JP2002332370A - Crosslinked polyolefin resin foam and its preparation process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crosslinked polyolefin resin foam which yields an expandable sheet showing an excellent extrusion property, shows an excellent stability at normal pressure expansion, contains fine expanded cells at either a low or high expansion ratio and has a substantially uniform product appearance and an excellent thickness uniformity. SOLUTION: The crosslinked polyolefin resin foam has a polyolefin resin (resin A) having an MFR of from 0.1 to 3 g/10 min and an extremely high molecular polyethylene (resin B1) having an intrinsic viscosity, measured in a decalin solvent at 135 deg.C, of from 5 to 40 dl/g. Here, the weight ratio of resin A to resin B1 is from 100:(0.01-20).

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 melt strength by increasing the molecular weight. However, polymerization time is not only increased, but also the cost is increased. As the molecular weight decreases, it becomes difficult to increase the desired melt strength. JP-A-5-95058 and JP-A-9-312
No. 30 proposes a polypropylene resin foam having a wide molecular weight distribution and containing a branched polymer in a polymer region, but it is very expensive to obtain a polymer material having many branches by polymerization of polypropylene. And Japanese Unexamined Patent Application Publication No.
Japanese Patent No. 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.

[0005] In the case of polyethylene resins, a method based on electron beam crosslinking is employed. However, if the degree of crosslinking is too high, it is difficult to control foaming of the expandable sheet. In addition, it is difficult to increase the degree of cross-linking with a linear low-density polyethylene by an electron beam, and when a resin having a high melt viscosity is used, there are problems such as an excessively high extrusion pressure and difficulty in uniformly dispersing a foaming agent.

[0006]

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

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by using the following constitution, it is possible to obtain a resin without changing the extrusion performance in the foaming sheet forming step. As a result, the foamed cells are fine and nearly uniform, and as a result, olefin-based crosslinked foams having excellent product appearance and thickness uniformity can be stably obtained from low expansion ratio to high expansion ratio. Heading that
The present invention has been reached.

[0008] That is, the gist of the present invention is that the MFR is 0.
A polyolefin resin (resin A) having a viscosity of 1 to 30 g / 10 minutes and an ultrahigh molecular weight polyethylene (resin B1) having an intrinsic viscosity of 5 to 40 dl / g measured in a decalin solvent at 135 ° C. And a weight ratio of the resin A: the resin B1 = 100: 0.01 to 20 in the crosslinked polyolefin resin foam.

Or a method of manufacturing the same.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The polyolefin resin (A) used in the present invention is not particularly limited as long as it has an MFR of 0.1 to 30 g / 10 minutes. Examples thereof include polypropylene (PP) and high-density polyethylene. (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), poly-1-butene, polyisobutylene, random copolymers of propylene with ethylene and / or 1-butene in any ratio or Block copolymers, ethylene-propylene-diene terpolymers in which the diene component is 50% by weight or less in all proportions of ethylene and propylene, polymethylpentene, copolymers of cyclopentadiene with ethylene and / or propylene Such as cyclic polyolefin, ethylene or propylene and 50 weight 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. Alone or 2
A mixture of more than one species can be used.

In the present invention, the polyolefin resin (A) includes PP, HDPE, LDPE, LLD
PE, at least one selected from ethylene-propylene random or block copolymer has high versatility,
It is preferable in that it is inexpensive.

The MFR of the polyolefin resin (A) used in the present invention is preferably 0.3 to 20 g / 10 minutes. The reason is that the resin A has an ultrahigh molecular weight polyethylene (resin B1) having an intrinsic viscosity of 5 to 40 dl / g as measured in a decalin solvent at 135 ° C. 0.1-5dl depending on
/ G low molecular weight to high molecular weight polyethylene (resin B
2) is also added) to maintain a good balance between the extrudability at the time of forming the foamable sheet and the melt viscosity of the resin at the time of foam molding after crosslinking the foamable sheet.
This is because a foam cell is preferable in obtaining a crosslinked olefin-based foam having a fine and uniform product appearance and excellent thickness uniformity. The MFR is measured according to JIS-K-6758 for a polypropylene-based resin and JIS-K-6760 for a polyethylene-based resin.

The MFR of the polyolefin resin (A)
Is less than 0.1 g / 10 minutes, the fluidity is not sufficient, it is difficult to form a foamable sheet, and the MFR is 30 g / min.
If the time exceeds 10 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 gas release occur on the surface, and good foam molding is performed. It is difficult to obtain goods.

