JP2024049031A - Heat-shrinkable film and manufacturing method of the same - Google Patents

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

The present invention relates to a heat-shrinkable film made of polyether ether ketone resin and a method for producing the same.

Polyether ether ketone resin is known to have excellent heat resistance, chemical stability, hydrolysis resistance, electrical insulation properties, and mechanical properties. Various methods have been proposed for producing resin films using this polyether ether ketone resin (see Patent Documents 1, 2, 3, 4, 5, 6, and 7).

For example, Patent Document 1 proposes a method of simultaneously molding and processing an engineering plastic melt and a laminate of the engineering plastic melt and a peelable resin film, and then peeling off the resin film to produce a thin engineering plastic film. Patent Document 2 also proposes a method of producing a thin engineering plastic film by extrusion coating one side of a release film with an engineering plastic melt, molding a laminate, and then peeling off the release film.

Patent Document 3 focuses on the true shear viscosity and extensional viscosity of polyether ether ketone resin and proposes a method for forming a polyether ether ketone resin film having a thickness of 5 μm or less by adjusting the distance from the tip of the die to the contact point where the polyether ether ketone resin comes into contact with the cooling roll. Patent Documents 4, 5, 6, and 7 disclose manufacturing methods for producing polyether ether ketone resin films by biaxial stretching. Furthermore, Patent Document 8 discloses a heat-shrinkable film using a highly heat-resistant resin.

JP 2007-21912 A Patent Publication No. WO2018/235436 Patent No. 6087257 Japanese Patent Application Laid-Open No. 63-256422 Japanese Patent Publication No. 7-64023 JP 2014-226881 A JP 2015-67683 A JP 2022-77687 A

However, in the case of Patent Document 1, although it is possible to obtain a thin engineering plastic film having excellent thickness uniformity with a thickness of less than 50 μm and a thickness variation of less than 10%, the heat shrinkability is small and there are problems with the functionality as a heat shrinkable film. Also, in the case of Patent Document 2, it is possible to obtain a thin engineering plastic film having excellent thickness uniformity and surface smoothness, but it also has small heat shrinkability and there are problems with the functionality as a heat shrinkable film.

In the case of Patent Document 3, it is effective for forming a polyether ether ketone resin film having a thickness of 5 μm or less, but the resin film obtained by this method has low heat shrinkability, which is problematic as a heat shrinkable film. In addition, in the cases of Patent Documents 4, 5, 6, and 7, the polyether ether ketone resin film after biaxial stretching is heat treated, resulting in a resin film with a heat shrinkage rate of 6% or less in the high temperature range, which is problematic as a heat shrinkable film.

Furthermore, in the case of Patent Document 8, polyphenylene sulfide resin is used to manufacture the heat-shrinkable film, but the melting point of this polyphenylene sulfide resin is around 280°C. Therefore, it melts at high temperatures of 300°C, causing serious problems in its use.

The present invention has been made in consideration of the above, and aims to provide a heat-shrinkable film that is expected to have improved heat shrinkability and can prevent melting at high temperatures of up to 300°C, as well as a method for producing the same.

After extensive research, the inventors focused on polyether ether ketone resin, which has the best heat resistance of all thermoplastic resins and also has excellent mechanical and electrical properties, and its degree of crystallinity, and completed the present invention.

That is, in order to solve the above problems, the present invention provides a resin film formed by molding an unstretched polyether ether ketone resin film having a crystallinity of 15% or less from a molding material containing at least a polyether ether ketone resin, and biaxially stretching the polyether ether ketone resin film,
The thermal dimensional change in the longitudinal and transverse directions at 170° C., 200° C., and 250° C. is −50% or more and −5% or less when measured in accordance with JIS K 7133.

The haze value at 200° C. and 250° C. is preferably 1% or more and 15% or less when measured in accordance with JIS K 7136.
It is also preferred that the maximum tensile strength at 23°C is 180 MPa or more and 290 MPa or less when measured in accordance with JIS K 7127, and the tensile modulus at 23°C is 3850 MPa or more and 4420 MPa or less when measured in accordance with JIS K 7127.
The storage modulus at 300° C. is preferably 1×10 ⁵ Pa or more and 1×10 ¹⁰ Pa or less when measured under conditions of a frequency of 1 Hz and a temperature increase rate of 3° C./min.

In order to solve the above problems, the present invention provides a method for producing a heat-shrinkable film according to claim 1 or 2,
The present invention is characterized in that an unstretched polyether ether ketone resin film having a crystallinity of 1% or more and 15% or less is molded by a molding method using a molding material containing at least a polyether ether ketone resin, and then the polyether ether ketone resin film is biaxially stretched at a stretching ratio of 1.5 times or more and 5 times or less.

After simultaneous biaxial stretching of the polyetheretherketone resin film, the polyetheretherketone resin film may be heat-treated at a temperature of (glass transition temperature of the polyetheretherketone resin film + 30)°C or higher and (melting point of the polyetheretherketone resin film) or lower to heat fix the film, if necessary, to adjust the thermal shrinkage properties.

Here, the molding material in the claims preferably contains at least 51% by mass or more and 100% by mass or less of polyether ether ketone resin. In addition, examples of molding methods for unstretched polyether ether ketone resin films include melt extrusion molding, calendar molding, and casting. Biaxial stretching may be performed continuously or batchwise. Furthermore, the heat-shrinkable film according to the present invention may have a single-layer structure, a two-layer structure, a three-layer structure, or the like, and can be used at least for insulating coatings for battery cells, box-shaped packaging materials, coating members for electric wires for motors, tubes, labels, and the like.

According to the present invention, polyether ether ketone resin is used, so it does not melt even at high temperatures of 300°C. In addition, since the molded unstretched polyether ether ketone resin film is biaxially stretched, high heat shrinkability can be expected, and a film with excellent heat shrinkability can be obtained. In addition, since a polyether ether ketone resin film with a crystallinity of 15% or less is biaxially stretched, it is expected that biaxial stretching will be easier.

According to the present invention, it is expected that the heat shrinkability can be improved, and it is possible to prevent melting at high temperatures of 300°C. In addition, since the crystallinity of the polyether ether ketone resin film is 15% or less, it is possible to suppress the occurrence of breakage, uneven stretching, pinholes, etc., in the polyether ether ketone resin film due to excessive stretching tension.

According to the invention described in claim 2, the tensile modulus of the heat-shrinkable film at 23°C is 3,850 MPa or more and 4,420 MPa or less when measured in accordance with JIS K 7127, so that the rigidity of the heat-shrinkable film can be improved and even if the thickness of the heat-shrinkable film becomes thin, ease of handling can be achieved.
According to the invention described in claim 3, the storage modulus of the heat-shrinkable film at 300°C is 1 x ¹⁰⁵ Pa or more and 1 x ¹⁰¹⁰ Pa or less when measured under conditions of a frequency of 1 Hz and a heating rate of 3°C/min, so that excellent heat resistance can be obtained.

According to the invention described in claim 4, a polyether ether ketone resin film with a crystallinity of 1% to 15% is biaxially stretched, which is expected to facilitate biaxial stretching. In addition, since the stretching ratio during biaxial stretching is 1.5 to 5.0 times, it is possible to obtain an excellent stretching effect while suppressing the thickness variation of the polyether ether ketone resin film, and it is also possible to prevent film tearing, stretching unevenness, and pinholes from occurring in the polyether ether ketone resin film.

According to the invention described in claim 5, the polyether ether ketone resin film is simultaneously biaxially stretched using the simultaneous biaxial stretching method, so that crystallization of the polyether ether ketone resin film can be suppressed, and since it can be not only stretched but also relaxed arbitrarily, it is possible to easily obtain a heat-shrinkable film in which bowing and anisotropy of molecular orientation are suppressed. In addition, since the complexity of the manufacturing work, such as considering balance as in the sequential biaxial stretching method, can be reduced, it is possible to improve the degree of freedom in setting the stretching conditions. Furthermore, if necessary, by subjecting the simultaneously biaxially stretched polyether ether ketone resin film to heat treatment, the heat shrinkage properties can be adjusted by the heat treatment and the heat setting of the polyether ether ketone resin film can be contributed.

1 is an overall explanatory diagram that illustrates a schematic view of a production apparatus in an embodiment of a heat-shrinkable film and a production method thereof according to the present invention. FIG. 2 is a perspective view illustrating a production apparatus according to a second embodiment of the heat shrinkable film and the production method thereof according to the present invention.

