JP5550819B2 - Manufacturing method of foamed rubber sheet - Google Patents

Description

  The present invention relates to a method for producing a foamed rubber sheet that can be suitably used as a gasket.

  Currently, foams are widely used as gaskets in various fields such as architecture, civil engineering, electricity, electronics, and vehicles. Examples of the foam used for such a gasket include a thermoplastic resin foam made of polyethylene resin, polypropylene resin, and the like, and a rubber foam made of synthetic rubber or natural rubber.

  Gaskets are used to fill gaps between various structures and prevent dust and moisture from entering the gaps between structures. This type of gasket is installed in a state in which a gasket made of a foam is compressed in a gap to be sealed, and the repulsive stress closes the gap with the interface to prevent intrusion of dust and moisture. As such a gasket, Patent Document 1 discloses a gasket made of a base made of a foam having elasticity within a predetermined range in hardness and density at 25% compression, and a plastic film fixed to one side of the base. Has been.

  However, since the gasket has an open cell structure, there has been a problem that it is impossible to prevent the intrusion of dust and moisture through the open cell.

  On the other hand, in recent years, particularly in the electric and electronics fields, lightweight, thinning, and miniaturization are rapidly progressing, and a thin gasket is required. However, since the rubber-based polymer has a high viscosity, it is difficult to reduce the thickness of the sheet in extrusion molding, and there is a limit to thinning the foamed rubber sheet.

  In addition, there is a method of thinning the molded foam rubber sheet by slicing, but sufficient thickness accuracy as a gasket cannot be secured, or the cross section of the bubble is exposed by slicing and the surface smoothness is lost. Therefore, it was not able to withstand practical use as a gasket.

JP 2001-100216 A

The present invention provides a method of manufacturing a sparkling Gomushi bets can be suitably used as a thin gasket thickness.

  The foamed rubber sheet of the present invention is characterized by containing a rubber-based polymer and having a skin layer formed on both sides and having a thickness of 0.2 to 1 mm.

  The rubber-based polymer is not particularly limited as long as it has rubber elasticity at room temperature, and examples thereof include natural rubber, synthetic rubber, and thermoplastic elastomer.

  Examples of the synthetic rubber include chloroprene rubber (CR), isoprene rubber (IR), butyl rubber (IIR), nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), urethane rubber, Fluorine rubber, acrylic rubber, silicone rubber and the like can be mentioned, and nitrile-butadiene rubber (NBR) is preferable. Examples of the thermoplastic elastomer include polystyrene-based thermoplastic elastomers and polyolefin-based thermoplastic elastomers.

The rubber-based polymer needs to be foamed by being foamed by stirring while blowing gas and finely dispersing the gas in the rubber-based polymer. More preferably, it is liquid at atmospheric pressure (1.01 × 10 ⁵ Pa) and 23 ° C. However, even if the rubber-based polymer is not liquid at 1 atm and 23 ° C., it is only necessary that the rubber-based polymer is softened by heating to ensure fluidity.

In addition, as a rubber-based polymer which is liquid at 1 atm (1.01 × 10 ⁵ Pa) and 23 ° C., liquid NBR (trade name “N280” manufactured by JSR Corporation), liquid butadiene rubber (trade name manufactured by Nippon Soda Co., Ltd.) “NISSO-PB”), liquid isoprene rubber (trade name “Kuraprene” manufactured by Kuraray Co., Ltd.) and the like are commercially available.

  The rubber polymer preferably has a radical polymerizable unsaturated double bond in the molecule. Thus, by having a radically polymerizable unsaturated double bond in the rubber-based polymer, as described later, the crosslinking efficiency at the time of crosslinking of the rubber-based polymer by irradiation with ionizing radiation or ultraviolet rays is improved. be able to. As a result, the foamed rubber sheet obtained is less likely to cause bubble breakage and bubble coalescence, and the stability of the bubbles is improved.

A skin layer is formed on both surfaces of the foam rubber sheet. This skin layer is a non-foamed layer having an apparent density of 500 kg / m ³ or more measured according to JIS K7222.

  This skin layer is not foamed as described above, and there is no bubble cross section on the surface. Therefore, when the foamed rubber sheet is used as a gasket, the skin layer of the foamed rubber sheet adheres to a member to be sealed such as a structure without a gap, and the foamed rubber sheet exhibits excellent sealing properties.

