JP7501571B2 - Heat-shrinkable film, box-shaped packaging material and battery cell, and method for manufacturing heat-shrinkable film - Google Patents

Description

The present invention relates to a heat-shrinkable film, a box-shaped packaging material, a battery cell, and a method for producing a heat-shrinkable film, and more particularly to a heat-shrinkable film, a box-shaped packaging material, and a battery cell that are excellent in durability after coating and coating retention.

Vehicle batteries used in hybrid cars and electric cars, and batteries used in power supply devices for charging natural energy and late-night power, are composed of multiple rectangular battery cells. The rectangular battery cells are covered with a heat-shrinkable film or tube for insulation, waterproofing, protection, etc.

As a package for a battery cell covered with the above-mentioned film, a rectangular package (see, for example, Patent Document 1) has been proposed in which a strip-shaped film 100 or the like is wrapped around a body portion 102 of a rectangular battery cell 101 as shown in FIG. 3. As a package for a battery cell covered with a tube, a package for a battery cell covered with a tube-shaped film 200 or the like as shown in FIG.
There have been proposals for a rectangular package in which the battery cell 101 is sealed and made into a bag shape into which a rectangular battery cell 101 is inserted. However, these packages do not necessarily adequately cover the battery cell 101, and when water accumulates at the bottom of the case into which the battery cell 101 is inserted due to condensation or the like, a short circuit may occur in the exposed portion of the battery cell 101.

4, the bottom of the battery cell 101 covered by the film 200 comes into contact with the seal, so the battery cell 101 covered by the film 200 may not be able to stand on its own. Furthermore, in recent years, there has been a trend to reduce the volume of the space occupied by the battery inside the vehicle in order to make the vehicle smaller, and this has made the heat dissipation of the battery an issue. As a technology for efficiently dissipating heat generated by the battery, there is a technology for dissipating heat from the battery cell 101 by heating the battery cell 1
There is an established technology for performing this from the bottom surface of the housing in which the battery cell 101 is housed. However, in the example shown in Fig. 4, the bottom surface of the battery cell 101 does not make sufficient contact with the housing, so heat dissipation may be poor.
To improve on these issues, a rectangular package has been proposed that has a gusset at the bottom to enable the battery cell 101 covered by the film 200 to stand on its own (see, for example, Patent Document 2).

In addition, in the case of the rectangular packaging body described in Patent Document 2, if the thickness of the film or the like is thin, it is possible to flatten the bottom by inserting a gusset into the bottom, but making the film or the like thinner makes it more likely to cause other problems such as tearing. Also, with a film or the like having a thickness generally required for covering battery cells, it may be difficult to process if a gusset is provided and multiple folds are performed to flatten the bottom, as in the rectangular packaging body described in Patent Document 2. One technique for dealing with this problem is to cut the film to create mountain folds 3, as shown in Figure 5.
It has been proposed to form a box-shaped packaging material unfolded body 300 having a cut portion 301 (see dashed line in FIG. 5) and a cut portion 302 (see solid line in FIG. 5), and to assemble the film into a box shape by heat sealing so that one end side 303 of the film is the inside of the box-shaped packaging body 400 and the other end side 304 of the film is the outside of the box-shaped packaging body 400 (see FIG. 6).

Utility Model Registration No. 3200706 Utility Model Registration No. 3195394

Conventionally, films or tubes made of vinyl chloride have been widely used as insulating coatings for these battery cells, but in recent years, there has been a demand for non-vinyl chloride due to environmental considerations and other reasons. In addition, in the case of vinyl chloride films or tubes, when vibrations are applied for a long period of time, particularly in vehicle applications, the film or tube may be torn due to friction between the housing and the film. In order to improve these problems, films or tubes made of polyester resins have been considered. However, polyester resin tubes or films are generally difficult to heat seal, and when processed into bag-shaped or box-shaped packages, poor adhesion and holes are likely to occur at the heat-sealed parts. In addition, from the perspective of long-term durability, tears and friction may occur, as with vinyl chloride films or tubes. Furthermore, polyester resin films or tubes also have the problem that secondary shrinkage occurs due to repeated cold and warm cycles, making the coating state prone to be poor.

When using a box-shaped packaging material unfolded body as shown in Fig. 5, high processing precision is required because the cut portion is L-shaped, and the L-shaped cut may expand during transportation, etc., leading to tearing of the box-shaped packaging material unfolded body, etc. Furthermore, when assembling into a box by heat sealing, high assembly precision is required because the L-shaped cut portion is used as the starting point for folding inward, and the assembly may easily become misaligned, resulting in poor heat sealing.
In order to deal with such a problem, it is effective to assemble a box-shaped packaging material development body as shown in FIG. 7 into a box-shaped package 600 (see FIG. 8) by heat sealing the box-shaped package.
However, when the box-shaped packaging material development body as shown in FIG. 7 is converted into a box-shaped packaging body 600 as shown in FIG.
In this case, in a part of the heat-sealed portion of the box-shaped package 600, the shrinkage direction of the overlapping film is a mixture of the main shrinkage direction and a direction perpendicular to the main shrinkage direction. Since the magnitude of secondary shrinkage differs between the main shrinkage direction and the direction perpendicular to the main shrinkage direction,
Another problem is that the film is prone to developing holes due to shifting in the area (near the heat-sealed portion).

The present invention has been made in consideration of the above problems, and has an object to provide a heat-shrinkable film, a box-shaped packaging material, and a battery cell that are excellent in durability and coating retention after coating.

As a result of intensive research, the present inventors have succeeded in obtaining a heat-shrinkable film that can solve the problems of the conventional techniques by setting the heat shrinkage rate in the main shrinkage direction, the heat shrinkage rate in the direction orthogonal to the main shrinkage direction, and the difference between the heat shrinkage rate in the main shrinkage direction and the heat shrinkage rate in the direction orthogonal to the main shrinkage direction within specific ranges in a polyester resin film, and have completed the present invention.

