JP2000344930A - Microporous film of polyolefin having high molecular weight and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a microporous polyolefin having high molecular weight and capable of adjusting the porosity and air permeability after the heat-treatment of a high-molecular weight polyolefin film in a liquid to form a microporous structure. SOLUTION: This process for the production of a microporous film of a high-molecular weight polyolefin comprises the heat-treatment for forming a microporous structure of a high-molecular weight polyolefin film in a 1st liquid to selectively melt or dissolve the amorphous part of the polyolefin at the treatment temperature, the immersion of the heat-treated film in a 2nd liquid, the drying of the film and the pressing of the product after drying the microporous film of high-molecular weight polyolefin.

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 microporous high molecular weight polyolefin film suitable for use as a filter material or a separator for non-aqueous batteries, and more particularly, to a method for suppressing the porosity of a microporous film. The present invention relates to a method for producing a high-molecular-weight polyolefin microporous film capable of increasing air permeability.

[0002]

2. Description of the Related Art A method for producing a high-molecular-weight polyolefin microporous film has hitherto been disclosed, for example, in Japanese Patent Publication No. 6-28.
No. 41, No. 6-53826, No. 7-1778
Various proposals have been made in, for example, Japanese Patent Application Laid-open No. 2 (1994).

[0003] In any of these methods, in order to obtain a microporous film, a high molecular weight polyolefin is added to a hydrocarbon solvent such as decane, dodecane, decalin, paraffin oil, or mineral oil, or a fatty acid such as a fatty acid, a fatty acid ester, or an aliphatic alcohol. After forming a film by adding a plasticizer composed of a hydrocarbon derivative, paraffin wax or a low molecular weight compound such as dioctyl phthalate or dibutyl sebacate, the low molecular weight compound is removed from the film to make it microporous. .

On the other hand, there has been proposed a method for producing a microporous film without adding a low-molecular-weight compound, as disclosed in Japanese Patent Publication Nos. 2-19141 and 6-18915. It is essential to stretch the film to make it microporous. Both methods are applied to polyethylene having a relatively low molecular weight (melt flow rate: 0.2 to 20 g / 10 min), and the tensile strength of the film is 0.02 GPa or less, or at most 0.03 GPa. is there.

Accordingly, the present applicant has previously filed Japanese Patent Application No.
No. 5501 proposed a method for obtaining a microporous film having high strength without adding a low molecular weight compound which needs to be removed from the microporous film to the polyolefin. In this method, a high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent is heat-treated, and if necessary, stretched before or after the heat treatment to make it porous. Etc., by selectively melting or dissolving the amorphous portion of the polyolefin in a first liquid, and then treating the heat-treated film with a first liquid that is compatible with the first liquid and has a higher boiling point than the first liquid. It is immersed in a second liquid having a low affinity with polyolefin and dried.

According to this method, a high-strength microporous film can be produced without passing through a low-molecular-weight compound extraction step of a plasticizer and / or a solvent in a polyolefin, and a film excellent in micropore closing property by heating can be obtained. can get.

[0007] The microporous film obtained by this method has a film physical property value in a range of porosity and air permeability suitable for a filter material and a separator for a non-aqueous battery.
These properties tend to increase the air permeability as the porosity increases, while the film strength decreases as the porosity increases. Therefore, how to balance these film properties is an important point in the manufacturing method.

However, the porosity and the air permeability of the microporous film vary depending on various factors such as the physical properties of the raw material film and the heat treatment conditions for making the microporous film. It was not easy to obtain a microporous film having air permeability.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a microporous film in which a high molecular weight polyolefin film is heat-treated in a liquid to make it microporous, and the porosity and air permeability of the microporous film are reduced. To provide a method for producing a microporous film of high molecular weight polyolefin, which can be adjusted after the microporation treatment.