In the present invention, the ultrahigh molecular weight polyethylene (resin B1) has an intrinsic viscosity of 5 to 40 dl / g measured at 135 ° C. in a decalin solvent, and a weight ratio of resin A: resin B1 = 100: 0. It needs to be blended so as to be from 01 to 20. When the intrinsic viscosity of the resin B1 measured at 135 ° C. in a decalin solvent is less than 5 dl / g, the melt viscosity and the melt strength decrease rapidly when the temperature of the resin is increased, and the gas generated by decomposition of the foaming agent is reduced. Since the resin cannot be held and escapes from the resin, the expansion ratio does not increase, and the surface of the product breaks and the smooth appearance cannot be obtained. The resin B1 has an intrinsic viscosity of 40 measured at 135 ° C. in a decalin solvent.
If it exceeds dl / g, the fluidity is not sufficient, and it is difficult to form a foamable sheet. The intrinsic viscosity of the resin B1 is preferably 8 to 30 dl / g, more preferably 10 to 10 dl / g.
20 dl / g. The resin B1 is 100
When the weight ratio is less than 0.01, the melt strength of the resin is reduced, the stability in foaming after crosslinking the sheet is insufficient, and the foam cells are enlarged, so that foaming on the surface and gas There is a problem that a dropout occurs and it is difficult to obtain a good foam molded article. On the other hand, if it exceeds 20, the fluidity is not sufficient,
There is a problem in that it is difficult to form a foamable sheet. The resin B1
Is preferably from 0.05 to 10, more preferably from 0.3 to 5.

[0015] In the present invention, it is preferable that the composition further comprises a low molecular weight to high molecular weight polyethylene (resin B2). The resin B2 has a limiting viscosity of 0.1 to 5 dl / g measured in a decalin solvent at 135 ° C., and is blended so that the weight ratio becomes resin B1: resin B2 = 100: 15 to 40. Is preferred. The intrinsic viscosity is 0.1
If it is less than dl / g, the ratio of foreign matter adhering during sheet molding may increase, which is not preferable. On the other hand, if the intrinsic viscosity exceeds 5 dl / g, the same as the resin B1,
The effect as the resin B2 cannot be expected. The resin B
The intrinsic viscosity of 2 is more preferably 0.5 to 3 dl / g. When the weight ratio is less than 15, the fluidity of the resin becomes insufficient, and it becomes difficult to form the foamable sheet,
It is not preferable because a good foam may not be obtained. When the weight ratio is more than 40, the melt viscosity and the melt strength decrease rapidly when the temperature of the resin is increased, and the foaming agent escapes from the resin without being able to hold the gas generated by decomposition and generation. As a result, the foaming ratio does not increase, and the surface of the product may be broken, and a smooth appearance may not be obtained. The weight ratio is more preferably from 20 to 35, and still more preferably from 25 to 30.

The resins B1 and B2 used in the present invention can be obtained as a mixture of the two by, for example, Ziegler polymerization described in JP-A-6-262679. It is also preferable to use a polyethylene resin (resin B) which is a body. At this time, the resin B, which is a mixture of the two, has an intrinsic viscosity of 5 to 40 dl / measured at 135 ° C. in a decalin solvent.
g of ultra high molecular weight polyethylene (resin B1) and 15 to 40% by weight of the low molecular weight to high molecular weight polyethylene (resin B2) of 15 to 40% by weight based on the ultra high molecular weight polyethylene. And the intrinsic viscosity is preferably 3.5 to 15 dl / g. More preferably, it is 7 to 13 dl / g.

In the present invention, the specific resin component (resin A + resin B1, resin A + resin B1 + resin B2, or resin A + resin B) is contained in the resin or polymer component.
Preferably 60% by weight or more (more preferably 75% by weight
The above is included. Further, as described in detail below, in order to complete the foam, a component other than a resin or a polymer such as a low molecular weight organic component or an inorganic component such as a foaming agent for foaming is generally used. However, in that case, the resin or polymer component is preferably 70% by weight or more (more preferably 80% by weight) in the foam.
The above is included.

