WO2017068893A1

WO2017068893A1 - Rubber composition, and crosslinked rubber product and method for producing same

Info

Publication number: WO2017068893A1
Application number: PCT/JP2016/077192
Authority: WO
Inventors: 英彦小栗; 茂樹川崎; 隆生山崎; 夕貴市川
Original assignee: 株式会社エラストミックス
Priority date: 2015-10-19
Filing date: 2016-09-14
Publication date: 2017-04-27
Also published as: CN107922665A; JP6814740B2; JPWO2017068893A1

Abstract

The present invention is a rubber composition that contains a rubber, and thermally-expandable microcapsules which undergo volumetric expansion through heating, and that is characterized in that the contained amount of the thermally-expandable microcapsules is 1.5-10.7 parts by mass with respect to 100 parts by mass of the rubber, and when a test piece including an uncrosslinked rubber composition that contains the rubber, the thermally-expandable microcapsules, a crosslinking agent, and a crosslinking accelerator is subjected to a heat treatment under conditions in which the temperature is 180°C, the frequency is 100 cpm, and the amplitude angle is 0.5 degrees in order to cause the crosslinking reaction and the volumetric expansion of the thermally-expandable microcapsules to proceed, a time difference Δt (= t₂ - t₁) between time t₁ when the test piece expanded by the heat treatment has exhibited the highest pressure, and time t₂ when an optimum crosslinking point defined in JIS K6300-2 is achieved, is 1.0-4.5 min.

Description

Rubber composition, crosslinked rubber product and method for producing the same

The present invention relates to a rubber composition containing rubber and a thermally expandable microcapsule that expands in volume by heating, and a microfoamed crosslinked rubber composition containing the expanded capsule obtained by using this rubber composition The present invention relates to a crosslinked rubber product having a low specific gravity and a method for producing the same.

In recent years, in order to save the environment and improve fuel efficiency, it has been desired to reduce the weight of vehicles such as automobiles, and as part of this, weight reduction is also required for structural parts. For example, studies have been made on reducing specific gravity using thermally expandable microcapsules for rubber parts for automobiles.
Patent Document 1 discloses a weather strip formed by extrusion-molding and vulcanizing a polymer material composition, and at least the surface side of only a contact portion in a seal portion that seals a gap to which the weather strip is applied is at least on the surface side. , 100 phr of ethylene / α-olefin / non-conjugated polyene copolymer, more than 50 phr to 120 phr of carbon black having an arithmetic average particle size of 60 nm or more, 100 phr or less of a softening agent, and thermally expandable microcapsules were blended. It is made of a polymer material composition, and the surface of the contact portion is formed with a heat-expandable microcapsule-derived uneven surface, and the carbon-based rough surface is formed on the surface of the heat-expandable microcapsule-derived uneven surface. A featured weatherstrip is disclosed.
Patent Document 2 discloses an ethylene / α-olefin / non-conjugated polyene copolymer of 100 phr, carbon black having an arithmetic average particle size of 60 nm or more, 50 phr to 100 phr, a softening agent of 100 phr or less, and a viscosity (25 ° C.) of 1000 cSt or more. A rubber material composition containing a silicone compound and thermally expandable microcapsules, and an automotive weather strip formed by extruding and vulcanizing the composition, wherein at least the surface of the weather strip contact portion An automotive weather strip is disclosed in which an uneven surface derived from carbon black is formed on the side and the specific gravity is 0.3 or more.
Patent Document 3 includes a matrix made of a polymer material and a plurality of capsules dispersed in the matrix, and a method for producing a molded article having irregularities formed on the surface due to expansion of the capsules, Prepare a green body that has an exposed shell part of the capsule that has been expanded and exposed to the surface, and an outer shell protrusion part of the capsule that has ruptured and protruded outward from the surface, and is then removed from the surface of the green body. A method of manufacturing a molded product such as a weather strip, which includes performing a finishing process for eliminating the shell protrusion, is disclosed.
Patent Document 4 discloses a foamed rubber molded article obtained by vulcanizing an unvulcanized rubber material blended with thermally expandable microcapsules to form a bubble space inside the rubber material. In the bubble space formed inside, a hole through which the internal gas permeates is formed in the shell of the thermally expandable microcapsule, and at least partly between the inner surface of the bubble space and the shell of the thermally expandable microcapsule. A foamed rubber molded product characterized in that a gap is formed is disclosed, and it is described that a weather strip is preferable as the foamed rubber molded product.

JP 2007-186559 A JP 2008-56748 A JP 2009-161587 A JP 2011-256223 A

Each of the molded articles in Patent Documents 1 to 4 has a structure in which expanded capsules are dispersed and contained in the vulcanized rubber matrix, so that the specific gravity is reduced, but only the surface layer is hardened. Surface roughness sometimes occurred.
An object of the present invention is an elastic rubber product made of a microfoamed crosslinked rubber composition containing an expanded capsule, and has a low specific gravity of less than 1.00, a suppressed surface roughness, etc., and an excellent appearance. It is to provide a rubber composition that can be efficiently produced with high productivity, a crosslinked rubber product, and a method for producing the same.

