JPS6169844A - Crosslinked synthetic resin foam - Google Patents

Abstract

PURPOSE:To obtain a crosslinked synthetic resin foam having excellent resistance to heat and low-temperature impact and high-temperature processability and suitable for use as an automobile trim and a substrate for pressure-sensitive adhesive type, by crosslinking and expanding an expandable olefin resin compsn. CONSTITUTION:A propylene/ethylene random block copolymer having an ethylene component content of 16-70wt% as resin component, a block coefficient (absorbance ratio of absorptions at 720cm<-1> and 731cm<-1> assignable to ethylene component in an infrared absorption spectrum) of 0.8 or above, a degree of isotacticity of 40% or above, a melt flow rate of 0.1-30 and a high-temperature side m.p. of 130-165 deg.C is used (an appropriate amount of an olefin polymer such as low-density or high-density polyethylene may be used together). An expandable resin compsn. consisting of said copolymer, a blowing agent, a crosslinking agent and other additives are crosslinked and expanded by any of conventional methods to obtain the purpose crosslinked synthetic resin foam.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides heat resistance, low-temperature impact resistance and This invention relates to a synthetic resin crosslinked foam with excellent high-temperature processability.

[Conventional technology]

Polyolefin resin foams are used in various fields because of their excellent cushioning properties, heat insulation properties, and the like. Among these polyolefin resin foams, polypropylene foam has the following characteristics compared to the same type of polyethylene foam:
Excellent heat resistance, tensile strength, bending strength, and thermoformability.

However, crystalline polypropylene resin generally has a high melting point, and the melting temperature of the resin is close to the decomposition temperature of the crosslinking agent and foaming agent, so it is difficult to melt and knead the resin without thermally decomposing them. Therefore, it was not possible to obtain a uniformly crosslinked and foamed molded article of good quality. Also,
A major drawback of crystalline polypropylene foam is that it is brittle at room temperature.

In order to improve these drawbacks, it is possible to mix polyethylene or use crystalline propylene as a base resin.
Ethylene random copolymer ('-P P P P P
-E -P P P P P -E -P P PPP
A propylene chain (
PP-) in which copolymerized ethylene molecules (E) are randomly distributed has been used (Japanese Patent Publication No. 38716/1983).

The former method of mixing polyethylene improves low-temperature impact properties, and the latter method of using copolymers has a lower melting point than propylene homopolymers, resulting in less crosslinking and blowing agents. It becomes possible to melt mix and mold the resin and these crosslinking agents and foaming agents without causing thermal decomposition.

[Problem that the invention seeks to solve]

In the former method of adding and mixing polyethylene to polypropylene, polypropylene and polyethylene are not compatible, so if the resulting foam is processed at high temperatures such as vacuum forming, the closed cells of the foam will burst and become open cells. However, the problem remains that the functionality of the foam is altered, such as loss of cushioning properties.

Furthermore, crosslinked foams using crystalline propylene-ethylene random copolymers such as the latter have significantly lower low-temperature impact resistance than conventional polyprolene foams, causing problems in use in cold regions.

This invention aims to eliminate these drawbacks, and aims to ensure that the crosslinking agent and foaming agent do not undergo thermal decomposition during melt mixing and molding, are crosslinked and foamed uniformly, and have good low-temperature impact resistance and high-temperature processability. The purpose is to provide a synthetic resin crosslinked foam of excellent quality.

[Means for solving problems]

This invention has an ethylene component of 16 to 70%, a blocking coefficient (absorbance ratio of absorption at 720 cm-' and 731 mark-1 caused by the ethylene component in an infrared absorption spectrum) of 0.8 or more, and an isotactic degree. 40% or more, melt flow rate (hereinafter referred to as MFR) 0.1 to 3
0. Propylene with a high temperature side melting point of 130-165℃
This synthetic resin crosslinked foam solves the above problems by crosslinking and foaming a foamable resin composition containing an ethylene random block copolymer as a resin component.

The propylene-ethylene random block copolymer used in this invention simultaneously polymerizes ethylene and propylene using a Ziegler-Natsuta type catalyst, and has a molecular arrangement of... -PPPPP-E-PPPPP-PPPP
P-EEEE-PPPPP-E-PPPPP-EEEE
- It has a structure in which ethylene is partially distributed in a random type and a block type in a propylene chain. That is, it is a copolymer that belongs to an intermediate type between a crystalline propylene-ethylene random copolymer and a crystalline propylene-ethylene prosodic copolymer.

