JP6814740B2 - Rubber composition, crosslinked rubber product and its manufacturing method - Google Patents

Description

The present invention is a rubber composition containing a rubber and a heat-expandable microcapsule that expands in volume by heating, and a crosslinked rubber composition in a slightly foamed state containing an expansion capsule obtained by using this rubber composition. The present invention relates to an elastic rubber product comprising a crosslinked rubber product having a low specific gravity and a method for producing the same.

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

JP-A-2007-186559 Japanese Unexamined Patent Publication No. 2008-56748 Japanese Unexamined Patent Publication No. 2009-161587 Japanese Unexamined Patent Publication No. 2011-256223

Since the molded articles in Patent Documents 1 to 4 have a structure in which expanded capsules are dispersed and contained in the vulcanized rubber matrix, the specific gravity is reduced, but only the surface layer becomes hard. Surface roughness may occur.
An object of the present invention is an elastic rubber product made of a crosslinked rubber composition in a slightly foamed state containing an expansion capsule, which has a low specific gravity of less than 1.00, suppresses surface roughness and the like, and has excellent appearance. It is an object of the present invention to provide a rubber composition capable of efficiently producing the product with high productivity, a crosslinked rubber product, and a method for producing the same.

The present inventors put a test piece containing rubber, a heat-expandable microcapsule that expands in volume by heating, and a cross-linking agent under the 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 was conducted in which the cross-linking reaction and the volume expansion of the heat-expandable microcapsules proceeded by heat treatment with the heat treatment, the time t ₁ when the test piece expanded due to the heat treatment and showed the maximum pressure, and JIS K6300- Injection molding is performed using an uncrosslinked rubber composition having a time difference Δt (= t _2- t ₁ ) from the time t ₂ at the optimum cross-linking point specified in 2 of 1.0 to 4.5 minutes. As a result, a crosslinked rubber product having a slightly expanded state slightly expanded from the shape of the cavity of the mold, having a low specific gravity of less than 1.00, suppressing surface roughness, etc., and having excellent appearance is efficiently produced. Since we were able to do so, we have completed the present invention. The slightly foamed state means that the upper limit of the volume-based expansion coefficient of the crosslinked rubber composition with respect to the uncrosslinked rubber composition is 15%.

The present invention is shown below.
1. 1. In a rubber composition containing rubber and heat-expandable microcapsules that expand in volume by heating,
The content of the heat-expandable microcapsules is 1.5 to 10.7 parts by mass with respect to 100 parts by mass of the rubber.
An uncrosslinked test piece composed of a rubber composition containing the rubber, the heat-expandable microcapsules, and a crosslinking agent is heat-treated at a temperature of 180 ° C., a frequency of 100 cpm, and an amplitude angle of 0.5 ° C. When a test was conducted in which the cross-linking reaction and the volume expansion of the heat-expandable microcapsules proceeded, the time t ₁ when the test piece expanded by the heat treatment and showed the maximum pressure, and JIS K 6300-2. A rubber composition characterized in that the time difference Δt (= t _2- t ₁ ) from the time t ₂ at the specified optimum cross-linking point is 1.0 to 4.5 minutes.
2. 2. Item 2. The rubber composition according to Item 1, wherein the maximum expansion temperature of the heat-expandable microcapsules is 140 ° C. or higher.
3. 3. Item 2. The rubber composition according to Item 1 or 2, wherein the heat-expandable microcapsules have a particle size of 18 to 50 μm.
4. The rubber composition according to any one of Items 1 to 3 above, wherein the heat-expandable microcapsules are those in which a liquid compound is encapsulated inside an outer shell made of a thermoplastic resin material.
5. The rubber composition according to any one of Items 1 to 4, wherein the rubber contains an ethylene / α-olefin rubber.
6. The rubber composition according to any one of Items 1 to 5, which further contains a cross-linking agent.
7. The rubber composition according to any one of the above items 1 to 6 used for injection molding.
8. Item 6. The rubber composition according to Item 6 or 7, wherein the completion time of the cross-linking reaction is 2 to 5 minutes.
9. A crosslinked rubber product produced by using the rubber composition according to item 6 above.
10. Item 2. The crosslinked rubber product according to Item 9, which is a grommet or rubber bush for a wire harness.
11. A method for producing a crosslinked rubber product, which comprises a step of injection molding the rubber composition according to the above item 6.

