JP2003119367A - Polylactic acid-based heat-shrinkable film - Google Patents

Abstract

(57) [Problem] To provide a film exhibiting good heat shrinkage characteristics while having biodegradability. SOLUTION: The polylactic acid (A) 55 whose composition ratio of L-lactic acid unit and D-lactic acid unit is 85/15 to 90/10.
Polylactic acid (B) 45 to 75% by weight and a composition ratio of L-lactic acid unit to D-lactic acid unit of 95/5 to 100/0.
A resin material consisting of a mixture of 92 to 97% by weight of a mixture with 25% by weight and 3 to 8% by weight of a chain-extended aliphatic-aromatic polyester is formed into a sheet shape.
A film obtained by stretching by a factor of up to 7 times, wherein the heat shrinkage in the main shrinkage direction is 40% or more at 80 ° C. and 60% or more at 100 ° C.
A heat shrinkable film having a heat shrinkage property of not more than 15%, a haze of not more than 10%, and an elongation in a direction orthogonal to the main shrinkage direction of not less than 200%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat-shrinkable film having biodegradability, and more specifically, two kinds of polylactic acid having different composition ratios of L-form and D-form and a chain-extended aliphatic group. -It relates to a uniaxially stretched heat-shrinkable film, which is made of an aromatic polyester and has specific shrinkage properties, which is particularly useful for shrink label applications.

[0002]

2. Description of the Related Art In a plastic container such as a glass bottle or a plastic bottle, a printed label is attached to display the name of contents or to decorate it.
A heat-shrinkable film is used as such a label. That is, by using a heat-shrinkable film,
By covering a bottle or the like with a predetermined film and subjecting it to heat treatment, the film shrinks, so that the bottle and the film can be integrated very easily. The heat-shrinkable film used for such labels and the like is required to have transparency, appropriate elasticity and compatibility with printing ink. Also,
In recent years, environmental problems have become particularly important, and recycling of bottles and the like is required. When recycling such a bottle or the like, the label with the name or the like printed thereon needs to be processed separately from the main body of the bottle or the like, and therefore, it is also necessary to easily separate the labels. Furthermore, it is desirable that the labels thus separated and collected can be disposed of by subjecting them to biodegradation. In order to satisfy these requirements, polylactic acid-based resins have attracted attention, and, for example, JP-A-5-212790.
Japanese Patent Laid-Open No. 7-256753, Japanese Patent Laid-Open No. 9-9
5605, JP-A-9-187863, etc.,
A heat-shrinkable film using a polylactic acid resin is disclosed.

[0003]

As the heat-shrinkable film used for the above-mentioned label and the like, it is desirable to exhibit sufficient heat-shrinkability while avoiding the influence on the contents and the container body. In particular, unlike glass bottles, etc., it is desirable that it is for a resin container, or if the contents are foods, chemicals, etc., it is possible to sufficiently heat shrink at a temperature as low as possible.
It is desirable to shrink 60% or more at 00 ° C. But,
The heat-shrinkable film described in JP-A-5-212790 or the like has been difficult to sufficiently heat-shrink at such a low temperature. Further, in order to improve the finish, the shrinkage rate of the film increases at a constant rate as much as possible with respect to the temperature rise during the heat treatment of the film,
That is, it is desirable that the heat shrinkage temperature-heat shrinkage rate relationship curve of the film be a gentle curve. However, the conventional heat-shrinkable film made of a polylactic acid-based resin material does not satisfy the above requirements, and the increase in the heat shrinkage temporarily stops at around 70 ° C., and the heat shrinkage temperature-heat shrinkage rate curve becomes a step. The heat shrinkage rate rapidly increases up to around 80 ° C., and reaches a level above that. To improve such characteristics,
A film prepared by blending a polylactic acid with a nucleating agent has been proposed (Japanese Patent Laid-Open No. 2001-226571), and although a considerable improvement effect is recognized, it is still insufficient, and the transparency of the film is slightly lowered. The problem of was left. The present invention has been made in order to solve the above-mentioned problems, and satisfies the requirements as a heat-shrinkable film used for the above-mentioned label and the like, while having biodegradability, a film exhibiting good heat-shrinkable properties. It is made for the purpose of providing.

