JPH09278908A - Drawing polypropylene film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a drawing polypropylene film, excellent in transparency and external appearance and capable of suitably using as a film for package because it is difficult to be injured when the films are together rubbed. SOLUTION: A drawing film containing 0.01-1wt.% of globular grains with a globularity degree of more than 0.8, which a 50% diameter in the volume integration distribution obtaining by a laser diffranction-scattering method is 0.5-5μm and the S value shown in the equation is 0.1 1, is obtained. However, D10, D50 and D90 respectively indicate 10%, 50% and 90% diameters in the volume integration distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a stretched polypropylene film which is excellent in transparency and appearance and is less likely to be scratched when the films are rubbed together, and can be suitably used as a packaging film.

[0002]

2. Description of the Related Art The smoother the surface of a stretched polypropylene film, the more excellent the transparency and the better the appearance. On the other hand, however, the films tend to come into close contact with each other to cause blocking, and the slipperiness also deteriorates, so that the aptitude for secondary processing such as slitting, printing, and bag making is deteriorated.

In order to solve such a problem, conventionally, a method of adding silica, zeolite or the like to the film to prevent the films from adhering to each other has been taken. (Japanese Patent Publication No. 52-16134 and Japanese Patent Laid-Open No. 62-39219) Recently, improvement of slipperiness has been attempted by using spherical inorganic oxides and organic polymers. (JP-A-7-145250
(Japanese Patent Laid-Open No. 7-26074)

[0004]

As the silica and zeolite, finely pulverized ones and synthetic spheres obtained by the sol-gel method have been used.

However, finely pulverized products tend to aggregate,
Addition of an amount necessary for surface modification causes poor dispersion, resulting in poor transparency and appearance. Further, generally, the effect on improving the slipperiness is small.

On the other hand, when spherical particles are used, the transparency and slidability are generally better than those obtained by fine pulverization. However, since the width of the particle size distribution is wide, the coarse particles contained in the film become a fish eye and deteriorate the appearance, and when the films are rubbed together, the film is easily scratched (hereinafter abbreviated as scratch property), It reduces the product value. Further, the fine particles do not affect the appearance and scratch properties, but do not contribute to the improvement of the blocking property, so that they are useless in the film. Therefore, in order to increase the concentration of spherical particles having an effective particle diameter, it is necessary to increase the total addition amount, which leads to an increase in cost.

An object of the present invention is to provide a stretched polypropylene film having excellent transparency, appearance and scratch resistance.

[0008]

As a result of intensive studies to solve the above problems, the present inventors have found that by adding a specific amount of spherical particles having a specific particle size and particle size distribution, the transparency can be improved. The inventors have found that a stretched polypropylene film having excellent appearance and being hardly scratched when the films are rubbed together is obtained, and the present invention has been completed.

That is, in the present invention, a spherical shape having a 50% diameter in a volume cumulative distribution by a laser diffraction scattering method of 0.5 to 5 μm and an S value represented by the following formula (1) of 0.1 to 1 It is a stretched polypropylene film containing 0.01 to 1% by weight of particles.

[0010]

[Equation 2]

(However, D10, D50, and D90 represent the 10% diameter, 50% diameter, and 90% diameter in the above volume cumulative distribution, respectively.)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The stretched polypropylene film of the present invention has a 50% diameter in a volume cumulative distribution of 0.5 to 5 μm according to a laser diffraction scattering method, and has the following formula (1).
0.01% of spherical particles having an S value of 0.1 to 1
It is characterized by containing ~ 1 wt%.

[0013]

(Equation 3)

(However, D10, D50, and D90 represent the 10% diameter, 50% diameter, and 90% diameter in the above volume cumulative distribution, respectively.) Here, the spherical particles mean the sphericity expressed by the formula (2). Is 0.
8 or more, preferably 0.9 or more.

[0015]

(Equation 4)

With the above-mentioned sphericity, the slipperiness and scratch resistance of the film are extremely good.

