JPS5830898B2 - Method for producing polyolefin foam - Google Patents

Description

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

For example, when polyolefin is foam-molded using an extruder in the same way as polystyrene, 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 permeation rate of polyolefin foam is significantly lower than that of polystyrene foam.

The process of expanding into a stable foam after shrinking in volume is called the maturation process.For example, in the case of a sheet with a thickness of 1 to 2 cm, it will take about 1 week to mature if left at room temperature. This 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 after ripening.

Such operations and the fact that they require a large storage space and a long time for 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, which consists of extruding a hydrocarbon polymer using a low-boiling hydrocarbon blowing agent, the above-mentioned hydrocarbon is , about 12 to 1 carbon atoms
Partial esters of 8 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.
An improved method is indicated which consists of adding 1 to 10 (by weight) cakes, preferably 0.1 to 3 (by weight) cakes, and encapsulating them in a polymer.

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 actual cases, fluorine-containing hydrocarbons are also used as blowing agents. Although fluorine-containing hydrocarbons have some effect in preventing shrinkage of the foam after extrusion, they are expensive and Methods that use large amounts of hydrocarbons 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 extrusion with the addition of partial esters of higher fatty acids such as stearic acid monoglyceride 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. In the case of sheets, it is necessary to rewind them.

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

The present inventor conducted research to obtain a polyolefin foam without the drawback of clumping, and as a result, discovered that triglycerides of higher fatty acids have excellent effects, leading to the present invention.

That is, in the present invention, 0.1 to 2 parts by weight of a nucleating agent and 0.1 to 10 parts by weight of higher fatty acid triglyceride are mixed with 100 parts by weight of polyolefin, and the mixture is supplied to an extruder, and the mixture is supplied to an extruder at a temperature below the softening temperature of the polyolefin. A method for producing a polyolefin foam, characterized in that a lower fatty hydrocarbon or a halogenated hydrocarbon having a boiling point of It is something.

In the present invention, polyolefin refers to homopolymers of olefins such as ethylene, propylene, butene, and pentene, or copolymers thereof, or copolymers containing these olefins with other vinyl monomers, or polymers thereof. means a mixture of unions.

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, magnesium silicate, calcium sulfate, and magnesium sulfate, as well as metal salts such as silicon oxide, aluminum oxide, curk, and magnesia. Contains oxides.

The decomposable blowing agent is an organic compound that mainly generates nitrogen gas when heated, and azodicarboxylic acid amide is preferable, but in addition, N,N'-dinitrosopencumethylenetetramine, 4,4-oxybisbenzene Examples include sulfonyl hydrazide.

In addition, the carbon dioxide gas generating agent is citric acid and hydrogen carbonate I-IJ
A mixture of an organic acid and a carbonate or bicarbonate, etc., can be mentioned.

These nucleating agents are effective in producing microcellular foams and are used in amounts of 0.1 to 2 weights per weight of polyolefin.

Suitable triglycerides of higher fatty acids to be used in the present invention include saturated fatty acids having 12 to 20 carbon atoms, particularly triglycerides of stearic acid, permitic acid, or mixtures thereof.

Animal oils and fats such as beef tallow, liver fat, and whale oil, as well as natural fats and oils such as soybean oil, olive oil, cacao butter, cottonseed oil, and castor oil, contain oleic acid, lylunic acid, or chiffrein in addition to lumitic acid and stearic acid. Hydrogenated oils and fats obtained by hydrogenating these oils and fats contain a large amount of oleic acid, lylic acid, lysyllic acid, lumitic acid, stearic acid, and hydroxystearic acid. These hardened oil-resistant products can be used in the method of the present invention.

In the method of the present invention, these higher fatty acid triglycerides are used in an amount of 0.1 to 10% by weight φ relative to the polyolefin.
added.

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

On the other hand, if 10 weight or more of higher fatty acid triglyceride is added, the surface of the foamed molded product becomes less slippery.
It tends to be difficult to obtain beautiful molded bodies.