A preferred embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the heat-shrinkable film in this embodiment is a heat-shrinkable resin film formed by molding a single layer of an unstretched polyether ether ketone resin film 2 having a crystallinity of 15% or less using a molding material 1 containing at least polyether ether ketone resin, and then biaxially stretching this polyether ether ketone resin film 2 at a stretch ratio of 5 times or less. By being used for battery cells, packaging materials, electrical wire coatings, etc., the film will contribute to the achievement of Goal 9 of the SDGs (the United Nations' international goals for sustainable development, consisting of 17 global goals and 169 targets (achievement criteria)) adopted at the United Nations Summit.

Molding material 1 is prepared with polyetheretherketone (PEEK) resin as the main component, and contains 51% by mass or more and 100% by mass or less, preferably 75% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less of this polyetheretherketone resin.

Polyether ether ketone resin is a crystalline thermoplastic resin consisting of arylene groups, ether groups, and carbonyl groups, and is made of resins described in the literature, for example, [Asahi Research Center Co., Ltd.: PEEK, a super engineering plastic growing in cutting-edge applications (part 1)], and is characterized by excellent mechanical properties, light weight, electrical properties, hydrolysis resistance, heat resistance, chemical resistance, etc. A specific example of this polyether ether ketone resin is polyether ether ketone resin represented by chemical formula (1).

In this chemical formula, n is 10 or more, preferably 20 or more, from the viewpoint of improving mechanical properties. The polyether ether ketone resin may be a homopolymer consisting of only the repeating unit of chemical formula (1), but may also have repeating units other than chemical formula (1). In addition, the proportion of the chemical structure of chemical formula (1) in the polyether ether ketone resin is 51 mol% or more, preferably 70 mol% or more, more preferably 85 mol% or more, and even more preferably 95 mol% or more, relative to 100 mol% of the polyether ether ketone resin. This is because, within this range, a heat-shrinkable film having excellent heat resistance, mechanical properties, electrical insulation, etc. can be obtained.

Polyetheretherketone resins may be used in the form of block copolymers, random copolymers, or modified products with other copolymerizable monomers, as long as the effects of the present invention are not impaired. Polyetheretherketone resins usually have a melting point of 320°C or higher and 360°C or lower, preferably 335°C or higher and 345°C or lower, and are generally used in a form suitable for molding into powder, granules, or pellets. The melting point (unit: °C) of polyetheretherketone resins can be determined by thermal analysis using a differential scanning calorimeter.

Examples of such polyether ether ketone resin products include Victrex Powder series and Victrex Granules series manufactured by Victrex, Vestakeep series manufactured by Diesel-Evonik, and KetaSpire PEEK series manufactured by Solvay Specialty Polymers.

Methods for producing polyether ether ketone resins include, for example, those 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, and Japanese Patent No. 5702283. A representative production method is not particularly limited, but includes a method in which an aromatic diol component and an aromatic dihalide component (wherein one of the components contains at least a component having a carbonyl group) are polycondensed in the presence of an alkali metal salt and a solvent at a temperature range of 150°C to 400°C.

An example of an aromatic diol component is hydroquinone, and an example of an aromatic dihalide component is 4,4'-difluorobenzophenone. An example of an alkali metal salt is inorganic potassium carbonate, and an example of a solvent is diphenyl sulfone. After the polycondensation reaction is complete, the product can be pulverized, washed with acetonitrile, methanol, ethanol, water, etc., and then dried.

When using polyether ether ketone resin, the crystallization temperature may be appropriately adjusted by modifying the terminal groups (usually halogen atoms) with alkaline sulfonate groups (sodium sulfonate groups, potassium sulfonate groups, lithium sulfonate groups, etc.), but it is preferable to use the resin without modifying the terminal groups.

The apparent shear viscosity of the polyether ether ketone resin, when the apparent shear rate is 1.0×10 ² sec ^-1 at a temperature of 375° C., is within the range of 1.0×10 ² Pa·s to 1.0×10 ⁴ Pa·s, preferably 2.0×10 ² Pa·s to 5.0×10 ³ Pa·s, more preferably 2.5×10 ² Pa·s to 2.5×10 ³ Pa·s, and even more preferably 5.0×10 ² Pa·s to 2.0×10 ³ Pa·s.

This is because, when the apparent melt viscosity is less than 1.0×10 ² Pa·s, the melt tension of the molten polyether ether ketone resin is small, causing problems in film formability and further deteriorating mechanical properties, making it difficult to biaxially stretch the polyether ether ketone resin film 2. On the other hand, when the apparent melt viscosity exceeds 1.0×10 ⁴ Pa·s, it becomes difficult to melt extrude the polyether ether ketone resin. The apparent shear viscosity of this polyether ether ketone resin can be measured using a commercially available shear viscosity/extensional viscosity measuring device.

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 can be added to molding material 1 as needed, provided that the characteristics of the present invention are not impaired.

In addition to polyether ether ketone resin, molding material 1 may also include 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, polyester resins such as polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polyethylene naphthalate (PEN) resin, polyimide (PI) resin, etc. polyamide resins such as polyamideimide (PAI) resin and 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, polyamide 46 (PA46) resin, and other polyamide resins, polysulfone (PSU) resin, polyethersulfone ( polysulfone resins such as polyphenylene sulfone (PPSU) resin and polyphenylene sulfide (PPS) resin, polyphenylene sulfide ketone resin, polyarylene sulfide resins such as polyphenylene sulfide sulfone resin and polyphenylene sulfide ketone sulfone resin, polytetrafluoroethylene (PTFE) resin, polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) resin, tetrafluoroethylene-hexafluoropropyl copolymer (FE Fluorine resins such as vinylidene fluoride (PVdF) resin, tetrafluoroethylene-ethylene copolymer (ETFE) resin, polychlorotrifluoroethylene (PCTFE) resin, vinylidene fluoride (PVdF) resin, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin, and acid-modified fluororesins, and thermoplastic resins such as polycarbonate (PC) resin, polyarylate (PAR) resin, polyacetal (POM) resin, liquid crystal polymer (LCP), and aliphatic polyketone resin can be selectively added.

In addition to the polyether ether ketone resin, various additives, such as crystal nucleating agents, antioxidants, heat stabilizers, slipping agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, and coloring inhibitors, can also be added to the molding material 1, provided that the object of the present invention is not impaired. Furthermore, the polyether ether ketone resin of the molding material 1 can contain particles, in which case inorganic particles or organic particles are preferably used.

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.

In contrast, the organic particles may be one of the following: crosslinked particles of dimethylpolysiloxane, crosslinked particles of polymethoxysilane-based compounds, cured polyorganosilsesquioxane particles, crosslinked particles of polystyrene-based compounds, crosslinked particles of acrylic-based compounds, crosslinked particles of polyurethane-based compounds, crosslinked particles of polyester-based compounds, crosslinked particles of fluorine-based compounds, and fullerenes, which may be used alone or in combination of two or more of them.

The average particle size of the inorganic particles and organic particles is preferably in the range of 0.01 μm to 5.0 μm. The average particle size is preferably 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 will be small and the handling properties may be reduced. On the other hand, if it exceeds 5.0 μm, the polyether ether ketone resin film 2 will be easily torn during biaxial stretching, and the optical properties, mechanical properties, electrical properties, and water absorption properties of the heat-shrinkable film will be deteriorated.

One method for measuring the average particle size of inorganic or organic particles is to calculate the weight average diameter using the circle equivalent diameter obtained by image processing of a transmission electron microscope photograph of the particles.

The amount of the particles added is preferably in the range of 0.01 to 3.0 parts by mass, preferably 0.03 to 2.0 parts by mass, more preferably 0.05 to 1.5 parts by mass, and even more preferably 0.05 to 1.0 parts by mass, based on 100 parts by mass of polyether ether ketone resin. This is because if the amount added is less than 0.01 parts by mass, handling properties are insufficient. On the other hand, if the amount added exceeds 3.0 parts by mass, the unstretched polyether ether ketone resin film 2 becomes easily torn during biaxial stretching, and the optical properties, mechanical properties, electrical properties, and water absorption of the heat-shrinkable film are deteriorated.

If it is desired to prevent aggregation of inorganic or organic particles or to improve affinity with polyether ether ketone resin, the molding material 1 may contain, within a range that does not impair the properties of the heat-shrinkable film, for example, a silane coupling agent [vinyl trimethoxysilane, vinyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-aminopropyl ethoxysilane, p-styryl trimethoxysilane, 3-methacryloxypropyl methyl dimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropyl triethoxysilane, 3-acryloxypropyl trimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyl trialkoxysilane, 3-mercaptopropyl methyl dimethoxysilane, 3-isocyanatopropyl triethoxysilane, 3-trimethoxysilylpropyl succinic anhydride, imidazole silane, etc.], a titanate coupling agent [isopropyl triisostearate, yl titanate, isopropyl(dioctylpyrophosphate) titanate, isopropyl tris(N-aminoethyl-aminoethyl) titanate, tetraoctylbis(di-tridecylphosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, bis(dioctylpyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate It is possible to treat with various coupling agents such as isopropyl dimethacryl isostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate, tetraisopropyl (dioctyl phosphite) titanate, etc., and aluminate coupling agents such as acetoalkoxyaluminum diisopropylate.

