JPH0698729B2 - Laminated film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laminated film comprising an ultrahigh molecular weight polyolefin microporous film and at least one reinforcing porous base material.

[Prior Art] Polyolefin microporous membranes are used in various applications such as battery separators, electrolytic condenser diaphragms, various filters, moisture-permeable waterproof clothing, reverse osmosis filtration membranes, ultrafiltration membranes and microfiltration membranes.

Conventionally, such a microporous polyolefin membrane is prepared by, for example, mixing and microdispersing a pore-forming agent composed of fine powder such as a different polymer in the polyolefin, and then extracting the pore-forming agent by a mixed extraction method in which the polyolefin phase is a solvent. A phase separation method that creates a porous structure by micro-phase separation. A strain such as stretching is applied to a polyolefin molded product in which different kinds of solids are micro-dispersed to cause interface destruction between different kinds of solids and create pores to make them porous. It is manufactured by a stretching method or the like.

Recently, an ultra-high molecular weight polyolefin that can be formed into a high-strength and high-elasticity film has been developed, and various high-strength films or microporous membranes made of this have been proposed.

For example, JP-A-58-5228 discloses that ultra high molecular weight polyethylene is dissolved in a non-volatile solvent, a gel such as a fiber or a film is molded from this solution, and the gel containing this solvent is subjected to an extraction treatment with a volatile solvent. Disclosed is an ultrahigh molecular weight polyolefin fiber or film obtained by heat drawing.

Further, JP-A-60-242035 discloses that a gel-like sheet is formed from a solution obtained by heating and dissolving ultrahigh molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more in a solvent, and the amount of solvent in the gel-like sheet is 10 to 80. The thickness obtained by removing the residual solvent after desolvation treatment to 10% by weight and then heating and stretching is 10μ
Disclosed is a microporous membrane of ultra-high molecular weight polyethylene having m or less, breaking strength of 200 kg / cm ² or more, and porosity of 30% or more.

[Problems to be Solved by the Invention] However, since the ultrahigh molecular weight polyethylene microporous membrane obtained in this manner is relatively thin, it is not suitable for applications requiring high strength. Therefore, if an attempt is made to increase the amount of the polymer solution cast on the support in order to increase the film thickness, the cooling rate will decrease and the crystallization will not proceed so easily that stretching will be difficult and the strength and emptyness of the resulting microporous film will be reduced. Porosity decreases. Also, when forming a gel-like sheet by extruding an ultra-high molecular weight polyethylene solution from a die, increasing the film thickness causes large swell and neck-in when exiting the die, making it difficult to form a film of uniform thickness. . If the film thickness of the microporous film is increased in order to increase the strength as described above, a microporous film having a satisfactory pore size and porosity cannot always be obtained.

Therefore, it is also possible to laminate the polyolefin microporous membrane on an appropriate porous support, but when it is heat-sealed or adhered with an adhesive as in the conventional case, the pore diameter and the porosity of the microporous membrane also change, It was found that a satisfactory laminated film could not be obtained. Therefore, an object of the present invention is to provide a laminated membrane in which a microporous membrane and a reinforcing porous base material are laminated without substantially changing the pore size and porosity of the microporous membrane.

[Means for Solving Problems] As a result of earnest research in view of the above object, the present inventors have found that the microporous membrane can be formed by fusing the microporous membrane and the reinforcing porous base material at intermittent portions. The inventors have found that the pore size and porosity do not substantially change, and have conceived the present invention.

That is, the laminated film of the present invention comprises an ultra high molecular weight polyolefin microporous film and a reinforcing porous substrate, and the microporous film and the microporous film so that the pore diameter and porosity of the microporous film do not substantially change. It is characterized in that the reinforcing porous base material is fused at intermittent portions.

