JP2009191241A - Crosslinked foamed sheet, laminated crosslinked foamed sheet and method for manufacturing crosslinked foamed sheet or laminated crosslinked foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crosslinked foamed sheet which is excellent in compressive flexibility and the repulsive stress of which is hardly deteriorated even when arranged in a compressed state over a long period of time and to provide a laminated crosslinked foamed sheet and methods for manufacturing the crosslinked foamed sheet and the laminated crosslinked foamed sheet. <P>SOLUTION: The crosslinked foamed sheet comprises a rubber-based resin and has 90-100 wt.% gel fraction. The method for manufacturing the crosslinked foamed sheet of the rubber-based resin comprises the steps of: melting/kneading a foamable resin composition containing a pyrolytic foaming agent and a crosslinking agent; molding the kneaded foamable resin composition into a foamable resin sheet; irradiating the obtained foamable resin sheet with ionizing radiation to crosslink the foamable resin sheet and prepare a foamable crosslinked resin sheet; heating the foamable crosslinked resin sheet to foam the foamable crosslinked resin sheet or foam and then crosslink the foamable crosslinked resin sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a crosslinked foamed sheet, a laminated crosslinked foamed sheet of the above-mentioned crosslinked foamed sheet and a synthetic resin layer, and methods for producing these.

  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, in the above gasket, the foam constituting the gasket has low compression flexibility, so that the structure is deformed by the repulsive stress that the foam tries to recover its shape from the compressed state, or the structure is deformed by the deformation of the structure. There was a problem that the infiltration of dust and moisture could not be prevented because the gap expanded.

  Therefore, a gasket excellent in compression flexibility is required, and an open-cell foam has been proposed as such a gasket. In the open cell foam, gas (air) escapes to the outside of the foam through the communicating portion of the bubbles during compression, so that there is almost no repulsive stress due to the gas (air) and compression flexibility is good.

  However, when the above open cell foam is used as a gasket, there has been a problem that dust and moisture enter through the communicating portion of the bubbles.

  On the other hand, when a closed cell foam in which the bubbles are partitioned by a partition in a three-dimensional lattice shape is used as a gasket, the repulsive stress of the closed cell foam is relieved over time, and the interface between the closed cell foam and the structure is reduced. As a result, the contact surface pressure is reduced and a gap is generated at the interface of the structure, resulting in a problem that it cannot function effectively as a gasket.

JP 2001-100216 A

  The present invention provides a cross-linked foamed sheet and a laminated cross-linked foamed sheet that are excellent in compression flexibility and whose repulsion stress is less likely to be lowered even when placed in a compressed state for a long period of time, and methods for producing these.

  The crosslinked foamed sheet of the present invention is characterized by containing a rubber-based resin and having a gel fraction of 90 to 100% by weight.

  The rubber-based resin constituting the crosslinked foamed sheet is not particularly limited as long as it has rubber elasticity at room temperature. Natural rubber, 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, etc., and crosslinked foam with excellent cushioning and durability In view of obtaining a sheet, chloroprene rubber (CR), butyl rubber (IIR), nitrile-butadiene rubber (NBR), and styrene-butadiene rubber (SBR) are preferable, and nitrile-butadiene rubber (NBR) is more preferable. Nitrile-butadiene rubber (NBR) is also referred to as nitrile rubber or acrylonitrile-butadiene copolymer rubber, and styrene-butadiene rubber (SBR) is a copolymer rubber of styrene and butadiene, also referred to as styrene rubber.

  And when the gel fraction of the crosslinked foamed sheet is low, the value of compression set of the crosslinked foamed sheet is increased, and the shape recoverability of the crosslinked foamed sheet is lowered, so it is limited to 90 to 100% by weight, 95 ~ 100% by weight is preferred.

In addition, the gel fraction of a crosslinked foamed sheet is measured in the following way. Ag is measured for the crosslinked foamed sheet. A good solvent for the polymer compound containing the rubber-based resin constituting the crosslinked foamed sheet is selected. The crosslinked foamed sheet is immersed in a good solvent at 120 ° C. for 24 hours, the insoluble matter is filtered through a 200-mesh wire mesh, the residue on the wire mesh is vacuum-dried, and the weight (Bg) of the dry residue Z ₁ is measured.

