JPH1112383A - Porous film, its production and air-permeable adhesive member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an olefin-based porous film excellent in mechanical strength and production efficiency and also the denseness and uniformity of its porous structure and porosity, to provide a method for producing the above porous film, and to obtain an air-permeable adhesive member using the above porous film. SOLUTION: This porous film, which consists of an olefin-based resin film, is so designed that the olefin-based resin defines a porous structure through providing voids among the films or fibers resulted from being crosslinked to three-dimensional network structure. This porous film is obtained by the following method: an olefin-based resin film partially crosslinked to three-dimensional network structure is swollen or partially dissolved with a good solvent whose temperature causes no crystallization of the olefin-based resin, and the good solvent intruded into the film after treated with the good solvent is removed by the aid of a poor solvent. The other objective air-permeable adhesive member is obtained by bearing one side or both sides of the above porous film with air-permeable adhesive layer(s). By the above-mentioned method, the objective porous film with stable quality presenting porousness at least comparable to those of conventional porous films can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an olefin-based porous film having excellent strength and easy to produce, a method for producing the same, and a breathable adhesive member using the same.

[0002]

2. Description of the Related Art Conventionally, the field of filters such as filtration membranes and separation membranes, the field of waterproofing in clothing and buildings that transmit water vapor and block the water, the field of packaging for heating elements such as disposable warmers, and the use of ion permeability have been used. Olefin-based porous films used in various fields such as battery diaphragm fields, especially those with fine pores, are formed by molding a molten mixture of polyethylene and polypropylene and a good solvent, and an uncrosslinked film having a crystalline structure And those produced by an extraction method in which a good solvent dispersed and contained therein is eluted and removed through a poor solvent (JP-B-60-23130, JP-B-6-104736, JP-A-6-104736). JP-A-53-32342, JP-A-55-60537, JP-A-60-35
036, JP-A-3-155045).

[0003] However, there is a problem that the strength is poor and the material is easily broken. Therefore, a porous film in which the strength is improved by adding polyethylene having an ultrahigh molecular weight or a branched structure has been proposed. However, it is difficult to uniformly disperse ultra-high molecular weight polyethylene due to differences in softening points and molecular weights, etc. The structure is difficult to be formed, and the regions such as ultra-high molecular weight polyethylene and the crystallization region contribute to the strength improvement.Therefore, it is necessary to increase those regions in order to improve the strength. There was a problem that was difficult to achieve. It is considered that the non-penetration of the good solvent into the crystallization region is due to the fact that the good solvent is released during the crystallization and does not stop in the crystallization region.

[0004] On the other hand, a porous film formed by a stretching method for stretching a film is also known, and a method of increasing the stretching ratio by increasing the stretching ratio or biaxial stretching has been proposed. However, also in this case, the porous structure is based on the fibrillation of the amorphous region by stretching the film, and since the film strength depends on the crystallization region, it is difficult to make the porous structure dense and homogenous. It was also difficult to improve the porosity because of the necessity of a crystallization region for maintaining strength.

[0005]

The present invention relates to an olefin-based porous film which is excellent in film strength and production efficiency, is excellent in denseness, homogeneity and porosity of a porous structure, a method for producing the same, and air permeability using the same. The task is to develop an adhesive member.

[0006]

The present invention relates to a porous material comprising an olefin-based resin film, wherein the olefin-based resin forms a porous structure with voids between fibers or films crosslinked in a three-dimensional network structure. A step of swelling or partially dissolving the film, and a good solvent at a temperature at which the olefin resin does not crystallize, with the olefin resin film partially crosslinked to a three-dimensional network structure, and the olefin resin film after the good solvent treatment A method for producing a porous film having at least a step of removing a good solvent that has penetrated the film through a poor solvent, and a permeable adhesive member having a permeable adhesive layer on one or both surfaces of the porous film. To provide.

[0007]

According to the present invention, by treating a film with a good solvent at a temperature at which the olefin resin does not crystallize,
A film or fiber made of an olefin-based resin cross-linked in a three-dimensional network structure exhibits high strength, and a good solvent efficiently penetrates into the non-cross-linked portion of the non-crystalline state between the films or fibers to even out the film. Swells and / or partially dissolves well. As a result, voids are formed between the crosslinked films or fibers, and a dense porous structure having excellent uniformity and porosity (opening ratio) can be formed. Also exhibit excellent strength, exhibit porous properties equal to or higher than those of conventional products, and provide a porous film of stable quality with high production efficiency.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The porous film of the present invention comprises a film in which an olefin resin is crosslinked in a three-dimensional network structure or a film having a porous structure with voids between fibers. An example is shown in FIG. 1 is a porous film. The production of the porous film according to the present invention is, for example, a step of swelling or partially dissolving an olefin resin film partially cross-linked to a three-dimensional network structure with a good solvent at a temperature at which the olefin resin does not crystallize, After the step, a method of removing a good solvent that has entered the film via a poor solvent through a poor solvent can be carried out by a method having a method.

