JPS5830896B2 - Method for producing polyolefin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyolefin foam such as polyethylene or polypropylene, and particularly to a method for producing a polyolefin foam having a high expansion ratio using non-crosslinked polyolefin.

When polyolefin is foam-molded using an extruder in the same way as polystyrene, for example, the foam extruded from the tip of the extruder once foams and expands, then shrinks significantly, and then gradually shrinks 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 lower than that of polystyrene foam.

The process of expanding into a stable foam after shrinking in volume is called the aging process. For example, in the case of a polyethylene foam sheet immediately after extrusion with a thickness of 1 to 2, it will last for about 1 week if left at room temperature. A maturing time of 3 to 5 days is required even in a heated room at 60°C.

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

This operation and the fact that it requires a large amount of storage space and time for aging are extremely disadvantageous in industrial production. The present invention was completed as a result of intensive research in order to obtain a polyolefin foam free of polyolefin.

Many methods are already known for obtaining polyolefin foams by extrusion.

For example, Japanese Patent Publication No. 46-43997 discloses that in an extrusion process for producing polyolefin foam, which consists of extruding an olefin polymer using a low-boiling hydrocarbon blowing agent, the above-mentioned hydrocarbon is , about 12 carbon atoms
A partial ester of ~18 fatty acids and a polyol with 3 to 6 hydroxyl groups, based on the weight of the polymer,
An improvement method is shown in which the addition of 0.1 to 10 (by weight), preferably 0.1 to 3 (by weight) φ is included in the polymer.

However, this method uses partial esters of fatty acids to prevent the bubbles of the extruded polyolefin foam from collapsing. cannot be obtained.

In this example, a fluorine-containing hydrocarbon is used as a blowing agent. Although the fluorine-containing hydrocarbon has a certain effect of preventing shrinkage of the polyolefin foam after extrusion, it is expensive. , it is not desirable to use large amounts of this.

Japanese Patent Publication No. 46-8587 discloses that the cells of the polyolefin multifoam are made extremely fine and homogeneous, and the polyolefin foam has elasticity,
In order to produce a polyolefin foam with excellent heat insulation properties and a beautiful appearance, we use a foam regulator consisting of a 3-component mixture of acid salts, carbonates, or bicarbonates of polyhydric carboxylic acids and fatty acid monoglycerides. However, in order to obtain a polyolefin foam, if a cell regulator that mainly generates carbon dioxide gas, such as the above-mentioned acid salts of polyhydric carboxylic acids or baking soda, is used, this air regulator will release air. It is easy to decompose due to moisture inside, and the properties of the raw material composition before being fed to the extruder vary and are not constant.Also, the tip of the extruder nozzle gets dirty, and impurities accumulate at the extrusion mouth of the nozzle, narrowing the gap and causing the sieve. ,
Another disadvantage is that the surface of the extruded polyolefin foam is contaminated or has a striated pattern.

The present invention is the result of intensive research in order to eliminate these drawbacks. 100 parts by weight of polyolefin is decomposed with 0.1-2 parts by weight of inorganic fine powder and 130'C or higher to mainly generate nitrogen gas. 0.01-3 parts by weight of a gas generating agent is mixed and supplied to the extruder, and 0.3-5 parts by weight of higher fatty acid ester of polyhydric alcohol is mixed in advance with the mixture or separately press-fitted into the extruder. A lower aliphatic hydrocarbon or a halogenated hydrocarbon having a boiling point below the melting point of the polyolefin is press-mixed into the molten polyolefin mixture and extruded from the tip of an extruder to obtain a polyolefin foam. The gist of this paper is a method for producing a polyolefin foam.

In the present invention, polyolefins are homopolymers of olefins such as ethylene, butene, and pentene, or copolymers of these, or copolymers of these olefins with other vinyl monomers, or copolymers of these olefins with other vinyl monomers. means a mixture of polymers.

In particular, it is suitably used for non-crosslinked low density polyethylene.

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, as well as silicon oxide, aluminum oxide,
It is a fine powder of metal oxides such as talc and magnesia that does not decompose at the heating temperature inside the extruder.

These inorganic fine powders smooth the rotation of the extruder screw and are useful as nucleating agents in foam production, and are effective in making the bubbles finer. However, if too much is mixed in, the bubbles will be destroyed and foaming will be hindered. Not only does the body surface become noticeably less smooth, but gas also tends to escape more easily.

Therefore, the inorganic fine powder is 0.1-2
It is preferable that parts by weight are mixed.

Generally, in extrusion molding of foam, there is a tendency for impurities and other substances to accumulate (build up) at the tip of the mold extrusion port of the extruder.

This tendency is particularly noticeable when carbon dioxide gas generating agents such as baking soda or acid salts of polyhydric carboxylic acids are used, and this buildup contaminates and scratches the surface of the molded product. Furthermore, the gap between the extrusion ports is reduced and the thickness of the molded product is reduced.