Therefore, the amount of the higher fatty acid triglyceride added is preferably 0.1 to 10% by weight, particularly 2 to 6% by weight φ relative to the polyolefin.

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

That is, the polyolefin and the nucleating agent are thoroughly mixed,
This is fed into a heated extruder from an extruder horn, a polyolefin is melted and mixed, and a higher fatty acid triglyceride and a lower fatty acid hydrocarbon or a halogenated hydrocarbon, or a mixture thereof is press-fitted therein, 10
A foam is obtained by extruding into the atmosphere from a die controlled at 0 to 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 extruded by the method of the present invention, as in the case where stearic acid monoglyceride is added, shows almost no shrinkage immediately after extrusion, and therefore hardly any post-foaming, ie, expansion upon standing.

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.

Furthermore, although the obtained foamed molded product differs depending on the thickness of the sheet and the size of the rod-shaped body or plate-shaped body, in both cases, the foaming agent in the molded body differs from the case of partial esters of higher fatty acids such as stearic acid monoglyceride. The gas dissipates quickly, so there is no need for long-term storage for secondary processing after manufacture.

In order to obtain a polyethylene foam sheet with a 40 times foaming thickness of 1 mrn, hydrogenated beef tallow oil was used as the higher fatty acid triglyceride according to the method of the present invention, and the amount of residual gas in the resulting foam sheet was measured. As shown in the figure, it is well understood that the residual gas in the foam sheet dissipates more quickly than when stearic acid monostearate is used.

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

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, there is no accumulation of f [substances caused by decomposition at the extrusion port of the extruder attached to the extruder, there is no slippage of the resin in the extruder, and there is no miscibility of the blowing agent. Since the extrusion is carried out uniformly and extruded stably, the continuous production of foam using an extruder can be carried out over a long period of time, which is effective in reducing the production cost.

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, practical examples of the present invention will be shown.

Example 1 Non-crosslinked low density polyethylene (MIIO23, Secret Concubine 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 through the extruder's conch.

The extruder is successively heated to about 200° C. from this feed section, and the mixture is melted and mixed and sent to the tip of the extruder by a screw.

On the other hand, hydrogenated beef tallow oil (stearic acid triglyceride approx. 63
150 kg of permitic acid triglyceride (containing about 27% permitic acid triglyceride) and about 15 parts by weight of butane were put into an extruder.
/ffl and 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
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.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the dissipation rate of the blowing agent gas when hardened beef tallow oil is added to obtain a polyethylene foam sheet with a thickness of 1 mm and 40 times the expansion by the method of the present invention. For reference, an example in which stearic acid monoglyceride was added is also shown. In the drawing, the vertical axis indicates the amount of gas remaining in the foam sheet, and the numerical value is the weight of the resin used on land. The horizontal axis is elapsed time (minutes). Line 1 shows 2.711 parts by weight of hardened beef tallow oil based on polyethylene, and line 2 shows the same <3.
It shows the amount of residual gas when 800 parts by weight is added. Line 3 shows the amount of residual gas when stearic acid monoglyceride is used in place of hardened beef tallow oil at a weight of 2.71 fbrjf based on polyethylene.

Claims (1)

[Scope of Claims] 1.0.00 nucleating agent per 100 parts by weight of polyolefin.
1-2 parts by weight, higher fatty acid triglyceride 0.1-1
A lower aliphatic hydrocarbon or 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 to form foam. 2. A method for producing a polyolefin foam, characterized in that the higher fatty acid triglyceride is a triglyceride of lumitic acid, stearic acid, or a mixture thereof.3. Method 4 for producing a polyolefin foam according to claim 1, in which the polyolefin is polyethylene; 4. The polyolefin according to claim 1, in which the nucleating agent is an inorganic fine powder, a decomposition type blowing agent, or a carbon dioxide gas generating agent. Foam manufacturing method