The ultrahigh molecular weight polyolefin used in the present invention has a weight average molecular weight of 5 × 10 ⁶ or more, preferably 1 × 10 ⁶ to 15
It is in the range of × 10 ⁶ . When the weight average molecular weight is less than 5 × 10 ⁵ , a microporous membrane having a high elastic modulus and a high strength, which is a characteristic of an ultrahigh molecular weight polyolefin, cannot be obtained. On the other hand, the upper limit is not particularly limited, but those exceeding 15 × 10 ⁶ are inferior in moldability in forming a gel-like sheet.

Examples of such ultra-high molecular weight polyolefins include crystalline homopolymers or copolymers obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Of these, ultra-high molecular weight polyethylene mainly composed of ethylene is preferable. In the above ultra-high molecular weight polyolefin, various additives such as an antioxidant, an ultraviolet absorber, a lubricant, an anti-blocking agent, a pigment, a dye and an inorganic filler may be added to the ultra-high molecular weight polyolefin as needed within a range not impairing the object of the present invention. Can be added at.

The reinforcing porous substrate can be formed of any thermoplastic resin woven fabric, non-woven fabric, porous film, porous sheet or porous film as long as it can be joined to the microporous film. Preferred thermoplastic resins include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyamides such as nylon, etc., but polyolefins are preferred from the viewpoint of bondability with ultra-high molecular weight polyolefin microporous membrane and chemical resistance. .

As an example of the woven fabric, for example, a film obtained by uniaxially stretching a film of high-density polyethylene or polypropylene is woven, and the weaving degree is 1000 to 1500 denier and the thickness is 0.05 to 2 mm.
There is a stretched tape yarn cloth with a basis weight of 10 to 100 g / m ² .
In addition, a thermoplastic resin is extruded in a net shape from a circular die, and an extruded net having a thread thickness of 0.3 to 3 mm, a thickness of 0.3 to 3 mm and a mesh size of 1 to 10 mm can also be used.

An example of a non-woven fabric is a thermoplastic resin having a diameter of 0.5 to 5
The thickness is 0.05-2mm, and the basis weight is 5-
There are non-woven fabrics with 500g / m ² and air permeability of 0.1-100cc / cm ² / sec. In addition, a pore-forming agent made of fine powder such as a different polymer is mixed with a polyolefin to microdisperse it, and then a mixed extraction method of extracting the pore-forming agent, and a porous structure is obtained by microphase-separating the polyolefin phase with a solvent. The polyolefin porosity obtained by the phase separation method, in which a polyolefin molded product in which different kinds of solids are micro-dispersed is subjected to strain such as stretching to cause interfacial destruction between different kinds of solids to generate pores and become porous Membranes are also available.

Further, a melt-extrusion foam-formed porous sheet made of the same thermoplastic resin or a porous film perforated by mechanical, heat, light, radiation or the like can be used.

Next, a method for producing a microporous membrane of ultrahigh molecular weight polyolefin will be described.

First, an ultrahigh molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more is heated and dissolved in a solvent to prepare a solution. The solvent is not particularly limited as long as it can sufficiently dissolve the ultrahigh molecular weight polyolefin. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, decalin and paraffin oil,
Alternatively, there may be mentioned mineral oil fractions having boiling points corresponding to these, but a non-volatile solvent such as paraffin oil is preferable in order to obtain a gel-like molded product having a stable solvent content.

The heating dissolution is performed with stirring at a temperature at which the ultrahigh molecular weight polyolefin is completely dissolved in the solvent. The temperature varies depending on the polymer and solvent used, but is in the range of 140 to 250 ° C. in the case of ultrahigh molecular weight polyethylene, for example. The concentration of the ultrahigh molecular weight polyolefin solution is preferably 1 to 10% by weight. If the concentration is too high, it will be difficult to prepare a uniform solution. In addition, in heating and melting, it is preferable to add an antioxidant in order to prevent oxidative deterioration of the polyolefin.

Next, the heated solution of the ultra-high molecular weight polyolefin is extruded in a sheet form from a die or cast on a support and rapidly cooled.
Quench at a rate of at least 50 ° C / min to below the gelling temperature,
For example, in the case of polyethylene, the temperature is up to 90 ° C or lower, preferably 50 to 60 ° C. This rapid cooling is performed with a water bath, an air bath, a solvent bath, or the like.

