JPH044236A - Polyolefin composition for crosslinked foam - Google Patents

Abstract

PURPOSE:To provide the title composition capable of giving foams having uniform, fine pores and improved in mechanical strength, elongation and anisotropy, comprising a polyolefin resin, foaming agent and polycarboxylic ester at specified proportion. CONSTITUTION:The objective composition comprising (A) 100 pts.wt. of a polyolefin resin (pref. a blend of PP and PE), (B) 1-30 (pref. 3-20) pts.wt, of a foaming agent (e.g. azodicarbonamide) and (C) 0.5-10 (pref. 1.0-7) pts.wt. of a polycarboxylic ester [pref. an aromatic dicarboxylic ester of the formula (R and R' are each 1-30C alkyl)].

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a polyolefin composition for crosslinked foam, and in particular to a foam having uniform and fine cells and having improved strength, elongation and anisotropy. The present invention relates to a polyolefin composition for crosslinked foam that provides the following properties.

[Prior art and problems to be solved by the invention] Polyolefin resin foams have excellent mechanical strength, flexibility, texture, heat resistance, chemical resistance, etc., and are used as interior materials for automobiles,
It is widely used as insulation materials, cushioning materials for sporting goods and food packaging, as well as other sound-deadening materials and exterior materials.

In such a foam, its foam regulating property is important, and it is desirable that the cell diameters be approximately the same and have a desired diameter. For example, if the average cell diameter is 400
There are many bubbles with a diameter of 1 mm or more in the foam of ~600 μs (20 bubbles with a diameter of 1 mm or more in the sheet foam)
1 or more), the final product will have poor texture. In addition, when foaming is performed using a conventional vertical foaming furnace, anisotropy tends to occur due to the weight of the semi-molten sheet, and this can also cause anisotropy in physical properties such as tensile strength and tensile elongation in the resulting foam. It had become.

Furthermore, in the case of polypropylene resin, crosslinking (gelation) is performed by electron beam irradiation, etc., which is performed before the foaming process.
If the gelation rate is small, it is difficult to achieve a high expansion ratio due to gas leakage, and conversely, if the gelation rate is too high, there is a problem that air bubbles communicate with each other internally, causing blisters, etc. . Therefore, in order to obtain a foam with a desired cell diameter, it is necessary to control the gelation rate within a narrow range, and therefore the crosslinking conditions such as electron beam irradiation are controlled within a narrow range.

In order to solve these problems with foams, there are methods of adding surfactants such as fatty acid esters and their metal salts, fatty acid amines, fatty acid amides, and glycols, or methods of adding polyethylene wax, atactic polypropylene, etc. is being carried out. Although foam regulating properties are improved to some extent by such methods, the additives may separate and ooze out during the foam manufacturing process, and the above-mentioned additive components may decompose due to their lack of heat resistance. There is a problem that foam regulating properties tend to deteriorate. Further, the problem of gelation rate has not been improved at all.

Therefore, the purpose of the present invention is to maintain the heat resistance, flexibility, heat insulation, cushioning properties, etc. of polyolefin crosslinked foams, have fine and uniform cell diameters, and improve anisotropy such as strength and elongation. It is an object of the present invention to provide a composition capable of obtaining a foam with a high expansion ratio and a wide optimum range of gelation rate.

[Means to solve the problem]

As a result of intensive research in view of the above issues, the present inventors have developed a composition in which a foaming agent and a polycarboxylic acid ester are added to a polyolefin resin, and after molding, crosslinking with ionizing radiation, and then foaming. The resulting foam retains the heat resistance, flexibility, heat insulation, and cushioning properties of polyolefin crosslinked foam, has fine and uniform cell diameters, and has improved anisotropy such as strength and elongation. The inventors have discovered that foaming is possible at a high expansion ratio over a wide range of gel fractions, and have conceived the present invention.

That is, the polyolefin composition for crosslinked foam of the present invention contains (a) (a) based on 100 parts by weight of the polyolefin resin;
b) 1 to 30 parts by weight of a blowing agent; and (c) 0.5 to 10 parts by weight of a polyhydric carboxylic acid ester.

The present invention will be explained in detail below.

In the present invention, (a) polyolefin resins include ethylene, propylene, butene-1, hexene-1,
Homopolymers of lead olefins such as 4-methylpentene-1, copolymers of propylene and ethylene or other α-olefins, copolymers of two or more of these α-olefins, or homopolymers of these Examples include blends of polymers, copolymers, and homopolymers and copolymers.

Among these, a mixture of polypropylene and polyethylene is preferred from the viewpoint of physical properties as a foam.