Of this copolymer, the ethylene content is from 16 to
At 70% by weight, the block coefficient (B), which is a measure of the blockiness of the contained ethylene, is 0.8 or more, the isotactic degree is 40% or more, the MRR is 0.1 to 30, and the high temperature side melting point is 130 to 165. ℃ is used.

In addition, the block coefficient (B) is the ratio of the absorbance (A) of the absorption at 720 (J-' and 731 marks 1 m-' caused by the ethylene component) in the infrared absorption spectrum of the copolymer measured at room temperature. Yes, A/73 of B=720cm-'
1 ell-' is the value indicated by A, of which 7
The absorption at 20 cm-' is due to block-copolymerized ethylene. Therefore, the larger the value of the block coefficient (B), the more ethylene chains copolymerized in a block manner in the propylene chain.

In addition, the high temperature side melting point is determined by scanning calorimetry (DSC method) or differential thermal analysis (DTA method) at a heating rate of 10°C/min,
The melting point on the high temperature side in the case of

In the present invention, the propylene-ethylene random block copolymer preferably has an ethylene content of 16 to 70 weight %, with the ethylene content of the block portion being 15 to 69 weight %. Further, the random portion of ethylene controls the melting point on the high temperature side, and its content is preferably 1 to 15% by weight. Increasing the ethylene content in the block portion improves low-temperature impact resistance, and also prevents closed cells from flowing during high-temperature processing, such as when polyethylene is mixed with a propylene-ethylene random copolymer. Never.

If the ethylene content is less than 16% by weight, the high temperature side melting point will be higher than 165°C or the low temperature impact strength will be poor. Moreover, when the ethylene content exceeds 70% by weight, the properties of polypropylene are almost lost, and the mechanical strength, elongation rate at high temperatures, and heat resistance deteriorate significantly. Furthermore,
The yield in the resin polymerization step becomes low and the cost becomes high.

[Effect]

The propylene-ethylene random block copolymer having the above-mentioned properties used in this invention has a high-temperature melting point in the range of 130 to 165°C, and the melting point of other propylene resins (polypropylene homopolymer; 165 to 165°C).
175°C, propylene-ethylene block copolymer; 1
60-170°C), the crosslinking agent, foaming agent, etc. do not thermally decompose during melt mixing or molding, and this melting point is suitable for producing a crosslinked foam having uniform fine cells.

In addition, among other propylene-based resins, propylene-ethylene random copolymers also have a melting point of 125 to 165°C,
Suitable for crosslinking agents, foaming agents, etc. that do not decompose thermally, but
This resin has the disadvantage that low-temperature impact resistance is significantly reduced, and is therefore undesirable.

In addition, the melting point can be adjusted by adjusting the ethylene content of the random portion, and in the propylene-ethylene random block copolymer of the present invention, the ethylene content is suitable in the range of 16 to 70% by weight. A range of melting points is obtained.

On the other hand, the low-temperature impact resistance of a crosslinked foam made of a propylene-ethylene copolymer is related to the block coefficient (B) in the propylene chain of copolymerized ethylene; , the impact resistance is insufficient, and the impact resistance of crystalline propylene-ethylene random copolymers is extremely low.

In addition, in the propylene-ethylene random block copolymer of this invention, the isotactic degree and MF
The preferred range of R is an isotactic degree of 40% or more, MF
The reason why R is limited to 0.1 to 30 is because if the isotactic degree is lower than 40%, the mechanical properties such as heat resistance and bending strength, which are characteristics of polypropylene foam, will deteriorate.
If R is less than 0.1, the melt viscosity will be too high and moldability will deteriorate, while if R exceeds 30, it will be difficult to adjust the foaming viscosity.

The synthetic resin foam of this invention is made of such propylene-
Although an ethylene random block copolymer is used, it can be manufactured by a method generally used for manufacturing crosslinked foams.

That is, for example, a foamable resin composition consisting of a propylene-ethylene random protox copolymer, a blowing agent, a crosslinking accelerator, etc. is fed into an extruder, extrusion molded, and then this molded product is subjected to electron beam irradiation. After crosslinking, it can be produced by foaming by heating to a temperature higher than the decomposition temperature of the foaming agent.

