JPH0259171B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing spherical polyolefin resin particles. BACKGROUND OF THE INVENTION Conventionally, foamed molded bodies have been manufactured using materials such as polystyrene and crosslinked low-density polyethylene, for example, by a bead molding method using pre-expanded particles. On the other hand, since polyolefin resins, especially polypropylene resins and linear low-density polyethylene, have excellent mechanical strength, heat resistance, chemical resistance, oil resistance, etc., the applicant has researched the development of foam molded products using polyolefin resins. As a result of our efforts, we succeeded in developing a method for obtaining pre-expanded particles and a method for obtaining foam molded articles using the pre-expanded particles, which we have already proposed. However, polystyrene can be obtained by suspension polymerization and low-density polyethylene can be obtained by cross-linking process to obtain spherical particles, and the pre-expanded particles obtained using these resin particles are spherical, whereas polypropylene resin In the case of linear low-density polyethylene, pre-expanded particles can be obtained using non-crosslinked resin particles, but on the other hand, it is difficult to obtain pre-expanded particles with a uniform shape, and the pre-expanded particles are not suitable for molding. Since it was difficult to fill the mold efficiently, it was difficult to obtain a uniform foam molded product. Therefore, the applicant of this patent dispersed polypropylene resin particles in a dispersion medium using a dispersant made of basic magnesium carbonate, talc, aluminum oxide, or a mixture thereof, and then heated the resin particles to a temperature of 10°C or more above the melting point of the resin particles. It has been found that spherical polypropylene resin particles can be obtained by this method, and has already been proposed. An object of the present invention is to provide a method for producing spherical polyolefin resin particles that is a further improvement over the above-mentioned conventional technique. That is, in the present invention, polyolefin resin particles are dispersed in a dispersion medium together with a dispersant having the ability to prevent fusion between the resin particles in a state containing a volatile plasticizer, and the melting point of the resin particles is -5°C or higher and the melting point is +10°C. ℃
The gist of the present invention is a method for producing spherical polyolefin resin particles, which is characterized by heating to a temperature below. In the present invention, the material of the polyolefin resin particles includes, for example, polypropylene homopolymer,
Examples include polypropylene resins such as ethylene-propylene random copolymers and ethylene-propylene block copolymers, and linear low-density polyethylene (hereinafter referred to as LLDPE) obtained by copolymerization of ethylene and α-olefin. . Furthermore, the polyolefin resin particles can be formed into pellets using an extruder, pulverized using a pulverizer, polymerized granules, etc., and have a weight of 6 mg/piece or less, especially 5 mg/piece. The following are preferred. Examples of volatile plasticizers used in the present invention include aliphatic hydrocarbons such as propane, butane, pentane, hexane, hebutane, etc.
Cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane,
Dichlorodifluoromethane, dichlorotetrafluoromethane, methyl chloride, ethyl chloride,
Preferred are halogenated hydrocarbons such as methylene chloride, low polymerized olefins such as isobutene oligomers, etc., which are easily removed by volatilization after heat treatment and have plasticity at high temperatures.
The amount of volatile plasticizer used is usually 5 to 50 parts by weight per 100 parts by weight of the resin particles. If the amount of volatile plasticizer is less than 5 parts by weight, the plasticizing effect may not be sufficiently exhibited. Furthermore, even if the amount exceeds 50 parts by weight, the plasticizing effect does not improve significantly, so there is no positive effect in using more than this amount. In the present invention, the dispersant having the ability to prevent fusion between resin particles is one that prevents fusion between resin particles when used in an appropriate amount and promotes spheroidization when stirred in a dispersion medium. Examples include insoluble inorganic fine powders such as aluminum oxide fine powder, magnesium oxide, carbon black, and titanium oxide powder, and surfactants. As the above-mentioned surfactant, any of anionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used, and these may be used in combination.
Specific examples of preferred anionic surfactants include calcium stearate, sodium stearate, aluminum stearate, sodium oleate, calcium oleate, calcium palmitate, higher fatty acid salts such as bovine fatty acid metal salts, and sodium alkylbenzenesulfonate. Examples include alkylbenzene sulfonates such as, other alkyl sulfate ester salts, alkylnaphthalene sulfonates, and the like. Further, specific examples of preferable cationic surfactants include alkylamine salts, quaternary ammonium salts, etc., and specific examples of preferable amphoteric surfactants include alkyl betaines. Nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene fatty acid ester may be used in combination with the above-mentioned various surfactants. Particularly preferred dispersants for use in the present invention are mixtures of aluminum oxide and metal soap, and mixtures of aluminum oxide powder and cationic surfactants. The appropriate amount of dispersant to be used varies depending on the type of dispersant, type of polyolefin resin, agglomeration treatment conditions, etc., so it must be confirmed experimentally, but in general, it should be confirmed experimentally for 100 parts by weight of polyolefin resin particles. , in the range of 0.05 to 5 parts by weight. Examples of the dispersion medium in which the resin particles are dispersed include water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but water is usually preferred. The amount of the dispersion medium used is usually 100 parts by weight or more per 100 parts by weight of the resin particles. In the present invention, the resin particles are heated to a temperature that is greater than or equal to the melting point of the resin particles -5°C and less than the melting point +10°C. If the heating temperature is lower than the melting point -5° C., it will be difficult to form spheres, making it impossible to achieve the object of the present invention. Furthermore, if the heating temperature is higher than the melting point +10°C, the ability to prevent fusion between particles will decrease, and energy loss will occur. Further, it is preferable to maintain the heating temperature for a certain period of time or more after reaching the desired temperature. After the spheroidization process is carried out in this way, it is either taken out to a low temperature region together with the dispersion medium, or it is kept at a predetermined temperature.
After cooling to a temperature of 100°C or less, the particles are taken out of the system to obtain spherical particles. In the present invention, the melting point of the resin particles was measured by differential scanning calorimetry (DSC). In this measurement method, the specimen is set at 10℃/10℃ in a nitrogen atmosphere.
Raise the temperature to 200℃ at a rate of 10℃/min, then increase the temperature to 200℃ at a rate of 10℃/min.
The apex of the melting peak when the temperature was lowered to 50°C and then raised again at a rate of 10°C/min was taken as the melting point, and when there were multiple peaks, the average temperature was taken as the melting point. The spherical polyolefin resin particles obtained by the present invention can be effectively used, for example, in the production of pre-expanded particles of the resin. In this method for producing pre-expanded particles, for example, resin particles, a volatile blowing agent, and a dispersion medium are placed in a closed container, the temperature is raised to a predetermined temperature while stirring, and the pressure inside the container is set to be equal to or higher than the vapor pressure of the volatile blowing agent. This is carried out by opening one end of the container while maintaining the pressure below, and simultaneously releasing the resin particles and dispersion medium from inside the container into a low-pressure atmosphere. The pre-expanded particles thus obtained have less variation in particle shape and also less variation in cell diameter (number of cells). In addition, a foamed molded article can be obtained using the pre-expanded particles obtained as described above, and since the shape of the pre-expanded particles is uniform, it can be efficiently filled into a mold for molding, and variations in cell diameter can be avoided. Since the amount is small, a foamed molded article having uniform and excellent physical properties can be obtained. As explained above, according to the production method of the present invention, spherical polyolefin resin particles can be obtained at relatively low temperatures, and when these spherical resin particles are used, for example, in the production of pre-expanded particles, the shape, cell diameter, etc. It has the advantage that it is possible to obtain pre-expanded particles with uniform properties, and furthermore, the foamed molded article obtained using the pre-expanded particles has excellent physical properties. Examples 1 to 7 and Comparative Examples 1 to 4 1000 g of polyolefin resin particles, the volatile plasticizer shown in Table 1, a dispersing agent, and water as a dispersion medium were placed in the autoclave of 5, and while stirring, the temperature was 115 to 175.
After heating to a temperature of .degree. C. and maintaining it for 1 hour, it was cooled to room temperature and taken out of the autoclave. The shape of the obtained resin particles was observed. The melting points of the polyolefin resins used in the present examples and comparative examples are as follows. Polyolefin resin Melting point (°C) Propylene homopolymer 165 Ethylene-propylene random copolymer 145 Ethylene-propylene block copolymer 163 LLDPE resin Melting point (°C) Ethylene-butene 1 copolymer 124 Also, Example 2 and Comparative Example 2 The resin particles obtained in the above are shown in FIGS. 1 and 2, respectively.

