JP2737786B2 - Method for producing highly transparent stretched polypropylene film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a highly transparent stretched polypropylene film. More specifically, the present invention relates to a method for producing a highly transparent stretched polypropylene film formed by stretching a sheet having specific characteristics.

[Conventional technology]

Polypropylene is a polymer having relatively excellent transparency, but is a crystalline polymer, and can have various degrees of transparency depending on molding conditions. Method of controlling crystallinity or spherulite size by copolymerizing with other olefins such as ethylene for the purpose of further improving transparency, or method of reducing spherulite by adding nucleating agent, molded product There are known methods for increasing the cooling rate of spherulites to reduce spherulites. These methods have a certain effect, and a method of controlling the size of spherulite is particularly useful.

[Problems to be solved by the invention]

It is useful to control the size of spherulites, but in the case of stretched films, even if the transparency of the original sheet is equally good, there is a difference in transparency when stretched. The film may be extremely opaque.

An object of the present invention is to provide a method for producing a highly transparent stretched polypropylene film that has solved the above-mentioned problems.

[Means for solving the problem]

The present inventors have conducted a rigorous analysis on the conventional film having a difference in transparency, and found that the obtained stretched film has almost no difference in the X-ray diffraction spectrum, and also has a difference in the size of the spherulite. Even without the film, the transparency may be largely different, and it has been found that the cause is that the surface smoothness of the stretched film is largely different.

The present inventors have conducted intensive studies based on this finding,
The present inventors have found that stretching a sheet satisfying specific conditions can provide a stretched film excellent in transparency, which was not conventionally known, and completed the present invention.

That is, in the present invention, a high-crystalline polypropylene resin composition comprising a homopolymer of propylene or a copolymer with a small amount of another α-olefin and containing polyallyltrimethylsilane was extruded and taken out from a die. The ratio of the intensity of the diffraction line attributed to the β-crystal to the total sum of the intensity of the diffraction line attributed to the α- and β-crystals obtained by measuring the X-ray diffraction spectrum on at least the surface thereof is 0.02 or less. This is a method for producing a highly transparent stretched polypropylene film, comprising stretching a sheet obtained by cooling the film.

Hereinafter, the method for producing a film of the present invention will be described in detail. The method for producing a stretched film of the present invention is characterized by the properties of the sheet at the preceding stage, and the intensity of the diffraction lines attributed to α- and β-crystals obtained by measuring the sheet at least on its surface with an X-ray diffraction spectrum. It is necessary that the ratio of the intensity of the diffraction line attributed to the β crystal to the sum of The smaller the ratio of the intensity of the diffraction line attributed to the β crystal (hereinafter, simply referred to as the ratio of the β crystal), the better, preferably 0.

There are various methods for producing such a sheet, and a large amount of polyallyltrimethylsilane must be added. The relatively rapid cooling of the sheet extruded from the die when forming the sheet. Stretch from the thinnest sheet possible. By combining these conditions, it is possible to reduce the ratio of β crystals to 0.02 or less. The requirements vary depending on the polypropylene used, but in the laboratory, it is also possible to add an additive for increasing the crystallization temperature and rapidly cool the sheet to make the ratio of β crystals substantially zero. However, industrially, it can be attained by using polypropylene to which polyallyltrimethylsilane is added, and by molding under conditions that allow relatively rapid cooling of the sheet.

The polypropylene used in the present invention is not particularly limited as long as it is highly crystalline. Not only a propylene homopolymer but also a statistical copolymer with ethylene, butene, hexene, etc. can be used. 0.
Those containing other olefins of about 1 mole ratio or less can be used. The melt flow rate measured at 230 ° C. and preferably having a molecular weight of about 0.1 to 10 can be used.

In the present invention, the ratio of β crystals was measured using a K-Cu line according to the following definition. For example, a wide-angle X-ray diffraction spectrum of the sheet surface of Comparative Example 1 will be described with reference to FIG.
The value of 2θ in the wide-angle X-ray diffraction spectrum is about 13.8 ° C., 16.6 ° C.
The peaks at 18.3 ° C. and 18.3 ° C. are defined as α crystals, and the intensity is represented by the peak height. Similarly, a peak of about 15.8 other than 2θ is defined as a β crystal, and the intensity is similarly represented by the peak height. (TURNER JORES et al. Makromol. Chemie vol. 75, 134
According to (1964). ).

〔Example〕

 Hereinafter, the present invention will be further described with reference to Examples.

Example 1 A vibration mill equipped with two crushing pots having an inner volume of 0.97 and containing 2.2 kg of steel balls having a diameter of 12 mm was prepared. , Α-trichlorotoluene (3 ml) was added, and the mixture was ground for 40 hours. 15g of the co-ground product thus obtained
Was placed in a 200 ml flask, 80 ml of titanium tetrachloride and 80 ml of toluene were added, and the mixture was stirred at 100 ° C. for 30 minutes. Thereafter, the supernatant was removed, 80 ml of titanium tetrachloride and 80 ml of toluene were added in the same manner, and the mixture was stirred at 100 ° C. for 30 minutes, and the solid obtained by removing the supernatant was repeatedly washed with n-hexane to prepare a transition metal. A catalyst slurry was obtained. When a part was sampled and the titanium content was analyzed, it was 1.9 wt%.

