JPH06339991A - Production of heat-shrinkable polyester-based film - Google Patents

Abstract

PURPOSE:To provide a film having heat-shrinkable properties stabilized in the specified direction by setting the rate of heat shrinkage of the specified temperature in the specified numerical value or more in at least either of the longitudinal direction and the cross direction and also stretching the film so that the rate of shrinkage in the point of intersection is regulated to the specified numerical value or more. CONSTITUTION:A heat-shrinkable polyester-based film is applied to the various wrapping materials and formed of composition containing copolymerized polyester which incorporates terephthalic acid and ethylene glycol as a main component. In the case, the rate of heat shrinkage of the film in hot air of 100 deg.C is set in >=30% in at least either of the longitudinal direction and the cross direction. The film is so stretched that the rate of shrinkage in the point of intersection is regulated to >=5%. By the way, the film is preheated at the temperature not lower than Tg of the composition containing copolymerized polyester and at the temperature not higher than (Tg+80 deg.C). Thereafter the film is stretched at the temperature not lower than (Tg+75 deg.C) which is lower than the preheating temperature in 9/10 and below of the whole stretching process region and stretched at the temperature not higher than (Tg+60 deg.C)which is lower than the stretching temperature in 1/10 or more of the others while exceeding four times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat-shrinkable polyester film (including a sheet) which exhibits particularly preferable properties in the field of packaging materials for coating, binding, and packaging.
The same shall apply hereinafter).

[0002]

BACKGROUND ART A tube-shaped body formed of a heat-shrinkable plastic film is, for example, a container, a bottle (including a plastic bottle: the same applies hereinafter), a can, a long object (pipe, rod, wood, various rod-shaped bodies). Etc.) etc. (hereinafter abbreviated as containers)
For covering, bundling or exterior use, particularly covering a part or the whole of these caps, shoulders, trunks, etc.,
In addition to being used for the purpose of marking, protection, bundling, improvement of commercial value, etc., fields such as boxes, bottles, plates, sticks, notebooks, etc., such as integrated packaging or skin packs, etc. It is widely used in Japan and is expected to be used for applications utilizing shrinkage and shrinkage stress.

Conventionally, a heat-shrinkable film such as polyvinyl chloride, polystyrene, polyethylene, or hydrochloric acid rubber has been used for the above-mentioned applications, and this is made into a tube-shaped body and then covered with the above-mentioned containers or heat-shrinked by integrated packaging. It was However, these films have poor heat resistance and have a drawback that they are apt to melt or burst when subjected to boil treatment or retort treatment and the film state cannot be maintained. Furthermore, in applications that require printing, the occurrence of printing pinholes (fine irregularities based on the fisheye due to additives in the film and gel of polymer) is observed due to poor ink transfer,
Even if the printing could be performed successfully, there is a problem that the shrinkage of the film (normal temperature shrinkage) gradually progresses to cause a dimensional change in the printing pitch.

That is, the above-mentioned conventional techniques using general-purpose heat-shrinkable films such as polyvinyl chloride, polystyrene, and polyethylene have the following problems. (a) Lack of near-uniaxial shrinkage In conventional applications where it is ideal that even if a large shrinkage in a certain direction is exhibited but no shrinkage occurs in the direction orthogonal to this, the conventional film is completely unsuitable. is there. For example, considering the case where a shrink label is attached to the bottle surface by shrinking in the horizontal direction, shrinking in the vertical direction of the label, that is, in the vertical direction of the bottle means that the label shrinks without the label coming to a predetermined position. However, this causes poor appearance. In order to prevent this, it is necessary to reduce the shrinkage in the longitudinal direction, but if the film is simply oriented in the transverse direction for this purpose, it is immediately understood from the common sense of the nature of polymer chemicals. Similarly, it is easy to tear, and it becomes easy to become fibrin, so the strength becomes weak. Considering that the strength in the longitudinal direction is important for preventing bottle breakage especially when the bottle drops, simple unidirectional stretching cannot be said to be a good method. In many other cases, it cannot be used unless it has impact resistance. From such a point, it is desired to develop a film which exhibits a sufficiently large shrinkage in a certain specific direction in a certain specific temperature range, but exhibits an extremely small shrinkage in a direction perpendicular thereto.

