JP3998860B2 - High molecular weight polyolefin microporous film and method for producing the same - Google Patents

Description

【００６０】
【発明の効果】
本発明によれば、高分子量ポリオレフィンフィルムの微多孔化のための熱処理を、処理温度において該ポリオレフィンの非晶性部分を選択的に溶融又は溶解させる第１の液体中で行い、ついで熱処理したフィルムを、第２の液体に浸漬したのち乾燥する高分子量ポリオレフィン微多孔フィルムの製造方法において、得られる微多孔フィルムの空孔率と透気度を調整することができ、用途に応じた膜物性を得ることができる。
【図面の簡単な説明】
【図１】本発明において高分子量ポリオレフィンフィルムを製造するための成形装置の一例を示す正面断面図である。
【図２】本発明において、処理前フィルムを熱処理する際に該フィルムを固定するための金枠の一例を示す図である。
【符号の説明】
１ 押出機
２ 溝付シリンダー
３ 第１スクリュー
１０ トーピド
１１ 圧力計
２０ スクリューダイ
２０Ａ 第２スクリュー先端部
２０Ｂ スクリューダイ中間部
２０Ｃ スクリューダイ出口
２１ 第２スクリュー
２２ アウターダイ
２３ マンドレル
２４ 気体流路
２５ エアリング
２６ 安定棒
２７ 防風筒
３０ パリソン
３１ インフレーションフィルム
３２ ネジ
３３ 金枠[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high-molecular-weight polyolefin microporous film suitable for filter media and non-aqueous battery separator applications. More specifically, the present invention can suppress the porosity of the microporous film and increase air permeability. The present invention relates to a method for producing a high molecular weight polyolefin microporous film.
[0002]
[Prior art]
Various methods for producing a high-molecular-weight polyolefin microporous film have been proposed so far, for example, in Japanese Patent Publication No. 6-2841, Japanese Patent Publication No. 6-53826, Japanese Patent Publication No. 7-177872, and the like.
[0003]
In order to obtain a microporous film, all of these methods include hydrocarbon solvents such as decane, dodecane, decalin, paraffin oil and mineral oil, fatty acid hydrocarbon derivatives such as fatty acid, fatty acid ester and aliphatic alcohol in order to obtain a microporous film. Then, a plasticizer made of a low molecular weight compound such as paraffin wax, dioctyl phthalate, dibutyl sebacate or the like is added to form a film, and then the low molecular weight compound is removed from the film to make it microporous.
[0004]
On the other hand, as shown in Japanese Patent Publication Nos. 2-19141 and 6-18915, methods for producing a microporous film without adding a low molecular weight compound have also been proposed. In order to do so, it is essential to stretch the film. Both methods are applied to polyethylene having a relatively low molecular weight (0.2 to 20 g / 10 min in melt flow rate), and the tensile strength of the film is 0.02 GPa or less, or 0.03 GPa at most. is there.
[0005]
Therefore, the present applicant previously obtained a microporous film having high strength in Japanese Patent Application No. 9-205501 without adding a low molecular weight compound that needs to be removed from the microporous film to the polyolefin. Proposed for the method. In this method, a high-molecular-weight polyolefin film substantially free of a plasticizer and / or a solvent is heat-treated, and if necessary, it is made porous by stretching treatment before or after the heat treatment. In the first liquid, the amorphous part of the polyolefin is selectively melted or dissolved, and then the heat-treated film is compatible with the first liquid and has a boiling point higher than that of the first liquid. It is soaked and dried in a second liquid that is low and inferior in affinity with polyolefin.
[0006]
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 polyolefin, and a film excellent in micropore blocking property by heating can be obtained.
[0007]
By the way, the microporous film obtained by this method has film property values in the range of porosity and air permeability suitable for filter media and non-aqueous battery separators, but these physical properties are generally empty. If the porosity increases, the air permeability tends to increase. On the other hand, if the porosity increases, the film strength decreases. Therefore, how to balance these film properties is an important point in the manufacturing method.
