JP7542929B2 - Polypropylene resin and silicone rubber bonded material and manufacturing method thereof - Google Patents

Description

The present invention relates to a joint between polypropylene resin and silicone rubber and a method for producing the same.

Silicone rubber is used in many fields due to its excellent heat resistance, cold resistance, weather resistance, electrical insulation, and safety, and is often used as a part combined with organic resins and metals. Polypropylene resin, a type of polyolefin resin, is the second most produced synthetic resin after polyethylene resin, and has a low specific gravity and excellent mechanical strength, processability, and scratch resistance. However, polypropylene resin is known as a difficult-to-adhere material, and a method has yet to be found to develop strong adhesion between polypropylene resin and silicone rubber that will reliably cause cohesive failure.

As an example of the study of adhesion between polypropylene resin and silicone rubber, Japanese Patent Laid-Open Publication No. 60-247556 (Patent Document 1) proposes the addition of an epoxy compound, an acid anhydride, an acrylic-modified silane, or an oxirane containing an unsaturated hydrocarbon to an addition-curing silicone composition; however, although cohesive failure was achieved with polyethylene resin, sufficient adhesive strength was not achieved with polypropylene resin.
Japanese Patent Laid-Open No. 60-084335 (Patent Document 2) describes providing a silane coupling agent layer containing aminosilane and vinylsilane on vulcanized silicone rubber, and then simultaneously heating and vulcanizing a silicone/polyolefin copolymer and a thermoplastic resin on top of the layer; however, this method makes it difficult to mold silicone rubber onto polypropylene resin.
Japanese Patent Laid-Open Publication No. 2004-210894 (Patent Document 3) describes bonding a chlorinated polyolefin resin to a silicone-based sealant via an aminosilane compound and/or a ketimine compound. However, the inventors' investigations showed that polypropylene resin coated with only aminosilane, particularly without pretreatment, did not exhibit sufficient adhesive strength to addition-curing silicone resin.
In addition, in JP 2009-1555358 A (Patent Document 4), a moisture-curing silicone rubber composition is adhered to various resin substrates, including polypropylene resin, via a silicon oxide film formed by burning an organosilicon compound, which is also partially implemented in the present invention. However, in the inventors' investigations, none of the primer treatments combining the silane coupling agent contained in each composition in the examples provided strong adhesion to addition-curing silicone rubber.
Furthermore, JP 2013-244652 A (Patent Document 5) proposes providing a primer layer mainly composed of methylhydrogenpolysiloxane on a polypropylene resin substrate that has been treated with a silicon oxide film (Itro treatment), and then heat-molding an addition-curing silicone rubber. However, the inventors' investigations did not reveal that an adhesive strength strong enough to cause cohesive failure of the addition-curing silicone rubber could be obtained.

Japanese Unexamined Patent Publication No. 60-247556 Japanese Patent Application Laid-Open No. 60-084335 JP 2004-210894 A JP 2009-155358 A JP 2013-244652 A

Therefore, the present invention aims to provide a bonded article in which polypropylene resin and silicone rubber are firmly bonded, and a method for producing the same.

As a result of intensive research conducted by the inventors in order to achieve the above object, the inventors discovered that strong adhesion between polypropylene resin and silicone rubber can be obtained by applying a primer composition containing as essential components a silane compound in which a gamma-aminopropyl group is bonded to a silicon atom and a silane compound containing an epoxy group to a polypropylene resin substrate that has been subjected to plasma treatment or silicon oxide film treatment, drying the composition to form a primer layer, and then heat-curing a silicone rubber composition on the primer layer, thereby completing the present invention.

Therefore, the present invention provides the following bonded polypropylene resin and silicone rubber and its manufacturing method.

＜1＞
A bonded article in which polypropylene resin and silicone rubber are bonded with the following primer composition.
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) A primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule.

＜2＞
A first step of performing a dry treatment on a surface of a polypropylene resin substrate;
After the first step,
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) a second step of applying a primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule to the surface of the substrate dry-treated in the first step and drying the composition to form a primer layer;
After the second step,
and a third step of applying a silicone rubber composition to the surface of the primer layer and curing the composition by heating to form a silicone rubber layer.

＜3＞
3. The method for producing a bonded article of polypropylene resin and silicone rubber according to <2>, wherein the dry treatment is a plasma treatment or a silicon oxide film treatment.

