Fluororesin film and its manufacturing method

Abstract

To provide a film having good dimensional stability, low haze, good yield rate in circuit formation, and capable of achieving both transparency and heat resistance, and a method of manufacturing the same.SOLUTION: A film made of tetrafluoroethylene-based polymer has a thickness of 100 to 200 μm, a haze of 8% or less, a thermal shrinkage rate after 30 minutes heating at 180°C both in the flow direction and the width direction of -1% or more and +1% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tetrafluoroethylene polymer film and a method for producing the same. [Background technology]

[0002] As electronic devices become lighter and more compact, flexible printed circuit boards (FPCs) are widely used as a lightweight, flexible wiring material to address the wiring volume and space limitations within devices. In recent years, the speed of transmitted signals on printed circuit boards has increased, leading to increasingly higher signal frequencies. Accordingly, there is a strong demand for FPCs to have low dielectric properties (low dielectric constant, low dielectric dissipation factor) in the high-frequency range. To meet these demands, substrate films composed of low-dielectric-properties materials such as liquid crystal polymer (LCP), syndiotactic polystyrene (SPS), and polyphenylene sulfide (PPS) have been proposed as alternatives to conventional polyimide (PI) and polyethylene terephthalate (PET) substrate films for FPCs. Meanwhile, with the pursuit of improved design for electronic devices, opportunities for FPCs to be used in visible locations are increasing, such as flexible devices such as flexible displays and touch panels, and electronic devices that use reflowed semiconductor elements such as LEDs, etc. In such electronic devices, FPCs must also be transparent.

[0003] PI film has excellent heat resistance, but transparency is an issue. PET film has excellent transparency, but poor heat resistance, and when used in flexible printed wiring boards, the heat generated during reflow can cause warping and dimensional changes in the substrate. Tetrafluoroethylene polymers such as polytetrafluoroethylene (PTFE) have high transparency and excellent physical properties such as chemical resistance, water and oil repellency, heat resistance, and electrical properties. They also have a lower dielectric constant and lower dielectric dissipation factor than materials such as PI, LCP, SPS, and PPS, making them suitable for use as transparent, reflow-resistant FPC substrate films. On the other hand, tetrafluoroethylene polymers have poor dimensional stability and are prone to misalignment during circuit processing. For this reason, Patent Document 1 proposes a method of removing distortion by annealing the film after it has been formed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 203243 Summary of the Invention [Problem to be solved by the invention]

[0005] Tetrafluoroethylene-based polymers have crystallinity, and the crystals tend to grow during the cooling process of the molten molded product, so the resulting film tends to have a large haze even though it has a high light transmittance. Furthermore, when the film becomes thick, distortion is difficult to eliminate even by heat treatment as in the method of Patent Document 1, and the film has poor dimensional stability, so that heat treatment may impair the flatness of the film.

[0006] As a result of extensive research, the present inventors have discovered a film that has good dimensional stability, low haze, good yield in circuit formation, and is capable of achieving both transparency and heat resistance. The object of the present invention is to provide a film having the above properties and a method for producing the same. [Means for solving the problem]

[0007] The present invention has the following aspects. <1> An extrusion-molded film made of a tetrafluoroethylene-based polymer, having a thickness of 100 to 200 μm, a haze of 8% or less, and a thermal expansion rate of -1 to +1% in both the machine direction and width direction of the film after heating at 180°C for 30 minutes. <2> The tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). <1> Film. <3> the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer containing units based on perfluoro(alkyl vinyl ether) and having a polar functional group, or a tetrafluoroethylene-based polymer containing 2.0 to 5.0 mol % of units based on perfluoro(alkyl vinyl ether) based on all units and having no polar functional group; <1> or <2> Film. <4> The melting temperature of the tetrafluoroethylene-based polymer is 260 to 320°C. <1> ~ <3> Any of the films.

[0008] <5> The aforementioned <1> ~ <4> The method for producing any one of the films described above by a T-die casting method includes extruding the tetrafluoroethylene-based polymer in a molten state from a die, and then sandwiching the film between two temperature-controlled rolls to cool it. <6> The temperatures of the two temperature-controlled rolls are 150 to 250°C for one and 80 to 150°C for the other. <5> Manufacturing method. <7> The method comprises an extrusion molding apparatus having a kneading section and a hopper connected to the kneading section, and when pellets of a tetrafluoroethylene-based polymer having a melting temperature of 260 to 320°C are charged into the hopper and the molten mixture melted and kneaded in the kneading section is discharged from a T-die to produce a film, the method further comprises an operation of adjusting the temperature of the pellets at a connecting section of the hopper with the kneading section to a range of (the melting temperature - 200) to (the melting temperature - 100)°C, and then supplying the pellets to the kneading section. <5> or <6> Manufacturing method. <8> The diameter of the pellet is 1.0 to 4.0 mm. <5> ~ <7> A manufacturing method of any of the above.

[0009] <9> The hopper is a multi-stage hopper having a first stage and a second stage arranged closer to the kneading section than the first stage, <5> ~ <8> A manufacturing method of any of the above. <10> The pressure in the step closest to the kneading section of the hopper is 1000 Pa or less. <5> ~ <9> A manufacturing method of any of the above. <11> The extrusion molding apparatus includes a T-die connected to the kneading section on the opposite side of the hopper in the axial direction, and a static mixer provided between the kneading section and the T-die. <5> ~ <10> A manufacturing method of any of the above. <12> The method further comprises the steps of extruding the tetrafluoroethylene-based polymer in a molten state from a T-die and heating the molten tetrafluoroethylene-based polymer in a non-contact heating section before the polymer contacts a first cooling roll. <5> ~ <11> A manufacturing method of any of the above. <13> the difference between the temperature of the tetrafluoroethylene-based polymer in the T-die and the temperature of the first cooling roll is 250°C or less; <12> Manufacturing method. <14> the absolute value of the difference between the temperature of the tetrafluoroethylene-based polymer in the T-die and the temperature of the non-contact heating section is 70°C or less; <12> or <13> Manufacturing method.

