JPH0655850B2 - Method for producing porous polyolefin membrane having permeability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a method for producing a polyolefin permeable porous membrane. Specifically, it relates to a method for producing a permeable porous membrane made of a polyolefin resin having fine pores. More specifically, it relates to a method for producing a permeable porous membrane by mixing a high molecular weight polyolefin and its plasticizer with an extruder to carry out inflation molding to obtain a film, and extracting and removing the plasticizer from the film.

<Prior Art and Problems Thereof> Conventionally, a polyolefin porous film has been produced, for example, by the following method.

A method in which the resin is mixed with a later extractable material, for example, paraffin wax, filler / plasticizer, other polymer, and the extractable material in the sheet is removed after forming the sheet. (JP-A-55-60537, 53-16077, 5
6-159128) However, since these methods add the above-mentioned extractable substances, it is difficult to form a film stably and at high speed, it is difficult to obtain a film having high air permeability and high strength, and the strength is low and brittle. In addition, the thickness of the film (or sheet) cannot be reduced, and it takes a long time to extract, which is a drawback. A method of stretching the film after extraction and removal to increase the strength is also shown, but it has a drawback that the process is complicated and the production cost is significantly increased because a stretching machine is used.

As another method, for example, there is a method in which a thermoplastic resin is melt-stretched, the resulting film is further stretched, and further heat-treated to form a porous film (Japanese Patent Laid-Open No. 46-40119, etc.). It has the drawbacks that it is difficult to increase air permeability, that it is very easy to tear in one direction, and that the process is complicated and the productivity cannot be increased.

<Purpose of the Invention> The present invention aims to provide a method for producing a high-performance porous permeable film at high speed with a simple process by eliminating the above-mentioned drawbacks of the conventional method.

<Means for Solving Problems> In the method of the present invention, when the melt is extruded while the high molecular weight polyethylene and the plasticizer are mixed by using an extruder, the inflation molding under extremely special conditions is used. The present invention relates to a method for obtaining a permeable film by obtaining a film and extracting and removing a plasticizer therefrom.

The gist of the present invention is to obtain a high molecular weight polyolefin (A) 5 to 70 having an intrinsic viscosity [η] in decalin of 135 ° C. of 3 dl / g or more.
A mixture of 95 to 30 wt% of wt% and a plasticizer (B) having a boiling point not lower than the melting point of (A) and soluble in a solvent is extruded into a cylinder using an annular die, and the expansion ratio is set to 50 times or more. A method for producing a porous polyolefin membrane having permeability, which comprises subjecting a film to a film by inflation molding and treating the resulting film with a solvent to extract and remove the component (B).

The features of the present invention are as follows.

The air permeability greatly depends on the porosity, but by using a high molecular weight polyolefin, stable molding can be performed even when a large amount of a plasticizer is used. Therefore, a film having a high porosity can be obtained and high air permeability can be obtained.

To obtain high air permeability, make the film thinner 1
Although it is one of the means, since high molecular weight polyolefin is used, strength or toughness can be secured even if it is thin.

Thin for the purpose of (specifically 200μ or less)
Various means are conceivable as the means for obtaining the film, but when molded by a special inflation method with the expansion ratio of 50 times or more as in the present invention, molecular orientation occurs biaxially at a temperature above the melting point of the polyolefin polymer. Therefore, a thin film with high air permeability and well-balanced vertical and horizontal strength can be obtained with a simple device structure. As a comparison, some cases using other means are shown.

a) T-die molding: If the die clearance is narrowed to obtain a thin-walled product, uneven flow and rough skin occur, and stable molding cannot be performed. Further, when the melt of the composition discharged from the T-die is stretched to be thinned, the composition can be stretched only in the uniaxial direction (the drawing direction), so that the pores of the finally obtained permeable porous film are crushed and the air permeability is reduced. It drops significantly. Also, the strength becomes very anisotropic.

b) Biaxially stretched below the melting point: If the sheet obtained by the T die molding as described above is biaxially stretched at a temperature above the melting point, a film with well-balanced longitudinal and lateral strength can be obtained. When a high molecular weight polymer is used as a material as in the present invention, the pores are largely crushed, and in this case also, the air permeability is greatly reduced. Further, in this case, a biaxial stretching machine is also required, which complicates the production process.

Next, a specific method of the present invention will be described in detail below.