＜4＞
The method for producing a bonded product of polypropylene resin and silicone rubber according to <1> or <2>, wherein the component (A) is at least one selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, and 3-aminopropylmethyldiethoxysilane.

＜5＞
The method for producing a bonded product of polypropylene resin and silicone rubber according to any one of <1> to <4>, wherein the primer layer formed by applying and drying the primer composition has a coverage of 0.05 to 5 g/ ^m2 .

＜6＞
The method for producing a bonded product of polypropylene resin and silicone rubber according to any one of <2> to <5>, wherein the silicone rubber composition contains the following components (C) to (F):
(C) an organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms per molecule: 100 parts by mass; (D) a reinforcing silica having a specific surface area of 50 to 500 ^m2 /g as measured by the BET method: 10 to 100 parts by mass; (E) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: in an amount such that there are 0.5 to 5 moles of hydrosilyl groups in component (E) per mole of alkenyl groups in component (C); (F) a platinum group metal catalyst: 0.5 to 1,000 ppm, calculated as the mass of platinum group metal, relative to component (C).

By using the manufacturing method of the present invention, a bonded product in which polypropylene resin and silicone rubber are firmly bonded can be obtained. Polypropylene resin is used for a variety of purposes, such as home appliances, stationery, automobile parts, toys, and sporting goods, and if silicone rubber of different hardness and color can be firmly bonded to it, it is useful for adjusting the texture (anti-slip, etc.) and adding design features.

The present invention will be explained in more detail below.

The present invention relates to a bonded article in which polypropylene resin and silicone rubber are bonded together using the following primer composition.
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) A primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule.

The method for producing a bonded article of the present invention further comprises the steps of:
A first step of performing a dry treatment on a surface of a polypropylene resin substrate;
After the first step,
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) a second step of applying a primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule to the surface of the substrate dry-treated in the first step and drying the composition to form a primer layer;
After the second step,
and a third step of applying a silicone rubber composition to the surface of the primer layer and curing the composition by heating to form a silicone rubber layer.

Polypropylene Resin The polypropylene resin substrate used in the present invention is not particularly limited, and polypropylene resins of various melting points and molecular weights can be used. Generally, polypropylene resins are classified into three types according to the form of copolymerization: homopolymers, which are single polymers of propylene only; random copolymers containing ethylene at a ratio of 4.5% by weight or less; and block copolymers containing ethylene-propylene copolymers in which ethylene is copolymerized after polymerization of homopolymers, and any of these can be used.

Silicone rubber The silicone rubber used in the present invention is not particularly limited, but is preferably an addition-curing type silicone rubber containing an alkenyl group-containing organopolysiloxane, reinforcing silica, an organohydrogenpolysiloxane, and a platinum group metal catalyst. Either millable type rubber that can be plasticized and mixed with a kneading roll or an internal mixer, or liquid rubber that is liquid or paste-like before curing can be used.

First step: dry treatment of the surface of the polypropylene resin substrate In the present invention, dry treatment of the polypropylene resin surface before forming the primer layer is an essential step. In general, examples of dry treatment include plasma treatment, corona treatment, flame treatment, silicon oxide film treatment (Itro treatment), UV treatment, and excimer treatment. When the dry treatment is performed, hydrophilicity is expressed, for example, by generating a hydrophilic group having an oxygen atom. This can improve the reactivity of the propylene resin with the primer composition. In the present invention, among these dry treatments, plasma treatment or silicon oxide film treatment is particularly preferred because it can stably obtain strong adhesion.

The plasma treatment used in the present invention is a method of treating the surface of a substrate under reduced pressure using argon or oxygen plasma, and the plasma output, gas flow rate, degree of vacuum, treatment time, etc. can be adjusted. The treatment conditions can be adjusted based on the wettability and spreading of the primer composition, and the contact angle of liquids such as water.

The silicon oxide film treatment used in the present invention is also called Itro treatment, and is a method in which a silane compound or the like is introduced into a fuel gas for forming a flame, and the flame is used to treat the surface of the substrate. After treatment, a large number of fine particles mainly composed of silicon dioxide are formed on the surface of the substrate, improving the reactivity with the primer composition. The degree of surface treatment can be adjusted by the size and shape of the flame, the distance between the burner and the substrate, the moving speed of the burner, the treatment time, etc. The treatment conditions can be adjusted based on the wettability and spreading of the primer composition, and the contact angle of liquids such as water. In addition, effective procedures for this silicon oxide film treatment are described in detail in JP 2003-238710 A.

