Fluororesin film and method for producing the same

Abstract

Provided is a film constituted by a tetrafluoroethylene-based polymer, the film having a thickness of 100-200 μm, a haze of 8% or less, and a thermal expansion / contraction rate, after heating for 30 minutes at 180℃, of -1% to +1%, inclusive, in both a width direction and a flow direction thereof.

Description

Technical Field

[0001] The present invention relates to a film of a tetrafluoroethylene-based polymer and a method for producing the same.

Background Art

[0002] As the weight reduction and miniaturization of electronic devices progress, flexible printed circuit boards (FPCs) are widely adopted as lightweight and flexible wiring materials to address the wiring amount and space limitations within the devices. In recent years, as the transmission signals in printed circuit boards have become faster, the frequency of signals has increased. Along with this, FPCs are strongly required to have low dielectric characteristics (low dielectric constant, low dielectric tangent) in the high-frequency region. In response to such requirements, as a base film used for FPCs, base films composed of liquid crystal polymers (LCPs), syndiotactic polystyrenes (SPSs), polyphenylene sulfides (PPSs), etc., which have low dielectric characteristics, have been proposed in place of conventional polyimides (PIs) and polyethylene terephthalates (PETs). On the other hand, with the pursuit of improving the designability of electronic devices, the opportunities for using FPCs in places visible to people, such as flexible devices like flexible displays and touch panels, and electronic devices that use semiconductor elements such as LEDs by reflow, are increasing. In such electronic devices, etc., it is necessary for the FPC to have transparency.

[0003] Although PI films are excellent in heat resistance, they have problems in transparency. PET films are excellent in transparency but have low heat resistance, and when used in flexible printed circuit boards, warping and dimensional changes of the base material due to heat during reflow become issues. Tetrafluoroethylene-based polymers such as polytetrafluoroethylene (PTFE) have high transparency and are excellent in physical properties such as chemical resistance, water and oil repellency, heat resistance, and electrical properties. They also have a low dielectric constant and a low dielectric tangent compared to materials such as PI, LCP, SPS, and PPS. Therefore, they can be used as a base film for FPCs that are transparent and have excellent reflow resistance. On the one hand, tetrafluoroethylene-based polymers have poor dimensional stability and are prone to displacement during circuit processing. Therefore, Patent Document 1 proposes a method of removing the strain by annealing treatment (heat treatment) after film formation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Tetrafluoroethylene-based polymers have crystallinity, and the crystals are likely to grow during the cooling process of the melt-molded body. Therefore, the obtained film is likely to have a large haze even if the light transmittance is high. Also, when the film becomes thick, even if heat treatment is performed as in the method of Patent Document 1, the strain is difficult to be eliminated, and due to poor dimensional stability, the flatness of the film may be impaired by the heat treatment.

[0006] As a result of intensive studies, the present inventor has found a film having good dimensional stability, low haze, good yield in circuit formation, and capable of achieving both transparency and heat resistance. An object of the present invention is to provide a film having the above characteristics and a method for producing the same.

Means for Solving the Problems

[0007] The present invention has the following aspects. <1> An extruded film composed of a tetrafluoroethylene-based polymer, having a thickness of 100 to 200 μm, a haze of 8% or less, and a thermal expansion rate after heating at 180°C for 30 minutes of -1 to +1% in both the flow direction and the width direction of the film. <2>The film according to <1>, wherein the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). <3>The film according to <1> or <2>, wherein the tetrafluoroethylene-based polymer contains units based on perfluoro(alkyl vinyl ether) and is a tetrafluoroethylene-based polymer 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) with respect to all units and having no polar functional group. <4>The film according to any one of <1> to <3>, wherein the melting temperature of the tetrafluoroethylene-based polymer is 260 to 320°C.

[0008] <5>A method for producing the film according to any one of <1> to <4> by a T-die casting method, which includes an operation of discharging the tetrafluoroethylene-based polymer from a die in a molten state and extruding it, and sandwiching and cooling the film between two temperature-controlled rolls. <6>The production method according to <5>, wherein the temperature of one of the two temperature-controlled rolls is 150 to 250°C and the temperature of the other is 80 to 150°C. <7>The production method according to <5> or <6>, further including an operation of adjusting the temperature of the pellets at the connection portion of the hopper to the kneading portion to the range of (the melting temperature - 200) to (the melting temperature - 100)°C and then supplying the pellets to the kneading portion when producing a film by discharging a melt-kneaded product melted and kneaded in the kneading portion from a T-die after charging pellets of a tetrafluoroethylene-based polymer having a melting temperature of 260 to 320°C into the hopper and providing an extrusion molding apparatus having a kneading portion and a hopper connected to the kneading portion. <8>The production method according to any one of <5> to <7>, wherein the diameter of the pellets is 1.0 to 4.0 mm.

[0009] <9>The manufacturing method according to any one of <5> to <8>, wherein the hopper is a multi-stage hopper including a first-stage portion and a second-stage portion disposed closer to the kneading portion than the first-stage portion. <10>The manufacturing method according to any one of <5> to <9>, wherein the pressure in the stage portion closest to the kneading portion of the hopper is 1000 Pa or less. <11>The manufacturing method according to any one of <5> to <10>, wherein the extrusion molding apparatus includes a T-die connected to the opposite side of the hopper in the axial direction of the kneading portion, and a static mixer provided between the kneading portion and the T-die. <12>The manufacturing method according to any one of <5> to <11>, further including an operation of discharging the tetrafluoroethylene-based polymer from the T-die in a molten state and heating the molten tetrafluoroethylene-based polymer with a non-contact heating unit before contacting the first cooling roll. <13>The manufacturing method according to <12>, wherein 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. <14>The manufacturing method according to <12> or <13>, wherein 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 unit is 70°C or less.

