JPS6227100B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polypropylene composition, particularly a polypropylene composition for use in films with excellent transparency and anti-blocking properties. Although polypropylene film has excellent transparency, it has the disadvantage that blocking occurs easily between the films. For the purpose of improving blocking properties, small amounts of inorganic fine particles such as element dioxide, talc, calcium carbonate, magnesium oxide, and kaolin are mixed with polypropylene. On the other hand, with the development of highly active catalysts, methods for polymerizing polypropylene with a low content of atactic polypropylene have been developed, for example, in JP-A-47-34478 and JP-A-49-49.
It has been proposed in No. 59094, No. 50-126590, No. 50-123182, etc. The polypropylene obtained by these methods has a granular form, unlike the conventional powder form. When a stretched film is produced from a mixture of granular polypropylene, silicon dioxide, and other additives, either as it is or once made into pellets, the blocking resistance of the resulting film is improved, but the transparency is poor. Getting worse. That is, when an object is viewed through such a film, it appears blurred due to distortion. In particular, in the case of a film using a mixture, the deterioration in transparency is more remarkable. Although the cause of this is not clear, it is thought to be caused by poor dispersion of silicon dioxide into granular polypropylene. When other anti-blocking agents such as talc and kaolin are used, excellent transparency can be obtained without deterioration of transparency, but if the film is operated for several days in a row, streaks will appear in the longitudinal direction of the film. Another drawback arises in that the number of streaks increases with the passage of operating time. As a result of various studies on these points, the present inventors have found that a polypropylene composition in which inorganic fine powder selected from talc, kaolin, etc. and silicon dioxide are blended in a specific ratio as an anti-blocking agent to granular polypropylene, The present inventors have discovered that it is possible to obtain a film with good transparency without deterioration of transparency and without streaks, and have come to provide the present invention. In the present invention, 0.1 to 1.0 parts by weight of at least one type of inorganic fine powder having a layered structure such as talc, kaolin, pyrophyllite, and sericite and 0.01 to 0.5 parts by weight of silicon dioxide are added to 100 parts by weight of granular polypropylene. , inorganic fine powder/silicon dioxide 1 to 50 (weight ratio)
This is a polypropylene composition formed by blending in the following range. In the present invention, polypropylene includes a homopolymer of propylene, a random copolymer of propylene and other olefins, a block copolymer of propylene and other olefins, and a blend of polypropylene with a small amount of these copolymers. , a general term for blends of polypropylene and small amounts of other polyolefins. The granular polypropylene used in the present invention is
It does not contain more than 1% by weight of particles of 100μ or less, preferably does not contain less than 5% by weight of particles of 200μ or less, and generally has an average particle size of 1000μ or less, especially
Polypropylene with a diameter of 300 to 1000 μ and an apparent specific gravity of 0.5 g/ml or more. Note that the average particle diameter was measured by a sieve method and expressed as a weight average. Various methods for producing the granular polypropylene of the present invention are known, such as JP-A-47-34478 and JP-A-49
-59094, No. 50-126590, No. 50-123182, etc., highly active catalysts, such as particle diameters of 10 to 50
When using titanium trichloride having a specific surface area in μ of 80 m ² /g or more, polypropylene with a relatively sharp particle size distribution can be obtained. The granular polypropylene to which the present invention can be particularly effectively applied has a particle size distribution according to the Rosin-Rammlar equation, that is, R(Dp)=100exp{-(Dp/Dl) ⁿ } (However, Dp indicates the diameter (μ) of the polypropylene particles, and R (Dp) is the cumulative weight percent remaining on the sieve, that is, Dp
The percentage by weight of larger particles is indicated, Dl is the particle size characteristic number and is expressed as the particle diameter when R(Dp)=36.8% by weight, and n is a uniform number. ), 100≦Dp≦1200, 0≦R(Dp)≦100, 100≦
This is a case in which Dl≦800 and n≧2.5, and 1% by weight or more of particles of 100μ or less and 1% by weight or more of particles of 1200μ or more are not contained. In the present invention, the inorganic fine powders used as antiblocking agents are all natural substances having a layered crystal structure. Examples include inorganic fine powders such as talc, kaolin, pyrofluorite, and sericite. That is, talc is 3MgO・4SiO ₂・H ₂ O
It is a mineral with a layered structure shown by the structural formula, and its theoretical weight composition is SiO ₂ 63.5%, MgO 31.7%,
H ₂ O 4.8%, the pure one is white,
Depending on the amount of impurities, it appears pale blue, pale green, or brown. Pyrofluorite also has a layered structure similar to the above-mentioned talc, and its structural formula is Al ₂ O ₄ · SiO ₂ · H ₂ O, and the theoretical weight composition is SiO ₂ 66.7%, Al ₂ O ₃ 28.3
%, H ₂ O 5.0%. Kaolin also includes minerals such as kaolinite, dateskite, and halloysite, of which kaolinite is the most representative. These structural formulas are Al ₂ O ₃・2SiO ₂・
2H ₂ O, the theoretical weight composition is Al ₂ O ₃ 39.5
%, SiO ₂ 46.5%, H ₂ O 14%. Furthermore, sericite is a crystal with a flat plate-like layered structure, and is also called sericite, and its structural formula is K ₂ O.3Al ₂ O _{3.6SiO 2.2H 2} O. In addition, the other antiblocking agent component 2
As silicon oxide, it is possible to use either one produced by a dry method, such as the product name "Aerosil 200" (manufactured by Nippon Aerosil Co., Ltd.), or one produced by a wet method, such as white carbon or silica gel. In particular, the average particle diameter is 0.5 to 15μ (measured by Coulter counter method and expressed as weight average diameter).
Preferably, it is within this range. The amount of the above-mentioned antiblocking agent added to granular polypropylene is such that at least one inorganic fine powder selected from the group consisting of talc, kaolin, pyrofluorite, and sericite is added to 100 parts by weight of granular polypropylene. The amount of silicon dioxide is 0.1 to 1.0 parts by weight, and the amount of silicon dioxide is 0.01 to 0.5 parts by weight. If it is outside these ranges, problems such as poor transparency of the film and streaks will occur. Furthermore, although the mixing ratio of the inorganic filler to silicic acid dioxide in the present invention is not particularly limited, it is generally preferable to use the inorganic filler/silicon dioxide weight ratio in the range of 1 to 50 for excellent transparency. This is preferred because a film can be obtained. In the present invention, it is not clear why a combination of inorganic fine powder such as talc, kaolin, pyrofluorite, and sericite with silicon dioxide results in a transparent film without a decrease in transparency and without streaks. The present inventors believe as follows. In other words, the streaks that occur when inorganic fine powder such as talc is used alone are caused by solid matter such as additive particles, decomposed additive solids, and degraded polymers remaining in the lip of the T-die, which causes scratches on the film. It is expected that the solids will form streaks, and by using silicon dioxide in combination, the solids will not stay in the lip of the die and will always remain solid.
There are no streaks because it is washed away by silicon oxide,
Furthermore, since the amount of silicon dioxide added is small, it is thought that a transparent film without deterioration in transparency can be obtained. The method for producing a stretched film using the composition of the present invention is not particularly limited, and a composition in which 100 parts by weight of the above-mentioned granular polypropylene is blended with a predetermined amount of inorganic fine powder such as talc and silicon dioxide is T-die extruded. A uniaxially or biaxially (sequentially or simultaneously stretched) stretched film may be obtained using a machine.
The composition used in the present invention may contain heat stabilizers, antistatic agents, weather stabilizers, lubricants, nucleating agents, pigments, flame retardants, etc., in amounts commonly used. The present invention will be described below with reference to Examples, but the present invention is not limited thereto. In the Examples, the properties of the films were evaluated using the following evaluation method. Transparency It is expressed as the number of legible films when the films are stacked 100 mm apart from the printed type (6 points) and the type is observed with the naked eye through the film. Formation of streaks ×... Streaks appear within 2 days of continuous operation 0... Streaks appear after 3 to 5 days of continuous operation ◎... Haze level at which streaks do not appear after 5 days or more of continuous operation ASTM-D- 1003-59T. Further, the granular polypropylene used in the examples is shown in the following table.