In the present invention, the foamable resin composition can be a propylene-ethylene random block copolymer mixed with other olefin polymers. That is, the propylene-ethylene random block copolymer of the present invention has a very high ethylene content in the block portion, so it has a much higher ethylene content than propylene-ethylene block copolymers and propylene homopomers with an ethylene content of 15% by weight or less. , has very good compatibility with polyethylene, making it possible to mix with other olefin resins, making it easy to modify, making it possible to create soft to hard foams, and even when processed at high temperatures, it remains independent. Very little loss of bubbles.

Examples of such olefin polymers include low density polyethylene, high density polyethylene, polypropylene, etc., and copolymers thereof. The blending ratio of these resins is appropriately selected depending on the intended foam. In general, it is desirable for the propylene content in the total resin to be 20% or more, since physical properties such as heat resistance and mechanical strength can be maintained, and from the perspective of the purpose of this invention.

This foamable resin composition also contains heat stabilizers, antioxidants, fillers, plasticizers, flame retardants, colorants, and antistatic agents used in conventional foam molding, as long as they do not interfere with crosslinking or foaming. There is no problem in adding organic or inorganic substances such as

The blowing agent is a compound that is liquid or solid at room temperature and decomposes or vaporizes when heated above the melting point of the base resin, and is used as appropriate as long as it does not substantially interfere with molding or crosslinking. The decomposition temperature of this blowing agent is preferably in the range of 180 to 270 DEG C. Examples include azodicarbonamide, azodicarboxylic acid metal salts, etc. These blowing agents are mixed in appropriate amounts depending on the type and expansion ratio.

In addition, crosslinking accelerators include polymethacrylates of polyhydric alcohols such as trimethylolpropane trimethacrylate, and by adding these, electron beam irradiation crosslinking can be carried out smoothly and efficiently.

〔Example〕

Example 1 Ethylene content is 30% by weight, block coefficient (B) is 1
．． 37, Isotactic degree is 85%, VFR is 10.
0. 100 parts by weight of a propylene-ethylene random block copolymer with a high temperature side melting point of 157°C, 3 parts by weight of trimethylolpropane trimethacrylate, and 1 part by weight of a heat stabilizer were mixed in a mixer, and this mixture was transferred to a 120 maΦ extruder. The resin was extruded into a sheet with a width of 5001 m and a thickness of 163 mm at a resin temperature of 185°C. In this sheet, the foaming agent was uniformly dispersed, and the foaming agent did not decompose.

Next, this sheet is subjected to two steps using an electron beam accelerator. OM rad
After irradiating both sides, a foamed sheet was produced by foaming using a hot air foaming device with a furnace temperature of 260°C. The obtained foam sheet has uniform microbubbles, is white in color, and has a thickness of 3.0 mm.
Apparent density: 0.032 g/cm:l, degree of crosslinking: 4
It was 5%.

Comparative Example I 100 parts by weight of a propylene homopolymer with an MFR of 7.5 and a melting point of 165°C, 12 parts by weight of azocarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, and 1 part by weight of a heat stabilizer were mixed in a mixer, 1 as in Example 1
Extrusion molding was carried out using a 201 φ extruder. However, the resin temperature could not be lowered below 197°C, and the foaming agent decomposed within the extruder, making it impossible to obtain a good sheet.

Comparative Example 2 Propylene-ethylene block copolymer 1 with an ethylene content of 2.5% by weight, an MFR of 6.0, and a melting point of 166°C
00 parts by weight, 12 parts by weight of azodicarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, 1 part by weight of heat stabilizer
Parts by weight were mixed using a mixer and extrusion molded using a 120-diameter extruder in the same manner as in Example 1. However, the resin temperature is 194℃
The blowing agent could not be lowered further, and the blowing agent decomposed in the extruder, making it impossible to obtain a good sheet.

Comparative Example 3 100 parts by weight of a propylene-ethylene random copolymer with an ethylene content of 2.6% by weight, an MFR of 7.0, a block coefficient (B) of 0, an isotactic degree of 86%, and a melting point of 154°C , 12 parts of abdicarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, and 1 part by weight of a heat stabilizer were mixed in a mixer, and as in Example 1, 120 parts of
0φ extruder, resin temperature 180℃, width 500mm, thickness 1
．． A 3 vm sheet was molded.

Next, this sheet is subjected to 2. OM r ad
After irradiating both sides, a foamed sheet was produced by foaming in a hot air foaming device with a furnace temperature of 260°C. This foam sheet has a thickness of 3. On, apparent density is 0,033 g/cm
', the degree of crosslinking was 46%.