According to the rubber composition of the present invention, the heat-expandable microcapsules are expanded into a slightly foamed state by being subjected to a molding method using heat treatment in the presence of a cross-linking agent, and the specific gravity is as low as less than 1.00. It is suitable for the production of crosslinked rubber products that suppress surface roughness and have excellent appearance.
According to the method for producing a crosslinked rubber product of the present invention, it is possible to efficiently obtain a crosslinked rubber product in a slightly foamed state having a low specific gravity of less than 1.00, suppressing surface roughness and the like and having excellent appearance. it can. Further, since the rubber composition having specific properties is used, mass production of crosslinked rubber products having a small variation in specific gravity as a whole can be advanced in a short time. Therefore, it is suitable for continuous production by injection molding or the like.

It is the schematic which shows the method of determining the time t ₁ and t ₂ which concerns on this invention. It is the schematic which shows the cord bush which is an example of the crosslinked rubber product of this invention. It is schematic cross-sectional view which shows the article which integrated the grommet which is another example of the crosslinked rubber product of this invention with a wire harness. It is the schematic sectional drawing which shows the manufacturing method of the integrated product of FIG.

1. 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, and is injection-molded by blending a cross-linking agent. It is applied to the production of crosslinked rubber products by a conventionally known molding method, particularly preferably 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 sulphurization or peroxide cross-linking, such as natural rubber, butadiene rubber, syndiotactic-1,2-polybutadiene (SPB) -containing butadiene rubber. Polymers of diene-based monomers such as SPB-containing natural rubber, isoprene rubber, butyl rubber, and chloroprene rubber; acrylonitrile-diene copolymer rubber such as acrylonitrile-butadiene rubber, nitrile chloroprene rubber, and 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. Etc. can be used. Of these, ethylene / α-olefin rubber is preferable, and ethylene / α-olefin / diene copolymer rubber is particularly preferable from the viewpoint of heat resistance and weather resistance in crosslinked rubber products.

The ethylene / α-olefin / diene copolymer rubber is a ternary copolymer obtained by copolymerizing ethylene, an α-olefin, and a diene.
Examples of the α-olefin include propylene, 1-butene, 2-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-hexene, 5-methyl-1-hexene, 1-octene, 1 Examples thereof include −nonen, 5-ethyl-1-hexene, 1-decene, 1-dodecene, 3-methyl-1-butene and the like, and among these, compounds having 3 to 5 carbon atoms are preferable.
The diene is preferably a non-conjugated diene, for example, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,7-octadien, 1,9-decadien, 3,6-dimethyl-. 1,7-Octadiene, 4,5-dimethyl-1,7-octadien, 5-methyl-1,8-nonadien, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 2, 5-Norbornene and the like can be mentioned. Of these, 5-ethylidene-2-norbornene is preferred.

The content ratio of the ethylene unit, the unit derived from α-olefin and the unit derived from diene constituting the ethylene / α-olefin / diene copolymer rubber is preferable when the total of these is 100% by mass. 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 type of the above rubber, or may contain two or more types of the rubber.

1-2. Thermally expandable microcapsules This component preferably contains an encapsulating substance (gas, or solid or liquid that evaporates by heating) that increases its occupied volume by heating inside an outer shell made of a resin material. It is a particulate microcapsule.
The heat-expandable microcapsules are microcapsules that expand in volume by heating to preferably 135 ° C. or higher, more preferably 140 ° C. or higher, further 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 heat-expandable microcapsules is preferably 140 ° C. or higher, more preferably 145 ° C. to 200 ° C., and particularly preferably 150 ° C. to 180 ° C. When the heat-expandable microcapsules having such properties are heated, the contained substance expands in volume and the resin material constituting the outer shell softens, so that capsules (expanded capsules) expanded by internal pressure can be obtained. In the present invention, the heat-expandable microcapsules are more preferably those in which a liquid compound is encapsulated inside an outer shell made of a resin material (resin composition).