[0010] <15>A laminate having a layer made of any one of the films of <1> to <4> and a base material layer made of a base material other than such a film.

Advantages of the Invention

[0011] According to the present invention, there are provided a film having good dimensional stability, low haze, good yield in circuit formation, and capable of achieving both transparency and heat resistance, and a method for manufacturing the same. According to the present invention, it is possible to provide a film having a thickness of around 100 μm, which is particularly preferable as a base material for an antenna substrate. The film of the present invention is useful as a colorless, transparent, and low-loss antenna substrate.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] The following terms have the following meanings. "Film thickness" is the average value of the measured values obtained by measuring the film thickness at 10 points at equal distances in the width direction using a contact thickness gauge DG-525H (manufactured by Ono Sokki Co., Ltd.) with a measuring head AA-026 (Φ10 mm, SR7). "Melting temperature of the polymer" is the temperature corresponding to the maximum value of the melting peak measured by differential scanning calorimetry (DSC) method. "Unit" in a polymer means an atomic group based on one molecule of the monomer formed by polymerization of the monomer. The unit may be a unit directly formed by a polymerization reaction, or a unit in which a part of the unit is converted into another structure by treating the polymer. Hereinafter, the unit based on monomer a is also simply referred to as "monomer a unit". "Glass transition point of the polymer" is a value measured by analyzing the polymer by dynamic viscoelasticity measurement (DMA) method.

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

[0015] In the film of ordinary thermoplastic fluororesin, molding strain resulting from its manufacturing method (melt molding method by extrusion molding) remains. 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 and contraction rate of -1 to +1% in both the MD and TD directions, with small distortion and sufficient uniformity in each direction, excellent dimensional stability, and even when the thickness is 100 to 200 μm, the haze is 8% or less, showing excellent transparency. Therefore, even in a laminate having such a film layer, since the distortion is small and sufficiently uniform, it is considered to have excellent thermal shock resistance, suppressed deformation, and excellent dimensional stability. For example, the laminate of the present invention having a metal foil as the base material layer has high thermal shock resistance when forming through-holes or vias during processing it into a printed wiring board, and as a result, it is easy to obtain a printed wiring board with less likelihood of wire breakage.

[0016] The thermal expansion and contraction rate of the film is measured as follows. First, a 12 cm square test piece having two sides along the MD and two sides along the TD is cut out from the film. Next, line segments with a length of 10 cm are drawn on the surface of the obtained test piece in the MD and TD directions respectively. Next, this test piece is placed in an oven at 180 °C for 30 minutes for heating and then taken out, naturally cooled to 25 °C, and then the length of the line segment is measured again. The thermal expansion rate is a value 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 rate is the rate of change (percentage) in the length of the line segment before and after heating. Note that a negative value indicates an expansion of the film, and a positive value indicates a contraction of the film. The thermal expansion 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%. If the thermal expansion 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 based on tetrafluoroethylene (TFE) (TFE units). 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 moldability 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 from 75 to 125°C, more preferably from 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. PAVE includes CF 2 =CFOCF 3 , C.F. 2 =CFOCF 2 CF 3 and CF 2 =CFOCF 2 CF 2 CF 3 (PPVE) is preferred, with PPVE being more preferred.

[0019] The F polymer preferably has a polar functional group. The polar functional group may be contained in the units in the F polymer or may be contained in the end groups of the main chain of the F polymer. As the latter aspect, there may be mentioned an F polymer having a polar functional group as an end group derived from a polymerization initiator, a chain transfer agent, etc., and an F polymer having a polar functional group obtained by subjecting the F polymer to plasma treatment or ionizing radiation treatment. As the polar functional group, a hydroxyl group-containing group and a carbonyl group-containing group are preferable. As the hydroxyl group-containing group, a group containing an alcoholic hydroxyl group is preferable, and -CF 2 CH 2 OH and -C(CF 3 ) 2 OH are more preferable. The carbonyl group-containing group is a group containing a carbonyl group (>C(O)), and as the carbonyl group-containing group, a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH 2 ), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)- etc.) and a carbonate group (-OC(O)O-) are preferable, and an acid anhydride residue is more preferable.

[0020] When the F polymer has a carbonyl group-containing group, the number of carbonyl group-containing groups in the F polymer is preferably 10 to 5000, more preferably 100 to 3000, and even more preferably 800 to 1500 per 1×10 6 carbons in the main chain. 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 International Publication No. 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 preferable. These F polymers are likely to form microspherulites in the molded article, and the adhesiveness with other components is likely to increase. As a result, it is easier to obtain a molded article excellent in surface smoothness, adhesiveness and electrical properties.

[0022] Polymer (1) is preferably a polymer containing TFE units, PAVE units, and units based on monomers having polar functional groups, and more preferably a polymer containing these units in this order at 90 to 99 mol%, 0.5 to 9.97 mol%, and 0.01 to 3 mol% with respect to all units. Further, as the monomer having a polar functional group, itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH") are preferable. Specific examples of Polymer (1) include the polymers described in International Publication No. 2018 / 16644.

