JP2001011228A - Foam and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foam which comprises a thermoreversibly crosslinkable resin and has a fine cell diameter thereby exhibiting improved dynamic properties, looking ultra-white and presenting a good appearance, and furthermore is excellent in recyclability, and to provide a method for preparing the same. SOLUTION: This foam comprises a thermoreversibly crosslinkable resin which flows at a flow beginning temperature Tc( deg.C) or above and has a crosslinked structure at Tc-40( deg.C) or below, and has an average cell diameter of at least 0.1 μm and not more than 30 μm and a void content of at least 20% and not more than 99%. The foam can be prepared by injecting a blowing agent soluble in a thermoreversibly crosslinkable resin into the resin at a temperature where the melt index (MI) of the resin is at least 1.5, cooling the resin down to a temperature where the MI of the resin is not more than 1.0 and allowing it to expand at a discharge opening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam comprising a thermoreversible crosslinkable resin having a fine foam diameter and excellent in recyclability, and a method for producing the foam.

[0002]

2. Description of the Related Art In recent years, crosslinked foams have excellent heat resistance, light weight, heat insulation and sound insulation, and are easy to mold by various processing methods. It is widely used in the field of industrial materials such as heat insulating materials for building and building applications, adhesive tapes, packing and packaging materials.

[0003] Foams include non-crosslinked foams and crosslinked foams. Non-crosslinked foams are mainly produced by the extrusion foaming method. A crosslinked foam is manufactured by adding a foaming agent to a thermoplastic resin, forming the sheet into a sheet, introducing a crosslinked structure, and thermally decomposing the foaming agent to foam. Methods for crosslinking the crosslinked foam include radiation and electron beam irradiation, a method using a thermally decomposable crosslinking material such as an organic peroxide, and a method of introducing an alkoxylyl group and subjecting it to a condensation reaction.

In general, crosslinked resin foams have better physical properties such as heat resistance and strength than non-crosslinked resin foams, and have higher heat moldability. However, the conventional crosslinked resin foam does not exhibit melt fluidity unless heated to a temperature close to the decomposition temperature of the resin, and thus has the drawback that remelt molding is substantially difficult and recyclability is poor.

On the other hand, in the field of foams, foams having many finer cells are desired. Such a foam has a small decrease in the mechanical properties of the foam,
It has features such as high whiteness, and is expected to be applied in the field of reflectors for surface light sources, print receiving papers, and the like. As a production method thereof, a method of continuously supplying a supercritical liquid to a thermoplastic resin and foaming the same as disclosed in Japanese Patent No. 2625576 is exemplified. In order to obtain such a fine foam continuously by extrusion foaming, it is necessary to modify the melting characteristics of the thermoplastic resin, and usually,
An object is achieved by improving the melt viscosity of a thermoplastic resin, introducing a branched chain structure, introducing a partially crosslinked structure, and the like. However, at present, it is not possible to obtain a foam having a large number of fine cells that is still satisfactory as a product by conventional resin modification alone.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoreversible crosslinkable material having a fine foam diameter, improved mechanical properties, super white appearance and excellent recyclability. An object of the present invention is to provide a resin foam and a method for producing the foam.

[0007]

The foam of the present invention exhibits fluidity at a flow starting temperature Tc (° C.) or higher, and Tc-40.
(° C.) or less, a foam made of a thermoreversible crosslinkable resin having a crosslinked structure, having an average foamed diameter of 0.1 μm to 3 μm
A foam having a pore size of 0 μm or less and a porosity of 20% or more and 99% or less, and further has the following preferred embodiment. (a) The flow start temperature Tc is 240 ° C. or less. (b) The degree of crosslinking of the thermoreversible crosslinking resin at room temperature is 5% or more 8
0% or less. (c) The specific gravity of the foam is 0.5 or less. (d) The foam is composed of closed cells. (e) Having a non-foamed layer on at least one side. (f) A thermoplastic resin having a degree of crosslinking at room temperature of 3% or less is blended. (g) It must be stretched at least uniaxially. (h) The thermoreversible crosslinkable resin is a polyolefin resin. Further, in the method for producing a foam of the present invention, a foaming agent which is soluble in a thermoreversible crosslinkable resin having a resin having a melt index (MI) of 1.5 or more is injected into the foam. A method for producing a foam, characterized in that the foam is cooled at a certain resin temperature and then foamed at a discharge port, or a foam soluble in a thermoreversible crosslinkable resin having a resin temperature of MI of 1.5 or more. A method for producing a foam, comprising injecting an agent, cooling the resin to a resin temperature having an MI of 0.5 or less, discharging the resin in an unfoamed state, and then rapidly heating to foam the foam.

In the method for producing a foam of the present invention, it is preferable that a soluble blowing agent is injected in a supercritical state.

[0009]

Embodiments of the present invention will be described below in detail.

The foam of the present invention has a flow starting temperature Tc.
(C) or more shows fluidity, and Tc-40 (C) or less is a foam made of a thermoreversible crosslinkable resin having a crosslinked structure, having an average foamed diameter of 0.1 μm or more and 30 μm or less, and This is achieved when the porosity of the foam is from 20% to 99%. That is, the present inventors use a thermo-reversible cross-linkable resin having a cross-linking structure at a foaming temperature or lower and exhibiting melt fluidity at the time of melt-kneading. They have found what the body can achieve and arrived at the present invention.

Here, the flow start temperature Tc is a temperature at which the melt index (MI) becomes 0.1, and having a crosslinked structure means a state in which the degree of crosslinking is 5% or more. . The thermoreversible crosslinkable resin that satisfies such characteristics is not particularly limited as long as it satisfies such characteristics.
No. 062 and 7-94029, an unsaturated carboxylic anhydride-modified polyolefin resin, a polyhydric alcohol compound having at least two or more hydroxyl groups in a molecule and an organic carboxylic acid. A resin composition comprising a reaction accelerator such as a metal salt;
A resin composition comprising a carboxylic acid anhydride-modified olefin-based resin and a compound containing two or more hydroxyl groups as disclosed in JP-A-106578 is mentioned.

The skeletal resin of the thermoreversible crosslinkable resin referred to in the present invention is not particularly limited, but polyolefin resins such as polyethylene, polypropylene and polymethylpentene, polyamide resins such as nylon 6, nylon 66, and polyethylene terephthalate. And polyester resins such as polybutylene terephthalate and polyethylene-2,6-naphthalate, polyacetal resins, polyphenylene sulfide resins, and the like.
These may be modified. Among them, in the present invention, the thermoreversible crosslinkable resin more preferably used is a polyolefin resin, more preferably,
It is a polypropylene resin.

