Method for manufacturing heat-shrinkable film

Abstract

To provide a heat-shrinkable film which can expect improvement of heat shrinkability and can prevent melting in a high temperature range of 300°C, and a manufacturing method of the same.SOLUTION: A heat-shrinkable film is formed by melt-extrusion molding an unstretched polyether ether ketone resin film 2 having a degree of crystallization of 15% or less by at least a polyether ether ketone resin-containing molding material 1, and biaxially stretching the polyether ether ketone resin film 2, wherein heating dimensional change rates in longitudinal and lateral directions at 170°C, 200°C and 250°C are -50% or more and -5% or less when measured according to JIS K 7133. The unstretched polyether ether ketone resin film 2 is biaxially stretched, which can improve heat shrinkability and can obtain an excellent heat-shrinkable film. The polyether ether ketone resin film 2 having a degree of crystallization of 15% or less is biaxially stretched, which can expect facilitation of biaxial stretching.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention is made of a polyether ether ketone resin. Method for manufacturing heat-shrinkable film This concerns... [Background technology]

[0002] Polyether ether ketone resins are known for their excellent heat resistance, chemical stability, hydrolysis resistance, electrical insulation properties, and mechanical properties. Various methods have been proposed for manufacturing resin films using these polyether ether ketone resins (see Patent Documents 1, 2, 3, 4, 5, 6, and 7).

[0003] For example, Patent Document 1 proposes a method for producing a thin-film engineering plastic film by simultaneously molding a laminate of an engineering plastic molten material and a releaseable resin film, and then peeling off the resin film. Patent Document 2 also proposes a method for producing a thin-film engineering plastic film by extruding an engineering plastic molten material onto one side of a release film, forming the laminate, and then peeling off the release film.

[0004] Patent Document 3 proposes a method for forming a polyetheretherketone resin film with a thickness of 5 μm or less by focusing on the true shear viscosity and extensional viscosity of the polyetheretherketone resin and adjusting the distance from the tip of the die to the contact point where the polyetheretherketone resin comes into contact with the cooling roll. Furthermore, Patent Documents 4, 5, 6, and 7 disclose a manufacturing method for producing polyetheretherketone resin film by biaxial stretching. In addition, Patent Document 8 discloses a heat-shrinkable film using a high heat-resistant resin. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-21912 [Patent Document 2] WO2018 / 235436 publication [Patent Document 3] Patent No. 6087257 [Patent Document 4] Japanese Patent Publication No. 63-256422 [Patent Document 5] Special Publication No. 7-64023 [Patent Document 6] Japanese Patent Publication No. 2014-226881 [Patent Document 7] Japanese Patent Publication No. 2015-67683 [Patent Document 8] Japanese Patent Publication No. 2022-77687 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the case of Patent Document 1, although it is possible to obtain a thin-film engineering plastic film with excellent thickness uniformity with a thickness of less than 50 μm and thickness unevenness of less than 10%, it has low thermal shrinkage and has functional problems as a heat-shrinkable film. Similarly, in the case of Patent Document 2, although it is possible to obtain a thin-film engineering plastic film with excellent thickness uniformity and surface smoothness, it also has low thermal shrinkage and has functional problems as a heat-shrinkable film.

[0007] In the case of Patent Document 3, although it is effective for molding polyetheretherketone resin films with a thickness of 5 μm or less, the resin film obtained by this method has low thermal shrinkage, which is problematic as a heat-shrinkable film. Also, in the cases of Patent Documents 4, 5, 6, and 7, the polyetheretherketone resin film is heat-treated after biaxial stretching, resulting in a resin film with a thermal shrinkage rate of 6% or less in the high-temperature range, which is problematic as a heat-shrinkable film.

[0008] Furthermore, in the case of Patent Document 8, a polyphenylene sulfide resin is used in the production of a heat-shrinkable film, but the melting point of this polyphenylene sulfide resin is around 280°C. Therefore, it will melt in a high-temperature range of 300°C, causing a serious obstacle to its use.

[0009] The present invention has been made in view of the above, and aims to provide a heat-shrinkable film that can be expected to have improved heat shrinkability and prevent melting in a high-temperature range of 300°C. Manufacturing method

Means for Solving the Problems

[0010] As a result of intensive research, the inventors of the present invention focused on the polyether ether ketone resin, which has the best heat resistance among thermoplastic resins and also excellent mechanical and electrical properties, and the crystallinity, and completed the present invention.

[0011] That is, in the present invention, in order to solve the above problems, A method for producing a heat-shrinkable film, comprising: melting and kneading a molding material containing at least polyetheretherketone resin; continuously extruding the molten polyetheretherketone resin into a strip shape using a T-die; and cooling the extruded polyetheretherketone resin by sandwiching it between a pressure roll and a cooling roll, thereby forming an unstretched polyetheretherketone resin film with a crystallinity of 1% to 15% into a strip shape with a thickness of 10 μm to 1000 μm; The cooling roll is a metal roll, and the temperature of this metal roll is set to be between [glass point transfer of polyetheretherketone resin -100]°C and [glass point transfer of polyetheretherketone resin +50]°C. The molded polyetheretherketone resin film is simultaneously biaxially stretched at a stretching ratio of 1.5 to 5 times to form a strip with a thickness of 5 μm to 100 μm. The heat-shrinkable film has a heating dimensional change rate in the longitudinal and transverse directions at 170°C, 200°C, and 250°C that is between -50% and -5% when measured according to JIS K 7133; the total light transmittance before heating, after heating at 200°C, and after heating at 250°C for 10 minutes at 200°C and 250°C is 80% or more when measured according to JIS K 7361-1; the haze values ​​after heating at 200°C and 250°C are 1% and 5% each when measured according to JIS K 7136; and the storage modulus in the longitudinal and transverse directions at 300°C is 1 × 10 when measured under conditions of a frequency of 1 Hz and a heating rate of 3°C / min. 5 Pa or more 1×10 10 It is characterized by having a Pa level of 70% to 300% elongation at tensile fracture in both the longitudinal and transverse directions at 23°C.

[0014] In addition, after the polyether ether ketone resin film is simultaneously biaxially stretched, if necessary, the polyether ether ketone resin film may be heat-treated and heat-fixed at a temperature of [glass transition temperature of the polyether ether ketone resin film + 30]°C or higher and [melting point of the polyether ether ketone resin film]°C or lower to adjust the heat shrinkage characteristics.

[0015] ​Here, the molding material in the claims preferably contains at least 51% to 100% by mass of polyetheretherketone resin. Furthermore, methods for molding the unstretched polyetheretherketone resin film include melt extrusion, calendering, or casting. Biaxial stretching may be carried out continuously or in batches. Moreover, the heat-shrinkable film according to the present invention is not particularly limited to a single-layer, double-layer, or triple-layer structure, and can be used for applications such as insulating coatings for battery cells, box-shaped packaging materials, and wires for motors, etc. Covering materials, labels, etc. It can be used for this purpose.

[0016] According to the present invention, since a polyetheretherketone resin is used, it does not melt even at high temperatures of 300°C. Furthermore, since the molded, unstretched polyetheretherketone resin film is biaxially stretched, high thermal shrinkage can be expected, and a film with excellent thermal shrinkage properties can be obtained. In addition, since a polyetheretherketone resin film with a crystallinity of 15% or less is biaxially stretched, the biaxial stretching process can be made easier. [Effects of the Invention]

[0017] According to the present invention, improved thermal shrinkability can be expected, and melting at high temperatures of 300°C can be prevented. Furthermore, by simultaneously biaxially stretching a strip-shaped unstretched polyetheretherketone resin film with a crystallinity of 1% to 15%, a high-value-added heat-shrinkable film with high isotropy in both the longitudinal and transverse directions can be obtained. In addition, by stretching a strip-shaped unstretched polyetheretherketone resin film with excellent thickness accuracy of 10 μm to 1000 μm using a T-die to 5 μm to 100 μm, a heat-shrinkable film with suppressed reduction in tensile strength can be obtained. Moreover, since the tensile elongation at break (longitudinal and transverse directions) at 23°C is 70% to 300%, the risk of problems such as breakage, cracking, and tearing during use of the heat-shrinkable film can be eliminated, and a decrease in the flexibility of the heat-shrinkable film can be expected. Furthermore, the dimensional change rates in the longitudinal and transverse directions when heated at 170°C, 200°C, and 250°C are between -50% and -5% when measured in accordance with JIS K 7133, ensuring an appropriate shrinkage rate for a heat-shrinkable film. Moreover, it prevents excessive shrinkage, eliminating the risk of tearing in the heat-shrinkable film. Additionally, the total light transmittance before heating, after heating at 200°C, and after heating at 250°C for 10 minutes are all 80% or higher when measured in accordance with JIS K 7361-1, preventing loss of transparency that would make it difficult to confirm the color and shape of the contents or covering contents. Furthermore, the haze values ​​after heating to 200°C and 250°C are between 1% and 5% respectively when measured in accordance with JIS K 7136, thus preventing the loss of transparency in the heat-shrinkable film. In addition, the storage modulus of the heat-shrinkable film at 300°C is 1 × 10⁻¹⁰ when measured under conditions of a frequency of 1 Hz and a heating rate of 3°C / min. 5 Pa or more 1×10 10 Since it is below Pa, excellent heat resistance can be expected. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram illustrating the manufacturing apparatus in an embodiment of the method for manufacturing a heat-shrinkable film according to the present invention. [Figure 2] This is a schematic perspective diagram illustrating a manufacturing apparatus in a second embodiment of the method for manufacturing a heat-shrinkable film according to the present invention. [Modes for carrying out the invention]

[0022] A preferred embodiment of the present invention will now be described with reference to the drawings. In this embodiment, as shown in Figure 1, an unstretched polyetheretherketone resin film 2 with a degree of crystallinity of 15% or less is formed as a single layer using a molding material 1 containing at least a polyetheretherketone resin, and this polyetheretherketone resin film 2 is biaxially stretched at a stretching ratio of 5 times or less to form a heat-shrinkable resin film. This film is used in battery cells, packaging materials, wire coatings, etc., and contributes to achieving Goal 9 of the SDGs (Sustainable Development Goals, which are the United Nations' international goals for sustainable development, consisting of 17 global goals and 169 targets (achievement criteria)) adopted at the UN Summit.

