WO2019027001A1

WO2019027001A1 - Multilayer film manufacturing method

Info

Publication number: WO2019027001A1
Application number: PCT/JP2018/029037
Authority: WO
Inventors: 諭中村; 亮石黒; 共祐片本
Original assignee: 株式会社日本製鋼所
Priority date: 2017-08-02
Filing date: 2018-08-02
Publication date: 2019-02-07
Also published as: TW201911625A; JP2019029282A; JP6876571B2; CN111033800A; CN117080676A; TWI736787B

Abstract

A multilayer film manufacturing method provided with: a step of removing from an original rolled film (22) a pore forming material; a step of applying a coating liquid including fine particles, using a second roll (26) while causing first rolls (27, 28) and the second roll to contact the original rolled film; a step of stretching the original rolled film in a width direction in a state in which the coating liquid has fluidity; and a step of drying the coating liquid to form a multilayer film to which a fine particle layer has been fixed. During coating, the angle formed by a line connecting the rotating axis position of at least one of the first rolls and the rotating axis position of the second roll and the direction in which the original rolled film is pressed by the second roll is not less than 0° and not more than 150°.

Description

Method of manufacturing multilayer film

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

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

As an example, a coating liquid prepared by mixing ceramic fine particles such as alumina and silica, which are inorganic materials, and a solvent is applied to the surface of a stretched film, and then the solvent is dried, thereby comprising these fine particles on the surface of the stretched film. The method of providing a film is used (refer patent document 1 and patent document 2). Moreover, the method of providing the film | membrane comprised from these resin materials on the surface of a stretched film is also used by apply | coating resin materials, such as polyamide and a polyimide which are organic materials, on the surface of a stretched film. The organic material and the inorganic material may be mixed and used (see Patent Document 3 and Patent Document 4).

Japan JP 2013-114751 Japan JP 2014-203680 gazette Japanese Patent Laid-Open Publication 2009-21265 Japanese Patent No. 4460028

In a stretched film used as a LIB separator, generally, micropores are formed due to the movement of lithium ions and the like. The fine pores can be formed, for example, by mixing a solvent as a material of a stretched film, forming a film, and then extracting the solvent or the like (so-called wet method). However, when using this method, since the micropores may be clogged due to shrinkage or the like of the stretched film in the process of extracting the solvent or the like, the solvent or the like is generally extracted to reopen the clogged micropores. After that, the stretched film is restretched. In this re-stretching, adjusting the size of the microporous is also performed.

By the way, when a film (hereinafter, also referred to as “fine particle layer”) composed of various kinds of fine particles is disposed on a stretched film to improve the heat resistance described above, the viewpoint of downsizing of the manufacturing system, rationalization of manufacturing processes, etc. Therefore, it may be preferable to provide a fine particle layer on the stretched film at a time before the above-described re-stretching. However, since the fine particle layer is less likely to be deformed than the material constituting the stretched film, it is feared that cracking of the fine particle layer and peeling of the fine particle layer from the stretched film may occur in the re-stretching process. In other words, when the fine particle layer is provided on the stretched film before various stretching processes including re-stretching, there is a possibility that the fine particle layer can not be maintained in a properly fixed state on the stretched film.

One of the objects of the present invention is to provide a method for producing a multilayer film in which the fine particle layer can be properly fixed to the surface of the stretched film.

[1] In the first aspect of the present invention, a method of producing a multilayer film is
A method for producing a multilayer film, in which a fine particle layer composed of fine particles is provided on the surface of a porous film,
Removing the porous forming material from a raw film comprising a resin material constituting the film and the porous forming material;
A pair of first rolls abut on one surface of the raw film at two different positions in the carrying direction of the raw film after the removing step, and the pair of first rolls in the carrying direction A coating liquid containing the fine particles is applied to the raw film using the second roll while the second roll is in contact with the other surface of the raw film at a position sandwiched between , Coating process,
A lateral stretching step of stretching the raw film in the width direction while maintaining the flowability of the coating liquid applied to the raw film;
A fixing step of drying the coating liquid to fix the fine particle layer on the film to form the multilayer film;
Equipped with
In the applying step, the second roll presses the raw film along a predetermined pressing direction, and when viewed from the direction along the rotation axis of the second roll, the second roll presses at least one of the first rolls. The inter-roll angle, which is the angle between a line segment connecting the rotational axis position and the rotational axis position of the second roll and the pressing direction, is 0 ° or more and 150 ° or less.

