JPS5830897B2 - Method for producing polyolefin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing polyolefin foams such as polyethylene and polypropylene.

For example, when polyolefin is foam-molded using an extruder in the same manner as polystyrene, the foam extruded from the tip of the extruder once foams and expands, then reaches a significant shoulder line, and then gradually collapses over a long period of time. It expands into a foam with a certain density.

This is believed to be due to the fact that the gas permeability of polyolefin foam is significantly better than that of polystyrene foam.

The process of expanding into a stable foam after shrinking in volume is called the maturing process. For example, in the case of a sheet with a thickness of 1 to 2 mm, it will take about 1 week to mature if left at room temperature. However, it requires aging for several hours or more even in a room at 60°C.

In particular, when the foam is a sheet, it is stored by being rolled up into a roll, so it must be rolled up loosely, and it must be turned over again after ripening.

The large storage space and time required for such operations and ripening are extremely disadvantageous in industrial production.

Various improvement methods are known to improve this problem.

For example, Japanese Patent Publication No. 46-43997 discloses that in an extrusion process for producing a polyolefin foam by extruding a hydrocarbon polymer using a low-boiling hydrocarbon blowing agent, the above-mentioned hydrocarbon is , about 12 carbon atoms
Partial esters of 18 fatty acids and polyols of 3 to 6 hydroxyl groups were prepared in a proportion of 0.05% by weight based on the weight of the polymer.
1-10% (by weight), preferably 0.1-3% (by weight)
In addition, improved methods have been shown that consist of encapsulation in polymers.

However, this method uses partial esters of fatty acids to prevent the foam from collapsing in the extruded polyolefin foam, and although the density of the extruded polyolefin foam does not change to some extent, it is not necessarily stable. do not have.

In this example, a fluorine-containing hydrocarbon is used as a blowing agent. Although the fluorine-containing hydrocarbon has the effect of preventing the shrinkage of the foam after extrusion to some extent, it is expensive and the fluorine-containing hydrocarbon Methods that use large amounts of hydrocarbons and the like are not preferred.

Furthermore, if a partial ester of a higher fatty acid, such as stearic acid monoglyceride, is added in an amount sufficient to prevent foam collapse, stearic acid monoglyceride has a strong lubricant effect, causing slippage between the barrel in the extruder and the polyolefin resin. , stable extrusion of the resin by the screw is inhibited.

In addition, foams obtained by adding partial esters of higher fatty acids such as stearic acid monoglyceride and extruding them have a slow dissipation of the gas used as a blowing agent, and must be stored for a long period of time to degas them. Also, in the case of sheets, it is necessary to rewind them.

The long-term storage and deaeration process of the foam is extremely uneconomical in factory production, as it cannot be shipped quickly.

As a result of research to obtain a polyolefin foam that does not have any drawbacks, the present inventor found that polyoxyethylene higher fatty acid ester not only improves the above-mentioned drawbacks, but also unexpectedly has an extremely excellent antistatic effect. This finding led to the present invention.

That is, the present invention provides 100 parts by weight of polyolefin, 0.1 to 2 parts by weight of the nucleating agent, % formula % [wherein, R1 is a higher alkanoyl group having a carbon number of 12 to 20, R2 is R, or a hydrogen atom, and n is an integer of 2 to 10, respectively] A polyoxyethylene higher fatty acid ester represented by 0.
A lower aliphatic hydrocarbon or a halogenated hydrocarbon having a boiling point below the softening temperature of the polyolefin is mixed into the molten polyolefin and extruded from the tip of the extruder. The gist of the present invention is a method for producing a polyolefin foam, which is characterized by obtaining a foam.

In the present invention, polyolefin refers to homopolymers of olefins such as ethylene, propylene, butene, and pentene, or copolymers thereof, or copolymers of vinyl monomers mainly composed of these olefins, or polymers thereof. It means a combination of.

Examples include high-density polyethylene, low-density polyethylene, crosslinked polyethylene, and polypropylene.

Examples of the nucleating agent include inorganic fine powder, decomposable foaming agents, carbon dioxide gas generating agents, etc., and each may be used alone or a mixture of these may be added.

Inorganic fine powders include metal salts of inorganic acids such as calcium carbonate, magnesium carbonate, calcium phosphate, magnesium phosphate, calcium silicate, magnesium silicate, calcium sulfate, and magnesium sulfate, silicon oxide, aluminum oxide, curcum, and magnesia. Contains oxides of metals such as.