[0010]

The process for producing a microporous high molecular weight polyolefin film according to the present invention has been proposed in order to achieve the above-mentioned object, and is intended for making microporous high molecular weight polyolefin films. The heat treatment is performed in a first liquid that selectively melts or dissolves the amorphous portion of the polyolefin at a processing temperature, and then the heat-treated film is immersed in a second liquid and then dried to obtain a high molecular weight polyolefin microporous material. A method for producing a film, wherein the microporous film is compressed after drying.

In the production method of the present invention, the high-molecular-weight polyolefin film before the treatment is a polyolefin-impermeable film having a limiting viscosity [η] of 4 dl / g or more, which does not substantially contain a plasticizer and / or a solvent. Is preferred.

Further, in the production method of the present invention, the high-molecular-weight polyolefin film before the processable treatment may have a crystallinity of 40.
% Or more.

[0013] In the manufacturing method of the present invention, it is preferable that the heat treatment is performed while restraining the film.

In a preferred embodiment of the production method of the present invention, the first liquid is a lower aliphatic alcohol, a lower aliphatic ketone, a lower aliphatic ester, a halogenated hydrocarbon, a hydrocarbon, a nitrogen-containing organic compound, an ether. It is desirably at least one liquid selected from the group consisting of water containing water, glycol, silicone oil and surfactant.

In a preferred embodiment of the production method of the present invention, the second liquid is a liquid having a boiling point of 120 ° C. or lower and is substituted with fluorine or a hydrocarbon compound substituted with fluorine and chlorine. Or an ether compound having at least one hydrocarbon group substituted with fluorine or substituted with fluorine and chlorine.

[0016] In a preferred embodiment of the production method of the present invention, it is desirable that the compression of the microporous film is performed by a roll press.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A high molecular weight polyolefin film used in the method for producing a high molecular weight polyolefin microporous film of the present invention, a microporous method (heat treatment), a first liquid, a second liquid, and an obtained film The compression method will be described in detail below.

[High-Molecular-Weight Polyolefin Film] The high-molecular-weight polyolefin used as a raw material for forming a film is obtained by subjecting ethylene, propylene and an α-olefin having 4 to 8 carbon atoms to single or two or more polymerization by slurry polymerization using a Ziegler catalyst. And obtained by polymerization. Preferred copolymers are copolymers of ethylene with a small amount of propylene or one or more of α-olefins having 4 to 8 carbon atoms. In the case of polyethylene copolymer, the amount of comonomer is 5
It is preferably at most mol%. Particularly preferred among these are ethylene homopolymers.

Intrinsic viscosity [η] of high molecular weight polyolefin
Is preferably 4 dl / g or more, more preferably 4 to 25 dl / g, and particularly for the purpose of obtaining a high-strength microporous film, the intrinsic viscosity [η] is preferably 5 to 20 dl / g.

The film can be formed by a conventionally known inflation film method, T-die method or the like, and the high molecular weight polyolefin film used in the present invention is preferably a plane oriented film. Among them, the general method of forming an inflation film is described in detail in "Plastic Extrusion Molding and Its Application" by Keiji Sawada, published by Seibundo Shinkosha (196
6 years)], Vol. 4, Chapter 2, which is performed with polyethylene or polypropylene.

In the T-die film forming method, when the film is melt-drawn, the film to be formed is uniaxially oriented.
After molding, the film must be plane-oriented by post-processing, but the inflation film molding method is preferable because the film can be plane-oriented at the time of molding by appropriately selecting the expansion ratio.

A preferable condition for forming the blown film is to make the draft ratio and the expansion ratio large. The draft ratio is the ratio between the outflow speed of the film resin at the lip exit of the blown film die and the take-off speed of the cooled and solidified tube film, and the expansion ratio is the diameter of the cooled and solidified tube film and the inflation film. It is the ratio to the average diameter of the die. In a normal case, the draft ratio is appropriately adjusted in a range of 2 or more, but a preferable range is 3 or more, and the expansion ratio is appropriately adjusted in a range of 1.1 to 20 times. Blown film of high molecular weight polyolefin is, for example,
It can be manufactured by the method described in detail in US Pat.

