JPH10292059A - Production of air-permeable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an air-permeable film having a uniform thickness, good air permeability and good high-speed orientability. SOLUTION: This air-permeable film is produced by uniaxially orienting a film made from a composition comprising 30-50 pts.wt. polyolefin resin and 70-50 pts.wt. inorganic filler. The polyolefin resin used is a mixture comprising 80-98 wt.% linear low-density polyethylene having a melt index of 0.8-5.0 g/10 min and a density of 0.910-0.940 g/cm<3> and 20-2 wt.% linear low-density polyethylene having a melt index of 0.01-0.5 g/10 min and/or high-density polyethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gas-permeable film having a uniform thickness and good gas permeability.

[0002]

2. Description of the Related Art Hitherto, many methods have been proposed for producing a breathable film by stretching a film containing a polyolefin resin and an inorganic filler in a uniaxial or biaxial direction to generate voids communicating with the film. . And
This breathable film is used for various applications such as sanitary materials, medical materials, building materials, battery separators, and the like.
When the film is stretched to generate voids, if the stretching ratio is too high, the molecular orientation in the resin increases, the rigidity of the film increases, and the softness of the film is impaired, so it is necessary to reduce the stretching ratio. However, when the stretching ratio is low, local necking that occurs at the start of stretching remains in the product film, resulting in poor uniformity in thickness and the formation of spots on the film. In recent years, the line speed at the time of film formation has been increasing in order to improve productivity. However, when the line speed is increased, a spot pattern tends to be more remarkable.

As a method for solving such a problem, for example, Japanese Patent Publication No. 5-35734 discloses a composition to which a known third component is added.
No. 253 proposes a method of adding a branched low-density polyethylene. However, although these methods are effective for this problem to some extent, they have not been sufficiently solved.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a gas permeable film having a uniform thickness, good air permeability, and good high-speed stretchability.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the polyolefin resin has a melt index of 0.8 to 5.
0 g / 10 min, density 0.910 to 0.940 g / cm
And linear low density polyethylene 80 to 98 wt% of ^3, linear low density melt index 0.01 to 0.5 g / 10 min polyethylene and / or high density polyethylene 2
It has been found that a mixture with 0 to 2% by weight may be used.

That is, the present invention relates to a method for producing a breathable film by stretching a film comprising a composition of 30 to 50 parts by weight of a polyolefin resin and 70 to 50 parts by weight of an inorganic filler at least in a uniaxial direction. Melt index of 0.8 to 5.0 g as a polyolefin resin
/ 10 min, a linear low density polyethylene having a density of 0.910 to 0.940 g / cm ³ , 80 to 98% by weight, and a melt index of 0.01 to 0.5 g / 10 min, and / or a high density linear low density polyethylene. Density polyethylene 20 ~
A method for producing a breathable film, comprising using a mixture with 2% by weight.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a linear low-density polyethylene is a copolymer composed of α-olefin having a molecular skeleton of C3 to C8 and ethylene. The former linear low-density polyethylene has a density of 0.910 to 0.940 g /
cm ³ , the melt index is 0.8 to 5.0 g / 1
It's 0 minutes. When the density of the linear low-density polyethylene is less than 0.910 g / cm ³ , the uniform stretchability deteriorates, and when it exceeds 0.940 g / cm ³ , the softness of the stretched film is impaired. Melt index 0.8g /
If the time is less than 10 minutes, it is difficult to obtain a uniform film due to abnormal flow when extruding the film, and 5.0.
If it exceeds g / 10 minutes, the uniform stretchability will deteriorate.

The specific linear low-density polyethylene to be mixed has a melt index of 0.01 to 0.5 g / 10
Minutes. Melt index is 0.01g / 1
If the time is less than 0 minutes, the mixing with the former linear low-density polyethylene becomes poor, and if it exceeds 0.5 g / 10 minutes, a film having a uniform thickness cannot be obtained.

The high-density polyethylene is a homopolymer of ethylene having a density of 0.950 to 0.970 g / cm ³ . Melt index is 0.01-0.5g
/ 10 minutes is preferred. Melt index is 0.
When it is less than 01 g / 10 minutes, the mixing with the linear low-density polyethylene becomes poor, and when it exceeds 0.5 g / 10 minutes, a film having a uniform thickness cannot be obtained.

In the present invention, the polyolefin resin has a melt index of 0.8 to 5.0 g / 10.
Min, a linear low-density polyethylene having a density of 0.910 to 0.940 g / cm ³ , 80 to 98% by weight, preferably 88 to 98% by weight.
96% by weight and a melt index of 0.01 to 0.5
g / 10 min linear low density polyethylene and / or high density polyethylene 20 to 2% by weight, preferably 12 to 4%
% By weight. 20% by weight of linear low density polyethylene and / or high density polyethylene to be mixed
If it exceeds, the occurrence of voids due to stretching is reduced, and only a film having poor air permeability can be obtained. Further, the softness of the film becomes poor, and the film easily tears in the stretching direction. On the other hand, if it is less than 2% by weight, it is difficult to obtain a film having a uniform thickness.