This requires frequent cleaning.

When baking soda or the like is used, the build-up cannot be prevented even by adding inorganic fine powder, and the extrusion port must be cleaned many times, which is a fatal flaw in the continuous operation of the foam by the extruder. It will become.

Examples of the polyhydric alcohol of the polyhydric alcohol higher fatty acid ester used in the present invention include glycerin, pentaerythritol, sorbitol, sorbitan, mannitol, etc.
Examples include dipentaerythritol and diglycerin.

Examples of higher fatty acids include saturated or unsaturated monovalent higher fatty acids having 10 to 30 carbon atoms, such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, and linoleic acid; These include beef fatty acids, bran oil fatty acids, coconut oil fatty acids, etc., which contain higher fatty acids.

In the present invention, compounds in which these polyhydric alcohols and higher fatty acids form ester bonds are used, but it is preferable that one or more hydroxyl groups remain in a free state in one molecule of the ester.

Examples include, for example, lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, pentaerythritol monocaprate, pentaerythritol monooleate, pentaerythritol monolaurate, dipentaerythritol distearate.
These include sorbitan monooleate, sorbitan sesquibran oil fatty acid ester, sorbitan monostearate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, mannicun monolaurate, etc.

These polyhydric alcohol fatty acid esters are used in an amount of 0.5 to 3 parts by weight per 100 parts by weight of the polyolefin.

Higher fatty acid esters of polyhydric alcohols are closely related to the aging time of the molded product, and if kept, if 0.1 part by weight of stearic acid monoglyceride is used based on the polyolefin, maximum shrinkage will occur 20 minutes after extrusion molding. Thereafter, it gradually expanded and continued to expand even after being left at room temperature for 4 days.

On the other hand, when 1 part by weight or 2 parts by weight of stearic acid monoglyceride is added, the density of the molded article hardly changes immediately after extrusion.

As a result, the closed cells are round, the thickness of the cell membrane does not change, and a firm molded product is obtained.

However, if more than 5 parts by weight of higher fatty acid ester of polyhydric alcohol is mixed in, not only will it not be useful for shrinkage and high foaming after extrusion, but also slippage will occur during the transfer of the molten resin in the extruder, resulting in a constant amount. extrusion becomes impossible.

That is, a foamed sheet with a constant thickness or a homogeneous cell structure cannot be obtained.

Therefore, the amount of higher fatty acid ester of polyhydric alcohol added is preferably 0.7 to 2.0 parts by weight based on the polyolefin.

Further, the gas generating agent used in the present invention is an organic compound that mainly generates nitrogen gas when heated to 130° C. or higher, and specifically, azodicarboxylic acid amide is suitable, but
Other examples include N,N'-dinitrosopentamethylenetetramine 4-4oxybisbenzenesulfonyl hydrazide.

These gas generating agents, together with the inorganic fine powder, are essential as nucleating agents for obtaining a molded article having minute and uniform bubbles.

It is added in an amount of 0.01-3 parts by weight per 100 parts by weight of polyolefin.

If the amount added is less than this, it will not contribute to the miniaturization of bubbles, and if it is more than this amount, buildup will occur at the extrusion port.

When a decomposition accelerator is mixed into azodicarboxylic acid amide and the decomposition temperature is lowered to below 130°C, the resin decomposes before it melts in the extruder and escapes to the hopper in one direction, causing the resin to foam into fine bubbles. Does not contribute.

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

That is, for example, a polyolefin, an inorganic fine powder, and a gas generating agent are thoroughly mixed, and this is fed from the hopper of an extruder into a heated extruder, the polyolefin is melt-mixed, and a higher fatty acid ester of a polyhydric alcohol and a lower A foam is obtained by injecting an aliphatic hydrocarbon, a halogenated hydrocarbon, or a mixture thereof and extruding it into the atmosphere from a die controlled at 100 to 150°C.

The shape of the foam is regulated by the shape of the die, and can be extruded into rods, plates, sheets, and other shapes.

The foam extruded by the method of the present invention exhibits almost no shrinkage immediately after extrusion and therefore does not undergo post-foaming, ie, expansion upon standing.

Therefore, the process of aging the foam is not necessary, and the time and effort such as storage for aging and unwinding of the rolled sheet are omitted, so the method of the present invention is extremely useful as an industrial production method for polyolefin foam. Useful.

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. It has become possible.

Further, according to the resin composition of the present invention, continuous production of foam by the extruder can be carried out for a long time without impurities generated by decomposition being deposited on the extrusion port of the die attached to the extruder. , contributing to lower manufacturing prices.

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 conventional aging process can be obtained.

Next, examples of the present invention will be shown together with comparative examples.

Example 1 Non-crosslinked polyethylene (MIIO23, density 0.920
, melting point 115°C) 100 parts by weight, 0.5 parts by weight of talc,
0.05 parts by weight of azodicarboxylic acid amide is 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.