[0010] <15> The aforementioned <1> ~ <4> and a substrate layer made of a substrate other than the film. [Effects of the Invention]

[0011] According to the present invention, a film having good dimensional stability, low haze, high yield in circuit formation, and both transparency and heat resistance, and a method for producing the same are provided. According to the present invention, a thick film having a thickness of about 100 μm, which is particularly preferred as a base material for an antenna substrate, can be provided. The film of the present invention is useful as a colorless, transparent, and low-loss antenna substrate. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is a schematic diagram showing one embodiment of a film production apparatus used in Method 1. [Figure 2] 1 is a schematic diagram illustrating one embodiment of an extrusion molding device that can be used in the present invention. [Figure 3] FIG. 1 is a schematic diagram showing one embodiment of a film production apparatus used in Method 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following terms have the following meanings: The "film thickness" is the average value of the measurements taken at 10 points at equal intervals across the width of the film using a contact thickness gauge DG-525H (manufactured by Ono Sokki Co., Ltd.) with a probe AA-026 (Φ10 mm, SR7). The "melting temperature of a polymer" is the temperature corresponding to the maximum value of the melting peak as measured by differential scanning calorimetry (DSC). The term "unit" in a polymer refers to an atomic group based on one molecule of a monomer formed by polymerization of the monomer. The unit may be a unit formed directly by a polymerization reaction, or may be a unit in which a portion of the unit is converted into a different structure by processing the polymer. Hereinafter, a unit based on monomer a will also be referred to simply as a "monomer a unit." The "glass transition temperature of a polymer" is a value measured by analyzing a polymer using dynamic mechanical analysis (DMA).

[0014] The film of the present invention is an extrusion-molded film made of a tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer"), has a thickness of 100 to 200 μm, a haze of 8% or less, and a thermal expansion rate of -1 to +1% in both the machine direction (hereinafter referred to as MD) and the width direction (hereinafter referred to as TD) of the film after heating at 180°C for 30 minutes. The film of the present invention may be a roll film in a wound state. Furthermore, as the laminate of the present invention having a layer made of the film of the present invention and a base layer made of a base material other than the film of the present invention, a laminate made of the film of the present invention and a metal foil is preferred. This laminate made of the film of the present invention and a metal foil can be suitably used as an FPC by cutting it to a predetermined length and processing the metal foil into a transmission circuit (including vias), and is suitable, for example, as an antenna substrate that is colorless, transparent, and has excellent electrical properties. The layer made of the film of the present invention will be referred to hereinafter as "F polymer layer", and a substrate layer made of a substrate other than the film of the present invention will be referred to hereinafter simply as "substrate layer" unless otherwise specified.

[0015] Ordinary melt processible fluororesin films have residual molding distortion due to their manufacturing method (melt molding by extrusion). By appropriately controlling the cooling conditions of the resin film during molding as described below, the film of the present invention has a thermal expansion rate of -1 to +1% in both MD and TD, with small and sufficiently uniform distortion in each direction, excellent dimensional stability, and excellent transparency with a haze of 8% or less even at a thickness of 100 to 200 μm. Therefore, even in a laminate having such a film layer, distortion is small and sufficiently uniform, and therefore it is considered that the laminate has excellent thermal shock resistance, deformation is suppressed, and dimensional stability is excellent. For example, the laminate of the present invention having a metal foil as a base layer has high thermal shock resistance when forming through holes or vias when processing it into a printed wiring board, and as a result, a printed wiring board that is less likely to break is easily obtained.

[0016] The thermal expansion / contraction rate of a film is measured as follows. First, a 12 cm square test piece with two sides along the MD and two sides along the TD is cut out from the film. Next, a 10 cm line is drawn in the MD and TD on the surface of the obtained test piece. Next, the test piece is heated in an oven at 180°C for 30 minutes, then removed and allowed to cool naturally to 25°C, and the length of the line is measured again. The thermal expansion / contraction rate is calculated according to the formula: {(length of the line segment before heating) - (length of the line segment after heating)} / (length of the line segment before heating) x 100. In other words, the thermal expansion / contraction rate is the percentage change in the length of the line segment before and after heating. Note that a negative value indicates expansion of the film, and a positive value indicates contraction of the film. The thermal expansion and contraction rate of the film of the present invention is -1 to +1% in both MD and TD of the film, preferably -0.8 to +0.8%, and more preferably -0.5 to +0.5%. When the thermal expansion and contraction rate is within the above range, wrinkles due to distortion of the film are less likely to occur even when heated.

[0017] The F polymer in the present invention is a polymer containing units (TFE units) based on tetrafluoroethylene (TFE). The F polymer in the present invention is heat-meltable, and its melting temperature is preferably 260 to 320°C, more preferably 275 to 315°C, and even more preferably 290 to 310°C. In this case, the molding processability of the F polymer and the mechanical strength of the film of the present invention are easily balanced. The glass transition point of the F polymer is preferably 75 to 125°C, more preferably 80 to 100°C.

[0018] Examples of F polymers include polytetrafluoroethylene (PTFE), polymers containing TFE units and units based on perfluoro(alkyl vinyl ether) (PAVE) (PAVE units) (PFA), and polymers containing units based on hexafluoropropene (HFP) (FEP), with PFA being preferred. Preferred PAVEs are CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (PPVE), with PPVE being more preferred.

[0019] The F polymer preferably has a polar functional group. The polar functional group may be contained in a unit in the F polymer or in a terminal group of the main chain of the F polymer. Examples of the latter include an F polymer having a polar functional group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer having a polar functional group obtained by treating an F polymer with plasma or ionizing radiation. The polar functional group is preferably a hydroxyl group-containing group or a carbonyl group-containing group. As the hydroxyl group-containing group, a group containing an alcoholic hydroxyl group is preferred, and -CF2CH2OH and -C(CF3)2OH are more preferred. The carbonyl group-containing group is a group containing a carbonyl group (>C(O)). Preferred carbonyl group-containing groups include a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.) and a carbonate group (-OC(O)O-), and more preferred are acid anhydride residues.

[0020] When the F polymer has a carbonyl group-containing group, the number of carbonyl group-containing groups in the F polymer is 1×10 6 The number per unit is preferably 10 to 5000, more preferably 100 to 3000, and further preferably 800 to 1500. The number of carbonyl group-containing groups in the F polymer can be quantified by the composition of the polymer or the method described in WO 2020 / 145133.

