JPH09124832A - Polyloefin-based resin preliminary foamed particle and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject preliminary foamed particles not causing aggregation and blocking and enabling shortening of molding and cooling time, etc., in an internal die molding by decreasing an inorganic dispersing agent attached to polyolefin-based preliminary foamed particles to a specific amount or below. SOLUTION: The amount of an inorganic dispersing agent attached to the surface of polyolefin-based preliminary foamed particles is regulated to <=300ppm. In order to obtain polyolefin-based preliminary foamed particles satisfying the conditions, the amount of the inorganic dispersing agent attached to the surface of the polyolefin-based preliminary foamed particles is reduced by cleaning with an aqueous solution (e. g. an acidic aqueous solution of chlorous acid, hypochlorous acid, hydrochloric acid, nitric acid, etc.) capable of dissolving the dispersing agent. The preliminary foamed particles are obtained by releasing a water dispersed material comprising polyolefin-based resin particles, an inorganic dispersing agent and a volatile foaming agent at a temperature near the melting point of the resin particles under pressure not lower than steam pressure of the foaming agent and not higher than the pressure in a pressure container.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polyolefin resin pre-expanded particles and a method for producing the same, and more specifically, it is applied to an in-mold foam molding method, which does not cause aggregation or blocking and reduces molding pressure. The present invention also relates to polyolefin resin pre-expanded particles capable of shortening the molding cooling time and a method for producing the same.

[0002]

2. Description of the Related Art Pre-expanded polyolefin resin particles used in an in-mold molding method are most commonly produced by heating resin particles containing a volatile foaming agent or a pyrolytic foaming agent. However, this method has the drawbacks that not only it is difficult to obtain particles having a high expansion ratio, but also the expansion ratio varies greatly and pre-expanded particles tend to shrink.

In addition to the above method, polyolefin resin particles containing a volatile foaming agent are dispersed in water in a pressure vessel, the dispersion is stirred under high temperature and high pressure, and then discharged under low pressure atmosphere. Is known to obtain pre-expanded particles (Japanese Patent Publication No. 56-1344). However, this method is an efficient method in that the foaming agent can be continuously impregnated into the resin particles and the foaming can be performed continuously with the same apparatus. Since the resin particles are easily aggregated in the container and the resin particles are discharged at a high speed under a low pressure atmosphere at a considerably high temperature,
There is a problem that the obtained pre-expanded particles are likely to cause blocking.

As means for preventing such aggregation in the pressure vessel and blocking of the released pre-expanded particles, generally, an inorganic material such as calcium carbonate, basic magnesium carbonate, basic zinc carbonate or basic calcium phosphate is used. The combined use of particles and anionic surfactants is known.
However, even in this method, when the amount of the inorganic dispersant is small, it causes aggregation in the pressure-resistant container and blocking when it is released outside the container, while when it is large, aggregation and blocking are prevented. , The inorganic dispersant remains on the surface of the obtained pre-expanded particles, inhibits fusion between the pre-expanded particles during in-mold foam molding, and lowers the mechanical strength of the obtained molded article. Problem occurs.

As a method for solving this problem, a method of using ultrafine aluminum oxide or titanium oxide having a particle size of 1 to 100 μm as an inorganic dispersant (Japanese Patent Laid-Open No. 19-19 / 1982).
No. 5131) has been proposed, but the fact is that the above problems have not been sufficiently solved.

[0006]

Therefore, in view of the above situation, the present inventors have found that the amount of the inorganic dispersant adhering to the surface of the pre-expanded particles as an agent for improving the fusion property without causing aggregation or blocking is extremely small. As a result of extensive studies aimed at obtaining pre-expanded particles, when the amount of the inorganic dispersant attached to the obtained pre-expanded particles is below a certain amount, the molding cooling time of in-mold molding is shortened and the fusion property is improved. I found that is remarkable.

[0007]

That is, the first aspect of the present invention
In the second aspect of the present invention, the polyolefin resin pre-expanded particles are characterized in that the inorganic dispersant attached to the surface of the polyolefin pre-expanded particles is 300 ppm or less.
Is a polyolefin resin characterized by washing an inorganic dispersant adhering to the surface of polyolefin pre-expanded particles with an aqueous solution capable of dissolving the dispersant to reduce the amount of the adhering inorganic dispersant. A method for producing pre-expanded particles,
Each is a content.

