JPH11302430A - Preparation of open-cell, crosslinked foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation process wherein an open-cell, crosslinked foam which comprises an olefin resin, exerts a high compression recovery, sealing property and airlightness and has a high open-cell ratio, uniform cells and a high expansion ratio, is easily obtained. SOLUTION: An open-cell and crosslinked foam is prepared by heat molding 100 pts.wt. ethylene resin with a density of from 0.840 to 0.900 g/cm<3> or an ethylene resin polymerized by using a metallocene catalyst containing a tetravalent transition metal, from 1 to 30 pts.wt. heat-decomposable blowing agent and from 0.3 to 3 pts.wt. crosslinking agent in a non-crosslinked state, then heating them under an atmospheric pressure, crosslinking and foaming them so that the maximum value of (degree of crosslinking/decomposition degree of heat-decomposable blowing agent) is 20 or smaller to obtain a crosslinked foam and communicating the cells of this crosslinked foam through mechanical deformation. Here, the dynamic viscoelasticity obtained after heat molding the above ethylene resin at a non-crosslinked state is from 2.0×10<3> to 5.0×10<3> Pa.S at 135 deg.C, 10 Hz.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an open-cell crosslinked foam.

[0002]

2. Description of the Related Art Conventionally, as a method of producing a crosslinked foam made of an olefin resin, a method of cross-linking an olefin resin foamable sheet containing a pyrolytic foaming agent and then decomposing the pyrolytic foaming agent is used. A method of foaming by heating above the temperature,
Alternatively, a method is generally used in which the expandable olefin-based resin composition is heated in a closed mold under pressure to perform crosslinking, and then depressurized to foam.

[0003] The crosslinked foam produced by the above method is generally a closed cell having a very fine cell structure.
In addition, since the cell membrane is tough, the cells hardly break even when subjected to mechanical deformation, and it has been difficult to obtain an open-cell crosslinked foam. Therefore, most of the open-celled crosslinked foams conventionally available on the market are made of urethane-based resins, but olefin-based resins have much higher weather resistance, chemical resistance and water resistance than urethane-based resins. Therefore, various methods for producing an open-celled crosslinked foam made of an olefin resin have been studied.

[0004] As a conventionally known method for obtaining an open-celled olefin-based resin crosslinked foam, for example, a water-soluble powder such as starch is added to an olefin-based resin and kneaded.
Examples include a method of eluting and removing a water-soluble powder, a method of sintering an olefin-based resin powder, and the like. The expansion ratio of an open-cell crosslinked foam obtained by these methods is about 2 to 3 times, There is a problem that a product having a high expansion ratio cannot be obtained.

Japanese Patent Application Laid-Open No. 57-191027 discloses that a foamable olefin resin composition is heated under normal pressure to simultaneously perform crosslinking and foaming, followed by mechanical deformation to form bubbles. Are shown. According to this method, an open-celled olefin-based resin crosslinked foam having excellent compression recovery properties and sealing properties can be obtained.However, when the expansion ratio is increased, it becomes easy to simultaneously perform crosslinking and foaming, In addition, there is a problem that bubbles are likely to be non-uniform.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an olefin resin which has excellent compression recovery properties, sealability and airtightness, a high open cell ratio, uniform cells and a high expansion ratio. An object of the present invention is to provide a production method by which an open-celled crosslinked foam can be easily obtained.

[0007]

According to the present invention, there is provided a process for producing an open-cell crosslinked foam having a density of 0.840 to 0.900 g.
/ Cm ^{3 of} an ethylene-based resin (hereinafter referred to as “ethylene-based resin (a)”) or an ethylene-based resin polymerized using a metallocene catalyst containing a tetravalent transition metal (hereinafter referred to as an “ethylene-based resin (b)”). 100 parts by weight, 1 to 30 parts by weight of a pyrolytic foaming agent and 0.3 to 3 parts by weight of a crosslinking agent are heat-molded in a non-crosslinked state, and then heated under normal pressure to obtain (crosslinking degree / heat). Cross-linking and foaming so that the maximum value of the decomposition type foaming agent) becomes 20 or less to form a cross-linked foam, and the cells of the cross-linked foam are communicated by applying mechanical deformation, and The dynamic viscoelasticity of the ethylene-based resin (a) or the ethylene-based resin (b) after heat-molding in a non-crosslinked state is 2.0 × 10 ³ at 135 ° C. and 10 Hz.
It is characterized by 5.0 × 10 ³ Pa · s.