In general, a thermoreversible crosslinkable resin means that a polymer chain forms a three-dimensional network structure by a chemical bond or a physical bond below a certain temperature. These bonds are dissociated and no longer form a three-dimensional network structure, and this structure formation is reversible during the temperature raising process and the temperature lowering process.

Examples of the thermoreversible crosslinkable resin include, for example, an unsaturated carboxylic anhydride-modified polyolefin resin, a polyhydric alcohol compound having at least two or more hydroxyl groups in a molecule, and a metal salt of an organic carboxylic acid. And the like, and a resin composition component composed of a reaction accelerator.

The polyolefins used for producing this modified polyolefin include ethylene, propylene, 1-butene, 1-hexene and 4-methyl-1-.
Homopolymers of olefins such as pentene or random or block copolymers of two or more of these olefins, or vinyl acetate, acrylic acid, methacrylic acid, acrylates based on these olefins,
It is a binary or multi-component copolymer with a methacrylate or the like. Specifically, high-density polyethylene, low-density polyethylene, polypropylene, ethylene-propylene random copolymer, ethylene-vinyl acetate copolymer, ethylene-
Butene-1 copolymer, propylene-butene-1 copolymer, ethylene-acrylate copolymer, ethylene-maleic anhydride-acrylate copolymer, zinc salt of ethylene-methacrylic acid copolymer, etc. is there. These may be used alone or in combination of two or more.

The unsaturated carboxylic anhydride used as the graft monomer includes, for example, maleic anhydride,
Itaconic anhydride, endic anhydride, citraconic anhydride, 1-butene-3,4-dicarboxylic anhydride, alkenyl succinic anhydride having at most 18 carbon atoms having a double bond at a terminal, and having many carbon atoms And alkadienyl succinic anhydride having a double bond at the terminal which is both 18. These may be used alone or in combination of two or more. Of these, maleic anhydride and itaconic anhydride are preferred.

The unit derived from the unsaturated carboxylic anhydride in the modified polyolefin is preferably in the range of 0.1 to 20% by weight, more preferably 1 to 10% by weight. If the unit derived from the acid anhydride is less than 0.1% by weight, the crosslinking density, which is the object of the present invention, becomes insufficient, which is not preferable. On the other hand, if it exceeds 20% by weight, properties such as flexibility and mechanical strength expected of the modified polyolefin are impaired, which is not preferable.

In order to produce the modified polyolefin used in the present invention, any known method can be employed. That is, a solution in which a polyolefin is dissolved in a solvent, a radical initiator and an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride are mixed and reacted, and a solution grafting method in which a denaturation is performed in an extruder in the absence of a solvent. A radiation grafting method using an electron beam or the like can be used. Furthermore, after graft modification by these methods,
It is preferable to remove unreacted substances, reaction by-products, and the like by washing with a solvent.

Examples of the polyhydric alcohol compound having at least two hydroxyl groups in the molecule include glycols such as ethylene glycol, diethylene glycol and triethylene glycol; 1,4-butanediol, 1,6
-Hexanediol, 1,8-octanediol, 1,
Alcohol compounds such as 10-decanediol, trimethylolethane, trimethylolpropane, and pentaerythritol; albitol, sorbitol, xylose, arabinose, glucose, galactose, sorbose,
Saccharides such as fructose, palatinose, maltotriose, and marezitose; saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyolefin oligomer having a plurality of hydroxyl groups, ethylene-hydroxyethyl (meth) acrylate [(meth) acrylate is , Methacrylates and acrylates. The same applies to the following.] Polymers having a plurality of hydroxyl groups in the molecule such as copolymers; 1,3-dihydroxypropane, 2,2-dimethyl-1,3-dihydroxypropane, trimethylolethane, 1,1,1 -Trimethylolpropane, 1,1,1
-Trimethylolhexane, 1,1,1-trimethyloldodecane, 2-cyclohexyl-2-methylol-
1,3-dihydroxypropane, 2- (p-methylphenyl) -2-methylol-1,3-dihydroxypropane, pentaerythritol, glycerin, diglycerin, hexadiglycerin, octaglycerin, decaglycerin, etc. to ethylene oxide or propylene oxide Glycerin monostearate, glycerin monooleate,
Glycerin monolaurate, glycerin monocaprylate, glycerin monohexanoate, glycerin monophenethyl ester, glycerin monopropionate, diglycerin monostearate, diglycerin distearate, diglycerin monooleate, diglycerin monohexano Eate, diglycerin dioctanoate, tetraglycerin monostearate, tetraglycerin tristearate, tetraglycerin tetrastearate,
Tetraglycerin trihexanoate, tetraglycerin monophenethyl ester, hexaglycerin monostearate, hexaglycerin distearate, hexaglycerin pentastearate, hexaglycerin trioleate, hexaglycerin monolaurate, hexaglycerin pentalaurate, decaglycerin Polyglycerin alkyl esters such as monostearate, decaglycerin octasterate, decaglycerin pentaoleate, decaglycerin dilaurate, pentadecaglycerin distearate, pentadecaglycerin decaoleate, and octadecaglycerin tetrastearate;
Sorbitan monostearate, sorbitan monooleate, sorbitan monolaurate, sorbitan monocaprylate, sorbitan monohexanoate, sorbitan monophenethyl ester, sorbitan monopropionate, sorbitan tristearate, sorbitan alkyl such as sorbitan tetrastearate Esters and the like. The melting point of these polyhydric alcohol compounds is preferably 300 ° C. or less in consideration of the thermal deterioration of the modified polyolefin. These polyhydric alcohol compounds can be used alone or in combination of two or more.

The amount of the polyhydric alcohol used is such that the molar ratio of the hydroxyl group contained in the polyhydric alcohol compound to the unit derived from the unsaturated carboxylic anhydride contained in the modified polyolefin is 0.01 to 10. It is preferably in the range, more preferably in the range of 0.05 to 5. When the molar ratio is less than 0.01, it is insufficient to introduce an effective amount of the crosslinked structure into the composition. When the molar ratio exceeds 10, the crosslinked structure may be formed at a processing temperature at the time of molding. It is not preferable because it is not completely dissociated and molding becomes extremely difficult. Further, the unit derived from the unsaturated carboxylic anhydride contained in the modified polyolefin is 0.1 to 1 unit.
When it is in the range of% by weight, the molar ratio of the hydroxyl group contained in the polyhydric alcohol compound is more preferably in the range of 0.1 to 5.

The reaction accelerator is a compound which activates the carbonyl group contained in the unit derived from the unsaturated carboxylic anhydride contained in the modified polyolefin to promote the reaction between the hydroxyl group and the acid anhydride group. . There are various types of such reaction accelerators. One example is a metal salt of an organic carboxylic acid.

