JPH0480239A - Resin composition for crosslinked foam - Google Patents

Abstract

PURPOSE:To obtain the title composition which can give a highly heat-resistant foam excellent in formability of sheet and good in mechanical properties without detriment to the characteristic properties of polypropylene by mixing a specified propylene/ethylene random copolymer with a linear low-density polyethylene and a blowing agent in a specified ratio. CONSTITUTION:This composition comprises 20-90wt.% propylene/ethylene ran dom copolymer (a) of an ethylene content of 0.2-1wt.% and a melt flow rate of 1-50g/10min at 230 deg.C under a load of 2.16kg, 80-10wt.% linear low-density polyethylene (b) copolymerized with a 4, 6 or 8 C alpha-olefin and having a density of 0.905-0.94g/cm<2> and a melt index of 1-20g/10min at 190 deg.C under a load of 2.16kg and 1-30pts.wt. blowing, per 100pts.wt. total of components (a) and (b), blowing agent (c).

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a resin composition for crosslinked foam, and in particular improves the moldability of raw sheets without substantially impairing the mechanical properties and heat resistance characteristic of polypropylene. The present invention relates to a resin composition for a crosslinked foam that provides a foam with excellent secondary processability and high heat resistance.

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

Among them, polyethylene foam has a low melting point and is flexible,
Excellent texture, elongation, etc. On the other hand, polypropylene foam has excellent mechanical strength such as tensile strength and bending strength, heat resistance, and secondary processability of the foam such as vacuum forming and stamping molding, and has a high melting point. Molecular cleavage progresses considerably, and the foam cells tend to become large and non-uniform.

Furthermore, since ordinary blowing agents begin to decompose at a relatively low temperature of about 170°C, they are not very suitable for polypropylene resins having a high melting point.

On the other hand, since blowing agents with high decomposition temperatures generate only a small amount of gas, a polyhydrous blowing agent is required to obtain a sufficiently high expansion ratio, which poses the problem of being uneconomical.

Therefore, is it possible to use a propylene-ethylene random copolymer with a relatively low melting point and an ethylene content of about 3% by weight or more? The problem with the composition is that it does not have sufficient heat resistance.

Therefore, the present inventors proposed a resin composition for crosslinked foam made of a propylene-ethylene random copolymer containing a trace amount of ethylene (Japanese Patent Application Laid-Open No. 63-69837).

However, the foam obtained from the above composition does not necessarily have sufficient physical properties at high temperatures or at room temperature, and it is necessary to strictly control the molding conditions of the raw sheet.

In addition, various compositions of propylene-ethylene random copolymers, etc., which have a relatively low melting point, and linear low-density polyethylene, which has good compatibility with the propylene-ethylene random copolymer and has excellent moldability, have been disclosed.

In addition, resin compositions containing 10% by weight or more of linear low-density polyethylene copolymerized with ethylene and α-olefin having 4 or more carbon atoms, ethylene or butene content of 1 to 15% by weight. % of ethylene or butene-propylene copolymer and a polyethylene resin copolymerized with a common olefin having 4 or more carbon atoms and having a density of less than 0.900 g/af and a melt index of 0.5 to 30 g/10 min, and an ethylene-propylene copolymer having a gel fraction power within the range of 0 to 70%, and the ethylene-propylene copolymer
Blend polymers with polyethylene resin having a gel fraction difference of 18% to +8% with propylene copolymer, etc. No. 102234) is disclosed.

However, each of the above-mentioned compositions does not necessarily have sufficient moldability of the raw sheet, or the heat resistance (high heat resistance) of the obtained foam at a high temperature of about 140°C. That is, the above-mentioned prior arts do not disclose any means for producing a resin composition for crosslinked foam that has both moldability of a raw sheet and high heat resistance. In this way, conventionally it has been impossible to obtain a well-balanced foam that has both physical properties at room temperature and high heat resistance.