  The selection of the good solvent for the polymer compound including the rubber resin may be performed based on the Merck index (Merck Index) published by Merck (USA). For example, good solvents for natural rubber, isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR) include nonpolar hydrocarbon solvents such as hexane, cyclohexane, benzene, and toluene. Since nitrile-butadiene rubber (NBR) has high polarity, methyl ethyl ketone (2-butanone), which is a polar solvent, is a good solvent.

Next, the additive extracted in the good solvent is identified by liquid chromatography, and the total weight (Cg) is measured. Subsequently, the additive contained in the dry residue Z ₁ is again used with the good solvent, and the additive remaining in the dry residue Z ₁ is again heated while heating the good solvent as necessary. Extract into a good solvent. The additive extracted in the good solvent is identified by liquid chromatography, and the total weight (Dg) is measured. Subsequently, the residue Z ₂ after the extraction is burned, and the total weight (Eg) of the inorganic filler remaining after the burning is measured.

Here, when carbon black is contained in the crosslinked foamed sheet, if the residue Z ₂ is burned, the carbon black is also lost. Therefore, separately from the above, a crosslinked foamed sheet of Ag is prepared and this crosslinked foamed sheet is used. The amount of carbon black (Fg) is quantified about the sheet | seat using the thermogravimetric analyzer. The thermogravimetric analyzer is commercially available from Seiko Instruments Inc. under the trade name “EXTRAR6000”.

The gel fraction of the crosslinked foamed sheet can be calculated based on the following formula.
Gel fraction of crosslinked foamed sheet (wt%)
= 100 x (B-D-E-F) / (A-C-D-E-F)

  Furthermore, a crystalline resin and a high softening point resin may be blended in the crosslinked foamed sheet for the purpose of improving moldability and dimensional stability.

  The crystalline resin is not particularly limited, and examples thereof include polyethylene, polypropylene, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl acetate copolymer, and ethylene-vinyl chloride copolymer.

  The high softening point resin is not particularly limited, and examples thereof include rosin resins, terpene resins, petroleum resins, and the like, and terpene resins are preferred from the viewpoint of foamability of the foamable crosslinked resin sheet described later. .

  In addition, the additive may be added to the crosslinked foamed sheet in the range which does not impair the physical property. Such additives include softeners, plasticizers, antioxidants, fillers, stabilizers, UV absorbers, anti-aging agents, pigments, colorants, fungicides, flame retardants, antistatic agents, plasticizers Etc. Specifically, for example, acrylic resins such as poly (meth) acrylic acid alkyl ester, polyvinyl chloride resins such as polyvinyl chloride; paraffins such as chlorinated paraffin, waxes, and dry oils such as linseed oil , Softeners (or plasticizers) such as animal and vegetable oils, petroleum oils, various low molecular weight resins, phthalates, phosphates, stearic acid and its esters, alkyl sulfonates, and tackifiers Agent), talc, calcium carbonate, bentonite, carbon black, fumed silica, aluminum silicate, fillers such as acetylene black and aluminum powder.

  When the compression set of the crosslinked foamed sheet is high, the crosslinked foamed sheet is inferior in shape recoverability, and the long-term water stoppage when used as a gasket may be reduced. 40% or less is more preferable, and 0 to 30% is particularly preferable. The compression set of the crosslinked foamed sheet was measured 24 hours after removing the compressive force by compressing under the conditions of a temperature of 70 ° C., a compression ratio of 50% and a compression time of 22 hours in accordance with JIS K6262. Value.

  Further, if the 50% compression stress measured by the method according to JIS K6767 in the crosslinked foamed sheet is high, the flexibility of the crosslinked foamed sheet becomes insufficient, and the crosslinked foamed sheet is used when the crosslinked foamed sheet is used as a gasket. Since the sheet cannot sufficiently follow the shape of the member to be sealed such as a structure and a gap may be formed between the part to be sealed and cause a sealing failure, 100 kPa or less is preferable, If it is too low, when the crosslinked foamed sheet is used as a gasket, the dust resistance and moisture resistance may be lowered, so 20 to 100 kPa is more preferable.

