JPS6291555A - Heat-shrinkable polyester film - Google Patents

Abstract

PURPOSE:To make beautiful and tight covering package and tying package possible, by providing a polyester film having such a heat shrinkability that its heat shrinkage factor in a direction of principal shrinkage has at lest a specified value and that the one in a direction perpendicular to the direction of principal shrinkage has the min. value at a specified temp. CONSTITUTION:A heat-shrinkable polyester film has such a heat shrinkability that is heat shrinkage factor at 80 deg.C is 30% or above, that the one at 100 deg.C is 50% or above and that the one in a direction perpendicular to the above direction of principal shrinkage has the min. value in a temp. region of 80+ or -25 deg.C. To obtain these film characteristics, it is desirable to use these film chracteristics, it is desirable to use a mixture of at least two polyesters, wherein the residue of an arom. dicarboxylic acid accounts for 30-90mol% of the mixture, or a copolyester. It is desirable that a difference heat shrinkage factor between the direction of principal shrinkage of the film and the direction perpendicular to said direction is 15% or below and a coefficient of planar orientation is 100-10<-3> or below.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to a heat-shrinkable polyester film (including sheets, hereinafter the same) that exhibits particularly suitable properties in the field of packaging materials such as covering and bundling. It is related to.

[Prior Art] Tubular bodies made of heat-shrinkable plastic film include, for example, containers, bottles (including plastic bottles), cans, sticks (pipes), etc.

For covering or bundling rods, wood, various rod-shaped bodies), etc. (hereinafter referred to as containers), especially the caps, shoulders, etc.
It is used to cover part or all of the body, etc., for purposes such as marking, protection, binding, and improving product value, as well as for boxes, bottles, boards, etc.
It is widely used in the fields of integrated packaging such as sticks, notebooks, etc., and packaging in close contact with items to be packaged such as skin packs, and is expected to be used in applications that take advantage of its shrinkage properties and shrinkage stress.

Conventionally, heat-shrinkable films made of polyvinyl chloride, polystyrene, polyethylene, hydrochloric acid rubber, etc. have been used for the above-mentioned purposes, and the film has been formed into a tube and then covered with the containers or packaged in a bundle and heat-shrinked.

However, these films have poor heat resistance and have the disadvantage that they melt or burst when subjected to boiling or retort processing, making it impossible to maintain the film-like structure.

Furthermore, in applications that require printing, pinholes (microscopic irregularities based on fish eyes caused by additives and polymer gels in the film) may occur due to poor ink transfer, and even if printing is successful, There was also a problem in that the film subsequently contracted (normal temperature storage II), resulting in a dimensional change in the printing pitch. On the other hand, tubes using polyester heat-shrinkable films have been made on a trial basis in the past, but they have not been able to achieve a sufficiently high heat-shrinkage rate in the desired direction, or There is a problem in that it is not possible to reduce thermal shrinkage in a direction perpendicular to the direction, and it has been difficult to apply the method to the above-mentioned applications.

[Problems to be Solved by the Invention] The above-mentioned conventional techniques using general-purpose heat-shrinkable films made of polyvinyl chloride, polystyrene, polyethylene, etc. have the following problems.

(a) Lack of nearly perfect uniaxial shrinkage The above-mentioned conventional films are completely unsuitable for applications where it is ideal to have large shrinkage in one direction but no shrinkage in the direction perpendicular to this. 0For example, if we consider attaching a shrink label to the surface of a bottle by shrinking it in the horizontal direction, shrinking the label in the vertical direction, that is, in the vertical direction of the bottle, means that the label will shrink up when it comes to a predetermined position. To prevent this, shrinkage in the vertical direction must be reduced, but if the film is simply oriented only in the horizontal direction for this purpose, due to the nature of polymeric chemicals, shrinkage in the vertical direction must be reduced. As can be easily understood from common sense, it is easy to tear, and it also becomes easy to fibrin, which weakens its strength. Simple unidirectional stretching is not a good method, especially considering that strength in the vertical direction is important to prevent bottles from breaking when the bottle is dropped, and it cannot be used for other purposes unless it has impact resistance. There are many cases.

From this point of view, it is desired to develop a film that has an extremely small shrinkage in a certain temperature range, but a sufficiently large shrinkage in the direction perpendicular to the temperature range.

(b) Insufficient heat resistance None of the conventional films described above can withstand high-temperature boiling or retort processing, making them unsuitable for sterilization. For example, when retort processing is performed, the conventional film breaks or ruptures during processing and loses all functionality. Therefore, it is desired to provide a heat-shrinkable film that can withstand boiling and retorting.