The metal salts of organic carboxylic acids include metal salts of fatty acids having 1 to 30 carbon atoms, such as acetic acid, propionic acid, butyric acid, octanoic acid, decanoic acid, lauric acid, and the like.
Myristic acid, palmitic acid, stearic acid, oleic acid, behenic acid and the like and the periodic table genus IA, IIA, IIB,
III Group B metals (eg, Li, Na, K, Mg, C
a, Zn, Al, etc.). More specific examples include lithium acetate, sodium acetate, magnesium acetate, aluminum acetate, potassium butyrate, calcium butyrate, zinc butyrate, sodium octanoate, calcium octanoate, potassium decanoate, magnesium decanoate,
Zinc decanoate, lithium laurate, sodium laurate, calcium laurate, aluminum laurate, potassium myristate, sodium myristate,
Aluminum myristate, sodium palmitate,
Examples include zinc palmitate, magnesium palmitate, sodium stearate, potassium stearate, calcium stearate, zinc stearate, sodium oleate sulfate, and sodium behenate. Of these, lithium laurate, sodium laurate, calcium laurate, aluminum laurate, potassium myristate, sodium myristate, aluminum myristate, sodium palmitate, zinc palmitate, magnesium palmitate, sodium stearate, potassium stearate , Calcium stearate, zinc stearate, sodium oleate and the like are preferred.

Another example of a metal salt of an organic carboxylic acid is a resin having a metal salt structure of a carboxylic acid. Examples of such a resin include metals of Group IA, Group IIA, Group IIB and Group IIIB of ethylene and a radical polymerizable unsaturated carboxylic acid (eg, Li, Na, K, Mg, Ca, Zn, Al).
Etc.) those having a structure obtained by copolymerizing a salt or those having a structure obtained by multiply copolymerizing ethylene and a metal salt of a radically polymerizable carboxylic acid with another radically polymerizable unsaturated carboxylic acid and / or a derivative thereof. No.

Further, polyethylene, polypropylene,
A structure in which a metal salt of a radically polymerizable unsaturated carboxylic acid (a free unsaturated carboxylic acid may be polymerized and then neutralized) is graft-polymerized on a polyolefin resin such as a free ethylene-propylene copolymer. And those having a structure in which a metal salt of a radically polymerizable carboxylic acid and another radically polymerizable unsaturated carboxylic acid and / or a derivative thereof are simultaneously co-grafted and polymerized on a polyolefin resin. Examples of the radically polymerizable unsaturated carboxylic acid and its derivative used herein include (meth) acrylic acid, maleic acid, fumaric acid, monomethyl maleate, monomethyl fumarate, monoethyl maleate, monoethyl fumarate, monobutyl maleate, fumarate Monobutyl acid, methyl (meth) acrylate, dimethyl maleate, dimethyl fumarate, diethyl maleate, diethyl fumarate, dibutyl maleate, dibutyl fumarate, and the like.

Another example of the reaction accelerator is a tertiary amine compound. Specific examples of the tertiary amine compound used here include trimethylamine, triethylamine, triisopropylamine, trihexylamine, trioctylamine, trioctadecylamine, dimethylethylamine, methyldioctylamine,
Dimethyloctylamine, diethylcyclohexylamine, N, N-diethyl-4-methylcyclohexylamine, diethylcyclododecylamine, N, N-diethyl-1-adamantamine, 1-methylpyrrolidine, 1-ethylpiperidine, quinuclidine, triphenyl Amine,
N, N-dimethylaniline, N, N-diethylaniline, N, N-dimethyl-m-phenetidine, 4-t-butyl-N, N-dimethylaniline and the like.

Other examples of the reaction accelerator include quaternary ammonium salts. Examples of the quaternary ammonium salt used herein include, for example, tetramethylammonium tetrafluoroborate, tetramethylammonium hexafluorophosphate, tetramethylammonium bromide, tetraethylammonium bromide, tetraethylammonium iodide, methyltri-n-butylammonium chloride, tetramethylammonium chloride Butylammonium bromide, tetrahexylammonium bromide, tetraheptylammonium bromide, phenyltrimethylammonium bromide, benzyltriethylammonium chloride and the like.

Further, a hydroxide of a metal belonging to Group IIA, IIB or IIIB or a halide of a metal belonging to Group IIA or IIB can be used as a reaction accelerator. Where IIA
Examples of the hydroxides of the metals of the genera, IIB, and IIIB include, for example, calcium hydroxide, magnesium hydroxide, and aluminum hydroxide. Examples of the halides of the metals of the IIA and IIB include, for example, Calcium chloride, calcium bromide, magnesium chloride and the like.

Further, oxo acids and genus IA, IIA, IIB
Salts of metals of the group IIIB can be used as reaction accelerators. Specific examples thereof include aluminum nitrate, calcium nitrate, zinc nitrate, magnesium nitrate, aluminum nitrate, sodium phosphate, calcium phosphate, sodium carbonate, calcium carbonate, magnesium carbonate, sodium sulfate, zinc sulfate, magnesium sulfate, aluminum sulfate, and chloric acid. Sodium, potassium chlorate, sodium iodate and the like. In addition, Li BF ₄ , Na B
F ₄ , KBF ₄ , Na PF ₆ , KPF ₆ , Na PC ₁₆ , Na
_{Fe C l4, Na Sn C l4} , Na Sb F 6, KSb F 6, N
alkali metal salts of _{a As F 6, Na As C} l6 like Lewis acids can also be used as a reaction accelerator.

Among the reaction accelerators exemplified above, metal salts of organic carboxylic acids are preferably used. In addition, two or more of the above various reaction accelerators can be used in combination as needed. The use amount of these reaction accelerators is in the range of 0.001 to 20 parts by weight, more preferably 0.01 to 15 parts by weight, based on 100 parts by weight of the modified polyolefin. When the amount is less than 0.001 part by weight, the reaction becomes too slow and it is difficult to effectively introduce a crosslinked structure into the composition. When the amount exceeds 20 parts by weight, the reaction rate is improved. Not only is it meaningless, but it is economically undesirable.

Further, the thermoreversible crosslinkable resin composition of the present invention can contain various additives, compounding agents, fillers, etc. within a range not to impair the properties of the composition. If these are specifically shown, an antioxidant (a heat stabilizer), an ultraviolet absorber (a light stabilizer), an antistatic agent, an antifogging agent, a flame retardant,
Examples include a lubricant (slip agent, anti-blocking agent), an inorganic filler such as a glass filler, an organic filler, a reinforcing agent, a coloring agent (dye or pigment), a foaming agent, and a fragrance. Further, other thermoreversible crosslinkable resins can be added to the resin composition of the present invention depending on the use and purpose.