And when the apparent density of the crosslinked foamed sheet is low, the crosslinked foamed sheet is brittle and the strength cannot be maintained, and when used as a gasket, the long-term water stoppage may be lowered. The foamed sheet is hard, the compression flexibility is reduced, the repulsive force at the time of compression is increased, the workability is deteriorated, and the sealed member such as a structure is deformed when used as a gasket, or Since the gap of the sealed portion may be enlarged due to the deformation of the sealed member, 30 to 200 kg / m ³ is preferable, and 30 to 150 kg / m ³ is more preferable. In addition, the apparent density of a crosslinked foamed sheet says the value measured by the method based on JISK7222.

  Furthermore, if the closed cell ratio of the crosslinked foamed sheet is low, the bubbles of the crosslinked foamed sheet communicate with each other and dust and moisture are likely to pass therethrough, and the dustproofness and moistureproofness may be reduced. Is preferable, and 90 to 100% is more preferable.

In addition, as a method for measuring the closed cell ratio of the crosslinked foamed sheet, first, a test piece having a flat square shape with a side of 5 cm and a constant thickness is cut out from the crosslinked foamed sheet. Subsequently, the weight W ₁ of the test piece is measured, and the thickness of the test piece is further measured to calculate the apparent volume V ₁ of the test piece.

Next, the value obtained as described above is substituted into the following equation (1) to calculate the apparent volume V ₂ occupied by the bubbles. The density of the resin constituting the test piece is ρg / cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ −W ₁ / ρ Formula (1)

Subsequently, the test piece is submerged in distilled water at 23 ° C. so that the distance from the upper surface of the test piece to the water surface is 100 mm, and a pressure of 15 kPa is applied to the test piece for 3 minutes. After that, the test piece is taken out from the distilled water, the water adhering to the surface of the test piece is removed, the weight W _{2 of the} test piece is measured, and the open cell ratio F ₁ is calculated based on the following formula (2). Thus, the closed cell rate F ₂ is obtained from the open cell rate F ₁ .
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂ Formula (2)
Closed cell ratio F ₂ (%) = 100−F ₁ Formula (3)

  Moreover, although the thickness of the said crosslinked foamed sheet is not specifically limited, 0.1-20 mm is preferable and 0.1-5 mm is more preferable in order to be used as a gasket.

  Furthermore, since the crosslinked foamed sheet contains a rubber-based resin, it has adhesiveness, and when the crosslinked foamed sheet is wound into a roll, the crosslinked foamed sheets adjacent to each other in the inner and outer directions are blocked. Therefore, a synthetic resin layer having no adhesiveness may be laminated and integrated on at least one surface of the crosslinked foamed sheet to form a laminated crosslinked foamed sheet.

  The synthetic resin constituting the synthetic resin layer (synthetic resin sheet) is not particularly limited, and examples thereof include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, and ethylene-vinyl acetate. Examples thereof include polyolefin resins such as polymers, and high density polyethylene is preferred.

  In addition, the softening point of the synthetic resin constituting the synthetic resin layer (synthetic resin sheet) is not particularly limited. However, if it is high, the foamability of the foamable laminated crosslinked sheet described later is lowered, and the resulting laminated crosslinked foamed sheet When the laminated crosslinked foamed sheet is used as a gasket due to insufficient flexibility, the laminated crosslinked foamed sheet cannot sufficiently follow the shape of the sealed member, and there is a gap between the sealed part. Since it may cause a sealing failure, 170 ° C. or lower is preferable, and if it is too low, the synthetic resin layer may be softened, which may adversely affect the compression set when used as a gasket. 90-130 degreeC is more preferable.

  When the compression set of the laminated crosslinked foamed sheet is high, the laminated crosslinked foamed sheet is inferior in shape recoverability, and the long-term water stoppage when used as a gasket may be reduced. The following is preferable, 40% or less is more preferable, and 0 to 30% is particularly preferable. The compression set of the laminated crosslinked foamed sheet was measured 24 hours after removing the compressive force after compressing under the conditions of a temperature of 70 ° C., a compression ratio of 50% and a compression time of 22 hours in accordance with JIS K6262. Value.