[0008]
However, the microporous film changes the porosity and air permeability of the film due to various factors such as the physical properties of the raw material film and the heat treatment conditions for microporosity, and the target porosity and air permeability are not necessarily the same. It was not easy to obtain a microporous film having
[0009]
[Problems to be solved by 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 adjusted after the microporous treatment. An object of the present invention is to provide a method for producing a high-molecular-weight polyolefin microporous film.
[0010]
[Means for Solving the Problems]
The method for producing a high molecular weight polyolefin microporous film according to the present invention has been proposed in order to achieve the above-mentioned object, Intrinsic viscosity [η] of 4 dl / g or more The heat treatment for making the high molecular weight polyolefin film microporous is performed in the first liquid that selectively melts or dissolves the amorphous portion of the polyolefin at the treatment temperature, and then the heat treated film is converted into the second liquid. A method for producing a high-molecular-weight polyolefin microporous film that is dipped in and dried, and is characterized by compressing the microporous film after drying.
[0011]
In the production method of the present invention, it is preferable that 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 that substantially does not contain a plasticizer and / or a solvent.
[0012]
Moreover, in the manufacturing method of this invention, it is preferable that the high molecular weight polyolefin film before the said processable is a plane orientation film with a crystallinity degree of 40% or more.
[0013]
Moreover, in the manufacturing method of this invention, it is preferable that the said heat processing is performed under restraint of a film.
[0014]
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, ether, glycol, Desirably, the liquid is at least one liquid selected from the group consisting of silicone oil and water containing a surfactant.
[0015]
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 is desirable.
[0016]
Moreover, in the preferable aspect of the manufacturing method of this invention, it is desirable that compression of the said microporous film is performed by a roll press.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The high molecular weight polyolefin film used in the method for producing a high molecular weight polyolefin microporous film of the present invention, the microporous method (heat treatment), the first liquid, the second liquid, and the compression method of the obtained film are described in detail below. Describe.
[0018]
[High molecular weight polyolefin film]
The high molecular weight polyolefin as a film forming raw material is obtained by polymerizing ethylene, propylene, and α-olefin having 4 to 8 carbon atoms, for example, by slurry polymerization using a Ziegler catalyst, alone or in combination of two or more. A preferred copolymer is a copolymer of ethylene and a single or a combination of two or more of a small amount of propylene or an α-olefin having 4 to 8 carbon atoms. In the case of a polyethylene copolymer, the amount of the comonomer is preferably 5 mol% or less. Of these, ethylene homopolymers are particularly preferred.
[0019]
The intrinsic viscosity [η] of the high molecular weight polyolefin is preferably 4 dl / g or more, more preferably 4 to 25 dl / g. For the purpose of obtaining a microporous film having a particularly high strength, the intrinsic viscosity [η] is 5 to 20 dl. / g is preferred.
[0020]
The film can be formed by a conventionally known inflation film method, T-die method or the like, but the high molecular weight polyolefin film used in the present invention is preferably a plane-oriented film. Of these, the general method for forming inflation films is described in detail in Chapter 4 of Chapter 4 of “Plastic Extrusion and Its Applications” (Keiji Sawada, published by Seibundo Shinkosha (1966)). Examples are those which are carried out with the polyethylenes and polypropylenes mentioned.
[0021]
In the T-die film molding method, when melt stretched, the film to be molded is uniaxially oriented. Therefore, after molding, the film must be surface-oriented by post-treatment. In the inflation film molding method, the expansion ratio is increased. By selecting appropriately, the film can be plane-oriented during molding, which is preferable.
[0022]
A preferable condition for forming the inflation film is to take a large draft ratio and expansion ratio. The draft ratio is the ratio of the flow rate of the film resin at the lip exit of the inflation film die to the take-up speed of the cooled and solidified tube film. The expansion ratio is the diameter of the cooled and solidified tube film and the inflation film. The ratio to the average diameter of the die. In the usual case, the draft ratio is appropriately adjusted in the range of 2 or more, but the preferable range is 3 or more, and the expansion ratio is appropriately adjusted in the range of 1.1 to 20 times.
A high-molecular-weight polyolefin inflation film can be produced, for example, by the method described in detail in JP-B-6-55433.