[0021] As the F polymer, a polymer (1) having a polar functional group containing TFE units and PAVE units, and a polymer (2) having no polar functional group containing TFE units and PAVE units and containing 2.0 to 5.0 mol % of PAVE units based on all units are preferred. These F polymers tend to form microspherulites in molded products, which increases adhesion to other components. As a result, molded products with excellent surface smoothness, adhesiveness, and electrical properties are more likely to be obtained.

[0022] Polymer (1) is preferably a polymer containing TFE units, PAVE units, and units based on a monomer having a polar functional group, more preferably a polymer containing these units in the following amounts, in that order, relative to the total units. Furthermore, preferred examples of the monomer having a polar functional group include itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH"). Specific examples of polymer (1) include the polymers described in WO 2018 / 16644.

[0023] Polymer (2) is composed only of TFE units and PAVE units, and preferably contains 95.0 to 98.0 mol% of TFE units and 2.0 to 5.0 mol% of PAVE units based on all units. The content of PAVE units in polymer (2) is preferably 2.1 to 5.0 mol%, more preferably 2.2 to 5.0 mol%, based on all units. The term "polymer (2) has no polar functional group" means that the number of carbon atoms constituting the polymer main chain is 1 × 10 6 This means that the number of polar functional groups possessed by the polymer is less than 500 per unit area. The number of polar functional groups is preferably 100 or less, and more preferably less than 50. The lower limit of the number of polar functional groups is usually 0. Polymer (2) may be produced using a polymerization initiator or chain transfer agent that does not generate a polar functional group as the terminal group of the polymer chain, or may be produced by fluorinating an F polymer having a polar functional group (such as an F polymer having a polar functional group derived from a polymerization initiator at the terminal group of the polymer main chain). Fluorination methods include methods using fluorine gas (see, for example, JP 2019-194314 A).

[0024] The film of the present invention may contain a resin other than the F polymer. However, the content of the F polymer in the film is preferably 80% by mass or more, and more preferably 100% by mass. Examples of resins other than the F polymer include epoxy resins, polyimide resins, polyamic acids (polyimide precursors), acrylic resins, phenolic resins, liquid crystalline polyester resins, polyolefin resins, modified polyphenylene ether resins, polyfunctional cyanate ester resins, polyfunctional maleimide-cyanate ester resins, polyfunctional maleimide resins, vinyl ester resins, urea resins, diallyl phthalate resins, melamine resins, guanamine resins, melamine-urea co-condensation resins, styrene resins, polycarbonate resins, polyarylate resins, polysulfones, polyaryl sulfones, aromatic polyamide resins, aromatic polyether amides, polyphenylene sulfides, polyaryl ether ketones, polyamideimides, and polyphenylene ethers.

[0025] The film of the present invention may further contain, for example, an inorganic filler, an organic filler, a thixotropic agent, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightening agent, a colorant, a conductive agent, a release agent, a surface treatment agent, a viscosity adjuster, a flame retardant, or the like.

[0026] Preferred inorganic fillers include boron nitride fillers, beryllia fillers (beryllium oxide fillers), silicate fillers (silica fillers, wollastonite fillers, talc fillers), and metal oxide fillers (cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, etc.). At least a portion of the surface of the inorganic filler may be surface-treated. Examples of surface treatment agents used for such surface treatment include polyhydric alcohols, saturated fatty acids, their esters, amines, paraffin wax, silane coupling agents, silicones, and polysiloxanes. The shape of the inorganic filler may be any of granular, needle-like (fibrous), plate-like, etc., and specific shapes include spherical, scale-like, layer-like, leaf-like, apricot-like, columnar, cockscomb-like, equiaxed, leaf-like, micaceous, block-like, flat, wedge-like, rosette-like, net-like, and prismatic.

[0027] The method for producing the film of the present invention will be described below: The film of the present invention can be produced preferably by a T-die casting method (a melt extrusion method using a T-die) from the viewpoint of being able to adjust the distortion of the film. The present inventors have found that the MD and TD distortions of films produced by the T-die casting method depend on the state (temperature, fluidity) of the molten F polymer and the cooling conditions, and are determined by the state of the molten F polymer extruded from the T-die until it is crystallized on a cooling roll. In other words, the present inventors have found that if the state of the F polymer and the cooling conditions are appropriately set to control the crystallization of the F polymer, the MD and TD heat shrinkage (distortion) of the resulting film will converge within a predetermined range, and due to the suppression of crystal growth, low haze can be achieved even in a relatively thick film of 100 to 200 μm.

[0028] The film manufacturing method of the present invention includes extruding the F polymer in a molten state from a T-die, and then sandwiching the film between two temperature-controlled rolls to cool it (Method 1). Preferably, one of the two temperature-controlled rolls has a temperature of 150 to 250°C, and the other has a temperature of 80 to 150°C. More preferably, one of the two temperature-controlled rolls is a metal roll controlled to 150 to 250°C, and the other is an elastic metal roll controlled to 80 to 150°C.

[0029] Figure 1 is a schematic diagram showing one embodiment of a film production apparatus used in Method 1. The production apparatus 10 shown in Figure 1 has a T-die 20, a first cooling roll (initial cooling roll) 30 arranged vertically below the T-die 20, a quenching roll 301, a second cooling roll 40 arranged alongside the first cooling roll 30, a take-up roll 50 that takes up the film 1, and transport rolls 61 and 62 arranged between the take-up roll 50 and the second cooling roll 40. The first cooling roll 30 may further be equipped with an air knife 70, and preferably is.

[0030] The F polymer is heated and melted in an extruder (not shown) connected to the T-die 20, and then fed into the T-die 20. The molten F polymer is extruded from the lip 21 of the T-die 20 toward the first cooling roll 30. The extruded molten F polymer then contacts the first cooling roll 30 and is cooled by being pinched between the first cooling roll 30 and the quenching roll 301. The F polymer then passes through the second cooling roll 40 and is transported by the transport rollers 61 and 62. The F polymer is then taken up as the film 1 onto the take-up roll 50. A temperature-controllable metal roll is preferably used as the first cooling roll 30, and an elastic metal roll is preferably used as the quenching roll 301.