The liquid compound which is the inclusion substance constituting the heat-expandable microcapsule preferably has a boiling point (atmospheric pressure condition) equal to or lower than the softening temperature of the resin material constituting the outer shell of the heat-expandable microcapsule. n-butane, isopentane, cyclopentane, n-pentane, isopentane, cyclopentane, n-hexane, 2-methylpentane, 2,2-dimethylbutane, cyclohexane, n-heptane, cycloheptane, n-octane, cyclooctane, etc. Hydrocarbons; 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 can be used. The liquid compound may be only one kind or two or more kinds. As the liquid compound, hydrocarbons are preferable, and low boiling point hydrocarbons having 4 to 5 carbon atoms are particularly preferable. The resin material constituting the outer shell preferably has thermoplasticity, and is preferably acrylonitrile, methacrylic acid, alkyl acrylate, alkyl methacrylic acid, vinyl chloride, vinylidene chloride, vinyl acetate, aromatic vinyl compound, and acrylic. Select from acids, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, acrylamide, substituted acrylamide, methacrylic acid, substituted methacrylicamide, 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 of the above. Examples of the thermoplastic resin include polyvinylidene chloride; vinylidene chloride / acrylonitrile copolymer, acrylonitrile-based (co) polymer such as polyacrylonitrile; acrylic (co) polymer such as polymethylmethacrylate; polychloride. Examples include vinyl. Of these, acrylonitrile-based (co) polymers are particularly preferable. The resin material (resin composition) can contain additives such as stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, and flame retardants.

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

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

The content of the heat-expandable microcapsules 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. It is ~ 10.7 parts by mass, preferably 1.8 to 10.5 parts by mass, and more preferably 2.0 to 10.2 parts by mass.

1-3. Other Ingredients The rubber composition of the present invention is a conventionally known compounding agent, such as a cross-linking agent, a cross-linking accelerator, or an organic substance, depending on the properties (wear resistance, conductivity, etc.) required for the cross-linked rubber product. Even if it contains a foaming agent, processing aid, filler, softener, antiaging agent, lubricant, flame retardant, stabilizer, antistatic agent, antibacterial / antifungal agent, slidability improver, colorant, etc. Good.

Examples of the cross-linking agent include sulfur; sulfur halides, and organic peroxides.
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, and 2,5-dimethyl-2,5-di (benzoylper). Oxy) hexane, di (tert-butylperoxy) diisopropylbenzene, 1,4-bis [(tert-butyl) peroxyisopropyl] benzene, di (tert-butylperoxy) benzoate, tert-butylperoxybenzoate, dik Milperoxide, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, tert-butyl peroxide, 2,5-dimethyl-2,5-di ( Examples thereof include tert-butylperoxy) -3-hexane.

The rubber composition of the present invention may contain only one kind of the above-mentioned cross-linking 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 content of the rubber is 100 parts by mass from the viewpoint of the crosslinking rate. It is preferably 0.4 to 8 parts by mass, and more preferably 0.5 to 6 parts by mass.

Examples of the cross-linking accelerator include N-cyclohexyl-2-benzothiazolyl sulfenamide, N-tert-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazolyl sulfenamide, and N. Sulfenamide compounds such as -oxyethylene-2-benzothiazolyl sulfeneamide, N, N'-diisopropyl-2-benzothiazolyl sulfenamide; sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate , Zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate and other dithiocarbamic acid compounds; tetramethylthium monosulfide, tetraethylthium monosulfide, tetraisopropyl thiuram monosulfide, tetra Thiuram compounds such as butyl thiuram monosulfide, tetrabenzyl thiuram monosulfide, tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetraisopropyl thiuram disulfide, tetrabutyl thiuram disulfide, tetrabenzyl thiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide; 2 -Thiazole compounds such as mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2- (4'-morpholinodithio) benzothiazole, 2-mercaptobenzothiazole zinc salt, 2-mercaptobenzothiazole cyclohexylamine salt, etc. Guanidin-based compounds such as 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide; Thiourea-based compounds such as diethylthiourea; Sodium isopropylxanthogenate, zinc isopropylxanthogenate, butyl Xanthogenic acid-based compounds such as zinc xanthogenate; metal methacrylates such as magnesium dimethacrylate and zinc dimethacrylate can be mentioned.

