Laminated film and method for producing laminated film

Abstract

Provided is a laminated film produced by co-extruding a liquid crystal polymer and an aromatic polyether ketone, the laminated film comprising: a liquid crystal polymer layer comprising the liquid crystal polymer; and aromatic polyether ketone layers comprising the aromatic polyether ketone, the aromatic polyether ketone layers being laminated on both surfaces of a liquid crystal polymer film. The degree of crystallinity of the aromatic polyether ketone layer is 40% or less, and the thickness of the liquid crystal polymer layer is 100 μm or more.

Description

Stacked film and method for manufacturing the same

[0001] The present invention relates to a stacked film and a method for manufacturing the same.

[0002] With the advancement of mobile communication technology, communication speed and capacity have increased, and the frequency used for communication has become higher. In the fifth-generation mobile communication system, the 3.7 GHz band and 4.5 GHz band in the Sub6 band, and the 28 GHz band in the millimeter-wave band are used. Furthermore, in the sixth-generation mobile communication system, frequency bands in the range of 90 GHz to 300 GHz are being considered. Since the transmission loss of a signal flowing through a circuit increases as the frequency becomes higher, a circuit with low transmission loss is required.

[0003] A circuit is composed of a conductor such as a copper wire through which a signal passes and an insulating material that holds it. In devices used for mobile communication such as smartphones, miniaturization and weight reduction are required, so a flexible printed circuit board (FPC) that is lightweight and can be freely bent is used, and a liquid crystal polymer film is used as the insulating material of the FPC. As a material that can be used for such an insulating material, a liquid crystal polymer film with reduced anisotropy and excellent smoothness is known (for example, Patent Document 1). Patent Document 1 discloses a method for manufacturing a stretched liquid crystal polymer film in which a liquid crystal polymer and a polyether ether ketone polymer (PEEK) are each melt-kneaded, these are supplied to a multi-manifold T-die and co-extruded to obtain a stacked film, and after stretching the stacked film, the PEEK layer is finally peeled off to adjust the surface roughness and surface orientation degree.

[0004] On the other hand, the signal flowing through the conductor tends to flow on the conductor surface as the frequency becomes higher due to the skin effect. It is known that the transmission loss due to this skin effect decreases as the thickness of the insulating material (dielectric material) increases (Non-Patent Document 1). Therefore, it is required that the thickness of the insulating material in a high-frequency circuit is 30 μm or more, preferably 50 μm or more.

[0005] International Publication No. 2024 / 004952

[0006] Yoshifumi Takada et al., "Analysis of the Influence of Wiring Structure and Material Properties on Transmission Characteristics," Proceedings of the 17th Annual Conference on Electronics Packaging, 2003.

[0007] However, the method described in Patent Document 1 has a problem in that the co-extruded PEEK layer and liquid crystal polymer layer tend to peel off, especially when the liquid crystal polymer layer is relatively thick, and when the laminated film is stretched, this peeling can cause rupture or perforation in the liquid crystal polymer layer. For this reason, it has been difficult to manufacture a stretched liquid crystal polymer film that is relatively thick and has few ruptures or perforations using the method described in Patent Document 1.

[0008] The object of the present invention is to provide a laminated film that can provide a stretched liquid crystal polymer film that is relatively thick and less prone to breakage and perforation, and a method for manufacturing a laminated film.

[0009] [1] One aspect of the present invention is a laminated film produced by co-extruding a liquid crystal polymer and an aromatic polyether ketone, comprising a liquid crystal polymer layer made of the liquid crystal polymer and an aromatic polyether ketone layer made of the aromatic polyether ketone laminated on both sides of the liquid crystal polymer layer, wherein the degree of crystallinity of the aromatic polyether ketone layer is 40% or less and the thickness of the liquid crystal polymer layer is 100 μm or more.

[0010] [2] Embodiment 2 of the present invention is a laminated film of Embodiment 1 in which the degree of crystallinity of the aromatic polyetherketone layer is 30% or less.

[0011] [3] A third aspect of the present invention is the laminated film according to claim 1 or 2, wherein the thickness of the aromatic polyetherketone layer is 50 μm or less.

