JPS6324457B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polypropylene sheet, and more specifically, when the smoothness and transparency of the sheet are improved, and solid phase molding is performed using the sheet,
This invention relates to a method for producing a polypropylene sheet that provides a molded article with high rigidity. Conventionally, polystyrene, polyvinyl chloride, etc. have been mainly used as transparent packaging materials. but,
Since these resins pose hygiene problems during use and disposal, the raw materials are being reviewed. Polypropylene is colorless and odorless, has a relatively light specific gravity, is strong, tough, and has a high surface hardness, so it has come to be evaluated as an alternative to the above-mentioned resins. However, conventional sheet thermoformed polypropylene products are inferior to polystyrene and polyvinyl chloride in rigidity, transparency, surface gloss, and thermoformability, and have low commercial value. However, recently, solid phase molding technology has been developed as a thermoforming technique using polypropylene sheets, and it has become possible to impart rigidity to polypropylene during the solid phase molding stage. However, the problems of transparency and surface gloss remain unsolved. As a result of repeated studies to solve these problems, the inventor of the present invention has found that it is possible to make the spherulites on both surfaces of a polypropylene sheet as fine and uniform as possible, and to increase the thickness of the fine spherulite layer. It has been found that this method is extremely effective in improving the surface gloss and transparency of thermoformed products, and in particular, warm solid-state air pressure forming can produce thermoformed products with high rigidity and excellent surface gloss and transparency. In addition, polypropylene has a specific melt index (hereinafter referred to as
Abbreviated as MI. ), and the surface temperature at the time of sheet forming is also set to a specific temperature, and when the first roll and second roll of the cooling roll are pressed together at the clamping pressure part, the first roll and the second roll are brought into surface contact. They discovered that this is effective and completed the present invention. In the present invention, after extruding polypropylene resin with an MI of 0.3 to 12 g/10 minutes in a molten state, the surface temperature is 10 to 10 minutes.
With respect to the tangent between the second cooling roll and the first cooling roll or Tatsuchiroll, which are set at 30°C or less, there is an incident angle of 10° on the first cooling roll or Tatsuchiroll.
This is a method for producing a polypropylene sheet, characterized by supplying and solidifying the polypropylene sheet at an angle of -45°. The polypropylene resin used in the present invention includes propylene homopolymers and random copolymers (propylene and α-olefin (content 1 to 6% by weight)).
copolymers), block copolymers ( _C2 component content: 5 to 15% by weight), and MI of 0.3 to 15%.
12g/10 minutes is fine. If the MI is less than 0.3 g/10 minutes, the discharge rate from the extruder will decrease, resulting in poor productivity and low rigidity of the polypropylene resin, which is not preferable. Moreover, if it exceeds 12 g/10 minutes, it becomes difficult to form a sheet due to its low viscosity. The resin temperature when extruding and molding this polypropylene resin from a T-die or the like is preferably 220 to 230°C. The higher the resin temperature, the better the surface gloss, but the lower the quenching effect, the more internal haze increases, and the lower the resin temperature, the better the overall transparency. However, if the resin temperature is lowered too much, the extrusion torque will increase and the discharge rate will decrease, which is undesirable.Also, if the resin temperature increases, the resin will deteriorate and the viscosity will decrease, making sheet molding difficult, which is undesirable. . Sheet molding of polypropylene resin can be carried out by a known method using a cooling roll. The inside of the cooling roll is a jacket through which a cooling medium passes, and a plurality of cooling rolls are used in combination. In this case, the surface temperature of the roll is maintained at 10 to 30°C. If the surface temperature is above 30°C, the transparency of the resulting sheet will decrease; on the other hand, the lower the temperature, the more transparent a product can be obtained, but below the dew point, water droplets may cause the sheet to become uneven in thickness, transparent, or
Since uneven gloss occurs, the lower limit temperature is usually set at 10°C. Note that the plurality of rolls may be kept at the same temperature, or the temperature may be lowered sequentially. Further, the sizes of the rolls are usually the same, as shown in FIG. As for the cooling roll, commercially available ones can be used, such as those made of metal materials such as aluminum and iron and coated with chrome or Teflon and finished with a mirror finish. In the present invention, when the polypropylene resin is supplied to the cooling roll, it is necessary to set the incident angle (θ) to 10 to 45 degrees with respect to the horizontal direction, as shown in FIG. To further explain the incident angle (θ), it means the angle at which the molten resin sheet is supplied to the first roll at the contact point between the rolls. If the incident angle is less than 10°, the molding speed must be extremely slow in order to provide a cooling effect to the first cooling roll or Tatsuchi roll side, improve surface gloss, and increase product transparency. If it exceeds 45 degrees, the surface of the sheet on the second cooling roll side will solidify and mirror transfer will not be possible, so the temperature of the first cooling roll or Tatsuchi roll must be increased, or the forming speed must be considerably increased. First, the cooling effect is extremely reduced, resulting in insufficient transparency of the product. According to the present invention, it is possible to obtain a polypropylene sheet that is smooth on both sides and has excellent surface gloss and transparency, and also has a good cooling effect during the production of the sheet, so that it can be produced efficiently. Another feature of the present invention is that a molded article with high rigidity can be obtained when solid phase molding is performed using the sheet. Since the polypropylene sheet obtained by the present invention has excellent transparency, it is particularly useful as a packaging material. Next, the present invention will be explained in detail with reference to examples. Examples 1 to 9 T-die sheet extrusion device with a diameter of 150 mm (L/D=
32) was used to mold polypropylene under the following molding conditions and cooling roll conditions to a width of 1300 mm and a thickness of
A 0.35mm sheet was obtained. Table 1 shows the results of measuring the physical properties of this sheet. (Molding conditions) Die temperature: 240℃, die lip opening 1.0mm (drawdown rate 35%), air gap: 80mm, molding speed:
20 mm/min, incident angle: 10°, 20°, 30° (cooling roll conditions) The three-roll system shown in Figure 1 was used. The roll was cooled by circulating temperature-controlled cooling water through a jacket inside the roll. In addition,
The diameter of each roll is 450 mm, the surface temperature is 20°C, and the rotation speed is 20 m/min. (Physical property measurement conditions) Haze (transparency parameter): Suga Test Instruments
Using a haze meter manufactured by Co., Ltd., the surface haze was determined by subtracting the internal haze from the total haze. In addition, internal haze was determined by applying silicone oil to the surface. Tensile modulus (rigidity parameter): JIS-K-
Measured in accordance with 6758. Physical properties of solid-phase molded products: Molding was performed in a #200 tray mold using a hot plate contact type vacuum-pressure molding machine, and transparency was evaluated visually and rigidity was evaluated in 4 grades by touch.