The degree of crosslinking of the foam of the present invention is 5 to 70.
%, More preferably from 10 to 70%, and even more preferably from 15 to 50%. If the degree of cross-linking is less than 5%, the gas of the foaming agent dissipates from the surface at the time of foaming, the foam easily breaks, and it becomes difficult to obtain a foam having a desired expansion ratio (density). If it exceeds 70%, excessive cross-linking and hardening occur, so that the impact resistance at low temperatures is deteriorated and cracks are easily generated, which is not preferable. This is because setting the degree of crosslinking as described above is preferable for obtaining an olefin-based crosslinked foam having excellent foam stability and foam cells in the crosslinked sheet, a nearly uniform product appearance and excellent thickness uniformity. In addition, such a crosslinking degree is measured by the following procedures. That is, a foam was shredded and precisely weighed 0.2 g (W ₀ g), and xylene was used as a solvent.
After extracting with an Soxhlet extractor at 24 ° C for 24 hours, remove insolubles, wash with pure xylene, further wash with acetone, heat with a vacuum dryer heated to 80 ° C for 4 hours, and completely remove volatiles Allow to cool naturally 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 (%) As a foaming agent for obtaining the foam of the present invention, an inorganic foaming agent, a volatile foaming agent, a decomposition-type foaming agent and the like are used.
Decomposable blowing agents are 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. It is preferred to add.

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

Examples of the stabilizer include pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and triethylene glycol-bis [3- (3-t-butyl-5- Methyl-4-hydroxyphenyl) propionate], phosphorus stabilizers such as tris (monononylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, dilauryl 3, A sulfur-based stabilizer such as 3′-thiodipropionate;
These can be used alone or in combination of two or more. The amount of the stabilizer is preferably 0.05 parts by weight or less based on 100 parts by weight of the polyolefin resin (A).

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 essential and optional components as described above 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.

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. As a crosslinking method, a method using ionizing radiation or ultraviolet light is known. Specifically, an electron beam is preferable. The irradiation energy is 0.2 to 15 Mr.
ad is preferable, and 0.5 to 10 Mrad is more 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 can be formed into various forms by thermoforming or the like.

[0030]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In Examples and Comparative Examples, unless otherwise specified.
“Parts” indicates parts by weight, with resin A being 100, and “%”.
Indicates weight%. In addition, various physical properties were measured by the following methods.

(1) Appearance of the sheet: The appearance of the foamable sheet was visually judged.

：: The sheet surface is smooth, and there is no aggregate of 1 mm or more when observed with transmitted light.

X: The sheet surface is non-uniform, and there are aggregates of 1 mm or more when observed with transmitted light.

(2) Degree of cross-linking: 0.2 g of shredded foam
(W ₀ g to) using xylene those precisely weighed as a solvent, after 24 hours extraction in Soxhlet extractor under 120 ° C., removed insoluble matter was washed with pure xylene were further washed with acetone 80 After heating for 4 hours in a vacuum dryer heated to ℃, the volatile components are completely removed, and then 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 (%) (3) 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 (cubic root of expansion ratio).

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

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

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

×: 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.

Here, the vicinity of the surface has a depth of 0 to 0 from the surface.
It refers to 0.5 mm.

(5) Appearance of molded article: Appearance of 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. Example 1 Low-density polyethylene (resin A) having a density of 922 kg / m ³ and MFR of 6 g / 10 min, and ultrahigh-molecular-weight polyethylene having an intrinsic viscosity of 10 dl / g measured at 135 ° C. in a decalin solvent (resin B1) And a polyethylene-based resin (B) having an intrinsic viscosity of 9 dl / g having a low molecular weight or high molecular weight polyethylene (resin B2) of 1.0 dl / g and a weight ratio of resin B1: resin B2 = 100: 20; Resin A: Resin B1 = 100: 5, 10.4 parts of azodicarbonamide as a decomposable foaming agent, and pentaerythrityl-tetrakis [methylene-3] as a heat stabilizer.
(3,5-Di-t-butyl-4-hydroxyphenyl)] propionate was uniformly mixed in an amount of 0.02 part by a Henschel mixer, and formed into a sheet having a thickness of 2 mm by an extruder. After irradiating this sheet with an absorption dose of 5.5 Mrad, the sheet was foamed at a foaming ratio of 30 times in a hot-air foaming furnace 50 ° C. higher than the decomposition temperature of the foaming agent. The thickness after foaming is 4.
A foam sheet having fine bubbles at 2 mm and a density of 32 kg / m ³ was obtained. Example 2 In Example 1, the ultra-high molecular weight polyethylene component (resin B
Sheet molding and foaming were carried out in the same manner as in Example 1 except that 1) was added so as to be 15 parts. Example 3 In Example 1, except that the intrinsic viscosity in decalin of the ultrahigh molecular weight polyethylene resin (resin B1) constituting the polyethylene resin (resin B) was 7.5 dl / g. In the same manner as in the above, sheet molding and foaming were performed. Example 4 In Example 1, the resin A was 50 parts by weight of a linear low molecular weight polyethylene (density: 920 kg / m ³ ; MFR: 8 g / 10 min) and low density polyethylene (density: 920 kg / m ³ ; MFR: 8 g / 10 min)
Was formed into a sheet in the same manner as in Example 1 except that 50 parts by weight of was used, and foaming was performed in the same manner as in Example 1 after applying an irradiation dose of 6 Mrad. Example 5 A sheet was formed in the same manner as in Example 1 except that the resin A used 100 parts by weight of a linear low molecular weight polyethylene (density: 926 kg / m ³ ; MFR: 22 g / 10 min).
After the application of Mrad, foaming was carried out in the same manner as in Example 1. Comparative Example 1 Low-density polyethylene as resin A (density 922 kg / m ³ ,
Sheeting and foaming were carried out in the same manner as in Example 1 except that ultrahigh molecular weight polyethylene (resin B1) was not added to 100 parts by weight of MFR (6 g / 10 min). Comparative Example 2 Linear low molecular weight polyethylene (density 926) as resin A)
(kg / m ³ ; MFR 22 g / 10 min), 100 parts by weight, ultra-high molecular weight polyethylene (resin B1) was added in an amount of 30 parts by weight, and low to high molecular weight polyethylene (resin B2) was not added. A sheet was formed in the same manner as in Example 1 except for the above.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

