JP2001055466A - Production of high-molecular weight polyolefin microporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly safe method for producing the subject microporous film excellent in physical property balance and large in average pore size through heat treatment of a high-molecular weight polyolefin film in a low-toxic, flame-retardant liquid causing no ozone layer depletion. SOLUTION: This method for producing the subject film comprises the following steps: a high-molecular weight polyolefin film is heat-treated in a 1st liquid which can selectively melt or dissolve the noncrystalline portion of the film at the heat treatment temperature, and the film thus heat-treated is then soaked in a 2nd liquid and subsequently dried; wherein the 1st liquid to be used is <=15 cst in viscosity at 30 deg.C, while the 2nd liquid to be used is a chlorine-free fluorocarbon-based compound.

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 high-molecular-weight polyolefin microporous film used for a filtration material, a separator for non-aqueous batteries, and the like.

[0002]

BACKGROUND OF THE INVENTION A method for producing a microporous film of high molecular weight polyolefin has been described, for example, in Japanese Patent Publication No.
No. -2841, No. 6-53826, No. 7-1
Various proposals have been made in, for example, US Pat.

[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 minutes), and the tensile strength of the film is 0.02 GPa or less, or at most 0.03 GPa. .

Accordingly, the present applicant has previously disclosed in Japanese Patent Application Laid-Open No. 10-3
No. 06168 proposes 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. Is performed by selectively melting or dissolving the amorphous portion of the polyolefin in a first liquid such as
Next, the heat-treated film is dipped in a second liquid that is compatible with the first liquid, has a lower boiling point than the first liquid, and has poor affinity for polyolefin, and is 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. By the way, as the second liquid used in this method, a hydrocarbon liquid such as chlorofluorocarbon is preferable from the viewpoint of low toxicity, nonflammability, and low corrosion. However, in recent years, hydrocarbons containing these chlorine atoms are hardly decomposed in the air due to their chemical stability, and destroy the ozone layer that protects the earth from the ultraviolet rays of the sun. It has become.

Therefore, the second liquid is converted from a hydrocarbon liquid such as chlorofluorocarbon to a perfluorocarbon liquid in which all the hydrogen atoms of the hydrocarbon are replaced with fluorine atoms, or a hydrocarbon liquid such as a fluorocarbon substitute. It is possible to change to a hydrofluorocarbon liquid or the like in which part of the hydrogen atoms are replaced with fluorine atoms and do not contain chlorine atoms, but only by this method, the porosity suitable for a filter material or a non-aqueous battery separator in the above method. It has been difficult to obtain a film property value with a good balance of air permeability, pore size, and the like.

[0008]

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, without destroying the ozone layer and having low toxicity. An object of the present invention is to provide a method for producing a high-molecular-weight polyolefin microporous film which is excellent in safety using a flame-retardant liquid, is excellent in balance of physical properties, and can increase the average pore diameter. Things.

[0009]

The process for producing a microporous high molecular weight polyolefin film according to the present invention comprises a heat treatment for making the high molecular weight polyolefin film microporous, and an amorphous portion of the polyolefin film at the processing temperature. Is carried out in a first liquid for selectively melting or dissolving, and then a heat-treated film is immersed in a second liquid and then dried to produce a high-molecular-weight polyolefin microporous film, wherein the first liquid is Viscosity (30 ° C)
Is 15 cst or less, preferably 1.5 to 15 cst, and the second liquid is characterized by using a fluorine-substituted hydrocarbon compound containing no chlorine atom.

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 contains substantially no plasticizer and / or solvent. Is preferred.

Further, in the production method of the present invention, the high molecular weight polyolefin film before the treatment has a crystallinity of 40%.
The above-mentioned plane-oriented film is preferable.

Further, in the manufacturing method of the present invention, it is preferable that the heat treatment is performed under the constraint of the film.

[0013] 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, it is desirable that the second liquid is a fluorine-substituted hydrocarbon compound having a boiling point of 120 ° C. or lower.

[0015]

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 features will be described in detail below.

[High-molecular-weight polyolefin film] The high-molecular-weight polyolefin 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 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 blown 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.

In any of the film forming methods,
One example of a suitable film to be used is an intrinsic viscosity [η].
With 4 to 25 dl / g, and the crystallinity is preferably 4
0% or more, more preferably 50% or more.
In the case of ethylene, preferably 60% or more, more preferably
60-70%, and the tensile strength in the machine direction is, for example,
0.04 GPa or more, tensile strength in the direction perpendicular to the machine direction
At a temperature of 40 ° C. and a humidity of 90
%, For example, 0.45 g · mm / m ^Two・ 24hr
The following impervious films are provided. With impermeable film
Has an air permeability of 10,000 in an air permeability test described below.
It is a film of more than second / 100cc. Of the resulting film
There is no particular limitation on the thickness, but handling in subsequent processing steps
5 to 500 μm, more preferably
Or 5 to 100 μm.

