KR20180087268A - Method for producing a composite membrane - Google Patents

Abstract

A method of producing a composite film comprising a porous substrate and a porous layer formed by coating a coating liquid containing a resin and a solvent on one or both surfaces of the porous substrate, the method comprising: (1) A process for applying a liquid on one side or both sides of a porous substrate, comprising the steps of: applying a liquid exuding from the inside to the outside of the rolled rotating member onto a porous substrate using a roll rotating member having an outer circumferential layer having a porous structure; (2) a step of coating a coating solution on one side or both sides of a porous substrate coated with a liquid to form a coating liquid layer; and (3) a step of coagulating the resin contained in the coating liquid layer, (4) a step of removing a solvent and a liquid from the composite membrane, and (4) a step of removing the solvent and the liquid from the composite membrane.

Description

Method for producing a composite membrane

The present invention relates to a method for producing a composite membrane.

Conventionally, a composite membrane having a porous layer on a porous substrate, such as a battery separator, a gas filter, and a liquid filter, is known. As a production method of this composite film, there is known a production method in which a coating liquid containing a resin and a solvent is coated on a porous substrate to form a coating liquid layer, and then the resin contained in the coating liquid layer is solidified to form a porous layer.

In the above-described production method, a part of the coating liquid coated on the porous substrate may seep into the porous substrate, or the solvent of the coating liquid may permeate into the porous substrate. Due to this phenomenon, a part of the resin in the coating liquid layer is solidified at an unexpected time, and the uniformity in the plane direction of the coating liquid layer is lowered. As a result, various physical properties of the composite film become uneven in the surface direction have.

As a means for solving the above problems, there is known a manufacturing method of coating a coating liquid on a porous substrate impregnated with a liquid, for example, as disclosed in Patent Documents 1 and 2. With this production method, since the solvent of the coating solution and the coating solution is hardly permeated into the inside of the porous substrate, the porous layer is likely to be uniformly formed in the surface direction.

Japanese Patent Application Laid-Open No. 2001-23602 Japanese Specification No. 2013-533370

From the viewpoint of production efficiency of the composite membrane, it is preferable to transport a porous substrate having a long porous substrate and a wide width at a high speed to coat the coating liquid. However, as the width of the porous substrate becomes wider and the conveying speed of the porous substrate becomes higher, the porous layer formed on the porous substrate tends to become uneven in the surface direction. There is a demand for a manufacturing method capable of producing a composite film excellent in uniformity in the plane direction even when a wide porous substrate is transported at a high speed.

An embodiment of the present disclosure was made under the above circumstances.

It is an object of the present invention to provide a method for producing a composite membrane capable of producing a composite membrane excellent in uniformity in the plane direction even when a wide porous substrate is transported at a high speed.

Specific means for solving the above-mentioned problems include the following aspects.

[1] A method for producing a composite film comprising a porous substrate and a porous layer formed on one or both surfaces of the porous substrate by coating a coating solution containing a resin and a solvent for dissolving or dispersing the resin,

(1) a step of applying a liquid compatible with the solvent to one or both surfaces of the porous substrate, using a roll rotating member having an outer peripheral layer having a porous structure, Applying the liquid leaking to the outer peripheral surface to the porous substrate,

(2) a step of coating the coating liquid on one side or both sides of the porous substrate coated with the liquid to form a coating liquid layer,

(3) a step of coagulating the resin contained in the coating liquid layer to obtain a composite film having a porous layer containing the resin on one side or both sides of the porous substrate,

(4) a step of removing the solvent and the liquid from the composite membrane

≪ / RTI >

[2] The method for producing a composite membrane according to [1], wherein the outer peripheral layer of the rolled rotating member is a porous ceramic layer.

[3] The method for producing a composite membrane according to [1] or [2], wherein the outer circumferential layer of the rolled rotating member is a porous layer having an average pore size of 2 μm or more and 20 μm or less.

[4] The method according to any one of [1] to [4], wherein the step (2) is carried out by using a first coating means for coating one surface and a second coating means for coating the other surface , And the step of sequentially coating the coating liquid on both surfaces of the porous substrate one by one. [Claim 3] The method for producing a composite film according to any one of [1] to [3]

[5] The method according to any one of [1] to [4], wherein the step (2) is a step of coating the coating solution using a coating means in which the pressing means for pressing the porous substrate to the coating means is not disposed. Lt; RTI ID = 0.0 > 1, < / RTI >

[6] The process for producing a composite film according to any one of [1] to [5], wherein the transport speed of the porous substrate is 20 m / min or more in the step (2).

[7] The method for producing a composite membrane according to any one of [1] to [6], wherein the step (1) is a step of applying the liquid to the porous substrate in an amount of 1 g / m 2 or more and 30 g / m 2 or less.

[8] The method for producing a composite membrane according to any one of [1] to [7], wherein the porous substrate is a polyolefin microporous membrane.

According to the embodiments of the present disclosure, there is provided a composite film manufacturing method capable of producing a composite film excellent in uniformity in the plane direction even when a wide porous substrate is transported at a high speed.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a conceptual diagram showing an embodiment of the manufacturing method of the present disclosure; Fig.
2 is a conceptual view showing an embodiment of the manufacturing method of the present disclosure;
3 is a schematic view showing an embodiment of a rolled rotating member;
4A is a schematic view of the shaft 14;
4b is a schematic view of the shaft 14. Fig.
5A is a schematic view showing one embodiment of a coating process;
5B is a schematic view showing one embodiment of the coating process.

Hereinafter, an embodiment will be described. These explanations and examples are for illustrating the embodiments and do not limit the scope of the embodiments.

In the present specification, the numerical range indicated by using " ~ " indicates a range including numerical values before and after " ~ " as the minimum value and the maximum value, respectively.

In this specification, the term " process " is included in the term when the intended purpose of the process is achieved, even if it can not be clearly distinguished from other processes as well as independent processes.

In the present specification, the term " machine direction " means a longitudinal direction in a porous substrate and a composite film produced in a long phase, and " width direction " means a direction perpendicular to " machine direction ". The " machine direction " may be referred to as " MD direction ", and the " width direction "

In the present disclosure, " commercial " with respect to a liquid means that they can be mutually combined to form a homogeneous solution.

≪ Method for producing composite membrane &

The production method of the present disclosure is a method for producing a composite film comprising a porous substrate and a porous layer provided on one side or both sides of the porous substrate. The manufacturing method of the present disclosure includes coating a coating liquid containing a resin and a solvent that dissolves or disperses the resin to form a porous layer. More specifically, the following steps (1) to (4) are carried out And a porous layer is provided on one side or both sides of the porous substrate.

