CN111033800A

CN111033800A - Manufacturing method of multilayer film

Info

Publication number: CN111033800A
Application number: CN201880050293.0A
Authority: CN
Inventors: 中村谕; 石黑亮; 片本共祐
Original assignee: Japan Steel Works Ltd
Current assignee: Japan Steel Works Ltd
Priority date: 2017-08-02
Filing date: 2018-08-02
Publication date: 2020-04-17
Also published as: WO2019027001A1; JP6876571B2; CN117080676A; JP2019029282A; TWI736787B; TW201911625A

Abstract

The method for manufacturing a multilayer film comprises the following steps: removing the porous forming material from the raw material film (22); a step of bringing first rollers (27, 28) and a second roller (26) into contact with the raw material film and applying a coating liquid containing fine particles using the second roller; stretching the raw material film in a width direction with the coating liquid having fluidity; and a step of drying the coating liquid to form a multilayer film having the microparticle layer fixed thereto. In the coating process, an angle formed by a line segment connecting the rotation axis position of at least one first roller and the rotation axis position of a second roller and the direction of pressing the raw material film by the second roller is more than 0 DEG and less than 150 deg.

Description

Method for producing multilayer film

Technical Field

The present invention relates to a method for producing a multilayer film.

Background

Conventionally, stretched films have been used for various products. For example, a stretched film made of a polyolefin material is used as a separator for a lithium ion battery (hereinafter referred to as "LIB"). In order to improve the heat resistance of such a separator, an organic material or an inorganic material may be disposed on the surface of the stretched film.

As an example, there is used a method of applying a coating liquid obtained by mixing ceramic fine particles such as alumina or silica as an inorganic material with a solvent to the surface of a stretched film and then drying the solvent to provide a film composed of the fine particles on the surface of the stretched film (see patent documents 1 and 2). In addition, a technique of applying a resin material such as polyamide or polyimide as an organic material to the surface of a stretched film to provide a film made of the resin material on the surface of the stretched film is also used. In addition, the organic material and the inorganic material may be used in combination (see patent documents 3 and 4).

Prior art documents

Patent document 1: japanese laid-open patent publication No. 2013-114751

Patent document 2: japanese unexamined patent application publication No. 2014-203680

Patent document 3: japanese patent application laid-open No. 2009-21265

Patent document 4: japanese patent No. 4460028 publication

Disclosure of Invention

Problems to be solved by the invention

The stretched film used as a separator for LIB is usually formed to be microporous for movement of lithium ions and the like. The micropores can be formed, for example, by a method (so-called wet method) in which a solvent or the like is mixed with a resin that is a material of the stretched film, the film is formed into a film, and then the solvent or the like is extracted. However, in the case of using this method, the micropores may be clogged due to shrinkage of the stretched film during extraction of the solvent or the like, and therefore, in general, the stretched film is stretched again after extraction of the solvent or the like in order to reopen the clogged micropores. In addition, in this secondary drawing, the size of the micropores is also adjusted.

However, in the case where a film made of various fine particles (hereinafter, also referred to as "fine particle layer") is disposed on the stretched film in order to improve the heat resistance, it is sometimes preferable to provide the fine particle layer on the stretched film at a point before the re-stretching from the viewpoints of downsizing of the production system, rationalization of the production process, and the like. However, since the fine particle layer is generally less likely to deform than the material constituting the stretched film, there is a possibility that cracks in the fine particle layer, peeling of the fine particle layer from the stretched film, or the like may occur during the re-stretching process. In other words, if the fine particle layer is provided on the stretched film before various stretching steps including re-stretching, the fine particle layer may not be properly fixed to the stretched film.

An object of the present invention is to provide a method for producing a multilayer film capable of appropriately fixing a microparticle layer to the surface of a stretched film.