[0004]

According to the present invention, 55 to 75% by weight of polylactic acid (A) having a composition ratio of L-lactic acid unit and D-lactic acid unit of 85/15 to 90/10 and L-lactic acid are used. Unit 92 to 9 and a polylactic acid (B) 45 to 25% by weight in which the composition ratio of the D unit and the D-lactic acid unit is 95/5 to 100/0.
A film obtained by molding a resin material comprising 7% by weight and 3-8% by weight of a chain-extended aliphatic-aromatic polyester into a sheet and stretching the sheet in one direction by 4 to 7 times. The heat shrinkage in the main shrinkage direction is 40% or more at 80 ° C., 60% or more at 100 ° C., and the heat shrinkage ratio in the direction orthogonal to the main shrinkage direction is 15% or less at 100 ° C. At the same time, the haze is 10% or less and the elongation in the direction orthogonal to the main shrinkage direction is 200% or more. In addition, the heat-shrinkable film of the present invention preferably contains 0.01 to 0.1 part by weight of a nucleating agent with respect to 100 parts by weight of the resin material, and 100 parts by weight of the resin material, It is desirable to add 0.01 to 0.2 parts by weight of the inorganic fine particles. Furthermore, in the heat-shrinkable film of the present invention, it is desirable that the heat shrinkage rate in the main shrinkage direction is increased by 5 to 15% per temperature rise of 5 ° C within the range of 65 to 85 ° C. It is desirable that the shrinkage is 3 to 10% higher than the thermal shrinkage at 90 ° C. in the same direction.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The resin material constituting the heat-shrinkable film of the present invention comprises two types of polylactic acid having different composition ratios of L-lactic acid units and D-lactic acid units (hereinafter referred to as L / D ratio). It comprises (A) and (B) and a chain-extended aliphatic-aromatic polyester.

The polylactic acid (A) and polylactic acid (B) used in the present invention are obtained by condensation polymerization or ring-opening polymerization of L-lactic acid or lactide which is a cyclic dimer thereof and D-lactic acid or lactide. It is a copolymer. For polylactic acid, L or D-
There are lactic acid homopolymers and various copolymers having different composition ratios of L-lactic acid units and D-lactic acid units, and further, those containing lactic acid mixed with a small amount of hydroxycarboxylic acid as a copolymerization component are also included. Examples of such hydroxycarboxylic acid include glycolic acid, 3-hydroxybutyric acid, and 4
Examples include -hydroxyvaleric acid and 6-hydroxycaproic acid. As the polylactic acid, various types of polylactic acid as described above are commercially available under the trade names such as “Lacea” (manufactured by Mitsui Chemicals, Inc.) and “Lacty” (manufactured by Shimadzu Corporation). The polylactic acid (A) and the polylactic acid (B) used in the present invention include not only a polymer consisting of lactic acid alone but also a small amount of the above-mentioned hydroxycarboxylic acid as a copolymerization component, and the weight average. The molecular weight is not particularly limited, but from the viewpoint of film strength, moldability, etc., about 10,000 to 1,000,000 is suitable, and about 30,000 to 500,000 is particularly preferable.

The polylactic acid (A) and polylactic acid (B) used in the present invention have L / D ratios of 85/15 to
90/10 and 95/5 to 100/0, and the mixing ratio is (A) 55 to 75% by weight and (B) 45 to, respectively.
Must be 25% by weight. When the L / D ratio in the polylactic acid (A) and the polylactic acid (B) and the mixing ratio of both deviate from the above ranges, the low-temperature shrinkage characteristics of the heat-shrinkable film and the preferable heat shrinkage temperature-heat shrinkage rate relationship curve are If it is not obtained and is heat-attached to the adherend as a shrinkable label, it tends to cause wrinkles and the like.

The chain-extended aliphatic-aromatic polyester used in the present invention is a polyfunctional aliphatic-aromatic polyester obtained by polycondensing an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid with an aliphatic diol. It is a biodegradable resin in which an aliphatic-aromatic polyester is branched and chain-extended by reacting with (Table 1
No. 500907, etc.) from "BSF Corporation"
It is commercially available under the trade name of "COFLEX". Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, etc., and examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalic acid, etc. Examples thereof include ethylene glycol, propanediol, butanediol and the like, and adipic acid / terephthalic acid / 1,4-butanediol can be mentioned as a desirable combination of each monomer component. Examples of the polyfunctional substance include compounds containing a plurality of NCO groups (isocyanurate, diisocyanate, etc.) and polyfunctional epoxides.