[0023] The molding material 1 is prepared with polyetheretherketone (PEEK) resin as the main component, and contains this polyetheretherketone resin in an amount of 51% to 100% by mass, preferably 75% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0024] Polyether ether ketone resin is a crystalline thermoplastic resin composed of arylene groups, ether groups, and carbonyl groups, and is the type of resin described in literature such as [Asahi Research Center Co., Ltd.: Super Engineering Plastics Growing in Advanced Applications - PEEK (Part 1)], and is characterized by excellent mechanical properties, lightness, electrical properties, hydrolysis resistance, heat resistance, and chemical resistance. A specific example of this polyether ether ketone resin is the polyether ether ketone resin represented by chemical formula (1).

[0025] [ka]

[0026] In this chemical formula, n should be 10 or more, preferably 20 or more, from the viewpoint of improving mechanical properties. The polyetheretherketone resin may be a homopolymer consisting only of repeating units of chemical formula (1), but it may also have repeating units other than those of chemical formula (1). Furthermore, the proportion of the chemical structure of chemical formula (1) in the polyetheretherketone resin should be 51 mol% or more, preferably 70 mol% or more, more preferably 85 mol% or more, and even more preferably 95 mol% or more, based on 100 mol% of the polyetheretherketone resin. This is because, within this range, a heat-shrinkable film with excellent heat resistance, mechanical properties, electrical insulation, etc., can be obtained.

[0027] The polyether ether ketone resin can also be used as a block copolymer, random copolymer, or modified form with other copolymerizable monomers, as long as the effects of the present invention are not impaired. Furthermore, the polyether ether ketone resin typically has a melting point of 320°C to 360°C, preferably 335°C to 345°C, and is generally used in powder, granular, or pelletized forms suitable for molding. The melting point (in °C) of the polyether ether ketone resin can be determined by thermal analysis using a differential scanning calorimeter.

[0028] Examples of polyether ether ketone resin products include the Victrex Powder series and Victrex Granules series from Victrex Corporation, the Vestakeep series from DiceCell Evonik Corporation, and the Keetasspire PEEK series from Solvay Specialty Polymers Corporation.

[0029] Examples of the method for producing a polyetheretherketone resin include the production methods described in JP-A-50-27897, JP-A-51-119797, JP-A-52-38000, JP-A-54-90296, JP-B-55-23574, JP-B-56-2091, Patent No. 5702283, and the like. As a typical production method, although not particularly limited, there is a method in which an aromatic diol component and an aromatic dihalide component (wherein at least one of the components contains a component having at least a carbonyl group) are polycondensed in the presence of an alkali metal salt and a solvent within a temperature range of 150°C or higher and 400°C or lower.

[0030] Examples of the aromatic diol component include hydroquinone, and examples of the aromatic dihalide component include 4,4'-difluorobenzophenone. Examples of the alkali metal salt include inorganic potassium carbonate, and examples of the solvent include diphenyl sulfone. After completion of the polycondensation reaction, it can be pulverized and washed with acetone, methanol, ethanol, water, etc. and dried.

[0031] When using the polyetheretherketone resin, the crystallization temperature may be appropriately adjusted by modifying the terminal group (usually a halogen atom) with an alkaline sulfonic acid group (sodium sulfonate group, potassium sulfonate group, lithium sulfonate group, etc.), etc., but it is preferably used without modifying the terminal group.

[0032] The apparent shear viscosity of the polyetheretherketone resin is 1.0×10 2 sec -1 in the case of, 1.0×10 2 Pa·s or more and 1.0×10 4 Pa·s or less, preferably 2.0×10 2 Pa·s or more and 5.0×10 3 Pa·s or less, more preferably 2.5×10 2 Pa·s or more and 2.5×10 3 Pa·s or less, still more preferably 5.0×10 2 Pa·s or more and 2.0×103 It is considered to be within the range of Pa·s or less.

[0033] This is because the apparent melt viscosity is 1.0 × 10⁻⁶ 2 If the apparent melt viscosity is less than Pa·s, the melt tension of the molten polyether ether ketone resin is low, causing problems with film moldability and further reducing mechanical properties, making biaxial stretching of the polyether ether ketone resin film 2 difficult. In contrast, if the apparent melt viscosity is 1.0 × 10⁻⁶ 4 If the viscosity exceeds Pa·s, melt extrusion molding of the polyether ether ketone resin becomes difficult. The apparent shear viscosity of this polyether ether ketone resin can be measured using a commercially available shear viscosity / extensional viscosity measuring device.

[0034] In addition to polyether ether ketone resin, polyarylene ether ketone resins such as polyether ketone (PEK) resin, polyether ketone ketone (PEKK) resin, polyether ether ketone ketone (PEEKK) resin, and polyether ketone ether ketone ketone (PEKEKK) resin may be added to molding material 1 as needed, within a range that does not impair the properties of the present invention.

[0035] Furthermore, the molding material 1 includes polyether ether ketone resin, as well as polyolefin resins such as polyethylene (PE) resin, polypropylene (PP) resin, polymethylpentene (PMP) resin and polystyrene (PS) resin, acid-modified olefin resins such as maleic anhydride-modified polyethylene resin and maleic anhydride-modified polypropylene resin, polyethylene terephthalate (PET) resin, polyester resins such as polybutylene terephthalate (PBT) resin and polyethylene naphthalate (PEN) resin, and polyimide (PI). Polyamide resins such as polyamide-imide (PAI) resin, polyetherimide (PEI) resin, polyamide 4T (PA4T) resin, polyamide 6T (PA6T) resin, modified polyamide 6T (modified PA6T) resin, polyamide 9T (PA9T) resin, polyamide 10T (PA10T) resin, polyamide 11T (PA11T) resin, polyamide 6 (PA6) resin, polyamide 66 (PA66) resin, and polyamide 46 (PA46) resin, polysulfone (PSU) resin, polyethersulfone Polysulfone resins such as (PES) resin and polyphenylene sulfone (PPSU) resin, polyphenylene sulfide (PPS) resin, polyphenylene sulfide ketone resin, polyphenylene sulfide sulfone resin and polyphenylene sulfide ketone sulfone resin, polyarylene sulfide resins, polytetrafluoroethylene (PTFE) resin, polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin, tetrafluoroethylene-hexafluoropropyl copolymer (FEP) resin, tetrafluoroethylene-ethylene copolymer (ETFE) resin, polychlorotrifluoroethylene (PCTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororesins such as vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin and acid-modified fluororesins, polycarbonate (PC) resin, polyarylate (PAR) resin, polyacetal (POM) resin, liquid crystal polymer (LCP), and aliphatic polyketone resin can be selectively added.

[0036] In addition to the polyether ether ketone resin, various additives such as nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and color inhibitors may be added to the molding material 1, as long as they do not impair the objectives of the present invention. Furthermore, the polyether ether ketone resin of the molding material 1 may contain particles, in which case inorganic particles or organic particles are preferably used.

[0037] Examples of inorganic particles include metal oxides such as silica, alumina, titanium dioxide, and zirconia, as well as barium sulfate, calcium carbonate, aluminum silicate, calcium phosphate, mica, talc, kaolin, clay, and zeolite. Among these, metal oxides such as silica, alumina, titanium dioxide, and zirconia are preferred. Silica is particularly preferred.

[0038] In contrast, as organic particles, one of the following can be used alone or in combination: dimethylpolysiloxane crosslinked particles, polymethoxysilane crosslinked particles, polyorganosilsesquioxane cured particles, polystyrene crosslinked particles, acrylic crosslinked particles, polyurethane crosslinked particles, polyester crosslinked particles, fluorine crosslinked particles, or fullerene.

[0039] The average particle size of the inorganic and organic particles is preferably in the range of 0.01 μm to 5.0 μm. Preferably, the average particle size is in the range of 0.05 μm to 3.0 μm, more preferably 0.07 μm to 2.0 μm, and even more preferably 0.1 μm to 1.0 μm. This is because if the average particle size is less than 0.01 μm, the surface roughness becomes small, which can reduce handling properties. On the other hand, if it exceeds 5.0 μm, the polyetheretherketone resin film 2 becomes more prone to tearing during biaxial stretching, and the optical properties, mechanical properties, electrical properties, and water absorption of the heat-shrinkable film deteriorate.

[0040] One method for measuring the average particle diameter of inorganic and organic particles is to use the equivalent circular diameter obtained by image processing from transmission electron microscope images of the particles, and then calculate the weight-average diameter.

[0041] The amount of the above-mentioned particles to be added is preferably in the range of 0.01 parts by mass to 3.0 parts by mass, more preferably 0.03 parts by mass to 2.0 parts by mass, more preferably 0.05 parts by mass to 1.5 parts by mass, and even more preferably 0.05 parts by mass to 1.0 part by mass, when the amount of polyetheretherketone resin is 100 parts by mass. This is because if the amount added is less than 0.01 parts by mass, the handling properties will be insufficient. On the other hand, if it exceeds 3.0 parts by mass, the unstretched polyetheretherketone resin film 2 will become prone to tearing during biaxial stretching, and the optical properties, mechanical properties, electrical properties, and water absorption of the heat-shrinkable film will deteriorate.

[0042] To prevent aggregation of inorganic or organic particles, or to improve affinity with polyether ether ketone resin, a silane coupling agent [vinyltrimethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-aminopropylethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3- -Methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltrialkoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-isocyanatetopropyltriethoxysilane, 3-trimethoxysilylpropyl succinic anhydride, imidazolesilane, etc.], titanate coupling agents [isopropyltriisostearo Iol titanate, isopropyl(dioctyl pyrophosphate) titanate, isopropyl tris(N-aminoethyl-aminoethyl) titanate, tetraoctylbis(di-tridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl) phosphite titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, bis(dioctyl pyrophosphate) ethylene titanate, isopropyltrioctanoyl titanate Treatment can be carried out with various coupling agents such as isopropyl dimethacrylate isostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl isostearoyl diacrylic titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumylphenyl titanate, tetraisopropyl(dioctyl phosphite) titanate, aluminate coupling agents such as acetalkoxyaluminum diisopropylate.

