JPH0592470A - Manufacture of polypropylene sheet excellent in transparency - Google Patents

Abstract

PURPOSE:To improve the transparency of a sheet without reducing the thermal formability of a polypropylene sheet. CONSTITUTION:Polypropylene is fusion-extruded on a cooling drum like a sheet, and after its cooling it is rolled between the rolls of the surface temperature of 100-120 deg.C at the rolling ratio of 1.1-1.4, whereby the globular crystal on the surface of the sheet is crushed and its transparency is made excellent. The sheet excellent in transparency may be obtained without using the special cooling method such as water cooling. Since the thermal formability of said sheet is not reduced, it is preferably used for the use of forming such as for PTP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is suitable as a PTP packaging material used for packaging pharmaceutical tablets, capsules, etc.
The present invention relates to a method for producing a polypropylene sheet having good transparency.

[0002]

2. Description of the Related Art Polyvinyl chloride sheets have been widely used as sheets for PTP packaging, and polypropylene sheets are mostly used despite the advantage that the moisture permeability is lower than that of polyvinyl chloride sheets. Not not. The main reason for this is that the transparency of polypropylene sheets is significantly inferior to that of polyvinyl chloride sheets. That is, in the method of extruding molten polypropylene in a sheet shape on a cooling surface such as a cooling drum to cool, the surface of the sheet in contact with the cooling drum is rapidly cooled,
The surfaces that are not in contact with each other have a low cooling rate, and spherulites are generated to roughen the surface and reduce the transparency.

As a method for improving the transparency of a polypropylene sheet, (1) a method of adding a nucleating agent such as dibenzylidene sorbitol to polypropylene, (2) a method of stretching the polypropylene sheet while cooling it from a molten state, ( 3) There is a method of rapidly cooling a molten polypropylene sheet to a temperature of 30 ° C. or lower by a water cooling method.
The method (1) has a drawback of deteriorating thermoformability such as vacuum forming and pressure forming, and the method (2) also impairs the thermoformability due to the orientation of the sheet. It has the drawback of requiring means.

[0004]

The present invention provides a simple and highly productive cooling drum method for improving transparency without deteriorating thermoformability. Surface temperature 1 after melt extrusion and cooling
A method for producing a polypropylene sheet having good transparency, which comprises rolling at a rolling ratio of 1.1 to 1.4 between rolls at 00 to 120 ° C.

The present invention will be described in detail below. In the present invention, as the polypropylene resin, propylene homopolymer or propylene and ethylene, α such as butene-1
-A copolymer with an olefin can be used. Among them, those having a melt flow index (MI, unit g / 10 minutes) of 1 to 4 measured under the conditions of JIS-K7210 are preferable, and a propylene homopolymer is more preferable in terms of the balance between transparency and thermoformability. It is suitable. If the MI is less than 1, the transparency will be poor, and if the MI is more than 4, the sheet will be sticky during thermoforming and the formability will be poor. If necessary,
Other thermoplastic resins such as hydrogenated petroleum resin, antioxidant, ultraviolet absorber, polyethylene and ethylene-propylene copolymer may be added.

Melt extrusion and cooling of polypropylene is
It can be carried out by a known technique. That is, the resin is supplied to an extruder, melted, and extruded from a T die onto a cooling surface such as a cooling drum or a cooling belt to be cooled to obtain an unstretched sheet. The temperature of the cooling surface is appropriately in the range of 60 to 80 ° C. The surface of this sheet, which is not in contact with the cooling surface, is not rapidly cooled, and spherulites are generated, so that the transparency is low. In particular, this phenomenon becomes remarkable in the case of a thick sheet used for thermoforming.

Next, the sheet is rolled between a pair of rolls. By this rolling, the spherulites generated on one surface of the sheet are crushed, and the transparency of the sheet can be improved.
The surface temperature of the roll is set in the range of 100 to 120 ° C. If it is less than 100 ° C, the effect of improving transparency is insufficient,
On the other hand, if it exceeds 120 ° C., crystallization due to heat progresses and the formability is lowered. The roll can heat only the side where spherulites are generated (the surface that did not contact the cooling surface),
Both rolls are preferably temperature controlled.

The rolling ratio (ratio of sheet thickness before rolling and sheet thickness after rolling) is preferably in the range of 1.1 to 1.4. If the rolling ratio is less than 1.1, the transparency improving effect is small,
If it exceeds 1.4 times, the crystallinity increases due to the orientation, resulting in poor moldability.

The sheet cooled by the cooling surface does not necessarily have to be cooled to near room temperature.
As long as it has sufficient shape retention and is cooled to a temperature lower than the crystallization start temperature of polypropylene, the rolling treatment can be performed even at a relatively high temperature. Alternatively, the cooled sheet may be wound up once and rolled in another step while being rewound.

Since the rolled sheet has a temperature lower than about 130 ° C., which is the crystallization start temperature of polypropylene resin, it may be naturally air-cooled without any cooling means, but it may be forced by air blowing. It is also preferable to perform cooling.

The sheet according to the present invention is suitable for use in applications such as PTP packaging and blister packaging after thermoforming such as vacuum forming and pressure forming, and its thickness is not particularly limited, 200-500 μm, especially 200-4
It is about 00 μm.

[0012]

EFFECTS OF THE INVENTION According to the present invention, it is possible to improve the transparency without deteriorating the thermoformability without requiring a special device or means such as a water cooling method, and it is suitable for molding applications such as PTP. Sheets are obtained.

[0013]

【Example】

Examples 1 to 4 Polypropylene (homopolymer, MI = 2) in which 0.1 part by weight of zita-sialybutyl-p-cresol and 0.1 part by weight of calcium stearate were blended.
Was melted and kneaded by an extruder having a cylinder diameter of 40 mm, and cast on a cooling drum having a surface temperature of 70 ° C. by a T die having a temperature of 240 ° C. to obtain a non-stretched sheet. Subsequently, rolling was performed at a rolling ratio shown in Table 1 between a pair of rolls having a surface temperature of 110 ° C. to form a sheet having a width of 200 mm and a thickness of 300 μm, which was subjected to pressure forming with a PTP molding machine to evaluate formability. The moldability was evaluated as "good" when the shape after molding was visible in the shape, and "bad" when the shape after molding was not visible in the shape. The transparency (haze) of the obtained sheet was measured according to JIS-K7105. The results are shown in Table 1.

Comparative Example A sheet having a thickness of 300 μm was prepared in the same manner as in Example 1 except that rolling with a roll was not performed, and the same evaluation as in Example 1 was performed.

[Table 1] From the above results, it is understood that by rolling in the rolling ratio range of 1.1 to 1.4, the transparency can be significantly improved without impairing the formability.

(Examples 5 to 8) The same unstretched sheet as in Example 1 was rolled at a rolling ratio of 1.3 with the temperature of the rolling roll changed as shown in Table 2 to prepare a sheet of 300 μm. The same evaluation as in Example 1 was performed. The results are shown in Table 2.

[Table 2]

From these results, it is understood that the surface temperature of the roll to be rolled is preferably in the range of 100 to 120 ° C.

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Claims (1)

[Claims] 1. A surface temperature of 100 to 120 ° C. after melt-extruding polypropylene into a sheet on a cooling surface and cooling.
A method for producing a polypropylene sheet having good transparency, which comprises rolling between the rolls at a rolling ratio of 1.1 to 1.4.