JPS6253813A - Manufacture of laminated porous film - Google Patents

Abstract

PURPOSE:To obtain a porous film not having a pinhole at all, by a method wherein a laminated porous film obtained by stretching the porous film composed of thermoplastic resin longitudinally at a specific draw ratio by a roll heated at the temperature of less than the fusion point of the resin after the porous film has been preheated by laminating two or more sheets of the porous film. CONSTITUTION:As for combination of the qualities of the materials of thermoplastic resin two or more sheets of which are stuck together, polyethylene and polypropylene are used, a roll stretching machine is used to stretch these porous films longitudinally and preheating of the porous film is performed by a preheating roll of the inside of the stretching machine. The temperature of the roll at the time of stretching is less than the fusion point of the thermoplastic resin constituting the porous film by 70 deg.C-1 deg.C. A longitudinal draw ratio is between the lowest draw ratio to be obtained by an expression of lowest draw ratio=1.15+[fusion point ( deg.C) of said resin - temperature ( deg.C) of heating roll]/100 and 15 times. A laminated porous film obtained through this longitudinal stretching is stretched laterally at the lateral draw ratio of 1.2-5 times [lateral draw ratio (time) = film width at outlet of lateral stretching machine/ film width at inlet of lateral stretching machine] in a lateral direction further.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a laminated porous membrane in which two or more porous membranes are bonded together. In particular, the present invention obtains a porous membrane with no pinholes by bonding two or more layers together to form a laminated porous membrane, and the resulting laminated porous 1
In general, medical diaphragms, pharmaceutical and food membranes, battery separators, etc.
Used in industrial applications.

(Prior art and its problems) There are various methods for producing the porous 1112, such as micro phase separation method and stretching method, but when creating micropores in any of the methods, the probability of occurrence differs depending on the manufacturing method, but the porous structure It is difficult to avoid the occurrence of pinholes (coarse holes), which are defects in

A pinhole is a coarse pore that deviates from the pore size distribution of a porous membrane toward the larger pore size. For example, average pore size 0.1g
m, refers to coarse pores of several μm in a porous membrane with a maximum effective pore diameter of 0.3 gm.

When a single pore pattern containing such pinholes is used as a single-port microfilter, fine particles and bacteria up to several micrometers in size pass through it, and it no longer functions as a microfilter.

In addition, when a polyolefin porous membrane is used as a diaphragm for an oxygenator, due to the water repellency of the polyolefin and the water pressure resistance of the micropores, only gas can pass through without blood.
If a pinhole exists, the water pressure resistance will be low, causing blood leakage at low pressure, and the device will no longer function as an artificial lung.

To prevent pinholes, it is necessary to inspect the membrane, find the presence of pinholes, and either remove this area or plug it with IJ. A common method for detecting pinholes is to use a continuous pinhole detector using laser, light, high voltage, or the like.

However, with existing pinhole detectors.

Only pinholes larger than a few gm of lO can be detected, and M7tm
Furthermore, it is difficult to detect pinholes smaller than 1 gm.

On the other hand, known methods for producing a membrane in which two sheets of porous 11!2 are bonded together include: (1) A method of applying an adhesive partially or entirely to the adhesive.

■Method of distributing hot melt agent between porous membranes and heat bonding with heated nip rolls.

■Method of heating and pressing porous membranes with heated nip rolls.

There are other methods. However, when porous membranes are bonded together using these methods, the pores are closed by the adhesive or hot melt agent because the bonding is performed using an adhesive or a hot melt agent in the method (2). In addition, with method (2), the membrane does not adhere even if it is pressed at a low temperature.If it is pressed at a high temperature, the membrane adheres, but the pores are collapsed due to the melting of the thermoplastic resin, and the function as a porous membrane is significantly deteriorated. descend. For this reason, this is not a preferable method for bonding the porous j0 together.

In particular, the membrane obtained by the method (■■) contains substances that are eluted from adhesives and hot melt agents, and is therefore unsuitable for use as oral membranes for medical and pharmaceutical food applications, battery separators, and the like.

Further, as a conventional technique, there is a method of stretching and bonding a plurality of non-porous polymer films. In this method, films with good flatness are overlapped by adhering to each other, and therefore, a laminated porous film in which two or more porous films are bonded together cannot be obtained.

As mentioned above, it is difficult to obtain a single porous or multi-layered porous film with no pinholes using known methods. (Objective of the Invention) The present invention has solved the above-mentioned problems. The purpose of this invention is to provide a porous membrane that has no pinholes at all.

