JP2002363850A - Porous sheet and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-elongation porous sheet having high tensile elongation at break, and further to provide a method for producing the porous sheet. SOLUTION: This sheet is obtained by compressing a nonwoven fiber assembly comprising a thermally bondable conjugate fiber consisting of a thermoplastic resin A having X deg.C melting point, and a thermoplastic resin B having Y deg.C melting point (X>Y), and has 0.01-100 μm average pore diameter and >=40% tensile elongation at break.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous sheet obtained by stretching a non-woven fiber aggregate made of a heat-adhesive conjugate fiber and a method for producing the same.

[0002]

2. Description of the Related Art Porous sheets having through holes are used in various applications such as separators for medical and industrial applications, separators for batteries and separators for electrolytic capacitors. In particular, a porous sheet made of a thermoplastic fiber is preferably used not only for a separator but also for a sanitary material such as a disposable diaper because a through hole can be easily obtained by stretching a nonwoven fabric. However, since the porous sheet is stretched at a high magnification because it is necessary to reduce the size of the pores, the porous sheet has drawbacks such that the tensile elongation at break is very small, and the porous sheet is easily broken when processed into a product. There is still room for improvement.

[0003]

SUMMARY OF THE INVENTION An object of the present invention involves a porous sheet having a large tensile elongation at break and a high elongation, and a complicated manufacturing process simply by changing processing conditions such as a draw ratio and a melting temperature. It is an object of the present invention to provide a method for producing a high elongation porous sheet which allows a wide selection of the average pore size of the porous sheet without requiring the same.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems. As a result, it was found that the intended purpose was achieved by employing the following configuration, and the present invention was completed based on this finding. (1) Thermoplastic resin A having a melting point of X ° C. and melting point of Y ° C. (X> Y)
A sheet obtained by consolidating a nonwoven fiber aggregate made of a heat-adhesive conjugate fiber composed of a thermoplastic resin B, and the sheet has an average pore size of 0.01 to 100 μm,
A porous sheet having a tensile elongation at break of 40% or more. (2) The porous sheet according to the above (1), wherein the thermoplastic resin A is polypropylene and the thermoplastic resin B is polyethylene. (3) The above (1), wherein the thermoplastic resin A is polyethylene terephthalate and the thermoplastic resin B is polyethylene.
Item 8. The porous sheet according to item 1. (4) Thermoplastic resin A having a melting point of X ° C. and a melting point of Y ° C. (X> Y)
A nonwoven fiber aggregate composed of a thermo-adhesive conjugate fiber composed of a thermoplastic resin B is heated at a melting temperature of Y ° C. or more and less than X ° C., subjected to a pressure treatment, and compacted in a thickness direction to form a sheet. The method for producing a porous sheet according to any one of the above (1) to (3), wherein the sheet is stretched at least in a uniaxial direction at a stretching temperature of Y ° C. or lower.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The porous sheet of the present invention is a sheet obtained by compacting a nonwoven fiber aggregate made of a heat-adhesive conjugate fiber. Further, the porous sheet of the present invention has an average pore size of 0.1.
01-100 μm, and the tensile elongation at break is 40% or more. The porous sheet of the present invention has a thickness of 0.01 to 100 μm.
Can be manufactured by selecting an average pore size of the above, so that it is possible to flexibly cope with applications in various fields. Further, by having a tensile breaking elongation of 40% or more, even when deformation such as kinking, twisting, and elongation occurs during processing into a product, breakage is unlikely to occur. The tensile elongation at break is preferably in the range of 40 to 150%, and more preferably in the range of 60 to 100% from the viewpoint of ease of processing.