The inventors have made a test piece containing rubber, a thermally expandable microcapsule that expands in volume by heating, and a crosslinking agent under conditions of a temperature of 180 ° C., a frequency (vibration frequency) of 100 cpm, and an amplitude angle of 0.5 degrees. When a test is performed in which the cross-linking reaction and the volume expansion of the thermally expandable microcapsule are progressed by heat treatment, the time t ₁ when the test piece expands to show the maximum pressure by the heat treatment and JIS K6300- Injection molding using an uncrosslinked rubber composition having a time difference Δt (= t ₂ −t ₁ ) of 1.0 to 4.5 minutes with respect to the time t ₂ at the optimum crosslinking point defined in 2. As a result, it is possible to efficiently produce a crosslinked rubber product having a fine foamed state slightly expanded from the shape of the cavity of the mold, a specific gravity as low as less than 1.00, suppressing surface roughness, etc., and having excellent appearance. From being able to book Which resulted in the completion of the Akira. The finely foamed state means that the upper limit of the volume-based expansion coefficient of the crosslinked rubber composition relative to the uncrosslinked rubber composition is 15%.

The present invention is shown below.
1. In a rubber composition containing rubber and thermally expandable microcapsules that expand in volume by heating,
The content of the thermally expandable microcapsule is 1.5 to 10.7 parts by mass with respect to 100 parts by mass of the rubber.
An uncrosslinked test piece made of a rubber composition containing the rubber, the thermally expandable microcapsule, and a crosslinking agent is heat-treated under conditions of a temperature of 180 ° C., a frequency of 100 cpm, and an amplitude angle of 0.5 degrees. When a test for advancing the cross-linking reaction and the volume expansion of the thermally expandable microcapsules was performed, the time t ₁ when the test piece expanded to show the maximum pressure due to the heat treatment, and JIS K6300-2 A rubber composition characterized in that a time difference Δt (= t ₂ −t ₁ ) with respect to a time t ₂ at the specified optimum crosslinking point is 1.0 to 4.5 minutes.
2. Item 2. The rubber composition according to Item 1, wherein the thermal expansion microcapsule has a maximum expansion temperature of 140 ° C or higher.
3. Item 3. The rubber composition according to Item 1 or 2, wherein the particle diameter of the thermally expandable microcapsule is 18 to 50 μm.
4). Item 4. The rubber composition according to any one of Items 1 to 3, wherein the thermally expandable microcapsule is obtained by encapsulating a liquid compound in an outer shell made of a thermoplastic resin material.
5). Item 5. The rubber composition according to any one of Items 1 to 4, wherein the rubber comprises ethylene / α-olefin rubber.
6). Furthermore, the rubber composition as described in any one of said claim | item 1 thru | or 5 containing a crosslinking agent.
7). Item 7. The rubber composition according to any one of Items 1 to 6, which is used for injection molding.
8). Item 8. The rubber composition according to Item 6 or 7, wherein the completion time of the crosslinking reaction is 2 to 5 minutes.
9. 7. A crosslinked rubber product produced using the rubber composition according to item 6.
10. Item 10. The crosslinked rubber product according to Item 9, which is a grommet for a wire harness or a rubber bush.
11. A method for producing a crosslinked rubber product, comprising a step of injection molding the rubber composition according to Item 6.

According to the rubber composition of the present invention, by subjecting it to a molding method using heat treatment in the presence of a crosslinking agent, the thermally expandable microcapsules are expanded into a finely foamed state, and the specific gravity is as low as less than 1.00, It is suitable for the production of a crosslinked rubber product that is suppressed in surface roughness and has excellent appearance.
According to the method for producing a crosslinked rubber product of the present invention, it is possible to efficiently obtain a microfoamed crosslinked rubber product having a low specific gravity of less than 1.00, suppressing surface roughness and having excellent appearance, with high productivity. it can. Moreover, since a rubber composition having specific properties is used, mass production of a crosslinked rubber product having a small variation in specific gravity as a whole can be carried out in a short time. Therefore, it is suitable for continuous production by injection molding or the like.

Method for determining the time t ₁ and t ₂ according to the present invention is a schematic diagram showing a. It is the schematic which shows the cord bush which is an example of the crosslinked rubber product of this invention. It is a schematic sectional drawing which shows the articles | goods which integrated the grommet which is the other example of the crosslinked rubber product of this invention with the wire harness. It is a schematic sectional drawing which shows the manufacturing method of the integrated object of FIG.

1. Rubber composition The rubber composition of the present invention is an uncrosslinked composition containing rubber and heat-expandable microcapsules that expand in volume by heating in a specific ratio. The present invention is applied to the production of a crosslinked rubber product by a conventionally known molding method, particularly preferably by injection molding, using a machine, an extruder, a compressor, a roll or the like.

1-1. Rubber This component is preferably an uncrosslinked rubber capable of sulfur vulcanization or peroxide crosslinking, such as natural rubber, butadiene rubber, butadiene rubber containing syndiotactic-1,2-polybutadiene (SPB), Polymers of diene monomers such as SPB-containing natural rubber, isoprene rubber, butyl rubber, chloroprene rubber; acrylonitrile-diene copolymer rubbers such as acrylonitrile-butadiene rubber, nitrile chloroprene rubber, nitrile isoprene rubber; styrene-butadiene Styrene / diene copolymer rubber such as rubber, styrene / chloroprene rubber, styrene / isoprene rubber; Ethylene / α-olefin rubber such as ethylene / α-olefin copolymer rubber, ethylene / α-olefin / diene copolymer rubber Etc. can be used. Of these, ethylene / α-olefin rubbers are preferred, and ethylene / α-olefin / diene copolymer rubbers are particularly preferred from the viewpoints of heat resistance and weather resistance in crosslinked rubber products.