The ethylene resin (a) used in the present invention
Examples thereof include linear low-density polyethylene and low-density polyethylene, and these may be used alone or in combination of two or more. Linear low-density polyethylene is obtained by copolymerizing ethylene with an α-olefin other than ethylene. Examples of the α-olefin other than ethylene include propylene, 1-butene, 1-pentene, and 4-methyl-. Examples thereof include 1-pentene, 1-hexene, 1-heptene, and 1-octene. Among them, ethylene resin (a) having a density range described below is easily obtained.
-Octene is preferred.

When the density of the ethylene-based resin (a) decreases, it becomes difficult to polymerize itself from the monomer, and when the density increases, the compression recovery, sealing property, and airtightness of the obtained open-cell crosslinked foam decreases. So, 0.840-0.900g
/ Cm ³ , preferably 0.840 to 0.89
0 g / cm ³ .

As a method for obtaining the ethylene-based resin (a), a method in which polymerization is carried out using a metallocene catalyst containing a tetravalent transition metal described later is preferable.

An olefin resin other than the ethylene resin (a) (hereinafter referred to as "olefin resin (a)") may be blended with the ethylene resin (a). As the olefin-based resin (a), any of those conventionally used for foams can be used. For example, linear low-density polyethylene,
Low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component, ethylene-ethyl acrylate containing ethylene as a main component, polypropylene, ethylene-propylene copolymer containing propylene as a main component Examples thereof include coalesce, polybutene, and ethylene-butene copolymer containing butene as a main component, and these may be used alone or in combination of two or more. The linear low-density polyethylene is obtained by copolymerizing ethylene with an α-olefin other than ethylene,
Examples of the α-olefin other than ethylene include the same as those described above.

The amount of the olefin-based resin (a) is limited to 80% by weight or less, and preferably 50% or less, because the larger the amount of the olefin-based resin (a), the lower the compression recovery property, sealing property and airtightness of the obtained open-cell crosslinked foam. % By weight or less. In the present invention, the ethylene resin (a) is replaced with the olefin resin (a).
Is also referred to as an ethylene-based resin (a) when the ethylene-based resin (a) is no longer the main component.

The ethylene resin (b) used in the present invention
Is polymerized using a metallocene catalyst containing a tetravalent transition metal, for example, linear low-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component, ethylene Examples thereof include ethylene-ethyl acrylate as a main component, and these may be used alone or in combination of two or more. The linear low-density polyethylene is obtained by copolymerizing ethylene with an α-olefin other than ethylene.
Examples of the olefin include the same ones as described above. Among them, 1-octene is preferable because an ethylene-based resin (b) having a density range described later is easily obtained.

When the density of the ethylene-based resin (b) decreases, the polymerization itself from the monomer becomes difficult, and when the density increases, the compression recovery, sealing property, and airtightness of the obtained open-cell crosslinked foam decreases. So 0.840 ~ 0.920g
/ Cm ³ , more preferably 0.840-0.
It is 890 g / cm ³ .

An olefin resin other than the ethylene resin (b) (hereinafter referred to as "olefin resin (b)") may be blended with the ethylene resin (b). As the olefin-based resin (b), any resin conventionally used for foams can be used. For example, linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ethylene as the main component Ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate mainly composed of ethylene, polypropylene, ethylene-propylene copolymer mainly composed of propylene, polybutene, ethylene-butene copolymer mainly composed of butene, etc. These may be used alone or in combination of two or more. The linear low-density polyethylene is obtained by copolymerizing ethylene with an α-olefin other than ethylene,
Examples of the α-olefin other than ethylene include the same as those described above.