  If the total thickness of the foamed rubber sheet is thin, when the foamed rubber sheet is used as a gasket, the followability and adhesion to the sealed member of the gasket will be reduced, and if it is thick, the foamed rubber sheet will recover its shape from the compressed state. Since the structure is deformed by the repulsive stress, and the gap between the structures is enlarged by the deformation of the structure, it is limited to 0.2 to 1 mm, and preferably 0.2 to 0.5 mm.

  If the thickness tolerance of the foamed rubber sheet is large, a gap may be generated between the sealed member such as a structure and the gasket when used as a gasket, which can sufficiently prevent the intrusion of dust and moisture. Since there is a possibility that it cannot be performed, ± 10% or less is preferable. In addition, the thickness tolerance of a foamed rubber sheet means what was measured based on JISK7676.

When the apparent density measured in accordance with JIS K7222 in the foamed rubber sheet is low, the foamed rubber sheet is brittle and the dimensional stability is lowered, so the workability is lowered and the workability is lowered, or as a gasket When used, the long-term sealability may decrease, and if it is high, the foamed rubber sheet is hard, the compression flexibility decreases, the repulsive force during compression increases, and when used as a gasket, Since a member to be sealed such as a structure may be deformed or the gap of the portion to be sealed may be enlarged due to deformation of the member to be sealed, 50 to 500 kg / m ³ is preferable. The apparent density of the foam rubber sheet refers to that measured based on JIS K7222.

  Further, if the 50% compressive stress measured by a method according to JIS K6767 in a foamed rubber sheet is high, the foamed rubber sheet has insufficient flexibility, and when used as a gasket, the shape of the member to be sealed is sufficient. In some cases, there is a gap between the part to be sealed and this may cause a sealing failure.If it is low, the foamed rubber sheet is brittle and the dimensional stability cannot be maintained, so the workability is poor. When it is used as a gasket, the long-term sealability may be deteriorated, so 20 to 200 kPa is preferable.

  Next, the manufacturing method of the said foamed rubber sheet is demonstrated. The method for producing the foamed rubber sheet is not particularly limited, but when the rubber-based polymer is in a liquid state, it remains as it is, and when the rubber-based polymer is in a solid state, it is heated to have a fluid state. The gas is mixed and finely dispersed in the rubber polymer by mechanically (physically) stirring while blowing the gas into the rubber polymer.

  The stirring device that mechanically stirs while blowing gas into the rubber polymer is not particularly limited, and the rubber polymer and gas are supplied to the stirring unit by a metering pump, and the rubber polymer and gas are mixed in the stirring unit. A mixer that stirs and mixes the mixture is included. Such a stirrer is, for example, a stirrer commercially available from Chilling Industries Co., Ltd. under the trade name “Vibro Mixer” or a stirrer commercially available from Primix Co., Ltd. under the trade name “Pipeline Homomixer”. Etc. are preferable.

  The gas blown into the rubber-based polymer is preferably a gas that does not interfere with the crosslinking of the rubber-based polymer by ionizing radiation or ultraviolet rays described later, and examples thereof include inert gases such as nitrogen gas, helium gas, neon gas, and argon gas. Nitrogen gas is preferred because it is inexpensive and can be used easily.

  Furthermore, the foaming ratio of the foamed rubber sheet finally obtained can be adjusted by adjusting the volume of the gas blown into the rubber-based polymer. In addition, when the stirring part of the stirring device is not a closed system, a part of the blown gas may be dispersed in the atmosphere without being dispersed in the rubber-based polymer, so determine the volume of the blown gas. In this case, it is necessary to consider the capacity for the gas to diffuse into the atmosphere.

  The bubble size (maximum diameter) of the gas dispersed in the rubber polymer can be adjusted by the stirring speed, the stirring time and the viscosity of the rubber polymer. If the rubber polymer is sufficiently stirred after the gas is blown, a foamed rubber polymer having a uniform cell size can be obtained.