The present invention provides the following [1] to [13].
[1] A single-layer or multi-layer heat-shrinkable film having a resin layer containing a polyester resin as a main component on at least one side of the film,
A heat-shrinkable film that satisfies the following a) to d).
a) the polyester resin contains a copolymer polyester resin; b) the heat shrinkage rate in the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 40% or more and 65% or less; c) the heat shrinkage rate in the direction orthogonal to the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 4% or more and 15% or less; d) the heat shrinkage rate difference between the heat shrinkage rate in the main shrinkage direction and the heat shrinkage rate in the direction orthogonal to the main shrinkage direction when immersed in 99°C hot water for 10 seconds (heat shrinkage rate in the main shrinkage direction - heat shrinkage rate in the direction orthogonal to the main shrinkage direction) is 30% or more and 55% or less. [2] The heat shrinkable film according to [1], which satisfies the following e) to g):
e) The heat of crystalline fusion (ΔHm) when heated at a rate of 10° C./min, as measured by differential scanning calorimetry, is 20 J/g or less. f) The absolute value of the fusion temperature difference (FT1-FT2) between the fusion temperature (FT1) between one surface and the fusion temperature (FT2) between the other surface and the other surface is 20° C. or less. g) The neck-in ratio after immersion in 70° C. warm water for 10 seconds is 5.0% or less. [3] The copolymerized polyester resin contains terephthalic acid and ethylene glycol as copolymerization components, and further contains 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,3
- containing at least one selected from the group consisting of propanediol and isophthalic acid,
The heat shrinkable film according to [1] or [2].
[4] The copolymer polyester resin contains, as a copolymerization component, 15 mol% or more of a diol component other than ethylene glycol, based on 100 mol% of the total amount of the diol components.
] The heat-shrinkable film according to any one of the preceding claims.
[5] In the Taber abrasion test according to JIS K7204, the abrasive wheel is subjected to a specified load of 4
The heat-shrinkable film according to any one of [1] to [4], in which when a load of 0.9 N is applied and the turntable is rotated at a constant speed of 70 revolutions per minute, the abrasion mass of the surface of the test piece per 1000 revolutions is 25 mg or less.
[6] The heat-shrinkable film according to any one of [1] to [5], which has a volume resistivity of 1×10 ¹⁴ Ω·cm or more.
[7] The heat-shrinkable film according to any one of [1] to [6], having a dielectric breakdown voltage of 8 kV or more.
[8] The heat-shrinkable film according to any one of [1] to [7], which is for insulating coating.
[9] The heat-shrinkable film according to any one of [1] to [8], which is for covering a battery cell.
[10] The heat-shrinkable film according to any one of [1] to [9], which is cut into a box-shaped packaging material development body.
[11] A box-shaped packaging material using the heat-shrinkable film described in [10] above, characterized in that it has a folding processing section and a heat-sealing section.
[12] A battery cell, characterized in that it is covered with the box-shaped packaging material described in [11] above.
[13] A method for producing a heat shrinkable film according to any one of [1] to [10] above, wherein the stretching ratio in the main shrinkage direction is 3.0 times or more and the stretching ratio in the direction perpendicular to the main shrinkage direction is 1.3 times or more.
A method for producing a heat-shrinkable film, comprising at least a step of stretching the film by at least 2 times.

According to the present invention, it is possible to realize a heat-shrinkable film, a box-shaped packaging material, and a battery cell that are excellent in durability after coating and coating retention.

FIG. 1 is an explanatory diagram of dimensions of a box-shaped package in a heat cycle test according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the dimensions of an aluminum metal block used in a heat cycle test according to an embodiment of the present invention. FIG. 3 is an illustration of a prior art battery cell coating with a film. FIG. 4 is an explanatory diagram of a battery cell covered with a tube according to the prior art. FIG. 5 is a schematic diagram of a box-shaped packaging material unfolded body in the first embodiment of the present invention. FIG. 6 is a schematic diagram of a box-shaped package according to the first embodiment of the present invention. FIG. 7 is a schematic diagram of a box-shaped packaging material unfolded body in the second embodiment of the present invention. FIG. 8 is a schematic diagram of a box-shaped package according to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following preferred embodiments.

In this specification, the term "mainly composed of" means that other components can be included within a range that does not impair the action and effect of the resin contained as the main component.
The term "main component" does not limit the specific content, but the content of the entire constituent components is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.
The content of the component is 100% by mass or less.The heat shrinkable film according to the present embodiment will be described in detail below.

<Embodiment>
The heat-shrinkable film according to the present embodiment is a single-layer or multi-layer heat-shrinkable film having a resin layer containing a polyester resin as a main component on at least one surface of the film,
The heat-shrinkable film satisfies the following a) to d).
a) the polyester resin contains a copolymer polyester resin; b) the heat shrinkage rate in the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 40% or more and 65% or less; c) the heat shrinkage rate in the orthogonal direction to the main shrinkage direction (hereinafter simply referred to as the "orthogonal direction") when immersed in 99°C hot water for 10 seconds is 4% or more and 15% or less; d) the difference in heat shrinkage rate between the main shrinkage direction and the orthogonal direction when immersed in 99°C hot water for 10 seconds (heat shrinkage rate in the main shrinkage direction - heat shrinkage rate in the orthogonal direction) is 30% or more and 55% or less

[Polyester Resin]
First, the polyester resin used in the resin layer of the heat shrinkable film will be described.
The polyester resin is a thermoplastic resin obtained by polymerizing a copolymerization component containing a dicarboxylic acid component and a diol component as constituent raw materials.

The heat-shrinkable film of this embodiment is a single-layer or laminated heat-shrinkable film having a resin layer containing a polyester resin as a main component on at least one side of the film, and it is necessary that the polyester resin contains a copolymer polyester resin.

(Copolyester)
The copolymer polyester used in the present embodiment is a copolymer containing terephthalic acid as a dicarboxylic acid component, ethylene glycol as a diol component, and further containing at least one of a dicarboxylic acid component other than the terephthalic acid and ethylene glycol and a diol component. The copolymer polyester may be used alone or in combination of two or more kinds.

Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2,5-dichloroterephthalic acid, 2-methylterephthalic acid, 4,4-stilbene dicarboxylic acid, 4,4-biphenyl dicarboxylic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, bisbenzoic acid, bis(p-carboxyphenyl)methane, anthracene dicarboxylic acid, 4,4-diphenyl ether dicarboxylic acid, 4,4-diphenoxyethane dicarboxylic acid, 5-Na sulfoisophthalic acid, and ethylene-bis-p-benzoic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, 1,3-cyclohexane dicarboxylic acid, and 1,4-cyclohexane dicarboxylic acid. These dicarboxylic acid components may be used alone or in combination of two or more. Among these, the dicarboxylic acid is preferably an aromatic dicarboxylic acid, more preferably terephthalic acid or isophthalic acid, from the viewpoint of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoint of durability and coating retention after coating. Also, it is more preferable to use terephthalic acid as the main component.

The amount of terephthalic acid in the copolymerization components is, from the viewpoint of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoint of durability and coating retention after coating, preferably 75 mol% or more, more preferably 80 mol% or more, and even more preferably 85 mol% or more, and is preferably 100 mol% or less, relative to 100 mol% of the total amount of the dicarboxylic acid components.

Examples of the diol component include ethylene glycol, 1,4-butanediol,
Neopentyl glycol, diethylene glycol, polytetramethylene glycol, 1,
Examples of the diol component include aliphatic diols such as 3-propanediol, and alicyclic diols such as 1,4-cyclohexanedimethanol.
Among these, the diol component is preferably ethylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-butanediol from the viewpoint of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoint of durability and coating retention after coating.
4-Cyclohexanedimethanol is preferred, 1,4-butanediol and 1,4-cyclohexanedimethanol are particularly preferred, and ethylene glycol is more preferred as the main component.

The amount of ethylene glycol in the copolymerization component is, from the viewpoint of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoint of durability after coating and coating retention, preferably 40 mol% or more, more preferably 45 mol% or more, and even more preferably 50 mol% or more, and is preferably 85 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less, relative to 100 mol% of the total amount of the diol component.

In addition, the blending amount of the diol component other than ethylene glycol in the copolymerization components is, from the viewpoint of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoint of durability after coating and coating retention, preferably 15 mol % or more, more preferably 20 mol % or more, and is preferably 60 mol % or less, more preferably 55 mol % or less, and even more preferably 50 mol % or less, relative to 100 mol % of the total amount of the diol components.

The copolymerized polyester resin used in the present invention preferably contains terephthalic acid and ethylene glycol as copolymerization components, and further contains at least one component having low crystallinity, for example, 1,4-butanediol, neopentyl glycol, diethylene glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,3-propanediol, and isophthalic acid, from the viewpoints of preventing holes and poor adhesion in the heat-sealed portion of the heat-shrinkable film, and from the viewpoints of durability and coating retention after coating.
It is particularly preferred that the alcohol comprises 1,4-butanediol, 1,4-cyclohexanedimethanol, and isophthalic acid.