Example 2 70 parts by weight of the same propylene-ethylene random block copolymer as in Example 1, MFR 4.0, density 0.
30 parts by weight of low density polyethylene of 922 g/cm";
8 parts by weight of azodicarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, and 0.5 parts by weight of a heat stabilizer are mixed in a mixer, and this mixture is heated to a resin temperature of 180°C by a 120 Tsuru Φ extruder to a width soom and a thickness It was extruded into a 1.5 m sheet. The foaming agent was uniformly dispersed in this sheet, and the sheet was smooth with no decomposition of the foaming agent.

Next, this sheet was heated to 1.3 M rad using an electron beam accelerator.
After irradiating both sides, a foamed sheet was produced by foaming using a hot air foaming device with a furnace temperature of 260°C. The obtained foam sheet has uniform fine cells, is white, and has a thickness of 3.5 mm. l
va, apparent density 0.0413g/cra", degree of crosslinking 4
It was 7%.

Comparative Example 4 50 parts by weight of a crystalline propylene-ethylene block copolymer with an ethylene content of 4.0% by weight, an MFR of 8.0, and a melting point of 162°C, an MFR of 4.0, and a density of 0.922.
50 parts by weight of low-density polyethylene of g/am3, 8 parts by weight of azodicarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, and 0.5 parts by weight of a heat stabilizer were mixed in a mixer, and the mixture was mixed in a 120 mΦ extruder in the same manner as in Example 2. Extruded. However, the resin temperature could not be lowered below 192''C, and the blowing agent decomposed in the extruder, making it impossible to obtain a good sheet.

Comparative Example 5 Ethylene content: 4.5% by weight, MFR: 8.0, block coefficient (B): 0.3, isotactic degree: 75%
, 50 parts by weight of a crystalline propylene-ethylene random copolymer with a melting point of 140°C, an MFR of 4.0, and a density of 0.9.
50 parts by weight of low-density polyurethane powder of 22 g/am', 8 parts by weight of azodicarbonamide, 3 parts by weight of trimethylolpropane trimethacrylate, and 0.5 parts by weight of a heat stabilizer were mixed in a mixer, and the mixture was prepared in the same manner as in Example 2. A foamed sheet having a thickness of 3.0 mm, an apparent density of 0.051 g/cm', and a degree of crosslinking of 46% was obtained.

Next, the physical properties of the foamed sheets obtained in Examples 1 and 2 and Comparative Examples 3 and 5 were measured. The results are shown in Table 1.

Next, the foamed sheets obtained in Examples 1 and 2 and Comparative Examples 3 and 5 were vacuum formed, and the maximum drawing ratio of vacuum forming and the change in the closed cell ratio of the foamed sheets before and after forming were measured. It was as shown in Table 2. (Margins below) Table 1 Note) Measurement of tensile strength and elongation; Measurement was performed by punching out a test piece with a No. 1 dumbbell and pulling it in the longitudinal direction at a speed of 500 m/min.

Impact resistance test: Based on the Elmendorf method.

Table 2 Note 1) The maximum drawing ratio (L/D) for vacuum forming is measured by varying the depth of the vacuum forming mold and measuring the maximum depth at which the molded part breaks (L).
was measured and expressed as the ratio (L/D) of the diameter (D) of the molded part.

2) Closed cell ratio: Measured using an air comparison density tester.

In addition, before molding, the closed cell ratio of the foamed sheets of Examples 1 and 2 was 92% and 90%, respectively, but after molding, it was 88% and 84%, respectively, and the decrease in the closed cell ratio was slight. It showed the same good resilience as before molding.

On the other hand, the foamed sheet of Comparative Example 5 had a closed cell ratio of 43%, which was 89% before molding, and had very poor compression recovery properties and no resilience.

Claims (1)

[Claims] 1. Ethylene component is 16 to 70% by weight, block coefficient (
7 caused by the ethylene component in the infrared absorption spectrum
Absorbance ratio of absorption at 20 cm^-^1 and 731 cm^-^1) is 0.8 or more, isotactic degree is 40% or more, melt flow rate (MFR) is 0.1 to 30, and high temperature side melting point is 130. A synthetic resin crosslinked foam, characterized in that it is formed by crosslinking and foaming an olefin resin foamable composition mainly composed of a propylene-ethylene random block copolymer at a temperature of ~165°C. 2. The synthetic resin crosslinked foam according to claim 1, wherein the olefin resin foamable composition comprises a mixture of the propylene-ethylene random block copolymer and another olefin polymer.