It is preferable that the film used in the present invention contains substantially no plasticizer and / or solvent. Substantially free means that a large amount of plasticizer and / or solvent is not added to the raw material polyolefin. Therefore, various additives used in addition to the polyolefins, such as heat stabilizers, weather stabilizers, lubricants, antiblocking agents, slip agents, pigments, dyes, etc., are blended within a range that does not impair the object of the present invention. However, the upper limit is preferably 10% by weight or less in total, more preferably 5% by weight or less.

In any of the film forming methods, a preferable film obtained is one having an intrinsic viscosity [η] of 4 to 25 dl / g and a crystallinity of preferably 40% or more, more preferably 50% or more. In the case of polyethylene in particular, it is preferably at least 60%, more preferably 6%.
0 to 70%, 0.04 GP in machine direction tensile strength
at least 0.04G in tensile strength in the direction perpendicular to the machine direction
It is an air-impermeable film having a Pa of not less than 40 Pa and a moisture permeability coefficient of, for example, 0.45 g · mm / m ² · 24 hr or less under conditions of a temperature of 40 ° C. and a humidity of 90%. The impermeable film is a film having an air permeability of 10,000 seconds / 100 cc or more in an air permeability test described later. The thickness of the obtained film is not particularly limited, but is preferably 5 to 500 μm, more preferably 5 to 1 for convenience of handling in the subsequent processing steps.
00 μm.

The film used for the microporous treatment of the present invention is preferably plane-oriented. The plane orientation in the present invention means that the crystal is biaxially oriented. That the film is biaxially oriented means that among the unit crystals of the polyolefin in the film plane, either the a-axis or the b-axis other than the c-axis corresponding to the molecular chain direction is mainly perpendicular to the film plane. It refers to a state in which it exists and a state in which, for example, the c-axis other than the axis is almost non-oriented in the film plane. The axis perpendicular to the film plane is usually the a-axis in the case of polyethylene, and is usually the b-axis in the case of other polyolefins.

This state can be confirmed by observation with an X-ray diffractometer as follows. In other words, when the X-rays are incident on the film placed in the equator direction from the end (END) direction of the film and the diffraction pattern is observed,
In the case of polyethylene, the orientation coefficient fa (in the case of other polyolefins, fb) is at least 0.2 or more, and the machine axis direction of the film is arranged so as to be in the meridian direction. And the diffraction pattern was observed when the diffraction coefficient was −0.0.
It is in a state where it is 2 or more and 0.2 or less.

The method of obtaining and calculating the orientation coefficients fa, fb, and fc is described in “X-ray diffraction of polymer (upper)” [LEROY
E. FIG. ALEXANDER, translated by Ichiro Sakurada, Doujin Kagaku]
As described in the section on the preferred orientation. Especially fc
Exceeds 0.2 (c-axis oriented state) or when fa is 0.2
In the case of a film having a crystallinity lower than the above, even if the crystallinity satisfies the above condition, it may not be possible to make the film microporous by heat treatment.

[Heat Treatment] The above-mentioned heat treatment for making the high molecular weight polyolefin film microporous is performed in a first liquid which selectively melts or dissolves the amorphous portion of the polyolefin at the treatment temperature. Such a first liquid has a moderate affinity for a high molecular weight polyolefin.
The conditions of the heat treatment vary depending on the state of the atmosphere, but in the case of polyethylene, for example, usually 100 ° C. to 145 ° C.
It is preferable to carry out at a temperature of 10 seconds to 10 minutes under such a condition that the crystallinity after the treatment is increased by about 10 to 20% as compared to before the treatment. At this time, the film is preferably fixed in at least one direction, more preferably in two directions, and particularly in two orthogonal directions so as to prevent shrinkage. If shrinkage is forced, the preferred shrinkage tolerance is 10% in the length and width directions.
Within.

