JPH0753756A - Thermally shrinkable porous polyester film - Google Patents

Abstract

PURPOSE:To prepare the subject film which is almost free from defects such as wrinkles, strain, and nonuniform shrinkage, has a beautiful finished appear ance, and has cushioning properties and hence is excellent in the prevention of breakage of a glass container when used for packaging or labelling it. CONSTITUTION:This porous polyester film has an apparent specific gravity of 0.4-1.3 and exhibits a shrinkage in the direction of the main shrinkage of 40% or higher and a shrinkage in the direction transverse to the main shrinkage of 20% or lower both when heated for 1min with air at 100 deg.C, and exhibits a shrinkage in the direction of the main shrinkage of 12% or higher when heated for 10sec with air at 100 deg.C to shrink the film by 40% and then heated for 10sec with.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film which is suitable as a packaging material used for coating, binding, exterior packaging, etc. In particular, the present invention relates to a void-containing heat-shrinkable polyester film having a beautiful finished appearance and a cushioning property, which has extremely few defects such as wrinkles, distortion, and shrinkage spots when heat-shrinked.

[0002]

2. Description of the Related Art Heat-shrinkable films are used for coating various containers such as bottles (including glass and plastic bottles) and cans; and for coating long objects such as pipes, rods, wood and various rod-shaped bodies, It is used for bundling and exterior. For example, such a heat-shrinkable film is used to cover a part or the whole of the bottle cap, shoulder, and body for the purpose of marking, protection, bundling, improvement of commercial value and the like. Heat-shrinkable film can also be used for boxes, bottles, plates,
It is also used for the purpose of accumulating and packing a plurality of sticks, notebooks, etc., and for the purpose of closely adhering a film to an object to be packaged and packaging with the film (skin package). In the above application, the shrinkability and shrinkage stress of the film are utilized.

Polyvinyl chloride, polystyrene, polyethylene, chlorinated rubber and the like are used as the material of the film. Usually, the above-mentioned film is molded into a tube, and the tube-shaped film is put on a bottle, or after pipes are accumulated and the tube-shaped film is put on the bottle, it is heat-shrinked to wrap or bind the film. To do.

However, the conventional heat-shrinkable film has poor heat resistance and cannot be subjected to high-temperature boil treatment or retort treatment (high-temperature sterilization treatment for producing retort food). For example, when subjected to retort processing, conventional films break during processing.

Conventional films also have poor adhesion to ink. For example, even if a polyvinyl chloride film is printed, a good printing state cannot be obtained due to poor adhesion between the ink and the film. Furthermore, since the polyvinyl chloride film lacks heat resistance, gels of polymers and additives are likely to be partially formed during film formation, which causes pinholes on the printed surface. .

The above-mentioned conventional film shrinks with time after the film is manufactured. Therefore, the contraction causes a change in the printing pitch, and high-precision printing cannot be performed.

On the other hand, a heat-shrinkable film using polyester, which is excellent in heat resistance, weather resistance and solvent resistance, has been proposed. However, this heat-shrinkable polyester film has problems that the heat shrinkage in a desired direction is insufficient, or the heat shrinkage in a direction orthogonal to the direction cannot be reduced. It was Such a problem can be solved by optimizing the copolymerization composition of the raw material polyester, as disclosed in, for example, JP-A-63-156833.

However, the films obtained by these methods also have a problem that the shrinking speed is too fast, and when the film is heat-shrinked, wrinkles, distortions, shrinkage spots, etc. occur on the film, which is beautiful. It is difficult to obtain a good appearance.

Further, the film has no cushioning property, and there is a problem that when the glass container or the like is packaged or labeled and transported or sold, the glass container or the like is easily damaged by an impact. Therefore, a heat-shrinkable polyester film having a high commercial value, which has an excellent effect of preventing bottle breakage due to its cushioning property, is desired.

[0010]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and an object thereof is to obtain a sufficiently large heat shrinkage ratio and to provide wrinkles, distortions, and shrinkage spots when heat shrinks. It has very few defects such as, has a beautiful appearance, and the film itself has an appropriate cushioning property.
It is an object of the present invention to provide a heat-shrinkable polyester film containing voids, which has an effect of preventing bottle breaking against glass containers and the like.

