JPH082990B2 - Expandable thermoplastic resin particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to expandable thermoplastic resin particles, and more specifically, expandable thermoplastic resin particles are pre-expanded and the expanded particles are expanded in a mold cavity. The present invention relates to expandable thermoplastic resin particles that can promote mutual fusion of expanded particles during molding and do not impair the ability of the resulting molded article or the like to prevent leakage.

[Conventional technology]

The expandable thermoplastic resin particles are, for example, polystyrene particles, which are impregnated in an aqueous suspension with a slightly swelling amount of a readily volatile aliphatic hydrocarbon such as pentane, or the polystyrene particles are On the other hand, it is manufactured by a method of impregnating a small amount of a solvent having solubility such as toluene and cyclohexane with a foaming agent such as butane. In order to obtain the expandable thermoplastic resin molded body economically and industrially, the expandable thermoplastic resin particles are pre-foamed in advance and filled in the mold cavity of the molding machine in which small holes and the like are punched, and pressurized steam is added. By injecting and heating to above the softening point to fuse and integrate the respective pre-expanded particles, a molded product according to the mold cavity can be obtained. In this case, it is desired that the fusion property at the time of molding is good, the molding time is shortened, and the ability to prevent the obtained cup or the like from remaining is not hindered.

[Problems to be Solved by the Invention]

When the expandable thermoplastic resin particles used for this purpose contain those having good affinity such as pentane, the softening point becomes low, and the particles tend to coalesce and agglomerate during pre-expansion. The agglomerated coalesced particles block the particle transfer pipe or the molding die cavity filling passage, which becomes an obstacle in the molding process. Therefore, it is known to previously coat the expandable thermoplastic resin particles with, for example, metal soap or talc powder so as not to agglomerate during pre-expansion. On the other hand, such a surface coating tends to inhibit fusion between resin particles during molding. Further, a method of adding a substance that promotes fusion between the expanded particles during molding is also known. The foamed molded product thus obtained has a good fusion state of each foamed particle when it is broken, and the surface of each particle does not appear at all and the fusion bonding is 100.
%, The fused surface is not perfect surface adhesion, and fine capillaries open to the outside. For example, when a dye solution containing a surfactant is added, the aqueous solution can be confirmed by passing between particles and seeping out to the outer wall. For example, even if a cup using ordinary expandable ethylene resin particles is in a normal molding state, if regular coffee is put and left for a long time, the coffee permeates the outer wall of the cup through the gap between the foamed particles in about 30 minutes. In addition, when used as a container for instant cup noodles or the like and storing the product for a certain period such as in the summer, the oil and fat of the powdered soup gradually seeps out, so it cannot be used as a container for these foods.

On the other hand, there are also proposals such as JP-A-59-41339 to prevent the exudation of aqueous solutions and fats and oils through the fusion surface,
These compositions and the like tend to hinder the mutual fusion of the foamed particles during molding, which requires extension of the molding heating time, resulting in reduced productivity. In addition, for example, when a triglyceride of a saturated higher fatty acid (Japanese Patent Publication No. 60-23783), a higher fatty acid (Japanese Patent Publication No. 58-49569), and a hardened oil (Japanese Patent Publication No. 59-28339) are used together to promote fusion. Although the fusion between the expanded particles during molding is improved, the results show that the ability to prevent the exudation of aqueous solutions such as cups and oils and fats is significantly impaired.

Therefore, if the expandable thermoplastic resin particles can be prevented from exuding and the productivity is not deteriorated, the application can be expanded and the productivity can be improved.

It is an object of the present invention to solve the above-mentioned problems and to provide highly productive expandable thermoplastic resin particles that do not exude.

[Means for solving the problem]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, have found that the expandable thermoplastic particles surface-treated with polyethylene wax are effective, and have completed the present invention. It was

That is, the present invention, in the expandable thermoplastic resin particles containing a hydrocarbon having a boiling point lower than the softening point in the thermoplastic resin particles, a crystalline ethylene polymer, molecular weight 400 ~ 900, melting point 85 ℃ ~ 110. The gist of the expandable thermoplastic resin particles is that the thermoplastic resin particles are coated with 0.005 to 0.05% by weight of polyethylene wax having a temperature of ° C.

[Action]

 The configuration and operation of the present invention will be described.

Examples of the thermoplastic resin particles to be used in the present invention include styrene or methylstyrene homopolymers and copolymers. Examples of the foaming agent include volatile hydrocarbons having a boiling point lower than the softening point of the resin particles such as propane, n-butane, i-butane, n-pentane, i-pentane and dichlorofluoromethane. The blowing agent is impregnated in an autoclave with a dispersion using an aqueous suspension in an amount of 1-10% by weight.