The amount of the olefin resin (b) is as follows:
When the content increases, the compression recovery property, sealing property and airtightness of the obtained open-celled crosslinked foam decrease, so the content is limited to 80% by weight or less, preferably 50% by weight or less, more preferably 35% by weight or less. In the present invention, an ethylene-based resin (b) in which the ethylene-based resin (b) is no longer a main component as a result of blending the olefin-based resin (b) with the ethylene-based resin (b) is also referred to as an ethylene-based resin (b).

Hereinafter, a method of performing polymerization using the above-described metallocene catalyst containing a tetravalent transition metal will be described in detail. In general, a metallocene compound is a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. In the present invention, at least one of tetravalent transition metals such as titanium, zirconium, hafnium, nickel, palladium, and platinum is used. A compound in which a cyclopentadienyl ring or an analog thereof is present as a ligand (ligand) is used.

As the ligand, other than the cyclopentadienyl ring, for example, a cyclopentadienyl oligomer ring, an indenyl ring, a cyclopentadienyl group substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon monosubstituted metalloid group. An enyl ring or an indenyl ring is exemplified. In addition to such ligands, for example, a monovalent anion or divalent anion chelate of chlorine or bromine, a hydrocarbon group,
Alkoxides, arylalkoxides, aryloxides, amides, arylamides, phosphides, arylphosphides and the like may be coordinated to the transition metal.

Examples of the hydrocarbon group in which the cyclopentadienyl ring and the indenyl ring are substituted include a methyl group, an ethyl group, a propyl group, a butyl group, an isobutyl group, and the like.
Examples thereof include an amyl group, an isoamyl group, a hexyl group, a 2-ethylhexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a cetyl group, and a phenyl group.

Specific examples of such a metallocene compound include, for example, cyclopentadienyltitanium tris (dimethylamide), methylcyclopentadienyltitanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl Silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium chloride, Methylphenylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, indenyl titanium tris (dimethylamide), indenyl titanium tri (Diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n-
Propylamide) and the like.

The metallocene compound functions as a catalyst when the ethylene resin is polymerized by changing the type of metal or the structure of the ligand and combining it with a specific cocatalyst. Specifically, polymerization is performed in a system in which methylaluminoxane (MAO), a boron compound, or the like is added as a cocatalyst to a metallocene compound. The usage ratio of the cocatalyst to the metallocene compound is usually 10 to 1,000,000 times, preferably 50 to 5,000 times.

The polymerization conditions are not particularly limited, and examples thereof include a solution polymerization method using an inert medium, a bulk polymerization method in which substantially no inert medium is present, and a gas phase polymerization method. Generally, the polymerization temperature is from -100 ° C to 300 ° C, and the polymerization pressure is from normal pressure to 100 kg / cm ² .

In the present invention, a pyrolytic foaming agent and a crosslinking agent are added to the ethylene-based resin (a) or the ethylene-based resin (b), and the mixture is melt-kneaded by a kneader mixer or the like, and is pressurized or any other known one. According to the method, the mixture is heated and molded into a desired shape while maintaining a non-crosslinked state. After being heat-molded into a desired shape, it is heated under normal pressure to a temperature equal to or higher than the decomposition start temperature of the thermal decomposition type foaming agent and to a temperature equal to or higher than the decomposition start temperature of the cross-linking agent. Is crosslinked and foamed so that the maximum value is 20 or less, to form a crosslinked foam, and the cells of the obtained crosslinked foam are communicated by applying mechanical deformation.