[0031] An example of an elastic metal roll is a roll whose surface is made of a metal material such as stainless steel, and whose space between the metal surface and the shaft is filled with an elastic material such as a fluid or rubber. The elastic metal roll, for example, comprises a substantially cylindrical, rotatable shaft, a cylindrical metal thin film that covers the outer surface of the shaft and contacts the film, and a fluid sealed between the shaft and the metal thin film. The fluid provides elasticity to the elastic metal roll, enabling roll compression molding at low linear pressure. The present invention utilizes this property to contribute to the control of film cooling conditions. The material of the shaft roll can be stainless steel. The metal thin film is preferably made of stainless steel and has a thickness of 2 to 5 mm. The metal thin film is preferably flexible or bendable, and preferably has a seamless structure without welded joints. A metal elastic roll equipped with such a metal thin film is excellent in durability, and if the metal thin film is mirror-finished, it can be handled in the same way as a normal mirror-finished roll. From the viewpoint of obtaining a film with excellent surface smoothness, it is more preferable that the surface of the metal elastic roll is a mirror-finished roll. Commercially available metal elastic rolls include the UF roll from Hitachi Zosen Corporation and the SF roll from Chiba Machinery Industry Co., Ltd.

[0032] By sandwiching the molten F polymer between the quenching roll 301, which is preferably a metal elastic roll, and the first cooling roll 30, which is preferably a metal roll, and cooling it, the film is rapidly cooled, suppressing crystal growth and reducing haze, and also reducing the accumulation of strain on the film sandwiched between the first cooling roll and the quenching roll. The temperature of the first cooling roll 30 is preferably 150 to 250°C, and the temperature of the quenching roll 301 is preferably 80 to 150°C from the viewpoint of being able to cool the film rapidly. Both the first cooling roll and the quenching roll are preferably configured to have a mechanism for passing a heat medium, and preferably have a dual mechanism for repeatedly passing the heat medium back and forth in the axial direction. The temperature of the first cooling roll and the temperature of the quenching roll both refer to the temperature of the heat medium. When the quenching roll is a metallic elastic roll, the temperature range is preferably such that the properties of the metallic elastic roll itself are not impaired.

[0033] In Method 1, it is preferable to further provide an air knife 70 at a position immediately after the molten F polymer is sandwiched between the first cooling roll 30 and the quenching roll 301. The air knife 70 has the role of cooling the molten F polymer and pressing it against the first cooling roll 30 by blowing a slit-shaped air stream from a slit nozzle uniformly in a line in the width direction of the first cooling roll 30 onto the line where the molten F polymer contacts the first cooling roll 30. Like the quenching roll 301, it has the effect of increasing the cooling efficiency of the F polymer, suppressing haze in the resulting film, and reducing the thermal expansion / contraction rate. The temperature of the air blown out from the air knife is preferably 150 to 200° C., more preferably 170 to 200° C. If it is 150° C. or higher, the thermal expansion rate of the film is small, and if it is 200° C. or lower, the haze tends to be small. The flow rate of the air blown out from the air knife is preferably 10 to 20 m / sec.

[0034] The film production method of the present invention further includes, in addition to Method 1, a method in which a film is produced from pellets of F polymer having a melting temperature of 260 to 320°C using, for example, an extrusion molding apparatus 11 shown in Figure 2 (Method 2). Fig. 2 is a conceptual diagram showing one embodiment of an extrusion molding apparatus used in Method 2. In the following explanation, the right side in Fig. 2 (forward in the direction of transport of the molten kneaded material) will be referred to as the "front end" and the left side (rear in the direction of transport) as the "base end."

[0035] The extrusion molding apparatus 11 shown in Figure 2 includes a hopper 2 and a kneading section 3 that communicates with the hopper 2. The kneading section 3 of this embodiment is configured as a single-screw kneader having a cylinder 31 and one screw 32 rotatably provided within the cylinder 31. Use of a single-screw kneader makes it easier to prevent deterioration of the F polymer when the pellets are melt-kneaded. In this case, when the total length of the screw 32 is L (mm) and the diameter is D (mm), the effective length (L / D), which is the ratio of the total length L to the diameter D, is more preferably 30 to 45. If the effective length is within the above range, sufficient shear stress can be applied to the F polymer while preventing deterioration of the F polymer, and temperature unevenness of the molten kneaded product can be easily reduced.

[0036] A gear box 33 and a motor 34 are arranged in this order on the base end side of the cylinder 31. A gear (not shown) is connected to the tip of a rotary shaft 341 of the motor 34, and this gear meshes with a predetermined gear (not shown) in the gear box 33. The gear box 33 accelerates or decelerates the rotational motion of the rotary shaft 341 and transmits it to the rotary shaft 331. The tip end of the rotary shaft 331 is connected to the base end side of the screw 32. With this configuration, the rotation of the motor 34 is transmitted to the screw 32, causing the screw 32 to rotate at a predetermined rotation speed. As a result, the molten kneaded material is transported from the base end side (left side) to the tip end side (right side) in FIG.

[0037] A heater 35 is provided on the outer periphery of the cylinder 31. The pellets (F polymer) supplied into the cylinder 31 are melted by the heat of the heater 35, mixed (kneaded) by the rotation of the screw 32, and transported toward the tip side. As a result, the pellets are melted and kneaded, and the molten and kneaded mixture is extruded from the tip opening 311 of the cylinder 31. A T-die 5 is disposed at the tip end side of the cylinder 31 (the opposite side of the hopper 2 in the axial direction of the kneading section 3). The molten mixture extruded from the tip opening 311 of the cylinder 31 is discharged from the lower end opening (discharge port) of the T-die 5, and thereafter, as described in Method 1, an F polymer film is produced. Here, the T-die 5 in FIG. 2 can be understood to correspond to the T-die 20 in FIG. 1 (or FIG. 3, which will be described later). Although not shown, the T-die 5 is also provided with a heater.

[0038] In this embodiment, a static mixer 6 is provided between the cylinder 31 (kneading section 3) and the T-die 5. This static mixer 6 is an element that divides, converts, or reverses the flow path of the molten kneaded material to stir the molten kneaded material. By providing such a static mixer 6, it is possible to prevent unnecessary external force from being applied to the molten and kneaded material, and therefore the molten and kneaded material can be uniformly kneaded while suppressing deterioration of the molten and kneaded material.