[0012] [4] Embodiment 4 of the present invention is a laminated film according to any of embodiments 1 to 3, wherein the length in the longitudinal direction is 10 m or more.

[0013] [5] Embodiment 5 of the present invention is a method for manufacturing a laminated film, comprising the steps of obtaining an unsolidified laminated film by co-extruding a liquid crystal polymer and a crystalline resin using a T-die, and winding and solidifying the unsolidified laminated film on a cast roll at a temperature of 150°C or lower, wherein the air gap, which is the distance between the exit of the T-die and the contact position between the cast roll and the unsolidified laminated film, is 100 mm or less.

[0014] [6] Embodiment 6 of the present invention is a method for manufacturing a laminated film according to Embodiment 5, wherein the air gap is 50 mm or less.

[0015] According to the laminated film of the present invention, it is possible to manufacture a stretched liquid crystal polymer film that is relatively thick and less prone to breakage and perforation.

[0016] Figure 1 is a schematic diagram illustrating the method for manufacturing a laminated film according to an embodiment of the present invention.

[0017] <Laminated Film> The laminated film of the present invention is composed of a liquid crystal polymer layer and a pair of aromatic polyetherketone layers laminated on both sides of the liquid crystal polymer layer. The laminated film of the present invention is used to manufacture a stretched liquid crystal polymer film by stretching it and then peeling the aromatic polyetherketone layers from the liquid crystal polymer layer.

[0018] <Liquid Crystal Polymer Layer> The liquid crystal polymer layer is a film made of a liquid crystal polymer. The liquid crystal polymer is not particularly limited, but liquid crystal polyesters that exhibit thermotropic liquid crystal properties are preferred. Examples of such liquid crystal polyesters include aromatic polyesters that exhibit liquid crystal properties when melted, synthesized from monomers such as aromatic diols, aromatic carboxylic acids, and hydroxycarboxylic acids. Specifically, examples include polycondensates of ethylene terephthalate and parahydroxybenzoic acid, polycondensates of phenol and phthalic acid and parahydroxybenzoic acid, and polycondensates of hydroxynaphthoic acid and parahydroxybenzoic acid. In particular, from the viewpoint of excellent mechanical properties, electrical properties, heat resistance, etc., an aromatic polyester liquid crystal polymer is preferred, which has 6-hydroxy-2-naphthoic acid and its derivatives as its basic structure and contains at least one monomer component selected from the group consisting of parahydroxybenzoic acid, terephthalic acid, isophthalic acid, 6-naphthalenedicarboxylic acid, 4,4'-biphenol, bisphenol A, hydroquinone, 4,4-dihydroxybiphenol, ethylene terephthalate, and their derivatives. Each liquid crystal polyester can be used individually or in any combination and ratio of two or more types. The liquid crystal polymer content is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass, based on the total amount of the liquid crystal polymer layer.

[0019] The synthesis method for liquid crystal polyesters is not particularly limited and can be one of known methods, but for example, melt polymerization, melt acidolysis, slurry polymerization, etc., can be applied. When applying these polymerization methods, acylation or acetylation may be carried out according to conventional methods.

[0020] The liquid crystal polymer may contain polymers such as fluororesins, polyolefins, polycycloolefins, polyetherimides, and silicone-modified polyetherimides, as well as release agents such as higher fatty acids having 10 to 25 carbon atoms, higher fatty acid esters, higher fatty acid amides, and higher fatty acid metal salts; chain extenders such as aliphatic carbodiimides, alicyclic carbodiimides, and aromatic carbodiimides; colorants such as dyes, pigments, and carbon black; organic fillers, inorganic fillers, hollow particles, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, flame retardants, lubricants, antistatic agents, surfactants, rust inhibitors, foaming agents, defoamers, and fluorescent agents, to the extent that they do not excessively impair the effects of the present invention. These polymers and additives can be incorporated into the molten resin composition during the formation of the laminated film. Furthermore, each of these polymers and additives can be used individually or in combination of two or more. The content of polymers and additives is not particularly limited, but from the viewpoint of moldability and thermal stability, it is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, and even more preferably 0 to 30% by mass, relative to the total amount of the liquid crystal polymer layer. These polymers and additives may be added to the liquid crystal polymer in advance, or they may be added to the liquid crystal polymer when forming the liquid crystal polymer film described later.