The ethylene / α-olefin / diene copolymer rubber is a terpolymer obtained by copolymerizing ethylene, α-olefin and diene.
Examples of the α-olefin include propylene, 1-butene, 2-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 5-methyl-1-hexene, 1-octene, 1 -Nonene, 5-ethyl-1-hexene, 1-decene, 1-dodecene, 3-methyl-1-butene and the like are mentioned, among which compounds having 3 to 5 carbon atoms are preferable.
The diene is preferably a non-conjugated diene, such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, 3,6-dimethyl- 1,7-octadiene, 4,5-dimethyl-1,7-octadiene, 5-methyl-1,8-nonadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 2, 5-norbornadiene and the like can be mentioned. Of these, 5-ethylidene-2-norbornene is preferred.

The ethylene / α-olefin / diene copolymer rubber constituting the ethylene unit, the α-olefin-derived unit and the diene-derived unit are preferably contained in a proportion of 100% by mass, respectively. Is 50 to 70% by mass, 25 to 50% by mass and 1 to 15% by mass, more preferably 55 to 65% by mass, 30 to 45% by mass and 5 to 12% by mass.

The rubber composition of the present invention may contain only one kind of the rubber or two or more kinds.

1-2. Thermally expandable microcapsules This component is preferably encapsulated in an outer shell made of a resin material, which is an encapsulated substance (a gas or a solid or liquid that evaporates by heating) that increases its occupied volume by heating. Particulate microcapsules.
This thermally expandable microcapsule is preferably a microcapsule that expands in volume when heated to 135 ° C or higher, more preferably 140 ° C or higher, still more preferably 160 ° C to 185 ° C, and particularly preferably 170 ° C to 185 ° C. . The above temperature is generally referred to as “expansion start temperature”. The maximum expansion temperature of the thermally expandable microcapsule is preferably 140 ° C. or higher, more preferably 145 ° C. to 200 ° C., and particularly preferably 150 ° C. to 180 ° C. When the thermally expandable microcapsule having such properties is heated, the encapsulated substance expands in volume and the resin material constituting the outer shell is softened, so that a capsule (expanded capsule) expanded by the internal pressure is obtained. In the present invention, the thermally expandable microcapsule is more preferably one in which a liquid compound is encapsulated inside an outer shell made of a resin material (resin composition).

The liquid compound that is the inclusion substance constituting the thermally expandable microcapsule preferably has a boiling point (atmospheric pressure condition) that is not higher than the softening temperature of the resin material that constitutes the outer shell of the thermally expandable microcapsule. n-butane, isobutane, cyclobutane, n-pentane, isopentane, cyclopentane, n-hexane, 2-methylpentane, 2,2-dimethylbutane, cyclohexane, n-heptane, cycloheptane, n-octane, cyclooctane, etc. Hydrocarbon: Hydrofluoroether compounds such as C ₃ F ₇ OCH ₃ , C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H _{5 and the} like. The liquid compound may be only one type or two or more types. The liquid compound is preferably a hydrocarbon, particularly preferably a low-boiling hydrocarbon having 4 to 5 carbon atoms. The resin material constituting the outer shell is preferably thermoplastic, and acrylonitrile, methacrylonitrile, acrylic acid alkyl ester, methacrylic acid alkyl ester, vinyl chloride, vinylidene chloride, vinyl acetate, aromatic vinyl compound, acrylic resin. Selected from acids, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylamide, substituted acrylamide, methacrylamide, substituted methacrylamide, and polyfunctional compounds having two or more polymerizable carbon-carbon unsaturated bonds It is preferable to contain a thermoplastic resin containing a structural unit derived from at least one kind. Examples of the thermoplastic resin include: polyvinylidene chloride; acrylonitrile-based (co) polymers such as vinylidene chloride / acrylonitrile copolymer and polyacrylonitrile; acrylic (co) polymers such as polymethyl methacrylate; polychlorinated Vinyl etc. are mentioned. Of these, acrylonitrile-based (co) polymers are particularly preferred. The resin material (resin composition) can contain additives such as a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, and a flame retardant.

The shape of the heat-expandable microcapsule is spherical or elliptical, and the particle diameter measured by thermomechanical analysis (TMA) or the like gives an appropriate expansion coefficient and gives a crosslinked rubber product having a good surface skin. Therefore, it is preferably 17 μm or more, more preferably 18 to 50 μm.

The rubber composition of the present invention may contain only one kind of the above heat-expandable microcapsules, or may contain two or more kinds.

The content of the thermally expandable microcapsule contained in the rubber composition of the present invention is 1.5 when the content of the rubber is 100 parts by mass from the viewpoint of the specific gravity and strength of the obtained crosslinked rubber composition. Is 10.7 parts by mass, preferably 1.8-10.5 parts by mass, more preferably 2.0-10.2 parts by mass.

1-3. Other Components The rubber composition of the present invention is a conventionally known compounding agent, such as a crosslinking agent, a crosslinking accelerator, an organic compound, depending on the properties (abrasion resistance, conductivity, etc.) required for the crosslinked rubber product. Contains foaming agents, processing aids, fillers, softeners, anti-aging agents, lubricants, flame retardants, stabilizers, antistatic agents, antibacterial / antifungal agents, slidability improvers, colorants, etc. Good.