(C) Poor printability The above-mentioned conventional films each have their own drawbacks with respect to the occurrence of pinholes due to halftone printing, adhesion with a wide variety of inks, and the like. For example, in polyvinyl chloride, ink pinholes are likely to occur due to gel-like substances, and in continuous tube processing, pinholes will exist in the middle of a long film. If this is supplied to a fully automatic labeling machine, the product will be manufactured with pinholes left behind, so all products must be inspected at the end, and the labor and reprocessing required by sampling will significantly reduce the actual operating rate. do. If this pinhole defect were to be inspected and removed after printing, the film would have to be made into a continuous film again after being cut, and it would be necessary to connect it with adhesive tape. As a result, there are seams, and defective products occur due to the effects of the seams in that area and before and after, and defective packages must be removed during the process. Furthermore, in high-precision printing, the printing pitch decreases due to shrinkage of the film after printing (shrinkage over time), and moreover, it is difficult to manage because it constantly changes under the distribution temperature conditions.

Therefore, for polyvinyl chloride shrink film, etc., refrigerated trucks, low-temperature warehouses, etc. are required. For this reason, it is desired to provide a heat-shrinkable film that can be printed without pinhole defects and that does not change over time after printing.

(d) Craze occurrence Polystyrene is prone to craze and has poor chemical resistance.

Therefore, during use, it is easily damaged by chemicals and the printed surface becomes dirty. Therefore, a film with excellent chemical resistance and durability is desired.

(e) Problems with industrial waste In recent years, the amount of plastic bottles used has increased rapidly. When considering the recovery of these bottles, there is a problem that they cannot be recovered and reused, especially if a different type of film such as polyvinyl chloride or polystyrene is used to cover a polyester bottle.

Furthermore, polyvinyl chloride has the problem of corrosion due to chlorine gas, so a heat-shrinkable film that does not cause waste pollution is desired.

(f) Shrinkage spots The heat shrinkability of the above conventional film tends to lack homogeneity, and once heat is applied and areas with sufficient shrinkage and areas with insufficient shrinkage are formed separately, heat is applied again. However, no further re-shrinkage occurs and the surface becomes uneven. Therefore, it is desired to provide a heat-shrinkable film that does not cause shrinkage spots.

The present invention was made in view of these circumstances, and aims to provide a polyester film that is free from the defects described in (a) to (f) above.

[Means for solving the problems] The polyester film of the present invention has a heat shrinkage rate of 30% or more at 80°C, a heat shrinkage rate of 50% or more at 100'O, and The thermal shrinkage rate in the direction perpendicular to the curve shows a minimum value in the temperature range of 80±25°C.

[Function] The heat shrinkage rate, which is one of the basic characteristics of the film of the present invention, must first be 30% or more at 80°C. If the heat shrinkage rate at 80°C is less than 30%, the film When it is placed on the surface of an irregularly shaped packaged object and subjected to heat shrinkage, it is not possible to achieve the necessary shrinkage in each part, and in order to achieve the above shrinkage, it is necessary to heat the product to a considerably high temperature. However, there are restrictions on the heat resistance of the packaged items, which naturally narrows the range of application. For example, if the packaged item itself is a thermoplastic plastic product, it may deform or melt due to heat.

If such a case is assumed, it is recommended to exhibit a heat shrinkage rate of 40% or more at 80°C. As for the upper limit, 90% is appropriate. Again 1
It is necessary to have a heat shrinkage rate of 50% or more at 00°C, and if it is less than 50%, there is a strong risk that local shrinkage spots will occur. However, it is not preferable that it exceeds 95%. Also, when considering the thermal shrinkage behavior in the range from 80 to 100 degrees Celsius, if the thermal contraction rate at 80'O exceeds that at 100 degrees Celsius, something that has once been heat-shrinked at around 80 degrees Celsius is continuously heated. As time goes on, it becomes loose and loses the tightening force previously exerted by contraction stress.

Next, the heat shrinkage rate in the direction perpendicular to the shrinkage direction is generally desired to be small, especially 80±25
It is necessary that the thermal shrinkage rate in the perpendicular direction in the temperature range of 0.degree. C. be the minimum, and by doing so, we succeeded in obtaining a beautiful coating appearance due to the main shrinkage in one direction. As a result of achieving intensive shrinkage in the main shrinkage direction in the above temperature range, strong adhesion to the packaged item is obtained, so if it were to be heated further and cause larger shrinkage, Even if this occurs, the friction caused by the close contact prevents further shrinkage, and a beautiful and strong binding force is maintained.

