JPH0246061B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to expandable thermoplastic resin particles, and more specifically, the present invention relates to foamable thermoplastic resin particles, and more specifically, to a container etc. obtained by foam molding in a mold cavity, oil-based particles such as instant noodles, fried chicken, etc. The present invention relates to a container that prevents food products, oils and fats such as fat-containing foods, regular coffee, etc. from seeping out through the fused surface of foamed particles on the container wall.

The present invention also relates to an expandable thermoplastic resin particle composition for preventing water from seeping out from drain pans used in household air conditioners, etc., or for preventing ice water from seeping from portable ice boxes. .

Expandable thermoplastic resin particles are produced by, for example, impregnating polystyrene resin particles with an easily volatile aliphatic hydrocarbon such as pentane, which causes the particles to swell slightly, in an aqueous suspension, or It is produced by a method such as impregnating a blowing agent such as butane, which is constantly in the gaseous state, into an aqueous suspension containing a small amount of a solvent such as toluene which has a solubility in the air. The expandable thermoplastic resin particles thus obtained are used as a raw material for producing a foamed thermoplastic resin molded body.

In order to obtain it economically and industrially, expandable thermoplastic resin particles are pre-foamed in advance, and the pre-expanded particles are filled into a mold cavity of a molding machine with small holes etc., and then heated with pressurized steam. By heating above the softening point to fuse and integrate each pre-expanded particle, a molded article conforming to the mold cavity can be obtained.

The expandable thermoplastic resin particles used for this purpose tend to coalesce and form agglomerates during the pre-foaming process. If agglomerated coalescent particles are included, they will clog the transfer pipe or the filling hole of the mold cavity, causing trouble in the molding process. For this purpose, it is known to previously coat the surface of expandable thermoplastic resin particles with metal soap, talc, calcium carbonate, etc.

Zinc stearate is also sometimes used to prevent agglomeration. However, in this case, the amount used hardly exceeds 0.2%, and in the case of other metal salts, calcium salts, and magnesium salts, the effect is achieved with approximately half the amount used for zinc stearate. Most industrially manufactured and commercially available zinc stearate products have a particle size of 10 microns or more.

When the resulting foamed molded product is broken, even if each particle is in a good state of fusion, i.e., the surface of each particle on the fracture surface is completely fused and 100% fused, it is not a surface bond. Fine capillaries open to the outside. For example, when an aqueous dye solution containing a surfactant is introduced, it can be confirmed that the aqueous solution passes through the particle fusion surface and oozes out. Even if a pot obtained by a normal molding method using general expandable polystyrene particles is in a normal fused state, if you add regular coffee liquid containing 0.01% by weight of sodium alkylbenzene sulfonate and leave it for about 10 to 10 minutes. Within minutes, you can see the coffee passing through the gaps between each particle and seeping out onto the outer wall of the cup. These tips usually have no practical problems when used as drinking tips for coffee, etc., but if you store oily foods such as donuts, hamburgers, fried chicken, margarine, etc. that contain salad oil, beef tallow, etc. for a long time, they will gradually turn into oils and fats. oozed out of the container wall, making it unsuitable for use as containers for these foods. Furthermore, if instant noodles mixed with curry powder are stored and stored in a container, the yellow pigment of the curry powder will ooze out onto the outer wall of the container, contaminating the container and significantly reducing the commercial value of the container-attached instant noodles.

Furthermore, drain pans made of foamed thermoplastic resin molded products used in small household air conditioners are used with a paraffin film or the like formed on the surface of the molded product because drain water permeates over a long period of time. In addition, simple ice boxes made of foamed thermoplastic resin that are carried on excursions, etc., have ice water seeping out over a long period of time, reducing their commercial value.

By using a special mold during molding using the foamable styrene polymer, or by heating conditions to high temperatures to form a molten resin film on the surface of the foam molded product, oozing of oils and fats, etc. can be prevented. However, general-purpose expandable styrene polymer particles have poor heat resistance compared to this method, and the foam melts and shrinks, making it difficult to obtain a molded product with a beautiful appearance that can be used as an industrial product. In this case, the molding cycle time is significantly prolonged, resulting in poor productivity, and the chips obtained by such a method have weak flexural strength and brittle physical properties, which have disadvantages that make them difficult to use practically.