[0043] The amount of coupling agent to be added is in the range of 0.01 parts by mass to 5.0 parts by mass, preferably 0.1 parts by mass to 3.0 parts by mass, more preferably 0.5 parts by mass to 2.0 parts by mass, and even more preferably 0.5 parts by mass to 1.5 parts by mass, when the amount of inorganic or organic particles is 100 parts by mass. This is because if the amount added is less than 0.01 parts by mass, it may not be possible to prevent aggregation between particles or improve affinity to the polyether ether ketone resin, which may lead to a decrease in mechanical strength or a decrease in dispersibility in the polyether ether ketone resin. On the other hand, if the amount exceeds 5.0 parts by mass, the optical properties, mechanical properties, electrical properties, and water absorption of the heat-shrinkable film may deteriorate.

[0044] The unstretched polyetheretherketone resin film 2 is molded by a predetermined molding method to a crystallinity of 15% or less, preferably 1% to 15%, more preferably 3% to 13%, even more preferably 4% to 12%, and most preferably 4% to 10%. This is because if the crystallinity is less than 1%, it becomes difficult to manufacture the polyetheretherketone resin film 2. On the other hand, if the crystallinity exceeds 15%, the stretching tension becomes excessive, making the polyetheretherketone resin film 2 prone to tearing, uneven stretching, pinholes, etc., and making biaxial stretching difficult.

[0045] The degree of crystallinity of the unstretched polyetheretherketone resin film 2 is calculated using the following formula based on the results of thermal analysis using a differential scanning calorimeter.

[0046] Crystallinity (%)={(ΔHm-ΔHc) / ΔHx}×100…(Formula 1) Here, ΔHm is the crystal melting peak of the unstretched polyether ether ketone resin film. Heat energy (J / g) ΔHc: Recrystallization peak of unstretched polyether ether ketone resin film Heat energy (J / g) ΔHx: 100% crystallized unstretched polyether ether ketone resin fil This is the theoretical value of the melting energy of mu, which is 130 J / g.

[0047] Methods for molding unstretched polyetheretherketone resin film 2 include melt extrusion molding, calendering, and casting. Among these molding methods, melt extrusion molding, which allows for continuous extrusion molding of unstretched polyetheretherketone resin film 2 into strips, is optimal from the viewpoint of improving thickness accuracy, productivity, handling, and equipment simplification.

[0048] As shown in Figure 1, the melt extrusion molding method involves using a melt extrusion molding machine 10 to melt and knead a molding material 1 containing polyetheretherketone resin, continuously extruding the molten polyetheretherketone resin in a strip shape from a die 13 such as a T-die or a round die connected to the tip of the melt extrusion molding machine 10, and cooling the polyetheretherketone resin by sandwiching it between a pressure roll 17 and a cooling roll 18 to produce an unstretched polyetheretherketone resin film 2.

[0049] The melt extrusion molding machine 10 consists of, for example, a single-screw extrusion molding machine or a twin-screw extrusion molding machine, and a raw material inlet 11 for the molding material 1 is installed at the rear upper part. An inert gas supply pipe 12 is connected to this raw material inlet 11 to supply an inert gas such as helium gas, neon gas, argon gas, krypton gas, or nitrogen gas as needed. The supply of inert gas by this inert gas supply pipe 12 effectively prevents oxidative degradation, oxygen crosslinking, and thermal crosslinking of the molding material 1.

[0050] The melting temperature during melt kneading in the melt extrusion molding machine 10 is not particularly limited as long as it is a temperature at which melt kneading and dispersion is possible and the polyetheretherketone resin does not decompose. However, it is preferable that the temperature be in the range of above the melting point of the polyetheretherketone resin (hereinafter referred to as Tm) and below the thermal decomposition temperature of the polyetheretherketone resin.

[0051] Preferably, the temperature range is between [Tm of polyetheretherketone resin + 10]°C and [Tm of polyetheretherketone resin + 100]°C, more preferably between [Tm of polyetheretherketone resin + 20]°C and [Tm of polyetheretherketone resin + 70]°C, and even more preferably between [Tm of polyetheretherketone resin + 30]°C and [Tm of polyetheretherketone resin + 60]°C. The Tm (unit: °C) of the polyetheretherketone resin can be determined by thermal analysis using a differential scanning calorimeter.

[0052] Specifically, a temperature range of 360°C to 450°C is preferable, preferably 360°C to 420°C, and more preferably 370°C to 400°C. This is because if the temperature of the melt extrusion molding machine 10 during melt kneading is below the Tm of the polyether ketone resin, melt extrusion molding is not possible, and therefore unstretched polyether ketone resin cannot be produced. On the other hand, if the temperature is above the thermal decomposition temperature, it will lead to the decomposition of the polyether ketone resin.

[0053] The die 13 is connected to the tip of the melt extrusion molding machine 10 via a connecting pipe 14 and functions to continuously extrude a strip of polyetheretherketone resin downwards. There are various types of dies 13, but a T-die is preferred as it is capable of obtaining an unstretched polyetheretherketone resin film 2 with excellent thickness accuracy.

[0054] Preferably, a gear pump 15 and a filter 16 are installed in the connecting pipe 14 upstream of the die 13. The gear pump 15 functions to transfer the molding material 1, which has been melted and kneaded by the melt extrusion molding machine 10, to the downstream die 13 via the filter 16 at a constant flow rate and with high precision. The filter 16 also functions to separate unmelted polyetheretherketone resin and foreign matter from the molten polyetheretherketone resin and transfer the molten polyetheretherketone resin to the die 13.

[0055] The temperature of die 13 during extrusion is preferably in the range of Tm of the polyetheretherketone resin or less than the thermal decomposition temperature of the polyetheretherketone resin. Preferably, it is between [Tm of polyetheretherketone resin + 10]°C and [Tm of polyetheretherketone resin + 100]°C, more preferably between [Tm of polyetheretherketone resin + 20]°C and [Tm of polyetheretherketone resin + 70]°C, and even more preferably between [Tm of polyetheretherketone resin + 30]°C and [Tm of polyetheretherketone resin + 60]°C.

[0056] Specifically, a temperature range of 360°C to 450°C is preferable, preferably 360°C to 420°C, and more preferably 370°C to 400°C. This is because if the temperature is below the Tm of the polyetheretherketone resin, it is not possible to produce the unstretched polyetheretherketone resin film 2. Conversely, if the temperature is above the thermal decomposition temperature, it will lead to the decomposition of the polyetheretherketone resin, which is undesirable.

[0057] Below the die 13, a pair of crimping rolls 17 are rotatably supported, spaced apart and facing each other. Between this pair of crimping rolls 17, a plurality of cooling rolls 18 are rotatably supported, arranged in a line and sliding against each other. Of these cooling rolls 18, the upstream cooling roll 18 and the downstream cooling roll 18 slide against the circumferential surface of the crimping rolls 17, respectively. Each crimping roll 17 is configured to be reduced in diameter, and each cooling roll 18 is configured to be larger in diameter than the crimping rolls 17.

[0058] Downstream of the downstream crimping roll 17 of the pair of crimping rolls 17, a winding machine 20 is installed to wind the unstretched polyetheretherketone resin film 2 onto a rotatable winding tube 19. Between this winding machine 20 and the downstream crimping roll 17, a slitting blade 21 is positioned to move up and down to form slits in the lateral direction of the unstretched polyetheretherketone resin film 2. Between this slitting blade 21 and the winding machine 20, a necessary number of rotatable tension rolls 22 are supported to apply tension to the unstretched polyetheretherketone resin film 2 for smooth winding.

[0059] Each crimping roll 17 is adjusted to a temperature range of [Tg of polyetheretherketone resin glass transition temperature (hereinafter referred to as Tg) - 100]°C or higher and [Tg of polyetheretherketone resin + 50]°C or lower, preferably [Tg of polyetheretherketone resin Tg - 70]°C or higher and [Tg of polyetheretherketone resin Tg + 40]°C or lower, more preferably [Tg of polyetheretherketone resin Tg - 40]°C or higher and [Tg of polyetheretherketone resin Tg + 30]°C or lower, and even more preferably [Tg of polyetheretherketone resin Tg - 10]°C or higher and [Tg of polyetheretherketone resin Tg + 20]°C or lower. The Tg (unit: °C) of the polyetheretherketone resin can be determined by thermal analysis using a differential scanning calorimeter.

[0060] The specific temperature range is 50°C to 190°C, preferably 100°C to 180°C, more preferably 120°C to 170°C, and even more preferably 130°C to 160°C.

[0061] The reason the temperature of the compression roll 17 is within a specific range is that if it is below [Tg of polyetheretherketone resin - 100]°C, the melt-extruded strip of polyetheretherketone resin cannot be brought into close contact with the cooling roll 18, making it impossible to obtain a smooth, unstretched polyetheretherketone resin film 2. On the other hand, if it exceeds [Tg of polyetheretherketone resin + 50]°C, the degree of crystallinity will exceed 15%, and it will be impossible to adjust the degree of crystallinity to 15% or less. Methods for adjusting the temperature of the compression roll 17 include, for example, using a heat transfer medium such as air, water, or oil, using an electric heater, or using induction heating.

[0062] From the viewpoint of improving the adhesion between the unstretched polyether ether ketone resin film 2 and the cooling roll 18, a rubber layer is optionally formed on the circumferential surface of each pressure roll 17, including at least natural rubber, isoprene rubber, butadiene rubber, norbornene rubber, acrylonitrile butadiene rubber, nitrile rubber, urethane rubber, silicone rubber, and fluororubber. Inorganic compounds such as silica and alumina are selectively added to this rubber layer. Among these rubbers, silicone rubber and fluororubber, which have excellent heat resistance, are preferred.

[0063] The multiple cooling rolls 18 consist of, for example, metal rolls with a larger diameter than the crimping roll 17, and are rotatably supported below the die 13 to sandwich the strip-shaped polyetheretherketone resin between them and the crimping roll 17. Together with the crimping roll 17, they function to cool the polyetheretherketone resin film 2 in a short time while controlling its thickness within a predetermined range.

[0064] The cooling roll 18, like the compression roll 17, is adjusted to a temperature range of [Tg of polyetheretherketone resin - 100]°C or higher and [Tg of polyetheretherketone resin + 50]°C or lower, preferably [Tg of polyetheretherketone resin - 70]°C or higher and [Tg of polyetheretherketone resin + 40]°C or lower, more preferably [Tg of polyetheretherketone resin - 40]°C or higher and [Tg of polyetheretherketone resin + 30]°C or lower, and even more preferably [Tg of polyetheretherketone resin - 10]°C or higher and [Tg of polyetheretherketone resin + 20]°C or lower. The Tg (unit: °C) of the polyetheretherketone resin can be determined by thermal analysis using a differential scanning calorimeter.