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

The unstretched polyether ether ketone resin film 2 is formed by a specified forming method so that the crystallinity is 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 is difficult to manufacture the polyether ether ketone resin film 2. On the other hand, if the crystallinity exceeds 15%, the stretching tension becomes excessive, which makes the polyether ether ketone resin film 2 prone to tearing, uneven stretching, pinholes, etc., and makes biaxial stretching difficult.

The crystallinity of the unstretched polyether ether ketone resin film 2 is calculated by the following formula based on the results of thermal analysis using a differential scanning calorimeter.

Crystallinity (%)={(ΔHm−ΔHc)/ΔHx}×100 (Equation 1)
Where, ΔHm: crystalline melting peak of unstretched polyether ether ketone resin film
Heat capacity (J/g)
ΔHc: Recrystallization peak of unstretched polyether ether ketone resin film
Heat capacity (J/g)
ΔHx: 100% crystallized unstretched polyether ether ketone resin film
The theoretical melting energy of 130 J/g.

Methods for forming the unstretched polyether ether ketone resin film 2 include melt extrusion, calendar molding, and casting. Among these methods, the melt extrusion method, which can continuously extrude the unstretched polyether ether ketone resin film 2 into a strip shape, is optimal from the standpoints of improving the thickness accuracy, productivity, and handleability of the unstretched polyether ether ketone resin film 2, and simplifying the equipment.

As shown in FIG. 1, the melt extrusion molding method is a method of producing an unstretched polyether ether ketone resin film 2 by melt-kneading a molding material 1 containing polyether ether ketone resin using a melt extruder 10, continuously extruding the molten polyether ether ketone 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 extruder 10, and then sandwiching and cooling the polyether ether ketone resin between a pressure roll 17 and a cooling roll 18.

The melt extrusion molding machine 10 is, for example, a single-screw extrusion molding machine or a twin-screw extrusion molding machine, and has a raw material inlet 11 for the molding material 1 at the upper rear. This raw material inlet 11 is connected to an inert gas supply pipe 12 that supplies inert gases such as helium gas, neon gas, argon gas, krypton gas, and nitrogen gas as needed. The supply of inert gas from this inert gas supply pipe 12 effectively prevents oxidative deterioration, oxygen crosslinking, and thermal crosslinking of the molding material 1.

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 polyether ether ketone resin does not decompose, but it is preferably in the range of the melting point of the polyether ether ketone resin (hereinafter referred to as Tm) or higher and lower than the thermal decomposition temperature of the polyether ether ketone resin.

The Tm (unit: °C) of the polyetheretherketone resin is preferably from [Tm of polyetheretherketone resin + 10] °C to [Tm of polyetheretherketone resin + 100] °C, more preferably from [Tm of polyetheretherketone resin + 20] °C to [Tm of polyetheretherketone resin + 70] °C, and even more preferably from [Tm of polyetheretherketone resin + 30] °C to [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.

Specific temperatures are preferably in the range of 360°C to 450°C, preferably 360°C to 420°C, and more preferably 370°C to 400°C. This is because if the temperature during melt kneading in the melt extruder 10 is below the Tm of the polyether ketone resin, melt extrusion molding is not possible, and therefore unstretched polyether ether ketone resin cannot be produced. On the other hand, if the temperature is above the thermal decomposition temperature, the polyether ether ketone resin will decompose.

The die 13 is connected to the tip of the melt extruder 10 via a connecting pipe 14 and functions to continuously extrude a strip of polyether ether ketone resin downward. There are various types of dies 13, but a T-die is preferred because it is possible to obtain an unstretched polyether ether ketone resin film 2 with excellent thickness accuracy.

It is preferable that a gear pump 15 and a filter 16 are attached to the connecting pipe 14 upstream of the die 13. The gear pump 15 functions to transfer the molding material 1 melt-kneaded by the melt extrusion molding machine 10 at a constant flow rate and with high precision to the downstream die 13 via the filter 16. In addition, the filter 16 functions to separate unmelted polyetheretherketone resin and foreign matter from the molten polyetheretherketone resin and transfer the molten polyetheretherketone resin to the die 13.

The temperature during extrusion of the die 13 should be in the range of Tm of the polyetheretherketone resin or higher and lower than the thermal decomposition temperature of the polyetheretherketone resin. It is preferably in the range of [Tm of polyetheretherketone resin + 10]°C or higher and [Tm of polyetheretherketone resin + 100]°C or lower, more preferably in the range of [Tm of polyetheretherketone resin + 20]°C or higher and [Tm of polyetheretherketone resin + 70]°C or lower, and even more preferably in the range of [Tm of polyetheretherketone resin + 30]°C or higher and [Tm of polyetheretherketone resin + 60]°C or lower.

Specific temperatures are preferably in the range of 360°C to 450°C, more preferably 360°C to 420°C, and even 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 an unstretched polyetheretherketone resin film 2. Conversely, if the temperature is above the thermal decomposition temperature, it will lead to decomposition of the polyetheretherketone resin, which is not preferable.

Below the die 13, a pair of opposing pressure rolls 17 are rotatably supported at a distance from each other, and between the pair of pressure rolls 17, a number of cooling rolls 18 are rotatably supported in a row that slide against each other. Of the multiple cooling rolls 18, the upstream cooling roll 18 and the downstream cooling roll 18 each slide against the circumferential surface of the pressure roll 17. Each pressure roll 17 is configured to have a narrower diameter, and each cooling roll 18 is configured to have a larger diameter than the pressure roll 17.

Of the pair of pressure rolls 17, a winder 20 is installed downstream of the downstream pressure roll 17, which winds up the unstretched polyether ether ketone resin film 2 onto a rotatable winding tube 19. Between this winder 20 and the downstream pressure roll 17, a slit blade 21 that forms a slit in the lateral longitudinal direction of the unstretched polyether ether ketone resin film 2 is arranged so that it can be raised and lowered. Between this slit blade 21 and the winder 20, a required number of rotatable tension rolls 22 are supported on the shafts to apply tension to the unstretched polyether ether ketone resin film 2 to smoothly wind it up.

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

Specific temperature ranges are 50°C or higher and 190°C or lower, preferably 100°C or higher and 180°C or lower, more preferably 120°C or higher and 170°C or lower, and even more preferably 130°C or higher and 160°C or lower.

The reason why the temperature of the pressure roller 17 is in this range is that if the temperature is below [Tg of polyetheretherketone resin - 100] °C, the melt-extruded strip-shaped polyetheretherketone resin cannot be brought into close contact with the cooling roller 18, and therefore a smooth unstretched polyetheretherketone resin film 2 cannot be obtained. On the other hand, if the temperature exceeds [Tg of polyetheretherketone resin + 50] °C, the crystallinity exceeds 15%, and it is not possible to adjust the crystallinity to 15% or less. Methods for adjusting the temperature of the pressure roller 17 include, for example, a method using a heat medium such as air, water, or oil, a method using an electric heater, and a method using induction heating.

From the viewpoint of improving the adhesion between the unstretched polyether ether ketone resin film 2 and the cooling roll 18, the peripheral surface of each pressure roll 17 is coated with a rubber layer such as at least natural rubber, isoprene rubber, butadiene rubber, norbornene rubber, acrylonitrile butadiene rubber, nitrile rubber, urethane rubber, silicone rubber, fluororubber, etc. as necessary, and inorganic compounds such as silica and alumina are selectively added to this rubber layer. Of these rubbers, it is preferable to select silicone rubber or fluororubber, which have excellent heat resistance.

The multiple cooling rolls 18 are, for example, metal rolls with a larger diameter than the pressure roll 17, and are rotatably supported below the die 13 to sandwich the polyether ether ketone resin extruded in a strip shape between them and the pressure roll 17. Together with the pressure roll 17, they function to cool the polyether ether ketone resin film 2 in a short period of time while controlling its thickness within a predetermined range.

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

Specific temperature ranges are 50°C or higher and 190°C or lower, preferably 100°C or higher and 180°C or lower, more preferably 120°C or higher and 170°C or lower, and even more preferably 130°C or higher and 160°C or lower.