Therefore, the object of the present invention is to provide a polypropylene material that has excellent moldability for raw sheets without substantially impairing the mechanical properties and heat resistance specific to polypropylene, has good mechanical properties, is excellent in secondary processability, and has high heat resistance. It is an object of the present invention to provide a resin composition for a crosslinked foam that provides a foam with properties.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventors have conducted intensive research on a resin composition for crosslinked foam containing a propylene-ethylene random copolymer and linear low-density polyethylene as resin components, and have found that the resin composition has a predetermined ethylene content. A composition containing a propylene-ethylene random copolymer, linear low-density polyethylene copolymerized with a specific toolefin, and a blowing agent, or substantially impairing the mechanical properties and heat resistance specific to polypropylene. The present inventors have discovered that a foam can be obtained which has excellent moldability of the raw sheet, good mechanical properties, excellent secondary processability, and high heat resistance without any problems, and has conceived the present invention.

That is, the resin composition for crosslinked foam of the present invention has (a) an ethylene content of 0.2 to 1% by weight and a melt flow rate (230° C., 2.16 kg load) of 1 to 50 g/]0.
Propylene-ethylene random copolymer 20-90 min
(b) Copolymerized lead olefin with 4.6 or 8 carbon atoms, density 0.905 to 0.94 g/cd
The melt index (190℃, 2.16kg load) is 1~20g/'10 minutes of linear low density polyethylene 8.
0 to 10% by weight, FC + the propylene-ethylene random copolymer (a) ten linear low-density polyethylene (
It is characterized by containing 1 to 30 parts by weight of a blowing agent based on a total of 100 parts by weight of b).

The present invention will be explained in detail below.

In the present invention, the fa) propylene-ethylene random copolymer is a copolymer of a repeating unit derived from propylene and a repeating unit derived from ethylene in a random manner.

The ethylene content in the propylene-ethylene random copolymer (a) is 0.2 to 1.0% by weight, preferably 0.3 to 0.8% by weight. Ethylene content in propylene-ethylene random copolymer: 0.2% by weight
If the amount is less than 1.0% by weight, the flexibility and formability of the original sheet will not be sufficient, and if it exceeds 1.0% by weight, the mechanical strength, heat resistance, and secondary processability such as vacuum forming and stamping will decrease.

In addition, the above (al propylene-ethylene random copolymer) is 1 to 50 g/10 min, preferably 3 to 30 g/10 min.
Minute melt flow rate (MFR, JISK7210,
load 2, 16 kg, 230°C).

In the present invention, (b) linear low density polyethylene is a linear copolymer obtained by copolymerizing ethylene with a small amount of α-olefin having 4.6 or 8 carbon atoms. Carbon number 4.6
Or as the α-olefin of 8, for example, butene-
1, hexene, 4-methylpentene-1, octene-
You can win or win first prize.

The content of ethylene in the linear low density polyethylene is usually about 85 to 99 mol%, particularly 90 to 9 mol%.
7 mol% is preferred. Linear low density polyethylene copolymerized with such α-olefins has a temperature of 0°905 to 0.9
40 g/crt, preferably 0.910-0.9
A density of 35 g/d and a melt flow rate (MF
R, JISK7210, load 2.16kg, 190°C
).

The blending ratio of the above-mentioned (al propylene-ethylene random copolymer) and (b) linear low density polyethylene copolymerized with lead olefin having 4.6 or 8 carbon atoms is as follows:
(a) Propylene-ethylene random copolymer + (b)
Linear low density polyethylene is 100 weight i (a
l Propylene-ethylene random copolymer or 20-90
% by weight, preferably 40 to 90% by weight, and (b) linear low density polyethylene 10 to 80% by weight, preferably 10 to 60% by weight. fa) If the propylene-ethylene random copolymer is less than 20% by weight ((b) if the linear low density polyethylene exceeds 80% by weight), the mechanical strength and high heat resistance, which are the characteristics of polypropylene resin, are sufficient. On the other hand, if (a) the propylene-ethylene random copolymer exceeds 90% by weight ((b) if the linear low-density polyethylene exceeds 10% by weight), the low-temperature formability of the raw sheet and the room temperature The physical properties etc. are not sufficient and the soft feel of the foam is also impaired.

In the present invention, the blowing agent (c) is a compound that is liquid or solid at room temperature, or decomposes or vaporizes when heated above the melting point of polypropylene, and substantially inhibits forming such as sheeting and crosslinking reactions. Any material can be used as long as it does not interfere with the decomposition temperature or 180 to 270°.
C range is preferred.