[First liquid] The first liquid having a suitable affinity for the high molecular weight polyolefin is defined as a crystal of the film when the film before the treatment of the high molecular weight polyolefin is immersed in the first liquid at the processing temperature. It does not act on the part but penetrates mainly into the amorphous part, selectively melts or melts the amorphous part, and crystallizes part of it by cooling, so that the overall crystallinity can be increased. is there. Therefore, a solvent having remarkably excellent affinity and dissolving polyolefin crystals in a heat treatment temperature range is excluded.

It should be noted that having an affinity for a high molecular weight polyolefin means that the liquid is sufficiently compatible with the high molecular weight polyolefin film, and can be rephrased as having a low surface tension. And the scale is 100 in contact angle.
It is a liquid having a temperature of not more than 90 °, preferably not more than 90 °, more preferably not more than 80 ° (the surface tension can be measured by a conventional method using a commercially available automatic contact angle meter).

The term “liquid that does not dissolve the high molecular weight polyolefin crystals in the heat treatment temperature range” means that the melting point of the high molecular weight polyolefin is secondarily determined in the presence of a liquid by a differential scanning calorimeter (DSC) equipped with a solution cell. When observed, compared to the case of high molecular weight polyolefin alone,
It is a liquid that does not lower its melting point by 20 ° C. or more. Since the affinity of the liquid for the high-molecular-weight polyolefin varies depending on the treatment temperature, a suitable affinity can be obtained by selecting the treatment temperature and the type of the liquid, and the effect of the porous structure can be maximized.

The first liquid having the above properties includes:
Lower aliphatic alcohols such as ethanol, propanol, butyl alcohol and amyl alcohol; lower aliphatic ketones such as acetone, methyl ethyl ketone and cyclohexanone; lower aliphatic esters such as ethyl formate and butyl acetate; carbon tetrachloride Halogenated hydrocarbons such as trichloroethylene, perchlorethylene, chlorobenzene, etc .; hydrocarbons such as heptane, cyclohexane, octane, decane, dodecane, paraffin oil, molten paraffin wax, etc .; pyridine, formamide, dimethylformamide etc. Nitrogen-containing organic compounds; methyl ether, ethyl ether, dioxane,
Preferred examples include ethers such as butyl cellosolob; glycols such as monoethylene glycol, diethylene glycol, and triethylene glycol; silicone oil; warm water and hot water to which a surfactant is added. These liquids can also be used as a mixture of two or more.

Among such first liquids, hydrocarbons are preferred, and heptane, cyclohexane, octane, decane, dodecane and paraffin oil are particularly preferred. Among the first liquids, the viscosity at 30 ° C. is 15
It is more preferred that it is not more than cst, preferably 0.1 to 10 cst.

The heat treatment temperature depends on the kind of the polyolefin and the kind of the liquid, but for example, as described above, in the case of polyethylene, it is usually 100 ° C. to 145 ° C., preferably 115 ° C. to 140 ° C. In the case of polyolefins other than polyethylene, the processing temperature is usually 50 ° C to 150 ° C, preferably 80 ° C to 140 ° C.
Generally, the processing time is 10 seconds to 10 minutes, preferably 30 seconds to 5 minutes after the film before processing reaches the processing temperature.
Minutes, and a higher processing temperature can shorten the processing time. In addition, it is preferable to avoid an unnecessary processing time because there is a possibility that the tensile strength of the microporous film may be reduced.