It is preferable that the film used in the present invention does not substantially contain a plasticizer and / or a solvent, but it means that the raw material polyolefin does not contain a large amount of a plasticizer and / or a solvent. Means
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. The upper limit is preferably 10% by weight or less in total, more preferably 5% by weight.
% By weight or less.

The film used in 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 X-ray is directed from the through (THROUGTH) 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 for 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 heat treatment for making the high-molecular-weight polyolefin film microporous is performed in a first liquid that 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.
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.

Examples of the first liquid having the above properties include lower aliphatic alcohols such as propanol, butyl alcohol and amyl alcohol; lower aliphatic ketones such as cyclohexanone; dodecane, paraffin oil, and molten paraffin wax. Hydrocarbons; nitrogen-containing organic compounds such as formamide; ethers such as butyl cellosolov; monoethylene glycol, diethylene glycol,
Glycols such as triethylene glycol; halogenated hydrocarbons; lower aliphatic esters; silicone oils and the like are more preferred.

When the present inventors use a fluorine-substituted hydrocarbon compound described later as the second liquid, the first liquid is preferably used to obtain a microporous membrane suitable for a filter or a separator for a non-aqueous battery. As a result of intensive search, if the viscosity of the first liquid at 30 ° C. is 15 cst or less, preferably 1.5 to 15 cst, more preferably 1.5 to 10 cst, the fluorine-substituted carbon It has been found that it is possible to obtain a microporous membrane having excellent compatibility with a hydrogen-based compound and suitable for a filter medium and a separator for a non-aqueous battery, particularly a microporous membrane having a suitable average pore diameter.

Among such first liquids, hydrocarbons are preferable, heptane, cyclohexane, octane, decane, dodecane and paraffin oil are preferable, and dodecane and paraffin oil are particularly preferable. These liquids can also be used as a mixture of two or more.

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. In the present invention, a fluorine-substituted hydrocarbon-based compound containing no chlorine atom is used. In the present invention, examples of the fluorine-substituted hydrocarbon compound include hydrofluorocarbon, hydrofluoroether, and hydrofluoroalcohol. These are low-toxicity, flame-retardant, low-corrosion liquids that do not destroy the ozone layer. Preferably, the second liquid has a lower boiling point than 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-nonafluorobutyl-methyl ether (boiling point 60 ° C), 1,1,1,2,
2,3,3,4,4-nonafluorobutyl-ethyl ether (boiling point 78
° C).

Hydrofluoroalcohol is a fluorinated alcohol in which a part of hydrogen atoms of alcohols is substituted only by fluorine atoms and does not contain chlorine atoms, and has a boiling point of 120 ° C.
The following are preferred. Specific examples of these include propanol pentafluoride (boiling point 81 ° C.), propanol tetrafluoride,
Trifluoroethanol and the like can be mentioned.

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. As a preferable allowable range of shrinkage in the case where shrinkage is forced, for example, a standard of 10% or less in the length and width directions can be mentioned.

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 a high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent is used, and a heat treatment for making microporous is performed, it is necessary to obtain a film having a higher tensile strength. In order to adjust the porosity and pore diameter of the film, the film may be stretched simultaneously with the heat treatment or may be stretched 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.

[Microporous Film of High Molecular Weight Polyolefin] The microporous film obtained in the present invention is excellent in strength, particularly tensile strength and piercing strength, despite having a microporous structure. In addition, it has suitable membrane properties as a filter material and a separator for a non-aqueous battery as described below. In particular, according to the production method of the present invention, the average pore diameter can be increased as compared with the case where chlorofluorocarbon is used as the second liquid. This is preferable because it shows excellent charge / discharge cycle characteristics and high-temperature storage characteristics of the battery when applied to a non-aqueous battery separator.

The porosity can be selected, for example, in the range of 25 to 60% or more by appropriately selecting the heat treatment of the film before treatment and the stretching treatment as necessary. Air permeability is Gurley value, for example, 1900 seconds / 10
0 cc or less, preferably 1500 seconds / 100 cc or less. The tensile strength is, for example, 0.05 GPa or more, and preferably 0.08 GPa or more in all directions, calculated based on the actual cross-sectional area of the film, depending on the selection of the porosity value. The average pore diameter is not particularly limited, for example, 0.01
To 1.0 μm.