[0023]
The film used in the present invention preferably 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 polyolefin. Accordingly, various additives usually added to polyolefins such as heat stabilizers, weathering stabilizers, lubricants, antiblocking agents, slip agents, pigments, dyes and the like are blended within a range that does not impair the purpose of the present invention. May be But The upper limit of the total amount is preferably 10% by weight or less, more preferably 5% by weight or less in terms of the total amount.
[0024]
In any film forming method, a suitable film to be obtained has an intrinsic viscosity [η] of 4 to 25 dl / g, and preferably has a crystallinity of 40% or more, more preferably 50% or more, Particularly in the case of polyethylene, it is preferably 60% or more, more preferably 60 to 70%, the tensile strength in the machine direction is 0.04 GPa or more, and the tensile strength in the direction perpendicular to the machine direction is 0.04 GPa or more. The moisture permeability coefficient is, for example, 0.45 g · mm / m at 40 ° C and 90% humidity. ² ・ Impermeable film of 24hr or less. The air-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 100 μm, for convenience in handling in subsequent processing steps.
[0025]
The film used for the microporous treatment of the present invention is preferably plane-oriented. In the present invention, the term “plane orientation” means that the crystal is biaxially oriented. The fact that the film is biaxially oriented means that any one of the a-axis and b-axis other than the c-axis corresponding to the molecular chain direction is mainly perpendicular to the film plane among the unit crystals of polyolefin within the film plane. A state in which the film exists and the c-axis other than the axis, for example, is distributed almost non-oriented in the film plane. In the case of polyethylene, the axis perpendicular to the film surface is usually the a axis, and in the case of other polyolefins, the axis is usually the b axis.
[0026]
This state can be confirmed as follows by observation with an X-ray diffractometer. That is, when the film is arranged in the equator direction from the end (END) direction of the film and X-rays are incident and the diffraction pattern is observed, in the case of polyethylene, the orientation coefficient fa (fb in the case of other polyolefins) is at least When the film has a mechanical axis direction of 0.2 or more and the meridian direction, the X-ray is incident from the THROUGTH direction and the diffraction pattern is observed, the orientation coefficient fc is −0. It is in a state where it is 2 or more and 0.2 or less.
[0027]
The method for obtaining the orientation coefficients fa, fb, and fc and the calculation method thereof are described in “X-ray diffraction of polymer (top)” [LEROY E., et al. As described in the section on preferred orientations by ALEXANDER, translated by Ichiro Sakurada, Chemical Doujin.
In particular, when fc is more than 0.2 (c-axis orientation state) or when fa is less than 0.2, even if the crystallinity satisfies the above conditions, the film cannot be microporous. There is a case.
[0028]
〔Heat treatment〕
The heat treatment for microporousizing the high molecular weight polyolefin film 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 the high molecular weight polyolefin. The conditions of the heat treatment vary depending on the atmospheric conditions. For example, in the case of polyethylene, the crystallinity after treatment is usually 10 ° C. to 10 ° C. at a temperature of 100 ° C. to 145 ° C. for 10 seconds to 10 minutes. It is preferable to carry out under conditions that increase by about 20%. 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. The preferred shrinkage tolerance when shrinkage is forced is within 10% in the length and width directions.
[0029]
[First liquid]
The first liquid having a moderate affinity with the high molecular weight polyolefin means that when the high molecular weight polyolefin pretreatment film is immersed in the first liquid at the processing temperature, it does not act on the crystal portion of the film and is mainly non-conductive. By penetrating the crystalline part, selectively melting or dissolving the amorphous part, and crystallizing a part thereof by cooling, the crystallinity as a whole can be increased. Accordingly, the affinity is remarkably excellent, and the solvent that dissolves the polyolefin crystal in the heat treatment temperature range is excluded.
[0030]
In addition, having affinity with high molecular weight polyolefin means that a liquid fully adapts to a high molecular weight polyolefin film, and it can be paraphrased that surface tension is small. The scale is a liquid having a contact angle of 100 degrees or less, preferably 90 degrees or less, and more preferably 80 degrees or less (the surface tension can be measured by a conventional method using a commercially available automatic contact angle meter).
