JPS5847409B2 - Method for manufacturing polyolefin foam sheet - Google Patents

Description

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

For example, when polyolefin is foam-molded using an extruder in the same way as polystyrene, the foam sheet extruded from the tip of the extruder has a stronger transparency than a polystyrene-filled sheet because the cells are coarser. .

In addition, a foam sheet with coarse cells lacks flexibility and does not have a good feel, which is disadvantageous when used as a cushioning material or packaging material.

When a polyolefin foam sheet is extruded, it once foams and expands, then shrinks significantly, and then gradually expands over a long period of time to form a foam sheet having a certain density.

The process of expanding into a stable foam after shrinking in volume is called the maturation process. For example, in the case of a foam sheet with a thickness of 1 to 2 mm, it takes about a week to mature if left at room temperature. 3 to 5 even in a room at 60℃
It takes a long time to mature.

In particular, since foamed sheets are stored by being rolled up into a roll, they must be rolled up loosely and must be turned over again after ripening.

Such operations and the fact that a large amount of storage space and time are required for ripening are extremely disadvantageous in industrial production.

The present inventors have discovered that when a polyolefin foam sheet is extruded, adding a higher fatty acid ester of a polyhydric alcohol, such as stearic acid monoglyceride, can suppress the shrinkage and expansion after extrusion, making it possible to omit the aging process. However, it has been found that when a higher fatty acid ester of a polyhydric alcohol is added, the bubbles become larger, the transparency of the resulting foamed sheet increases, and the degree of milky whiteness tends to decrease.

For example, Japanese Patent Publication No. 46-8587 describes a method for producing a polyolefin foam having fine cells.
In order to make the cells of the polyolefin foam extremely fine and homogeneous and to produce a polyolefin foam with excellent elasticity and heat insulation properties and a beautiful appearance, acid salts, carbonates, or bicarbonates of polyhydric carboxylic acids are used. The use of a cell control agent consisting of a ternary mixture of salts and fatty acid monoglycerides has been shown, but in order to obtain polyolefin foams,
If you use the above-mentioned foam control agent that generates carbon dioxide gas, it will decompose due to moisture in the air, stain the tip of the extruder nozzle, and contaminate the surface of the extruded polyolefin foam. The disadvantage is that there are variations in the

The present inventor conducted research to develop a method for manufacturing a beautiful polyolefin foam sheet that does not have these drawbacks, and found that by adding polybutene with an average molecular weight of 300 to 1,500, the bubbles are fine, there is no transparency, and the sheet is milky white. good,
Moreover, the present invention was completed based on the discovery that even if a higher fatty acid ester of a polyhydric alcohol such as stearic acid monoglyceride is used, a polyolefin foam sheet without coarsening of the cells can be obtained. .1-2% by weight, and 0.01 of a gas generating agent that decomposes at temperatures above 130°C to mainly generate nitrogen gas.
-3% by weight of polybutene with an average molecular weight of 300-1500 (0.05-5% by weight) was mixed and fed to the extruder.
Alternatively, the polybutene and higher fatty acid ester of polyhydric alcohol (0.3-5% by weight) are mixed in advance into the mixture, or alternatively, the mixture is press-fitted into the extruder and lower aliphatic hydrocarbon having a boiling point below the melting point of the polyolefin or The gist of this invention is a method for producing a polyolefin foam sheet, which comprises press-mixing a halogenated hydrocarbon into the mixture heated and melted in an extruder and extruding it from the tip of the extruder to obtain a polyolefin foam sheet. .

In the present invention, polyolefin refers to a homopolymer of olefins such as ethylene, propylene, polyisobutylene, butadiene rubber, a copolymer thereof, or a copolymer containing these olefins with other vinyl monomers as a main component. , or a mixture of these polymers.

% non-crosslinked low density polyethylene is preferably used.

In the present invention, the polybutene added to the polyolefin has an average molecular weight of 300-1500.

These polybutenes are liquid, and as their molecular weight increases, their viscosity increases and mixing becomes difficult.

In particular, polybutene having a molecular weight of 420-630 is preferably used.

The polybutene is mixed in an amount of 0.05-5% by weight with respect to the polyolefin.

If the amount is less than 0.05% by weight, the desired effect of making the cells finer will not be sufficiently exhibited, and if it is more than 5% by weight, the effect will not be further enhanced and is therefore unnecessary.

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,
Contains metal oxides such as talc and magnesia.