The heat-adhesive conjugate fiber used in the present invention is:
This is a composite fiber composed of a thermoplastic resin A having a melting point of X ° C., which is at least two kinds of thermoplastic resins having a melting point difference, and a thermoplastic resin B having a melting point of Y ° C. (X> Y). The difference between the melting points (XY) of the thermoplastic resin is preferably 10 ° C. or more, more preferably 15 ° C. or more. In order for the composite fiber to have good thermal adhesiveness, the thermoplastic resin A is used as a fiber-forming component, the thermoplastic resin B is used as an adhesive component, and the thermoplastic resin B extends in the length direction of the fiber surface. It is preferable to use a composite fiber having a structure that is continuously exposed and simultaneously coated with the thermoplastic resin A. Examples of the composite form of the heat-adhesive composite fiber include concentric sheath-core type, eccentric sheath-core type, side-by-side type, sea-island type, and hollow type. Also,
The shape may be not only a circular cross section but also an irregular cross section. In view of the thermal adhesiveness, a composite fiber having a concentric sheath-core, eccentric sheath-core, and side-by-side composite form is preferable. Above all, a heat-adhesive conjugate fiber having a concentric sheath-core structure is more preferable since it has stable heat-adhesive properties. The thermoadhesive conjugate fiber used in the present invention can be produced by using a spinneret capable of producing the composite form, a conjugate spinning device, a drawing device, and the like, as necessary.

The composite fiber used in the present invention has a melting point of X ° C.
In the case of a concentric sheath-core composite fiber having the thermoplastic resin A as a core component and the thermoplastic resin B having a melting point of Y ° C. (X> Y) as a sheath component, the weight ratio of the thermoplastic resin A: the thermoplastic resin The weight ratio of B is preferably in the range of 25:85 to 85:25, and more preferably in the range of 30:70 to 70:30. If the weight ratio of the thermoplastic resin B is significantly lower than 25, the amount of the sheath component may be insufficient and the core component may not cover the entire surface along the fiber length direction. Is completely difficult to obtain by thermocompression bonding. On the other hand, when the weight ratio of the thermoplastic resin B is much higher than 85, the sheet tends to be stiff because the amount of the core component for maintaining the strength of the obtained sheet is insufficient.

[0008] The combination of the thermoplastic resin A and the thermoplastic resin B used for the heat-adhesive conjugate fiber is Y ° C or higher, X
A combination that can be heat-treated at a temperature of less than about 0 ° C. to form a nonwoven fiber aggregate made of a thermoadhesive conjugate fiber composed of thermoplastic resin A and thermoplastic resin B by thermocompression bonding or the like to form a sheet. It can be used without any problems. For example, when the combination is represented by thermoplastic resin B / thermoplastic resin A, high-density polyethylene / propylene copolymer, linear low-density polyethylene / propylene copolymer, low-density polyethylene / propylene copolymer, propylene Other α
-Binary or terpolymer / propylene copolymer with olefin, linear low-density polyethylene / high-density polyethylene, low-density polyethylene / high-density polyethylene, propylene with other α-olefins Terpolymer or terpolymer / polyethylene terephthalate, propylene homopolymer / polyethylene terephthalate, various polyethylene / polyethylene terephthalates, low melting thermoplastic polyester / polyethylene terephthalate, various polyethylene / nylon 6, various polypropylene / nylon 6, nylon 6 / nylon 66, nylon 6 / thermoplastic polyester and the like.

[0009] Among these, a combination comprising polypropylene and polyethylene, which are polyolefins,
It is preferable from the viewpoint of heat adhesion, chemical resistance, and lightness. Polypropylene is particularly preferable as a separation membrane or a separator because it has high heat resistance among polyolefins and can withstand even a high temperature environment such as boiling. As the combination, low-density polyethylene / propylene homopolymer, linear low-density polyethylene / propylene homopolymer, high-density polyethylene / propylene homopolymer,
Examples thereof include an ethylene-propylene-butene-1 terpolymer / propylene homopolymer and an ethylene-propylene binary copolymer / propylene homopolymer. Further, a combination of a polyolefin and a polyester, particularly a combination of a polyethylene and a polyester, is preferred from the viewpoint of thermal adhesion. Examples of such combinations include low density polyethylene / polyethylene terephthalate, linear low density polyethylene / polyethylene terephthalate, and high density polyethylene / polyethylene terephthalate.