[0023] Polymer (2) consists 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 with respect to 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% with respect to all units. Note that Polymer (2) having no polar functional group means that the number of polar functional groups of the polymer is less than 500 per 1×10 6 carbon atoms constituting the polymer main chain. The number of the above polar functional groups is preferably 100 or less, more preferably less than 50. The lower limit of the number of the above polar functional groups is usually 0. Polymer (2) may be produced using a polymerization initiator, a chain transfer agent, etc. that do not generate a polar functional group as the end 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 end group of the polymer main chain). Examples of the fluorination treatment method include a method using fluorine gas (see Japanese Patent Application Laid-Open No. 2019-194314, etc.).

[0024] The film of the present invention may contain resins other than the F polymer. However, the content of the F polymer contained in the film is preferably 80% by mass or more, more preferably 100% by mass. Examples of resins other than the F polymer include epoxy resins, polyimide resins, polyamic acids which are 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, polysulfone, polyallyl sulfone, aromatic polyamide resins, aromatic polyether amides, polyphenylene sulfide, polyallyl ether ketone, polyamideimide, and polyphenylene ether.

[0025] The film of the present invention may further contain, for example, inorganic fillers, organic fillers, thixotropy-imparting agents, defoaming agents, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brightening agents, colorants, conductive agents, mold release agents, surface treatment agents, viscosity regulators, flame retardants, and the like.

[0026] Preferred inorganic fillers include boron nitride fillers, beryllia fillers (fillers of beryllium oxides), silicate fillers (silica fillers, wollastonite fillers, talc fillers), and metal oxide (cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, etc.) fillers. Further, at least a part of the surface of the inorganic filler may be surface-treated. Examples of the surface treatment agent used for such surface treatment include polyhydric alcohols, saturated fatty acids, their esters, amines, paraffin waxes, silane coupling agents, silicones, and polysiloxanes. The shape of the inorganic filler may be any of granular, acicular (fibrous), plate-like, etc. Specific shapes include spherical, scaly, layered, foliated, almond-shaped, columnar, cockscomb-shaped, equiaxed, leaf-shaped, mica-shaped, block-shaped, flat plate-shaped, wedge-shaped, rosette-shaped, reticulated, and prismatic.

[0027] Hereinafter, the method for manufacturing the film of the present invention will be described. From the viewpoint of being able to adjust the strain of the film, the film of the present invention can preferably be manufactured by the T-die casting method (melt extrusion method using a T-die). The present inventors have found that the MD and TD strains of the film 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 until the molten F-polymer discharged from the T-die crystallizes on the cooling roll. In other words, if the state of the F-polymer and the cooling conditions are appropriately set to control the crystallization of the F-polymer, the thermal shrinkage rates (strains) in the MD and TD directions of the obtained film converge within a predetermined range, and due to the suppression of crystal growth, the present inventors have found that a relatively thick film of 100 to 200 μm can achieve low haze.

[0028] The method for manufacturing the film of the present invention includes an operation of discharging the F-polymer from the T-die in a molten state and performing extrusion molding, and sandwiching the film between two temperature-controlled rolls for cooling (this method 1). Preferably, the temperature of one of the two temperature-controlled rolls is 150 to 250°C, and the temperature of the other is 80 to 150°C. More preferably, one of the two temperature-controlled rolls is a metal roll controlled at 150 to 250°C, and the other is a metal elastic roll controlled at 80 to 150°C.

[0029] FIG. 1 is a schematic view showing an embodiment of a film manufacturing apparatus used in the present method 1. The manufacturing apparatus 10 shown in FIG. 1 includes a T-die 20, a first cooling roll (first cooling roll) 30 disposed vertically below the T-die 20, a quenching roll 301, a second cooling roll 40 provided in parallel with the first cooling roll 30, a winding roll 50 for winding the film 1, and conveying rolls 61 and 62 disposed between the winding roll 50 and the second cooling roll 40. Further, the first cooling roll 30 may further include an air knife 70, and it is preferable to include it.

[0030] The F-polymer is melted by heating in an extruder (not shown) connected to the T-die 20 and supplied into the T-die 20. The molten F-polymer is discharged from the lip 21 of the T-die 20 toward the first cooling roll 30. Next, the discharged molten F-polymer contacts the first cooling roll 30 and is cooled by being sandwiched between the first cooling roll 30 by the quenching roll 301. Further, the F-polymer is conveyed by the conveying rollers 61 and 62 after passing through the second cooling roll 40. Thereafter, the F-polymer is wound around the winding roll 50 as the film 1. As the first cooling roll 30, it is preferable to use a metal roll capable of temperature control, and as the quenching roll 301, it is preferable to use a metal elastic roll.

[0031] Examples of the metal elastic roll include a roll in which the surface is made of a metal material such as stainless steel and the space between the surface metal material and the shaft roll is filled with an elastic material such as a fluid or rubber. The metal elastic roll is composed of, for example, a substantially cylindrical shaft roll rotatably provided, a cylindrical metal thin film disposed so as to cover the outer peripheral surface of this shaft roll and contacting the film-like object, and a fluid enclosed between these shaft roll and the metal thin film. The fluid causes the metal elastic roll to exhibit elasticity and has the property that roll pressure bonding forming is possible at a low line pressure. In the present invention, such a property is utilized to contribute to the control of the film cooling conditions. Examples of the material of the shaft roll include stainless steel. The metal thin film is made of stainless steel, and its thickness is preferably 2 to 5 mm. The metal thin film is preferably flexible or bendable, and preferably has a seamless structure without a welded joint. The metal elastic roll provided 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 manner as a normal mirror 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 roll. Examples of commercially available metal elastic rolls include the UF roll of Hitachi Zosen Corporation and the SF roll of Chiba Machinery Industry Co., Ltd.

