JP2002275297A - Cross-linked polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cross-linked polyolefin resin foam having excellent extrudability of a foaming sheet and stability during thick foaming, having a fine cell diameter of the foam ranging from a low to a high expansion ratios and excellent uniform smoothness of a product appearance and thickness uniformity. SOLUTION: This cross-linked polyolefin resin foam is obtained by adding a polytetrafluoroethylene-containing mixture comprising polytetrafluoroethylene particles having <=10 μm particle diameter and an organic polymer to a polyolefin resin having 0.1-30 g/10 min MFR. Thereby, the cross-linked polyolefin resin foam having an improved melt strength of the resin, resultantly a fine cell diameter and excellent uniform smoothness of product appearance and uniformity of thickness ranging from a low to a high expansion ratios is stably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyolefin foam having excellent surface smoothness from a low expansion ratio to a high expansion ratio, which solves the drawbacks of conventional foams using a crosslinked polyolefin resin.

[0002]

2. Description of the Related Art As a method for obtaining a foam of an olefin resin, an extrusion foaming method in which an olefin resin is melt-kneaded with a foaming agent in an extruder and then extruded under a low pressure to foam the foam,
A method of press-foaming resin beads containing a foaming agent in a heatable container, or a method of once forming a foamable sheet, subjecting the foamable sheet to cross-linking with an electron beam or the like, and then foaming under normal pressure. Widely adopted.

[0003] In the normal pressure foaming method for olefin resins, foaming is performed by expanding a blowing agent in a molten mixture. However, since olefin resins are generally crystalline, when the temperature of the resin is increased, the melting temperature of the resin increases. Viscosity and melt strength decrease rapidly, the foaming agent decomposes, and the generated gas cannot be retained, escapes from the resin and does not increase in foaming ratio, and the product surface has a smooth appearance due to foam breakage. Can not be obtained. Conversely, if the foaming temperature is lowered or the degree of crosslinking is increased in order to increase the melt viscosity or melt strength of the resin, sufficient and uniform foaming will not be achieved. In the normal pressure foaming, in order to make the foam cells of the foam uniform and fine, the surface is smooth and the thickness uniformity is excellent, not only the melt viscosity at the time of foaming but also the melt strength is kept high. This is very important.

For polypropylene, there is a method of increasing the melt viscosity and the melt viscosity and melt strength by increasing the molecular weight. However, not only the polymerization time is increased but also the cost is increased, the flowability is deteriorated, and resin foaming is caused to occur. , And the molecular weight is reduced, and as a result, it is difficult to increase the intended melt strength. JP-A-5-95058 and JP-A-9-950
Japanese Patent No. 31230 proposes a polypropylene resin foam having a wide molecular weight distribution and containing a branched polymer in a polymer region. However, it is very expensive to obtain a polymer material having many branches by polymerization of polypropylene. JP-A-6-234878 proposes a polypropylene that causes long-chain branching by electron beam crosslinking, but it is difficult to control the degree of crosslinking and the price is high. In the case of a polyethylene resin, a method by electron beam crosslinking is employed, but if the degree of crosslinking is too high, it is difficult to control the foaming sheet during foaming. In addition, it is difficult to increase the degree of cross-linking by electron beams in linear low-density polyethylene,
If a resin having a high melt viscosity is used, there are problems that the extrusion pressure becomes too high and the foaming agent is difficult to be uniformly dispersed.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the extrudability of a foamable sheet and the stability during normal pressure foaming, and the foam cells of the foam are fine and nearly uniform from low to high expansion ratios. An object of the present invention is to provide an olefin-based crosslinked foam excellent in product appearance and thickness uniformity.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a small amount of polytetrafluoroethylene comprising polytetrafluoroethylene particles having a particle diameter of 10 μm or less and an organic polymer. By adding the containing mixture to a polyolefin resin having a limited MFR, the melt strength of the resin is improved without changing the extrusion performance during foaming sheet molding. As a result, the foam cells are fine and nearly uniform, and the product appearance is improved. It has been found that olefin-based crosslinked foams having excellent uniformity of thickness and thickness can be stably obtained from low expansion ratio to high expansion ratio, and have reached the present invention.