In the present invention, the mixing ratio of the chain-extended aliphatic-aromatic polyester to the mixture of polylactic acid (A) and polylactic acid (B) should be 3 to 8% by weight. If it is less than 3% by weight, the elongation in the direction orthogonal to the main shrinkage direction of the film will be small, and if it is more than 8% by weight, the transparency of the film will be poor.

It is desirable to add a nucleating agent to the resin material used in the present invention. As the nucleating agent, dibenzylidene sorbitol, bis (p-methylbenzylidene) sorbitol, bis (p-ethylbenzylidene) sorbitol, hydroxy-di (t-Bt benzoic acid) aluminum,
Examples thereof include bis (4-t-Bt-phenyl) phosphate phosphate salt.

Specifically, "EC-1" (manufactured by EC Chemical Co., Ltd.), "Gel All MD", "Gel All DH" (manufactured by Shin Nippon Rika Co., Ltd.), "NC-4" (manufactured by Mitsui Chemicals, Inc.), A
"L-PTBBA" (manufactured by Shell Chemical Co., Ltd.), "Adeka Stab NA-10", "Adeka Stab NA-11", "Adeka Stab NA-21" (manufactured by Asahi Denka Kogyo Co., Ltd.) and the like are exemplified as commercially available products. Also, among the nucleating agents,
A substance having a melting point of 350 ° C. or lower is desirable because it exhibits more effect. The nucleating agent is generally added to a crystalline polymer such as polypropylene in order to improve transparency, impact resistance, dimensional stability and the like. By blending the agent with polylactic acid, it is possible to improve the heat shrinkage characteristics such as optimization of the shrinkage curve of the heat shrinkable film and to expand the appropriate stretching temperature range in the production of the film.

The blending ratio of the nucleating agent is the resin material 100 described above.
It is preferably 0.01 to 0.1 parts by weight with respect to parts by weight. If it is less than 0.01 part by weight, the effect of improving heat shrinkage properties and the like is small, and if it exceeds 0.1 part by weight, the effect of improving the content or more cannot be expected. The kneading of polylactic acid, which is the main component of the resin material, and the nucleating agent is preferably performed at a temperature higher than the melting point of the nucleating agent.

The resin material used in the present invention preferably contains inorganic fine particles in order to improve the slipperiness of the films. Examples of the inorganic fine particles include inorganic substances such as silica, talc and kaolin, and the average particle size is 1
.About.7 .mu.m, and the compounding amount is 0.
About 0.1 to 0.2 parts by weight is desirable. Blending amount 0.01
If it is less than 0.2 parts by weight, the effect of improving the slipperiness of the film is poor, and if it exceeds 0.2 parts by weight, the transparency of the film is impaired.

The resin material used in the present invention includes:
Other components may be added within a range not departing from the spirit of the present invention. Examples of such additive components include antioxidants, ultraviolet absorbers, antiblocking agents, lubricants, antistatic agents, plasticizers, heat stabilizers, pigments, dyes, fillers, hindered amine light stabilizers, Various polymers (for example, EVA resin) can be mentioned.

The heat-shrinkable film of the present invention is made of the above-mentioned resin material and has biodegradability and can be used for labels and the like, and has transparency, moderate elasticity and printing. It exhibits compatibility with ink.
The method of molding into a film is not particularly limited,
Various well-known film forming methods and stretching treatment methods can be appropriately used. For example, a means for stretching a sheet-shaped product by an extrusion method, a calender method, a casting method or the like by a roll method, a tenter method (transverse stretching machine) or the like can be applied. The stretching may be performed in a single stage or in multiple stages.

The heat shrinkable film of the present invention is required to have the heat shrinkage rate satisfying the following requirements, and the resin material according to the present invention can be used. 1) The heat shrinkage in the main shrinkage direction is 40% or more at 80 ° C. 2) The heat shrinkage in the main shrinkage direction is 100% or more and 60% or more. 3) The heat shrinkage in the direction orthogonal to the main shrinkage direction is 15% or less at 100 ° C. The heat-shrinkable film of the present invention, like a uniaxially stretched film, has a different draw ratio depending on the direction, and the main shrinkage direction means the direction in which the shrinkage ratio is the highest, and usually the draw ratio is the highest. Means the direction being processed. Therefore, in the direction orthogonal to the main shrinkage direction, not only unstretched but also stretched to some extent is included.