Examples of the polypropylene used in the present invention include a propylene homopolymer, a binary copolymer of propylene and an α-olefin other than propylene, or a terpolymer. Further, these copolymers may be a mixture of two or more kinds. Further, these copolymers may be any of a random copolymer and a block copolymer. In addition, as an α-olefin other than propylene, ethylene, 1-butene, 1-pentene, 1-
Examples thereof include α-olefins having 2 to 12 carbon atoms such as hexene and 1-octene, and these may be used in combination. When a propylene homopolymer is used as the polypropylene, the peak of the melting point is usually 162.
It is around ° C. However, when a binary random copolymer of propylene and ethylene or a ternary random copolymer of propylene and ethylene or butene is used, the peak of the melting point can be adjusted by the production conditions. Accordingly, polypropylene having a melting point range of 120 to 162 ° C can be arbitrarily selected and used. Further, polypropylene having a melt flow rate (MFR: a value measured in accordance with the condition 14 in JIS K7210 Table 1) of 2 to 150 g / 10 minutes is suitable because it is suitable for fiberization.

Examples of the polyethylene used in the present invention include an ethylene homopolymer and a binary copolymer of ethylene and a monomer other than ethylene.
Further, these copolymers may be a mixture of two or more kinds. Further, these copolymers may be any of a random copolymer and a block copolymer. As monomers other than ethylene, propylene, 1-butene, 1-
C3-C3 such as pentene, 1-hexene and 1-octene
12, α-olefins, vinyl esters such as vinyl acetate, acrylates such as ethyl acrylate, methacrylates such as methyl methacrylate, carbon monoxide and the like. You may. A specific copolymer of ethylene and an α-olefin other than ethylene has a density of 0.910 to 0.1.
925 g / cm ³ low density polyethylene, density 0.9
26~0.940g / cm ³ of linear low density polyethylene, the density can be mentioned high density polyethylene 0.941~0.980g / cm ^3. In particular, the melt flow rate (MI: JIS K 7210, condition 4 in Table 1)
Polyethylene having a value of 2 to 100 g / 10 min.

Further, the polypropylene and polyethylene used in the present invention may be modified products. For example,
When using polypropylene, an organic silane compound or an unsaturated carboxylic acid or a derivative thereof can be used as a modifier. Specifically, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, tetrahydrophthalic acid and norbornene dicarboxylic acid, maleic anhydride, itaconic anhydride, tetrahydrophthalic anhydride and norbornene dicarboxylic anhydride, etc. An example is an unsaturated carboxylic anhydride. Among them, maleic acid and maleic anhydride, which are most excellent in practical performance, are preferable. In the case where a modified product is used in the present invention, the modification rate of the used modified product, for example, the grafting ratio when modifying maleic anhydride on polypropylene is usually desirably 1 to 10%. .

As the polyethylene terephthalate used in the present invention, among the ordinary polyethylene terephthalates which are commercially available or industrially used, polyethylene terephthalate which is commercially available especially for fibers can be used.
Specifically, polyethylene terephthalate having an intrinsic viscosity in the range of 0.50 to 1.20 can be preferably used.

The thermoplastic resin A or the thermoplastic resin B may contain generally used antioxidants, hindered amine weathering agents, ultraviolet absorbers, surfactants such as antifogging agents and antistatic agents, antiblocking agents, A slip agent, an antibacterial agent, an antifungal agent, a pigment, and the like can be blended as needed within a range not to impair the effects of the present invention. Further, in order to lower the softening temperature and improve the flexibility of the thermoplastic resin, ethylene-diene elastic copolymer, ethylene-propylene elastic copolymer, styrene polymerized with a single-site catalyst or a known multi-site catalyst. -An elastic copolymer such as a butadiene elastic copolymer may be added to the thermoplastic resin A or the thermoplastic resin B.