【table】

[Table] Example 8 and Comparative Example 5 1000 g of the resin particles obtained in Example 2 or non-heat-treated resin particles were placed in the autoclave of 5.
Add 200 g of dichlorodifluoromethane, 15 g of basic magnesium carbonate, and 3000 g of water, open one end of the container, and reduce the pressure inside the container to 35 Kg/cm ² and the temperature to 145
Pre-foaming was carried out while maintaining the temperature at °C. The shape, cell diameter, and shape variations of the obtained pre-expanded particles were measured, and the amount of resin particles remaining in the autoclave was also measured. The results are shown in Table 2. Further, the obtained pre-expanded particles were filled into a mold for molding, heated and foamed to obtain a foamed molded article. The moldability during molding was investigated. The results are also shown in Table 2. The pre-expanded particles obtained in Example 8 are shown in FIG. 3, and the pre-expanded particles obtained in Comparative Example 5 are shown in FIG. 4.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a perspective view showing resin particles obtained by the present invention, FIG. 2 is a perspective view showing resin particles obtained by a method other than the present invention, and FIG. 3 is a perspective view showing resin particles obtained by the present invention. FIG. 4 is a perspective view showing pre-expanded particles produced using resin particles obtained by a method other than the present invention.

Claims (1)

[Claims] 1 Polyolefin resin particles are dispersed in a dispersion medium together with a dispersant having the ability to prevent fusion between the resin particles in a state containing a volatile plasticizer, and the melting point of the resin particles is -5°C or higher and the melting point is lower than +10°C. A method for producing spherical polyolefin resin particles, the method comprising heating to a certain temperature.