[0021] The thickness of the liquid crystal polymer layer is 100 μm or more, preferably 120 to 500 μm, and more preferably 175 to 300 μm. As described above, the laminated film of the present invention is used to produce a stretched liquid crystal polymer film by stretching it. From the viewpoint of reducing anisotropy, the stretching of the laminated film needs to be carried out at a stretching ratio of 3 to 4 times. By setting the thickness of the liquid crystal polymer layer within the above range, the stretched liquid crystal polymer film obtained by stretching the laminated film of the present invention can be made relatively thick, with a thickness of 30 μm or more.

[0022] The melting point of the liquid crystal polymer is preferably 250 to 380°C, more preferably 280 to 350°C. The glass transition temperature of the liquid crystal polymer is preferably 90 to 150°C, more preferably 100 to 120°C.

[0023] <Aromatic Polyetherketone Layer> The aromatic polyetherketone layer is provided to prevent the film from breaking when the liquid crystal polymer layer is stretched. Specific examples of aromatic polyetherketones that make up the aromatic polyetherketone layer include polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyetheretherketoneketone (PEEKK).

[0024] The degree of crystallinity of the aromatic polyetherketone layer is 40% or less, preferably 30% or less, and more preferably 25% or less. The lower limit of the degree of crystallinity of the aromatic polyetherketone layer is not particularly limited, but is usually 10% or more. By setting the degree of crystallinity of the aromatic polyetherketone layer within the above range, even though the liquid crystal polymer layer is relatively thick at 100 μm or more, the laminated film can be made to have excellent adhesion between the liquid crystal polymer layer and the aromatic polyetherketone layer. Therefore, it is possible to suppress the occurrence of breakage and perforation at the delamination points between the liquid crystal polymer layer and the aromatic polyetherketone layer during the stretching of the laminated film. As a result, breakage and perforation of the stretched liquid crystal polymer film obtained using the laminated film can be reduced.

[0025] The degree of crystallinity of the aromatic polyetherketone layer is expressed by the following formula. In the following formula, the density measurement of the aromatic polyetherketone layer can be measured, for example, based on JIS Z 8837. In the following formula, the density of amorphous aromatic polyetherketone (0% crystallinity) and the density of crystalline aromatic polyetherketone (100% crystallinity) are not particularly limited, but literature values ​​can be used. Degree of crystallinity of aromatic polyetherketone layer (%) = (Density measurement of aromatic polyetherketone layer - Density of amorphous aromatic polyetherketone) / (Density of crystalline aromatic polyetherketone - Density of amorphous aromatic polyetherketone PEEK) × 100

[0026] The thickness of the aromatic polyetherketone layer is preferably 100 μm or less, more preferably 5 to 50 μm, and even more preferably 10 to 35 μm.

[0027] In conventional techniques, when obtaining a laminated film by co-extruding a liquid crystal polymer and an aromatic polyether ketone, if the liquid crystal polymer layer in the laminated film is relatively thick (100 μm or more), the adhesion between the co-extruded liquid crystal polymer layer and the aromatic polyether ketone layer decreases, making the liquid crystal polymer layer and the aromatic polyether ketone layer more prone to delamination during stretching of the laminated film. This is thought to be because, when the liquid crystal polymer layer is thick, the laminated film co-extruded from the extruder is not cooled as a whole, making it difficult for the interface between the liquid crystal polymer layer and the aromatic polyether ketone layer to cool and solidify. As a result, the aromatic polyether ketone near the interface crystallizes and becomes prone to shrinkage.

[0028] In contrast, the laminated film of the present invention has a crystallinity of 40% or less of the aromatic polyetherketone layer, thereby suppressing the shrinkage of the aromatic polyetherketone layer during the manufacturing of the laminated film. Therefore, although the liquid crystal polymer layer of the laminated film of the present invention is relatively thick, at 100 μm or more, delamination from the liquid crystal polymer layer due to the shrinkage of the aromatic polyetherketone layer is suppressed. In other words, the laminated film of the present invention has excellent adhesion between the liquid crystal polymer layer and the aromatic polyetherketone layer. By stretching the laminated film of the present invention, even if the liquid crystal polymer layer is relatively thick, the entire liquid crystal polymer layer can be stretched uniformly without causing delamination. Accordingly, the laminated film of the present invention makes it possible to manufacture a stretched liquid crystal polymer film that is relatively thick and has reduced breakage and perforation.