The spherical particles used in the present invention have an S value of 0.1 to 1, which is a measure of particle size distribution, and have a specific narrow particle size distribution close to a single particle size. Here, the S value is the 50% diameter in the volume cumulative distribution by the laser diffraction scattering method, 90
It is a value obtained by the formula (1) from the% diameter and the 10% diameter.

Since the particle size distribution is narrow, it is possible to minimize the amount of addition for developing the desired performance. In order to obtain better film performance, the S value is 0.3 to 0.8.
It is preferable to use one selected from the above. If the S value is larger than 1, the proportion of coarse particles increases, so that the scratch resistance and the appearance are deteriorated. Also, if the S value is smaller than 0.1 and is too close to the single particle size, the spherical particles are likely to cause secondary aggregation, and the secondary aggregated particles deteriorate the appearance of the film.

The 50% diameter is 0.5 to 5 μm, preferably 1 to 3 μm. If it is less than 0.5 μm, blocking resistance is insufficient, and if it is more than 5 μm, scratch resistance and appearance are poor.

The addition amount of the spherical particles used in the present invention is 0.0
It is 1 to 1% by weight, preferably 0.03 to 0.5% by weight. If it is less than 0.01% by weight, blocking resistance and slipperiness will be insufficient, and if it is more than 1% by weight, the appearance will be poor.

If the dynamic friction coefficient of the packaging film is in the range of 0.2 to 0.3, the suitability for packaging machines will be good.

As described above, in the present invention, since the spherical particles to be used have a specific narrow particle size distribution close to a single particle size, the addition amount for exhibiting desired performance is the minimum, and the appearance is excellent. A stretched polypropylene film having excellent scratch resistance and scratch resistance is obtained. Since the stretched polypropylene film of the present invention has such characteristics, it can be suitably used as a packaging film.

The spherical particles used in the present invention are not particularly limited, and known particles can be used without any limitation as long as the particle diameter is within the above range. Examples of the spherical particles that can be preferably used include inorganic oxides and organic polymers.

The types of the inorganic oxide and the organic polymer are not particularly limited, but they are generally available, have good dispersibility in polypropylene, and are close to the refractive index of polypropylene and do not impair the transparency of the film. Is preferred. As such an inorganic oxide, in the present invention, silica, silica-alumina, silica-zirconia,
A composite oxide containing silica such as silica-titania as a main component, for example, 50 mol% or more can be preferably used.

In order to impart particularly excellent slipperiness and scratch resistance, it is preferable to use a spherical molten inorganic oxide. The method for producing the spherical molten inorganic oxide is not particularly limited, but in particular, the inorganic oxide synthesized by a known method such as a sol-gel method is heated at a temperature of 2000 to 3000 ° C. to melt the surface and then cooled. The above method is preferable in order to obtain a film having good physical properties.

As the organic polymer, silicone resin particles, silicone rubber particles, polyamide particles, condensed resin particles having a triazine ring, crosslinked polystyrene particles, crosslinked polymethyl acrylate, and crosslinked polymethyl methacrylate particles are preferably used. it can.

In order to impart particularly excellent transparency, it is preferable to use crosslinked polymethylmethacrylate particles having a refractive index extremely close to that of polypropylene. The method for producing the crosslinked polymethylmethacrylate is not particularly limited, but suspension polymerization, emulsion polymerization and the like are preferably used. In addition, in order to control the particle size distribution, classification after polymerization is also used as needed.

As the polypropylene used in the present invention, known polypropylene can be used without limitation. Specific examples thereof include homopolypropylene, a propylene-α-olefin copolymer having an α-olefin content other than propylene of 10 mol% or less, or a mixture thereof. Examples of the above α-olefin include ethylene, 1-butene, and 1
-Pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene and the like can be mentioned. Moreover, you may mix | blend another resin as needed. In that case, considering the transparency and the like, the content of the other resin is preferably 50% by weight or less.

The stretched polypropylene film of the present invention may be a monolayer film or a laminated film laminated with another resin layer capable of being laminated. In particular, a laminated polypropylene film having two or more layers, in which the stretched polypropylene film is laminated on at least one outermost surface layer, is favorably used as a heat seal film or the like.

