JPS63219B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing a heat-shrinkable polyolefin resin molded article. Heat-shrinkable resin moldings are used in a wide variety of applications, including various packaging materials, coating materials, and protective coating materials for connecting parts of long products such as pipelines and electric wires and cables. There are various methods for producing such heat-shrinkable resin molded bodies, but the molded bodies are required to have various advanced properties, such as excellent heat resistance and heat deformation properties. To meet these demands, measures such as introducing crosslinking into commonly used thermoplastic polymers or blending other high-melting point polymers have been taken, and in recent years, methods have also been taken to impart certain functions to the polymer materials used. Improved molded bodies have also been proposed. For example, heat-recovery deformability during melting is an important factor in determining the performance of heat-shrinkable molded products made of polyolefin.Furthermore, in order to obtain advanced functions for the molded products, they must have impact resistance,
It is important that the material also has tear resistance. In order to achieve all of these factors, it is generally necessary to make various changes to the crosslinking density of the heat-shrinkable resin molded product, or to embed heat-resistant woven fabric with high elasticity in order to improve the melt properties. A means to do so has been added. As mentioned above, various efforts have been made to provide the various properties required for heat-shrinkable resin molded products.
Although improvements have been made, these processing methods basically utilize a technique that stretches a crosslinked resin molding and gives the constituent polymers of the molding a memory effect called stretching. The introduction of crosslinking is central to these technologies. By the way, when producing this type of heat-shrinkable resin molding, the proportion of the crosslinking process in the product cost is often 50% or more, and therefore a method that can perform the crosslinking process at low cost is desired. . In the case of crosslinking by electron beam irradiation, there are significant restrictions depending on the form of the crosslinked molded product, specifically the final molded product such as a sheet, film, or tube, especially its thickness, and the possibility of mixing crosslinking agents. In the case of chemical crosslinking, there are various problems in the crosslinking process, such as the need to perform delicate molding operations on uncrosslinked products mixed with a crosslinking agent at a temperature range that does not cause decomposition of the crosslinking agent. I couldn't escape it. As a result of intensive studies to solve this problem, the inventors have found that certain types of blended polymers have approximately the same heat shrinkability without any crosslinking by appropriately determining extrusion conditions and selecting blended products. They discovered that a resin molded article could be produced and completed this invention. That is, in this invention, a mixture is obtained by mixing 5 to 50% by weight of a thermoplastic crystalline polymer other than the polyolefin with a higher melting point than the polyolefin, and the mixture is heated while providing conditions that allow the high melting point resin to melt. This is a method for producing a heat-shrinkable polyolefin resin molded article, which is characterized by forming a desired molded article by extrusion molding and uniaxially stretching the obtained molded article by 7 to 15 times. The heat-shrinkable polyolefin-based resin molded article according to the present invention is considered to be a molded article composed of a polyolefin as a matrix and a thermoplastic crystalline polymer on the other hand as a unique composite structure, and when this is stretched, the latter becomes the former. It is presumed that the fibers are uniformly dispersed and oriented in the fibers and exhibit the effect of solving the above-mentioned problem. That is, the melting point of a crystalline polymer is generally determined by the ratio of melting enthalpy and melting entropy.
When the molecular species are different, each has a unique value, but a high melting point polymer has a low melting entropy and a high melting point. That is, this is because the rigidity of the molecular chain is maintained even when melted. On the other hand, the compatibility of polymers can be evaluated by the solubility parameter, which is also related to the rigidity of the molecular chains via the cohesive energy density of the molecular chains, and as a result, the compatibility is determined by the melting point of the blended polymer. There are properties that are closely related. This is the reason why a thermoplastic crystalline polymer having a high melting point other than polyolefin is mixed with the polyolefin in the present invention. Next, the reason why this invention exhibits the same effect as crosslinking, that is, crosslinking substitute function and shrinkage function without performing crosslinking, is that the high melting point polymer is oriented as a fine fibrous aggregate, and these It is estimated that this effect is due to the surface tension of the molten polyolefin that forms small voids and fills these voids. Further, the provision of anisotropy through deformation called stretching, that is, the deformation of the fibrous aggregate of the base polyethylene and high melting point polymer due to this deformation, contributes to maintaining shrinkage in the temperature range above the melting point of the polyolefin. It is considered that The polyolefin used in this invention includes hydrocarbon polymer compounds such as high-density polyethylene, low-density polyethylene, polypropylene, poly-4-methylpentene-1, and polybutene, and copolymers of two or more of these. . The material to be blended with this polyolefin is a thermoplastic crystalline polymer other than the above-mentioned polyolefin, which has a melting point higher than that of the polyolefin, particularly preferably about 20° C. or higher. Preferred are fiber-forming non-polyolefins. Specifically, nylon 6, nylon
Examples include polyamide resins such as 12, nylon 66, and nylon 8, unsaturated polyester resins such as PET and PBT, and polysulfone resins such as polycarbonate. The reason why it is preferable for these to have a melting point 20°C or more higher than that of polyolefin is that below this limit, the compatibility of the resin is good, so this high melting point polymer is not arranged in a sufficient fibrous shape during extrusion molding, and the effect of this invention is This is because it is difficult to obtain. These thermoplastic crystalline polymers are mixed in an amount of 5 to 50% by weight, preferably 5 to 40% by weight, based on the polyolefin. If the amount is less than this, the object of the present invention cannot be achieved, and if it exceeds this amount, the hardness of the molded product will increase and the properties as a shrinkable material will be impaired, making it unsuitable. The above-mentioned two materials may be mixed in a manner that allows the materials to be fed into the extruder hopper with good workability, such as by sufficiently mixing pellets in a V-type blender. Next, the mixture of these two materials is extruded into a molded body of the desired shape using an extruder. The direct cause of the appearance of a structure arranged in the form of fibers is the difference in compatibility of the blended resins, and normally, if a molded product is obtained using an extrusion device for thermoplastic plastics, It does not require any special efforts. Therefore, consideration should be given to adopting a screw shape with high kneading efficiency, for example, using a twin-screw extruder, and furthermore, setting the cylinder temperature of the extruder based on the melting point of the polymer on the high melting point side. Specifically, the center part of the cylinder is kept at a temperature of 20 to 40 degrees Celsius above the melting point of the high melting point resin so that it can be sufficiently melted, and the die part is kept at a temperature of 5 degrees Celsius above the melting point of the high melting point resin.
It is desirable to keep the temperature ~10°C lower. Next, the obtained molded body is preferably stretched uniaxially at a temperature as low as possible and at a high magnification. Specifically, a stretching temperature of 10° C. lower than the melting point of the polyolefin used, for example, a stretching temperature of 15 to 60° C. for low density polyethylene, and a stretching ratio of 7 to 15 are suitable. The stretching method may be any method such as contacting with a hot plate, stretching in a hot fluid such as heated air, gas, water, or oil, or using hot rolls. As is clear from the above description and the examples below, this invention provides an excellent heat-shrinkable molded product by simply mixing polyolefin with a thermoplastic crystalline polymer having a higher melting point than polyolefin, without any crosslinking. It is possible to solve the above-mentioned problems associated with crosslinking in terms of cost and work during production, and its industrial value is extremely large. This invention will be explained below using specific examples. Examples 1 to 3 and Comparative Examples 1 and 2 V-shape was obtained by changing 15 to 30% by weight of nylon 6 (Toray Industries, Amilan CM1021 melting point 216 °C) to low density polyethylene (MI 0.8, melting point 111 °C). A mixture was obtained by mixing in a blender for 30 minutes. This mixture was extruded into a sheet of 160 mm width x 0.2 mm thickness using a 40 mmφ extruder (extrusion temperature: 250°C at the center of the cylinder,
die head 210℃). The obtained sheet is rolled with a 300mm width rolling roll.
It was enlarged 10 times at a temperature of 60°C. For comparison, a crosslinked polyethylene film and an uncrosslinked film were obtained by crosslinking the film obtained using only polyethylene at 20 Mrad of γ rays, and the heat shrinkability of these films was examined and the results are shown in Table 1 below. Indicated.