Step (1): As a step of applying a liquid (also referred to as a " pretreatment liquid ") compatible with a solvent of a coating liquid to one surface or both surfaces of the porous substrate, a roll rotating member having an outer peripheral layer having a porous structure (Also referred to as " pre-treatment step ") of applying a pretreatment liquid exuding from the inside of the roll rotating member to the outer circumferential surface.

Step (2): A step of coating a coating liquid on one side or both sides of a porous substrate coated with a pretreatment liquid to form a coating liquid layer (also referred to as " coating step ").

Step (3): A step of coagulating the resin contained in the coating liquid layer to obtain a composite film having a porous layer containing the resin on one side or both sides of the porous substrate (also referred to as " solidification step ").

Step (4): Step of removing the solvent of the coating liquid and the pretreatment liquid from the composite film (also referred to as " solvent removal step ").

The step (3) may be a wet process or a dry process. The details of the wet process and the dry process will be described later.

As the step (4), for example, the step of washing the composite membrane and / or the step of drying the composite membrane may be mentioned.

The manufacturing method of the present disclosure may further include a step of preparing a coating solution for preparing the coating solution used in the step (2).

1 is a conceptual diagram showing an embodiment of a manufacturing method of the present disclosure. In Fig. 1, a roll of a porous base material (a roll obtained by winding a long porous base material) to be provided for producing a composite membrane is placed on the left side of the figure, and a roll on which a composite membrane is wound is placed on the right side in the figure . The embodiment shown in Fig. 1 has a coating solution preparing step, a pre-treating step, a coating step, a solidifying step, a washing step, and a drying step. In this embodiment, the coagulation step is performed in a wet manner, and the water washing step corresponds to the solvent removing step (the drying step may also be equivalent to the solvent removing step). In this embodiment, a preprocessing step, a coating step, a coagulating step, a water washing step, and a drying step are successively performed in sequence, and a coating solution preparing step is performed in accordance with the execution time of the coating step. Details of each step will be described later.

2 is a conceptual diagram showing another embodiment of the manufacturing method of the present disclosure. In Fig. 2, on the left side in the drawing, a roll of a porous substrate (a roll obtained by winding a long porous substrate) provided for the production of a composite membrane is placed, and a roll on which a composite membrane is wound is placed on the right side in the figure. The embodiment shown in Fig. 2 has a coating solution preparing step, a pre-treating step, a coating step, and a solidifying step. In this embodiment, the coagulation step is performed in a dry manner, and the coagulation step is also a solvent removal step. In the present embodiment, a preprocessing step, a coating step, and a solidifying step (which is also a solvent removing step) are successively carried out successively, and a coating solution preparing step is carried out in accordance with the execution time of the coating step. Details of each step will be described later.

In the manufacturing method of the present disclosure, the pretreatment step is a step of applying a liquid (pretreatment liquid) compatible with the solvent of the coating liquid coated on the porous substrate to one surface or both surfaces of the porous substrate before the coating process. The pretreatment liquid is a liquid compatible with the solvent of the coating liquid, so that the coating liquid does not interfere with affinity to the surface of the porous substrate, and therefore, the adhesion between the porous substrate and the porous layer is not hindered. Since the coating liquid is applied to the porous substrate containing liquid by performing the pretreatment step, permeation of the coating liquid and the solvent of the coating liquid into the porous substrate is suppressed, and a part of the resin in the coating liquid layer is solidified It is inhibited from solidifying beforehand. As a result, the porous layer is easily formed uniformly in the surface direction, and as a result, a composite film having excellent uniformity in the plane direction can be produced.

In the manufacturing method of the present disclosure, the pretreatment step is a step of applying a pretreatment liquid that seeps from the inside of the roll rotating member to the outer circumferential surface of the roll rotating member with an outer circumferential layer having a porous structure. By using the roll rotating member, even when the wide porous substrate is transported at a high speed, the pre-treatment liquid can be applied to the porous substrate with high uniformity. As a result, Area and can be manufactured at high speed. Therefore, the production method of the present disclosure is excellent in the productivity of the composite membrane. Further, the rolled rotating member is advantageous from the viewpoint of scattering of the pretreatment liquid at the time of applying the pretreatment liquid.

The reason why the composite membrane has excellent uniformity in the plane direction is that the film thickness of the composite membrane and / or the force (peel strength) when the porous layer is peeled off from the porous substrate, Which means that there is little unevenness.

Hereinafter, each step of the manufacturing method of the present disclosure will be described in detail.

[Coating solution preparation step]

The manufacturing method of the present disclosure may have a coating solution preparing process for preparing a coating solution to be provided in a coating process. The manufacturing method of the present disclosure does not require a coating solution preparing step, and the coating solution already prepared and stored in the coating step may be provided.

The coating liquid preparing step is a step of preparing a coating liquid containing a resin and its solvent. The coating solution is prepared by dissolving or dispersing the resin in a solvent. The coating liquid may contain a component other than a resin and a solvent, for example, a filler. The resin or filler used for preparing the coating liquid, that is, the resin or filler contained in the porous layer will be described in detail in the section of [porous layer] to be described later.

Examples of the solvent (also referred to as " good solvent ") for dissolving the resin used for preparing the coating liquid include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, . From the viewpoint of forming a porous layer having a good porous structure, it is preferable to mix a phase separating agent that induces phase separation in a good solvent. Examples of the phase-separating agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. The phase separation agent is preferably mixed with a good solvent in such a ratio that the viscosity of the coating solution suitable for the coating can be ensured.

The solvent used for preparing the coating liquid preferably contains 50 mass% or more (more preferably 60 mass% or more) of the good solvent and 10 mass% to 50 mass% ( More preferably 10% by mass to 40% by mass). From the viewpoint of forming a good porous structure, it is preferable that the coating liquid contains the resin at a concentration of 3% by mass to 10% by mass, and the filler is contained at a concentration of 10% by mass to 90% by mass.

For the preparation of the coating liquid, a homogenizer, a glass bead mill, a ceramic bead mill or the like can be used in order to improve the solubility and dispersibility of the resin and the filler in a solvent. Further, in order to increase the dispersion efficiency, the resin or the filler may be pre-dispersed in a dispersant before being mixed with a solvent.

The viscosity of the coating liquid is preferably from 0.1 Pa · s to 5.0 Pa · s from the viewpoint of coating ability on the porous substrate. The viscosity of the coating liquid can be controlled by the composition ratio of the solvent, the resin and the filler.

[Pretreatment process]

The pretreatment step is a step of applying a liquid (pretreatment liquid) compatible with the solvent of the coating liquid to one surface or both surfaces of the porous substrate. The pretreatment step is a step of applying a pretreatment liquid that seeps from the inside of the roll rotating member to the outer circumferential surface of the roll substrate using a roll rotating member having an outer circumferential layer having a porous structure.

