JPH06136167A - Production of porous film or sheet - Google Patents

Abstract

PURPOSE:To obtain a method for producing a porous film or sheet which does not allow a liquid, such as water, to permeate, has uniform and excellent air and moisture permeabilities and is excellent in chemical resistance, dust-freeness and electrical characteristics by mixing at least two dispersions of synthetic resins or high-molecular materials having poor compatibility with each other, applying the mixture on a support and melting it to form a film. CONSTITUTION:A dispersion of a thermoplastic resin (A) is mixed with a dispersion containing a high-molecular material (B) having poor compatibility with the resin A and different in melting point and the mixture is applied on a support, melted and formed into film, thus giving a film or sheet. This film or sheet is stretched at least in one direction at a temperature lower than the melting points of the resin A and the material B.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the production of a porous film or sheet which is impermeable to liquids such as water and has excellent breathability and moisture permeability as well as chemical resistance, dust resistance and electrical characteristics. It is about the method.

[0002]

2. Description of the Related Art Conventionally, a porous film is formed by, for example, forming a film from a resin composition obtained by adding an inorganic filler to a polyolefin resin, and stretching the film, or a porous film obtained by stretching the film. It is obtained by extracting the soluble filler from the film with water, acid or alkali.

However, according to these methods, the presence of the inorganic filler in the porous film may not provide the required properties such as chemical resistance and electrical properties, which limits its use. There was a drawback.

Therefore, recently, there has been proposed a method for stretching a film formed by melt-kneading two or more kinds of thermoplastic resins having poor compatibility as described below.

That is, first, in the first method for producing a porous film, a mixture of a thermoplastic resin A and a thermoplastic resin B having poor compatibility with the resin A and having a melting point of at least 20 ° C. higher is used. Melt and knead at a temperature above the melting point of resin B, form into a sheet at a temperature higher than the melting point of resin A and lower than the melting point of resin A, and then stretched in at least one direction at a temperature lower than the melting point of resin A. (JP-A-58-198536).

As a second method for producing a porous film, 100 parts by weight of a polyolefin resin (A) and a thermoplastic resin (B) 10 to 1 having a low compatibility with (A) are used.
Melt and knead a resin mixture containing 100 parts by weight as an essential component,
The extruded film or sheet is (A) and (B) in a temperature range of not less than 10 ⁶ poises and not more than 300 ° C. and having substantially no shear rate 1- A film or sheet obtained by heat-treating for 60 seconds and then rapidly cooling is stretched in at least uniaxial direction (JP-A-63-63).
-270748).

[0007]

In the above method, the melting points are different, and the interface between the main component resin A and the high melting point thermoplastic resin B dispersed in a so-called island shape therein is stretched. Although it is made to be porous, in a film obtained by an ordinary extrusion machine, a thermoplastic resin B having a high melting point is formed into a film by deformation due to a shearing force inside the extruder or drawdown at a die outlet. Since the film is stretched in the flow direction and is transformed into a linear or layered form, when this film is stretched, the uniaxial stretching in the flow direction of the film shows that the effective interfacial area for generating pores is very small. Therefore, voids are less likely to occur, and the resulting film has a very small tear strength in the flow direction.

In addition, when the film is uniaxially stretched in the axial direction, the pores generated by the stretching may only have a small porosity, and the required air permeability may not be obtained.

Further, even when the biaxial stretching is carried out, it is more advantageous than when the uniaxial stretching is carried out in the flow or axial direction to generate the voids, but the holes are also two-dimensionally generated in the film surface direction and three-dimensionally formed. Therefore, a stretched film having a large porosity cannot be obtained in either uniaxial stretching or biaxial stretching.

Further, in the unstretched film and the stretched film in which the high melting point thermoplastic resin B is dispersed in layers, a phenomenon of peeling parallel to the film surface is also observed, and the delamination strength of the film becomes extremely weak. There are challenges.

On the other hand, in the above-mentioned method, although the above-mentioned problems are somewhat improved, since the thermoplastic resin is used in both of them, the same problem occurs.

In fact, although the porous film obtained by the above-mentioned method has some improvement in moisture permeability, it cannot be said that the tensile strength is sufficient.

In particular, the films obtained by the above-mentioned methods (1) and (2) are both resin mixtures containing a polyolefin resin (A) and a thermoplastic resin (B) poor in compatibility with this (A) as essential components. Is melt-kneaded and the extruded film or sheet is stretched. When the melt-kneaded resin mixture is extruded into a film, the (A) and (B) have poor compatibility, As a result of separation or deviation between the two, it is difficult to obtain a uniform film or sheet, and there are serious problems such as variations in air permeability and moisture permeability.

