization, for example, hexamethyldisilazane, trimethylchlorosilane, or the like.

Here, the surface treatment of (C) aerosol silica with (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane may be directly performed on the surface-untreated aerosol silica. This may be applied to fumes silica that has been surface-treated with hexamethyldisilazane, trimethylchlorosilane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane or the like (hereinafter, referred to as other treatment agents). Further, as will be described later, the surface treatment with 1,3-divinyl-1,1,3,3-tetramethyldisilazane and the surface treatment with the other treatment agent may be performed at the same time.

(C) The surface treatment of the aerosol silica can be carried out by a usual method. That is, the fumes silica before being blended into the composition can be surface-treated in advance by the dry method or the wet method shown below. In the dry method, the aerosol silica is placed in a reaction vessel and heated to 100 to 170 ° C. under normal pressure or reduced pressure with stirring to obtain an excess amount of 1,3-divinyl-1,1,3,3-tetramethyldi. This is a method in which vapor of silazane is supplied to react with a hydroxyl group on the surface of aerosol silica, and then dry nitrogen gas is supplied to remove the unreacted silicaan with ammonia produced as a by-product. In the wet method, fumigant silica is dispersed in a hydrocarbon, 1,3-divinyl-1,1,3,3-tetramethyldisilazane is added with stirring, and if necessary, the mixture is stirred with heating. This is a method in which the surface-treated silica that has settled is separated and dried by allowing it to stand after the reaction.

Further, (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane is blended in a system in which (C) fumigant silica is mixed with the component (A), and the temperature is 161 ° C. or lower. Knead with heat for 2 to 6 hours to react (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane with the hydroxyl group on the surface of (C) aerosolized silica, and reduce the pressure if necessary. It is also possible to adopt an in-process treatment method for removing by-products.

When the surface treatment of (C) aerosol silica is performed by the in-process treatment method, a small amount of water may be added in order to promote the reaction. In addition, in a system in which (A) component and (C) fuzzy silica are mixed, (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane and others such as hexamethyldisilazane are added. Treatment agent can be blended. Then, (C) the fumes silica is simultaneously subjected to the surface treatment with (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane and the surface treatment with the other treatment agents described above. You may.

The blending amount of the fumes silica (C) is 1 to 50 parts by mass, preferably 5 to 30 parts by mass with respect to 100 parts by mass of the component (A). (C) If the blending amount of the aerosol silica is less than 1 part by mass, the silicone rubber mold obtained by curing the composition cannot obtain sufficient hardness, and the large mold may bend due to its own weight, which is preferable. Absent. On the other hand, if the blending amount of (C) aerosolized silica exceeds 50 parts by mass, the hardness of the cured product becomes too large, and it becomes difficult to remove the resin replica from the silicone rubber mold.

The blending amount of (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane is preferably 0.05 to 1.0 parts by mass with respect to 100 parts by mass of the component (A). Is 0.1 to 0.8 parts by mass. Sufficient hardness and mechanical properties when the amount of (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane is less than 0.05 parts by mass with respect to 100 parts by mass of the component (A). A cured product having the above is not obtained, and the demoldability of the resin replica from the silicone rubber mold is deteriorated. Further, when the blending amount of (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane exceeds 1.0 part by mass, the cured product becomes a gel, and the resin replica is molded and removed. I can't get a mold that can be molded.

<(E) Polyorganohydrogensiloxane>
The polyorganohydrogensiloxane which is the component (E) has a monofunctional siloxane unit represented by the formula: R ² ₂ HSiO _1/2 and a tetrafunctional siloxane unit represented by the formula: SiO _4/2 (Q). A resin-like polyorganohydrogensiloxane having a unit) and having a hydrogen atom content of 0.5 to 1.2% by mass of the molecular weight of the polyorganohydrogensiloxane. The polyorganohydrogensiloxane of the component (E) acts as a cross-linking agent when its Si—H group reacts with the alkenyl group of the components (A) and (B). Further, the Si—H group of the component (E) also reacts with the alkenyl group (vinyl group) of (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane, resulting in a cured product. It has the effect of improving mechanical strength.