  Then, the above-mentioned foamed rubber-based polymer is applied to the release treatment surface of the release sheet that has been subjected to the release treatment on one surface so as to have a thickness of 0.2 to 1 mm. Thereafter, the foamed rubber sheet can be obtained by irradiating the rubber-based polymer with ionizing radiation or ultraviolet rays to cross-link the rubber-based polymer. The coating apparatus for applying the rubber-based polymer to the release treatment surface of the release sheet is not particularly limited as long as the rubber-based polymer can be applied thinly. Examples thereof include a die coater, a roll coater, and a knife coater. It is done. The release sheet is not particularly limited, and examples thereof include those obtained by performing release treatment such as silicone treatment on one surface of paper or a synthetic resin sheet.

  Moreover, you may manufacture a foamed rubber sheet in the following ways other than the said manufacturing method. Two release sheets having a release treatment on one surface are prepared, and the two release sheets are arranged in a state where these release treatment surfaces face each other and have an interval of 0.2 to 1 mm. And the above-mentioned foamed rubber-based polymer is supplied between the two release sheets. Thereafter, the foamed rubber sheet can be obtained by irradiating the rubber-based polymer with ionizing radiation or ultraviolet rays to cross-link the rubber-based polymer. In addition, although the same thing as the above-mentioned is used as a release sheet, at least one release sheet needs to be able to permeate | transmit ionizing radiation or an ultraviolet-ray.

  The ionizing radiation is not particularly limited, and examples thereof include electron beams, α rays, β rays, γ rays, and electron beams are preferable. If the irradiation amount of ionizing radiation is small, the crosslinking of the rubber-based polymer may be insufficient and bubbles may be broken or bubbles may be coalesced. Since the rubber-based polymer may be deteriorated too much, 0.1 to 3 Mrad is preferable.

Moreover, if the irradiation amount of ultraviolet rays is small, the crosslinking of the rubber polymer may be insufficient and bubbles may be broken or bubbles may be united. If the irradiation amount is large, the crosslinking density of the rubber polymer is too high. Since a rubber-type polymer may deteriorate, 300-10000 mJ / cm < ² > is preferable.

  The light source for irradiating ultraviolet rays is not particularly limited. For example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, an excimer laser, a chemical lamp, a black light lamp, a microwave excitation mercury lamp, a metal halide lamp. Sodium lamps, halogen lamps, xenon lamps, fluorescent lamps, sunlight, and the like. These may be used alone or in combination of two or more.

  The foamed rubber sheet thus obtained has skin layers on both sides.

  Moreover, you may contain a photoradical generator in a rubber-type polymer, before making it foam. Such a photo radical generator is not particularly limited. For example, a compound that decomposes by light such as ultraviolet light or visible light to generate a radical, a compound that generates a radical by extracting hydrogen, energy transfer such as electron transfer, and the like. And the like.

  Specifically, the photo radical generator is not particularly limited, and examples thereof include 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, α-hydroxy-α, α′-dimethyl. Acetophenone derivative compounds such as acetophenone, methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, benzoin ether compounds such as benzoin ethyl ether and benzoin propyl ether, ketal derivative compounds such as benzyldimethyl ketal, halogenated ketones, acylphossine Fin oxide, acyl phosphonate, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-N, N-dimethylamino-1- (4 -Morpholinophenyl) -1 Butanone, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, bis (η5-cyclopentadienyl) bis (Pentafluorophenyl) titanium, bis (η5-cyclopentadienyl) bis [2,6-difluoro-3- (1H-py-1-yl) phenyl] titanium, anthracene, perylene, coronene, tetracene, benzanthracene, Phenothiazine, flavin, acridine, ketocoumarin, thioxanthone derivative, benzophenone, acetophenone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, isopropyl Thioxanthone, and the like, may also be alone, or two or more are used alone.

  If the amount of the photo radical generator added to the rubber polymer is small, the photoreactivity of the rubber polymer may not be improved. If it is large, the light transmittance of the rubber polymer will decrease, and the light irradiation surface Since crosslinking occurs only on the surface and the photoreactivity of the rubber-based polymer located deep from the surface may be insufficient, 0.001 to 10 parts by weight is preferable with respect to 100 parts by weight of the rubber-based polymer. 0.01 to 5 parts by weight is more preferable.

  Moreover, you may make the rubber-type polymer contain the compound which has a radically polymerizable unsaturated group before making it foam. Thus, by including the compound having a radical polymerizable unsaturated group, the crosslinking efficiency of the rubber-based polymer by ionizing radiation or ultraviolet rays is improved.