The copolymerized polyester resin used in the present embodiment can be obtained by adjusting the dicarboxylic acid component and the diol component as copolymerization components to predetermined component amounts, and first subjecting these copolymerization components to an esterification reaction and then subjecting them to a polycondensation reaction according to a known method.

The polyester resin used in the present embodiment contains the above-mentioned copolymer polyester resin, and may contain, for example, polyethylene terephthalate (homopolyester) consisting of only terephthalic acid and ethylene glycol and one or more types of copolymer polyester, may consist of only one type of copolymer polyester, or may contain two or more types of copolymer polyesters having different compositions.

<Layer structure of film>
The heat-shrinkable film according to the present embodiment may have a resin layer containing a polyester resin as a main component on at least one side (for example, the front or back side) of the film. That is, the heat-shrinkable film may have a resin layer containing a polyester resin as a main component on one side (the front or back side) of the film, or on both sides (the front and back sides).

The layer structure of the heat-shrinkable film can be appropriately selected as necessary from the viewpoint of required quality, application, etc., and may be a single-layer film of a resin layer containing a polyester resin as a main component, or a multi-layer film in which another resin layer is laminated on a resin layer containing a polyester resin as a main component. In addition, the heat-shrinkable film may further be provided with a deposition layer, various coating layers, etc., as necessary.

The resin layer mainly composed of the polyester resin may contain various additives, if necessary, in addition to the polyester resin, within a range that does not impair the effects of the present invention. Examples of additives include ultraviolet absorbers, light stabilizers, antioxidants, hydrolysis inhibitors, stabilizers, colorants, antistatic agents, lubricants, inorganic fillers, various resins, etc. These may be used alone or in combination of two or more.

<Method of producing heat shrinkable film>
The method for producing the heat-shrinkable film is not particularly limited. When the heat-shrinkable film is a single-layer film, it can be produced by a known method such as a T-die method or a tubular method. When the heat-shrinkable film is a laminated film, it can be produced by, for example, a method of co-extrusion using a plurality of extruders, or a method of laminating the resins constituting each layer by forming them into sheets separately and then using a press method, a roll nip method, or the like.

The heat shrinkable film is uniaxially or biaxially stretched by a roll stretching method, a tenter stretching method, a tubular stretching method, a long distance stretching method, or the like. In particular, the heat shrinkable film according to the present embodiment is
Preferably it is a biaxially oriented film.

The shape of the heat shrinkable film is not particularly limited and may be either planar or tubular. From the viewpoints of productivity and printability on the inner surface, however, a planar shape is preferred.
As a method for producing a flat film, for example, in the case of a monolayer film, a method can be exemplified in which the resin or resin composition used in the resin layer is melted using an extruder, extruded from a T-die, and cooled and solidified by a chilled roll to obtain a film. In the case of a laminated film, the above method can be used to co-extrude using multiple extruders. The obtained film can be roll-stretched in the longitudinal direction and tenter-stretched in the transverse direction, and then annealed, cooled, and optionally subjected to corona discharge treatment, etc., to produce a flat film stretched in a uniaxial or biaxial direction. In addition to the above-mentioned T-die method, a method can also be applied in which a film stretched in a uniaxial or biaxial direction by a tubular method is cut open to produce a flat film.

Biaxial stretching may be performed simultaneously in the film take-up direction (machine direction) and in the direction perpendicular to the film take-up direction (transverse direction), but sequential biaxial stretching in which one of the directions is performed first is more effective. In sequential biaxial stretching, either the film take-up direction or the direction perpendicular to the film take-up direction may be stretched first.

The stretching temperature is appropriately changed depending on the softening temperature of the resin constituting the heat shrinkable film and the application of the heat shrinkable film. From the viewpoint of reducing the neck-in ratio, the stretching temperature is preferably 60° C. or higher, more preferably 70° C. or higher, even more preferably 85° C. or higher, even more preferably 90° C. or higher, and is preferably 130° C. or lower, more preferably 120° C. or lower.

Usually, the direction in which the film has a higher stretch ratio when biaxially stretched becomes the main shrinkage direction in which the heat shrinkage rate is high when the film is shrunk by applying heat.
The stretching ratio in the main shrinkage direction is appropriately determined depending on the components of the heat shrinkable film, the stretching means, the stretching temperature, and the product form. The stretching ratio in the main shrinkage direction is 3.0 times or more, preferably 4.0 times or more, more preferably 5.0 times or more, and is 7.0 times or less, preferably 6.0 times or less.

Even in applications requiring shrinkage characteristics in almost one direction, such as insulating the coating of battery cells used in vehicle batteries, it is also effective to stretch the material in the perpendicular direction to an extent that does not impair the shrinkage characteristics.

The stretching temperature in the case of stretching in the orthogonal direction is typically in the range of 60° C. to 100° C. The stretching method is preferably roll stretching, and within this temperature range, the film can be stretched uniformly without sticking to the roll. As for the stretching ratio, the greater the stretching ratio, the better the break resistance, but the greater the thermal shrinkage rate, which may affect the covering properties, so the stretching ratio is 1.3 times or more, preferably 1.4 times or more, and 2.0 times or less, preferably 1.8 times or less.

In addition, the heat-shrinkable film can be given and retained its shrinkability by cooling the heat-shrinkable film promptly after stretching within a time period during which the molecular orientation of the stretched film does not relax.

The thickness of the heat-shrinkable film is not particularly limited as long as it satisfies the volume resistivity and dielectric breakdown voltage described below. From the viewpoints of abrasion resistance, insulation, and the characteristics of general polyester-based heat-shrinkable films, the film thickness (absolute average thickness) is preferably 80 μm or more.
It is more preferably 85 μm or more, and even more preferably 90 μm or more. In addition, the thickness of the film is preferably 120 μm or less from the viewpoint of the necessity of processing such as folding, the cost, etc. The insulating properties are related to the film thickness (absolute average thickness), and generally, the thicker the film, the higher the insulating properties and the more insulating properties can be secured.

The heat shrinkable film according to the present embodiment thus produced satisfies the following requirements b) to d).
b) The heat shrinkage rate in the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 40% or more and 65% or less. c) The heat shrinkage rate in the orthogonal direction when immersed in 99°C hot water for 10 seconds is 4% or more and 15% or less.
d) When immersed in 99°C hot water for 10 seconds, the difference in heat shrinkage between the main shrinkage direction and the cross direction (heat shrinkage in the main shrinkage direction - heat shrinkage in the cross direction) is 30% or more and 55% or less.

<Heat shrinkage rate>
The heat shrinkage rate of the heat shrinkable film in the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 40% or more, preferably 42% or more, more preferably 44% or more, 65% or less, preferably 63% or less, and more preferably 60% or less. If the heat shrinkage rate of the heat shrinkable film in the main shrinkage direction is equal to or more than the lower limit, as shown in Figures 6 and 8, when the heat shrinkable film is processed into a box-shaped package and placed over a battery cell, and then shrunk with a shrinker to cover the battery cell, there is no risk of moisture entering between the battery cell and the heat shrinkable film due to condensation or the like due to inability to tightly adhere to the battery cell. Furthermore, if the heat shrinkage rate of the heat shrinkable film in the main shrinkage direction is equal to or less than the upper limit, there is no risk of large shrinkage in the orthogonal direction when the heat shrinkable film is shrunk with a shrinker. Here, the "main shrinkage direction" means the direction in which the shrinkage rate is the largest when immersed in 99°C hot water for 10 seconds.

