JPH0674342B2 - Method for producing colored polyolefin resin pre-expanded particles and method for producing expanded molded article - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing colored polyolefin resin pre-expanded particles and a method for producing a foamed molded product using the particles.

[Conventional technology]

The bead method polyolefin-based resin foam molding has cushioning properties,
Since it has excellent heat insulation and chemical resistance and is lightweight,
Widely used for heat insulating materials, containers, containers, etc. These products are used in the natural color (milky white) of the polyolefin resin foam molded product, but recently, to prevent stains on the molded product, to enhance the sense of quality of the content product, and to distinguish it, colored products There is a growing demand for adoption.

Usually, the following method is used to obtain a colored bead method polyolefin resin molded product.

(1) A method of applying or spraying a paint or the like on a bead method polyolefin resin molded body of a natural color that is usually practiced, (2) When manufacturing pellets of a polyolefin resin as a raw material, dyes or pigments are previously added. After kneading, and using this to produce pre-expanded particles, a usual method of in-mold molding, (3) expandable polystyrene resin mixed with a dye or pigment in a solvent compatible with the resin, and liquid Or a method of mixing a paste toner.

However, the method (1) is not practical for practical use because the adhesive strength of the coating material to the polyolefin resin is weak, the drying step is required after coating, and the coating cost is high. I have a problem. In addition, the method (2) has a problem of mixing colored pre-expanded particles in the pre-expansion step to the storage tank line, which requires time and effort for switching and cleaning, and cannot be put to practical use in terms of productivity and cost unless the lot size reaches a certain level. Have difficulty. Further, in the method of (3), even if such a method is applied to a polyolefin resin, at the time of prefoaming,
There is a problem that the dye or pigment adhering to the surface migrates to the foaming agent, the aqueous solution, or the steam, and the desired concentration of color cannot be obtained.

[Problems to be solved by the invention]

In the method for producing the pre-expanded particles of the polyolefin resin, a major difference from the pre-expanded particles of the polystyrene resin is the gas permeability (foaming agent retention) of the base resin. That is, polystyrene resin has low gas permeability,
An expandable polystyrene resin containing a foaming agent is put in a container such as a drum and transported, and immediately after being stored in a molding factory, or in the case of a long time, stored for 2 months to 3 months, and then pre-foamed and molded.

On the other hand, the polyolefin resin has a large gas permeability, and the expandable polyolefin resin containing the foaming agent needs to be prefoamed immediately after being impregnated with the foaming agent.
In most cases, pre-foaming is done by the raw material manufacturer, not at the molding factory. Further, the foaming agent in the polyolefin resin pre-expanded particles obtained in this way is also completely dispersed in 1 to 2 days. Therefore, in order to produce colored pre-expanded particles, a method of stirring and mixing dyes and pigments with pre-expanded particles can be considered in practice, but polyolefin resins have poor adhesion with dyes and pigments and The foamed particles are light, and furthermore, it is difficult to uniformly stir and mix due to static electricity generated by stirring and mixing, and therefore it is difficult to uniformly color. In addition, because the adhesion of dyes and pigments to the colored pre-expanded particles is weak, the dye or pigment easily peels off from the pre-expanded particles that appear to be colored at first glance, and the coloring device, transportation piping, storage tank, etc. It is contaminated and very difficult to clean.

As a result of intensive studies to eliminate the above-mentioned drawbacks, the present inventors have been able to easily and economically produce colored polyolefin resin pre-expanded particles and foamed molded products thereof in which these drawbacks have been improved. We have found a suitable method for the production of particles and shaped bodies.

[Means for solving problems]

That is, the first aspect of the present invention is to mix and color a dye or a pigment or a mixture thereof dissolved or dispersed in an organic solvent that dissolves or swells a polyolefin resin, and a polyolefin resin pre-expanded particle. A method for producing colored polyolefin resin pre-expanded particles, which is characterized by the second aspect of the present invention, in which a dye or a pigment or a mixture thereof is dissolved or dispersed in an organic solvent that dissolves or swells a polyolefin resin, and A method for producing a colored polyolefin resin foam molded article, which comprises filling colored polyolefin resin pre-expanded particles obtained by mixing and coloring with a polyolefin resin pre-expanded particles in a mold and heat-sealing them. Is the content of each.