In particular, the shrinkage in the main shrinkage direction is performed in this temperature range to complete the adhesion to the packaged object, and the
Even if the temperature exceeds ±25℃, the frictional force and restraining force caused by the close contact with the packaged item will make it difficult for further shrinkage to occur, so in this temperature range where particularly large shrinkage occurs, The fact that the contraction of the protein was suppressed is of important significance. Next, pitch change during the natural flow process after printing is reduced by using a polyester polymer with a glass transition temperature of 35° C. or higher and a mixture thereof. Especially when used in summer or in high temperature areas, it is preferable to use polyester polymers with a glass transition temperature of 45° C. or higher and mixtures thereof.

As a means to obtain the above properties, it is recommended to select a copolymer or a mixture thereof containing 30 to 90 mol% of aromatic dicarboxylic acid residues. Examples of such polyesters include terephthalic acid, isophthalic acid,
L or more types selected from dibasic acids such as adipic acid, orthophthalic acid, "t! bacic acid, and naphthalene dicarboxylic acid, and one type selected from diols such as ethylene glycol, butanediol, neopentyl glycol, and cyclohexane dimetatool. Examples of polyester polymers produced by the above method include polyethylene terephthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyethylene α, β
Non-limiting examples include -bis(2-chloro or 2-methoxyphenoxy)ethane-4°4'-dicarboxylic acid osylate.

A polyester/polyether block copolymer can also be mixed with these polyesters to the extent that transparency is not impaired. The preferred intrinsic viscosity of the film base material is from 0.50 to 1.3 clfL/g, and as long as it satisfies this intrinsic viscosity value, these polymers may account for 70% by weight or more. , a polymer having a lower degree of polymerization or a higher degree of polymerization may be mixed. A film obtained using such a polymer by an extrusion method or a calendering oil introduction method has a strength of 2.5 to 7 times in one direction, preferably 3.0 times.
The film is stretched from 1.0 times to 2.0 times, preferably from 1.1 times to 1.8 times in a direction perpendicular to the above direction. Stretching in the first direction is performed to obtain a high heat shrinkage rate, and stretching in the second direction is performed to improve the impact resistance and tear resistance of the film initially stretched in one direction. It is extremely effective in solving sexual problems.

However, when stretched more than 2.0 times, the thermal shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, resulting in a wavy finish. To suppress this waving, increase the heat shrinkage rate to 15.
% or less, preferably 8 to 9% or less, more preferably 7% or less
% or less is recommended. There is no particular restriction on the stretching means, and methods such as roll stretching, long gap stretching, and tenter stretching are applicable, and the shape does not matter whether it is flat or tubular.

Further, the stretching may be carried out by successive biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. Furthermore, the film of the present invention is stretched in one axis in the longitudinal direction, one axis in the transverse direction, two axes in the longitudinal and transverse directions, etc. In particular, in biaxial stretching, stretching in the longitudinal and transverse directions is carried out sequentially in one direction or the other. is effective, and the order of stretching does not matter whichever comes first.When simultaneous biaxial stretching is performed, the stretching order may be simultaneous in the longitudinal and lateral directions, longitudinal first, or lateral first, and the heat setting in these stretchings can be done depending on the purpose. It is recommended to pass through a heating zone of 30 to 150° C. for about 1 second to 30 seconds in order to prevent dimensional changes under high summer temperatures, although this may be carried out accordingly. Further, expansion up to 70% may be applied either before or after such processing. In particular, it is preferable to stretch in the main direction and relax in the non-shrinkage direction (direction perpendicular to the main shrinkage direction), and it is better not to stretch in the perpendicular direction.

In order to exhibit the preferable characteristics of the present invention, it is necessary to use only the above-mentioned stretching ratio, and the average glass transition temperature (
Preheating and stretching at a temperature higher than Tg), for example around Tg + 80''C, is also an effective means.In particular, the above treatment temperature for stretching in the main direction (main shrinkage direction) is determined by the heat shrinkage rate in the direction perpendicular to the direction. and as mentioned above, 80
It is extremely important to bring the minimum value within the temperature range of ±25°C. Further, after stretching, by cooling the film while maintaining it in a stretched or tensioned state and applying stress to the film, or by cooling it further successively, the back and forth shrinkage characteristics become better and more stable.0 The thickness of the film of the present invention Although there are no particular limitations on the height, a range of about 1 to 600 lumens is advantageous from a practical standpoint.