In order to produce the thermoreversible crosslinkable resin composition, a modified polyolefin, a polyhydric alcohol and a reaction accelerator may be mixed by various means. As a mixing method, dry blending may be performed using a mixer such as a Henschel mixer or a tumbler generally used in the field of olefin polymers, or kneading such as a Banbury mixer, a kneader, an extruder and a roll mill. Melting and kneading using a mixer. At this time, a uniform mixture can be obtained by dry-blending in advance and melt-kneading the resulting mixture. Further, each component can be melt-mixed at the time of molding the resin composition of the present invention. That is, each component can be mixed (dry-blended) in the form of pellets or powder, and can be melt-mixed in an extruder or an injection molding machine by utilizing a production stage of a film or the like.

Further, other thermoreversible crosslinkable resins include carboxylic acid anhydride-modified olefin-based resins, basically, a copolymer of α-olefin and ethylenically unsaturated carboxylic acid anhydride, There is a graft of an α-olefin resin with an ethylenically unsaturated carboxylic anhydride.

As the α-olefin in the former copolymer, for example, ethylene, propylene, butene-1,
4-methylpentene-1, hexene-1 and the like. Examples of the latter ethylenically unsaturated carboxylic anhydride include 2-octen-1-yl succinate anhydride, 2-dodecene-1-yl succinate anhydride and 2-octadecene-1-yl succinate. Anhydride, maleic anhydride, 2,3-dimethylmaleic anhydride, bromomaleic anhydride, dichloromaleic anhydride, citraconic anhydride, itaconic anhydride, 1-butene-3,4-dicarboxylic acid Anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride, 1,2,3,6-tetrahydrophthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, exo-3,6- Epoxy-1,2,3,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, methyl-5-norbornene-2,3
-Dicarboxylic anhydride, endo-bicyclo [2.2.2]
Oct-5-ene-2,3-dicarboxylic anhydride, bicyclo [2.2.2] oct-7-ene-2,3,5,6
-Tetracarboxylic anhydride and the like.

Examples of the former copolymer include a binary copolymer of the α-olefin and the ethylenically unsaturated carboxylic anhydride, and an ethylenically unsaturated copolymer such as acrylic acid, methacrylic acid and maleic acid. Saturated carboxylic acid compounds, vinyl acetate, methyl acrylate, ethylenically unsaturated ester compounds such as methyl methacrylate, acrylamide, methacrylamide, ethylenically unsaturated amide compounds such as N-methylacrylamide, styrene, acrylonitrile,
It may be a ternary or higher multi-component copolymer obtained by copolymerizing other ethylenically unsaturated compounds such as methacrylonitrile. Among these copolymers, a binary or multi-component copolymer of ethylene and an ethylenically unsaturated carboxylic anhydride, particularly maleic anhydride, is preferred, and these copolymers are conventionally known, It can be produced by a polymerization method such as lump, solution and suspension.

The α-olefin resin in the latter graft is, for example, a homopolymer of ethylene (branched or linear) such as low density / medium density / high density polyethylene, ethylene and propylene, Butene-1, 3-
Copolymers with α-olefins such as methylbutene-1, pentene-1, 3-methylpentene-1, 4-methylpentene-1, hexene-1, octene-1, and decene-1;
Ethylene resins such as ethylene and vinyl esters such as vinyl acetate, copolymers of acrylic acid, methacrylic acid, or other monomers such as esters thereof, homopolymers of propylene, propylene, ethylene, butene- 1,3-methylbutene-1, pentene-1,3-methylpentene-
Copolymers with α-olefins such as 1,4-methylpentene-1, hexene-1, octene-1, decene-1, propylene, isoprene, 1,3-butadiene, 1,3
Propylene resins such as copolymers with other monomers such as diene compounds such as pentadiene, 1,4-hexadiene, 1,5-hexadiene and 1,9-decadiene, and butene-1,4-methylpentene; -1, hexene-1 etc. α
-Olefin homopolymers and copolymers.

As the ethylenically unsaturated carboxylic acid anhydride, those similar to the above-mentioned copolymers can be used. Among these grafts, those obtained by grafting an ethylenically unsaturated carboxylic acid anhydride, particularly maleic anhydride, to an ethylene-based resin or a propylene-based resin are preferable. It can be produced by a grafting method such as kneading, solution or suspension.

The content of the ethylenically unsaturated carboxylic anhydride unit as the carboxylic anhydride-modified olefin resin is preferably at least 0.1% by weight, particularly preferably at least 1.0% by weight. It is essential that the average number of bonds as a carboxylic anhydride group per molecule of the modified olefin-based resin, which is obtained from the multiplier of the number-average molecular weight of the modified olefin-based resin and this content, is two or more.
If the average number of bonds is less than 2, the degree of crosslinking of the composition becomes insufficient, and the object of the present invention cannot be achieved in terms of heat resistance. As the carboxylic acid anhydride-modified olefin resin of the component (A) in the present invention, a modified olefin resin may be an unmodified olefin resin as long as the average number of bonds per carboxylic acid anhydride group per molecule is satisfied. It may be diluted with a resin.

The hydroxyl group-containing compound of the component (B) which forms a crosslink by bonding to the carboxylic acid anhydride group of the carboxylic acid anhydride-modified olefin resin does not have a hydroxyl group bonded to a primary carbon atom. It is essential that the compound has two or more hydroxyl groups bonded to secondary carbon atoms. Here, when the number of hydroxyl groups bonded to the secondary carbon atom is less than 2, the degree of crosslinking of the composition becomes insufficient, and the object of the present invention cannot be achieved in terms of heat resistance. Even if the number of hydroxyl groups bonded to the primary carbon atom is two or more, when the compound has a hydroxyl group bonded to the primary carbon atom, the dissociation of crosslinks as a composition becomes insufficient, and the object of the present invention in melt fluidity is as follows. Is difficult to achieve.

As the hydroxyl group-containing compound, specifically, for example, 2,2,4,4-tetramethyl-1,3-
Cyclobutanediol, 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol,
1,4-cyclohexanediol, 1,4-cyclooctanediol, 1,5-cyclooctanediol, 1,
3,5-cyclohexanetriol, inositol and the like, among which 1,2-cyclopentanediol,
1,3-cyclopentanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,
4-cyclohexanediol, 1,4-cyclooctanediol, 1,5-cyclooctanediol, 1,3
5-Cyclohexanetriol is preferred.

As the hydroxyl group-containing compound, specifically, for example, 2,3-butanediol, 2,4-pentanediol, 2,5-hexanediol, 1,1,1,1
5,5,5-hexafluoro-2,2,4,4-pentane tetrol and the like can be mentioned, among which 2,3-butanediol, 2,4-pentanediol and 2,5-hexanediol are preferable. .