If the above-mentioned leakage phenomenon can be prevented, new uses of expandable thermoplastic resin particles for packaging containers and containers for oils, fats, fatty foods, etc. will be expanded, and the present inventors have conducted extensive research on this point. The invention has been completed. That is, in the present invention, a hydrocarbon having a boiling point lower than the softening point of the resin particles is used as a blowing agent in the thermoplastic resin particles in an amount of 1 to 10
% by weight of expandable thermoplastic resin particles, the surface of which is coated with 0.2 to 0.4% by weight of zinc stearate having a particle diameter of 10 microns or less and 90% or more. The main points are as follows.

The expandable thermoplastic resin particles in the present invention are styrene or methylstyrene homopolymers, styrene-maleic anhydride copolymers, or combinations of styrene and acrylic esters or methacrylic esters, such as styrene methyl methacrylate or acrylate. Examples include copolymers.

As the blowing agent, easily volatile hydrocarbons having a boiling point lower than the softening point of the resin particles, such as propane, n-butane, i-butane, n-pentane, neopentane, and dichlorofluoromethane, are used. Expandable resin particles can be obtained by, for example, impregnating the resin particles with these blowing agents in an aqueous suspension by heating them in an autoclave.
The blowing agent is usually impregnated into the resin particles in an amount of 1 to 10% by weight.

In the present invention, the effect of the zinc stearate coated on the surface of the expandable thermoplastic resin particles is better as the particle size becomes smaller, and the average particle size is 3 to 8 microns, and fine particles with at least 90% of the particles being 10 microns or less. obtained from.

This zinc stearate is coated in an amount of 0.2 to 0.4% by weight on the expandable resin particles. The amount covered is
If it is less than 0.2% by weight, it is difficult to obtain the effect of sufficiently preventing the oozing of oils and fats and water, and if it exceeds 0.4% by weight, it is too much and tends to inhibit the fusion of the foam particles during molding, which is not preferable.

The zinc stearate referred to here may be used alone, but from the viewpoint of cost, it is preferable to use industrial zinc stearate, for example, a zinc salt of a mixed fatty acid with 14 to 20 carbon atoms containing 60% or more of stearic acid. It is.

In the present invention, by using nonionic cellulose ether in addition to zinc stearate as a coating agent, the desired effect can be further improved or the amount of zinc stearate used can be reduced. A sizing material that can be used for this purpose is coated on the expandable resin particles in an amount of 0.0005 to 0.01% by weight.

Nonionic cellulose ethers used in the present invention include methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, hydroxyethylcellulose, and the like. The amount of nonionic cellulose ether coated is
If it is less than 0.0005% by weight, it is difficult to obtain the effect of sufficiently stopping the oozing of oils and fats and aqueous solutions, and if it exceeds 0.01% by weight, it is too much.

There are various methods for coating expandable resin particles with zinc stearate and nonionic cellulose ether. For example, after sufficiently mixing the expandable resin particles and the nonionic cellulose ether aqueous solution using a drum blender, zinc stearate can be added and further mixed to adhere the coating agent to the surface of the resin particles.

The foam molded article formed from the expandable thermoplastic resin particles of the present invention is extremely difficult to exude oil and water due to factors such as the melting point of zinc stearate, the size of the powder particles, and the solubility in the polymer and solvent. This is because the repellency properties of fatty acids, particularly due to the orientation of the terminal methyl groups, are exhibited in this usage method.

Among common metal soaps, stearates other than zinc, such as magnesium, calcium, and aluminum, and zinc salts other than stearate, such as laurate and myristate, had significantly inferior results compared to zinc stearate. .

The finer the particle size of zinc stearate, the easier it is to achieve the desired effect, and the amount of zinc stearate used can be small.

It is also believed that nonionic cellulose ether exerts its film-forming ability, adhesion, and caking properties on the surface of foamed particles and the fused surface between foamed particles during pre-foaming or molding, thereby preventing oil and water from seeping out. The desired effect is remarkable compared to other adhesives such as sodium alginate and sodium polyacrylate. In addition, the effect becomes more pronounced when used in combination with zinc stearate.