However, if the range is narrowed down to a more preferable range based on current market needs, it is about 4 to 380 gm, and in the above application example, a range of 6 to 250 ILm is practical. The plane orientation coefficient of the film thus obtained was 100×
It is preferably 10-3 or less. Planar orientation coefficient is 100×
This is because if it exceeds 10-3, it becomes easy to break due to an impactful external force and becomes easy to tear even by the slightest external trauma.

On the other hand, the birefringence is preferably 15×10-3 to 160×10-3; if the birefringence is less than 15×10-3, the thermal shrinkage rate and shrinkage stress in the longitudinal direction will be insufficient, and if it exceeds 160×10-3, there will be scratch resistance. This results in a decrease in force and impact strength, and even if it is made into a film, its usefulness in practical use decreases.

The film of the present invention will be explained below from the viewpoint of its use.

Packaging applications Particularly in the packaging of foods, beverages, pharmaceuticals, etc., boiling processing, retort processing, and aseptic packaging are used to extend the shell life, but existing heat-shrinkable films are not sufficient for these processes. The film of the present invention can withstand heat sterilization by boiling treatment and retort treatment, and the original appearance of the film as well as the finish due to heat shrinkage are good.
It has higher heat shrinkage stress than VC and has excellent cohesiveness.

Therefore, it is possible to strongly cover or bind and package heavy items or deformed molded items without causing them to collapse. In addition, at the heat shrinkage rate level of 50 to 70% required for packaging, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction is the lowest value, so it has broad heat shrinkability, so it can be used for shrink wrapping from the initial stage of heat shrinkage. The completion process is carried out in the temperature range (80°C) showing the minimum shrinkage amount.
±25'O). As a result, a feature was obtained in which the error in finished dimensions was reduced.

In packaging that uses heat shrinkability, it is common to continue heating after the heat shrinkage is complete (the state where the package adheres to the packaged item and is unable to shrink any further, even if it has the ability to shrink further). This is a standard procedure that plays an important role in accommodating numerous product variations and achieving perfect shrinkage. At this time, if the shrinkage ability of the film has reached saturation, the film will undergo linear expansion due to the subsequent heating, and even though you have taken the pains to shrink it properly, it will instead become loose. come '
In order to prevent such a situation, the present invention recommends increasing the shrinkage stress and further stretching after stretching as described above. Moreover, in this point, the meaning of orientation as used in the present invention exists.

This will be described in more detail below.

(a) Unidirectional shrinkability: One of the roles of shrinkage film is to prevent the destruction of the packaged items and the collapse of the package, and for this purpose, it must have high impact resistance and be large in the main direction. It is necessary to obtain the shrinkage rate. In this respect, it was found that the film of the present invention has a high shrinkage rate and high impact resistance, so that beautiful packaging can be obtained, and it also exhibits excellent durability in terms of protecting the packaged items. This trend was confirmed by the drop bag test. Furthermore, due to the almost perfect unidirectional shrinkability, the finished dimensional error after shrink wrapping became extremely small. This means that the heat shrinkage rate in the direction perpendicular to the main direction is low and, for example, when formed into a tube, the finished dimensional error in the length direction of the tube is extremely small and excellent.

(b) #Thermal properties: All conventional general-purpose films cannot withstand high-temperature boiling or retort processing, making them unsuitable for sterilization. For example, when retort processing is performed, the conventional films are It will be destroyed and ruptured, and all functions will be lost. In contrast, the film of the present invention can be subjected to heat treatments such as boiling and retorting, and exhibits excellent usefulness as a heat-shrinkable film.

(c) Printability: Each of the above conventional films has its own drawbacks in terms of pinhole formation due to halftone printing, adhesion with a wide variety of inks, and the like. For example, polyvinyl chloride film has a large number of ink pinholes due to gel-like substances, and when the film is processed continuously, pinholes existing in the middle of the long film must be removed by inspection. The effort required for this quality inspection significantly reduces the actual operating rate during processing. Moreover, after removing the pinhole part, it will be fixed with adhesive tape to add it.
This portion becomes thicker, and in the case of a long rolled product, not only the existence of the seam portion itself becomes a problem, but also the problem that the thick portion deforms several layers of the film.

Furthermore, seasonal temperature changes after the film is printed, especially shrinkage over time due to long-term storage, would normally be a problem, requiring distribution using refrigerated trucks or low-temperature warehouses, but the present invention eases these restrictions. succeeded in doing so.

