JPH10237200A - Porous film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having the same moisture permeability, film strength, touch, thickness accuracy and productivity as those of conventional ones and having a small thickness in high thickness accuracy, and to provide a method for producing the same. SOLUTION: This porous film is produced by monoaxially orienting a film obtained from a resin composition comprising 25-65wt.% of a polyolefin resin and 75-35wt.% of an inorganic filler, and satisfies the relations of the inequalities: 1<=A<=1.5C, 0.02C<=B<=0.5C and 5<=C<=25 wherein A is the maximum particle diameter (μm) of the inorganic filler; B is the average particle diameter (μm) of the inorganic filler; and C is the thickness (μm) of the porous film. At least 40wt.% of the inorganic filler particles have particle diameters of >=1μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a porous film and a method for producing the same. More specifically, the present invention relates to a porous film having reduced moisture permeability, film strength, texture, thickness accuracy, productivity, and the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, there has been proposed a method for producing a porous 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 porous film is used for sanitary materials, medical materials, clothing materials,
It is used for various purposes such as building materials and battery separators. In particular, in recent years, in applications to sanitary materials such as disposable diapers, demand for inexpensive films has been spurred, and thinning of films has become an important issue. It is well known that thinning of a film causes a reduction in the strength of the film, and attempts have been made to improve the tensile and tear strength by bonding the film to a nonwoven fabric or the like. However,
Since the air permeability of the bonding portion with the nonwoven fabric is impaired, there is a problem that the moisture permeability is reduced.

[0003] For the above reasons, a thin film having high moisture permeability is desired, but the following problems are obstacles.
In order to reduce the thickness of the film, for example, in the case of extrusion molding, a method of reducing the amount of extrusion can be considered, but this is not preferable because it leads to a reduction in the production amount. Therefore, a method of increasing the film take-up speed is generally used, but the moisture permeability of the film tends to decrease with an increase in the take-up speed. That is, the moisture permeability tends to decrease as the thickness decreases. Therefore, as a method of increasing the moisture permeability, a method of increasing the stretching ratio, increasing the amount of the inorganic filler to be added, and the like are considered. However, in any of these methods, stretching of the film is apt to occur, resulting in a decrease in productivity.
Under such circumstances, a porous film having high moisture permeability, high productivity, and reduced thickness, and a method for producing the same are desired.

For example, JP-A-64-81831 discloses that (a) 30 to 70% by weight of a polyolefin resin,
(B) A microporous film characterized in that a mixture comprising 70 to 30% by weight of a filler surface-treated with a metal salt of a saturated fatty acid is melt-molded into a sheet or film, and then the sheet or film is stretched. Is disclosed. The filler has an average particle size of 1 μm.
m, preferably in the range of 0.01 to 0.5 μm.

Japanese Patent Application Laid-Open No. 4-227748 discloses that (a) α-α having a density of 0.910 to 0.945 g / cm ³ , a melt flow rate of 0.01 to 20 g / 10 min, and a carbon number of 6 or more. Olefin or diolefin comonomer 1
A linear ethylene copolymer having a boiling normal hexane extraction amount of 20% by weight or less, containing (b) an average particle size of 10 μm or less and a bulk density of 0.1 to 0.7 g / c.
particulate inorganic filler m ^3, (c) 80~ saturated or unsaturated fatty acid esters consist of each component of the component (a) is 20 to 80 wt% and component (b) 9 to 40 carbon atoms
Component (c) is added in an amount of 0.1 to 100 parts by weight of 20% by weight.
Disclosed is a filler-containing stretched film comprising a resin composition having a blending ratio of １５15 parts by weight and having a tear strength MD of 10 g or more. It is described that the component (b) is a granular inorganic filler having an average particle diameter of 10 μm or less, preferably 0.1 to 5 μm, and more preferably 0.5 to 2 μm.

Further, JP-A-7-97474 discloses that
(A) a resin comprising 60 to 85% by volume of polyethylene having a density of 0.87 to 0.94 g / cm ³ , and (b) 15 to 40% by volume of an inorganic filler having a variation coefficient of particle diameter of 0.8 or less. A method for producing a porous film in which a composition is formed into a film and stretched in at least one direction is disclosed. The average particle size of the inorganic filler is preferably 1/5 or less of the thickness of the film.
It is described that it is selected from the range of 7 μm.