In the first aspect, in the coating step, the coating liquid is applied to the raw film while the second roll presses the raw film. In particular, according to experiments and studies conducted by the inventor, the coating liquid is placed in a state in which the first roll and the second roll are disposed such that the above-described roll-to-roll angle is 0 ° or more and 150 ° or less. It has been revealed that the adhesion between the fine particles contained in the coating liquid and the raw film is remarkably improved by applying the raw film. Furthermore, in the transverse stretching step, the raw film is stretched in the width direction in a state in which the coating liquid has fluidity (in other words, a state in which the coating liquid is not completely dried). As a result, the coating liquid flows following the stretching of the raw film, so the final multilayer film is compared to the case in which the coating liquid is completely dried to form the fine particle layer and the transverse drawing is performed. Cracks, peeling, etc. of the fine particle layer provided on Therefore, according to the manufacturing method which concerns on a 1st side, microparticles | fine-particles can be fixed appropriately on the surface of a stretched film.

[2] According to a second aspect of the present invention, in the first aspect,
In the transverse stretching step,
Including a preliminary step of preheating and a main step of stretching in the width direction under heating;
The preliminary drying amount which is the reduction amount of the coating liquid before and after the preliminary process in the preliminary process is 20 wt% or less,
The main drying amount which is the reduction amount of the coating liquid before and after the main step in the main step is 20 wt% or less.

According to experiments and studies conducted by the inventor of the second aspect, in the preheating step and the present step included in the transverse drawing step, the reduction amount of the coating liquid is set to 20 wt% or less. It has been clarified that the followability of the coating liquid to film stretching can be improved. Therefore, according to the manufacturing method which concerns on a 2nd side surface, microparticles | fine-particles can be further appropriately fixed on the surface of a stretched film.

[3] In the third aspect of the present invention, in the second aspect,
The preliminary step is
Including a process of heating the raw film so that the amount of heat per unit area given to the raw film is 1.5 kW / h or less,
The main process is
The method includes heating the raw film so that the amount of heat per unit area given to the raw film is 1.2 kW / h or less.

According to experiments and studies conducted by the inventor of the third aspect, the heat amount per unit area given to the raw film in the preliminary step is set to 1.5 kW / h or less, and the raw film is produced in this step It is clear that setting the amount of heat per unit area to be less than or equal to 1.2 kW / h given to can adjust the amount of decrease of the coating liquid as defined in the above-mentioned second aspect. Therefore, according to the manufacturing method which concerns on a 3rd side, microparticles | fine-particles can be further appropriately fixed to the surface of a stretched film.

[4] In the fourth aspect of the present invention, in any one of the first to third aspects,
The application process is
A process is included in which the ratio G / L of the rotational speed G of the second roll to the transport speed L of the raw film is greater than 0 and 10 or less.

According to experiments and studies conducted by the inventor of the fourth aspect, the ratio G / L of the rotational speed G of the second roll to the transport speed L of the original film is set to a value larger than 0 and 10 or less. By setting, it is clear that the coating liquid can be applied so as to have a desired thickness. Therefore, according to the manufacturing method which concerns on a 4th side, microparticles | fine-particles can be further appropriately fixed on the surface of a stretched film.

[5] In a fifth aspect of the present invention, in any one of the first to fourth aspects,
The fixing step is
A process of fixing the fine particle layer on the surface of the raw film is realized by gradually drying the coating liquid under heating while stretching the raw film in the transport direction.

According to the fifth aspect, after the micropores of the raw film are opened by the transverse drawing step (that is, the above-described redrawing), the fine particle layer can be formed on the surface of the raw film. Accordingly, since the fine particle layer is not formed at the time of the lateral stretching step, cracking, peeling, and the like of the fine particle layer finally provided in the multilayer film are suppressed. Furthermore, the degree of micropore opening can be adjusted by stretching the raw film in the transport direction. Therefore, according to the manufacturing method which concerns on a 5th side, microparticles | fine-particles can be fixed appropriately on the surface of the stretched film which has a micropore of a desired opening degree.

[6] In the sixth aspect of the present invention, in any one of the first to fifth aspects,
The multilayer film is used as a lithium ion battery separator.

According to the sixth aspect, the method for producing a multilayer film according to any one of the first to fifth aspects described above can be applied to a method for producing a lithium ion battery separator having high industrial value.

