JPH01203439A - Porous film and production thereof - Google Patents

Abstract

PURPOSE:To obtain the present film, excellent in moisture and air permeability, water resistance and flexibility and suitable as rain apparels, disposable diapers, packaging materials, etc., by blending a polyolefinic resin with specific magnesium hydroxide, melt forming a film and drawing the resultant film. CONSTITUTION:The aimed film obtained by blending (A) 100pts.wt. polyolefinic resin with (B) 50-400pts.wt., preferably 60-200pts.wt. magnesium hydroxide, having 0.3-2.0mum, preferably 0.5-1.0mum average particle diameter and <=10m<2>/g, preferably 0.5-5.0m<2>/g specific surface area and subjected to surface treatment, then melt forming a film and drawing the resultant film in at least an uniaxial direction at >=1.1 times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porous film and a method for producing the same, and more specifically to a porous film made of a polyolefin resin and surface-treated magnesium hydroxide, and its production method. This relates to a manufacturing method.

[Prior art]

BACKGROUND ART Porous films obtained by blending a polyolefin resin with an organic or inorganic incompatible substance in a specific ratio, melting the film by a known method, and then stretching the film have been known.

However, when calcium carbonate is used as a substance incompatible with polyolefin resin, the stress due to stretching is concentrated on the aggregates or coarse particles due to the presence of coarse particles due to the agglomeration of particles and the wide particle size distribution. Therefore, stretch breakage easily occurs at low magnification, making it difficult to obtain a thin film. Further, even if no stretching breakage occurs, holes with a pore diameter of 0.1 au+ or more are formed, resulting in a decrease in water pressure resistance and poor functionality as a porous film. In addition, there was a drawback that the film was too rigid and dry.

In order to improve flexibility and create uniform porosity at low magnification, a method has been developed in which a liquid compound is added to the polyolefin resin and filler.For example, as a liquid compound,
Liquid polybutadiene and liquid polybutene (JP-A-57-4
7334), liquid polyhydroxy saturated hydrocarbon (JP-A-57-203520), liquid polyisoprene rubber (JP-A-58-149925), or polyhydroxy saturated hydrocarbon and epoxy group-containing organic compound (JP-A-58-149925). JP-A-59-140235) is added.

However, these additives have the problem of not forming uniform pores unless they are blended in large amounts, or of eluting when they come into contact with solvents or chemicals.

Further, when these liquid compounds are added, interfacial peeling between the filler and the polyolefin resin matrix becomes difficult to occur, resulting in a problem that air permeability and moisture permeability are reduced.

These liquid additives have been further improved; for example, JP-A-62-129321 proposes the use of silicone oil, but since it is also liquid like the above-mentioned additives, it does not cause stickiness on the surface due to embossment. The problem was that it was unavoidable.

To compensate for the above-mentioned disadvantages such as stickiness and do not contain additives, it has been proposed to use calcium carbonate, which is composed of two particle parts, a coarse particle part and a fine particle part, as an incompatible substance (Japanese Patent Application Laid-open No. 62-201941), but it has the disadvantage that the particles are difficult to handle and that the air permeability of the obtained film is uneven because it is difficult to uniformly disperse the two particle parts. Ta.

Similarly, it has been proposed that barium sulfate is used as an incompatible substance without additives (Japanese Patent Application Laid-open No. 129240/1982). This material has characteristics such as good stretchability, high moisture permeability, uniform and fine pore size, excellent flexibility, and high physical strength in the direction of stretching.Furthermore, since there are no particularly large particles, A thin film is obtained.

However, since barium sulfate has a high specific gravity, the resulting porous film has a high specific gravity of 20 g/rr per basis weight.
There is a problem that a film having a diameter of f or less cannot be stably obtained industrially.

In addition, barium sulfate has a high Mohs hardness of 3.0 to 3.8, which poses a problem in that a part of the cylinder of the extruder is easily worn out.

Various studies have been conducted on porous films obtained from substances incompatible with polyolefin resins and their manufacturing methods, but there are problems with the properties such as moldability and quality of porous films, as shown above. It has its drawbacks.

[Problem to be solved by the invention]

An object of the present invention is to provide a porous film that does not contain liquid compounds and is made of polyolefin resin, has excellent tensile properties, moisture permeability, air permeability, and production stability, and is thin in thickness and can be produced with a low basis weight. It is in.

[Means to solve the problem]

In order to achieve the above-mentioned problem, the present inventors have made extensive studies,
We have finally arrived at the present invention.

That is, the present invention uses 100 parts by weight of a polyolefin resin, an average particle size of 0.3 to 2.0 μm, and a specific surface area of 10 μm.
rr/g or less, and a resin composition consisting of 50 to 400 parts by weight of surface-treated magnesium hydroxide is melt-formed into a film and then stretched at least 1.1 times in one axis direction. The present invention provides a porous film and a method for producing the same.