The decomposable blowing agent is an organic compound that mainly generates nitrogen gas when heated, and azodicarboxylic acid amide is suitable; Bisbensene sulfonyl hydrazide and the like can be mentioned.

Further, examples of the carbon dioxide gas generating agent include a mixture of an organic acid and a carbonate or bicarbonate, such as citric acid and sodium hydrogen carbonate.

These nucleating agents are effective in producing foams with fine cells and are used in an amount of 0.1 to 2 weight percent based on the polyolefin.

The polyoxyethylene higher fatty acid ester used in the present invention is a compound represented by the above general formula, and specifically, polyoxyethylene (n=4) mono or civalmitic acid ester, polyoxyethylene (n=4) Examples include mono- or distearic acid esters.

The polyoxyethylene higher fatty acid ester has a surfactant effect, and in the present invention, one having an HLB value (hydrophilicity-lipophilicity ratio) of 4 to 11 is preferable.

For example, in polyoxyethylene monostearate,
The relationship between n and the HLB value is as follows.

n 2 4 10 25 40 4-
5HLB 4.0 6.5], 1,0 15.0
Thick ones of 17.5 to 18.0 HLB have the effect of making bubbles finer, but have poor affinity with polyolefins, and for example, with N-40 substances, extrusion stability tends to be inhibited.

Therefore, it is most preferable to have an HLB of 4 to 11 as having fine bubbles and no extrusion fluctuations.

In the method of the present invention, these polyoxyethylene higher fatty acid esters have a content of 0.1 to 1 with respect to the polyolefin.
0% by weight added.

When the amount added is less than 0.1%, the extruded foam shrinks to a maximum within 20 to 120 minutes after extrusion, and then gradually expands.
It continues to expand even after being left at room temperature for 4 days.

That is, long-term aging is required.

On the other hand, if 10% by weight or more of polyethylene higher fatty acid ester is added, the surface of the foamed molded product becomes less slippery, and it tends to be difficult to obtain a beautiful molded product.

Therefore, the amount of polyoxyethylene higher fatty acid ester added is preferably 0.1 to 10% by weight based on the polyolefin.

The polyolefin foam of the present invention is produced by conventional methods using a conventional extruder.

That is, for example, by thoroughly mixing the polyolefin and the nucleating agent,
This is fed into a heated extruder from the hopper of the extruder, polyolefin is melted and mixed, and polyoxyethylene higher fatty acid ester and lower aliphatic hydrocarbon or halogenated hydrocarbon or a mixture thereof are pressurized into the mixture. A foam is obtained by extruding into the atmosphere from a die controlled at ~150°C.

The shape of the foam is regulated by the shape of the die, and can be extruded into a rod, plate, sheet, or other desired shape.

The foam pressed by the method of the present invention, as in the case of adding stearic acid monoglyceride, shows almost no shrinkage immediately after extrusion, and therefore hardly expands when left to stand after extrusion.

Therefore, there is no need for a step of aging the foam, and the time and effort of storage for aging, unwinding of the rolled sheet, etc. can be omitted.

Moreover, the resulting foamed molded product varies depending on the thickness of the sheet and the size of the rod or plate, but unlike the case of partial esters of higher fatty acids such as stearic acid monoglyceride, the foaming agent in the molded product also collapses. Gas dissipates quickly,
Therefore, there is no need for long-term storage for secondary processing after production.

Therefore, the method of the present invention is extremely useful as a method for industrially producing polyolefin foams.

Furthermore, the foam obtained by the method of the present invention has an extremely excellent antistatic effect.

Using polyoxyethylene (n=4) monostearate, stearic acid monoglyceride, hardened beef tallow oil, and hardened soybean oil, the static electricity attenuation degree of the resulting foam was measured, and the results were as follows.

The foam used was a board with an original thickness of 5 Qmm, and the static electricity attenuation was measured using a static meter manufactured by Muroto Shokai at an applied voltage of 8 KV, a sensitivity of 1010-5 O, and a height of the applied sensing part of 2 Q mm.

The average values of each sample measured three times were as follows.

Hydrogenated soybean oil and hydrogenated beef tallow oil are mainly composed of a mixture of stearic acid triglyceride and palmitic acid triglyceride.

The amount of each additive added is expressed as % by weight relative to the polyolefin, and is an amount that can sufficiently exhibit the effect of preventing shrinkage after extrusion and foaming.

