JPH0316967B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing spherical polypropylene resin particles. BACKGROUND ART Foam molded bodies have conventionally been manufactured using polystyrene or crosslinked polyethylene as a material, for example, by a bead molding method using pre-expanded particles. On the other hand, since polypropylene resin has excellent mechanical strength, heat resistance, chemical resistance, oil resistance, etc., the applicant has conducted research on the development of foam molded products using polypropylene resin, and has developed a method for obtaining pre-expanded particles. We have successfully developed a method to obtain a foamed molded product using the pre-expanded particles, and have already proposed it. However, spherical resin particles can be obtained for polystyrene by a suspension polymerization method and for polyethylene by a crosslinking process, and the pre-expanded particles obtained using these resin particles are spherical, whereas in the case of polypropylene resins. Although pre-expanded particles can be obtained using non-crosslinked resin particles, it is difficult to obtain uniform spherical pre-expanded particles, and the pre-expanded particles cannot be efficiently filled into a mold. However, there is still room for improvement in that it is difficult to obtain a uniform foamed molded product. The purpose of the present invention is to provide a method for producing spherical polypropylene resin particles that eliminates the drawbacks of the prior art, and as a result of intensive research to achieve the above object, the present inventors have The particles are dispersed in a dispersion medium using aluminum hydroxide as a dispersant, and the melting end temperature of the resin particles is adjusted while stirring.
The present inventors have discovered that spherical polypropylene resin particles can be obtained by heating to a temperature higher than Tm, and have completed the present invention. That is, in the present invention, polypropylene resin particles are dispersed in a dispersion medium using 0.5 parts by weight or more of aluminum hydroxide as a dispersant based on 100 parts by weight of the resin particles, and the melting end temperature Tm of the resin particles is adjusted while stirring.
The gist of the present invention is a method for producing spherical polypropylene resin particles, which is characterized by heating to a temperature above. In the present invention, examples of the material of the polypropylene resin particles include propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, etc., and these can be used alone or in combination. However, ethylene-propylene random copolymer is particularly preferred. In addition, the polypropylene resin particles can be pelletized by an extruder or pulverized by a pulverizer, and may have any shape, but the weight of the resin particles is 6 mg/piece or less. is preferable, and particularly preferably 5 mg/piece or less. The aluminum hydroxide used as a dispersant in the present invention usually has a particle size of 1 μm or less, preferably 0.5 μm or less. The aluminum hydroxide above is polypropylene resin particles.
It is used in an amount of 0.5 parts by weight or more, preferably 1 to 3 parts by weight, per 100 parts by weight. If the amount of aluminum hydroxide added is less than 0.5 part by weight, sphericalization of the resin particles, which is the object of the present invention, cannot be expected. Further, even if a dispersant other than those mentioned above, such as basic zinc carbonate, calcium phosphate, calcium carbonate, etc., is used, no effect of spheroidization can be expected. However, these dispersants may also be added to the extent that they do not impede the effects of the present invention.
