JPH0665698B2 - Method for manufacturing polyolefin resin foam sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyolefin-based resin foam sheet by extrusion foam molding, and particularly to a method for producing a polyolefin-based resin foam sheet having fine and fine cells.

(B) Conventional technology Conventionally, decomposition type foaming agents during extrusion foaming of polyolefin resins include inorganic foaming agents such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, azide compounds, and sodium borohydride. Etc. and organic foaming agents such as 4-4′oxybisbenzenesulfonyl hydrazide, dinitropentamethylenetetramine, azodicarbonamide, trihydrazinohydrazine, etc. are used. These foaming agents are mixed with a raw material resin and then extruded. A method of supplying to a machine and extruding is known as a method of obtaining a low-foaming polyolefin-based foamed sheet. Among these, inorganic carbon dioxide generators such as sodium bicarbonate and ammonium bicarbonate are relatively inexpensive, but when heated to the foaming temperature in the extruder, decomposition occurs very slowly and the amount of gas generated must be adjusted. However, it has a drawback that it is difficult. Therefore, the use of the above-mentioned organic foaming agent has become mainstream.

In this regard, the inventors of the present invention combine an inorganic carbon dioxide generator with a weak acid as a foaming aid to accelerate the decomposition, and to adjust the timing of such decomposition, either or both of them have a melting point of 40 to 40. We have already made a proposal to coat with a coating agent at 120 ° C (Japanese Patent Publication No. 60-11).
(975 publication). Then, by extrusion-foaming using such a foaming agent, it is possible to efficiently manufacture a low-foaming polyolefin resin foam sheet having good surface smoothness and fine and dense cells, which has been difficult to manufacture in the past.

(C) Problems to be Solved by the Invention This invention was made by further developing the above knowledge.

That is, with the foaming agent used by coating the above-mentioned inorganic carbon dioxide generating agent and acid, a foamed sheet having finer bubbles than in the conventional case can be obtained. It is desirable from the viewpoint of product quality (for example, improvement in appearance and printability).

Therefore, the present invention is intended to provide a method for efficiently producing a low-expansion polyolefin resin foam sheet having a special surface gloss in which cells are finely densified.

(D) Means for Solving the Problems From the above viewpoints, the inventors of the present invention have conducted diligent research and studies, and as a result, by using the coating agent-coated foaming agent with a fine particle size of 60 mesh or less, The present inventors have found the fact that a low-foaming sheet in which cells are extremely finely densified can be efficiently obtained, and arrived at the present invention.

Thus, according to the present invention, in a method for producing a foamed sheet by extrusion-foaming a polyolefin-based resin containing a foaming agent at a temperature of a softening point or higher, a combination of an inorganic carbon dioxide foaming agent and a weak acid is used as a foaming agent, Both or one of them is coated with 5 to 50% by weight of a coating agent having a melting point of 40 to 120 ° C., and is added to the above polyolefin resin in a powder form which is atomized to a particle size of 60 mesh or less. A method for producing a polyolefin-based resin foam sheet is provided.

The polyolefin resin in the present invention refers to a thermoplastic resin obtained by polymerizing or copolymerizing olefins such as ethylene, propylene, butene, isoprene, and pentene, and ethylene-vinyl acetate, ethylene-ethyl acrylate, etc. Besides polymers, ionomers and the like are also included.

Examples of the inorganic carbon dioxide generator in the present invention include carbonates or bicarbonates of alkali metals or alkaline earth metals, as well as ammonium carbonate and ammonium bicarbonate. Of these, sodium bicarbonate is preferably used. Further, these may be a mixture of two or more kinds. All of these are available as powders.

The weak acids used in the present invention include oxalic acid, malonic acid,
Maleic acid, fumaric acid, succinic acid, itaconic acid, citraconic acid, adipic acid, formic acid, acetic acid, probionic acid, butyric acid, stearic acid, oleic acid, caprylic acid, enanthic acid, caproic acid, valeric acid, lactic acid, tartaric acid, citric acid Acids, phthalic acid, benzoic acid, benzene sulfonic acid, toluene sulfonic acid, chloroacetic acid, organic acids such as diglycolic acid, inorganic acids such as boric acid and acidic salts such as potassium acid tartrate, and citric acid is used. preferable. These may be a mixture of two or more. All of these are available as powders.