The present invention has been completed in view of the above technical problems, and a dispersion of two or more kinds of synthetic resins or polymer substances having poor compatibility is mixed and coated on a support. After that, by melting and forming a film, liquid such as water does not permeate, and it has uniform and excellent breathability and moisture permeability, and
It is an object of the present invention to provide a method for producing a porous film / sheet which is excellent in chemical resistance, dust resistance, and electrical characteristics.

[0015]

In order to achieve the above-mentioned object, the present invention provides a dispersion of a thermoplastic resin (A) and a thermoplastic resin (A) having poor compatibility and a melting point. A film or sheet obtained by mixing dispersions containing different polymer substances (B), applying the mixture on a support, and then melting and film-forming the thermoplastic resin (A) and the polymer It is characterized in that it is stretched in at least one direction at a temperature lower than the melting point of the substance (B).

The present invention will be described in detail below. The thermoplastic resin (A) used in the present invention is not particularly limited as long as it is a thermoplastic resin and can be formed into a film or a sheet.

Specific examples of the thermoplastic resin (A) include, for example, polyolefin resin, polystyrene resin, polyvinyl chloride resin, polyamide resin, polyacrylate resin, polyester resin, polycarbonate resin or Examples include thermoplastic polyurethane-based resins, and among these, from the viewpoint of molding / workability and various characteristics of the film or sheet, manufacturing cost, etc.,
A polyolefin resin is particularly desirable.

Examples of the polyolefin resin include linear low-density polyethylene, high-pressure polyethylene, low-pressure polyethylene, polypropylene, ethylene-propylene copolymers, polybutadiene, ionomer resin, ethylene-vinyl acetate copolymer resin and the like. Examples of the polyolefin resin, among these, those using linear low-density polyethylene, the production or processability of the film or sheet is further excellent, and the production cost is significantly low,
Moreover, it is most preferable that the obtained porous film / sheet has high mechanical strength.

In the present invention, the dispersion liquid of the thermoplastic resin (A) is formed. The concentration of the resin (A) component in the dispersion liquid is preferably 20 to 60% by weight. If the concentration is less than 20% by weight, the concentration becomes too thin and the apparatus becomes large, it takes a long time to remove the dispersion medium such as water, the treatment of the dispersion medium becomes difficult, and It is not preferable because it is difficult to form a thick film. On the other hand, when it exceeds 60% by weight, the concentration becomes too high and it becomes difficult to uniformly mix it with the polymer substance described later, or the coating property is poor. Since it becomes difficult, it is not preferable. From these viewpoints, the concentration of the resin (A) component is preferably 20 to 60% by weight.

When the thermoplastic resin (A) is dispersed in a dispersion medium such as water, the average particle size of the resin (A) is preferably in the range of 0.1 to 50 μm. However, if it is less than 0.1 μm, the resin (A) is too fine and rises in the air during handling to deteriorate the working environment or the handling property is not desirable, while if it exceeds 50 μm, the dispersibility becomes poor. , It becomes difficult to obtain a uniform dispersion liquid, and it takes time to melt and form a film, which lowers workability.
It is not preferable because it is difficult to obtain a uniform film or tape. Therefore, from these viewpoints, the average particle size is 0.3 to
It is desirable to set it in the range of 50 μm.

In the present invention, with respect to the dispersion liquid of the thermoplastic resin (A) and the thermoplastic resin (A),
A dispersion liquid containing a polymer substance (B) having poor compatibility and different melting points is mixed.

Examples of the polymer substance (B) include at least one selected from thermoplastic resins, thermosetting resins and rubber-based substances.

The thermoplastic resin as the polymer substance (B) is not particularly limited as long as it has poor compatibility with the thermoplastic resin (A) and has a different melting point.

In this case, the thermoplastic resin as the polymer substance (B) is selected from the above-mentioned thermoplastic resins by combination with the thermoplastic resin (A) used, with respect to the thermoplastic resin (A). Therefore, those having poor compatibility and different melting points may be selected and used.

The thermosetting resin as the polymer substance (B) is not particularly limited, but specifically, for example, bisphenol A epoxy resin, novolac epoxy resin, halogenated epoxy resin, or the like. Epoxy resin, alkyd resin, amino alkyd resin, silicone resin, unsaturated polyester resin, thermosetting polyurethane resin, polyimide thermosetting resin, polybenzimidazole thermosetting resin, urea resin, melamine resin, resorcinol resin Resins Phenolic resins or xylene resins may be mentioned.