The second step of forming a primer layer on the substrate surface dry-treated in the first step is a primer composition used in the present invention for forming a primer layer on the substrate surface dry-treated in the first step.
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) A primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule.
Each component is described in detail below.

(A) Silane Compound with 3-Aminopropyl Group Bonded to Silicon Atom The silane compound with 3-aminopropyl group bonded to silicon atom of component (A) is a key material of the present invention, and its use provides strong adhesion. The silane compound has one or more 3-aminopropyl groups bonded to silicon atom in one molecule, preferably one or two, more preferably one.
Furthermore, groups bonded to silicon atoms other than the 3-aminopropyl group include groups selected from alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 6 carbon atoms, and those having one or more alkoxy groups per molecule are preferred.
Specific examples of the silane compound of component (A) include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, di(3-aminopropyl)dimethoxysilane, and di(3-aminopropyl)diethoxysilane. The component (A) can be used alone or in appropriate combination of two or more.
Known aminosilanes include silane compounds in which an N-2-(aminoethyl)-3-aminopropyl group, an N-(1,3-dimethyl-butylidene)propylamino group, or an N-phenyl-3-aminopropyl group is bonded to a silicon atom, but none of these can provide strong adhesion.

(B) Silane compound having an epoxy group-containing organic group As the silane compound having an epoxy group-containing organic group of component (B), a known compound can be used. The silane compound has one or more epoxy group-containing organic groups bonded to silicon atoms in one molecule, preferably one or two, more preferably one.
Furthermore, examples of groups bonded to silicon atoms other than the epoxy group-containing organic group include groups selected from alkyl groups having 1 to 10 carbon atoms and alkoxy groups having 1 to 6 carbon atoms, and those having one or more alkoxy groups per molecule are preferred.
Specific examples of the silane compound of component (B) that are easily available and have high reactivity include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The component (B) can be used alone or in appropriate combination of two or more types.

The mixing ratio of components (A) and (B) in the primer composition is preferably a molar ratio of amino groups to epoxy groups of 2:8 to 8:2, more preferably 3:7 to 7:3, and even more preferably 4:6 to 6:4.

The (A) and (B) components can also be used by diluting them with a solvent. The solvent is not limited as long as it dissolves the (A), (B) and other optional components, and any known solvent can be used. The solvent may be used alone or in combination of two or more depending on the evaporation rate during application and drying of the primer composition. Specific examples of the solvent include aromatic hydrocarbons such as xylene, toluene, and benzene; aliphatic hydrocarbons such as heptane and hexane, aromatic/aliphatic mixed hydrocarbons such as ligroin and rubber volatile oil; chlorinated hydrocarbons such as trichloroethylene, perchloroethylene, and methylene chloride; esters such as ethyl acetate; ketones such as methyl isobutyl ketone, methyl ethyl ketone, and cyclohexanone; aliphatic alcohols such as ethanol, isopropanol, and butanol; ethers such as diethyl ether; and silicone-based solvents. Among these, aliphatic alcohols are preferred, and aliphatic alcohols having 1 to 6 carbon atoms, which are easy to dry, are particularly preferred. The reason for this is that in the primer composition, the amino group and epoxy group in the silane compound react, opening the epoxy group and generating a hydroxyl group, but in the aliphatic alcohol, the reaction between this hydroxyl group and the silicon atom in the silane compound is suppressed, which increases the storage stability of the primer solution.

The amount of solvent to be blended is preferably such that the components (A), (B) and other optional components account for 0.1 to 20% by mass of the primer composition, and more preferably 0.5 to 10% by mass.

Examples of the method for applying the primer composition include brush application and spraying. The amount of application is adjusted by the application method, the number of applications, the concentration of the primer composition, etc., and can be estimated from the change in weight after drying. The amount of application of the primer composition is preferably 0.05 to 5 g/ ^m2 , and more preferably 0.1 to 2 g/ ^m2 . If the amount of application is less than 0.05 g/ ^m2 , sufficient adhesive strength may not be obtained, and if it exceeds 5 g/ ^m2 , the primer layer may be easily destroyed by external stress.