[0007] That is, the gist of the present invention is that the MFR is 0.
1-30 g / 10 min polyolefin resin (A)
For 100 parts by weight, a polytetrafluoroethylene-containing mixture (B) comprising polytetrafluoroethylene particles having a particle diameter of 10 μm or less and an organic polymer has a polytetrafluoroethylene content of 0% in the mixture (B). 0.1 to 20 parts by weight, and the degree of crosslinking is 5
To 70% of a crosslinked polyolefin resin foam.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The polyolefin resin (A) used in the present invention is, for example, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (L).
DPE), linear low density polyethylene (LLDPE),
Poly-1-butene, polyisobutylene, random copolymer or block copolymer in any ratio of propylene and ethylene and / or 1-butene, diene component in 50% by weight or less in any ratio of ethylene and propylene Certain ethylene-propylene-diene terpolymers, cyclic polyolefins such as polymethylpentene, copolymers of cyclopentadiene with ethylene and / or propylene, 50% by weight of ethylene or propylene
The following, for example, vinyl acetate, alkyl methacrylate, acrylic acid ester, aromatic alkyl ester, random copolymers with vinyl compounds such as aromatic vinyl, block copolymers or graft copolymers, and the like. May be used alone or in combination of two or more.

In the present invention, as the polyolefin resin (A), PP, HDPE, LDPE, LLDP
E, at least one selected from ethylene-propylene random or block copolymers is preferred in that it has high versatility and is inexpensive.

The polyolefin resin (A) used in the present invention preferably has an MFR of 0.1 to 30 g / 10 minutes, more preferably 0.3 to 20 g / 10 minutes. The extrudability at the time of preparing the foamable sheet by adding the containing mixture (B) and the melt viscosity of the resin at the time of foam molding after crosslinking the foamable sheet are maintained in a well-balanced manner. This is preferable for obtaining an olefin-based cross-linked foam having fine cells and uniform product appearance and excellent thickness uniformity. In addition, the polypropylene resin is JIS-K-67.
58, polyethylene resin was measured according to JIS-K-6760.

If the MFR of the polyolefin resin (A) is less than 0.1 g / 10 minutes, the fluidity is not sufficient, and it is difficult to form a foamable sheet, and the MFR is 30 g / 1.
If the time exceeds 0 minutes, the melt strength of the resin is reduced, the stability in foaming after crosslinking the sheet is insufficient, and the foam cells are enlarged, foaming and degassing occur on the surface,
It is difficult to obtain a good foam molded product. The degree of crosslinking in the foam of the present invention is preferably 10 to 70%, and more preferably 1 to 70%.
It is preferable that the content be 5 to 50% in order to obtain an olefin-based crosslinked foam having excellent foam stability and foam cells, and a uniform product appearance and excellent thickness uniformity. In addition, such a degree of crosslinking is obtained by chopping the foam into 0.2 g.
A finely weighed (W ₀ g) sample was treated with xylene as a solvent.
After extraction with a Soxhlet extractor at 20 ° C. for 24 hours, insolubles were taken out, washed with pure xylene, further washed with acetone, and heated with a vacuum dryer heated to 80 ° C. for 4 hours.
After completely removing volatile components, the mixture is naturally cooled at room temperature. The weight (W ₁ g) of this product is measured, and the degree of crosslinking is determined by the following equation.