  Further, if the 50% compressive stress measured by the method according to JIS K6767 in the laminated crosslinked foamed sheet is high, the flexibility of the laminated crosslinked foamed sheet becomes insufficient, and the laminated crosslinked foamed sheet is used as a gasket. The laminated cross-linked foam sheet cannot sufficiently follow the shape of the member to be sealed, and a gap may be formed between the part to be sealed and cause a sealing failure. If it is too high, when the laminated crosslinked foamed sheet is used as a gasket, the dustproof property and moistureproof property may be lowered, so 20 to 100 kPa is more preferable.

  Although the thickness of the said laminated crosslinked foamed sheet is not specifically limited, In order to be used as a gasket, 0.1-20 mm is preferable and 0.1-5 mm is more preferable.

  Further, if the thickness of the synthetic resin layer is thin, tearing may occur at the time of foaming. On the other hand, if it is thick, the 50% compressive stress of the laminated crosslinked foamed sheet may become too high. .

  Furthermore, an adhesive layer may be laminated and integrated on one surface of the crosslinked foamed sheet and the laminated crosslinked foamed sheet. The pressure-sensitive adhesive is not particularly limited, and examples thereof include a urethane-based pressure-sensitive adhesive and a rubber-based pressure-sensitive adhesive. A urethane-based pressure-sensitive adhesive is preferable because it has excellent adhesion and removability.

  Next, the manufacturing method of the crosslinked foamed sheet of this invention is demonstrated. First, a foamable resin composition obtained by adding a crystalline resin, a high softening point resin or an additive as necessary to the rubber-based resin, the pyrolyzable foaming agent, and the crosslinking agent, if necessary, a Banbury mixer, After kneading with a kneader such as a pressure kneader, the temperature is continuously below the decomposition temperature of the pyrolytic foaming agent and below the 1-minute half-life temperature of the crosslinking agent using a calendar, extruder, conveyor belt casting, etc. A foamable resin sheet is formed by melting and kneading in the process.

  The pyrolytic foaming agent contained in the foamable resin composition is not particularly limited, and examples thereof include azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, 4,4-oxybis. (Benzenesulfonyl hydrazide) and the like may be mentioned, and these may be used alone or in combination of two or more.

  And when there is little content of the thermal decomposition type foaming agent in the said foamable resin composition, while the foamable crosslinked resin sheet mentioned later may not foam, when large, when foaming a foamable crosslinked resin sheet, 1 to 30 parts by weight is preferable with respect to 100 parts by weight of the rubber-based resin, and 4 to 20 parts by weight is more preferable.

  Moreover, it does not specifically limit as a crosslinking agent contained in the said foamable resin composition, For example, an organic peroxide, sulfur, a sulfur compound etc. are mentioned, An organic peroxide is preferable. Examples of the organic peroxide include diisopropylbenzene hydroperoxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butyl perbenzoate, cumyl hydroperoxide, t-butyl hydroperoxide, 1, 1-bis (t-butylperoxy) -3,3,5-trimethylhexane, n-butyl-4,4-bis (t-butylperoxy) valerate, α, α'-bis (t-butylperoxy) Isopropyl) benzene, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexyne-3, t-butylperoxycumene and the like. Examples of the sulfur compound include tetramethylthiuram disulfide, Tetramethylthiuram monosulfide, N-cyclohexyl-2- Emissions benzothiazole sulfenamide, N-t-butyl-2-benzothiazole sulfenamide, sulfur monochloride, and the like sulfur dichloride.

  And as said crosslinking agent, that whose 1-minute half life temperature is higher than the decomposition temperature of a thermally decomposable foaming agent is preferable. This is because by using a cross-linking agent having a half-life temperature higher than the decomposition temperature of the thermal decomposable foaming agent for 1 minute, the foamable cross-linked resin sheet described later can be cross-linked while being foamed or foamed. Because it can.

  In addition, the decomposition temperature of the said thermal decomposition type foaming agent is a decomposition temperature of the thermal decomposition type foaming agent described in the 98th-99th pages of the "foaming molding technology of various polymers" issued from the technical information association. . In addition, when a plurality of pyrolyzable foaming agents are used in the foamable resin composition, the decomposition temperature of the pyrolyzable foaming agent having the highest decomposition temperature among those pyrolyzable foaming agents. It is preferable to use a crosslinking agent having a high half-life temperature of 1 minute.