If desired, the thermosetting resin composition contains a curing agent, a curing accelerator, and a curing agent corresponding to each thermosetting resin.
Additives such as catalysts are blended.

Specific examples of this additive include boron trifluoride monoethylamine, dicyandiamide, aromatic amines, acid anhydrides, imidazoles and hydrazide adducts.

In this case, the compounding ratio of the additive varies depending on the thermosetting resin and the additive used, but is generally 0.1 to 30 parts by weight of the additive with respect to 100 parts by weight of the thermosetting resin. It is desirable to do.

Further, the rubber substance as the polymer substance (B) is not particularly limited, and specific examples thereof include natural rubber and synthetic rubber.

The natural rubber is not particularly limited as long as it is a rubber obtained from a growing plant.

The synthetic rubber is not particularly limited as long as it is a rubber other than the natural rubber, and specifically, for example, thermoplastic elastomer, styrene butadiene rubber, acrylonitrile butadiene rubber, butadiene rubber, isoprene rubber. , Chloroprene rubber, chlorosulfonated polyethylene, ethylene propylene rubber, butyl rubber, silicone rubber, polysulfide rubber, fluororubber, urethane rubber, acrylic rubber, polyisobutylene, isoprene, adduct rubber or chlorinated rubber, and hydrochloric acid rubber.

Specific examples of the thermoplastic elastomer include styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SI).
-S) Further, a styrene block polymer such as styrene-ethylene / butylene-styrene (S-EB-S) may, for example, be mentioned.

In the present invention, the above polymer substance (B)
The concentration of the polymer substance (B) in the dispersion is preferably 20 to 60% by weight. If the concentration is less than 20% by weight, the concentration becomes too thin. It is not preferable because the apparatus becomes large, it takes a long time to remove the dispersion medium such as water, and the treatment of the dispersion medium becomes difficult. On the other hand, when it exceeds 60% by weight, the concentration becomes too high. However, it is not preferable because it becomes difficult to uniformly mix with a polymer substance described later and coatability becomes difficult. From these viewpoints, the concentration of the polymer substance (B) is 25 to 5
It is preferably 5% by weight.

When the polymer substance (B) is dispersed in a dispersion medium such as water, the average particle size of the polymer substance (B) is preferably in the range of 0.1 to 50 μm. If the particle size is less than 0.1 μm, the polymer substance (B) is too fine, and is not desirable because it floats up in the air during handling and the working environment deteriorates, and the handling property deteriorates.
When it is more than μm, the dispersibility becomes poor and it becomes difficult to obtain a uniform dispersion liquid, which makes it difficult to obtain a uniform film or tape, or causes film breakage during stretching in a subsequent step, which is not preferable. From these viewpoints, it is desirable that the average particle diameter be in the range of 0.3 to 50 μm.

As for the mixing ratio of the thermoplastic resin (A) and the polymer substance (B), 10 to 100 parts by weight of (B) are mixed with 100 parts by weight of (A),
When the compounding ratio of (B) is less than 10 parts by weight, it is difficult to obtain a porous film or sheet having desired air permeability and moisture permeability, while when it exceeds 100 parts by weight, a film layer as a base material is used. Alternatively, the sheet layer (A) and the dispersed phase (B) are reversed, and a porous film or sheet having good air permeability or moisture permeability cannot be obtained.

In the present invention, when the thermoplastic resin (A) and the polymer substance (B) to be mixed are selected, this (A) and (B) are mixed so as to be more evenly mixed. It is desirable that the true densities of (B) are selected to be equal or almost equal to each other.

Further, when the true specific gravities of the thermoplastic resin (A) and the polymer substance (B) to be mixed are different from each other, the two are more uniformly mixed, so that the average of these (A) and (B) It is desirable to change the particle size.

The method for producing the porous film / sheet of the present invention is realized by the method described below. First, a dispersion liquid of a thermoplastic resin (A) which is a base resin and a dispersion liquid of a polymer substance (B) which is a dispersed phase are mixed and coated on a support such as a separator to form a dispersion medium. After the removal, the film or sheet obtained by melting and forming a film may be stretched in at least one direction at a temperature lower than the melting points of the thermoplastic resin (A) and the polymer substance (B). .

In this case, since the dispersion liquid of the thermoplastic resin (A) and the dispersion liquid of the polymer substance (B) are mixed, the dispersion medium serves as a buffer, and the dispersion liquids (A) and (B) are uniform. The size of the nuclei dispersed in the film layer or the sheet layer can be adjusted very easily by the average particle size of (B), that is, the film or film having a uniform sea-island structure. Therefore, a sheet is obtained, and therefore, by stretching this uniform film or sheet in at least one direction, liquid such as water does not permeate, and is uniform, and also has excellent breathability and moisture permeability. It is possible to obtain a porous film / sheet having excellent chemical resistance, dust resistance, and electrical characteristics.

