JPH061873A - Production of polyolefin resin foam - Google Patents

Abstract

PURPOSE:To produce a polyolefin resin foam with a good moldability without producing any defective molding due to accelerated crosslinking when a crosslinkable polyolefin resin is used and without causing defects in adhesive properties of the foam by extrusion foaming using a fluorocarbon blowing agent considered not to destroy the ozone layer. CONSTITUTION:A resin compsn. contg. 100 pts.wt. polyolefin resin and 0.5-4 pts.wt. 15-22C primary fatty acid amide and a fluorocarbon blowing agent considered not to destroy the ozone layer are melt mixed under pressure to give a foamable mixture, which is extruded into a low-pressure zone and thereby foamed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyolefin resin foam by an extrusion foaming method using a non-specific chlorofluorocarbon as a foaming agent. More specifically, it has good foam moldability and dimensional stability over time. In addition, the present invention relates to a method for producing a polyolefin resin foam in which the poor adhesion of the foam due to the addition of the shrinkage inhibitor is improved.

[0002]

2. Description of the Related Art Generally, a method for producing a polyolefin resin foam is a chemical foaming method in which a resin is kneaded with a pyrolytic chemical foaming agent, molded into a predetermined shape, and then heated and foamed above the decomposition temperature of the foaming agent. A typical method is the extrusion foaming method in which a gas or a volatile liquid having a boiling point below the melting point of a resin such as butane, pentane, or dichlorodifluoromethane is pressed into a molten resin and then discharged into a low pressure region to foam. is there.

In the extrusion foaming method, generally, a polyolefin resin is put into an extruder to be melted, a foaming agent is pressed in from the middle of the extruder, further melt-kneaded, and then extruded and foamed from a die to form a foam. Is getting Blowing agents used in the extrusion foaming method are roughly classified into hydrocarbons and halogenated hydrocarbons.

[0004] Hydrocarbons have a high gas escape rate through the foam film of the foam, so that they tend to easily shrink with time, lack dimensional stability, and require a long aging period after foaming. There is a drawback that.

On the other hand, most of the halogenated hydrocarbons are
While having the same drawbacks as hydrocarbons, dichlorodifluoromethane (CFC-12) and dichlorotetrafluoroethane (CFC-114) have a small dimensional change over time in the resulting foam, and therefore foam for extrusion foaming. Widely used as an agent. However, CFC-12 and CFC-1
Most of the CFCs such as 14 have a large ozone layer depleting power, and thus are being globally abolished as specific CFCs that should be regulated from the viewpoint of global environment protection.

[0006] Hydrogen-containing fluorocarbons and chlorine-free fluorocarbons that are less likely to damage the ozone layer are being developed as CFCs (non-specific CFCs) that substitute CFCs of CFCs. Among them, for example, monochlorodifluoromethane (HCFC-22),
Monochlorodifluoroethane (HCFC-142b),
Alternatively, since these mixtures have good foaming properties, it is possible to substitute specific CFCs in extrusion foaming of polyolefin resins. However, since these non-specific freons have a higher gas escape rate than CFCs, they tend to cause cell shrinkage over time, lack the dimensional stability of the foam over time, and require a long aging period after foaming. And

Therefore, when these non-specific CFCs are used as a foaming agent in extrusion foaming, it is necessary to add a relatively large amount of shrinkage inhibitor. However, since (1) many shrinkage inhibitors act as lubricants, when the addition amount is large, the resin slips strongly in the extruder and causes extrusion fluctuation. (2) Silane-grafted polyethylene In the case of crosslinkable polyolefin resin such as
When a shrinkage inhibitor such as a fatty acid ester or metallic soap is used, these act as a cross-linking agent or a cross-linking catalyst, so that cross-linking gelation is promoted and extrusion molding is difficult,
(3) Since most shrinkage inhibitors belong to surfactants, they have poor compatibility with non-polar polyolefin resins and ooze out onto the surface of the foam, and as a result, between the foam and other materials, or foaming. There is a problem that the body cannot be bonded with an adhesive (for example, an acrylic adhesive) between the bodies.