[Liquid Substitution and Drying] The microporous film that has been heat-treated in the first liquid is immersed in the second liquid, replaced with the liquid, and then dried. [Second Liquid] The second liquid that is liquid-replaced with the first liquid is preferably a liquid that is compatible with the first liquid and has poor affinity for polyolefin. And, in the present invention, in particular, a hydrocarbon compound substituted with fluorine or substituted with fluorine and chlorine, or having at least one hydrocarbon group substituted with fluorine or substituted with fluorine and chlorine Ether compounds are preferred. In the present invention, as the hydrocarbon compound substituted with fluorine or substituted with fluorine and chlorine, hydrofluorocarbon is an ether compound having at least one hydrocarbon group substituted with fluorine or substituted with fluorine and chlorine. Examples thereof include hydrofluoroether. These are low-toxic, flame-retardant liquids that do not destroy the ozone layer. In the present invention, the boiling point of the second liquid is
Preferably, it is lower than the boiling point of the first liquid.

The hydrofluorocarbon is a fluorinated hydrocarbon compound in which a part of hydrogen atoms of a hydrocarbon is substituted only by a fluorine atom and does not contain a chlorine atom, and preferably has a boiling point of 120 ° C. or less. Examples of these are 1,1,1,
2,3,4,4,5,5,5-decafluoropentane (boiling point 55 ° C), 1,1,
2,2,3,3,4,4-octafluorobutane (boiling point 44 ° C), 1,1,2,
2,3,3,4-heptafluorocyclopentane (boiling point: 82 ° C.) and the like.

The hydrofluoroether is a fluorinated ether in which a part of hydrogen atoms of ethers is substituted only by a fluorine atom and does not contain a chlorine atom, and preferably has a boiling point of 120 ° C. or less. Examples of these are 1,2,2,2,-
Tetrafluoroethyl-heptafluoropropyl ether (boiling point 40 ° C), 1,1,1,2,3,3-hexafluoro-2-heptafluoropropoxy-3- (1,2,2,2-tetrafluoroethoxy ) -Propane (boiling point 104 ° C), 1,1,1,2,2,3,3,4,4-nonafluoro-methyl ether (boiling point 60 ° C), 1,1,1,2,2,3,3 ,
4,4-nonafluoro-ethyl ether (boiling point 78 ° C.) and the like.

The treated film immersed in the second liquid is preferably fixed in at least one direction and most preferably in two orthogonal directions so as to suppress shrinkage during immersion as in the heat treatment. is there. If shrinkage is forced, the preferred range of shrinkage is within 10% in the length and width directions.

The immersion in the second liquid is preferably performed by heating the second liquid and / or applying ultrasonic vibration to the second liquid. The temperature for heating the second liquid varies depending on the type of liquid, but is preferably 30 ° C.
Above, more preferably 30 ° C. to the boiling point of the second liquid,
More preferably, it is the boiling point of the second liquid. By immersing in the second liquid at 30 ° C. or higher, the first liquid is efficiently replaced with the second liquid in a short time. Therefore, the immersion time in the second liquid is greatly reduced, and particularly in continuous production, the film running length in the liquid tank can be significantly reduced. Moreover, the good properties of the microporous film are hardly impaired. The atmospheric pressure may be normal pressure, under pressure, or under reduced pressure, but usually at normal pressure.

The microporous film immersed in the second liquid is dried. After drying, heat setting may be performed to remove wrinkles in the film, adjust the porosity and film thickness, and reduce the surface friction coefficient of the film. As the conditions for the heat setting, a temperature, a processing time, and the like in a gas (air) atmosphere are appropriately selected.

[Stretching] In the present invention, when performing a heat treatment for making the high molecular weight polyolefin film microporous, in order to obtain a film having a higher tensile strength, or to adjust the porosity and pore diameter of the film. Stretching may be performed simultaneously with the heat treatment, or may be performed before and after the heat treatment.

The stretching is performed at a temperature lower than the melting point of the film before heat treatment. Although the lower limit of the stretching temperature depends on the type of the high molecular weight polyolefin, it is around the melting point of the film −40 ° C. If the high molecular weight polyolefin is polyethylene, 100
° C to 145 ° C. The stretching ratio is 150% or more, preferably 150% to 500% in the case of uniaxial stretching.
It is. In the case of uniaxial stretching, uniaxial stretching with a constant width is preferred. In the case of biaxial stretching, the area ratio is 150% or more, preferably 150% to 2500%.

