JPH11302437A - Preparation of high-molecular-weight polyolefin finelyporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve productivity of a finely-porous film by carrying out a heat treatment of a high-molecular-weight polyolefin film containing not a plasticizer nor a solvent in a specific liquid to make the film finely porous followed by an ultrasonic treatment in a liquid which is less affinitive to the polyolefin. SOLUTION: A high-molecular-weight polyolefin film containing not a plasticizer nor a solvent of a crystallinity of not less than 40% is subjected to a heat treatment at 100-145 deg.C for 10 sec-10 min. The film is then introduced into a vessel 1 containing a first liquid which has a boiling point of not less than the heat treatment temperature and can melt or dissolve selectively the amorphous part of the polyolefin. In the vessel 1, the film is stretched by not less than 150%, at the temperature of about 40 deg.C lower than the melting point of the film, to make the film finely porous. Then, this film is introduced to vessels 2a and 2b containing a second liquid having an affinity with the first liquid, a lower boiling point and a weaker affinity with the polyolefin than the first liquid. In these vessels, an ultrasonic treatment is carried out at 10-45 deg.C and a normal pressure with an ultrasonic wave of a frequency of 15-70 kHz.

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, for example, a filter material or a non-aqueous battery separator.

[0002]

2. Description of the Related Art A method for producing a microporous film of high molecular weight polyolefin has hitherto been disclosed, for example, in Japanese Patent Publication No.
No. 1, Tokuhei 6-53826, Tokuhei 7-17782
Various proposals have been made. In any of these methods, a hydrocarbon solvent such as decane, dodecane, decalin, paraffin oil, or mineral oil, a fatty acid, a fatty acid ester, or a fatty acid hydrocarbon derivative such as an aliphatic alcohol is added to a high molecular weight polyolefin to obtain a microporous film. After adding a plasticizer comprising a low molecular weight compound such as paraffin wax or dioctyl phthalate or dibutyl sebacate to form a film, the low molecular weight compound is removed from the film. Japanese Patent Publication No. Hei 6-2841 discloses that a low molecular weight compound is removed from a film in order to obtain a higher strength microporous film.
A method of stretching the obtained film has been proposed.

On the other hand, as shown in Japanese Patent Publication No. 2-19141 and Japanese Patent Publication No. 6-18915, a method for producing a microporous film without adding a low molecular weight compound has been proposed. These methods require stretching the film to make it microporous, and in each case the molecular weight is MFR.
Since a polyethylene as low as 0.2 to 20 g / 10 min is used, its tensile strength is limited to 0.02 GPa or less, or at most 0.03 GPa, and its industrial use is limited.

[0004]

SUMMARY OF THE INVENTION The present applicant has previously obtained a microporous film having high strength without adding a low molecular weight compound which requires a step of removing from a film according to Japanese Patent Application No. 9-205501. The method for was proposed.
In this method, a high-molecular-weight polyolefin substantially free of a plasticizer and / or a solvent is heat-treated to make it porous, and further subjected to a stretching treatment as necessary. This is performed by selectively melting or dissolving the amorphous portion, and is immersed 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 wash it.

An object of the present invention is to improve the above method to produce a high-molecular-weight polyolefin microporous film with high productivity, and to provide a production method particularly suitable for continuous production.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a high molecular weight polyolefin film substantially free of a plasticizer and / or a solvent, having a boiling point higher than a heat treatment temperature and selectively melting or dissolving an amorphous portion of the polyolefin. Heat treatment is performed in the first liquid to make it microporous, and then immersed 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. The method for producing a microporous high molecular weight polyolefin film to be washed is characterized in that ultrasonic treatment is performed while the film is immersed in a second liquid.

[0007] Another invention is directed to a first method for selectively melting or dissolving a high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent, having a boiling point not lower than a heat treatment temperature and selectively melting or dissolving an amorphous portion of the polyolefin. Heat treatment is performed in a liquid to make it microporous. Then, it is compatible with the first liquid, has a lower boiling point than the first liquid, and has a low affinity for polyolefin, and is immersed in the second liquid to be washed. In the method for producing a microporous molecular weight polyolefin film, the temperature of the second liquid is set to 30 ° C. or higher, and in a preferred invention, the second liquid is boiled.