The present invention will be explained in detail below.

In the present invention, polyolefin resins include polypropylene (PP), low density polyethylene (LDPE), high density polyethylene (■Ko E), linear low density polyethylene (
L-LDPE), homopolymers such as polybutene, ethylene-propylene copolymers, ethylene-butylene copolymers,
Copolymers such as ethylene-vinyl acetate copolymers, and
It is a blend of these.

Linear low density polyethylene is a type of ethylene-α-olefin copolymer, and the α-olefins copolymerized here include butene-1,4-methylpentene-1, hexene-I, octene-1, Decene-1, Dodecene-1
and so on.

Suitable magnesium hydroxide in the present invention has an average particle size of 0.3 to 2.0 μm, preferably 0.5 to 1.0 μm.

If the average particle size is less than 0.3μ, it will not be possible to obtain a good porous film, and if it is larger than 2.0μ, the film will have poor stretchability, such as breakage, and the pore size will become large. The function as a sex film becomes inferior.

In addition, the specific surface area is 10nf/g or less, and 0.5 to 5
．． A range of 0 m2/g is more preferable.

When the specific surface area exceeds 1 Onl/g, the shape of magnesium hydroxide becomes amorphous, plate-like, etc., resulting in a wide particle size distribution, resulting in a decrease in film stretchability and failure to make the film porous.

Incidentally, the magnesium hydroxide used in the present invention can be easily manufactured by the manufacturing method described in JP-A-60-176918, and those manufactured by this manufacturing method are preferred.

In the present invention, it is essential to surface-treat the above-mentioned magnesium hydroxide, and when magnesium hydroxide without surface treatment is used, agglomeration of magnesium hydroxide occurs, resulting in poor dispersibility. Therefore, uniform whitening is not achieved and the stretchability is significantly reduced.

The amount of surface-treated magnesium hydroxide used is 50 to 400 parts by weight, preferably 60 to 200 parts by weight, per 100 parts by weight of the polyolefin resin. If the amount used is less than 50 parts by weight, the porosity will be insufficient and the number of communicating pores will be reduced, making it impossible to obtain sufficient air permeability and moisture permeability. If it is used in excess of 400 parts by weight, the rigidity of the film will increase. , the forming and stretching properties of the sheet-like material are reduced.

As the surface treatment agent used in the present invention, fatty acids, fatty acid metal salts, and fatty acid amides are suitable, and those that are solid at room temperature are particularly preferred. Fatty acids, fatty acid metal salts, and fatty acid amides include stearic acid, sodium stearate, calcium stearate, palmitic acid, sodium palmitate, calcium palmitate, myristic acid, sodium myristate, calcium myristate, lauric acid, sodium laurate, and lauric acid. Examples include calcium phosphate, oleic acid, sodium oleate, calcium oleate, stearamide, oleic acid amide, and particularly preferred are sodium stearate, sodium palmitate, sodium myristate, sodium laurate, and sodium oleate. .

The surface-treated magnesium hydroxide is prepared by adding calcium hydroxide to an aqueous magnesium chloride solution and causing the reaction, and the product is aged to produce and precipitate magnesium hydroxide. Next, an aqueous solution of a fatty acid metal salt is added to the filtered and water-washed precipitate, spread on the surface, evaporated to dryness, and finely pulverized. Alternatively, it can be obtained by blending a predetermined amount of fatty acid, fatty acid metal salt, or fatty acid amide with magnesium hydroxide, mixing with a Henschel mixer, and spreading the mixture on the surface of magnesium hydroxide.

The fatty acid, fatty acid metal salt, or fatty acid amide is preferably used in an amount of 10% by weight or less, more preferably 2 to 5% by weight, based on magnesium hydroxide.

Furthermore, other inorganic fillers such as barium sulfate and calcium carbonate may be added as the M filler in addition to the surface-treated magnesium hydroxide, within a range that does not impede the effects of the present invention.

In addition, heat stabilizers, heat stabilizers, and
There is no problem in adding ultraviolet stabilizers, antistatic agents, pigments, fluorescent agents, etc.

Next, a method for manufacturing a porous film of the present invention will be explained.

First, surface-treated magnesium hydroxide is added to polyolefin resin along with other additives, and then mixed using a Henschel mixer, super mixer, or tumbler type mixer, and then subjected to conventional single or twin screw extrusion. Knead and pelletize using a machine.

Next, these pellets are formed into a film using an inflation molding machine or a T-die molding machine.

At this time, it is also possible to directly mold using an extruder without pelletizing.

Thereafter, stretching is performed at least 1.1 times in at least one axis direction. Stretching may be performed in multiple stages or biaxially.