In the present invention, a web or a nonwoven fabric can be used as the nonwoven fiber aggregate. The web used in the present invention is obtained by a production method according to the purpose, application, fiber length and fineness of the heat-adhesive conjugate fiber. When the fiber length of the heat-adhesive conjugate fiber is 20 to 125 mm, a web can be manufactured by a carding machine or a random webber method.
At this time, by setting the fiber length to 25 to 75 mm, the card passing property is improved, and a web with a better texture can be obtained. Further, the fiber length of the composite fiber is 3 to 20.
In the case of mm, a web can be manufactured by an air lay method or a papermaking method. The fineness suitable for these production methods is
1 to 35 dtex. When the heat-adhesive conjugate fiber is a long fiber, a web can be directly produced by spinning by a method such as a melt blow method, a spun bond method, and a flash spun method. The fineness suitable for these production methods is
0.8 to 11.0 dtex, more preferably,
It is 1.7 to 5.5 dtex. The nonwoven fabric used in the present invention can be manufactured by subjecting the web to a process such as a thermocompression bonding method, a hot air heating method, a high pressure water column flow entanglement method, and a needle punching method. The non-woven fiber aggregate may be not only a heat-adhesive conjugate fiber but also other fibers as long as the effects of the present invention are not impaired. Further, as the nonwoven fiber aggregate, it is more preferable to use a nonwoven fabric than a web from the viewpoints of transportability, easy processability, and uniformity of basis weight.

Hereinafter, the method for producing the porous sheet of the present invention will be described in detail.

A thermoplastic resin A having a melting point of X ° C. and a melting point of Y ° C. (X
A non-woven fiber aggregate made of a thermo-adhesive conjugate fiber composed of the thermoplastic resin B of> Y) is produced. In addition, you may use a commercially available nonwoven fabric. The sheet is obtained by thermocompression bonding of the nonwoven fabric fiber aggregate. Specifically, the nonwoven fabric fiber assembly is heated by hot air at a melting temperature of Y ° C. or higher and lower than X ° C. to melt and soften the thermoplastic resin B, and then pressurized simultaneously with cooling between a pair of rolls in the thickness direction. An example is a method in which the sheet is compacted into a sheet. Further, as another manufacturing method, a method in which the nonwoven fiber aggregate is heated by a hot plate to melt and soften the thermoplastic resin B, and then pressed and cooled by a pair of cooling plates can be exemplified.
The temperature at which the nonwoven fiber aggregate is melt-softened is equal to or higher than the melting point Y ° C. of the thermoplastic resin B constituting the heat-adhesive conjugate fiber.
It is preferable to carry out at a temperature lower than the melting point temperature X ° C. of the thermoplastic resin A. When thermocompression bonding is performed at a temperature equal to or higher than the melting point of the thermoplastic resin A constituting the thermoadhesive conjugate fiber, the conjugate fiber in the sheet may lose its properties without retaining its fiber shape. Further, when thermocompression bonding is performed at a melting point of less than Y ° C. of the thermoplastic resin B constituting the heat-adhesive conjugate fiber, there is a possibility that a hole is formed in the sheet.

Next, after the obtained sheet is preheated at a temperature of Y ° C. or lower, or at a stretching temperature of Y ° C. or lower, the sheet is stretched uniaxially or biaxially to obtain a porous sheet. The stretching method for making this porous can be performed by a general stretching method employed when stretching a sheet or a film. In stretching the sheet, not only uniaxial stretching but also simultaneous and sequential secondary stretching can be applied. When the above-mentioned uniaxial stretching is applied, the above-mentioned sheet is made of thermoplastic resin B
At a melting point of Y ° C. or lower and a speed of 0.01 to 100 m / min.
It may be stretched by a factor of 5 to 5. When the simultaneous biaxial stretching is applied, the sheet is moved in one direction at a speed of 0.01 to 100 m / min at a melting point Y ° C. or lower of the thermoplastic resin B.
Times to 5 times, the speed is 0.01 to 1 in the direction of 90 ° in this direction.
What is necessary is just to stretch simultaneously 1 to 5 times at 00 m / min. When the above-mentioned sequential biaxial stretching is applied, the above-mentioned sheet is melted at a melting point of the thermoplastic resin B of not higher than Y ° C. and at a speed of 0.0 ° C.
The film is stretched 1 to 5 times at a rate of 1 to 100 m / min, and is further stretched in a direction at 90 ° to the stretching direction at a melting point of Y ° C. or less of the thermoplastic resin B at a speed of 0.01 to 100 m / min. What is necessary is just to stretch 5 times. Note that the stretching temperature is preferably equal to or lower than the melting point of the thermoplastic resin B, Y ° C. If the stretching is performed at a temperature exceeding the melting point Y ° C. of the thermoplastic resin B, the surface of the stretched product tends to be fuzzy, resulting in poor smoothness. Further, the stretching ratio is preferably 1 to 5 times, and if it greatly exceeds 5 times, the upper surface of the stretched product tends to be fluffy, and similarly, the smoothness tends to be poor.

