JPH0577697B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to polyolefin resin particles whose particle surface layer is halogenated, particularly polyolefin resin particles which contain an easily volatile blowing agent and whose particle surface layer is halogenated. The present invention relates to a manufacturing method. (Prior Art and Problems) The polyolefin resin particles of the present invention whose surface layer portions are halogenated are a novel substance that has not been described in any literature. Conventionally, highly elastic resin foams have been manufactured using polyethylene, polypropylene, and compositions in which polyethylene is blended with polystyrene as raw resins. However, when these raw material beads contain an easily volatile foaming agent, they have extremely poor retention of the foaming agent, and therefore cannot be sold as raw material beads like expandable polystyrene; Currently, they are commercially available as foamed pre-expanded particles or foamed molded bodies. As a measure to overcome this drawback, after halogenating the surface layer of polyethylene particles in aqueous suspension,
A patent application was made in 1980 for a method of impregnating with an easily volatile foaming agent.
-97548. however,
This invention aims to improve foaming agent retention by forming a film with gas barrier properties on the resin surface by halogenating the surface layer of polyolefin resin particles. Although the agent retention has improved compared to conventional products, it may not be sufficient depending on the type of resin. It has also become clear that the ease of halogenation and foaming agent retention vary widely depending on the method of manufacturing the particles used. (Means for Solving the Problems) The present invention essentially solves these problems, and provides a completely novel method for producing polyolefin resin particles that has not existed in the past. That is, the present invention is characterized by dispersing polyolefin resin pellets obtained by the hot cut method in water, irradiating the pellets with ultraviolet rays in the presence of halogen gas to halogenate the surface layer of the pellets, and impregnating the pellets with an easily volatile blowing agent. The content is a method for producing polyolefin resin particles. The polyolefin resins mentioned here include low-density polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-propylene random copolymer, ethylene-vinyl acetate copolymer, ethylene-styrene copolymer, and vinegar. These include bistyrene copolymer, chlorinated polyethylene, etc., and these may be used alone or in combination with each other.
Further, other resins may be mixed with these polyolefin resins. In this case, the polyolefin resin is at least 50% by weight.
Further, these polyolefin resins may be crosslinked with peroxide or the like. A typical method for resin granulation is extrusion pelletization. There are two further types of extrusion methods: one is the strand cut method in which the resin extruded from the die is pulled out, cooled, and then cut, and the other is the strand cut method in which the resin extruded from the die is arbitrarily cut on the spot. This is a hot cut method where the length is cut. In the strand cut method, the resin is cooled and hardened after applying tension, so that residual strain exists in the segments within the pellet. If this pellet is directly halogenated, the pellet surface cannot be uniformly halogenated due to the distortion of the segments, and an incompletely shaped halogenated film is formed. When pellets whose surfaces are halogenated in this way are impregnated with an easily volatile blowing agent, the internal pressure is dissipated through the thin part of the halogenated film, and the gas barrier property, which is the first feature of the present invention, is fully exhibited. It becomes a difficult situation. Also, when foaming these pellets, if the surface halogenated film is uneven, the internal unhalogenated part will be exposed from the thin part of the film when the surface stretches, and the foaming agent will escape from there. Moreover, since halogenated polyolefin and normal polyolefin have different physical properties such as tensile strength, it becomes difficult to obtain a foam with a high degree of foaming. As described above, the problem of distortion of segments within pellets has a very important meaning in making effective use of the technology of halogenating the surface layer of polyolefin resin particles. In the present invention, hot-cut pellets are used instead of strand-cut pellets. In this way, residual distortion within the pellet can be minimized. The hot cut method used in the present invention does not pull out the resin and rapidly cool it as in the strand cut method, but cuts the resin extruded from the die on the spot, so the distortion during extrusion is reduced. Although present, large tensile strain as in the strand cut method does not remain, and the pellet surface becomes relatively uniform.
By halogenating the surface layer of these pellets, resin particles having a more uniform halogenated layer can be produced. Although the diameter of the pellets at this time is not limited in any way, those of 1 to 2 mm are usually used. Easily volatile blowing agents include propane, butane,