The foam of the present invention has excellent extrudability at the foaming sheet molding stage and stability at the time of normal pressure foaming due to the resin composition, and its foam cells are fine from low to high foaming ratio. It is. This has made it possible to provide an olefin-based crosslinked foam having a nearly uniform product appearance and excellent thickness uniformity.

Continued on the front page F term (reference) 4F074 AA16 AA17 AA18 AA20 AA21 AA22A AA22B AA23A AA23B AA24 AA25A AA25B AA32A AA32B AA32D AA54 AA98 AB05 AC19 AC20 AC26 AC30 AC32 AC34 AD10 BA12 DA14 BA03 DA16 BB031 BB032 BB033 BB061 BB071 BB101 BB111 BB121 BB151 BC021 DE226 EQ016 EU186 FD010 FD030 FD170 FD326

Claims (6)

[Claims] 1. A polyolefin resin (resin A) having an MFR of 0.1 to 30 g / 10 minutes and an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 5 to 40 dl / g measured at 135 ° C. in a decalin solvent. (Resin B1), and the weight ratio of the resin A: the resin B1 = 100: 0.01 to 2
0. A crosslinked polyolefin-based resin foam characterized by being 0. 2. A low molecular weight or high molecular weight polyethylene (resin B2) having an intrinsic viscosity of 0.1 to 5 dl / g measured at 135 ° C. in a decalin solvent, and a weight ratio of the resin B1 : The crosslinked polyolefin resin foam according to claim 1, wherein the resin B2 is 100: 15 to 40. 3. The crosslinked polyolefin resin foam according to claim 1, wherein the degree of crosslinking is 5 to 70%. 4. A polyolefin resin (resin A) having an MFR of 0.1 to 30 g / 10 minutes and an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 5 to 40 dl / g measured in a decalin solvent at 135 ° C. (Resin B1) is obtained by blending the resin A: resin B1 = 100: 0.01 to 20 in a weight ratio to obtain a crosslinked polyolefin-based resin foam by subjecting the mixture to crosslinking and foaming. A method for producing a crosslinked polyolefin-based resin foam characterized by the following. 5. A polyolefin resin (resin A) having an MFR of 0.1 to 30 g / 10 minutes and an ultrahigh molecular weight polyethylene having an intrinsic viscosity of 5 to 40 dl / g measured at 135 ° C. in a decalin solvent. (Resin B1) and 0.1 to 5d
l / g of low to high molecular weight polyethylene (resin B
2) A polyethylene resin (resin B) having an intrinsic viscosity of 3.5 to 15 dl / g having the weight ratio of the resin B
1: A crosslinked polyolefin-based resin foam obtained by subjecting the resin B2 = 100: 15 to 40 and the resin A: resin B1 = 100: 0.01 to 20 to be blended and foamed. A method for producing a crosslinked polyolefin-based resin foam, characterized in that a foam is obtained. 6. The method for producing a crosslinked polyolefin resin foam according to claim 4, wherein the crosslinking is carried out at a degree of crosslinking of 5 to 70%.