As the olefin-based resin, an appropriate resin containing an olefin such as ethylene or propylene can be used according to the purpose of use, and is not particularly limited. Incidentally, examples thereof include linear or other low-density polyethylene or medium-density polyethylene, high-density polyethylene or ultra-high-molecular-weight polyethylene, blends of two or more of the above-mentioned polyethylenes, other polyolefins such as polypropylene, one or two or more. A blend of at least one kind of polyethylene and another kind of polyolefin, a copolymer of two or more kinds of olefins such as an ethylene-propylene copolymer and an ethylene-propylene-diene copolymer, and a blend thereof are given.

[0010] One or more of the above-mentioned olefin-based resins may be combined with an olefin- (meth) acrylate-based copolymer such as an olefin-ethyl acrylate copolymer or an olefin- (meth-acrylate) such as an olefin-methacrylic acid copolymer. 1) one of olefin-vinyl copolymers composed of one or more of olefins such as ethylene and propylene and other appropriate vinyl monomers, such as acrylic acid copolymers and olefin-vinyl acetate copolymers; A kind or a blend of two or more kinds is also an example of the olefin-based resin.

In the above, when the blended olefin-based resin is used, a polymer which does not greatly differ in crystallization temperature, speed, softening point, and molecular weight from the viewpoints of mixing with a homogeneous material and good film-forming properties. It is preferable to use a combination of The blending can be performed by an appropriate mixing method, but a method using a mixing roll, a Banbury mixer, a twin-screw kneader, a Henschel mixer, or the like is preferable from the viewpoint of film forming properties by homogeneously mixing the components.

The olefin-based resin film can be formed by an appropriate method such as a casting method, a molding method by melting, and a calender rolling method. From the viewpoint of production efficiency and the like, an extrusion molding method via a T die, an inflation die, or the like is preferable. The film to be subjected to the good solvent treatment is a polyethylene resin film or a polyethylene resin film and a polypropylene resin film.
It may be a laminate film of two or three or more layers of an olefin-based resin film, such as a laminate film of three or more layers. Further, the film to be subjected to the good solvent treatment may be a film which has been subjected to a stretching treatment by an appropriate method such as roll rolling or uniaxial or biaxial and annealed.

The thickness of the olefin-based resin film can be appropriately determined according to the purpose of use and the like.
00 μm, especially 5 to 300 μm, especially 10 to 200 μm. In the formation of the above-mentioned film, for example, a softener, an inorganic filler or a pigment, an antioxidant or an ultraviolet stabilizer, an antistatic agent or a flame retardant, a lubricant or a fluorescent agent may be added to the porous film. Can be added to the film as needed. Also, a good solvent that is solid at room temperature can be previously blended in the film. When a laminate film having three or more layers is formed, it is particularly advantageous to previously mix a good solvent into at least an intermediate film layer in order to make the entire film evenly porous.

The partial crosslinking of the olefin resin film is
Cross-linking olefin resin into a three-dimensional network structure, such as a method of irradiating appropriate radiation such as electron beam or ultraviolet light, a method of mixing a cross-linking agent into the olefin resin and performing a cross-linking treatment by heating or / and irradiation. It can be performed by applying an appropriate method that can be processed. Rather than processing efficiency,
Partial cross-linking by electron beam irradiation is preferred. By such a partial cross-linking treatment, even if the olefin resin is treated with a good solvent at a temperature that does not crystallize, the heat-resistant film portion or fiber portion in which the resin does not swell and dissolve due to cross-linking of the three-dimensional network structure is evenly distributed in the film. As well as being densely formed,
A film having excellent strength is formed. In addition, while maintaining the film state, the uncrosslinked portion between the membrane portion or the fiber portion can be non-crystallized through a good solvent to uniformly swell or / and partially dissolve to form a dense porous material. can do.