[0032] The molten F polymer is preferably sandwiched and cooled between a quenching roll 301 which is preferably a metal elastic roll and a first cooling roll 30 which is preferably a metal roll, so that the film can be rapidly cooled to suppress crystal growth and reduce haze, and the accumulation of strain on the film sandwiched between the first cooling roll and the quenching roll can be reduced. 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 rapidly cooling the film. In addition, both the first cooling roll and the quenching roll preferably have a structure having a mechanism for passing a heat medium, and more preferably have a duplex mechanism in which the heat medium reciprocates axially and repeatedly passes through. The temperature of the first cooling roll and the temperature of the quenching roll both mean the temperature of the heat medium. When the quenching roll is a metal elastic roll, it is preferably within a temperature range that does not impair the characteristics of the metal elastic roll itself.

[0033] In the first method 1, it is preferable that the air knife 70 is further provided at the position immediately after the molten F polymer is sandwiched between the first cooling roll 30 and the quenching roll 301. The air knife 70 cools the molten F polymer and presses it against the first cooling roll 30 by linearly and uniformly blowing a slit-shaped air flow in the width direction of the first cooling roll 30 on the line where the molten F polymer contacts the first cooling roll 30. Similar to the quenching roll 301, it has the effect of increasing the cooling efficiency of the F polymer, suppressing the haze of the obtained film, and reducing the thermal shrinkage 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 shrinkage rate of the film becomes 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 / s.

[0034] The method for producing the film of the present invention further includes, in the first method 1, a method for producing a film from pellets of an F polymer having a melting temperature of 260 to 320 °C using, for example, the extrusion molding apparatus 11 shown in FIG. 2 (the second method). FIG. 2 is a conceptual diagram showing an embodiment of the extrusion molding apparatus used in the second method. In the following description, the right side in FIG. 2 (the front in the transfer direction of the molten kneaded material) will be referred to as the "tip" and the left side (the rear in the transfer direction) will be referred to as the "base end".

[0035] The extrusion molding apparatus 11 shown in FIG. 2 includes a hopper 2 and a kneading section 3 communicating with the hopper 2. The kneading section 3 of the present embodiment is composed of a single-screw kneader having a cylinder 31 and a single screw 32 rotatably provided in the cylinder 31. By using a single-screw kneader, it is easy to prevent the F polymer from deteriorating when melting and kneading the pellets. 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) represented by 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, while preventing the deterioration of the F polymer, sufficient shear stress can be applied to the F polymer, and it is easy to reduce the temperature unevenness of the melt-kneaded product.

[0036] On the base end side of the cylinder 31, a gear box 33 and a motor 34 are arranged in order. A gear (not shown) is connected to the tip of the rotating shaft 341 of the motor 34, and this gear meshes with a predetermined gear (not shown) in the gear box 33. In the gear box 33, the rotational motion of the rotating shaft 341 is accelerated or decelerated and transmitted to the rotating shaft 331. The tip of the rotating shaft 331 is connected to the base end side of the screw 32. With such a configuration, the rotation of the motor 34 is transmitted to the screw 32, and the screw 32 is rotated at a predetermined rotational speed. As a result, the melt-kneaded product is transferred from the base end side (left side) to the tip side (right side) in FIG. 2.

[0037] Further, a heater 35 is provided on the outer peripheral portion of the cylinder 31. The pellets (F polymer) supplied into the cylinder 31 are melted by the heating of the heater 35, and at the same time, are mixed (kneaded) by the rotation of the screw 32 and transferred toward the tip side. As a result, the pellets are melted and kneaded, and the melt-kneaded product is extruded from the tip opening 311 of the cylinder 31. A T-die 5 is arranged on the tip side of the cylinder 31 (the side opposite to the hopper 2 in the axial direction of the kneading section 3). The melt-kneaded product 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, an F-polymer film is manufactured as described in Method 1. Here, it may be understood that the T-die 5 in FIG. 2 corresponds to the T-die 20 in FIG. 1 (or FIG. 3 described later). Although not shown, a heater is also provided on the T-die 5.

[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 melt-kneaded material to stir the melt-kneaded material. By installing such a static mixer 6, it is not necessary to apply an unnecessary external force to the melt-kneaded material, so that deterioration of the melt-kneaded material can be suppressed and kneading can be performed uniformly.

[0039] A hopper 2 is arranged on the proximal end side of the cylinder 31. The hopper 2 of this embodiment is composed of a two-stage hopper including a funnel-shaped first-stage portion 21 and a funnel-shaped second-stage portion 22 arranged on the kneading section 3 (cylinder 31) side with respect to the first-stage portion 21. A heater 211 and a pump P1 are connected to the first-stage portion 21. Thereby, the pellets supplied into the first-stage portion 21 can be heated under reduced pressure. The first-stage portion 21 is connected to the second-stage portion 22 via a connection portion 212. A heater 221 and a pump P2 are connected to the second-stage portion 22. Thereby, the pellets supplied into the second-stage portion 22 can be heated under reduced pressure. The second-stage portion 22 is connected to the cylinder 31 via a connection portion 222. The inner surface (inner circumferential surface) of the hopper 2 (the first-stage portion 21 and the second-stage portion 22) is preferably coated with a resin film. That is, it is preferable that the inner surface of the hopper 2 is resin-lined. Thereby, it is possible to sufficiently prevent the softened pellets from adhering to the inner surface of the hopper 2. Examples of the constituent material of the resin film include fluororesins such as PTFE.