- Pretreatment liquid -

The pretreatment liquid is a liquid which is applied to the porous substrate before the coating process for the purpose of inhibiting the penetration of the coating liquid and the solvent of the coating liquid into the porous substrate.

Examples of the pretreatment solution include the following (i) to (iv).

(i) a liquid of the same kind as the positive solvent contained in the coating liquid.

(ii) a liquid of the same kind as the phase separator contained in the coating liquid.

(iii) a good solvent contained in the coating liquid and a good solvent of the other kind, and compatible with both solvents contained in the coating liquid.

(iv) at least two selected from (i) to (iii).

Examples of the above (i) and (iii) include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide and dimethylformamide. Examples of (ii) include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol and the like.

As the pretreatment liquid, a liquid containing at least the above-mentioned (i) or (iii) is preferable from the viewpoint of suppressing the solidification of the resin at the interface between the pretreatment liquid and the coating liquid before the solidification step, Is more preferable, and a liquid having the same composition as the solvent of the coating liquid is particularly preferable. Specifically, it contains 50 mass% or more (more preferably 60 mass% or more) of the above (i) and 10 mass% to 50 mass% (more preferably 10 mass% ) Is preferable.

The application amount of the pretreatment liquid to the porous substrate is preferably 1 g / m 2 to 30 g / m 2. If the coating amount of the pretreatment liquid is 1 g / m < 2 > or more, penetration of the solvent of the coating liquid and the coating liquid into the porous substrate can be sufficiently suppressed. In view of the above, the amount of the pretreatment liquid applied is more preferably 3 g / m 2 or more, and more preferably 5 g / m 2 or more. On the other hand, if the coating amount of the pretreatment liquid is 30 g / m < 2 > or less, unevenness in coating of the coating liquid is unlikely to occur. In view of the above, the coating amount of the pretreatment liquid is more preferably 20 g / m 2 or less, and more preferably 15 g / m 2 or less.

The temperature of the pretreatment liquid when applied to the porous substrate is, for example, 10 to 50 캜.

When the coating of the coating liquid is carried out on only one side of the porous substrate, in the pretreatment step, the pretreatment liquid may be applied to only the surface of the porous substrate, or only the surface of the opposite side may be coated with the pretreatment liquid, .

When the coating liquid is applied to both surfaces of the porous substrate, the pretreatment liquid may be applied only to one surface of the porous substrate in the pretreatment step, or the pretreatment liquid may be applied to both surfaces of the porous substrate.

- a roll-

In the manufacturing method of the present disclosure, the roll rotating member used for applying the pretreatment liquid is a member having an outer circumferential layer having a porous structure, and the pretreatment liquid exudes from the inside to the outer circumferential surface through the porous structure.

Examples of the material of the outer peripheral layer of the rolled rotating member include inorganic materials such as ceramics, metal, and glass; And organic materials such as synthetic resin (for example, urethane, polypropylene, polyester, fluorine resin, nylon) and cellulose. The material of the outer circumferential layer of the rolled rotating member is preferably a material having durability against the pretreatment liquid. For example, an organic material such as synthetic resin or cellulose may be dissolved in an organic solvent such as N-methylpyrrolidone or dimethylacetamide. Therefore, when an organic solvent is used as the pretreatment liquid, When the organic material is applied to the layer, the outer layer may be dissolved or broken. On the other hand, organic materials such as synthetic resin and cellulose are difficult to dissolve in an aqueous solvent. Therefore, when an aqueous solvent is used as the pretreatment liquid, an organic material can be applied to the outer circumferential layer of the rolled rotating member. That is, the material of the outer peripheral layer of the rolled rotating member needs to be selected in consideration of the content solubility of the pretreatment liquid.

Specific examples of the outer layer of the rolled rotating member include porous ceramics, foamed urethane, nonwoven fabric of resin fibers, nonwoven fabric of glass fibers, nonwoven fabric of metal fibers, woven fabric of natural fibers, nonwoven fabric of natural fibers, .

The outer circumferential layer of the rolled rotating member is preferably porous ceramics. Porous ceramics have high solubility in water for an organic solvent and an aqueous solvent, and the porous structure is hardly damaged by a pretreatment liquid. Therefore, when the porous ceramics is applied to the outer circumferential layer of the roll-shaped rotary member, the kinds of the solvent that can be used as the pretreatment liquid can be broadened, and various kinds of coating layers can be formed. In addition, since the surface smoothness of the porous ceramics is high, it is difficult to scratch the porous substrate. Since the porous ceramics has a porous structure having a high curvature ratio, the pre-treatment liquid slowly permeates to the outer circumferential surface and is thinly placed on the outer circumferential surface, so that it is easy to control the application amount of the pre-treatment liquid.

The outer circumferential layer of the rolled rotating member is preferably a porous layer having an average pore size of 2 to 20 占 퐉. When the average pore diameter of the outer circumferential layer is within the above range, it is easy to control the amount of the pretreatment liquid exuding on the outer circumferential surface. In view of the above, the average pore size of the outer circumferential layer is preferably 2 占 퐉 or more, more preferably 5 占 퐉 or more, preferably 20 占 퐉 or less, and more preferably 10 占 퐉 or less. The average pore size of the outer circumferential layer of the rolled rotating member is a value measured by a mercury porosimetry method using a thermometer.

The outer circumferential layer of the rolled rotating member may be a single porous layer or a multi-layer porous layer obtained by laminating the same kind of material or different materials. When the outer peripheral layer of the rolled rotating member is a multilayer, it is preferable that at least the outermost peripheral layer is a porous ceramic.

The outer circumferential layer of the rolled rotating member has a layer thickness of, for example, 5 mm to 10 mm. The axial length of the outer peripheral layer of the rolled rotating member is not particularly limited as long as it is not less than the width of the porous substrate, and is, for example, a length of +0 cm to +50 cm with respect to the width of the porous substrate. The outer diameter of the rolled rotating member is, for example, 50 mm to 200 mm.

The roll rotating member may be a driving roll rotated by a motor or a driven roll rotating in accordance with the conveyance of the porous substrate.

Embodiments of the roll-shaped rotary member will be described below with reference to the drawings, but it goes without saying that the manufacturing method of the present disclosure is not limited to these examples.

3 is a schematic view showing an example of a roll-shaped rotating member. The roll-shaped rotary member 10 shown in Fig. 3 has an outer peripheral layer 12 and a shaft 14.

The outer peripheral layer 12 is a layer having a porous structure. The outer peripheral layer 12 is disposed on the outer peripheral surface of the shaft 14 and constitutes the outer peripheral surface of the rolled rotating member 10. [ The outer peripheral layer 12 is, for example, porous ceramics. The pretreatment liquid seeps from the inner peripheral surface side of the outer peripheral layer 12 to the outer peripheral surface through the porous structure.