[Table] Comparative Examples 1 and 2 Sheets were obtained under the same conditions as in Example 1, except that polypropylene A (see Examples) was used and the incident angle of the molten resin sheet was set to 0° or 50°. The physical properties of the obtained sheet were measured and the results are shown in Table 2. Comparative Examples 3 to 5 Polypropylene A (see Examples) was used, the incident angle of the molten resin sheet was 20°, and the temperature of each roll of the three rolls was 5°C (Comparative Example 3) and 45°C (Comparative Example 4). A sheet was obtained in the same manner as in Example 1 except that the temperature was 80°C (Comparative Example 5). The physical properties of this sheet were measured and the results are shown in Table 2.

【table】

[Table] *1, *2: Same as Table-1
*: Water droplets appear on the roll surface and the surface is uneven.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.
In the figure, 1 is the first roll or tatsuchi roll, 2
is the second roll, 3 is the third roll, 4 is the extruder, 5
is a sheet.

Claims (1)

[Claims] 1. After extruding a polypropylene resin with a melt index of 0.3 to 12 g/10 minutes in a molten state, a second cooling roll whose surface temperature is set to 10 to 30°C and a first
A method for producing a polypropylene sheet, characterized in that the polypropylene sheet is supplied to a first cooling roll or tatsuchi roll at an incident angle of 10 to 45 degrees with respect to a tangent to the cooling roll or tatsuchi roll and solidified.