(Structure of the Invention) The present invention involves stacking two or more porous films made of thermoplastic resin, preheating them, and then heating the rolls to a temperature of 70°C below the melting point of the resin to 1°C below the melting point, at a minimum stretching ratio of 1. 15+
['Melting point (''C) of the resin - heating roll temperature (''O)]
A method for producing a laminated porous membrane characterized by stretching in the longitudinal direction to a minimum stretching ratio (fold) obtained by the formula of /100 to 15 times or less, and a laminated porous membrane obtained by longitudinal stretching, further comprising: This is a method for producing a laminated porous membrane characterized by transverse stretching of 1.2 to 5 times.

(Embodiments and effects) The thermoplastic resin in the present invention includes polyethylene,
Polyolefin resins such as polypropylene and their copolymers, fluorine resins such as polyvinylidene fluoride and ethylene-tetrafluoroethylene copolymers, polyamide resins such as nylon 6 and nylon 66, and thermoplastic resins such as polyester resins. Either is fine.

Among these thermo-III plastic resins, polyolefin resins are preferred. Furthermore, polyethylene and polyethylene copolymers mainly composed of polyethylene are more preferred.

The combination of thermoplastic resin materials that bond two or more sheets together is
For example, similar combinations such as M1 combination of polyethylene and polypropy L/7 can be used. A combination of the same kind, such as a combination of polyethylene and a copolymer mainly composed of polyethylene, is more preferable, and it is most preferable that the materials are exactly the same, such as polyethylene and polyethylene.

For porous membranes that bond two or more sheets together, the thickness is 20gm-
1mm, pores; $10-85%, pore diameter 0°O1-37
zm is preferred; if the film thickness is less than 20 gm, the tensile strength is weak and stretching is difficult. Also, the thickness of 11 is 1mm.
If the thickness exceeds 100%, it is too thick and difficult to stretch. Stomata = 141
If the porosity is less than 0%, the function of the pores 11 will be low and undesirable. If the porosity exceeds 85%, the strength of the membrane will be weak and stretching will be difficult.

For stretching in the longitudinal direction, a commonly used roll stretching machine is sufficient. Preheating of the porous membranes to be bonded is preferably carried out using a preheating roll in a roll stretching machine, but preheating may also be performed using external infrared rays, a heater, or the like.

The roll temperature during stretching is 70° C. below the melting point of the thermoplastic resin constituting the porous membrane to 1° C. below the melting point. A particularly preferred temperature is from 50°C below the melting point of the resin to 1"C below the melting point.

If the roll temperature is lower than 100°C below the melting point, the membrane may break during stretching, the peel strength of the membrane may decrease, etc., making it impossible to obtain a stable laminated porous membrane; If the temperature is too high, the resin may melt, resulting in a decrease in membrane function and membrane rupture, which is undesirable.

Further, the preheating temperature of the porous membranes to be bonded together is not particularly limited, as long as it is equal to or lower than the heating roll temperature.

The longitudinal stretching ratio is preferably the minimum stretching ratio (times) to 1.15 + [melting point (°C) of the resin - heating roll temperature ('O)]/Zoo to 15 times.
If the longitudinal stretching ratio is less than the minimum stretching ratio, the films cannot be bonded together.

Furthermore, if the stretching ratio exceeds 15 times, the film will break during stretching. Within this range, the longitudinal stretching ratio is preferably (minimum stretching ratio + 0.5) times to 10 times, more preferably (minimum stretching ratio + 1.0) times to 8 times. The stretching ratio at this time is determined by the speed ratio of the low speed roll and the high speed roll in the roll stretching machine used. That is, stretching time + (times) = speed of high speed roll/speed of low speed roll.

Further, longitudinal stretching may be performed multiple times to bond two or more porous membranes together. In this case, the stretching ratio is determined by the product of the respective stretching ratios. Even if the laminated porous layer 1 obtained by stretching is further stretched in the lateral direction, the desired laminated porous layer 1 will not be formed.
You can get a sense of obscurity. For stretching in the lateral direction, a lateral stretching machine such as an ordinary tenter stretching machine 11 is sufficient.

The transverse stretching ratio at this time is 1.2 to 5 times, preferably 1
．． It is 5 to 3 times. The method for determining the transverse stretch ratio at this time is: transverse stretch ratio (times) = lll5 at the exit of the transverse stretcher! Width/film width at the inlet of the transverse stretching machine.

After longitudinal stretching, winding and further transverse stretching, or continuous transverse stretching after longitudinal stretching, either method is acceptable. It is 70°C below the melting point of the resin and 1°C below the melting point, preferably 50°C below the melting point of the resin and 1°C below the melting point.

The number of porous membranes to be laminated in the present invention is 2 or more if 2 or more.
There is no particular limitation on the number of sheets or three sheets.

The thickness of the laminated porous membrane prepared according to the present invention is as follows.

10 μm to 2 mm, preferably 20 JLm to 500 lm, more preferably 50 gm to 200 lm.
.