The shaft 14 is a hollow member made of, for example, a metal (stainless steel, aluminum, iron, brass, copper, or the like). Both ends in the axial direction of the shaft 14 are held in a bearing (not shown) so that the shaft 14 becomes rotatable (freely). The pretreatment liquid flows through the hollow portion of the shaft 14.

The shaft 14 has a through hole in its outer circumferential surface in a region where the outer circumferential layer 12 is disposed. 4A and 4B are schematic views of the shaft 14 with the outer circumferential layer 12 removed from the rolled rotating member 10 and show one example of the through hole that the shaft 14 has on the outer circumferential surface. The through hole 16a shown in Fig. 4A has a circular opening in the form of a plurality of openings arranged in a periodic manner. The through hole 16b shown in Fig. 4B is a slit orthogonal to the axial direction of the shaft 14, and a plurality of slits are arranged at predetermined intervals. The pretreatment liquid migrates from the hollow portion of the shaft 14 to the outer peripheral layer 12 through the through hole 16a (or the through hole 16b).

One embodiment of the shaft 14 is a hollow member having both ends open in the axial direction. In this embodiment, the pretreatment liquid flows through the hollow portion of the shaft 14 in one direction in the axial direction, and a part of the pretreatment liquid passes through the through hole 16a (or the through hole 16b) (12). Then, the pretreatment liquid seeps into the outer peripheral surface through the porous structure of the outer peripheral layer 12. It is preferable that the pretreatment liquid flowing out of the shaft 14 without shifting to the outer peripheral layer 12 is circulated to the hollow portion of the shaft 14. [

In another embodiment of the shaft 14, one end is an opening end, the other end is a closing end, the hollow portion is divided into two long axially spaced portions by a partitioning member, Which is a hollow member. In this embodiment, the pretreatment liquid flows into the one chamber from the opening end of the shaft 14, and flows from the closed end side to the other chamber. Part of the pretreatment liquid migrates to the outer circumferential layer 12 through the through hole 16a (or the through hole 16b) while flowing through the two chambers. Then, the pretreatment liquid seeps into the outer peripheral surface through the porous structure of the outer peripheral layer 12. It is preferable that the pretreatment liquid flowing out of the shaft 14 without shifting to the outer circumferential layer 12 is circulated to the hollow portion of the shaft 14. [

[Coating process]

The coating step is a step of coating a coating liquid containing a resin and a solvent on one side or both sides of a porous substrate to form a coating liquid layer.

The coating step is carried out after the pretreatment step, before the pretreatment liquid disappears from the porous substrate by drying. It is preferable that the time from when the pretreatment liquid is applied to the porous substrate to when the coating liquid is applied is, for example, within 5 minutes.

Examples of the coating method of the coating liquid on the porous substrate include die coating, roll coating, gravure coating, bar coating, knife coating and the like.

One embodiment of the coating process is a process of coating a coating solution using a coating means in which a pressing means for pressing the porous substrate against the coating means is not disposed. In this embodiment, the coating means is not in surface contact with the porous substrate, but the coating means comes into linear contact with the porous substrate in the width direction to coat the coating liquid. The present embodiment is preferable from the viewpoint that the transport speed of the porous substrate can be increased, but the higher the transport speed of the porous substrate becomes, the more easily the non-uniformity of the porous layer is likely to become present. According to the manufacturing method of the present disclosure, even when the coating process adopts the present embodiment and the conveying speed of the porous substrate is increased, a composite film excellent in uniformity in the plane direction can be produced. Examples of coating methods employing the present embodiment include die coating, roll coating, and gravure coating.

One embodiment of the coating process includes a first coating means for coating one surface and a second coating means for coating the other surface, which are arranged opposite to each other with the porous substrate interposed therebetween, On both sides of the substrate.

In one embodiment of the coating process, the first coating means for coating one surface and the second coating means for coating the other surface, which are spaced apart from each other in the transport direction of the porous substrate, This is a step of sequentially coating one side of the porous substrate on both sides thereof. This embodiment will be described with reference to Figs. 5A and 5B. Fig. 5A and 5B are schematic views showing an embodiment of a coating process, respectively.

The embodiment shown in Fig. 5A is a die coating method in which the support roll 51, the die coater 21 (first coating means), the die coater 22 (Second coating means) and a support roll 52 are arranged in this order. The die coater 21 and the die coater 22 are disposed apart from each other in the transport direction of the porous substrate 71. In the embodiment shown in Fig. 5A, since the backup roll (the pushing means for pressing the porous substrate against the coating means) is not disposed in the die coater 21 and the die coater 22, The coater 22 contacts the porous base material 71 in a linear direction in the width direction without being in surface contact with the porous base material 71. [ Although a backup roll may be disposed in the die coater 21 and the die coater 22, it is preferable that the backup roll is not disposed from the viewpoint that the transport speed of the porous substrate can be increased.

5A, the coating liquid is coated on one surface of the porous substrate 71 by the die coater 21 and then the coating liquid is coated on the other surface of the porous substrate 71 by the die coater 22. Subsequently, Coat the surface with a coating solution.

The embodiment shown in Fig. 5B is a coating method in which the coating method is a gravure coating and the support roll 51, the gravure coater 41 (first coating means), the gravure coater 42 (Second coating means) and a support roll 52 are arranged in this order. The gravure coater 41 and the gravure coater 42 are disposed apart from each other in the transport direction of the porous substrate 71. The gravure coater 41 and the gravure coater 42 are not provided with the backup rolls (the pressing means for pressing the porous substrate to the coating means) 71 in the width direction without touching the surface of the porous substrate 71 in the surface direction. The backup rolls may be disposed in the gravure coater 41 and the gravure coater 42, but it is preferable that no backup rolls are disposed from the viewpoint of increasing the conveying speed of the porous substrate.

5B, a coating liquid is coated on one side of the porous substrate 71 by the gravure coater 41 and then the coating liquid is coated on the other side of the porous substrate 71 by the gravure coater 42. Next, Coat the surface with a coating solution.

As shown in Figs. 5A and 5B, in the embodiment in which the two coating means are spaced apart in the transport direction of the porous substrate and the coating is performed one by one, the two coating means are disposed opposite to each other with the porous substrate interposed therebetween, The porous substrate is hardly scratched, the layer thickness of the coating liquid layer is easily controlled on the surface, and the conveying speed of the porous substrate can be increased. According to the manufacturing method of the present disclosure, it is possible to manufacture a composite film excellent in uniformity in the plane direction even when the conveying speed of the porous substrate is increased by adopting the embodiment in which coating is performed one by one as described above.