Examples of the raw material resin for the polyolefin pre-expanded particles used in the present invention include low density polyethylene, linear low density polyethylene, medium density polyethylene,
High density polyethylene, ethylene-vinyl acetate copolymer,
Polypropylene, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-
Propylene block copolymer, ethylene-propylene-
Examples thereof include butene terpolymer, and these may be used alone or as a mixture of two or more kinds.

If necessary, for example, one or more raw materials such as a nucleating agent such as talc, an ultraviolet absorber, an antistatic agent, a heat stabilizer, a flame retardant, a colorant, and a filler may be used. It may be blended into the resin. Further, as the resin, a polyolefin resin crosslinked by peroxide or electron beam irradiation may be used, or a non-crosslinked polyolefin resin may be used in combination.

The polyolefin-based pre-expanded particles are obtained by, for example, dispersing the raw material resin particles and a volatile foaming agent in water in a pressure vessel in the presence of an inorganic dispersant or an anionic surfactant to obtain the melting point of the raw material resin particles. From -25 ° C to + 10 ° C,
Preferably, the resin particles are heated to a temperature in the range of −20 ° C. to + 5 ° C. to impregnate the volatile foaming agent into the resin particles, and the temperature and pressure in the container are controlled under a pressure higher than the vapor pressure of the volatile foaming agent. It can be obtained by discharging the mixture of the resin particles and water under a lower pressure atmosphere than in the container while keeping the same, but the method is not limited to this.

Examples of the volatile foaming agent used in the present invention include hydrocarbons or halogenated hydrocarbons having a boiling point of −50 to 120 ° C., such as normal butane and isobutane, and these may be used alone or in combination of two or more kinds. Used. The amount of these volatile foaming agents used is set in consideration of the type of foaming agent, the ratio of the amount of resin in the container to the space volume in the container, and it is possible to obtain pre-expanded particles of various magnifications. . Examples of the inorganic dispersant include calcium carbonate, basic magnesium carbonate, basic zinc carbonate, basic calcium phosphate and the like, and these are used alone or in combination of two or more kinds.

The amount of the inorganic dispersant remaining on the surface of the pre-expanded particles can be reduced by immersing the pre-expanded particles in an aqueous solution in which the inorganic dispersant can be dissolved. The aqueous solution in which the inorganic dispersant can be dissolved is, for example, an acidic aqueous solution containing one or more of chlorous acid, hypochlorous acid, hydrochloric acid, perchloric acid, nitrous acid, nitric acid, sulfuric acid and the like. It is necessary to adjust the pH of the acidic aqueous solution to 3 or less, preferably 1 or less. An aqueous solution having a pH of more than 3 is insufficient to dissolve the inorganic dispersant adhering to the surface of the pre-expanded particles, and an aqueous solution having a pH of 3 or less, preferably a pH of 1 or less, does not contain the inorganic dispersant. It becomes possible to reduce the amount of the inorganic dispersant that dissolves and adheres to the surface to 300 ppm or less, and as a result, the fusion property between the pre-expanded particles can be improved. The pre-expanded particles immersed in the acidic aqueous solution are thoroughly washed with water to remove the acidic aqueous solution and the dissolved inorganic salt. If the acidic aqueous solution remains, corrosion inside the line occurs, and if the inorganic salt remains, it becomes a fusion inhibitor between the pre-expanded particles.

The polyolefin resin pre-expanded particles of the present invention treat the obtained pre-expanded particles to reduce the amount of the inorganic dispersant adhering to the surface thereof. Even in the case of producing pre-expanded particles by releasing in an atmosphere, a sufficient amount of the inorganic dispersant is present in the pressure vessel and at the time of release, so that aggregation in the pressure vessel and blocking at the time of release are sufficient. To be prevented.

[0014]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples. In the following description,% means% by weight and part means part by weight, unless otherwise specified.

Examples 1 to 4 and Comparative Examples 1 to 4 Ethylene-propylene random copolymer (resin density 0.
90 g / cm ³ , melt flow index 8.2 g / 1
0 minutes, ethylene content 3.0%, crystal melting point 154 ° C) 1
0.2 part of powdery talc was blended with 00 part, and the blended product was extruded with a 50 mm single screw extruder to give pellets of about 2 mg / grain. 100 parts of the obtained pellets (50k
g) was placed in a pressure-resistant container of 200 L capacity having a stirrer, and tricalcium phosphate (manufactured by Ohira Chemical Industry Co., Ltd.) 2.0
Parts and normal paraffin sodium sulfonate 0.0
Dispersed in 300 parts of water in the presence of 3 parts. While stirring the dispersion, 12 parts of isobutane was added, and the dispersion was heated to 154 ° C. At this time, gaseous isobutane was added to adjust the internal pressure of the pressure vessel to the pressure shown in Table 1. Next, while maintaining the pressure in the pressure vessel with gaseous isobutane, a dispersion liquid of pellets and water was discharged into the atmosphere through a circular orifice having a diameter of 4 mm attached to the rear end of a discharge valve having an inner diameter of 25 mm. , Pre-expanded particles were obtained. The true magnification of the obtained pre-expanded particles was measured.