[0008] Still another aspect of the present invention is to provide a high molecular weight polyolefin film substantially free of a plasticizer and / or a solvent, which has a boiling point not lower than a heat treatment temperature and selectively melts or dissolves an amorphous portion of the polyolefin. Heat treatment in the liquid is performed to make microporous, then immersed in the second liquid that is compatible with the first liquid, has a lower boiling point than the first liquid, and is inferior in affinity with polyolefin, and is washed. In the method for producing a microporous film of a high-molecular-weight polyolefin, ultrasonic treatment is performed while the film is immersed in a second liquid at 30 ° C. or higher.

In the above invention, the temperature of the second liquid is set to 3
The invention in which the film is washed at 0 ° C. or higher is preferable,
The invention of boiling the second liquid is more preferred. In particular, the latter invention used in combination with ultrasonic treatment is even more preferred. In the latter invention, in which the temperature of the second liquid is set to 30 ° C. or higher, or the second liquid is boiled, the first liquid can be replaced by the second liquid in a short time, and therefore, particularly for continuous production. Are suitable.

Another invention is characterized in that the polyolefin film is continuously fed into the second liquid. As a result, the microporous film is continuously produced, and the running length of the film can be significantly reduced. Yet another invention is
The second liquid used in each of the above inventions is characterized by being a low-boiling hydrocarbon, and still another invention is characterized in that the second liquid is a chlorine-fluorine-substituted low-boiling hydrocarbon.
Still another invention is characterized in that the second liquid is a low boiling halogenated hydrocarbon.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The high molecular weight polyolefin film, the first liquid, the second liquid, the processing method, and the characteristics of the obtained film used in the method for producing a microporous high molecular weight polyolefin film of the present invention are described in detail below. I do.
[High-molecular-weight polyolefin film] The high-molecular-weight polyolefin used as a raw material for forming the film is ethylene
Propylene and an α-olefin having 4 to 8 carbon atoms,
For example, by slurry polymerization using a Ziegler catalyst,
It is obtained by polymerization alone or in combination of two or more. Preferred copolymers are copolymers of ethylene and a small amount of propylene or an α-olefin having 4 to 8 carbon atoms, alone or in combination of two or more.

In the case of a polyethylene copolymer, the amount of the comonomer is preferably at most 5 mol%. Particularly preferred among these are ethylene homopolymers. The intrinsic viscosity [η] of the high molecular weight polyolefin is 4 dl / g or more, preferably 4 to 25 dl / g. In particular, for the purpose of obtaining a high-strength microporous film, the intrinsic viscosity [η] is 5 to 20 dl / g.
Is preferred.

The film does not substantially contain a plasticizer and / or solvent, but does not contain substantially means that a large amount of plasticizer and / or solvent is not added to the raw material polyolefin. Various additives usually used in addition to polyolefins such as heat stabilizers, weather stabilizers, lubricants, anti-blocking agents, slip agents, pigments, dyes, etc., even if they are blended within a range that does not impair the purpose of the present invention. Good, but the upper limit is preferably 10% by weight or less in total amount,
More preferably, it is at most 5% by weight.

The film can be formed by a conventionally known blown film method, T-die method or the like. Among them, the method of forming a blown film is described in detail in "Plastic Extrusion Molding and Its Application" by Keiji Sawada, published by Seibundo Shinkosha (19
66)], Vol. 4, Chapter 2, general methods such as those performed with polyethylene or polypropylene.

[0015] Compared with the blown film forming method, in the case of the T-die film forming method, the formed film is uniaxially oriented when melt-stretched.
The film must be plane-oriented by post-processing, but in the blown film molding method, the film can be plane-oriented at the time of film formation by appropriately selecting the expansion ratio at the time of molding.