[0008]

An object of the present invention is to use a non-specific CFC which does not damage the ozone layer as a foaming agent and has a good moldability by an extrusion foaming method. In some cases, it is an object of the present invention to provide a method for producing a polyolefin-based resin foam that does not cause molding failure due to accelerated cross-linking and does not cause poor adhesion of the foam.

The inventors of the present invention have earnestly studied various compounds acting as shrinkage inhibitors in extrusion foaming of polyolefin resins using non-specific CFC as a foaming agent, and as a result, primary fatty acid amide having 15 to 22 carbon atoms has been found. When used in a specific ratio, it has good extrusion foaming moldability, does not cause molding failure even when using a crosslinkable polyolefin resin, and exudes to the surface of the foam to improve adhesiveness. I found that there is no problem such as hindrance. The present invention has been completed based on these findings.

[0010]

According to the present invention, a resin composition containing 100 parts by weight of a polyolefin resin and 0.5 to 4 parts by weight of a primary fatty acid amide having 15 to 22 carbon atoms, and a non-specification Provided is a method for producing a polyolefin resin foam, which comprises melt-kneading chlorofluorocarbon under pressure, and extruding the obtained foamable mixture into a low-pressure region for foaming.

The present invention will be described in detail below. Examples of the polyolefin resin used in the present invention include:
Polyethylene, crosslinkable ethylene copolymer, polypropylene, crosslinkable propylene copolymer, polybutene, polybutadiene, ethylene-propylene copolymer, crosslinkable ethylene-propylene copolymer, ethylene or propylene and α-olefin copolymer , Ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, copolymer of ethylene and acrylic acid derivative, ethylene-vinyl chloride copolymer, ethylene-styrene copolymer and the like. These polyolefin resins can be used alone or in admixture of two or more.

If necessary, a cell nucleating agent, a crosslinking catalyst, an antioxidant, a lubricant, a pigment, an antistatic agent, etc. can be appropriately added to the polyolefin resin.

Examples of the bubble nucleating agent include talc, silica, calcium carbonate, calcium stearate, calcium silicate, baking soda and the like. Examples of the crosslinking catalyst include silanol condensation catalysts such as dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, stannous acetate, stannous caprylate, tin naphthenate, zinc caprylate, and zinc stearate. Examples of antioxidants include phenols, organic thioacids, organic phosphoric acids, organic amines, and organic tins.

In the present invention, the polyolefin resin 100
0.5 to 4 parts by weight of primary fatty acid amide having 15 to 22 carbon atoms is added to parts by weight. This carbon number is 15-22
The primary fatty acid amide serves as a shrinkage-preventing agent for a polyolefin resin foam.

When a compound generally used as a surfactant or a lubricant such as a fatty acid ester or metallic soap is added as a shrinkage inhibitor, the extrusion moldability is poor, or the compound exudes and adheres to the surface of the polyolefin resin foam. Of the crosslinkable polyolefin resin, and promotes crosslinking to cause molding failure. On the other hand, a primary fatty acid amide having 15 to 22 carbon atoms can be stably extrusion-foamed with a relatively small amount of use and exhibits a good shrinkage-preventing action, as well as a crosslinkable polyolefin resin. However, it does not cause molding defects and does not impair the adhesiveness of the foam. Even fatty acid amides other than primary fatty acid amides having 15 to 22 carbon atoms cannot exert these effects.

Examples of the primary fatty acid amide having 15 to 22 carbon atoms include stearic acid amide and behenic acid amide. These can be used alone or in combination of two or more. The usage ratio is 0.5 to 4 parts by weight with respect to 100 parts by weight of the polyolefin resin. If this proportion is too small, the effect of preventing shrinkage is small, and if it is too large, stable extrusion moldability is impaired.

The foaming agent used in the present invention is a non-specific chlorofluorocarbon such as HCFCs which has no fear of environmental problems such as ozone layer destruction. Examples of non-specific CFCs include monochlorodifluoromethane (HCFC-22), monochlorodifluoroethane (HCFC-142b), monochlorotetrafluoroethane (HCFC-124), difluoroethane (HFC-152a), and mixtures of two or more thereof. Is mentioned. Among these non-specific CFCs, monochlorodifluoromethane (HCFC-22), monochlorodifluoroethane (HCFC-142b), and mixtures thereof are particularly preferable from the viewpoint of foaming characteristics.