The rubber composition of the present invention may contain only one kind of the above-mentioned cross-linking accelerator, or may contain two or more kinds. In the present invention, the cross-linking accelerator preferably contains a sulfenamide-based compound, and a combination of this sulfenamide-based compound with another cross-linking accelerator such as a thiuram-based compound or a dithiocarbamic acid-based 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 mass by mass when the content of the rubber is 100 parts by mass from the viewpoint of scorch stability and crosslinking rate. Parts, more preferably 1.5 to 8 parts by mass, still more preferably 2 to 6 parts by mass.
When the cross-linking accelerator is composed of a sulfenamide compound and another cross-linking accelerator such as a thiuram compound or a dithiocarbamic acid compound, the preferable content ratio of the sulfenamide compound and the other cross-linking accelerator is , Is as follows. The content of the other cross-linking accelerator is preferably 120 parts by mass or less, more preferably 5 to 110 parts by mass, and further preferably 55 to 105 parts by mass when the content of the sulfenamide compound is 100 parts by mass. It is a department.

Examples of the organic foaming agent include 4,4'-oxybis (benzenesulfonylhydrazide), azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, p-toluenesulfonylhydrazide, hydrazodicarbonamide, and barium azocarboxyde. The rate etc. can be mentioned.

When the rubber composition of the present invention contains an organic foaming agent, the upper limit of the content is to give a crosslinked rubber product having a good surface surface. Therefore, when the content of the rubber is 100 parts by mass, It is preferably 1.0 part by mass, more preferably 0.7 part by mass, and even more preferably 0.5 part by mass.

Examples of the processing aid include zinc oxide; higher fatty acids such as ricinoleic acid, stearic acid, partiminic acid, and lauric acid; salts of higher fatty acids such as barium stearate, zinc stearate, and calcium stearate; ricinoleic acid, stearic acid, and partimine. Examples thereof include 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, aluminum hydroxide and the like.

Examples of the softener include petroleum-based softeners such as process oil, lubricating oil, paraffin and vaseline; fatty oil-based softeners such as castor oil, flaxseed oil, rapeseed oil and palm oil; tall oil; sub; beeswax and carnauba wax. , Lanorin and other waxes; fatty acids or fatty acid salts such as ricinoleic acid, palmitic acid, barium stearate, calcium stearate, zinc laurate; synthetic polymers such as petroleum resin, atactic polypropylene, kumaron inden resin and the like. ..

Examples of the antiaging agent include naphthylamine compounds, diphenylamine compounds, p-phenyldiamine compounds, quinoline compounds, hydroquinone derivatives, monophenol compounds, thiobisphenol compounds, hindered phenol compounds, and phosphite esters. Examples include compounds.
Examples of the lubricant include paraffin wax, liquid paraffin, paraffin-based synthetic wax, polyethylene wax, zinc stearate, hydroxystearic acid, fatty acid amide, fatty acid ester, silicone gel, silicone oil, silicone powder, silicone-containing polymer, and silicone graft. Examples include polymers.

In the present invention, preferable rubber compositions that provide excellent crosslinked rubber products in the presence of a crosslinking agent are rubber containing ethylene / α-olefin rubber and thermally expandable microcapsules having a maximum expansion temperature of 140 ° C. to 175 ° C. It is a composition containing and. The cross-linking agent used is preferably a cross-linking agent composed of a sulfenamide-based compound and a thiuram-based compound.