[0039] A hopper 2 is disposed on the base end side of the cylinder 31. The hopper 2 in this embodiment is configured as a two-stage hopper including a funnel-shaped first stage 21 and a funnel-shaped second stage 22 disposed closer to the kneading section 3 (cylinder 31) side than the first stage 21. A heater 211 and a pump P1 are connected to the first stage 21. This allows the pellets supplied into the first stage 21 to be heated under reduced pressure. The first step portion 21 is connected to the second step portion 22 via a connecting portion 212 . A heater 221 and a pump P2 are connected to the second stage 22. This allows the pellets supplied into the second stage 22 to be heated under reduced pressure. The second step portion 22 is connected to the cylinder 31 via a connection portion 222 . The inner surface (inner peripheral surface) of the hopper 2 (first stage 21 and second stage 22) is preferably coated with a resin film. That is, the inner surface of the hopper 2 is preferably lined with a resin. This can sufficiently prevent the softened pellets from adhering to the inner surface of the hopper 2. The resin film can be made of a fluororesin such as PTFE.

[0040] The pellets used in Method 2 may contain components other than the F polymer, but the content of the F polymer is preferably 80% by mass or more, and more preferably 100% by mass. Examples of components other than the F polymer include the above-mentioned other resins and additives. The pellets may be spherical or cylindrical in shape, with cylindrical being preferred. The pellets preferably have a diameter of 1.0 to 4.0 mm. Pellets with such a diameter can be heated thoroughly to the inside when heated in the hopper 2 while preventing bridging (clogging) in the hopper 2.

[0041] In Method 2, F polymer pellets are preheated in hopper 2 and then fed to kneading section 3. The melted and kneaded mixture is then extruded from T-die 5 to produce a film. The temperature of the pellets at the junction 222 between hopper 2 and kneading section 3 is adjusted to a range of (X-200) to (X-100)°C, where X is the melting temperature of the F polymer. The temperature of the pellets at the junction 222 between hopper 2 and kneading section 3 is preferably (X-175) to (X-125)°C. Specifically, the pellet temperature is preferably 70 to 225°C, more preferably 105 to 195°C. In this case, bridging within hopper 2 due to softening of the pellets is less likely to occur. Furthermore, temperature unevenness of the molten mixture within kneading section 3 is sufficiently reduced, making it easier to obtain a film with a uniform thickness and free of fisheyes.

[0042] The pressure in the second stage 22 (the stage closest to the kneading section 3) is preferably lower than the pressure in the first stage 21, and is preferably 1000 Pa or less, and more preferably 100 Pa or less. This allows the air in the pellets to be sufficiently removed, preventing the formation of a heat insulating layer by the air and making it easier to prevent temperature unevenness from occurring in the molten kneaded product in the kneading section 3. The softened pellets are supplied to the kneading section 3. The rotation speed of the screw 32 is preferably 10 to 50 ppm. The heating temperature by the heater 35 is more preferably (X+30) to (X+50)°C. Melting and kneading the pellets under the above conditions makes it easier to form a homogeneous melt-kneaded product with little temperature variation, and as a result, makes it easier to obtain the film of the present invention. The molten kneaded material is supplied to a T-die 5 via a static mixer 6 and extruded from the T-die 5. The molten kneaded material extruded from the T-die 5 is formed into a film as described in Method 1 and taken up on a take-up roll. Furthermore, the extrusion molding device 11 may have a cutter as needed.

[0043] According to Method 2, the surging phenomenon is highly suppressed, and the polymer is uniformly melted and kneaded without excessive heat history to form a film. This makes it easy to produce a wide film with few defects (fisheyes) and sufficient length in the transverse direction. The number of fisheyes in the film of the present invention is 2 The lower limit of the number of fisheyes is 0.

[0044] The film manufacturing method of the present invention further includes a method in which, in Method 1 or Method 2, the F polymer is extruded in a molten state from a T-die and the molten F polymer is heated in a non-contact heating section before contacting the first cooling roll (Method 3). Fig. 3 is a schematic diagram showing one embodiment of a film production apparatus used in Method 3. The production apparatus 101 shown in Fig. 3 is similar to the production apparatus 10 in Method 1, except that it further includes a pair of heaters (non-contact heating units) 80 arranged opposite each other between the T-die 20 and the first cooling roll 30.

[0045] The F polymer is heated and melted in an extruder (not shown) connected to the T-die 20 and fed into the T-die 20. The molten F polymer is extruded from the lip 21 of the T-die 20 toward the first cooling roll 30. The extruded molten F polymer is then heated without coming into contact with the heaters 80 as it passes between the pair of heaters 80. It then comes into contact with the first cooling roll 30 and is pressed against the first cooling roll 30 by the quench roll 301 to be cooled. At this time, an air knife 70 installed perpendicular to the tangent to the first cooling roll 30 may be used to blow a slit-shaped air stream uniformly in a line across the width of the first cooling roll 30, thereby cooling the molten F polymer and pressing it against the first cooling roll 30. After passing through the second cooling roll 40, the F polymer is transported by transport rollers 61 and 62 and taken up as a film 1 on the take-up roll 50.

[0046] According to this configuration, the molten F polymer discharged from the T-die 20 is maintained at a high temperature by heating with the heater 80, even while reaching the first cooling roll 30. Therefore, the molten F polymer flowing down toward the first cooling roll 30 maintains a relatively high fluidity, and is less likely to become stretched due to its own weight or the tensile force of the first cooling roll 30. As a result, it is presumed that the occurrence of the bowing phenomenon (orientation of the F polymer in MD and TD) is suppressed when the molten F polymer is formed into a film, and a film with small MD and TD distortion (thermal expansion and contraction rate) as described above can be obtained.

[0047] 3, the F polymer extruded from the T-die 20 is heated by the heater 80 from both sides in the thickness direction, resulting in high temperature uniformity in the thickness direction and excellent effectiveness in suppressing the occurrence of the bowing phenomenon. Furthermore, from the viewpoint of further improving the effectiveness in suppressing the occurrence of the bowing phenomenon, it is preferable to configure the heater 80 so that the temperature of the F polymer can also be uniform in the width direction. In this case, for example, the width of the heater 80 can be designed to be sufficiently larger than the length of the F polymer in the width direction.