The inorganic filler is, for example, calcium carbonate,
Examples include barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica, talc and the like. Of these, calcium carbonate and barium sulfate are particularly preferred. The average particle size of the inorganic filler is preferably 20 μm or less, more preferably 10 μm or less,
Most preferably, the thickness is 0.5 to 5 μm. The inorganic filler is preferably subjected to a surface treatment in order to improve the dispersibility with the resin. As the surface treatment agent, those capable of rendering the surface hydrophobic by coating the surface of the inorganic filler are preferable, and examples thereof include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

The composition ratio of the polyolefin resin and the inorganic filler is such that the polyolefin resin is 50 to 30 parts by weight, preferably 45 to 35 parts by weight, and the inorganic filler is 5 to 35 parts by weight.
It is in the range of 0 to 70 parts by weight, preferably 55 to 65 parts by weight. When the amount of the inorganic filler is less than 50 parts by weight, adjacent voids formed by peeling off the interface between the polyolefin-based resin and the inorganic filler are not communicated with each other, and air permeability cannot be obtained. On the other hand, when the amount exceeds 70 parts by weight, elongation during stretching of the film is lost, and stretching becomes difficult.

The film of the present invention is basically composed of the above-mentioned linear low-density polyethylene, a specific linear low-density polyethylene high-density polyethylene, and an inorganic filler. The dispersant may be added in an amount of 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the above components. Examples of the dispersant include saturated or unsaturated fatty acid esters having 9 to 40 carbon atoms, triglycerides using saturated or unsaturated fatty acids having 2 to 30 carbon atoms, monohydric higher alcohols or derivatives thereof, higher fatty acid amides, higher amines Liquid or waxy components such as alcohol derivatives selected from saturated or unsaturated dihydric or higher alcohols, homopolymers, copolymers, ether compounds, amine compounds, amide compounds and ester compounds of the alcohols Can be used. These can be used alone or in combination of two or more.

In addition to the above-mentioned dispersants, additives generally used for resin compositions, such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, etc. A wetting agent, a lubricant, an anti-fogging agent, an anti-blocking agent, an antistatic agent, a slip agent, a coloring agent and the like may be added.

The breathable film of the present invention is prepared by, for example, mixing the above-mentioned polyolefin resin, inorganic filler, and if necessary, a dispersant and other additives using a Henschel mixer, a super mixer, a tumbler type mixer or the like. ,
The mixture is heated and kneaded with a single-screw or twin-screw extruder, a kneader or the like, and pelletized. Next, the pellets are molded at a temperature equal to or higher than the melting point of the polyolefin resin, preferably equal to or higher than the melting point + 20 ° C. and lower than the decomposition temperature, by a known molding method such as an extruder equipped with a T-die or the like or an inflation molding machine equipped with a circular die. Melting and film formation using a machine. In some cases, it is also possible to form a film directly on a molding machine without pelletizing. The formed film is formed at room temperature to the softening point of the resin (JIS K-) by a known method such as a roll method and a tenter method.
(Measured by the method specified in 6760), the film is stretched at least in a uniaxial direction, and the interfacial separation between the polyolefin resin and the inorganic filler is caused to produce a breathable film. Stretching may be performed in one step or may be performed in multiple steps. Since the stretching ratio is related to the breaking of the film at the time of stretching, the air permeability of the obtained film, the soft feeling of the film, and the like, it is not preferable that the stretching ratio is too high or too low. From such a viewpoint, the stretching ratio in the present invention is 1.2 to 5 times, preferably 1.5 to 3 times. In the case of biaxial stretching, a method of first performing uniaxial stretching in a machine direction or a direction perpendicular to the machine direction, and then performing a second axis stretching in a direction perpendicular to the machine direction, and a machine direction, and There is a method in which biaxial stretching is performed at the same time in a direction making a right angle. Either method can be applied. Further, after stretching, a heat setting treatment may be performed as needed to stabilize the form of the obtained aperture. As the heat-setting treatment, at a temperature lower than the softening point to the melting point of the resin, 0.1 to
A method of performing heat treatment for 100 seconds can be given.

The thickness of the breathable film of the present invention is not particularly limited, but is usually about 10 to 100 μm. If it is less than 10 μm, the film is easily broken,
When the thickness exceeds μm, the film becomes hard and soft like cloth.
It is not preferable because it is difficult to form a breathable film having a good texture.