[0031]
The liquid that does not dissolve the high molecular weight polyolefin crystals in the heat treatment temperature range is, for example, when the melting point of the high molecular polyolefin is observed with a second run in the presence of the liquid by a differential scanning calorimeter (DSC) equipped with a solution cell. 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 with respect to the high-molecular-weight polyolefin also varies depending on the treatment temperature, an appropriate affinity can be obtained by selecting the treatment temperature and the type of the liquid, and the effect of porosity can be maximized.
[0032]
Examples of the first liquid having the above properties include lower aliphatic alcohols such as ethanol, propanol, butyl alcohol, and amyl alcohol; lower aliphatic ketones such as acetone, methyl ethyl ketone, and cyclohexanone; ethyl formate and butyl acetate. Lower aliphatic esters such as carbon tetrachloride, halogenated hydrocarbons such as trichloroethylene, perchloroethylene, chlorobenzene, etc .; carbonization such as heptane, cyclohexane, octane, decane, dodecane, paraffin oil, molten paraffin wax, etc. Hydrogen; Nitrogen-containing organic compounds such as pyridine, formamide, dimethylformamide, etc .; Ethers such as methyl ether, ethyl ether, dioxane, butyl cellosolve, etc .; monoethylene glycol, diethylene glycol , Glycols such as triethylene glycol; silicone oil; hot water containing a surfactant, such as hot water is preferred.
These liquids can also be used as a mixture of two or more.
[0033]
Among such first liquids, hydrocarbons are preferable, and heptane, cyclohexane, octane, decane, dodecane, and paraffin oil are particularly preferable. Among the first liquids, the viscosity at 30 ° C. is 15 cst or less, preferably 0.1 to 10 cst.
[0034]
Although the heat treatment temperature depends on the type of polyolefin and the type of liquid, 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 treatment temperature is usually 50 ° C. to 150 ° C., preferably 80 ° C. to 140 ° C. In general, the processing time is 10 seconds to 10 minutes, preferably 30 seconds to 5 minutes after the pre-processing film reaches the processing temperature. If the processing temperature is increased, the processing time can be shortened. In addition, it is preferable to avoid the processing time more than necessary because it may reduce the tensile strength of the microporous film.
[0035]
[Liquid replacement and drying]
The film that has been microporous by heat treatment in the first liquid is dipped in the second liquid to be liquid-substituted, 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 inferior in affinity with the polyolefin. In the present invention, in particular, at least one hydrocarbon compound substituted with fluorine or substituted with fluorine and chlorine, or a hydrocarbon group substituted with fluorine or substituted with fluorine and chlorine is contained. Ether compounds are preferred. In the present invention, the hydrocarbon compound substituted with fluorine or substituted with fluorine and chlorine is an ether compound in which the hydrofluorocarbon has at least one hydrocarbon group substituted with fluorine or substituted with fluorine and chlorine. Examples thereof include hydrofluoroether. These are low toxicity, flame retardant liquids that do not destroy the ozone layer.
In the present invention, the boiling point of the second liquid is preferably lower than the boiling point of the first liquid.
[0036]
Hydrofluorocarbons are preferably fluorinated hydrocarbon compounds in which some of the hydrogen atoms of the hydrocarbon are substituted with only fluorine atoms and do not contain chlorine atoms, and have a boiling point of 120 ° C. or lower. Specific examples thereof include 1,1,1,2,3,4,4,5,5,5-decafluoropentane (boiling point 55 ° C.), 1,1,2,2,3,3,4, Examples include 4-octafluorobutane (boiling point 44 ° C.) and 1,1,2,2,3,3,4-heptafluorocyclopentane (boiling point 82 ° C.).
[0037]
The hydrofluoroether is preferably a fluorinated ether in which part of the hydrogen atoms of the ether is substituted with only a fluorine atom and does not contain a chlorine atom, and has a boiling point of 120 ° C. or less. Specific examples thereof include 1,2,2,2, -tetrafluoroethyl-heptafluoropropyl ether (boiling point 40 ° C.), 1,1,1,2,3,3-hexafluoro-2-heptafluoropropylene. Roxy-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).