Degree of crosslinking = (W ₁ / W ₀ ) × 100 (%) The polytetrafluoroethylene-containing mixture (B) used in the present invention comprises polytetrafluoroethylene particles having a particle diameter of 10 μm or less and an organic polymer. It is necessary that the polytetrafluoroethylene in the mixture does not form an aggregate of 10 μm or more. Such a polytetrafluoroethylene-containing mixture has a particle size of 0.05 to 1 μm.
m obtained by mixing an aqueous dispersion of polytetrafluoroethylene particles with an aqueous dispersion of organic polymer particles and coagulating or spray-drying the mixture, or polytetrafluorocarbon having a particle size of 0.05 to 1 μm. Emulsion polymerization of a monomer having an ethylenically unsaturated bond in a dispersion obtained by mixing an aqueous dispersion of ethylene particles and an aqueous dispersion of organic polymer particles, followed by coagulation or spray-drying to obtain a powder. It is preferable to use a powder obtained or a powder obtained by converting these powders into a master batch with the above-mentioned polyolefin resin.

As raw materials for the polytetrafluoroethylene particle dispersion, Fluon AD-1 and AD-936 manufactured by Asahi ICI Fluoropolymer Co., Ltd., and Polyflon D-1 and D-2 manufactured by Daikin Industries, Ltd. Teflon 30J manufactured by the Company can be cited as a representative example.

The organic polymer constituting the polytetrafluoroethylene-containing mixed powder (B) used in the present invention includes:
Although not particularly limited, those having high compatibility with the olefin resin are preferred from the viewpoint of dispersibility when blended into the polyolefin resin (A).

Specific examples of the monomer for forming the organic polymer include styrene, p-methylstyrene, o-methylstyrene, p-chlorostyrene, o-chlorostyrene, p-methoxystyrene, and o-methoxystyrene. Styrene, α
-Styrene-based monomers such as methylstyrene: methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid-
(Meth) acrylate monomers such as 2-ethylhexyl, dodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, acrylonitrile, Vinyl cyanide monomers such as methacrylonitrile: vinyl ether monomers such as vinyl methyl ether and vinyl ethyl ether: vinyl carboxylate monomers such as vinyl acetate and vinyl butyrate: ethylene, propylene, isobutylene, etc. Olefin-based monomers: Diene-based monomers such as butadiene and isoprene can be exemplified. These monomers can be used alone or in combination of two or more.

Among these monomers, styrene-based monomers, (meth) acrylate-based monomers, and olefin-based monomers are preferable in terms of compatibility with the polyolefin-based resin (A). The body can be mentioned. Preferred are those containing at least 20% by weight of one or more monomers selected from the group consisting of long-chain alkyl (meth) acrylate monomers having 6 or more carbon atoms, styrene and olefin monomers. Can be mentioned.
Particularly, a long-chain alkyl (meth) acrylate monomer having 12 to 24 carbon atoms is preferable.

The content of polytetrafluoroethylene in the polytetrafluoroethylene-containing mixture (B) used in the present invention is preferably 0.01 to 20 parts by weight.

The polytetrafluoroethylene-containing mixture (B) used in the present invention is prepared by charging an aqueous dispersion of a polytetrafluoroethylene-containing material into hot water in which metal salts such as calcium chloride and magnesium sulfate are dissolved. Then salt out,
It is obtained by drying after coagulation, powdered by spray drying, or masterbatch of the powder using a polyolefin resin (A).

Normal polytetrafluoroethylene fine powder forms aggregates of 100 μm or more in the step of recovering the powder from the state of the particle dispersion, so that it is difficult to uniformly disperse it in the thermoplastic resin. On the other hand, the polytetrafluoroethylene-containing mixture (B) used in the present invention has a dispersion in the polyolefin-based resin (A) because polytetrafluoroethylene alone does not form a domain having a particle diameter of more than 10 μm. The properties are extremely excellent. As a result, in the resin composition of the present invention, polytetrafluoroethylene is efficiently fiberized in the polyolefin-based resin (A), and the melt strength of the resin composition is maintained while maintaining the extrudability of the resin at the time of molding the expandable sheet. And as a result, the foam cells are finer,
A foam having an excellent uniform appearance can be obtained.

