JPH0715023B2 - Crosslinked plastic foam and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a crosslinked plastic foam having excellent mechanical strength and having fine cells, and a method for producing the same.

(Prior Art) Conventionally, as a cross-linked plastic foam, a cross-linked foam using a polyolefin resin such as LDPE has been widely known because of its low price, and is used for various purposes. However, the foam is a tensile insulation, elongation, skin peeling strength, etc. for applications requiring particularly mechanical strength such as a heat insulating material for lithographic plates which is laminated with a steel plate and bent, and a base material for adhesive tape. Was required, and thin sheets were required to have a small cell diameter at the same time, which was not sufficiently satisfactory.

In addition, a crosslinked polyolefin foam is formed by molding a polyolefin resin in which a foaming agent is kneaded, and then irradiating it with an electron beam to crosslink it and then heating it to foam it, and molding a polyolefin resin in which a crosslinking agent and a foaming agent are kneaded. rear,
It is manufactured by a method of chemical crosslinking for heating to crosslink and foam.

However, the foam obtained by the electron beam cross-linking foaming method has a limitation in the penetration depth into the above-mentioned molded body due to the ability of the irradiator, and if the molded body is thick, a uniform foam cannot be obtained. The foam produced by the chemical cross-linking method is superior to the electron beam cross-linking method in that a thick product can be continuously produced, but it has a defect that the cell diameter is coarse and the appearance is inferior.

(Problems to be Solved by the Invention) The present inventors have proposed a method for continuously producing a crosslinked foam having excellent mechanical strength, fine cell size, and good appearance in a chemical crosslinking method under normal pressure. As a result of conducting a variety of studies,
This is a cross-linked foam having excellent mechanical strength and having a uniform cell size and fineness.

(Means for Solving the Problems) The crosslinked plastic foam of the present invention has a linear low density polyethylene of 95 to 70 parts by weight, a chlorinated polyethylene of 5 to 30 parts by weight, and a total of 100 parts by weight of the above two kinds. On the other hand, a composition containing 1 to 10 parts by weight of a thermoplastic polyester resin is crosslinked and foamed.

Further, the method for producing the crosslinked plastic foam of the present invention,
95 to 70 parts by weight of linear low-density polyethylene, 5 to 30 parts by weight of chlorinated polyethylene, and a foaming agent in a composition containing 1 to 10 parts by weight of a thermoplastic polyester resin based on 100 parts by weight of the above-mentioned two kinds. After the cross-linking agent is mixed and molded, it is heated to cross-link and foam, or the above-mentioned composition is mixed with a foaming agent,
It is characterized in that after molding, it is irradiated with an electron beam to crosslink and then heated to foam.

In the present invention, the linear low-density polyethylene is, for example, ethylene propylene by an ionic polymerization reaction under medium and low pressure,
Butene-1, Penten-1, Hexene-1, Octene-
An appropriate number of short chain branches are introduced into a linear backbone polymer by copolymerizing a small amount of an α-olefin such as 1,4-methylpentene-1, thereby making the density within the range of ordinary high pressure low density polyethylene. It is a polymer reduced to.
Its density is 0.95~0.940g / cm ^3, melt index 0.5
It is preferably about 10 g / 10 minutes.

The reason why chlorinated polyethylene is added to low density polyethylene in the present invention is to improve the mechanical strength of the foam by adding chlorinated polyethylene. If the added amount is less than 5 parts by weight, bubbles are added. Is not uniform and the mechanical properties are not improved, and when it exceeds 30 parts by weight, the appearance of the foam is impaired.

The reason why the thermoplastic polyester resin is added to the linear low-density polyethylene in the present invention is that the bubble diameter of the foam can be made finer by adding the thermoplastic polyester resin. If it is less than 1 part by weight, the bubbles cannot be made finer, and 10
If it exceeds the weight part, the resin is apt to deteriorate during foaming, and the desired foam cannot be obtained.

The softening point of the thermoplastic polyester resin is 50 °
A temperature in the range of 120 ° C is preferable, and a temperature of 50 ° C or lower causes severe softening during heating and foaming, resulting in poor workability. Also, if the temperature is 120 ° C. or higher, the appearance at the time of molding by extrusion or the like is inferior.

Further, the foaming agent used in the method of the present invention is composed of a substance that decomposes by heat to generate oris,
Examples are azodicarbonamide, dinitrosopentamethylenetetramine, diphenyl-4,4-disulfonylhydrazide.

The amount of the foaming agent added is appropriately selected depending on the expansion ratio of the desired foam, but is usually 5 to 30 parts by weight with respect to 100 parts by weight of the resin composition.

Examples of the cross-linking agent for cross-linking the foam in the present invention include dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide,
2-5-dimethyl-2,5-di (t-butyloxy) hexane and the like, and the addition amount thereof is 0.1 to 2 parts by weight of the crosslinking agent with respect to 100 parts by weight of the resin composition.