Examples of the crosslinking agent include sulfur; sulfur halides; organic peroxides and the like.
Examples of the sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. Examples of the sulfur halide include sulfur monochloride and sulfur dichloride.
Examples of the organic peroxide include benzoyl peroxide, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (benzoylperoxide). Oxy) hexane, di (tert-butylperoxy) diisopropylbenzene, 1,4-bis [(tert-butyl) peroxyisopropyl] benzene, di (tert-butylperoxy) benzoate, tert-butylperoxybenzoate, dic Milperoxide, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, ditert-butyl peroxide, 2,5-dimethyl-2,5-di ( tert-butylperoxy) -3-hexene and the like.

The rubber composition of the present invention may contain only one kind of the above-mentioned crosslinking agent, or may contain two or more kinds.

When the rubber composition of the present invention contains a crosslinking agent, the content thereof is preferably 0.2 to 10 parts by mass when the rubber content is 100 parts by mass from the viewpoint of crosslinking speed. The amount is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 6 parts by mass.

Examples of the crosslinking accelerator include N-cyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolylsulfenamide, N -Sulfenamide compounds such as oxyethylene-2-benzothiazolylsulfenamide, N, N'-diisopropyl-2-benzothiazolylsulfenamide; sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate Dithiocarbamate compounds such as zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, tetramethylthiuram monosulfide, Traethylthiuram monosulfide, tetraisopropylthiuram monosulfide, tetrabutylthiuram monosulfide, tetrabenzylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetraisopropylthiuram disulfide, tetrabutylthiuram disulfide, tetrabenzylthiuram disulfide, tetrakis ( 2-ethylhexyl) thiuram compounds such as thiuram disulfide; 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2- (4′-morpholinodithio) benzothiazole, zinc salt of 2-mercaptobenzothiazole, 2 -Thiazole compounds such as cyclohexylamine salt of mercaptobenzothiazole; 1,3-diphenylguanidi Guanidine compounds such as 1,3-di-o-tolylguanidine and 1-o-tolylbiguanide; thiourea compounds such as diethylthiourea; xanthogenic acid such as sodium isopropylxanthate, zinc isopropylxanthate, zinc butylxanthate System compounds; metal salt of methacrylic acid such as magnesium dimethacrylate and zinc dimethacrylate.

The rubber composition of the present invention may contain only one kind of the above crosslinking accelerator, or may contain two or more kinds. In the present invention, the crosslinking accelerator preferably contains a sulfenamide compound, and a combination of the sulfenamide compound and another crosslinking accelerator such as a thiuram compound or a dithiocarbamic acid compound is particularly preferable. preferable.

When the rubber composition of the present invention contains a crosslinking accelerator, the content thereof is preferably 1 to 10 masses from the viewpoint of scorch stability and crosslinking rate when the rubber content is 100 parts by mass. Part, more preferably 1.5 to 8 parts by weight, still more preferably 2 to 6 parts by weight.
When the crosslinking accelerator is composed of a sulfenamide compound and another crosslinking accelerator such as a thiuram compound or a dithiocarbamic acid compound, the preferred content ratio of the sulfenamide compound and the other crosslinking accelerator is Is as follows. The content of the other crosslinking accelerator is preferably 120 parts by mass or less, more preferably 5 to 110 parts by mass, still more preferably 55 to 105 parts by mass, when the content of the sulfenamide compound is 100 parts by mass. Part.

Examples of the organic blowing agent include 4,4′-oxybis (benzenesulfonylhydrazide), azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, p-toluenesulfonylhydrazide, hydrazodicarbonamide, barium azocarboxyl. Rate and the like.

When the rubber composition of the present invention contains an organic foaming agent, the upper limit of the content gives a crosslinked rubber product having a good surface skin, so when the rubber content is 100 parts by mass, Preferably it is 1.0 mass part, More preferably, it is 0.7 mass part, More preferably, it is 0.5 mass part.

Examples of the processing aid include zinc oxide; higher fatty acids such as ricinoleic acid, stearic acid, palmitic acid and lauric acid; salts of higher fatty acids such as barium stearate, zinc stearate and calcium stearate; ricinoleic acid, stearic acid and palmitic acid And esters of higher fatty acids such as acid and lauric acid.

Examples of the filler include carbon black, corn starch, calcium carbonate, clay, talc, diatomaceous earth, silica, alumina, aluminum sulfate, barium sulfate, calcium sulfate, basic magnesium carbonate, and aluminum hydroxide.

Examples of the softener include petroleum-based softeners such as process oil, lubricating oil, paraffin and petrolatum; fatty oil-based softeners such as castor oil, linseed oil, rapeseed oil and coconut oil; tall oil; sub; beeswax and carnauba wax Waxes such as lanolin; fatty acids or fatty acid salts such as ricinoleic acid, palmitic acid, barium stearate, calcium stearate, zinc laurate; synthetic polymers such as petroleum resins, atactic polypropylene, coumarone indene resins, etc. .

Examples of the anti-aging agent include naphthylamine compounds, diphenylamine compounds, p-phenyldiamine compounds, quinoline compounds, hydroquinone derivatives, monophenol compounds, thiobisphenol compounds, hindered phenol compounds, and phosphite esters. Compounds and the like.
The above lubricants include paraffin wax, liquid paraffin, paraffin synthetic wax, polyethylene wax, zinc stearate, hydroxystearic acid, fatty acid amide, fatty acid ester, silicone gel, silicone oil, silicone powder, silicone-containing polymer, silicone graft Examples thereof include polymers.