(d) Craze: Film craze during and after heat shrinkage does not occur in the present invention. In particular, crazes do not occur even after boiling or retorting.

(e) Problems with industrial waste In recent years, the use of plastic bottles in addition to glass bottles has rapidly spread. When considering the recovery of such bottles, it is preferable that they be made of a homogeneous material, and it is advantageous in this respect to apply the film of the present invention to the packaging of polystyrene bottles.

Furthermore, the film of the present invention does not generate harmful gases such as chlorine gas during heat shrinkage. Particularly in recent years, heat-shrinkable films have attracted attention for their simple packaging, bundling properties, and adhesion properties, and are being widely used as automated, resource-saving packaging, but the fact that they do not emit harmful gases is also important. It becomes a requirement.

(f) Shrinkage unevenness: The film of the present invention has a large shrinkage rate and high shrinkage stress,
Even during the secondary heating, if the heating continues, the material will show a tendency to shrink, so no shrinkage spots will occur.

Examples will be described below, and the measurement methods used in the examples are as follows.

1. Haze Measured based on JIS-K f3714.

2. The distance between the heat shrinkage sample marks is 200 mm, and the film is 15 mm wide.
It was cut into mm pieces and measured at each temperature.

For heating, hot air at 80°C and 100''O was used for 1 minute each.

3. Longitudinal Heat Shrinkage The temperature was gradually changed from the minimum temperature of 50°C to 150°C, and the heat shrinkage rate was measured for each. By plotting each data, the temperature exhibiting the lowest thermal contraction was determined.

4. Birefringence index One-plane orientation coefficient The refractive index in each of the vertical, horizontal, and thickness directions was measured using an Abbe refractometer.

5. Impact strength using a pendulum impact tester (Toyo Seiki Rui), 23
It was seasoned at 165% RH and measured for 24 hours.

6. Durability against bag breakage: 180 mm long and 120 mm wide 7) A bag was made, 1 & oml of water was put into the bag, and the bag was sealed. The bag was allowed to fall naturally at different heights and the breakage of the bag was investigated.

Items that burst at a height of 40 cm or less: “Fragile” 40~? 5c
Items that rupture at m: "poor" or "slightly inferior" items that rupture at 75-80cI11: "good" at 90cm
Items that rupture under the above conditions: "Excellent" [Example] Example 1 and Comparative Examples 1 to 3 Polyester-based polymer of polyethylene (tele/iso) phthalate copolymer (tele/iso ratio = 78/22) with intrinsic viscosity Polymerize to 0.80di/g, and add 2
A melt-extruded unstretched film was prepared by mixing 0.04% (by weight) of silicon oxide.

The film was stretched 1.2 times in the machine direction, then 4.2 times in the transverse direction, and then cooled while being stretched about 20% in the transverse direction to have a birefringence of 98X10- with the transverse direction being the main shrinkage direction.
3, plane orientation coefficient is 31×10-3.80℃ and 100
Thickness 4 whose heat shrinkage rate at °C is 52% and 72%, respectively.
07zm heat-shrinkable polyester film obtained had a minimum longitudinal heat shrinkage rate of 4.1% at 87°C. Table 1 shows the results of comparing the properties of this film with those of typical heat-shrinkable films conventionally used. In the same table, Comparative Example 1 is a polyvinyl chloride film, Comparative Example 2 is a polyethylene film, and Comparative Example 3 is a polystyrene film.

The films of Comparative Examples in Table 1 did not exhibit the "temperature that gave the minimum longitudinal heat shrinkage rate", but simply had a tendency that the lower the temperature, the lower the heat shrinkage rate. On the other hand, the film of the present invention effectively exists at a temperature at which it exhibits the minimum longitudinal heat shrinkage rate (direction perpendicular to the main shrinkage direction), and when used for coating purposes, it provides a beautiful appearance. When each of the above films was formed into a tube shape by aligning the height direction of the plastic bottle with the longitudinal direction of the film, and this was placed over the bottle and heat-shrinked at 87℃, there was no significant dimensional change in the height direction of the bottle. The invented film had the smallest and most uniform finish. The comparative film had an asymmetrical appearance. When the film was subjected to retort treatment, large shrinkage and melting phenomena were observed in some parts of the comparative example, and bag breakage or local tearing was observed.