Further, as the hydroxyl group-containing compound, specifically, for example, 4,4'-isopropylidene-dicyclohexanol, α, α'-bis (4-hydroxycyclohexyl) -1,4-diisopropylbenzene,
α, α'-bis (4-hydroxycyclohexyl)-
1,4-diisopropylcyclohexane, 4,4′-methylenebis (cyclohexanol), 2,2′-methylenebis (4-methylcyclohexanol) and the like, among which 4,4′-isopropylidene-dicyclohexanol , Α, α′-bis (4-hydroxycyclohexyl) -1,4-diisopropylbenzene, α, α′-
Bis (4-hydroxycyclohexyl) -1,4-diisopropylcyclohexane is preferred.

The composition ratio of the carboxylic anhydride-modified olefin resin and the hydroxyl group-containing compound in the thermoreversible crosslinkable resin composition is such that the ratio of the number of hydroxyl groups to the number of carboxylic anhydride groups is 0.1 to 10%. Is preferably set, and more preferably 0.2 to 5. Here, when the ratio of the number of hydroxyl groups to the number of carboxylic anhydride groups is less than 0.1, the degree of crosslinking as a composition becomes insufficient, and the composition does not become satisfactory in heat resistance. Insufficient dissociation,
Melt fluidity is not sufficiently satisfactory.

It is preferable that the carboxylic acid anhydride-modified olefin resin and the hydroxyl group-containing compound be used.
As long as the effects of the present invention are not impaired, components other than the above components may be contained. Specifically, for example, various commonly used additives, for example, antioxidants, ultraviolet absorbers, nucleation agents Agents, neutralizers, lubricants, antiblocking agents, dispersants, flow improvers, release agents, flame retardants, colorants, fillers, and the like can be added.

The carboxylic anhydride-modified olefin resin and the hydroxyl group-containing compound are mixed with other optional components by a Henschel mixer, ribbon blender, V-type blender, etc., and then mixed uniaxially or uniaxially. It can be prepared by melt-kneading with a multi-screw extruder, roll, Banbury mixer, kneader, Brabender or the like.

In particular, in the foam of the present invention, it is possible to blend the thermoreversible crosslinkable resin used in the present invention with a thermoplastic resin having a degree of crosslinkage at room temperature (25 ° C.) of 3% or less. it can. Examples of the thermoplastic resin having a degree of crosslinking at room temperature of 3% or less include polyolefin resins such as polyethylene, polypropylene and polymethylpentene, polyamide resins such as nylon 6 and nylon 66, polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2. Polyester resin such as 2,6-naphthalate, polyacetal resin, polyphenylene sulfide resin, and the like. These thermoplastic resins are preferably 10 parts by weight based on 100 parts by weight of the thermoreversible crosslinkable resin.
５０50 parts by weight.

The average foam diameter of the foam of the present invention is 0.1 μm.
m or more and 30 μm or less. More preferably 0.2 μm
Not less than 15 μm, more preferably 0.5 μm
Not less than 10 μm. The porosity of the foam of the present invention is 20% or more and 99% or less. More preferably,
30% or more and 95% or less, more preferably 50%
Not less than 90%. By having such a large number of fine cells, the mechanical properties are improved, and the foam becomes super white and has excellent appearance as compared with the conventional foam having large cells. Average foam diameter is 0.1μm or more 3
If the thickness is less than 0 μm or less, light scattering by air bubbles becomes insufficient, so that sufficient whiteness and luminance cannot be obtained, and it cannot be used for a reflector or a printing-oriented application. When the porosity is not 20% or more and 99% or less, the number of air bubbles is too small, so that not only sufficient light scattering is not caused, but also the cushioning property and the like are deteriorated, and the shock absorption and the printability are deteriorated. Become.

The flow start temperature Tc of the thermoreversible crosslinkable resin of the present invention is preferably 240 ° C. or lower. It is more preferably 230 ° C. or lower, and further preferably 220 ° C.
It is below ° C. When the flow start temperature Tc is 240 ° C. or lower, the foam has excellent thermal dimensional stability and easily controls the foaming temperature during the production of the foam to obtain a foam having a large number of extremely fine and uniform cells. be able to.

The thermoreversible crosslinkable resin of the present invention exhibits fluidity at a flow start temperature Tc. Here, the fluidity means that the melt index (MI) is 0.1 or more.

The thermoreversible crosslinkable resin of the present invention at room temperature (25
C) is preferably 5% or more and 80% or less. More preferably, it is 10% or more and 70% or less. More preferably, it is 20% or more and 60% or less.
When the degree of crosslinking at room temperature is 5% or more and 80% or less, the foam becomes a foam having excellent mechanical strength, and also has an excellent deep draw formability. In addition, it is preferable to have an appropriate degree of crosslinking in such a manner that, during foaming, bubbles do not burst or the cells do not grow too large, and a foam having fine cells of the present invention can be obtained, which is preferable. .

The specific gravity of the foam of the present invention is 0.5 g / cm
It is preferably ³ or less. More preferably, 0.4
g / cm ³ or less, more preferably 0.3 g / c 3
m ³ or less. When the specific gravity of the foam is 0.5 g / cm ³ or less, it is excellent in lightness, heat insulating properties, and cushioning properties, and can be widely used in fields such as heat insulating materials and cushioning materials. Further, it is preferable that the specific gravity is reduced, because the material cost is reduced and the cost is reduced.

The foam according to the present invention preferably comprises closed cells. A closed cell is a state in which bubbles are hardly connected. When the cells of the foam are closed cells, it is excellent in the heat insulating effect and also excellent in the cushioning property. As described above, while the foam cells are closed cells, in order to have a large number of fine cells, it is necessary that the thermoreversible crosslinkable resin according to the present invention is used.
It has been discovered by the inventors of the present invention.

The foam of the present invention can be in the form of a sheet, a rod, a lump, or the like, depending on the application, but is often prepared in the form of a sheet. The thickness of the sheet is more preferably 0.5 μm or more and 10,000 μm or less, and still more preferably 10 μm or more and 5,000 μm or less.

Further, the foam of the present invention preferably has a non-foamed layer on at least one surface. More preferably, it is good to have a non-foamed layer on both surfaces. A non-foamed layer is a layer in which no air bubbles exist. Thus, at least on one side, when a non-foamed layer is present, the surface roughness is reduced and extremely smooth compared to a foam without a non-foamed layer, and when used as a cushioning material for precision machinery, etc. It is preferable because fine scratches do not occur on precision machines. Further, when the foam of the present invention is used for a print receiving sheet, it is preferable because high-precision printing can be performed at the time of printing. The non-foamed layer is preferably mainly composed of a thermoreversible crosslinkable resin or a thermoplastic resin constituting the foamed layer, more preferably a thermoplastic resin having a degree of crosslinking at room temperature of 3% or less. Good to be. More preferably, it is good to be a polyolefin or polyester. Also, as the thickness of the non-foamed layer,
The thickness is preferably from 0.1 μm to 100 μm, more preferably from 1 μm to 50 μm.