The stretching may be performed in an air atmosphere,
In addition, as described in the above-described heat treatment, the heat treatment may be performed in contact with the first liquid to be subjected to heat treatment. The stretching method is
Uniaxial stretching that minimizes lateral width shrinkage (width drop), uniaxial stretching that prevents lateral shrinkage with a tenter clip, or sequential use of all tenter clips performed by a normal biaxial stretching tester Alternatively, simultaneous biaxial stretching, and further, continuous sequential biaxial stretching in which the first stage is stretched with a pair of rolls and then stretching in the transverse direction with a tenter clip, or continuous simultaneous biaxial stretching in a continuous tenter clip system can be applied.

[Compression] The high molecular weight polyolefin microporous film obtained by the above operation is
Has a film property of relatively high porosity in the treatment with the liquid. Therefore, although the air permeability also has a high value, in applications requiring film strength, a high porosity is not preferable because it lowers the strength. On the other hand, it is desired that the air permeability is always high. Therefore, in order to lower the porosity without significantly lowering the air permeability, the microporous film is compressed.

The compression may be performed simply by a flat plate press, but is preferably performed by a roll press in order to perform a continuous compression process. The compression pressure is appropriately determined so as to obtain a desired porosity, for example, a microporous film thickness of 10 to 1000 μm.
m, usually 1 to 200 kg / cm ² , preferably 1
It is 0 to 150 kg / cm ² .

[Microporous Film of High Molecular Weight Polyolefin] In the present invention, the microporous film of high molecular weight polyolefin obtained by the heat treatment has, for example, fibrils having a leaf-like and / or network shape as main components. A vein-like and / or mesh-like fibril is a state in which a fibril constituting a film has a thick stem fiber and a thin fiber connected to the outside thereof, and the thin fiber forms a complex network structure. Say.

In the microporous film obtained by the present invention, the voids formed between the fibrils can be narrowed without significantly reducing the air permeability. Regardless, it has excellent strength, especially tensile strength and piercing strength. In addition, it has suitable membrane properties as a filter material and a separator for a non-aqueous battery as described below.

The porosity is selected in the range of, for example, 25 to 60% or more by subjecting the microporous film to a compression treatment while selecting the heat treatment of the film before the treatment and, if necessary, the stretching treatment conditions. be able to.
The air permeability can be set to a Gurley value of 1900 seconds / 100 cc or less, preferably 1500 seconds / 100 cc or less. Tensile strength is calculated based on the actual cross-sectional area of the film, depending on the choice of porosity value, and is, for example, 0.1 mm in all directions.
It is at least 05 GPa, preferably at least 0.08 GPa. The average pore diameter is not particularly limited, but is, for example, 0.01 to 1.0 μm.

The above properties in the present invention can be measured by the following methods. 1. Intrinsic viscosity This is a value measured at 135 ° C in a decalin solvent. The measuring method was performed based on ASTM D4020. 2.Film thickness Tokyo Precision Co., Ltd.
-150 type).

3. Average pore diameter The maximum value of the pore diameter measured by a mercury porosimeter manufactured by Yuasa Ionics (Model Autoscan 33) was defined as the average pore diameter. 4. Porosity The weight of the sample film was measured, the density as 0.95 g / cm ³ , and the thickness as a dense film was calculated. Porosity (volume%) = [(To−Tw) / To] × 100 where To is the actual film thickness determined by a film thickness measuring instrument, and Tw is the porosity 0% calculated from the weight. Is the thickness as a film (dense film).

5. Tensile Strength Tensilon (Model RTM) manufactured by Orientec Co., Ltd.
100 type) at room temperature (23 ° C.). ASTM D8
It was measured and calculated based on Method A of 82 (sample width 15 mm). 6. Air permeability (Gurley test) In accordance with ASTM D727, the film was coated with a standard Gurley Densometer (B) manufactured by Toyo Seiki Seisaku-sho, Ltd.
(Gurley densometer). 7. Melting point The melting point in the present invention is a value measured by a differential scanning calorimeter (DSC) according to ASTM D3417.