Third Step of Forming a Silicone Rubber Layer on the Surface of the Primer Layer The silicone rubber composition used in the present invention for forming a silicone rubber layer on the surface of the primer layer is not particularly limited, but a preferred example is an addition-curing type silicone rubber composition containing the following components (C) to (F).
(C) an organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms per molecule: 100 parts by mass; (D) a reinforcing silica having a specific surface area of 50 to 500 ^m2 /g as measured by the BET method: 10 to 100 parts by mass; (E) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that there are 0.5 to 5 moles of hydrosilyl groups in component (E) per mole of alkenyl groups in component (C); (F) a platinum group metal catalyst: 0.5 to 1,000 ppm, calculated as platinum metal mass, relative to component (C).
Each component will be described in detail below.

（式（Ｉ）中、Ｒは同一又は異種の炭素数１～１２の１価炭化水素基を示し、ａは１．９５～２．０５の数である。） (C) Alkenyl-containing organopolysiloxane The (C) component preferably used in the silicone rubber composition is an organopolysiloxane having a degree of polymerization (or the number of silicon atoms in the molecule) of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms in one molecule. This (C) component is used as the main component (base polymer) of this composition. The (C) alkenyl-containing organopolysiloxane is preferably a raw rubber-like component (i.e., a non-liquid component with high viscosity and no self-flowability) at room temperature (25°C). The silicone rubber composition containing this alkenyl-containing organopolysiloxane as the main component is usually a millable type composition (i.e., a raw rubber-like composition that can be uniformly kneaded under shear stress by a kneader such as a roll mill). A representative example of the alkenyl-containing organopolysiloxane of component (C) is one represented by the average composition formula (I) shown below.

(In formula (I), R represents the same or different monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a number from 1.95 to 2.05.)

In the above average composition formula (I), R represents the same or different monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and specifically includes alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; fluoroalkyl groups such as 3,3,3-trifluoropropyl; alkenyl groups such as vinyl, allyl, and propenyl; aryl groups such as cycloalkenyl, phenyl, and tolyl; and aralkyl groups such as benzyl and 2-phenylethyl. Methyl, vinyl, phenyl, and trifluoropropyl groups are preferred, and methyl and vinyl groups are particularly preferred. It is preferable that methyl groups account for 80 mol % or more, and particularly 90 mol % or more of R, and it is further preferable that all R groups except for alkenyl groups are methyl groups.

Specific examples of the alkenyl-containing organopolysiloxane of component (C) include organopolysiloxanes whose main chain is made of dimethylsiloxane units, and dimethylpolysiloxanes whose main chain has diphenylsiloxane units having phenyl groups, vinyl groups, 3,3,3-trifluoropropyl groups, etc., methylvinylsiloxane units, methyl-3,3,3-trifluoropropylsiloxane units, etc., introduced into part of the main chain.

The organopolysiloxane of component (C) must have two or more (usually from 2 to 50, and particularly from 2 to 20) alkenyl groups, preferably vinyl groups, per molecule. For example, it is preferable that, relative to all R groups in the above average composition formula (I), 0.01 to 10%, and particularly 0.02 to 5%, be alkenyl groups.
The alkenyl group may be bonded to a silicon atom at the molecular chain terminal, or may be bonded to a silicon atom in the middle of the molecular chain (non-terminal), or may be both, but it is preferable that the alkenyl group contains at least an alkenyl group bonded to a silicon atom at both molecular chain terminals.Specifically, it is preferable that the molecular chain terminals are blocked with a dimethylvinylsilyl group, a methyldivinylsilyl group, a trivinylsilyl group, or the like.

In the above average composition formula (I), a is a number from 1.95 to 2.05, preferably from 1.98 to 2.02, and more preferably from 1.99 to 2.01. The molecular structure of the alkenyl-containing organopolysiloxane of component (C) is generally a straight-chain structure in which the main chain is basically composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ) and both molecular chain terminals are blocked with triorganosiloxy groups (R ₃ SiO _1/2 ), but it may also have a branched structure containing a small amount of branch units (RSiO _3/2 ) in the main chain within a range that does not impair rubber elasticity (R is the same as above).

The degree of polymerization of the organopolysiloxane of component (C) is from 100 to 10,000, preferably from 1,000 to 10,000, more preferably from 2,000 to 10,000, even more preferably from 3,000 to 8,000, and particularly preferably from 5,000 to 8,000. If the degree of polymerization is less than 100, sufficient rubber strength may not be obtained.
In this specification, the degree of polymerization is a value calculated as a weight average degree of polymerization from the number average molecular weight in terms of polystyrene in gel permeation chromatography (GPC) analysis measured under the following conditions.