[0065] The specific temperature range is 50°C to 190°C, preferably 100°C to 180°C, more preferably 120°C to 170°C, and even more preferably 130°C to 160°C.

[0066] The reason the temperature of the cooling roll 18 is within a specified range is that if it is below [glass transition point of polyetheretherketone resin - 100]°C, the strip-shaped polyetheretherketone resin, which is continuously melt-extruded, cannot be brought into close contact with the cooling roll 18, and therefore a smooth polyetheretherketone resin film 2 cannot be obtained. Conversely, if it exceeds [glass transition point of polyetheretherketone resin + 50]°C, the degree of crystallinity will exceed 15%, and it will not be possible to adjust the degree of crystallinity to 15% or less. Methods for adjusting the temperature of the cooling roll 18 and for cooling include methods using heat transfer fluids such as air, water, or oil, or electric heaters or induction heating.

[0067] After extruding the molding material 1 into a strip-shaped polyetheretherketone resin film 2, the unstretched polyetheretherketone resin film 2 is wound onto a pair of pressure rolls 17, a plurality of cooling rolls 18, a tension roll 22, and a winding tube 19 of a winding machine 20. Both sides of the unstretched polyetheretherketone resin film 2 are cut longitudinally with a slitting blade 21 and wound sequentially onto the winding tube 19 of the winding machine 20, thereby producing a long length of unstretched polyetheretherketone resin film 2.

[0068] The thickness of the unstretched polyetheretherketone resin film 2, which is cooled by the cooling roll 18 and manufactured, is preferably 10 μm or more and 1000 μm or less, preferably 30 μm or more and 750 μm or less, more preferably 50 μm or more and 500 μm or less, and even more preferably 50 μm or more and 250 μm or less. This is because if the thickness of the unstretched polyetheretherketone resin film 2 is less than 10 μm, the tensile strength of the unstretched polyetheretherketone resin film 2 decreases, which can lead to the breakage of the polyetheretherketone resin film 2 during biaxial stretching. On the other hand, if the thickness of the unstretched polyetheretherketone resin film 2 exceeds 1000 μm, it becomes difficult to manufacture the unstretched polyetheretherketone resin film 2.

[0069] Once the intermediate product, unstretched polyetheretherketone resin film 2, is manufactured, the unstretched polyetheretherketone resin film 2 wound onto the winding machine 20 is transferred to a separate biaxial stretching device and fed into it, where it is biaxially stretched to produce the finished product, a heat-shrinkable film. The heat-shrinkable film is a biaxially stretched film that is stretched in two axial directions: the longitudinal direction (sometimes referred to as the extrusion direction, machine axis direction, longitudinal direction, or MD) and the transverse direction (sometimes referred to as the direction perpendicular to the extrusion direction, width direction, or TD).

[0070] The reason for biaxial stretching of the unstretched polyetheretherketone resin film 2 is that thermal shrinkage cannot be expected in the unstretched state. Furthermore, in the case of uniaxial stretching, shrinkage does not occur in the unstretched direction, which presents problems for a heat-shrinkable film. In contrast, biaxial stretching of the unstretched polyetheretherketone resin film 2 using the biaxial stretching method allows for the maintenance of the mechanical properties, electrical properties, and low water absorption of a heat-shrinkable film, while increasing the thermal shrinkage rate and improving optical properties and heat resistance.

[0071] Biaxial stretching methods include sequential biaxial stretching and simultaneous biaxial stretching, and any of these methods is acceptable. Sequential biaxial stretching is possible at ultra-high speeds because the longitudinal and transverse stretching mechanisms are independent and relatively simple. However, when biaxial stretching crystalline resins such as polyetheretherketone resins using sequential biaxial stretching, the polyetheretherketone resin film 2 is cooled after longitudinal stretching. In crystalline resins, recrystallization proceeds at this point, and if the stretching stress within the polyetheretherketone resin film 2 increases during subsequent transverse stretching, optical properties such as haze value may deteriorate. Also, when stretched longitudinally, molecules tend to orient in the stretching direction, so if stretched transversely after longitudinal stretching, the polyetheretherketone resin film 2 may tear under certain conditions.

[0072] Therefore, in order to achieve the desired lateral stretching ratio, the molding conditions may be constrained, such as the need to consider the balance between the longitudinal and lateral stretching conditions, including adjusting the longitudinal stretching ratio in the preceding stage, and the limitations on the combinations of stretching ratios. Consequently, sequential biaxial stretching has the problem of being more complicated to optimize the stretching conditions compared to simultaneous biaxial stretching.

[0073] In contrast, simultaneous biaxial stretching, which stretches the polyetheretherketone resin film 2 simultaneously in the longitudinal and transverse directions, can suppress crystallization of the polyetheretherketone resin film 2. Moreover, since it allows for arbitrary relaxation as well as stretching, it is possible to easily obtain a polyetheretherketone resin film 2 with suppressed bowing and molecular orientation anisotropy. Furthermore, simultaneous biaxial stretching allows for simultaneous stretching of a resin in the longitudinal and transverse directions while the molecules are not oriented in a specific direction. This reduces the complexity of considering balance, as is the case with sequential biaxial stretching, and increases the freedom in setting stretching conditions. Therefore, simultaneous biaxial stretching is preferable to sequential biaxial stretching.

[0074] The stretching ratio during biaxial stretching should be 5.0 times or less in both the longitudinal and transverse directions, preferably between 1.5 and 5.0 times, more preferably between 1.7 and 4.0 times, even more preferably between 2.0 and 3.5 times, and most preferably between 2.0 and 3.0 times. This is because if the stretching ratio is less than 1.5 times, sufficient molecular orientation does not occur, resulting in a small stretching effect and causing variations in thickness. On the other hand, if it exceeds 5.0 times, the tensile tension becomes excessive, making it easy for the polyetheretherketone resin film 2 to tear, have uneven stretching, and produce pinholes during stretching.

[0075] The stretching temperature during biaxial stretching is in the range of [Tg -20 of the unstretched polyetheretherketone resin film]°C or higher and [Tg +50 of the unstretched polyetheretherketone resin film]°C or higher and [Tg +30 of the unstretched polyetheretherketone resin film]°C or lower, and more preferably [Tg +5 of the unstretched polyetheretherketone resin film]°C or higher and [Tg +20 of the unstretched polyetheretherketone resin film]°C or lower.

[0076] This is because if the stretching temperature is below [Tg -20 of the unstretched polyetheretherketone resin film]°C, the stretching tension becomes excessive, making the film prone to tearing, uneven stretching, and pinholes during stretching. In addition, it can cause the heat-shrinkable film to whiten. On the other hand, if the temperature exceeds [Tg +50 of the unstretched polyetheretherketone resin film]°C, the polyetheretherketone resin film 2 stretches under its own weight, which is why uneven stretching is likely to occur.

[0077] The manufactured heat-shrinkable film can be used as a finished product as is, but if necessary, the biaxially oriented polyetheretherketone resin film 2 can be heat-treated and heat-fixed to prevent natural shrinkage, adjust the heat shrinkage rate, adjust the heat shrinkage temperature, and adjust other heat shrinkage characteristics. The heat-fixing temperature in this case should be in the range of [Tg of polyetheretherketone resin film + 30]°C or higher and [Tm of polyetheretherketone resin film]°C or lower, preferably [Tg of polyetheretherketone resin film + 60]°C or higher and [Tm of polyetheretherketone resin - 20]°C or lower, and more preferably [Tg of polyetheretherketone resin + 90]°C or higher and [Tm of polyetheretherketone resin - 40]°C.

[0078] The heat setting time for the biaxially stretched polyetheretherketone resin film 2 is preferably in the range of 1 second to 10 minutes, more preferably 2 seconds to 7 minutes, more preferably 3 seconds to 5 minutes, and even more preferably 5 seconds to 2 minutes.

[0079] The heat setting process may be carried out in two or more stages, such as by dividing it into a heat treatment performed continuously after the stretching process and a separate heat treatment performed after the production of the biaxially oriented film. Furthermore, the heat setting process may be a tension-type heat treatment, in which the heat treatment is performed while maintaining the tension from the biaxial stretching process, or a relaxation-type heat treatment, which is performed simultaneously with the start of the heat treatment. Alternatively, a combination of tension-type and relaxation-type heat treatments may be performed, for example, by performing a tension-type heat treatment as the first heat treatment followed by a relaxation-type heat treatment as the second heat treatment.

[0080] The thickness of the heat-shrinkable film is not particularly limited, but for example, a range of 5 μm to 100 μm, preferably 10 μm to 75 μm, and more preferably 10 μm to 50 μm is preferable. This is because if the thickness is less than 5 μm, the tensile strength of the heat-shrinkable film decreases significantly, making it prone to breakage during manufacturing and reducing manufacturing efficiency. On the other hand, if the thickness exceeds 100 μm, the tensile tension becomes excessive, making it prone to tearing, uneven stretching, and pinholes during stretching.

[0081] The thermal shrinkage rate of heat-shrinkable films at 170°C, 200°C, and 250°C can be evaluated by the heating dimensional change rate measured in accordance with JIS K 7133. The heating dimensional change rates at 170°C, 200°C, and 250°C are preferably in the range where the heating dimensional change rate in the longitudinal direction of the resin film is -50.0% or more and -5.0%, and the heating dimensional change rate in the transverse direction of the resin film is -50.0% or more and -5.0%, preferably -35.0% or more and -7.5%, and the heating dimensional change rate in the transverse direction of the resin film is -35.0% or more and -7.5%, more preferably -25.0% or more and -12.0%, and the heating dimensional change rate in the transverse direction of the resin film is -25.0% or more and -10.0%, and even more preferably -22.0% or more and -10.0%, and the heating dimensional change rate in the longitudinal direction of the resin film is -20.0% or more and -9.3%.

