JPH11348064A - Manufacture of crosslinked open cell foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method, with which a crosslinked open cell foam made of an olefin-based resin, excellent in compressional recovery properties, sealing properties airtightness and heat resistance and high in open cell rate can be easily obtained. SOLUTION: A crosslinked foam is produced by molding an olefin-based resin, a thermal decomposition type foaming agent and two specified kinds of organic peroxides A and B under heat in non-crosslinked state and then heating up to a temperature, at which the organic peroxide A is halved in one minute under a normal pressure, or higher and below a temperature, at which the organic peroxide B is halved in one minute, so as to set the maximum value of the ratio of the degree of crosslinking to the decomposition ratio of the thermal decomposition type foaming agent not more than 20 through crosslinking and foaming. The cells of the crosslinked foam are made to intercommunicate with one another by applying a mechanical deformation. After that, the resultant foam is heated up to a temperature, at which the organic peroxide B is halved in one minute, or higher so as to produce a crosslinked open cell foam.

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 and sealing properties can be obtained, but the crosslinking agent is decomposed simultaneously with the decomposition of the blowing agent. And there was a problem that heat resistance was insufficient.

As a method of improving the heat resistance by increasing the degree of cross-linking, for example, Japanese Patent Application Laid-Open No. 22345/1990 discloses a method of irradiating an ethylene resin with ionizing radiation. When an electron beam or the like is used, when the thickness of the foam becomes about 1 cm or more, the transparency of the electron beam is insufficient, so that the heat resistance is not improved, and the γ-ray or the like having good transparency as ionizing radiation is used. In the case of using, there was a problem that the dose rate was low, so that it was inefficient.

[0007]

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

[0008]

According to the present invention, there is provided a method for producing an open-cell crosslinked foam, comprising:
1 to 30 parts by weight of a thermal decomposition type foaming agent, (A) 0.2 to 2 organic peroxides having a half-life temperature of 150 ° C. or more and less than 185 ° C. for 1 minute
Parts by weight and (B) 0.2 to 2 parts by weight of an organic peroxide having a half-life temperature of 185 to 200 ° C. for 1 minute in a non-crosslinked state, and then heat-molded. The mixture is heated to a temperature equal to or higher than the half-life temperature for one minute and lower than the half-life temperature for one minute of the organic peroxide (B) so that the maximum value of (degree of crosslinking / decomposition rate of the thermal decomposition type foaming agent) becomes 20 or less. Then, the cells of the crosslinked foam are communicated by applying mechanical deformation to the crosslinked foam, and then heated to a temperature equal to or higher than the half-life temperature of the organic peroxide (B) for 1 minute or more.

As the olefin resin used in the present invention, any resin conventionally used for foams can be used.
Generally, ethylene-based resins, propylene-based resins and mixtures thereof are used.

When the density of the ethylene-based resin is reduced, it becomes difficult to polymerize from a monomer, and when the density is increased, the compression recovery property, sealing property and airtightness of the open-cell crosslinked foam are reduced. those ~0.910g / cm ³ (hereinafter, referred to as "ethylene-based resin (a)") are preferred, it is more preferred 0.840~0.890g / cm ^3. As such an ethylene-based resin, for example,
Linear low-density polyethylene may be used, 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 propylene, 1-butene, and 1-butene.
Pentene, 4-methyl-1-pentene, 1-hexene,
1-heptene, 1-octene, and the like.
Octene is preferred.

When the amount of the ethylene resin (a) is too small, the compression recovery, sealing property and airtightness of the open-cell cross-linked foam decrease, so that the olefin resin should be contained in an amount of 20% by weight or more. preferable.

As a method for obtaining the ethylene resin (a), for example, a method of polymerizing using a metallocene compound containing a tetravalent transition metal can be mentioned.

Hereinafter, a method of performing polymerization using a 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, a compound in which at least one cyclopentadienyl ring or an analog thereof is present as a ligand (ligand) on a tetravalent transition metal such as titanium, zirconium, hafnium, nickel, palladium, or platinum 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,
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 metallocene compounds include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, 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 during the polymerization of the ethylene resin 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 for example, a solution polymerization method using an inert medium, a bulk polymerization method in which substantially no inert medium is present, a gas phase polymerization method and the like can be employed. Generally, the polymerization temperature is from -100 ° C to 300 ° C, and the polymerization pressure is from normal pressure to 100 kg / cm ² .