[0007]

However, according to the findings of the present inventors, the inorganic filler having the particle size and the particle size distribution described in the above-mentioned publication is used to have a thickness of 5 to 25 μm.
When a porous film is manufactured to a degree that the film is stretched when the film is stretched, in particular, the stretch break occurs starting from an inorganic filler having a particle diameter larger than the thickness of the film, It was found that this stretching breakage was accelerated as the stretching ratio was increased. Furthermore, the moisture permeability of the porous film decreases as the thickness becomes thinner, and only by paying attention to the average particle diameter, coefficient of variation, etc. of the inorganic filler used as in the conventional method, a porous film having a practically small thickness is used. It was extremely difficult to obtain a conductive film.

However, in view of the above-mentioned problems, it is an object of the present invention to maintain thickness accuracy, film strength, texture, etc. equal to those of conventional ones, and have a high moisture permeability even if the thickness is small, and An object of the present invention is to provide a porous film having good properties and a method for producing the same.

[0009]

Means for Solving the Problems The present inventors have made intensive studies and as a result, according to the thickness of the target porous film,
The inventors have found that the above object can be achieved by controlling the maximum particle size, the average particle size, and the like of the inorganic filler to be used, and have finally reached the present invention.

That is, the present invention relates to a porous film obtained by stretching a film obtained from a resin composition containing 25 to 65% by weight of a polyolefin resin and 75 to 35% by weight of an inorganic filler in at least a uniaxial direction. The maximum particle size of the filler, the average particle size of the inorganic filler, and the thickness of the porous film are expressed by the following formula (1) [Equation 7].

[0011]

1 ≦ A ≦ 1.5C (1), Equation (2) [Equation 8]

[0012]

0.02C ≦ B ≦ 0.5C (2) and Equation (3) [Equation 9]

[0013]

5 ≦ C ≦ 25 (3) [In the formulas (1) to (3), A is the maximum particle size (μm) of the inorganic filler, and B is the average particle size (μm) of the inorganic filler. ), C
Indicates the thickness (μm) of the porous film], and at least 40% by weight of the inorganic filler has a particle size of 1 μm or more.

Another aspect of the present invention provides a method for producing a porous film by stretching a film having the above composition at least in a uniaxial direction, wherein the above formulas (1) to (3) are satisfied.
A method for producing a porous film, characterized in that at least 40% by weight of an inorganic filler having a particle size of 1 μm or more is used.

In the present invention, the thickness (μm) of the porous film, the maximum particle size (μm) of the inorganic filler, the average particle size (μm), and the weight ratio (% by weight) of 1 μm or more are described in the following Examples. It means the value measured by the method described in the examples.

A feature of the present invention is that when producing a porous film having the above composition, the above formulas (1) to (3) are satisfied and at least 40% by weight depending on the thickness of the target porous film. In other words, a thin porous film having a thickness of 5 to 25 μm is produced by using an inorganic filler having a particle diameter of 1 μm or more without causing stretching breakage or the like. In addition, by using the inorganic filler having such a particle shape, even when the thickness is reduced, the moisture permeability does not decrease, and the same thickness accuracy, texture, rigidity, and mechanical strength as those conventionally known are maintained. This has the effect of obtaining a porous film. Furthermore, even when the porous film is stretched at a high magnification when producing a porous film, the film is free from stretching breakage.

Therefore, the porous film of the present invention can be used in various fields such as sanitary materials, medical materials, clothing materials, building materials, battery separators and the like. In particular, it can be particularly suitably used as a material for a product such as a disposable diaper, which is inexpensive and requires a large thickness.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The porous film of the present invention can be produced by melt-forming a resin composition containing a specific amount of a polyolefin resin and an inorganic filler to form a film, and stretching the obtained film in at least one axial direction.