[0082] This is because, if the dimensional change rate due to heating in the vertical and horizontal directions is less than -5.0% (or if it expands), it is not possible to ensure an appropriate shrinkage rate for the heat-shrinkable film. As a result, adhesion to the packaged contents or coated contents is poor, and there is a risk that substances that contaminate or corrode the packaged contents or coated contents may penetrate between the heat-shrinkable film and the packaged contents or coated contents. On the other hand, if the dimensional change rate due to heating in the vertical and horizontal directions exceeds -50.0%, the shrinkage rate becomes excessive, which can damage the packaged contents or coated contents, or cause the heat-shrinkable film to tear.

[0083] The optical properties of heat-shrinkable films can be evaluated by their total light transmittance and haze value. First, when measuring the total light transmittance of a heat-shrinkable film, the film is measured before and after heating at 200°C and 250°C for 10 minutes, in accordance with JIS K 7361-1, under conditions of 23°C ± 2°C and 50% RH ± 5% RH. The total light transmittance of the heat-shrinkable film before and after heating at 200°C and 250°C for 10 minutes should be 70% or higher, preferably 75% or higher, more preferably 80% or higher, and even more preferably 85% or higher. This is because good transparency can be expected when the total light transmittance of the heat-shrinkable film is 70% or higher. In contrast, if it is less than 70%, transparency is lost, making it difficult to confirm the color and shape of the contents or covering contents.

[0084] Next, the haze value of the heat-shrinkable film can be measured before and after heating at 200°C and 250°C for 10 minutes. When measuring the haze value of this heat-shrinkable film, the resin film before and after heating at 200°C and 250°C for 10 minutes is measured in accordance with JIS K 7136, under conditions of 23°C ± 2°C and 50% RH ± 5% RH. The haze value of the heat-shrinkable film before and after heating at 200°C and 250°C for 10 minutes should be in the range of 15.0% or less, preferably 1% to 15.0%, more preferably 1% to 10.0%, even more preferably 1% to 5.0%, and most preferably 1% to 2.5%. This is because if the haze value exceeds 15%, transparency is impaired, making it difficult to discern the color and shape of the packaged contents or covering contents.

[0085] The mechanical properties of a heat-shrinkable film can be evaluated by its tensile properties, which can be measured in accordance with JIS K 7127. Ideally, the tensile properties of this heat-shrinkable film should be such that the maximum tensile strength (longitudinal and transverse directions) at 23°C is 100 MPa or higher, the elongation at break at 23°C (longitudinal and transverse directions) is 50% or higher, and the tensile modulus (longitudinal and transverse directions) at 23°C is 3000 MPa or higher.

[0086] The maximum tensile strength (longitudinal and transverse directions) of the heat-shrinkable film at 23°C is 100 MPa or more, preferably 150 MPa or more, more preferably 180 MPa or more, even more preferably 200 MPa or more, and most preferably 180 MPa to 290 MPa. This is because if the maximum tensile strength at 23°C is less than 100 MPa, the heat-shrinkable film does not have sufficient toughness, which can lead to problems such as breakage, cracking, and tearing during use.

[0087] While there are no specific restrictions on the upper limit of the maximum tensile strength, it is preferable to keep it below 500 MPa. This is because if the maximum tensile strength of the heat-shrinkable film exceeds 500 MPa, the adhesion to the packaged or coated contents will be poor, and there is a risk that substances that contaminate or corrode the packaged or coated contents may penetrate between the heat-shrinkable film and the packaged or coated contents.

[0088] Furthermore, the tensile elongation at break (longitudinal and transverse directions) at 23°C should be 50% or more, preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, even more preferably 50% to 300%, and most preferably 80% to 300%. This is because if the tensile elongation at break is less than 50%, the heat-shrinkable film does not have sufficient toughness, which may lead to problems such as breakage, cracking, or tearing when using the heat-shrinkable film. There is no particular upper limit to the tensile elongation at break, but it is preferable to keep it at 300% or less. This is because if the tensile elongation at break of the heat-shrinkable film exceeds 300%, the flexibility of the heat-shrinkable film decreases, and handling tends to worsen as the thickness of the heat-shrinkable film decreases.

[0089] The tensile modulus of the heat-shrinkable film at 23°C is 3000 MPa or higher, preferably 3500 MPa or higher, more preferably 4000 MPa or higher, even more preferably 4200 MPa or higher, and most preferably in the range of 3850 MPa to 4420 MPa. This is because, within this range, the rigidity is excellent, and the heat-shrinkable film tends to be easy to handle even when its thickness is reduced. Furthermore, if the tensile modulus of the heat-shrinkable film is less than 3000 MPa, the rigidity becomes insufficient, and there is a risk that the heat-shrinkable film may be punctured by contents or coverings with protrusions, or at the corners of polygonal structures such as rectangles or triangles.

[0090] While there are no specific upper limits on the tensile modulus, it is preferable to keep it below 6000 MPa. This is because if the tensile modulus of the heat-shrinkable film exceeds 6000 MPa, the adhesion to the packaged or coated contents will be poor, and there is a risk that contaminating or corrosive substances may penetrate between the heat-shrinkable film and the packaged or coated contents.

[0091] The heat resistance of a heat-shrinkable film can be expressed by its storage modulus at 300°C. To obtain excellent heat resistance, the storage modulus at 300°C is 1.0 × 10⁻¹⁰ when measured under conditions of a frequency of 1 Hz and a heating rate of 3°C / min. 5 Pa or higher, comfort level 1.0 × 10 6 Pa or higher, more preferably 1.0 × 10 7 It is desirable that the storage modulus is Pa or higher. This means that the storage modulus at 300°C is 1.0 × 10⁻⁶. 5 If the Pa value is less than Pa, sufficient heat resistance cannot be obtained in high-temperature ranges. Therefore, when left in high-temperature ranges of 300°C or higher, the heat-shrinkable film softens, causing it to tear after packaging or covering the contents.

[0092] The upper limit of the storage modulus of a heat-shrinkable film at 300°C is not particularly limited, but is approximately 1.0 × 10⁻⁶. 10 A value of Pa or less is desirable. This is because the storage modulus is 1.0 × 10⁻⁶. 10 This is because exceeding Pa results in poor adhesion between the heat-shrinkable film and the contents of the packaging or covering, potentially allowing contaminating or corrosive substances to penetrate between the heat-shrinkable film and the contents of the packaging or covering.

[0093] The electrical properties of heat-shrinkable films can be evaluated by volume resistivity, dielectric breakdown voltage, relative permittivity, and dielectric loss tangent. The volume resistivity of heat-shrinkable films can be measured in accordance with JIS C 2139-3-1. From the perspective of ensuring superior insulation, this volume resistivity should be 1.0 × 10⁻⁶. 14 Ω·cm or greater, preferably 1.0 × 10⁻⁶ 15 Ω·cm or more, more preferably 1.0 × 10 16 A value of Ω·cm or higher is preferable. The upper limit of volume resistivity is preferable as long as it is high, and there are no particular restrictions, but it is usually 1 × 10⁻⁶. 18 A value of Ω·cm or less is preferable.

[0094] When heat-shrinkable film is used, for example, as a coating for battery cells, the volume resistivity is 1.0 × 10⁻⁶ 14A resistance of Ω·cm or higher ensures excellent insulation performance, and even if an overvoltage is applied to the battery cell, it can withstand the stress without being destroyed, thus preventing problems caused by electrical short circuits in the battery cell.

[0095] The dielectric breakdown voltage of the heat-shrinkable film can be measured in accordance with IEC 60243-1 at 23°C ± 2°C and 50%RH ± 5%RH. The dielectric breakdown voltage of this heat-shrinkable film is preferably 1.0kV or higher, more preferably 1.5kV or higher, more preferably 2.0kV or higher, and even more preferably 3.0kV or higher. This is because a dielectric breakdown voltage of 1.0kV or higher indicates excellent insulation properties, allowing the film to maintain resistance without breakdown even under overvoltage, thus preventing problems caused by electrical short circuits in battery cells and other devices. While a higher dielectric breakdown voltage is preferable and not particularly limited, it is typically 20kV or lower.

[0096] The relative permittivity of a heat-shrinkable film can be evaluated at frequencies of 1 GHz and 28 GHz. The relative permittivity at 1 GHz is preferably measured by the cavity resonator perturbation method, and the relative permittivity at 28 GHz is preferably measured by the Fabry-Perot method. The relative permittivity of a heat-shrinkable film at 23°C and frequencies of 1 GHz and 23°C and 28 GHz should be 3.5 or less, preferably 3.4 or less, and more preferably 3.3 or less. This is because a relative permittivity of 3.5 or less in a heat-shrinkable film provides excellent insulation. While a lower lower limit is preferable for the relative permittivity at 1 GHz and 28 GHz, there are no particular restrictions; however, in practical terms, it should be 1.1 or higher.

[0097] The dielectric loss tangent of a heat-shrinkable film can be evaluated at frequencies of 1 GHz and 28 GHz. The dielectric loss tangent at 1 GHz is preferably measured by the cavity resonator perturbation method, while the cavity resonator perturbation method at 28 GHz is preferably measured by the Fabry-Perot method. The dielectric loss tangent of the heat-shrinkable film at 23°C and frequencies of 1 GHz and 23°C and 28 GHz should be 0.010 or less, preferably 0.008 or less, more preferably 0.007, and even more preferably 0.006 or less. This is because excellent insulation can be expected if the dielectric loss tangent of the heat-shrinkable film is 0.010 or less. The lower limit of the relative permittivity at 1 GHz and 28 GHz is preferable as low as possible, and is not particularly restricted, but practically it is 0.0001 or higher.

[0098] The water absorption rate of a heat-shrinkable film can be measured in accordance with JIS K 7209 Method A under conditions of 23°C ± 2°C. The water absorption rate of this heat-shrinkable film is preferably 10% or less, more preferably 8% or less, more preferably 6% or less, and even more preferably 4% or less. This is because if the water absorption rate of the heat-shrinkable film is 10% or less, the film maintains high electrical insulation properties even in high-temperature and high-humidity environments. While there is no particular lower limit to the water absorption rate of heat-shrinkable film 1, it is practically 0.01% or higher.

[0099] According to the above, by biaxially stretching the molded, unstretched polyetheretherketone resin film 2 and setting the dimensional change rate in the longitudinal and transverse directions at 170°C, 200°C, and 250°C to be between -50% and -5%, the heat shrinkability can be improved, and a film with excellent heat shrinkability can be obtained. Furthermore, since the unstretched polyetheretherketone resin film 2 with a crystallinity of 1% to 15% is biaxially stretched, the biaxial stretching process can be made easier. In addition, since simultaneous biaxial stretching is performed, a high-value-added heat-shrinkable film with high isotropy in the longitudinal and transverse directions can be obtained.