The foam of the present invention is preferably stretched in at least one direction. More preferably, it is good to be stretched in the biaxial direction. After stretching in the biaxial direction, the film may be further stretched in the longitudinal and / or transverse directions. After being stretched in the biaxial direction, it may be heat-treated. Since the mechanical properties are dramatically improved by stretching, it can be used in a wide range of fields such as heat insulating materials, cushioning materials, packing materials, print receiving papers, and surface light source reflectors.

Next, the method for producing the foam of the present invention will be described in detail.

The foam of the present invention has a melt index (MI) of 1.0 or less after injecting a soluble foaming agent into a thermoreversible crosslinkable resin having a resin temperature of 1.5 or more. It is obtained by cooling to the resin temperature and foaming at the outlet. Further, in order to extrude and foam the thermoreversible crosslinkable resin, it is necessary to inject a foaming agent soluble at a resin temperature at which the MI at which the crosslinked structure decreases and the molten state becomes MI is 1.5 or more. Thereafter, in order to foam the resin so as to have a large number of fine bubbles, the resin can be obtained by cooling the resin temperature to a temperature at which the MI becomes 1.0 or less and foaming the resin at the discharge port.

As another method, a foaming agent soluble in a thermoreversible crosslinkable resin having a resin temperature MI of 1.5 or more is injected, and then cooled to a resin temperature MI of 0.5 or less. However, it can also be obtained by discharging in an unfoamed state and then rapidly heating to foam. At this time, the resin temperature is set at M to discharge in an unfoamed state.
It can also be obtained by cooling and molding to a temperature at which I becomes 0.5 or less, and then rapidly raising the temperature to the foaming temperature to foam.

As a method of melt extrusion, a commercially available extruder is used to supply a thermoreversible crosslinkable resin to a supply section, and the resin is rotated by rotating a screw in a heated cylinder section in the extruder. The molten resin that has been melted and sent out of the extruder is guided to a die through a heated channel (polymer tube). If necessary, a gear pump may be provided to remove foreign substances and denatured polymer through a filter and to improve the quantitative supply. The polymer guided in this manner is widened to a required width inside the die serving as the discharge port, discharged from the die, and formed into a sheet-like material or a molded body using a casting drum or a mold that is a known cooling method. Cooled, solidified.

Here, as an extruder for melting the thermoreversible crosslinkable resin, a known single-screw or twin-screw extruder can be used. As the screw of the extruder, an optimum screw may be used according to the properties of the thermoreversible crosslinkable resin to be applied and the properties of the soluble gas to be injected. The setting of the temperature for heating the thermoplastic resin in the extruder depends on the MI of the thermoreversible crosslinkable resin up to the portion where the soluble foaming agent is injected.
Is 1.5 or more. More preferably, MI is 3.0 or more, and still more preferably, MI is 5.0 or more. Thereafter, in order to foam at the discharge port, the resin is cooled to a resin temperature at which the MI is 1.0 or less. On the other hand, in order to extrude in an unfoamed state, the resin is cooled to a resin temperature at which the MI is 0.5 or less and extruded.

As a method for injecting a soluble foaming agent into a resin in the present invention, a method in which a carbon-soluble foaming agent is injected into a resin in a molten state in an extruder is preferable. Further, it is more preferable to inject a soluble foaming agent while applying a pressure of several MPa or more at a vent portion of an extruder having a vent port. Such high pressures are advantageously obtained in an extruder. It is important that the soluble foaming agent is completely dissolved in the resin in the extruder. If there is a portion that remains in a gaseous state without being dissolved, it will remain as large bubbles and will not be usable. As the extruder with a vent port, there are a single-screw extruder, a twin-screw extruder, a tandem extruder in which extruders are connected in series, and the like, which is selected according to a required application. Further, in order to improve the degree of dispersion of the foaming agent in the molten thermoplastic resin, a static mixer may be arranged at the tip of the extruder having a vent.
If the injection of the blowing agent into the thermoplastic resin is before the extruder,
It is difficult to uniformly dissolve the foaming agent in the molten thermoplastic resin. Even if a foaming agent is injected after the extruder, it is difficult to uniformly dissolve it.

As a method for injecting such a foaming agent into a resin, it is preferable to use a tandem extruder in which two or more extruders are connected in series as an extruder. As mentioned above, it is important that the blowing agent be completely dissolved in the molten resin. For this purpose, it is preferable to increase the pressure in the extruder after press-fitting the foaming agent into the extruder. The structure in which the pressure increases as it flows through the extruder completely dissolves the blowing agent. In order to obtain such a pressure distribution structure, it is preferable to use a tandem extruder in which two or more extruders are connected in series.

[0062] The tandem extruder means that the basic function of the extruder is divided into two units, that is, the first extruder melts the resin and the second extruder supplies a fixed amount. In addition, shear heat generation can be suppressed while increasing the discharge amount. Inject the foaming agent with the first extruder, dissolve it,
It is preferable to take operating conditions that completely dissolve the gas remaining in the second extruder. Even when a tandem extruder is used, the screw shape is different from a normal screw shape and is preferably a screw shape having a sealing mechanism for preventing a backflow of the blowing agent. That is, in the first extruder, it is preferable to provide a ring and a seal mechanism on the raw material supply side rather than the position where the foaming agent is press-fitted, to prevent the gas from flowing backward. If such a seal mechanism is not provided, the gas is likely to flow backward because the pressure on the raw material supply side is lower.

Specific examples of the soluble foaming agent used in the present invention include an inert gas such as carbon dioxide, nitrogen gas, helium, xenon and neon, and a hydrocarbon such as ethane, butane, cyclohexane, benzene and xylene. And halogenated hydrocarbons such as chloroform, carbon tetrafluoride, ethyl fluoride and ethane tetrafluoride, and organic compounds such as acetone and ethyl methyl ketone. More preferably, an inert gas such as carbon dioxide gas or nitrogen gas is used. The blowing agent is 1
Only one type may be used, or two or more types may be used in combination.

The soluble foaming agent in the present invention is preferably injected into a molten resin in a supercritical state. Here, the supercritical state is a temperature higher than the critical temperature of a certain substance,
In addition, it is in a state of a critical pressure or higher, and exhibits intermediate physical properties between gas and liquid. When the soluble foaming agent is not in a supercritical state, the solubility in the thermoplastic resin is low, and the dissolution rate in the resin is low, which is not preferable.