In the porous sheet of the present invention, the average pore diameter in the range of 0.01 to 100 μm can be selected from a wide range by simply changing the sheet processing conditions and the stretching processing conditions without complicated manufacturing steps. Can be. For example, in order to obtain a porous sheet having a small average pore size, the processing temperature, which is one of the processing conditions for the sheet, is set to around the melting point X ° C. of the thermoplastic resin A, and the other processing conditions include the stretching temperature and the stretching ratio. You may want to lower the conditions. Conversely, in order to obtain a porous sheet having a large average pore size, the processing temperature, which is one of the processing conditions for the sheet, is set at around the melting point Y ° C. of the thermoplastic resin B, and the stretching temperature is set at the melting point Y ° C. of the thermoplastic resin B. It is advisable to increase the stretching magnification condition to the vicinity.

The surface of the porous sheet of the present invention may be coated with a surface treating agent such as a surfactant, if necessary.
In addition, the porous sheet can be used not only as a single layer but also as a laminate of two or more layers, another nonwoven fabric, and a layer laminated with a semipermeable membrane. Further, the porous sheet may be used not only as a flat sheet but also wound around a cylinder and used as a tape after slitting. It can be used not only for separators such as battery separators, but also for applications such as cylindrical filters and wind filters.

[0021]

EXAMPLES The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In addition, the measuring method and evaluation method in an Example and a comparative example were implemented by the following method.

(1) Porosity: Calculated by the following equation. Porosity = void volume / total sheet volume × 100 = (water-containing weight−absolute dry weight) × specific gravity of water / total sheet volume × 100 (2) Average pore diameter and maximum pore diameter (μm): ASTM F
316-86 and ASTM E128, P
erm-porometer (PORUS MATER
IALs INC. Made by bubble point method)
The average flow pore diameter obtained from the measurement was taken as the average pore diameter value, and the maximum pore diameter was taken as the maximum pore diameter value. (3) Surface properties: The surface state of the stretched sheet was visually determined. (4) Melting point (° C.): DSC measuring device (Seiko Electronics S
SC-5000) using a temperature range of 40 ° C to 300 ° C,
The temperature was measured at a heating rate of 20 ° C./min, and the top of the endothermic peak was determined and defined as the melting point. (5) Tensile breaking strength (MPa) and tensile breaking elongation (%): Tensile breaking strength and tensile breaking elongation were measured in accordance with JIS K7127 "Method for tensile testing plastic films and sheets", No. 1 test piece.

Example 1 As a nonwoven fiber aggregate made of a porous sheet material, the melting point was 1
The basis weight is composed of a composite component fiber having a core component of 62 ° C. polypropylene and a linear low-density polyethylene having a melting point of 121 ° C. as a sheath component. The weight ratio of the sheath core is 50% / 50%, and the single-fiber fineness is 2.4 dtex. An 80 g / m ² composite spunbonded nonwoven fabric is heated at a melting temperature of 140 ° C. to be melt-softened, and then a pressure of 5 m / min is applied between a pair of cooling rolls set at a surface temperature of 50 ° C. To make a 0.1 mm sheet. Further, after the obtained sheet was preheated at 100 ° C. for 120 seconds, using a pantograph-type biaxial stretching machine, the stretching temperature was 100 ° C., and the speed was 3 m / m.
The sheet was uniaxially stretched by a factor of 2.5 to obtain a sheet. Using the obtained porous sheet, the average pore diameter, the maximum pore diameter, the tensile elongation at break, and the like were measured according to a predetermined test method, and the surface state was visually observed. Table 1 shows the results of these evaluations.