  The compound having a radically polymerizable unsaturated group is not particularly limited. For example, one radically polymerizable double bond such as a styryl group, an acryloyl group, a methacryloyl group, a vinyl ester group, or a vinyloxy group may be present in one molecule or The compound which has 2 or more is mentioned, It may be used independently or 2 or more types may be used together.

  The compound having a styryl group as a radically polymerizable unsaturated group is not particularly limited, and examples thereof include styrene, indene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, p-chloromethylstyrene, and p-methoxy. Styrene, p-tert-butoxystyrene, divinylbenzene and the like can be mentioned, and these may be used alone or in combination of two or more.

The compound having an acryloyl group or a methacryloyl group as a radical polymerizable unsaturated group is not particularly limited, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and n-butyl (meth) acrylate. , Tert-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, isomyristyl (meth) acrylate, Stearyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, glycidyl (Meth) acrylate, tetrahydrofurfuryl (meth) acrylate, hexanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) Acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) ) Acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, 2-hydroxyethyl (meth) Acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxy Hexyl (meth) acrylate, 3-hydroxy-3-methylbutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-[(meth) acryloyloxy] ethyl-2-hydroxyethylphthalic acid, 2 - etc. and [(meth) acryloyloxy] ethyl-2-hydroxypropyl _{phthalate, CH 2 = CH-C (} O) O-CH 2 CH 2 O- [C (O) CH 2 CH 2 CH 2 CH 2 CH _{2 O] n-H (n} = 1~10), CH 2 = C (CH 3) _{-C (O) O-CH 2} CH 2 O- [C (O) CH 2 CH 2 CH 2 CH 2 CH 2 O] n-H (n = 1~10), CH 2 = CH-C (O) _{O- (CH 2 CH 2 O)} n-H (n = 1~12), CH 2 = C (CH 3) -C (O) O- (CH 2 CH 2 O) n-H (n = 1~ _{12), CH 2 = CH-} C (O) O- [CH 2 CH (CH 3) O] n-H (n = 1~12), CH 2 = C (CH 3) -C (O) O- _{[CH 2 CH (CH 3)} O] n-H (n = 1~12), CH 2 = C (CH 3) -C (O) O- (CH 2 CH 2 O) n- [CH 2 CH ( _{CH 3) O] m-H} (n = 1~12), CH 2 = CH-C (O) O- (CH 2 CH 2 O) n- [CH 2 CH (CH 3) O] m-H ( _{n = 1~12), CH 2 =} C (CH 3) -C (O) O- (CH 2 CH 2 O) n- (C _{2 CH 2 CH 2 CH 2 O} ) m-H (n = 1~12), CH 2 = CH-C (O) O- (CH 2 CH 2 O) n- (CH 2 CH 2 CH 2 CH 2 O ) m-H (n = 1~12 ), CH 2 = CH-C (O) O- (CH 2 CH 2 O) n-CH 3 (n = 1~10), CH 2 = C (CH 3) _{-C (O) O- (CH 2} CH 2 O) n-CH 3 (n = 1~30), CH 2 = CH-C (O) O- [CH 2 CH (CH 3) O] n-CH _{3 (n = 1~10), CH} 2 = C (CH 3) -C (O) O- [CH 2 CH (CH 3) O] n-CH 3 (n = 1~10), CH 2 = C _{(CH 3) -C (O)} O- (CH 2 CH 2 O) n- [CH 2 CH (CH 3) O] m-H (n = 1~10), CH 2 = CH-C (O) _{O- (CH 2 CH 2 O)} n- [CH 2 CH (CH 3) O] m-H (n = 1 _{10), CH 2 = CH-} C (O) O- [CH 2 CH (CH 3) O] n-C (O) -CH = CH 2 (n = 1~20), CH 2 = C (CH 3 ) -C (O) O- [CH 2 CH (CH 3) O] n-C (O) -C (CH 3) = CH 2 (n = 1~20), CH 2 = CH-C (O) _{O- [CH 2 CH 2 O]} n-C (O) -CH = CH 2 (n = 1~20), CH 2 = C (CH 3) -C (O) O- [CH 2 CH 2 O] n-C (O) -C ( CH 3) = CH 2 (n = 1~20) , and the like, may be also alone, or two or more are used alone.

  The compound having a vinyl ester group as a radically polymerizable unsaturated group is not particularly limited, and examples thereof include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinyl benzoate, and vinyl cinnamate. Even if it is used independently, 2 or more types may be used together.