[0100] Furthermore, since the stretching ratio during simultaneous biaxial stretching is between 1.5 and 5.0 times, it is possible to obtain an excellent stretching effect while suppressing thickness variations, and moreover, it is possible to prevent film tearing, uneven stretching, and pinholes from occurring in the polyetheretherketone resin film 2 during simultaneous biaxial stretching. In addition, because polyetheretherketone resin is used, it does not melt even in the high temperature range of 300°C, so it does not cause serious problems in manufacturing or use. Moreover, if the polyetheretherketone resin film 2 that has been simultaneously biaxially stretched is heat-fixed as a heat-shrinkable film, it is possible to prevent natural shrinkage.

[0101] Next, Figure 2 shows a second embodiment of the present invention, in which the melt extrusion molding machine 10 is divided into first and second melt extrusion molding machines 10A and 10B, and a cast roll 30, a biaxial stretching machine 31, a take-up machine 35, and a winding machine 36 are sequentially arranged downstream of these first and second melt extrusion molding machines 10A and 10B to manufacture a two-layer heat-shrinkable film.

[0102] The first melt extrusion molding machine 10A is, for example, a melt extrusion molding machine 10 similar to that of the first embodiment, and functions to melt and knead a molding material 1 containing polyetheretherketone resin and continuously extrude this molding material 1 into a die 13 such as a T-die. In contrast, the second melt extrusion molding machine 10B melts and kneads a differently formulated molding material 1 containing additives such as polyetheretherketone resin, an antistatic agent, a low dielectric material, or a heat dissipation material, and functions to continuously extrude this molding material 1 upstream of the die 13 to merge it with the molding material 1 of the first melt extrusion molding machine 10A.

[0103] The molding material 1 from the first and second melt extrusion molding machines 10A and 10B, which have merged, are extruded together from the die 13 to form a laminate of a thick polyetheretherketone resin layer and a thin polyetheretherketone resin layer. The cast roll 30 is installed downstream of the first and second melt extrusion molding machines 10A and 10B and the die 13, and functions to form the molten strip-shaped polyetheretherketone resin into a sheet.

[0104] The biaxial stretching machine 31 is installed downstream of the cast roll 30 and has ovens 32 for blowing hot air on both the left and right sides, and stretches the sheeted, unstretched polyetheretherketone resin film 2 simultaneously in the longitudinal and transverse directions. The biaxial stretching machine 31 has a pair of left and right running rails 33 that can be expanded and contracted in the width direction, arranged in a roughly V-shape in plan, and each running rail 33 is formed by a pair of opposing guide rails, on which a clip 34 runs. The clip 34 is attached to a link mechanism that runs across the pair of guide rails, and an independent gripping part for resin film is installed at the tip of this link mechanism.

[0105] Such a biaxial stretching machine 31 stretches the unstretched polyetheretherketone resin film 2 in the lateral direction by spreading a pair of running rails 33 in the lateral direction, and stretches the unstretched polyetheretherketone resin film 2 in the longitudinal direction by narrowing a pair of running rails 33 in the lateral direction.

[0106] The take-up machine 35 is installed downstream of the biaxial stretching machine 31 and functions to take up the biaxially stretched polyetheretherketone resin film 2. The winding machine 36 is installed downstream of the take-up machine 35 and functions to wind the biaxially stretched polyetheretherketone resin film 2, in other words, the heat-shrinkable film, onto a winding tube. The other parts are the same as in the above embodiment and will not be described.

[0107] In this embodiment, the same effects and advantages as in the above embodiment can be expected. Moreover, since it is not necessary to transfer the unstretched polyetheretherketone resin film 2 wound on the winding machine 20 to a separate biaxial stretching device for biaxial stretching, it is clear that the manufacturing process can be made faster and easier. Furthermore, since the heat-shrinkable film can be formed into a two-layer structure with different thicknesses and compositions, significant improvements in functionality can be expected.

[0108] In the above embodiment, the molten polyether ether ketone resin was pressed against the cooling roll 18 using the pressure roll 17, but the invention is not limited to this. For example, the molten strip of polyether ether ketone resin may be pressed against the cooling roll 18 using an electrostatic application method (or pinning method) or an air knife. Furthermore, when cooling the molten polyether ether ketone resin, methods such as pressing the molten strip of polyether ether ketone resin against a metal belt, spraying water onto the molten strip of polyether ether ketone resin, or immersing the molten strip of polyether ether ketone resin in water may be employed.

[0109] Furthermore, at least one of the front or back surfaces of the heat-shrinkable film may be subjected to surface activation treatments such as corona treatment, plasma treatment (including vacuum plasma treatment and atmospheric pressure plasma treatment), ultraviolet treatment, or Itro treatment. Additionally, various properties can be added and its value further enhanced by printing, various functional coatings, lamination, etc. Moreover, the melt extrusion molding machine 10 can be divided into first, second, and third melt extrusion molding machines to produce a three-layer heat-shrinkable film. [Examples]

[0110] The following describes the heat-shrinkable film according to the present invention. Manufacturing method Examples of this will be described along with comparative examples. [Example 1] First, in order to produce an unstretched polyetheretherketone resin film, a commercially available polyetheretherketone resin (product name: Keetasspire PEEK KT-851NL SP, manufactured by Solvays Pestultipolymers Japan Co., Ltd., hereinafter abbreviated as "KT-851NL SP") was prepared, and this polyetheretherketone resin was placed in a dehumidifying dryer heated to 160°C and dried for more than 12 hours. The polyetheretherketone resin will be abbreviated as "PEEK resin" below.

[0111] Next, the PEEK resin was placed in a single-screw extruder equipped with a T-die as shown in Figure 1 and melted and kneaded. This melted and kneaded PEEK resin was continuously extruded from the T-die of the single-screw extruder and cooled by being sandwiched between multiple pressure rolls and cooling rolls, thereby extruding the unstretched PEEK resin film into a strip shape. During this process, the temperature of the single-screw extruder was adjusted to 380-400°C, the temperature of the T-die was adjusted to 400°C, and the temperature of the connecting pipe linking the single-screw extruder and the T-die was adjusted to 400°C. When the PEEK resin was fed into the single-screw extruder, nitrogen gas was supplied at 18 L / min through an inert gas supply pipe. The temperature of the molten PEEK resin was measured at the T-die inlet, and the measured temperature was 397°C.

[0112] After extruding the unstretched PEEK resin film, both ends of the continuous unstretched PEEK resin film were cut with a slitting blade and sequentially wound onto a winding tube of a winding machine to produce unstretched PEEK resin film. In this process, as shown in Figure 1, the unstretched PEEK resin film was sequentially wound onto multiple cooling rolls at 150°C, a pair of silicone rubber crimping rolls, and a 6-inch winding tube located downstream of these.

[0113] The Tg of KT-851NL SP was measured using a differential scanning calorimeter (SII Nano Technologies Co., Ltd., product name: High-Sensitivity Differential Scanning Calorimeter X-DSC7000) in accordance with JIS K 7121, under conditions of a heating rate of 10°C / min. The measured Tg of KT-851NL SP was 146°C. The Tg of unstretched PEEK resin film was also measured using a differential scanning calorimeter (SII Nano Technologies Co., Ltd., product name: High-Sensitivity Differential Scanning Calorimeter X-DSC7000) in accordance with JIS K 7121, under conditions of a heating rate of 10°C / min. The measured Tg of unstretched PEEK resin film was 145°C.

[0114] The apparent shear viscosity of PEEK resin was measured using a twin capillary rheometer R6000 (manufactured by IMATEK: product name) after drying the PEEK resin at 160°C for 12 hours. Specifically, 40g of PEEK resin was first placed into the barrel using capillary dies: φ1.0mm × 16mm (long die), φ1.0mm × 0.25mm (short die), barrel diameter: 15mm, temperature: 375°C. The piston was then pushed in at a speed of 50mm / min until the pressure reached 0.9MPa on the long die side and 0.3MPa on the short die side. Once the pressure reached the predetermined value, it was held in that state for 6 minutes.

[0115] Then, the piston is pushed again at a speed of 50 mm / min until the pressure reaches 0.9 MPa on the long die side and 0.3 MPa on the short die side. Once the pressure reaches the predetermined value, the predetermined apparent shear rate (10, 20, 30, 50, 80, 100, 200, 300, 800 sec) is applied. -1 The apparent shear viscosity was determined by measuring the viscosity under the following conditions: apparent shear rate of 100 sec. -1 The apparent shear viscosity of KT-851NL SP in this context is 1.00 × 10⁻⁶. 3 It was Pa·s.

[0116] To determine the crystallinity of the unstretched PEEK resin film, approximately 8 mg of the sample was weighed from the unstretched PEEK resin film and measured using a differential scanning calorimeter (SII Nanotechnologies Corporation, product name: EXSTAR7000 series X-DSC7000) at a heating rate of 10°C / min within a measurement temperature range of 20°C to 380°C. The calorific value was calculated from the heat energy (J / g) of the crystallization peak and the heat energy (J / g) of the recrystallization peak obtained using the following formula. The resulting PEEK resin film had a crystallinity of 9.2%.

[0117] Crystallinity (%)={(ΔHm-ΔHc) / ΔHx}×100…(Formula 1) Here, ΔHm: the heat energy (J / g) of the crystal melting peak of the unstretched PEEK resin film. ΔHc: Heat energy (J / g) of the recrystallization peak of unstretched PEEK resin film. ΔHx: The theoretical value of the melting energy of 100% crystallized PEEK resin. It is 130 J / g.

[0118] The thickness of the unstretched PEEK resin film was measured using a micrometer (Mitutoyo Corporation, product name: Coolant-Proof Micrometer, code MDC-25PJ). For the measurement, 10 arbitrary points were measured in the transverse direction of the unstretched PEEK resin film, and the average value was taken as the film thickness.