[0029] Furthermore, conventionally, due to insufficient adhesion between the liquid crystal polymer layer and the aromatic polyetherketone layer, it was not possible to prevent delamination of the liquid crystal polymer layer and the aromatic polyetherketone layer throughout the entire laminated film when manufacturing long laminated films. In contrast, in the present invention, by setting the crystallinity of the aromatic polyetherketone layer to 40% or less, excellent adhesion between the liquid crystal polymer layer and the aromatic polyetherketone layer can be achieved throughout the entire laminated film, even when the laminated film is made long. Therefore, according to the laminated film of the present invention, breakage and perforation are reduced, and long stretched liquid crystal polymer films can be manufactured. The length in the longitudinal direction of the laminated film is preferably 10 m or more, more preferably 50 m or more, and even more preferably 100 m or more. The length in the longitudinal direction of the laminated film is not particularly limited, but is usually 1000 m or less.

[0030] <Method for Manufacturing Laminated Film> A laminated film can be manufactured by a method comprising the steps of: obtaining an unsolidified laminated film by co-extruding a liquid crystal polymer and an aromatic polyether ketone using a T-die; and solidifying the unsolidified laminated film by winding it on a cast roll at a temperature of 150°C or lower.

[0031] In the process of obtaining an unsolidified laminated film, a method for forming multilayer extruded films can be used for co-extrusion using a T-die. Specifically, examples include the feed block method, in which molten liquid crystal polymer and aromatic polyether ketone supplied from two extruders are supplied to a feed block and combined before being extruded in a film form from a T-die, and the multi-manifold method, in which molten liquid crystal polymer and aromatic polyether ketone are supplied separately to the T-die and extruded in layers in a film form. From the viewpoint of improving the smoothness of the liquid crystal polymer film obtained using the laminated film, it is preferable to apply the multi-manifold method, taking into account cases where the viscosity and flow characteristics of the liquid crystal polymer and aromatic polyether ketone differ during melting.

[0032] The temperature of the cylinder of the extruder that extrudes the liquid crystal polymer is preferably 230 to 360°C, and more preferably 280 to 350°C. The amount of liquid crystal polymer discharged by the extruder is not particularly limited and can be set appropriately according to the target thickness of the liquid crystal polymer layer.

[0033] The temperature of the cylinder of the extruder that extrudes the aromatic polyetherketone is preferably 340 to 400°C, and more preferably 350 to 380°C. The amount of aromatic polyetherketone discharged by the extruder is not particularly limited and can be set appropriately according to the target thickness of the aromatic polyetherketone layer.

[0034] Figure 1 is a schematic diagram illustrating the manufacturing method of the laminated film in this embodiment. Next, as shown in Figure 1, the unsolidified laminated film 10 extruded from the T-die 1 is wound up by a cast roll 2 at a temperature of 150°C or lower to solidify the unsolidified laminated film 10. The temperature of the cast roll 2 is 150°C or lower, preferably 140°C or lower, and more preferably 100°C or lower. Although not particularly limited, the temperature of the cast roll 2 is usually 30°C or higher. By keeping the temperature of the cast roll 2 within the above range, even when the liquid crystal polymer layer is relatively thick, the unsolidified laminated film 10, especially the interface between the liquid crystal polymer layer and the aromatic polyetherketone layer, can be appropriately cooled. Furthermore, by keeping the temperature of the cast roll 2 within the above range, even when the unsolidified laminated film 10 is made in a long length of 10 m or more, the interface between the liquid crystal polymer layer and the aromatic polyetherketone layer can be appropriately cooled. As a result, the crystallinity of the aromatic polyetherketone layer can be controlled to 40% or less. This improves the adhesion between the liquid crystal polymer layer and the aromatic polyether ketone layer, reducing the occurrence of breakage and perforation of the liquid crystal polymer film during stretching of the laminated film.