In the method for foaming a polyolefin resin of the present invention, a mixture of a polyolefin resin and a desired additive is charged into an extruder and melt-kneaded according to a conventional method.
The foaming agent is press-fitted into the extruder through an injection port provided in the barrel of the extruder, the resin and the foaming agent are melt-kneaded under pressure, and then extruded from a mold having a predetermined shape into a low-pressure region to foam. The press-fitting amount of non-specific freon of the foaming agent can be appropriately determined according to the desired expansion ratio, but is usually about 10 to 35 parts by weight with respect to 100 parts by weight of the polyolefin resin.

[0019]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The method of evaluating the characteristics is as follows.

<Moldability> ∘: Very good moldability and beautiful foam appearance ◯: Good moldability, good foam appearance Δ: Moldability is slightly insufficient, foam appearance is slightly poor x: Crosslinking promoted Poor moldability and poor appearance of foam

<Shrinkage with time> ⊚: No shrinkage with time ◯: Recovered within 1 day Δ: Shrinked slightly (recovered within 1 to 2 days) ×: Shrinked with time

<PVC adhesive tape (acrylic adhesive)
Adhesiveness with> ◎: Very good (foam skin material destruction 40% or more) ○: Good (foam skin material destruction 40% or less) △: A little insufficient (foam skin material destruction 10% or less) ×: Poor (Peeling of interface)

[Examples 1 to 4 and Comparative Examples 1 to 6] Density 0.
Low density polyethylene or crosslinkable polyethylene (silane-grafted polyethylene) having a melt index (MI) of 2.0 at 925 g / cm ³ and 190 ° C., in the proportions shown in Table 1, a cell nucleating agent (talc) and a silanol condensation catalyst (dibutyl). Tin diacetate) and various shrinkage inhibitors are mixed, supplied to a single screw extruder (L / D = 28) having a diameter of 40 mm, melt-kneaded, and then from a foaming agent injection port provided in the center of the extruder, A 60:40 mixture of HCFC-142b and HCFC-22 was pressed in at a ratio such that the expansion ratio was 30 times. Then, a die in which the melt-kneaded foamable composition was attached to the tip of the extruder (inner diameter 3.0 mmφ, outer die diameter 5.8)
(mmφ) was extruded into the atmosphere and foamed simultaneously with the discharge. Table 1 collectively shows the evaluation results of the moldability, shrinkage property over time, and adhesiveness of the foam.

[0024]

[Table 1]

As is clear from Table 1, when a fatty acid amide compound having a carbon number of 15 to 22 represented by stearic acid amide or behenic acid amide is used, the adhesiveness between the obtained polyolefin resin foam and the adhesive is improved. Is also ensured, and in the case of crosslinkable polyolefins, poor moldability due to accelerated crosslinking is avoided.

[0026]

EFFECTS OF THE INVENTION According to the present invention, in extrusion foaming of a polyolefin-based resin using a non-specific CFC, the moldability is good, and in the case of a crosslinkable polyolefin-based resin, molding defects due to accelerated crosslinking are not caused. Also provided is a method for producing a polyolefin-based resin foam that does not cause poor adhesion of the foam. The foam produced by the method of the present invention is excellent in secondary workability because it is possible to adhere other members or foams of the same type to each other using an adhesive.

Claims (2)

[Claims] 1. A resin composition containing 100 parts by weight of a polyolefin resin and 0.5 to 4 parts by weight of a primary fatty acid amide having 15 to 22 carbon atoms, and non-specific CFCs are melt-kneaded under pressure to obtain A method for producing a polyolefin-based resin foam, which comprises extruding the foamable mixture thus obtained into a low-pressure region for foaming. 2. The production method according to claim 1, wherein the non-specific CFC is monochlorodifluoromethane (HCFC-22) and / or monochlorodifluoroethane (HCFC-142b).