[0119] Next, an unstretched PEEK resin film was simultaneously biaxially stretched using a commercially available simultaneous biaxial stretching machine that stretches in both the longitudinal and transverse directions. Specifically, the unstretched PEEK resin film was simultaneously biaxially stretched by 2.0 times in the longitudinal direction and 2.0 times in the transverse direction using a tenter method. During this process, the preheating section of the heating furnace of the simultaneous biaxial stretching machine was heated to 90°C for 30 seconds, and then heated to 155°C for 120 seconds while stretching by 2.0 times in both the longitudinal and transverse directions. The ends of the biaxially stretched PEEK resin film obtained in this way were cut with a slitting blade and sequentially wound onto a winding tube of a winding machine to produce a heat-shrinkable film.

[0120] After manufacturing the heat-shrinkable film, its thickness, heat shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption were evaluated and summarized in Table 1. Heat shrinkage characteristics were evaluated by the rate of change in dimensions upon heating, optical properties by total light transmittance and haze, mechanical properties by maximum tensile strength, elongation at tensile break and tensile modulus, heat resistance by storage modulus at 300°C, electrical properties by volume resistivity, electrical dielectric breakdown strength, and relative permittivity and dielectric loss tangent at 1 GHz and 28 GHz, and water absorption by water absorption rate.

[0121] • Film thickness of heat-shrinkable film The thickness of the heat-shrinkable film was measured using a micrometer (Mitutoyo Corporation, product name: Coolant-Proof Micrometer, code MDC-25PJ). For measurement, 10 arbitrary points were measured along the transverse direction of the heat-shrinkable film, and the average value was taken as the film thickness.

[0122] • Thermal shrinkage properties of heat-shrinkable films The thermal shrinkage characteristics of the heat-shrinkable film were evaluated by the rate of change in dimensions during heating. To measure this rate of change in dimensions during heating, a test piece cut from the heat-shrinkable film to a size of 120 mm in the longitudinal direction × 120 mm in the transverse direction was used in accordance with JIS K 7133. 100 mm gauge marks were marked on the longitudinal and transverse directions of the test piece, and the length between the gauge marks was measured with calipers. The test piece was then placed in an oven at 170°C, 200°C, and 250°C for 10 minutes. After 10 minutes of heating, the test piece was allowed to cool naturally to 23°C, and then the length between the gauge marks was measured again at 23°C ± 2, 50 ± 5% RH. The rate of change in dimensions during heating was calculated using the following formula.

[0123] Heating dimensional change rate (%) = {(L - L0) / L0} × 100 Here, L0: Distance between gauge marks before the test (mm) L: Distance between markings after heating (mm)

[0124] • Total light transmittance of heat-shrinkable film The total light transmittance of the heat-shrinkable film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: NDH-8000) in accordance with JIS K 7361-1, under conditions of 23°C ± 2°C and 50%RH ± 5%RH. The specific measurement method for total light transmittance involved first cutting the heat-shrinkable film into test specimens measuring 120mm in length and 120mm in width. The total light transmittance of these specimens was measured before and after heating in an oven at 200°C and 250°C for 10 minutes. The measurement of total light transmittance of the specimens heated at 200°C and 250°C for 10 minutes involved placing the specimens in the oven at 200°C and 250°C for 10 minutes, allowing them to cool naturally to 23°C ± 2°C, and then measuring under conditions of 23°C ± 2°C and 50%RH ± 5%RH.

[0125] • Haze of heat-shrinkable film The haze of the heat-shrinkable film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: NDH-5000) in accordance with JIS K 7136, under conditions of 23°C ± 2°C and 50%RH ± 5%RH. Specifically, to measure the haze of the heat-shrinkable film, a test piece was first cut to a size of 120 mm in the vertical direction and 120 mm in the horizontal direction. This test piece was heated in an oven at 200°C and 250°C for 10 minutes. After heating, the test piece was allowed to cool naturally to 23°C ± 2°C, and then measured under conditions of 23°C ± 2°C and 50%RH ± 5%RH.

[0126] • Mechanical properties of heat-shrinkable films The mechanical properties of the heat-shrinkable film were evaluated by measuring the maximum tensile strength, elongation at tensile break, and tensile modulus at 23°C. Mechanical properties were measured in both the longitudinal and transverse directions. Measurements were performed in accordance with JIS K 7127, under the conditions of a tensile speed of 50 mm / min, a temperature of 23°C ± 2°C, and a relative humidity of 50% RH ± 5% RH.

[0127] • Heat resistance of heat-shrinkable film The heat resistance of the heat-shrinkable film was evaluated by its storage modulus (E') at 300°C. This storage modulus was measured in both the longitudinal and transverse directions. Specifically, to measure the longitudinal storage modulus, a sample measuring 60mm in the longitudinal direction × 6mm in the transverse direction was used; to measure the transverse storage modulus, a sample measuring 6mm in the longitudinal direction × 60mm in the transverse direction was used. For the measurement of the storage modulus, a viscoelastic spectrometer (product name: RSA-G2, manufactured by T.S. Instruments Japan) was used in tensile mode under the following conditions: frequency 1Hz, strain 0.1%, heating rate 3°C / min, measurement temperature range -60 to 360°C, and check interval 21mm. The storage modulus at 300°C was then determined.

[0128] • Electrical properties of heat-shrinkable films The electrical properties of the heat-shrinkable film were evaluated by volume resistivity, dielectric breakdown voltage, relative permittivity at 1 GHz and 28 GHz, and dielectric loss tangent.

[0129] • Volume resistivity of heat-shrinkable film The volume resistivity of the heat-shrinkable film was measured in accordance with JIS C2139-3-1 under conditions of 23°C ± 2°C and 50%RH ± 5%RH. Specifically, the measurement method involved first cutting the heat-shrinkable film to a size of 100 mm in the vertical direction and 100 mm in the horizontal direction to create a test specimen. This specimen was left to stand for 24 hours under conditions of 23°C ± 2°C and 50%RH ± 5%RH. After standing, the specimen was attached to the electrode of a measuring instrument [HIOKI E.E. CORPORATION, product name: Flat plate electrode SME-8310]. With the specimen attached to the electrode of the measuring instrument, a voltage of 500V was applied, and the resistance value after 1 minute was measured using a measuring instrument [HIOKI E.E. CORPORATION, product name: Super insulation meter SM-8220], and the volume resistivity was calculated using the following formula.

[0130] Volume resistivity (Ω cm)=(19.6 / t)×Rv Here, t: thickness of the test specimen (cm) Rv: Measured volume resistance (Ω)

[0131] • Dielectric properties of heat-shrinkable film [Frequency: 1 GHz] The relative permittivity and dielectric loss tangent of the heat-shrinkable film at a frequency of 1 GHz were measured using a network analyzer (Anritsu MS46122B) by the cavity resonator perturbation method. Dielectric properties around 1 GHz were measured using a 1 GHz cavity resonator (Keycom TMR-1A) in accordance with ASTM D2520. These dielectric property measurements were performed under conditions of 23°C ± 1°C and 10% RH ± 5% RH.

[0132] • Dielectric properties of heat-shrinkable film [Frequency: 28GHz] The relative permittivity and dielectric loss tangent of the heat-shrinkable film at a frequency of 28 GHz were measured using a vector network analyzer A (Agilent Technologies, product name: Vector Network Analyzer E8361A) and the Fabry-Perot method, a type of open-type resonator method. An open-type resonator (Keycom, Fabry-Perot resonator Model No. DPS03) was used as the resonator.

[0133] For the measurements, a heat-shrinkable film for high-frequency circuit boards was placed on the sample stage of an open-type resonator jig, and measurements were taken using the Fabry-Perot method, a type of open-type resonator method, with a vector network analyzer. Specifically, the relative permittivity and dielectric loss tangent were measured using a resonance method that utilizes the difference in resonance frequencies between the sample stage without the heat-shrinkable film and the sample stage with the heat-shrinkable film.

[0134] • Water absorption (%) of heat-shrinkable film The water absorption of the heat-shrinkable film was evaluated by its water absorption rate, which was measured in accordance with JIS K 7209 A method under conditions of 23°C ± 2°C. Specifically, first, the heat-shrinkable film was cut to a size of 100 mm in the vertical direction × 100 mm in the horizontal direction to form a test specimen, and this specimen was dried in an oven adjusted to 50°C for 24 hours. After drying the test specimen for 24 hours, it was placed in a desiccator and cooled to room temperature, after which the mass of the test specimen was measured. Subsequently, the test specimen was immersed in distilled water at 23°C ± 2°C for 14 days, then removed from the distilled water, the moisture on the surface of the removed test specimen was wiped off with paper, and the mass of the test specimen was immediately measured. The water absorption rate was calculated using the following formula, and the results are shown in Table 1.

[0135] Water absorption rate (%)={(m2-m1) / m1}×100 Here, m1: Mass of the test specimen before immersion (mg) m2: Mass of the test specimen after immersion (mg)

[0136] [Example 2] Using the unstretched PEEK resin film produced in Example 1, simultaneous biaxial stretching was performed in the same manner as in Example 1 to produce a heat-shrinkable film with a different thickness than that of Example 1. However, the stretching ratio was changed to 2.5 times in the longitudinal direction and 2.5 times in the transverse direction for simultaneous biaxial stretching. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1, and the results are summarized in Table 1.

[0137] [Example 3] Using KT-851NL SP, a commercially available PEEK resin used in Example 1, unstretched PEEK resin films of different thicknesses were manufactured in the same manner as in Example 1. The film thickness and crystallinity of these unstretched PEEK resin films were evaluated in the same manner as in Example 1.

[0138] After producing an unstretched PEEK resin film, this unstretched PEEK resin film was simultaneously biaxially stretched using the same method as in Example 1 to produce a heat-shrinkable film with a different thickness than that of Example 1. In this case, the simultaneous biaxial stretching was carried out with a stretching ratio of 2.0 times in the longitudinal direction and 2.0 times in the transverse direction. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1, and the results are summarized in Table 1.

[0139] [Table 1]

[0140] [Example 4] Using the unstretched PEEK resin film produced in Example 3, a heat-shrinkable film with a different thickness from that of Example 1 was produced by simultaneous biaxial stretching in the same manner as in Example 1. The simultaneous biaxial stretching was carried out with a stretching ratio of 2.6 times in the longitudinal direction and 2.5 times in the transverse direction. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1 and are listed in Table 2.