The reason why the temperature of the cooling roll 18 is in this range is that if the temperature is below [glass transition point of polyetheretherketone resin - 100] °C, the continuous melt extrusion molded strip-shaped polyetheretherketone resin cannot be brought into close contact with the cooling roll 18, and therefore a smooth polyetheretherketone resin film 2 cannot be obtained. Conversely, if the temperature exceeds [glass transition point of polyetheretherketone resin + 50] °C, the crystallinity exceeds 15%, and it is not possible to adjust the crystallinity to 15% or less. Methods for adjusting the temperature and cooling the cooling roll 18 include methods using heat media such as air, water, oil, etc., or electric heaters and induction heating.

After the molding material 1 is extruded into a strip-shaped polyether ether ketone resin film 2, this unstretched polyether ether ketone resin film 2 is wound around a pair of pressure rolls 17, multiple cooling rolls 18, a tension roll 22, and a winding tube 19 of a winding machine 20, and both sides of the unstretched polyether ether ketone resin film 2 are cut in the longitudinal direction with a slit blade 21. The film is then wound up sequentially around the winding tube 19 of the winding machine 20, producing a long unstretched polyether ether ketone resin film 2.

The thickness of the unstretched polyether ether ketone resin film 2 produced by cooling with the cooling roll 18 is preferably 10 μm to 1000 μm, more preferably 30 μm to 750 μm, more preferably 50 μm to 500 μm, and even more preferably 50 μm to 250 μm. This is because if the thickness of the unstretched polyether ether ketone resin film 2 is less than 10 μm, the tensile strength of the unstretched polyether ether ketone resin film 2 decreases, which leads to breakage of the polyether ether ketone resin film 2 during biaxial stretching. On the other hand, if the thickness of the unstretched polyether ether ketone resin film 2 exceeds 1000 μm, it becomes difficult to produce the unstretched polyether ether ketone resin film 2.

After the intermediate product, unstretched polyether ether ketone resin film 2, is produced, the unstretched polyether ether ketone resin film 2 wound on the winder 20 is transferred to a separate biaxial stretching device and fed therein for biaxial stretching to produce the finished heat-shrinkable film. The heat-shrinkable film is a biaxially stretched film that is stretched in two directions: the longitudinal direction (sometimes called the extrusion direction, machine axis, longitudinal direction, or MD) and the transverse direction (sometimes called the direction perpendicular to the extrusion direction, width direction, or TD).

The reason why the unstretched polyether ether ketone resin film 2 is biaxially stretched by the biaxial stretching method is that, when it is unstretched, heat shrinkage cannot be expected. Also, when it is uniaxially stretched, there is no shrinkage in the direction that is not stretched, which creates problems as a heat shrinkable film. In contrast, if the unstretched polyether ether ketone resin film 2 is biaxially stretched by the biaxial stretching method, the mechanical properties, electrical properties, and low water absorption of the heat shrinkable film can be maintained, the heat shrinkage rate can be increased, and the optical properties and heat resistance can be improved.

Biaxial stretching methods include sequential biaxial stretching and simultaneous biaxial stretching, and either method may be used. Sequential biaxial stretching is a relatively simple mechanism in which the longitudinal and transverse stretching mechanisms are independent, making ultra-high speed stretching possible. However, when a crystalline resin such as polyether ether ketone resin is biaxially stretched by sequential biaxial stretching, the polyether ether ketone resin film 2 is cooled once after longitudinal stretching in the sequential biaxial stretching process. Recrystallization progresses in the crystalline resin, and if the stretching stress in the polyether ether ketone resin film 2 increases during the subsequent transverse stretching, the optical properties such as the haze value may deteriorate. In addition, when stretched in the longitudinal direction, the molecules tend to be oriented in the stretching direction, so when stretched in the transverse direction after longitudinal stretching, the polyether ether ketone resin film 2 may tear depending on the conditions.

Therefore, in order to achieve the desired transverse stretch ratio, the molding conditions may be restricted, such as by considering the balance between the longitudinal and transverse stretching conditions, such as adjusting the longitudinal stretch ratio in the previous stage, and by limiting the combination of stretch ratios. Therefore, the sequential biaxial stretching method has the problem that optimization of the stretching conditions is complicated compared to the simultaneous biaxial stretching method.

In contrast, the simultaneous biaxial stretching method, which stretches the film in both the longitudinal and transverse directions at the same time, can suppress crystallization of the polyether ether ketone resin film 2, and can also be freely relaxed in addition to stretching, making it easy to obtain a polyether ether ketone resin film 2 in which bowing and anisotropy of molecular orientation are suppressed. In addition, the simultaneous biaxial stretching method can simultaneously stretch a resin in a state in which the molecules are not oriented in a specific direction in both the longitudinal and transverse directions, reducing the complexity of having to consider balance as in the sequential biaxial stretching method, and increasing the freedom in setting the stretching conditions. Therefore, the simultaneous biaxial stretching method is preferable to the sequential biaxial stretching method.

The stretching ratio during biaxial stretching is 5.0 times or less in both the longitudinal and transverse directions, preferably 1.5 times to 5.0 times, more preferably 1.7 times to 4.0 times, even more preferably 2.0 times to 3.5 times, and most preferably 2.0 times to 3.0 times. This is because if the stretching ratio is less than 1.5 times, sufficient molecular orientation does not occur, the stretching effect is small, and it may also cause thickness variations. On the other hand, if it exceeds 5.0 times, the tensile tension becomes too large, and the polyether ether ketone resin film 2 is likely to break during stretching, have uneven stretching, or have pinholes.

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

This is because if the stretching temperature is less than [Tg of unstretched polyether ether ketone resin film - 20]°C, the stretching tension becomes excessive, which can easily cause film tearing, uneven stretching, and pinholes during stretching. In addition, this can cause the heat-shrinkable film to whiten. On the other hand, if the temperature exceeds [Tg of unstretched polyether ether ketone resin film + 50]°C, the polyether ether ketone resin film 2 will stretch under its own weight, which can easily cause uneven stretching.

The heat-shrinkable film produced may be used as a finished product as it is, but if necessary, the biaxially stretched polyether ether ketone resin film 2 may be heat-treated to heat-set, which can prevent natural shrinkage and adjust the heat shrinkage characteristics, such as adjusting the heat shrinkage rate and heat shrinkage temperature. The heat-setting temperature in this case should be in the range of [Tg of polyether ether ketone resin film + 30]°C to [Tm of polyether ether ketone resin film]°C, preferably [Tg of polyether ether ketone resin film + 60]°C to [Tm of polyether ether ketone resin - 20]°C, and more preferably [Tg of polyether ether ketone resin + 90]°C to [Tm of polyether ether ketone resin - 40]°C.

The heat setting time for the biaxially stretched polyether ether ketone 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.

The heat setting may be carried out in two or more separate steps, such as a heat treatment carried out continuously after the stretching step and a separate heat treatment carried out after the biaxially stretched film is produced. The heat setting may also be a tension heat treatment in which the heat treatment is carried out while maintaining the tension during biaxial stretching, or a relaxation heat treatment carried out simultaneously with the start of the heat treatment. A combination of tension heat treatment and relaxation heat treatment may also be carried out, for example by carrying out a tension heat treatment as the first heat treatment and then a relaxation heat treatment as the second heat treatment.

The thickness of the heat-shrinkable film is not particularly limited, but is preferably, for example, 5 μm to 100 μm, preferably 10 μm to 75 μm, and more preferably 10 μm to 50 μm. This is because if the thickness is less than 5 μm, the tensile strength of the heat-shrinkable film is significantly reduced, making it more likely to break during production and reducing production efficiency. On the other hand, if the thickness exceeds 100 μm, the tensile tension becomes too large, making it more likely that the film will break during stretching, that stretching will be uneven, and that pinholes will form.

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

This is because if the rate of change in dimensions due to heat in the longitudinal and transverse directions is less than -5.0% (or if it stretches), it is not possible to ensure an appropriate shrinkage rate for the heat-shrinkable film, resulting in poor adhesion to the packaged or coated contents and the risk of substances that contaminate or corrode the packaged or coated contents penetrating between the heat-shrinkable film and the packaged or coated contents. On the other hand, if the rate of change in dimensions due to heat in the longitudinal and transverse directions exceeds -50.0%, the shrinkage rate becomes too high, damaging the packaged or coated contents and causing tears in the heat-shrinkable film.

The optical properties of a heat-shrinkable film can be evaluated by its total light transmittance and haze value. First, when measuring the total light transmittance of a heat-shrinkable film, the heat-shrinkable film is measured before and after heating at 200°C and 250°C for 10 minutes in accordance with JIS K 7361-1 under an environment 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 is preferably 70% or more, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. This is because when the total light transmittance of the heat-shrinkable film is 70% or more, good transparency can be expected. On the other hand, when it is less than 70%, transparency is lost, making it difficult to confirm the color and shape of the contents and the coated contents.