The thermal decomposition type foaming agent has a low decomposition initiation temperature, the foaming property is reduced, and the higher the decomposition initiation temperature, the more likely it is to generate abnormal bubbles. Therefore, the decomposition initiation temperature of the ethylene-based resin (a) or ethylene-based resin (b) is low. ) Is preferably 20 ° C. or more higher than the melting point (peak temperature in DSC) of 20 to 15
Those that are 0 ° C. higher are more preferred. Further, when the decomposition end temperature is low, the foaming property is reduced, and when the decomposition end temperature is high, foaming is often not completely completed.
Those at 0 ° C. are preferred. Examples of such a thermal decomposition type foaming agent include azodicarbonamide (decomposition start temperature = about 200 ° C., decomposition end temperature = about 210 ° C.), N,
N′-dinitrosopentamethylenetetramine (decomposition start temperature = about 200 ° C., decomposition end temperature = about 205 ° C.), 4,
4′-oxybisbenzenesulfonyl hydrazide (decomposition start temperature = about 155 ° C., decomposition end temperature = about 160 ° C.) and the like may be used alone or in combination of two or more. Among them, azodicarbonamide is preferable because the amount of generated gas, safety in handling, and the like are excellent. If the amount of the thermal decomposition type foaming agent is too small, a desired expansion ratio cannot be obtained, and if it is large, the maximum value of (degree of crosslinking / decomposition rate of the thermal decomposition type foaming agent) tends to exceed 20, so that the ethylene resin It is limited to 1 to 30 parts by weight based on 100 parts by weight of (a) or the ethylene-based resin (b), and may be appropriately adjusted according to a desired expansion ratio.

It is preferable to add a foaming aid in order to adjust the decomposition temperature, decomposition rate, etc. of the pyrolytic foaming agent. As the foaming auxiliary, any conventionally known one can be used, and examples thereof include zinc oxide, urea or a derivative thereof, and a stearate such as magnesium stearate.
These may be used alone or in combination of two or more. The combination and the amount of addition are appropriately adjusted according to the desired expansion ratio, cell shape, and the like.

When the decomposition rate of the crosslinking agent is increased,
The maximum value of (crosslinking degree / decomposition rate of the thermal decomposition type foaming agent) easily exceeds 20, and when it is slow, when the decomposition rate of the thermal decomposition type foaming agent becomes high, outgassing occurs and bubbles become uneven. Therefore, it is preferable that the half-life temperature for one minute (hereinafter, referred to as “half-life temperature”) is 150 to 190 ° C. As such a crosslinking agent, for example, dicumyl peroxide (half-life temperature =
About 171 ° C), 1,1-di (t-butylperoxy)-
3,3,5-trimethylcyclohexane (half temperature = about 151 ° C.), α, α′-bis (t-butylperoxyisopropyl) benzene (half temperature = about 182 ° C.), t-
Butyl peroxycumene (half temperature = about 178 ° C.) and the like. If the amount of the crosslinking agent is too small, a desired degree of crosslinking cannot be obtained, and if the amount is too large, the maximum value of (degree of crosslinking / decomposition rate of the thermal decomposition type foaming agent) tends to exceed 20, so that the ethylene resin (a) Alternatively, the amount is limited to 0.3 to 3 parts by weight based on 100 parts by weight of the ethylene-based resin (b), and may be appropriately adjusted according to a desired degree of crosslinking.

Further, it is preferable to add a crosslinking aid because the dynamic viscoelasticity of the ethylene resin tends to be in the range described later. As the crosslinking assistant, a polyfunctional monomer is used. For example, triallyl isocyanurate, divinylbenzene, trimethylolpropane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (Meth) acrylate,
Examples thereof include 1,10-decanediol (meth) acrylate, triallylic acid triallyl ester, ethylvinylbenzene, and diallyl phthalate, and these may be used alone or in combination of two or more. Among them, triallyl isocyanurate is preferred because of its excellent affinity with the resin. When the amount of the crosslinking aid is small, the degree of crosslinking does not increase, and when the decomposition rate of the thermal decomposition type foaming agent increases, gas escape occurs and bubbles become non-uniform, and when the amount increases, crosslinking proceeds more than necessary. Since the open cell ratio of the obtained open-cell crosslinked foam decreases, the ethylene-based resin (a)
Or 0.3 parts by weight based on 100 parts by weight of the ethylene resin (b).
It is preferably from 5 to 5 parts by weight, and may be appropriately adjusted according to a desired degree of crosslinking.

The temperature and time for heat-molding into a desired shape in the above-mentioned non-crosslinked state differ depending on the resin used, the crosslinking agent and the like. For example, when dicumyl peroxide is used as the crosslinking agent, it is 130 to 140. About 10 to 30 minutes at a suitable temperature.