[0011]

The heat-shrinkable polyester film containing voids of the present invention has a heat shrinkage ratio of 40% or more in the main shrinkage direction when heated with hot air at 100 ° C. for 1 minute, A void-containing heat-shrinkable polyester film having a content of 20% or less in the direction orthogonal to the main shrinkage direction, which is heated with hot air at 100 ° C. for 10 seconds to shrink the film by 40%, and then 130 The heat shrinkage rate when heated with hot air at 0 ° C. for 10 seconds is 12% or more in the main shrinkage direction, and the apparent specific gravity is 0.4 or more and 1.3 or less.

The present invention will be described in detail below.

As the dicarboxylic acid component constituting the polyester used in the present invention, any of aromatic dicarboxylic acids including terephthalic acid constituting the ethylene terephthalate unit, aliphatic dicarboxylic acids and alicyclic dicarboxylic acids can be used. Can be done. Aromatic dicarboxylic acids other than terephthalic acid include benzenedicarboxylic acids such as isophthalic acid, orthophthalic acid, and 5-tert-butylisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid; 4,4′-dicarboxylate. Dicarboxybiphenyls such as diphenyl and 2,2,6,6-tetramethylbiphenyl-4,4'-dicarboxylic acid; 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid and substitution thereof Body; 1,2
-Diphenoxyethane-4,4'-dicarboxylic acid and substituted products thereof. As the aliphatic dicarboxylic acid,
Oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, pimelic acid, suberic acid, undecanoic acid, dodecanedicarboxylic acid, brassic acid, tetradecanedicarboxylic acid, tapsinic acid, nonadecanedicarboxylic acid, doco Examples include sandicarboxylic acid and substitution products thereof. As the alicyclic dicarboxylic acid, 4,
4'-dicarboxycyclohexane and its substitution products.

As the diol component constituting the polyester used in the present invention, any of aliphatic diols such as ethylene glycol constituting an ethylene terephthalate unit, alicyclic diols and aromatic diols can be used. Aliphatic diols other than ethylene glycol include diethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, 1,10-decanediol, neopentyl glycol, 2-methyl-2-ethyl-1,3-propanediol. , 2-diethyl-1,3-propanediol, 2-
Examples include ethyl-2-n-butyl-1,3-propanediol. Examples of the alicyclic diol include 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol. Examples of aromatic diols include ethylene oxide adducts of bisphenol compounds such as 2,2-bis (4′-β-hydroxyethoxydiphenyl) propane and bis (4′-β-hydroxyethoxyphenyl) sulfone; xylylene diglycol, Examples include polyalkylene glycol such as polyethylene glycol and polypropylene glycol.

The polyester used in the present invention can be formed from the above dicarboxylic acids and diols. In order to prepare the polyester, it is usually preferable to use one or more dicarboxylic acids and diols in combination, respectively, whereby the properties as a heat-shrinkable film can be improved. The types and contents of the dicarboxylic acid component and the diol component used in combination can be appropriately determined based on desired film characteristics, economic efficiency and the like.

The heat-shrinkable polyester film of the present invention is a composition containing at least one polyester obtained from the above dicarboxylic acid component and diol component. In the heat-shrinkable polyester film of the present invention, it is preferable that 40 to 90 mol% of the whole polyester contained is an ethylene terephthalate unit. When the content of the ethylene terephthalate unit is less than 40 mol% of the total polyester, the heat resistance of the film is low, the film cannot withstand high temperature boil treatment or retort treatment, and the manufacturing cost becomes high. . On the other hand, when it exceeds 90 mol%, the secondary shrinkage ratio becomes low, and wrinkles, distortions, shrinkage plaques, etc. of the film when heat-shrinked occur, and a beautiful finished appearance cannot be obtained.

Any of the polyesters used in the present invention can be manufactured by conventional methods. For example, a direct esterification method in which a dicarboxylic acid and a diol are directly reacted;
A polyester or a copolyester is prepared by a transesterification method or the like in which a dicarboxylic acid dimethyl ester is reacted with a diol. Each of these methods may be a batch method or a continuous method.

In general, the copolyester has a low melting point, so that it has a problem that it is difficult to handle when dried. Therefore, the copolyester is preferably used as a mixture with the homopolyester. Examples of the homopolyester include polyethylene terephthalate, polyethylene naphthalate, and poly (1,4-cyclohexene dimethylene terephthalate), and polyethylene terephthalate is particularly preferable in that it is economical because it is inexpensive.

The polyester composition used in the present invention may contain various additives as required. Examples of the additive include titanium dioxide, fine particle silica,
Lubricants such as kaolin and calcium carbonate, foaming agents, antistatic agents, antiaging agents, anti-UV agents, and coloring agents such as dyes are available.