Examples of the ethylene resin other than the ethylene resin (a) (hereinafter referred to as “ethylene resin (b)”) include linear low density polyethylene, low density polyethylene, medium density polyethylene, and high density polyethylene. Polyethylene, ethylene-vinyl acetate copolymer containing ethylene as a main component,
Examples thereof include an ethylene-ethyl acrylate copolymer containing ethylene as a main component, 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.As the α-olefin other than ethylene,
The same thing as the above is mentioned.

As the propylene resin, for example,
Examples thereof include polypropylene and a copolymer with an α-olefin other than propylene containing propylene as a main component, and these may be used alone or in combination of two or more. Examples of the α-olefin other than propylene include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene and the like.

The thermal decomposition type foaming agent used in the present invention has low foaming properties when the decomposition start temperature is low, and tends to cause uneven foaming such as abnormal air bubbles when the decomposition start temperature is high. Is preferably higher by 20 to 70 ° C. than the melting point (peak temperature in DSC) of In addition, when the decomposition end temperature is low, the foaming property is reduced, and when the decomposition end temperature is high, foaming is often incompletely completed. Therefore, the decomposition end temperature is preferably 150 to 210 ° C. As such a thermal decomposition type foaming agent, for example, azodicarbonamide (decomposition start temperature = about 200 ° C., decomposition end temperature = about 21
0 ° C.), N, N′-dinitrosopentamethylenetetramine (decomposition start temperature = about 200 ° C., decomposition end temperature = about 20 ° C.)
5 ° C.), 4,4′-oxybisbenzenesulfonyl hydrazide (decomposition start temperature = about 155 ° C., decomposition end temperature = about 160 ° C.) and the like.
More than one species may be used in combination. Above all, azodicarbonamide is preferred because it is excellent in the amount of generated gas, handling safety, and the like. The addition amount of the thermal decomposition type foaming agent is appropriately adjusted according to the desired expansion ratio. However, if the amount is small, the desired expansion ratio cannot be obtained. Since the maximum value of the decomposition rate of the blowing agent) easily exceeds 20, it is limited to 1 to 30 parts by weight based on 100 parts by weight of the olefin resin.

Organic peroxide (A) used in the present invention
Is 1 minute half-life temperature (hereinafter referred to as “half-life temperature”)
50 ° C. or higher and lower than 185 ° C., for example, dicumyl peroxide (half 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-life = about 182 ° C), t-butylperoxycumene (half-life = about 178 ° C) and the like. Or two or more of them may be used in combination.

If the amount of the organic peroxide (A) is too small, a desired degree of crosslinking cannot be obtained, and if it is too large, the maximum (crosslinking degree / decomposition rate of the thermal decomposition type foaming agent) in the later-described crosslinking and foaming step will be increased. Since the value easily exceeds 20, it is limited to 0.2 to 2 parts by weight based on 100 parts by weight of the olefin resin.

The organic peroxide (B) used in the present invention
Has a half-life temperature of 185 to 200 ° C., for example, 1,1,3,3-tetramethylbutyl hydroperoxide (half-life temperature = about 190 ° C.), di-t-butyl peroxide (half-life temperature = about 192) ° C), 2,5-dimethyl-2,5-di (t-butylperoxy) 3-hexene (half temperature = about 193 ° C), and these may be used alone or in combination of two or more. Is also good.

As the amount of the organic peroxide (B) decreases, the heat resistance of the obtained open-celled crosslinked foam decreases,
If the amount increases, crosslinking proceeds more than necessary, so that the amount is limited to 0.2 to 2 parts by weight based on 100 parts by weight of the olefin resin.

If the total amount of the organic peroxide (A) and the organic peroxide (B) is too small, a desired degree of crosslinking cannot be obtained. If the amount is too large, crosslinking proceeds more than necessary. 0.4 parts per 100 parts by weight of olefin resin
~ 3 parts by weight are preferred.

In the present invention, a crosslinking aid, a foaming aid, and an inorganic additive may be added to the olefin resin, the pyrolytic foaming agent, the organic peroxide (A) and the organic peroxide (B), if necessary. The mixture is melt-kneaded with a kneader mixer or the like, and then heat-molded into a desired shape while maintaining a non-crosslinked state by a conventionally known arbitrary method such as a press, and then heated under normal pressure, crosslinked and foamed. To form a crosslinked foam.

Examples of the crosslinking aid include triallyl isocyanurate, divinylbenzene, trimethylolpropane tri (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and 1,9-nonanediol di (meth) acrylate. ) Acrylate, 1,10-decanediol di (meth) acrylate, triallylic acid triallyl ester, ethylvinylbenzene, diallyl phthalate, etc., which may be used alone or in combination of two or more. Good. Among them, triallyl isocyanurate is preferable because of its excellent affinity with the resin.