If the stretching ratio is less than 1.1 times, the film will not be sufficiently porous.

Further, after stretching, heat setting may be performed to increase the morphological stability of the holes.

In order to improve the printability and adhesion of the porous film, surface treatment such as corona discharge treatment can also be performed.

Air permeability is determined by the amount of surface-treated magnesium hydroxide used, particle size, stretching ratio, etc., but since magnesium hydroxide is thermally decomposed into magnesium oxide and water, the resulting sheet material has no melting properties. Microscopic cavities are created by the foaming of water generated during membrane formation, and the stretching facilitates porosity and communication, resulting in improved air permeability and moisture permeability.

〔Example〕

The present invention will be explained below with reference to Examples.

The method for evaluating the physical properties of the film used in this example is as follows.

(1) Strength: A film of 25 mm (width) x 100 mm (length) was pulled at a tensile speed of 200 ma+/sin using a Tensilon tensile tester, and the strength at break was measured in MD (machine direction) and TD (perpendicular to the flow direction), respectively. It was measured.

(2) Moisture permeability: Measured according to ASTM E96-66(D).

(3) Hole: Hole diameter is 0.1. The number of pores of cIm or more was measured.

Examples 1 to 6, Comparative Examples 1 to 9 100 parts by weight of linear low density polyethylene with old = 2.0 and ρ = 0.92 (Shishiko E) was added with the fillers shown in Table 1. T
Each of the porous films was extruded using a die molding machine and stretched at the stretching ratio shown in Table 2 to have the thickness of the porous film.

Next, the film was stretched at 80°C in the -axis or two-wheel direction at the stretching ratio shown in Table 2 to obtain a porous film.

The physical properties shown above were measured for the obtained film, and the results are shown in Table 2.

In Comparative Example 7, it was not possible to pelletize, and in Comparative Examples 2, 6, 8, and 9, stretching was attempted, but there were many stretching breaks, and a porous film could not be obtained.

Example 7.8 Instead of linear low density polyethylene (L-LDPE),
In Example 7, low density polyethylene (LDPE) with MI = 2.0, ρ = 0.92 and low density polyethylene (LDPE) with MI = 2.0, ρ =
In Example 8, high-density polyethylene (HOPE) of 0.96 was replaced with linear low-density polyethylene (L-LDPE Rito, III = 1.5, ρ) of
A porous film was obtained in the same manner as in Example 2, except that polypropylene (PP) of 0.90 was used at a ratio of 3 nia.

The results of measuring the physical properties of the obtained film are shown in Table 2. [Effects of the invention] As is clear from the examples, the filler has an average particle diameter of 0.3 to 2.0 μm and a specific surface area of IOm/g or less. By using magnesium hydroxide that has undergone surface treatment, the following effects can be obtained.

(1) Compared to barium sulfate, it causes less secondary aggregation and has better dispersibility, so even if the amount added is small, high moisture permeability and uniform pore size distribution can be obtained.

(2) Since it has excellent stretchability and has a lower specific gravity than barium sulfate, a thin porous film with a basis weight of 10 g/rrf or less can be stably obtained industrially.

(3) As for extrudability, since magnesium hydroxide has a small Mohs hardness of 2.0 to 3.0, there is little wear on the cylinder of the extruder, allowing long-term use of the device and improving productivity.

The porous film of the present invention has excellent moisture permeability, air permeability, water resistance, and flexibility, and can be used for waterproof clothing such as rain gear, etc.
Disposable diapers, leak-proof films for sanitary materials, packaging materials,
Suitable for use as battery separators, filtration materials, etc. Also, due to its air permeability and moisture permeability, no condensation occurs, making it suitable for wallpaper and sheets for building materials.

Claims (1)

[Claims] 1. 100 parts by weight of polyolefin resin, 50% magnesium hydroxide having an average particle size of 0.3 to 2.0 μm, a specific surface area of 10 m^2/g or less, and surface-treated. ~
After melting and film-forming a resin composition consisting of 400 parts by weight,
A porous film characterized by being stretched at least 1.1 times in one direction. 2. The porous film according to claim 1, wherein the surface treatment is with a fatty acid, a fatty acid metal salt, or a fatty acid amide. 3. 100 parts by weight of polyolefin resin and an average particle size of 0
．． 3 to 2.0 μm, specific surface area is 10 m^2/g,
and surface-treated magnesium hydroxide 50-400
1. A method for producing a porous film, which comprises blending parts by weight, then melting and forming the film, and then stretching the film by a factor of 1.1 or more in at least one axis. 4. The method for producing a porous film according to claim 3, wherein the surface treatment is surface treatment with a fatty acid, a fatty acid metal salt, or a fatty acid amide.