If shrinkage occurs in the heat-shrinkable film, it may not be able to cover part of the battery cell during the shrinking process, and the insulating properties may be reduced. Even if the battery can be covered at this stage, there is no room for size and shape, and the repeated rise and fall in temperature of the battery mounting part of the car will cause secondary shrinkage in the heat-shrinkable film, increasing the risk that part of the battery cell will not be covered. In addition, secondary shrinkage can cause cracks at the edge of the heat seal (
In this case, the shear force due to shrinkage of the heat shrink film (near the electrode) increases, increasing the risk of cracking. In addition to controlling the heat shrinkage rate, it is also possible to address the above risks by increasing the height of the heat shrink film. However, this would result in the use of a large amount of unnecessary material, which is undesirable from a cost perspective, and would also result in the film covering parts that do not need to be covered, such as electrodes. Therefore, in terms of quality design, it is preferable to set the heat shrinkage rate of the heat shrink film to an appropriate level, rather than addressing the issue by increasing the dimensions of the heat shrink film.

The heat shrinkage rate of the heat shrinkable film in the orthogonal direction when immersed in 99°C hot water for 10 seconds is 4% or more, preferably 5% or more, more preferably 6% or more, 15% or less, preferably 14% or less, and more preferably 12% or less. If the heat shrinkage rate of the shrinkable film in the orthogonal direction is equal to or more than the lower limit, the rigidity in the orthogonal direction due to the orthogonal orientation of the film is sufficient, and cracks due to shear force caused by shrinkage at the edge of the heat sealed portion due to secondary shrinkage are unlikely to occur. If the heat shrinkage rate of the heat shrinkable film in the orthogonal direction is equal to or less than the upper limit, no significant shrinkage occurs in the orthogonal direction when the heat shrinkable film is shrunk by a shrinker.

The heat shrinkage difference between the heat shrinkage in the main shrinkage direction and the heat shrinkage in the orthogonal direction when the heat shrinkage film is immersed in warm water at 99° C. for 10 seconds (heat shrinkage in the main shrinkage direction−heat shrinkage in the orthogonal direction) is 30% or more, preferably 31% or more, more preferably 32% or more, and is 55% or less, preferably 53% or less, and more preferably 50% or less.
% or less. If the difference between the heat shrinkage rate in the main shrinkage direction and the heat shrinkage rate in the orthogonal direction is within the above upper and lower limits, the film is less affected by the shrinkage rate in the direction orthogonal to the main shrinkage direction during heat shrinkage in the main shrinkage direction, and can be uniformly shrunk during heat shrinkage. When the film is shrunk onto a covering, it can be uniformly adhered to the covering. For example, when the covering is a battery cell, moisture does not enter between the heat shrinkable film and the film due to condensation, etc., which is preferable.

Moreover, it is preferable that the heat shrinkable film according to the embodiment further satisfies the following e) to g).
e) The heat of crystalline fusion (ΔHm) when heated at a rate of 10°C/min, as determined by differential scanning calorimetry, is 20 J/g or less. f) The absolute value of the fusion temperature difference (FT1-FT2) between the fusion temperature (FT1) between one surface and the fusion temperature (FT2) between the other surface and the same is 20°C or less. g) The neck-in ratio after immersion in 70°C warm water for 10 seconds is 5.0% or less.

<Crystal melting heat (ΔHm)>
The heat shrinkable film preferably has a crystalline fusion heat (ΔHm) of 20 J/g or less when the film is heated at a heating rate of 10° C./min according to JIS K7122 using differential scanning calorimetry. If the crystalline fusion heat (ΔHm) is 20 J/g or less, the phenomenon that the temperature at which heat sealing is possible varies depending on the location does not occur, and the heat sealing does not become unstable. The crystalline fusion heat (ΔHm) of the heat shrinkable film is particularly preferably 18 J/g or less,
It is more preferable that the elasticity is 16 J/g or less.

Generally, when a film is made of raw materials with low crystallinity, it is difficult for a distribution of high and low crystallinity to occur depending on the location of the film, and there are no restrictions on the film processing method and processing conditions. On the other hand, when a film is made of raw materials with high crystallinity, not only the crystallinity of the front and back sides is likely to differ from each other depending on the processing method and processing conditions of the film, but also the crystallinity of the same side is likely to differ depending on the location of the film, so that a distribution of crystallinity may occur depending on the film processing method and processing conditions. Therefore, the heat of crystal fusion (ΔHm) of the raw material of the heat shrinkable film is 20 J/g or less, so that the occurrence of a distribution of crystallinity due to the film processing method and processing conditions can be prevented.

<Fusing temperature difference (FT1-FT2)>
The heat shrinkable film has a fusion temperature (FT1) between one surface (e.g., the surface of the heat shrinkable film facing the covering body) and a fusion temperature (FT2) between the other surface (e.g., the back surface of the heat shrinkable film facing the covering body).
The absolute value of the fusion temperature difference (FT1-FT2) between the fusion temperatures (FT2) of the two heat-shrinkable films is preferably 20°C or less, more preferably 15°C or less, and even more preferably 10°C or less. If the absolute value of the fusion temperature difference (FT1-FT2) is 20°C or less, when one side (e.g., the front side) and the other side (e.g., the back side) of the heat-shrinkable film are heat-sealed together, even if the heat-sealing process is performed under conditions with a lower fusion temperature, defects such as insufficient heat sealing and poor adhesion do not occur. Furthermore, even if the heat-sealing process is performed under conditions with a higher fusion temperature, defects such as holes due to overheating do not occur in the sealed portion of the side with the lower fusion temperature. Thus, even when one side and the other side are heat-sealed together, the fusion temperature difference (
When the absolute value of FT1-FT2) is 20° C. or less, heat sealing can be carried out suitably.

In the present embodiment, the fusion temperature is measured under the following conditions. First, a heat shrinkable film is cut into a size of 60 mm in the horizontal direction and 30 mm in the vertical direction, and the two sides of the heat shrinkable film are overlapped, and then the heat seal bar is set in a heat sealer having a 10 mm wide heat seal bar with the longitudinal and lateral directions aligned. Then, the sealing temperature is increased by heating from one side at each predetermined temperature at 5°C intervals, heat sealing is performed at a pressure of 0.1 MPa for 60 seconds, and the sealed portion is peeled off after leaving it to stand for 10 seconds. This is repeated three times (N=3), and the highest temperature at which all the films can be peeled off without breaking is the fusion temperature.

<Neck-in rate>
The neck-in ratio of the heat-shrinkable film when immersed in 70°C hot water for 10 seconds is preferably 5.0% or less, more preferably 3.5% or less, and more preferably 2.1% or less. If the neck-in ratio is 5.0% or less, the repeated increase and decrease in temperature of the battery mounting part described above will cause the shrinkage and neck-in to proceed little by little, and the problem of part of the battery cell being exposed will not occur. By satisfying both the heat shrinkage ratio and the neck-in ratio, the heat-shrinkable film will not suffer from coating defects even when used for a long period of time, and will be able to maintain excellent insulation and waterproof properties. The neck-in ratio can be adjusted by the stretching conditions during film production, etc.