As mentioned above, the resin composition of the present invention
The amount of the polytetrafluoroethylene component in the polytetrafluoroethylene-containing mixture (B) is 0.01 to 20% by weight based on the polyolefin resin (A) having an FR of 0.1 to 30 g / 10 minutes. It was blended so that it would be within the range of parts. If the amount of the polytetrafluoroethylene component (B) is less than 0.01 part by weight, sufficient melt strength cannot be obtained, and if it exceeds 20 parts by weight, the fluidity becomes insufficient and the foamable sheet has This is because molding becomes difficult and a good foam cannot be obtained.

As the foaming agent for obtaining the foam of the present invention, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent and the like are used, and a decomposable foaming agent is used in view of the balance with the foaming temperature. Is preferred.

As the decomposition type foaming agent, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like can be used. These foaming agents can be appropriately mixed and used. The amount of the foaming agent varies depending on the type of the foaming agent, the desired expansion ratio, and the like, but the amount of addition is 0.1 to 20 parts by weight of the decomposable foaming agent per 100 parts by weight of the polyolefin resin (A). Is preferred.

In the present invention, a foam control agent may be further added to the melt-kneaded product of the resin and the foaming agent. Examples of the cell regulator include inorganic powders such as talc and silica, acidic salts of polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate.
It is preferable to add the foam control agent in a range of 13 parts by weight or less based on 100 parts by weight of the resin (except when a large amount of the inorganic filler is added to the resin).

In the present invention, a desired quality can be obtained by adding a stabilizer, a lubricant, an inorganic filler and the like to the melt-kneaded product of the resin and the foaming agent according to the purpose.

Examples of the stabilizer include pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4). -Hydroxyphenyl) propionate], phosphorus stabilizers such as tris (monononylphenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, dilauroyldipropionate, etc. Examples thereof include sulfur-based stabilizers, and these can be used alone or in combination of two or more. The compounding amount of such a stabilizer is polyolefin resin (A) 10
0.05 parts by weight or less with respect to 0 parts by weight is preferred.

Representative examples of the lubricant include sodium, calcium, and magnesium salts of saturated or unsaturated fatty acids such as lauric acid, palmitic acid, oleic acid, and stearic acid. These may be used alone or in combination of two or more. These can be used in combination. The amount of the lubricant is preferably 0.1 to 2 parts by weight based on 100 parts by weight of the polyolefin resin (A).

Representative examples of the inorganic filler include, for example, calcium carbonate, talc, glass fiber, magnesium carbonate, mica, kaolin, calcium sulfate, aluminum hydroxide, magnesium hydroxide, silica, clay, zeolite and the like. These can be used alone or in combination of two or more. The amount of the inorganic filler is preferably 1 to 50 parts by weight based on 100 parts by weight of the polyolefin resin (A).

Further, in the present invention, a desired quality can be obtained by adding a flame retardant, a pigment or the like to the melt-kneaded product of the resin and the foaming agent according to the purpose.

A prescribed amount of each of the above essential and optional components is blended, and the resin composition is adjusted using a usual kneader such as a roll, a Banbury mixer, or an extruder.
Preferably, it is a foamable sheet. Further, a master pellet (master batch) containing the polytetrafluoroethylene-containing mixture (B) at a high concentration may be diluted with the polyolefin-based resin (A) to form a resin composition. At this time, the amount of polytetrafluoroethylene is 0.01 to 20 parts by weight based on 100 parts by weight of the total amount of the polyolefin resin (A).
It is preferable to be blended so as to be parts by weight. Further, the polyolefin resin (A) to be diluted and the remaining polyolefin resin (A) may not be the same.

As a method for obtaining the foam of the present invention, the resin composition and the foaming agent are melt-extruded, formed into a sheet,
This sheet is crosslinked to obtain a crosslinked polyolefin resin sheet for foaming. Examples of the crosslinking method include ionizing radiation and ultraviolet rays, and specifically, an electron beam is preferable. The irradiation energy is preferably from 0.2 to 15 Mrad, more preferably from 0.5 to 10 Mrad. The degree of cross-linking caused by the irradiation energy is preferably 5 to 70%. If the degree of cross-linking is less than 5%, the gas of the blowing agent is dissipated from the surface at the time of foaming, so that the foam is easily broken, and the foam having a desired expansion ratio (density) is obtained. On the other hand, if it exceeds 70%, excessive cross-linking and hardening occur, so that the impact resistance at low temperatures is deteriorated and cracks are liable to occur, which is not preferable. After the crosslinking, the sheet is foamed by a method exemplified by a vertical (horizontal) hot air foaming method and a foaming method in a chemical bath.

