JPS59105035A - Production of microporous sheet - Google Patents

Abstract

PURPOSE:To obtain a uniformly hazed, homogeneous microporous sheet, by laminating a thermoplastic resin sheet containing a filler of a finer particle diameter with a thermoplastic resin sheet containing a filler of a larger particle diameter, and stretching the laminate. CONSTITUTION:A thermoplastic resin such as vinyl chloride resin or acrylic resin is mixed with a filler, particle diameter <=1mu, (e.g., calcium carbonate or common salt), and the mixture is molded into a thermoplastic resin sheet (hereinafter, abbreviated as sheet A). Separately, a thermoplastic resin sheet containing a filler having a particle diameter larger than that of the filler used in sheet A (hereinafter, abbreviated as sheet B) is prepared so that the thickness of sheet B is at least three times that of sheet A. Sheet A is laminated with sheet B, and the laminate is stretched to obtain the purpose microporous sheet which is a porous sheet in which the B side consists of the microporous sheet and the diameters of the pores of sheet B side are larger than those of sheet A side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a microporous sheet made of a novel thermoplastic resin by a dry method.

Specifically, the method for producing a microporous sheet is characterized in that a plurality of thermoplastic resin sheets each containing a filler having a specified particle size are laminated and then stretched.

In recent years, porous sheets of synthetic resin have been used in fields such as battery separators and separation of blood and emulsions. Sheets used in these fields have, for example, microporous sheets with a pore size of 001μ or less, and have excellent filterability,
Materials with excellent chemical resistance and strength are required.

Conventionally, methods for manufacturing porous sheets include, for example, a dry method in which a filler is mixed into a thermoplastic resin and then formed and the resulting sheet is stretched, or a sheet is formed by mixing a filler into a thermoplastic resin. There is a wet method in which the filler is then extracted with a solvent or the like.

However, in the former dry method, the pore size of the sheet generally depends on the particle size of the filler and the stretching ratio, and in order to obtain a uniform pore size, it is necessary to make the particle size of the filler used uniform and the stretching ratio uniform. It is necessary to That is, in general, when a porous sheet is obtained by stretching a sheet material filled with a large amount of inorganic filler, it is important to uniformly achieve the whitening phenomenon during stretching, that is, the interfacial peeling phenomenon between the filler and the resin matrix. is important. Conventionally, in order to achieve such a uniform whitening phenomenon, inorganic fillers have been subjected to surface treatment, or interfacial peeling has been achieved by preliminary micro-stretching at the lowest possible temperature within the temperature range above the glass transition point and below the softening point. This is achieved through methods such as implementation. however,
In order to obtain a microporous sheet, when a large amount of inorganic filler with a particle size of 1 μm or less is used, it is difficult to achieve a uniform whitening phenomenon. That is, even if a large amount, particularly 50% by weight or more, of an inorganic filler with a particle size of 1 μm or less is filled and the above-mentioned method is used, a porous sheet that is locally stretched and homogeneous during stretching cannot be obtained, and it is not possible to obtain a porous sheet that is locally stretched during stretching. Problems such as breakage occurred before the magnification was reached, and no microporous sheet was substantially obtained.

On the other hand, in the latter wet method, the pore size of the sheet after the filler has been extracted is determined by the particle size of the filler, so that a uniform microporous sheet can be obtained. Also known is a method of producing a microporous sheet having high porosity by further stretching this sheet. However, these wet methods use inorganic chemicals or organic solvents to extract fillers, plasticizers, etc., and are therefore time-consuming, costly, and complicated. Furthermore, a method for manufacturing synthetic paper by laminating and stretching sheets containing fillers has been disclosed (Japanese Patent Publication No. 50-58665, Japanese Patent Publication No. 57-49011).

However, although the manufacturing method of such synthetic paper shows microporous formation by stretching, its purpose is mainly to maintain and improve strength, and the laminated sheets are cannot be said to have good permeability. On the other hand, the present invention is clearly different, as it aims to produce a microporous sheet in which the surface layer is finely porous and the base layer is also highly porous.

As a result of intensive research to achieve the above object, the present inventors have found that by laminating a resin sheet containing a filler with a specific fine particle size onto a specific resin sheet in advance, stretching becomes possible. The inventors have discovered that a microporous sheet can be easily obtained and have provided the present invention.

That is, the present invention provides a thermoplastic resin sheet containing a filler with a maximum particle size of 1 μm or less (hereinafter referred to as A sheet), and a thermoplastic resin sheet containing a filler with an average particle size larger than the above particle size (hereinafter referred to as A sheet). This is a method for producing a microporous sheet, which is characterized by laminating and then stretching a sheet (referred to as B sheet).

The microporous sheet FiA obtained by the method of the present invention is a sheet in which the sheet surface is microporous, and the B sheet surface has a larger pore diameter than the A sheet surface.