In the present invention, polypropylene is not limited to a homopolymer of propylene, but includes block copolymers or random copolymers of propylene and other lead olefins such as ethylene. Particularly preferred is a propylene ethylene random copolymer. In the case of random copolymers with ethylene, the ethylene content is preferably 1 to 15% by weight. Such polypropylene usually has a melt flow rate of 0.2 to 80 g/10 m1n) (MFR5JISK7210, load 2.
16 kg, 230°C).

In the present invention, polyethylene has a melt flow rate of 0.1 to 50 g/10 min, a density (ASTM 01505
) is 0.955 to 0.885 g/ant, and also includes copolymers with olefins having about 4 to 20 carbon atoms. Examples of such polyethylene include low-density polyethylene, linear low-density polyethylene, and high-density polyethylene, with linear low-density polyethylene being particularly preferred. Linear low density polyethylene is usually 0.5 to 20g/
10 minute melt index (ML load 2゜16kg,
190°C), and 0.910 to 0.940g/cm!
It has a density of

When the polyolefin resin is composed of a propylene-ethylene random copolymer and a linear low-density polyethylene, the proportion of the propylene-ethylene random copolymer is preferably 20 to 90% by weight, particularly preferably 30% by weight. ~80% by weight, linear low density polyethylene is preferably 80-10% by weight, particularly preferably 70-20% by weight.
Weight%.

In the present invention, (6) a blowing agent is a compound that is liquid or solid at room temperature, but decomposes or vaporizes when heated above the melting point of the polyolefin used, and is used in forming such as sheets and crosslinking reactions. Unless it substantially interferes with
Any one can be used, but the decomposition temperature is 180 to 270
Preferably, the temperature is within the range of °C. A specific example is:
azodicarbonamide)', azodicarboxylic acid metal salt, dinitrosopentamethylenetetramine, hydrazodicarbonamide, p-toluenesulfonyl semicarbazide, S
Examples include trihydrazinotridine.

The above-mentioned (b) blowing agent is usually used in an amount of 1 to 30 parts by weight, preferably 3 to 20 parts by weight, based on 100 parts by weight of the polyolefin resin (a), depending on the type and expansion ratio. The amount added can be changed as desired.

In the present invention, the polyvalent carboxylic acid ester (c) is not particularly limited as long as it is stable during the manufacturing process, and aliphatic polyvalent carboxylic acid esters, aromatic polyvalent carboxylic acid esters, etc. can be used. .

Preferably, it is an aromatic polycarboxylic acid ester, and more preferably an aromatic dicarboxylic acid ester.

The aromatic dicarboxylic acid ester is represented by the following formula: (wherein R and Ro represent an alkyl group having 1 to 30 carbon atoms). Among such aromatic dicarboxylic acid esters, those having a structure in which two ester groups are arranged at ortho positions are particularly preferable, and specific examples include diisononyl phthalate (DINF) and dioctyl phthalate (DOP). .

The amount of polycarboxylic acid ester (c) added above is (a
) 0°5 per 100 parts by weight of polyolefin resin
~10 parts by weight, preferably 1.0 to 7 parts by weight.

If the polyhydric carboxylic acid ester is less than 0.5 parts by weight, the effect of its addition will not be sufficient, and if it exceeds 10 parts by weight, sheet molding and foam molding will become difficult, which is not preferable.

In the present invention, in addition to the above-mentioned components, it is preferable to add a crosslinking aid in order to carry out the crosslinking reaction smoothly and efficiently. Examples of crosslinking aids that can be used in the present invention include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol pentaacrylate, diallyl phthalate, diallyl maleate, and the like. When using an organic peroxide for crosslinking, the amount of crosslinking aid added is (a) polyolefin resin 100%
0.5 to 5.0 parts by weight, preferably 1 part by weight
．． 0 to 3.0 parts by weight.

In the Ikemi invention, various other compounding agents, specifically rubber substances, other resins, pigments, various fillers, flame retardants, antioxidants, etc., are used for the purpose of improving the properties of polyolefin. can be mixed as appropriate.

The composition for a crosslinked polyolefin foam of the present invention comprises (a) a polyolefin as described above, (a) a blowing agent, and (c) a blowing agent;
) It can be obtained by kneading the polyhydric carboxylic acid ester, a crosslinking aid, other compounding agents, etc., which are blended as necessary, using a kneader, Henschel mixer, extruder, etc. The kneading temperature may be set appropriately depending on the base polyolefin resin, but when a mixture of propylene-ethylene random copolymer and linear low density polyethylene is used as the polyolefin resin, it is usually 16
The temperature is 0 to 180°C.

Moreover, crosslinking and foaming of this composition can be performed as follows.