[GPC measurement conditions]
Developing solvent: toluene Flow rate: 0.6 mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-H
TSKgel SuperH5000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (toluene solution with a concentration of 0.5% by mass)

The alkenyl-containing organopolysiloxane of component (C) may be used alone or in combination of two or more types with different molecular structures or degrees of polymerization.

The alkenyl-containing organopolysiloxane of component (C) can be obtained by known methods, such as (co)hydrolyzing and condensing one or more organohalogenosilanes, or by ring-opening polymerization of a cyclic polysiloxane using an alkaline or acidic catalyst.

(D) Reinforcing Silica The reinforcing silica of the component (D) preferably used in the above silicone rubber composition can be the reinforcing silica fine powder usually used in silicone rubber compositions.The reinforcing silica of the component (D) can be, for example, fumed silica, dry silica such as calcined silica, wet silica such as precipitated silica, etc., and among them, fumed silica is preferred from the viewpoint of heat resistance.
The specific surface area measured by the BET method is preferably 50 to 500 m ² /g, more preferably 100 to 400 m ² /g, and particularly preferably 100 to 300 m ² /g. If the specific surface area is less than 50 m ² /g, the mechanical strength may be insufficient. If the specific surface area is greater than 500 m ² /g, industrial production may be difficult.

If necessary, the surface of this reinforcing silica may be hydrophobized with a known treating agent such as chlorosilane or hexamethyldisilazane.

The amount of reinforcing silica (D) added to the silicone rubber composition is preferably 10 to 100 parts by mass, more preferably 20 to 70 parts by mass, and particularly preferably 30 to 60 parts by mass, per 100 parts by mass of the alkenyl group-containing organopolysiloxane (C). If the amount is less than 10 parts by mass, the amount is too small to provide a sufficient reinforcing effect, and if it exceeds 100 parts by mass, processability may deteriorate and mechanical strength may decrease.

（式（ＩＩ）中、Ｒ²は互いに独立に同一又は異種の炭素数１～１０の非置換又は置換の１価炭化水素基である。ｂは０．７～２．１、ｃは０．００１～１で、かつｂ＋ｃは０．８～３を満足する数である。） (E) Organohydrogenpolysiloxane The component (E) that is preferably used in the above silicone rubber composition is an organohydrogenpolysiloxane having at least two, and preferably three or more, hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in each molecule. It is preferably an organohydrogenpolysiloxane that is liquid at room temperature and is represented by the following average composition formula (II):

(In formula (II), ^R2 's are each independently the same or different, unsubstituted or substituted monovalent hydrocarbon groups having 1 to 10 carbon atoms; b is a number that satisfies 0.7 to 2.1, c is a number that satisfies 0.001 to 1, and b+c is a number that satisfies 0.8 to 3.)

In formula (II), R ² 's are each independently the same or different and are unsubstituted or substituted monovalent hydrocarbon groups having 1 to 10 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, and propyl.

In addition, in formula (II), b is a number that satisfies 0.7 to 2.1, preferably 0.8 to 2, c is a number that satisfies 0.001 to 1, preferably 0.01 to 1, and b+c is a number that satisfies 0.8 to 3, preferably 0.9 to 2.7.

The organohydrogenpolysiloxane of component (E) has at least two hydrosilyl groups (2 to 300), preferably three or more (e.g., 3 to 200), and more preferably four or more (e.g., 4 to 100) per molecule, and these may be at the ends of the molecular chain, in the middle of the molecular chain (non-terminal), or both. The organohydrogenpolysiloxane may have a silicon atom count (or degree of polymerization) of usually 2 to 300, preferably 3 to 200, and more preferably 4 to 100 per molecule, and preferably has a viscosity at 25°C of 0.5 to 1,000 mPa·s, more preferably 1 to 500 mPa·s, and particularly preferably 5 to 300 mPa·s. The viscosity is measured at 25°C using a rotational viscometer as described in JIS K 7117-1:1999.

The amount of the organohydrogenpolysiloxane blended is preferably 0.1 to 30 parts by weight, and more preferably 0.3 to 10 parts by weight, per 100 parts by weight of the organopolysiloxane of component (C).
This organohydrogenpolysiloxane is also blended so that the molar ratio of hydrosilyl groups to the total alkenyl groups in component (C) is preferably in the range of 0.5 to 5, more preferably in the range of 0.8 to 3, and can also be in the range of 1 to 2.5. When using an organohydrogenpolysiloxane, if the blending amount of the organohydrogenpolysiloxane is too small, crosslinking may be insufficient, resulting in poor rubber properties such as strength and elongation, whereas if the blending amount is too large, there may be too many crosslinking points (too high crosslinking density), similarly resulting in poor rubber properties.