Examples of the coating agent having a melting point of 40 to 120 ° C. used in the present invention include paraffins, waxes (for example, polyethylene wax), fatty acid esters of polyhydric alcohols including vegetable oil and animal oil (for example, stearic acid of glycerin and ethylene glycol, olein). Acid and montanic acid esters and mixtures thereof) and fatty acid amides (eg hardened tallow amide, stearyl amide, palmityl amide, oleyl amide and linolein amide). In addition to this, it has a melting point of 40 to 120 and does not react with the weak acid and carbon dioxide generator described above.
Those having a temperature of ° C can be used.

In the present invention, as a method for coating the foaming agent with the coating agent, there are various methods. After drying the carbon dioxide generating agent and the weak acid respectively, an appropriate amount of the coating agent is added to both or one of them and heated. It is suitable to use a crushed solid obtained by coating with stirring and cooling. Also, it is usually suitable to coat both of them.

At this time, it is necessary to carry out pulverization to a particle size of at least 60 mesh or less. Here, “60 mesh or less” means a particle size that passes at least a Tyler standard 60 mesh sieve. Usually, it is preferable that the particle size is 80 mesh or less. If a particle size larger than 60 mesh is used, it is not suitable because the improvement of the fineness of bubbles cannot be expected.

At this time, the coating obtained by crushing was transferred to a stirrer,
It is preferable to reheat while stirring to a temperature close to the melting point of the coating agent, or to recoat the coating agent to adjust the coating state of the foaming agent as uniformly as possible.

Further, in the above coating method, the coating agent is 5 to 5 times for each of the carbon dioxide generating agent and the weak acid.
50% by weight, preferably 10 to 20% by weight, is used. If it is less than 5% by weight, the coating amount is insufficient, and if it exceeds 50% by weight, the bubbles are coarsened and the uniformity thereof is lowered, and the cost is not suitable.

The coating agent-coated carbon dioxide generator and / or the coating agent-coated weak acid thus obtained is used by being added to the polyolefin resin raw material. At this time, it is suitable that the addition ratio of the carbon dioxide generator and the weak acid is 3: 1 to 1: 2, and the addition amount to the polyolefin resin is 0.2 to 6.0 wt.
% Is suitable.

By subjecting such a polyolefin resin composition to extrusion foam molding using an ordinary extruder, a low foam polyolefin resin foam sheet can be obtained. At this time, other additives such as a nucleating agent, a filler, a coloring agent, a flame retardant, and an ultraviolet absorber may be appropriately added to the polyolefin resin composition.

In particular, 30 wt% of inorganic fine powder may be mixed as a filler. These include talc, mica, calcium carbonate, kaolin, clay, diatomaceous earth, silica, alumina and the like, with a particle size of 325 mesh pass being preferred. A volatile foaming agent may also be used in combination.

(E) Work The carbon dioxide generator and the weak acid, whose contact with each other has been blocked by the coating of the coating agent, do not readily react at room temperature, but the coating agent melts at the temperature at which the polyolefin resin is extruded. And efficiently generate fine carbon dioxide bubbling. And, these coating agent coating itself, because it is finely dispersed to 60 mesh or less and finely dispersed in the polyolefin-based resin, in synchronism with the action of generating the fine carbon dioxide, extremely fine bubbles (for example, It acts to perform foaming with a surface bubble diameter of 0.2 mm or less).

Therefore, the obtained foamed sheet has a soft surface luster, and can be used as a food container or a packaging container for sheet molding.

Further, the clogging of the screen attached between the extruder screw and the mold inlet is reduced, and the number of times of screen replacement is reduced.

(F) Example Example 1 After sufficiently drying sodium bicarbonate (powder) and citric acid (powder), 20 wt% of hardened tallow amide (melting point 98 ° C.) was added to each, and the melting point of hardened tallow amide or more was exceeded. After heating and stirring, the mixture was thoroughly mixed, and after cooling, it was pulverized with a stone and this was repeated to obtain finely divided coatings of 60 mesh pass each. Transfer these separately to a stirrer, reheat while stirring to near the melting point of the hardened beef tallow amide, and cool.
A coated sodium bicarbonate and coated citric acid with a particle size of 60 mesh or less was obtained.