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 is measured before and after heating at 200°C and 250°C for 10 minutes in accordance with JIS K 7136 under an environment 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 is preferably 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 and it becomes difficult to grasp the color and shape of the packaged contents or coated contents.

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. 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 more, the tensile elongation at break (longitudinal and transverse directions) at 23°C is 50% or more, and the tensile modulus (longitudinal and transverse directions) at 23°C is 3000 MPa or more.

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 or more and 290 MPa or less. 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, and problems such as breakage, cracking, and tearing may occur when the heat-shrinkable film is used.

The upper limit of the maximum tensile strength is not particularly limited, but it is preferably 500 MPa or less. 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.

The tensile elongation at break (longitudinal and transverse directions) at 23°C is 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, and there is a risk of problems such as breakage, cracking, and tearing occurring when the heat-shrinkable film is used. There is no particular restriction on the upper limit of the tensile elongation at break, but it is preferably 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 the handleability tends to deteriorate when the heat-shrinkable film becomes thinner.

The tensile modulus of the heat-shrinkable film at 23°C is 3000 MPa or more, preferably 3500 MPa or more, more preferably 4000 MPa or more, even more preferably 4200 MPa or more, and most preferably in the range of 3850 MPa to 4420 MPa. This is because within this range, the film has excellent rigidity and tends to be easy to handle even if the film is thin. In addition, if the tensile modulus of the heat-shrinkable film is less than 3000 MPa, the rigidity is insufficient and the heat-shrinkable film may be broken by contents or coverings with protrusions, or the corners of polygonal structures such as rectangles and triangles.

The upper limit of the tensile modulus is not particularly limited, but it is preferably 6000 MPa or less. 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 substances that contaminate or corrode the packaged or coated contents may penetrate between the heat-shrinkable film and the packaged or coated contents.

The heat resistance of the heat shrinkable film can be expressed by the storage modulus at 300° C. From the viewpoint of obtaining excellent heat resistance, the heat shrinkable film preferably has a storage modulus at 300° C. of 1.0×10 ⁵ Pa or more, more preferably 1.0×10 ⁶ Pa or more, and even more preferably 1.0×10 ⁷ Pa or more, when measured under conditions of a frequency of 1 Hz and a temperature increase rate of 3° C./min. This is because, when the storage modulus at 300° C. is less than 1.0×10 ⁵ Pa, sufficient heat resistance cannot be obtained in a high temperature range, and the heat shrinkable film softens when left in a high temperature range of 300° C. or more, and breaks after packaging or covering the packaged or covered contents.

The upper limit of the storage modulus of the heat-shrinkable film at 300° C. is not particularly limited, but is preferably not more than 1.0×10 ¹⁰ Pa. This is because, if the storage modulus exceeds 1.0×10 ¹⁰ Pa, the 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.

The electrical properties of the heat shrinkable film can be evaluated by the volume resistivity, dielectric breakdown voltage, relative dielectric constant, and dielectric loss tangent. The volume resistivity of the heat shrinkable film can be measured in accordance with JIS C 2139-3-1. From the viewpoint of ensuring better insulation, this volume resistivity is 1.0×10 ¹⁴ Ω·cm or more, preferably 1.0×10 ¹⁵ Ω·cm or more, and more preferably 1.0×10 ¹⁶ Ω·cm or more. The upper limit of the volume resistivity is preferably as high as possible, and is not particularly limited, but is usually 1×10 ¹⁸ Ω·cm or less.

When a heat-shrinkable film is used, for example, to cover a battery cell, if the volume resistivity is 1.0 x ¹⁰ Ω·cm or more, excellent insulating performance can be ensured, and even when an overvoltage is applied to the battery cell, the film can be resistant to breakdown and prevent problems caused by electrical shorts in the battery cell.

The breakdown voltage of the heat shrinkable film can be measured at 23°C ± 2°C and 50% RH ± 5% RH in accordance with IEC 60243-1. The breakdown voltage of this heat shrinkable film is 1.0 kV or more, preferably 1.5 kV or more, more preferably 2.0 kV or more, and even more preferably 3.0 kV or more. This is because if the breakdown voltage of the heat shrinkable film is 1.0 kV or more, it has excellent insulation properties and can maintain its resistance without breaking down even when an overvoltage is applied, preventing problems caused by electrical shorts in battery cells, etc. The higher the upper limit of the breakdown voltage of the heat shrinkable film, the better, and although there is no particular limit, it is usually 20 kV or less.

The dielectric constant of the heat shrinkable film can be evaluated at frequencies of 1 GHz and 28 GHz. The dielectric constant at 1 GHz is preferably measured by the cavity resonator perturbation method, and the dielectric constant at 28 GHz is preferably measured by the Fabry-Perot method. The dielectric constant of the heat shrinkable film at 1 GHz and 23°C and 28 GHz is preferably 3.5 or less, more preferably 3.4 or less, and even more preferably 3.3 or less. This is because a heat shrinkable film with a dielectric constant of 3.5 or less has excellent insulation properties. The lower the lower limit of the dielectric constant at 1 GHz and 28 GHz, the better, and there is no particular restriction, but in practice it is 1.1 or more.

The dielectric loss tangent of the heat shrinkable film can be evaluated at frequencies of 1 GHz and 28 GHz. The dielectric loss tangent at a frequency of 1 GHz is measured by the cavity resonator perturbation method, and the cavity resonator perturbation method at a frequency of 28 GHz is preferably measured by the Fabry-Perot method. The dielectric loss tangent of the heat shrinkable film at a frequency of 1 GHz at 23°C and a frequency of 28 GHz at 23°C is 0.010 or less, preferably 0.008 or less, more preferably 0.007, and even more preferably 0.006 or less. This is because if the dielectric loss tangent of the heat shrinkable film is 0.010 or less, excellent insulation properties can be expected. The lower limit of the relative dielectric constant at a frequency of 1 GHz and a frequency of 28 GHz is preferably as low as possible, and is not particularly limited, but is 0.0001 or more in practical use.

The water absorption rate, which indicates the water absorption rate of a heat shrinkable film, can be measured in an environment of 23°C ± 2°C in accordance with JIS K 7209 A method. The water absorption rate of this heat shrinkable film is 10% or less, 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 heat shrinkable film maintains high electrical insulation even in a high temperature and humidity environment. The lower limit of the water absorption rate of the heat shrinkable film 1 is not particularly limited, but in practical use it is 0.01% or more.

According to the above, the molded unstretched polyether ether ketone resin film 2 is biaxially stretched to set the thermal dimensional change rate in the longitudinal and transverse directions at 170°C, 200°C, and 250°C to -50% or more and -5% or less, so that the heat shrinkability can be improved and an excellent heat shrinkable film can be obtained. In addition, since the unstretched polyether ether ketone resin film 2 having a crystallinity of 1% or more and 15% or less is biaxially stretched, it is expected that biaxial stretching will be facilitated. In addition, since simultaneous biaxial stretching is performed during biaxial stretching, a high added-value heat-storing film having high isotropy in the longitudinal and transverse directions can be obtained.

In addition, since the stretching ratio during simultaneous biaxial stretching is 1.5 times or more and 5.0 times or less, an excellent stretching effect can be obtained while suppressing thickness variation, and it is possible to prevent film tearing, stretching unevenness, and pinholes from occurring in the polyether ether ketone resin film 2 during simultaneous biaxial stretching. In addition, since polyether ether ketone resin is used, it does not melt even in the high temperature range of 300°C, and does not cause serious problems in production and use. Furthermore, if the simultaneously biaxially stretched polyether ether ketone resin film 2 is subjected to a heat treatment, it is possible to heat fix the heat-shrinkable film and prevent natural shrinkage.

Next, FIG. 2 shows a second embodiment of the present invention. In this case, the melt extruder 10 is divided into a first and a second melt extruder 10A and 10B, and a cast roll 30, a simultaneous longitudinal and transverse biaxial stretching machine 31, a take-up machine 35, and a winding machine 36 are sequentially arranged downstream of the first and second melt extruders 10A and 10B to produce a two-layer heat-shrinkable film.

The first melt extruder 10A is, for example, a melt extruder 10 similar to that of the first embodiment, and functions to melt and knead a molding material 1 containing polyether ether ketone resin, and continuously extrude this molding material 1 into a die 13 such as a T-die. In contrast, the second melt extruder 10B melts and kneads a molding material 1 of a different composition containing additives such as polyether ether ketone resin, antistatic agents, low dielectric materials, and heat dissipation materials, and continuously extrudes this molding material 1 upstream of the die 13 to join the molding material 1 of the first melt extruder 10A.