[0040] The pellets used in this method 2 may contain components other than the F-polymer, but the content of the F-polymer is preferably 80% by mass or more, more preferably 100% by mass. Examples of the components other than the F-polymer include the other resins and additives described above. In addition, examples of the shape of the pellets include spherical and cylindrical shapes, with a cylindrical shape being preferred. The diameter of the pellets is preferably 1.0 to 4.0 mm. With pellets of such a diameter, while preventing bridging (jamming) in the hopper 2, when heated in the hopper 2, the inside can be sufficiently heated (warmed).

[0041] In the present method 2, after pre-heating the F-polymer pellets in the hopper 2, they are supplied to the kneading section 3, and the melt-kneaded product melted and kneaded in the kneading section 3 is discharged from the T-die 5 to produce a film. At this time, the temperature of the pellets at the connection portion 222 of the hopper 2 to the kneading section 3 is adjusted to the range of (X - 200) to (X - 100)°C. Here, X is the melting temperature of the F-polymer. The temperature of the pellets at the connection portion 222 of the hopper 2 to the kneading section 3 is preferably (X - 175) to (X - 125)°C. The specific temperature of the pellets is preferably 70 to 225°C, and more preferably 105 to 195°C. In this case, bridging in the hopper 2 due to softening of the pellets is less likely to occur. Also, since the temperature unevenness of the melt-kneaded product in the kneading section 3 is sufficiently reduced, a film having a uniform thickness and free from the generation of fish eyes is easily obtained.

[0042] The pressure in the second-stage section 22 (the section closest to the kneading section 3) is preferably lower than the pressure in the first-stage section 21, preferably 1000 Pa or less, and more preferably 100 Pa or less. Thereby, the air inside the pellets can be sufficiently removed, preventing the formation of a heat-insulating layer by air and making it easy to prevent temperature unevenness from occurring in the melt-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. If the pellets are melt-kneaded under the above conditions, a homogeneous melt-kneaded product with little temperature unevenness is easily formed. As a result, the film of the present invention is more easily obtained. The melt-kneaded product is supplied to the T-die 5 via the static mixer 6 and discharged from the T-die 5. The melt-kneaded product discharged from the T-die 5 is formed into a film as described in the present method 1 and wound around the winding roll. Further, the extrusion molding apparatus 11 may have a cutting machine if necessary.

[0043] According to the second method, while highly suppressing the surging phenomenon, the polymer is uniformly melted and kneaded without giving an excessive heat history, and thus the film is formed. Therefore, a wide film having a sufficient length in the short side direction and having few defects (fish eyes) can be easily manufactured. The number of fish eyes in the film of the present invention is preferably less than 0.05 per 1 m of the film. 2 The lower limit of the number of fish eyes is 0.

[0044] The method for producing the film of the present invention further includes, in the first method or the second method, a method of discharging the F polymer from the T die in a molten state and heating the molten F polymer in a non-contact heating unit before contacting the first cooling roll (the third method). FIG. 3 is a schematic view showing an embodiment of a film production apparatus used in the third method. The production apparatus 101 shown in FIG. 3 is the same as the production apparatus 10 in the first method, except that it further has a pair of heaters (non-contact heating units) 80 arranged opposite to each other between the T die 20 and the first cooling roll 30.

[0045] The F polymer is melted by heating in an extruder (not shown) connected to the T die 20 and supplied into the T die 20. The molten F polymer is discharged from the lip 21 of the T die 20 toward the first cooling roll 30. Next, when the discharged molten F polymer passes between the pair of heaters 80, it is heated without contacting the heaters 80, contacts the first cooling roll 30, and is pressed against the first cooling roll 30 by the quenching roll 301 and cooled. At this time, by linearly and uniformly blowing a slit-shaped air flow in the width direction of the first cooling roll 30 with an air knife 70 installed in a direction perpendicular to the tangent line in contact with the first cooling roll 30, the molten F polymer can be cooled and pressed against the first cooling roll 30. Further, after passing through the second cooling roll 40, the F polymer is conveyed by the conveying rollers 61 and 62 and wound around the winding roll 50 as the film 1.

[0046] According to such a 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. For this reason, the molten F polymer flowing downward toward the first cooling roll 30 maintains relatively high fluidity, so it is not easily stretched by its own weight or the tensile force of the first cooling roll 30. As a result, it is presumed that the occurrence of the boiling phenomenon (orientation of the F polymer in the MD and TD) is suppressed during film formation, and a film with small MD and TD distortion (thermal expansion rate) as described above can be obtained.

[0047] In particular, in the configuration shown in FIG. 3, since the F polymer discharged from the T die 20 is heated by the heaters 80 from both sides in the thickness direction, the temperature uniformity in the thickness direction is high, and the effect of suppressing the occurrence of the above-mentioned boiling phenomenon is excellent. Further, from the viewpoint of further improving the effect of suppressing the occurrence of the boiling phenomenon, it is preferable to configure the heater 80 so that the temperature in the width direction of the F polymer can also be made uniform. In this case, for example, the width of the heater 80 may be designed to be sufficiently larger than the length in the width direction of the F polymer.