These inorganic fine powders smooth the rotation of the extruder screw and are useful as nucleating agents in foam production, and are effective in producing foam with fine cells, but if used in large quantities, they may is destroyed, making it easier for gas to escape.

Inorganic fine powder is 0.1-2% by weight based on polyolefin
is used.

Generally, in extrusion molding of foam, impurities and other substances tend to accumulate (build up) at the tip of the mold of the extruder.

This tendency is particularly noticeable when a carbon dioxide gas generating agent is used, and the formation of pill build-up contaminates and scratches the surface of the molded product, further reducing the thickness of the molded product.

Therefore, it is necessary to stop the operation and clean it frequently, and continuous operation is not possible.

By adding inorganic fine powder, this pill-up can be prevented from occurring and continuous operation is possible.

The gas generating agent used in the present invention is an organic compound that mainly generates nitrogen gas when heated to a temperature of 130° C. or higher, and specifically, azodicarboxylic acid amide is suitable.

Other examples include N,N'-dinitrosopentamethylenetetramine and 4,4-oxybisbenzenesulfonylhydrazide.

These gas generating agents, together with the inorganic fine powder, contain fine,
Moreover, it is useful as a nucleating agent for obtaining a molded article having uniform cells, and is 0.01-
3% by weight is added.

In the method of the present invention, a higher fatty acid ester of a polyhydric alcohol can be added in order to prevent shrinkage and expansion of the foamed sheet after extrusion molding and to shorten or omit the aging time.

The polyhydric alcohols of higher fatty acid esters of polyhydric alcohols include, for example, glycerin, pentaerythritol, sorbitol, sorbitan, mannitol, mannitan, dipentaerythritol, diglycerin, and the like.

Examples of higher fatty acids include saturated or fully saturated monovalent higher fatty acids having 10 to 30 carbon atoms, such as cabric acid, lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, and linoleic acid; These include beef fatty acids, cassava 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 are ester bonded 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, sorbitasomono These include oleate, sorbitan sesquiseed oil fatty acid ester, sorbitan monopalmitate, sorbitan monolaurate, sorbitan monostearate, mannitan monooleate, mannitan monolaurate, and the like.

These fatty acid esters of polyhydric alcohols have a ratio of 0.0% to the polyolefin. 5-3% by weight is used.

Higher fatty acid esters of polyhydric alcohols are closely related to the aging time of the molded product. For example, when stearic acid monogceride is used in an amount of 0.1% by weight based on the polyolefin, maximum shrinkage occurs 20 minutes after extrusion molding, and then Even if it gradually expands and is left at room temperature for 4 days, it still continues to expand.

On the other hand, when 2% or 3% of stearic acid monoglyceride is added, the density of the molded product 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 foam sheet can be obtained.

However, if the higher fatty acid ester of polyhydric alcohol is used in excess, the surface of the molded product will become difficult to stick to, and it will be difficult to obtain a beautiful foamed sheet.

Therefore, the amount of higher fatty acid ester of polyhydric alcohol added is 0. 3-5% by weight
is suitable.

Further, the higher fatty acid ester of polyhydric alcohol also has an antistatic effect, and for this purpose, addition of 0.01% by weight is sufficient to achieve this effect.

The polyolefin foam sheet obtained by the method of the present invention has fine closed cells, and compared to a polyolefin foam sheet that does not contain polybutene, transparency is significantly improved and a foam sheet with good opalescence can be obtained. Furthermore, in order to enhance the whiteness, it is also possible to add a small amount of a white pigment such as titanium oxide or zinc oxide.

In addition, suitable pigments may be added to provide other coloring.

The pigment to be added is preferably one that is stable against heating in the extruder, and therefore metal oxides are preferred.

However, it is of course possible to use heat-stable organic pigments.

These pigments are generally added in amounts of 0.1-1% by weight.

If more than 1% by weight is used, it will be difficult to mix uniformly with the resin, and there is a risk that pigment-induced unevenness will occur in the produced foam sheet.

The production of polyolefin foam sheet by the method of the present invention is as follows:
This can be carried out using a conventional extruder and a conventionally known method.

That is, for example, a polyolefin, a polybutene, an inorganic fine powder, a gas generating agent, and if necessary a pigment and a fatty acid ester of a polyhydric alcohol are thoroughly mixed, and this is fed from a hopper of an extruder into a heated extruder, Polyolefin is melted and mixed, a blowing agent made of a lower aliphatic hydrocarbon, a halogenated hydrocarbon, or a mixture thereof is press-fitted into the mixture, and the mixture is extruded into the atmosphere in the form of a sheet through a nozzle heated to 100-150°C. A foamed sheet is obtained.