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

FIG. 1 is a schematic block diagram showing a LIB separator manufacturing system according to the present invention. Fig.2 (a) is a concrete block diagram of the in-line coater of FIG. 1, FIG.2 (b) and FIG.2 (c) are schematic which shows the roll angle specified by a gravure roll and a near roll. FIG. 3 is a schematic configuration view showing an in-line adhesive coating method for BOPET in another form of FIG. 1. FIG. 4 is a schematic configuration view showing an in-line ceramic coating method for a separator in another form of FIG. 1. FIG. 5 is a block diagram of a demonstration device of a LIB separator manufacturing system according to the present invention. FIG. 6 is a schematic block diagram showing the main part of the demonstration device of FIG. FIG. 7 is an explanatory view showing a coating thickness adjusting condition in the in-line coater of FIG. FIG. 8 is an explanatory view showing the transverse stretching / drying conditions for the in-line coater of FIG. FIG. 9 is an explanatory view of a peel strength measurement test for the separator in the present invention. FIG. 10 is a schematic block diagram showing a conventional off-line LIB separator manufacturing system. FIG. 11 is a schematic block diagram showing a conventional off-line type off-line coater.

Hereinafter, an embodiment of the multilayer film manufacturing method according to the present invention will be described in the case where it is applied to a separator manufacturing system for LIB (hereinafter, also simply referred to as “system”). In the present system, an in-line coater is provided between the extractor and the lateral stretcher in terms of downsizing of the system, rationalization of the manufacturing process, and the like.

First, prior to describing the system according to the present invention, a conventional system will be briefly described with reference to FIGS. 10 and 11. FIG. The conventional system comprises the wet separator manufacturing system 1 of FIG. 10 and the off-line coater 8 of FIG. In FIG. 10, the wet separator manufacturing system 1 includes an extruder 2, a cast roll 3, a longitudinal stretcher 4, a first horizontal stretcher 5, and an extractor 6 in order from the upstream side 9 to the downstream side 10. And a second transverse stretcher 7. An off-line coater 8 is provided on the downstream side 10 of the second horizontal stretching machine 7 or at another place. The off-line coater 8 is not an in-line configuration that falls within the line of the wet separator manufacturing system 1 but is independent as an off-line configuration.

The specific configuration of the off-line coater 8 is shown in FIG. The film 122 for a separator delivered from the unwinding part 121 is dried by the first, second and

third dryers

123, 124 and 125 after the solution containing the ceramic fine particles is applied by the coater head 120. Thereafter, the separator 122A is wound by the winding unit 126.

On the other hand, in the embodiment of the system to which the method for manufacturing a multilayer film according to the present invention shown in FIG. 1 is applied, the wet separator manufacturing system 1 has the 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 comprising a resin material constituting the film 22 and a porous forming material (for example, 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. The same reference numerals as shown in FIG. 10 are used for substantially the same parts as the above-described conventional system. It should be noted that from the time when the resin extruded from the extruder 2 passes through the cast roll 3 to form the film 22, the film 22 is subjected to various treatments and until just before the LIB separator (multilayer film) is finally obtained. We call it "raw film".

In the extractor 6, washing and solvent extraction (removal) processing is performed. A slurry-like coating liquid in which ceramic fine particles are mixed with an aqueous solvent or an organic solvent is applied on the film 22 by the inline coater 8A on the downstream side, and a separator 22A is formed. The sheet-like separator 22A sent from the in-line coater 8A to the downstream side 10 is stretched in the width direction by the second transverse stretcher 7 disposed immediately after the in-line coater 8A and wound by the winding mechanism 23 . The average particle size of the ceramic fine particles used in this example is more than 10 μm and 400 μm or less.

Here, the “average particle diameter” in the present embodiment was determined by a laser diffraction scattering method. Specifically, measurement is performed according to JIS Z8825 using MT3300 manufactured by Microtrack Bell Corporation. Then, the average particle diameter is specified by analyzing the particle size distribution measured and calculated by the device using an automatic arithmetic processing device.