[0141] [Example 5] First, as the commercially available PEEK resin, KT-851NL SP in Example 1 was replaced with Victrex Granules 450G (Victrex Corporation; hereinafter abbreviated as "450G"), and unstretched PEEK resin films of different thicknesses were manufactured using the same method as in Example 1. At this time, the apparent shear viscosity of 450G at 375°C was measured using the same method as in Example 1. The measurement showed that the apparent shear rate of 450G at 375°C was 100 sec. -1 The apparent shear viscosity at 450G is 1.32 × 10⁻⁶. 3 It was Pa·s.

[0142] After producing an unstretched PEEK resin film, this unstretched PEEK resin film was simultaneously biaxially stretched using the same method as in Example 1 to produce a heat-shrinkable film with a different thickness than that of Example 1. The simultaneous biaxial stretching was performed with stretching ratios of 3.0 times in the longitudinal direction and 3.0 times in the transverse direction. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1 and are listed in Table 2.

[0143] [Example 6] Using the unstretched PEEK resin film produced in Example 5, the thickest heat-shrinkable film was produced by simultaneous biaxial stretching in the same manner as in Example 1. The simultaneous biaxial stretching was performed with stretching ratios of 2.5 times in the longitudinal direction and 3.0 times in the transverse direction. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1 and are listed in Table 2.

[0144] [Table 2]

[0145] [Comparative Example 1] The unstretched PEEK resin film with a thickness of 50 μm and a crystallinity of 9.2% prepared in Example 1 was used as a heat-shrinkable film without stretching, and its film thickness, heat shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption were evaluated using the same method as in Example 1, and the results are summarized in Table 3.

[0146] [Comparative Example 2] An unstretched PEEK resin film with a thickness of 50 μm and a crystallinity of 9.2%, prepared in Example 1, was stretched to twice its length only in the longitudinal direction using a metal roll heated to 160°C to produce a heat-shrinkable film. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1, and the results are summarized in Table 3.

[0147] [Comparative Example 3] An unstretched PEEK resin film with a thickness of 50 μm and a crystallinity of 9.2%, prepared in Example 1, was stretched to 2.0 times its original size in the transverse direction only, using the same method as in Example 1, to produce a heat-shrinkable film. In this process, the preheating section of the heating furnace was heated to 90°C for 30 seconds, and then the film was stretched to 2.0 times its original size in the transverse direction while being heated to 155°C for 120 seconds. The film thickness, thermal shrinkage characteristics, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1 and are listed in Table 3.

[0148] [Comparative Example 4] Using the PEEK used in Example 1, an unstretched PEEK resin film was manufactured under the same conditions as in Example 1, and this unstretched PEEK resin film was used as a heat-shrinkable film. The film thickness and crystallinity of the unstretched PEEK resin film were evaluated using the same method as in Example 1 and are shown in Table 3. The heat shrinkage properties, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1, and the results are shown in Table 3.

[0149] [Comparative Example 5] Using the PEEK resin used in Example 1, an unstretched PEEK resin film was manufactured under the same conditions as in Example 1, and this unstretched PEEK resin film was used as a heat-shrinkable film. However, in Example 1, the film was sandwiched between a pressure roll heated to 150°C and a cooling roll, whereas in Comparative Example 5, it was sandwiched between a pressure roll heated to 220°C and a cooling roll. The film thickness, crystallinity, thermal shrinkage properties, optical properties, mechanical properties, heat resistance, electrical properties, and water absorption of the obtained heat-shrinkable film were evaluated using the same method as in Example 1, and the results are shown in Table 3.

[0150] [Table 3]

[0151] [Results] In each example, the dimensional change rate of the heat-shrinkable film at 200°C was -10% or more in both the longitudinal and transverse directions, demonstrating excellent heat shrinkage characteristics. Furthermore, the total light transmittance of the heat-shrinkable film remained above 80.0% even after heating at 200°C for 10 minutes, and the haze remained below 2.0% even after heating at 200°C for 10 minutes, ensuring excellent transparency. Regarding the mechanical properties of the heat-shrinkable film, the maximum tensile strength was above 180 MPa and the elongation at tensile strength was above 70%, indicating sufficient toughness. In addition, the tensile modulus of elasticity was above 3800 MPa, indicating sufficient rigidity.

[0152] In each example, the storage modulus of the heat-shrinkable film at 300°C is 8.50 × 10⁻⁶. 7 The heat resistance of the heat-shrinkable film was above Pa, and no decrease in heat resistance was observed. Furthermore, the electrical properties of the heat-shrinkable film showed a volume resistivity of 1 × 10⁻⁶. 16 The dielectric constant was Ω·cm or higher, the dielectric breakdown voltage was 4.0kV or higher, the relative permittivity at 1GHz was 3.1 or lower, the dielectric loss tangent was 0.0031 or lower, and the relative permittivity at 28GHz was 3.2 or lower, with a dielectric loss tangent of 0.0054 or lower. No decrease in insulation properties was observed with biaxial stretching. Furthermore, the water absorption of the heat-shrinkable film was 0.35% or lower, and no decrease was observed with biaxial stretching.

[0153] In contrast, in Comparative Example 1, although the low-crystallinity PEEK resin film used in Example 1 before biaxial stretching had no problems with heat resistance, electrical properties, and water absorption, its heating dimensional change rate was small (-3.0% or less), making it unsuitable for use as a heat-shrinkable film. Furthermore, the haze value was 34% or higher, resulting in poor transparency, and the tensile modulus of elasticity in mechanical properties was less than 3000 MPa, leading to poor rigidity and handling problems.

[0154] Comparative Example 2 is an example using a heat-shrinkable film obtained by stretching the unstretched PEEK resin film used in Example 1, before biaxial stretching, only in the longitudinal direction. Although this heat-shrinkable film had no problems with heat resistance, electrical properties, or water absorption, it was found to be unsuitable as a heat-shrinkable film because the dimensional change rate in the transverse direction during heating was 0.86% due to stretching only in the longitudinal direction. Furthermore, its mechanical properties were poor, with a tensile modulus in the transverse direction of 2798 MPa, which is less than 3000 MPa, resulting in low rigidity and handling problems.

[0155] Comparative Example 3 is an example using a heat-shrinkable film obtained by uniaxially stretching only the transverse direction of the unstretched PEEK resin film used in Example 1 before biaxial stretching. Although this heat-shrinkable film also had no problems with heat resistance, electrical properties, and water absorption, it was found to be unsuitable as a heat-shrinkable film because the dimensional change rate in the longitudinal direction due to heating was small at -1.36% due to the transverse stretching. Furthermore, regarding mechanical properties, the tensile modulus in the longitudinal direction was 2852 MPa, which is less than 3000 MPa, resulting in low rigidity and problems with handling.

[0156] Comparative Example 4 is an example using a heat-shrinkable film made from an unstretched PEEK resin film. While this heat-shrinkable film showed no problems with electrical properties or water absorption, its heat shrinkage characteristics were small due to its unstretched nature, with a dimensional change rate of -5.08% in the longitudinal direction and 1.30% in the transverse direction. Therefore, it was found to be unsuitable as a heat-shrinkable film. Furthermore, its optical properties also deteriorated; the haze value increased to 16.5% after heating at 200°C for 10 minutes, resulting in a loss of transparency. Its heat resistance was also poor, with a storage modulus of 1.0 × 10⁻⁶ at 300°C.5 The pressure was below Pa, which caused problems. Furthermore, the mechanical properties were also problematic, as the tensile modulus was below 3000 MPa, resulting in low rigidity and handling difficulties.

[0157] Comparative Example 5 is an example using a heat-shrinkable film made from an unstretched PEEK resin film with a crystallinity of 21.1%. Although this heat-shrinkable film showed no problems with heat resistance, electrical properties, or water absorption, it was found to be unsuitable as a heat-shrinkable film because it was an unstretched film, resulting in small heat shrinkage characteristics with a dimensional change rate of -4.46% in the longitudinal direction and 1.46% in the transverse direction. Furthermore, the optical properties were also poor, with a haze value of 53% or more, indicating a loss of transparency. In addition, the tensile modulus in the transverse direction of the mechanical properties was less than 3000 MPa, resulting in poor rigidity and handling problems. [Industrial applicability]

[0158] The heat-shrinkable film according to the present invention Manufacturing method It is used in the manufacturing of battery cells, box-shaped packaging materials, wire insulation materials, and labels. [Explanation of Symbols]

[0159] 1 Molding material 2. Polyether ether ketone resin film (PEEK resin film) 10. Melt extrusion molding machine 10A First melt extrusion molding machine 10B First and second melt extrusion molding machines 13 dice 17 Crimping Roll 18 Cooling Rolls 20 Winder 30 Cast Roll 31. Simultaneous biaxial stretching machine (vertical and horizontal) 35. Pickup machine 36 Winder

Claims

[Claim 1] A method for producing a heat-shrinkable film, comprising: melting and kneading a molding material containing at least a polyetheretherketone resin; continuously extruding the molten polyetheretherketone resin into a strip shape using a T-die; and cooling the extruded polyetheretherketone resin by sandwiching it between a pressure roll and a cooling roll, thereby forming an unstretched polyetheretherketone resin film with a crystallinity of 1% to 15% into a strip shape with a thickness of 10 μm to 1000 μm, wherein The cooling roll is a metal roll, and the temperature of this metal roll is set to be between [glass point transfer of polyetheretherketone resin -100]°C and [glass point transfer of polyetheretherketone resin +50]°C. The molded polyetheretherketone resin film is simultaneously biaxially stretched at a stretching ratio of 1.5 to 5 times to form a strip with a thickness of 5 μm to 100 μm. A method for manufacturing a heat-shrinkable film, characterized in that the heat-shrinkable film has a heating dimensional change rate in the longitudinal and transverse directions at 170°C, 200°C, and 250°C that is between -50% and -5% when measured in accordance with JIS K 7133; the total light transmittance before heating, after heating at 200°C, and after heating at 250°C for 10 minutes at 200°C and 250°C is 80% or more when measured in accordance with JIS K 7361-1; the haze values ​​after heating at 200°C and after heating at 250°C are 1% or more and 5% or less, when measured in accordance with JIS K 7136; the storage modulus in the longitudinal and transverse directions at 300°C is 1 × 10⁵ Pa or more and 1 × 10¹⁰ Pa or less when measured under conditions of a frequency of 1 Hz and a heating rate of 3°C / min; and the tensile elongation at break in the longitudinal and transverse directions at 23°C is 70% or more and 300% or less.

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