Moreover, it can be manufactured over a wide range of porosity of 30 to 90% and pore diameter of 0.02 to 5 gm. The peel strength of the laminated porous membrane according to the present invention is l g/cm width,
Practically speaking, it can be used as a single porous membrane.

According to the present invention, two or more porous membranes in which pinholes exist can be fused and integrated into a single layer without impairing their permeability, and in this case, two or more porous membranes with pinholes can be integrated into one layer without impairing their permeability. Since there is no probability that the holes in the porous membrane will form a ball and communicate with each other, a composite porous membrane having no pinholes at all can be obtained as a result. By eliminating pinholes, reliability as a porous membrane is significantly improved, making it suitable for medical diaphragms,
It can be used for various purposes such as oral membranes for pharmaceuticals and foods, and separators for internal use.

That is, the laminated porous membrane according to the present invention can be used as a microfilter for filtering particles and bacteria with higher precision than known microfilters. In addition, the laminated porous membrane is
Useful for medical purposes.

For example, when a laminated porous membrane made of polyolefin resin is used as a septum for human lungs, there are no pinholes, so it is possible to obtain a highly reliable artificial lung without blood leakage due to pinholes. .

In addition, 1. The iAM layer porous J pattern is useful as a separator for alkaline batteries, lithium batteries, and other various primary batteries and secondary batteries. In applications such as separators for alkaline batteries, microfilters, etc., which are used in water or aqueous solutions, oxyethylene and oxypropylene may be used, vaguely, to the extent that the effects of the present invention are not impaired. Water wettability can be imparted by attaching a commercially available surfactant such as a block copolymer or sodium alkylbenzene sulfonate before or after stretching.

The present invention will be explained below with reference to Examples, but the present invention is not limited thereto in any way.

(Examples 1 to 9) Two polyethylene porous membranes (melting point 130°C) obtained by the method described in JP-A-55-131028 were preheated with a wire and then longitudinally stretched with a roll stretching machine to form two sheets. Pasted together. Table 1 shows the porous membranes to be laminated, the lamination conditions, the 'A separation strength of the laminated porous membranes, and the occurrence of pinholes. T again! As an example of the functions of the laminated porous membrane obtained in Example 3, Table 2 shows a comparative example in which the laminated porous membrane obtained in Example 3 and the same porous membrane as in Example 3 were stretched under the same conditions.

(Example 10) Three sheets of porous polyethylene (melting point 125°C) obtained by the method described in JP-A-55-131028 were stacked and preheated to 80°C, and then stretched 4 times longitudinally using a roll stretching machine. A laminated porous membrane was obtained by bonding three layers together. The peel strength of the two interfaces of the obtained laminated porous membrane was 30 g/C.
m4114. After stacking two polyethylene porous membranes (melting point 130"C) obtained by the method described in JP-A-55-131028 and preheating to 80°C, they were stretched 3 times longitudinally using a roll stretching machine. A laminated porous membrane was obtained by bonding two sheets together. This was further stretched twice in the transverse direction using a tenter stretching machine. The peel strength of the obtained laminated porous membrane was 5 g/cm.
There were no pinholes in the width. The width of the film was approximately equal to that of a □ membrane obtained by stretching one sheet 3 times vertically and 2 times horizontally.

Table 2 (Effects of the Invention) According to the present invention, porous holes having no pinholes at all can be obtained by a relatively simple means, and the invention is extremely useful industrially.

Claims (5)

[Claims] (1) Two or more porous films made of thermoplastic resin are stacked together, preheated, and then heated to a temperature of 70°C below the melting point of the resin to 1°C below the melting point, at the minimum stretching ratio (times).
= 1.15 + [melting point of the resin (°C) - heating roll temperature (
A method for producing a laminated porous membrane, characterized by stretching in the longitudinal direction to a minimum stretching ratio (times) obtained by the formula of 15 times or less obtained by the formula: [° C.]]/100. (2) The method for producing a laminated porous membrane according to claim 1, wherein the thermoplastic resin is a polyolefin resin. (3) The method for producing a laminated porous membrane according to claim 2, wherein the polyolefin resin is polyethylene or a copolymer thereof. (4) The method for producing a laminated porous membrane according to claim 3, wherein the roll temperature is 60 to 129°C. (5) Two or more porous membranes made of thermoplastic resin are stacked together, preheated, and then heated to a temperature of 70°C below the melting point of the resin to 1°C below the melting point, at the minimum stretching ratio (times).
= 1.15 + [melting point of the resin (°C) - heating roll temperature (
°C)]/100, the laminated porous membrane is uniaxially stretched in the longitudinal direction to a minimum stretching ratio (times) of 15 times or less, and is further stretched in the transverse direction by 1.2 times to 5 times. A method for manufacturing a laminated porous membrane.