The characteristics 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. Viscosity of first liquid Measured at 30 ° C. using a Canon-Fenske viscometer according to JIS K2238. 3. Thickness Tokyo Precision Co., Ltd. Thickness measuring instrument Miniax (Model DH
-150 type).

4. 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. 5. Porosity The sample film weight was measured, the density as 0.95 g / cm ³ , the thickness as a dense film was obtained by calculation, and the porosity was obtained by the following equation from the relationship with the value obtained by the above-mentioned film thickness measuring device. 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).

6. Tensile Strength Tensilon (Model RTM) manufactured by Orientec
100 type) at room temperature (23 ° C.). ASTM D8
It was measured and calculated based on Method A of 82 (sample width 15 mm). 7. 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). 8. Melting point The melting point in the present invention is a value measured by a differential scanning calorimeter (DSC) according to ASTM D3417.

9. 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. 10.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.

[0051]

EXAMPLES (Example 1) In a blown film manufacturing apparatus shown in FIG. 1, a blown film made of polyethylene was manufactured using 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: 136
° C, bulk density: 0.45 g / cm ³ )
Extruder, joint (J) shown in FIG. 1, die base (D
1) Set the temperature of the die tip (D2) to 200
℃, 180 ℃, 160 ℃, 160 ℃, the first screw rotation speed 21 rpm, the second screw rotation speed 4.5 rp
m, and compressed air is blown from a gas flow path of 8 mmφ extending inside the second screw, the mandrel and the stabilizing rod shaft while taking in with a pinch roll at a speed of 7.7 m / min. Parison with outer die inside diameter 53
By inflating the film to 8.5 times the diameter of mmφ, a high-molecular-weight polyethylene blown film having a folding width of 710 mm and a thickness of 14 μm was produced stably.

<Microporization (Heat Treatment)> Using the obtained blown film, a heat treatment was carried out 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 121 ° 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 )
C. and put in a bath for 3 minutes. This was taken out and air-dried at room temperature, and then the film was removed from the metal frame to obtain a measurement sample. Table 1 shows the physical properties of the obtained microporous film.

Example 2 The same procedure as in Example 1 was carried out except that a paraffin oil having a viscosity (30 ° C.) of 11 cst was used instead of the paraffin oil having a viscosity of 6 cst, and the heat treatment temperature was changed to 123 ° C. Table 1 shows the physical properties of the obtained microporous film. (Comparative Example 1) Instead of paraffin oil having a viscosity of 6 cst,
Using paraffin oil of viscosity (30 ° C) 18 cst,
The operation was performed in the same manner as in Example 1 except that the heat treatment temperature was set to 125 ° C. Table 1 shows the physical properties of the obtained microporous film.

(Comparative Example 2) Instead of 1,1,1,2,2,3,3,4,4-nonafluoro-ethyl ether, 1,3-dichloro-1,1,2,2,
Using 3-pentafluoropropane, set the temperature of the immersion tank to 4
The procedure was performed in the same manner as in Example 1 except that the temperature was set to 0 ° C. Table 1 shows the physical properties of the obtained microporous film.

[0056]

[Table 1]

[0057]

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, the heat-treated film is immersed in a second liquid and then dried, and then dried using a low-toxicity, flame-retardant and non-destructive liquid ozone layer. Microporous films suitable for materials and separators for non-aqueous batteries can be manufactured. Further, the average pore diameter of the microporous membrane can be increased as compared with the case where chlorofluorocarbon is used as the second liquid.

[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 Continuing on the front page (72) Inventor Masaaki Ohashi 6-1-2, Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture F-term in Mitsui Chemicals, Inc. 4F074 AA16 CB03 CB17 CB28 CC04Y CC04Z CC28Z CC32Y CC32Z CC45 DA02 DA03 DA08 DA10 DA23 DA43 DA49

Claims (6)

[Claims] 1. A heat treatment for microporizing a high molecular weight polyolefin film in a first liquid which selectively melts or dissolves an amorphous portion of the polyolefin film at a treatment temperature. To
A method for producing a high-molecular-weight polyolefin microporous film which is immersed in a second liquid and then dried, wherein a first liquid having a viscosity (30 ° C.) of 15 cst or less is used, and chlorine atoms are added to the second liquid. A method for producing a high-molecular-weight polyolefin microporous film, characterized by using a fluorine-substituted hydrocarbon-based compound not containing. 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 liquid according to claim 1, wherein the second liquid is a fluorine-substituted hydrocarbon compound having a boiling point of 120 ° C. or lower.
3. The method for producing a high-molecular-weight polyolefin microporous film described in 1. above.