Means for solving the problems

[1] In the first aspect of the present invention, a method for manufacturing a multilayer film is a method for manufacturing a multilayer film in which a fine particle layer made of fine particles is provided on a surface of a porous film, and the method for manufacturing a multilayer film includes:

a removing step of removing the porous forming material from a raw material film containing a resin material constituting the film and the porous forming material;

a coating step of coating a coating liquid containing the fine particles onto the raw material film using a pair of first rollers in a state where the pair of first rollers are in contact with one surface of the raw material film at two different positions in a conveying direction of the raw material film subjected to the removal step, and a second roller is in contact with the other surface of the raw material film at a position sandwiched between the pair of first rollers in the conveying direction;

a transverse stretching step of stretching the raw material film in a width direction while maintaining a state in which the coating liquid applied to the raw material film has fluidity; and

a fixing step of forming the multilayer film by drying the coating liquid to fix the fine particle layer to the film,

in the coating step, the second roller presses the raw material film in a predetermined pressing direction, and an angle between rollers, which is an angle formed by a line segment connecting a rotation axis position of at least one of the first rollers and a rotation axis position of the second roller, and the pressing direction, is 0 ° or more and 150 ° or less when viewed in a direction along the rotation axis of the second roller.

In the first aspect, in the coating step, the second roller presses the raw material film and applies the coating liquid to the raw material film. In particular, it has been found from experiments and examinations conducted by the inventors that when the coating liquid is applied to the raw material film in a state where the first roller and the second roller are arranged so that the angle between the rollers is 0 ° to 150 °, adhesion between fine particles contained in the coating liquid and the raw material film is significantly improved. In the transverse stretching step, the raw film is stretched in the width direction in a state where the coating liquid has fluidity (in other words, in a state where the coating liquid is not completely dried). Thus, the coating liquid flows following the stretching of the raw material film, and therefore, compared with the case where the transverse stretching is performed in a state where the coating liquid is completely dried to form the fine particle layer, the cracking, peeling, and the like of the fine particle layer finally provided in the multilayer film can be suppressed. Thus, according to the production method of the first aspect, the fine particles can be appropriately fixed to the surface of the stretched film.

[2] In a second aspect of the present invention, in addition to the first aspect,

the transverse stretching step includes a preliminary step of performing preheating and a main step of performing stretching in the width direction under heating,

the amount of the coating liquid reduced before and after the preliminary step in the preliminary step, i.e., the preliminary drying amount, is 20 wt% or less,

the amount of decrease in the coating liquid before and after the main step in the main step, that is, the main drying amount, is 20 wt% or less.

In the second aspect, it has been found from experiments and examinations conducted by the inventors that the following ability of the coating liquid to the stretching of the raw material film can be improved by setting the amount of decrease of the coating liquid to 20 wt% or less in the preheating step and the main step included in the transverse stretching step. Thus, according to the production method of the second aspect, the fine particles can be more appropriately fixed to the surface of the stretched film.

[3] In a third aspect of the present invention, based on the second aspect,

the preliminary step includes a treatment of heating the raw material film so that the amount of heat per unit area imparted to the raw material film is 1.5kW/h or less,

the main step includes a treatment of heating the raw material film so that the amount of heat per unit area imparted to the raw material film is 1.2kW/h or less.

As for the third aspect, it has been found from experiments and examinations conducted by the inventors that the amount of decrease in the coating liquid is adjusted to be the second aspect by setting the amount of heat per unit area applied to the raw material film to 1.5kW/h or less in the preliminary step and 1.2kW/h or less in the main step. Thus, according to the production method of the third aspect, the fine particles can be more appropriately fixed to the surface of the stretched film.

[4] In a fourth aspect of the present invention, in addition to any one of the first to third aspects,

the coating step includes a process in which the ratio G/L of the rotational speed G of the second roller to the transport speed L of the raw material film is greater than 0 and 10 or less.

In the fourth aspect, it has been found from experiments and examinations performed by the inventors that the coating liquid can be applied to a desired thickness by setting the ratio G/L of the rotation speed G of the second roller to the transport speed L of the raw material film to a value greater than 0 and 10 or less. Thus, according to the production method of the fourth aspect, the fine particles can be more appropriately fixed to the surface of the stretched film.

[5] In a fifth aspect of the present invention, in addition to any one of the first to fourth aspects,

the fixing step includes a process of fixing the fine particle layer to the surface of the raw material film by stretching the raw material film in the transport direction and gradually drying the coating liquid under heating.

According to the fifth aspect, after the micropores of the raw material film are opened by the transverse stretching step (i.e., the above-described secondary stretching), the microparticle layer can be formed on the surface of the raw material film. Thus, the micro particle layer is not formed at the time of the transverse stretching step, and therefore cracking, peeling, and the like of the micro particle layer finally provided as the multilayer film can be suppressed. Further, the degree of opening of the micropores can be adjusted by stretching the raw material film in the conveying direction. Thus, according to the production method of the fifth aspect, the fine particles can be appropriately fixed to the surface of the microporous stretched film having a desired degree of opening.

