JPH04323023A - Manufacture of transparent polypropylene sheet - Google Patents

Abstract

PURPOSE:To obtain a more transparent P P sheet by rolling polypropylene (P P) to be a specific drawing ratio at the temperature of a melting point or lower, and rendering the surface smooth thereafter. CONSTITUTION:A polymeric material supplied in a hopper 1 as pellets is continuously extruded by means of an extruder 2 for heating and kneading pellets and the molten resin is cool-solidified as advancing in the inner part of a die 3 and then fully solidified in the proximity of an outlet of the die to be molded as a sheet. In the case of manufacturing a P P sheet by a hot extruding method or the like in this manner, the P P sheet molded to be relatively thick in the aforegoing process is subsequently passed through a rolling machine 6 and the P P is rolled to be a ratio of 3 or more at the temperature of a melting point or lower, after that, of which surface is processed to be made smooth by a surface processing machine 7. In this way, by rolling at the drawing ratio of 3 or more, the grain boundary is allowed to be destroyed to thereby obtain a P P sheet with high transparency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing sheets of polymeric materials, particularly polypropylene.

0002

[Prior art] Conventionally, thick plastic sheets (
(usually 5 mm or more) are manufactured by extruding molten resin from a die. This manufacturing method is called hot extrusion, and the process is as shown below. That is, as shown in FIG. 2, the polymer material supplied as pellets to the hopper 1 is continuously extruded by an extruder 2 that heats and kneads the pellets, and is mixed into a die 3. The die 3 is cooled with water, and the polymer material mixed in in a molten state cools and solidifies as it moves through the die, becomes completely solid near the die exit, and exits the die 3 as a sheet 4. go.

[0003] Also, in the production of thinner sheets,
As shown in FIG. 3, there is also a method in which the molten resin extruded from the die 3 is wound around a roll 5 and cooled and solidified. This is commonly called calendering. However, in these methods, there was a further problem to be solved regarding the transparency of the sheet.

0004

[Problems to be Solved by the Invention] Polypropylene (hereinafter referred to as PP) sheets manufactured by conventional methods are opaque regardless of the manufacturing method used. Table 1 shows the measurement results of haze H of PP sheets manufactured by the conventional method. Haze H is an index that indicates the opacity of a plastic sheet, and H=1
00% represents complete opacity and H=0% represents complete transparency. If H<5%, it can be considered transparent in practical terms.

This haze measurement method is based on ASTM D1
003. All PP sheets manufactured using conventional methods exhibit a haze of 90% or more and are completely opaque even when observed with the naked eye. In view of the above points, the present invention provides a method for manufacturing a transparent PP sheet.

[0006]

[Table 1]

[0007]

[Means for Solving the Problems] The gist of the present invention is to provide a transparent polypropylene, which is characterized by rolling polypropylene at a temperature below its melting point to a stretching ratio of 3 or more, and then smoothing the surface of the polypropylene. The method for manufacturing polypropylene sheets.

[0008] The present invention will be explained in detail below based on the drawings. First, the inventors conducted many studies and clarified the cause of the opacity of conventional sheets. Table 2 shows the internal transparency of sheets manufactured by the conventional method. Since the internal haze value is over 90%, these sheets are completely opaque inside the board itself. This can be confirmed by observation using a polarizing microscope, and this is because the polymer has clear grain boundaries.

[0009]

[Table 2]

Based on the above results, the inventors conducted many experiments and found that the inside of the plate becomes transparent if it is rolled at a total stretch ratio of 3 or more (FIG. 4). This is because the above-mentioned grain boundaries are destroyed by rolling. In particular, it can be seen that transparency comparable to that of glass can be obtained if the material is rolled at a drawing ratio of 5 or more (here, total drawing ratio=thickness of the material/final thickness of the rolled material). FIG. 4 shows the material PP and the material temperature at 140°C.

However, as shown in FIG. 4, the total haze including the surface texture shows a considerably large value. This is because the plate surface deteriorates more than the raw material due to rolling. Therefore, it is impossible to use the rolled material as a transparent sheet, and it is necessary to improve the surface properties.

FIG. 1 shows the manufacturing method of the present invention. The equipment used in this manufacturing method is mainly a rolling mill 6 and a surface treatment device 7. In rolling mill 6, the total stretching ratio is 3, which is necessary to make the inside of the plate transparent.
The above rolling is performed to obtain a rolled material 8. It is preferable to heat the material 4 to a temperature below its melting point in order to obtain sufficient deformability. As for the rolling method, rolling may be performed in one direction, or if necessary, rolling may be performed in two or more directions. Regarding the number of passes, if a predetermined thickness cannot be obtained with one pass, multiple passes may be performed.

The surface treatment device 7 improves the surface properties of the rolled material 8 that have deteriorated due to rolling. As the surface treatment method, surface grinding, polishing, transparent resin coating, etc. can be selected and applied as appropriate. The surface quality after surface treatment is R
It is necessary that a=0.1 μm or less (measurement distance: 200 μm).

[0014]

[Examples] Examples of the present invention are shown in Table 3, and comparative examples are shown in Table 4.

[0015]

[Table 3]

[0016]

[Table 4]

[0017]

According to the present invention, since the crystal grain boundaries of the polymer can be destroyed, it is possible to produce transparent PP sheets.

[Brief explanation of the drawing]

FIG. 1 shows the manufacturing process in the present invention.

FIG. 2 shows a conventional method for manufacturing a polymer sheet (hot extrusion method).

FIG. 3 shows a conventional method for manufacturing a polymer sheet (calender molding method).

FIG. 4 shows the effect of making the PP sheet transparent by rolling.

[Explanation of symbols]

1 Hopper 2　Extruder 3 Constant temperature die 4 Polymer sheet 5 Rolling roll 6 Rolling mill 7 Surface treatment equipment

Claims (1)

[Claims] [Claim 1] Polypropylene at a temperature below its melting point
A method for producing a transparent polypropylene sheet, which comprises rolling the sheet to the above stretching ratio, and then smoothing the surface of the sheet.