Food containers such as eating and drinking utensils, and molded products such as food containers molded from the expandable thermoplastic resin particles of the present invention include beef tallow, soybean oil, rapeseed oil, etc.
Direct inclusion of oily and fatty foods such as lard, mayonnaise, curry dressing sauce, butter, margarine, white sauce, yogurt, ice cream, instant ramen, stew, donuts, hamburgers, and fried chicken to the outside of containers etc. It suppresses the exudation of oils or pigments for a long period of time, enabling applications that were previously impossible.

In the same way, it is expected that the man-hours required for constructing the drain pan of the household air conditioner will be reduced, and the value of products such as portable ice boxes and fresh fish boxes will be improved.

The present invention will be explained in detail below with reference to Examples.

Example 1 Expandable polystyrene resin with a diameter of 0.3 to 0.6 mm containing 5.5% by weight of n-pentane as a blowing agent
Add 0.001% by weight of methyl hydroxypropyl cellulose aqueous solution to 1000g and cover the surface.
Next, 3.0 g of zinc stearate having an average particle size of about 5 μm and 90% less than 10 μm was added to coat the surface to obtain resin particles.

This is foamed in a batch-type pre-foaming device in a stream of normal-pressure steam at 95°C in 5 minutes to a bulk of 100 g while stirring with a rotating blade to uniformly heat the entire product. Particles were obtained. Contents after aging and drying pre-expanded grains in the atmosphere for 6 hours
450c.c., filled into a 2mm thick socket, 1.8
After heating with water vapor at Kg/cm ² (gauge pressure) for 7 seconds and cooling with water, a polystyrene resin foam molded product in the form of a polystyrene resin foam was obtained.

Pour the seasoning soup containing curry powder that comes with the instant noodles into the resulting pot for about 8 minutes.
The entire cotup was wrapped tightly in vinylidene chloride resin film and placed in an oven at 60°C, and the yellow pigment of the curry powder was observed to pass between the foam particles on the cotup wall and come out on the outer wall of the cotup. It was confirmed that there was no oozing even after 100 hours had passed, and there was no problem in practical use as a container for instant curry noodles.

Example 2 Expandable polystyrene resin particles used in Example 1
3.3 g of zinc stearate having an average particle diameter of about 3 to 5 μm and 90% of the particle size of 10 μm or less was added to 1000 g to uniformly coat the surface to obtain coated expandable polystyrene resin particles.

This was pre-foamed in the same manner as in Example 1 to obtain a polystyrene foam molded polystyrene resin. Example 1
I added curry powder and tested it in the same way.
After 15 hours, exudation of yellow pigment was observed on the outer surface of the pot wall. However, it was recognized that the results were superior to those of Comparative Example 1.

Example 3 Expandable polystyrene resin particles used in Example 1
Add 0.0005% by weight of methyl cellulose and 2.4g of zinc stearate having an average particle size of about 3 to 5μ and less than 10μ to 1000g and stir in a container to uniformly coat the surface to obtain coated expandable polystyrene resin particles. Ta. When we put salad oil mixed with rapeseed oil and soybean oil into the resulting pot and left it to stand, we observed that it passed through the fused surface of the foam particles on the pot wall and oozed out to the outer surface, but it did not ooze even after 50 hours had passed. There was no offer.

Comparative Example 1 Expandable polystyrene resin used in Examples 1 and 2
1000g of zinc stearate used in Example 1
When a test was carried out on a pot prepared in the same manner as in Example 1 except that 1.5 g was coated on the surface and curry powder was added thereto, yellow pigment was found to ooze out on the outer surface of the pot wall after 2 hours. When the molded product obtained in Comparative Example 1 was broken, each foamed particle was completely torn, and the degree of fusion was 100%, which was the best.

Comparative Example 2 A pot was prepared in exactly the same manner as in Example 1, except that zinc stearate, a general industrial product with an average particle size of 10 to 15 μm and a maximum particle size of 30 to 40 μm, was used, and curry powder was added thereto. When the test was carried out, it was observed that yellow pigment oozed out on the outer surface of the pot wall after 10 hours, and when compared with the results obtained in Example 1, a large difference was observed.