The physical properties of the breathable film produced by the present invention can be freely determined depending on the filling ratio, type, particle size, blending ratio of high-density polyethylene, and drawing conditions (drawing direction, drawing ratio, drawing temperature, etc.) of the inorganic filler. However, when the film thickness is in the range of 10 to 100 μm, JIS-Z0208 (40 ° C., 90%, CaCl ₂
The moisture permeability measured by the method specified in
0 to 20000 g / m ² · 24 hr).

A breathable film having such properties has moderate breathability, moisture permeability, feeling, and excellent mechanical properties. Therefore, sanitary materials such as disposable paper diapers, body fluid absorbing pads, bed sheets, medical materials such as surgical gowns, base materials for hot compresses, clothing materials such as jumpers and raincoats,
It can be used very suitably as a building material such as a wallpaper, a roof waterproof material, a desiccant, a moisture proofing agent, a deoxidizing agent, a disposable body warmer, a packaging material such as freshness preserving packaging, a food packaging, and a battery separator.

[0019]

The present invention will now be described more specifically with reference to the following examples. Note that the present invention is not limited to these examples. The melt index (hereinafter referred to as MI), moisture permeability, and film thickness uniformity shown in the examples are values measured by the following methods. (1) Melt index (g / 10 minutes) It is measured at a temperature of 190 ° C. and a load of 2160 g by a method specified in ASTM D-1238-57T (E). (2) Moisture permeability (g / m ² · 24 hr) JIS-Z02 at a temperature of 40 ° C. and a relative humidity of 90%
08 (CaCl ₂ method). (3) Uniformity of film thickness Three samples (machine direction (hereinafter, referred to as vertical direction): 100 cm, direction perpendicular to the machine direction (hereinafter, referred to as horizontal direction): 5 cm) are sampled from the air-permeable film, Thickness measuring machine (PE) for a total of 300 measurement points at 1 cm intervals
ACOCK, UPLIGHT DIAL GUAG
E NO. 25), the average thickness (X), the maximum thickness (MAX), and the minimum thickness (MIN) are obtained, and [(MAX) − (MIN)] / (X) is calculated. Uniformity of film thickness.

Example 1 Linear low-density polyethylene (Ultzex 2021L, trade name, manufactured by Mitsui Petrochemical Industries, Ltd., density: 0.920 g / cm ³ , melt index (MI): 2) in 40 parts by weight of polyolefin resin 0.1 g / 10 min) to 38 parts by weight (95% by weight in the polyolefin resin) of a high-density polyethylene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: HIZEX 8000F, density: 0.950, MI: 0.0)
3) 2 parts by weight (5% by weight in the polyolefin resin)
Calcium carbonate (made by Dowa Calfine Co., Ltd., trade name:
After mixing 60 parts by weight (SST-40, average particle size: 1.0 μm) with a tumbler mixer, the mixture was uniformly kneaded at 220 ° C. using a tandem kneading extruder, and processed into pellets. The pellets were melt-formed at 240 ° C. using an extruder equipped with a T-die,
A preheated roll heated to 2 mm was uniaxially stretched in the machine direction at a stretching ratio of 2.0 times at a line speed of 20 m / min and at a stretching speed of 200 m / min to obtain a breathable film having a thickness of 40 μm. Table 1 shows the moisture permeability and the uniformity of the thickness of the obtained breathable film.

Example 2 The polyolefin resin of Example 1 was replaced with a linear low-density polyethylene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: Ultzex 2021L, density: 0.920 g / cm ³ , melt index (MI): 2) .1 g / 10 min) to 36 parts by weight (90 parts by weight in the polyolefin resin), linear low-density polyethylene (Ultzex 2005HC, manufactured by Mitsui Petrochemical Industries, Ltd., density: 0.923 g / c)
m ³ , melt index: 0.5 g / 10 min) A breathable film was obtained in the same manner as in Example 1, except that 4 parts by weight (10% by weight in the polyolefin resin) was used. Table 1 shows the obtained characteristics.

Example 3 The polyolefin resin of Example 1 was replaced with a linear low-density polyethylene (Ultzex 2021L, trade name, manufactured by Mitsui Petrochemical Industries, Ltd., density: 0.920 g / cm ³ , melt index (MI): 2) 0.1 g / 10 min) to 38 parts by weight (95% by weight in the polyolefin resin) of a high-density polyethylene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: HIZEX 8000F, density: 0.950, MI: 0.0)
3) 1 part by weight (2.5% by weight in polyolefin resin), linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Ultzex 2005HC, density:
0.923 g / cm ³ , melt index: 0.5 g
/ 10 min) A breathable film was obtained in the same manner as in Example 1, except that 1 part by weight (2.5% by weight in the polyolefin resin) was used. Table 1 shows the obtained characteristics.