  And when there is little content of the crosslinking agent in the said foamable resin composition, when a crosslinked foamed sheet is not fully bridge | crosslinked, compression set may become large and shape recoverability may fall, but when many Since the foamability of the foamable crosslinked resin sheet to be described later may be lowered, 2 to 18 parts by weight is preferable with respect to 100 parts by weight of the rubber-based resin, and 4 to 12 parts by weight is more preferable.

  The foamable resin composition may contain an additive as long as the physical properties of the obtained crosslinked foamed sheet are not impaired.

  Examples of the additive include a foaming aid, a crosslinking aid, a vulcanization accelerator, a vulcanization acceleration aid, and a vulcanization retarder. Specifically, for example, vulcanization accelerators and vulcanization accelerators such as aldehyde ammonias, aldehyde amines, guanidines, thiazoles, sulfenamides, turums, dithiocarbamic acids, xanthogenic acids, thioureas; Vulcanization retarders such as organic acids such as phthalic anhydride, benzoic acid and salicylic acid, amines such as N-nitroso-diphenylamine and N-nitroso-phenyl-β-naphthylamine; acrylics such as poly (meth) acrylic acid alkyl esters And polyvinyl chloride resins such as polyvinyl chloride and the like.

  Next, the foamable resin sheet is cross-linked by irradiating the foamable resin sheet obtained as described above with ionizing radiation to produce a foamable cross-linked resin sheet. The ionizing radiation is not particularly limited, and examples thereof include electron beams, α rays, β rays, and γ rays, and electron beams are preferable.

  Also, if the irradiation amount of ionizing radiation to the foamable resin sheet is small, the foamable resin sheet is insufficiently crosslinked, and foaming may occur when foaming the foamable crosslinked resin sheet, If the amount is too large, the crosslink density of the foamable crosslinked resin sheet becomes too high, the foamability of the foamable crosslinked resin sheet decreases, the flexibility of the resulting crosslinked foamed sheet becomes insufficient, and the crosslinked foamed sheet is used as a gasket. When used, the crosslinked foamed sheet cannot sufficiently follow the shape of the member to be sealed, and a gap may be formed between the part to be sealed and cause a sealing failure. ~ 3 Mrad is preferred.

  Subsequently, the foamable crosslinked resin sheet is foamed or foamed and then further crosslinked with a crosslinking agent to produce a crosslinked foamed sheet. In order to crosslink the foamable crosslinked resin sheet with the crosslinking agent while foaming, the foamable crosslinked resin sheet is heated to a temperature equal to or higher than the decomposition temperature of the thermally decomposable foaming agent and equal to or higher than the 1 minute half-life temperature of the crosslinking agent. By decomposing the thermally decomposable foaming agent and the crosslinking agent, the foamable crosslinked resin sheet may be crosslinked in parallel with foaming. In order to crosslink the foamable crosslinked resin sheet with the crosslinking agent after foaming, the foamable crosslinked resin sheet is brought to a temperature not lower than the decomposition temperature of the pyrolytic foaming agent and lower than the half-life temperature of the crosslinking agent for 1 minute. A foamed crosslinked resin sheet is foamed by heating to decompose the pyrolytic foaming agent to produce a crosslinked foamed sheet, and then the crosslinked foamed sheet is heated to a temperature equal to or higher than the half-life temperature of the crosslinking agent for 1 minute. What is necessary is just to bridge | crosslink a crosslinked foamed sheet by decomposing | disassembling an agent. In addition, since the further heating after preparation of a crosslinked foamed sheet causes the surface of a crosslinked foamed sheet to become rough, it is preferable to bridge | crosslink with a crosslinking agent, foaming a foamable crosslinked resin sheet.

  As described above, in the method for producing a crosslinked foamed sheet, the foamable resin sheet is crosslinked with ionizing radiation to produce a foamable crosslinked resin sheet having a melt viscosity suitable for foaming, and then the foamable crosslinked resin sheet. Since the foamed crosslinked resin sheet can be easily adjusted to have a melt viscosity suitable for foaming, a crosslinked foamed sheet having a desired apparent density and excellent compression flexibility can be obtained.

  Further, in the method for producing a crosslinked foamed sheet, the foamable crosslinked resin sheet crosslinked by ionizing radiation is further crosslinked with a crosslinking agent while foaming or after foaming, so that it is crosslinked to a preferable gel fraction range. As a result, it is possible to obtain a crosslinked foamed sheet having a low compression set with a reduced amount of plastic deformation.

