JPH0238098B2 - - Google Patents

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 by laminating a plurality of thermoplastic resin sheets containing fillers each having a specified particle size and thickness, and then stretching the sheets. 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 are required to have micropores with a pore diameter of 1 μm or less, and to have excellent filterability, chemical resistance, strength, etc. Conventionally, methods for manufacturing porous sheets include:
For example, a dry method involves mixing a filler in a thermoplastic resin and stretching the resulting sheet, or a method in which a mixture of a filler in a thermoplastic resin is formed into a sheet, and then the filler is extracted with a solvent or the like. There are wet methods etc. 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 uniform and the stretching ratio uniform. There is a need 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 ensure that the whitening phenomenon during stretching, that is, the interfacial peeling phenomenon between the filler and the resin matrix, occurs uniformly. 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, when a large amount of inorganic filler with a particle size of 1 μm or less is used to obtain a microporous sheet, it is difficult to achieve a uniform whitening phenomenon. That is, the particle size
Even if a large amount of inorganic filler of 1μ or less is filled, especially 50% by weight or more, and the above-mentioned method is used, a porous sheet that is locally stretched and homogeneous cannot be obtained during stretching, and it is not possible to obtain a porous sheet that is locally stretched at a predetermined stretching ratio. Trouble such as breakage occurred before the sheet was completely broken, and a microporous sheet could not be obtained substantially. On the other hand, in the latter wet method, the pore size of the sheet after the filler has been extracted is substantially 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 producing synthetic paper by laminating and stretching sheets containing fillers has been disclosed (Japanese Patent Publication No. 50-38665, 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. In order to achieve the above object, the present inventors have conducted intensive research and found that stretching is possible by laminating a resin sheet containing a specific amount of a filler with a specific fine particle size onto a specific resin sheet in advance. The present inventors have discovered that a desired microporous sheet can be easily obtained and have provided the present invention. That is, the present invention uses 30 to 80 particles of filler with a particle size of 1μ or less.
Thermoplastic resin sheet (A) containing % by weight, and the sheet (A)
A method for producing a microporous sheet, which comprises laminating the thermoplastic resin sheet (B) with a thermoplastic resin sheet (B) having a thickness three times or more and containing 30 to 80% by weight of a filler having a particle size larger than the above particle size, and then stretching the sheet. It is. The microporous sheet obtained by the method of the present invention is A
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 sheets containing a specific amount of filler with a specific particle size are laminated to a specific thickness and then stretched. That is, in general, after mixing a predetermined amount of a very small filler with a particle size of 1μ or less into a thermoplastic resin, the sheet (A sheet) is in a netting stretched state, that is, it is stretched from one part and the stretched pores are non-uniform. 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 sheet to have the desired microporosity is the A sheet, and since the A sheet alone cannot be stretched, it is laminated together with the B sheet, and the B sheet is a type of sheet for stretching the A sheet. This is an auxiliary seat. After laminating and stretching, these become a series of porous sheets, but at this time, at least one surface (one side) is microporous (a microporous sheet made by stretching the A sheet), and the other sheets have a porosity larger than that. That's fine. 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, the A sheet has a maximum particle size of 1μ or less,
Preferably, a filler with a particle diameter of 0.01 to 0.5μ is used, whereas a filler with an average particle size of generally 1 to 50μ, preferably 3 to 20μ, and a larger particle size than that of the filler in the A sheet is used for the B sheet. It is necessary. B
If the particle size of the filler contained in the sheet is smaller than the particle size of the filler in the A sheet, the A sheet may be partially stretched during stretching, resulting in nonuniform stretching pores, and in some cases, the A sheet may not be uniform. Breakage may occur before the stretching ratio is reached. Fillers which can be used in the present invention are fillers normally mixed into rubber or plastics, such as calcium carbonate, gypsum, calcium sulfite, calcium phosphate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, magnesium sulfate, water. Japanese silicic acid, anhydrous silicic acid, soda ash, sodium chloride,
Sodium sulfate, clay, various cements, volcanic ash, shirasu, titanium oxide, iron oxide, carbon black, various metal powders, other inorganic substances or organic metal salts mainly composed of inorganic substances, etc., and generally have an average particle size of 50 microns or less. It has the following. In particular, the filler to be mixed into the A sheet is one that has been finely pulverized to less than 1μ, or one that has been synthesized.