Like the heat-shrinkable film according to the present invention,
When the film satisfies the above three requirements, it exhibits sufficient heat shrinkability at low temperature and in a short time, and can be mounted on a container or the like with good finish. Further, when used as a label or the like, it is possible to reduce the deformation of the printed characters, patterns, or the like. In particular, when the heat shrinkage of the film is 70% or more at 100 ° C., the film can be more tightly attached to the container or the like by the low-temperature heat treatment that can avoid the influence on the contents and the container.

Further, as a characteristic of the heat shrinkage ratio, it is desirable that the heat shrinkage ratio in the main shrinkage direction is increased by 5 to 15% per 5 ° C. temperature rise within the temperature range of 65 to 85 ° C. The fact that the rate of increase of the heat shrinkage in the main shrinkage direction with respect to the temperature rise is within the above range indicates that the heat shrinkage has an appropriate rising curve with respect to the temperature rise, and that the packaging without uneven shrinkage is It is possible and the quality of shrink wrapping is improved.

With respect to the heat shrinkage in the main shrinkage direction, 1
The heat shrinkage at 00 ° C is 3 to 10 than the heat shrinkage at 90 ° C.
It is desirable to be large. Thermal shrinkage at 100 ° C and 90
The difference in the heat shrinkage ratio at ℃ within the above range is 90
Even in the temperature range of up to 100 ° C., the heat shrinkage ratio shows a gentle rising curve with respect to the temperature rise.

The heat-shrinkable property of the heat-shrinkable film of the present invention, that is, the property of affecting the attachability of the shrinkable label to the adherend is as described above, but the heat-shrinkable film of the present invention is As a characteristic, the haze has a transparency of 10% or less, and it is necessary that the elongation in the direction orthogonal to the main shrinkage direction is 200% or more. If the haze exceeds 10%, the commercial value of the label will be reduced, and if the elongation in the direction orthogonal to the main shrinkage direction is less than 200%, the film will be easily cut in the stretching step and post-processing, which is not preferable. .

In the present invention, when the film is stretched in the main shrinkage direction, its stretching ratio is set within the range of 4 to 7 times in order to satisfy the above-mentioned requirements and predetermined required physical properties such as film strength. There must be. The stretching temperature is
10 to 30 ° C from the glass transition temperature of the resin material used
Higher temperatures are desirable and 70-80 ° C is the optimum stretching temperature range. If the temperature is lower than this temperature range, the film is likely to be broken or whitened, and if the temperature is higher than this temperature range, uniform stretching becomes difficult. Further, in the present invention, it is desirable to slightly stretch the film in a direction orthogonal to the main shrinkage direction of the film. The stretching temperature at this time is appropriately the same as or a few degrees lower than the temperature at which the film is stretched in the main shrinking direction, and the stretching ratio is, for example, at a stretching temperature of 72 ° C. of 1.05 to 1. 1 is suitable. If the stretching ratio is out of this range, when the shrinkable label is attached to a plastic bottle or the like, the shrinkage in the vertical direction becomes excessively large, or conversely extends, which is not preferable.

The present invention not only excels in heat shrinkage properties of the heat shrinkable film, but also has a property that a suitable stretching temperature range is wide in the stretching step for producing the heat shrinkable film. Therefore, the tolerance of the stretching condition is large, and stable production of the heat-shrinkable film is easily performed.

The heat-shrinkable film of the present invention is particularly suitable for use as a label attached to a bottle or the like, but can be appropriately applied to other uses.

[0024]

EXAMPLES Next, the contents of the present invention will be described in more detail by way of examples. The physical properties of the heat-shrinkable films shown in Examples and Comparative Examples were measured by the test methods described below.

(1) Elongation at break Length 10 with the direction perpendicular to the main shrinkage direction being the longitudinal direction.
A film sample was prepared by sampling to a size of 0 mm / width 10 mm, and using a Tensilon tensile tester, room temperature 23 ° C./distance between chucks 50 mm / pulling speed 200.
The elongation (%) at the time of breaking the sample was measured under the condition of mm / min.