The microporous sheet of the present invention may be a composite sheet obtained by laminating sheet A and sheet B and then stretching the sheet, and is a general term that also includes sheets obtained by peeling sheet B from the stretched sheet.

The most important thing in the present invention is that each sheet containing a filler of a specific particle size is laminated and then stretched. That is, in general, after mixing a predetermined amount of a very small filler with a particle size of 1 μ or less into a thermoplastic resin, the sheet (A sheet) is in a necking stretched state, that is, it is stretched from one part and the stretched pores are nonuniform. Not only this, but also phenomena such as cutting occur before the desired stretching ratio is reached.

However, by laminating a specific auxiliary sheet (B sheet) to the sheet, it becomes possible to obtain a stretched microporous sheet in which the A sheet is also uniformly whitened.

In the present invention, the final sheet having the desired microporosity is the A sheet, and since the A sheet alone cannot be stretched, the KB sheet is also stretched, and the B sheet is a type of sheet for stretching the A sheet. This is an auxiliary sheet. After laminating and stretching, these become a series of porous sheets, but at least one surface (one side)
It is sufficient that the porosity is microporous (a microporous sheet obtained by stretching sheet A), and the other sheets have a porosity larger than the porosity.

In the present invention, it is important to specify the particle size of the filler contained in each of the two types of sheets, that is,
A sheet has a maximum particle size of 1μ or less, preferably 0.01~
In contrast to the use of a filler of 0.5 μm, the average particle size of the B sheet is generally 1 to 50 μm, preferably 3 to 20 μm, and the particle size is larger than that of the filler of the A sheet. is necessary.

Fillers that can be used in the present invention include fillers that are normally mixed into rubber or plastics, such as calcium carbonate, gypsum,
Calcium sulfite.

Calcium phosphate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide.

Magnesium sulfate, aqueous silicic acid, silicic anhydride, soda ash, sodium chloride, sodium sulfate.

Clay, various cements, volcanic ash, shirasu, titanium oxide,
These include iron oxide, carbon black, various metal powders, other inorganic substances, or organic metal salts mainly composed of inorganic substances, and generally have an average particle size of 50 microns or less.

In particular, the filler to be mixed into the six sheets is one that has been finely pulverized to 1μ or less, or one that has been synthesized to a size of 1μ or less, and the latter is particularly preferred as a method of obtaining a uniform particle size, and the filler that belongs to this category As such, calcium carbonate, magnesium hydroxide, silicic anhydride, titanium oxide, etc. are preferably used. Further, the particle size of the filler filled in the A sheet in the present invention may be set to have a maximum particle size of 1 μm or less in advance, or may be made to be 1 μm or less at a stage such as cross-wire of the resin. These are the amount that can maintain the desired porosity in the resin,
Preferably 30-80% by weight, particularly preferably 50-8%
Add so that the content is 0% by weight.

In the present invention, for the purpose of improving the dispersibility of the inorganic filler in the resin matrix and improving the uniform stretchability in the stretching process, heat-resistant plasticizers, erasing agents, or surfactants are added to the inorganic powder in advance. It is particularly suitable for A sheet to use one whose surface has been treated with process oil or the like. The amount of these surface treating agents varies depending on the particle size, but is usually 3 to 100 parts by weight based on the amount filled.

In the present invention, various additives other than those mentioned above, such as pigments, stabilizers, flame retardants, etc., may be mixed simultaneously or separately.

As the thermoplastic resin used in the present invention, known thermoplastic resins can be used without particular limitation. For example, vinyl chloride 4i4JIL vinyl acetate resin, polystyrene.

A　B　s resin, acrylic resin, polyethylene.

Examples include polypropylene, fluororesin, polyamide resin, acetal resin, polycarbonate, cellulose plastic, and polyolefin such as polypropylene is generally preferably used from the viewpoint of processability and chemical resistance. Thermoplastic resin sheets containing the fillers shown above generally have a thickness of 0.03-30.

The laminating method is to mix the above composition and then
After forming the sheets individually by calender molding or extrusion molding, the sheets are bonded together by compression molding, or by coextruding the molten composition of A resin and B resin from a T-die or cylindrical gouer. Alternatively, a general two-layer molding method such as forming two layers on the A sheet by extrusion lamination may be adopted. At this time, regarding the thickness of the A sheet and the B sheet, when stretching the laminated sheet, if the A sheet is thicker than the B sheet, the A
Since the stretchability of the sheet is poor, in order to alleviate this condition, it is preferable that the thickness of the B sheet is 6 times or more that of the A sheet. When laminating the A sheet and the B sheet, if the composition and physical properties such as melting point of the sheets are significantly different, the strength of the laminated part may decrease, and in some cases, peeling may occur. Usually the same type of resin is used, but different types of resin can also be used.

Next, the laminated sheet is stretched in at least one direction, preferably in two axial directions, to obtain a porous sheet. Although known stretching methods and equipment may be used, pores are usually formed in the sheet by stretching the sheet by 165 times or more, preferably about 2 times, at a temperature below the melting point of the thermoplastic resin.