8. Crystallinity The crystallinity in the present invention is measured by a differential scanning calorimeter (DSC).
When the melting point was measured under the conditions shown in ASTM D3417, the heat of fusion measured simultaneously was used and calculated as a ratio to the value of the theoretical heat of crystal dissolution. 9.Puncture strength Orientec Tensilon tensile tester (Model: RT
(M100 type) at 23 ° C. at a crosshead speed of 120 mm / min. As the piercing needle, a needle having a needle tip of 0.5 mmR and a diameter of 1 mm was used, and the force when the needle pierced the film was defined as the piercing strength. The piercing film was fixed with a 15 mmφ circular fixed frame.

[0053]

EXAMPLES (Experimental Example 1) In a blown film manufacturing apparatus shown in FIG. 1, a polyethylene blown film was manufactured using one having the following specifications. <Specification of Apparatus> First screw outer diameter of the extruder 50 mmφ First screw effective length 1100 mm First screw flight pitch 30 mm (constant) First screw compression ratio 1.8 Screw die effective length 1490 mm (L / D = 28) Die outlet outer die inner diameter 53mmφ Die outlet mandrel outer diameter 45mmφ Second screw outer diameter 70mmφ Second screw effective length 238mm Second screw flight pitch 25mm (constant) Second screw compression ratio 1.0 Stable rod outer diameter 39mmφ Stable rod Length: 600 mm Gas flow path: 8 mmφ Other components include a stabilizer, a pinch roll, and a product winder (not shown).

<Production of blown film> Polyethylene (intrinsic viscosity [η]: 7.5 dl / g, melting point: 13
Using a powdered resin having a temperature of 6 ° C. and a bulk density of 0.45 g / cm ³ ), the extruder and the set temperature of the joint portion (J), the die base portion (D1) and the die tip portion (D2) shown in FIG.
0 ° C., 180 ° C., 160 ° C., 160 ° C., the first screw rotation speed was 21 rpm, and the second screw rotation speed was 4.5.
rpm, and while taking in with a pinch roll at a speed of 7.7 m / min, compressed air was blown from an 8 mmφ gas flow path extending inside the second screw, the mandrel and the stabilizer rod shaft, Outer die inner diameter 5 with parison
Inflate to 8.5 times 3mmφ, fold width 710mm,
A high-molecular-weight polyethylene blown film having a thickness of 13.5 μm was produced stably.

<Microporization (Heat Treatment)> Using the obtained blown film, a heat treatment was performed as follows. The inflation film 32 was sandwiched between a pair of stainless steel frames 33 shown in FIG. 2 and fixed to the upper and lower frames by screws 34, thereby fixing the four sides of the film.
In this state, the viscosity (30 ° C.) heated to 122 ° C. 6 cst
Into a tank filled with paraffin oil, heat-treated for 1 minute, then taken out of the heat-treatment tank, and 1,1,1,2,2,3,3,4,4 with the film fixed to the metal frame 70 filled with -nonafluorobutyl-ethyl ether (C ₄ F ₉ OC ₂ H ₅ )
It was thrown into a bath at ℃ and immersed for 30 seconds. This was taken out and air-dried at room temperature to obtain a 33 μm-thick microporous film.
Remove the film from the metal frame, press pressure 30k at 50k
The film was compressed under the condition of g / cm ² until the film thickness became 26 μm. Table 1 shows the physical properties of the microporous film before and after the compression operation.

(Experimental Example 2) The same procedure as in Experimental Example 1 was conducted except that the pressing pressure of the microporous film was 100 kg / cm ² and the thickness of the film after compression was 21 μm. Table 1 shows the physical properties of the microporous film before and after the compression operation.
It was shown to.