In this case, the base material layer is homopolypropylene having excellent mechanical performance among the above-mentioned polypropylenes,
Propylene-ethylene copolymers, ethylene-propylene-1-butene copolymers, and blends containing these polypropylenes as the main components are used, and the surface layer has propylene-ethylene excellent in heat sealability among the above polypropylenes. A copolymer, a propylene-1-butene copolymer, etc. can be used.

It is also a preferred embodiment to add another polyolefin to polypropylene which is a material resin for the surface layer. Examples of other polyolefins include polyethylene, ethylene-α-olefin copolymers, and propylene-α-olefin copolymers having an α-olefin content other than propylene of more than 10 mol%.

In the case of a laminated film, the spherical particles are blended in at least the outermost layer on one side. In this case, the content of the spherical particles in the surface layer resin must be within the above range. In addition, the base material layer is also generally uniaxially or biaxially stretched.

The stretched polypropylene film of the present invention is selected to have a thickness of 10 to 70 μm depending on the application. In addition, in the laminated film, when a polyolefin other than polypropylene is added to the surface layer, the transparency of the film is likely to decrease, so the surface layer thickness is 40% or less of the total film thickness, and particularly 30% or less. It is preferable that

The stretched polypropylene film of the present invention comprises
It is uniaxially or biaxially stretched. The production method is not particularly limited, but polypropylene powder or pellets and spherical particles are sufficiently mixed, melt-extruded, and preferably stretched 3 to 7 times in the film flow direction (MD), and further in that direction. It is possible to obtain it by stretching 7 to 12 times in the direction (TD) at right angles to. In the case of a laminated film, polypropylene constituting each layer is coextruded and then stretched by the above method, or the polypropylene of the base material layer is melt extruded and is preferably stretched 3 to 7 times in MD. Then, a method of melt-extruding the polypropylene of the surface layer thereon and stretching it 7 to 12 times in TD is preferably adopted.

[0035]

As described above, the stretched polypropylene film of the present invention is excellent in blocking resistance, transparency and appearance by adding a specific amount of spherical particles having a specific particle size and particle size distribution. In addition, it has an excellent property that it is hard to be scratched when the films are rubbed together, which is not possible with a conventional polypropylene film.

Since the particles used in the present invention are spherical and have a high degree of sphericity, it is considered that they have better slipperiness than other finely pulverized silica and synthetic particles.

Furthermore, since the spherical particles of the present invention have a narrow particle size distribution in a specific range and a small number of coarse particles, it is considered that scratches are less likely to occur when the films are rubbed together, fish eyes are small, and the appearance is good.

Also, since there are few fine particles that do not contribute to the film performance, the amount of addition for exhibiting the desired performance can be minimized.

The stretched polypropylene film of the present invention comprises
Since it has the above-mentioned excellent performance, it can be suitably used as various packaging materials for foods, fibers, sundries, cigarettes, cassette tapes and the like.

[0040]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

The physical properties of the films in the following Examples and Comparative Examples were measured by the following method after the film was manufactured and cured at 40 ° C. for 3 days.

(1) Transparency The haze value of the film was measured according to JIS-K-6714.

(2) Appearance The number of fish eyes having a length of 0.01 mm or more was observed with a transmission optical microscope, and the following 5 grades were evaluated.

1 point: 100 pieces / mm ² or more 2 points: 60 to 99 pieces / mm ² 3 points: 30 to 59 pieces / mm ² 4 points: 10 to 29 pieces / mm ² 5 points: 0 to 9 pieces / mm ² (3) Scratch resistance In order to evaluate the scratch resistance when the films were rubbed together, two films were prepared and one film (20 ×
30 cm) was fixed as the lower film. The other film is used as the upper film, and the diameter of the upper film is 10 cm.
A load of 4.6 kg was applied on the area of the circle to contact the lower film, and the upper film was rubbed horizontally for 20 cm 5 times. The haze value before and after performing the above operation was measured, and it was evaluated that scratches were less likely to occur as the change in the haze value was smaller.

(4) Sliding property The dynamic friction coefficient was measured according to ASTM-D-1894.

