JPH0356170B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polypropylene stretched film with excellent rigidity. Polypropylene stretched film, especially biaxially stretched film, has excellent optical properties such as transparency and gloss, and relatively good mechanical properties such as tensile strength and rigidity, making it suitable for a wide range of applications such as food packaging and textile packaging. It is used. However, depending on the application, these properties are not fully satisfied, and in particular, the film is inferior to cellophane, polyester stretched film, etc. in terms of film rigidity, so the field of use is greatly restricted. . For this reason, various studies have been made to improve the rigidity of stretched polypropylene films, but no method has been found that satisfies both stretchability and film rigidity. For example, attempts have been made to increase the stretching ratio during stretching, but there is a limit to the improvement in rigidity because membrane tearing tends to occur during stretching, which reduces productivity. In addition, there is a method of using highly crystalline polypropylene as the polypropylene, but there is a limit to the high crystallization of polypropylene that can be applied because film tearing and stretching unevenness occur during stretching, making normal film formation difficult. However, there is a limit to the improvement in rigidity by highly crystalline polypropylene because the rigidity of the stretched film that is attempted to be improved by changing the stretching conditions, such as the stretching ratio, decreases. In view of these circumstances, the present inventors conducted various studies in order to obtain a method for producing a polypropylene stretched film with excellent rigidity and no problem with the above-mentioned stretching processability. It has been discovered that a stretched film with excellent rigidity can be obtained without deteriorating the stretching processability by stretching using a blend formed by adding the above-mentioned compounds, and the present invention has been achieved based on this discovery. That is, the general formula RCONH (CH ₂ ) nNHCOR (where R is an aliphatic hydrocarbon group having 11 to 21 carbon atoms,
n represents an integer from 1 to 10. This is a method for producing a polypropylene stretched film with excellent rigidity, which comprises stretching in at least one direction a blend obtained by adding 0.5 to 5 parts by weight of a bisamide compound represented by the following formula. The polypropylene used in the present invention is defined by the isotactic pentad fraction of the boiling heptane insoluble portion and the content of the boiling heptane soluble portion, which are determined as follows. After completely dissolving 5 g of polypropylene in 500 ml of boiling xylene, the temperature was lowered to 20°C and left for 4 hours. Thereafter, it is separated into a xylene soluble part and an insoluble part at 20°C. Next, the xylene-insoluble portion at 20° C. is further subjected to Soxhlet extraction with boiling n-heptane for 8 hours to separate it into an extraction residue and an extract. This extraction residue is used as the boiling heptane insoluble part. What is boiling heptane soluble part?20
It is the sum of the xylene soluble portion and the boiled n-heptane extract. The weight percentage of the boiling heptane soluble portion is determined from the weight of the boiling heptane soluble portion and the total weight of the polypropylene subjected to measurement. Isotactic pentad fraction is A.
Macromolecules 6 925 by Zambelli et al.
(1978), i.e. ¹³ C−
It is the isotactic fraction in pentad units in a polypropylene molecular chain measured using NMR. However, regarding peak attribution,
Macromolecules 8 , 687 (1975)
The revised version of Macromolecules 6 , 925 (1973) has been described, so this will be used as the basis. The highly crystalline polypropylene used in the present invention has an isotactic pentad fraction in the boiling heptane insoluble part of 0.955 or more, preferably 0.960 or more, and a content of the boiling heptane soluble part of 9.0% by weight or less, preferably 2.0 to Must be 8.0% by weight. That is, the isotactic pentad fraction of the boiling heptane insoluble portion is less than 0.955, or even if the isotactic pentad fraction of the boiling heptane insoluble portion is 0.955 or more, the content of the boiling heptane soluble portion is 9.0. If the amount of polypropylene exceeds the weight percentage, it is impossible to obtain a stretched film with excellent rigidity, which is the object of the present invention. Such polypropylene used in the present invention is, for example, JP-A No. 53-1989, which is filed by the same applicant as the present application and is known before the filing date of the present application.
