JP2998032B2 - Manufacturing method of polyolefin resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a polyolefin resin foam having uniform fine cells.

<Prior art> Conventionally, polyolefin resin foams have been produced in large quantities as foams of polyethylene resin, polypropylene resin, etc., and have been used in a wide variety of applications. As for the body, an extremely uniform fine foam has not yet been obtained.

On the other hand, since cyclodextrin (hereinafter abbreviated as CD) forms inclusion compounds with various compounds, synthetic resin products containing CD inclusion compounds such as fragrances, rust preventives, insecticides, and antibacterials have been developed. It has been proposed (Japanese Patent Publication No. 63-6588). A crosslinking agent comprising a CD inclusion compound of an isocyanate compound has also been proposed (JP-A-60-152535). However, no example has been found in which CD is applied to foam production technology.

<Problems to be Solved by the Invention> The present inventors have found that when producing a polyolefin resin foam,
The present inventors have found that the presence of CD in the system contributes to the uniformity and size of cells in the polyolefin-based resin foam, and has led to the present invention.

That is, an object of the present invention is to provide a method for obtaining a polyolefin-based resin foam having extremely uniform fine cells.

<Means for Solving the Problems> The present invention provides a system in which a natural and / or modified CD is present in a system in which a polyolefin-based resin, a decomposable foaming agent, and at least one of a crosslinking agent and a crosslinking aid are blended. This is achieved by a method for producing a polyolefin-based resin foam to be foamed in a state where the foam is formed.

The polyolefin resin in the present invention is, for example, polyethylene, ethylene-propylene copolymer, ethylene-butene copolymer, polypropylene, polypropylene copolymer, etc. produced by high-pressure method, medium-pressure method, low-pressure method, etc. The present invention relates to a polypropylene copolymer, particularly ethylene-
It is effective to apply to a propylene copolymer.

In the method for producing a polyolefin resin foam of the present invention, CD is present in a conventional foam in which a mixture of a polyolefin resin and a decomposable foaming agent is blended with at least one of a crosslinking agent and a crosslinking aid. There is a feature in making it work.

In order to produce a foam having uniform fine cells,
It is necessary to uniformly disperse the added foaming agent, cross-linking agent and cross-linking aid in the resin, but a mixture of a polyolefin-based resin, a decomposable foaming agent and one or more cross-linking agents and cross-linking aids By allowing CD to be present therein, the decomposition-type foaming agent, the crosslinking agent, and the crosslinking aid can be uniformly dispersed in the polyolefin resin. Note that the crosslinking agent and the crosslinking aid each include at least one kind.

As the foaming method of the present invention, various foaming methods such as a normal pressure foaming method, a pressure foaming method, an extrusion foaming method and a bead foaming method can be employed.

The decomposition type foaming agent in the present invention is a compound that decomposes by heating to generate 50 to 200 cc / g of gas. Typical examples thereof include sodium hydrogen carbonate, ammonium carbonate, azodicarbonamide, azobisisobutyronitrile and the like. This decomposition type foaming agent is preferably used in an amount of 1 to 30 parts by weight, particularly 3 to 15 parts by weight, based on 100 parts by weight of the resin.

A cross-linking agent is a substance that is decomposed by giving thermal energy to generate radicals. Typical examples thereof include peroxides such as dicumyl peroxide and tert-butyl cumyl peroxide. This crosslinking agent is resin 100
It is preferable that the amount is 0.02 to 5 parts by weight, particularly 0.1 to 1 part by weight with respect to parts by weight.

The crosslinking aid promotes crosslinking of the resin, and is, for example, a polyfunctional compound such as diallyl phthalate or divinylbenzene. The amount of the crosslinking aid is preferably 3 to 30 parts by weight, particularly preferably 5 to 15 parts by weight based on 100 parts by weight of the resin.

The natural CD in the present invention is a donut-like non-reducing oligosaccharide in which glucose is produced by reacting an enzyme with starch and glucose is cyclically linked by α-1,4 bonds. It is preferable that the number of constituent glucoses is 6 to 8 since the inside diameter of the pores is appropriate for inclusion of the organic peroxide.

Constituent glucose has 6 pores of α-CD, 7 β-CD and 8 γ-CD, each having a pore diameter of about 4.5 °, 7.0 ° and 8.5 °, and a pore depth of 7.0 °. is there.

The modified CD in the present invention is obtained by modifying a natural CD by a chemical reaction. For example, natural CD is dimethylated or trimethylated.

Specifically, glucose constituting α-CD, β-CD or γ-CD is obtained by methylating each hydroxyl group of C-2 and C-6, or C-2, C-3 and C-6. Each hydroxyl group is methylated.

Modified CD is obtained by reacting natural CD with barium oxide and dimethyl sulfate or methyl iodide.

This CD is used in an amount of 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the resin.

Hereinafter, a preferred foaming method in the present invention will be described more specifically.