The molding material 1 from the merged first and second melt extruders 10A and 10B is extruded together through the die 13 to form a thick polyetheretherketone resin layer and a thin polyetheretherketone resin layer. The cast roll 30 is installed downstream of the first and second melt extruders 10A and 10B and the die 13, and functions to form the molten ribbon-shaped polyetheretherketone resin into a sheet.

The longitudinal and transverse simultaneous biaxial stretching machine 31 is installed downstream of the cast roll 30, and has hot air blowing ovens 32 on both the left and right sides, and simultaneously biaxially stretches the unstretched polyether ether ketone resin film 2 in the longitudinal and transverse directions. This longitudinal and transverse simultaneous biaxial stretching machine 31 is equipped with a pair of left and right running rails 33 that can be expanded and contracted in the width direction, in a roughly V-shaped plan view, and each running rail 33 is formed by a pair of opposing guide rails, and a clip 34 runs on the pair of guide rails. A link mechanism that runs across the pair of guide rails is attached to the clip 34, and an independent resin film gripper is installed at the tip of this link mechanism.

Such a simultaneous longitudinal and transverse biaxial stretching machine 31 stretches the unstretched polyether ether ketone resin film 2 in the transverse direction by widening a pair of running rails 33 in the transverse direction, and stretches the unstretched polyether ether ketone resin film 2 in the longitudinal direction by narrowing the pair of running rails 33 in the transverse direction.

The take-up machine 35 is installed downstream of the longitudinal and transverse simultaneous biaxial stretching machine 31 and functions to take up the simultaneously biaxially stretched polyether ether ketone resin film 2. The winding machine 36 is installed downstream of the take-up machine 35 and functions to wind up the simultaneously biaxially stretched polyether ether ketone resin film 2, in other words, the heat-shrinkable film, onto a winding tube. The other parts are the same as those in the above embodiment, so the explanation will be omitted.

In this embodiment, the same effects as those of the above embodiment can be expected, and since there is no need to transfer the unstretched polyether ether ketone resin film 2 wound on the winder 20 to a separate biaxial stretching device for biaxial stretching, it is clear that the manufacturing process can be expected to be quicker and easier. In addition, since the heat-shrinkable film can be formed into a two-layer structure with different thicknesses and compositions, high functionality can be expected.

In the above embodiment, the molten polyetheretherketone resin is pressed against the cooling roll 18 by the pressure roll 17 to adhere to the cooling roll 18, but the present invention is not limited to this. For example, the molten polyetheretherketone resin may be adhered to the cooling roll 18 by using an electrostatic application method (or a pinning method) or an air knife. In addition, when cooling the molten polyetheretherketone resin, the molten polyetheretherketone resin may be adhered to a metal belt or the like, water may be sprayed onto the molten polyetheretherketone resin, or the molten polyetheretherketone resin may be poured into water.

At least one of the front and back surfaces of the heat shrinkable film may be subjected to a surface activation treatment such as a corona treatment, a plasma treatment such as a vacuum plasma treatment or an atmospheric plasma treatment, an ultraviolet treatment, or an Itro treatment. In addition, various properties can be added by applying printing, various functional coatings, lamination, etc., to further improve the value of the film. Furthermore, the melt extruder 10 can be divided into a first, second, and third melt extruder to produce a heat shrinkable film with a three-layer structure.

EXAMPLES Hereinafter, examples of the heat shrinkable film and the method for producing the same according to the present invention will be described together with comparative examples.
Example 1
First, in order to prepare an unstretched polyether ether ketone resin film, a commercially available polyether ether ketone resin (manufactured by Solvay Spessruty Polymers Japan, Inc., product name KetaSpire PEEK KT-851NL SP (hereinafter abbreviated as "KT-851NL SP")) was prepared, and this polyether ether ketone resin was placed in a dehumidifying dryer heated to 160°C and dried for 12 hours or more. The polyether ether ketone resin is hereinafter abbreviated as "PEEK resin".

Next, the PEEK resin was set in a single-screw extruder with a T-die as shown in Figure 1 and melt-kneaded. The melt-kneaded PEEK resin was continuously extruded from the T-die of the single-screw extruder and cooled by being sandwiched between a number of pressure rolls and a cooling roll, thereby extruding an unstretched PEEK resin film into a strip shape. At this time, the temperature of the single-screw extruder was adjusted to 380-400°C, the temperature of the T-die to 400°C, and the temperature of the connecting pipe connecting the single-screw extruder and the T-die 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 inlet of the T-die, and was found to be 397°C.

After the unstretched PEEK resin film was extruded in this manner, both ends of the continuous unstretched PEEK resin film were cut with a slit blade and sequentially wound around a winding tube of a winding machine to produce an unstretched PEEK resin film. At this time, the unstretched PEEK resin film was sequentially wound around multiple cooling rolls at 150°C, a pair of pressure rolls made of silicone rubber, and a 6-inch winding tube located downstream of these, as shown in Figure 1.

The Tg of KT-851NL SP was measured using a differential scanning calorimeter (manufactured by SII Nanotechnologies, product name: High-sensitivity differential scanning calorimeter X-DSC7000) in accordance with JIS K 7121 at a heating rate of 10°C/min. The Tg of KT-851NL SP was measured at 146°C. The Tg of the unstretched PEEK resin film was measured using a differential scanning calorimeter (manufactured by SII Nanotechnologies, product name: High-sensitivity differential scanning calorimeter X-DSC7000) in accordance with JIS K 7121 at a heating rate of 10°C/min. The Tg of the unstretched PEEK resin film was measured at 145°C.

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

Thereafter, the piston was again pushed in at a speed of 50 mm/min until the pressure reached 0.9 MPa on the long die side and 0.3 MPa on the short die side, and when the pressure reached a predetermined value, the apparent shear viscosity was measured at predetermined apparent shear rates (10, 20, 30, 50, 80, 100, 200, 300, 800 sec ^-1 ) to determine the apparent shear viscosity. The apparent shear viscosity of KT-851NL SP at an apparent shear rate of 100 sec ^-1 was 1.00 x 10 ³ Pa·s.

The crystallinity of the unstretched PEEK resin film was measured by weighing out about 8 mg of a measurement sample from the unstretched PEEK resin film and using a differential scanning calorimeter (manufactured by SII Nanotechnologies, product name: EXSTAR7000 series X-DSC7000) at a heating rate of 10°C/min over a measurement temperature range of 20°C to 380°C. The heat quantity (J/g) of the crystal melting peak and the heat quantity (J/g) of the recrystallization peak obtained at this time were used to calculate the crystallinity using the following formula. The crystallinity of the obtained PEEK resin film was 9.2%.

Crystallinity (%)={(ΔHm−ΔHc)/ΔHx}×100 (Equation 1)
Here, ΔHm: heat of crystal melting peak of unstretched PEEK resin film (J / g)
ΔHc: Heat quantity (J / g) of the recrystallization peak of the unstretched PEEK resin film
ΔHx: theoretical melting energy of 100% crystallized PEEK resin,
130 J/g.

The thickness of the unstretched PEEK resin film was measured using a micrometer (Mitutoyo Corporation, product name: Coolant Proof Micrometer, code MDC-25PJ). Measurements were taken at 10 random locations in the lateral direction of the unstretched PEEK resin film, and the average value was taken as the film thickness.

Next, the unstretched PEEK resin film was simultaneously biaxially stretched using a commercially available simultaneous biaxial stretching machine that simultaneously stretches in the longitudinal and transverse directions. Specifically, the unstretched PEEK resin film was simultaneously biaxially stretched 2.0 times in the longitudinal direction and 2.0 times in the transverse direction using a tenter system. At this time, the temperature of the preheating part of the heating furnace of the simultaneous biaxial stretching machine was heated to 90°C for 30 seconds, and then stretched 2.0 times in the longitudinal direction and 2.0 times in the transverse direction while heating at 155°C for 120 seconds. Both ends of the biaxially stretched PEEK resin film thus obtained were cut with a slit blade and sequentially wound around the winding tube of a winding machine to produce a heat-shrinkable film.

After producing the heat-shrinkable film, the thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics, and water absorption of this heat-shrinkable film were evaluated and the results are summarized in Table 1. Heat shrinkage characteristics were evaluated by the rate of dimensional change upon heating, optical characteristics were evaluated by the total light transmittance and haze, mechanical characteristics were evaluated by the maximum tensile strength, tensile elongation at break, and tensile modulus, heat resistance was evaluated by the storage modulus at 300°C, electrical characteristics were evaluated by the volume resistivity, electrical breakdown strength, and the relative dielectric constant and dielectric loss tangent at 1 GHz and 28 GHz, and water absorption was evaluated by the water absorption rate.