1-4. Method for Producing Rubber Composition The rubber composition of the present invention can be produced by mixing each component according to a conventional method.
Preferred production methods are a step of kneading rubber with a compounding agent excluding heat-expandable microcapsules, a cross-linking agent and a cross-linking accelerator (first kneading step), and a obtained kneaded product (hereinafter, "first kneaded product"). ”), And a step (mixing step) of mixing the heat-expandable microcapsules, a cross-linking agent, a cross-linking accelerator, and another compounding agent in sequence.
In the first kneading step, for example, a Banbury mixer, an intermixer, a kneader or the like can be used.
In the above mixing step, the first kneaded product is mixed with the heat-expandable microcapsules, the cross-linking agent and the cross-linking accelerator, and for example, using an open roll or the like, preferably 20 from the expansion start temperature of the heat-expandable microcapsules. Kneading is carried out at a temperature lower than ° C., more preferably 100 ° C. or lower, further preferably 60 ° C. to 90 ° C., and particularly preferably 70 ° C. to 80 ° C. The first kneaded product used at this time is preferably cooled to 50 ° C. or lower. The mixing time in the above mixing step is usually 30 seconds to 10 minutes.

1-5. Performance of rubber composition In the present invention, the rubber composition for forming a crosslinked rubber product having a low specific gravity, suppressing surface roughness, etc. and having excellent appearance is a rubber prepared by the above method and a heat-expandable microcapsule. , A test piece (an uncrosslinked test piece) is prepared using a composition containing a cross-linking agent (hereinafter referred to as "composition (A)"), and the temperature is 180 ° C., the frequency (vibration frequency) is 100 cpm, and the amplitude angle is increased. When a crosslinked rubber composition is formed by performing a test in which the crosslinking reaction and the volume expansion of the heat-expandable microcapsules proceed by heat treatment under the condition of 0.5 ° C., the test piece expands by this heat treatment. and the time _{t 1} when the maximum pressure and the optimum crosslinking points defined by JIS K6300-2 (optimum pressure硫点) time difference Δt between the time _{t 2} when the ₍₌ t 2 -t ₁₎ is The rubber composition takes 1.0 to 4.5 minutes, preferably 1.5 to 3.5 minutes, and more preferably 2.0 to 2.7 minutes.
The contents of the heat-expandable microcapsules and the cross-linking agent contained in the composition (A) are preferably 1.5 to 10.7 parts by mass and 0.2 to 10 parts by mass, respectively, with respect to 100 parts by mass of the rubber. It is a department.
When the composition (A) contains a cross-linking accelerator, the content ratio thereof is preferably 1 to 10 parts by mass with respect to 100 parts by mass of rubber. As the cross-linking accelerator, the above-exemplified components can be used. When two or more kinds of cross-linking accelerators are used, it is preferable to use the sulfenamide compound in combination with other cross-linking accelerators such as thiuram compound and dithiocarbamic acid compound, and the ratio of the amount used is as described above. Is.

The above test can be performed using a device to which a method according to JIS K6300-2 can be applied, and the times t ₁ and t ₂ are determined based on the curve shown in FIG. The first axis shows the expansion pressure of the uncrosslinked test piece made of the composition (A). When the heat treatment is started, the cross-linking reaction gradually proceeds, and the thermally expandable microcapsules expand at the initial stage. Then, after the maximum pressure exerted on the test piece at time t _1, although the outer shell of some of the inflation capsule rupture or melt, cross-linked rubber composition of microfoaming state by expansive capsules are formed, the inflation pressure Stabilizes. On the other hand, the second axis shows the torque of the crosslinked rubber composition, and the drawn curve is generally called 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 crosslinked rubber products, and for example, a crosslinked rubber product can be produced within 6 minutes, preferably within 5 minutes by injection molding. Therefore, the rubber composition of the present invention is suitable for mass production of crosslinked rubber products.