Polypropylene resin (PP) 100 parts by weight, hardened tallow amide-coated sodium bicarbonate obtained above 0.5 parts by weight (as pure sodium bicarbonate) and hardened tallow amide coated citric acid 0.5 parts by weight (as pure citric acid) In addition, 0.8 part by weight of talc as a nucleating agent was uniformly mixed and supplied to a normal extruder (diameter 90 mmφ), and extrusion molding was performed according to a conventional method at an extrusion rate of 55 kg / hour (using a 200 mmφ circular die). ).

After cutting out the extruded cylindrical foam, a porous polypropylene sheet having a fine bubble and a smooth surface with a foaming ratio of about 1.8 times, an average thickness of 0.82 mm and a width of 400 mm was obtained. When the average bubble diameter on the surface was measured with a microscope, it was 0.21 mm.

Example 2 Polyethylene wax (low molecular weight polyethylene; softening point: about 101 ° C.) was used as a coating agent, the coating amount was 30% by weight, the amount of each foaming agent was 0.7 parts by weight, and ethylenebisamide 0.1 part by weight as a nucleating agent. Extrusion was carried out in the same manner as in Example 1 except that parts were used. The results are shown in Table 1.

Example 3 A stearic acid crude product (melting point: about 60 as a coating agent
Extrusion molding was carried out in the same manner as in Example 1 except that 20% by weight of (.degree. C.) was used, only citric acid was coated, and the amounts of the foaming agent and the nucleating agent were slightly changed. The uncoated sodium bicarbonate was used in the form of fine powder as it was mixed with the polypropylene resin. The results are shown in Table 1.

Example 4 The same as Example 1 except that 20% by weight of montanic acid ethylene glycol ester wax (melting point: about 71 ° C.) was used as a coating agent, the particle size was 80 mesh or less, the amount of the blowing agent was changed, and the nucleating agent was removed. Was extruded by various methods. The results are shown in Table 1.

Example 5 Extrusion was carried out in the same manner as in Example 1 except that 15% by weight of a fatty acid polyhydric alcohol ester (melting point: about 87 ° C.) was used as a coating agent to reduce the amount of a foaming agent. The results are shown in Table 1.

Example 6 Extrusion molding was performed in the same manner as in Example 1 except that a polyethylene resin (PE) was used instead of the polypropylene resin as the base resin. The results are shown in Table 1.

Example 7 Extrusion molding was performed in the same manner as in Example 2 except that 0.8 part by weight of butane was added as a volatile foaming agent during extrusion. The results are shown in Table 1.

Comparative Examples 1 to 4 Table 1 also shows comparative examples under the following conditions.

Comparative Example 1 Sodium bicarbonate and citric acid were directly added and used without coating treatment, and extrusion foaming was performed according to Example 1.

Comparative Example 2 Sodium bicarbonate and citric acid were coated with liquid paraffin, and extrusion foaming was performed according to Example 1.

Comparative Example 3 20% hardened tallow amide was added to sodium bicarbonate and citric acid for coating, and the resulting mixture was crushed to a 30-mesh pass, and extrusion foaming was performed according to Example 4.

(Comparative Example 4) Extrusion foaming was carried out in accordance with Example 1 using a coating having a particle size of 50 mesh and 0.9 parts by weight of butane.

The results are also shown in Table 1.

As described above, according to the production method of the present invention, it is understood that the low-foaming polypropylene and polyethylene sheets having fine and fine cells can be efficiently obtained.

(G) Effect of the Invention According to the production method of the present invention, it is possible to efficiently produce a low-foaming (usually 1.2 to 3 times) polyolefin resin sheet with extremely fine and dense cells, which has been difficult to produce conventionally. The obtained sheet is of high quality having a good surface gloss and further improved surface smoothness, which is also advantageous in terms of printability and the like.

Claims (3)

[Claims] 1. A method for producing a foamed sheet by extrusion-foaming a polyolefin-based resin containing a foaming agent at a temperature equal to or higher than a softening point, wherein an inorganic carbon dioxide generator and a weak acid are used in combination as a foaming agent. A polyolefin characterized in that both or one of them is coated with 5 to 50% by weight of a coating agent having a melting point of 40 to 120 ° C. and is added to the above polyolefin resin in a powder form which is atomized to a particle size of 60 mesh or less. Of manufacturing a resin foam sheet. 2. The method according to claim 1, wherein the inorganic carbon dioxide generator and the weak acid are sodium bicarbonate and citric acid. 3. The production method according to claim 1, wherein the coating agent is any one of waxes, resin acid esters of polyhydric alcohols, and fatty acid amides.