(5) Blocking property A film piece of 4 cm × 30 cm was cut out to have a thickness of 3 mm.
It overlapped so that it might become. Film sample at temperature 3
After being left in an atmosphere of 0 ° C. and 70% RH for 24 hours, a pressure of 20 kg / cm ² was applied to the film sample for 30 seconds using a press machine. Then, both ends of the film sample were fixed with a jig, and the bending strength was measured using an autograph (manufactured by Shimadzu Corporation).

Examples 1 to 6 and Comparative Examples 1 to 4 Spherical polymethylmethacrylate particles having the properties shown in Table 1 were added to polypropylene having a melt index of 2.0 g / 10 minutes and an isotacticity of 98.4%. In addition to the compounding ratio shown in Table 1, glyceryl monostearate and N-hydroxyethyl-N '-(2-
Stearylethyl) octadecylamine (0.5% by weight), erucic acid amide (0.03% by weight) and calcium stearate (0.04% by weight) were added and melt-kneaded. The resin was extruded from a T-die, and a stretched film having a thickness of 20 μm was obtained by a biaxial stretching machine using a tenter method. The surface was subjected to a corona discharge treatment of 30 W · min / m ² according to a conventional method.

The transparency, scratch resistance, appearance, slipperiness (dynamic friction coefficient) and blocking property of these films were measured, and the results are shown in Table 1.

[0049]

[Table 1]

Examples 7 to 9 and Comparative Examples 5 to 6 Polypropylene having a melt index of 2.0 g / 10 minutes and an isotacticity of 98.4%, and particles having the characteristics shown in Table 2 were blended as shown in Table 2. In addition, glyceryl monostearate and N-hydroxyethyl-N '-(2-stearylethyl) octadecylamine were added as antistatic agents in an amount of 0.3% by weight, and erucic acid amide was added in an amount of 0.03%.
% By weight and 0.04% by weight of calcium stearate were added and melt-kneaded. The above resin was extruded through a T-die and a stretched film having a thickness of 50 μm was obtained by a tenter method biaxial stretching machine. The surface was subjected to a corona discharge treatment of 30 W · min / m ² according to a conventional method.

The transparency, scratch resistance, appearance, slipperiness (dynamic friction coefficient) and blocking property of these films were measured, and the results are shown in Table 2.

[0052]

[Table 2]

Examples 10 to 12 and Comparative Examples 7 to 8 Polypropylene having a melt index of 2.0 g / 10 minutes and an isotacticity of 98.4% was added to glyceryl monostearate and N-hydroxyethyl as antistatic agents.
N ′-(2-stearylethyl) octadecylamine (0.5% by weight), erucic acid amide (0.03% by weight) and calcium stearate (0.04% by weight) were added and melt-kneaded. Used as a composition. on the other hand,
Particles having the characteristics shown in Table 3 were added to a propylene-ethylene random copolymer having an ethylene content of 3 mol% at the compounding ratio shown in Table 3 to obtain a resin composition for a surface layer.

Using the resin composition for the base layer and the surface layer described above, a tenter biaxial stretching machine was used to obtain a three-layer laminated film in which the surface layers were laminated on both sides of the base layer.
The surface was subjected to a corona discharge treatment of 25 W · min / m ² . The thickness of each layer was 2/26/2 μm.

The transparency, scratch resistance, appearance, slipperiness (dynamic friction coefficient) and blocking property of these films were measured, and the results are shown in Table 3.

[0056]

[Table 3]

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Claims (2)

[Claims] 1. A spherical particle having a 50% diameter in a volume cumulative distribution of 0.5 to 5 μm by a laser diffraction scattering method and an S value of 0.1 to 1 represented by the following formula (1). A stretched polypropylene film comprising 0. 1 to 1% by weight. [Equation 1] (However, D10, D50, and D90 represent the 10% diameter, 50% diameter, and 90% diameter in the above volume cumulative distribution, respectively.) 2. A laminated polypropylene film having two or more layers, wherein the outermost layer on at least one side is composed of the stretched polypropylene film according to claim 1.