Examples of the polyolefin resin used in the present invention include polypropylene, random or block copolymers of propylene and ethylene, terpolymers of propylene, ethylene and butene, low density polyethylene, linear low density polyethylene, medium density polyethylene. Examples include, but are not limited to, high density polyethylene, ethylene-vinyl acetate copolymer, copolymer of ethylene and acrylic acid or a metal salt of acrylic acid, polybutene-1, poly-4-methylpentene-1 and the like. Not something. These resins may be used alone or in combination of two or more. Further, a mixture of the above resin and an inorganic or organic filler may be used.

Among the polyolefin resins, crosslinked or non-crosslinked propylene-ethylene copolymer and polyethylene resin are particularly preferable.

The method for producing the pre-expanded polyolefin resin particles used in the present invention is not particularly limited, and any method obtained may be used.

For example, a volatile foaming agent, a polyolefin resin particle and a dispersant are dispersed and suspended together with water in a pressure tight container, and then heated to a predetermined temperature and pressure, and then the polyolefin resin particle and water are placed in a low pressure range. Pre-expanded particles obtained by releasing into, a volatile foaming agent or a polyolefin-based resin particles impregnated with an inorganic gas is placed in a pressure resistant container, pre-expanded particles obtained by heating with steam or the like in the container, After heating and kneading the polyolefin resin and the foaming agent with an extruder or the like and then cooling, after extruding as an extruded foam strand from a porous die provided at the tip of the extruder,
Examples include pre-expanded particles obtained by cutting the expanded strand into a suitable length with a cutter or the like.
Pre-expanded particles having substantially closed cells can be used even if they are obtained by any method.

The density of the polyolefin resin pre-expanded particles is not particularly limited, but for example, a density of about 0.01 to 0.3 g / cm ³ and an average cell diameter of about 100 to 1000 μm is used.

The dyes and pigments used in the present invention are not particularly limited, and examples thereof include azo dyes, aminoazo dyes, diazo dyes, anthraquinone dyes, aminoanthraquinone dyes, nigrosine dyes, and cyanine blue and pigments such as carbon black. To be

As the organic solvent used in the present invention, those having a property of dissolving or swelling a polyolefin resin are used, and for example, acetone is used for a polypropylene resin,
Chloroform, ethyl acetate, n-heptane, toluene,
p-xylene, ethyl ether and the like, and for polyethylene resins, acetone, ethyl alcohol, ether, methyl acetate, cyclohexane, petroleum ether, benzene, methyl ethyl ketone, toluene and the like can be mentioned, and these can be used alone or in combination of two or more. Used.

Examples of the coloring method include a method of dissolving or dispersing a dye, a pigment, or a mixture thereof in an organic solvent, and stirring and mixing the dye and the pre-expanded particles in a mixing device. Any mixing device may be used, such as a ribbon blender, a Henschel type mixer, or a super mixer, and may be appropriately selected depending on the mixing ability and the desired degree of coloring.

As described above, the polyolefin-based pre-expanded particles are light in weight and static electricity generated by stirring in the mixing device may take a long time to uniformly mix, or the uniform mixing may be difficult. . In such a case, it is desirable that the pre-expanded particles be subjected to antistatic treatment prior to the mixing treatment with the dye or the like. The antistatic agent is not particularly limited, and known ones such as anionic surfactants, cationic surfactants and nonionic surfactants may be used alone or in combination of two or more.

The colored pre-expanded particles obtained as described above are filled in a usual in-mold foam molding method, that is, filled in a mold, heat-fused and cooled, and taken out from the mold as a molded body.

In the present invention, even when the adhesive strength of the colored pre-expanded particles to the particles such as the dye is slightly insufficient, the adhesive strength is improved by heating during molding.

〔Example〕

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

Examples 1 to 16 and Comparative Examples 1 to 3 (a) Production of raw material pre-expanded particles A and B of ethylene-properene random copolymer-("Noblene" manufactured by Sumitomo Chemical Co., Ltd., ethylene content 3.3% by weight) Pellets (one particle weight about 1.8 mg, DSC melting point T _M 143.
5 ° C) 100 parts (parts by weight, the same applies hereinafter), 20 to 35 parts of dichlorodifluoromethane, 1.5 parts of powdered basic tribasic calcium phosphate as dispersant and 0.006 parts of n-paraffin sodium sulfonate together with 300 parts of water in a pressure resistant container. Preparation, 145
Heated to ° C. The pressure in the container at this time is about 17 to 30 kg / c.
m was ² -G. Then, while keeping the pressure inside the container at 17 to 30 kg / cm ² -G while injecting dichlorodifluoromethane, open the valve at the bottom of the pressure resistant container to open the water dispersion with a pore size of 4 m.
Pre-expanded particles were discharged under atmospheric pressure through an mφ orifice plate to obtain pre-expanded particles having an expansion ratio of 18 times (raw material pre-expanded particles A) and 53 times (raw material pre-expanded particles B).