The thickness of the heat shrinkable film was measured using a micrometer (manufactured by Mitutoyo Corporation, product name: Coolant Proof Micrometer, code MDC-25PJ). Measurements were taken at 10 random locations in the lateral direction of the heat shrinkable film, and the average value was taken as the film thickness.

-Heat shrinkage properties of heat shrinkable film The heat shrinkage properties of the heat shrinkable film were evaluated by the rate of change in dimensions upon heating. In measuring the rate of change in dimensions upon heating, a test piece was cut out of the heat shrinkable film to a size of 120 mm in the longitudinal direction x 120 mm in the transverse direction in accordance with JIS K 7133, and a 100 mm mark was drawn on the test piece in the longitudinal and transverse directions, and the length between the mark was measured with a caliper. Then, the test piece was placed in an oven at 170°C, 200°C, and 250°C and heated for 10 minutes. After heating for 10 minutes, the test piece was naturally cooled to 23°C, and the length between the mark was measured again at 23°C±2, 50±5% RH, and the rate of change in dimensions upon heating was calculated by the following formula.

Heat dimensional change rate (%)={(L−L ₀ )/L ₀ }×100
Where L ₀ : Gauge length before test (mm)
L: Gauge distance after heating (mm)

Total light transmittance of heat shrinkable film The total light transmittance of the heat shrinkable film was measured in accordance with JIS K 7361-1 using a haze meter [manufactured by Nippon Denshoku Industries Co., Ltd., model: NDH-8000] under an environment of 23°C ± 2°C and 50% RH ± 5% RH. The specific method of measuring the total light transmittance was to first cut the heat shrinkable film into a size of 120 mm in the vertical direction × 120 mm in the horizontal direction to prepare a test piece. The total light transmittance of this test piece was measured before and after heating in an oven at 200°C and 250°C for 10 minutes. The measurement of the total light transmittance of the test piece heated at 200°C and 250°C for 10 minutes was performed by placing the test piece in an oven at 200°C and 250°C and heating it for 10 minutes, and after heating, allowing the test piece to cool naturally to 23°C ± 2°C, and then performing the measurement under an environment of 23°C ± 2°C and 50% RH ± 5% RH.

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 an environment of 23°C±2°C and 50% RH±5% RH in accordance with JIS K 7136. When specifically measuring the haze of the heat shrinkable film, the heat shrinkable film was first cut into a size of 120 mm in the vertical direction × 120 mm in the horizontal direction to prepare a test piece, which was then heated in an oven at 200°C and 250°C for 10 minutes, and after heating, the test piece was naturally cooled to 23°C±2°C and then measured in an environment of 23°C±2°C and 50% RH±5% RH.

Mechanical Properties of Heat Shrinkable Film The mechanical properties of the heat shrinkable film were evaluated in terms of maximum tensile strength, tensile elongation at break, and tensile modulus at 23°C. The mechanical properties were measured in the longitudinal and transverse directions. The measurements were performed in accordance with JIS K 7127 under 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.

Heat Resistance of Heat Shrinkable Film The heat resistance of the heat shrinkable film was evaluated by the storage modulus (E') of the heat shrinkable film at 300°C. The storage modulus of this heat shrinkable film was measured in the longitudinal and transverse directions of the heat shrinkable film. Specifically, when measuring the storage modulus in the longitudinal direction of the heat shrinkable film, a piece was cut out to a size of 60 mm in the longitudinal direction x 6 mm in the transverse direction, and when measuring the storage modulus in the transverse direction, the piece was cut out to a size of 6 mm in the longitudinal direction x 60 mm in the transverse direction and measured. When measuring the storage modulus, a viscoelasticity spectrometer (manufactured by TS Instruments Japan, product name: RSA-G2) was used in a tensile mode under the conditions of a frequency of 1 Hz, a strain of 0.1%, a heating rate of 3°C/min, a measurement temperature range of -60 to 360°C, and a check distance of 21 mm, and the storage modulus at 300°C was obtained.

Electrical Properties of Heat Shrinkable Film The electrical properties of the heat shrinkable film were evaluated in terms of volume resistivity, dielectric breakdown voltage, dielectric constant at 1 GHz and 28 GHz, and dielectric loss tangent.

Volume resistivity of heat shrinkable film The volume resistivity of the heat shrinkable film was measured in accordance with JIS C2139-3-1 under an environment of 23°C ± 2°C and 50% RH ± 5% RH. As a specific measurement method, first, the heat shrinkable film was cut into a size of 100 mm in the vertical direction × 100 mm in the horizontal direction to prepare a test piece, and this test piece was left to stand for 24 hours under an environment of 23°C ± 2°C and 50% RH ± 5% RH. After standing, the test piece was attached to the electrode part of a measuring instrument [manufactured by HIOKI EE Corporation, product name: electrode for plate samples SME-8310]. After the test piece was attached to the electrode part of the measuring instrument in this way, an applied voltage of 500 V was applied, and the resistance value after 1 minute was measured using a measuring instrument [manufactured by HIOKI EE Corporation, product name: Super insulation meter SM-8220], and the volume resistivity was calculated according to the following formula.

Volume resistivity (Ω cm) = (19.6/t) × Rv
Where t: thickness of test piece (cm)
Rv: Measured volume resistance (Ω)

・Dielectric properties of heat shrinkable film [frequency: 1 GHz]
The dielectric constant and dielectric loss tangent of the heat shrinkable film at a frequency of 1 GHz were measured by a cavity resonator perturbation method using a network analyzer [Network Analyzer MS46122B manufactured by Anritsu Corporation]. The measurement of the dielectric properties near 1 GHz was performed in accordance with ASTM D2520 using a cavity resonator 1 GHz [Model: TMR-1A manufactured by Keycom Corporation]. The measurement of the dielectric properties was performed in an environment of temperature: 23°C ± 1°C and humidity: 10% RH ± 5% RH.

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

For the measurements, a heat-shrinkable film for high-frequency circuit boards was placed on the sample stage of the open resonator fixture, and measurements were performed using the Fabry-Perot method, a type of open resonator method, with a vector network analyzer. Specifically, the relative dielectric constant and dielectric loss tangent were measured using a resonance method that utilizes the difference in resonance frequency between when there is no heat-shrinkable film on the sample stage and when there is.

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

Water absorption rate (%) = {(m ₂ -m ₁ )/m ₁ } x 100
Here, m ₁ : mass (mg) of the test piece before immersion
_m2 : Mass of test piece after immersion (mg)

Example 2
The unstretched PEEK resin film produced in Example 1 was used and simultaneously biaxially stretched in the same manner as in Example 1 to produce a heat shrinkable film having a thickness different from that of Example 1. However, the simultaneous biaxial stretching was performed at a stretch ratio of 2.5 times in the longitudinal direction and 2.5 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3
Unstretched PEEK resin films of different thicknesses were produced using the same method as in Example 1, using the KT-851NL SP used in Example 1 as a commercially available PEEK resin, and the film thickness and crystallinity of these unstretched PEEK resin films were evaluated using the same method as in Example 1.

After the unstretched PEEK resin film was produced, this unstretched PEEK resin film was simultaneously biaxially stretched in the same manner as in Example 1 to produce a heat shrinkable film having a thickness different from that of Example 1. In this case, the simultaneous biaxial stretching was performed at a stretch ratio of 2.0 times in the longitudinal direction and 2.0 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 4
The unstretched PEEK resin film produced in Example 3 was simultaneously biaxially stretched in the same manner as in Example 1 to produce a heat shrinkable film having a thickness different from that of Example 1. The simultaneous biaxial stretching was performed at a stretch ratio of 2.6 times in the longitudinal direction and 2.5 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Example 5
First, the commercially available PEEK resin was changed from KT-851NL SP in Example 1 to Victrex Granules 450G (product name of Victrex Corporation; hereinafter abbreviated as "450G"), and unstretched PEEK resin films of different thicknesses were produced in the same manner as in Example 1. In this case, the apparent shear viscosity of 450G at 375°C was measured in the same manner as in Example 1. When measured, the apparent shear viscosity of 450G at 375°C and an apparent shear rate of 100 sec ^-1 was 1.32 x ¹⁰³ Pa·s.

After the unstretched PEEK resin film was produced, this unstretched PEEK resin film was simultaneously biaxially stretched in the same manner as in Example 1 to produce a heat shrinkable film having a thickness different from that of Example 1. The simultaneous biaxial stretching was performed by changing the stretching ratio to 3.0 times in the longitudinal direction and 3.0 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Example 6
The unstretched PEEK resin film produced in Example 5 was used to produce the thickest heat-shrinkable film by simultaneous biaxial stretching in the same manner as in Example 1. The simultaneous biaxial stretching was performed at a stretch ratio of 2.5 times in the longitudinal direction and 3.0 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 1
The unstretched PEEK resin film having a film thickness of 50 μm and a crystallinity of 9.2% produced in Example 1 was made into a heat-shrinkable film without being stretched. The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics, and water absorption properties of this heat-shrinkable film were evaluated in the same manner as in Example 1, and the results are summarized in Table 3.