The polyorganohydrogensiloxane of the component (E) is preferably composed of the monofunctional siloxane unit and the Q unit, but in addition to these units, the formula: R ² ₂ SiO _2/2 or the formula: R ² HSiO. It can have a bifunctional siloxane unit represented by _2/2 .

In the formulas representing the monofunctional siloxane unit and the bifunctional siloxane unit, R ² is an independently substituted or unsubstituted alkyl group, respectively. Examples of the unsubstituted alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and the like. Examples of the substituted alkyl group include a halogen-substituted alkyl group such as a chloromethyl group, a 3-chloropropyl group, a 3,3,3-trifluoropropyl group, and a cyanoalkyl group such as a 3-cyanopropyl group. A methyl group is preferable as R ² .

In the polyorganohydrogensiloxane of the component (E), the content of the Si—H group is 0.5 to 1.2% by mass of the molecular weight. When the content of Si—H groups is less than 0.5% by mass, the composition may be inferior in curability. If the content of Si—H groups exceeds 1.2% by mass, a cured product having good mechanical properties may not be obtained.
As the component (E), one type can be used alone or two or more types can be used in combination.

The viscosity (23 ° C.) of the resin-like polyorganohydrogensiloxane as the component (E) is preferably in the range of 1 to 100 mPa · s. (E) When the viscosity of the resin-like polyorganohydrogensiloxane is less than 1 mPa · s, the strength of the cured silicone rubber becomes insufficient. If the viscosity exceeds 100 mPa · s, the curability of the composition deteriorates. The viscosity of the resin-like polyorganohydrogensiloxane (E) is more preferably 1 to 50 mPa · s.
Further, the (E) resin-like polyorganohydrogensiloxane preferably has a weight average molecular weight (Mw) of 500 to 2,000. (E) When the Mw of the resin-like polyorganohydrogensiloxane is less than 500, the strength of the cured silicone rubber becomes insufficient. On the other hand, when Mw exceeds 2,000, the curability of the composition deteriorates.

The blending amount of the component (E) is the alkenyl group in the component (A), the alkenyl group in the component (B), and (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane. The amount of Si—H group in the component (E) is 0.5 to 5.0 mol with respect to 1 mol in total with the alkenyl group of. More preferably, it is in the range of 1.0 to 3.0 mol. If the Si—H group in the component (E) is less than 0.5 mol, the curing reaction does not proceed and it may be difficult to obtain a cured product. If the Si—H group in the component (E) exceeds 5.0 mol, the physical properties such as elasticity of the cured silicone rubber deteriorate. Further, since a large amount of unreacted Si—H groups remain in the cured product, the physical properties may change with time.

<(F) Platinum compound>
The platinum-based compound as the component (F) is a catalyst that promotes the addition reaction (hydrosilylation reaction) between the alkenyl group in the components (A) and (B) and the Si—H group in the component (E). .. The (F) platinum-based compound is the alkenyl group (vinyl group) in the (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane and Si—H in the component (E). It also promotes the addition reaction with the group. The platinum-based compound described later has a high catalytic ability for the addition reaction near room temperature.

Examples of the platinum-based compound (F) include platinum chloride, a reaction product of platinum chloride and alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, and a platinum-phosphine complex. A reaction product of chloroplatinic acid and an alcohol, a platinum-vinylsiloxane complex, and the like are particularly preferable from the viewpoint of good solubility in the components (A) and (E) and catalytic activity.

The content of the platinum-based compound (F) is an amount that is 1 to 100 mass ppm in terms of platinum atoms with respect to the component (A). It is preferably 2 to 50 mass ppm. (F) If the content of the platinum-based compound is less than 1 mass ppm, the curing rate is slow and the curing is not completely completed even if a sufficient time is taken, so that the silicone rubber mold has adhesiveness and the prototype (mother mold). ), And the releasability of the duplicated product from the silicone rubber mold is reduced. When the content of the platinum-based compound (F) exceeds 100 mass ppm, the curing rate is excessively increased, so that workability such as casting of the composition after blending each component is lowered. In addition, platinum-based compounds are expensive and therefore uneconomical.