The foamed sheet or plate foam can be formed into various forms by thermoforming or the like.

[0032]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the following description, “parts” indicates parts by weight,
"%" Indicates% by weight, and various physical properties were measured by the following methods.

(1) Solid content concentration: 170 ° C.
And dried for 30 minutes.

(2) Particle size distribution, weight average particle size: A solution obtained by diluting a particle dispersion with water was used as a sample solution, and a dynamic light scattering method (ELS800, manufactured by Otsuka Electronics Co., Ltd., temperature: 25 ° C., scattering angle: 90) Degree).

(3) Degree of crosslinking: The foam was finely cut and weighed precisely at 0.2 g (W ₀ g).
After extraction with a Soxhlet extractor at 20 ° C. for 24 hours, the insoluble matter was taken out, washed with pure xylene, further washed with acetone, and heated with a vacuum dryer heated to 80 ° C. for 4 hours.
After completely removing volatile components, the mixture is naturally cooled at room temperature. The weight (W ₁ g) of this product is measured, and the degree of crosslinking is determined by the following equation.

Degree of crosslinking = (W ₁ / W ₀ ) × 100 (%) (4) Stability at the time of foaming; fixed intervals (L ₁ m) between the cross-linked foamed polyolefin resin sheets collected at a width of 10 mm
m), put a load of twice the weight of the sheet on the lower end of the sheet, suspend it in a hot air oven at 250 ° C., and after 1 minute, set the length between the marked lines on the foam (L ₂ mm). ) And calculate the ratio (L _{2 /} L ₁ ).

：: The ratio is 1.2 times or less the theoretical magnification of expansion (triple root of expansion ratio).

×: The ratio is 1.2 times or more the theoretical magnification of expansion (triple root of expansion ratio).

(5) Foam Cell State: The cross section of the foam sheet was visually observed.

：: The cell size in the vicinity of the surface of the sheet and in the center does not exceed twice.

X: The ratio of the size of the cell in the vicinity of the surface of the sheet to the size of the cell in the center is twice or more.

(6) Appearance of molded article: The appearance of the foam sheet was visually judged.

：: There is no foam on the sheet surface and the sheet is smooth.

C: Foam breaks were observed on the sheet surface, and the sheet was not smooth.

Examples 1-4 <Polytetrafluoroethylene-containing mixed powder (hereinafter referred to as B-
No. 1. ) Production> First, stirrer, condenser,
A separable flask equipped with a thermocouple and a nitrogen inlet was charged with 190 parts of distilled water, 1.5 parts of sodium dodecylbenzenesulfonate, 100 parts of styrene, and 0.5 part of cumene hydroperoxide, and heated at 40 ° C. under a nitrogen stream. The temperature rose. Then, 0.001 part of iron sulfate, 0.003 part of disodium ethylenediaminetetraacetate, 0.2 of Rongalit salt
A mixture of 4 parts of distilled water and 10 parts of distilled water was added, and radical polymerization was performed. After the end of the heat generation, the temperature in the system was maintained at 40 ° C. for 1 hour to complete the polymerization, and a styrene polymer particle dispersion (hereinafter, referred to as P-1) was obtained.

The solid content concentration of P-1 was 33.3%, the particle size distribution showed a single peak, and the weight average particle size was 96 n.
m.

On the other hand, as a polytetrafluoroethylene-based particle dispersion, Fluon AD manufactured by Asahi ICI Fluoropolymer Co., Ltd.
396 was used. AD396 has a solid content of 63.0%.
And containing 5 parts of polyoxyethylene alkyliphenyl ether per 100 parts of polytetrafluoroethylene. The particle size distribution of AD396 showed a single peak, and the weight average particle size was 290 nm.