In the present invention, a preferable rubber composition that provides an excellent crosslinked rubber product in the presence of a crosslinking agent includes a rubber containing an ethylene / α-olefin rubber and a thermally expandable microcapsule having a maximum expansion temperature of 140 ° C. to 175 ° C. It is a composition containing these. The crosslinking agent to be used is preferably a crosslinking agent comprising a sulfenamide compound and a thiuram compound.

1-4. Manufacturing method of rubber composition The rubber composition of the present invention can be manufactured by mixing each component according to a conventional method.
A preferable production method includes a step of kneading a rubber and a compounding agent excluding a thermally expandable microcapsule, a crosslinking agent and a crosslinking accelerator (first kneading step), and an obtained kneaded product (hereinafter referred to as “first kneaded product”). And a step of mixing a thermally expandable microcapsule, a crosslinking agent, a crosslinking accelerator, and another compounding agent (mixing step).
In the first kneading step, for example, a Banbury mixer, an intermixer, a kneader or the like can be used.
In the mixing step, the first kneaded product is blended with a heat-expandable microcapsule, a crosslinking agent, and a crosslinking accelerator, and, for example, using an open roll or the like, preferably from the expansion start temperature of the heat-expandable microcapsule. The kneading is carried out at a temperature lower by at least 0 ° C., more preferably at most 100 ° C., further preferably at 60 ° C. to 90 ° C., particularly preferably at 70 ° C. to 80 ° C. It is preferable that the said 1st kneaded material used at this time is what was lowered | hung to 50 degrees C or less. The mixing time in the mixing step is usually 30 seconds to 10 minutes.

1-5. Performance of Rubber CompositionIn the present invention, a rubber composition that forms a crosslinked rubber product having a low specific gravity, reduced surface roughness, etc. and excellent in appearance is prepared by the rubber, thermally expandable microcapsule, and A test piece (uncrosslinked test piece) is prepared using a composition containing a crosslinking agent (hereinafter referred to as “composition (A)”), and the temperature is 180 ° C., the frequency (vibration frequency) is 100 cpm, and the amplitude angle. When this was heat-treated under the condition of 0.5 degree and the cross-linking reaction and the volume expansion of the heat-expandable microcapsule were advanced to form a cross-linked rubber composition, the test piece expanded by this heat treatment. The time difference Δt (= t ₂ −t ₁ ) between the time t ₁ when the maximum pressure is shown and the time t ₂ at the optimum crosslinking point (optimum vulcanization point) defined in JIS K6300-2 is 1.0-4.5 minutes, preferably Is a rubber composition which takes 1.5 to 3.5 minutes, more preferably 2.0 to 2.7 minutes.
The content ratio of the heat-expandable microcapsules and the crosslinking agent contained in the composition (A) is preferably 1.5 to 10.7 parts by mass and 0.2 to 10 parts by mass with respect to 100 parts by mass of the rubber, respectively. Part.
When the composition (A) contains a crosslinking accelerator, the content is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the rubber. As the crosslinking accelerator, the above-exemplified components can be used. When two or more types of crosslinking accelerators are used, a combination of a sulfenamide-based compound and another crosslinking accelerator such as a thiuram-based compound or a dithiocarbamic acid-based compound is preferable. It is.

The above test can be performed using an apparatus to which a method according to JIS K6300-2 can be applied, and times t ₁ and t ₂ are determined based on the curve shown in FIG. The first axis indicates the expansion pressure of an uncrosslinked test piece made of the composition (A). When the heat treatment is started, the crosslinking reaction proceeds gradually, and the thermally expandable microcapsules expand at the initial stage. Then, after the pressure applied to the test piece reaches the maximum at time t ₁ , although the outer shell of some of the expanded capsules ruptures or melts, a slightly foamed crosslinked rubber composition is formed by the expanded capsules, and the expansion pressure Stabilizes. On the other hand, the second axis indicates the torque of the crosslinked rubber composition, and the drawn curve is generally referred to as a “vulcanization curve”. This vulcanization curve, the optimum crosslinking points defined by JIS K6300-2 (optimum pressure硫点), i.e., crosslinked maximum torque (maximum vulcanizing large torque) _{T H} and a crosslinking minimum torque (maximum vulcanizing small torque) and _{T L} the _{T E} is the difference is 100 percent, _{T E} value can be obtained time (tc90) when 90% (90% crosslinked progression rate), to do this and the time _{t 2.} The above Δt can be calculated from the obtained t ₁ and t ₂ .

The rubber composition of the present invention is excellent in productivity of a crosslinked rubber product. For example, the crosslinked rubber product can be produced by injection molding within 6 minutes, preferably within 5 minutes. Therefore, the rubber composition of the present invention is suitable for mass production of crosslinked rubber products.