<Other ingredients>
The silicone rubber composition for molding of the present invention may contain other components as long as the characteristics of the present invention are not impaired. For example, as a filler, silica-based powders such as fused silica, pulverized quartz, and diatomaceous earth, those treated with ordinary surface treatment agents such as polyorganosiloxane and hexamethyldisilazane, calcium carbonate, and silicate. Aluminum, titanium oxide, zinc oxide, iron oxide, carbon black and the like can be blended. Since these fillers impair transparency, it is preferable not to mix them when the silicone rubber mold requires transparency.

Further, in order to prolong the curing time of the composition at room temperature and improve workability such as injection, a control agent (curing retarder) that suppresses the hydrosilylation reaction can be blended. Examples of the curing retarder include a vinyl group-containing cyclic organopolysiloxane such as vinylcyclotetrasiloxane, triallyl isocyanurate, alkylmaleate, acetylene alcohols and their silane or siloxane modified products, hydroperoxide, and tetramethyl. Examples thereof include ethylenediamine and benzotriazole.
In the present invention, it is preferable to use vinylcyclotetrasiloxane, specifically 1,3,5,7-tetramethyltetravinylcyclotetrasiloxane as the curing retarder.

In addition to the silicone rubber composition for molding of the present invention, pigments, plasticizers, flame retardant imparting agents, thixotropy imparting agents, antibacterial agents, antibacterial agents, adhesive imparting agents and the like may be added as required. May be blended.

In the silicone rubber composition for molding according to the embodiment of the present invention, each component (A) to (F) and other components to be blended as needed are uniformly mixed by a mixing means such as a universal kneader or a kneader. It can be prepared by kneading into. Usually, a composition consisting of a component group containing (E) component and a composition consisting of a component group containing (F) component are separately prepared and stored, and both compositions are uniformly prepared immediately before use. Although it is used after being mixed with, it is also possible to store all the components in the same container in the presence of a curing retarder.

The viscosity of the silicone rubber composition for molding of the present invention is not particularly limited, but is preferably in the range of 3,000 to 1,000,000 mPa · s as a value measured with a rotational viscometer at 23 ° C. If the viscosity is less than 3,000 mPa · s, a cured product having sufficient rubber strength may not be obtained. On the other hand, if the viscosity exceeds 1,000,000 mPa · s, the fluidity of the composition deteriorates, and it becomes difficult to mold the silicone rubber mold. From the viewpoint of molding (casting) workability, a more preferable viscosity is 5,000 to 200,000 mPa · s.

When the silicone rubber composition for molding of the present invention is stored in a plurality of containers, it is uniformly mixed and defoamed, and when it is stored in one container, it is extruded as it is to form the entire prototype (mother mold). Cast or apply and cure to wrap or on a portion of the surface of the prototype. In this way, a silicone rubber mold is produced. Curing can be carried out at room temperature, but curing may be accelerated by heating at 40 ° C to 150 ° C. After curing, the silicone rubber mold is removed from the prototype, and a molding resin such as urethane resin or epoxy resin is cast into the obtained silicone rubber mold. Then, after curing at a curing temperature according to the type of molding resin, the molded product is removed from the silicone rubber mold. In this way, a replica made of the molding resin can be obtained.

The hardness of the cured product of the silicone rubber composition for molding of the present invention is preferably 35 to 50 as measured by an A-type hardness tester. When the hardness of the cured product is less than 35, the silicone rubber mold is deformed when the molded product is removed from the silicone rubber mold, and it is difficult to use the cured product repeatedly as a mold. Further, when the hardness of the cured product exceeds 50, the silicone rubber mold is hard to be deformed, so that the mold removal property is lowered, and it is difficult to remove the molded product from the silicone rubber mold.