In a flask with an inner volume of 200 ml, toluene 40 m under a nitrogen atmosphere
l, 10.0 g of the above-mentioned transition metal catalyst, 24.0 ml of diethylaluminum chloride, 14 ml of methyl p-toluate and 20 ml of triethylaluminum were added and mixed.
After placing the autoclave in a 300 g autoclave and replacing the gas phase with propylene, 20 N of hydrogen was added, then propylene was added, and propylene was added to a pressure of 5 kg / cm ² gauge. The polymerization was continued until the amount of the mixture reached 50 kg. Then, unreacted propylene was purged, methanol 20 was added, the mixture was stirred at 90 ° C., and the obtained slurry was purified by washing with water. The slurry was filtered, the powder was separated and dried at 80 ° C., 60 mmHg for 12 hours.

Analysis of the obtained powder showed a boiling n-heptane extraction residual ratio of 97.7% and an intrinsic viscosity of 1.72 (hereinafter abbreviated as η) measured with a tetralin solution at 135 ° C.

On the other hand, a master powder containing a polymer of allyltrimethylsilane was produced using the above transition metal catalyst.
In a 300 ml flask, 5 g of a transition metal catalyst, 5 ml of diethylaluminum chloride and 10 ml of allyltrimethylsilane,
The slurry was added to 10 ml of toluene and stirred at 60 ° C. for 2 hours. Then, the slurry was placed in an autoclave having an internal volume of 3, and then heptane 1, methyl p-toluate (0.6 ml) and trimethylaluminum (5 ml) were added. The pressure was adjusted to 5 kg / cm ² gauge, and then the polymerization was carried out at an internal temperature of 60 ° C. at a constant pressure until the charged amount of propylene became 500 g. By treating in the same manner as in the above method, a polymer of allyltolumethylsilane is obtained.
A master powder containing 12000 ppm was obtained.

Next, the known antioxidant, the above copolymer and master powder were mixed by an extruder to obtain a composition containing 10 ppm of a polymer of allyltrimethylsilane. 40 m of this composition
The sheet was formed into a sheet having a thickness of 550 μm using an extruder having an mΦ at an extrusion temperature of 250 ° C. and a sheet cooling temperature of 80 ° C. Next, 5 × at 155 ° C. using a biaxial stretching machine manufactured by TM Long.
The film was stretched 7 times to obtain a stretched film. The ratio of β crystal in this sheet and the physical properties of the film are shown in the table. In the table, transparency is indicated by haze and visual evaluation results.

 Haze Compliant with ASTM D1003.

Comparative Row 1 The procedure was the same as in Example 1 except that the sheet thickness was 1300 μm. The evaluation results are shown in the table.

Comparative Example 2 The procedure of Example 1 was repeated, except that the propylene homopolymer obtained in Example 1 was used and only an antioxidant was added. The results are shown in the table.

Example 2 Same as Example 1 except that the sheet cooling temperature (chill roll surface temperature) was 20 ° C. and the sheet thickness was 1300 μm. The results are shown in the table.

Comparative Example 3 Using the homopolymer of propylene obtained in Example 1, instead of polyallyltrimethylsilane, 12
0.1 part by weight of 4-di (ethylbenzylidene) sorbitol is added to 100 parts by weight of polypropylene, the sheet cooling temperature (chill roll surface temperature) is 90 ° C., and the sheet thickness is 1300 μm.
Other than the above, the procedure was the same as in Example 1. The results are shown in the table.

FIG. 1 shows a wide-angle X-ray diffraction spectrum of one surface of the sheet used for producing the stretched sheet of the present invention.
No crystals are observed. For reference, the wide-angle X-ray diffraction spectrum of the surface of the sheet of Comparative Example 1 which is not in contact with the roll is shown in FIG. 2, but considerable β crystals are observed.

[Effects of the Invention] By carrying out the method of the present invention, a stretched film which is extremely excellent in transparency and can be used for various applications can be obtained, and is extremely industrially valuable.

[Brief description of the drawings]

FIG. 1 shows a wide-angle X-ray diffraction spectrum of one surface of a sheet used for producing a stretched sheet of the present invention, and FIG. 2 shows a wide-angle of a surface of a sheet of Comparative Example 1 which is not in contact with a roll. 3 shows an X-ray diffraction spectrum.

 ──────────────────────────────────────────────────の Continuing from the front page Judge of the colleague Jinro Ono Judge Yumiko Niki Judge Minoru Kina (56) References JP-A-58-87024 (JP, A) JP-A-59-198122 (JP, A)

Claims (1)

(57) [Claims] 1. A sheet obtained by extruding a highly crystalline polypropylene resin composition comprising a homopolymer of propylene or a copolymer with a small amount of another α-olefin and containing polyallyltrimethylsilane, and taking out from a die. The ratio of the intensity of the diffraction line attributed to the β-crystal to the total sum of the intensity of the diffraction line attributed to the α- and β-crystals obtained by measuring at least the surface with an X-ray diffraction spectrum is 0.02 or less. A method for producing a stretched highly transparent polypropylene film, comprising stretching a sheet obtained by cooling as described above.