In the normal pressure foaming method, a sheet obtained by melt-kneading a decomposable foaming agent, a cross-linking agent, a cross-linking aid and CD with a polyolefin resin at a temperature higher than the melting point of the resin and lower than the decomposition temperature of the foaming agent is further added to the foaming agent. Is heated above the decomposition temperature and foamed under normal pressure. Generally, sufficient viscoelasticity of the polymer is required to hold the gas generated by decomposition at the decomposition temperature of the blowing agent,
For this purpose, a method has been developed in which polymers are cross-linked with a cross-linking agent and a cross-linking aid to give optimal viscoelasticity and melt viscosity for foaming, and these methods may be applied. Among the polyolefin resins, particularly the polypropylene resin has a higher melting point than the polyethylene resin, so that it is difficult to mix the foaming agent, the crosslinking agent, and the crosslinking assistant with the resin and knead them uniformly. However, in the present invention, the coexistence of CD makes it easy to uniformly knead the resin, the foaming agent and the crosslinking agent, and the crosslinking aid, so that it is possible to produce a polyolefin-based resin having uniform fine bubbles, It is particularly effective for the production of polypropylene resins.

In addition, polypropylene resins generally have a higher melting point than polyethylene, which inevitably increases the foaming temperature, makes crosslinking more difficult, easily decomposes the polymer, and causes a sudden change in viscosity due to the high crystallinity of the polymer. Is more difficult to foam than polyethylene. However, when such a polypropylene-based resin is foamed, CD can coexist with a decomposable foaming agent, a cross-linking agent, and a cross-linking aid to solve these problems at once and form a uniform and fine foam. it can.

In the pressure foaming method of another invention of the present invention, a polypropylene resin, a foaming agent, and a mixture obtained by adding a CD to a crosslinking agent are filled in a closed mold, and heated under pressure to form a crosslinking agent. And the foaming agent is decomposed and rapidly expanded and foamed by the pressure change due to the pressure release. Also in this case, in order to further enhance the crosslinking effect, it is preferable to add a crosslinking aid to the above-mentioned mixed system. The pressure foaming method includes a one-stage method and a two-stage method, and either method may be used.

As a specific method of one step method, the type hollow in the mold by filling the mixture narrowing scissors two sheets of iron plate, a pressure of 10~250kg / cm ² on the plate surface of the mold, the blowing agent The internal pressure generated by decomposition is contained, and the pressure is released when the crosslinking is completed. The temperature ranges from 160 to 270 ° C, at which the melting of the polymer, the decomposition of the cross-linking agent and the decomposition of the blowing agent occur, in particular 200 to 230 ° C
Is preferred.

The method of the present invention is particularly preferable when polyethylene-propylene is used as a raw material resin and a pressure foaming method is employed, since a foam having more uniform and fine cells can be obtained.

Extrusion foaming is a method in which a thermoplastic resin containing a foaming agent is extruded from a die in a molten state to expand the resin by a change in pressure from a high pressure state to normal pressure, and to foam the resin. It can be applied to the first invention.

<Example> 100 PHR of polypropylene resin (FX-40, manufactured by Mitsubishi Yuka) is mixed with 5 PHR of azodicarbonamide (Vinifor AC # 3, manufactured by Eiwa Chemical Co.) with a mixing roll (at 160 ° C for 5 minutes).
After that, 0.25 PHR of dicumyl peroxide included in β-CD
And 10 PHR of divinylbenzene were added and kneaded, and kneading was performed for a total of 10 minutes.

Pour the kneaded material into a 100 × 100 × 5mm mold, make a heated press sheet at 160 ° C, and insert it between presses, 210 ° C, 2
When heating and pressurizing were performed at 00 kg / cm ² for 7 minutes and the pressure was released, a polypropylene foam having an apparent density of 0.0316 and fine and uniform air bubbles was obtained.

<Comparative Example> Among the blends of the examples, those in which dicumyl peroxide was not included by CD and 2.5 PHR was added, the polymer adhered to the mold, and a uniform foam could not be obtained.

<Effect of the Invention> In the method of the present invention, in the foaming method of a polyolefin resin, by adding CD, the method has extremely fine air bubbles which could not be obtained at all, and the air bubbles have excellent uniformity. A foam is obtained.

Furthermore, the foam obtained by the method of the present invention has excellent surface appearance.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 9/00-9/42

Claims (3)

(57) [Claims] 1. A method comprising foaming a system containing a polyolefin resin, a decomposable foaming agent, and at least one of a crosslinking agent and a crosslinking aid in the presence of natural and / or modified cyclodextrin. A method for producing a characteristic polyolefin resin foam. 2. The method according to claim 1, wherein the polyolefin resin is a polypropylene resin. 3. A method for producing a polypropylene resin foam, comprising heating a polypropylene resin, a foaming agent, a crosslinking agent, and a natural and / or modified cyclodextrin under pressure.