The conveying speed of the porous substrate in the coating step is preferably 20 m / min or more, more preferably 30 m / min or more, and more preferably 40 m / min or more, from the viewpoint of production efficiency. According to the manufacturing method of the present disclosure, even when a wide porous substrate is transported at a high speed (for example, 20 m / min or more), a composite film excellent in uniformity in the plane direction can be produced. It is preferable that the above-mentioned conveying speed is somewhat faster from the viewpoint of producing a composite film having better uniformity in the plane direction, and the above range is preferable. The upper limit of the conveying speed is preferably 150 m / min or less, more preferably 100 m / min or less, from the viewpoint of suppressing occurrence of coating irregularity.

The coating amount of the coating liquid is, for example, 10 g / m 2 to 60 g / m 2 as the total of both surfaces.

[Solidification process]

The coagulation step includes a wet step of bringing the coating liquid layer into contact with the coagulating liquid to solidify the resin contained in the coating liquid layer to obtain a porous layer; And a dry process in which the solvent contained in the coating liquid layer is removed to solidify the resin contained in the coating liquid layer to obtain a porous layer. Since the dry process tends to be dense in the porous layer as compared with the wet process, the wet process is preferable from the viewpoint of obtaining a good porous structure.

In the wet process, it is preferable that the porous substrate having the coating liquid layer is immersed in the coagulating solution, and more specifically, the coagulating bath containing the coagulating solution is preferably passed.

The coagulating solution used in the wet process is generally a mixed solvent of a good solvent used for preparing a coating solution and a phase separating agent and water. The mixing ratio of the good solvent and the phase separation agent is preferably adjusted to the mixing ratio of the mixed solvent used for preparation of the coating solution. The concentration of water is suitably 40% by mass to 80% by mass with respect to the total amount of coagulating solution from the viewpoints of formation of a porous structure and productivity. The temperature of the coagulating liquid is, for example, 20 to 50 캜.

When the solidification step is a dry process, the solidification step is also a solvent removal step. By this step, the liquid component (the solvent of the pretreatment liquid and the coating liquid applied to the porous substrate) contained in the composite film is removed. The method for removing the liquid component from the composite membrane is not particularly limited, and for example, a method of contacting the composite membrane with the exothermic member; A method of conveying a composite membrane in a chamber in which temperature and humidity are adjusted; And a method of applying hot air to the composite membrane. When heat is applied to the composite membrane, the temperature is, for example, 50 DEG C or higher, and is not higher than the melting point of the porous substrate.

[Washing step]

An embodiment of the manufacturing method of the present disclosure has a water washing step of employing a wet process in the coagulation process and washing the composite film after the coagulation process. The water washing step is a step carried out for the purpose of removing liquid components other than water contained in the composite membrane (a pretreatment liquid applied to a porous substrate, a solvent for a coating liquid, and a coagulating liquid solvent). When the solidification step is a wet process, the washing step corresponds to the solvent removing step. Specifically, the washing process is preferably carried out by conveying the composite membrane in a water bath. The water temperature of the water for washing is, for example, 0 ° C to 70 ° C.

[Drying process]

One embodiment of the manufacturing method of the present disclosure has a drying step of removing water from the composite membrane after the water washing step. The drying process may also be equivalent to the solvent removal process. The method of removing water from the composite membrane is not limited, and for example, a method of contacting the composite membrane with a heat generating member; A method of conveying a composite membrane in a chamber in which temperature and humidity are adjusted; And a method of applying hot air to the composite membrane. When heat is applied to the composite membrane, the temperature is, for example, 50 DEG C or higher, and is not higher than the melting point of the porous substrate.

The manufacturing method of the present disclosure may employ the following embodiments from the viewpoint of coating quality or productivity.

As a part of the coating solution preparing process, a process of passing the solvent through the filter before mixing with the resin is performed for the purpose of removing the foreign substance from the solvent for preparing the coating solution. The suspended particle size of the filter used in this treatment is, for example, 0.1 to 100 m.

A stirrer is provided in a tank for carrying out a coating solution preparing process, and the coating solution is always stirred with an agitator to suppress sedimentation of solid components (for example, filler) in the coating solution.

- The piping for transporting the coating liquid from the coating liquid preparation process to the coating process is circulated, and the coating liquid is circulated in the piping to suppress the aggregation of the solid components in the coating liquid. In this case, it is preferable to control the temperature of the coating liquid in the pipe constantly. The length of the pipe is, for example, 20 m.

A filter is installed in the middle of a piping for transporting the coating liquid from the coating liquid preparing process to the coating process, thereby removing coagulated matter and / or foreign matter from the coating liquid.

· As a pump for supplying the coating liquid from the coating liquid preparation process to the coating process, for example, a pulsating flow rate metering pump is provided.

Between the upstream of the pretreatment process and / or between the pretreatment process and the coating process, a static eliminator is disposed to remove the surface of the porous substrate.

A housing is provided around the coating means to keep the environment of the coating process clean and to control the temperature and humidity of the atmosphere in the coating process.

A sensor for detecting the coating amount is disposed downstream of the coating means to correct the coating amount in the coating process.

Hereinafter, the porous base material and the porous layer of the composite membrane will be described in detail.

[Porous substrate]

In the present disclosure, a porous substrate means a substrate having voids or pores therein. As such a substrate, a microporous membrane; A porous sheet made of fibrous material such as a nonwoven fabric or paper; And a composite porous sheet obtained by laminating one or more other porous layers on the microporous membrane or the porous sheet. In the present disclosure, a microporous membrane is preferable from the viewpoint of thinning of the composite membrane and strength. The microporous membrane means a membrane having a plurality of micropores therein and a structure in which these micropores are connected to each other so that gas or liquid can pass from one side to the other side.

As the material of the porous substrate, a material having electrical insulation is preferable, and either organic material or inorganic material may be used.

As the material of the porous substrate, a thermoplastic resin is preferable from the viewpoint of giving a shutdown function to the porous substrate. The shutdown function refers to a function of preventing the thermal runaway of the battery by blocking the movement of ions when the composite material is applied to the battery separator and the constituent material dissolves to close the pores of the porous substrate when the battery temperature rises . As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200 占 폚 is suitable, and polyolefin is particularly preferable.

As the porous substrate, a microporous membrane containing a polyolefin (" polyolefin microporous membrane ") is preferable. As the polyolefin microporous membrane, for example, there can be mentioned a polyolefin microporous membrane which has been applied to a conventional battery separator. Of these, it is preferable to select a polyolefin microporous membrane having sufficient mechanical properties and material permeability.

The polyolefin microporous membrane preferably contains polyethylene from the viewpoint of exhibiting a shutdown function, and the content of polyethylene is preferably 95% by mass or more with respect to the total mass of the polyolefin microporous membrane.