The polyolefin resin used in the present invention comprises:
Monoolefin polymers such as ethylene, propylene and butene and copolymers thereof are used as main components. For example, polyethylene resins such as low-density polyethylene, linear low-density polyethylene (ethylene-α-olefin copolymer), medium-density polyethylene, and high-density polyethylene;
Examples include polypropylene resins such as polypropylene and ethylene-polypropylene copolymer, poly4-methylpentene, polybutene, ethylene-vinyl acetate copolymer, and mixtures thereof.

The polyolefin resin may be a resin produced using a multi-site catalyst such as a Ziegler catalyst or a resin produced using a single-site catalyst such as a metallocene catalyst. Of these, polyethylene resins are preferred, and ethylene-α
-A linear low density polyethylene resin which is an olefin copolymer and a low density polyethylene are particularly preferred. Also, in consideration of the moldability, stretchability, etc. of the film, the melt index of the polyolefin resin is 0.2 to 7 g / 10 m
It is preferably about in. The above resins may be used alone or as a mixture of two or more.

The inorganic filler used in the present invention has a maximum particle size and an average particle size satisfying the above-mentioned formulas (1) to (3) according to the thickness of the target porous film, and , At least 40% by weight have a particle size of 1 μm or more.

According to the findings of the present inventors, a porous film obtained by stretching a resin film containing an inorganic filler tends to have a lower moisture permeability as the thickness of the film is reduced. In order to reduce the thickness of the film, it is common to increase the take-off speed of the film when the extrusion speed is constant, but the moisture permeability of the porous film tends to decrease as the take-up speed increases. It is in. That is,
The moisture permeability tends to decrease as the thickness decreases.

As a result of extensive studies by the present inventors, when a resin film containing an inorganic filler is stretched to form pores in the film, the inorganic filler having a particle size of 1 μm or more mainly causes voids in the voids. It has been found that the inorganic filler having a particle diameter of less than 1 μm does not significantly contribute to the opening of the voids, and that the tendency becomes more remarkable by reducing the thickness of the film. In addition, among the inorganic fillers used, when the ratio of the inorganic fillers having a particle size of less than 1 μm increases, dispersibility in the resin layer is reduced due to aggregation or the like, which causes the film to break during stretching. I found that. Therefore, the method of simply increasing the absolute amount of the inorganic filler having a particle size of 1 μm or more increases the absolute amount of the inorganic filler having a particle size of less than 1 μm. As a result, the film may be broken at the time of stretching, which is not suitable as a means for forming a good void and improving the moisture permeability.

As described above, the amount of the inorganic filler having a particle diameter of 1 μm or more affects the breakage of the film during stretching and the moisture permeability of the obtained porous film. That is, the particle size is 1
By limiting the proportion of particles having a particle size of μm or more to a specific value or more, voids can be effectively generated at the time of stretching, and furthermore, it becomes possible to prevent synergistic aggregation of fine inorganic filler particles. is there. By such means, even when the thickness of the porous film is reduced, a decrease in the moisture permeability of the obtained film can be suppressed, and the film can be prevented from being broken during stretching. Considering such points comprehensively, in the present invention, at least 40% by weight of the total amount of the inorganic filler used is an inorganic filler composed of particles having a particle size of 1 μm or more. Preferably at least 45% by weight
It is. The upper limit of the weight ratio occupied by particles of 1 μm or more is:
There is no particular limitation based on the above reasons.

In the present invention, the above-mentioned inorganic filler is used. However, satisfying such conditions alone does not completely prevent problems such as breaking of the film when producing a porous film. The inorganic filler used in the production of the porous film is usually, regardless of the average particle size,
It contains particles having a particle size larger than the film thickness to some extent. According to the findings of the present inventors, it has been found that when the thickness of the film is reduced, the film breaks at the time of stretching, starting from the vicinity of the large-diameter particles.
That is, there is a preferred maximum particle size depending on the thickness of the porous film. From this viewpoint, in the present invention, the maximum particle size (A) of the inorganic filler is selected so as to satisfy the above-mentioned formula (1) in relation to the thickness (C) of the porous film. Preferably, the following equation (4) [Equation 10]

[0026]

10 ≦ 1 ≦ A ≦ 1.4C (4) (where A represents the maximum particle size (μm) of the inorganic filler, and C represents the thickness (μm) of the porous film). Such an inorganic filler is used. By adopting such a configuration, the film does not break during stretching even when the thickness of the film is reduced or the film is stretched at a high magnification, and the productivity is remarkably improved.