In the present embodiment, the neck-in ratio is a value measured as follows. First, a heat-shrinkable film is cut into a size of 140 mm or more in the main shrinkage direction and 100 mm in the orthogonal direction, and attached to a fixed frame jig with an inner length of 140 mm and a width of 120 mm, with the main shrinkage direction and the inner length direction aligned, and both ends fixed at a length of 140 mm in the main shrinkage direction. Then, the heat-shrinkable film attached to the fixed frame jig is immersed in a hot water bath at 70° C. for 10 seconds, and then immersed in cold water at 30° C. or less for 10 seconds to determine the maximum heat shrinkage ratio in the orthogonal direction, and the value obtained by dividing the heat shrinkage ratio by 2 is the neck-in ratio.

The shrinkable film of the present embodiment satisfies the above physical properties b) to d), and preferably further satisfies the physical properties e) to g). A film satisfying such physical properties can be obtained, for example, by using the above-mentioned polyester resin and, when producing a heat-shrinkable film, going through a process of stretching at a stretching ratio of 3.0 or more in the main shrinkage method and at a stretching ratio of 1.3 or more in the direction perpendicular to the main shrinkage direction.

<Wear resistance>
In addition, the heat shrinkable film of the present embodiment preferably has the following abrasion resistance.
In a Taber abrasion test in accordance with JIS K7204, when a specified load of 4.9 N is applied to an abrasive wheel and a turntable is rotated at a constant speed of 70 revolutions per minute, the heat-shrinkable film preferably has an abrasion mass of 25 mg or less, more preferably 22 mg or less, even more preferably 20 mg or less, and particularly preferably 18 mg or less per 1,000 revolutions on the surface of the test piece.

If the wear mass of the heat shrinkable film is 25 mg or less, the insulation property will not be impaired by the occurrence of rubbing caused by vibration between the housing in which the battery cell is inserted and the insulating material covering the battery cell, resulting in the occurrence of holes and the like. In general, from the viewpoint of maintaining insulation property, a covering material that is prone to holes or the like caused by physical rubbing is not preferable. In particular, in batteries used for vehicles, the housing that houses the battery cell and the insulating material covering the battery cell may be rubbed due to vibration, so the wear resistance of the insulating material is an important factor in terms of the required quality. The wear mass can be appropriately adjusted by selecting an appropriate material, stretching conditions during film production, etc.

<Volume resistivity>
The heat-shrinkable film preferably has a volume resistivity of 1× ¹⁰ Ω·cm or more, and more preferably 1× ¹⁰ Ω·cm or more. If the heat-shrinkable film has a volume resistivity of 1× ¹⁰ Ω·cm or more, the film can ensure insulation performance and can withstand an overvoltage applied to the battery cell without breaking down, thereby preventing problems caused by electrical shorts in the battery cell.

<Breakdown voltage>
The heat-shrinkable film has a breakdown voltage of preferably 8 kV or more, more preferably 10 kV or more, and even more preferably 11 kV or more. If the heat-shrinkable film has a breakdown voltage of 8 kV or more, the heat-shrinkable film can ensure insulation performance and can withstand overvoltage without breaking down, thereby preventing problems caused by electrical shorts in the battery cells. There is no particular limit to the upper limit of the breakdown voltage of the heat-shrinkable film, and it is, for example, 20 kV or less.

<Intrinsic Viscosity of Film>
The intrinsic viscosity of the heat shrinkable film is preferably 0.50 dl/g or more and 1.10 dl/g or less. If the intrinsic viscosity of the heat shrinkable film is 0.50 dl/g or more, the film can be easily formed, and a film having sufficient physical properties and strength can be obtained.
If the intrinsic viscosity is 0.55 dl/g or less, the film can be stably extruded. From the viewpoint of further improving the above-mentioned effects, the intrinsic viscosity of the heat-shrinkable film is more preferably 0.55 dl/g or more, even more preferably 0.60 dl/g or more, and more preferably 1.0 dl/g or less, and even more preferably 0.90 dl/g or less. The intrinsic viscosity of the film is a value obtained by precisely weighing 1 g of a measurement sample, dissolving it in a mixed solvent of phenol/1,1,2,2-tetrachloroethane (mass ratio 1:1) to prepare a solution with a concentration of 0.01 g/cm ³ , and measuring the relative viscosity ηr with the solvent at 30°C.

<Shrinkage stress>
The shrinkage stress of the heat-shrinkable film is not particularly limited, but the maximum shrinkage stress when immersed in silicone oil at 80° C. for 1 minute is preferably 7.0 MPa or less, more preferably 5.0 MPa or less, and more preferably 1.0 MPa or more, and most preferably 2.0 MPa or less.
If the heat-shrinkable film has a shrinkage stress of 7.0 MPa or less, problems such as peeling of the sealed portion will not occur when the heat-shrinkable film is used to cover an object to be covered, and if the shrinkage stress is 1.0 MPa or more, the heat-shrinkable film is less likely to wrinkle after covering, and wrinkles will not hinder the arrangement of the battery cells when they are incorporated into an electric circuit or the like.

The heat-shrinkable film according to the present embodiment can also be cut appropriately to be used as a box-shaped packaging material of a desired shape. This box-shaped packaging material can be suitably used as an insulating packaging material for battery cells, etc.
The heat-shrinkable film can be processed into packaging materials by various processes such as cutting, folding, and gluing. The shape of the packaging materials can be, for example, a box or a bag.
The heat-shrinkable film can be cut into a box-shaped unfolded cut piece, which can then be folded and bonded by heat sealing or the like to form a box-shaped packaging material.

The above-mentioned box-shaped packaging material can be expanded without any particular limitation as long as it can be processed into a box-shaped packaging material. For example, as shown in Figs. 5 and 7, a film is cut to form mountain folds (see broken lines 301 in Fig. 5 and 501 in Fig. 7) and cuts (see broken lines 302 in Fig. 5 and 50 in Fig. 7).
5 and 7. The box-shaped packaging material development bodies shown in FIGS. 5 and 7 can be processed to have the box-shaped packaging material development bodies shown in FIGS. 6 and 8.
The package may be a box-shaped package as shown in FIG.

For example, in the box-shaped packaging material development body 500 shown in FIG.
The other end sides 503 and 504 of the film are the inside of the box-shaped packaging body 600.
00 is placed on the outside of the box-shaped package 600 (see FIG. 8).
It can be said that:

As described above, in the box-shaped packaging body 600, in a part of the heat-sealed portion, the shrinkage direction of the film overlaps with the main shrinkage direction (505 in FIG. 7) and the orthogonal direction (503, 504 in FIG. 7). Therefore, when the box-shaped packaging body 600 is produced using a conventional heat-shrinkable film, a shift occurs due to a difference in shrinkage rate when secondary shrinkage occurs, and defects such as holes are likely to occur in the heat-sealed portion.
On the other hand, the heat-shrinkable film according to the present embodiment satisfies the above-mentioned a) to d), and therefore can suppress the occurrence of secondary shrinkage. Therefore, when the box-shaped packaging body 600 is produced using the heat-shrinkable film according to the present embodiment, defects such as holes are unlikely to occur.

As described above, according to the embodiment, the heat shrinkage rate in the main shrinkage direction, the heat shrinkage rate in the perpendicular direction, and the difference in heat shrinkage rate are within a predetermined range, so that durability and coating retention after coating are not impaired, and holes at the edge of the heat-sealed portion can be prevented. This prevents crystallinity distribution in the shrink film, and even when one side (front side) of the heat-shrinkable film is bonded to the other side (back side), there is no adhesion failure, and it is possible to prevent the occurrence of tears and sudden neck-in during heat shrinkage. In addition, the insulation, abrasion resistance,
Since the resulting film is excellent in all qualities such as coating retention and durability, it is possible to realize a heat-shrinkable film that can prevent holes and poor adhesion in the heat-sealed portions.