A preferable condition for forming a film is to set a large draft ratio and expansion ratio. The draft ratio is the flow rate 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 average diameter of the cooled and solidified tube film and the average of the blown film die. It is the ratio of diameters. 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. The blown film can be produced, for example, by the method described in JP-B-6-55433.

In either method, the resulting film has an intrinsic viscosity [η] of 4 to 25 dl / g and a crystallinity of preferably 60% or more, more preferably 60 to dl / g.
70%, tensile strength in the machine direction of 0.04 GPa or more, tensile strength in the direction perpendicular to the machine direction of 0.04 GPa or more, and a moisture permeability coefficient of 0.45 g at a temperature of 40 ° C. and a humidity of 90%. It is an impermeable film of not more than mm / m ² · 24 hr. 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 for the convenience of handling in the subsequent processing steps.
To 500 μm, more preferably 5 to 100 μm
It is.

The crystallinity of the film determined from the heat of crystal dissolution by a differential scanning calorimeter (DSC) is preferably 60% or more, more preferably 60 to 70% in the case of polyethylene. In the case of a polyolefin other than polyethylene, the crystallinity of the film is preferably at least 40%, more preferably at least 50%.

The film of the present invention is preferably plane-oriented. The plane orientation in the present invention means that the crystal is biaxially oriented. The fact that the film is biaxially oriented means that among the unit crystals of the polyolefin in the film plane, the a-axis and the b-axis other than the c-axis corresponding to the molecular chain direction.
Any of the axes refers to a state in which the axis mainly exists perpendicular to the film surface and a state other than the axis, for example, the c-axis is almost non-oriented in the film surface. 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. That is, when the film is arranged in the equator direction from the end (END) direction of the film and X-rays are incident thereon and the diffraction pattern is observed, the orientation coefficient fa for polyethylene is at least (fb for other polyolefins). 0.2 or more, and the film was arranged so that the machine axis direction was the meridian direction, and when an X-ray was incident from the through direction (THROUGTH) and the diffraction pattern was observed, the orientation coefficient fc was −
It is in a state of being 0.2 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 heat treatment of the above-mentioned film varies depending on the atmosphere conditions. For example, in the case of polyethylene, the crystallinity after the treatment is usually set at a temperature of 100 ° C to 145 ° C for 10 seconds to 10 minutes. Is preferably increased by about 10 to 20% as compared to before the treatment. At this time, the film is preferably secured in at least one direction, most preferably in two directions, to prevent shrinkage. If shrinkage is forced, the preferred range of shrinkage is 10% or less in the length and width directions.

Even if the above-mentioned film has a degree of crystallinity of 60% or more, it is necessary to perform heat treatment for the purpose of further increasing the degree of crystallinity in order to secure a high porosity after microporous formation. Is preferred. The operation of increasing the crystallinity of the film may be a heat treatment involving stretching. When the film is fixed in two directions, the film becomes microporous by the above-described processing. When a specific first liquid described later is used, a microporous film can be obtained by washing the liquid in a fixed state.

[First Liquid] The first liquid is a liquid having an appropriate affinity for a high molecular weight polyolefin. Having moderate newtability with high molecular weight polyolefin,
When a high molecular weight polyolefin film is formed and immersed in the first liquid at the processing temperature, it does not act on the crystalline part of the film but penetrates mainly into the amorphous part, selectively melts or melts, and cools. When this is done, a part thereof is crystallized, and the crystallinity can be increased as a whole. 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 the affinity with the high molecular weight polyolefin means that the liquid is sufficiently adapted to 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 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” refers to, for example, a differential scanning calorimeter (DSC) equipped with a solution cell, and the melting point of the high molecular weight polyolefin is determined by a second run in the presence of a liquid. It is a liquid that does not lower its melting point by 20 ° C. or more compared to the melting point of a high molecular weight polyolefin alone when observed. 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.