When cross-linking occurs in the step of heat molding, the maximum value of (degree of cross-linking / decomposition rate of the thermal decomposition type foaming agent) exceeds 20, and bubbles are communicated by applying mechanical deformation in a later step. However, only those having an extremely low open cell ratio can be obtained. In addition, when this step is not performed, the viscosity of the resin is not adjusted, and the open cell ratio and the compression recovery of the obtained open cell crosslinked foam are reduced. The non-crosslinked state in the present invention is a state in which the degree of crosslinking is 0%.

The degree of crosslinking in the present invention is a value measured by the following method. First, about 100 mg of the foam at any time is precisely weighed in the thickness direction, immersed in 100 ml of xylene at 120 ° C. for 24 hours, and then filtered through a 200-mesh stainless steel wire mesh, and the insoluble material on the wire mesh is removed. Vacuum dry the minute. Next, the weight of the insoluble portion is precisely weighed, and the degree of crosslinking is calculated as a percentage by the following equation. Degree of crosslinking (%) = (weight of insoluble matter (mg) / weight of weighed foam (mg)) × 100

When the dynamic viscoelasticity of the ethylene-based resin (a) or the ethylene-based resin (b) after being heat-molded into a desired shape in a non-crosslinked state is reduced, the shape of the bubbles is maintained during foaming. However, if the size is large, the bubbles do not grow during foaming and a high expansion ratio cannot be obtained. Therefore, at 135 ° C. and 10 Hz, 2.0 × 10 ³ -5.
It is limited to 0 × 10 ³ Pa · s.

The dynamic viscoelasticity referred to in the present invention is a value measured by a dynamic viscoelasticity measuring instrument (manufactured by Rheometrics Scientific FFE, model “RMS800”) on a parallel plate having a diameter of 25 mm. .

Next, crosslinking and foaming are carried out. At any point in the process, (degree of crosslinking / decomposition rate of the thermally decomposable foaming agent) is
When the size is increased, even if mechanical deformation is applied to the obtained crosslinked foam, the cells do not communicate, and an open-cell crosslinked foam cannot be obtained. Therefore, the maximum value is limited to 20 or less.

The decomposition rate of the above-mentioned pyrolytic foaming agent is a ratio of the expansion ratio at the time of measuring the degree of cross-linking to the expansion ratio of the obtained cross-linked foam, expressed as a percentage. calculate. Decomposition rate (%) = (expanded expansion ratio / expanded expansion ratio of obtained crosslinked foam) × 100 The expansion ratio is a density measured using an electronic hydrometer (trade name “ED120T” manufactured by Mirage Co., Ltd.). (G / cc)
Is the reciprocal of

The temperature and time for crosslinking and foaming are as follows:
Although it depends on the resin used, the thermal decomposition type foaming agent, the cross-linking agent, and the like, it is usually preferable that the temperature is 150 to 200 ° C. and the time is 10 to 90 minutes.

In the crosslinking and foaming steps, when the dynamic viscoelasticity of the ethylene resin (a) or the ethylene resin (b) is reduced, the shape of the bubbles is not maintained, and abnormal bubbles are generated. Since the cells do not grow and a foam having a high expansion ratio cannot be obtained, the dynamic viscoelasticity at a crosslinking degree of 30% is
1.0 × 10 ^{4 to} 5.0 × 10 ⁴ P at 175 ° C., 1 Hz
a · s is preferred.

Therefore, in the present invention, the resin component has a dynamic viscoelasticity after heat molding in a non-crosslinked state at 135 ° C. and 2.0 × 10 ^{3 to} 5.0 × 1 at 10 Hz.
0 ³ a Pa · s, and the dynamic viscoelasticity 175 ° C. when crosslinking degree 30%, 1.0 × 10 ⁴ in 1 Hz to 5.0 × 10
It is more preferable to use an ethylene-based resin (a) or an ethylene-based resin (b) having a pressure of ⁴ Pa · s.

Although the crosslinked foam obtained by the above method has closed cells, the cells are communicated by applying mechanical deformation to obtain the open-cell crosslinked foam of the present invention.