  The compound having a vinyloxy group as a radically polymerizable unsaturated group is not particularly limited, and examples thereof include n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, tert-amyl vinyl ether, cyclohexyl vinyl ether, 2- Ethylhexyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2-chloroethyl vinyl ether, ethylene glycol butyl vinyl ether, tritylene glycol methyl vinyl ether, benzoic acid (4-vinyloxy) butyl, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, Tetraethylene glycol divinyl ether, butane-1,4 Diol-divinyl ether, hexane-1,6-diol-divinyl ether, cyclohexane-1,4-dimethanol-divinyl ether, di (4-vinyloxy) butyl isophthalate, di (4-vinyloxy) butyl glutarate, succinic acid Di (4-vinyloxy) butyl, trimethylolpropane trivinyl ether, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 6-hydroxyhexyl vinyl ether, cyclohexane-1,4-dimethanol-monovinyl ether, diethylene glycol monovinyl ether, 3- Examples include aminopropyl vinyl ether, 2- (N, N-diethylamino) ethyl vinyl ether, urethane vinyl ether, and polyester vinyl ether. Or more may be used in combination.

  Among the compounds having the above-mentioned radical polymerizable unsaturated group, the radically polymerizable unsaturated group is highly reactive and can efficiently crosslink the rubber-based polymer immediately after irradiation with ionizing radiation or ultraviolet rays. A compound having an acryloyl group or a methacryloyl group is preferably used.

  If the amount of the compound having a radically polymerizable unsaturated group added to the rubber-based polymer is small, the effect of the addition may not be obtained, and if it is large, the rubber-based polymer itself may be inhibited from crosslinking. The amount is preferably 1 to 5 parts by weight per 100 parts by weight of the rubber polymer.

In addition, when the rubber-based polymer has a radically polymerizable unsaturated double bond in the molecule, a compound containing a mercapto group (hereinafter referred to as a “mercapto group-containing compound” is used for the purpose of increasing the crosslinking efficiency by irradiation with ionizing radiation or ultraviolet rays. "there is that) you added.

  The mercapto group-containing compound preferably has two or more mercapto groups that react with radically polymerizable unsaturated double bonds, and has three or more mercapto groups that react with radically polymerizable unsaturated double bonds. More preferably. Examples of the mercapto group-containing compound include trimethylolpropane tris-3-mercaptopropionate, tris-[(3-mercaptopropionyloxy) -ethyl] -isocyanurate, and the like. The polyvalent mercapto group-containing compound is commercially available from Sakai Chemical Industry Co., Ltd. under the trade name “Polythiol”.

  If the amount of the mercapto group-containing compound added to the rubber-based polymer is small, the effect of the addition may not be obtained. If the amount is large, the resulting foamed rubber sheet may be hardened. 1-10 weight part is preferable with respect to a part.

  Furthermore, for the purpose of adjusting the expansion ratio of the foamed rubber sheet, a general-purpose foaming agent is added to the rubber-based polymer before foaming, and in addition to foaming the rubber-based polymer by mechanically stirring and foaming, The rubber-based polymer may be further foamed.

  When the foaming agent is contained in the rubber-based polymer, the foaming of the rubber-based polymer with the foaming agent may be performed at any point in the manufacturing process of the foamed rubber sheet. Since the dimensional stability of the foamed rubber sheet is improved, it is preferable that the foaming agent is decomposed by heating and the rubber-based polymer is foamed with the foaming agent before the rubber-based polymer is crosslinked.

  The foaming agent is not particularly limited as long as it decomposes by heating and generates a foaming gas. For example, azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, 4,4-oxybis ( Benenesulfonyl hydrazide) and the like, and may be used alone or in combination of two or more.

  If the amount of the foaming agent added to the rubber-based polymer is small, the effect of the addition may not be obtained. If the amount is large, the foam-based foam may break down due to decomposition and foaming. 1-3 parts by weight is preferable with respect to 100 parts by weight.

  Furthermore, a general-purpose additive may be added to the foamed rubber sheet for the purpose of adjusting mechanical properties and stability. Examples of the additive include a vulcanization accelerator, a vulcanization retarder, a foaming aid, a crosslinking aid, an antioxidant, a filler, a stabilizer, an ultraviolet absorber, a pigment, a flame retardant, an antistatic agent, a plasticizer, A filler etc. are mentioned.