As described above, the polyester film of the present invention has an apparent specific gravity of 0.4 or more and 1.3 or less, and has a large number of cavities in the film. In order to obtain such a film, the polyester composition used usually contains a thermoplastic resin that is incompatible with the polyester.

As the thermoplastic resin which is incompatible with the polyester, polyolefin resin, polystyrene resin,
Examples include polyacrylic resin, polycarbonate resin, polysulfonic acid resin, and the like.

The polyester composition thus obtained is preferably amorphous and has a glass transition temperature (Tg) of 50 ° C. or higher. If the Tg is less than 50 ° C., the secondary shrinkage rate becomes low, and wrinkles, distortions, shrinkage marks and the like of the film when heat-shrinked occur, and a beautiful finished appearance cannot be obtained. The intrinsic viscosity when the various components of the polyester composition are mixed is preferably 0.50 to 1.3 d / g. If the intrinsic viscosity is less than 0.50 d / g, the strength may decrease, and
If it exceeds / g, the strength of the obtained film may not be increased beyond a certain level and may be economically disadvantageous.

The above polyester composition is formed into a film by a known method (for example, extrusion method, calender method). The shape of the film is, for example, a plane shape or a tube shape, and is not particularly limited. The obtained film is, for example, stretched in a predetermined one direction (main stretching direction) in a range of 2.5 to 7.0 times, preferably 3.0 to 6.0 times under predetermined conditions described later. To be done. 4.0
Double to 6.0 is more preferable, and 4.5 to 6.0 is most preferable. In the direction orthogonal to the main stretching direction, 1.
It is stretched in the range of 0 to 2.0 times, preferably 1.1 to 1.8 times. Either may be first in the order of this stretching. Stretching in the main stretching direction is performed to obtain a high heat shrinkage ratio in this direction. Stretching in the direction orthogonal to the main stretching direction is performed in order to improve the impact resistance of the obtained film and to alleviate the property of being easily torn in one direction. When the stretching ratio in the right-angled direction exceeds 2 times, the heat-shrinkability in the direction orthogonal to the main shrinkage direction becomes too large, and the finish when heat-shrinked becomes uneven in a wavy state. The film stretched at the above ratio is usually
The shrinkage in the direction orthogonal to the shrinkage in the main stretching direction is preferably 15% or less, more preferably 8 to 9% or less, and further preferably 7% or less. The film having such a shrinkage ratio has a uniform finish when subjected to heat treatment.

As a stretching method, a usual method is adopted. Examples thereof include roll stretching method, long gap stretching method, tenter stretching method, and tubular stretching method. In any of these methods, the stretching is performed by sequential biaxial stretching and simultaneous biaxial stretching.
Axial stretching, uniaxial stretching, and combinations thereof can be performed. In the above-mentioned biaxial stretching, stretching in the longitudinal and transverse directions may be performed simultaneously, but sequential biaxial stretching in which either one is performed first is effective, and the longitudinal and lateral directions may be performed first.

During the stretching, for example, the film is heated at a temperature not lower than Tg of the polyester forming the film, for example, not lower than Tg (Tg + 80 ° C.). When this heating is performed during the stretching in the main stretching direction (which becomes the “main shrinkage direction”), heat shrinkage in the direction orthogonal to the direction (main shrinkage direction) can be suppressed. When the temperature range is (Tg + 80 ° C. ± 25 ° C.), the heat shrinkage ratio in the direction orthogonal to the main shrinkage direction is almost the minimum.

After the above stretching, the following operations such as heat setting, stretching and cooling can be preferably performed.

After stretching the film, heat setting is usually performed. For example, after stretching the film,
It is recommended to pass the film through a heating zone of 30 ° C to 150 ° C for about 1 to 30 seconds. This is called heat set. By performing this heat setting, it is possible to prevent the dimensional change of the film under high temperature and high humidity conditions such as high temperature in summer.

Furthermore, after the above stretching, the film obtained by cooling the film while keeping it in a stretched or tensioned state while applying stress, or by cooling the film continuously after releasing the tensioned state after the treatment. The shrinkage property by heating is more favorable and stable.

In the heat-shrinkable polyester film of the present invention thus obtained, the heat shrinkage ratio (primary heat shrinkage ratio) in the main shrinkage direction at 100 ° C. is 40% or more. If the heat shrinkage ratio is less than 40%, when the film is heat-shrinked along the surface of the irregularly-shaped package, the necessary shrinkage cannot be achieved in detail, and the primary heat It would have to be heated to high temperatures to achieve the shrinkage. On the other hand, since the heat resistance of the packaged object is also limited, the application range of the film is narrowed, which is not preferable.