In the method of the present invention, the olefin resin film partially crosslinked into a three-dimensional network structure is made porous by swelling and / or swelling the film with a good solvent at a temperature at which the olefin resin does not crystallize. After partial dissolution, the removal is performed by removing the good solvent that has entered the film via the poor solvent. This makes it possible to obtain a high-strength porous film with stable quality by a simple operation through simple equipment that does not require complicated equipment. The temperature of the good solvent may be any temperature at which the olefin-based resin forming the film does not crystallize, but from the viewpoint of processing efficiency and the like, a temperature as close as possible to the temperature at which the crosslinked portion of the three-dimensional network structure does not dissolve. In particular, it is preferably near the melting point of the olefin resin.

The treatment with a good solvent may be performed, for example, by dipping an olefin resin film in a heating bath of a good solvent.
It can be carried out by an appropriate method in which the film and the good solvent come into contact. As the good solvent, an appropriate solvent that can dissolve the olefin resin can be used. From the viewpoint of the stability of the bath when a heating bath is used, liquid paraffin, mineral oils such as process oils, plasticizers such as phthalate esters, adipic esters and sebacate esters, one kind of solid paraffin wax or the like Two or more are preferably used, and a surfactant may be used in combination. Above all, liquid paraffin or a combination system of liquid paraffin and other components is preferred.

The swelling rate and the degree of partial dissolution of the olefin resin film are determined by the type of the good solvent and the combination thereof.
It is possible to control the porosity such as the pore diameter and the aperture ratio, and the working speed. By immersing the film in a liquid paraffin bath at a temperature near the melting point of the olefin resin film, the desired swelling or / and partial dissolution treatment is usually performed within 2 minutes, especially within 1 minute, especially within 30 seconds. It can be carried out.

In the treatment with the above-mentioned good solvent, the olefin resin film is laminated on a porous substrate such as nonwoven fabric or paper made of polyester fiber or polyamide fiber having higher heat resistance, and then subjected to the treatment. Can also be offered. Thereby, when the olefin-based resin film comes into contact with the heating bath, the film shape can be maintained more favorably. Such a porous substrate,
The porous film can be provided for practical use by bonding it as it is.

The olefin-based resin film after the treatment with the good solvent is treated with a poor solvent after performing other treatments as necessary, and the good solvent that has entered the film is removed to complete the porous treatment. I do. As the poor solvent, an appropriate solvent that dissolves a good solvent and does not dissolve or hardly dissolve an olefin resin can be used. By the way, as an example,
Examples thereof include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, and chlorine-containing organic solvents such as methylene chloride and trichloroethylene.

The treatment with the poor solvent may be carried out, for example, by dipping the olefin resin film treated with the good solvent in a bath of the poor solvent also serving as cooling, for example, by appropriately contacting the good solvent in the film or the film with the poor solvent. Can be performed in a simple manner. Thereby, the good solvent in the film dissolves in the poor solvent and is extracted and removed, and the partially dissolved olefin resin precipitates in the poor solvent.

The porous film obtained by treating with a poor solvent is
If necessary, it can be washed with an alcohol such as methanol or the like and put to practical use. In this case, the drying treatment using hot air or the like is performed at a temperature of 50 ° C.
When the temperature is about ℃, it is preferable to carry out the treatment in a state where tension is applied by an appropriate method using a tenter or the like so as not to shrink the film.

As described above, in the present invention, an appropriate treatment can be performed between the treatment with a good solvent and the treatment with a poor solvent. There is no particular limitation on the processing. Incidentally, examples thereof include a stretching treatment for the purpose of controlling the pore size, improving the strength, stability, and transparency of the film.

The above stretching treatment can be carried out by an appropriate method such as a uniaxial or biaxial method. However, the roll compression rolling method is more preferable in terms of uniformity of the film thickness, densification and fineness of holes, and improvement of film strength. Is advantageous. Also, from the viewpoint of enhancing the transparency of the porous film, it is more advantageous to use a method in which the film is supplied between rolls having a thin gap for condensing and compressing the film, and the film is drawn out from between the rolls at a higher speed than the supply speed to carry out a stretching treatment. The stretching treatment can be performed after the treatment with the poor solvent.

The porosity of the porous film of the present invention can be confirmed by, for example, an enlarged view using an electron microscope or the like, when measuring strength or elongation, or when measuring air permeability or water permeability. When magic ink is applied to the film surface,
The ink can be easily and directly confirmed, for example, rather than being sucked and oozing out from the back surface.