In addition, when the amount of polybutene and higher fatty acid ester of polyhydric alcohol is relatively large, these substances may be mixed by increasing pressure from the middle of the extruder.

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

Example 1 Non-crosslinked polyethylene (MI value 0.3, density 0.920
, melting point 115°C), 0.2 parts by weight of polybutene (average molecular weight 470), 0.1 parts by weight of stearic acid monoglyceride, 0.5 parts by weight of talc, and 0.05 parts by weight of azodicarboxylic acid amide in a ribbon blender. Mix well and feed into the extruder from the extruder hopper.

From this supply section, the extruder is sequentially heated to about 200° C., and the mixture is melted and mixed and sent to the tip of the extruder by a screw.

About 15 parts by weight of butane is 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° C. at the tip of the extruder to obtain a polyethylene foam sheet.

By the same method as in Example 1 above, with the following formulation:
Polyethylene foam sheets were produced in each case.

The foamed sheet obtained was as shown in Table 1.

From Table 1 above, for example, the following can be clearly understood.

If a large amount of talc is used (Comparative Example 1), a foamed sheet with good opalescence can be obtained, but properties such as appearance and feel are not good.

In particular, in Comparative Example 1, large and small bubbles were mixed, and the bubbles appeared coarse in appearance.

Comparative Examples 2 and 3, in which polyethylene glycol was used without using polybutene, had the disadvantage that the cells were coarse and the foam sheets were highly transparent.

This is remarkable in Comparative Example 3 in which a large amount of stearic acid monoglyceride was used.

In Example 5, although a large amount of stearic acid monoglyceride was used, a good foamed sheet was obtained.

According to the method for manufacturing a polyolefin foam sheet of the present invention, a foam sheet having fine and uniform cells can be obtained by using only a very small amount of inorganic fine powder, gas generating agent, etc., and therefore the foaming ratio can be increased. You can get a good foam sheet.

For example, a polyethylene foam sheet having a foaming capacity of 40 to 60 times can be easily obtained by the method of the present invention.

Furthermore, since pill-up does not occur at the mouth of the extruder, beautiful foam sheets can be continuously produced.

Furthermore, even if a higher fatty acid ester of a polyhydric alcohol such as stearic acid monoglyceride is added, the bubbles do not become coarse, so a high quality foam sheet can be obtained, which has an anti-electro-electrical effect and has almost no shrinkage or expansion after extrusion. Therefore, there is no need to unwind the foam sheet, ripen it, etc.

As mentioned above, the polyolefin foam sheet obtained by the method of the present invention is composed of fine and uniform cells, has a smooth surface, is highly flexible, has a good texture, has a good degree of opalescence, and has a good appearance. Therefore, it can be widely used as various cushioning materials, packaging materials, decorative materials, etc.

Claims (1)

[Claims] 1. Polyolefin is mixed with 0.1-2% by weight of an inorganic fine powder and 0.01-3% by weight of a gas generating agent that decomposes at a temperature of 130°C or higher to mainly generate nitrogen gas. 0.05-5 wt. A method for producing a polyolefin foam sheet, which comprises press-mixing a hydrocarbon or a halogenated hydrocarbon into the mixture heated and melted in an extruder, and extruding the mixture from the tip of the extruder to obtain a polyolefin foam sheet. 2. The method for producing a polyolefin foam sheet according to claim 1, wherein the polyolefin is polyethylene. 3 Mix 0.1-2% by weight of an inorganic fine powder and 0.01-3% by weight of a gas generating agent that decomposes at a temperature of 130°C or higher to mainly generate nitrogen gas with polyolefin and feed the mixture to an extruder. , 0.05-5% by weight of polybutene with an average molecular weight of 300-1500 and 0.3-5% by weight of higher fatty acid ester of polyhydric alcohol are mixed into the mixture in advance, or the mixture is press-fitted into an extruder to form a polyolefin. A polyolefin foam sheet is obtained by press-mixing a higher aliphatic hydrocarbon or a halogenated hydrocarbon having a boiling point below the melting point into the heated and melted mixture in an extruder and extruding it from the tip of the extruder. A method for producing polyolefin foam sheets. 4. The method for producing a polyolefin foam sheet according to claim 3, wherein the polyolefin is polyethylene.