When cross-linking using an electron beam, an ordinary electron beam, γ
It is performed by irradiating radiation such as α rays and α rays, and the irradiation amount varies depending on the thickness of the foamed molded product, but is usually 1 Mrad to 10 M.
This is done within the range of rad.

(Examples) Examples (1) to (5) As shown in Table 1, linear low-density polyethylene having MI 1.0 and a density of 0.92 g / cm ³ was added to chlorinated polyethylene (Eraslen 404).
B, manufactured by Showa Denko KK and thermoplastic polyester resin (softening point
A foaming agent (Vinihol AC ^# 1) was added to the composition containing 102 ° C.
After adding 15 parts by weight of Eiwa Chemical Industry Co., Ltd.) and 0.8 parts by weight of a cross-linking agent (dicumyl peroxide, manufactured by Mitsui Petrochemical Industry Co., Ltd.), melt-kneading with a pressure kneader (5) and stripping with an open roll. , Pelletized. This pellet
A 2 mm thick sheet was obtained by extruding at 140 ° C. using a 40 mmφ extruder. This sheet was heated on a wire mesh type belt conveyor to carry out cross-linking foaming to obtain a cross-linked plastic foam of the present invention having a thickness of 6 mm.

Comparative Example (1) As shown in Table 1, a high-pressure low-density polyethylene having an MI of 1.0 g / 10 min and a density of 0.921 g / cm ³ was added with a foaming agent and a cross-linking agent in the same manner as in the example and pelletized into a sheet. A comparative example crosslinked plastic foam was obtained by molding and heating to cause crosslink expansion.

Comparative Example (2) As shown in Table 1, the same linear low-density polyethylene as that used in the example was used, to which a foaming agent and a cross-linking agent were added, pelletized, and molded into a sheet. Then, it was heated to be crosslinked and foamed to obtain a comparative crosslinked plastic foam having a thickness of 6 mm.

Comparative Example (3) As shown in Table 1, a composition in which only chlorinated polyethylene was added to the same linear low-density polyethylene as in the example, a foaming agent and a crosslinking agent were added in the same manner as in the example, and pelletized. Molded into a rear sheet and heated to crosslink and foam to a thickness of 6 mm
A cross-linked plastic foam was obtained.

Comparative Examples (4) to (5) As shown in Table 1, the same composition as that of the Examples except that the linear low-density polyethylene, chlorinated polyethylene and thermoplastic polyester were mixed in different mixing ratios was used. A foaming agent and a cross-linking agent were added to and pelletized, then molded into a sheet, and heated to cross-link and foam to obtain a cross-linked plastic foam of Comparative Example having a thickness of 6 mm.

Example (5) 15 parts by weight of a foaming agent was added to the same composition as in Example (1), pelletized in the same manner as in Example (1), and molded into a sheet, followed by irradiation with an electron beam of 4 Mrad. Cross-linking was performed by irradiation, and then heat-foaming was performed in a heating furnace to obtain a cross-linked plastic foam of the present invention having a thickness of 6 mm.

With respect to the thus obtained crosslinked plastic foam of the present invention and the crosslinked plastic foam of the comparative example, the appearance, density, rebound resilience and cell diameter were measured as the characteristics. The results are as shown in Table 1.

(Effect) As described in detail above, according to the crosslinked plastic foam of the present invention, the appearance is beautiful because it has excellent mechanical strength and the cell diameter is uniform and fine, and it is suitable for heat insulating ceiling materials, base materials for adhesive tapes, and household sundries products. It is extremely useful when applied.

Claims (3)

[Claims] 1. A linear low-density polyethylene 95 to 70 parts by weight,
Chlorinated polyethylene 5 to 30 parts by weight, and the total of the above two types
A crosslinked plastic foam obtained by crosslinking and foaming a composition containing 1 to 10 parts by weight of a thermoplastic polyester resin with respect to 100 parts by weight. 2. Linear low-density polyethylene 95 to 70 parts by weight,
Chlorinated polyethylene 5 to 30 parts by weight, and the total of the above two types
A method for producing a crosslinked plastic foam characterized by mixing a foaming agent and a crosslinking agent into a composition containing 1 to 10 parts by weight of a thermoplastic polyester resin with respect to 100 parts by weight, molding the mixture, and then heating the mixture to crosslink and foam. . 3. Linear low-density polyethylene 95 to 70 parts by weight,
Chlorinated polyethylene 5 to 30 parts by weight, and the total of the above two types
A crosslinked plastic characterized by mixing a foaming agent in a composition containing 1 to 10 parts by weight of a thermoplastic polyester resin with respect to 100 parts by weight, molding the mixture, irradiating it with an electron beam to crosslink it, and then heating it to foam it. Method for producing foam.