The pre-expanded particles thus obtained are shown in Table 1 at respective pH values.
Was immersed in an aqueous hydrochloric acid solution, washed thoroughly with water, and then dried, and the amount of calcium phosphate salt remaining on the surface of the pre-expanded particles was measured. 4 these pre-expanded particles with a molding machine P110 (manufactured by Toyo Metal Co., Ltd.)
It was filled in a mold of 50 mm × 300 mm × 60 mm, and the foamed particles were heated and fused with steam to obtain a foamed molded body. In this case, the molding pressure at which the fusion rate was 60% and the molding cooling time at this molding pressure were measured. Table 1 shows the measurement results.
The true magnification, the amount of calcium phosphate remaining on the surface, the molding pressure and the molding cooling time were determined by the following methods.

(A) True magnification formula; (true magnification) = [resin density before foaming (g / cm ³ )] /
(Density of pre-expanded particles (g / cm ³ )] (B) Surface residual calcium phosphate amount formula: [Weight of residual calcium phosphate surface (g)] =
(Weight of calcium phosphate salt adhering to surface of pre-expanded particles used for measurement (g)] / (weight of pre-expanded particles used for measurement (g)] × 100 × 10000 (ppm). Forming pressure Make a notch with a depth of 2 mm from the surface of the formed body, and break it with this part as a back, without breaking at the interface of the particles, the rate at which the particles themselves break is 60% (water vapor pressure) (D) Molding cooling time The time of the water cooling step was defined as the molding cooling time.

Examples 5 to 8 and Comparative Examples 5 to 8 Linear low density polyethylene (resin density 0.92 g / cm ³ ) as polyolefin resin particles, melt flow index 1.0 g / 10 minutes, crystal melting point 121 ° C. ) And 0.01 parts of talc were used to obtain pellets in the same manner as in Example 1. Next, 100 parts of the obtained pellets were used, 16 parts of isobutane was added, and the heating temperature of the dispersion liquid was set to 114.
Pre-expanded particles were obtained in the same manner as in Example 1 except that the temperature and the internal pressure of the pressure vessel were changed as shown in Table 1. The obtained pre-expanded particles were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0019]

[Table 1]

As is clear from the results shown in Table 1, the residual amount of the inorganic dispersant remaining on the surface of the pre-expanded particles was 30%.
It can be seen that when the content is 0 ppm or less, the molding pressure is lowered and the molding cooling time is shortened.

[0021]

INDUSTRIAL APPLICABILITY The pre-expanded particles of the present invention treat the produced pre-expanded particles to reduce the amount of the inorganic dispersant adhering to the surface of the pre-expanded particles. Since there is a dispersant, for example, agglomeration in the pressure-resistant container or blocking at the time of discharge from the pressure-resistant container does not pose a problem, and further, a large reduction in molding pressure and a reduction in molding cooling time are achieved. This makes it possible to reduce the cost of utilities and the like in the molding process, the productivity is greatly improved, and its usefulness is outstanding.

Claims (3)

[Claims] 1. A polyolefin resin pre-expanded particle, wherein the inorganic dispersant adhering to the surface of the polyolefin pre-expanded particle is 300 ppm or less. 2. An inorganic dispersant adhering to the surface of the polyolefin pre-expanded particles is washed with an aqueous solution capable of dissolving the dispersant to reduce the amount of the adhering inorganic dispersant. Method for producing pre-expanded polyolefin resin particles. 3. The polyolefin-based pre-expanded particles are volatile at a temperature near the melting point of the resin particles, in an aqueous dispersion of polyolefin-based resin particles, an inorganic dispersant and a volatile foaming agent in a pressure resistant container. The polyolefin-based material according to claim 2, which is obtained by releasing the foaming agent into an atmosphere of a pressure lower than that in the pressure vessel while keeping the temperature and pressure in the pressure vessel constant under a pressure higher than the vapor pressure of the foaming agent. Method for producing pre-expanded resin particles.