In the heat-shrinkable polyester film of the present invention, the heat shrinkage at 100 ° C. in the direction orthogonal to the main shrinkage direction is 20% or less, preferably 15% or less, and preferably 10% or less. It is more preferable that there is. When the heat shrinkage rate of the film exceeds 20%, when the film is used as a label for shrinking, the film greatly shrinks along the longitudinal direction of the container,
Distortion and curling of the edges occur, which is not preferable.

Further, the film of the present invention is heated with hot air at 100 ° C. for 10 seconds, and the film is heated in the main shrinkage direction to 40 ° C.
After the heat shrinkage of 10%, the heat shrinkage in the main shrinkage direction (secondary heat shrinkage) when heated with hot air of 130 ° C. for 10 seconds is 12% or more, and preferably 14% or more. If the secondary heat shrinkage ratio is less than 12%, defects such as wrinkles, distortions, and shrinkage unevenness occur in the film when heat-shrinked, and a beautiful appearance cannot be obtained, which is not preferable.

The above polyester composition usually contains a thermoplastic resin, which is present in the unstretched film in the form of fine particles. When the unstretched film is stretched, cavities are generated around the fine particles, and as a result,
Many fine cavities are formed inside the film. Voids also form around the particles of inert particles that are less familiar to the polyester when present in the composition. further,
When the composition contains a foaming agent, the function of the foaming agent causes voids when heated.

The polyester film of the present invention thus has a large number of fine voids inside, and its apparent specific gravity is 0.4 or more and 1.3 or less, preferably 0.6 or more and 1.3 or less. is there. When the apparent specific gravity exceeds 1.3, the void content in the film, that is, the cushioning property of the film is reduced, which is not preferable. When the apparent specific gravity is less than 0.4, the void content in the film becomes too large, and the strength and shrinkage of the film decrease.

The plane orientation coefficient of the film of the present invention is 100.
It is preferably × 10 ⁻³ or less. Plane orientation coefficient is 10
When it exceeds 0 × 10 ⁻³ , the strength of the obtained film is lowered and the film is apt to be broken even by a small amount of external damage. When such a film is wound around the outer surface of a bottle and used as a reinforcing material, a sufficient reinforcing effect cannot be obtained.

The birefringence of the film of the present invention is 15 × 1.
It is preferably 0 ^{−3 to} 160 × 10 ⁻³ . When the birefringence is less than 15 × 10 ⁻³ , the heat shrinkage and shrinkage stress in the main shrinkage direction of the obtained film are low. When the birefringence exceeds 160 × 10 ⁻³ , the obtained film is easily broken by external scratches and the impact strength becomes low, so that the film is not practical.

The thickness of the film of the present invention is 6 to 250 μm.
It is preferably in the range of. Film thickness is 6 μm
If it is less than 250 μm, the strength may be deteriorated and the handleability of the film may be deteriorated. If it exceeds 250 μm, it may be expensive.

The void-containing heat-shrinkable polyester film of the present invention is excellent in cushioning property because it has many fine voids in addition to good heat-shrinkability. Such a film is used by packaging or labeling a glass container or the like and applying heat to shrink the film. This allows transportation and sale without damaging the glass container or the like.

[0038]

EXAMPLES The present invention will be described below with reference to examples. The measuring methods used in this example and comparative examples are shown below.

(1) Primary heat shrinkage rate The film is cut into a width of 15 mm to form a tape-shaped sample, and a marked line is drawn in a gap of 200 mm in the longitudinal direction. This sample is heated with hot air at 100 ° C. for 1 minute, and the shrinkage rate is measured.

(2) Secondary heat shrinkage ratio Both ends of the film are fixed to a metal frame with a slack of 40% of the length of the film in the main shrinkage direction,
Heat the film with hot air at 100 ° C for 10 seconds,
Shrink until the slack disappears. This heat-shrinkable film is cut into a tape-shaped sample with a width of 15 mm, and a marked line is drawn in a gap of 200 mm in the longitudinal direction.
This sample is heated with hot air at 130 ° C. for 10 seconds, and the shrinkage rate is measured.

(3) Apparent specific gravity The film was accurately cut into a square of 5.00 cm × 5.00 cm, and the thickness was measured at 50 points, and the average thickness was t.
μm. The weight of this film was measured up to 0.1 mg and this was taken as wg, and the apparent specific gravity was calculated by the following formula.