[0038]
The treated film immersed in the second liquid may be fixed in at least one direction, most preferably in two orthogonal directions, so as to suppress shrinkage during immersion as in the case of heat treatment. The preferred shrinkage tolerance when shrinkage is forced is within 10% in the length and width directions.
[0039]
It is preferable that the immersion in the second liquid is performed by heating the second liquid and / or applying ultrasonic vibration to the second liquid.
The temperature when heating the second liquid varies depending on the type of liquid, but is preferably 30 ° C. or higher, more preferably 30 ° C. to the boiling point of the second liquid, and even 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 shortened, and the film running length in the liquid tank can be greatly shortened particularly in continuous production. In addition, the good properties of the microporous film are rarely impaired.
The atmospheric pressure may be normal pressure or increased pressure, and may be reduced pressure, but is usually performed at normal pressure.
[0040]
The microporous film immersed in the second liquid is dried. After drying, heat setting may be performed to remove film wrinkles, adjust porosity and film thickness, and reduce the surface friction coefficient of the film. As conditions for heat setting, temperature, processing time, and the like are appropriately selected in a gas (air) atmosphere.
[0041]
[Stretching]
In the present invention, when performing heat treatment for making the high molecular weight polyolefin film microporous, to obtain a film having a higher tensile strength, to adjust the porosity and pore diameter of the film, Stretching may be performed before and after heat treatment.
[0042]
Stretching is performed below the melting point of the film before heat treatment. Although the minimum of extending | stretching temperature is based also on the kind of high molecular weight polyolefin, it is about melting | fusing point-40 degreeC of a film. If the high molecular weight polyolefin is polyethylene, the temperature is 100 ° C to 145 ° C. In the case of uniaxial stretching, the draw ratio is 150% or more, preferably 150% to 500%. In the case of uniaxial stretching, constant width uniaxial stretching is preferred. In the case of biaxial stretching, the surface magnification is 150% or more, preferably 150% to 2500%.
[0043]
The stretching may be performed in an air atmosphere, or may be performed in contact with the first liquid to be heat-treated as described in the heat treatment section above.
The stretching method is uniaxial stretching that minimizes lateral width shrinkage (width drop), uniaxial stretching that prevents transverse shrinkage with a tenter clip, or all that is performed with a normal biaxial stretching tester. Sequential or simultaneous biaxial stretching by the tenter clip method, and further, continuous sequential biaxial stretching by stretching the first stage with a pair of rolls and then stretching in the transverse direction by a tenter clip, or continuous simultaneous biaxial stretching by the continuous tenter clip method. Applicable.
[0044]
〔compression〕
The high-molecular-weight polyolefin microporous film obtained by the above operation has film properties having a relatively high porosity by treatment with the first liquid and the second liquid. Therefore, although the air permeability has a high value, in applications that require film strength, a high porosity is not preferable because the strength is lowered. On the other hand, it is desired that the air permeability is always high. Therefore, the microporous film is compressed in order to reduce the porosity without reducing the air permeability so much.
[0045]
The compression may be simply 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, when the microporous film thickness is 10 to 1000 μm, it is usually 1 to 200 kg / cm. ² , Preferably 10 to 150 kg / cm ² It is.
[0046]
[High molecular weight polyolefin microporous film]
In the present invention, the high-molecular-weight polyolefin microporous film obtained by heat treatment contains, for example, veins and / or mesh-like fibrils as main constituent elements. A vein and / or mesh-like fibril is a state in which a fibril constituting a film has a thick trunk fiber and a thin fiber connected to the outside, and the thin fiber forms a complex network structure. Say.
[0047]
Since the microporous film obtained in the present invention can narrow the gap formed between the fibrils without significantly reducing the air permeability, it has a high air permeability, Excellent strength, especially tensile strength and puncture strength.
In addition, it has film properties suitable as a filter medium and a nonaqueous battery separator as described below.
[0048]
The porosity can be selected in the range of, for example, 25 to 60% or more by selecting the heat treatment of the pre-treatment film and, if necessary, the stretching treatment conditions and compressing the microporous film. .
The air permeability can be 1900 seconds / 100 cc or less, preferably 1500 seconds / 100 cc or less in terms of Gurley value.