[6] In a sixth aspect of the present invention, in addition to any one of the first to fifth aspects,

the multilayer film is used as a separator for a lithium ion battery.

According to the sixth aspect, the method for producing a multilayer film of any one of the first to fifth aspects can be applied to a method for producing a lithium ion battery separator, which is industrially highly valuable.

Effects of the invention

According to the present invention, fine particles can be appropriately fixed to the surface of the stretched film.

Drawings

Fig. 1 is a schematic configuration diagram showing a LIB spacer manufacturing system according to the present invention.

Fig. 2(a) is a specific configuration diagram of the inline coater of fig. 1, and fig. 2(b) and 2(c) are schematic diagrams showing a roll angle defined by a gravure roll and a proximity roll.

Fig. 3 is a schematic configuration diagram showing another embodiment of fig. 1, illustrating a BOPET in-line adhesive application method.

Fig. 4 is a schematic configuration diagram showing another embodiment of fig. 1, which illustrates an on-line ceramic coating method for a spacer.

Fig. 5 is a block diagram of a verification device of the LIB spacer manufacturing system according to the present invention.

Fig. 6 is a schematic configuration diagram showing a main part of the authentication apparatus of fig. 5.

Fig. 7 is an explanatory view showing coating thickness adjustment conditions of the in-line coater of fig. 1.

Fig. 8 is an explanatory view showing conditions of transverse stretching and drying in the inline coater of fig. 1.

Fig. 9 is an explanatory view of a peel strength measurement test for a separator according to the present invention.

Fig. 10 is a schematic configuration diagram showing a conventional off-line spacer manufacturing system for LIBs.

Fig. 11 is a schematic configuration diagram showing a conventional off-line type off-line coater.

Detailed Description

Hereinafter, an embodiment of the multilayer film manufacturing method according to the present invention will be described in a case where the method is applied to a LIB spacer manufacturing system (hereinafter, also simply referred to as "system"). In the present system, the inline coater is provided between the extractor and the transverse stretcher from the viewpoint of downsizing of the system, rationalization of the manufacturing process, and the like.

First, prior to the description of the system of the present invention, a conventional system will be briefly described with reference to fig. 10 and 11. The conventional system includes the wet separator manufacturing system 1 of fig. 10 and the off-line coater 8 of fig. 11. In fig. 10, a wet separator manufacturing system 1 includes an extruder 2, a casting roll 3, a longitudinal stretcher 4, a first transverse stretcher 5, an extractor 6, and a second transverse stretcher 7 in this order from an upstream side 9 to a downstream side 10. An off-line coater 8 is provided on the downstream side 10 of the second cross-stretching machine 7 or at another location. The off-line coater 8 is not an in-line structure entering the production line of the wet separator manufacturing system 1, but is independent as an off-line structure.

The specific structure of the off-line coater 8 is shown in fig. 11. The separator film 122 fed out from the winding-out section 121 is coated with a solution containing ceramic fine particles by a coating head 120, and then dried by first, second, and

third dryers

123, 124, and 125. Then, the separator 122A is wound by the winding unit 126.

In contrast, in the embodiment of the system shown in fig. 1 to which the method for producing a multilayer film of the present invention is applied, the wet separator production system 1 has an extruder 2 on the upstream side 9. The film 22 extruded from the die 2A of the extruder 2 toward the downstream side 10 is a raw film containing a resin material constituting the film 22 and a porous forming material (e.g., a solvent or the like). The film 22 is stretched by the longitudinal stretcher 4 and the first transverse stretcher 5, and then supplied to the extractor 6. In addition, the same reference numerals as those shown in fig. 10 are used for substantially the same portions as those of the above-described conventional system. In addition, the film 22 from the time when the resin extruded from the extruder 2 passes through the casting roll 3 to become the film 22 to the time immediately before undergoing various processes to finally obtain the spacer for LIB (multilayer film) is referred to as a "raw film".

The extractor 6 performs cleaning and extraction (removal) of the solvent. The separator 22A is formed by applying a slurry-like coating liquid in which ceramic fine particles are mixed with an aqueous solvent or an organic solvent to the film 22 by the downstream inline coater 8A. The sheet-like separator 22A fed from the inline coater 8A to the downstream side 10 is stretched in the width direction by the second transverse stretcher 7 disposed immediately after the inline coater 8A and is wound up by the winding mechanism 23. The ceramic fine particles used in the present example had an average particle diameter of more than 10 μm and not more than 400 μm.