The polyethylene wax used in the present invention is particularly a linear crystalline ethylene homopolymer having a molecular weight of 400 to 9
It is in the range of 00 and its melting point is 85-110 ° C.
This is used in a finely divided form. For example, a crystalline polyethylene wax having a molecular weight of 500 and a melting point of 88 ° C. and a molecular weight of 700 and a melting point of 99 ° C. has the most excellent effect. Even with similar polyethylene wax, the molecular weight is 2000 and the melting point is
Those of 126 ° C show almost no effect of the present invention. This is due to the molding temperature of the expandable styrenic resin particles, and the maximum temperature of the molded product is usually 105 to 120 ° C, and the polyethylene wax melts or becomes close to it at the time of molding. It is considered that it is an essential requirement to affect

In addition, even if Fischer-Tropsch wax (fine particles) and petroleum wax microcrystalline wax (fine powder) in the same melting point range are used, the effect of accelerating fusion between the foamed particles at the time of molding, which is the effect of the present invention, can be obtained. Absent.

In using them, they may be used alone or in combination within the above range. These polyethylene waxes are 5-30
It is used as a micron fine powder, and there are various methods for uniformly adhering and coating the surfaces of resin particles. For example, a drum blender may be used for rotational mixing with the expandable thermoplastic resin particles. The specified polyethylene wax adhered to the surface of the expandable thermoplastic resin particles is partially melted in saturated steam at around 100 ° C during pre-expansion and is rotated and stirred in the foaming tank to make it more uniform. Is molded into a cup, etc.

In this case, a higher fatty acid metal salt such as zinc stearate may be used in combination. Zinc stearate has the effect of adhering each particle during pre-expansion, preventing agglomeration, releasing from the molding die, improving slippage of the molded product, regular coffee in cups, instant noodle soup The effect of preventing exudation of the like is enhanced.

As higher fatty acid metal salt, stearic acid, lauric acid,
Zinc, magnesium, calcium, aluminum salts of higher fatty acids such as myristic acid, and the like.
Zinc stearate is often used.

The polyethylene wax specified in the present invention is preferably used in an amount of 0.005 to 0.05% by weight, more preferably 0.005 to 0.02% by weight, based on the expandable thermoplastic resin particles. If the amount used is less than 0.005% by weight, it is difficult to obtain the effect of sufficiently promoting fusion at the time of molding, and if it exceeds 0.02% by weight, the effect is insufficient, and the ability to prevent residue such as cups tends to be impaired. Therefore, it has a feature that the amount used may be extremely small. When a higher fatty acid metal salt is used in combination, the amount used is 0.05 to 0.25% by weight, preferably 0.15 to 0.2.
% By weight. The feature of the present invention is that the foam formed from the expandable thermoplastic resin particles, for example, regular coffee in a cup, an aqueous solution of soup of instant noodles, etc. It is to promote fusion and contribute to improvement of molding productivity.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1. 1000 g of expandable polystyrene resin particles having a diameter of 0.3 to 0.6 mm containing 5.5% by weight of n-pentane as a foaming agent and polywax 655 fine powder product as polyethylene wax (composition: ethylene homopolymer having a molecular weight of 700, melting point 99 ° C.) 0.1 g (Peterlite Co., Ltd.) and 2.0 g zinc stearate were added, and the mixture was stirred in a container so as to cover the surface of the resin particles, to obtain coated expandable polyethylene resin particles.

The whole was uniformly heated in normal pressure saturated steam at 90 ° C. in a rotary stirring type pre-expansion device, and foamed in 5 minutes so that the bulk volume became 100 g /, to obtain pre-expanded particles.

After the pre-expanded particles were aged and dried in the air for 6 hours, they were filled in a cup-shaped molding die with an internal volume of 500cc and a wall thickness of 2mm to obtain 2.0kg /
After heating with cm ² steam for 4.0 seconds and cooling, a polystyrene resin foam-molded body molded from the molding die hole was obtained.
Powder soup used for instant noodles in the obtained cup
Add 10 g and 5 g of water, stir and mix, and coat the slurry soup on the entire inner wall of the cup, then wrap the entire cup in a vinylidene chloride film so that it is sealed, and leave it in an oven at 60 ° C to remove the brown pigment from the soup. It was observed that they passed between the foamed particles of the cup wall and exuded to the outer surface of the cup.

As a result, it was confirmed that there was no bleeding even after 24 hours, and that it can be put to practical use as an instant noodle container.

Example 2 The same as in Example 1 except that the polywax 655 fine powder product was changed to polywax 500 fine powder product (composition: ethylene homopolymer having a molecular weight of 500, melting point 88 ° C. manufactured by Peterlite Co., Ltd.).
The cup was molded with a heating time of 2 seconds. The same exudation preventing effect was as good as in Example 1.

Comparative Example 1 Example 1 except that polyethylene wax was not used
When molded in the same manner as above, fusion between the foamed particles of the molded cup was poor, the cup was fragile, and exudation of instant noodle soup was observed in 5 hours, which was not practical Met. The heating time was required to be 6.0 seconds in order to improve the fusion during the molding, which was a content that significantly reduced the productivity.