Example 4 Hydrogenated castor oil (trade name: Custerwax, manufactured by Ito Oil Co., Ltd.) was added to 100 parts by weight of all components in Example 1.
5 parts by weight, dehydrated castor oil (manufactured by Ito Oil Co., Ltd., trade name:
DCO) was added and mixed with a tumbler mixer, and then a breathable film was obtained in the same manner as in Example 1.
Table 1 shows the obtained characteristics.

[0024]

[Table 1] A: Mitsui Petrochemical Co., Ltd. Ulto-Zex 2021L B: Mitsui Petrochemical Co., Ltd. Hi-Zex 8000F C: Mitsui Petrochemical Co., Ltd. Ulto-Zex 2005HC D: Mitsui Petrochemical Co., Ltd. Ulto-Xex 2005HC 50% + Mitsui Petrochemical Hizex 8000F 50% E: Mitsui Petrochemical Co., Ltd. Mirason F312 F: Dehydrated castor oil Ito Oil Co., Ltd. DCO 50% + hydrogenated castor oil Ito Oil Co., Ltd. Castor wax 50% G: Refined castor oil Ito Oil ( stock)

Comparative Example 1 A polyolefin resin was used as a linear low-density polyethylene (Ultzex 2021 manufactured by Mitsui Petrochemical Co., Ltd.)
L, density: 0.920 g / cm ³ , MI: 2.1 g / 1
(0 minutes) was changed to 40 parts by weight (100% by weight in the polyolefin resin) to produce a breathable film in the same manner as in Example 1. Table 2 shows the obtained characteristics.

Comparative Example 2 Polyolefin resin was used as a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name Ultzex 2021L,
Density: 0.920 g / cm ³ , MI: 2.1 g / 10
36% by weight of polyolefin-based resin (90% by weight) and branched low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name Mirason F312, density: 0.925 g / cm3)
A gas permeable film was produced in the same manner as in Example 1 except that the melt index was changed to 4 parts by weight (10% by weight in the polyolefin resin). Table 2 shows the obtained characteristics.

Comparative Example 3 A polyolefin resin was used as a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name Ultzex 2021L).
Density: 0.920 g / cm ³ , MI: 2.1 g / 10
Min) 40 parts by weight (100% by weight in polyolefin resin), and the total of polyolefin and calcium carbonate is 1
Refined castor oil (Ito Oil Co., Ltd.)
Was added in the same manner as in Example 1 except that 3 parts by weight of the gas-permeable film was added. Table 2 shows the obtained characteristics.

Comparative Example 4 A polyolefin resin was used as a linear low-density polyethylene (manufactured by Mitsui Petrochemical Co., Ltd., trade name Ultzex 2021L).
Density: 0.920 g / cm ³ , MI: 2.1 g / 10
Min) A breathable film was produced in the same manner as in Example 4 except that the amount was changed to 40 parts by weight (100% by weight in the polyolefin resin). Table 2 shows the obtained characteristics.

[0029]

[Table 2] A: Mitsui Petrochemical Co., Ltd. Ulto-Zex 2021L B: Mitsui Petrochemical Co., Ltd. Hi-Zex 8000F C: Mitsui Petrochemical Co., Ltd. Ulto-Zex 2005HC D: Mitsui Petrochemical Co., Ltd. Ulto-Xex 2005HC 50% + Mitsui Petrochemical Hizex 8000F 50% E: Mitsui Petrochemical Co., Ltd. Mirason F312 F: Dehydrated castor oil Ito Oil Co., Ltd. DCO 50% + hydrogenated castor oil Ito Oil Co., Ltd. Castor wax 50% G: Refined castor oil Ito Oil ( stock)

[0030]

The method for producing a breathable film of the present invention comprises:
Even if high-speed stretching at a low magnification is performed, a film having good air permeability, good thickness uniformity, and no spots can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04 B29L 7:00 (72) Inventor Takayuki Kajiwara 2-1-1 Tango-dori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemicals Co., Ltd. Inside the company (72) Inventor Katsumi Senba 2-1-1 Tangodori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Tsutomu Iseki 2-1-1 Tangodori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Within Chemical Co., Ltd. (72) Inventor Toshiyuki Enomoto 2-1-1 Tango-dori, Minami-ku, Nagoya, Aichi Prefecture Inside Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Taro Ichikawa 2-1-1, Tango-dori, Minami-ku, Nagoya, Aichi Prefecture Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a breathable film by stretching a film comprising a composition of 30 to 50 parts by weight of a polyolefin resin and 70 to 50 parts by weight of an inorganic filler at least in a uniaxial direction. The melt index is 0.8 to 5.0 g / 10 min, and the density is 0.1.
80 to 98% by weight of a linear low-density polyethylene of 910 to 0.940 g / cm ³ and a melt index of 0.01
-0.5 g / 10 min linear low density polyethylene and / or
Alternatively, a method for producing a breathable film, comprising using a mixture with 20 to 2% by weight of high-density polyethylene.