[0048] The temperature of the F polymer in the T die 20 is X 1 [℃], and the temperature of the heater 80 is Z 1 When the temperature is specified as [℃], the absolute value of the difference (|X 1 -Z 1 |) is preferably 70°C or less, more preferably 30 to 50°C. In this case, the temperature of the F polymer can be maintained sufficiently high until it reaches the first cooling roll 30 while preventing deterioration of the F polymer. When the die temperature and the die lip temperature are different, X 1 means the die temperature. In addition, the temperature of the first cooling roll 30 is set to Y 1 When [℃] is specified, the difference (X 1 -Y 1 ) is preferably 250°C or less, more preferably 200°C or less, and even more preferably 125 to 175°C. In this case, the degree of cooling of the F polymer by the first cooling roll 30 becomes more appropriate, so that distortions in the MD and TD are less likely to remain in the obtained film 1, and deformation due to insufficient cooling can also be suitably prevented. Specifically, Y 1 The heating temperature is preferably 150 to 250°C.

[0049] Furthermore, from the viewpoint of further improving the effect of suppressing the occurrence of the bowing phenomenon during cooling by the first cooling roll 30, it is preferable to configure the first cooling roll 30 so that the temperatures of the F polymer in the MD and TD can be made uniform. Therefore, the first cooling roll 30 preferably has a mechanism for passing a heat medium therethrough, and more preferably has a dual mechanism for passing the heat medium back and forth in the axial direction. 1 means the temperature of the heat transfer medium.

[0050] 3, a pair of heaters 80 are provided, but only one may be provided. Also, the non-contact heating unit may be configured with a blower device that blows hot air instead of the heater 80.

[0051] In all of Methods 1 to 3, the thickness of the molten F polymer before contacting the first cooling roll 30 (thickness t in FIGS. 1 and 3) is preferably 100 to 200 μm. In this case, the accuracy of heating by the heater 80 and cooling by the first cooling roll 30 is improved, and the resulting film 1 is less likely to have residual distortion in the MD and TD.

[0052] If the ratio of the opening of the lip 21 of the T-die 20 to the thickness of the final film 1 (draw ratio) is large, the molecular chains of the polymer contained in the F polymer become strongly stretched, and the polymer molecules tend to be oriented. As a result, the MD and TD distortions remaining in the film 1 tend to increase. Therefore, a draw ratio of 50 or less is preferred. The peripheral speed of the first cooling roll 30 (peripheral speed S in Figs. 1 and 3) is more preferably 2 to 20 m / min from the viewpoint of further reducing the MD and TD distortions remaining in the film 1. The temperature of the second cooling roll 40 is more preferably 30 to 90°C.

[0053] The F polymer (film 1) after being separated from the first cooling roll 30 may be subjected to a surface treatment capable of introducing adhesive functional groups into its surface. Examples of such surface treatments include discharge treatments such as corona discharge treatment and plasma treatment, plasma graft polymerization treatment, light irradiation treatments such as electron beam irradiation and excimer UV light irradiation, itro treatment using a flame, and wet etching treatment using metallic sodium. This surface treatment introduces polar functional groups such as hydroxyl groups, carbonyl groups, and carboxyl groups onto the surface of the film 1, thereby improving adhesion to other surfaces.

[0054] The laminate of the present invention (hereinafter also referred to as "the present laminate") will be described below. The present laminate is a laminate in which an F polymer layer (a layer made of the film of the present invention) and a substrate layer are laminated in this order. The present laminate is preferably obtained by laminating the film of the present invention and a film-like or sheet-like substrate other than the film of the present invention using a roll-to-roll method, for example, at a melting temperature of the F polymer to 400°C, or by overlapping the two and then heat-pressing them at a melting temperature of the F polymer to 400°C.

[0055] Examples of materials for the substrate layer in the present laminate include metals and resins. Examples of resins include thermoplastic resins, non-thermofusible resins, uncured curable resins, and cured curable resins. Metals and heat-resistant resins are particularly preferred. The substrate layer in the present laminate is preferably a layer formed from a film-like or sheet-like substrate, and metal foil and heat-resistant resin film are preferred as the film-like or sheet-like substrate. The substrate layer in the present laminate may also be a resin layer or a metal layer formed on the surface of the film of the present invention by coating, plating or other means.

[0056] When the substrate layer in the present laminate is a layer formed from a metal foil, the ten-point average roughness of the surface of the metal foil is preferably 0.01 μm or more and 0.5 μm or less. In this case, the film of the present invention and the metal foil tend to adhere more firmly. Therefore, the laminate having the film of the present invention with high thickness accuracy and the printed circuit board obtained by processing the same tend to exhibit remarkable electrical properties. Specifically, when the substrate layer in the present laminate is made of metal foil, the dielectric loss tangent of the F polymer layer of the present laminate at a frequency of 10 GHz is preferably 0.0001 to 0.0020.

[0057] Examples of materials for the metal foil include iron, copper, nickel, titanium, aluminum, and alloys thereof (stainless steel, nickel 42 alloy, etc.). As the metal foil, rolled copper foil and electrolytic copper foil are preferred. The surface of the metal foil may be subjected to an anti-rust treatment (formation of an oxide film such as chromate). The surface of the metal foil may also be treated with a silane coupling agent. In this case, the treatment area may be a part of the surface of the metal foil, or the entire surface. The thickness of the metal foil is preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm.

[0058] Alternatively, a carrier-attached metal foil containing two or more layers of metal foil may be used. Examples of carrier-attached metal foils include carrier-attached copper foils consisting of a carrier copper foil (thickness: 10 to 35 μm) and an ultrathin copper foil (thickness: 2 to 5 μm) laminated on the carrier copper foil via a release layer. The use of such carrier-attached copper foils enables the formation of fine patterns by the MSAP (modified semi-additive) process. The release layer is preferably a metal layer containing nickel or chromium, or a multilayer metal layer formed by laminating such metal layers. A specific example of the metal foil with a carrier is "FUTF-5DAF-2" manufactured by Fukuda Metal Foil and Powder Co., Ltd.

[0059] The substrate layer of the laminate may be a metal layer formed by a vapor deposition method or a plating method. The metal layer can be formed, for example, by forming a metal seed layer on the surface of the film of the present invention by a sputtering method or an electroless plating method, and then growing a metal from the seed layer by an electrolytic plating method. Before forming the seed layer, the surface of the film of the present invention may be surface-treated. Examples of surface treatment methods include annealing treatment, corona treatment, plasma treatment, ozone treatment, excimer treatment, and silane coupling treatment. Metals that can be plated by electroless plating include copper and nickel. Examples of metals in the seed layer include copper, nickel, chromium, nichrome alloys, and titanium alloys. An example of the metal to be plated by electrolytic plating is copper.