Examples of the foaming aid include zinc oxide, urea or derivatives thereof, and stearate salts such as magnesium stearate. These may be used alone or in combination of two or more.

The above-mentioned inorganic additive facilitates communication of the cells of the crosslinked foam in the step of applying mechanical deformation described later, and inorganic fillers conventionally used for foams can be used. Calcium, talc, metal oxides and the like can be mentioned, and these may be used alone or in combination of two or more.

The conditions for heat-molding into a desired shape in the non-crosslinked state are as follows: resin used, organic peroxide (A),
It varies depending on the type and amount of the organic peroxide (B) and the like, and may be determined as appropriate. For example, when dicumyl peroxide is used as the organic peroxide (A), the temperature is 130 to
Suitably heating at 140 ° C. for 10 to 30 minutes.

The non-crosslinked state referred to in the present invention is a state in which the degree of crosslinking is 0%, and when crosslinking occurs in the heating molding step, bubbles are generated in the step of applying mechanical deformation described later. No communication and the open cell ratio is reduced. When the step of heat molding is not performed, the viscosity of the resin is not adjusted, so that the open cell ratio and the compression recovery of the open-cell crosslinked foam are reduced.

The degree of crosslinking referred to in the present invention is a value measured by the following method. First, about 50 mg of the foam at any time is precisely weighed in the thickness direction, and the bubbles are crushed.
After immersion in 100 ml of xylene at 20 ° C. for 24 hours, 2
The mixture is filtered through a 00 mesh stainless steel wire mesh, and the insoluble matter on the wire mesh is vacuum dried at 80 ° C. for 5 hours. 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

Next, cross-linking and foaming are carried out under normal pressure to obtain a cross-linked foam. When the value of (degree of cross-linking / decomposition rate of thermal decomposition type foaming agent) at any time in this step increases, it will be described later. Since the bubbles do not communicate in the step of applying mechanical deformation and the open cell ratio is reduced, the maximum value is limited to 20 or less.

The decomposition rate of the pyrolytic foaming agent according to the present invention is as follows:
For the expansion ratio of the obtained cross-linked foam, the value of the ratio of the expansion ratio at the time of measuring the degree of cross-linking is a value shown as a percentage,
It is calculated by the following equation.

Decomposition rate (%) = ｛Expanded expansion ratio (cc)
/ G) / expansion ratio of the obtained crosslinked foam (cc / g)}
× 100

The expansion ratio is the reciprocal of the density (g / cc) measured using an electronic hydrometer (trade name “ED120T” manufactured by Mirage Co., Ltd.).

The conditions for the above crosslinking and foaming depend on the type and amount of the resin, the pyrolytic foaming agent, the organic peroxide (A), the organic peroxide (B), and the like, and are determined as appropriate. But usually at a temperature of 150 to 180 ° C.,
Heat for 90 minutes.

The obtained crosslinked foam has closed cells, but the cells are opened by mechanical deformation to open the cells, and then reheated to obtain the open-cell crosslinked foam of the present invention.

As the method for applying the mechanical deformation, any conventionally known method may be employed. For example, the crosslinked foam may be rolled at a constant speed by two rolls at a thickness of 1 to 10 mm. %.
The step of applying mechanical deformation may be performed only once or may be repeated a plurality of times.

The reheating step is performed to decompose the organic peroxide (B) and increase the degree of crosslinking, and the heating temperature is limited to a temperature equal to or higher than the half temperature of the organic peroxide (B). The heating conditions include the type and amount of the resin and the organic peroxide (B) used,
It depends on the thickness of the cross-linked foam, the expansion ratio, and the like, and may be determined as appropriate. However, usually, the lower the heating temperature, the lower the decomposition rate of the organic peroxide (B), and the higher the heating temperature, the more the resin deteriorates. It is preferable to heat at 170 to 200 ° C. for 10 to 20 minutes.

In addition, when the increase in the degree of crosslinking due to the reheating step decreases, the effect of improving the heat resistance decreases.
% Or more, more preferably 10% or more.

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.

[0046]

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.