When producing a relatively thick microporous film, a heated solution of an ultrahigh molecular weight polyolefin is rapidly cooled and extruded into a sheet form from a die. The quenching rate is likewise 50 ° C./min or more and is carried out up to the gelling temperature, for example up to 90 ° C. in the case of polyethylene, preferably up to 50-60 ° C. The die can be cooled by circulating cooling water in the die or by immersing the die in water, but the type of refrigerant used and the cooling method are not limited to this.

It is expected that when the ultrahigh molecular weight polyolefin solution gels, the resistance increases and it becomes difficult to extrude from the die, but the present inventors have unexpectedly discovered that the polyolefin gel can be extruded relatively easily. The reason for this is not clear, but it is considered that the ultrahigh molecular weight polyolefin gel swollen with a non-volatile solvent such as paraffin oil has low resistance to the die opening having a relatively wide slit width. Therefore, it is possible to obtain a sheet of ultra-high molecular weight polyolefin gel having a relatively wide range, for example, a thickness of 0.5 to 20 mm, preferably 1 to 10 mm. The extrusion rate depends on the temperature of the solution, the temperature of the refrigerant, and the length of the cooling portion, but is usually 2-3 cm to 2-3 m / min.

The gel-like sheet is then desolvated. The desolvation treatment can be carried out by a method of immersing the gel-like sheet in an easily volatile solvent and extracting and drying, a method of compressing, a method of heating, or a method by a combination thereof. An extraction method using an easily volatile solvent is preferable in order to remove the solvent without significantly changing it, but a method in combination with a compression method is effective in shortening the extraction time. As this easily volatile solvent,
Examples thereof include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, ethers such as diethyl ether and dioxane. These solvents are appropriately selected according to the solvent used for dissolving the ultrahigh molecular weight polyolefin, and used alone or as a mixture.

The removal amount of the solvent in the gel-like sheet is at least 10% by weight with respect to the solvent contained, and the ultrahigh molecular weight polyolefin contained in the gel-like sheet is 10 to 90% by weight, preferably 10 to 60% by weight. It is necessary to perform desolvation treatment so that the amount becomes%. If the amount of solvent removed from the gel-like sheet is less than 10% by weight with respect to the solvent, and the polyolefin contained in the gel-like sheet is less than 10% by weight, the gel-like sheet is highly swollen with the solvent. It is easy to cause the gel to dissolve in the heat drawing. In addition, uneven stretching is likely to occur partially, and it is difficult to obtain a stretch-molded product having a uniform thickness, and it is not preferable from the viewpoint of handling such as exudation of the solvent during stretching. On the other hand, if the solvent is removed until the content of the polyolefin contained in the gel-like sheet exceeds 90% by weight, the network of the gel-like sheet becomes too dense and stretching cannot be performed at a high magnification, resulting in high elastic modulus and high strength. A microporous film cannot be obtained. The removal amount of the solvent contained in the gel-like sheet can be adjusted by the amount of the volatile solvent with respect to the gel-like sheet, the time, the compression pressure of the gel-like sheet, or the like.

Further, in the solvent removal treatment of the gel-like sheet with the easily volatile solvent, the gel-like sheet shrinks in the three axial directions as the easily volatile solvent absorbed in the gel-like sheet instead of the non-volatile solvent evaporates. Easy to bend. Therefore, in order to prevent this, and to obtain a raw sheet that is smooth and has a small shrinkage in the biaxial (longitudinal and lateral) directions and is capable of being stretched uniformly and at a high ratio, the gel-like sheet should be selectively shrunk in the thickness direction. Is preferred. The contraction rate is
It is preferably 50% or more, preferably 70% or more in the thickness direction, and 20% or less in the biaxial direction. Selective shrinkage of the gel-like sheet in the thickness direction is performed by, for example, adhering the gel-like sheet to a smooth support, grasping from the biaxial direction, or sandwiching it with a porous plate to remove the volatile solvent. It can be performed by a method of evaporating.