(Experimental Example 3) The microporous film obtained in Experimental Example 1 before the compression treatment was rolled at a temperature of 30 ° C. and a compression pressure of 50%.
A compression treatment was performed through a roll at kg / cm ² .
Table 1 shows the physical properties of the microporous film before and after the compression operation.

(Comparative Experimental Example) The microporous film obtained in Experimental Example 1 before the compression treatment was treated at 132 ° C. instead of the compression treatment.
Under an atmosphere of 90 seconds. The physical properties of this film before and after the heat setting operation are shown in Table 1 together with the physical properties of each experimental example.

[0059]

[Table 1]

[0060]

According to the present invention, the heat treatment for making the high-molecular-weight polyolefin film microporous is performed in the first liquid which selectively melts or dissolves the amorphous portion of the polyolefin at the treatment temperature. Then, in a method for producing a high-molecular-weight polyolefin microporous film, in which the heat-treated film is immersed in a second liquid and then dried, the porosity and air permeability of the obtained microporous film can be adjusted. Appropriate film properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an example of a molding apparatus for producing a high molecular weight polyolefin film in the present invention.

FIG. 2 is a view showing one example of a metal frame for fixing a film before processing in the present invention when the film is heat-treated.

[Explanation of symbols]

 Reference Signs List 1 extruder 2 grooved cylinder 3 first screw 10 torpedo 11 pressure gauge 20 screw die 20A second screw tip 20B screw die middle part 20C screw die outlet 21 second screw 22 outer die 23 mandrel 24 gas flow path 25 air ring 26 Stabilizing rod 27 Windproof tube 30 Parison 31 Inflation film 32 Screw 33 Metal frame

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 23:02 (72) Inventor Masaaki Ohashi 6-1-2, Waki, Waki-machi, Kuga-gun, Yamaguchi Prefecture Mitsui Chemicals (72) Inventor Hiroshi Koizumi 1-2-1, Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term (reference) 4F074 AA17 AA24 AA26 CB03 CB05 CB17 CB27 CB28 CC03Z CC27Z CC28Z CC29Z CC32Y DA43 DA49

Claims (7)

[Claims] 1. A heat treatment for microporousization of a high molecular weight polyolefin film is performed at a processing temperature in a first liquid that selectively melts or dissolves an amorphous portion of the polyolefin, and then heat-treats the film. A method for producing a microporous high molecular weight polyolefin film, comprising: immersing the microporous film in a second liquid, followed by drying, and compressing the microporous film after drying. 2. The high-molecular-weight polyolefin film before the treatment is a polyolefin-impermeable film having an intrinsic viscosity [η] of 4 dl / g or more, which does not substantially contain a plasticizer and / or a solvent. A method for producing a high-molecular-weight polyolefin microporous film. 3. The method for producing a microporous high molecular weight polyolefin film according to claim 1, wherein the high molecular weight polyolefin film before the treatment is a plane oriented film having a degree of crystallinity of 40% or more. 4. The method for producing a high-molecular-weight polyolefin microporous film according to claim 1, wherein the heat treatment is performed under constraint of the film. 5. The first liquid is a lower aliphatic alcohol, a lower aliphatic ketone, a lower aliphatic ester, a halogenated hydrocarbon, a hydrocarbon, a nitrogen-containing organic compound, an ether, a glycol, a silicone oil, a surfactant. The method for producing a microporous high molecular weight polyolefin film according to claim 1, which is at least one liquid selected from the group consisting of water containing: 6. The second liquid has at least one fluorine-substituted or fluorine- and chlorine-substituted hydrocarbon compound or a fluorine-substituted or fluorine- and chlorine-substituted hydrocarbon group having a boiling point of 120 ° C. or lower. The method for producing a high-molecular-weight polyolefin microporous film according to claim 1 or 5, which is an ether compound. 7. The method according to claim 1, wherein the compression of the microporous film is performed by a roll press.