Example 4 Diameter containing 5.5% by weight butane as blowing agent and 1.5% by weight cyclohexane as blowing aid
3.5 g of the same zinc stearate and 0.01% by weight of hydroxyethyl cellulose as in Example 1 were stirred in a container to uniformly coat 1000 g of expandable polystyrene particles of 1.0 to 1.5 mm to obtain coated expandable polystyrene resin particles.

The obtained expandable polystyrene resin particles were subjected to the same method as in Example 1 to obtain pre-expanded particles having a bulk ratio of 40 g/. The pre-expanded particles were left in the air for 6 hours to dry, then filled into a box-shaped mold with a wall thickness of 10 mm.
After heating and cooling for 30 seconds using water vapor at 0.7 Kg/cm ² (gauge pressure), the product was taken out from the mold to obtain a molded expandable polystyrene product.

Add 1 g of sodium alkylbenzenesulfonate to 1 part water, and Eriochrome Black to the box-shaped molded product.
A solution in which T2g was dissolved and dispersed was put in and observed to seep out to the outside, but there was no seepage even after 2 hours had passed, confirming that there was very little water seeping out over a long period of time.

Comparative Example 3 Expandable polystyrene resin particles used in Example 4
1000 g was uniformly coated with 1.5 g of zinc stearate, and a leakage test of the colored liquid was conducted in the same manner as in Example 4. As a result, oozing was observed after 5 minutes.

Comparative Example 4 Expandable polystyrene resin particles used in Example 4
Zinc stearate 5.0 same as Example 1 to 1000g
g and 0.02% by weight of hydroxyethylcellulose were coated on the surface in the same manner, and the resulting coated expandable polystyrene resin particles were molded in the same manner as in Example 4.

When the molded product is broken, in the case of Example 4,
Compared to all (100%) of each foamed particle being torn,
In the case of Comparative Example 4, each expanded particle was only about 70%, and the degree of fusion between the particles was poor.

Further, when a leakage test of the colored liquid was carried out in the same manner as in Example 4, slight seepage was observed after 24 hours.

Claims (1)

[Scope of Claims] 1. Expandable plastic resin particles containing 1 to 10% by weight of a hydrocarbon having a boiling point lower than the softening point of the resin particles as a blowing agent in the thermoplastic resin particles. 1. An expandable thermoplastic resin particle, characterized in that the resin particle is coated with 0.2 to 0.4% by weight of zinc stearate having a particle diameter of 10 microns or less on the surface thereof. 2. The expandable thermoplastic resin particles according to claim 1, wherein the thermoplastic resin is a polystyrene resin. 3. The foamability according to claim 2, wherein the polystyrene resin is a styrene polymer, a methylstyrene polymer, a styrene-maleic anhydride copolymer, or a copolymer of styrene and an acrylic ester or a methacrylic ester. Thermoplastic particles. 4. The expandable thermoplastic resin particles according to claim 1, wherein the zinc stearate is fine particles having an average particle size of about 3 to 8 microns. 5. A hydrocarbon having a boiling point lower than the softening point of the resin particle is used as a blowing agent in the thermoplastic resin particle in an amount of 1 to 10% by weight based on the resin particle. A foamable thermoplastic characterized in that the resin particles are coated with 0.2 to 0.4% by weight of zinc stearate, which is 90% or more in the size of 10 microns or less, and are further coated with 0.0005 to 0.01% by weight of nonionic cellulose ether. resin particles. 6. The expandable thermoplastic resin particles according to claim 5, wherein the thermoplastic resin is a polystyrene resin. 7. The foam according to claim 6, wherein the polystyrene resin is a styrene polymer, a methylstyrene polymer, a styrene-maleic anhydride copolymer, or a copolymer of styrene and an acrylic ester or a methacrylic ester. thermoplastic resin particles. 8. The expandable thermoplastic resin particles according to claim 5, wherein the zinc stearate is fine particles having an average particle size of about 3 to 8 microns.