Specific examples thereof include azodicarbonamide, azodicarboxylic acid metal salt, dinitrosopentamethylenetetramine, hydrazocycarbocyamide, p-toluenesulfonyl semicarbazide, and s-trihydrazinotriazine. These blowing agents include (a) propylene-
Ethylene random copolymer (b) Used in a range of 1 to 30 parts by weight per 100 parts by weight of the linear low-density polyethylene (hereinafter referred to as the resin component), and optionally depending on the type and expansion ratio of each. The amount of mixture can be changed.

In the present invention, in addition to the above-mentioned (al propylene-ethylene random copolymer, (b) linear low-density polyethylene, and blowing agent), a peroxide can be added in order to carry out a crosslinking reaction. When the crosslinking reaction is carried out using ionizing radiation, it is not necessary to use an organic peroxide.When using an organic peroxide, it is preferable that the temperature is above the decomposition temperature of about 150°C. , methyl ethyl ketone peroxide (182°C), t-butylperoxyisopropyl carbonate (153°C), cycumyl peroquine 1-(171°C), cumene hydroperoxide (255°C), 2.5 Dimethyl-2,5-one (t-
butylperoxy)hexane (179°C), 2.5-
Examples include dimethyl-2,5-cy(t-butylperoxy)l\xin-3 (193°C) and so-t-butylperoxyphthalate (+59°C). These organic peroxides are added in an amount of 0.01 to 1.0 parts by weight per 100 parts by weight of the resin component.
It is used in a proportion of 0 parts by weight, preferably 0.05 to 0.5 parts by weight.

Further, in order to carry out the crosslinking reaction smoothly and efficiently, it is preferable to add a crosslinking aid. Examples of crosslinking coagents that can be used in the present invention include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol pentaacrylate, diallyl phthalate, diallyl maleate, and the like. The amount of the crosslinking aid added is 0.5 to 7 parts by weight per 100 parts by weight of the resin component.
．． 0 parts by weight, preferably 1.0. ~4.0 parts by weight.

In other matters inventions, various other compounding agents, specifically rubber substances, other resins, pigments, various fillers, flame retardant substances, oxidation An inhibitor can be mixed as appropriate.

Next, a method for producing a crosslinked foam using a composition consisting of the above-mentioned components will be described.

First, as described above, (al propylene-ethylene random copolymer, (b) linear low density polyethylene copolymerized with an α-olefin having 4.6 or 8 carbon atoms, (c) a blowing agent, and if necessary, Organic peroxides, crosslinking aids, and other compounding agents are mixed in kneaders, Henschel mixers,
Knead using an extruder or the like. At this time, it is necessary that the melt-kneading temperature be lower than the decomposition temperature of the blowing agent. The preferred melt crosstalk temperature is 155 to +70'c.

Thereafter, the kneaded product is extruded from a die such as an extruder to form a molded product such as a sheet. At this time, set the temperature of the dice to 15
It is preferable to control the temperature within the range of 5 to 170°C.

The molded product obtained in step 2 is then crosslinked, or
As for the formation method of the crosslinked structure, in addition to the method using organic peroxide as mentioned above, there are conventional methods such as irradiation with ionizing radiation such as alpha rays, beta rays (electron beams), and γ rays, and methods using heating. It is possible to adopt the method described. Among these methods, a method by irradiation with ionizing radiation is preferred, and crosslinking by irradiation with an electron beam is particularly preferred. The amount of radiation irradiated varies depending on the type and amount of organic peroxide and crosslinking aid, and the degree of crosslinking, but is generally 0.1 to 50 Mr.
ad, preferably 1 to 30 Mrad.

The thus crosslinked resin composition for a crosslinked foam is foamed at a temperature higher than the melting point of the resin component, preferably at 230°C.
It can be carried out by heating to a temperature of C or higher, more preferably 240 to 270C.

The heating time required for foaming is usually 0.5 to 5 minutes.