(F) Platinum Group Metal Catalyst Examples of the component (F) that is preferably used in the above silicone rubber composition include platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, platinum bisacetoacetate, palladium-based catalysts, rhodium-based catalysts, and the like.

The amount of component (F) to be added can be a catalytic amount, and is usually preferably 0.5 to 1,000 ppm, and more preferably 1 to 500 ppm, calculated as platinum metal mass relative to component (C).

The curing conditions for the silicone rubber composition are preferably 100-180°C for 10 seconds to 30 minutes, and more preferably 120-160°C for 20 seconds to 20 minutes. After molding the silicone rubber composition onto the primer layer (i.e., after the first curing), it is preferable to carry out a post-cure (secondary curing) to improve adhesion and the compression set of the cured product. The post-cure conditions, taking into account the heat resistance temperature and melting point of the polypropylene resin, are preferably 100-180°C for 30 minutes to 100 hours, and more preferably 120-160°C for 1 to 8 hours.

The silicone rubber composition may be molded by any method, including injection molding, compression molding, extrusion molding, and transfer molding.

The present invention will be specifically explained below with examples and comparative examples, but the present invention is not limited to the following examples.

[Base silicone rubber compound]
100 parts by mass of an organopolysiloxane consisting of 99.9 mol% dimethylsiloxane units, 0.075 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxane units, with a weight average degree of polymerization of approximately 6,000 and a vinyl group amount of 1.4 x ^10-5 mol/g, 25 parts by mass of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) with a specific surface area of 200 ^m2 /g measured by the BET method, 4 parts by mass of dimethyldimethoxysilane and 0.15 parts by mass of methylvinyldimethoxysilane as surface treatment agents, and 1 part by mass of hydrochloric acid (pH = 3) were kneaded in a kneader and heat-treated at 180°C for 1 hour to obtain a silicone-based compound.

[Silicone rubber composition (addition crosslinking)]
To 100 parts by mass of the base silicone rubber compound, 0.05 parts by mass of a platinum catalyst (Pt concentration: 1% by mass), 0.025 parts by mass of ethynylcyclohexanol, and 0.8 parts by mass of methylhydrogendimethylpolysiloxane (average degree of polymerization: 40, hydrosilyl group amount: 0.014 mol/g) both ends of which are blocked with trimethylsiloxy groups and have an average of 20 hydrosilyl groups on the side chains were mixed using a two-roll mill.

[Silicone rubber composition (peroxide crosslinking)]
100 parts by mass of the base silicone rubber compound was mixed with 0.6 parts by mass of bis(4-methylbenzoyl) peroxide using a two-roll mill.

[Silane Compound]
As silane compounds having an amino group, 3-aminopropyltriethoxysilane (KBE-903, manufactured by Shin-Etsu Chemical Co., Ltd.) and N-2-(aminoethyl)-3-aminopropylsilane (KBM-603, manufactured by Shin-Etsu Chemical Co., Ltd.) were prepared. As silane compounds having an epoxy group, 3-glycidoxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (KBM-303, manufactured by Shin-Etsu Chemical Co., Ltd.) were prepared. As a silane compound having a vinyl group, vinyltriethoxysilane (KBE-1003, manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared.

[Primer composition]
A primer composition was prepared by adding one or two types of a specific silane compound to isopropyl alcohol, and the amount of each was 5% by mass. When two types of silane compounds were used, the amino group, epoxy group, and vinyl group were adjusted to be equimolar. After the primer composition was prepared, it was stirred with a shaker for 1 hour, and the primer composition was applied and dried the next day or later. When the primer composition was applied by brush coating, the mass after drying was approximately 0.5 g/ ^m2 . Drying was performed by leaving it at room temperature for more than 2 hours.

[Adhesive substrate]
A polypropylene resin substrate having a width of 25 mm, a length of 100 mm and a thickness of 2 mm was obtained from Test Piece Corporation.

[Plasma treatment]
The surface of the polypropylene resin substrate was washed with ethanol, dried, and then subjected to surface treatment using a plasma dry cleaner (ODC210, manufactured by Yamato Scientific Co., Ltd.) under conditions of a high-frequency output of 100 W, an oxygen flow rate of 100 mL/min, and a vacuum degree of 60 Pa for 1 minute.