1-6. Crosslinked rubber composition A crosslinked rubber composition can be obtained 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, and hot air heating. Can be formed.
By heating the rubber composition at a temperature preferably 5 ° C. or higher, more preferably 5 ° C. to 30 ° C. higher, and further preferably 10 ° C. to 20 ° C. higher than the expansion start temperature of the heat-expandable microcapsules. , The cross-linking agent acts to cross-link the rubber three-dimensionally. Further, the heat-expandable microcapsules expand to become expansion capsules, and the expansion capsules are contained in a dispersed state in a matrix made of crosslinked rubber having a three-dimensional crosslinked structure. Thereby, a crosslinked rubber composition in a slightly foamed state having excellent elasticity can be obtained. In the crosslinked rubber composition of the present invention, some of the heat-expandable microcapsules may rupture after expansion, but most of the expanded capsules are contained in a substantially uniform size. Even when the raw rubber composition contains a compounding agent other than the cross-linking agent, the compounding agent is dispersed in a matrix made of cross-linked rubber having a three-dimensional cross-linked structure.
The average particle size of the expanded capsule is preferably 18 to 50 μm.

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

2. 2. Cross-linked rubber product The cross-linked rubber product of the present invention is an elastic rubber product made of a slightly foamed cross-linked rubber composition containing an expansion capsule, which is produced by using a rubber composition containing a cross-linking agent. The shape of the crosslinked rubber product of the present invention can be adapted to the purpose, application and the like. The shape of the crosslinked rubber product can be a simple shape such as a plate body, a rod body, or a tubular body, or a complicated shape having through holes, irregularities, curved surfaces, thin-walled parts, thick-walled parts, and the like. Since the crosslinked rubber product of the present invention uses the rubber composition of the present invention as a manufacturing raw material, when an injection molding machine, an extruder, a compressor, a roll, or the like is used, surface roughness and the like are suppressed and the appearance is improved. It is an excellent crosslinked rubber product with low specific gravity and has 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, flash mount moldings, and sealing materials. Of these, preferred embodiments are rubber bushes and grommets.

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

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

The grommet is an annular component having a through hole that fits into the opening of an object. FIG. 3 illustrates a grommet 24 in which the outer peripheral portion of the large-diameter tubular portion 28 is inscribed in an opening formed in a panel (not shown), and the wire harness 22 is internally fitted in the through hole. It is a schematic cross-sectional view. FIG. 3 shows an integrated body 20 including a wire harness portion 22 and a grommet portion 24.

