JPH0367491B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing a thermoplastic resin sheet,
Specifically, the present invention relates to a method for rapidly and stably producing a thermoplastic resin sheet with excellent transparency, uniformity, thermoformability, etc. Conventionally, transparent containers have been thermoformed using thermoplastic resin sheets, and polyvinyl chloride resins and polystyrene resins are often used as such thermoplastic resins. However, polyvinyl chloride resin has problems in terms of toxicity and heat resistance. Further, polystyrene resins have a problem in that they do not have sufficient heat resistance or impact resistance. Therefore, it is possible to use polyolefin resin, but relatively highly crystalline films and sheets have poor transparency, which is a major drawback compared to conventional ones, and it is difficult to use them as various packaging containers. . For this reason, various methods have been proposed for obtaining transparent sheets for thermoforming. For example, a method of manufacturing containers by heating a crystalline plastic sheet to a temperature above its melting point, rapidly cooling it, and then air-forming it at a temperature below its melting point (Japanese Patent Publication No. 57-17689)
Publication No.). A method of manufacturing a thermoforming sheet by setting the surface roughness of both sides of a thermoplastic synthetic resin sheet to 0.7 μRMS or less, and then applying uniaxial stretching of 3 times or less to the sheet (Japanese Patent Application Laid-Open No. 128673/1983) Public bulletin). Against isotactic polypropylene
A sheet made of a resin containing 0.01 to 2.0 wt% of a nucleating agent and having a surface roughness of 0.7 μRMS or less is stretched 1.02 to 3 times in one direction at a temperature lower than its melting point, and the resulting uniaxially oriented sheet is Method for manufacturing transparent containers by thermoforming at a temperature lower than the melting point
94371). However, in the above method, since a preformed sheet is reheated, reheating causes deterioration of the resin and uneven heating, and increases energy costs. Moreover, uniform cooling and rapid cooling are insufficient, and the resulting sheet does not have sufficient transparency. Furthermore, there are problems such as sagging and wrinkles of the sheet during thermoforming, making it impossible to obtain molded products with excellent transparency and uniformity. In addition, in the method (2), although the raw sheet itself is inferior in transparency, the transparency is attempted to be improved by secondary stretching. however,
In this method, the stretching ratio is usually as high as 1.5 to 2.5 times, but the transparency is not necessarily sufficient. Furthermore, if the stretching ratio is increased in order to improve transparency, the thermoformability deteriorates significantly, and there is a drawback that the film tears in the MD direction, making it impossible to form it. Moreover, in order to obtain a transparent container, a certain degree of stretching by deep drawing is required, and uniform transparency cannot be obtained due to uneven stretching, and vacuum forming requires a high degree of sheet orientation.
The major drawback is that it cannot be used because of its low heat resistance. Furthermore, although the stretching ratio can be made relatively lower in the method compared to the method in (2), the uniform kneading properties of the nucleating agent are not sufficient, resulting in problems such as plate-out and mucus in the die during sheet forming. Furthermore, there are health and safety issues, and transparency and uniformity are not always sufficient. As mentioned above, the conventional methods have various drawbacks, and it has not yet been possible to obtain containers with excellent transparency and good thermoformability. An object of the present invention is to eliminate the above-mentioned conventional drawbacks and provide a method for producing a thermoplastic resin sheet having excellent transparency and a wide range of thermoformability. That is, the present invention melt-extrudes a thermoplastic resin in the form of a film, introduces the extruded molten resin film into a slit in the direction of cooling water flow, rapidly cools it, and then adjusts the melting point or The present invention provides a method for producing a thermoplastic resin sheet, which is characterized by stretching at a stretching ratio of 1.02 to 3.00 times at a temperature below the softening point. There are various thermoplastic resins used as raw materials in the present invention, such as polyolefins such as polypropylene, polyethylene, and propylene copolymers; polyesters such as polyethylene terephthalate and polybutylene terephthalate;