(2) Transparency Based on JIS K 7105, the total light transmittance and the diffuse transmittance were determined, and the haze of the film sample was calculated by the following formula. Haze (%) = (diffuse transmittance / total light transmittance) × 100

(3) Heat Shrinkage Property Heat Shrinkage Ratio in the Main Shrinkage Direction With the main shrinkage direction as the longitudinal direction, length 100 mm / width 10
Create a film sample sampled to the size of mm, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃
Then, the sample was immersed in a warm water bath at 100 ° C. for 10 seconds and calculated by the following formula. Thermal shrinkage (%) = {(length before immersion-length after immersion) /
Length before immersion} × 100 Further, based on the above measured values, an increase in the heat shrinkage rate at every 5 ° C. temperature rise in the temperature range of 65 to 85 ° C. and 90 ° C.
The increase in the heat shrinkage rate with increasing temperature from 100 to 100 ° C. was calculated. Heat shrinkage rate in the direction orthogonal to the main shrinkage direction A length 10
A film sample sampled in a size of 0 mm / width 10 mm was prepared, the sample was immersed in a hot water bath at 100 ° C. for 10 seconds, and calculated by the above formula.

(4) Appropriate stretching temperature The stretching temperature is varied at 70 to 80 ° C. at 2 ° C. intervals,
For a film having a thickness of 50 μm obtained by stretching 5 times in the main shrinkage direction under each stretching temperature condition, stretching satisfying the above-mentioned heat shrinkage property requirement regarding the increase in the heat shrinkage ratio in the main shrinkage direction with the temperature rise of the present invention. The presence or absence of temperature and its range were confirmed.

(5) Finishing test for mounting The length is 240 mm and the width is 8 with the main contraction direction as the longitudinal direction.
Both ends of a film sample sampled to a size of 0 mm were solvent-sealed, and a cylindrical film having a circumference of 230 mm was covered on a 500 ml rectangular PET bottle having a length of 218 mm in the circumferential direction. This was passed through a steam tunnel having an inlet temperature of 80 ° C. and an outlet temperature of 85 ° C. for 10 seconds, and the film sample was brought into close contact with the PET bottle by heat shrinkage. The mounting finish of 10 PET bottles mounted with the film sample was visually observed and evaluated according to the following criteria. ◯: Almost no defective parts such as wrinkles, bending, shrinkage distortion, etc., and good appearance Δ: Some defective parts, poor appearance 2 to 4 ×: Same defective parts, poor appearance 5 More than a book

Example 1 The composition ratio of L-lactic acid unit and D-lactic acid unit was 87.3 / 1.
The weight average molecular weight is 2.7 and the composition ratio of L-lactic acid unit and D-lactic acid unit is 98.9 / 1.1, and 70% by weight of polylactic acid (A) having a weight average molecular weight of about 190,000. Mixture with 30% by weight of polylactic acid (B) having a molecular weight of about 200,000 9
5 parts by weight, 5 parts by weight of chain-extended aliphatic-aromatic polyester (trade name "ECOFLEX", manufactured by BSF Corporation), and 0.05 parts by weight of silica fine particles were uniformly mixed. The mixture was made into pellets by an extruder set at 210 ° C., and the pellets were supplied to a T-die extruder and extrusion-molded into a sheet having a thickness of 250 μm. First, the sheet was stretched in the longitudinal direction to 1.07 times the original size at a temperature set at 72 ° C. using a roll device, and then applied to a tenter device, and the temperature was set at 2 ° C. intervals in the range of 70 to 80 ° C. Then, it was stretched in the transverse direction to 5 times the dimension after longitudinal stretching. Table 1 shows the evaluation results of the obtained stretched film. However,
Of the evaluation results in the table, those outside the proper stretching temperature range are those of the stretched film obtained by transverse stretching at a temperature of 76 ° C (the same applies to the following Examples and Comparative Examples).

Example 2 Same as Example 1 except that the mixing ratio of polylactic acid (A) and polylactic acid (B) was 65% by weight of polylactic acid (A) and 35% by weight of polylactic acid (B). As a blend, a stretched film was obtained by the same method and conditions as in Example 1. Table 1 shows the evaluation results of the obtained stretched film.

Example 3 Except that the blending amount of the mixture of polylactic acid (A) and polylactic acid (B) was 93 parts by weight, and the blending amount of the chain-extended aliphatic-aromatic polyester was 7 parts by weight. The same composition as in Example 2 was used to obtain a stretched film by the same method and conditions as in Example 1. Table 1 shows the evaluation results of the obtained stretched film.