[0035] The air gap G, which is the distance between the exit (lip tip) of the T-die 1 and the contact position between the unsolidified laminated film 10 and the cast roll 2, is 100 mm or less, preferably 80 mm or less, more preferably 60 mm or less, and even more preferably 50 mm or less. Although not particularly limited, the air gap G is usually 10 mm or more. By setting the air gap G within the above range, the degree of crystallinity of the aromatic polyetherketone layer can be appropriately controlled. This improves the adhesion between the liquid crystal polymer layer and the aromatic polyetherketone layer, and reduces the occurrence of breakage and perforation of the liquid crystal polymer film when the laminated film is stretched.

[0036] When winding the unsolidified laminated film 10 with the cast roll 2, it is preferable to bring the touch roll 3 into contact with the side of the laminated film opposite to the side in contact with the cast roll 2. The temperature of the touch roll 3 is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 100°C or lower. From the viewpoint of adjusting the degree of crystallinity of the two aromatic polyetherketone layers laminated on both sides of the liquid crystal polymer layer to be of the same degree, it is preferable to set the temperatures of the cast roll 2 and the touch roll 3 to be the same.

[0037] <Method for Manufacturing Stretched Liquid Crystal Polymer Film> The laminated film of the present invention can be suitably used in the manufacture of stretched liquid crystal polymer films. Specifically, a stretched liquid crystal polymer film can be obtained by stretching the laminated film of the present invention in the width direction (TD direction) and then peeling off the aromatic polyetherketone layer.

[0038] While there are no particular limitations on the method for stretching the laminated film, the tenter transverse stretching method, in which the laminated film is clamped at both ends with clips and then heated and stretched, is preferred. The stretching ratio is preferably 3 to 4 times. By setting the stretching ratio within the above range, the anisotropy of the resulting stretched polymer film can be reduced. The stretching speed is preferably 1 to 5000% / min, more preferably 50 to 2500% / min. In addition, stretching in the longitudinal direction (MD direction) may be added as needed to adjust the degree of surface orientation after stretching.

[0039] The stretching of the laminated film is preferably carried out under conditions such that the surface temperature of the laminated film during stretching (the target stretching temperature) is below the melting point of the liquid crystal polymer. The target stretching temperature is more preferably 30 to 200°C lower than the melting point of the liquid crystal polymer, even more preferably 80 to 200°C lower, and particularly preferably 100 to 170°C lower. Furthermore, the target stretching temperature is preferably above the glass transition temperature of the liquid crystal polymer. The target stretching temperature of the laminated film can be adjusted by appropriately setting the stretching speed and the temperature when stretching the laminated film (the furnace temperature of the stretching apparatus).

[0040] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[0041] <Density and Crystallinity of the PEEK Layer> The PEEK layer was peeled from the laminated film, and the density of the PEEK layer was measured at 23°C using an automated true density analyzer BELPycno (manufactured by Microtrac-Bel Co., Ltd.) with helium as the measuring gas, according to JIS Z 8837 (gas pycnometer method). The degree of crystallinity of the PEEK layer was determined using the measured density based on the following formula: Degree of crystallinity of the PEEK layer (%) = (Measured density of the PEEK layer - Density of amorphous PEEK) / (Density of crystalline PEEK - Density of amorphous PEEK) × 100 Note that the density of amorphous PEEK was 1.2629 g / cm³. ３ Density of crystalline PEEK: 1.3820 g / cm³ ３ That's what I decided.

[0042] <Adhesion between LCP layer and PEEK layer> The obtained laminated film was wound around a 3-inch core (plastic cylinder) with an outer diameter of 84.2 mm for 1 m along the longitudinal direction of the film and then unwound. In the laminated film, the portion wound around the 3-inch core was observed, and the presence or absence of peeling between the LCP (liquid crystal polymer) layer and the PEEK layer was evaluated as follows. Also, when the LCP layer and the PEEK layer peeled off during film formation and a laminated film could not be obtained, it was evaluated as D as follows. A: No peeling between the LCP layer and the PEEK layer B: Peeling between the LCP layer and the PEEK layer is within 1 place C: Peeling between the LCP layer and the PEEK layer is less than 5 places D: Peeling between the LCP layer and the PEEK layer occurred during film formation, or peeling between the LCP layer and the PEEK layer is 5 places or more