[For production]

The crosslinked foam resin composition of the present invention comprises a propylene-ethylene random copolymer having a specific ethylene content and a linear low-density polyethylene copolymerized with an α-olefin having 4.6 or 8 carbon atoms. , and a foaming agent. Such a composition does not substantially impair the mechanical properties and high heat resistance characteristic of polypropylene, and has excellent moldability as a raw sheet, as well as foams with good mechanical properties and excellent secondary processability. give.

The reason why such an effect is obtained is not necessarily clear, or the propylene-ethylene random copolymer having an ethylene content within the range of the present invention has high heat resistance and high tensile properties at room temperature and high temperature. has. Furthermore, linear low-density polyethylene copolymerized with a common olefin having 4.6 or 8 carbon atoms has the effect of suppressing deterioration of physical properties at high temperatures, and has excellent flexibility and moldability.

Therefore, a composition containing a resin having such characteristics can suppress the deterioration of the moldability of the raw sheet, and when made into a crosslinked foam, can exhibit high tensile properties over a wide range of room temperature and high temperature. This is thought to be because strength can be obtained.

Example C] The present invention will be explained in more detail with reference to the following specific examples.

In each of the Examples and Comparative Examples, the following linear low-density polyethylene was used.

[+] Linear low density polyethylene/LLDPE■: [Octene-I (as comonomer)
c8), melt index (Ml, 190℃
, 2.16 kg load) 4.0 g/10 min, density 0.
935g/CM) ・LLDPE■: [Hexene-1 (as comonomer)
c6), melt index (ML 190℃
, 2.1'6kg load) 2.5g/10min, density 0.9
20g/crt) ・LLDPE■: [Butene-1 (c
4), melt index (old, 190℃, 2.16kg load) 4.0g710
(Ethylene content and melt flow rate shown in Table 1)
Propylene-ethylene random copolymer (RPP) having (MFR 1230°C, 2.16 kg load),
15 parts by weight of azodicarbonamide as a blowing agent and 3 parts by weight of a crosslinking agent are added to 100 parts by weight of a resin component made by blending linear low-density polyethylene of the type shown in the table in the proportions shown in Table 1. , an antioxidant, a heat stabilizer, and a neutralizing agent, and mix the mixture to 300 to 700% using a Henschel mixer.
After mixing at 0 rpm for 2 to 5 minutes, transfer to a twin screw extruder (40 m
mφ, length/diameter (L/D)=28) and extruded at an extrusion temperature of 170°C to pelletize.

The pellets are processed using a single-axis sheet molding machine (50 mmφ, L/D
-28, with a T-die) and extruded at the extrusion temperature shown in Table 1 to create a sheet with a thickness of 1.0 mm.

Regarding the raw sheet thus obtained, the lowest extrudable temperature and the appearance of the sheet were measured to evaluate its moldability.

The results are also shown in Table 1.

Next, this sheet was irradiated with a 750 kV electron beam at a dose of 8 Mrad to effect crosslinking. Thereafter, approximately 2 portions of the mixture were placed in an air oven at 250°C to decompose the foaming agent and foamed approximately 25 times.

For the crosslinked foam sheet thus obtained, the apparent density after foaming, tensile strength at 23°C, specific strength,
The elongation at break, tear strength, tensile strength at high temperature (+30'C), specific strength, elongation at break, and heat resistance were measured.

The results are also shown in Table 1.

Comparative Example 1.2 Ethylene content and melt flow rate shown in Table 1)
(MFR, 230°C, 2.16 kg load);
A blowing agent, a crosslinking aid, and an oxidizing agent were added to 100 parts by weight of a resin component containing linear low-density polyethylene of the type shown in the table in the proportions shown in Table 1 in the same manner as in Example 1. An inhibitor, a heat stabilizer, and a neutralizing agent were added to form pellets.

A raw sheet and a crosslinked foam sheet were prepared from the pellets in the same manner as in Example 1.

Regarding the raw sheet and crosslinked foam sheet thus obtained, the minimum temperature at which the raw sheet can be extruded, the appearance of the sheet, the apparent density after foaming, the tensile strength at 23°C, specific strength, elongation at break, and Tear strength, under high temperature (130°
The tensile strength, specific strength, elongation at break, and heat resistance in C) were measured in the same manner as in Example 1.

The results are also shown in Table 1.