The heat-shrinkable film according to the above embodiment has excellent insulation properties, durability, abrasion resistance and coating retention after coating, and therefore can be suitably used in fields where these qualities are required, such as the insulating coating of battery cells that constitute batteries used in vehicle batteries used in hybrid cars and electric cars, and power supply devices for charging natural energy and late-night electricity.

Examples performed to clarify the effects of the present invention will be described below. Note that the present invention is not limited to the following examples and comparative examples. In the following examples, the take-up direction (flow direction) of the laminated film is the "machine direction" (MD).
tion), and the direction perpendicular to the "vertical direction" is referred to as the "transverse direction" (TD).

First, the present inventors prepared the heat-shrinkable film according to the above-mentioned embodiment, and measured the "heat shrinkage rate in the main shrinkage direction", the "heat shrinkage rate in the perpendicular direction", and the "heat shrinkage rate in the main shrinkage direction" of the prepared heat-shrinkable film.
The relationship between the "thermal shrinkage difference" and the heat cycle test was investigated. The various measurement conditions are shown below.

<Evaluation method>
(1) Heat shrinkage rate The heat shrinkable films obtained in the examples and comparative examples were cut into pieces measuring 20 mm in MD and 100 mm in TD, and immersed in a 99°C hot water bath for 10 seconds, and then immersed in cold water at 30°C or lower for 10 seconds to measure the amount of shrinkage in the main shrinkage direction. Also, the heat shrinkable films obtained in the examples and comparative examples were cut into pieces measuring 20 mm in TD and 100 mm in MD, and immersed in a 99°C hot water bath for 1
After immersing for 10 seconds, the sample was immersed in cold water at 30°C or less for 10 seconds to measure the amount of shrinkage in the orthogonal direction. The thermal shrinkage percentage is expressed as a percentage of the amount of shrinkage to the original size before shrinkage. The difference between the thermal shrinkage percentage in the main shrinkage direction and the thermal shrinkage percentage in the orthogonal direction was calculated. As a reference value, the temperature of the hot water bath was set to 80°C, and the amount of shrinkage in the main shrinkage direction and the amount of shrinkage in the orthogonal direction at 80°C were measured in the same manner to calculate the thermal shrinkage percentage.

(2) Heat of crystal fusion (ΔHm)
In accordance with JIS K7122, a differential scanning calorimeter (model number: Diamond DSC) was used.
The heat of fusion (ΔHm) was calculated from the peak area of a thermograph obtained when the heat-shrinkable film was heated at a heating rate of 10° C./min using a thermometer (manufactured by PerkinElmer Japan).

(3) Fusion temperature (FT)
The heat shrinkable films obtained in the Examples and Comparative Examples were cut to a size of 60 mm in TD and 30 mm in MD, two sheets of heat shrinkable film were stacked on each side, and the TD of the heat shrinkable film was aligned with the longitudinal direction of the heat seal bar in a heat sealer having a 10 mm wide heat seal bar, and the film was heated from one side at a specified temperature and heat sealed at a pressure of 0.1 MPa for 60 seconds. The film was then left to stand for 10 seconds and the sealed portion was peeled off. The above was repeated three times (N=3).
The maximum temperature at which all the films could be peeled off without breaking was taken as the fusion temperature. The sealing temperatures were set at intervals of 5° C. The fusion temperature (FT1) between one side (front side) of the heat-shrinkable film, the fusion temperature (FT2) between the other side (reverse side) of the heat-shrinkable film, and the absolute value of the fusion temperature difference (FT1-FT2) were measured.

(4) Neck-in ratio The heat-shrinkable films obtained in the Examples and Comparative Examples were cut into a size of 140 mm or more in the main shrinkage direction and 100 mm in the orthogonal direction, and attached to a fixing frame jig with an inner length of 140 mm and a width of 120 mm with the main shrinkage direction and the inner length direction aligned, with both ends fixed at a length of 140 mm in the main shrinkage direction, and then immersed in a hot water bath at 70° C. for 10 seconds, and then immersed in cold water at or below 30° C. for 10 seconds. Thereafter, the maximum heat shrinkage ratio in the orthogonal direction was measured, and the measured value was divided by 2 to obtain the neck-in ratio (%).

(5) Abrasion resistance (abrasion mass)
The heat-shrinkable films obtained in the Examples and Comparative Examples were subjected to a Taber abrasion test in accordance with JIS K7204. A test piece was fixed to the rotating table of a Taber abrasion tester (model number: "Rotary Abraser No. 410", manufactured by Toyo Seiki Seisakusho Co., Ltd.) and subjected to a prescribed abrasion wheel CS-
A specified load of 4.9 N was applied to the abrasive wheel, and the turntable was rotated 1000 times at a constant speed of 70 revolutions per minute. The abrasion was evaluated as follows based on the abrasion mass per 1000 revolutions on the surface of the test piece. The evaluation criteria are as follows. Evaluations of "○" and "△" are within the acceptable range.
◯: Wear mass 20 mg or less △: Wear mass over 20 mg and 25 mg or less ×: Wear mass over 25 mg

(6) Volume Resistivity The volume resistivity of the heat shrinkable films obtained in the Examples and Comparative Examples was measured in accordance with JIS K 6911. The heat shrinkable film was cut into a size of 100 mm in MD and 100 mm in TD, and a volume resistivity measuring device (manufactured by Advantest Corporation) was used to contact two electrodes on the front and back surfaces, apply a direct current voltage of 500 V, and measure the current flowing between the electrodes after 1 minute to determine the volume resistivity value.

(7) Breakdown Voltage The breakdown voltage of the heat-shrinkable films obtained in the Examples and Comparative Examples was measured in accordance with JIS C 2110. After a test piece was sandwiched between two electrodes of a breakdown voltage tester (manufactured by Haraguchi Kogyo Co., Ltd.), the voltage was increased at 1 kV/sec to determine the voltage at the moment when breakdown occurred.

(8) Heat Cycle Test Evaluation As shown in FIG. 1, the heat-shrinkable films 10 obtained in the examples and comparative examples were subjected to a heat cycle test under the sealing conditions shown in Table 1, with a length of 95 mm (see L1), a width of 25.5 mm (see L2), and a depth of 150 mm.
After processing it into a box shape of 9 mm (see L3), as shown in Figure 2, it is cut into a rectangular battery cell.
A box-shaped aluminum metal block 20 having a length of 0 mm (see L4), width of 25 mm (see L5), and depth of 145 mm (see L6) was covered with hot air at 120° C. for 30 seconds. If holes were formed in the seal at this stage, the following heat cycle test was not performed.
Next, the samples were held at -40°C and 65°C for 0.5 hours, respectively, and then the temperature was increased and decreased by 0.
A heat cycle of 5 hours was carried out 1000 times, and the film covering the aluminum metal block 20 was evaluated for perforation (durability) of the heat-sealed portion. The evaluation criteria are shown below. A rating of "◯" is within the acceptable range.
○: No holes △: Holes less than 10 mm in total at the edge (nearby) of the heat-sealed part ×: Holes more than 10 mm in total at the edge (nearby) of the heat-sealed part, or holes in the sealed part Furthermore, the film's ability to cover and retain the aluminum metal block 20 was evaluated. The evaluation criteria are as follows. A rating of "○" is within the acceptable range.
○: Coverage is normal △: Battery cell is partially exposed ×: Holes were formed in the seal, and the heat cycle test could not be performed

(9) Measurement of Intrinsic Viscosity The intrinsic viscosity (IV) of the heat shrinkable films obtained in the examples and comparative examples was
The relative viscosity ^ηr of the solution to the solvent at 30° C. was measured.