Examples of the first liquid include lower aliphatic alcohols such as ethanol, propanol, butyl alcohol and amino alcohol; lower aliphatic ketones such as acetone, methyl ethyl ketone and cyclohexanone; ethyl formate and acetic acid Lower aliphatic esters such as butyl, etc .; halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene, perchloroethylene, chlorobenzene, etc .; hydrocarbons such as heptane, cyclohexane, octane, decane, dodecane, etc .; pyridine, formamide, Nitrogen-containing organic compounds such as dimethylformamide and the like; methyl ether, ethyl ether, dioxane,
Ethers such as butyl cellosolob. Further, glycols such as monoethylene glycol, diethylene glycol, triethylene glycol and the like, and silicon oil generally used as a heating medium are also preferable liquids.

These liquids can also be used as a mixture of two or more. Warm water or hot water to which a surfactant is added is also effective, but benzene, xylene,
Tetralin is not preferred because it dissolves high molecular weight polyolefins at the heat treatment temperature. Suitable first liquids for polyethylene and polypropylene are liquids of octane, decane, dodecane, paraffin oil, molten paraffin wax and liquids based on them, and liquids of at least one or more of these.

The heat treatment temperature depends on the kind of the polyolefin and the kind of the liquid, but is, for example, 100 to 145 ° C., preferably 115 to 140 ° C. in the case of polyethylene as described above. The processing temperature for polyolefins other than polyethylene is usually 50
C. to 150.degree. C., preferably 80.degree. C. to 140.degree. 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. The higher the processing temperature, the shorter 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.

The film formed by the blown film forming machine is a tube or a film which is wound by being pinched by a pinch roll. Therefore, in the case of heat treatment or additional stretching treatment, for example, one end is cut off to form a single film. Treated as In the case of the blown film, compared with the T-die film molding, there is no need to cut off both ends (ears) as in the case of the T-die film.

[Second Liquid] The second liquid is compatible with the first liquid, has a lower boiling point than the liquid, and has a lower affinity for the polyolefin than the liquid. The film subjected to the heat treatment in the liquid is then immersed in the second liquid and washed. Even during washing, the treated film is preferably fixed in at least one direction, most preferably in two directions, so as to suppress shrinkage. If shrinkage is forced, the preferred range of shrinkage is 10% or less in the length and width directions.

Examples of the second liquid that can be used include low-boiling hydrocarbons such as hexane and heptane, chlorine-substituted low-boiling hydrocarbons such as methylene chloride, and 1,2-dichloro-2,2,2. 2-trifluoroethane, 1,1-dichloro-1-fluoroethane, 1,3-dichloro-1,
1,2,2,3-pentafluoropropane, 2,2
Chlorine fluorine-substituted low-boiling hydrocarbons such as 3,3,3-pentafluoropropanol can be mentioned.

The washing with the second liquid is performed by heating the second liquid and / or sonicating the film in the second liquid. The temperature at which the second liquid is heated varies depending on the type of the liquid, but is 30 ° C. or higher, preferably 30 to 100 ° C., and more preferably 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 running length of the film can be significantly reduced. Further, the good properties of the porous film are hardly impaired.

The pressure may be normal pressure, increased pressure, or reduced pressure, but is usually normal pressure. When performing ultrasonic treatment, the wavelength of the ultrasonic wave used is usually 15 to 70.
The ultrasonic treatment can be carried out at a frequency of KHz, preferably 40 to 60 KHz, by immersing the ultrasonic generator in the liquid or by attaching the ultrasonic generator to the outer wall of the tank.

The ultrasonic treatment is desirably used in combination with the heating of the second liquid. The liquid temperature during the ultrasonic treatment is, for example, 10 to 45 ° C. The dried microporous film may be heat-set for removing wrinkles of the film, adjusting the porosity and film thickness, and reducing the coefficient of surface friction of the film. The conditions at the time of heat setting are appropriately selected such as the temperature and the processing time in a gas (air) atmosphere.

[Stretching] The present invention provides a method for producing a high-molecular-weight polyolefin microporous film in which a polyolefin-impermeable film substantially containing no plasticizer and / or solvent is heat-treated to be microporous. There is
During the heat treatment, the film may be stretched at the same time as the heat treatment, or may be stretched before and after the heat treatment in order to obtain a film having a higher tensile strength or to adjust the porosity and pore diameter of the film.