The in-line coater 8A is configured as shown in FIG. 2 (a). The film 22 extracted and processed by the extractor 6 is conveyed toward the gravure roll 26 (second roll) of the doctor chamber 25 through a plurality of guide rolls 24. The film 22 is subjected to the above-described coating treatment in a state of being sandwiched in the thickness direction by the gravure roll 26, the pair of entrance side near rolls 27, and the exit side near rolls 28 (a pair of first rolls). Is sent to the second transverse drawing machine 7 as a separator 22A of The inlet near roll 27 and the outlet near roll 28 are in contact with one surface of the film 22 at two different positions in the transport direction of the film 22. The gravure roll 26 is in contact with the other surface of the film 22 at a position where the gravure roll 26 is sandwiched between the entry side near roll 27 and the exit side near roll 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 near rolls 27 and 28 can be adjusted by a variable mechanism (not shown). Specifically, as shown in FIGS. 2 (b) and 2 (c), the gravure roll 26 presses the film 22 along a predetermined pressing direction (see the arrow in the figure), and When viewed from the direction along the axis of rotation of the roller, the angle formed by the line connecting the axis of rotation 26a of at least one of the inlet side near roll 27 and outlet side near roll 28 and the axis of rotation 26a of the gravure roll 26 and the pressing direction. It arrange | positions so that (theta) (henceforth "the angle between rolls") may be 0 degree or more and 150 degrees or less. The roll-to-roll angle θ can be adjusted by moving the position of the gravure roll 26 back and forth (that is, to the left and right in the figure). When the inter-roll angle θ is 0 °, at least one of the inlet side near roll 27 and the outlet side near roll 28 and the gravure roll 26 are in a positional relationship adjacent to each other in the left and right in the drawing.

As shown in FIG. 2A, the gravure roll 26 has, on its surface, a gravure pattern 26A in which a square screed 40 including a rhombus is engraved in a regular arrangement. The crucible 40 defines a recess on the inner side, and when applying the coating liquid to the film 22 as described later, the coating liquid may be conveyed toward the film 22 while the coating liquid is stored inside. it can. The gravure pattern 26A is configured such that the angle θ (θ = 45 ° in FIG. 2) of the vertical line 26B with respect to the rotational direction R of the gravure roll 26 is 0 ° ≦ θ ≦ 90 °. Further, the ratio of the short side to the long side of the square ridge 40 is 0 <L ≦ 1. The height of the wall of the crucible 40 is 0 μm <H ≦ 1 mm. The gravure roll 26 has 0 pieces <N ≦ 500 pieces of ridges 40 in 1 inch square. The inline coater (gravure coater) 8A does not have the drying function (dryer) of only the drying which the conventional offline coater 8 has, and is also used as the drying function of the second horizontal stretching machine 7.

In the in-line coater system shown in FIG. 1, the drying furnace required for the off-line coater shown in FIG. 10 is also used as the drying function of the second transverse stretcher 7 in the separator manufacturing system. That is, the drying furnace conventionally used is omitted. Further, since the delivery and take-up mechanism 23 is also used in the system, only the in-line coater 8A may be disposed after the extractor 6 in the wet separator manufacturing system 1 and in front of the second transverse stretcher 7.

Then, the coating method of the coating liquid in the system shown in FIG. 1 is demonstrated. First, an example of a coating method used for well-known BOPET (Bioxially-Oriented Polyethylene terephthalate) etc. is shown in FIG. 3 as a comparison object. In this example, an adhesive layer is finally formed on the surface of the film 22. First, a coating solution is prepared in which about 10 wt% of polyurethane resin and the like that finally becomes an adhesive layer is dissolved in about 90 wt% of water. The coating liquid is applied onto the film 22 with a thickness of about 4 μm before transverse stretching in a state containing water. In the preheating step in the second horizontal stretching machine 7, after the water is evaporated from the coating solution, the film 22 is stretched by about 4 times in the width direction. As a result, finally, a layer of polyurethane resin or the like having a thickness of about 1 μm (that is, an adhesive layer) is laminated in a film 22 shape. At the time of stretching in the width direction, the polyurethane resin or the like is still in a flowable state (for example, in a state like a paste) even after evaporation of water in the coating liquid, so the film 22 is stretched. Even if it is allowed to move, the deformation of the film 22 can be followed in a state of being stuck to the film 22.

On the other hand, unlike the example of FIG. 3, when the coating liquid containing ceramic fine particles is applied by the in-line coater system shown in FIG. 1 to form the fine particle layer on the film 22, the coating liquid in the second horizontal stretching machine 7 In the state of being applied on the film 22, it will be transversely stretched. In addition, in the production of the LIB separator, the micropores in the film 22 blocked in the extraction (removal) process are opened by this transverse drawing, and the porous film 22 (multilayer film) is formed. . Here, if the method of forming the adhesive layer shown in FIG. 3 is used as it is, there is a concern that peeling or cracking of the fine particle layer may occur during the stretching of the film 22. Therefore, the method for producing a multilayer film according to the present invention is used.