(10) Shrinkage Stress The heat-shrinkable films obtained in the Examples and Comparative Examples were stretched for 70 mm in the main shrinkage direction and 10 mm in the perpendicular direction.
The specimen was cut into a size of 1 mm and fixed to a load cell with a chuck distance of 50 mm so as not to cause slack. The specimen was then immersed in a silicon bath at 80±0.5°C and the maximum stress was measured for 1 minute. The shrinkage stress was calculated using the following formula (2).
Contraction stress (MPa) = load applied to load cell (N) / cross-sectional area of sample piece (mm ² )
Formula (2)

Example 1
A copolymerized polyester resin obtained by copolymerizing a copolymerization component having a dicarboxylic acid component of 98 mol % of terephthalic acid and 2 mol % of isophthalic acid, and a diol component of 55 mol % of ethylene glycol, 30 mol % of 1,4-cyclohexanedimethanol, and 15 mol % of 1,4-butanediol was melt-kneaded at 240° C. or more and 260° C. or less. Then, the copolymerized polyester resin was extruded by an extruder.
The unstretched film was taken up by a cast roll at 45° C. and cooled to solidify, to obtain an unstretched film. Next, the unstretched film obtained was stretched in the machine direction (MD) at a preheating temperature of 73° C. and a stretching temperature of 78° C. using a machine direction stretching machine.
The film was then stretched 1.45 times in a longitudinal direction to obtain a longitudinally stretched film. The longitudinally stretched film was then stretched 5.0 times in a transverse direction (TD) at a preheating temperature of 100° C. and a stretching temperature of 84° C. using a film tenter, and then heat-treated at 100° C. to obtain a heat-shrinkable film (intrinsic viscosity: 0.77) having a thickness of 100 μm.
The sample preparation and sealing conditions for the heat cycle test were 180° C. and maintained for 1 second. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

Example 2
A heat shrinkable film (intrinsic viscosity: 0.77 dl/g) was produced and evaluated in the same manner as in Example 1, except that the unstretched film obtained was stretched 1.6 times in the machine direction (MD) using a machine stretching machine. The sample production sealing condition for the heat cycle test was to hold at 180°C for 1 second. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

Example 3
A heat-shrinkable film (intrinsic viscosity: 0.77 dl/g) was produced and evaluated in the same manner as in Example 1, except that the unstretched film obtained was stretched 1.6 times in the machine direction (MD) using a machine-direction stretching machine, and the heat treatment temperature of the film tenter was set to 105° C. The sample production sealing condition for the heat cycle test was held at 180° C. for 1 second. The evaluation results of the obtained heat-shrinkable film are shown in Table 1 below.

(Comparative Example 1)
A copolymerized polyester resin obtained by copolymerizing a copolymerization component having a dicarboxylic acid component of 98 mol % of terephthalic acid and 2 mol % of isophthalic acid, and a diol component of 55 mol % of ethylene glycol, 30 mol % of 1,4-cyclohexanedimethanol, and 15 mol % of 1,4-butanediol was melt-kneaded at 240°C to 260°C. Then, the copolymer was extruded by an extruder and kneaded for 5 hours.
The film was taken up by a casting roll at 5°C and cooled to solidify, to obtain an unstretched film. Next, the unstretched film obtained was stretched 5.0 times in the transverse direction (TD) at a preheating temperature of 100°C and a stretching temperature of 90°C using a film tenter, and then heat-treated at 75°C to obtain a heat-shrinkable film with a thickness of 100 μm (intrinsic viscosity: 0.77 dl/g). The sample preparation sealing condition for the heat cycle test was held at 180°C for 1 second. The evaluation results of the obtained heat-shrinkable film are shown in Table 1 below.

(Comparative Example 2)
A copolymerized polyester resin obtained by copolymerizing a copolymerization component having a dicarboxylic acid component of 90 mol % of terephthalic acid and 10 mol % of isophthalic acid, and a diol component of 65 mol % of ethylene glycol, 20 mol % of 1,4-cyclohexanedimethanol, and 15 mol % of 1,4-butanediol was melt-kneaded at 240° C. or higher and 260° C. or lower. Then, the copolymerized polyester resin was extruded by an extruder.
The film was taken up by a cast roll at 35°C and cooled to solidify, to obtain an unstretched film. Next, the unstretched film obtained was stretched 2.2 times in the transverse direction (TD) at a preheating temperature of 110°C and a stretching temperature of 88°C using a film tenter, and then heat-treated at 91°C to obtain a heat-shrinkable film with a thickness of 100 μm (intrinsic viscosity: 0.78 dl/g). The sample preparation sealing condition for the heat cycle test was held at 180°C for 1 second. The evaluation results of the obtained heat-shrinkable film are shown in Table 1 below.

(Comparative Example 3)
A heat shrinkable film (intrinsic viscosity:
The heat cycle test sample preparation and sealing conditions were 180° C. and 1 second retention. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

(Comparative Example 4)
The dicarboxylic acid component is 100 mol % of terephthalic acid, and the diol component is 90 mol % of ethylene glycol.
A copolymer polyester resin obtained by copolymerizing copolymerization components of 5 mol % of glycerol and 5 mol % of 1,4-butanediol was melt-molded using a single-screw extruder equipped with a round die at the tip,
The tube was immediately immersed in cold water to obtain a tubular product. The obtained tubular product was continuously fed to the next stretching step. In the stretching step, the tubular product was fed at a constant speed while applying pressure from compressed gas to the inside of the tube from one end, and then heated with hot water at 90°C. It was passed through a cylindrical tube that was cooled to regulate the stretch ratio in the radial direction, and stretched at a stretch ratio of 1.05 times in the longitudinal direction (MD) and 1.67 times in the transverse direction (TD). The tube after stretching cooled in the cylindrical tube was sandwiched between a pair of nip rolls to maintain the stretching tension, and taken up as a stretched tube (heat-shrinkable film). The film had a thickness of 80 μm.
A heat-shrinkable film (intrinsic viscosity: 0.72 dl/g) was obtained. The sample preparation and sealing conditions for the heat cycle test were a temperature of 230° C. and a holding time of 1.5 seconds. The evaluation results of the obtained heat-shrinkable film are shown in Table 1 below.