The average particle size of the inorganic filler affects the dispersibility and stretchability of the polyolefin resin and the inorganic filler, good void opening, air permeability, moisture permeability, etc. of the resulting porous film. Effect. In consideration of improving these properties, in the present invention, the average particle size (B) of the inorganic filler
Is selected so as to satisfy the above equation (2) in relation to the thickness (C) of the porous film. Preferably, the following formula (5) [Equation 11]

[0028]

[Equation 11] 0.02C ≦ B ≦ 0.4C (5) More preferably, the following equation (6) [Equation 12]

[0029]

0.03C ≦ B ≦ 0.4C (6) [wherein B represents the average particle size (μm) of the inorganic filler, and C represents the thickness (μm) of the porous film]. Use satisfactory inorganic fillers. By adopting such a configuration, it is possible to open a void capable of exhibiting waterproofness and moisture permeability while maintaining good air permeability, and further, dispersibility of particles in a polyolefin resin, stretchability of a film. Can be made favorable.

In the present invention, any inorganic filler can be used without any limitation as long as it satisfies the above particle size. As an inorganic filler, for example,
Calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide,
Examples include zinc oxide, magnesium oxide, titanium oxide, silica, and talc. Of these, calcium carbonate and barium sulfate are preferred.

These inorganic fillers are subjected to a surface treatment to improve the dispersibility with the polyolefin resin, promote the interfacial separation with the resin, and prevent the absorption of moisture from the outside. Are preferred. As the surface treating agent, those capable of making 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.

Further, the inorganic filler is preferably of a rounded shape for the purpose of improving the dispersibility in the resin and the releasability at the interface with the resin. As the inorganic filler having a rounded shape, for example, it is preferable to use a ball mill after coarse particles are obtained by a roller mill in a step of pulverizing a rough stone, and the sharp projections of the particles are dropped.

The composition ratio of the polyolefin resin and the inorganic filler affects the moldability and stretchability of the film, the air permeability and the moisture permeability of the obtained film. When the amount of the inorganic filler is less than 35% by weight, adjacent voids obtained by interfacial peeling between the polyolefin resin and the inorganic filler are not communicated with each other, and a porous film having good air permeability, moisture permeability, etc. is obtained. I can't get it. Further, when the amount of the inorganic filler is 7
If the amount exceeds 5% by weight, it is not preferable because, when a film is formed, poor forming such as stretch breakage occurs, or the stretchability is lowered, and sufficient stretching cannot be performed. From this viewpoint, the composition ratio of the polyolefin resin and the inorganic filler is 25 to 65% by weight of the polyolefin resin and 75 to 3% by weight of the inorganic filler.
Preferably it is 5% by weight. More preferably, the polyolefin resin is 30 to 60% by weight, and the inorganic filler is 70% by weight.
４０40% by weight.

In the porous film of the present invention, a drawing aid such as a fatty acid ester, a stabilizer, an antioxidant, a coloring agent, an ultraviolet absorber, a flame retardant, a deodorant, Other additives such as antibacterial agents may be added.

Next, a method for producing the porous film of the present invention will be exemplified. For example, after mixing the above-mentioned polyolefin resin, an inorganic filler, a stretching aid such as a fatty acid ester and other additives as necessary with a Henschel mixer, a super mixer, a tumbler type mixer or the like, a single or twin screw type The mixture is kneaded using an extruder and pelletized. Then, 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 possible to form a film directly with a molding machine without pelletizing.

The formed film is formed at least at room temperature and below the softening point of the resin (value measured by the method specified in JIS K-6760) by a known method such as a roll method or a tenter method. A porous film is produced by stretching in a uniaxial direction to cause interfacial separation between the polyolefin resin and the inorganic filler. Stretching may be performed in one step or may be performed in multiple steps. The stretching ratio is unfavorable if the ratio is too high or too low, because it is related to film breakage during stretching, air permeability, moisture permeability and the like of the obtained film. From this viewpoint, the stretching ratio is preferably at least 1.2 to 8 times in the uniaxial direction. More preferably, it is 1.2 to 7 times. When biaxially stretching, first uniaxially stretching in the machine direction, or in a direction perpendicular to it, then a method of stretching the second axis in a direction perpendicular to that direction, and in the machine direction, or perpendicular to it And a method of simultaneously biaxially stretching in the direction of を, and any method can be applied.