1-6. Crosslinked rubber composition By subjecting a rubber composition containing a crosslinking agent to a conventionally known heating method or molding method (described later) such as press heating, steam heating, oven heating, hot air heating, etc., a crosslinked rubber composition is obtained. Can be formed.
By heating the rubber composition at a temperature that is preferably 5 ° C. or more higher than the expansion start temperature of the thermally expandable microcapsule, more preferably 5 to 30 ° C., more preferably 10 to 20 ° C. The rubber is three-dimensionally cross-linked by the action of the cross-linking agent. Further, the thermally expandable microcapsule expands to form an expanded capsule, and the expanded capsule is contained in a dispersed state in a matrix made of a crosslinked rubber having a three-dimensional crosslinked structure. Thereby, the crosslinked rubber composition of the fine foaming state which has the outstanding elasticity can be obtained. In the crosslinked rubber composition of the present invention, some of the thermally expandable microcapsules may be ruptured after expansion, but most of the expanded capsules are contained in a substantially uniform size. When the raw rubber composition contains a compounding agent other than the crosslinking agent, this compounding agent is dispersed in a matrix made of a crosslinked rubber having a three-dimensional crosslinked structure.
The average particle diameter of the expanded capsule is preferably 18 to 50 μm.

The specific gravity (according to JIS K6268 A method) of the crosslinked rubber composition is preferably less than 1.00, more preferably 0.92 to 0.99, and still more preferably 0.96 to 0.99.

2. Cross-linked rubber product The cross-linked rubber product of the present invention is an elastic rubber product made of a micro-foamed cross-linked rubber composition containing expanded capsules, which is produced using a rubber composition containing a cross-linking agent. The shape of the crosslinked rubber product of the present invention can be determined according to the purpose, application and the like. The shape of the crosslinked rubber product can be a simple shape such as a plate, a rod, or a cylinder, or a complex shape having a through hole, unevenness, curved surface, thin portion, thick portion, and the like. Since the crosslinked rubber product of the present invention uses the rubber composition of the present invention as a raw material for production, when an injection molding machine, an extruder, a compressor, a roll, or the like is used, surface roughness is suppressed and the appearance is improved. An excellent low specific gravity crosslinked rubber product with a smooth skin.

Examples of the crosslinked rubber product of the present invention include rubber bushes such as cord bushes, grommets, weather strips, glass runs, side moldings, flush mount moldings, sealing materials, and the like. Of these, preferred embodiments are rubber bushes and grommets.

The rubber bush is a component that is disposed between members or that holds or fixes a linear member or the like. 2A and 2B illustrate a cylindrical cord bush 10 as a rubber bush. FIG. 2A is a plan view (top view), FIG. 2B is a sectional view (longitudinal sectional view), and FIG. 2C is a side view. (Code insertion part side).

The cord bush 10 in FIG. 2 includes a cord insertion portion 14 into which a cord to be held is inserted at one end side, and the cord inserted from the cord insertion portion 14 side at the other end side is an outer peripheral surface of the cord by its own elasticity. A cord holding portion 18 that is elastically deformed so as to be fastened. Further, the cord insertion portion 14 side and the cord holding portion 18 side are hermetically separated from the inner peripheral surface of the cord bush 10 and elastically deformed so that the inserted cord is fastened to the outer peripheral surface of the cord by its own elasticity. Thus, the valve portion 16 for improving the cord retention is provided. 2 is provided with a flange portion 12 having a roundness.

The grommet is an annular part having a through hole to be fitted into the opening of the object. FIG. 3 illustrates a grommet in which the outer periphery of the large-diameter cylindrical portion 28 is inscribed in an opening formed in a panel (not shown), and the grommet 24 in which the wire harness 22 is fitted in the through hole is illustrated. FIG. In FIG. 3, the integrated object 20 which consists of the wire harness part 22 and the grommet part 24 is shown.

3. Method for Producing Crosslinked Rubber Product The method for producing the crosslinked rubber product is not particularly limited, and may be a method using an injection molding machine, an extruder, a compressor, a roll, or the like. In particular, a method using an injection molding machine capable of performing mass production continuously in a short time is suitable, and the method for producing a crosslinked rubber product according to the present invention includes injection molding of the rubber composition of the present invention containing a crosslinking agent. The process of carrying out is provided.
The processing temperature of the rubber composition when producing the crosslinked rubber product is appropriately selected according to the type of rubber, the expansion start temperature of the thermally expandable microcapsule, etc., but the surface roughness of the crosslinked rubber product is suppressed. Therefore, the temperature is preferably 5 ° C. or more higher than the expansion start temperature of the thermally expandable microcapsule, more preferably 5 ° C. to 30 ° C., and still more preferably 10 ° C. to 20 ° C. The heating time (crosslinking reaction completion time) is preferably 2 to 5 minutes, more preferably 2 to 3.5 minutes. That is, the molding time in the injection molding process is preferably 1 to 6 minutes, more preferably 2 to 5 minutes, and further preferably 2 to 3.5 minutes.
In the present invention, a crosslinked rubber product having a smooth surface and excellent appearance can be obtained by an injection molding process. However, the production method of the present invention can be applied to the surface of a molded product as necessary after the injection molding process. Or the finishing process etc. of removing the unnecessary part in an edge part etc. can be provided.

Hereinafter, a method of manufacturing the integrated product 20 of the wire harness 22 and the grommet 24 shown in FIG. 3 by injection molding will be described with reference to FIG.