The stretching is performed at a temperature lower than the melting point of the film before processing. 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
But not 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 heat treatment, the heat treatment may be performed under the contact with the first liquid which has a suitable affinity for the high molecular weight polyolefin and does not dissolve the film before the polyolefin treatment at the stretching treatment temperature. The stretching method is uniaxial stretching that minimizes lateral width shrinkage (width drop), uniaxial stretching that prevents lateral shrinkage with a tenter clip,
Sequential or simultaneous biaxial stretching by an all tenter clip method performed in a normal biaxial stretching tester, further stretching the first stage with a pair of rolls, and then continuous sequential biaxial stretching to stretch in the transverse direction with a tenter clip, or The continuous simultaneous secondary clip stretching of the continuous tenter clip method can be applied.

The microporous film obtained by the present invention is excellent in strength, particularly tensile strength, despite having a microporous structure. The porosity can be selected, for example, in the range of 30 to 60% by appropriately selecting the heat treatment of the film before treatment and, if necessary, the stretching treatment. Air permeability is, for example, 1900 seconds / 100 in Gurley value
cc or less, preferably 1500 seconds / 100 cc or less.

Although the tensile strength depends on the selection of the porosity, it is calculated based on the actual cross-sectional area of the film and is, for example, 0.05 GPa or more, preferably 0.08 GP in all directions.
a or more. Therefore, the microporous high molecular weight polyolefin film of the present invention also has, for example, the following characteristics.

That is, (a) the porosity is 25% or more, preferably 30% or more, and (b) the air permeability is 1900 sec / 100 cc.
Or less, preferably 1500 seconds / 100 cc or less, and (c) a tensile strength of 0.05 GPa or more, preferably 0.08 GPa
As described above, (d) the air-impermeable temperature is 140 ° C. or lower, preferably 1
30 ° C. to 137 ° C., (e) a microporous high molecular weight polyolefin film having an intrinsic viscosity [η] of 4 dl / g or more, preferably 4 dl / g to 25 dl / g.

The above characteristics in the present invention can be measured by the following methods. [Intrinsic viscosity] The intrinsic viscosity in the present specification is a value measured at 130 ° C in a decalin solvent. The measurement method is AST
Performed based on MD4020. [Measurement of Film Thickness] The film thickness was measured using a film thickness measuring instrument Miniax (model DH-150) manufactured by Tokyo Seimitsu Co., Ltd.

[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. [Porosity] The sample film weight was measured, and the density was 0.95.
g / cm ³ and calculate the thickness as a dense film by calculation,
It was determined in relation to the value obtained by the above-mentioned film thickness measuring device.

[0044]

(Equation 1)

Here, T _o is the actual thickness of the film determined by a film thickness measuring instrument, and T _w is the porosity 0 calculated from the weight.
The thickness of the film as a percentage. [Tensile strength] The tensile strength was measured at room temperature (23 ° C) with a tensile tester Tensilon (model RTM100) manufactured by Orientec. A
It was measured and calculated by the method A of STM D882 (sample width 15 mm).

[Measurement of air permeability (Gurley test)] AST
According to MD727, the film was measured with a standard Gurley Densometer (Gurley Densometer: Type B Gurley Densometer manufactured by Toyo Seiki Seisaku-sho, Ltd.). [Measurement of Melting Point] The melting point referred to in the present invention is ASTM.
It is a value measured by a differential scanning calorimeter (DSC) according to D3417.

[Crystallinity] The crystallinity according to the present invention was measured by a differential scanning calorimeter (DSC) according to ASTM D3417.
When the melting point was measured under the conditions shown in (1), the amount of heat of fusion measured at the same time was used and calculated as a ratio to the value of the theoretical crystal heat of fusion. [Measurement of Orientation Coefficient] The orientation coefficient was measured using an X-ray diffractometer (model number RU300) manufactured by Rigaku Corporation.