Comparative Example 2
The unstretched PEEK resin film having a film thickness of 50 μm and a crystallinity of 9.2% produced in Example 1 was stretched twice in only the longitudinal direction by a metal roll heated to 160° C. to produce a heat-shrinkable film.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are summarized in Table 3.

Comparative Example 3
A heat-shrinkable film was produced by stretching the unstretched PEEK resin film having a thickness of 50 μm and a crystallinity of 9.2% produced in Example 1 only in the transverse direction by 2.0 times in the same manner as in Example 1. At this time, the preheating part of the heating furnace was heated to 90° C. for 30 seconds, and then heated to 155° C. for 120 seconds while stretching the film by 2.0 times in the transverse direction.
The film thickness, heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 3.

Comparative Example 4
An unstretched PEEK resin film was produced using the PEEK used in Example 1 under the same conditions as in Example 1, and this unstretched PEEK resin film was used as a heat shrinkable film as is. The film thickness and crystallinity of the unstretched PEEK resin film were evaluated in the same manner as in Example 1 and are shown in Table 3.
The heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorbency of the obtained heat shrinkable film were evaluated in the same manner as in Example 1, and the results are shown in Table 3.

Comparative Example 5
An unstretched PEEK resin film was produced under the same conditions as in Example 1 using the PEEK resin used in Example 1, and this unstretched PEEK resin film was used as a heat shrinkable film as it was. However, while in Example 1 the film was sandwiched between a pressure roll and a cooling roll heated to 150°C, in Comparative Example 5 the film was sandwiched between a pressure roll and a cooling roll heated to 220°C.
The film thickness and crystallinity of the obtained heat shrinkable film, as well as the heat shrinkage characteristics, optical characteristics, mechanical characteristics, heat resistance, electrical characteristics and water absorption properties were evaluated in the same manner as in Example 1, and the results are shown in Table 3.

[Results]
In each example, the heat shrinkable film had a thermal dimensional change rate of -10% or more in both the longitudinal and transverse directions at 200°C, and good heat shrink properties were obtained. The heat shrinkable film also had a total light transmittance of 80.0% or more even after 10 minutes of heating at 200°C, and a haze of 2.0% or less even after 10 minutes of heating at 200°C, and excellent transparency was ensured. The mechanical properties of the heat shrinkable film were a maximum tensile strength of 180 MPa or more, and a tensile elongation of 70% or more, and the film had sufficient toughness. In addition, the tensile modulus was 3800 MPa or more, and the film had sufficient rigidity.

In each example, the heat shrinkable film had a storage modulus of 8.50×10 ⁷ Pa or more at 300° C., and no deterioration in the heat resistance of the heat shrinkable film was observed. The electrical properties of the heat shrinkable film were a volume resistivity of 1×10 ¹⁶ Ω·cm or more, a breakdown voltage of 4.0 kv or more, a relative dielectric constant of 3.1 or less at 1 GHz, a dielectric loss tangent of 0.0031 or less, and a relative dielectric constant of 3.2 or less at 28 GHz, a dielectric loss tangent of 0.0054 or less, and no deterioration in the insulating properties due to biaxial stretching was observed. Furthermore, the water absorption of the heat shrinkable film was 0.35% or less, and no deterioration due to biaxial stretching was observed.

In contrast, in the case of Comparative Example 1, the low-crystalline PEEK resin film before biaxial stretching used in Example 1 is a heat-shrinkable film, so although there are no problems with heat resistance, electrical properties, and water absorption, the rate of dimensional change upon heating was small at -3.0% or less, and it was found to be unsuitable as a heat-shrinkable film. In addition, the haze value was 34% or more, so transparency was not achieved, and the tensile modulus of elasticity, a mechanical property, was 3000 MPa or less, so rigidity deteriorated and problems arose with handling.

Comparative Example 2 is an example in which a heat-shrinkable film was used in which the unstretched PEEK resin film used in Example 1 before biaxial stretching was stretched only in the longitudinal direction. This heat-shrinkable film had no problems with heat resistance, electrical properties, or water absorption, but because it was stretched only in the longitudinal direction, the dimensional change upon heating in the transverse direction was 0.86%, proving that it is not suitable as a heat-shrinkable film. In addition, in terms of mechanical properties, the transverse tensile modulus was 2798 MPa, which is less than 3000 MPa, so the rigidity was low and problems arose with handling.

Comparative Example 3 is an example in which a heat-shrinkable film was used in which the unstretched PEEK resin film used in Example 1 before biaxial stretching was uniaxially stretched in the horizontal direction only. This heat-shrinkable film also had no problems with heat resistance, electrical properties, and water absorption, but because it was stretched in the horizontal direction, the thermal dimensional change rate in the vertical direction was small at -1.36%, making it unsuitable as a heat-shrinkable film. In terms of mechanical properties, the tensile modulus in the vertical direction was 2852 MPa, which is less than 3000 MPa, so the rigidity was low and problems with handling were recognized.

Comparative Example 4 is an example using a heat shrinkable film made of an unstretched PEEK resin film. This heat shrinkable film also had no problems with electrical properties and water absorption, but because it was an unstretched film, the heat shrinkable properties were small, at -5.08% in the longitudinal direction and 1.30% in the transverse direction, and it was found to be inappropriate as a heat shrinkable film. In addition, the optical properties were such that the haze value rose to 16.5% by heating at 200°C for 10 minutes, and transparency was lost. The heat resistance was also problematic, with a storage modulus at 300°C of less than 1.0 x 10 ⁵ Pa. Furthermore, the mechanical properties were such that the tensile modulus was 3000 MPa or less, resulting in low rigidity and problems with handling.

Comparative Example 5 is an example using a heat-shrinkable film made of unstretched PEEK resin film with a crystallinity of 21.1%. This heat-shrinkable film also had no problems with heat resistance, electrical properties, or water absorption, but because it was an unstretched film, the heat-shrinkable properties were small, with a thermal dimensional change rate of -4.46% in the longitudinal direction and 1.46% in the transverse direction, and it was found to be unsuitable as a heat-shrinkable film. In addition, the optical properties were such that the haze value was 53% or more and transparency was lost. Furthermore, the mechanical properties of the tensile modulus were such that the transverse tensile modulus was 3000 MPa or less, resulting in poor rigidity and problems with handling.

The heat-shrinkable film and its manufacturing method according to the present invention are used in the manufacturing fields of battery cells, box-shaped packaging materials, electrical wire coverings, tubes and labels.

1 Molding material 2 Polyether ether ketone resin film (PEEK resin film)
REFERENCE SIGNS LIST 10 melt extruder 10A first melt extruder 10B first and second melt extruders 13 die 17 pressure roll 18 cooling roll 20 winder 30 casting roll 31 longitudinal and transverse simultaneous biaxial stretching machine 35 take-up machine 36 winder

Claims (5)

A heat-shrinkable film is formed by molding an unstretched polyether ether ketone resin film having a crystallinity of 15% or less from a molding material containing at least a polyether ether ketone resin, and biaxially stretching the polyether ether ketone resin film,
A heat-shrinkable film, characterized in that the rate of dimensional change upon heating in the longitudinal and transverse directions at 170°C, 200°C, and 250°C is -50% or more and -5% or less when measured in accordance with JIS K 7133. The heat-shrinkable film according to claim 1, which has a maximum tensile strength at 23°C of 180 MPa or more and 290 MPa or less when measured in accordance with JIS K 7127, and a tensile modulus at 23°C of 3850 MPa or more and 4420 MPa or less when measured in accordance with JIS K 7127. 3. The heat-shrinkable film according to claim 1, which has a storage modulus at 300° C. of from 1×10 ⁵ Pa to 1×10 ¹⁰ Pa when measured under conditions of a frequency of 1 Hz and a heating rate of 3° C./min. A method for producing a heat-shrinkable film according to claim 1 or 2, characterized in that an unstretched polyether ether ketone resin film having a crystallinity of 1% to 15% is formed by a molding method using a molding material containing at least polyether ether ketone resin, and then the polyether ether ketone resin film is biaxially stretched at a stretch ratio of 1.5 to 5 times. The method for producing a heat-shrinkable film according to claim 4, in which the polyetheretherketone resin film is subjected to simultaneous biaxial stretching, and then heat-treated at a temperature of not less than [glass transition temperature of the polyetheretherketone resin film + 30]°C and not more than [melting point of the polyetheretherketone resin film] to heat-set it.

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