  What is necessary is just to adjust the expansion ratio of the said crosslinked foamed sheet so that a crosslinked foamed sheet may become a desired apparent density, and 5-30 times are preferable.

  Next, a method for producing a laminated crosslinked foamed sheet in which a synthetic resin layer is laminated and integrated on one surface of the crosslinked foamed sheet will be described. The method for producing a laminated cross-linked foam sheet is the same as the method for producing a cross-linked foam sheet described above, wherein a synthetic resin layer is laminated and integrated on one surface of a foam resin sheet to produce a foam laminate sheet, and the foam laminate sheet is ionized. This foamable cross-linked sheet is produced by cross-linking the foamable laminated sheet by irradiating a radiative radiation to produce a foamable cross-linked cross-linked sheet in which the foamable cross-linked resin sheet and the synthetic resin layer are laminated and integrated. Is heated to a temperature equal to or higher than the softening point of the synthetic resin constituting the synthetic resin layer to foam the foamable cross-linked crosslinked sheet or after foaming, and then crosslinked with a crosslinking agent.

  The synthetic resin layer can be laminated and integrated on one side of the foamable resin sheet. The synthetic resin sheet separately prepared on one side of the foamable resin sheet can be heat-sealed and integrated. The synthetic resin layer can be integrated on one side of the foamable resin sheet. A method of laminating and integrating a resin sheet by extrusion lamination, a method of laminating and integrating a synthetic resin sheet on one side of a foamable resin sheet, a synthetic resin sheet on one side of a foamable resin sheet by coextrusion Examples of the method include lamination and integration, and a method of extrusion laminating a synthetic resin sheet on one surface of a foamable resin sheet and a method of coextrusion are preferable. The synthetic resin sheet can be manufactured by a general-purpose method such as a T-die method, an inflation method, a calendar molding method, or a solution casting method, and the synthetic resin sheet is laminated and integrated on one surface of the foamable resin sheet by coextrusion. In the case of using the method for converting to T, the T die method and the inflation method are preferable.

  In order to crosslink the foamable laminated cross-linked sheet with a crosslinking agent while foaming, the foamable laminated cross-linked sheet is cross-linked at a temperature equal to or higher than the softening point of the synthetic resin constituting the synthetic resin layer and above the decomposition temperature of the thermally decomposable foaming agent. What is necessary is just to bridge | crosslink in parallel with foaming a foamable laminated bridge | crosslinking sheet | seat by heating at the temperature more than the 1 minute half life temperature of an agent, and decomposing | disassembling a thermal decomposition type foaming agent and a crosslinking agent.

  In order to crosslink the foamable laminated cross-linked sheet with a cross-linking agent after foaming, the foamable multi-layer cross-linked sheet has a softening point of the synthetic resin constituting the synthetic resin layer or higher and a decomposition temperature of the pyrolytic foaming agent. A laminated crosslinked foamed sheet is produced by heating the crosslinked agent to a temperature lower than the half-life temperature of 1 minute of the crosslinking agent to decompose the pyrolytic foaming agent and foaming the foamable laminated crosslinked sheet. The laminated cross-linked foamed sheet may be crosslinked by heating the sheet to a temperature equal to or higher than the 1 minute half-life temperature of the crosslinking agent to decompose the crosslinking agent.

  In addition, since the further heating after preparation of a crosslinked foamed sheet causes the roughness of the surface of a crosslinked foamed sheet, it is preferable to bridge | crosslink with a crosslinking agent, foaming a foamable laminated crosslinked sheet.

  In this way, by heating the foamable laminated crosslinked sheet at a temperature equal to or higher than the softening point of the synthetic resin constituting the synthetic resin layer, the synthetic resin layer constituting the foamable laminated crosslinked sheet becomes flexible and expandable. Since foaming of the foamable cross-linked resin sheet constituting the multi-layer cross-linked sheet is not hindered, it is possible to obtain a multi-layer cross-linked foam sheet excellent in compression flexibility having a cross-linked foam sheet having a desired apparent density.