Example 4 A resin material was used as a nucleating agent (trade name "ADEKA STAB NA-21").
(Asahi Denka Kogyo KK, melting point: about 230 ° C.) A stretched film was obtained by the same method and conditions as in Example 1, except that 0.03 parts by weight was added. Table 1 shows the evaluation results of the obtained stretched film.

Comparative Example 1 Example 2 except that the blending amount of the mixture of polylactic acid (A) and polylactic acid (B) was 100 parts by weight, and the chain-extended aliphatic-aromatic polyester was not blended. A stretched film was obtained in the same manner and conditions as in Example 1, except that the same composition was used. Table 1 shows the evaluation results of the obtained stretched film.

Comparative Example 2 Except that the amount of the mixture of polylactic acid (A) and polylactic acid (B) was 90 parts by weight and the amount of the chain-extended aliphatic-aromatic polyester was 10 parts by weight. Example 2
A stretched film was obtained in the same manner and conditions as in Example 1, except that the same composition was used. The evaluation results of the obtained stretched film are shown in Table 1.
Shown in.

Comparative Example 3 Same as Example 1 except that the mixing ratio of polylactic acid (A) and polylactic acid (B) was 50% by weight of polylactic acid (A) and 50% by weight of polylactic acid (B). As a blend, a stretched film was obtained by the same method and conditions as in Example 1. Table 1 shows the evaluation results of the obtained stretched film.

Comparative Example 4 A stretched film was prepared by the same method and conditions as in Example 1, except that 95 parts by weight of polylactic acid (A) was added and no polylactic acid (B) was added. Got Table 1 shows the evaluation results of the obtained stretched film.

Comparative Example 5 Polylactic acid (A) and polylactic acid (B) used in Example 1
Example 1 except that a polylactic acid having a composition ratio of L-lactic acid unit and D-lactic acid unit of 93.8 / 6.2 and a weight average molecular weight of about 210,000 was used instead of the mixture of A stretched film was obtained in the same manner and conditions as in Example 1, except that the same composition was used. Table 1 shows the evaluation results of the obtained stretched film.

[0039]

[Table 1]

[0040]

EFFECT OF THE INVENTION The heat-shrinkable film according to the present invention is biodegradable, exhibits excellent heat-shrinkable properties, has a good wearing finish, and is for producing such a heat-shrinkable film. Since it has a wide stretching temperature range, it is easy to manufacture, and it is possible to provide a high-quality shrinkable label which is excellent in transparency, moderate elasticity, and compatibility with printing ink.

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Claims (5)

[Claims] 1. A polylactic acid (A) 55 having a composition ratio of L-lactic acid units and D-lactic acid units of 85/15 to 90/10.
75% by weight, polylactic acid (B) 45-2 having a composition ratio of L-lactic acid unit and D-lactic acid unit of 95/5 to 100/0
A resin material composed of 92 to 97% by weight of a mixture with 5% by weight and 3 to 8% by weight of a chain-extended aliphatic-aromatic polyester is molded into a sheet, and the sheet is unidirectionally 4 to 4.
A 7-fold stretched film having a heat shrinkage in the main shrinkage direction of 40% or higher at 80 ° C and 60% or higher at 100 ° C, and a heat shrinkage ratio in the direction orthogonal to the main shrinkage direction of 100 ° C. A heat-shrinkable film having a heat shrinkage property of 15% or less, a haze of 10% or less, and an elongation of 200% or more in a direction orthogonal to the main shrinkage direction. 2. The heat-shrinkable film according to claim 1, wherein 0.01 to 0.1 part by weight of a nucleating agent is mixed with 100 parts by weight of the resin material. 3. The heat-shrinkable film according to claim 1, wherein 0.01 to 0.2 parts by weight of inorganic fine particles are mixed with 100 parts by weight of the resin material. 4. The heat-shrinkable film according to claim 1, wherein the heat shrinkage in the main shrinkage direction increases by 5 to 15% per 5 ° C. temperature rise within the range of 65 to 85 ° C. 5. The heat-shrinkable film according to claim 1, wherein the heat shrinkage at 100 ° C. in the main shrinkage direction is 3 to 10% higher than the heat shrinkage at 90 ° C. in the same direction.