JPS58101136A - Preparation of polypropylene sheet having improved transparency - Google Patents

Abstract

PURPOSE:To prepare a sheet having improved transparency, by blending a polypropylene resin having a low MFI with dibenzylidene sorbitol or its nucleus- substituted derivative as a transparent nucleating agent, extruding the blend from the tip of a die at a specific temperature. CONSTITUTION:Polypropylene resin having a melt flow index of 0.1-1.5g/10min is blended with dibenzylidene sorbitol or its nucelus-substituted derivative as a transparent nuclating agent, and extruded from the tip of a die regulated at 260-350 deg.C, preferably 270-320 deg.C, to form a sheet. The amount of the transparent nucleating agent is 0.05-0.5wt% based on the resin. The rise in MFI of the prepared sheet is a little, blow molding and vacuum molding are carried out smoothly, useful as a container material such as tray, cup, etc. requiring the transparency of substances put in the container.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a sheet with excellent transparency using polypropylene 41 resin having a low melt flow index (hereinafter abbreviated as MFI).

More specifically, when extruding a polypropylene resin with a low MFI containing a transparent nucleating agent to form a sheet, a specific transparent nucleating agent is used and the temperature at the tip of the die is set to a high temperature range outside the normal temperature range. The present invention relates to a method for producing a polypropylene sheet with excellent transparency.

Polyvinyl chloride, polystyrene, polypropylene, polyethylene, A as plastic materials for sheet processed products
Many materials such as BS are used, but among these, polypropylene is superior in terms of heat resistance, oil resistance, water vapor permeability, food hygiene, etc., and is used in the field of packaging containers such as various trays and cups. It has been rapidly used in recent years.

Pressure forming and vacuum forming are generally used as methods for forming containers from sheets, but polypropylene sheets have the disadvantage that they tend to sag when heated, resulting in an MFI of 0. Its use is limited to low speeds of 1 to 1.5 f/10 min. Furthermore, since the transparency of polypropylene resin when used as a container is inferior to that of polyvinyl chloride and polystyrene, various attempts have been made to improve the transparency of polypropylene sheets.

When the MIFI is high, for example, 2f710 min or more, a sheet with good transparency can be obtained by adding 0.05 to 0.5 g of a transparent nucleating agent to polypropylene and extruding the sheet by a conventional method. However, the MFI used in pressure forming and vacuum forming is 0.1 to 1.5.
At present, sheets made from polypropylene which is heated at f/10 minutes cannot be sufficiently improved in transparency using this method.

Therefore, the inventors of the present invention conducted intensive studies with the aim of producing a sheet with excellent transparency using polypropylene with a low MFI. As a result, the following method was used to produce a polypropylene sheet with excellent transparency and suitable for air pressure forming and vacuum forming. The present invention was achieved by discovering that the following can be obtained.

That is, the present invention contains a transparent nucleating agent and has an MFI of 0.1 to 1.5.
f/10 minutes to form a sheet by extruding a polypropylene resin containing dibenzylidene sorbitol or its nuclear substituted derivative as a transparent nucleating agent, and extruding from a die tip controlled at 260 to 350°C. This is a method for manufacturing a polypropylene sheet with improved transparency, which involves sheet molding.

In the present invention, dibenzylidene sorbitol and its nuclear substituted derivatives are particularly used, and lower alkyl substituted derivatives of ~5 are commonly used. The amount added is preferably in the range of 0.05 to 05% by weight based on the polypropylene resin. If the amount added is less than the above range, the effect of improving transparency will be small, and if it is more than the above range, it will bleed onto the surface and conversely impair transparency. It is also possible to use other nucleating agents, such as benzoic acid, benzoic acid, and sebacic acid.

The addition of dibenzylidene sorbitol or its nuclear substituted derivative is carried out by a known method, and is usually mixed with the polypropylene polymer powder and other additives in a high-speed rotating mixer such as a Henschel mixer.

The polypropylene resin used in the present invention includes homopolymers of propylene and random copolymers with other α-olefins, such as ethylene, MF
I, 0.1 to 1.5 f/10 minutes is used.

Particularly in the case of propylene homopolymers, the effect of improving transparency is remarkable.

The polypropylene resin may be pre-added with an antioxidant, an ultraviolet absorber, an antistatic agent, and a small amount of polyethylene, ethylene-propylene copolymer, or the like. Measurement of MFI is performed according to the method described in ASTM-D1238-65T.

In the method of the present invention, the temperature at the die tip of the extruder is
The temperature is controlled at 60 to 350°C, preferably 270 to 520°C, and molded into a sheet. On the other hand, in the extrusion molding of ordinary polypropylene sheets, the die temperature is 20
If the die temperature is 260°C or higher, the MPI of polypropylene will increase sharply, and the resulting sheet will sag significantly when heated.
It is unsuitable for pressure forming and vacuum forming, and odor is generated due to thermal decomposition, making it unsuitable for use as packaging containers.