The latter is particularly preferable as a method for obtaining a uniform particle size, and calcium carbonate, magnesium hydroxide, silicic anhydride, titanium oxide, etc. are preferably used in this category. In addition, even if the particle size of the filler filled in the A sheet in the present invention is set in advance to a maximum particle size of 1μ or less,
Alternatively, the thickness may be set to 1μ or less at a stage such as kneading the resin. These are added in an amount sufficient to maintain the desired porosity in the resin, preferably 30 to 80% by weight, particularly preferably 50 to 80% by weight. That is, if the filler content in each of the two types of sheets is less than 30% by weight, the number of effective communicating pores in the resin will decrease and the desired porous sheet will not be obtained; If it exceeds this, the fillers tend to aggregate with each other, making it difficult to form into a sheet and causing breakage during stretching. In the present invention, in order to improve the dispersibility of the inorganic filler in the resin matrix and to improve the uniform stretchability in the stretching process, heat-resistant plasticizers, lubricants, 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 oil or the like. The amount of these surface treatment 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 resin, vinyl acetate resin, polystyrene, ABS resin,
Acrylic resin, polyethylene, polypropylene,
Fluorine resin, polyamide resin, acetal resin,
Examples include polycarbonate and cellulose plastic, but polyolefins such as polypropylene are generally preferred from the viewpoint of processability and chemical resistance. Thermoplastic resin sheets containing the fillers shown above generally have a thickness of 0.03 to 3 mm. The laminating method is to knead the above composition, then individually mold the sheets by calender molding or extrusion molding, and then bond the sheets together by compression molding, or by using a T-die or cylindrical shape. A two-layer sheet may be formed by co-extruding the melted composition of resin A and resin B from a die, or a general two-layer sheet may be formed by extrusion lamination on top of the A sheet. A molding method is adopted. At this time, regarding the thickness of the A sheet and the B sheet, when stretching the laminated sheet, if the thickness of the A sheet is thicker than the thickness of the B sheet, the stretchability of the A sheet will be inferior.
In order to alleviate this condition, the thickness of sheet B must be
It is necessary to make it at least three times the size of the sheet. When laminating A sheet and 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. The sheets are usually made of the same type of resin, 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. Regarding the stretching direction and device, known ones can be used, but usually,
Pores are formed in the sheet by stretching it 1.5 times or more, preferably about 2 times, at a temperature below the melting point of the thermoplastic resin. Moreover, it is also possible to peel off the B sheet after stretching. The resulting microporous sheet generally has a thickness of 0.03 to 3 mm and a porosity of 60 to 90.
%, and the maximum pore diameter is 1μ or less, the pore size 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 is, or it can be 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 such as alcohol, it may be made into a microporous sheet made only of resin, which 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 Porosity [%] = [W ₁ −W ₀ /W ₁ −W ₂ ]×100 W ₀ ; Weight of sample in air W ₁ ; Weight of water content of sample W ₂ ; Weight of sample in water Weight (2) Air permeability ~ According to JIS P8117. (3) Maximum pore diameter ~ According to ASTM F-316-70 (using ethanol) Example 1 and Comparative Examples 1 and 2 Heavy calcium carbonate (manufactured by Shiroishi Calcium Co., Ltd., trade name: Whiten-B, particle size 7μ) 70 A composition consisting of 30% by weight of polypropylene powder (manufactured by Tokuyama Soda Co., Ltd., trade name: Tokuyama Polypro YE-120), and 3.0 PHR of polyester plasticizer (manufactured by Dainippon Ink Co., Ltd., trade name: Polycizer W-2300). After kneading with a 3″ roll at 200℃, the thickness is 0.3m/m with a press machine.
A sheet (sheet B) was created. Then, using the fillers and dispersants shown in Table 1, the thickness of 0.1
m/m sheet (sheet A), the above sheet (B) and sheet (A) were laminated at 170℃ in a formwork with a thickness of 0.35 m/m, and pressed to a thickness of 0.35 m. /m sheet was obtained. Next, the sheet was simultaneously biaxially stretched to 2x2 times vertically and horizontally at 130°C using an experimental biaxial stretching machine, and the physical properties of the obtained sheet are shown in the right column of Table 1 (No. 1
-4). Note that No. 4 shows the results of Comparative Example 1, a stretched sheet consisting only of sheet (B). Nos. 1 to 3 have smaller pore diameters than No. 4, and the sheet (B)
The side surface was found to be microporous with microfibrillation. Electron micrographs of the sheet (B) side surface and the sheet (A) side surface of No. 1 are shown in FIGS. 1 and 2, respectively. Further, as Comparative Example 2, sheet (B) and sheet (A) containing No. 1 filler were prepared in the same manner, and 2
When a sheet of laminated press sheets having a thickness of m/m was stretched, breakage occurred and the stretched sheet could not be obtained.