FIG. 4 is a schematic cross-sectional view of an injection mold 30 including a first mold 32 and a second mold 34, and is a view in which the wire harness 22 is disposed and the mold is closed. The remaining space in the mold after the wire harness 22 is arranged becomes a cavity 38 for the grommet 24.
First, the mold 30 for injection molding was formed above the first mold 32 at a temperature higher by 5 ° C. or more, more preferably by 10 ° C. to 20 ° C. than the expansion start temperature of the thermally expandable microcapsule. A fluid rubber composition heated to a temperature of 100 ° C. to 120 ° C. is supplied from the raw material introduction hole 36 to fill the cavity 38. This state is preferably maintained for 1 to 6 minutes, more preferably 2 to 5 minutes, and further preferably 2 to 3 minutes. Next, after the temperature of the injection mold 30 is set to 160 ° C. to 185 ° C., the mold is opened, and the integrated product 20 including the wire harness portion 22 and the grommet portion 24 is discharged.
Since the grommet portion 24 in the obtained integrated product 20 includes the expanded capsule, the grommet portion 24 is in a finely foamed state and is larger in size than the cavity 38. The expansion rate based on volume is usually 5 to 10%.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In the following, “part” is based on mass unless otherwise specified.

1. 1. Production and evaluation of rubber composition 1-1. Raw material components The raw material components used in the production of the rubber composition are as follows.
1-1-1. Rubber EPDM “EP57F” (trade name) manufactured by JSR Corporation was used.
1-1-2. Thermally expandable microcapsules (1) M1
A thermally expandable microcapsule “Matsumoto Microsphere FN-78D” (trade name) manufactured by Matsumoto Yushi Seiyaku Co., Ltd. was used. The expansion start temperature is 100 ° C. to 120 ° C., the maximum expansion temperature is 150 ° C. to 165 ° C., and the particle size is 35 to 50 μm.
(2) M2
Thermally expandable microspheres “ADVANCELL EMH204” (trade name) manufactured by Sekisui Chemical Co., Ltd. were used. The expansion start temperature is 115 ° C. to 125 ° C., the maximum expansion temperature is 165 ° C. to 175 ° C., and the particle size is 38 to 44 μm.
(3) M3
Thermally expandable microspheres “ADVANCEL EMH302” (trade name) manufactured by Sekisui Chemical Co., Ltd. were used. The expansion start temperature is 130 ° C. to 140 ° C., the maximum expansion temperature is 160 ° C. to 170 ° C., and the particle size is 18 to 24 μm.
(4) M4
A thermally expandable microcapsule “Matsumoto Microsphere FN-180D” (trade name) manufactured by Matsumoto Yushi Seiyaku Co., Ltd. was used. The expansion start temperature is 140 ° C. to 155 ° C., the maximum expansion temperature is 175 ° C. to 185 ° C., and the particle size is 35 to 45 μm.

1-1-3. Cross-linking agent Sulfur “Jinhua stamp fine powder sulfur 200 mesh” (trade name) manufactured by Tsurumi Chemical Co., Ltd. was used.
1-1-4. Cross-linking accelerator (1) A1
N-cyclohexyl-2-benzothiazolylsulfenamide “Noxeller CZ-G” (trade name) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.
(2) A2
Tetramethylthiuram disulfide “Noxeller TT-P” (trade name) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.
(3) A3
Tetraethylthiuram disulfide “Noxeller TT-G” (trade name) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.
(4) A4
Zinc dibutyldithiocarbamate “Noxeller BZ-P” (trade name) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd. was used.
(5) A5
Zinc dimethyldithiocarbamate “Noxeller PZ” (trade name) manufactured by Ouchi Shinsei Chemical Co., Ltd. was used.

1-1-5. Organic foaming agent 4,4′-oxybis (benzenesulfonylhydrazide) “Neocerbon N # 1000S” (trade name) manufactured by Eiwa Chemical Industry Co., Ltd. was used.
1-1-6. Filler (1) F1
Carbon black “Asahi # 60” (trade name) manufactured by Asahi Carbon Black was used.
(2) F2
Calcium carbonate “Super SS” (trade name) manufactured by Maruo Calcium Co., Ltd. was used.
1-1-7. Softening agent Process oil “Fukor process P400” (trade name) manufactured by Fuji Kosan Co., Ltd. was used.
1-1-8. Lubricant Ultra high molecular weight silicone polymer “BY27-002” (trade name) manufactured by Toray Dow Corning Silicone Co., Ltd. was used.

1-2. Production and Evaluation of Rubber Composition Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4
Using the raw material components in the quantitative ratios shown in Table 1, rubber compositions C1 to C14 were produced in the following manner.
Using a kneader “1.7L MIXTRON BB mixer” (trade name) manufactured by Kobe Steel, rubber was kneaded under conditions of a temperature of 100 ° C. and a rotation speed of 60 rpm, and then a thermally expandable microcapsule, a crosslinking agent, and a crosslinking accelerator. The compounding agent except the agent was added and kneading was continued under the same conditions as described above. And it knead | mixed further on the conditions of temperature 50 degreeC, front side rotational speed 22rpm, and rear side rotational speed 20rpm using the Kansai roll company mixing roll machine, and prepared the 1st kneaded material.
Next, the first kneaded product, the thermally expandable microcapsule, the cross-linking agent, and the cross-linking accelerator are kneaded under the same conditions as described above using a mixing roll machine manufactured by Kansai Roll Co. A sheet made of material was obtained.
Thereafter, this sheet was cut into a 5-gram test piece, and a crosslinking test was performed using a Rubber Process Analyzer “RPA2000” (model name) manufactured by Alpha Technologies. The measurement conditions are a temperature of 180 ° C., a frequency (vibration frequency) of 100 cpm, and an amplitude angle of 0.5 degrees. This measurement to obtain a graph as shown in FIG. 1, the computer processing, obtain the _{t 1} and _{t 2,} further wherein: the Delta] t ₌ t 2 -t _1, to obtain a Delta] t (see Table 1).