As a method of applying mechanical deformation, any conventionally known method may be employed. For example, a crosslinked foam is passed between two rolls rotating at a constant speed, and the thickness of the crosslinked foam is set to 1 And a method of compressing to a thickness of about 10%. The mechanical deformation may be applied only once or may be applied a plurality of times.

In the production method of the present invention, additives such as an antibacterial agent, a flame retardant, a deodorant, a pigment and the like may be added as needed as long as the physical properties are not impaired.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0042]

EXAMPLES In Examples and Comparative Examples, the following resins were used. LLDPE1: polymerized using a metallocene catalyst containing a tetravalent transition metal, having a density of 0.870 g / c
m ³ , linear low-density polyethylene copolymerized with 1-octene having a melting point of 60 ° C. (trade name “EG8200” manufactured by Dow Chemical Company) LLDPE2: using a metallocene catalyst containing a tetravalent transition metal Polymerized to a density of 0.9
Linear low-density polyethylene copolymerized with 1-octene having a melting point of 98 ° C. and a melting point of 98 g / cm ³ (manufactured by Dow Chemical Company, trade name: FW1650)

LDPE1: density of 0.895 g / c
m ³ , low-density polyethylene having a melting point of 113 ° C. (manufactured by Sumitomo Chemical Co., Ltd., trade name “EUL400”) LDPE2; density: 0.918 g / cm ³ , melting point: 10
6 ° C low-density polyethylene (manufactured by Sumitomo Chemical Co., Ltd., trade name “G
807 ") LDPE3: density 0.920 g / cm ³ , melting point 11
8 ° C low-density polyethylene (Mitsubishi Chemical Corporation, trade name “L
E520H ”) LDPE4: density of 0.932 g / cm ³ , melting point of 12
0 ° C low-density polyethylene (Sumitomo Chemical Co., trade name “F
203-0 ")

EVA1: an ethylene-vinyl acetate copolymer having a vinyl acetate content of 15% by weight and a melting point of 93 ° C. (trade name “H2021” manufactured by Sumitomo Chemical Co., Ltd.) EVA2: a vinyl acetate content of 20% by weight, melting point Is 83
° C ethylene-vinyl acetate copolymer (trade name “Ultracene 2233” manufactured by Tosoh Corporation)

(Examples 1 to 3) The resin components (LLDPEs 1 and 2, LDPEs 1 to 4 and E
VA1 and 2), azodicarbonamide, dicumyl peroxide, triallyl isocyanurate and zinc oxide are melt-kneaded at 110 ° C. by a kneader mixer, and then introduced into a mold having a concave portion of 30 cm long × 30 cm wide × 5 cm deep. Then, the concave portion was sealed with another mold having a smooth surface, and heated at 135 ° C. for 25 minutes to mold. The degree of crosslinking after molding was 0%, and the dynamic viscoelasticity of the resin component at 135 ° C. and 10 Hz was as shown in Table 1. In addition, 1
It was crosslinked and foamed by heating in an oven at 75 ° C. for 60 minutes to obtain a crosslinked foam. The maximum value of (degree of crosslinking / decomposition rate of the thermal decomposition type foaming agent) in the heating step was 20 or less, and the obtained crosslinked foam was closed cell. The resin component was molded into a 2 mm sheet, and the sheet was accelerated at an acceleration voltage of 750 k.
The dynamic viscoelasticity at 175 ° C. and 1 Hz when cross-linking was performed by irradiating 3.5 Mrad with an electron beam of v so that the degree of cross-linking became 30% was as shown in Table 1.

Next, the obtained cross-linked foam was sliced to a thickness of 5 cm, compressed to 2 mm in thickness by using two constant-speed rolls having a rotation speed of 5 rpm and a diameter of 100 mm, and air bubbles were communicated. A crosslinked foam was obtained. The expansion ratio and open cell ratio of the obtained open-cell crosslinked foam were as shown in Table 1.