[Table] Examples 4-5, Comparative Examples 3-4 Isotactic polypropylene (MI0.9,
Polycarbonate resin (Teijinsha, Panlite K1300 melting point approx. 230°C) in the amount shown in Table 2
℃) and mixed for 35 minutes using a V-type blender to obtain a mixture. This mixture was extruded into a 4.5 mmφ rod product using a 40 mmφ screw type extruder and uniaxially stretched under the conditions shown in the table. For comparison, uniaxially stretched polypropylene rods were obtained under exactly the same conditions without the addition of polycarbonate resin, and their heat shrinkability was investigated and is shown in the same table.

[Table] Examples 6 to 8 Nylon 6 (Toray Industries, Amiran CM1201, melting point 215-220°C) was added in the amount shown in Table 3 to high-density polyethylene (MI 0.9, melting point 130°C) in a V-type blender. and mixed to obtain a mixture. This mixture was extruded into a sheet having a width of 150 mm and a thickness of 0.3 mm using a screw type extruder having a diameter of 40 mm, and the resulting sheet was uniaxially stretched 15 times in hot water at 90°C. The amount of heat shrinkage of the obtained stretched sheet was examined and the results are shown in the same table.

[Table] As is clear from the results in the above tables, the product of the present invention, that is, the product made of the mixture polymer, has the same heat shrinkage force as that of polyolefin alone and crosslinked, without any crosslinking. It is also clear that various demands for properties can be met by selecting the stretching conditions or changing the amount of blended polymer as in Examples 4-5 or 6-8.

Claims (1)

[Claims] 1. Mix 5 to 50% by weight of a polyamide resin or a polysulfone resin with a melting point higher than that of the polyolefin to obtain a mixture,
A heat-shrinkable polyolefin resin characterized in that this mixture is formed into a desired molded body by extrusion molding while providing conditions that allow the high melting point resin to melt, and the resulting molded body is uniaxially stretched 7 to 15 times. Method for manufacturing a molded object.