The polyolefin used in the present invention includes ethylene, propylene, 4-methyl-1-pentene, 3-methyl-1.
A polymer obtained by polymerizing monomers such as butene, 1-butene, 1-hexene or a copolymer of these monomers. When the molecular weight is represented by the intrinsic viscosity [η] in decalin at 135 ° C., it is 3 dl / g or more, preferably 5 dl / g.
g or more. When it is less than 3 dl / g, the moldability is extremely poor when mixed with a plasticizer and molded as shown below.

The role of the plasticizer is to improve the extrudability of a high-molecular weight polymer in an extruder or the formability in inflation molding, and secondly to make the film porous and permeable by extracting and removing it in a later step. Is to bring. Considering this role, the plasticizer is required to have good compatibility with polyolefin and to be soluble in a solvent and to be easily removed by extraction. Even if the plasticizer is liquid at room temperature, it can be mixed with the polymer by devising a special device, but slippage is likely to occur when mixing with the polymer, and mixing is difficult, so plasticizers that have a boiling point above the melting point of polyolefin at the room temperature are solid. The agent is appropriate. Specifically, higher aliphatic alcohols such as paraffin waxes, capryl alcohol, lauryl alcohol, palmityl alcohol and stearyl alcohol are most suitable.

The boiling point of the plasticizer is required to be higher than the melting point of the polymer. However, if the plasticizer vaporizes during molding, it causes inconveniences such as lowering of working environment due to smoking and generation of bubbles in the molded product. This is because the boiling point of the plasticizer is preferably 10 ° C. or more higher than the melting point of the polyolefin used.

The mixing ratio of the polyolefin and the plasticizer is 95 to 30 wt% of the plasticizer with respect to 5 to 70 wt% (% by weight) of the polyolefin, more preferably 10 to 60 wt% of the polyolefin,
90 to 40 wt% of plasticizer. If the amount of the plasticizer is 95% or more, the moldability particularly during inflation molding becomes poor, and if it is 30% or less, the extrudability becomes poor and high air permeability cannot be obtained.

Next, inflation molding can be carried out by supplying a dry blend of polyolefin and a plasticizer to an apparatus for molding ordinary polyethylene or the like. However, as shown in Japanese Patent Application No. 60-214146 by the present inventors, a kneading effect can be obtained by cooling a part of the supply part to prevent vaporization of the plasticizer or by carrying out extrusion in a two-stage system. It can be raised and stable molding can be performed.

In inflation molding, the composition melt-mixed by an extruder is extruded as a tubular melt-molded product from an annular die attached to the tip of the extruder, and air is blown into the tubular body to expand the film, thereby achieving a thin film. However, in the method of the present invention, the blow-up ratio (BUR) is
(Diameter of tubular body / diameter of annular slit of die) and draft rate (DR) (take-off speed / extrusion speed) are set to be large. The expansion ratio (BUR × DR) is 50 times or more, preferably 1
It is more than 00 times, and a film having a thickness of several μ can be stably obtained.

In the present invention, although it depends on the product to be obtained, more stable moldability can be obtained by installing an air ring and cooling like the molding of ordinary polyethylene or the like.

Thus, the film is obtained by inflation molding under an extremely high expansion ratio. The plasticizer is extracted and removed from the obtained film. For example, when paraffin waxes are used as the plasticizer, heptane, hexane, ligroin, toluene, xylene, chloroform, etc., liquid aliphatic at normal temperature, alicyclic or It is carried out by immersing the film in a solvent such as an aromatic hydrocarbon or a halide thereof, or spraying the solvent on the film. Higher aliphatic alcohols such as stearyl alcohol can be removed by immersing them in lower alcohols such as methanol, ethanol and butanol. Further, it is more preferable to raise the temperature of these solvents for use in order to increase the extraction speed. For example, with a 50μ film using stearyl alcohol as a plasticizer, 50 ° C
If it is immersed in ethanol, it can be extracted and removed in about 10 seconds, but with a 200μ sheet, it takes about 200 seconds.
From this, it is better to form a thick sheet, extract the plasticizer and then stretch it to obtain a thin film, and then extract it after forming the originally thin film by inflation molding with a high expansion ratio, as in the present invention. It turns out that the production efficiency is very high.

The porous permeable film obtained as described above is used for various moisture permeable films, battery separators, etc. because of its high strength, good vertical / horizontal balance, high tear strength and high air permeability. I can do things. In addition, it has excellent fractionation of particles (open holes) and can be used as a microfilter.

<Examples> Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Various physical properties shown in the specification and examples of the present invention were measured according to the following methods.

-Porosity (%): (Void volume / Porous film volume) x
100-Air permeability (sec / 100cc): JIS-P-811
The air permeation time (second) of 100 cc of air was measured by a Gurley type densometer according to No. 7.