According to the silicone rubber composition for molding of the present invention, a urethane resin having good releasability (demoldability) and particularly improved mechanical properties even without blending non-reactive silicone oil or It is possible to obtain a silicone rubber mold that exhibits excellent molding durability even for an epoxy resin. The silicone rubber mold obtained from the composition of the present invention does not need to be coated with an external mold release agent or the like at the time of molding, and is also a molded product (replica) obtained by using this silicone rubber mold. Since it is not necessary to perform cleaning with a solvent before painting or plating, it is possible to shorten the work time and significantly reduce the cost, including the molding work and all the work associated therewith.
Therefore, the silicone rubber composition for molding of the present invention is particularly useful in the field of molding that requires a high degree of mold removal, such as prototype molding.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. In Examples and Comparative Examples, "parts" means "parts by mass" and "%" means "% by mass", and all physical property values such as viscosity are 23 ° C. and 50% relative humidity. Indicates the value at. The weight average molecular weight (Mw) is a value measured using a GPC apparatus using toluene as a solvent (manufactured by Tosoh Corporation, apparatus name; HLC-8220 GPC) and converted into polystyrene.

Further, in the following description, the M unit, the M ^vi unit, the D unit, the ^DH unit and the Q unit each represent a siloxane unit represented by the following formula.
M unit ………… (CH ₃ ) ₃ SiO _1/2
M ^V unit _{............ (CH 3) 2 (CH} 2 = CH) SiO 1/2
^MH unit ………… (CH ₃ ) ₂ HSiO _1/2
D unit ………… (CH ₃ ) ₂ SiO _2/2
D ^V units _{............ (CH 3) (CH 2} = CH) SiO 2/2
^DH unit ………… (CH ₃ ) HSiO _2/2
Q unit ………… SiO _4/2

Example 1
And 100 parts of dimethylpolysiloxane with both terminals blocked with vinyldimethylsiloxy groups (A) viscosity of 10,000 mPa · s, consist (B) M units, ^{M v} and Q units, these molar ratio of M: ^{M V: Q = 5: 1} : 8 and resinous polymethylvinylsiloxane 2 parts Mw of 3,000, and fumed silica 20 parts of (C) BET specific surface area of ^{300m 2 / g, (D)} 1 , 3-Divinyl-1,1,3,3-tetramethyldisilazane 0.15 part, hexamethyldisilazane 8 part, and water 1 part were placed in a universal kneader and kneaded at room temperature for 2 hours. The mixture was kneaded at 150 ° C. for 2 hours under reduced pressure.

Then, after cooling to room temperature, 0.15 parts of (F) chloroplatinic acid-vinylsiloxane complex (platinum concentration 2%) and 0.1 part of 1,3,5,7-tetramethyltetravinylcyclotetrasiloxane were added. After being added and uniformly dispersed, a resin-like polymethylhydrogensiloxane (viscosity 22 mPa · s, Mw870) consisting of (E1) ^MH units and Q units and containing 0.9% of hydrogen atoms bonded to silicon atoms. ) 1.6 parts were added and mixed uniformly to obtain a silicone rubber composition. The viscosity of the obtained composition was 50,000 mPa · s.

Examples 2-4, Comparative Examples 1-7
Each component shown in Table 1 was blended in the composition shown in the same table and mixed in the same manner as in Example 1 to obtain a polyorganosiloxane composition having the viscosity shown in the table.
The components listed in Table 1 are as follows.
[Resin-like polymethylvinylsiloxane]
............ M units consist ^{D V} and Q units, these molar ratio of ^{M: D V: Q = 6} : 1: Mw at 8 3,000 resinous polymethylvinylsiloxane [(E2 ) Resin-like polymethylhydrogensiloxane]
………… Resin-like polymethylhydrogensiloxane (viscosity 17 mPa · s, Mw790) consisting of ^MH units and Q units and containing 1.0% of hydrogen atoms bonded to silicon atoms.
[Linear polymethylhydrogensiloxane]
………… Unit formula: MD ^H ₂₀ D ₂₀ M linear polymethylhydrogensiloxane

Next, the hardness and demolding property of the cured product obtained from the polyorganosiloxane compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 7 were measured and evaluated as shown below. The measurement result is the mole of the Si—H group in the component (C) with respect to the total of the vinyl group in the component (A), the vinyl group in the component (B) and the vinyl group in the component (E) in the composition. It is shown in Table 1 together with the ratio (H / Vi ratio).