[0043] <Breakage and perforation during stretching> After stretching the laminated film, the range within 100 m in the longitudinal direction of the film was observed, and the cumulative number of defective products such as breakage and perforation of the stretched liquid crystal polymer film was counted and evaluated as follows. A: The number of defective products is less than 5 B: The number of defective products is 5 or more and less than 10 C: The number of defective products is 10 or more and less than 50 D: The number of defective products is 50 or more or evaluation is impossible

[0044] <Example 1> Liquid crystal polymer (LCP, manufactured by Polyplastics Co., Ltd., LAPEROS A950RX) was supplied to a twin-screw extruder (screw diameter 32 mm) and melt-kneaded at 300 °C. Also, polyetheretherketone (PEEK, manufactured by Daicel-Evonik, VESTAKEEEP 3300G) was supplied to a single-screw extruder (screw diameter 40 mm) and melt-kneaded at 380 °C. These molten polymers were supplied to a multi-manifold T-die, and the PEEK layer was laminated on both sides of the LCP layer and extruded, and cooled with a cast roll and a touch roll to produce a laminated film with a thickness of 175 μm for the LCP layer, a thickness of 30 μm for each of the PEEK layers on both sides, and a total thickness of 235 μm. At this time, the distance (air gap) from the lip tip of the T-die to the point where the film touches the cast roll was 50 mm, and the temperatures of the cast roll and the touch roll were both 80 °C. The crystallinity of the PEEK layer was 22%, and the adhesion between the LCP layer and the PEEK layer was good.

[0045] The laminated film thus produced was stretched 3.5 times in the width direction (TD) at a conveying speed of 3 m / min (stretching speed: 625% / min) using a tenter-type transverse stretching machine (furnace temperature: 320°C), and the PEEK film was peeled off to obtain a stretched liquid crystal polymer film with a thickness of 50 μm. The results are shown in Table 1.

[0046] <Examples 2 to 6> A laminated film was produced and stretched in the same manner as in Example 1, except that the LCP discharge amount, the cast roll temperature, the touch roll temperature, the PEEK discharge amount, and the air gap were changed as shown in Table 1. The results are shown in Table 1.

[0047] <Comparative Example 1> A laminated film was produced in the same manner as in Example 1, except that the cast roll temperature was set to 180°C. The crystallinity of the PEEK layer was as high as 42%, and the LCP layer and the PEEK layer were peeled off, so stretching could not be performed. The results are shown in Table 2.

[0048] <Comparative Examples 2 and 3> A laminated film was produced in the same manner as in Comparative Example 1, except that the cast roll temperature and the air gap were changed as shown in Table 2. The crystallinity of the PEEK layer exceeded 40% in both cases, and the LCP layer and the PEEK layer were peeled off, so stretching could not be performed. The results are shown in Table 2.

[0049]

[0050] <s

[0051] 1... T-die 2... Cast roll 3... Touch roll 10... Uncured laminated film G... Air gap

Claims

1. A laminated film manufactured by co-extruding a liquid crystal polymer and an aromatic polyether ketone, comprising: a liquid crystal polymer layer made of the liquid crystal polymer; and an aromatic polyether ketone layer made of the aromatic polyether ketone laminated on both sides of the liquid crystal polymer layer, wherein the degree of crystallinity of the aromatic polyether ketone layer is 40% or less, and the thickness of the liquid crystal polymer layer is 100 μm or more.

2. The laminated film according to claim 1, wherein the degree of crystallinity of the aromatic polyetherketone layer is 30% or less.

3. The laminated film according to claim 1 or 2, wherein the thickness of the aromatic polyetherketone layer is 50 μm or less.

4. The laminated film according to claim 1 or 2, wherein the length in the longitudinal direction is 10 m or more.

5. A method for manufacturing a laminated film, comprising the steps of: obtaining an unsolidified laminated film by co-extruding a liquid crystal polymer and a crystalline resin using a T-die; and solidifying the unsolidified laminated film by winding it on a cast roll at a temperature of 150°C or lower, wherein the air gap, which is the distance between the exit of the T-die and the contact position between the cast roll and the unsolidified laminated film, is 100 mm or less.

6. The method for manufacturing a laminated film according to claim 5, wherein the air gap is 50 mm or less.

Images