The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene from the viewpoint of having heat resistance to such an extent that it does not readily rupture when exposed to high temperatures. Examples of such a polyolefin microporous membrane include a microporous membrane in which polyethylene and polypropylene are present in a single layer. In such a microporous membrane, it is preferable to include 95 mass% or more of polyethylene and 5 mass% or less of polypropylene from the viewpoint of compatibility between the shutdown function and heat resistance. From the viewpoint of compatibility between the shutdown function and heat resistance, the polyolefin microporous membrane having a laminated structure of two or more layers, at least one layer containing polyethylene, and at least one layer containing polypropylene desirable.

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight of 100,000 to 5,000,000. If the weight average molecular weight of the polyolefin is 100,000 or more, sufficient mechanical properties can be secured. On the other hand, if the weight average molecular weight of the polyolefin is 5,000,000 or less, the shutdown characteristics are good and the film is easily formed.

As a method for producing a polyolefin microporous membrane, a method of extruding a molten polyolefin resin from a T-die to form a sheet, subjecting the sheet to crystallization, stretching, and then heat treatment to form a microporous membrane; A method in which a polyolefin resin melted together with a plasticizer such as liquid paraffin is extruded from a T-die, cooled and formed into a sheet, stretched, and then the plasticizer is extracted and heat treated to form a microporous membrane.

Examples of the porous sheet made of fibrous material include polyesters such as polyethylene terephthalate; Polyolefins such as polyethylene and polypropylene; Heat-resistant resins such as aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyether ketone, and polyether imide; Nonwoven fabric, paper, etc., made of fibrous material such as cellulose. The heat-resistant resin refers to a resin having a melting point of 200 ° C or higher, or a resin having no melting point and having a decomposition temperature of 200 ° C or higher.

Examples of the composite porous sheet include sheets in which a functional layer is laminated on a porous sheet made of a microporous membrane or a fibrous material. Such a composite porous sheet is preferable from the viewpoint of enabling additional functional addition by the functional layer. As the functional layer, for example, a porous layer made of a heat-resistant resin or a porous layer made of a heat-resistant resin and an inorganic filler can be mentioned from the viewpoint of imparting heat resistance. Examples of the heat-resistant resin include one or two or more heat-resistant resins selected from aromatic polyamide, polyimide, polyether sulfone, polysulfone, polyether ketone and polyetherimide. As the inorganic filler, metal oxides such as alumina; And metal hydroxides such as magnesium hydroxide. Examples of the composite method include a method of coating a functional layer on a microporous membrane or a porous sheet; A method of bonding the microporous membrane or the porous sheet and the functional layer with an adhesive; And a method of thermocompression bonding a microporous membrane or a porous sheet and a functional layer.

The width of the porous substrate is preferably 0.3 m to 3.0 m from the viewpoint of suitability to the manufacturing method of the present disclosure. According to the manufacturing method of the present disclosure, even when a wide porous substrate (for example, a width of 0.5 m or more) is transported at a high speed, a composite film excellent in uniformity in the plane direction can be produced.

The length of the porous substrate is preferably 50 m or more from the viewpoint of suitability to the manufacturing method of the present disclosure.

The thickness of the porous substrate is preferably 5 占 퐉 to 50 占 퐉 in view of mechanical strength.

The breaking extension of the porous substrate is preferably 10% or more in the MD direction, more preferably 20% or more, more preferably 5% or more, and more preferably 10% or more in the TD direction from the viewpoint of mechanical strength. The fracture elongation of the porous substrate is obtained by performing a tensile test at a tensile rate of 100 mm / min in an atmosphere at a temperature of 20 캜 using a tensile tester.

The gel value (JIS P8117: 2009) of the porous substrate is preferably 50 sec / 100 cc to 800 s / 100 cc from the viewpoint of mechanical strength and material permeability.

The porosity of the porous substrate is preferably 20% to 60% from the viewpoints of mechanical strength, handling property, and material permeability.

The average pore diameter of the porous substrate is preferably 20 nm to 100 nm from the viewpoint of the material permeability. The average pore size of the porous substrate is a value measured using a permeometer according to ASTM E1294-89.

[Porous layer]

In the present disclosure, the porous layer has a plurality of micropores therein and has a structure in which these micropores are connected, and is a layer in which gas or liquid can pass from one surface to the other.

When the composite membrane is applied to a battery separator, it is preferable that the porous layer is an adhesive porous layer that can be adhered to the electrode. It is preferable that the adhesive porous layer is present on both surfaces of the porous substrate rather than only on one side of the porous substrate.

The thickness of the porous layer is preferably 0.5 m to 5 m on one side of the porous substrate from the viewpoint of mechanical strength.

The porosity of the porous layer is preferably 30% to 80% from the viewpoints of mechanical strength, handling property, and material permeability.

The average pore size of the porous layer is preferably 20 nm to 100 nm from the viewpoint of the material permeability. The average pore size of the porous layer is a value measured using a permeometer according to ASTM E1294-89.

The porous layer is formed by coating a coating solution containing at least a resin and a solvent thereof. Therefore, the porous layer contains at least a resin. The porous layer may further include a filler or the like. Hereinafter, the components of the coating liquid and the resin contained in the porous layer will be described.

[Suzy]

The type of resin contained in the porous layer is not limited. As the resin contained in the porous layer, a resin having a function of immobilizing a filler (so-called binder resin) is preferable. When the composite membrane is produced by a wet process, the resin contained in the porous layer is preferably a hydrophobic resin from the viewpoint of suitability for production. When the composite membrane is applied to a battery separator, it is preferable that the resin contained in the porous layer be stable to an electrolyte solution, electrochemically stable, has a function of immobilizing inorganic particles, and can adhere to an electrode. The porous layer may contain one resin or two or more kinds of resins.

Examples of the resin include homopolymers or copolymers of vinylnitriles such as polyvinylidene fluoride, polyvinylidene fluoride copolymer, styrene-butadiene copolymer, acrylonitrile and methacrylonitrile, polyethylene oxide and polypropylene Oxides and the like are preferable. Among them, polyvinylidene fluoride and polyvinylidene fluoride copolymer (these are referred to as " polyvinylidene fluoride resin ") are particularly preferable.

As the polyvinylidene fluoride resin, a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride); A copolymer of vinylidene fluoride and another copolymerizable monomer (polyvinylidene fluoride copolymer); And mixtures thereof. Examples of the monomer copolymerizable with vinylidene fluoride include tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichlorethylene, vinyl fluoride, etc. One or more kinds of monomers can be used . The polyvinylidene fluoride resin can be produced by emulsion polymerization or suspension polymerization.