As is clear from the above table, polyoxyethylene (n=
4) Foams obtained by adding monostearate have a low degree of charge from the beginning, and moreover, the degree of attenuation after 30 seconds is 80% or more, and generally, if 50% attenuation occurs within 30 seconds, it is difficult to charge. It is clear that the antistatic effect is significant.

Further, according to the method of the present invention, a molded product having fine bubbles, a smooth and beautiful surface, and a high expansion ratio can be stably obtained.

Conventionally, it has not been possible to obtain a foamed molded product with a high expansion ratio using non-crosslinked low density polyethylene, but according to the method of the present invention, it is possible to obtain a polyethylene foamed molded product with a foaming ratio of 60 to 70 times, for example. became possible.

Furthermore, according to the resin composition of the present invention, impurities caused by decomposition do not accumulate at the extrusion port of the extruder attached to the extruder, and there is no slippage of the resin in the extruder, so that the blowing agent can be mixed uniformly. Since foams can be extruded stably, continuous production of foams using an extruder can be carried out over a long period of time, which is effective in reducing production costs.

Furthermore, according to the present invention, without using an expensive fluorine-containing hydrocarbon blowing agent, a hydrocarbon such as butane can be used.
A polyolefin foam with a high expansion ratio that does not require a maturing step can be obtained.

Next, examples of the present invention will be shown.

Example 1 Non-crosslinked low density polyethylene (MIIO23, density 0.
920, melting point 115°C) 100 parts by weight and talc 0.
7 parts by weight were thoroughly mixed in a rebore blender and fed into the extruder from the hopper of the extruder.

The extruder is sequentially heated to about 200°C from this supply section,
The above mixture is melt-blended and sent to the tip of the extruder by means of a screw.

-Capolyoxyethylene (n=4) monostearate 4
．． 66 parts by weight and about 15 parts by weight of butane in an extruder.
Press the mixture under a pressure of 50 kg/ci to mix well.

In this way, a foamed rod-shaped body having a diameter of 18 mm was obtained from the die cooled to about 110° C. at the tip of the extruder.

This foam has an expansion ratio of approximately 60 times, and the cells are fine and
It was uniform, with almost no shrinkage or expansion from the tip immediately after extrusion, and the surface was beautiful even during continuous production.

Example 2 Non-crosslinked low density polyethylene (MIIO23, density 0.
920. 100 parts by weight (melting point 115°G) and 0 talc
．． 7 parts by weight were thoroughly mixed in a tumbler blender and fed into the extruder from the hopper of the extruder.

From this feed, the extruder is successively heated to about 200'C, and the mixture is melt-blended and delivered to the tip of the extruder by means of a screw.

- 2.81 parts by weight of polyoxyethylene (n=2) monostearate and about 15 parts by weight of butane are forced into an extruder under a pressure of 150 kg/crj and mixed well.

In this way, a foamed sheet with a thickness of about 1.2 mm was obtained from the die cooled to about 110° C. at the tip of the extruded material.

This foam has a foaming ratio of approximately 45 times, and the cells are fine and
Moreover, it was uniform, with almost no shrinkage or expansion due to its size immediately after extrusion, and the surface was beautiful even during continuous production.

Claims (1)

[Claims] 1 0 nucleating agent per 100 parts by weight of polyolefin
, 1 to 2 parts by weight, general formula % formula % [In the formula, R1 is a higher alkanoyl group having 12 to 20 carbon atoms, R2 is the same as R1 or a hydrogen atom, and n is an integer of 2 to 10, respectively. ] Polyoxyethylene higher fatty acid ester 0
．． A lower aliphatic hydrocarbon or a halogenated hydrocarbon having a boiling point below the softening temperature of the polyolefin is mixed into the molten polyolefin and extruded from the tip of the extruder. A method for producing a polyolefin foam, the method comprising: obtaining a foam. 2. The method for producing a polyolefin foam according to claim 1, wherein the polyoxyethylene higher fatty acid ester is a polyoxyethylene mono- or cibalmitic acid ester, a polyoxyethylene mono- or distearic acid ester, or a mixture thereof. 3. The method for producing a polyolefin foam according to claim 1, wherein the polyolefin is polyethylene. 4. The method for producing a polyolefin foam according to claim 1, wherein the nucleating agent is an inorganic fine powder, a decomposable blowing agent, or a carbon dioxide gas generating agent.