Example 2 A sheet was produced under the same processing conditions as in Example 1 except that the sheet was heated at a melting temperature of 160 ° C. and uniaxially stretched 1.2 times. Table 1 also shows the evaluation results.

Example 3 A sheet was produced under the same processing conditions as in Example 1 except that the film was heated at a melting temperature of 160 ° C. and uniaxially stretched 2.5 times. Table 1 also shows the evaluation results.

Example 4 A sheet was manufactured under the same processing conditions as in Example 1 except that the film was heated at a melting temperature of 160 ° C. and uniaxially stretched 3.5 times. Table 1 also shows the evaluation results.

Example 5 As a nonwoven fiber aggregate made of a porous sheet material, the melting point was 2
A core component is polyethylene terephthalate at 60 ° C., and a linear low-density polyethylene having a melting point of 121 ° C. is a sheath component. The weight ratio of the sheath core is 50% / 50%, and the single-fiber fineness is 2.6 dte.
A sheet was manufactured according to Example 1, except that a composite spunbond nonwoven fabric having a basis weight of 80 g / m ^{2 and} composed of composite long fibers x was used and heated at a melting temperature of 160 ° C.
Table 1 shows the results of these evaluations.

Comparative Example 1 A sheet was produced under the same processing conditions as in Example 1 except that heating was performed at a melting temperature of 100 ° C. (the melting point of the linear low-density polyethylene used for the sheath component was 121 ° C.). Table 1 also shows the evaluation results.

Comparative Example 2 A sheet was produced under the same processing conditions as in Example 1 except that heating was performed at a melting temperature of 180 ° C. (the melting point of the polypropylene used as the core component was 162 ° C.). Table 1 also shows the evaluation results.

Comparative Example 3 As a nonwoven fiber aggregate of the material of the porous sheet, the melting point was 1
Using a regular spunbond nonwoven fabric with a basis weight of 80 g / m ² composed of 100% polypropylene at 62 ° C,
A sheet was produced under the same processing conditions as in Example 1 except that the sheet was heated at a melting temperature of 162 ° C. Table 1 also shows the evaluation results.

[0031]

[Table 1]

[0032]

The porous sheet of the present invention has a large tensile elongation at break and a high elongation as compared with the conventional product, so that it is difficult to be torn by the stress during the secondary processing. It can be used preferably. Further, by using the method for producing a porous sheet of the present invention, the average pore diameter can be selected from a wide range of 0.01 to 100 μm without complicated production steps simply by changing the processing conditions such as the draw ratio and the melting temperature. It is possible to provide a porous sheet that can easily cope with various fields.

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Claims (4)

[Claims] 1. A thermoplastic resin A having a melting point of X ° C. and a melting point of Y ° C.
A sheet obtained by consolidating a nonwoven fiber aggregate made of a heat-adhesive conjugate fiber composed of a thermoplastic resin B (X> Y), wherein the sheet has an average pore size of 0.01 to 100 μm.
m, and a porous sheet having a tensile elongation at break of 40% or more. 2. The porous sheet according to claim 1, wherein the thermoplastic resin A is polypropylene and the thermoplastic resin B is polyethylene. 3. The porous sheet according to claim 1, wherein the thermoplastic resin A is polyethylene terephthalate and the thermoplastic resin B is polyethylene. 4. A thermoplastic resin A having a melting point of X ° C. and a melting point of Y ° C.
(X> Y) Non-woven fiber aggregate composed of a thermo-adhesive conjugate fiber composed of thermoplastic resin B is heated at a melting temperature of Y ° C. or more and less than X ° C., subjected to a pressure treatment, The sheet is compacted, and the sheet is stretched at least in a uniaxial direction at a stretching temperature of Y ° C. or less.
4. The method for producing a porous sheet according to any one of 3.