The obtained porous film can be used for various purposes according to the prior art. In particular, those having excellent porosity (opening ratio) and strength can be preferably used as a battery separator because the ion permeability is proportional to the porosity. In this case, the fineness of the pores advantageously shortens the time required for the olefin-based resin to melt due to a rise in temperature to form a film that blocks the pores and blocks ions, and thus advantageously functions to improve the temperature sensing ability.

In practical use of the porous film, FIG.
As illustrated in FIG. 3, a permeable adhesive layer 2 may be provided on one or both sides of the porous film 1 to form a permeable adhesive member. The air-permeable adhesive layer can be formed by an appropriate method such as a method of spray-coating an adhesive or a heat-activatable adhesive, a method of pattern coating in a streak or a dot pattern, or a method of forming and depositing into a fibrous form. And can also be formed as a stretched porous film of a hot melt adhesive film.

The above-mentioned air-permeable adhesive member is such that a porous film can be adhered and laminated with another member through the air-permeable adhesive layer. An appropriate adhesive substance such as an adhesive or a hot-melt adhesive can be used. In the case where the adhesive layer has room temperature adhesiveness such as an adhesive layer, it is preferable to temporarily protect the adhesive layer with the separator 3 as shown in the figure until practical use.

[0028]

【Example】

Example 1 A low-density polyethylene was formed through a T-die of an extruder to form a film having a thickness of 40 µm, and the film was irradiated with an electron beam at 3 Mrad (30 Gry) to partially crosslink into a three-dimensional network structure. Thereafter, it was introduced into a liquid paraffin bath at 115 ° C. and immersed for 20 seconds.
Was introduced into a toluene bath equipped with a stirrer, and immersed for 30 seconds to remove paraffin, thereby precipitating partially dissolved polyethylene to obtain a porous film.

Example 2 A porous film was obtained in the same manner as in Example 1 except that medium density polyethylene was used instead of low density, and the temperature of the liquid paraffin bath was 120 ° C.

Example 3 A porous film was obtained in the same manner as in Example 1 except that high-density polyethylene was used instead of low-density, and the temperature of the liquid paraffin bath was 130 ° C.

Example 4 A porous film was obtained in the same manner as in Example 1 except that a blend of 70 parts by weight of low-density polyethylene and 30 parts by weight of polypropylene was used as the olefin resin, and the temperature of the liquid paraffin bath was 120 ° C. Was.

Example 5 A porous film was obtained in the same manner as in Example 1 except that the partial cross-linking treatment was carried out by irradiation with an electron beam of 1 Mrad (10 Gry).

Example 6 A porous film was obtained in the same manner as in Example 1 except that the partial cross-linking treatment was performed by irradiation with an electron beam of 5 Mrad (50 Gry).

Comparative Example An attempt was made to form a porous film in the same manner as in Example 1 except that a film not subjected to partial crosslinking treatment by electron beam irradiation was introduced into a liquid paraffin bath. However, when introduced into the liquid paraffin bath, the polyethylene was dissolved, the original shape was lost, and no porous film was obtained.

Evaluation Test The pores (openings) of the porous film obtained in the examples were obtained.
The ratio, tensile strength, and porous state in cross section (TEM cross section observation) were examined, and the results are shown in the following table.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is a sectional view of another embodiment.

FIG. 3 is a sectional view of still another embodiment.

[Explanation of symbols]

 1: porous film 2: air-permeable adhesive layer 3: separator

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kihachi Suzuki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (5)

[Claims] 1. A porous material comprising an olefin-based resin film, wherein the olefin-based resin forms a porous structure with voids between fibers or films cross-linked in a three-dimensional network structure. the film. 2. The film according to claim 1, wherein the olefin resin film is a film made of low density, medium density or high density polyethylene, a film made of a blend of two or more olefin resins, or an olefin resin film. A porous film which is a laminated film having three or more layers. 3. The porous film according to claim 1, wherein the olefin resin film has been partially cross-linked. 4. A step of swelling or partially dissolving an olefin resin film partially cross-linked to a three-dimensional network structure with a good solvent at a temperature at which the olefin resin does not crystallize, and the olefin after the good solvent treatment. A method for producing a porous film, comprising at least a step of removing a good solvent that has entered a resin film via a poor solvent into the film. 5. A gas-permeable adhesive member having a gas-permeable adhesive layer on one or both surfaces of the porous film according to claim 1.