[Table] Examples 1 to 10, Comparative Examples 1 to 3 With the composition shown in Table 1, granular polypropylene, silica, inorganic fine powder, and 2,6-di-t-butyl para-cresol as an antioxidant were added. 0.2% by weight, 0.1% by weight of "Irganox 1010" (trade name of Geigy), and 0.1% by weight of calcium stearate were mixed uniformly with a super mixer, and then pelletized with a pelletizer to obtain pellets of a polypropylene composition. Each of the above pellets was formed into a sheet with a thickness of 1 mm using a T-die method biaxial stretching machine at a resin temperature of 280°C, and this sheet was stretched 5 times in the longitudinal direction at 140°C, and then using a transverse stretching machine. , 8 horizontally at 160℃
A film with a thickness of 25 μm was obtained by stretching the film twice. The obtained film was subjected to corona discharge treatment so that the wetting index was 40 dyne/cm. The film made of each polypropylene composition was examined for transparency and the presence or absence of streaks.
It was measured. The results are shown in Table 1, Examples.

【table】

Claims (1)

[Scope of Claims] 1. 100 parts by weight of granular polypropylene, 0.1 to 1.0 parts by weight of inorganic fine powder having a layered structure, and an average particle size.
A polypropylene composition comprising 0.01 to 0.5 parts by weight of silicon dioxide having a particle size of 0.5 to 15μ, in an inorganic fine powder/silicon dioxide ratio of 1 to 50 (weight ratio). 2. The polypropylene composition according to claim 1, wherein the inorganic fine powder having a layered structure is at least one selected from the group consisting of talc, kaolin, pyrophyllite, and sericite. 3. Granular polypropylene has the general formula R(Dp)=100exp{-(Dp/Dl) ⁿ } (where, Dp represents the diameter (μ) of the polypropylene particles, and R(Dp) represents the cumulative weight percent remaining on the sieve, i.e. Dp
The percentage by weight of larger particles is indicated, Dl is the particle size characteristic number and is expressed as the particle diameter when R(Dp)=36.8% by weight, and n is a uniform number. ), 100≦Dp≦1200, 0≦R(Dp)≦100, 100≦
2. The composition according to claim 1, wherein the composition satisfies Dl≦800 and n≧2.5 and does not contain 1% by weight or more of particles with a size of 100μ or less and 1% by weight or more with particles of 1200μ or more. 4. The composition according to claim 1, wherein the inorganic fine powder has an average particle diameter of 0.5 to 15μ. 5. The composition according to claim 1, which is used for a film having excellent transparency and blocking resistance.