Stretching is performed by heating the original sheet of desolvated gel-like sheet,
It is carried out at a predetermined magnification by an ordinary tenter method, roll method, inflation method, rolling method or a combination of these methods. Biaxial stretching is preferable, and either longitudinal / transverse simultaneous stretching or sequential stretching may be used.

The stretching temperature is not higher than the melting point of the ultrahigh molecular weight polyolefin + 10 ° C., preferably in the range from the crystal dispersion temperature to below the crystal melting point. For example, in the case of polyethylene, the temperature is 90 to 140 ° C, more preferably 100 to 130 ° C. If the stretching temperature exceeds the melting point + 10 ° C, the molecular chains cannot be oriented by stretching due to the melting of the resin. On the other hand, if the stretching temperature is lower than the crystal dispersion temperature, the softening of the resin is insufficient, the film is easily broken during stretching, and high-stretching cannot be performed.

The stretching ratio varies depending on the thickness of the raw fabric, but is at least 2 times or more in the uniaxial direction, preferably 5 to 20 times, and the surface magnification is 10 times or more, preferably 25 to 400 times. Area magnification is 10
If it is less than twice, the stretching is insufficient and a highly elastic and high-strength microporous membrane cannot be obtained. On the other hand, if the areal magnification exceeds 400 times, there are restrictions on the stretching device, stretching operation, etc.

The stretch-molded product is immersed in the above-mentioned volatile solvent to extract and remove the residual solvent, and then the solvent is evaporated to dry. It is necessary to extract the solvent until the solvent in the stretch-molded product is less than 1% by weight.

The ultra high molecular weight polyolefin microporous membrane produced as described above has a porosity of 30% or more and a through pore diameter of 0.001 to 0.5 μ.
m. The film thickness can be 10 μm or less depending on the manufacturing method.

The microporous membrane and the reinforcing porous substrate are joined by intermittent fusion bonding. Such fusion is preferably performed by calendering when the porous substrate is a woven fabric or extraction net, and by embossing when it is a non-woven fabric or a porous membrane. As the processing device, various devices used for ordinary heat sealing, high frequency sealing, ultrasonic sealing and the like can be used. If the fused portion is too large, the change in pore size and porosity of the microporous membrane will be too large. Therefore, the fused portion preferably has an average width of 5 mm or less, preferably 2 mm or less. Further, the proportion of the fused portion is 1 to 50%, preferably 5 to 25% of the whole. If it is less than 1%, the joining is insufficient and 50
If it exceeds%, the pore diameter and the porosity are too low.

In such fusion, the fusion temperature is, for example, 70 to 140 ° C. for the polyethylene microporous membrane and 100 to 170 ° C. for the polypropylene microporous membrane. Although slight pressure is applied during fusion, an auxiliary material such as paper may be used as a cushion material for protecting the polyolefin microporous film.

[Examples] Examples of the present invention will be shown below. The test method in the examples is as follows.

(1) Thickness of microporous membrane: A cross section was measured by a scanning electron microscope.

(2) Thickness of laminated film: measured with a micrometer.

(3) Tensile 0.2% deformation load: Measured according to ASTM D882.

(4) Tensile breaking load: Measured according to ASTM D882.

(5) Pure water permeation rate: After incorporating the laminated membrane into a flat membrane module, water was passed through with a distilled water / ethanol mixed solution (50/50 volume ratio) to perform a hydrophilic treatment, and after thoroughly washing with distilled water,
It was determined by measuring the amount of permeation of the filtrate when a water pressure of 380 mmHg was applied.

(6) Protein inhibition rate: When a physiological saline solution containing 0.05% by weight of γ-globulin (manufactured by Sigma, molecular weight 156,000) was circulated under a differential pressure of 380 mmHg using the module described in (5) above. In addition, the concentration of γ-globulin contained in the filtrate was determined by measuring the absorbance at 280 nm, and calculated by the following formula.