Further, using a rubber composition as a molding material, a heated press apparatus “37T press” (trade name) manufactured by Iwaki Kogyo Co., Ltd. was used for processing at a temperature of 180 ° C. and a pressure of 16 MPa to obtain a crosslinked rubber sheet having a thickness of 2 mm. It was. Then, this crosslinked rubber sheet was visually observed, and the following criteria were used to determine whether or not there was residue on the surface due to the rupture of the expanded capsule and whether there was rough skin (see Table 1).
(1) Foam residue adhering to the surface ○: None △: Slightly observed ×: Seen in large quantities (2) Roughness of the surface skin ○: Smooth △: Slightly rough ×: Rough The

Furthermore, a grommet for a wire harness was continuously produced by injection molding using the rubber composition as a molding material under the conditions of a temperature of 180 ° C. and a time of 90 to 360 seconds. The cycle time at this time was measured, and the productivity was determined according to the following criteria.
○: 1.5 to 3.5 minutes Δ: 3.6 to 5.0 minutes ×: 5.0 minutes exceeded

2. Production and Evaluation of Crosslinked Rubber Products Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-4
Rubber compositions C1 to C10 and C11 to C14 were respectively subjected to injection molding to produce grommets. Specifically, in the configuration shown in FIG. 4, a part of the wire harness 22 is disposed so as to be exposed to the cavity 38 formed by the molds 32 and 34, and the cavity 38 is extruded. A rubber composition heated to 80 ° C. by a machine and brought into a fluidized state is supplied from the raw material introduction hole 36 of the injection mold 30 set at 180 ° C. (injection time 9 to 12 seconds) to fill the cavity 38 It was. After 160 seconds, the injection mold 30 was opened. The integrated object 20 which consists of the wire harness part 22 and the grommet part 24 was obtained by the above operation. The grommets 24 obtained in Examples 2-1 to 2-10 had an expansion coefficient of 5 to 10% with respect to the cavity 38 on the volume basis.

In Comparative Example 2-1 using the rubber composition C11, since Δt exceeded 4.5 minutes, the specific gravity was 1.00, the cycle time exceeded 5 minutes, and the productivity was insufficient. In Comparative Examples 2-2 to 2-3 using the rubber compositions C12 and C13, a grommet portion 24 having a high specific gravity and having foam residue attached to the surface was obtained. In Comparative Example 2-4 using the rubber composition C14, although the specific gravity was low, a grommet portion 24 having a poor surface skin was obtained. On the other hand, in the grommets 24 of Examples 2-1 to 2-10 obtained by using the rubber compositions C1 to C10, such defects were not observed and the appearance was good.

The rubber composition of the present invention is suitable for production of general and industrial crosslinked rubber products. For example, members for vehicles such as grommets, weather strips, glass runs, side moldings, flush mounting moldings; rubbers such as cord bushes Bush; particularly suitable for the production of sealing materials and the like.

10: Cord bush, 12: Flange part, 14: Cord insertion part, 16: Valve part, 18: Cord holding part, 20: Integrated product of wire harness and grommet, 22: Wire harness (part), 24: Grommet (part) ), 26: small diameter cylindrical part, 28: large diameter cylindrical part, 30: injection mold, 32: first mold, 34: second mold, 36: raw material introduction hole, 38: cavity

Claims

In a rubber composition containing rubber and thermally expandable microcapsules that expand in volume by heating,
The content of the thermally expandable microcapsule is 1.5 to 10.7 parts by mass with respect to 100 parts by mass of the rubber.
An uncrosslinked test piece made of a rubber composition containing the rubber, the thermally expandable microcapsule, and a crosslinking agent is heat-treated under conditions of a temperature of 180 ° C., a frequency of 100 cpm, and an amplitude angle of 0.5 degrees. When the cross-linking reaction and the volume expansion of the thermally expandable microcapsule proceed, the time t 1 when the test piece expands to show the maximum pressure by the heat treatment is defined by JIS K6300-2. A rubber composition characterized in that a time difference Δt (= t 2 −t 1 ) with respect to a time t 2 at the optimum crosslinking point is 1.0 to 4.5 minutes.
The rubber composition according to claim 1, wherein the maximum expansion temperature of the thermally expandable microcapsule is 140 ° C or higher.
The rubber composition according to claim 1 or 2, wherein the particle diameter of the thermally expandable microcapsule is 18 to 50 µm.
The rubber composition according to any one of claims 1 to 3, wherein the thermally expandable microcapsules are obtained by encapsulating a liquid compound inside an outer shell made of a thermoplastic resin material.
The rubber composition according to any one of claims 1 to 4, wherein the rubber contains an ethylene / α-olefin rubber.
Furthermore, the rubber composition as described in any one of Claims 1 thru | or 5 containing a crosslinking agent.
The rubber composition according to any one of claims 1 to 6, which is used for injection molding.
The rubber composition according to claim 6 or 7, wherein the completion time of the crosslinking reaction is 2 to 5 minutes.
A crosslinked rubber product produced using the rubber composition according to claim 6.
The cross-linked rubber product according to claim 9, which is a grommet for a wire harness or a rubber bush.
A method for producing a crosslinked rubber product comprising a step of injection molding the rubber composition according to claim 6.