As a mixer used for mixing the dispersion liquid of the thermoplastic resin (A) which is the base resin and the dispersion liquid of the polymer substance (B) which is the dispersed phase, there are known mixers such as homomixers and dispersers. A mixer is included.

When the uniformly mixed resin mixture of (A) and (B) is formed into a film or sheet, the resin mixture is coated on a support such as a separator and the dispersion medium is removed. Melting and film formation may be performed, and the film formation temperature at this time is at least higher than the melting point of the thermoplastic resin (B). Therefore, it is not necessary to carry out above the melting point of the polymer substance (B).

Further, in the present invention, as another method for molding the resin mixture uniformly mixed as described above into a film or sheet, the resin mixture is melted and kneaded, and a known molding apparatus and molding are used. The method may be used, and for example, an inflation molding machine, a T-die molding machine, a calender roll, various extruders, etc. can be adopted.

In this case, since this resin mixture is uniformly mixed, it is almost uniform in the molten state, and a uniform film or sheet can be obtained by kneading this.

In the present invention, the obtained film or sheet is machined in a longitudinal direction, that is, in one direction, by using a known stretching machine such as a roll stretching machine, a simultaneous biaxial stretching machine, a sequential biaxial stretching machine or a tenter stretching machine. Alternatively, it may be stretched in the lengthwise and crosswise directions, that is, in two directions. By stretching in this way, fine communication holes are formed, the quality is stable, and moreover, a porous film / sheet excellent in uniformity and breathability and moisture permeability is obtained. You can get it.

In this case, the stretching direction may be one direction,
It is desirable to stretch in two directions in order to obtain a more uniform porous film / sheet having excellent breathability and moisture permeability at a relatively low stretch ratio.

In the present invention, in forming the porous film / sheet, the stretching ratio of the unstretched film / sheet is 2 to 7 times in one direction, and if it is less than 2 times, the unstretched portion remains. Since uneven stretching may occur, a uniform film or sheet may not be obtained in some cases, while exceeding 7 times may cause breakage, which is not desirable.

When the unstretched film or sheet is stretched, the stretching ratio is (length × width) 2 in the case of bidirectional stretching.
It is 10 to 10 times, and if it is less than 2 times, unstretched portions remain and uneven stretching occurs, so it may not be possible to obtain a uniform film or sheet, or it may be difficult to obtain the required breathability and moisture permeability. If it exceeds, it may break, which is not desirable.

In the present invention, the stretching ratio means a value obtained by dividing the dimension after the stretching treatment by the dimension before the stretching treatment.

The temperature during this stretching is 20 to 1
It is desirable to set the temperature to 30 ° C., particularly 60 to 110 ° C., and if the above conditions are not satisfied, it will break or become porous, but it will be difficult to obtain communicating pores with independent bubbles, and breathability and moisture permeability will be obtained. May be damaged, which is not desirable.

In this way, a porous film / sheet is obtained, which is impermeable to liquids such as water and uniform, and has excellent breathability and moisture permeability. .

By the way, in the present invention, the porous film / sheet obtained as described above is subjected to an annealing treatment, if desired, to thereby reduce the final magnification from, for example, 4 times to 2 times. The post-treatment may improve the air permeability and moisture permeability of the porous film / sheet, and further the strength. In this case, the annealing temperature is preferably in the range of 50 to 200 ° C. If the temperature is lower than 50 ° C, the temperature is too low and the fluidity of the polymer becomes poor, so that it may not be possible to uniformly set a predetermined draw ratio. On the other hand, if the temperature exceeds 200 ° C, the polymer melts and becomes porous. 70 to 130 ° C. is particularly desirable because it may be lost.

In the present invention, the porous film
An appropriate amount of additives such as an antioxidant, an ultraviolet stabilizer, an antistatic agent, a lubricant, and a fluorescent agent, which are usually used, may be added within a range that does not deteriorate the physical properties of the sheet.

[0053]

The present invention, which has the above-mentioned constitution, mixes the dispersion liquid of the thermoplastic resin (A) which is the base resin with the dispersion liquid of the polymer substance (B) which is the dispersion phase. The dispersion medium such as the above acts as a buffer and has the effect of uniformly mixing the (A) and (B).