Apparent specific gravity = w / 5 × 5 × t × 10000.

(4) Cavity content It was calculated by the following formula.

Cavity content (volume%) = 100 × (1-true specific volume / apparent specific volume) where true specific volume = x ₁ / d ₁ + x ₂ / d ₂ + x ₃ / d ₃ + ...
-+ X _i / d _i + ... Apparent specific volume = 1 / apparent specific gravity In the above formula, x _i represents the weight fraction of each component i in the polyester composition, and d _i represents the true specific gravity of each component i. .
The value of the true specific gravity d _i is 1.40 when each component is a polyester resin, and is 1. when the component is a general-purpose polyethylene resin.
05, 0.91 was used for the crystalline polypropylene resin.

(5) Cushion property A dial gauge (KK Ozaki Co., Ltd.) equipped with a 3 mmφ circular flat-bottomed probe was used, and the measurement pressure was 10 gf /
The film thickness t ₀ was measured in cm ² . Then, a weight was placed in that state to raise the measurement pressure to 5 kgf / cm ² , and 10 seconds after the weight was placed, the thickness t ₁ of the film was measured. Thirty seconds after the weight was placed, the weight was removed and the thickness t ₂ of the film was measured. From the thicknesses t ₀ , t ₁ and t _{2 of} the film thus measured,
The compression rate and recovery rate of the obtained film were calculated according to the following formula. The larger the compression rate and the recovery rate are, the better the cushioning property is, and the larger the bottle breaking prevention effect is.

[0046]

[Equation 1]

(6) Finished state after shrinkage In order to use the film as a shrinkable label, metallic film printing was performed to form a cylindrical shape (tube). This is 1.5
It was put on a rectangular PET bottle having a capacity of 1 liter and passed through a shrink tunnel. The temperature conditions of the shrink tunnel were 100 ° C. in the first zone and 140 ° C. in the second zone, and the retention time of the bottle was 4.5 seconds in the first zone and 5 seconds in the second zone. The finished state of the obtained label after shrinkage was visually evaluated for wrinkles, distortion during printing, and shading of printing due to shrinkage unevenness.

Example 1 95 mol% of terephthalic acid and 5 mol% of adipic acid as dicarboxylic acid, 63 mol% of ethylene glycol as diol component, 2 mol% of diethylene glycol, and 35 mol% of 1,4 cyclohexanedimethanol. Containing 0.05% by weight of silicon dioxide having an average particle diameter of 2.4 μm, an intrinsic viscosity of 0.70 dl
/ G of copolyester was obtained. A polyester composition prepared by blending this copolymerized polyester and crystalline polypropylene (thermoplastic resin incompatible with polyester) having a melt flow index of 2.5 g / 10 min at a ratio of 90:10 (weight ratio) is kneaded. It was melt-extruded from a T-die at 285 ° C. by a twin-screw extruder, electrostatically adhered to a cooling roll and solidified to obtain an unstretched film having a thickness of 200 μm. Table 1 shows the composition of the copolyester except silicon dioxide in the polyester composition, the content of each component, and the name and blending amount of the thermoplastic resin which is incompatible with the polyester. Table 1 also shows the polyester compositions used in Examples 2 to 4 and Comparative Examples 1 to 3.

This unstretched film was preheated at 110 ° C. for 6 seconds and then stretched 5.0 times in this direction so that a predetermined one direction was the main shrinkage direction. The temperature conditions during stretching are 80 ° C until half of the whole process, and 85 ° C for the other half.
Set to. After stretching, heat treatment was performed at 90 ° C. for 5 seconds.
At the time of this heat treatment, a relaxation treatment of 3% in the main shrinkage direction and 0.2% in the direction orthogonal to the main shrinkage direction was performed to obtain a heat shrinkable film of 40 μm.

With respect to the obtained heat-shrinkable film, the primary heat-shrinkage rate, the secondary heat-shrinkage rate, the apparent specific gravity, and the void content are measured by the above-mentioned method, and the cushioning property and the compression ratio and the recovery ratio are measured. And the finished state after shrinkage was visually evaluated. The results are shown in Table 2. The results of the films obtained in Examples 2 to 4 and Comparative Examples 1 to 3 are also shown in Table 2.

From Table 2, it can be seen that the film of Example 1 has a high secondary heat shrinkage, a good finished state after shrinkage as a shrinkable label, and a high void content and excellent cushioning property. Recognize. When such a film is used as a label on a bottle, it has a great effect of preventing bottle breaking.