After the stretching, a heat-setting treatment may be performed, if necessary, in order to stabilize the form of the obtained holes. As the heat setting treatment, a method of performing a heat treatment at a temperature equal to or higher than the softening point of the resin and lower than the melting point for 0.05 to 100 seconds may be used. When obtaining a thin film, depending on the desired film thickness, a method of reducing the extrusion discharge amount of the extruder, a method of increasing the film take-up speed, and simultaneously reducing the extrusion discharge amount and increasing the take-up speed. There is a method of increasing the extrusion discharge amount and a method of simultaneously increasing the take-off speed, and any of these methods can be applied. When higher rationality and productivity are required, a method of simultaneously increasing the extrusion discharge amount and the take-up speed is more preferable.

The manufacturing method as described above is particularly effective when the thickness is 5 to 2
It is effective for producing a thin porous film having a thickness of 5 μm. That is, the porous film according to the present invention has a thickness of 5 to 25 μm. Therefore, the porous film of the present invention is suitably used for applications requiring a small thickness of the film, for example, as a disposable diaper or a backsheet for a body fluid absorbing pad.

[0039] The porous film of the present invention is made of ASTM-E
96 (40 ° C., 60%, conditions of the water method) having a moisture permeability of 1800 to 5000 g / m.
It is in the range of ² · 24hr.

The porous film having such physical properties has excellent air permeability, moisture permeability and waterproofness, thickness accuracy, texture, and moderate mechanical properties even when the thickness is reduced. Therefore, sanitary materials such as disposable diapers, body fluid absorbing pads, bed sheets, clothing materials such as surgical gowns, clothing materials such as jumpers and raincoats, wallpaper materials, roof waterproof materials, building materials such as house wraps, and keeping freshness It can be suitably used in the field of packaging materials such as packaging and food packaging, battery separators and the like. In particular, excellent productivity of thin thickness, breathability,
Since it has moisture permeability, it is most suitable as a material for articles that require particularly low price, such as disposable diapers and pads for absorbing body fluid.

[0041]

EXAMPLES The present invention will be described in more detail with reference to the following examples. Note that the present invention is not limited to these examples. Melt index (hereinafter referred to as MI), moisture permeability, air permeability, film thickness, maximum particle diameter of inorganic filler, particle weight% of 1 μm or more, average particle diameter, number of stretching cuts, uniformity of thickness shown in Examples The properties, stiffness, and tensile strength are values measured by the following methods.

(1) Melt index (g / 10 mi)
n) Measured at a temperature of 190 ° C. and a load of 2160 g by the method specified in ASTM D-1238-57T (E). (2) Moisture permeability (g / m ² · 24 hr) ASTM-E9 at a temperature of 40 ° C. and a relative humidity of 60%
Measured by the method specified in 6 (Water method).
The test time is 24 hours. (3) Air permeability (sec / 100 ml) Measured according to the method specified in JIS P-8117. (4) Maximum particle size (μm) of inorganic filler Laser diffraction type particle size distribution analyzer (manufactured by Shimadzu Corporation, type:
SA-CP type).
The particle size becomes 100.0% by rounding off the second decimal place. (5) Particle size of inorganic filler of 1 μm or more by weight% The cumulative weight% of particles having a particle size of 1 μm or more is measured by the particle size distribution measuring device described in (4).