In addition to polyamides such as nylon-6 and nylon-6.6, polycarbonate; polystyrene; polyvinyl chloride and the like can be mentioned. Among these, crystalline thermoplastic resins such as polyolefin, polyester, and polyamide are particularly preferred. In the present invention, a nucleating agent, surfactant, lubricant, antioxidant, etc. may be added as necessary. In the present invention, the raw material resin is melt-extruded into a film. As a method for melt-extruding the raw resin into a film, a T-die method, which is usually used for forming sheets, etc., can be used. The molten resin film extruded in this way is then introduced into a slit through which cooling water flows, but at this time it is preferable that the film is extruded under conditions to ensure excellent transparency. In other words, it is preferable to extrude under conditions that make the surface of the membrane as smooth as possible, for example by using a die with no scratches on the surface or by extruding at a relatively high die exit temperature. is preferred. The thickness of the molten resin film thus extruded is usually 3 mm or less, preferably 0.1 to 2.0 mm. Next, the transparent molten resin film extruded as described above is introduced into a slit through which cooling water flows and is rapidly cooled. That is, the cooling water is caused to flow through the slits in a flowing state, and the molten film-like material is introduced therein in the direction in which the cooling water flows, thereby rapidly cooling it. The material of the slit portion is not particularly limited and may include metal, plastic, wood, cloth, etc. Further, the slit portion may be constructed of a pair of endless belts or a pair of rolls kept at a predetermined interval. In particular, by forming the slit portion in two or more stages, it is possible to obtain an excellent product with even higher productivity. The width of the slit is not particularly limited, but is usually 20 mm or less, preferably 10 mm or less, and more preferably 6 mm or less. Further, as the cooling water, only water or an aqueous solution containing an organic or inorganic thickener is used, but an aqueous solution containing a thickener is preferable in terms of uniform cooling and surface smoothness. Here, various organic thickeners can be used, such as natural polymer substances, semi-synthetic products, and synthetic products. Natural polymer substances include sweet starch, potato starch,
Starches such as wheat starch; mannans such as konjac; seaweeds such as agar and sodium alginate; vegetable mucilages such as gum tragacanth and gum arabic; microbial mucilages such as dextran and levan; glue, gelatin, casein, collagen, etc. There are many proteins, etc. Semi-synthetic products include cellulose-based substances such as viscose, methylcellulose, and carboxymethylcellulose; starch-based substances such as soluble starch, carboxymethyl starch, and dialdehyde starch. In addition, synthetic products include polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, and the like. On the other hand, inorganic thickeners include silica sol, alumina sol, clay, water glass, and various metal salts. In addition to aqueous solutions prepared by adding these thickeners to water, viscous substances such as polyethylene glycol, polypropylene glycol, and silicone oil can also be used alone. The viscosity of the aqueous solution with added thickener should be between 2 and 3000 centipoise (CP), preferably between 3 and 1000 CP. In addition, the temperature of the cooling water is preferably -10℃ to +50℃, and especially when manufacturing sheets with a thickness of 0.2 mm or more, the liquid temperature should be 20℃ or less, particularly preferably 10℃ or less, to prevent haze spots from occurring. Effective. In this way, a thermoplastic resin sheet is produced by rapidly cooling the molten resin film to usually 100°C or lower, preferably 60°C or lower. Note that in order to further improve the transparency of this sheet, it is preferable to add an annealing step. In other words, this sheet is heated to a temperature below its melting point or softening point, usually 10 to 60°C below its melting point or softening point.
By heating using a heating roll or the like in a low temperature range, preferably in a temperature range 20 to 50° C. lower than the melting point or softening point, even better transparency can be obtained. Further, the transparent sheet obtained by quenching in this manner is stretched at a stretching ratio of 1.02 to 3.00 times at a temperature below its melting point or softening point to produce a stretched thermoplastic resin sheet. In other words, the quenched transparent sheet is heated below its melting point or softening point.
Preferably a temperature 5 to 70°C lower than the melting point or softening point, more preferably 5 to 70°C lower than the melting point or softening point.