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

[0049] Also, even when cooling by the first cooling roll 30, from the viewpoint of further improving the effect of suppressing the occurrence of the boiling phenomenon, it is preferable to configure the first cooling roll 30 so that the temperatures of the F polymer in the MD and TD directions can be made uniform. Therefore, the first cooling roll 30 preferably has a configuration having a mechanism for passing a heat medium, and more preferably has a double mechanism in which the heat medium reciprocates in the axial direction and repeatedly passes through. Note that the temperature Y 1 of the first cooling roll 30 means the temperature of the heat medium.

[0050] In the configuration shown in FIG. 3, a pair of heaters 80 are arranged, but only one of them may be arranged. Also, the non-contact heating unit may be configured by a blowing device that blows hot air instead of the heater 80.

[0051] For any of the first to third methods, the thickness of the molten F polymer (thickness t in FIGS. 1 and 3) before contacting the first cooling roll 30 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 remaining MD and TD strains in the obtained film 1 are less likely to remain.

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

[0053] The F polymer (film 1) after detaching from the first cooling roll 30 may be subjected to a surface treatment capable of introducing an adhesive functional group on its surface. Examples of such surface treatment include discharge treatment such as corona discharge treatment and plasma treatment, plasma graft polymerization treatment, radiation treatment such as electron beam irradiation and excimer UV light irradiation, flame treatment, and wet etching treatment using metallic sodium. By this surface treatment, polar functional groups such as hydroxy group, carbonyl group, and carboxy group are introduced on the surface of the film 1, and as a result, the adhesiveness with other surfaces is further enhanced.

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

[0055] Examples of the material of the base material layer in this laminate include metals and resins. Examples of the resin include thermoplastic resins, non-thermally fusible resins, uncured products of curable resins, cured products of curable resins, and the like. In particular, metals and heat-resistant resins are preferable. The base material layer in this laminate is preferably a layer formed from a film-like or sheet-like base material. As the film-like or sheet-like base material, metal foil and heat-resistant resin film are preferable. The base material layer in this laminate may also be a resin layer or a metal layer formed on the surface of the film of the present invention by means such as coating or plating.

[0056] When the base material layer in this 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 are more likely to adhere firmly. Therefore, in the laminate having the film of the present invention with high film thickness accuracy and the printed circuit board obtained by processing the same, the electrical characteristics are likely to be remarkably exhibited. Specifically, when the base material layer in this laminate is made of a metal foil, the dielectric tangent of the F-polymer layer of this laminate at a frequency of 10 GHz is preferably 0.0001 to 0.0020.

[0057] Examples of the material of the metal foil include iron, copper, nickel, titanium, aluminum, and alloys thereof (such as stainless steel and nickel 42 alloy). As the metal foil, rolled copper foil and electrolytic copper foil are preferable. The surface of the metal foil may be subjected to rust prevention treatment (formation of an oxide film such as chromate). Further, the surface of the metal foil may be treated with a silane coupling agent. The treatment range at that time 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] Further, as the metal foil, a carrier-attached metal foil containing two or more metal foils may be used. Examples of the carrier-attached metal foil include a carrier-attached copper foil composed of a carrier copper foil (thickness: 10 to 35 μm) and an ultra-thin copper foil (thickness: 2 to 5 μm) laminated on the carrier copper foil via a release layer. By using such a carrier-attached copper foil, it is possible to form a fine pattern by the MSAP (Modified Semi-Additive) process. As the above-mentioned release layer, a metal layer containing nickel or chromium and a multi-layer metal layer in which this metal layer is laminated are preferable. A specific example of the carrier-attached metal foil is the product named "FUTF-5DAF-2" manufactured by Fukuda Metal Foil & Powder Co., Ltd.

[0059] The base material layer of the present laminate may be a metal layer formed by a vapor deposition method and 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 further growing the 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 the surface treatment method include annealing treatment, corona treatment, plasma treatment, ozone treatment, excimer treatment, and silane coupling treatment. Examples of the metal plated by the electroless plating method include copper and nickel. Examples of the metal in the seed layer include copper, nickel, chromium, nichrome alloy, titanium alloy, etc. Examples of the metal plated by the electrolytic plating method include copper.

[0060] When the base material layer in this laminate is a layer of a heat-resistant resin film, such a film contains one or more heat-resistant resins and may be a single-layer film or a multilayer film. Glass fibers, carbon fibers, etc. may be embedded in the heat-resistant resin film. When the base material layer is a layer of a heat-resistant resin film, this laminate preferably has a structure in which the film of the present invention is laminated on both sides of the base material 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 this laminate is significantly reduced, and warping is less likely to occur. Examples of the heat-resistant resin include polyimide, polyarylate, polysulfone, polyallylsulfone, aromatic polyamide, aromatic polyetheramide, polyphenylene sulfide, polyallyl ether ketone, polyamideimide, liquid crystal polyester, and liquid crystal polyester amide, and polyimide (particularly, aromatic polyimide) is preferred.

[0061] In this laminate which is a heat-resistant resin film having the film of the present invention on both sides, its thickness (total thickness) is preferably 220 μm or more, more preferably 250 μm or more. The above 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 above ratio is preferably 5 or less. In this case, the characteristics of the heat-resistant resin film (high yield strength, difficult plastic deformability) and the characteristics of the F-polymer layer (low water absorption) are exhibited in good balance.