Tear strength (g): Measured according to JIS-P-8110.

Tensile strength (kg / cm ^2): conforms to ASTM D-882.

Example 1 20 wt% of high molecular weight polyethylene powder having an intrinsic viscosity [η] = 13.5 and 80 wt% of stearyl alcohol were dry-blended in a plastic bag, and the blended product was fed to a 40 mmφ extruder and melt-mixed in the extruder. The mixture was fed in a molten state to a 20 mmφ extruder. An annular die having an outer diameter of 30 mm and an inner diameter of 29 mm installed at the tip of the extruder was extruded as a cylindrical melt-molded product at a resin temperature of 190 ° C., and air was blown into the inside of the cylindrical body for inflation molding. At this time, water cooling was performed from under the hopper of the 40 mmφ extruder to half the length of the supply section using a water cooling jacket. The inflation molding conditions are DR (draft ratio) = 11.1 and BUR (blow-up ratio) = 5.
Conducted in 1. The molding was performed stably. This film was immersed in ethanol at 55 ° C. for 15 seconds to extract and remove stearyl alcohol. After extraction and removal, a white permeable porous film was obtained.

The physical properties of the film are a film thickness of 5 μ and a porosity of 68.
%, Air permeability 10 sec / 100 cc, tensile strength vertical 27
It was 0 and the width was 250 kg / cm ² .

Comparative Example 1 Using the same raw material and extruder as in Example 1, a T die with a width of 20 cm was installed at the tip of a 20 mmφ extruder, and the following tests were conducted.

1) The test was conducted with a clearance of 0.2 mm,
The sheet could not be extruded stably.

2) When the clearance was set to 0.5 mm and the draft rate (DR) was increased, the melt started to break at DR = 3.5. That is, it was difficult to reduce the thickness to 100 μm or less by T-die molding.

Comparative Example 2 T-die molding was performed as in Comparative Example 1. The die clearance is 0.5 mm and DR = 3. The thickness of the obtained film was 170μ. The film was treated with ethanol to remove stearyl alcohol, but it took 4 minutes. The physical properties of the obtained permeable porous film were as follows.

Film thickness 95μ, porosity 56%, air permeability 830se
c / 100 cc.

Compared to Example 1, it shows that the pores are collapsed and the air permeability is greatly reduced.

Comparative Example 3 T-die molding was performed in the same manner as Comparative Example 2. The die clearance is 1.0 mm and DR = 1.0. This sheet was stretched 4 times lengthwise and 4 times widthwise at a temperature of 120 ° C. using a biaxial stretching machine, and the film was immersed in ethanol at 55 ° C. for 15 minutes in the same manner as in Example 1 to extract and remove stearyl alcohol. The physical properties of the obtained permeable porous film are as follows. Film thickness 32μ, porosity 52%, air permeability 58
0 sec / 100 cc, tear strength vertical 7 g, horizontal 7 g.

Example 2 Molded with DR and BUR shown in Table-1, the outer diameter of the die was 3
The inner diameter of the die is changed without changing 0 mm, and the other is the first embodiment.
A permeable porous membrane was obtained in the same manner as in. The results are shown in Table-1.
Shown in.

<Effect of the Invention> According to the method of the present invention, it becomes possible to produce a porous polyolefin film having gas permeability with high efficiency, and the obtained film is very excellent in strength.

For example, filters, film applications that require transparency,
A very suitable film can be obtained by using it.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B29L 7:00 4F

Claims (5)

[Claims] 1. The intrinsic viscosity [η] in decalin at 135 ° C. is 3
High molecular weight polyolefin (A) of dl / g or more 5 to 70 wt
% And a mixture of 95 to 30 wt% of a plasticizer (B) having a boiling point not lower than the melting point of (A) and soluble in a solvent is extruded into a cylinder using an annular die, and the expansion ratio is set to 50 times or more and inflation is performed. A process for producing a porous polyolefin membrane having permeability, which comprises molding to obtain a film, and treating the obtained film with a solvent to extract and remove the component (B). 2. The method according to claim 1, wherein [η] of the high molecular weight polyolefin (A) is 5 dl / g or more. 3. The method according to claim 1, wherein the plasticizer (B) is solid at room temperature. 4. High molecular weight polyolefin (A) 10-60
The manufacturing method according to any one of claims 1 to 3, wherein a mixture of wt% and a plasticizer (B) of 90 to 40 wt% is used. 5. The manufacturing method according to any one of claims 1 to 4, wherein inflation molding is performed with a development magnification of 100 times or more.