(6) Average Particle Size (μm) of Inorganic Filler From the specific surface area measured using the air permeation method based on JIS M-8511, the particle size is calculated based on the following formula. Average particle size (μm) = 6 × 10 ⁴ / (true specific gravity × specific surface area (cm ² / g)) Here, the true specific gravity is a value according to JIS K-5101. (7) Number of Stretch Breaks (Times / hr) The porous film is manufactured continuously for 8 hours under the conditions shown in each Example and Comparative Example, and how many times the film undergoes stretch breaks is observed. The value converted to the number of times per hour is defined as the number of stretching breaks. (8) Film thickness (μm), uniformity of film thickness From a porous film, a sample [vertical direction (hereinafter, referred to as MD): 110 cm, horizontal direction (hereinafter, referred to as TD): 5c
m], and a total of 300 measurement points are determined on the MD at 1 cm intervals. Thickness measuring machine (manufactured by PEACOCK,
Format: UPGRIDDIAL GUAGE NO. 2
The thickness is measured using 5), and the average thickness (X), the maximum thickness (MAX), and the minimum thickness (MIN) are determined. The obtained average thickness (X) is rounded to the nearest whole number to give a film thickness. Further, [(MAX-MIN)] / (X) is calculated, and the calculated value is defined as the uniformity of the film thickness. (9) Rigidity (mm) Measured in accordance with the method (cantilever method) specified in JIS L-1096. (10) Tensile strength (Kg / 25mm) Measured according to the method specified in JIS P-8113. The measurement conditions were: test piece size 25 mm width x 100 m
m length, measurement temperature 23 ° C., tensile speed 200 m / min. The strength at break is measured for MD and TD, respectively.

Example 1 Linear low-density polyethylene (manufactured by Mitsui Petrochemical Industries, Ltd.)
Product name: Ultzex 2021L, density: 0.920
g / cm ³ , MI: 2.1 g / 10 min) 40% by weight and calcium carbonate (Dowa Calfine Co., Ltd.)
(Trade name: MD-2, average particle diameter 1.2 μm, maximum particle diameter 15 μm, 1 μm or more particles 46% by weight), 60% by weight, and castor oil (Ito Oil Co., Ltd., Trade name: Rhombus A 3% by weight was added and mixed with a tumbler mixer, then uniformly kneaded at 200 ° C. using a tandem type extruder and processed into pellets. 9. Kneading, melting and extruding the pellets at 240 ° C. using an extruder equipped with a T-die;
After forming a film at a take-off speed before stretching of 0 m / min,
The film was uniaxially stretched in the machine direction at a stretch ratio of 2 times between the preheated roll and the stretch roll heated to obtain a porous film 1. The resulting porous film 1 has moisture permeability, air permeability, film thickness, thickness uniformity, rigidity and tensile strength, and
The number of stretching breaks was measured by the above method. The results obtained are shown in [Table 1]. The porous film 1 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Examples 2 to 8 and Comparative Examples 1 and 2 Example 1 was repeated except that the take-up speed before stretching, the film thickness, the stretching ratio, and the amount of the inorganic filler were changed as shown in Table 1.
In the same manner as in the above, porous films 2 to 8 and 10 to 11 were produced. Each physical property of each of the obtained porous films was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 1].
The porous films 2 to 4 do not deteriorate in moisture permeability due to the reduction in thickness, and also have productivity, thickness accuracy, texture,
Both strengths were good. The productivity, moisture permeability, air permeability, thickness accuracy, texture, and strength of the porous films 5 to 8 were good even when the stretching ratio was increased. Porous film 1
0 is excellent in moisture permeability and air permeability, but poor in productivity.
Although the porous film 11 has good productivity, it is not preferable because both moisture permeability and air permeability are insufficient.