Here, the "average particle diameter" in the present embodiment is obtained by a laser diffraction scattering method. Specifically, the measurement was carried out by a method in accordance with JIS Z8825 using MT3300 manufactured by Microtrac-bel. The particle size distribution measured and calculated by the device is analyzed by an automatic arithmetic processing device, and the average particle diameter is determined.

The inline coater 8A is configured as shown in fig. 2 (a). The film 22 subjected to the extraction process by the extractor 6 is conveyed to a gravure roll 26 (second roll) of a doctor chamber 25 via a plurality of guide rolls 24. The film 22 is subjected to the above-described coating treatment while being sandwiched in the thickness direction by the gravure roll 26, the pair of entrance-side approach rollers 27, and the exit-side approach roller 28 (the pair of first rollers), and thereafter is conveyed as a sheet-like separator 22A to the second cross stretcher 7. The entrance-side approach roller 27 and the exit-side approach roller 28 abut against the surface of one side of the film 22 at two different positions in the conveying direction of the film 22. The gravure roll 26 is in contact with the other surface of the film 22 at a position sandwiched between the entrance-side approach roller 27 and the exit-side approach roller 28 in the transport direction. The gravure roll 26 has a mechanism (not shown) for rotating the gravure roll 26.

The positional relationship between the gravure roll 26 and the proximity rolls 27 and 28 can be adjusted by a variable mechanism, not shown. Specifically, as shown in fig. 2 b and 2 c, the gravure roll 26 is arranged so as to press the film 22 in a predetermined pressing direction (see the arrow in the drawing), and so that an angle θ (hereinafter also referred to as "inter-roll angle") formed by a line segment connecting the rotation axis 28a of at least one of the entrance-side approach roll 27 and the exit-side approach roll 28 and the rotation axis 26a of the gravure roll 26 and the pressing direction becomes 0 ° or more and 150 ° or less, when viewed from a direction along the rotation axis of the gravure roll 26. The inter-roller angle θ can be adjusted by moving the position of the gravure roller 26 forward and backward (i.e., leftward and rightward in the drawing). When the inter-roller angle θ is 0 °, at least one of the entrance-side approach roller 27 and the exit-side approach roller 28 and the gravure roller 26 are in a positional relationship adjacent to each other in the left-right direction in the drawing.

As shown in fig. 2(a), the gravure roll 26 has an intaglio pattern 26A engraved on its surface in a regular array with quadrangular dams 40 having diamond shapes. The banks 40 are formed with concave portions on the inner side thereof, and when the coating liquid is applied to the film 22 as described later, the coating liquid can be stored on the inner side and transported to the film 22. The intaglio pattern 26A is configured such that an angle θ (θ is 45 ° in fig. 2) of the vertical line 26B with respect to the rotation direction R of the intaglio roller 26 is 0 ° to θ 90 °. In addition, the ratio of the short side to the long side of the quadrangular weir 40 is 0< L.ltoreq.1. The height of the wall of the weir 40 is 0 μm < H.ltoreq.1 mm. The gravure roll 26 has 0 dams 40 < n.ltoreq.500 at 1 inch square. The online coater (gravure coater) 8A does not have the drying function (dryer) of the conventional offline coater 8, which is only drying, but also uses the drying function of the second cross stretcher 7.

In the on-line coater system shown in fig. 1, the drying oven required for the off-line coater shown in fig. 10 doubles as a drying function of the second transverse stretcher 7 in the separator manufacturing system. Namely, the drying furnace used in the past is omitted. Since the pay-off/take-up mechanism 23 also serves as the system, the inline coater 8A may be disposed only after the extractor 6 and before the second cross-stretching machine 7 in the wet separator manufacturing system 1.