It can be obtained by the method described in No. 33289. Examples of the bisamide compound in the present invention include methylene bis stearamide, ethylene bis stearamide, hexamethylene bis stearamide, and the like. If the methylene number n of the bisamide compound exceeds 10, problems will occur in terms of compatibility, smoke generation, and odor, so it cannot be used. The amount of bisamide compound added is 0.5 to 5 parts by weight,
Preferably it is 1.0 to 3.0 parts by weight. Various additives such as antioxidants, lubricants, antistatic agents, antiblocking agents, etc. can be appropriately added to the polypropylene used in the present invention. The stretching process in the present invention can be carried out by a method commonly used in industry, such as roll stretching, tenter stretching, tubular stretching, and the like. When a stretched film is produced using the highly crystalline polypropylene specified in the present invention, a film with significantly higher rigidity can be obtained compared to when ordinary polypropylene is used, but there is a problem in that the stretching processability is reduced. There is. However, surprisingly, by adding the bisamide compound of the present invention, stretching processability can be significantly improved without causing a decrease in film stiffness. The effects of the present invention will be explained below with reference to Examples, but the present invention is not limited to these. The physical properties of the films in the Examples were measured by the following test methods. Young's modulus: A test piece with a width of 20 mm was taken from the longitudinal direction (MD) and the transverse direction (TD), and an S-S curve was taken using a tensile tester at a chuck interval of 60 mm and a tensile speed of 5 mm/min to measure the initial elastic modulus. . Example 1 The melt index was 2.2 g/10 min, and the isotactic pentad fraction of the insoluble part of boiling heptane was
0.967, the content of boiling heptane soluble part is 4.5% by weight
2.0 parts by weight of ethylene bisstearoamide as a bisamide compound is added and mixed to 100 parts by weight of highly crystalline polypropylene, and after pelletizing with a granulator, melt extrusion is performed at a resin temperature of 280°C, and then cooled to 30°C. A sheet with a thickness of 0.8 mm was obtained by rapidly cooling with a roll. The obtained sheet was stretched 4 times in the longitudinal direction at a stretching temperature of 140°C and 10 times in the transverse direction at a stretching temperature of 155°C at a predetermined stretching speed using a tenter-type sequential biaxial stretching device, followed by heat treatment at 140°C. By doing this, a biaxially stretched film with a thickness of about 20 μm was obtained. Comparative Example 1 A biaxially stretched film was prepared in the same manner as in Example 1 without adding a bisamide compound to the highly crystalline polypropylene in Example 1. Comparative example 2 Melt index as polypropylene
2.4 g/10 minutes, using polypropylene with an isotactic pentad fraction of boiling heptane insoluble part of 0.940 and a boiling heptane soluble part content of 7.5% by weight, and the same as Example 1 except that no bisamide compound was added. A biaxially stretched film was prepared by the method described in the following. Table 1 shows the stretchability and film properties in Example 1 and Comparative Examples 1 and 2 above.

[Table] Note (1) ○: Good stretching condition △: Stretching unevenness occurred ×: Film tearing As shown in Table 1, in Example 1 according to the present invention, the stretched film had significantly higher rigidity than Comparative Example 2. It can also be seen that the stretchability is significantly improved compared to Comparative Example 1.

Claims (1)

[Scope of Claims] 1. Based on 100 parts by weight of highly crystalline polypropylene, the isotactic pentad fraction of the boiling heptane insoluble part is 0.955 or more and the content of the boiling heptane soluble part is 9.0% by weight or less, General formula RCONH(CH ₂ ) nNHCOR (where R is an aliphatic hydrocarbon group having 11 to 21 carbon atoms,
n represents an integer from 1 to 10. 1. A method for producing a polypropylene stretched film with excellent rigidity, which comprises stretching in at least one direction a blend obtained by adding 0.5 to 5 parts by weight of a bisamide compound represented by the following formula.