  The crosslinked foamed sheet of the present invention is characterized by containing a rubber-based resin and having a gel fraction of 90 to 100% by weight. Therefore, the compression set is low and the shape recoverability is excellent. Therefore, the crosslinked foamed sheet can be widely used in the fields of architecture, civil engineering, electricity, electronics, vehicles and the like as a gasket that maintains an excellent repulsive force over a long period of time.

  And the manufacturing method of the crosslinked foamed sheet | seat of this invention crosslinks an expandable resin sheet with ionizing radiation, and after producing the expandable crosslinked resin sheet which has a melt viscosity suitable for foaming, this expandable crosslinked resin sheet Since the foamed crosslinked resin sheet can be easily adjusted to have a melt viscosity suitable for foaming, a crosslinked foamed sheet having a desired apparent density and excellent compression flexibility can be obtained. Therefore, the crosslinked foamed sheet obtained by the method for producing a crosslinked foamed sheet can be suitably used as a gasket excellent in compression flexibility.

  Furthermore, in the above-mentioned method for producing a crosslinked foamed sheet, the foamable crosslinked resin sheet crosslinked by ionizing radiation can be further crosslinked with a crosslinking agent while foaming or foaming, so that the gel fraction is 90 to 90%. A crosslinked foamed sheet having a low compression set of 100% by weight can be obtained.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
Nitrile-butadiene rubber (NBR, density: 0.96 g / cm ³ ) 100 parts by weight, azodicarbonamide (trade name “SO-L” manufactured by Otsuka Chemical Co., Ltd., decomposition temperature: 195 to 210 ° C.) 8 parts by weight and a crosslinking agent As a diisopropylbenzene hydroperoxide (Nippon Yushi Co., Ltd., trade name “Park Mill P”, 1 minute half-life temperature: 230 ° C.) 4 parts by weight of an expandable resin composition is supplied to an extruder and melt kneaded at 130 ° C. The foamed resin sheet was obtained by extrusion.

Subsequently, both surfaces of the foamable resin sheet were irradiated with an electron beam at an acceleration voltage of 500 keV for 0.8 Mrad to obtain a foamable crosslinked resin sheet. Then, by supplying the foamable crosslinked resin sheet to a foaming furnace and heating to 240 ° C., azodicarbonamide and diisopropylbenzene hydroperoxide are decomposed and crosslinked while foaming the crosslinked resin sheet, By cooling, a crosslinked foamed sheet having an apparent density of 100 kg / m ³ and a thickness of 1.0 mm was obtained.

(Example 2)
A crosslinked foamed sheet having an apparent density of 121 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the amount of the crosslinking agent was 8 parts by weight.

(Example 3)
A crosslinked foamed sheet having an apparent density of 155 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the amount of the crosslinking agent was 12 parts by weight.

Example 4
A crosslinked foamed sheet having an apparent density of 40 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the amount of azodicarbonamide was 16 parts by weight.

(Example 5)
A crosslinked foamed sheet having an apparent density of 38 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the amount of azodicarbonamide was 25 parts by weight.

(Example 6)
A crosslinked foamed sheet having an apparent density of 220 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the amount of the crosslinking agent was 16 parts by weight.

(Example 7)
Nitrile-butadiene rubber (NBR, density: 0.96 g / cm ³ ) 100 parts by weight, azodicarbonamide (trade name “SO-L” manufactured by Otsuka Chemical Co., Ltd., decomposition temperature: 195 to 210 ° C.) 8 parts by weight and a crosslinking agent As a diisopropylbenzene hydroperoxide (Nippon Yushi Co., Ltd., trade name “Park Mill P”, 1 minute half-life temperature: 230 ° C.) 4 parts by weight of an expandable resin composition is supplied to an extruder and melt kneaded at 130 ° C. Then, the foamable resin sheet is extruded, and on one surface of the foamable resin sheet, a high-density polyethylene film having a thickness of 40 μm serving as a synthetic resin layer (trade name “HD” manufactured by Tamapoly Co., Ltd., softening point of the high-density polyethylene: 125 ° C) by extrusion laminating, a foamable laminate sheet in which a foamable resin sheet and a high-density polyethylene film are laminated and integrated. To obtain the door.