Next, a method of applying the coating liquid in the system shown in fig. 1 will be described. First, as a comparative object, FIG. 3 shows an example of a coating method used for a well-known BOPET (Bioxialy-Oriented Polyethylene terephthalate: biaxially Oriented polyester film) or the like. In this example, an adhesive layer is finally formed on the surface of the film 22. First, a coating liquid is prepared by dissolving approximately 10 wt% of a urethane resin or the like which finally becomes an adhesive layer in approximately 90 wt% of water. The coating liquid was applied to the film 22 in a thickness of approximately 4 μm in a state of containing water before stretching in the transverse direction. In the preheating step in the second transverse stretcher 7, after the moisture is evaporated from the coating liquid, the film 22 is stretched approximately 4 times in the width direction. As a result, a layer of urethane resin or the like (i.e., an adhesive layer) having a thickness of about 1 μm is finally laminated in the form of a film 22. Since the urethane resin or the like is in a state of fluidity (for example, a state of paste) even after evaporation of moisture in the coating liquid at the time of stretching in the width direction, even if the film 22 is stretched, the film 22 can follow deformation of the film 22 in a state of being stuck to the film 22.

On the other hand, unlike the example of fig. 3, when a coating liquid containing ceramic fine particles is applied by the inline coater system shown in fig. 1 to form a fine particle layer on the film 22, the film 22 is transversely stretched in a state where the coating liquid is applied to the film in the second transverse stretcher 7. In the production of the spacer for LIB, when the extraction (removal) process is performed, the micropores in the clogged membrane 22 are opened by the transverse stretching, and a porous membrane 22 (multilayer membrane) is formed. Here, if the method of forming the adhesive layer shown in fig. 3 is followed without any change, the micro particle layer may be peeled or broken during the stretching of the film 22. Therefore, the method for producing a multilayer film of the present invention is used.

Specifically, as shown in fig. 4, unlike the BOPET shown in fig. 3, the film 22 (not shown) is first passed through the stretching section 31 while maintaining the coating liquid in a fluid state without drying the coating liquid too much in the preheating section 30. Further, by drying the coating liquid and thermally fixing the film after stretching, peeling or cracking of the fine particle layer can be suppressed. Various parameters of the stretching and drying steps may be set according to the requirements such as the type of the film 22 and the coating thickness.

For example, the coating liquid containing ceramic fine particles is constituted so as to contain approximately 30 to 40 wt% of ceramic fine particles, 60 to 70 wt% of a solvent, and the like. In particular, for use as a heat-resistant insulator, the coating liquid is constituted so as to contain approximately 40 wt% of alumina as ceramic fine particles and approximately 60 wt% of an aqueous solvent.

In the drying step of the separator 22A, the temperature and the air volume of the separator 22A are adjusted so that the amount of heat per unit area applied to the film in the preheating step (preliminary step) is 1.5kW/h or less. Thus, the amount of decrease in the coating liquid before and after the treatment, i.e., the amount of drying (preliminary drying amount), is suppressed to 20 wt% or less. In the subsequent transverse stretching step (main step), the temperature and the air volume are adjusted so that the amount of heat per unit area applied to the film is 1.2kW/h or less. Thus, the amount of reduction before and after the treatment, i.e., the amount of drying (main amount of drying), was suppressed to 20 wt% or less. Further, the unit area is, for example, 1m²。

The evaluation of the multilayer film produced by the system of the present invention will be described below. The physical property values described in the following evaluations were obtained by the methods shown below.

And (3) surface observation: the produced sheet was subjected to platinum vapor deposition with a thickness of 0.3nm by a vacuum vapor deposition apparatus (E-1045, manufactured by Hitachi Highesta Co., Ltd.). The surface of the sheet was observed by using an FE-SEM (SUPRA 55VP, manufactured by Carl Zeiss).

Peel strength: the measurement was carried out in accordance with JIS6854-1 using an automatic drawing machine (AG 20kNG, Shimadzu corporation). Specifically, fig. 9 shows an outline of a test for measuring the peel strength of the separator 22A. A low-tack tape 52 was stuck to the coating film 51 on the separator 22A on the stage 50, the coating film 51 was connected to a jig 54 provided with a load sensor 53 via the low-tack tape 52, and the maximum load of the jig 54 was measured as the peel strength.