  Examples of the vulcanization accelerator include aldehyde ammonias, aldehyde amines, guanidines, thiazoles, sulfenamides, turums, dithiocarbamic acids, xanthogenic acids, thioureas and the like.

  Examples of the vulcanization retarder include organic acids such as phthalic anhydride, benzoic acid and salicylic acid, and amines such as N-nitroso-diphenylamine and N-nitroso-phenyl-β-naphthylamine.

  Examples of the plasticizer include acrylic resins such as poly (meth) acrylic acid alkyl esters; paraffins such as chlorinated paraffin; drying oils such as waxes and linseed oil, animal and vegetable oils, petroleum oils, and various types. Low molecular weight resins; phthalic acid esters, phosphoric acid esters, stearic acid and esters thereof, and alkylsulfonic acid esters.

  Examples of the filler include talc, calcium carbonate, bentonite, carbon black, fumed silica, aluminum silicate, acetylene black, and aluminum powder.

  The foamed rubber sheet of the present invention is characterized by containing a rubber polymer and having a skin layer formed on both sides and having a thickness of 0.2 to 1 mm. The skin layer can be adhered to a member to be sealed such as a structure without a gap, and thus the foamed rubber sheet of the present invention exhibits excellent sealing properties when used as a gasket.

  Further, the method for producing a foamed rubber sheet of the present invention comprises foaming by stirring and foaming while blowing a gas into the rubber polymer, and then supplying the rubber polymer onto the release sheet, and ionizing the rubber polymer. Therefore, it is possible to stably produce a foamed rubber sheet having a small thickness and excellent compression flexibility.

  Furthermore, since the foamed rubber-based polymer is supplied onto the release sheet, when the foamed rubber sheet is produced by extrusion molding or calendar molding, the thick foamed rubber sheet is sliced in the thickness direction. Unlike the case of manufacturing, the obtained foamed rubber sheet has small thickness tolerance and excellent thickness accuracy.

And as mentioned above, foaming is carried out by stirring and foaming while blowing gas into the rubber polymer, and the foamed rubber polymer is supplied onto the release sheet, so that the thickness is 0.1 to 1 mm. A foamed rubber sheet having an apparent density of 50 to 500 kg / m ³ despite being thin can be easily obtained.

  And the non-foamed skin layer is formed on both surfaces of the obtained foamed rubber sheet, and there is no cell cross section. Therefore, when the foamed rubber sheet is used as a gasket, the sealed portion Excellent adhesion and exhibits excellent sealing performance.

(Example 1 )
Liquid nitrile-butadiene rubber (trade name “N280” manufactured by JSR Corporation, 1 atmosphere (1.01 × 10 ⁵ Pa), liquid at 23 ° C.) and bis (2,4,6-trimethylbenzoyl) phenylphosphine 3 parts by weight of oxide (trade name “Irgacure 819” manufactured by Ciba Specialty Chemicals) and 6 parts by weight of trimethylolpropane tris-3-mercaptopropionate (trade name “Polythiol TMMP” manufactured by Sakai Chemical Industry Co., Ltd.) were added. Mix evenly.

  Next, while feeding 1.5 times the amount of nitrogen gas into the nitrile-butadiene rubber with respect to the volume of the liquid nitrile-butadiene rubber, the nitrile-butadiene rubber was mechanically agitated using a hand mixer, and the nitrogen was added. The gas was foamed by mixing and finely dispersing the gas in nitrile-butadiene rubber. The stirring and mixing of the liquid nitrile-butadiene rubber and nitrogen gas were performed in a sealed container.

Next, the foamed nitrile-butadiene rubber was coated on the release-treated surface of the release paper so as to have a thickness of 0.25 mm, and then applied to the nitrile-butadiene rubber with a high-pressure mercury lamp (trade name “TOSCURE401” manufactured by Toshiba Lighting & Technology Corp.). ) Was irradiated with 2000 mJ / cm ² of ultraviolet light having a wavelength of 365 nm at an acceleration voltage of 300 eV to crosslink the nitrile-butadiene rubber.