Specifically, as shown in FIG. 4, unlike in the case of BOPET shown in FIG. 3, first, in the preheating zone 30, the moisture of the coating liquid is not dried so much, and the coating liquid maintains the fluidity state While the film 22 (not shown) is passed through the drawing zone 31. Then, by performing drying of the coating liquid and heat setting of the film after stretching, it is possible to suppress peeling and cracking of the fine particle layer. In addition, what is necessary is just to set the various parameters which concern on a extending | stretching and a drying process according to requirements, such as a kind of film 22, and coating thickness.

For example, a coating liquid containing ceramic fine particles can be configured to contain about 30 to 40 wt% of ceramic fine particles and 60 to 70 wt% of a solvent or the like. In particular, for heat-resistant separators, the coating liquid can be configured to contain about 40 wt% of alumina as ceramic particles and about 60 wt% of a water-based solvent.

In the drying step of the separator 22A, the temperature and the air amount of the separator 22A are adjusted so that the heat amount per unit area given to the film in the preheating step (preliminary step) is 1.5 kW / h or less. Thereby, the drying amount (preliminary drying amount) which is the reduction amount of the coating liquid before and behind this process is suppressed to 20 wt% or less. Further, in the subsequent transverse stretching step (this step), the temperature and the air flow are adjusted so that the heat quantity per unit area given to the film is 1.2 kW / h or less. Thereby, the dry amount (main dry amount) which is a reduction amount before and after this treatment is suppressed to 20 wt% or less. The unit area is, for example, 1 m ² .

Hereinafter, evaluation of the multilayer film manufactured using the system which concerns on this invention is demonstrated. Each physical property value described in the following evaluation is a value obtained by the method shown below.
Surface observation: The prepared sheet was subjected to platinum deposition with a thickness of 0.3 nm using a vacuum deposition apparatus (E-1045 manufactured by Hitachi High-Technologies Corporation). This sheet was subjected to surface observation using an FE-SEM (SUPRA 55 VP manufactured by Carl Zeiss).
Peeling strength: Carried out according to JIS 6854-1 using an autograph (AG · 20 kNG manufactured by Shimadzu Corporation). Specifically, a test outline for measuring the peel strength of the separator 22A is shown in FIG. The low adhesive tape 52 is attached to the coating film 51 on the separator 22A on the table 50, and the coating film 51 is connected to the jig 54 provided with the load cell 53 via the low adhesive tape 52. The maximum load of is measured as the peel strength.

Example 1
The coating liquid was simply applied and stretched using the apparatus shown in FIGS. 5 and 6. As the film 22, a commercially available polyethylene film (LL-XMTM) manufactured by Futamura Chemical Co., Ltd. was used. Nippon Zeon BM-2000M was used as the ceramic fine particles contained in the coating liquid. In order to make coating thickness conditions of a coating liquid constant, as shown in FIG. 7, rotational speed G (m / min) and film conveyance speed (= line speed. M / min) of the gravure roll 26 of the in-line coater 8A. The ratio G / L of L was controlled to be 0 <G / L ≦ 10. Specifically, the transport speed was set to 6 m / min, and G / L = 2, as the conditions under which the coating liquid can be coated uniformly on the film 22 in a particularly stable manner. The film 22 coated with the coating liquid under these conditions was treated so as to pass through the 10 zones of the transverse stretcher shown in FIG. The conditions shown in Example 1 of Table 1 below were set with the first zone at the entrance shown in FIG. 8 as the preheating unit, the second zone as the extension unit, and the remaining eight zones as the heat setting unit. In the stretched portion, the film 22 was stretched 1.2 times.

(Example 2)
It experimented on the conditions shown in Example 2 of Table 1 by setting film conveyance speed to 12 m / min on the same conditions as Example 1.

(Example 3)
It experimented on the conditions shown in Example 3 of Table 1 by setting film conveyance speed to 16 m / min on the same conditions as Example 1.

(Example 4)
It experimented on the conditions shown in Example 4 of Table 1 by making film conveyance speed into 20 m / min on the same conditions as Example 1.

(Example 5)
It experimented on the conditions shown in Example 5 of Table 1 by setting film conveyance speed to 24 m / min on the same conditions as Example 1.