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 and stirred to a temperature equal to or higher than the melting end temperature Tm of the resin particles, preferably at a temperature from higher than the melting end temperature Tm+5°C to lower than the melting end temperature Tm+40°C. If the heating temperature is lower than the melting end temperature, it is difficult to make the resin particles spherical, and the object of the present invention cannot be achieved. Further, it is preferable to maintain the heating temperature for 15 minutes or more after reaching the desired temperature. Further, it is preferable that the rotational speed of stirring is 230 rpm or more. In the present invention, the melting end temperature Tm of the resin particles
The measurements were carried out by differential scanning calorimetry (DSC). In this measurement method, it refers to the end temperature of the endothermic curve obtained when the sample is set and then heated at a rate of 10°C/min in a nitrogen atmosphere. The spherical polypropylene resin particles obtained by the present invention can be effectively used, for example, in the production of pre-expanded particles of the resin. The method for producing pre-expanded particles includes, for example, placing resin particles, a volatile blowing agent, and a dispersion medium in a closed container, raising the temperature to a predetermined temperature while stirring, and raising the pressure inside the container to a level higher than the vapor pressure of the volatile blowing agent. Alternatively, it may be carried out by opening one end of the container while maintaining the pressure below, and simultaneously releasing the resin particles and dispersion medium from the inside of 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). Furthermore, when producing pre-expanded particles, a dispersant is usually used and the dispersant adhering to the pre-expanded particles is washed and removed, but if the resin particles obtained by the present invention are used, the pre-expanded particles It is not necessary to wash the resin particles, and the amount of resin particles remaining in the closed container during the production of pre-expanded particles is also very small. 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 present invention, the resin particles are dispersed in a dispersion medium using 0.5 parts by weight or more of aluminum hydroxide as a dispersant for 100 parts by weight of polypropylene resin particles, and the resin particles are dispersed in a dispersion medium with stirring. Spherical resin particles can be obtained by heating to a temperature equal to or higher than the melting end temperature Tm of the particles, and when these spherical resin particles are used, for example, to produce pre-expanded particles, the pre-expanded particles are uniform in shape, cell diameter, etc. It has the advantage that foamed particles can be obtained, and the foamed molded product obtained using the pre-expanded particles has excellent physical properties. Hereinafter, the present invention will be explained in further detail with reference to Examples and Comparative Examples. Examples 1 to 7 and Comparative Examples 1 to 4 Polypropylene resin particles, dispersant, and water shown in Table 1 were placed in a container (autoclave) 5, stirred at a rotation speed of 250 rpm, and heated to the temperature shown in the table. After being held for 1 hour, the resin particles were cooled and the shape of the resulting resin particles was observed. In addition, the melting end temperature of the polypropylene resin used in this example and comparative example
Tm is as follows, and the DSC endothermic curve of the resin particles used in Example 1 is shown in Figure 7 (a in the figure).
indicates the baseline. ). Polypropylene resin Melting end temperature (°C) Propylene homopolymer 175 Ethylene-propylene random copolymer 157 Ethylene-propylene block copolymer 170 The results are shown in Table 1. Furthermore, the resin particles obtained in Example 3 are shown in FIG. 1, and the particles obtained in Comparative Examples 1 and 2 are shown in FIGS. 2 and 3, respectively. Example 8 and Comparative Examples 5 to 6 1000 g of resin particles shown in Table 2 and particulate aluminum oxide 3 were placed in a container (autoclave) of 5.
g, dichlorodifluoromethane 200 g, and water
Add 3000g and increase the pressure inside the container to 35Kg/cm ² while stirring.
(G) After setting the temperature to 145°C, one end of the container is opened while maintaining the pressure and temperature inside the container, and the resin particles and water are released under atmospheric pressure to foam the resin particles and pre-foam. Particles were obtained. The shape of the obtained pre-expanded particles, the cell diameter, the variation in shape, and the amount of resin particles remaining in the container were measured. Second result
Shown in the table. Next, each of the obtained pre-expanded particles was filled into a mold for molding, and heated and foamed to obtain a foamed molded article. Table 2 also shows the results of observing the quality of moldability during molding. The pre-expanded particles obtained in Example 8 are shown in FIG. 4, and the pre-expanded particles obtained in Comparative Examples 5 and 6 are shown in FIG. 5 and FIG. 6, respectively.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a plan view showing resin particles obtained in Example 3 of the present invention, FIGS. 2 and 3 are plan views showing resin particles obtained in Comparative Example 1 and Comparative Example 2, respectively, and FIG. The figure is a plan view of pre-expanded particles obtained in Example 8 using the resin particles obtained in Example 3, and FIGS. A plan view of the expanded particles, FIG. 7 shows the resin particles used in Example 1.
This is a DSC endothermic curve.

Claims (1)

[Claims] 1 Polypropylene resin particles, the resin particles
A spherical polypropylene characterized in that it is dispersed in a dispersion medium using 0.5 parts by weight or more of aluminum hydroxide per 100 parts by weight as a dispersant, and heated to a temperature equal to or higher than the melting end temperature Tm of the resin particles while stirring. Method for producing resin particles.