3. 3. Method for Producing Crosslinked Rubber Product The method for producing the crosslinked rubber product is not particularly limited, and a method using an injection molding machine, an extruder, a compressor, a roll, or the like can be used. In particular, a method using an injection molding machine capable of continuously mass-producing in a short time is preferable, and the method for producing a crosslinked rubber product in the present invention is an injection molding of a rubber composition of the present invention containing a crosslinking agent. Provide a step to do.
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 heat-expandable microcapsules, etc., but the surface roughness of the crosslinked rubber product is suppressed. Therefore, the temperature is preferably 5 ° C. or higher, more preferably 5 ° C. to 30 ° C. higher, and even more preferably 10 ° C. to 20 ° C. higher than the expansion start temperature of the thermally expandable microcapsules. 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 step is preferably 1 to 6 minutes, more preferably 2 to 5 minutes, and even more 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 the injection molding step, but the manufacturing method of the present invention is the surface of the molded product, if necessary, after the injection molding step. Alternatively, a finishing step such as removing an unnecessary portion at the end portion 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 molding die 30 including the first mold 32 and the second mold 34, in which the wire harness 22 is arranged and the mold is closed. After arranging the wire harness 22, the remaining space in the mold becomes the cavity 38 for the grommet 24.
First, the temperature of the injection molding die 30 was set to be 5 ° C. or higher, more preferably 10 ° C. to 20 ° C. higher than the expansion start temperature of the heat-expandable microcapsules, and was formed above the first mold 32. 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. Then, this state is held for preferably 1 to 6 minutes, more preferably 2 to 5 minutes, and further preferably 2 to 3 minutes. Next, after the temperature of the injection molding die 30 is set to 160 ° C. to 185 ° C., the die is opened and the integrated product 20 composed of the wire harness portion 22 and the grommet portion 24 is discharged.
Since the grommet portion 24 in the obtained integrated product 20 contains an expansion capsule, it is in a slightly foamed state and is larger in size than the cavity 38. The volume-based expansion coefficient 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 heat-expandable microcapsule "Matsumoto Microsphere FN-78D" (trade name) manufactured by Matsumoto Yushi Pharmaceutical 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
A heat-expandable microsphere "ADVANCEL EMH204" (trade name) manufactured by Sekisui Chemical Co., Ltd. was 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
A heat-expandable microsphere "ADVANCEL EMH302" (trade name) manufactured by Sekisui Chemical Co., Ltd. was 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 heat-expandable microcapsule "Matsumoto Microsphere FN-180D" (trade name) manufactured by Matsumoto Yushi Pharmaceutical 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 Tsurumi Chemical Industry Co., Ltd. sulfur "Kinkain fine powder sulfur 200 mesh" (trade name) was used.
1-1-4. Crosslink accelerator (1) A1
N-cyclohexyl-2-benzothiazolyl sulfeneamide "Noxeller CZ-G" (trade name) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. was used.
(2) A2
Tetramethylthiuram disulfide "Noxeller TT-P" (trade name) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. was used.
(3) A3
Tetraethyl thiuram disulfide "Noxeller TT-G" (trade name) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. was used.
(4) A4
Zinc dibutyldithiocarbamate "Noxeller BZ-P" (trade name) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. was used.
(5) A5
Zinc dimethyldithiocarbamate "Noxeller PZ" (trade name) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. was used.

1-1-5. Organic foaming agent 4,4'-oxybis (benzenesulfonyl hydrazide) "Neocerbon N # 1000S" (trade name) manufactured by Eiwa Kasei Kogyo Co., Ltd. was used.
1-1-6. Filler (1) F1
Carbon black "Asahi # 60" (trade name) manufactured by Asahi Carbon Black Co., Ltd. was used.
(2) F2
Calcium carbonate "Super SS" (trade name) manufactured by Maruo Calcium Co., Ltd. was used.
1-1-7. Softener A process oil "Fuccol Process P400" (trade name) manufactured by Fuji Kosan Co., Ltd. was used.
1-1-8. Lubricants An 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 Compositions Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4
The rubber compositions C1 to C14 were produced in the following manner using the above raw material components in the amount ratios shown in Table 1.
After kneading the rubber under the conditions of a temperature of 100 ° C. and a rotation speed of 60 rpm using a kneader "1.7 L MIXTRON BB mixer" (trade name) manufactured by Kobe Steel Co., Ltd., heat-expandable microcapsules, a cross-linking agent and cross-linking promotion The compounding agent excluding the agent was added, and kneading was continued under the same conditions as above. Then, using a mixing roll machine manufactured by Kansai Roll Co., Ltd., the first kneaded product was further kneaded under the conditions of a temperature of 50 ° C., a front rotation speed of 22 rpm and a rear rotation speed of 20 rpm.
Next, the first kneaded product, the heat-expandable microcapsules, the cross-linking agent, and the cross-linking accelerator were kneaded using a mixing roll machine manufactured by Kansai Roll Co., Ltd. under the same conditions as above, and the uncrosslinked rubber composition was obtained. I got a sheet of things.
Then, this sheet was cut into a test piece of 5 grams, and a cross-linking 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, the rubber composition was used as a molding material and processed using a heating press device "37T press" (trade name) manufactured by Iwaki Kogyo Co., Ltd. under the conditions of 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, the crosslinked rubber sheet was visually observed, and it was determined based on the following criteria whether or not there was residue deposits due to the rupture of the expanded capsule and whether or not there was rough skin on the surface (see Table 1).
(1) Foamed residue deposits on the surface ○: None △: Slightly seen ×: Large amount was seen (2) Rough surface skin ○: Smooth △: Slightly rough ×: Rough Ta