Example 9 Low density polyethylene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: Mirason F312, density: 0.925 g / cm ³ ,
Example 1 except that MI: 2.0 g / 10 min) was used.
In the same manner as in the above, a porous film 9 was produced. Each physical property of the obtained porous film was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 1]. The porous film 9 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 10 As an inorganic filler, calcium carbonate (trade name: NCC1010, manufactured by Nitto Powder Chemical Co., Ltd., average particle size: 1.3 μm)
m, maximum particle diameter 10 μm, 1 μm or more particles 64% by weight)
Except that the porous film 1 was used in the same manner as in Example 1.
2 was produced. Each physical property of the obtained porous film 12 was evaluated in the same manner as in Example 1, and the results are shown in [Table 2].
The porous film 12 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Examples 11 to 13 Porous films 13 to 15 were produced in the same manner as in Example 10, except that the take-up speed and the film thickness before stretching were changed as shown in Table 2. Each physical property of each of the obtained porous films was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous films 13 to 15 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 14 As an inorganic filler, barium sulfate (manufactured by Barite Industry Co., Ltd.)
(Trade name: B-20HD, average particle size 0.9 μm, maximum particle size 3 μm, 1 μm or more particles 50% by weight), and the stretching ratio was 5 times, except that the stretching ratio was 5 times. No. 16 was manufactured. The obtained porous film 16
Were evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous film 16 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 15 As an inorganic filler, calcium carbonate (trade name: NX23PS, manufactured by Nitto Powder Chemical Co., Ltd., average particle size: 1.0 μm)
m, maximum particle diameter 8 μm, 1 μm or more particles 54% by weight) except that porous film 17 was used in the same manner as in Example 1.
Was manufactured. Each physical property of the obtained porous film 17 was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous film 17 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Examples 16 to 18 Porous films 18 to 20 were produced in the same manner as in Example 15, except that the take-up speed before stretching and the film thickness were changed as shown in Table 2. Each physical property of each of the obtained porous films was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous films 18 to 20 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 19 As an inorganic filler, calcium carbonate (manufactured by Dowa Calfine Co., Ltd., trade name: SST-40, average particle size 1.1 μm)
m, maximum particle diameter 25 μm, 1 μm or more particles 49% by weight)
Except that the porous film 2 was used in the same manner as in Example 1.
1 was produced. Each physical property of the obtained porous film 21 was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous film 21 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 20, Comparative Examples 3 and 4 Porous films 22, 26 and 27 were produced in the same manner as in Example 19 except that the take-up speed before stretching and the film thickness were changed as shown in Table 2. . Each physical property of each of the obtained porous films was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous film 22 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength. As the porous films 26 and 27 are made thinner, the productivity is reduced, which causes a problem.

Example 21 As an inorganic filler, calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Caltex 5, average particle size 0.8 μm)
m, maximum particle size 4 μm, 1 μm or more particles 44% by weight) except that porous film 23 was used in the same manner as in Example 1.
Was manufactured. Each physical property of the obtained porous film 23 was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. The porous film 23 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 22 As an inorganic filler, calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: SUPER # 1700, average particle size: 1) was used.
Porous film 24 was produced in the same manner as in Example 1, except that 3 μm, the maximum particle diameter was 22 μm, and 1 μm or more particles were 77% by weight. Each physical property of the obtained porous film 24 was evaluated in the same manner as in Example 1, and the obtained results were shown in [Table 2].
Shown in The porous film 24 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Example 23 As an inorganic filler, calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: MC Coat S-20, average particle size: 1.20) was used.
Porous film 25 was produced in the same manner as in Example 1 except that 5 μm, the maximum particle diameter was 18 μm, and 1 μm or more particles were 75% by weight. Each physical property of the obtained porous film 25 was evaluated in the same manner as in Example 1, and the obtained results were shown in [Table 2].
Shown in The porous film 25 did not deteriorate in moisture permeability due to the reduction in thickness, and had good productivity, thickness accuracy, texture, and strength.

Comparative Examples 5 to 6 As an inorganic filler, calcium carbonate (manufactured by Dowa Calfine Co., Ltd., trade name: MD-1, average particle diameter 0.8 μm, maximum particle diameter 15 μm, 1 μm or more particles 36% by weight) The porous films 28 and 29 were produced in the same manner as in Example 1 except that the take-up speed before stretching and the film thickness were changed as shown in [Table 2]. Each physical property of each of the obtained porous films was evaluated in the same manner as in Example 1, and the obtained results are shown in [Table 2]. Although the productivity of the porous films 28 and 29 is good, moisture permeability and air permeability are reduced due to the reduction in thickness, which is problematic.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