In this case, the size of nuclei dispersed in the film layer or sheet layer can be adjusted very easily by the average particle size of (B), that is, a film or sheet having a uniform sea-island structure can be obtained. Therefore, by stretching this uniform film or sheet in at least one direction, liquids such as water are impermeable and uniform,
Moreover, it has an effect of obtaining a porous film / sheet which exhibits excellent breathability and moisture permeability, and has excellent chemical resistance, dust resistance, and electrical characteristics.

[0055]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited thereto. Examples 1 to 3 At a ratio shown in Table 1, a dispersion liquid (35% by weight of resin content) of a high-density polyethylene (HDPEMI 1.1 g / 10 minutes, average particle diameter 2 μm), which is a thermoplastic resin (A), and a polymer Material (B), polyester (PET average particle size 3μ
m) dispersion (resin content 35% by weight) or polypropylene (MI 8 g / 10 min, average particle size 4 μm) was thoroughly mixed with a homomixer, and then cast on a release paper with a coating machine to prepare a dispersion medium. The film was removed, further dried at the temperature shown in Table 1 and melted to form a film, and the release paper was peeled off to obtain a film.

Next, this film was unidirectionally stretched under the conditions shown in Tables 1 and 2 to obtain a porous film.

Comparative Example 1 100 parts by weight of high-density polyethylene (HDPE) and 25 parts by weight of polycarbonate (PC) were sufficiently kneaded by a twin-screw extruder and then extruded by a single-screw extruder under the conditions shown in Table 1. The film was formed.

Next, this film was stretched in one direction under the conditions shown in Tables 1 and 2 to obtain a porous film.

Comparative Example 2 100 parts by weight of high-density polyethylene (HDPE) and 45 parts by weight of polystyrene (PS) were sufficiently kneaded by a twin-screw kneader and then extruded by a single-screw extruder under the conditions shown in Table 1. Filmed

The obtained film was heat-treated at 210 ° C. for 10 seconds, and then stretched in one direction under the conditions shown in Tables 1 and 2 to obtain a porous film.

[0061]

[Table 1]

Tables 2 and 3 show the results obtained by measuring various characteristics of the above-mentioned Examples and Comparative Examples.

[0063]

[Table 2]

[0064]

[Table 3]

The dust-free property was determined by rotating a stainless steel rod in contact with the sample and measuring the lint number with a dust counter. The results are shown in Table 4.

[0066]

[Table 4]

Note 1) The tensile strength shown in Table 2 means the strength at break when a sample is sandwiched at a chuck interval of 40 mm using a tension universal tensile tester and pulled at a tensile speed of 300 mm / min.

Note 2) The moisture permeability shown in Table 3 is JIS L
It was measured by the moisture permeable cup method at -1099.

Note 3) The air permeability shown in Table 3 is JIS P
It was measured by the Gurley method in -8117.

The results shown in Tables 2 and 3 show that each of the examples exhibits excellent breathability and moisture permeability as compared with each of the comparative examples, and the tensile strength is also higher than that of each comparative example. , It is recognized that there is no difference.

The air permeability and the moisture permeability of the examples and the comparative examples were varied at a temperature of 23 ° C.
When measured under a relative humidity of 65%, both of the examples are ± 30% of the average value, whereas the comparative examples are both ± 60% of the average value. %
It was confirmed that the variation in each example was small.

[0072]

INDUSTRIAL APPLICABILITY The present invention provides a porous film / sheet which has the above-mentioned structure, is stable and homogeneous in quality, has no variation, and is extremely excellent in breathability and moisture permeability without using a special technique or device. It has the effect that it can be manufactured at low cost.

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Claims (4)

[Claims] 1. A dispersion liquid of a thermoplastic resin (A) and a dispersion liquid containing a polymer substance (B) having a poor compatibility and a different melting point with respect to the thermoplastic resin (A) are mixed. After coating on a support, the film or sheet obtained by melting and forming a film is applied in at least one direction at a temperature lower than the melting points of the thermoplastic resin (A) and the polymer substance (B). A method for producing a porous film or sheet, which comprises stretching. 2. The method for producing a porous film or sheet according to claim 1, wherein the polymer substance (B) is at least one selected from a thermoplastic resin, a thermosetting resin and a rubber-based substance. 3. The method for producing a porous film or sheet according to claim 1, wherein the rubber-based substance is natural rubber or synthetic rubber. 4. The compounding ratio of the thermoplastic resin (A) and the polymer substance (B) is 1 for (B) based on 100 parts by weight of (A).
The method for producing a porous film or sheet according to any one of claims 1 to 3, wherein the amount is 0 to 100 parts by weight.