[Degasification temperature] 1 mol of anhydrous lithium perchlorate was obtained by using propylene carbonate which had been previously dehydrated with a molecular sieve (manufactured by Wako Pure Chemical Industries, Ltd .: 4A) in a dry nitrogen atmosphere (water content: 50 ppm or less) as a solvent. Per liter of solution was prepared and this solution was impregnated into the film using a vacuum scan. This film is sandwiched between nickel electrodes, and an impedance meter (Mita Radio Research Laboratory model D-
52S), the volume electrical resistivity of the film was measured. The instrument and measurement method are described in Raman et al.'S report (FCLaman et al., JE.
Electrochem. Soc., Vol. 140, 51-53 (1993)).

The resistivity per volume at room temperature (23 ° C.) was defined as the volume electrical resistivity of the film, and the temperature at which the temperature was raised and the resistivity sharply increased was defined as the impermeable temperature. [High-Molecular-Weight Polyolefin Film] The high-molecular-weight polyolefin microporous film obtained in the present invention is mainly composed of, for example, fibrils in the form of veins, and microcrystals having an irregular size of 1 μm or less are formed on each fiber of the fibrils. It has a structure that is agglomerated. In such a case, the tensile strength is 0.05 GPa or more, preferably 0.08 GPa.
a microporous film having an impermeable temperature of 140 ° C. or less, preferably 130 ° C. to 137 ° C., which is not less than that of the conventional microporous polyolefin microporous film, and which has an excellent balance between tensile strength and impermeable temperature. It is also possible to get

EXAMPLES Example 1 As shown in FIG. 1, a tank 1 containing a liquid paraffin oil as a first liquid and a 1,1-difluoro-2,2,3,3 as a second liquid. -Pentafluoropropane (HCF
C-225), a raw film 3 composed of a high molecular weight polyethylene blown film having an intrinsic viscosity [η] of 7.6 dl / g and a thickness of 13.5 μm, using a processing apparatus composed of a plurality of tanks 2a and 2b each containing therein. , And heat-treated by passing through paraffin oil at 125 ° C. in the first tank 1 for 60 seconds to make it microporous, and then into the second tank 2a, and HCFC-2
25 (paraffin oil concentration: 6% by weight) for 30 seconds for washing, and paraffinyl was replaced with a chlorine-fluorinated hydrocarbon. The residual paraffin oil concentration in the film after the treatment (hereinafter referred to as “residual PO concentration”) was 60% by weight.

Here, the residual PO concentration is obtained as follows. Assuming that the weight of the treated film is W ₁ , the treated film is immersed in n-hexane, taken out after 5 hours, and the dried film is represented by W ₂ ,

(Equation 2) Example 2 The liquid temperature of the chlorine-fluorine-substituted low-boiling hydrocarbon of the second liquid was 4
The same raw film as in Example 1 was heat-treated under the same conditions as in Example 1 except that the temperature was set to 0 ° C. When the residual PO concentration in the film after the treatment was measured, it was 60% by weight.

Example 3 The liquid temperature of the chlorine-fluorine-substituted low-boiling hydrocarbon of the second liquid was adjusted to 5
The same raw film as in Example 1 was heat-treated under the same conditions as in Example 1 except that the temperature was set to 0 ° C. When the residual PO concentration in the film after the treatment was measured, it was 60% by weight.

Example 4 The liquid temperature of the chlorine-fluorine-substituted low-boiling hydrocarbon of the second liquid was 5
The same raw film as in Example 1 was heat-treated under the same conditions as in Example 1 except that the temperature was set to 0 ° C. When the residual PO concentration in the film after the treatment was measured, it was 56% by weight.

Comparative Example 1 The chlorine-fluorine-substituted low-boiling hydrocarbon of the second liquid was 22 to 2
The same raw film as in Example 1 was heat-treated at a room temperature of 3 ° C. and under the same conditions as in Example 1. Residual P in film after processing
When the O concentration was measured, it was 80% by weight.