According to the porous film provided by the present invention, the maximum particle size and the average particle size of the inorganic filler to be used are limited according to the desired thickness, and at least 40% by weight is 1 μm or more. Since a certain inorganic filler is used, the moisture permeability does not decrease even when the thickness is reduced, and has the same texture, moisture permeability, air permeability, rigidity, mechanical strength, and the like as those conventionally known. Moreover, it is a porous film that is uniformly stretched and thin and has high thickness accuracy. for that reason,
It can be used in various fields such as sanitary materials, medical materials, clothing materials, building materials, battery separators, and the like. In particular, it can be suitably used as a material for products, such as disposable diapers, which are inexpensive and are required to be thinner. Further, according to the production method of the present invention, not only a porous film having the above-described excellent properties can be obtained, but also, even when the film is stretched at a high magnification in production, the film is not stretched and the production is prevented. It can be manufactured with good efficiency.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04 105: 16 503: 04 B29L 7:00 (72) Inventor Katsumi Senba 2-1-1 Tangodori, Minami-ku, Nagoya-shi, Aichi Prefecture Address: Mitsui Toatsu Chemical Co., Ltd. (72) Takayuki Kajiwara 2-1-1 Tango-dori, Minami-ku, Nagoya-shi, Aichi Prefecture Mitsui Toatsu Chemical Co., Ltd. (72) Inventor: Shigeru Yano 2 Tango-dori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Tsutomu Iseki 2-1-1 Tango-dori, Minami-ku, Nagoya City, Aichi Prefecture In-house Mitsui Toatsu Chemical Co., Ltd. (72) Toshiyuki Enomoto Tango, Minami-ku, Nagoya City, Aichi Prefecture 2-1-1, Mitsui Toatsu Chemical Co., Ltd.

Claims (10)

[Claims] 1. A porous film obtained by stretching a film obtained from a resin composition containing 25 to 65% by weight of a polyolefin resin and 75 to 35% by weight of an inorganic filler in at least one axial direction, wherein the maximum amount of the inorganic filler is The particle diameter, the average particle diameter of the inorganic filler, and the thickness of the porous film are expressed by the following formula (1) [Equation 1] 1 ≦ A ≦ 1.5C (1) 0.02C ≦ B ≦ 0.5C (2) and Equation (3) [Equation 3] 5 ≦ C ≦ 25 (3) [Equation (1)- In (3), A is the maximum particle size (μm) of the inorganic filler, B is the average particle size (μm) of the inorganic filler, C
Indicates the thickness (μm) of the porous film], and at least 40% by weight of the inorganic filler has a particle size of 1 μm or more. 2. The porous film according to claim 1, wherein the polyolefin resin is at least one resin selected from linear low-density polyethylene and low-density polyethylene. 3. The porous film according to claim 1, wherein the inorganic filler is at least one compound selected from calcium carbonate and barium sulfate. 4. The stretch ratio of the porous film is 1.2 to 8
The porous film according to claim 1, which is twice as large. 5. The porous film having a moisture permeability of 1800 to 5
The porous film according to claim 1, wherein a 000g / m ² · 24hr. 6. A porous film obtained by forming a resin composition containing 25 to 65% by weight of a polyolefin resin and 75 to 35% by weight of an inorganic filler into a film, and then stretching the obtained film at least uniaxially. It is a manufacturing method, and a numerical formula (1) [Equation 4] 1 ≦ A ≦ 1.5C (1), a numerical formula (2) [Equation 5] 0.02C ≦ B ≦ 0.5C (2) and Equation (3) [Equation 6] 5 ≦ C ≦ 25 (3) [In Equations (1) to (3), A represents an inorganic filler. Maximum particle size (μm), B is average particle size of inorganic filler (μm), C
Indicates the thickness (μm) of the porous film], and at least 40% by weight of the inorganic filler has a particle size of 1 μm or more. 7. The method for producing a porous film according to claim 6, wherein the polyolefin resin is at least one resin selected from linear low-density polyethylene and low-density polyethylene. 8. The method for producing a porous film according to claim 6, wherein the inorganic filler is at least one compound selected from calcium carbonate and barium sulfate. 9. The stretch ratio of the porous film is 1.2 to 8
The method for producing a porous film according to claim 6, wherein the ratio is twice as large. 10. A porous film having a moisture permeability of 1800 to 1800.
Method for producing a porous film according to claim 6, wherein a 5000g / m ² · 24hr.