[Silicon oxide coating treatment]
The surface of the polypropylene resin substrate was washed with ethanol, dried, and then surface treatment was performed using a silicon oxide film treatment device (Flamebond FB-5, manufactured by Soft99 Corporation). The flame size was adjusted to about 4 cm, the distance between the nozzle and the substrate was 3 cm, and the burner travel speed was 40 cm/sec, and the burner was moved back and forth over the substrate three times. The loss of gloss on the substrate surface confirmed that the treatment had been performed.

[Adhesion]
The adhesiveness was evaluated with reference to the shear adhesion test in JIS K 6850:1999. The silicone rubber composition was cut to a thickness of 2 mm using a two-roll mill and cut to a size of 25 mm x 12.5 mm. The silicone rubber composition was sandwiched between two polypropylene resin substrates that had been plasma-treated or silicon oxide-treated, and heated for 2 hours in an oven set at 150°C. After removing from the oven and leaving at room temperature for 12 hours or more, the tensile tester (TENSOMETER 2020, manufactured by Alpha Technologies Japan LLC) was used to tensile in the opposite directions at 50 mm/min, and the maximum test force was recorded. The polypropylene resin substrate was chucked via a waterproof abrasive paper (#180, JIS standard) to prevent the chucked portion from slipping.

The test results are shown in Table 1. When a polypropylene resin substrate that had been plasma-treated or silicon oxide film-treated was treated with a primer that combined a silane compound having a 3-aminopropyl group and a silane compound having an epoxy group, strong adhesive strength was obtained, and the cured product of the silicone rubber composition (silicone rubber) did not undergo cohesive failure, or the chucked portion did not slip and break (non-destructive). A similar test was also carried out with a silane compound having an N-2-(aminoethyl)-3-aminopropyl group, but in both cases the interface peeled off easily.

Claims (6)

A bonded article in which polypropylene resin and the following silicone rubber are bonded with the following primer composition.
Silicone rubber:
(C) Organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(D) Reinforcing silica having a specific surface area measured by the BET method of 50 to 500 m ² /g: 10 to 100 parts by mass
(E) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the amount of hydrosilyl groups in component (E) is 0.5 to 5 moles per mole of alkenyl groups in component (C); and
(F) Platinum group metal catalyst: A cured product of a silicone rubber composition containing 0.5 to 1,000 ppm by mass of platinum group metal relative to the component (C).
Primer Composition:
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) A primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule. A first step of performing a dry treatment on a surface of a polypropylene resin substrate;
After the first step,
(A) a silane compound having a 3-aminopropyl group bonded to a silicon atom, and
(B) a second step of applying a primer composition containing a silane compound having one or more epoxy group-containing organic groups in one molecule to the surface of the substrate dry-treated in the first step and drying the composition to form a primer layer;
After the second step,
2. The method for producing a bonded article of polypropylene resin and silicone rubber according to claim 1, further comprising a third step of applying a silicone rubber composition to the surface of the primer layer and curing the composition by heating to form a silicone rubber layer. The method for producing a bonded product of polypropylene resin and silicone rubber according to claim 2, characterized in that the dry treatment is a plasma treatment or a silicon oxide film treatment. 4. The method for producing a bonded article of polypropylene resin and silicone rubber according to claim 2 or 3 , characterized in that component (A) is one or more members selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, and 3- aminopropylmethyldiethoxysilane. 5. The method for producing a bonded article of polypropylene resin and silicone rubber according to any one of claims 2 to 4, characterized in that the primer layer formed by applying and drying the primer composition has a weight of 0.05 to 5 g/ ^m2 . 6. The method for producing a bonded article of polypropylene resin and silicone rubber according to claim 2, wherein the silicone rubber composition contains the following components (C) to (F):
(C) an organopolysiloxane having a degree of polymerization of 100 to 10,000 and having two or more alkenyl groups bonded to silicon atoms per molecule: 100 parts by mass; (D) a reinforcing silica having a specific surface area of 50 to 500 ^m2 /g as measured by the BET method: 10 to 100 parts by mass; (E) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: in an amount such that there are 0.5 to 5 moles of hydrosilyl groups in component (E) per mole of alkenyl groups in component (C); (F) a platinum group metal catalyst: 0.5 to 1,000 ppm, calculated as the mass of platinum group metal, relative to component (C).