JPS6347740B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyolefin composition for biaxially oriented films. More specifically, the present invention relates to a biaxially oriented film composition comprising hydrotalcite and polyolefin having a specific particle size distribution. Polyolefin produced using a Ziegler type catalyst contains halogen compounds caused by the catalyst used, and if polyolefin containing a large amount of halogen compounds is molded as is, hydrogen halide will be generated during molding, causing rust in the molding machine. cause To prevent this, conventionally a method of removing the catalyst by washing with water or methanol, etc., and a method of adding a rust inhibitor have been used in combination. However, in recent years, highly active catalysts have been developed, and since the content of transition metal components in polyolefins is at a relatively low level, attempts have been made to omit the catalyst removal step. Conventionally, fatty acid metal salts such as calcium stearate have been frequently used as rust inhibitors for polyolefins. However, fatty acid metal salts have a small rust-preventing effect and need to be added in large quantities to polyolefins with a relatively high halogen content, which impairs the transparency and strength of the polyolefins.
On the other hand, a technique for preventing rust by blending a basic compound of an alkaline earth metal, alumina, aluminum hydroxide, etc. with polyolefin is known, and a method of blending hydrotalcite is also known. However, when we produced a biaxially stretched polyolefin film containing the above-mentioned basic inorganic metal compound, the film appeared to sparkle due to the large number of pores created by the peeling of the interface between the metal compound and polyolefin during film stretching. It turned out that there were problems with industrialization. The inventors of the present invention have made extensive studies on this problem, and have found that it is sufficient to use a metal compound powder having a specific particle size distribution, and have arrived at the present invention. That is, in the present invention, 20 μ
0.5% by weight or less of particles having a particle size of
and 0.005 to 2.0% of hydrotalcite with a particle size of 16μ or more is 2.0% by weight or less.
This is a polyolefin composition for biaxially oriented films containing 0.5% by weight. The polyolefins applied to the present invention are obtained by Ziegler type polymerization, and include polyethylene, polypropylene, poly-1-butene,
These include poly-4-methyl-1-pentene, ethylene-propylene copolymer, and ethylene-1-butene copolymer. Among these, titanium compounds supported on carriers containing magnesium and organometallic compounds of metals from Groups 1 to 3 of the periodic table are particularly effective for polyolefins with good transparency and mechanical properties. A remarkable effect can be obtained on polypropylene produced without a catalyst removal step by using a highly active catalyst consisting of. Next, hydrotalcite as used in the present invention is a hydrous basic carbonate of magnesium and aluminum, and the natural mineral is said to have a structure of Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O. In synthetic products, Mg/Al
with different ratios, e.g. Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .
3H ₂ O, Mg ₅ Al ₂ (OH) ₁₄ CO ₃・4H ₂ O, Mg ₁₀ Al ₂
(OH) ₂₂ (CO ₃ ) ₂・4H ₂ O, Mg ₈ Al ₂ (OH) ₂₀ CO ₃・
Examples include those having a structure such as 5H ₂ O.
Among these, Mg ₄ Al ₂ (OH) ₁₂ CO ₃・3H ₂ O
It is preferable that the structure is because the primary particles are large and easily become fine powder. The hydrotalcite used in the present invention has a particle size of 20μ or more in an amount of 0.5% by weight or less, and a particle size of 16μ or more in an amount of 2.0% by weight or less.
% by weight or less, and if the particle size is outside this range, many coarse pores will occur in the film when biaxially stretched, impairing the appearance. The amount of hydrotalcite to polyolefin is 0.005% to 0.5% by weight, preferably
The amount is in the range of 0.005% to 0.2% by weight, and if it is less than the above range, the rust prevention effect will be insufficient, and if it exceeds 0.5% by weight, the appearance of the film will be impaired. The composition of the present invention may contain antioxidants, ultraviolet absorbers, heat stabilizers, antistatic agents, lubricants, slip agents, tackifiers, antifogging agents, antiblocking agents, and the like. Next, examples will be shown. In the examples, the particle size distribution of hydrotalcite and the distribution of pores in the film were measured by the following method. (1) Particle size distribution 100 mg of the sample powder was placed in a mixture of 10 ml of 1% saline and 10 ml of methanol, stirred for 2 minutes using ultrasonic waves, and the resulting suspension was measured using a Coulter counter equipped with a 50 μm diameter column. (2) Distribution of pores in the film After cutting a test piece from any part of the film, immersing it in Canada balsam and fixing it with a slide glass, taking a 50x microphotograph.
The length and number of pores in the film were measured, and the distribution of pores per 4 cm ² of the film was determined. Examples 1 to 5, Comparative Examples 1 to 3 Using a highly active catalyst containing a titanium compound supported on magnesium chloride as one component, the powder shown in Table 1 was added to polypropylene obtained without performing a catalyst removal step. 0.1% by weight of synthetic hydrotalcite (Mg ₄ Al ₂ (OH) ₁₂ CO ₃・3H ₂ O) with a degree distribution and Irganox 1010 (manufactured by Ciba Geigy) and 2,6-di-tert-butyl as antioxidants. -4-
Methylphenol was added in an amount of 0.1% by weight and pelletized at 250°C using an extruder. Next, the pellets were melted at 270°C with an extruder, extruded through a coat hanger type die, cooled once with a chill roll, stretched 5 times in the longitudinal direction with a stretching roll at 130°C, and then stretched horizontally with a tenter at 155°C. A biaxially stretched polypropylene film having a thickness of 35 μm was obtained by stretching the film 7 times in the transverse direction using a stretching machine. The pore distribution and appearance of these films are shown in Table 2.

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Claims (1)

[Claims] 1. 0.005 to 0.5% of hydrotalcite having a particle size of 20μ or more is 0.5% by weight or less, and 2.0% by weight or less of a particle size of 16μ or more, based on the polyolefin. % by weight of a polyolefin composition for biaxially oriented film. 2. The composition according to claim 1, wherein the polyolefin is polypropylene. 3 Hydrotalcite is Mg ₄ Al ₂ (OH) ₁₂ CO ₃・
The composition according to claim 1, which has a structure of 3H ₂ O. 4. The composition according to claim 1 or 2, wherein the polyolefin is a polyolefin produced without a catalyst removal step.