The open cell ratio referred to in the present invention is ASTM.
It was calculated from the closed cell rate measured according to D 1940 62T by the following formula. Open cell rate (%) = 100-Closed cell rate (%)

Comparative Example 1 A predetermined amount of resin components (LLDPE1 and LLDPE2, LDPE1 to LDPE4 and EVA) shown in Table 1
1 and 2), azodicarbonamide, dicumyl peroxide, triallyl isocyanurate and zinc oxide were molded in the same manner as in Example 1. The degree of crosslinking after molding is 0%, and the dynamic viscoelasticity of the resin component at 135 ° C. and 10 Hz is as follows:
As shown in Table 1. Further, heating and crosslinking were carried out in the same manner as in Example 1 to obtain a crosslinked foam. The maximum value of (degree of crosslinking / decomposition rate of the thermal decomposition type foaming agent) in the heating step was 20 or less, and the obtained crosslinked foam was closed-celled, but had an expansion ratio of about 4 times. I could only get it. The dynamic viscoelasticity at 175 ° C. and 1 Hz when the resin component was crosslinked so as to have a degree of crosslinking of 30% as in Example 1 was as shown in Table 1.

Comparative Examples 2 and 3 A predetermined amount of resin components (LLDPE1 and LLDPE1, LDPE1 to LDPE4,
VA1 and 2), azodicarbonamide, dicumyl peroxide, triallyl isocyanurate and zinc oxide were molded in the same manner as in Example 1. Crosslinking degree after molding is 0%
The dynamic viscoelasticity of the resin component at 135 ° C. and 10 Hz was as shown in Table 1. Further, cross-linking and foaming were performed in the same manner as in Example 1, but the cells became extremely uneven, and a cross-linked foam was not obtained. In addition, when the resin component was crosslinked so as to have a degree of crosslinking of 30% as in Example 1, 1
The dynamic viscoelasticity at 75 ° C. and 1 Hz was as shown in Table 1.

(Evaluation of Compression Recovery Property) The thickness of the open-cell crosslinked foam obtained in the examples was measured 10 days after the roll compression, and the thickness recovery rate with respect to the thickness (5 cm) before the roll compression was determined. It was calculated by the following equation, and the value is shown in Table 1. Thickness recovery rate (%) = (thickness after 10 days (cm) / thickness before roll compression (cm)) × 100

(Evaluation of Appearance) In the examples, both sides of the open-cell crosslinked foam immediately after roll compression were visually observed,
The results are shown in Table 1, in which the case where no appearance defect such as uneven foaming was observed on the surface was evaluated as ○, and the case where the appearance defect was observed was evaluated as ×.

[0052]

[Table 1]

[0053]

According to the first aspect of the present invention, since it has the above-described structure, it has excellent compression recovery, sealing properties and airtightness, a high open cell ratio, and a high open-cell open-cell crosslinkability. A foam is easily obtained. In addition, since the dynamic viscoelasticity during or after cross-linking foaming is within a specific range, the cross-linked foam having good foam retention in the foaming step and uniform foam and high expansion ratio can be obtained. Obtained easily.

Claims (2)

[Claims] (1) a density of 0.840 to 0.900 g / cm;
100 parts by weight of an ethylene-based resin polymerized using a metallocene catalyst containing an ethylene-based resin or a tetravalent transition metal of ³ , 100 to 30 parts by weight of a pyrolytic foaming agent, and 0.3 to 0.3 parts of a crosslinking agent
3 parts by weight are heat-molded in a non-crosslinked state, and then heated under normal pressure, crosslinked and foamed so that the maximum value of (crosslinking degree / decomposition rate of the thermal decomposition type foaming agent) becomes 20 or less, crosslinked foaming. A method for producing an open-celled cross-linked foam which is made into a body and communicates by applying mechanical deformation to the cells of the cross-linked foam, wherein the dynamic viscosity of the ethylene resin after being heat-molded in a non-cross-linked state. Elasticity is 2.0 × 10 ³ at 135 ° C. and 10 Hz
A method for producing an open-cell crosslinked foam having a viscosity of 5.0 × 10 ³ Pa · s. 2. The dynamic viscoelasticity of the ethylene-based resin at a crosslinking degree of 30% is 175 ° C. and 1.0 × 10 ^{4 to} 5 at 1 Hz.
The method for producing an open-cell crosslinked foam according to claim 1, wherein the pressure is 0 × 10 ⁴ Pa · s.