<Measurement of hardness>
As shown in FIGS. 1A and 1B, a mother mold 2 made of acrylic resin (ABS resin) is arranged in the container 1, and a portion that wraps the mother mold 2 and measures the hardness has a predetermined thickness. The above polyorganosiloxane composition 3 was poured so as to be. The master mold 2 is a square columnar having a square cross section with a side of 6 mm, and three stepped portions (middle bottom portion, high bottom portion, low bottom portion) having different heights are formed on the bottom surface in the direction perpendicular to the paper surface. Has been done. Each of the insole portion, the high bottom portion, and the low bottom portion has a width of 2 mm, and the insole portion and the low bottom portion, and the insole portion and the high bottom portion each have a height difference of 2 mm.

Next, the polyorganosiloxane composition 3 was defoamed under reduced pressure and then heated at 50 ° C. for 14 hours to be cured. Next, after cooling the cured product to room temperature, the mother mold 2 was removed to obtain a silicone rubber mold 4 shown in FIG. The hardness of the portion indicated by the arrow of the silicone rubber mold 4 thus obtained was measured according to JIS K6251. In Comparative Examples 5 and 6, the cured product was in the form of a gel and it was difficult to separate it from the mother mold, so that a silicone rubber mold could not be obtained.

<Measurement of demoldability>
As shown in FIG. 2, an epoxy resin (manufactured by Axon, trade name: RS-505) 5 was injected into the silicone rubber mold 4 obtained above, and heated at 70 ° C. for 24 hours to cure. A temperature rise was observed due to heat generated by the curing reaction. After curing, it was cooled to room temperature, and then an epoxy resin molded product (replica) was pulled out from the silicone rubber mold 4. Then, the lightness and weight when pulling out the replica from the mold were examined. Demoldability was evaluated according to the following criteria.
[Evaluation]
◎: Light pulling ○: Slightly heavy pulling △: Heavy pulling ×: Silicone rubber mold partially destroyed

From Table 1, the following can be seen. That is, the silicone rubber mold formed by the silicone rubber compositions of Examples 1 to 4 in which each component (A) to (F) is blended in a predetermined composition specified in the present invention is in the range of 35 to 50. Has hardness (according to A-type hardness tester). These silicone rubber molds are excellent in demoldability to the epoxy resin replica, and the unevenness (step) formed on the bottom of the replica does not adhere to the bottom of the silicone rubber mold, and the pullability is good. is there.

On the other hand, in the silicone rubber composition of Comparative Example 1, a linear polyorganohydrogensiloxane as a cross-linking agent is blended instead of a resin, so that the strength of the silicone rubber mold is not sufficient. Absent. In addition, the duplicated product adheres to the mold, and when the duplicated product is pulled out from the silicone rubber mold, the mold is not broken, but the pulling out is heavy and the mold removal property is poor.

In the silicone rubber compositions of Comparative Examples 2 and 3, the blending amount of 1,3-divinyl-1,1,3,3-tetramethyldisilazane as the component (D) is 0 with respect to 100 parts of the component (A). Since it is less than .05 parts, a cured product having sufficient hardness and strength cannot be obtained, and the silicone rubber mold is broken when the duplicated product is pulled out from the silicone rubber mold, making it difficult to remove the mold. ing.
In the silicone rubber composition of Comparative Example 4, the blending amount of the resin-like polyorganosiloxane having three or more vinyl groups as the component (B) is less than 0.5 parts with respect to 100 parts of the component (A). Therefore, a cured product having sufficient hardness and strength cannot be obtained, and the silicone rubber mold is broken when the duplicated product is pulled out from the silicone rubber mold, making it difficult to remove the mold.