(Comparative Example 1) As shown in Table 1, a heat-shrinkable film was obtained in the same manner as in Example 1 except that a thermoplastic resin that was incompatible with polyester was not added.

The film obtained in Comparative Example 1 had a high secondary heat shrinkage and the finished state after shrinking as a shrinkable label was good, but there was no cavity in the film and the heat of Example 1 Cushioning property is inferior in terms of compression rate as compared with the shrinkable film.

Comparative Example 2 A heat-shrinkable film was obtained in the same manner as in Example 1 except that the composition of the copolyester was changed as shown in Table 1.

The film obtained in Comparative Example 2 has a high void content and excellent cushioning properties, but has a lower secondary heat shrinkage rate than the heat shrinkable film of Example 1 and has a finished state after shrinkage. Is also bad.

(Example 2) In Example 2, 90 mol% of terephthalic acid and 10 mol% of sebacic acid were used as the dicarboxylic acid, and ethylene glycol 4 was used as the diol component.
65 parts by weight of a copolyester composed of 8 mol%, 2 mol% of diethylene glycol and 50 mol% of neopentyl glycol, and 35 parts by weight of polyethylene terephthalate were used. 9 of these polyesters and crystalline polypropylene (thermoplastic resin that is incompatible with polyester) with a melt flow index of 2.5 g / 10 min.
A polyester composition which was blended and kneaded at a ratio of 0:10 (weight ratio) was obtained. A heat-shrinkable film was obtained in the same manner as in Example 1 using the polyester composition thus obtained.

The film obtained in Example 2 has a high secondary heat shrinkage, a good finished state after shrinkage as a shrinkable label, a high void content, and an excellent cushioning property.

(Example 3) Composition of copolymerized polyester, content of each component, content of copolymerized polyester and polyethylene terephthalate contained in polyester, name and blending amount of thermoplastic resin incompatible with polyester A heat-shrinkable film was obtained in the same manner as in Example 2 except that was changed as shown in Table 1.

The film obtained in Example 3 has a high secondary heat shrinkage, a good finished state after shrinking as a shrinkable label, a high void content, and an excellent cushioning property.

Example 4 Example 4 was carried out except that the composition of the copolymerized polyester, the content of each component, and the content of the copolymerized polyester and polyethylene terephthalate contained in the polyester were changed as shown in Table 1. Example 2
A heat-shrinkable film was obtained in the same manner as.

The film obtained in Example 4 has a high secondary heat shrinkage, a good finished state after shrinking as a shrinkable label, a high void content, and an excellent cushioning property.

Comparative Example 3 As shown in Table 1, a heat-shrinkable film was obtained in the same manner as in Example 2 except that a thermoplastic resin that was incompatible with polyester was not added.

The film obtained in Comparative Example 3 had a high secondary heat shrinkage and the finished state after shrinking as a shrinkable label was good, but there was no cavity in the film and the heat of Example 2 Cushioning property is inferior in terms of compression rate as compared with the shrinkable film.

[0064]

[Table 1]

The abbreviations in Table 1 indicate the following: T: terephthalic acid IPA: isophthalic acid SA: sebacic acid AA: adipic acid AZ: azelaic acid EG: ethylene glycol DEG: diethylene glycol CHDM: 1,4-cyclohexanedi Methanol NPG: Neopentyl glycol

[0066]

[Table 2]

[0067]

EFFECTS OF THE INVENTION According to the present invention, a heat-shrinkable film having excellent heat-shrinkability and having a beautiful appearance with few defects such as wrinkles, distortion, and shrinkage spots when heat-shrinked is obtained. To be This film also has a cushioning property due to the high void content, and is excellent in the bottle breaking prevention effect.
INDUSTRIAL APPLICABILITY The heat-shrinkable film of the present invention is useful as various packaging materials including shrink films for labels and has high utility value.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B29L 7:00 (72) Inventor Tsutomu Isaka 2-8 Dojimahama, Kita-ku, Osaka-shi, Osaka Toyo Spinning Co., Ltd.

Claims (1)

[Claims] 1. Cavity-containing heat having a heat shrinkage of 40% or more in the main shrinkage direction and 20% or less in the direction orthogonal to the main shrinkage direction when heated with hot air of 100 ° C. for 1 minute. A shrinkable polyester film, which is heated with hot air of 100 ° C. for 10 seconds to shrink the film by 40%, and then heated with hot air of 130 ° C. for 10 seconds. 12 in the main contraction direction
% Or more, and an apparent specific gravity of 0.4 or more and 1.3 or less, a polyester film.