(Comparative Example 5)
The dicarboxylic acid component is 100 mol % terephthalic acid, and the diol component is 6-ethylene glycol.
A heat shrinkable film (intrinsic viscosity: 0.76 dl/g) was prepared and evaluated in the same manner as in Comparative Example 4, except that a copolymerized polyester resin obtained by copolymerizing copolymerization components of 5 mol % of 1,4-cyclohexanedimethanol, 30 mol % of 1,4-cyclohexanedimethanol, and 5 mol % of 1,4-butanediol was used, and the film was stretched to a thickness of 70 μm. The sample preparation sealing conditions for the heat cycle test were holding at 180° C. for 1 second. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

(Comparative Example 6)
A copolymerized polyester resin obtained by copolymerizing a copolymerization component having a dicarboxylic acid component of 98 mol % of terephthalic acid and 2 mol % of isophthalic acid, and a diol component of 55 mol % of ethylene glycol, 30 mol % of 1,4-cyclohexanedimethanol, and 15 mol % of 1,4-butanediol was melt-kneaded at 240°C to 260°C. Then, the copolymer was extruded by an extruder and kneaded for 5 hours.
The film was taken up by a cast roll at 5°C and cooled to solidify, to obtain an unstretched film. Next, the unstretched film obtained was stretched 1.15 times in the machine direction (MD) at a preheat temperature of 70°C and a stretching temperature of 75°C using a machine direction stretching machine to obtain a machine direction stretched film. Next, the machine direction stretched film obtained was stretched 5.0 times in the transverse direction (TD) at a preheat temperature of 100°C and a stretching temperature of 84°C using a film tenter.
The mixture was heat-treated at 100° C. to give a heat-shrinkable film (intrinsic viscosity: 0.77d
The sample preparation and sealing conditions for the heat cycle test were 180° C. and 1 second retention. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

(Reference Example 1)
Instead of copolymer polyester resin, polyvinyl chloride was used and the thickness was 100 μm.
A heat shrinkable film was prepared and evaluated in the same manner as in Comparative Example 4, except that the heat cycle test was performed under the condition of sample preparation and sealing at 190° C. for 1 second. The evaluation results of the obtained heat shrinkable film are shown in Table 1 below.

As can be seen from Table 1, when the heat shrinkage rate in the main shrinkage direction (TD in this embodiment), the heat shrinkage rate in the orthogonal direction (MD in this embodiment), and the difference in heat shrinkage rate were within the specified ranges, no holes were generated at the edge (or in the vicinity) of the heat sealed portion in the heat cycle test, and good evaluation results were obtained (Examples 1, 2, and 3).
In contrast, when the difference in heat shrinkage was large and the heat shrinkage in the orthogonal direction was small, holes were generated at the edge (nearby) of the heat-sealed portion (Comparative Example 1, Comparative Example 3, Comparative Example 6). This result is considered to be due to the occurrence of shear in the heat-sealed film due to secondary shrinkage, which led to holes due to insufficient rigidity in the orthogonal direction.
Furthermore, when the heat shrinkage rate in the orthogonal direction was small, slight holes were generated in the heat-sealed portion (Comparative Example 2 and Comparative Example 5). This result is considered to be due to the fact that the heat shrinkage rate and the difference in heat shrinkage rate in the main shrinkage direction were within the specified range, but the slight holes were generated due to insufficient rigidity in the orthogonal direction.
In addition, when the absolute values of the heat of crystal fusion (ΔHm) and the fusion temperature difference (FT1-FT2) were too large, holes were formed in the sealed portion during heat sealing, making it impossible to perform the heat cycle test (Comparative Example 4). This result shows that the heat of crystal fusion (ΔHm) was too large, which caused a distribution of crystallinity in the heat-shrinkable film, making the heat seal unstable, and causing the fusion temperature difference (FT
It is believed that the absolute value of 1-FT2) was too large, and therefore when the front and back surfaces of the heat-shrinkable film were joined and sealed, poor adhesion occurred, making it impossible to conduct the heat cycle test.
Furthermore, when polyvinyl chloride was used, a part of the battery cell was exposed after the heat cycle test, and the insulation was insufficient (Reference Example 1). This result is believed to be due to the neck-in ratio being too high.
As described above, the heat shrinkable films according to Examples 1, 2, and 3 have insulating properties,
It was superior to Comparative Examples 1 to 6 and Reference Example 1 in all qualities such as abrasion resistance, coating retention, and durability.

REFERENCE SIGNS LIST 100, 200 Film 101 Battery cell 102 Body 201 One end 300 Unfolded box-shaped packaging material 301 Mountain fold 303 One end 302 Cut 304 Other end 400 Box-shaped packaging material 500 Unfolded box-shaped packaging material 501 Mountain fold 502 Cut 503, 504 Other end 505 One end 600 Box-shaped packaging material

Claims (11)

A single-layer or multi-layer heat-shrinkable film having a resin layer containing a polyester resin as a main component on at least one surface of the film,
The main shrinkage direction of the heat shrinkable film is a direction perpendicular to the film take-up direction,
The heat shrinkable film has a thickness of 80 μm or more,
A heat-shrinkable film that satisfies the following a) to c) and h).
a) The polyester resin comprises a copolymerized polyester resin, the copolymerized polyester resin comprises terephthalic acid and ethylene glycol as copolymerization components, and further comprises at least one selected from the group consisting of 1,4-butanediol, neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,3-propanediol, and isophthalic acid, and comprises 15 mol% or more of a diol component other than ethylene glycol relative to 100 mol% of the total amount of the diol components , with the proviso that the copolymerized polyester resin does not comprise a copolymerized polyester resin containing 6 mol% or more of a constituent unit derived from diethylene glycol;
b) The heat shrinkage ratio in the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 40% or more and 65% or less. c) The heat shrinkage ratio in the direction perpendicular to the main shrinkage direction when immersed in 99°C hot water for 10 seconds is 4% or more and 15% or less. h) The maximum shrinkage stress when immersed in 80°C silicone oil for 1 minute is 7.0 MPa or less. The heat shrinkable film according to claim 1, which satisfies the following d) to g):
d) When immersed in 99°C hot water for 10 seconds, the difference in heat shrinkage between the heat shrinkage in the main shrinkage direction and the heat shrinkage in the direction perpendicular to the main shrinkage direction (heat shrinkage in the main shrinkage direction - heat shrinkage in the direction perpendicular to the main shrinkage direction) is 30% or more and 55% or less. e) When heated at a rate of 10°C/min, the heat of crystalline fusion (ΔHm) is 20 J/g or less, as determined by differential scanning calorimetry. f) The absolute value of the fusion temperature difference (FT1 - FT2) between the fusion temperature (FT1) between one surface and the fusion temperature (FT2) between the other surface and the same is 20°C or less. g) The neck-in ratio after immersion in 70°C hot water for 10 seconds is 5.0% or less. The heat-shrinkable film according to claim 1 or 2, in which, in a Taber abrasion test conforming to JIS K7204, when a specified load of 4.9 N is applied to the abrasive wheel and the turntable is rotated at a constant speed of 70 revolutions per minute, the abrasion mass of the test piece surface per 1000 revolutions is 25 mg or less. 4. The heat-shrinkable film according to claim 1, which has a volume resistivity of 1×10 ¹⁴ Ω·cm or more. The heat-shrinkable film according to any one of claims 1 to 4, having a dielectric breakdown voltage of 8 kV or more. The heat-shrinkable film according to any one of claims 1 to 5, which is used for insulating coating. The heat-shrinkable film according to any one of claims 1 to 6, which is used for covering battery cells. The heat-shrinkable film according to any one of claims 1 to 7, which is cut into a box-shaped packaging material unfolded body. A box-shaped packaging material using the heat-shrinkable film according to claim 8, characterized in that it has a folding section and a heat-sealed section. A battery cell, characterized in that it is covered with the box-shaped packaging material described in claim 9. A method for producing a heat-shrinkable film according to any one of claims 1 to 8, comprising at least a step of stretching the film to a stretching ratio of 3.0 or more in the main shrinkage direction and to a stretching ratio of 1.3 or more in the direction perpendicular to the main shrinkage direction.

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