As the filtration device in the present invention, a known filter can be used. Filter types include cylindrical and disc-shaped filters,
There are leaf disks and the like in which disk-shaped ones are used in a stack, and it is selected according to the application and purpose. Further, these may be used in combination. The filtration accuracy (95% cut diameter) of the filter varies as necessary,
It is preferable that it is not more than 80 μm cut. More preferably, it is 0.5 μm or more and 100 μm or less. When the filtration accuracy of the filter is larger than 80 μm, it is difficult to collect foreign substances and denatured modified resin.

In the present invention, the resin pressure must be maintained at a high pressure from the extruder to just before the discharge port so that the foaming agent does not foam. If the resin pressure is reduced between the extruder and immediately before the discharge port, the foaming agent foams, and the bubbles grow to produce large bubbles, which is not preferable. As a method of maintaining the resin pressure at a high pressure just before the discharge port, it is preferable to provide a pressure control valve at the outlet of the extruder and also provide a pressure control mechanism at the discharge port.

In the present invention, when the foaming agent is completely dissolved in the resin and then foamed at the discharge port or when it is molded in a non-foamed state, it is important to rapidly quench and solidify. In order to cause foaming in the base, it is preferable that the pressure loss inside the base is high, and the pressure drop rate inside the base is also high. In this way, when the molten foaming agent is foamed at the same time as molding by the die,
If not rapidly quenched, bubbles will grow significantly and become large bubbles, making them unusable. Also, when a molded article is obtained in an unfoamed state, if it is not quenched and solidified, bubbles will be generated in the molded article, resulting in a defect. When it is discharged in an unfoamed state, it can be rapidly cooled and solidified and molded immediately, and then rapidly heated in a condensing-type radiation heater, heating medium tank or hot air tank, and foamed to obtain a foam. .

As the stretching method used in the present invention, sequential biaxial stretching, which is a known technique, or simultaneous biaxial stretching by a tubular method or a tenter method is preferable. More preferably,
Sequential biaxial stretching is preferably performed in which the film is stretched in the longitudinal direction by a plurality of aligned rolls, stretched in the transverse direction by a clip running on a tenter, and then heat-treated while being held by the clip in the tenter. Here, the order of the longitudinal stretching and the transverse stretching is not particularly limited, but it is difficult to uniformly longitudinally stretch the film which has been widened by the transverse stretching. It is also within the scope of the present invention to perform longitudinal stretching and / or transverse stretching again after longitudinal stretching and transverse stretching.

As the stretching method, the film may be stretched in the longitudinal direction and then stretched in the width direction, or may be stretched in the width direction and then stretched in the longitudinal direction. More preferably, they are simultaneously biaxially stretched. A foam that has been simultaneously biaxially stretched is preferable because the bubble diameter in the longitudinal direction and the width direction is relatively uniform, and since it is not stretched by a roll, the bubbles are less likely to collapse in the thickness direction. More preferably, the stretching is performed by a simultaneous biaxial tenter driven by a linear motor. The simultaneous biaxial tenter driven by a linear motor not only improves the productivity but also allows the film to be freely relaxed in the longitudinal and width directions, so that a film having a low heat shrinkage can be easily obtained.

In the present invention, the methods for evaluating each physical property value are as follows. (1) Average foam diameter and porosity The thickness section of the sample (foam) was measured with a scanning electron microscope for 1.0
A photograph taken at a magnification of 00 to 5,000 times is taken, and the diameter of at least 100 cells in the specified thickness range is applied to an image analyzer to determine the diameter of the bubbles. This average foam diameter is defined as the average foam diameter. At this time, all the bubble areas (M foam) in the measurement range are divided by the entire area of the measurement range,
The porosity is obtained by multiplying 100 times. (2) Specific gravity A sample was cut into a 100 × 100 mm square, and a minimum of 1 mm was obtained by attaching a measuring element (No. 7002) with a diameter of 10 mm to a dial gauge (No. 2109-10).
The thickness at the zero point is measured, and the average value d (μm) of the thickness is calculated. This sample was weighed with a direct reading balance and weighed w
(G) is read to the unit of 10-4 g. At this time, the specific gravity is set to w / d × 100. (3) Melt index (MI) The melt index at each temperature is JIS K7210.
It is measured according to (Method B). (4) Flow start temperature (Tc) The melt index (MI) of the resin is from 25 ° C. to 10 ° C.
The temperature when MI reaches 0.1 for the first time is defined as the flow start temperature (Tc). (5) Degree of Crosslinking (Gel Fraction) A sample (foam) is shredded and 0.2 g is precisely weighed. This was immersed in tetralin at 130 ° C., and heated for 3 hours with stirring to dissolve the dissolved portion. The insoluble portion was taken out and washed with acetone to remove tetralin, and then washed with pure water to remove acetone. Moisture is removed with a hot air dryer at 120 ° C., and the mixture is naturally cooled to room temperature (25 ° C.). The weight (W1) g of this product was measured, and the gel fraction was determined by the following equation, which was used as the degree of crosslinking.

Crosslinking degree = (0.2−W1 / 0.2) × 100 (%) (6) Optical Density One or several films are stacked, and an optical densitometer (TR9
27, manufactured by Macbeth Co., Ltd.). The thickness of the film and the optical density are plotted, and the optical density corresponding to a thickness of 100 μm is determined by interpolation or extrapolation.

[0072]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments.

Example 1 As a thermoreversible crosslinkable resin,
Umex 1010 (maleic anhydride-modified polyolefin resin) (94.6% by weight) and 2,5-hexanediol (5.4% by weight) manufactured by Sanyo Kasei Kogyo Co., Ltd. What was melt-kneaded for minutes was used. This thermoreversible crosslinkable resin (Tc = 22
The degree of crosslinking at 0 ° C. and ordinary temperature (25 ° C.) was supplied to a tandem extruder in which two extruders were connected in series. The first extruder has a screw length to diameter ratio L / D.
= 30 and the second one used L / D = 20. In the first extruder, a ring-shaped seal was applied to the screw at L / D = 15, and a blowing agent supply port was provided at L / D = 18. The first extruder was melted at 280 ° C., carbon dioxide gas was injected at 11 MPa from the gas supply port, and the extruder was extruded at a set temperature of 220 ° C. The molten resin extruded from the extruder was filtered by a filter pack through a short pipe, then formed into a sheet from a base via a pressure regulating valve, and discharged. The molten resin pressure immediately before the pressure control valve is set to be 22 MPa,
When discharging from the base, dissolved carbon dioxide gas foams,
Many bubbles were generated in the sheet. The sheet extruded from the die was quenched and solidified on a casting drum maintained at a surface temperature of 25 ° C. and wound up. The thickness of the obtained sheet was 1 mm, the average foamed diameter was 5 μm, and the porosity was 58%. The specific gravity of the sheet is 0.4 g /
cm ³ . Tables 1 and 2 show the obtained results.