Comparative Example 2 The same raw film as in Example 1 was heat-treated under the same conditions as in Comparative Example 1 except that the treatment time with the chlorine-fluorine-substituted low-boiling hydrocarbon was 50 seconds. PO remaining in the film after processing
When the concentration was measured, it was 60% by weight. The above results are shown in Table 1 below.

[0056]

[Table 1]

As can be seen from Table 1, when the temperature of the second liquid is raised to 30 ° C. or higher, and particularly to the boiling point of 54 ° C., the residual PO concentration is greatly reduced even if the processing time is the same as compared to the case of processing at room temperature. I was able to. As a result, the processing efficiency was increased, the running length of the film was shortened, and the tank in which the second liquid was put was able to be shortened.

[0058]

According to the first aspect of the present invention, a high-molecular-weight polyolefin substantially free of a plasticizer and / or a solvent is heat-treated in a first liquid to make it microporous, and then immersed in a second liquid. In the method for producing a high-molecular-weight polyolefin microporous film obtained by washing with water, the replacement of the second liquid with the first liquid is performed efficiently, the processing efficiency of the second liquid is increased, and the productivity is improved. At the same time, the running length of the film passing through the second liquid can be shortened, the size of the tank for storing the second liquid can be reduced, and the amount of the second liquid can be reduced.

According to the second aspect of the invention, the replacement of the second liquid with the first liquid is performed efficiently, and
Further, according to the fourth aspect of the present invention, the substitution is performed more efficiently, and the above-mentioned effect is further improved. According to the fifth aspect of the present invention, the microporous film is continuously produced, and the running length of the film is greatly reduced, so that the tank for storing the second liquid and the processing amount of the second liquid can be further reduced. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a processing apparatus used in the present invention.

[Explanation of symbols]

 1, 2, tank 3 ... raw film

Claims (8)

[Claims] 1. A high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent in a first liquid having a boiling point not lower than a heat treatment temperature and selectively melting or dissolving an amorphous portion of the polyolefin. High-molecular-weight polyolefin fine particles which are immersed and washed in a second liquid which is heat-treated to be microporous, compatible with the first liquid, has a lower boiling point than the first liquid, and is inferior in affinity for polyolefin; A method for producing a microporous film of a high molecular weight polyolefin, wherein the ultrasonic treatment is performed while the film is immersed in a second liquid. 2. A high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent in a first liquid having a boiling point not lower than a heat treatment temperature and selectively melting or dissolving an amorphous portion of the polyolefin. High-molecular-weight polyolefin fine particles which are immersed and washed in a second liquid which is heat-treated to be microporous, compatible with the first liquid, has a lower boiling point than the first liquid, and is inferior in affinity for polyolefin; A method for producing a microporous high molecular weight polyolefin film, wherein the temperature of the second liquid is set to 30 ° C. or higher in the method for producing a porous film. 3. The method for producing a microporous high molecular weight polyolefin film according to claim 2, wherein the second liquid is boiled. 4. A high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent in a first liquid having a boiling point not lower than a heat treatment temperature and selectively melting or dissolving an amorphous portion of the polyolefin. High-molecular-weight polyolefin fine particles which are immersed and washed in a second liquid which is heat-treated to be microporous, compatible with the first liquid, has a lower boiling point than the first liquid, and is inferior in affinity for polyolefin; In the method for producing a porous film, the second
A method for producing a high-molecular-weight polyolefin microporous film, comprising performing ultrasonic treatment in a state where the film is immersed in a liquid. 5. The method for producing a microporous high molecular weight polyolefin film according to claim 1, wherein the polyolefin film is continuously fed into the second liquid. 6. The method according to claim 1, wherein the second liquid is a hydrocarbon having a boiling point lower than the heat treatment temperature in the first liquid.
The method for producing a microporous high molecular weight polyolefin film according to any one of claims 1 to 5. 7. The method for producing a microporous high molecular weight polyolefin film according to claim 1, wherein the second liquid is a chlorine-fluorine-substituted low-boiling hydrocarbon. 8. The method for producing a microporous high molecular weight polyolefin film according to claim 1, wherein the second liquid is a halogenated hydrocarbon having a low boiling point.