First, the above-mentioned mixed material is extruded into a predetermined shape using a die such as an extruder. At this time, the extrusion temperature is appropriately controlled depending on the base polyolefin. Note that when using a mixture of propylene-ethylene random copolymer and linear low-density polyethylene, the extrusion temperature is
It is preferable to control the temperature within the range of 0 to 180°C.

The molded body thus obtained is then crosslinked,
Methods for forming a crosslinked structure include alpha rays, beta rays (electron beams),
Conventionally used methods such as irradiation with ionizing radiation such as gamma rays and heating may be employed. Among these methods, a method by irradiation with ionizing radiation is preferred, and crosslinking by electron beam irradiation is particularly preferred. The amount of radiation irradiated varies depending on the type and amount of the crosslinking agent, the degree of crosslinking, etc., but is generally 0.1 to 50 Mrad.
, preferably 1 to 30 Mrad.

The thus crosslinked composition of the present invention can be foamed by heating it to a temperature higher than the melting point of the resin component, preferably 200°C or higher, more preferably 230 to 270°C. The heating time required for foaming is usually (
1.5 to 5 minutes.

Generally, in order to obtain a foam with a sufficiently high expansion ratio, the gel fraction is controlled by setting the irradiation dose of ionizing radiation to an optimum value, and the decomposition temperature of the blowing agent is also set to an optimum value. However, in the composition of the present invention, the value of the gel fraction that can provide a sufficiently high foaming ratio is significantly wider than that of the conventional composition, so the range of the ionizing radiation irradiation amount and It is easy to control the decomposition temperature of the blowing agent.

[For production]

The polyolefin composition for crosslinked foam of the present invention has uniform fine cells, can maintain mechanical strength such as tensile strength, tensile elongation, and tear strength, and has a flexible and tenacious foam. .

Moreover, this polyolefin composition for crosslinked foam has good foam moldability even when polypropylene or polyethylene alone is used as a base resin, and when it is made into a sheet shape, it is easy to mold a raw sheet.

Moreover, the composition of the present invention allows the range of the ionizing radiation dose to be applied to obtain a foam having a desired expansion ratio to be significantly wider than conventional methods.

The reason why such various effects can be obtained is not necessarily clear, but there are uniform crosslinking effects due to the uniform dispersion of the crosslinking aid, uniform foaming effects due to the uniform dispersion of the blowing agent, and foam regulation due to the reduction of surface energy. This is thought to be due to various effects such as

In addition, when the composition of the present invention contains an antioxidant, the dispersion of the polycarboxylic acid ester is promoted, so that it has effects such as preventing surface oxidation during crosslinking due to ionizing radiation, etc. You can also expect

〔Example〕

The present invention will be explained in more detail by the following specific examples.

The following raw materials were used in each of the Examples and Comparative Examples.

[1] Polyolefin ■ Propylene-ethylene random copolymer/RPP:
[Mel)7o-Le-) (MFI?, 230
°C, 2.16 kg load) 9 g/10 min: ethylene content 4 wt%] ■Linear low density polyethylene/LLDPE: C melt flow rate 4 g/10 min, density 0.934 g/crl] ■Low density polyethylene - LDPE: Cyllufo-L/-) 3-4g/
10 minutes, density 01924 g/cut] [2] Polyvalent carboxylic acid ester ■Dioctyl phthalate/DOP: [manufactured by Shin Nihon Rika ■] ■Diisononyl phthalate/DINP: [manufactured by Shin Nippon Rika ■] Examples 1 to 6 and comparative examples 1 to 4 As shown in Table 1, various polyolefin resins (including blends), 15 parts by weight of azodicarboxylic acid amide (ADCA: made by Hydraulic Chemical Co., Ltd.) as a blowing agent, and trimethylol as a crosslinking agent. propane trimethacrylate)
(TMPT: manufactured by Shin Nakamura Chemical ■) and 1.5 parts by weight of tetrakis [methylene-3 (3,5-di-t) as an antioxidant.
-Butyl-4-hydroxyphenyl)propionate-toyomethane (I rganoxlolo, manufactured by Ciba Geigy)
0.5 parts by weight and further dioctyl phthalate or diisononyl phthalate as a polyhydric carboxylic acid ester, and using a Henschel mixer, 30 ° C., 500 r
After mixing for 2 minutes at pm, 50 mmφ with T-die,
It was supplied to an extruder having a length/diameter (L/D) of 28 and extruded at an extrusion temperature of 160 to 180°C to produce a sheet with a thickness of 1.0 mm.

Next, this sheet was irradiated with a 750 kV electron beam at a dose shown in Table 1 to effect crosslinking. Thereafter, it was placed in an air oven at 250° C. for 1.5 minutes to decompose the foaming agent and foam to about 30 times its original size.