(Comparative example 1)
Among the 10 zones of the transverse stretching machine shown in FIG. 8, the second zone of the entrance was shown in Example 1 of Table 1 as the preheating zone, the third zone as the stretching zone, and the remaining 4 zones as the heat setting zone. The conditions were set, and the others were conducted under the same conditions as in Example 1.

(Comparative example 2)
Of the 10 zones of the transverse stretching machine shown in FIG. 8, the second zone of the entrance is the preheating zone, the third zone is the stretching zone, and the remaining 4 zones are the heat setting zone, under the same conditions as in Example 2 of Table 1 above. Experimented with.

(Evaluation)
The results of the evaluation are shown in Table 2 below. In the SEM photographs of the conditions of Examples 1 to 2 and 3, it is observed that the fine particle layer of the ceramic fine particles is partially cracked by film stretching. The same applies to Comparative Examples 1 and 2. This is considered to be caused by stretching in a state in which the amount of heat given to the preheating portion and the stretching portion is large and the water content of the coating liquid is reduced.

When Examples 1 to 3 are compared, the state of cracking is improved and the peel strength tends to be improved as the amount of heat given to the preheating part and the drawing part is reduced. Furthermore, in Examples 4 and 5, no crack was 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, observation results of the fine particle layer of the multilayer film manufactured under optimum conditions using the off-line type LIB separator manufacturing system shown in FIG. The surface properties of the fine particle layer shown in the SEM images of Examples 4 and 5 manufactured using the system according to the present invention are substantially the same as those of this reference example, and the peel strengths show equal or higher values. As described above, by optimizing the heat quantity and the stretching conditions of the preheating unit and the stretching unit, the system according to the present invention can produce a multilayer film having mechanical properties equal to or more than the off-line LIB separator manufacturing system.

As described above, in the step of applying the coating liquid to the film 22, the gravure roll 26 applies the coating liquid to the film 22 while pressing the film 22. In particular, according to the above-described experiment and discussion, the coating liquid is applied to the film 22 in a state where the near rolls 27, 28 and the gravure roll 26 are disposed such that the inter-roll angle is 0 ° or more and 150 ° or less. By doing this, it was revealed that the adhesion between the fine particles contained in the coating liquid and the film 22 is significantly improved. Furthermore, in the transverse stretching step, the film 22 is stretched in the width direction in a state in which the coating liquid has fluidity (in other words, a state in which the coating liquid is not completely dried). As a result, the coating liquid flows following the stretching of the film 22. Therefore, compared with the case where the coating liquid is completely dried and the fine particle layer is formed, the multilayer film is finally formed into a multilayer film. Cracking and peeling of the provided particle layer are suppressed. Therefore, according to the manufacturing method which concerns on this embodiment, microparticles | fine-particles can be fixed appropriately on the surface of a stretched film.

Furthermore, according to the above-described experiments and considerations, in the preheating step and the present step included in the lateral stretching step, by setting the reduction amount of the coating fluid to 20 wt% or less, the coating fluid to the film 22 is stretched. It became clear that the followability could be improved.

Furthermore, according to the above-described experiments and considerations, the amount of heat per unit area given to the film 22 in the preliminary step is set to 1.5 kW / h or less, and the amount of heat per unit area given to the film 22 in this step is 1.2 kW. It has become clear that by setting the ratio to / h or less, the amount of decrease in the coating liquid can be adjusted to be set in the above-mentioned range.

Furthermore, according to the above-described experiments and considerations, the coating liquid is obtained by setting the ratio G / L of the rotational speed G of the gravure roll 26 to the transport speed L of the film 22 to a value larger than 0 and 10 or less. It has been found that it can be applied to have the desired thickness.

Furthermore, by arranging an in-line coater between the extractor and the transverse drawing machine to manufacture a multilayer film under the conditions described above, it is possible to use a stretched film that has hitherto been able to be manufactured only with an off-line manufacturing system. Production of a high heat resistant separator by coating of ceramic fine particles on the surface was inlined. Thereby, the manufacturing cost of the high heat resistant separator can be suppressed, and the productivity of the high heat resistant separator can be dramatically improved.