To 833 parts of AD396, 1167 parts of distilled water was added to obtain a polytetrafluoroethylene particle dispersion F-1 having a solid concentration of 26.2%. F-1 contains 25% of polytetrafluoroethylene particles and 1.2% of polyoxyethylene nonylphenyl ether.

A separable flask equipped with a stirrer, a condenser, a thermocouple and a nitrogen inlet was prepared by mixing 160 parts of F-1 (40 parts of polytetrafluoroethylene) and 181.8 parts of P-1 (60 parts of polystyrene). And stirred at room temperature for 1 hour under a nitrogen stream. Thereafter, the inside of the system was heated to 80 ° C. and kept for 1 hour. No solid matter was separated through a series of operations, and a uniform particle dispersion was obtained. The solid content concentration of the particle dispersion was 29.3%, the particle size distribution was relatively broad, and the weight average particle size was 168 nm.

341.8 parts of this particle dispersion was poured into 700 parts of 85 ° C. hot water containing 5 parts of calcium chloride, the solid content was separated, filtered and dried to obtain a mixed powder of polytetrafluoroethylene (B). -1) 98 parts were obtained.

After the above B-1 was shaped into a strip shape at 250 ° C. by a press molding machine, ultrathin sections were observed with a microtome without staining using a transmission electron microscope. Although polytetrafluoroethylene is observed as a dark area, 1
Aggregates exceeding 0 μm were not observed.

<Production of polytetrafluoroethylene-containing mixed powder (hereinafter referred to as B-2)> First, 0.1 part of azobisdimethylvaleronitrile was dissolved in a mixed solution of 75 parts of dodecyl methacrylate and 25 parts of methyl methacrylate. I let it. A mixture of 2.0 parts of sodium dodecylbenzenesulfonate and 300 parts of distilled water was added thereto, and the mixture was stirred at 10,000 rpm for 4 minutes with a homomixer, and then passed twice through a homogenizer at a pressure of 300 kg / cm ² to obtain a stable solution. A dodecyl methacrylate / tyl methacrylate pre-dispersion was obtained. This was charged into a separable flask equipped with a stirrer, a condenser, a thermocouple, and a nitrogen inlet, and stirred at an internal temperature of 80 ° C. for 3 hours under a nitrogen gas stream to carry out radical polymerization, and a dodecyl methacrylate / methyl methacrylate copolymer A particle dispersion (hereinafter referred to as P-2) was obtained.

The solid content concentration of P-2 was 25.1%, the particle size distribution showed a single peak, and the weight average particle size was 198.
nm.

160 parts (40 parts of polytetrafluoroethylene) of F-1 and 159.4 parts of P-2 (dodecyl methacrylate / methyl methacrylate copolymer 40)
Was charged into a separable flask equipped with a stirrer, a condenser, a thermocouple and a nitrogen inlet, and stirred at room temperature for 1 hour under a nitrogen stream. Thereafter, the temperature in the system was raised to 80 ° C., and 0.001 part of iron sulfate, 0.003 part of disodium ethylenediaminetetraacetate, 0.24 part of Rongalite salt, and 1 part of distilled water
After adding 0 parts of the mixed solution, a mixed solution of 20 parts of methyl methacrylate and 0.1 part of t-butyl peroxide was added dropwise over 30 minutes. After completion of the addition, the internal temperature was removed at 80 ° C. for 1 hour. The radical polymerization was completed. No solid content was separated through a series of operations, and a uniform particle dispersion was obtained. The solid content concentration of the particle dispersion was 28.5%, the particle size distribution was relatively broad, and the weight average particle size was 248 nm.

349.7 parts of this particle dispersion was poured into 600 parts of 75 ° C. hot water containing 5 parts of calcium chloride, the solid content was separated, filtered and dried, and the polytetrafluoroethylene-containing mixed powder (B -2) 97 parts were obtained.