[0047]

EXAMPLES (Examples 1 to 3, Comparative Examples 1 and 2) A predetermined amount of LLDPE shown in Table 1 (density = 0.870 g / cm ³⁾
Linear low-density polyethylene copolymerized with 1-octene, manufactured by Dow, trade name "EG8200"), LDPE
(Low-density polyethylene having a density of 0.932 g / cm ³ ,
Sumitomo Chemical Co., Ltd., trade name "F203-0"), azodicarbonamide, 1,1-di (t-butylperoxy) 3,
3,5-trimethylcyclohexane (half temperature = about 15
1 ° C.), dicumyl peroxide (half temperature = about 171)
° C), 1,1,3,3-tetramethylbutyl hydroperoxide (half temperature = about 190 ° C), 2,5-dimethyl-2,5-di (t-butylperoxy) 3-hexene (half temperature = about 190 ° C). 193 ° C.), melt kneading triallyl isocyanurate and zinc oxide at about 110 ° C. with a kneader mixer, then 30 cm long × 30 cm wide × 5 cm deep
Was placed in a mold having a concave portion, and 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%.

Next, the mixture was heated in an oven at 175 ° C. for 60 minutes to perform crosslinking and foaming, thereby obtaining 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 obtained cross-linked foam was sliced to a thickness of 5 cm, compressed to a thickness of 2 mm using a constant-speed roll having a rotation speed of 5 rpm and a diameter of 100 mm to communicate bubbles, and an open-cell cross-linked foam was obtained. (Hereinafter referred to as “open-cell crosslinked foam (1)”). The expansion ratio and the degree of crosslinking of the obtained open-cell crosslinked foam (1) were as shown in Table 2.

Further, the open-cell crosslinked foam (1)
Was heated in an oven at 180 ° C. for 15 minutes. The degree of crosslinking of the heated open-cell crosslinked foam (hereinafter referred to as “open-cell crosslinked foam (2)”) was as shown in Table 2.

The open-celled crosslinked foam (2) was evaluated for its open-cell properties and compression-recovery properties, and the heat resistance of the open-cell crosslinked foams (1) and (2) as follows.

(Evaluation of open cell properties) ASTM D-19
The open cell ratio was calculated from the closed cell ratio of the open-cell crosslinked foam (2) measured according to 40-62T by the following formula, and is shown in Table 2. Open cell rate (%) = 100-Closed cell rate (%)

(Evaluation of Compression Recovery) The thickness of the open-celled crosslinked foam (2) was measured 10 days after roll compression, and the thickness recovery ratio with respect to the thickness (5 cm) before roll compression was calculated by the following formula. , And the values are shown in Table 2.

Thickness recovery rate (%) = ｛thickness after 10 days (c)
m) / thickness before roll compression (cm)｝ × 100

(Evaluation of Heat Resistance) The dimensional change rate of the open-cell crosslinked foamed materials (1) and (2) at 110 ° C. was measured according to JIS K 6767 except that the temperature was changed to 110 ° C. The values are shown in Table 2.

Comparative Example 3 LLDPE, L shown in Table 1
After melt-kneading DPE, azodicarbonamide, 1,1,3,3-tetramethylbutyl hydroperoxide, triallyl isocyanurate and zinc oxide at about 110 ° C. using a kneader mixer, the length is 30 cm × 30 cm ×
It was introduced into a mold having a concave portion having a depth of 5 cm, 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%.

Next, when heated in an oven at 175 ° C. for 60 minutes, the cell diameter became extremely uneven, and no foam was obtained.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

According to the present invention, the open-cell crosslinked foam of the present invention has the above-mentioned structure, and therefore has excellent compression-recovery, sealability and airtightness, and has a high open-cell ratio. Obtained easily. Further, the degree of cross-linking can be increased as required, and an open-cell cross-linked foam excellent in heat resistance can be obtained.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 24

Claims (2)

[Claims] 1. An olefin resin (100 parts by weight), a pyrolytic foaming agent (1 to 30 parts by weight), and (A) a half-life temperature of 15 minutes per minute.
0.2 to 2 parts by weight of an organic peroxide having a temperature of 0 ° C or more and less than 185 ° C and (B) 0.2 to 2 parts by weight of an organic peroxide having a half-life temperature of 185 to 200 ° C for 1 minute in a non-crosslinked state. After molding, the organic peroxide (A) is heated under normal pressure to a temperature equal to or higher than the half-life temperature of 1 minute and lower than the half-life temperature of the organic peroxide (B) for 1 minute. Crosslinking and foaming to form a crosslinked foam such that the maximum value of the decomposition rate is 20 or less, and the cells of the crosslinked foam are communicated by applying mechanical deformation to the organic peroxide (B). A method for producing an open-cell, crosslinked foamed body, wherein the foamed body is heated to at least a half-life temperature for one minute. 2. An olefin resin having a density of 0.840.
~0.910g / cm ³ of the ethylene-based resin 20 wt%
The method for producing an open-cell crosslinked foam according to claim 1, which contains the above.