The resin contained in the porous layer is preferably a heat-resistant resin (a resin having a melting point of 200 DEG C or higher, or a resin having a melting point of 200 DEG C or higher and no decomposition temperature) from the viewpoint of heat resistance. Examples of the heat resistant resin include polyamide (nylon), wholly aromatic polyamide (aramid), polyimide, polyamideimide, polysulfone, polyketone, polyether ketone, polyether sulfone, polyether imide, And mixtures thereof. Of these, wholly aromatic polyamides are preferable from the viewpoints of easiness of forming a porous structure, binding property with inorganic particles, oxidation resistance, and the like. Of the wholly aromatic polyamides, meta-type wholly aromatic polyamides are preferable from the viewpoint of easy molding, and particularly preferable are poly-meta phenylene isophthalamides.

In the present disclosure, a particulate resin or a water-soluble resin may be used as the resin. Examples of the particulate resin include particles containing a resin such as a polyvinylidene fluoride resin, a fluorine rubber, and a styrene-butadiene rubber. The particulate resin can be dispersed in a dispersion medium such as water to be used for producing a coating liquid. Examples of the water-soluble resin include a cellulose resin, polyvinyl alcohol, and the like. The water-soluble resin can be used, for example, in the production of a coating solution by dissolving in water. The particulate resin and the water-soluble resin are favorable when the coagulation process is carried out dry.

[filler]

The filler may be either an inorganic filler or an organic filler. The filler preferably has a volume average particle diameter of the primary particles of 0.01 탆 to 10 탆, more preferably 0.1 탆 to 10 탆, still more preferably 0.1 탆 to 3.0 탆.

The porous layer preferably contains inorganic particles as a filler. The inorganic particles contained in the porous layer are preferably stable to an electrolyte solution and electrochemically stable. The porous layer may contain one kind of inorganic particles or two or more kinds of inorganic particles.

Examples of the inorganic particles include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide and boron hydroxide; Metal oxides such as silica, alumina, zirconia, and magnesium oxide; Carbonates such as calcium carbonate and magnesium carbonate; Sulfates such as barium sulfate and calcium sulfate; Clay minerals such as calcium silicate and talc. Among them, metal hydroxides and metal oxides are preferable from the viewpoints of imparting flame retardancy and antistatic effect. The inorganic particles may be surface-modified with a silane coupling agent or the like.

The particle shape of the inorganic particles is optional, and may be any of spherical, elliptical, plate, needle, and irregular. The volume average particle diameter of the primary particles of the inorganic particles is preferably from 0.01 m to 10 m, more preferably from 0.1 m to 10 m, and most preferably from 0.1 m to 10 m, from the viewpoints of moldability of the porous layer, material permeability of the composite membrane, Mu m to 3.0 mu m is more preferable.

When the porous layer contains inorganic particles, the ratio of the inorganic particles to the total amount of the resin and the inorganic particles is, for example, 30% by volume to 90% by volume.

The porous layer may contain an organic filler as a filler. Examples of the organic filler include crosslinked poly (meth) acrylic acid, crosslinked poly (meth) acrylate, crosslinked polysilicon, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine Particles composed of a crosslinked polymer such as resin, phenol resin, and benzoguanamine-formaldehyde condensate; Particles made of a heat-resistant resin such as polysulfone, polyacrylonitrile, aramid, polyacetal, and thermoplastic polyimide.

[Characteristics of composite membrane]

The thickness of the composite membrane is, for example, 5 m to 100 m, and in the case of a battery separator, for example, 5 m to 50 m.

The gully value (JIS P8117: 2009) of the composite membrane is preferably 50 sec / 100 cc to 800 sec / 100 cc from the viewpoint of mechanical strength and material permeability.

The porosity of the composite membrane is preferably 30% to 60% in terms of mechanical strength, handling property, and material permeability.

In the present disclosure, the porosity of the composite membrane is determined by the following formula. The porosity of the porous substrate and the porosity of the porous layer are the same.

(%) = {1- (Wa / da + Wb / db + Wc / dc + ... + Wn / dn) / t} 100

Wa, Wb, Wc, ... , Wn are constituent materials a, b, c, ... , mass (g / cm2) of n, da, db, dc, ... , dn represents the constituent materials a, b, c, ... (g / cm < 3 >) of n, and t is the film thickness (cm).

[Use of composite membrane]

Examples of the application of the composite membrane include a battery separator, a film for a capacitor, a gas filter, and a liquid filter. Particularly, a separator for a non-aqueous secondary battery can be cited as a particularly useful application.

(Example)

Hereinafter, the manufacturing method of the present disclosure will be described in more detail by way of examples. However, the production method of the present disclosure is not limited to the following examples.

≪ Evaluation method of quality of composite membrane &

The composite membranes prepared in the following Examples and Comparative Examples were evaluated by the following quality evaluation methods.

[Uniformity of film thickness]

The film thickness (mu m) of the composite film was measured at 20 points at intervals of 4 cm in the width direction by using a contact type thickness meter (MITTO CHEMICAL Co., LITEMATIC, measuring terminal: circumferential terminal having a diameter of 5 mm, applied load: , The average of 20 points was calculated and classified as follows.

A: Difference in film thickness between each measurement point with respect to average film thickness is less than 0.2 占 퐉

B: one measuring point with a difference in film thickness of 0.2 탆 or more and less than 0.5 탆 for the average film thickness, and the other measuring points are those for which the difference in film thickness is less than 0.2 탆

C: Two to four measurement points having a film thickness difference of not less than 0.2 μm and not more than 0.5 μm with respect to an average film thickness, and the other measurement points are a film thickness difference of less than 0.2 μm with respect to an average film thickness

D: Five or more measurement points having a film thickness difference of 0.2 占 퐉 or more and less than 0.5 占 퐉 with respect to the average film thickness, and the other measurement points are those having a film thickness difference of less than 0.2 占 퐉

E: at least five measuring points having a difference in film thickness of not less than 0.2 탆 and not more than 0.5 탆 for an average film thickness, and at least one measuring point having a film thickness difference of not less than 0.5 탆 for an average film thickness

[Uniformity of Peel Strength]

The composite membrane was cut into 1 cm in the TD direction and 10 cm in the MD direction from a total of five sites, one in the width direction, one inward and one 20 cm inward from one of the ends, one cm inward and 20 cm inward from the other end , And a mending tape of 3M was attached to one side to prepare a test piece. The mending tape was slightly peeled together with the immediately underlying porous layer from one end in the longitudinal direction of the test piece (that is, the MD direction of the composite membrane), and the two separated ends were grasped by Tensilon (RTC-1210A of Orientech) T-peel test was conducted. The tensile speed of the T-peel test was 20 mm / min. The load (N) at the time of peeling the porous layer from the porous substrate was measured, and the load from 10 mm to 40 mm was measured at intervals of 0.4 mm And the average was calculated. The average of the measured values of five test pieces was calculated and classified as follows.

A: The strength difference of each test piece is less than 0.02N with respect to the average strength of five test pieces.