[0062] Specific examples of this laminate include a metal foil, a metal-clad laminate having an F-polymer layer on at least one surface of the metal foil, a polyimide film, and a multilayer film having an F-polymer layer on both surfaces of the polyimide film. As a preferred embodiment of the laminate in which the base material layer is a heat-resistant resin film, the heat-resistant resin film is a polyimide film with a thickness of 20 to 100 μm, and examples include a three-layer film in which the film of the present invention, the polyimide film, and the film of the present invention are directly laminated in this order. In such an embodiment, the thicknesses of the two films of the present invention are the same and preferably 100 to 200 μm. Also, 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. The laminate of such an embodiment is most likely to exhibit the effects of the laminate described above.

[0063] Here, the outermost surface of the laminate (the surface opposite to the base material layer of the F-polymer layer) may be further surface-treated in order to further improve its linear expansibility and adhesiveness. Examples of the surface treatment method include annealing treatment, corona treatment, plasma treatment, ozone treatment, excimer treatment, and silane coupling treatment. Regarding the conditions in the annealing treatment, the temperature is preferably 120 to 180 °C, the pressure is preferably 0.005 to 0.015 MPa, and the time is preferably 30 to 120 minutes. Examples of the gas used in the plasma treatment include oxygen gas, nitrogen gas, noble gas (such as argon), 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 the laminate with an F-polymer layer (metal foil with an F-polymer layer) in which the base material layer is a metal foil is etched to form a transmission circuit, and a printed circuit board is obtained. Specifically, a printed circuit board can be manufactured by a method of etching the metal foil to process it into a predetermined transmission circuit or a method of processing the metal foil into a predetermined transmission circuit by an electrolytic plating method (semi-additive method (SAP method), MSAP method, etc.). The printed circuit board manufactured from the metal foil with an F-polymer layer has a transmission circuit formed from the metal foil and an F-polymer layer in this order. Specific examples of the configuration of the printed circuit board include transmission circuit / F-polymer layer / prepreg layer, transmission circuit / F-polymer layer / prepreg layer / F-polymer layer / transmission circuit. In the production of such a printed circuit board, an interlayer insulating film may be formed on the transmission line, or a coverlay film may be laminated on the transmission line. These interlayer insulating films and coverlay films may be formed of the film of the present invention.

[0065] As described above, the film of the present invention, its manufacturing method, and the laminate of the present invention have been described. However, 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, in the above-described configurations, any other arbitrary configuration may be added, or may be replaced with any configuration that exhibits the same function. Also, the manufacturing method of the present invention may have any other arbitrary steps added in the configurations of the above-described embodiments, or may be replaced with any step that produces the same effect.

Example

[0066] Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited thereto. Details of each component are shown below. [F polymer] F polymer 1: A polymer having an acid anhydride group, containing TFE units, NAH units, and PPVE units in this order at 98.0 mol%, 0.1 mol%, and 1.9 mol% (melting temperature 300 °C) F polymer 2: A polymer having no functional group, containing TFE units and PPVE units in this order at 98.0 mol% and 2.0 mol% (melting temperature 300 °C) Note that F polymer 1 has 1000 carbonyl group-containing groups per 1 × 10 6 main chain carbon atoms, and F polymer 2 has 40. [Pellet] Pellet 1: Pellets of F polymer 1 (diameter: 2.2 mm) [Measurement of haze] The haze (cloudiness) of the films obtained in each example etc. was measured in accordance with JIS K 7136 using NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.). [Thermal expansion rate] In accordance with JIS K7133:1999, after cutting the film into a size of 120 mm × 120 mm, a reference line of 100 mm was drawn in the film flow direction (MD) and the width direction (TD), and the length of the reference line was measured. After leaving the film standing in an oven at 180 °C for 30 minutes of heating and then naturally cooling it to 25 °C, the length of the reference line was measured again, and the elongation rate was calculated according to the following formula. Formula: {(Length of the reference line before heating) - (Length of the reference line after heating)} / (Length of the reference line before heating) × 100 [Film appearance] The film was left standing on the surface of a smooth glass, and the presence or absence of warping was confirmed and evaluated according to the following criteria. 〇: No warping is confirmed. ×: Warping is confirmed.

[0067] [Example 1] (1) Film production After charging F polymer 1 into an extruder at 350 °C, it was extruded from a T-die with a width of 1600 mm 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 quenching roll 301, which is a metal elastic roll controlled at 90 °C, and a first cooling roll 30 at 200 °C, and then, from an air knife (height 50 mm) installed in a direction perpendicular to the tangent line in contact with the first cooling roll and facing the first cooling roll, a slit-shaped air flow at 200 °C with a wind speed of 15 m / s was linearly and uniformly blown in the width direction of the first cooling roll 30 and pressed against the first cooling roll 30. Subsequently, after passing through a second cooling roll 40 at 90 °C, it was taken up and wound by winding rolls 61 and 62 heated to 90 °C. The haze of the obtained film (hereinafter referred to as PFA film 1) was 3%, and the thermal elongation rate after heating at 180 °C for 30 minutes was 0.2% in MD and -0.3% in TD. Note that a hopper is connected to the front stage of the kneading section of the extruder. For the input of F-polymer 1, pellets 1 were put into the hopper, and a pressure reduction treatment and a heat treatment were performed in the hopper at 100 Pa or less so that the temperature of the F-polymer at the connection part became 180°C. In addition, the molten F-polymer 1 extruded from the T-die was heat-treated at 320°C with a non-contact heater before contacting the quenching roll and the first roll. (2) Manufacture and evaluation of antenna substrate On the PFA film 1, by a roll-to-roll method, nickel-chromium alloy was sputtered to a thickness of 10 nm to form a nickel-chromium alloy layer. Then, on the nickel-chromium alloy layer, copper was sputtered to a thickness of 200 nm to form a copper layer. Further, after dry film resist was roll-laminated on the copper layer at 90°C, it was exposed and developed so that the mesh width became 6 μm. By copper sulfate electrolytic copper plating, the mesh part was plated to a thickness of 6 μm. Then, the dry film resist was peeled off, and then the copper layer and the 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 conduction was achieved was performed as conduction (〇) / no conduction (×). In addition, the haze of the antenna substrate after forming the mesh antenna was measured by the method described above. The film manufacturing conditions, film characteristics, and performance evaluation results as an antenna are shown in Table 1.