(example 1)

The coating and stretching of the coating liquid were performed easily using the apparatus shown in fig. 5 and 6. As the film 22, a polyethylene film (LL-XMTM) manufactured by Domura chemical Co., Ltd., commercially available was used. As the ceramic fine particles contained in the coating liquid, BM-2000M manufactured by ZENO, Japan was used. In order to make the coating thickness condition of the coating liquid constant, as shown in fig. 7, the ratio G/L between the rotation speed G (m/min) of the gravure roll 26 and the film transport speed (line speed m/min) L of the line coater 8A is controlled so as to be 0< G/L ≦ 10. Specifically, as a condition for stably and uniformly applying the coating liquid to the film 22, the transport speed is set to 6m/min and G/L is set to 2. The film 22 coated with the coating liquid under these conditions was processed through 10 stages of a transverse stretcher shown in fig. 8. The conditions shown in example 1 of table 1 below were set with the first section of the inlet shown in fig. 8 as the preheating section, the second section as the stretching section, and the remaining 8 sections as the heat fixing sections. In the stretching section, the film 22 was stretched 1.2 times.

[ Table 1]

(example 2)

An experiment was performed under the same conditions as in example 1 under the conditions shown in example 2 of table 1 with the film transport speed set at 12 m/min.

(example 3)

An experiment was performed under the same conditions as in example 1 under the conditions shown in example 3 of table 1 with the film transport speed set at 16 m/min.

(example 4)

Under the same conditions as in example 1, experiments were carried out under the conditions shown in example 4 of table 1 with the film transport speed set at 20 m/min.

(example 5)

Under the same conditions as in example 1, experiments were carried out under the conditions shown in example 5 of table 1 with the film transport speed set at 24 m/min.

Comparative example 1

The conditions shown in example 1 of table 1 were set with the second section of the entrance of the 10 sections of the transverse stretching machine shown in fig. 8 as the preheating section, the third section as the stretching section, and the remaining 4 sections as the heat fixing sections, and the experiment was performed under the same conditions as in example 1.

Comparative example 2

An experiment was performed under the same conditions as in example 2 of table 1, except that the second section of the inlet of the 10 sections of the transverse stretching machine shown in fig. 8 was a preheating section, the third section was a stretching section, and the remaining 4 sections were heat-fixing sections.

(evaluation)

The evaluation results are shown in table 2 below. In the SEM photographs under the conditions of examples 1 to 2 and 3, it was observed that the fine particle layer formed of the ceramic fine particles was locally cracked due to the film stretching. Comparative examples 1 and 2 are also contemplated. This is considered to be because the heat applied to the preheating section and the stretching section is large, and the stretching is performed in a state where the moisture content of the coating liquid is reduced.

[ Table 2]

In comparison with examples 1 to 3, the state of cracking was improved and the peel strength tended to be improved as the amount of heat applied to the preheating section and the stretching section was reduced. In examples 4 and 5, no cracks were observed in the fine particle layer, and the peel strength was further improved as compared with examples 1 to 3.

Table 2 shows, as a reference example, the observation results of the fine particle layers of the multilayer film produced under the optimum conditions using the off-line type spacer production system for LIB shown in fig. 10. In contrast to this reference example, the surface properties of the microparticle layers shown in the SEM images of examples 4 and 5 produced using the system of the present invention were almost the same, and the peel strength showed equal or higher values. In this way, if the heat and stretching conditions of the preheating section and the stretching section are optimized, a multilayer film having mechanical properties equivalent to or higher than those of an off-line type LIB spacer production system can be produced by the system of the present invention.

As described above, in the step of applying the coating liquid to the film 22, the gravure roll 26 presses the film 22 and applies the coating liquid to the film 22. In particular, as is clear from the above-described experiments and examinations, the

close rollers

27 and 28 and the gravure roll 26 are disposed so that the angle between the rollers is 0 ° to 150 °, and the coating liquid is applied to the film 22, whereby the adhesion between fine particles contained in the coating liquid and the film 22 is significantly improved. In the transverse stretching step, the film 22 is stretched in the width direction in a state where the coating liquid has fluidity (in other words, in a state where the coating liquid is not completely dried). Thus, the coating liquid flows following the stretching of the film 22, and therefore, compared to the case where the transverse stretching is performed in a state where the coating liquid is completely dried to form the fine particle layer, the cracking, peeling, and the like of the fine particle layer finally provided in the multilayer film can be suppressed. Thus, according to the production method of the present embodiment, the fine particles can be appropriately fixed to the surface of the stretched film.

Further, as is clear from the above-described experiments and examinations, the amount of decrease in the coating liquid in the preheating step and the main step included in the transverse stretching step is 20 wt% or less, whereby the following property of the coating liquid to the stretching of the film 22 can be improved.