B: Specimen with a difference in strength of less than 0.02 N and less than 0.04 N relative to the average strength of 5 specimens

C: Specimen with a strength difference of 0.04 N or more and less than 0.06 N with respect to the average strength of five specimens

D: Specimen with an intensity difference of less than 0.06 N and less than 0.08 N with respect to the average strength of five specimens

E: Specimen with an intensity difference of 0.08 N or more with respect to the average strength of five specimens

≪ Preparation of composite membrane &

[Example 1]

- Coating liquid preparation process -

(PMIA) was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (mass ratio 1: 1) and further aluminum hydroxide particles (Al (OH) ₃ , Volume average particle diameter of primary particles: 0.8 mu m) were dispersed to prepare a coating liquid. The composition (mass ratio) of the coating liquid was PMIA: Al (OH) ₃ : DMAc: TPG = 4: 16: 40: 40.

- Pretreatment process -

As a porous substrate, a polyethylene microporous membrane (film thickness 10 mu m) having a width of 0.8 m in the elongated phase was prepared. DMAc and TPG were mixed at a mass ratio of 1: 1 to prepare a pretreatment solution. As a means for applying the pretreatment liquid, a ceramic roll having a shape shown in Fig. 4 (a stainless steel-made hollow shaft in the shape shown in Fig. 4A and a roll having an outer circumferential layer of porous ceramics) having an outer diameter of 12 cm, m, a layer thickness of the outer circumferential layer of 5 mm, and an average pore diameter of the outer circumferential layer of 10 m).

The outer circumferential surface of the ceramic roll in which the pretreatment liquid was circulatingly supplied to the hollow shaft was brought into contact with the porous substrate during transportation to apply the pretreatment liquid to one side of the porous substrate.

- Coating process -

As shown in Fig. 5A, the two sides of the porous substrate coated with the pretreatment liquid were coated with a coating liquid on both sides by two die coaters disposed apart from each other in the transport direction of the porous substrate. A backup roll was not disposed in the two die coaters, and the die coater was linearly contacted with the porous substrate in the width direction to coat the coating liquid.

- Coagulation process -

The porous substrate obtained by coating the coating liquid on both sides was transported in a coagulation bath and immersed in a coagulating liquid (water: DMAc: TPG = 43: 40: 17 [mass ratio], liquid temperature: 30 ° C) to solidify the resin contained in the coating liquid layer, A composite membrane was obtained.

- Washing process, drying process -

The composite membrane was returned to a water bath controlled at a water temperature of 30 占 폚 and washed with water, and the water repellent composite membrane was passed through a drying apparatus equipped with a heating roll and dried.

Each of the above-mentioned steps was continuously carried out to produce a composite membrane having a porous layer on both surfaces of a polyethylene microporous membrane.

[Examples 2 to 3]

A composite membrane was prepared in the same manner as in Example 1 except that the conveying speed of the porous substrate in the coating step was changed as shown in Table 1. [

[Examples 4 to 5]

A composite membrane was prepared in the same manner as in Example 1, except that the application amount of the pretreatment liquid was changed as shown in Table 1.

[Example 6]

The procedure of Example 1 was repeated except that polymethenylene isophthalamide was changed to polyvinylidene fluoride (PVDF), and aluminum hydroxide particles were changed to alumina particles (Al ₂ O ₃ , volume average particle diameter of primary particles: 0.1 μm) A composite membrane was produced.

[Example 7]

A composite membrane was prepared in the same manner as in Example 1 except that poly (meta phenylene isophthalamide) was changed to polyvinylidene fluoride (PVDF) and aluminum hydroxide particles were not used.

[Comparative Example 1]

A composite membrane was prepared in the same manner as in Example 1 except that the pretreatment step was not carried out.

[Comparative Example 2]

The application means of the pretreatment liquid was changed to a towel cloth (width 1.3 m) at the height contacting with the porous substrate during transportation. A composite membrane was prepared in the same manner as in Example 1 except that the pretreatment liquid was supplied to the towel cloth and the porous substrate was transported while being brought into contact with the towel cloth to apply the pretreatment liquid to one side of the porous substrate.

[Comparative Example 3]

A composite membrane was prepared in the same manner as in Example 1 except that the application means of the pretreatment liquid was changed to a slot die coater.

Table 1 shows the results of the quality evaluation of each of the composite membranes of Examples 1 to 7 and Comparative Examples 1 to 3.

[Table 1]

The disclosure of Japanese Patent Application No. 2015-233612, filed on November 30, 2015, is hereby incorporated by reference in its entirety.

All publications, patent applications, and technical specifications described in this specification are herein incorporated by reference into the present specification to the same extent as if each individual publication, patent application, and technical specification were specifically and individually indicated to be incorporated by reference. do.

10: roll rotating member 12: porous layer
14: shaft 16a: through hole
16b: through hole 21, 22: die coater
41, 42: Gravure coater 51, 52: Support roll
71: Porous substrate

Claims (8)

A method for producing a composite film comprising a porous substrate and a porous layer formed on one or both surfaces of the porous substrate by coating a coating solution containing a resin and a solvent for dissolving or dispersing the resin,
(1) a step of applying a liquid compatible with the solvent to one or both surfaces of the porous substrate, using a roll rotating member having an outer peripheral layer having a porous structure, Applying the liquid leaking to the outer peripheral surface to the porous substrate,
(2) a step of coating the coating liquid on one side or both sides of the porous substrate coated with the liquid to form a coating liquid layer,
(3) a step of coagulating the resin contained in the coating liquid layer to obtain a composite film having a porous layer containing the resin on one side or both sides of the porous substrate,
(4) a step of removing the solvent and the liquid from the composite membrane
≪ / RTI > The method according to claim 1,
Wherein the outer circumferential layer of the rolled rotating member is a porous layer of ceramics. 3. The method according to claim 1 or 2,
Wherein the outer peripheral layer of the rolled rotating member is a porous layer having an average pore size of 2 占 퐉 or more and 20 占 퐉 or less. 4. The method according to any one of claims 1 to 3,
Wherein the step (2) is carried out by using a first coating means for coating one surface and a second coating means for coating the other surface, which are spaced apart from each other in the transport direction of the porous substrate, Wherein the porous substrate is coated on both sides of the porous substrate one by one. 5. The method according to any one of claims 1 to 4,
Wherein the step (2) is a step of coating the coating solution using a coating means not provided with a pressing means for pressing the porous substrate against the coating means. 6. The method according to any one of claims 1 to 5,
Wherein the conveying speed of the porous substrate is 20 m / min or more in the step (2). 7. The method according to any one of claims 1 to 6,
Wherein the step (1) is a step of applying the liquid to the porous substrate at 1 g / m 2 or more and 30 g / m 2 or less. 8. The method according to any one of claims 1 to 7,
Wherein the porous substrate is a polyolefin microporous membrane.

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