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

[0069] [Example 3] F polymer 1 was extruded from a T-die to a thickness of 125 μm without using a chill roll 301 (i.e., without sandwiching between the chill roll 301 and the first cooling roll 30), and without blowing air onto the molten F polymer 1 with an air knife at the first cooling roll. A film was produced in the same manner as in (1) of Example 1, except that the film was wound up via the first cooling roll (PFA film 3). Using the obtained PFA film 3, an antenna substrate and an antenna were fabricated in the same manner as in (2) of Example 1 and evaluated in the same manner. Table 1 shows the film production conditions, film properties, and performance evaluation results as an antenna for the obtained PFA film 3. The PFA film 3 had poor adhesion to the first cooling roll, and "air marks", which are marks where air had entered between the film and the first cooling roll, were observed, and the appearance was defective.

[0070] [Table 1]

Industrial Applicability

[0071] The film of the present invention is useful as a cover material for an antenna because it is transparent and has excellent dimensional stability. Further, the film of the present invention can be easily processed into a metal laminate (resin-coated metal foil), and the obtained processed article can be applied to various fields such as flexible printed circuit boards, antenna components, printed circuit boards, sports equipment, food industry supplies, etc., which have transparency, 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 the disclosure of the specification of the present invention.

Explanation of Reference Numerals

[0072] 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…Peripheral speed, 11…Extrusion molding apparatus, 2…Hopper, 21…First stage section, 211…Heater, 212…Connection section, P1…Pump, 22…Second stage section, 221…Heater, 222…Connection section, P2…Pump, 3…Kneading section, 31…Cylinder, 311…Tip opening, 32…Screw, 33…Gear box, 331…Rotating shaft, 34…Motor, 341…Rotating shaft, 35…Heater, 5…T-die, 6…Static mixer, L…Overall length, D…Diameter

Claims

**Claim 1** A method for manufacturing an extruded film composed of a tetrafluoroethylene-based polymer, the method comprising: extruding the tetrafluoroethylene-based polymer in a molten state from a die and forming it by extrusion; and sandwiching the film between two temperature-controlled rolls and cooling it, wherein the film has a thickness of 100 to 200 μm, a haze of 8% or less, a thermal shrinkage rate after heating at 180° C. for 30 minutes of -1 to +1% in both the flow direction and the width direction of the film, and the tetrafluoroethylene-based polymer is a tetrafluoroethylene-based polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). **Claim 2** The manufacturing method according to claim 1, wherein the tetrafluoroethylene-based polymer contains units based on perfluoro(alkyl vinyl ether) and is a tetrafluoroethylene-based polymer 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) with respect to all units and having no polar functional group. **Claim 3** The manufacturing method according to claim 1 or 2, wherein the melting temperature of the tetrafluoroethylene-based polymer is 260 to 320° C. **Claim 4** The manufacturing method according to any one of claims 1 to 3, wherein the temperature of one of the two temperature-controlled rolls is 150 to 250° C and the temperature of the other roll is 80 to 150° C. **Claim 5** The manufacturing method according to any one of claims 1 to 4, further comprising adjusting the temperature of the pellets at the connection portion of the hopper to the kneading portion to a range of (the melting temperature - 200) to (the melting temperature - 100)° C and then supplying the pellets to the kneading portion when manufacturing a film by discharging a melt-kneaded product melted and kneaded in the kneading portion from a T-die after charging pellets of a tetrafluoroethylene-based polymer having a melting temperature of 260 to 320° C into the hopper and providing an extrusion molding apparatus having a kneading portion and a hopper connected to the kneading portion. **Claim 6** The manufacturing method according to claim 5, wherein the diameter of the pellets is 1.0 to 4.0 mm. **Claim 7** The manufacturing method according to claim 5 or 6, wherein the hopper is a multi-stage hopper including a first-stage portion and a second-stage portion disposed closer to the kneading portion than the first-stage portion. **Claim 8** The manufacturing method according to any one of claims 5 to 7, wherein the pressure in the step portion closest to the kneading portion of the hopper is 1000 Pa or less.

9. The manufacturing method according to any one of claims 5 to 8, wherein the extrusion molding apparatus includes a T-die connected to the opposite side of the hopper in the axial direction of the kneading portion, and a static mixer provided between the kneading portion and the T-die.

10. The manufacturing method according to any one of claims 1 to 9, further comprising an operation of discharging the tetrafluoroethylene-based polymer from the T-die in a molten state and heating the molten tetrafluoroethylene-based polymer with a non-contact heating unit before contacting the first cooling roll.

11. The manufacturing method according to claim 10, wherein 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. The manufacturing method according to claim 10 or 11, wherein 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 unit is 70°C or less.

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