Further, as is clear from the above-described experiments and examinations, the amount of decrease in the coating liquid is adjusted to be within the above-described range by setting the amount of heat per unit area applied to the film 22 to 1.5kW/h or less in the preliminary step and 1.2kW/h or less in the main step.

Further, as is clear from the above-described experiments and examinations, the coating liquid can be applied to a desired thickness by setting the ratio G/L of the rotation speed G of the gravure roll 26 to the transport speed L of the film 22 to a value greater than 0 and 10 or less.

Further, by arranging an in-line coater between the extractor and the transverse stretcher and producing the multilayer film under the above-described conditions, it is possible to realize on-line production of a high heat-resistant separator obtained by applying ceramic fine particles to a stretched film, which has been produced only by an off-line production system. This can dramatically improve the productivity of the highly heat-resistant separator while suppressing the production cost of the highly heat-resistant separator.

In addition, as another feature of the method for manufacturing a multilayer film used in the present system, the ceramic fine particles have the above-described average particle diameter, and thus the adhesiveness of the ceramic fine particles to the film 22 is improved. Further, the inline coater 8A is configured by the gravure roll 26, the doctor chamber 25, the entrance-side approach roll 27, the exit-side approach roll 28, and the plurality of guide rolls 24, and thus the structure of the inline coater 8A can be miniaturized. This makes it easy to arrange an inline coater between the extractor 6 and the second cross stretcher 7. Further, the line coater 8A (gravure coater) is not provided with a drying function, and the dryer of the second transverse stretcher 7 is used as a dryer for drying, thereby greatly contributing to downsizing of the line coater 8A. The angle, height, and number of the banks 40 provided on the surface of the gravure roll 26 are set according to the type of material to be coated, and the like, thereby enabling optimum coating.

The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above embodiments, and modifications, improvements, and the like can be appropriately made. The material, shape, size, number, arrangement position, and the like of each component of the above-described embodiments are arbitrary as long as the present invention can be realized, and are not limited.

The present application is based on japanese patent application filed on 8/2 in 2017 (japanese patent application 2017-.

Usefulness in industry

The method for producing a multilayer film of the present invention can appropriately fix fine particles to the surface of a stretched film. The present invention having such an effect can be used for manufacturing a separator for a lithium ion battery, for example.

Description of the reference numerals

1 Wet type separator manufacturing System

2 extrusion press

2A mould

3 casting roll

4 longitudinal stretcher

5 first transverse stretcher

6 extraction machine

7 second transverse stretcher

8A on-line coating machine (gravure coating machine)

9 upstream side

10 downstream side

22 film (raw material film)

22A spacer

23 coiling mechanism

24 guide roller

25 scraper chamber

26 gravure roll (second roll)

26A intaglio pattern

27 entry side approach roll (first roll)

28 Exit side approach roll (first roll)

30 preheating section

31 stretch section

40 weir

R direction of rotation

Height H

Claims

1. A method for manufacturing a multilayer film having a fine particle layer made of fine particles provided on a surface of a porous film, comprising:

a coating step of coating a coating liquid containing the fine particles onto the raw material film using a pair of first rollers in a state where the pair of first rollers are in contact with one surface of the raw material film at two different positions in a conveying direction of the raw material film that has undergone the removal step, and a second roller is in contact with the other surface of the raw material film at a position sandwiched between the pair of first rollers in the conveying direction;

in the coating step, the second roller presses the raw material film in a predetermined pressing direction, and an inter-roller angle, which is an angle formed by a line segment connecting a rotation axis position of at least one of the first rollers and a rotation axis position of the second roller, and the pressing direction when viewed in a direction along the rotation axis of the second roller, is 0 ° or more and 150 ° or less.

2. The method for producing a multilayer film according to claim 1,

the amount of the coating liquid reduced before and after the preliminary step in the preliminary step, that is, the preliminary drying amount, is 20 wt% or less,

the amount of decrease of the coating liquid before and after the main step in the main step, that is, the main drying amount, is 20 wt% or less.

3. The method for producing a multilayer film according to claim 2,

4. The method for producing a multilayer film according to any one of claims 1 to 3,

5. The method for producing a multilayer film according to any one of claims 1 to 4,

6. The method for producing a multilayer film according to any one of claims 1 to 5,

the multilayer film is a separator for a lithium ion battery.