[0060] When the substrate layer in the present laminate is a layer of a heat-resistant resin film, the film contains one or more types of heat-resistant resin and may be a single-layer film or a multi-layer film. The heat-resistant resin film may have glass fibers, carbon fibers, or the like embedded therein. When the substrate layer is a layer of a heat-resistant resin film, the present laminate is preferably a laminate having a structure in which the film of the present invention is laminated on both sides of the substrate layer. In this case, since the film of the present invention is laminated on both sides of the heat-resistant resin film, the linear expansion coefficient of the present laminate is significantly reduced, and warping is unlikely to occur. Examples of heat-resistant resins include polyimide, polyarylate, polysulfone, polyarylsulfone, aromatic polyamide, aromatic polyetheramide, polyphenylene sulfide, polyaryletherketone, polyamideimide, liquid crystalline polyester, and liquid crystalline polyesteramide, and polyimide (particularly, aromatic polyimide) is preferred.

[0061] In the present laminate, which is a heat-resistant resin film having the film of the present invention on both sides, the thickness (total thickness) is preferably 220 μm or more, more preferably 250 μm or more. The thickness is preferably 500 μm or less. In such a configuration, the ratio of the total thickness of the two F polymer layers to the thickness of the heat-resistant resin film is more preferably 0.8 or more. The ratio is preferably 5 or less. In this case, the properties of the heat-resistant resin film (high yield strength, low plastic deformation resistance) and the properties of the F polymer layer (low water absorbency) are exhibited in a well-balanced manner.

[0062] Specific examples of the laminate include a metal clad laminate having a metal foil and an F polymer layer on at least one surface of the metal foil, and a multilayer film having a polyimide film and an F polymer layer on both surfaces of the polyimide film. A preferred embodiment of the present laminate in which the base layer is a heat-resistant resin film is a three-layer film in which the heat-resistant resin film is a polyimide film having a thickness of 20 to 100 μm, and a film of the present invention, a polyimide film, and a film of the present invention are laminated in this order in direct contact with each other. In this embodiment, the thickness of the two films of the present invention is the same, preferably 100 to 200 μm. Furthermore, the ratio of the total thickness of the two films of the present invention to the thickness of the polyimide film is preferably 0.5 to 5. A laminate in this embodiment is most likely to exhibit the effects of the laminate described above.

[0063] Here, the outermost surface of the present laminate (the surface of the F polymer layer opposite the substrate layer) may be further surface-treated in order to further improve its linear expansion properties and adhesiveness. Examples of the surface treatment method include annealing treatment, corona treatment, plasma treatment, ozone treatment, excimer treatment, and silane coupling treatment. The annealing conditions are preferably a temperature of 120 to 180° C., a pressure of 0.005 to 0.015 MPa, and a time of 30 to 120 minutes. Gases used in the plasma treatment include oxygen gas, nitrogen gas, rare gas (argon, etc.), hydrogen gas, ammonia gas, and vinyl acetate. These gases may be used alone or in combination of two or more.

[0064] The metal foil of this laminate (metal foil with F polymer layer), whose base layer is metal foil, is etched to form a transmission circuit, thereby obtaining a printed circuit board. Specifically, the printed circuit board can be manufactured by etching the metal foil to process it into a predetermined transmission circuit, or by processing the metal foil into a predetermined transmission circuit by electrolytic plating (semi-additive method (SAP method), MSAP method, etc.). A printed circuit board manufactured from metal foil with an F polymer layer has a transmission circuit formed from metal foil and an F polymer layer, in that order. Specific examples of the configuration of a printed circuit board include transmission circuit / F polymer layer / prepreg layer and transmission circuit / F polymer layer / prepreg layer / F polymer layer / transmission circuit. In the manufacture of such a printed circuit board, an interlayer insulating film may be formed on the transmission circuit, and a coverlay film may be laminated on the transmission circuit. These interlayer insulating films and coverlay films may be formed from the film of the present invention.

[0065] The film of the present invention, the method for producing the same, and the laminate of the present invention have been described above, but the present invention is not limited to the configurations of the above-described embodiments. For example, in the film of the present invention and the laminate of the present invention, any other structure may be added to the above-mentioned structure, or any structure that exhibits the same function may be substituted. Furthermore, the manufacturing method of the present invention may have any other steps added to the configuration of the above embodiment, or may be substituted with any other steps that produce the same effect. [Example]

[0066] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Details of each component are shown below. [F Polymer] F polymer 1: a polymer having an acid anhydride group, containing 98.0 mol%, 0.1 mol%, and 1.9 mol% of TFE units, NAH units, and PPVE units, in that order (melting temperature: 300°C); F polymer 2: a polymer having no functional group, containing 98.0 mol%, and 2.0 mol% of TFE units and PPVE units, in that order (melting temperature: 300°C). In addition, F polymer 1 has a carbonyl group-containing group with a main chain carbon number of 1 × 10 6 Each polymer has 1000 molecules, and F polymer 2 has 40 molecules. [pellet] Pellet 1: Pellet of F polymer 1 (diameter: 2.2 mm) [Haze measurement] The haze (cloudiness) of the films obtained in each example was measured in accordance with JIS K 7136 using NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.). [Thermal expansion / contraction rate] According to JIS K7133:1999, the film was cut into a size of 120 mm x 120 mm, and 100 mm gauge lines were drawn in the machine direction (MD) and cross direction (TD) of the film, and the length of the gauge lines was measured. The film was placed in an oven at 180°C for 30 minutes, then naturally cooled to 25°C, and the length of the gauge lines was measured again, and the expansion / contraction ratio was calculated according to the following formula. Formula: {(length of gauge line before heating) - (length of gauge line after heating)} / (length of gauge line before heating) x 100 [Film appearance] The film was placed on a smooth glass surface, and the presence or absence of warping (waviness) was checked and evaluated according to the following criteria. ◯: No warping (waviness) observed. ×: Warpage (waviness) is observed.