Example 2 and Comparative Example 4.5 Polyethylene containing 80 mol% of terephthalic acid residue (tere/
An iso)phthalate copolymer and a 60 mol% polyethylene (tele/iso)phthalate copolymer are mixed in a ratio of 90% (by weight) of the former and 10% (by weight) of the latter, based on the total weight of the mixture. 0.05% (by weight) of silicon dioxide was mixed therein.

Then it was stretched in the longitudinal direction at 78°C (conditions are shown in Table 2).
Then, after heating to 120° C. in the transverse direction, it was stretched in the transverse direction. After stretching, continue at 60°C while maintaining 20% elongation.
The film was cooled to a temperature of 50%, then subjected to a 5% relaxation treatment, and then wound up after cooling. The obtained film was 30J1. After applying corona discharge treatment to both sides of the stretched film, each film was formed into a tube using a polyurethane adhesive mixed with a curing agent.

Comparative Examples 4 and 5 in Table 2 are films with a longitudinal stretching ratio of 2.5 times and 3.5 times, and have a large shrinkage rate in the longitudinal direction and a shrinkage ratio in the main direction (
The temperature/degree range for obtaining sufficient shrinkage (in the transverse direction) does not match the temperature range in which the heat shrinkage rate in the direction perpendicular to the main direction (vertical direction) shows the minimum value, and the latter heat shrinkage rate exceeds 15%, and in the same practical test as in Example 1, the finish was extremely poor.

Example 3 A copolymerized polyester consisting of polyester/polycyclohexane dimethyl phthalate consisting of an acid component containing 90/10 mol% of terephthalic acid/isophthalic acid and an alcohol component containing 50,750 mol% of ethylene glycol/cyclohexane dimetatool was prepared with an intrinsic viscosity of 0.70dJl/g
After polymerizing to become
An unstretched film with a thickness of 178 gm was formed, then stretched 1.3 times in the machine direction at 85°C, and then stretched at 110° in the transverse direction.
The film was formed by stretching 4.5 times at 0°C and further stretching 15% in an atmosphere at 50°C. The finished film has a thickness of approximately 3
01Lm stretched film, and the properties are as shown in Table 3.

Example 4 Terephthalic acid/isophthalic acid/orthophthalic acid is 85/
An unstretched film was formed in the same manner as in Example 1 using a copolyester polymer consisting of an acid component of 1015 (mol%) and a glycol component of 8°/20 (mol%) of ethylene glycol/diethylene glycol. An unstretched film was obtained.

Next, it was stretched 1.8 times in the machine direction at 85°C, and then stretched 4.0 times in the cross direction at 150°C. Subsequently, it was stretched at 65° C. by 50% in the transverse direction and simultaneously relaxed by 30% in the longitudinal direction, and then cooled. The resulting film had a thickness of 35 pm and was a very favorable film having a high heat shrinkage in the transverse direction and at the same time a very low heat shrinkage in the machine direction. The characteristics are shown in Table 3.

Table 3 The small length M) was removed from the entire circumference.

[Effects of the Invention] Since the film of the present invention is configured as described above, it exhibits stable heat shrinkability in a specific direction, and can provide a beautiful and strong packaging state in covering packaging or bundling packaging. It also has various effects such as improved printing pitch stability, improved heat resistance, and improved impact strength, and can exhibit excellent utility value in a wide range of fields.

Claims (5)

[Claims] (1) Heat shrinkage rate at 80℃ is 30% or more, 100℃
A heat-shrinkable polyester film having a heat shrinkage rate of 50% or more, and a heat shrinkage rate in a direction perpendicular to the shrinkage direction that reaches a minimum value in a temperature range of 80±25°C. . (2) Polyester film has a glass transition temperature of 35
℃ or higher, a copolyester polymer, and a mixture of the polymer and at least one other polymer. The heat-shrinkable polyester film according to item 1. (3) The heat-shrinkable polyester film according to claim 1 or 2, which has a planar orientation coefficient of 100×10^-^3 or less. (4) A mixture or copolyester film of two or more polyesters in which aromatic dicarboxylic acid residues account for 30 to 90 mol%, and the heat shrinkage rate in one direction is 3.
0% or more, the heat shrinkage rate in the direction perpendicular to this is 15% or less, and the plane orientation coefficient is 100 x 10^-^3 or less. heat-shrinkable polyester film. (5) Maximum value of heat shrinkage stress at 80℃ is 0.95~
5kg/mm^2, maximum value is 1.0~ at 100℃
The heat-shrinkable polyester film according to any one of claims 1 to 4, which has a heat-shrinkable polyester film of 5 kg/mm^2.