The resulting foam had very fine bubbles and a large number of bubbles, and thus efficiently scattered visible light, and thus was excellent in whiteness. As a result, the optical density was 1.6.

Example 2 The same apparatus and conditions as in Example 1 were used, except that a thermoreversible crosslinkable resin (Tc = 240 ° C., degree of crosslinking 15%) was grafted with maleic anhydride-modified polypropylene resin (98. 7% by weight) and 1,3,5-cyclohexanetriol (1.3% by weight) were kneaded under the same conditions. Further, the temperature of the second-stage extruder is set to 250
Set to ° C. The thickness of the obtained sheet was 1 mm, the average foamed diameter was 10 μm, and the porosity was 52%.
The specific gravity of the sheet was 0.45 g / cm ³ , and the optical density was 1.4. Tables 1 and 2 show the obtained results.

Example 3 The same apparatus and conditions as in Example 1 were used except that a thermoreversible crosslinkable resin (Tc = 230 ° C., degree of crosslinking 20%) was grafted with a maleic anhydride-modified polypropylene resin (94. 9% by weight) and 1,3,5-cyclohexanetriol (5.1% by weight) were kneaded under the same conditions. The thickness of the obtained sheet was 1 mm, the average foamed diameter was 7 μm, and the porosity was 50%.
The specific gravity of the sheet was 0.4 g / cm ³ , and the optical density was 1.5. Tables 1 and 2 show the obtained results.

Example 4 The same apparatus and conditions as in Example 1 were used, except that the foaming agent injection pressure was set to 16 MPa, and the resin pressure immediately before the pressure control valve was set to 25 MPa. The thickness of the obtained sheet is 1 mm, and the average foamed diameter is 2 μm.
m, and the porosity was 70%. The specific gravity of the sheet was 0.25 g / cm ³ , and the optical density was 1.65. Tables 1 and 2 show the obtained results.

(Comparative Example 1) The same apparatus and conditions as in Example 1 were used, except that the temperature of the second-stage extruder was set to 260 ° C. The thickness of the obtained sheet is 1 mm, and the average foamed diameter is 6
0 μm and the porosity was 20%. The specific gravity of the sheet was 0.8 g / cm ³ , and the optical density was 0.6. Tables 1 and 2 show the obtained results.

(Comparative Example 2) Under the same apparatus and conditions as in Example 1, but using a thermoplastic resin for foaming, HMS-PP manufactured by Montell-JPO Co., Ltd. instead of the thermoreversible crosslinkable resin.
PF-814 (Tc = 170 ° C., modified polypropylene) was used. The thickness of the obtained sheet was 1 mm, the average foamed diameter was 50 μm, and the porosity was 25%.
The specific gravity of the sheet was 0.75 g / cm ³ , and the optical density was 0.66. Tables 1 and 2 show the obtained results.

Example 5 The same apparatus and conditions as in Example 1 were used, except that the temperature of the second-stage extruder was set to 210 ° C., and an unfoamed sheet was obtained. Rapid heating was performed to foam. The thickness of the obtained sheet is 1 mm, the average foam diameter is 1 μm, and the porosity is 7
It was 0%. The specific gravity of the sheet is 0.25 g / c.
m ³ and the optical density was 1.66. Tables 1 and 2 show the obtained results.

Example 6 The same apparatus and conditions as in Example 1 were used, except that the raw material used was the thermoreversible crosslinkable resin 8 of Example 1.
0 wt% and thermoplastic resin Montell-JPO Co., Ltd.
The ratio of HMS-PPPF-814 (20 wt%) manufactured by the company was blended and used. The thickness of the obtained sheet is 1 mm
The average foam diameter was 4 μm and the porosity was 60%. The specific gravity of the sheet was 0.3 g / cm ³ and the optical density was 1.5. Tables 1 and 2 show the obtained results.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

According to the present invention, a foam having many recyclable fine cells can be obtained. The foam of the present invention is made of a thermoreversible crosslinkable resin having a fine foam diameter, improved mechanical properties, super-white appearance and excellent recyclability, and particularly excellent printing base material. It is suitably used as a substrate for packaging, cards, labels, receiving paper for video printers, photographic paper, display boards, reflector base materials for surface light sources, heat insulating materials, cushioning materials and packing materials.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 101/16 C08L 101/00 F term (Reference) 4F074 AA17 AA24 AA24D AA26 AA28D AA28F AA43A AA48 AA57 AA66 AA71 AA87 AD04 AD10 AD11 AD13 BA32. FD150 FD328 GG02 GT00

Claims (12)

[Claims] 1. A foam made of a thermoreversible crosslinkable resin having a crosslinked structure at a flow start temperature Tc (° C.) or higher, and at Tc-40 (° C.) or lower, wherein the average foaming diameter is 0. .1 μm or more and 30 μm or less and a porosity of 2
Foam characterized by being 0% or more and 99% or less. 2. The foam according to claim 1, wherein the flow start temperature Tc is 240 ° C. or lower. 3. The foam according to claim 1, wherein the thermoreversible crosslinkable resin has a degree of crosslinking at room temperature of 5% or more and 80% or less. 4. The foam according to claim 1, wherein the specific gravity is 0.5 or less. 5. The foam according to claim 1, wherein the foam comprises closed cells. 6. The foam according to claim 1, wherein the foam has a non-foamed layer on at least one surface. 7. The foam according to any one of claims 1 to 6, wherein a thermoplastic resin having a degree of crosslinking at room temperature of 3% or less is blended. 8. The foam according to claim 1, wherein the foam is stretched in at least one axial direction. 9. The foam according to claim 1, wherein the thermoreversible crosslinkable resin is a polyolefin-based resin. 10. The melt index (MI) is 1.5.
A foaming method characterized by injecting a soluble foaming agent into the thermoreversible crosslinkable resin having the above resin temperature, cooling the resin to a resin temperature having an MI of 1.0 or less, and then foaming the resin at a discharge port. How to make the body. 11. The melt index (MI) is 1.5.
A soluble foaming agent is injected into the thermoreversible crosslinkable resin having the above resin temperature, cooled to a resin temperature having MI of 0.5 or less, discharged in an unfoamed state, and then rapidly heated. A method for producing a foam, characterized in that the foam is foamed. 12. The method for producing a foam according to claim 10, wherein a soluble foaming agent is injected in a supercritical state.