γ-globulin inhibition rate = {1- (γ-globulin concentration in filtrate / γ-globulin concentration in stock solution)} × 100 Reference Example 1 With 4.0% by weight of polyethylene having a weight average molecular weight (w) of 2 × 10 ^6. Liquid paraffin (64 cst / 40 ° C.) mixed with 100 parts by weight of 96.0% by weight, 0.125 parts by weight of 2,6-di-t-butyl-p-cresol (“BHT”, Sumitomo Chemical Co., Ltd.) and tetrakis [methylene] An antioxidant with 0.25 part by weight of 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate] methane (“Irganox 1010” manufactured by Ciba Geigy) was added and mixed. This mixed solution was filled in an autoclave equipped with a stirrer and stirred at 200 ° C. for 90 minutes to obtain a uniform solution.

This solution was filled in a heated mold and rapidly cooled to 15 ° C. to form a gel sheet having a thickness of 4 mm. This gel-like sheet was immersed in 250 ml of methylene chloride for 60 minutes, and then methylene chloride was evaporated and dried while being attached to a smooth plate to prepare a raw fabric having a liquid paraffin content of 82.9% by weight.

The obtained raw sheet was cut into 9 × 9 cm, set in a biaxial stretching machine, and simultaneously biaxially stretched 10 × 10 times at a temperature of 118 ° C. and a stretching speed of 30 cm / min. After washing the obtained stretched film with methylene chloride to remove residual liquid paraffin by extraction,
After drying and heat setting at 120 ° C., an ultrahigh molecular weight polyethylene microporous membrane having a thickness of 4 μm was obtained. The protein inhibition rate is 68.8
%, The water transmission rate was 957 / m ² .hr.atm.

Example 1 The ultra-high-molecular-weight polyethylene microporous membrane of Reference Example 1 was used as a polyethylene tape yarn cloth (Nisseki plastic walliff, basis weight 18 g / m ² , thickness 70 μm) and thin paper (basis weight 22 g / m ² ).
Sandwiched between them, pressure-bonded at a temperature of 105 ° C using a calender roll processor, the thin paper was peeled off, and a laminated film consisting of an ultrahigh molecular weight polyethylene microporous film and a polyethylene tape yarn cloth was formed. Obtained.
Table 1 shows the test results of this laminated film.

Example 2 The ultrahigh molecular weight polyethylene microporous membrane of Reference Example 1 was sandwiched between ^two polyethylene tape yarn cloths (Nisseki plastic walliff, basis weight 18 g / m ² , thickness 70 μm) and a calendar. Using a roll processor, pressure bonding was performed at a temperature of 110 ° C. to obtain a laminated film. Table 1 shows the test results of this laminated film.

Example 3 The extruded net made of polyethylene was used for the ultrahigh molecular weight polyethylene microporous membrane of Reference Example 1 (Netron made by Tokyo Polymer, yarn diameter 60
0 μm, thickness 600 μm, mesh size 2 mm) and thin paper (basis weight 22 g)
/ m ² ), sandwiched between them, pressure-bonded at a temperature of 100 ° C using a calender roll processor, and then peeled off the thin paper to obtain a laminated film consisting of polyethylene microporous film and polyethylene extruded net. It was Table 1 shows the test results of this laminated film.

Example 4 Two polypropylene non-woven fabrics made of the ultra-high-molecular-weight polyethylene microporous membrane of Reference Example 1 (Tapyrus manufactured by Tonen Petrochemical, grammage 30
sandwiched between g / m ² and 400 μm thick,
A laminated film was obtained by pressure bonding using an embossing machine at a temperature of 125 ° C. The test results of this laminated film are shown in Table 1.
Shown in.