(B) Production of pre-expanded particles C of raw material Cross-linked low-density polyethylene resin particles (average particle diameter 2.2 mm) containing 25 parts of dichlorodifluoromethane per 100 parts of polyethylene resin were preheated by steam heating in a pressure vessel. .

After leaving the pre-expanded particles at room temperature for 24 hours to remove water, and after holding for 150 minutes under atmospheric pressure at a temperature of 60 ° C,
Pre-expanded particles having an expansion ratio of 35 when the particles were taken out at room temperature were obtained.

(C) Production of Colored Pre-Expanded Particles The above pre-expanded particles A, B and C were each put into a 100-liter super mixer by 80 liters, and mixed and colored according to the formulation shown in Table 1.

That is, the pre-expanded particles and the antistatic agent dissolved in ethanol were placed in a supermixer and stirred for 2 minutes, then the dye and pigment mixed in the solvent were added and the mixture was stirred for 5 minutes to obtain colored pre-expanded particles. It was Table 1 shows the results of visual evaluation of color unevenness and color tint of the obtained pre-expanded particles.

(D) Production of colored expanded molded article The colored pre-expanded particles obtained as described above are put into a pressure resistant container, compressed by air pressure to 60 to 80% of the original volume, and then 250 × 270 × It was filled in a 50 mm block mold, heated and fused with steam, and then cooled, and the foamed molded product was taken out from the mold. After this molded product was dried at 60 ° C. for 24 hours, color unevenness and color tint of the molded product were evaluated, and the results are shown in Table 1.

In addition, the evaluation of the color unevenness and the color tint was performed based on the following evaluation criteria.

(1) Evaluation of colored pre-expanded particles Color unevenness: The difference in lightness and darkness between particles was visually judged; ◯: The difference in lightness and darkness was hardly noticed ×: The difference in lightness and darkness was obvious Color tint: Particles of white paper When sandwiched between them and crushed with a finger, it was visually judged whether or not the color was transferred to white paper; ◯: It was almost unknown whether or not the color was transferred ×: Color transfer was apparent (2) Colored molding Evaluation of body Color unevenness: The surface of the molded product was separated by about 1 m and visually inspected from an angle of 45 degrees to visually judge the difference in shade. ○: Substantially no difference in shade and a uniform color was seen. △: A slight shade difference was observed. Poor: A difference in light and shade is clearly recognized around the steam pores Color: Rubbing the surface of the molded product strongly with white paper 10 times, and visually observing the presence or absence of color migration to white paper; ◯: Whether or not migration has occurred It is almost unknown. △: White paper is stained darkly. ×: Color transition is obvious. As is clear from Table 1, according to the present invention, colored pre-expanded particles and molded articles can be produced by a simple method, and by treating with a proper amount of antistatic agent in advance, color unevenness can be more easily and efficiently obtained. A colored pre-expanded particle having a small amount of water is obtained. If a solvent having a high solubility and swelling property in polyolefin is used, pre-expanded particles and molded products having less color can be obtained.

[Action / effect]

As described above, according to the present invention, the colored pre-expanded particles and the molded product can be easily obtained with a simple apparatus, and therefore, it is extremely convenient to obtain the pre-expanded particles and the molded product of a small amount and multi-colored variety.

Claims (3)

[Claims] 1. Coloring, characterized in that a dye or pigment or a mixture thereof is dissolved or dispersed in an organic solvent that dissolves or swells a polyolefin resin, and the polyolefin resin pre-expanded particles are mixed and colored. Method for producing pre-expanded polyolefin resin particles. 2. The pre-expanded polyolefin resin particles are subjected to antistatic treatment, and then mixed and colored with a dye or pigment or a mixture thereof dissolved or dispersed in an organic solvent which dissolves or swells the polyolefin resin. 1. The manufacturing method according to 1. 3. A colored polyolefin obtained by mixing and coloring a dye or a pigment or a mixture thereof, which is dissolved or dispersed in an organic solvent for dissolving or swelling a polyolefin resin, and pre-expanded polyolefin resin particles. A method for producing a colored polyolefin resin foam-molded article, which comprises filling pre-expanded particles of a resin-based resin in a mold and heating and fusing the same.