The dried B-2 was shaped into strips at 220 ° C. by a press molding machine, and ultrathin sections were observed with a microtome without staining using a transmission electron microscope.
Although polytetrafluoroethylene was observed as a dark part, no aggregate exceeding 10 μm was observed.

<Production of master batch (hereinafter referred to as M-1) of mixed powder containing polytetrafluoroethylene> 75 parts of linear homopolypropylene pellets (EA7 manufactured by Nippon Polychem; MFR 1.2 g / 10 minutes) Of the mixed powder B-2 containing tetrafluoroethylene to 25
After blending parts and hand blending, the twin screw extruder (Wer
ner & Pfleiderer ZSK30), barrel temperature 200 ° C, screw rotation speed 200 rpm
m, melt-kneaded, shaped into pellets, and mixed with a polytetrafluoroethylene-containing mixed powder master batch (M
-1. ) Got.

In Examples 1 to 4, M-1 was used as a polytetrafluoroethylene-containing mixture, and a sheet to be subjected to foaming was prepared by mixing a polyolefin resin and a foaming agent in the proportions shown in Table 1 below. .

[0059]

[Table 1]

Next, the components of the resin composition shown in Table 1 were heated to a temperature at which the foaming agent was not decomposed, specifically, to 120 to 160 ° C. for a polyethylene resin and to 140 to 180 ° C. for a polypropylene resin. The sheet was introduced into a vented extruder, extruded from a die, and further irradiated with an electron beam to form a crosslinked sheet.

Table 2 summarizes the results obtained above.

[0062]

[Table 2]

As is clear from Table 2 above, the foams obtained in Examples 1 to 4 of the present invention have a uniform cell diameter, excellent smoothness in appearance, and excellent stability during foaming. there were.

On the other hand, the foam containing no polytetrafluoroethylene-containing mixture (B) shown in Comparative Example 1 had non-uniform bubbles and poor stability at the time of foaming. When the addition amount of the mixture (B-1) is large, there are problems such as unevenness of the surface during sheet molding, and a sheet having a stable thickness cannot be obtained.

[0065]

The crosslinked polyolefin resin foam of the present invention has excellent stability during foaming, and has a fine cell diameter.
The foam is uniform and the product appearance is smooth.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F074 AA16 AA17 AA24 AA39 AA97 AA98 AB05 AE06 BA13 BB25 CA21 CA29 CC04X CC04Y CC06X CC22X CC48 DA02 DA04 4J002 BB02W BB03W BB033 BB11W BB11W BB12 BB12WBB BC BB12W BB12B BB12W BB12W BB12W BB12W BB12W BD154 BE043 BF013 BF023 BG043 BG053 BG063 BG103 BL013 BL023 BP02W FA084 FD010 FD030 FD170 FD320

Claims (5)

[Claims] 1. A polytetrafluoroethylene comprising polytetrafluoroethylene particles having a particle diameter of 10 μm or less and an organic polymer per 100 parts by weight of a polyolefin resin (A) having an MFR of 0.1 to 30 g / 10 min. An ethylene-containing mixture (B) is blended so that the amount of the polytetrafluoroethylene component in the mixture (B) is 0.01 to 20 parts by weight, and the degree of crosslinking is 5 to 70%. Polyolefin resin foam. 2. The crosslinked polyolefin resin foam according to claim 1, wherein the polyolefin resin (A) is mainly a polyethylene resin. 3. The crosslinked polyolefin resin foam according to claim 1, wherein the foam contains at least 15% by weight of a linear low-density polyethylene having a density of 800 to 935 kg / m ³ . 4. The crosslinked polyolefin resin foam according to claim 1, wherein the polyolefin resin is mainly a polypropylene resin. 5. A polyolefin resin comprising 15 to 85% by weight of a polyethylene resin and 85 to 15% of a polypropylene resin.
The crosslinked polyolefin-based resin foam according to claim 1 or 4, which comprises a mixture of 1% by weight.