The gel fraction, tensile strength at 23°C, tensile elongation and tear strength, and thermal dimensional stability of the polyolefin crosslinked foam sheet thus obtained were measured.

In addition, the state of bubbles was visually observed on the sheet after foaming.

The results are also shown in Table 1.

Furthermore, in each of the above Examples, the compositions containing no polyhydric carboxylic acid ester were similarly made into foam sheets, and various physical properties were measured and the state of the cells was observed in the same manner as in Example 1.

The results are also shown in Table 1.

(1) Gel fraction: Calculated by immersing the foam sheet in boiling xylene for 24 hours, then measuring the weight of the insoluble matter.

(2) It is a value measured according to JIS K6767, and shows the value in the longitudinal direction (MO)/width direction (TD).

(3) This is a value measured according to JIS K6767, and indicates the value in the longitudinal direction (MD>/width direction (TO)).

(4) This is a value measured according to JIS K6767, and shows the value in the longitudinal direction (MO)/width direction (TO).

(The shrinkage rate ((%), longitudinal direction (MO)/width direction (TO)) was measured after being left at 5020°C or 90°C for 22 hours.

From the above results, the values of tensile strength, tensile elongation, and tear strength of the crosslinked foam sheets of each example are larger than those of the corresponding comparative examples, the anisotropy is also improved, and the thermal dimensional stability is was also good. This is thought to be because the foam made from the composition of the present invention has fine and uniform cells.

Example 7.8 and Comparative Example 5 Using the foam compositions of Example 4.5 and Comparative Example 4,
The irradiation dose of 750kV electron beam was 101rad, 12M.
rad (same conditions as Example 4), 14 Mrad,
Cross-linked foams were produced by changing the amount to 16 Mrad and 18 Mrad, respectively.

The gel fraction was measured for each crosslinked foam sheet.

In addition, foam moldability was evaluated based on the following criteria.

◎: Good foam surface, fine cells.

○: Has uniform and fine cells.

△: Slight gas leakage.

×: A large amount of gas escapes, the foaming ratio does not increase, or there is blistering due to the communication holes.

The results are also shown in Table 2.

From Table 2, it can be seen that the crosslinked foam sheets of Examples 7 and 8 exhibit good foam moldability when the electron beam irradiation dose is in the range of 12 to 16 Mrad. In addition, the electron beam irradiation amount was 10 Mra.
The conditions for crosslinking d and polypropylene resin are such that even with a very small amount of electron beam irradiation, a large amount of outgassing does not occur, and the crosslinking condition for polypropylene resin is that the amount of electron beam irradiation is 18 Mrad, which is a very large amount of electrons. It can be seen that even in the case of radiation exposure, a large amount of gas escapes and no blistering occurs due to the communication holes.

On the other hand, the crosslinked foam sheet of Comparative Example 5 shows good foam moldability when the electron beam irradiation amount is 12 Mrad, but when the electron beam irradiation amount is lower than that, it is difficult to maintain the bubbles. It became difficult to do so, resulting in a large amount of gas leakage, and when the electron beam irradiation amount was higher than that, the bubbles communicated with each other, resulting in gas leakage as well.

This is because the composition of the present invention using polypropylene as the polyolefin resin can maintain bubbles even at a low gel fraction, while preventing communication between the bubbles even at a high gel fraction. Moreover, it is thought that this is because the bubbles can be uniformly dispersed.

This indicates that the composition of the present invention allows crosslinking and foaming at a high expansion ratio over a wide range of electron beam irradiation doses.

〔Effect of the invention〕

As detailed above, the polyolefin composition for crosslinked foam of the present invention contains a polyolefin resin, a blowing agent, and a polyhydric carboxylic acid ester, so it has uniform and fine cells and has high strength. , good elongation, etc.

Furthermore, in the composition of the present invention, the conditions for controlling the irradiation amount of ionizing radiation when achieving a sufficiently high expansion ratio are significantly relaxed.

Applicant: Tonen Petrochemical Co., Ltd.

Claims (2)

[Claims] (1) Contains (b) 1 to 30 parts by weight of a blowing agent and (c) 0.5 to 10 parts by weight of polyhydric carboxylic acid ester based on 100 parts by weight of (a) polyolefin resin. A polyolefin composition for crosslinked foam. (2) In the polyolefin composition for crosslinked foam according to claim 1, the polyvalent carboxylic acid ester has the following general formula: ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R and R' are carbon A polyolefin composition for crosslinked foam, characterized in that it is an aromatic dicarboxylic acid ester represented by (1 to 30 alkyl groups).