[Table] Example 2 Heavy calcium carbonate (product name: White Saw)
B, particle size 7 μ, manufactured by Shiraishi Calcium Co., Ltd.) per 100 g, 70 wt% of the surface treated with 3 g (3PHR) of polyester plasticizer (product name: W-2300, manufactured by Dainippon Ink Co., Ltd.) and polypropylene (product given name:
YE−120, Tokuyama Polypro, Tokuyama Soda Co., Ltd.) 30wt
% was wound into a sheet with a thickness of 0.3 mm using a T-die extruder having a cylinder diameter of 30 mm (Sheet B). Next, 100g of magnesium hydroxide (product name: Kisuma 4AF, particle size 0.3μ, manufactured by Kyowa Chemical Co., Ltd.) was surface-treated with 10g (10PHR) of dioctyl phthalate (55wt%).
A pellet composition consisting of 45% by weight of polypropylene was extruded using the same extruder to a thickness of 70 μm, and laminated with the sheet B by extrusion lamination by nipping. The obtained laminated sheet was then successively stretched in the machine direction by 2.5 times at 80° C. and in the transverse direction by 2.5 times at 130° C. using an experimental stretching machine. The stretched sheet has a thickness of 0.25m/m, a porosity of 78%, an air permeability of 60 seconds, and a maximum pore diameter of 0.8μ.
It was a microporous sheet with unprecedented micropores and high permeability. Comparative Example 3 A composition consisting of 30% by weight of filler No.-1 in Table 1, 70% by weight of polypropylene, and 3.0 PHR of polyester plasticizer was kneaded in the same manner as in Example 1, and then 0.3 m/min.
A sheet of m was made and designated as sheet (B). Next, a sheet (A) with a thickness of 0.1 m/m, which is the same as No.-1 of Example 1.
The above sheet (B) was pressed in the same manner as in Example 1 to obtain a sheet with a thickness of 0.35 m/m. In addition, a sheet, which was the same as No. 2 of Example 1, was also produced by pressing the sheet (A) with a thickness of 0.1 m/m and the sheet (B). When each of the above-mentioned sheets was simultaneously biaxially stretched under the same conditions as in Example 1, all of the sheets were partially stretched from the initial stage and were not stretched uniformly, but were broken in the middle, resulting in a predetermined uniform microporosity. I couldn't get a sheet. Comparative Example 4 A sheet (B) with a thickness of 0.2 m/m having the same composition as in Example 1 was prepared, and a sheet (A) with the same composition and thickness as No.-1 of Example 1 was prepared. 0.2m/
After creating a sheet of 0.35 m/m, it was pressed under the same conditions as in Example 1 to obtain a sheet of 0.35 m/m. Then,
When simultaneous biaxial stretching was carried out under the same conditions as in Example 1,
The sheet was partially stretched and could not be stretched uniformly and was broken in the middle, making it impossible to obtain the desired uniform microporous sheet.

[Brief explanation of drawings]

FIG. 1 shows an electron micrograph of the surface of the (B) layer side of the microporous sheet shown in the example of the present invention, and FIG. 2 similarly shows the surface of the (A) layer side.

Claims (1)

[Claims] 1. A thermoplastic resin sheet (A) containing 30 to 80% by weight of a filler with a particle size of 1 μ or less, and 30 to 80% of a filler having a particle size larger than the above and having a thickness of 3 times or more that of the sheet (A). 1. A method for producing a microporous sheet, which comprises laminating a thermoplastic resin sheet (B) containing % by weight and then stretching the sheet.