The tensile strength is calculated on the basis of the actual cross-sectional area of the film and is, for example, 0.05 GPa or more, preferably 0.08 GPa or more in all directions, although it depends on the selection of the porosity value.
The average pore diameter is not particularly limited but is, for example, 0.01 to 1.0 μm.
[0049]
The said characteristic in this invention can be measured with the following method.
1. Intrinsic viscosity
It is a value measured at 135 ° C. with a decalin solvent. The measurement method was performed based on ASTM D4020.
2.Film thickness
It was measured with a film thickness measuring machine miniax (model DH-150 type) manufactured by Tokyo Seimitsu Co., Ltd.
[0050]
3.Average pore diameter
The maximum pore diameter measured with a mercury porosimeter manufactured by Yuasa Ionics Co., Ltd. (model autoscan 33) was taken as the average pore diameter.
4. Porosity
The sample film weight is measured and the density is 0.95 g / cm ^Three The thickness as a dense film was obtained by calculation, and was obtained by the following formula from the relationship with the value obtained by the film thickness measuring instrument.
Porosity (volume%) = [(To−Tw) / To] × 100
Here, To is the actual thickness of the film obtained with a film thickness measuring instrument, and Tw is the thickness of the film (dense film) having a porosity of 0% obtained by calculation from the weight.
[0051]
5.Tensile strength
This was carried out at room temperature (23 ° C.) with a tensile tester Tensilon (model RTM100) manufactured by Orientec. Measured and calculated based on ASTM D882 Method A (sample width 15 mm).
6. Air permeability (Gurley test)
The film was measured with a standard Gurley densometer (Gurley Densometer: B-type Gurley Densometer manufactured by Toyo Seiki Seisakusho) according to ASTM D727.
7.Melting point
The melting point in the present invention is a value measured by a differential scanning calorimeter (DSC) according to ASTM D3417.
[0052]
8. Crystallinity
The degree of crystallinity in the present invention is expressed as a ratio to the value of the theoretical crystal melting calorific value using the melting calorific value measured simultaneously when the melting point is measured by a differential scanning calorimeter (DSC) under the conditions shown in ASTM D3417. Obtained by calculation.
9. Puncture strength
Using a Tensilon tensile tester (Model: RTM100 type) manufactured by Orientec Co., Ltd., the measurement was performed at 23 ° C. and 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 pierces the film was defined as the piercing strength. The piercing film was fixed with a 15 mmφ circular fixed frame.
[0053]
【Example】
(Experimental example 1)
In the inflation film production apparatus shown in FIG. 1, a polyethylene inflation film was produced using the following specification.
<Device specifications>
Extruder first screw outer diameter 50mmφ
First screw effective length 1100mm
1st screw flight pitch 30mm (constant)
First screw compression ratio 1.8
Screw die effective length 1490mm (L / D = 28)
Die outlet outer die inner diameter 53mmφ
Die exit mandrel outer diameter 45mmφ
Second screw outer diameter 70mmφ
Second screw effective length 238mm
2nd screw flight pitch 25mm (constant)
Second screw compression ratio 1.0
Stabilizer outer diameter 39mmφ
Stabilizer bar length 600mm
Gas channel inner diameter 8mmφ
In addition, a stabilizer, a pinch roll, and a product winder (not shown) are provided.
[0054]
<Manufacture of inflation film>
Polyethylene (Intrinsic viscosity [η]: 7.5 dl / g, Melting point: 136 ° C., Bulk density: 0.45 g / cm ^Three ), The set temperatures of the extruder, the joint part (J), the die base part (D1) and the die tip part (D2) shown in FIG. 1 are 200 ° C., 180 ° C., 160 ° C. and 160 ° C., respectively. The first screw rotation speed was set to 21 rpm and the second screw rotation speed was set to 4.5 rpm. While taking up with a pinch roll at a speed of 7.7 m / min, it was extended into the second screw, the mandrel and the stabilizer rod shaft. Compressed air is blown from the existing 8mmφ gas flow path, and the parison is inflated 8.5 times the inner die inner diameter of 53mmφ to stabilize a high molecular weight polyethylene inflation film with a folding width of 710mm and a thickness of 13.5μm. And manufactured.