On the other hand, the amount of stearic acid monoglyceride added was changed as appropriate, and about 15 parts by weight of butane was forced into the extruder and mixed well.

The mixed resin was extruded into the atmosphere through a die having a circular extrusion port cooled to about 110 DEG C. at the tip of the extruder to obtain various polyethylene foam sheets.

That is, the average cell diameter and expansion ratio based on the difference in the amount of stearic acid monoglyceride added are as shown in the following table.

Further, the thickness change over time of the polyethylene foam sheets obtained in the above Examples and Comparative Example 1 is as shown in FIG. 1, where the vertical axis is the thickness and the horizontal axis is the time.

That is, in Comparative Example 1, maximum shrinkage was exhibited 20 minutes after extrusion, and expansion continued even after 6 days had passed.

However, in Examples 4 and 5, the desired thickness with a high expansion ratio (50 times) was obtained immediately after extrusion (approximately 20-30 seconds after extrusion from the die), and there was almost no change in the thickness even after several days. There is no.

In Example 2°3, there was some expansion immediately after extrusion.

In Example 1, slight shrinkage was observed, but this shrinkage was recovered after aging for about one day.

In addition, 5 of the cell structure inside the foam sheet obtained in Example 4
A 0x magnification micrograph is shown in Figure 2, and it is composed of uniform, fine bubbles.

On the other hand, for comparison, stearic acid monoglyceride 1.
A foamed sheet (Comparative Example 2) obtained in substantially the same manner as in Example 1 by mixing only 5 parts by weight and 0.5 parts by weight of talc (not containing azodicarboxylic acid amide) had an average cell diameter of 0.8.
~1 mm, the surface is not beautiful, and a 50x magnification micrograph of the bubbles inside shows that the bubbles are irregular as shown in Figure 3.

Furthermore, in this example, impurities were deposited on the extrusion port of the die 10 days after continuous production using the extruder, so it was cleaned.

However, 0.2 parts by weight of baking soda, 0 parts of monosodium citrate,
．． When a product containing 1 part by weight and 1.0 part by weight of stearic acid monoglyceride as a foam regulator was produced continuously in an extruder for one day, impurities accumulated at the extrusion port and had to be cleaned.

Example 2 A resin composition containing 0.7 parts by weight of talc, 0.5 parts by weight of azodicarboxylic acid amide and 2.0 parts by weight of stearic acid monoglyceride, and 20 parts by weight of butane as a blowing agent were press-fitted into an extruder. Except for this, extrusion foaming was carried out in the same manner as in Example 1 through three nozzles in diameter, and a polyethylene foam of approximately 70 times the size was obtained.

Example 3 Talc 0. Example 1 was obtained by extrusion and foaming in the same manner as in Example 1, except that the resin composition was mixed with 0.5 parts by weight of abdicarboxylic acid amide, and 1 to 2.0 parts by weight of sorbitan monostearate. A polyethylene foam sheet similar to No. 4, which was expanded approximately 50 times, was obtained.

Example 4 Extrusion foaming was carried out in the same manner as in Example 1 except that 0.05 parts by weight of N,N'-dinitrosopentamethylenetetramine was mixed in place of azodicarboxylic acid amide. A foam with good physical properties was obtained.

[Brief explanation of the drawing]

FIG. 1 is a line graph showing the change in thickness of the polyethylene foam sheets over time in Example 1 and Comparative Example 1, where the vertical axis shows the thickness of the foam sheet and the horizontal axis shows the change over time. Line 1 is a line showing the change in thickness of Example 1, line 2 is Example 2, line 3 is Example 3, line 4 is Example 4, and line 5 is a line showing the change in thickness of Comparative Example 1. FIG. 2 is a 50 times enlarged micrograph showing the cell structure inside the polyethylene foam sheet obtained in Example 4 of Example 1. FIG. 3 is a 50 times enlarged micrograph showing the cell structure inside the polyethylene foam sheet obtained in Comparative Example 2.

Claims (1)

[Claims] 1. 100 parts by weight of polyolefin, 0.1 part of inorganic fine powder
-2 parts by weight and 0.01 to 3 parts by weight of a gas generating agent that decomposes at 130°C or higher to mainly generate nitrogen gas and supplied to an extruder, and 0.3 parts by weight of higher fatty acid ester of polyhydric alcohol are mixed. -5 parts by weight is mixed in advance with the above mixture or separately press-injected into an extruder, and mixed with the above-mentioned polyolefin mixture in which a lower aliphatic hydrocarbon or halogenated hydrocarbon having a boiling point below the melting point of the polyolefin is melted. A method for producing a polyolefin foam, characterized in that the polyolefin foam is obtained by extruding it from the tip of an extruder. 2. The method for producing a polyolefin foam according to claim 1, wherein the polyolefin is polyethylene.