Hydrocarbons such as pentane, hexane, and heptane, Freon-11, Freon-12, Freon-114, and the like include, but are not particularly limited to, and these can be used alone or in combination. The amount of these blowing agents is preferably in the range of 10 to 40% by weight based on the resin content. If it is less than 10% by weight, preferred expandable particles cannot be obtained, and if it is less than 40% by weight, good expanded particles can be obtained, so it is wasteful to use a larger amount. In this invention, halogenating the particle surface means that, although it depends on the size of the polyolefin resin used, if the average diameter is 0.5 mm or more, as is generally used for bead molding, halogenating the particle surface 200μ from the particle surface. The degree of halogenation in the interior is determined by an X-ray microanalyzer, and the halogen concentration at the maximum peak of the concentration distribution is 10% by weight or more, preferably 15% by weight or more (estimated from the X-ray intensity ratio of a standard sample). In this case, the standard sample amount for determining the halogen concentration using an X-ray microanalyzer is a salt plate if the halogen is chlorine, sodium bromide if it is bromine, potassium iodide if it is iodine, and fluorite if it is fluorine. It is. From particle surface and particle surface
If the maximum halogen concentration of the halogen concentration distribution within the 200 μm is less than 10% by weight, the retention of the blowing agent will be extremely poor. In addition, the fact that the surface layer of the particle is more highly halogenated than the inside means that halogenation of only a very small amount near the surface of the particle is sufficient to improve the retention properties of the polyolefin resin particles. Not only that, but also the function of the original polyolefin resin is halogenated. Furthermore, it takes a lot of time to halogenate the entire particle after it has already been granulated, and productivity is extremely low. Alternatively, if the powdered polyolefin is halogenated before being granulated, it is possible to uniformly halogenate almost the entire part.
Not only does such work require a great deal of labor, but it is also inevitable that the cost will be high. In this way, halogenation to the inside of the particle is essentially unnecessary, but
There is no particular problem with halogenation as long as it is in a small amount compared to the particle surface layer and within a range that does not impair the original function of the polyolefin resin. The halogens used here include fluorine,
There are chlorine, bromine, and iodine, and any of them may be used, but chlorine is advantageous in terms of ease of handling and cost. Next, a method for producing polyolefin resin particles having a halogenated surface layer according to the present invention will be described. for example,
Polyolefin resin particles are dispersed in an aqueous suspension system, and the polyolefin resin particles are dispersed in an aqueous suspension system to obtain a solution near the melting point of polyolefin (melting point ±10°C).
After recovering the distortion, it is cooled, washed with water, and dried.
Obtain heat-treated pellets. Disperse this in water,
The resin surface layer is halogenated by UV irradiation in the presence of halogen gas. There is also a method of impregnating the obtained particles with an easily volatile blowing agent, or by dispersing polyolefin resin particles in water and impregnating them with an easily volatile blowing agent, and then irradiating the particles with ultraviolet rays in the presence of halogen gas to layer the particle surface. By halogenating the moiety, the resin particles which are the object of the present invention can be easily obtained. Depending on the type of resin, it is also possible to halogenate it without using ultraviolet rays. The polyolefin resin particles, easily volatile blowing agent, degree of halogenation, etc. during this production are as described above. The degree of halogenation in the production of resin particles can be controlled by the intensity of ultraviolet rays, the amount of ultraviolet rays, and the reaction temperature, and may be arbitrarily selected depending on the desired quality and the type of resin used. (Example) Next, the present invention will be explained with reference to an example. Example 1 100 parts by weight of polyethylene pellets (density 0.920, hot-cut product), 117 parts by weight of pure water, 0.025 parts by weight of AOS, and 3 parts by weight of Supertite were placed in the autoclave from 1, sealed, and heated to 130°C while stirring. After raising the temperature and holding it for 5 minutes, it was cooled to 50°C, the contents were taken out, washed with water, and dried to obtain heat-treated polyethylene. Next, 100 parts by weight of the above heat-treated polyethylene and 567 parts by weight of pure water were placed in a glass reactor, and the mixture was stirred.
After raising the temperature to 70°C and performing nitrogen substitution, ultraviolet rays were irradiated while flowing chlorine, and after 1.5 hours, surface chlorinated polyethylene with a degree of chlorination of 2.7 mol% was obtained.
Table 1 shows the foaming agent retention capacity when this resin was impregnated with butane as a foaming agent. Comparative Example 1 A surface layer chlorinated product of polyethylene (density 0.920) obtained by the strand cut method was obtained in the same manner as in Example 1 above. The degree of chlorination was 2.8 mol%.
Table 1 also shows the retention capacity when this resin was impregnated with a blowing agent (butane).

[Table] * The foaming agent retention rate over time is the foaming agent remaining rate at each point in time relative to the initial impregnated amount. Impregnated pellets were stored at 23°C.

Claims (1)

[Claims] 1. A foamable polyolefin characterized by dispersing polyolefin resin pellets obtained by a hot cut method in water, irradiating the pellets with ultraviolet rays in the presence of halogen gas to halogenate the surface layer of the pellets, and impregnating the pellets with an easily volatile foaming agent. Method for producing resin particles.