Heat to ~50°C lower temperature and perform roll stretching or roll rolling. Here, the sheet may be heated using a roll, an oven, or the like. Note that the stretching may be performed by biaxial stretching in addition to uniaxial stretching. Although the stretching ratio varies depending on the stretching conditions, it is sufficient as long as the shrinkage stress is about 0.2 to 30 kg/cm ² , and is usually 1.02 to 3.00 times, preferably 2 times or less. In other words, the stretching ratio has almost no effect on the transparency of the resulting sheet, so it depends on the conditions during thermoforming, but in general it is sufficient to carry out thermoforming to the extent that no bending or wrinkles occur. Determine by considering the degree of orientation required for the molded product. As described above, a thermoplastic resin sheet with excellent transparency can be produced. Furthermore, the thermoplastic resin sheet obtained by the method of the present invention can be processed by vacuum forming, pressure forming, plugging, etc., particularly at a temperature lower than its melting point or softening point, specifically at a temperature 5 to 50 degrees Celsius lower than its melting point or softening point. Various molded products can be obtained by thermoforming such as assisted air pressure molding and matt molding. According to the method of the present invention, a sheet with excellent transparency, uniformity, thermoformability, especially vacuum formability can be obtained. Furthermore, the method of the present invention has a low degree of stretching and excellent thermoformability. Therefore, according to the method of the present invention, sheets can be produced that have various strengths and rigidities from vacuum forming to pressure forming, and from shallow forming to deep drawing, and are suitable for the forming conditions and required physical properties of the formed product. can be obtained. Furthermore, according to the method of the present invention, sheets can be manufactured at high speed and stably, and furthermore, an annealing process can be easily incorporated into the method of the present invention, and as an effect of this, a sheet with better transparency can be obtained. I can do it. Therefore, the method of the present invention can be effectively used for manufacturing sheets for various packaging containers. Next, examples of the present invention will be shown. Examples 1 to 7 Isotactic polypropylene (melt index 2.0 g/10 minutes, melting point 168°C) was
T-die extrusion equipment (extruder 60mmφ, L/
A transparent molten resin film was extruded using a die (D = 28, die width 550 mm, die lip opening 1 mm). The extruded molten resin film is cooled by cooling devices A and B shown below.
and molded under the molding conditions shown in Table 1 to obtain a polypropylene sheet. Next, this sheet was heated to 130° C. using a heating roll, and then stretched at a predetermined stretching ratio shown in Table 1 to obtain a stretched polypropylene sheet. The obtained stretched polypropylene sheets were subjected to the prescribed thermoforming shown in Table 1, and the moldability and molded products were evaluated. The results are shown in Table 1. Cooling device A (single-stage slit) Slit height 50 mm, width 3 mm, water tank water level above the slit 5 mm, cooling water temperature 2°C Cooling device B (two-stage slit) First stage slit: height 50 mm, width 2 mm, water tank water level above the slit 5mm Second stage slit: height 10mm, width 4mm, water tank water level above the slit 10mm Cooling water temperature: 10℃ Example 8 In Example 1, high density polyethylene (density
0.960g/ ^cm3 , melt index 0.2g/10min,
The procedure of Example 1 was followed except that the sheet was heated to 110°C and then stretched to obtain a sheet with excellent transparency. Comparative Example 1 A sheet was produced in the same manner as in Example 3, except that stretching was not performed, thermoforming was performed, and the moldability and molded product were evaluated. The results are shown in Table 1. Reference Example 1 In Example 2, vacuum forming was performed at a forming temperature of 155° C. instead of air pressure forming, but the forming could not be completed. For this reason, when the molding temperature was raised to 165°C, the transparency and surface gloss of the molded product decreased significantly. 【table】

Claims (1)

[Scope of Claims] 1. A thermoplastic resin is melt-extruded into a film, and the extruded molten resin film is introduced into a slit in the direction of the flow of cooling water and rapidly cooled, and then the resin is melted and extruded. 1.02 at a temperature below the melting point or softening point
A method for producing a thermoplastic resin sheet, characterized by stretching at a stretching ratio of ~3.00 times. 2. The manufacturing method according to claim 1, wherein the slit is a two-stage slit.