In addition, as another feature of the method for producing a multilayer film used in the present system, when the ceramic fine particles have the above-described average particle diameter, the adhesiveness of the ceramic fine particles to the film 22 becomes good. Further, by configuring the inline coater 8A from the gravure roll 26, the doctor chamber 25, the inlet near roll 27, the outlet near roll 28, and the plurality of guide rolls 24, the configuration as the inline coater 8A can be miniaturized. Therefore, it is easy to arrange the in-line coater between the extractor 6 and the second transverse drawing machine 7. In addition, the inline coater 8A (gravure coater) is not provided with a drying function, and the use of the dryer of the second horizontal stretching machine 7 as a dryer for drying can greatly contribute to the miniaturization of the inline coater 8A. Further, optimum coating can be performed by setting the angle, height, and number of the above-described ridges 40 provided on the surface of the gravure roll 26 according to the type of the material to be coated, and the like.

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 embodiments described above, and appropriate modifications, improvements, etc. are possible. In addition, the material, shape, size, number, arrangement location, and the like of each component in the embodiment described above are arbitrary and not limited as long as the present invention can be achieved.

This application is based on Japanese Patent Application (Patent Application No. 201-7149893) filed on Aug. 2, 2017, the contents of which are incorporated herein by reference.

The method for producing a multilayer film according to the present invention can properly fix the fine particles on the surface of the stretched film. The present invention having this effect can be utilized, for example, in the manufacture of a lithium ion battery separator.

1 Wet Separator Manufacturing System 2 Extruder 2A Die 3 Cast Roll 4 Longitudinal Stretcher 5 First Horizontal Stretcher 6 Extractor 7 Second Horizontal Stretcher 8A In-line Coater (Gravure Coater)
9 upstream 10 downstream 22 film (raw film)
22A Separator 23 Take-up Mechanism 24 Guide Roll 25 Doctor Chamber 26 Gravure Roll (Second Roll)
26A Gravure Pattern 27 Entry Side Near Roll (1st Roll)
28 Exit near roll (1st roll)
30 preheating zone 31 stretching zone 40 堰 R rotation direction H height

Claims

A method for producing a multilayer film, in which a fine particle layer composed of fine particles is provided on the surface of a porous film,
Removing the porous forming material from a raw film comprising a resin material constituting the film and the porous forming material;
A pair of first rolls abut on one surface of the raw film at two different positions in the carrying direction of the raw film after the removing step, and the pair of first rolls in the carrying direction A coating liquid containing the fine particles is applied to the raw film using the second roll while the second roll is in contact with the other surface of the raw film at a position sandwiched between , Coating process,
A lateral stretching step of stretching the raw film in the width direction while maintaining the flowability of the coating liquid applied to the raw film;
A fixing step of drying the coating liquid to fix the fine particle layer on the film to form the multilayer film;
Equipped with
In the applying step, the second roll presses the raw film along a predetermined pressing direction, and when viewed from the direction along the rotation axis of the second roll, the second roll presses at least one of the first rolls. The inter-roll angle, which is the angle between the line segment connecting the rotational axis position and the rotational axis position of the second roll and the pressing direction, is 0 ° or more and 150 ° or less.
Method of manufacturing multilayer film.
In the method for producing a multilayer film according to claim 1,
In the transverse stretching step,
Including a preliminary step of preheating and a main step of stretching in the width direction under heating;
The preliminary drying amount which is the reduction amount of the coating liquid before and after the preliminary process in the preliminary process is 20 wt% or less,
The main drying amount which is a reduction amount of the coating liquid before and after the main step in the main step is 20 wt% or less.
Method of manufacturing multilayer film.
In the method for producing a multilayer film according to claim 2,
The preliminary step is
Including a process of heating the raw film so that the amount of heat per unit area given to the raw film is 1.5 kW / h or less,
The main process is
The method includes heating the raw film so that the amount of heat per unit area given to the raw film is 1.2 kW / h or less.
Method of manufacturing multilayer film.
In the method for producing a multilayer film according to any one of claims 1 to 3,
The application process is
Including a process in which the ratio G / L of the rotational speed G of the second roll to the transport speed L of the raw film is greater than 0 and 10 or less.
Method of manufacturing multilayer film.
In the method for producing a multilayer film according to any one of claims 1 to 4,
The fixing step is
And fixing the fine particle layer on the surface of the raw film by gradually drying the coating liquid under heating while stretching the raw film in the transport direction.
Method of manufacturing multilayer film.
In the method for producing a multilayer film according to any one of claims 1 to 5,
The multilayer film is a lithium ion battery separator.
Method of manufacturing multilayer film.