JPH07207056A - Extrusion foaming of polyolefin resin - Google Patents

Abstract

PURPOSE:To obtain a foam without causing the depletion of the ozonosphere by feeding a polyolefin resin into an extruder, melting the resin by heating, injecting a specified volatile blowing agent into the melt and extrusion-foaming the melt at atmospheric pressure. CONSTITUTION:A polyolefin resin is fed into an extruder and melted by heating. 10-35 pts.wt., per 100 pts.wt. polyolefin resin, volatile blowing agent comprising 5-22 wt. % 1,1-difluoro-ethane and 78-95wt.% carbon dioxide into the melt in the course of its transfer and mixed, and the melt is extrusion-molded into a specified shape at atmospheric pressure.

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 foam using a nonflammable foaming agent which does not destroy the ozone layer when a polyolefin resin is foamed.

[0002]

2. Description of the Related Art Conventionally, halogenated hydrocarbons and lower fatty hydrocarbons are pressed into a molten polyolefin resin from the middle of an extruder, and are mixed in a molten gel by cooling in the vicinity of the exit of the extruder. In other words, it is known to produce a sheet-shaped, tube-shaped or rod-shaped highly expanded polyolefin foam by discharging from a die into the atmosphere. At that time, among halogenated hydrocarbons, in recent years, due to the problem of ozone layer depletion, not only CFC but also HCFC which is an alternative CFC
It has been decided that it will eventually be abolished. For HFCs with zero ozone depletion potential,
Freon 134a, which is also nonflammable, is the most effective, but it has a problem that it is extremely difficult to obtain a highly expanded polyolefin foam because of its poor compatibility with resin and poor foaming efficiency.

[0003]

In order to solve such a problem, Japanese Patent Laid-Open No. 2-279739 discloses a polystyrene resin containing carbon dioxide, 1-chloro-1,1-difluoroethane (abbreviated as CFC 142b). And a mixture of dichlorodifluoromethane (Freon 12 for short) is disclosed as a blowing agent. However, Freon 142b
Is a FCFC and CFC 12 is a CFC, so it is destined to be totally abolished in recent years. CFC 142
From the mixing ratio of b (60 to 68% by weight), this foaming agent is in the range of combustible gas, and a large amount of cost is required for explosion-proof safety measures in all foaming equipment.

In order to overcome the above-mentioned drawbacks, the present invention provides a method for producing a polyolefin resin foam using a volatile foaming agent which does not destroy the ozone layer and has a nonflammability.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that volatile blowing agents such as Freon 152a having an ozone depletion potential of 0 and carbon dioxide in a certain ratio. It has been found that, by using the mixture, even if the flon 152a which is originally a combustible gas is used, it becomes a non-combustible gas and a polyolefin resin foam can be obtained. That is, according to the present invention, when the polyolefin resin is heated and melted in the extruder and transferred, two kinds of fluorocarbons 152a 5 to 22% by weight and carbon dioxide 78 to 95% by weight are provided during the transfer. Provided is a polyolefin-based resin foam characterized by adding an appropriate amount of a mixed volatile foaming agent, and then extruding and foaming into a predetermined shape under normal pressure.

The composition of the present volatile foaming agent, in which the amount of CFCs 152a which is a flammable gas is 22% by weight or less and the rest is mixed with carbon dioxide which is a nonflammable gas, behaves similarly to the nonflammable gas. This is a great advantage not only in handling gas but also in handling foam. On the other hand, Freon 152
When a is reduced to less than 5% by weight, it is difficult to adopt it in terms of quality because it is affected by increasing the expansion ratio of the foam. Also,
Regarding carbon dioxide, if it exceeds 95% by weight, the carbon dioxide tends to be hardly dissolved in the polyolefin resin, and when discharged from the die outlet, the volatile foaming agent and the resin are separated from each other, resulting in no foaming. The harmful effect of not giving to Next, the polyolefin resin in the main foaming means polyethylene, polypropylene, ethylene-propylene copolymer, ethylene or propylene and α-olefin copolymer, ethylene-vinyl acetate copolymer, polyethylene silane graft copolymer. Examples thereof include coalescing and the like, and these may be used alone or in combination of two or more kinds.

The addition amount of the volatile foaming agent in the present invention is
10 to 35 parts by weight, more preferably 15 to 30 parts by weight, based on 100 parts by weight of the polyolefin resin, is desirable for obtaining a highly expanded foam. Further, in the present invention, in addition to these components, a bubble nucleating agent such as talc, calcium carbonate, silica and heavy sour, or an antioxidant such as phenol type, organic thioacid type and organic amine can be added. It is also possible to add additives such as pigments, antistatic agents and lubricants.

[0008]

EXAMPLES Examples of the present invention will be described below. Examples 1 to 3 and Comparative Examples 1 to 2 Low density polyethylene Examples (MI: 1.5, density: 0.
924) was mixed with talc as a nucleating agent, and the mixture was supplied to a tandem extruder having a diameter of 75 mm and melt-kneaded. CFC 15 shown in Table 1 from the perforated foaming agent injection port of the first stage extruder.
2a and carbon dioxide were added at a predetermined mixing ratio. The amount of addition was adjusted so that the expansion ratio of the foam was 20 times or more. In the second-stage extruder, these were gradually kneaded while being further kneaded, and extruded into the atmosphere from a die at the exit end of the extruder and simultaneously foamed. Further, for comparison, the same material as in the example was supplied to the extruder, and the foaming agent shown in Table 1 was added to carry out extrusion foaming. These results are summarized in Table 1.

[0009]

[Table 1]

Examples 4 to 6 and Comparative Examples 3 to 4 Low density polyethylene resin (MI: 2.0, density: 0.9
25) to a linear low density polyethylene resin (MI: 2.
0, density: 0.919) and 100/10 (PHR) were mixed in the mixed resin, talc was mixed as a nucleating agent, and the same operations as in Examples 1 to 3 were performed. For comparison, the same material as in the example was supplied to the extruder, and the foaming agent shown in Table 2 was added to carry out extrusion foaming. The results are shown in Table 2.

[0011]

[Table 2]

[0012]

As described above, since the volatile foaming agent of the extrusion foaming method according to the present invention does not cause ozone layer depletion, it can be said that the volatile foaming agent can sufficiently cope with the movement toward the complete abolition of HCFC. Moreover, since the volatile foaming agent is within the range of a certain mixing ratio, not only the foaming property but also a partially foaming agent which is originally flammable has the same property as the noncombustible gas when mixed with other noncombustible gas. Therefore, it does not require a large cost for production equipment and the like, and its industrial value is great.

Claims (1)

[Claims] 1. A polyolefin resin is heated in an extruder,
When melted and transferred, a two-mixed volatile foaming agent composed of 5 to 22% by weight of 1,1-difluoroethane (hereinafter abbreviated as CFC 152a) and 78 to 95% by weight of carbon dioxide during the transfer. An extrusion foaming method for a polyolefin-based resin, which comprises press-fitting and then extruding and foaming into a predetermined shape under normal pressure.