[0055]
<Microporous (heat treatment)>
Using the obtained inflation film, heat treatment was performed as follows.
The four sides of the film were fixed by sandwiching the inflation film 32 between the pair of stainless steel metal frames 33 shown in FIG. In this state, it was put into a bath filled with 6 cst of paraffin oil having a viscosity (30 ° C.) heated to 122 ° C., heat-treated for 1 minute, taken out from the heat-treatment bath, and the film was fixed to a metal frame. 1,1,2,2,3,3,4,4-nonafluorobutyl-ethyl ether (C _Four F ₉ OC ₂ H _Five ) Was filled in a bath at 70 ° C. and immersed for 30 seconds. This was taken out and air-dried at room temperature to obtain a microporous film having a film thickness of 33 μm. Remove the film from the metal frame and press at 50 ° C / cm at 30 ° C. ² The film was compressed to a film thickness of 26 μm under the above conditions. The physical properties of the microporous film before and after the compression operation are shown in Table 1.
[0056]
(Experimental example 2)
In Experimental Example 1, the press pressure of the microporous film was 100 kg / cm. ² In the same manner as in Experimental Example 1, except that the film thickness after compression was 21 μm. The physical properties of the microporous film before and after the compression operation are shown in Table 1.
[0057]
(Experimental example 3)
The microporous film before compression treatment obtained in Experimental Example 1 was subjected to a roll temperature of 30 ° C. and a compression pressure of 50 kg / cm. ² Then, the compression treatment was performed through a roll. The physical properties of the microporous film before and after the compression operation are shown in Table 1.
[0058]
(Comparative experiment example)
The microporous film before compression treatment obtained in Experimental Example 1 was heat set for 90 seconds in an atmosphere at 132 ° C. instead of the compression treatment. 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]
【The invention's effect】
According to the present invention, the heat treatment for making the high molecular weight polyolefin film microporous is performed in the first liquid that selectively melts or dissolves the amorphous portion of the polyolefin at the treatment temperature, and then the heat treated film. In the method for producing a high-molecular-weight polyolefin microporous film that is immersed in the second liquid and then dried, the porosity and air permeability of the resulting microporous film can be adjusted, and the film physical properties according to the application can be adjusted. Obtainable.
[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 an example of a metal frame for fixing the film before heat treatment in the present invention.
[Explanation of symbols]
1 Extruder
2 Cylinder with groove
3 First screw
10 Torpido
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 Stabilizer
27 Windshield
30 Parison
31 Inflation film
32 screws
33 gold frame

Claims (6)

  A heat treatment for microporosity of a high molecular weight polyolefin film having an intrinsic viscosity [η] of 4 dl / g or more is performed in a first liquid that selectively melts or dissolves the amorphous part of the polyolefin at the treatment temperature, A method for producing a high-molecular-weight polyolefin microporous film, wherein the heat-treated film is immersed in a second liquid and then dried, wherein the microporous film is compressed after drying. A method for producing a film. The method for producing a high molecular weight polyolefin microporous film according to claim 1, wherein the high molecular weight polyolefin film before the treatment is a plane oriented film having a crystallinity of 40% or more. The method for producing a high-molecular-weight polyolefin microporous film according to claim 1 or 2 , wherein the heat treatment is performed under film restraint.   The first liquid is composed of water containing a lower aliphatic alcohol, a lower aliphatic ketone, a lower aliphatic ester, a halogenated hydrocarbon, a hydrocarbon, a nitrogen-containing organic compound, ether, glycol, silicone oil, and a surfactant. The method for producing a high-molecular-weight polyolefin microporous film according to claim 1, which is at least one liquid selected from the group. The second liquid is a fluorine-substituted or fluorine- and chlorine-substituted hydrocarbon compound having a boiling point of 120 ° C or lower, or an ether compound having at least one fluorine-substituted or fluorine- and chlorine-substituted hydrocarbon group. Item 5. The method for producing a high molecular weight polyolefin microporous film according to Item 1 or 4 .   The method for producing a high molecular weight polyolefin microporous film according to claim 1, wherein the microporous film is compressed by a roll press.

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