Ethylene content and melt flow rate shown in Table 1 (
A blowing agent, a crosslinking aid, an antioxidant, and a heat-resistant stabilizer were added to 100 parts by weight of a propylene-ethylene random copolymer (RPP) having an MFR of 1230°C and a load of 2.16 kg in the same manner as in Example 1. and a neutralizing agent were added to form pellets.

From these pellets, a raw material was sorted and a crosslinked foam sheet was created in the same manner as in Example 1.

Regarding the raw sheet and crosslinked foam sheet thus obtained, the minimum temperature at which the raw sheet can be extruded, the appearance of the sheet, the apparent density after foaming, the tensile strength at 23°C, specific strength, elongation at break, and Tear strength, under high temperature (130°
The tensile strength, specific strength, elongation at break, and heat resistance in C) were measured in the same manner as in Example 1.

The results are also shown in Table 1.

(1) A case in which no decomposition of the blowing agent was observed and a smooth appearance was evaluated as ○, and a case in which decomposition of the blowing agent was observed and the appearance was rough was evaluated as ×.

(This is a value measured according to 21 JIS K6767, and shows the average value in the longitudinal direction (MD) and the width direction (TD).

(3) Values measured according to JIS K6767, (
Tensile strength: kg/car)/(calculated based on the apparent density of the foam g/cII).

(4) It is a value measured according to JIS K6767, and shows the average value in the longitudinal direction (M D ) and the width direction (TD).

(5) This is a value measured according to JIS K6767, and shows the average value in the longitudinal direction (MD) and the width direction (TD).

f6) It is a value measured according to JIS K6767, and shows the average value in the longitudinal direction (MD) and the width direction (TD).

(7) Values measured according to JIS K6767, (
Calculated by tensile strength - kg/cnf) / (apparent density of foam g/crrf).

(This is a value measured according to 81 JIS K6767, and shows the average value in the longitudinal direction (M D ) and the width direction (TD).

(9) Longitudinal direction (after being left at +40°C for 24 hours)
MD) and the average (X) of the thermal deformation rate in the width direction (TD), or 0
% ◎, 0%〈X52% ○, 2%〈X≦10%
It was evaluated as △ and 10% as ×.

As is clear from Table 1, the foams of the compositions of Examples 1 to 7 have higher tensile strength, specific strength, elongation at break, and heat resistance at high temperatures than the foams of the composition of Comparative Example 1.2. Furthermore, compared to the foam of the composition of Comparative Example 3, the tensile strength, specific strength, elongation at break, and tear strength at room temperature are significantly superior.

In addition, in the composition of Comparative Example 4, since the melting point of the resin component was too high, the foaming agent decomposed during sheet extrusion, making it impossible to obtain a good raw sheet.

〔Effect of the invention〕

As detailed above, the resin composition for crosslinked foam of the present invention is a linear resin composition prepared by copolymerizing a propylene ethylene random copolymer with a predetermined ethylene content and an α-olefin having 4.6 or 8 carbon atoms. It contains low density polyethylene and a foaming agent. Such a composition does not substantially impair the mechanical properties and high heat resistance characteristic of polypropylene, and has excellent moldability as a raw material, as well as foams with good mechanical properties and excellent secondary processability. give.

Such a resin composition for crosslinked foam has surface properties,
Taking advantage of its flexibility, heat resistance, and mechanical properties, it is suitable for use in automobile interior materials, sporting goods, cushioning materials for food packaging, heat insulation materials, sound deadening materials, and other exterior materials.

Applicant: Tonen Petrochemical Co., Ltd.

Claims (1)

[Claims] (a) The ethylene content is 0.2 to 1% by weight, and the melt flow rate (230°C, 2.16kg load) is 1 to 50%.
g/10 min propylene-ethylene random copolymer 2
0 to 90% by weight, and (b) a copolymerized α-olefin having 4, 6 or 8 carbon atoms, with a density of 0.905 to 0.94 g/cm^3,
Linear low-density polyethylene 80-1 with a melt index (190°C, 2.16 kg load) of 1-20 g/10 minutes
(c) the propylene-ethylene random copolymer (a
) + 1 to 30 parts by weight of a blowing agent based on a total of 100 parts by weight of the linear low-density polyethylene (b).