Comparative Example 2 Instead of polyethylene wax, Sazol wax spray 30 (composition: Fischer, synthetic petroleum paraffin wax from coal by Tropsch method, freezing point 97-98 ° C)
A cup was molded in the same manner as in Example 1 except that fine powder having a particle size of 10 microns or less, manufactured by Sersol Chemical Co., Ltd. was used. The obtained cup had poor fusion between the foamed particles, and the cup was fragile and could not be put to practical use.

Comparative Example 3 Instead of polyethylene wax, microcrystalline wax Hi-Mic-3090 (composition: petroleum wax having a molecular weight of 700 to 800 and a large amount of low crystallinity isoparaffin and microparaffin, melting point 90 ° C, manufactured by Nippon Seiro Co., Ltd.) A cup was molded in the same manner as in Example 1 except that was used. However, in the obtained cup, fusion between the foamed particles was poor, and the cup was fragile and could not be put to practical use.

Example 3 1000 g of expandable polyethylene resin particles used in Example 1
Polywax 655 fine powder 0.1g and zinc stearate 2.0
g, an ethanol solution 0.5 of a fluorine-containing random copolymer as a fat / oil exudation inhibitor in a cup was added, and the mixture was stirred in a container so as to coat the surface of the resin particles, to obtain a foamed polystyrene resin particle-treated product.

Cup forming was carried out in the same manner as in Example 1, and a cup of normal quality was obtained with a heating time of 4.5 seconds. Put instant noodles and seasoning oyster containing curry powder in the obtained cup, wrap the entire cup so that it is sealed with a vinylidene chloride film and leave it in an oven at 60 ° C. The yellow pigment (oil and fat) of the curry powder is cup. It was observed that the noodles exuded to the outer wall, but they did not exude even after 100 hours, and it was confirmed that there was no practical problem as an instant noodle container.

Comparative Example 4 Example 3 except that no polyethylene wax was used.
When molding was carried out in the same manner as above, heating time was required to be 6.5 seconds in order to obtain a good cup, and a decrease in productivity of cup molding was observed.

Comparative Example 5 0.3 g of a higher fatty acid (containing 70% of ricinoleic acid) which has a fusion promoting effect at the time of molding instead of polyethylene wax
A cup was molded in the same manner as in Example 3 except that
The exudation preventing ability of the instant noodle oyster (oil and fat) was evaluated. Fusion during molding was performed normally, but bleeding was 3
It was observed in about 4 hours, and the inhibition of exudation preventing ability was largely observed, and it was difficult to put to practical use.

Example 4 5.5% by weight butane as a foaming agent and 1.5 as a foaming aid
Polywax 655 fine powder 0.3 and zinc stearate 2.0 g were added to 1000 g of expandable polyethylene particles in which polystyrene particles having a diameter of 1.0 to 1.5 mm were impregnated with cyclohexane at a weight percentage of 1.0 to 1.5 mm, and the mixture was stirred and surface-treated in a container.

Then, in the same manner as in Example 1, pre-expanded particles were obtained by foaming so that the bulk volume became 25 g /. Leave the pre-expanded particles in the air for 6 hours, fill them in a mold that can give a box-shaped molded product with a wall thickness of 20 mm, heat-mold for 25 seconds with 0.7 kg / cm ² steam, and after cooling, take out the molded product. Obtained. A solution in which 0.1 g of sodium alkylbenzene sulfonate and 0.1 g of eriochrome black T was dissolved and dispersed in water 1 was put into the box-shaped molded product, and seepage to the outer surface was observed. As a result, there was no bleeding even after 1 hour, and it was confirmed that this molded product formed an ice box and little bleeding of the aqueous solution.

Comparative Example 6 When the molding was carried out in the same manner as in Example 4 except that the polyethylene wax was removed, the heating time required for fusion bonding was 32 seconds, and a decrease in molding productivity was observed.

〔The invention's effect〕

Since the present invention is configured as described above,
In particular, it is possible to promote fusion between the expanded particles during molding without impairing the ability of the cup to prevent the aqueous solution, oil and fat, etc. from seeping out, which is extremely useful industrially.

Claims (2)

[Claims] 1. A foamable thermoplastic resin particle containing a thermoplastic resin particle having a hydrocarbon having a boiling point lower than the softening point of the resin particle, which is a crystalline ethylene homopolymer and has a molecular weight of 400 to 900, Polyethylene wax with a melting point of 85 ℃ ~ 110 ℃ is thermoplastic resin particles 0.005 ~ 0.05
Expandable thermoplastic resin particles, characterized in that they are coated by weight%. 2. The expandable thermoplastic resin particles according to claim 1, wherein the polyethylene wax is coated with 0.05 to 0.25% by weight of a higher fatty acid metal salt.