Subsequently, both surfaces of the foamable laminated sheet were irradiated with an electron beam at an acceleration voltage of 500 keV for 0.8 Mrad to obtain a foamable laminated crosslinked sheet. Then, the foamable laminated crosslinked sheet is supplied to a foaming furnace and heated to 240 ° C., thereby decomposing azodicarbonamide and the crosslinking agent, crosslinking the foamable laminated crosslinked sheet while foaming, and then cooling. As a result, a laminated crosslinked foamed sheet obtained by laminating and integrating a high-density polyethylene film having a thickness of 40 μm on one surface of a crosslinked foamed sheet having an apparent density of 112 kg / m ³ and a thickness of 1.0 mm was obtained.

(Comparative Example 1)
A crosslinked foamed sheet having an apparent density of 90 kg / m ³ and a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that no crosslinking agent was blended.

(Comparative Example 2)
When a crosslinked foamed sheet was produced in the same manner as in Example 1 except that the amount of azodicarbonamide was 35 parts by weight, a crosslinked foamed sheet was not obtained.

(Comparative Example 3)
Layered cross-linking in the same manner as in Example 7 except that a polyethylene terephthalate film (trade name “E5000” manufactured by Toyobo Co., Ltd., softening point of polyethylene terephthalate: 260 ° C., thickness: 50 μm) was used instead of the high-density polyethylene film. An attempt was made to produce a foamed sheet, but since the polyethylene terephthalate film was not softened in the foaming furnace, foaming of the foamable cross-linked resin sheet was hindered, and a good laminated cross-linked foam sheet could not be obtained.

(Comparative Example 4)
When a crosslinked foamed sheet was produced in the same manner as in Example 1 except that the amount of the crosslinking agent was 20 parts by weight, a crosslinked foamed sheet was not obtained.

  Next, the compression set and 50% compression stress of the crosslinked foamed sheet and laminated crosslinked foamed sheet obtained as described above, and the gel content of the crosslinked foamed sheet constituting the crosslinked foamed sheet and laminated crosslinked foamed sheet The rate, apparent density, and closed cell rate were measured as described above, and the results are shown in Table 1.

Claims (9)

A crosslinked foamed sheet containing a rubber-based resin and having a gel fraction of 90 to 100% by weight. A laminated crosslinked foamed sheet comprising a synthetic resin layer laminated and integrated on one surface of the crosslinked foamed sheet according to claim 1. A foamable resin sheet is formed by melt-kneading a foamable resin composition containing a rubber-based resin, a thermally decomposable foaming agent, and a crosslinking agent, and the foamable resin sheet is irradiated with ionizing radiation to form the foamable resin sheet. Crosslinking the sheet after cross-linking the sheet to produce a foamable cross-linked resin sheet, and then heating the foamable cross-linked resin sheet to cross-link while foaming or foaming the foamable cross-linked resin sheet. A method for producing a foam sheet. The foamable resin composition contains 1 to 30 parts by weight of a pyrolytic foaming agent and 2 to 18 parts by weight of a crosslinking agent with respect to 100 parts by weight of a rubber-based resin. A method for producing a crosslinked foamed sheet. The method for producing a crosslinked foamed sheet according to claim 3 or 4, wherein the rubber-based resin is a nitrile-butadiene rubber. The method for producing a crosslinked foamed sheet according to claim 3 or 4, wherein the one-minute half-life temperature of the crosslinking agent is higher than the decomposition temperature of the thermally decomposable foaming agent. The method for producing a crosslinked foamed sheet according to claim 3, wherein the irradiation amount of ionizing radiation is 0.1 to 3 Mrad. A foamable resin sheet is formed by melting and kneading a foamable resin composition containing a rubber-based resin, a pyrolytic foaming agent and a crosslinking agent, and a synthetic resin layer is laminated and integrated on one surface of the foamable resin sheet. After producing a laminate sheet, the foamable laminate sheet is cross-linked by irradiating the foamable laminate sheet with ionizing radiation to produce the foamable laminate crosslinked sheet. A method for producing a laminated crosslinked foamed sheet, wherein the foamable laminated crosslinked sheet is crosslinked while being foamed or foamed by heating at a temperature equal to or higher than a softening point of a synthetic resin constituting the resin layer. The method for producing a laminated cross-linked foamed sheet according to claim 8, wherein the synthetic resin layer is a polyolefin resin layer.