In the method of the present invention, if the temperature at the tip of the die is 260° C. or lower, a polypropylene sheet with improved transparency cannot be obtained even if a large amount of transparent nucleating agent is added.

The method of heating the tip of the die in the method of the present invention is as follows:
Although there are no particular limitations, for example, as shown in Figure 1, this can be achieved by placing a plate-shaped heater approximately 40 mm wide on the lip of the tip of the die at both the upper and lower ends, and adjusting the temperature using a dynamic resistor, for example. At this time, the temperature of the extrusion cylinder and the temperature of other equipment parts except the die tip are controlled in the same way as in normal extrusion molding.

In the method of the present invention, only the tip of the die is heated to 260 to 650°C.
The MFI of the sheet obtained by the present invention increases only slightly, making it suitable for pressure forming, vacuum forming, etc., and its transparency is significantly improved, making it easier to see the contents. A sheet is obtained that is suitable as a material for containers such as tray cups that require transparency.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Dibenzylidene sorbitol with methyl group substituted with 02
Polypropylene homopolymer containing MFI 0.3 f/10 minutes was extruded using an extruder with a screw diameter of 65 at an extrusion rate of 40 Kg/hr and a cylinder temperature of 2.
Sheet molding was carried out under conditions of 30°C, die temperature of 240°C, and die tip of 610°C. The die is a manifold type with a width of 700mm, and a width of 4'O at the tip, and a length of 70mm.
A plate-shaped heater of 0.800 W was used, which was set on both the upper and lower sides and had a structure in which the temperature at the tip could be controlled. The thickness of the obtained sheet was 0.5 mm, and the transparency, MFI measurements, and vacuum forming suitability tests were conducted as follows.

The transparency of the sheet was measured by holding a universal visual acuity chart 5 cWL away from the sheet and expressing the visual acuity value corresponding to clearly visible letters. In this case, the higher the value, the better the transparency. Vacuum forming suitability: vertical 100mm, horizontal 200mm
I vacuum-formed a tray with a depth of 40 mm and judged the presence or absence of sheet sag and uneven thickness of the molded product. The results are shown in Table-1.

In this example, a sheet with good transparency and good suitability for vacuum forming was obtained.

Example 2 Dibenzylidene sorbitol was extruded under conditions where the ethyl base was placed at a die tip temperature of 270°C to obtain a sheet with a wall thickness of 0.5°C. The sheet was evaluated in the same manner as in Example 1,
The results are shown in Table 1.

Example 6 M containing 0.5% by weight of dibenzylidene sorbitol
A propylene-ethylene random copolymer (ethylene content 6.0%) with a FI of 0.5 f/1o was produced using the same extruder as in Example 1, with a cylinder temperature of 260°C and a die temperature of 240°C.
A sheet with a wall thickness of 0.5 mm was obtained by extrusion at a die tip temperature of 540° C. The sheet was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 1 Using the same homopolymer as in Example 1, the tip of the die was
Extrusion molding was carried out in the same manner as in Example 1 except that the temperature was controlled at 0° C. to obtain a sheet having a wall thickness of 0.5 mm. Transparency was poor. Table 1 shows the evaluation results of the sheet.

Comparative Example 2 Using the same propylene resin as used in Example 2,
A sheet with a wall thickness of 0.5 cm was obtained by extrusion molding in the same manner as in Example 2 except that the temperature at the die tip was 380°C. Although the transparency was good, the sheet had a burnt odor, caused sagging during vacuum forming, and only molded products with uneven thickness were obtained.

Comparative Example 3 Extrusion was carried out in the same manner as in Example 1, except that the same homopolymer as in Example 1 was used and the temperature of the die body and tip was 310°C. However, the obtained sheet had a large uneven thickness. , it produced a burnt odor and had no commercial value.

Table 1

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a method of heating the tip of an extruder die suitable for carrying out the method of the present invention. In the diagram: 1, die tip heater 2, lip adjustment bolt 3 dieland bird 11r), 1 Yujin 341 + Gokako Sho also Goen 1st figure

Claims (1)

[Claims] Contains a transparent nucleating agent and has a melt flow index of 01 to 1.
When extruding a polypropylene resin at 5 f/10 minutes to form a sheet, the polypropylene resin contains dibenzylidene sorbitol or its nuclear substituted derivative as a transparent nucleating agent, and is extruded from the tip of a die controlled at 260 to 550°C. A method for producing a polypropylene diagonal tonneau with improved transparency, characterized by sheet molding.