Thereafter, the release paper was peeled off to obtain a foamed rubber sheet having a thickness of 0.25 mm and an apparent density of 390 kg / m ³ . A skin layer having an apparent density of 1000 kg / m ³ and a thickness of 0.01 mm was formed on both surfaces of the obtained foamed rubber sheet. The foam rubber sheet had a thickness tolerance of ± 5% and a 50% compressive strength of 180 kPa.

(Example 2 )
The thickness of the nitrile-butadiene rubber coated on the release-treated surface of the release paper was set to 0.8 mm instead of 0.25 mm, and the ultraviolet irradiation amount was set to 4000 mJ / cm ² instead of 2000 mJ / cm ² . Except that, a foamed rubber sheet having a thickness of 0.8 mm and an apparent density of 376 kg / m ³ was obtained in the same manner as in Example 1 . A skin layer having an apparent density of 1000 kg / m ³ and a thickness of 0.01 mm was formed on both surfaces of the obtained foamed rubber sheet. The foam rubber sheet had a thickness tolerance of ± 2% and a 50% compressive strength of 177 kPa.

(Example 3 )
A thickness of 0.25 mm and an apparent density of 65 kg / m ³ were the same as in Example 1 except that 15 times the amount of nitrogen gas was fed into the liquid nitrile-butadiene rubber with respect to the volume of the liquid nitrile-butadiene rubber. A foamed rubber sheet was obtained. A skin layer having an apparent density of 1000 kg / m ³ and a thickness of 0.005 mm was formed on both surfaces of the obtained foamed rubber sheet. The foam rubber sheet had a thickness tolerance of ± 8% and a 50% compressive strength of 46 kPa.

(Example 4 )
The thickness of the nitrile-butadiene rubber coated on the release-treated surface of the release paper was set to 0.8 mm instead of 0.25 mm, and the ultraviolet irradiation amount was set to 4000 mJ / cm ² instead of 2000 mJ / cm ² . In the same manner as in Example 1 except that 15 times the amount of nitrogen gas was fed into the liquid nitrile-butadiene rubber with respect to the volume of the liquid nitrile-butadiene rubber, the thickness was 0.8 mm and the apparent density was 63 kg / An m ³ foamed rubber sheet was obtained. A skin layer having an apparent density of 1000 kg / m ³ and a thickness of 0.005 mm was formed on both surfaces of the obtained foamed rubber sheet. The foam rubber sheet had a thickness tolerance of ± 4% and a 50% compressive strength of 46 kPa.

(Comparative Example 1)
Nitrile-butadiene rubber (trade name “N222L” manufactured by JSR) 100 parts by weight and azodicarbonamide (trade name “SO-L” manufactured by Otsuka Chemical Co., Ltd.) 8 parts by weight as a foaming agent are supplied to an extruder at 120 ° C. Then, it was melt kneaded and extruded to obtain a foamable rubber sheet having a thickness of 2.0 mm.

Next, the foamed rubber sheet was crosslinked by irradiating the foamed rubber sheet with 0.8 Mrad of an electron beam at an acceleration voltage of 800 keV on both surfaces. Then, the foamed rubber sheet having a thickness of 3.0 mm is cooled by supplying the foamable rubber sheet to a foaming furnace and heating it to 240 ° C. to decompose the azodicarbonamide to foam the foamable rubber sheet and then cooling the foamed rubber sheet. Obtained. By slicing the obtained foamed rubber sheet, a foamed rubber sheet having a thickness of 0.5 mm and an apparent density of 100 kg / m ³ was obtained. The skin layer was not formed on both surfaces of the obtained foamed rubber sheet, and the cell cross section was exposed. The thickness tolerance of the foamed rubber sheet was ± 24%. The 50% compressive strength was 56 kPa.

Claims (4)

After foaming by stirring and foaming while blowing a gas into a rubber polymer containing a compound containing a mercapto group, the rubber polymer is supplied onto a release sheet, and the rubber polymer is charged with ionizing radiation. Or the manufacturing method of the foaming rubber sheet characterized by irradiating with an ultraviolet-ray and bridge | crosslinking.   The method for producing a foamed rubber sheet according to claim 1, wherein the rubber polymer contains a photoradical generator.   The method for producing a foamed rubber sheet according to claim 1 or 2, wherein the rubber-based polymer contains a radically polymerizable unsaturated double bond.   The method for producing a foamed rubber sheet according to any one of claims 1 to 3, wherein the rubber-based polymer is a nitrile-butadiene rubber.