Example 5 A laminated film was obtained in the same manner as in Example 4, except that an ultrasonic sewing machine was used instead of the embossing roll processing machine to bond in a grid pattern with 10 mm intervals. Table 1 shows the test results of this laminated film.

Example 6 The ultra-high-molecular-weight polyethylene microporous membrane of Reference Example 1 was used as a polyethylene non-woven fabric (Tyvek made by Deupon, basis weight 75 g / m ² , thickness
Sandwiched between 150 μm) and thin paper (basis weight 22 g / m ² ), pressure-bonded at a temperature of 105 ° C. using an embossing roll machine, and then peeled off the thin paper to make ultra-high-molecular-weight polyethylene microporous. A laminated film composed of the film and a polyethylene non-woven fabric was obtained. Table 1 shows the test results of this laminated film.

Example 7 The ultra high molecular weight polyethylene microporous membrane of Reference Example 1 was sandwiched between a polyethylene porous membrane (pore size 0.5 μm, thickness 50 μm) and thin paper (basis weight 22 g / m ² ), and an embossing roll machine was used. After pressure-bonding with a temperature of 105 ° C., the thin paper was peeled off to obtain a laminated film composed of an ultrahigh molecular weight polyethylene microporous film and a polyethylene porous film. Table 1 shows the test results of this laminated film.

Comparative Example 1 A laminated film was obtained in the same manner as in Example 4 except that a calendering machine was used instead of the embossing roll processing machine. Table 1 shows the test results of this laminated film.

Comparative Example 2 A laminated film was obtained in the same manner as in Example 6 except that a calendering machine was used instead of the embossing roll processing machine. Table 1 shows the test results of this laminated film.

As shown in Table 1, as compared with the microporous membrane of the reference example, the laminated films shown in Examples 1 to 7 have an increased thickness and both the small deformation strength and the breaking strength are remarkably improved. I understand. This made it easier to handle. Further, it can be seen that the inhibition of proteins and the like due to the size of the pore diameter of the microporous membrane are hardly changed by the laminating process. Further, it was confirmed that the pure water permeation rate did not decrease due to the effective film area, and an excellent laminated film was obtained.

On the other hand, in Comparative Examples 1 and 2 in which the entire surface is heat-sealed, the effective film area is remarkably reduced, so that the pure water permeation rate is remarkably reduced, and a good laminated film is not obtained.

[Effects of the Invention] The laminated film of the present invention comprises an ultrahigh molecular weight polyolefin microporous film fused at intermittent portions and a reinforcing porous substrate, and the pore size and porosity of the microporous film are substantially impaired. It is not.
Further, since the porous film is bonded to the porous substrate with sufficient bonding strength, the entire laminated film has sufficient breaking strength. Therefore, the laminated membrane of the present invention is easy to handle and is suitable for various applications such as battery separators, diaphragms for electrolytic capacitors, ultraprecision filtration membranes, ultrafiltration membranes, and porous membranes for moisture-permeable waterproof clothing.

Claims (5)

[Claims] 1. A microporous membrane comprising an ultrahigh molecular weight polyolefin microporous membrane and at least one layer of a reinforcing porous base material so that the pore diameter and porosity of the microporous membrane do not substantially change. A laminated film, characterized in that the reinforcing porous substrate and the reinforcing porous substrate are fused at intermittent portions. 2. The laminated film according to claim 1, wherein the ultrahigh molecular weight polyolefin microporous film is 0.001.
A laminated film having a through hole diameter of 0.5 μm and a porosity of 30% or more. 3. The laminated film according to claim 1 or 2, wherein the ultra high molecular weight polyolefin is 5 ×.
A laminated film having a weight average molecular weight of 10 ⁵ or more. 4. The laminated film according to any one of claims 1 to 3, wherein the reinforcing porous substrate is a woven fabric, a non-woven fabric, a porous film, a porous sheet or a porous film. A laminated film comprising: 5. The laminated film according to any one of claims 1 to 4, wherein the microporous film and the reinforcing porous base material are fused by embossing. Characteristic laminated film.