It is also possible to peel off the B sheet after stretching. The resulting microporous sheet generally has a thickness of 0.03 to 5I! ll11. Porosity 60-90%.

When the maximum pore diameter is 1 μm or less, the pore diameter distribution is uniform and the strength is excellent. Therefore, after the microporous sheet obtained by the present invention is stretched, it can be used as it is, or extracted with an appropriate eluent, such as an acid or alkaline solution for inorganic powder, or an added plasticizer, etc. By extracting and removing the resin with an organic solvent, a microporous sheet consisting only of the resin may be obtained, and it can be used for a wide range of applications as described above.

EXAMPLES Hereinafter, examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

The method for measuring performance evaluation items is as follows.

1) Porosity Wo: weight of sample piece in air w + Water content weight of 9 sample pieces W2; Weight of sample piece in water 2) Air permeability ~ According to JISP8117.

3) Maximum pore diameter ~ According to A8TM Ii''-316-70 (using ethanol) Example 1 Heavy calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd.).

Product name: White No 81 (particle size 7μ) 70% by weight, polypropylene powder (manufactured by Tokuyama Soda Co., Ltd.).

A composition consisting of 30 weight (trade name: Tokuyama Polypro YE-120) and 3.0 PHR of a polyester plasticizer (manufactured by Dainippon Ink Co., Ltd., trade name: Polycizer W-2300) was mixed at 200C with a 3″ roll. After that, use a press to reduce the thickness to 0.
．． A 3% sheet B) was prepared. Next, a sheet A) having a thickness of 0.1X was prepared in the same manner using the filler and dispersant shown in Table 1, and the sheet (B) and sheet (A) were heated to a thickness of 0.1X at 170°C. They were laminated in a 351X mold and pressed to obtain a sheet with a thickness of 0.35%. Next, the sheet was simultaneously biaxially stretched at 1 soc in an experimental biaxial stretching machine to a ratio of 2x2 in the vertical and horizontal directions, and the physical properties of the obtained sheet are shown in the right column of Table 1 (A1 to A4). A4 is a comparative example and shows the results of a stretched sheet consisting only of sheet (B).

It was found that A1 to A3 had smaller pore diameters than A4, and the surface on the sheet (B) side was microfibrillated and microporous. Electron micrographs of the (B) side surface of A1 and the sheet (A) side surface are shown in Figures 1 and 2, respectively.
Shown in the figure.

Further, as a comparative example, when a sheet made by laminating press sheets of 2X thickness in the same manner as sheet) (B) and sheet) (A) containing the filler A1 was stretched, breakage occurred, and the stretching Didn't get a sheet.

1゛Fuji Example 2 3F for 100F of heavy calcium carbonate (trade name: Whiten-B, particle size 7μ, manufactured by Shiroishi Calcium Co., Ltd.)
(3PHR) polyester plasticizer (product name: W-
2300, manufactured by Dainippon Ink Co., Ltd.) 7
A pellet composition consisting of 0 wt% and 30 wt% of polypropylene (trade name 2YE-120, manufactured by Tokuyama Polyglo, Tokuyama Soda Co., Ltd.) was formed into a sheet with a thickness of 0-3 m+ using a T-die extruder with a cylinder diameter of 60 mm. (Sheet B). Next, magnesium hydroxide (product name: Kisuma 4)
A.F.

Particle size 0.6μ, Kyowa Kagakusha #) 10f (
A pellet composition consisting of 55 wt % of dioctyl phthalate (10 PHR) surface treated and 45 wt % of polypropylene was extruded using the same extruder to a thickness of 7011 mm.
Then, the sheet B was laminated with the sheet B by extrusion lamination 7.

The resulting laminated sheet was then stretched in the longitudinal direction by an experimental stretching machine.
It was successively stretched 2.5 times at 00 and 2.5 times at 160 L in the transverse direction. The stretched sheet has a thickness of 0.25% and a porosity of 78%.
9 Air permeability 60 seconds.

The maximum pore diameter is 0.8μ, and it has an unprecedented micro JL,
It was a microporous sheet with high permeability.

[Brief explanation of the drawing]

Figure 1 shows (B) the microporous sheet shown in the example of the present invention.
Similarly, FIG. 2 shows an electron micrograph of the layer side surface (A). Patent applicant Tokuyama Soda Co., Ltd.

Claims (1)

[Claims] 1) Thermoplastic resin sheet containing a filler with a particle size of 1 μ or less)
(A) and a thermoplastic resin sort (B) containing a filler larger than the above particle size are laminated and then stretched. 2) (B) The thickness of the sheet is ( 3) Thermoplastic resin sheet (A) still has a filler content of 60 to 80% (B)
Heavy view 9 (manufacturing method according to claim 1)