In the silicone rubber composition of Comparative Example 5, the blending amount of (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane was a predetermined ratio (1) with respect to 100 parts of the component (A). Since it exceeds 0 parts), the cured product becomes a gel, and a rubber-like mold capable of removing the duplicate product cannot be obtained.
In the silicone rubber composition of Comparative Example 6, the blending amount of the resin-like polyorganosiloxane having three or more vinyl groups as the component (B) is within a predetermined range (10 parts with respect to 100 parts of the component (A)). Since it exceeds the limit, the cured product becomes a gel, and a rubber mold capable of removing the duplicate product cannot be obtained.
In the silicone rubber composition of Comparative Example 7, as a resin-like polyorganosiloxane having an alkenyl group, a polyorganosiloxane containing three or more vinyl groups in D units instead of M units is blended. Therefore, the strength of the silicone rubber mold is not sufficient, and the demoldability of the duplicated product from the mold is deteriorated.

According to the silicone rubber composition for molding of the present invention, a silicone rubber mold having hardness suitable for molding and excellent releasability with respect to the molding resin can be obtained. This silicone rubber mold has excellent mold releasability, especially with respect to urethane resins and epoxy resins for prototype molding with improved mechanical properties and the like. Therefore, the silicone rubber composition for molding of the present invention is suitable for molding replicas that require a high degree of releasability, such as prototype molding. Furthermore, since it is not necessary to apply an external mold release agent at the time of molding and it is not necessary to add a non-reactive silicone oil to improve the mold release property, a resin that requires transparency and surface smoothness. Suitable for molding duplicates.

Claims (5)

(A) 100 parts by mass of polyorganosiloxane having two or more alkenyl groups bonded to a silicon atom in one molecule and having a viscosity at 23 ° C. of 1,000 to 200,000 mPa · s.
Formula (B): A monofunctional siloxane unit represented by R ¹ ₃ SiO _1/2 (in the formula, R ¹ is an alkenyl group or a substituted or unsubstituted alkyl group, respectively), and the formula: 0.5 to 10 parts by mass of polyorganosiloxane having a tetrafunctional siloxane unit represented by SiO _4/2 and having 3 or more alkenyl groups contained in the monofunctional siloxane unit in one molecule.
(C) 1 to 50 parts by mass of aerosol silica
(D) 1,3-Divinyl-1,1,3,3-tetramethyldisilazane 0.05 to 1.0 part by mass,
Formula (E): A monofunctional siloxane unit represented by R ² ₂ HSiO _1/2 (in the formula, R ² is an independently substituted or unsubstituted alkyl group), and formula: SiO _{4 /. The} polyorganohydrogensiloxane having a tetrafunctional siloxane unit represented by ₂ and having a hydrogen atom bonded to a silicon atom in an amount of 0.5 to 1.2% by mass based on the whole component is described in (A). ) The hydrogen atom in the component is 0.5 to 5.0 with respect to a total of 1 mol of the alkenyl group in the component, the alkenyl group in the component (B), and the alkenyl group in the component (D). Contains the amount to be mol and (F) the amount of catalyst of the platinum-based compound .
A silicone rubber composition for molding , wherein the fumigant silica (C) is surface-treated with (D) 1,3-divinyl-1,1,3,3-tetramethyldisilazane .
The first aspect of claim 1, wherein the component (A) is a linear polyorganosiloxane in which the main chain consists of repeating diorganosiloxane units and both ends of the molecular chain are sealed with a triorganosyloxy group. Silicone rubber composition for molding. The component (B) is _composed of a monofunctional siloxane unit represented by the formula: R ¹ ₃ SiO _1/2 and a tetrafunctional siloxane unit represented by the formula: SiO _4/2 , and is 1,000 to 10 The silicone rubber composition for molding according to claim 1 or 2, wherein it is a polyorganosiloxane having a weight average molecular weight of 000. The silicone rubber composition for molding according to any one of claims 1 to 3, wherein the hardness of the cured product obtained by curing the present composition is 35 to 50. The molding method according to any one of claims 1 to 4, wherein the content ratio of the platinum-based compound (F) with respect to the entire composition is 1 to 100 mass ppm in terms of platinum atoms. Silicone rubber composition.

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