[0067] [Example 1] (1) Film manufacturing After being fed into an extruder at 350 ° C, F polymer 1 was extruded from a 1600 mm wide T-die to a thickness of 125 μm. The die temperature was 350 ° C, and the die lip temperature was 370 ° C. The extruded molten F polymer 1 was sandwiched between a first cooling roll 30 at 200 ° C and a quenching roll 301, which was a metal elastic roll controlled at 90 ° C., and then, toward the first cooling roll, an air knife (height 50 mm) installed in a direction perpendicular to the tangent line contacting the first cooling roll was blown uniformly in a line in the width direction of the first cooling roll 30 at a wind speed of 15 m / sec. The first cooling roll 30 was pressed against the first cooling roll 30, and then passed through a second cooling roll 40 at 90 ° C. After that, it was taken up and wound by take-up rolls 61 and 62 heated to 90 ° C. The resulting film (hereinafter referred to as PFA film 1) had a haze of 3%, and the thermal expansion and contraction rates after heating at 180°C for 30 minutes were 0.2% in MD and -0.3% in TD. A hopper was connected to the upstream of the kneading section of the extruder, and F polymer 1 was added by placing pellets 1 in the hopper, reducing the pressure in the hopper to 100 Pa or less, and heating the hopper, adjusting the temperature of the F polymer at the connection section to 180°C. In addition, the molten F polymer 1 extruded from the T-die was heated to 320°C using a non-contact heater before contacting the quench roll and the first roll. (2) Antenna substrate manufacturing and evaluation A nickel-chromium alloy layer was formed on PFA film 1 by roll-to-roll sputtering to a thickness of 10 nm, and then a copper layer was formed on the nickel-chromium alloy layer by sputtering to a thickness of 200 nm. A dry film resist was then roll-laminated on top of the copper layer at 90°C, and then exposed and developed to a mesh width of 6 μm. The mesh portion was plated to a thickness of 6 μm by copper sulfate electrolytic copper plating. After that, the dry film resist was peeled off, and then the copper layer and nickel-chromium alloy layer formed by sputtering were removed by etching to obtain an antenna substrate. The electrical resistance of the obtained antenna substrate was measured, and the evaluation of whether or not electrical continuity was achieved was performed by rating it as conductive (◯) / non-conductive (×). In addition, the haze of the antenna substrate after forming the mesh antenna was measured by the method described above. Table 1 shows the film manufacturing conditions, film characteristics, and performance evaluation results as an antenna.

[0068] [Example 2] A film (PFA film 2) was produced in the same manner as in Example 1(1), except that F polymer 2 was used instead of F polymer 1 and air was not blown onto the molten F polymer 2 with an air knife on the first cooling roll. Using the obtained PFA film 2, an antenna substrate and an antenna were produced and evaluated in the same manner as in Example 1(2). The film production conditions, film properties, and antenna performance evaluation results are shown in Table 1.

[0069] [Example 3] A film (PFA film 3) was produced in the same manner as in (1) of Example 1, except that F polymer 1 was extruded from a T-die to a thickness of 125 μm, no quenching roll 301 was used (i.e., no sandwiching was performed between the quenching roll 301 and the first cooling roll 30), and air was not blown onto the molten F polymer 1 with an air knife on the first cooling roll, and the film was taken up via the first cooling roll. Using the obtained PFA film 3, an antenna substrate and an antenna were produced in the same manner as in (2) of Example 1, and evaluated in the same manner. The film production conditions, film properties, and antenna performance evaluation results for the obtained PFA film 3 are shown in Table 1. PFA film 3 had poor adhesion to the first cooling roll, and "air marks" were observed, which are marks caused by air getting between the film and the first cooling roll, and the appearance was poor.

[0070] [Table 1] [Industrial Applicability]

[0071] The film of the present invention is transparent and has excellent dimensional stability, making it useful as an antenna covering material. Furthermore, the film of the present invention can be easily processed into metal laminates (resin-coated metal foils), and the resulting processed articles can be applied to a variety of fields, including flexible devices such as transparent flexible printed circuit boards, antenna components, printed circuit boards, sports equipment, and food industry products, as well as wearable devices and medical devices that emphasize design. The entire contents of the specification, claims, abstract and drawings of Japanese Patent Application No. 2020-062167, filed on March 31, 2020, are hereby incorporated by reference as part of the disclosure of the specification of the present invention. [Explanation of symbols]

[0072] DESCRIPTION OF SYMBOLS 1...film, 10,101...manufacturing apparatus, 20...T-die, 21...lip, 30...first cooling roll, 301...quenching roll, 40...second cooling roll, 50...take-up roll, 61, 62...conveyor roll, 70...air knife, 80...heater, t...thickness, S...circumferential speed, 11...extrusion molding apparatus, 2...hopper, 21...first stage, 211...heater, 212...connection section, P1...pump, 22...second stage, 221...heater, 222...connection section, P2...pump, 3...kneading section, 31...cylinder, 311...tip opening, 32...screw, 33...gearbox, 331...rotating shaft, 34...motor, 341...rotating shaft, 35...heater, 5...T-die, 6...static mixer, L...total length, D...diameter

Claims

1. An extrusion-molded film made of a tetrafluoroethylene-based polymer, the film having a thickness of 100 to 200 μm, a haze of 8% or less, and a thermal expansion / contraction rate of −1 to +1% in both the machine direction and width direction of the film after heating at 180°C for 30 minutes, the tetrafluoroethylene-based polymer comprising a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether).

2. 2. The film according to claim 1, wherein the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer containing units based on perfluoro(alkyl vinyl ether) and having a polar functional group, or a tetrafluoroethylene-based polymer containing 2.0 to 5.0 mol% of units based on perfluoro(alkyl vinyl ether) based on all units and having no polar functional group.

3. 3. The film according to claim 1, wherein the melting temperature of the tetrafluoroethylene-based polymer is 260 to 320°C.

4. A film described in any one of claims 1 to 3, which is for use in printed circuit boards.

5. A film described in any one of claims 1 to 3, which is for use as an antenna substrate.

6. A laminate comprising a layer made of the film according to any one of claims 1 to 5 and a substrate layer made of a substrate other than said film.

7. The laminate described in claim 6, wherein the substrate layer is a metal foil.

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