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

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

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 2-2-2-3 using the rubber compositions C12 and C13, a grommet portion 24 having a high specific gravity and having foamed residue adhered to the surface was obtained. Further, in Comparative Example 2-4 using the rubber composition C14, a grommet portion 24 having a low specific gravity but a poor surface surface was obtained. On the other hand, in the grommet portion 24 of Examples 2-1 to 2-10 obtained by using the rubber compositions C1 to C10, such a defect was not observed and the appearance was good.

The rubber composition of the present invention is suitable for producing crosslinked rubber products for general use and industrial use, for example, vehicle members such as grommets, weather strips, glass runs, side moldings, flash mount moldings; rubbers such as cord bushes. Bush: Especially suitable for manufacturing sealing materials and the like.

10: Cord bush, 12: Flange part, 14: Cord insertion part, 16: Valve part, 18: Cord holding part, 20: Integrated wire harness and grommet, 22: Wire harness (part), 24: Grommet (part) ), 26: Small diameter cylinder, 28: Large diameter cylinder, 30: Injection molding mold, 32: 1st mold, 34: 2nd mold, 36: Raw material introduction hole, 38: Cavity

Claims (10)

In a rubber composition containing rubber , a heat-expandable microcapsule that expands in volume by heating , a cross-linking agent, and a cross-linking accelerator .
The content of the heat-expandable microcapsules is 1.5 to 10.7 parts by mass with respect to 100 parts by mass of the rubber.
The cross-linking agent is sulfur, and the content of the cross-linking agent is 0.2 to 10 parts by mass with respect to 100 parts by mass of the rubber.
The cross-linking accelerator has the following constitutions (1), (2) or (3).
(1) It is composed of a sulfenamide compound, a dithiocarbamic acid compound and a thiuram compound, and the total content of these compounds is 3.2 to 3.5 parts by mass with respect to 100 parts by mass of the rubber. (2) Sulfenamide-based compound and thiuram-based compound, and these compounds are each contained in 1.0 part by mass with respect to 100 parts by mass of the rubber (3) Sulfenamide-based compound and The rubber is composed of a thiuram compound, and the content of the sulfenamide compound and the thiuram compound is 2.0 parts by mass and 0.1 parts by mass, respectively, with respect to 100 parts by mass of the rubber. An uncrosslinked test piece composed of a rubber composition containing the heat-expandable microcapsules, a cross-linking agent, and a cross-linking accelerator is heat-treated under the conditions of a temperature of 180 ° C., a frequency of 100 cpm, and an amplitude angle of 0.5 degrees. Then, when the cross-linking reaction and the volume expansion of the thermally expandable microcapsules were allowed to proceed, the time t ₁ when the test piece expanded by the heat treatment and showed the maximum pressure, and JIS K 6300-2. A rubber composition, wherein the time difference Δt (= t _2- t ₁ ) from the time t ₂ at the specified optimum cross-linking point is 1.0 to 4.5 minutes. The rubber composition according to claim 1, wherein the maximum expansion temperature of the heat-expandable microcapsules is 140 ° C. or higher. The rubber composition according to claim 1 or 2, wherein the heat-expandable microcapsules have a particle size of 18 to 50 μm. The rubber composition according to any one of claims 1 to 3, wherein the heat-expandable microcapsules are those in which a liquid compound is encapsulated 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. The rubber composition according to any one of claims 1 to 5 , which is used for injection molding. The rubber composition according to any one of claims 1 to 6, wherein the completion time of the cross-linking reaction is 2 to 5 minutes. A crosslinked rubber product produced by using the rubber composition according to any one of claims 1 to 7 . The crosslinked rubber product according to claim 8 , which is a grommet or a rubber bush for a wire harness. A method for producing a crosslinked rubber product, which comprises a step of injection molding the rubber composition according to any one of claims 1 to 7 .

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