(B) Insufficient heat resistance None of the aforementioned conventional films can withstand high temperature boil treatment or retort treatment, and are unsuitable for sterilization treatment. For example, when the retort treatment is performed, the conventional film is broken or ruptured during the treatment, and all the functions of the film are lost. Therefore, it is desired to provide a heat-shrinkable film that can withstand boil treatment and retort treatment.

(C) Poor printability The above-mentioned conventional films have their own drawbacks with respect to the generation of pinholes due to halftone printing and the adhesion to a wide variety of inks. For example, in the case of polyvinyl chloride, ink pinholes are likely to occur due to gel, and in continuous tube processing, pinholes are present in the middle of a long film. If this is supplied to an automatic labeling machine, it will be commercialized with pinholes left, so it will be necessary to finally inspect all products, and the actual operation rate will decrease significantly due to the labor and reprocessing due to sampling To do. If this pinhole defect is to be inspected and removed at the stage after printing is completed, it will be returned to a continuous film after cutting, and it will be necessary to join it with an adhesive tape. Therefore, a seam is formed, and the appearance of the seam part and the part before and after the seam are deteriorated to cause a defective product, and this defective package must be removed during the process. In high-precision printing, the print pitch is reduced (shrinkage over time) due to the shrinkage of the film after printing, and this shrinkage over time constantly encounters difficulty in control under the conditions of flow temperature. Therefore, a polyvinyl chloride shrink film or the like requires a refrigerated vehicle or a low temperature warehouse.
From such a point, it is desired to provide a heat-shrinkable film which enables printing without pinhole defects and which does not change with time after printing.

(D) Generation of Craze Polystyrene film is apt to cause craze and has poor chemical resistance. Therefore, the printed surface is liable to be damaged by the chemical during use. Therefore, a film having excellent chemical resistance and durability is desired. (e) Industrial waste problem In recent years, the amount of plastic bottles used has increased rapidly. Considering the recovery of this bottle, there is a problem that it cannot be recycled for recovery, especially when a different film such as polyvinyl chloride or polystyrene is used for coating the polyester bottle. Furthermore, polyvinyl chloride has a problem of corrosion due to chlorine gas, and a heat-shrinkable film that does not cause waste pollution is desired.

(F) Shrinkage of Shrinkage The heat shrinkability of the above-mentioned conventional film tends to lack homogeneity, and once sufficient and insufficient areas of heat shrinkage are formed separately, heat is applied again. However, further re-contraction does not occur, and the surface has uneven unevenness. Furthermore, the most important point in terms of application is that, in high-speed shrink wrapping and labeling, spots tend to appear in areas where the shrinkage rate increases, and when metallic ink is used, shrinkage spots are apparently improved, but color spots In the case of, the difference in the partial shrinkage ratio after finishing appears as it is. Therefore, a more uniform shrinkage ratio is desired.

In contrast to the conventional film having the above-mentioned problems, a tube using a polyester heat-shrinkable film has been manufactured by trial so far, and has a sufficient heat shrinkage ratio in a desired direction. There is a problem that it can not be made high, and it is not possible to reduce the heat shrinkage in the direction orthogonal to the above direction, and the conventional polyester heat shrinkable film adheres to the packaged object at the large shrinkage part. However, this tendency is strong especially in high-speed packaging that requires high-speed short-time shrinkage. In particular, this phenomenon appears as color spots in the case of metallic printing ink, which is a serious problem in appearance of high quality products. Therefore, it has been difficult to expand to the above applications.

[0010]

The present invention has been made in view of such circumstances, and is a heat-shrinkable polyester film which does not have the defects as described in the above (a) to (f). The purpose of the present invention is to provide a method for producing.

[0011]

The method for producing a heat-shrinkable polyester film of the present invention is a polyester film comprising a copolymerized polyester-containing composition containing terephthalic acid and ethylene glycol as main components. The heat shrinkage in hot air is 30 in at least one of the longitudinal direction and the width direction of the film.
The main point is that the stretching is performed so that the shrinkage percentage at the intersection is 5% or more and the intersection point shrinkage rate is 5% or more.

Further, after the above-mentioned stretching is preheated at a temperature not lower than Tg of the copolymerized polyester-containing composition and not higher than Tg + 80 ° C., 9/10 or less of the entire stretching process area is not higher than Tg + 75 ° C. lower than the preheating temperature. The remaining 1/10 or more is Tg + 60 ° C., which is lower than the stretching temperature, and stretching more than 4 times is a preferred embodiment of the method of the present invention.

[0013]

The constituent material of the heat-shrinkable polyester film according to the method of the present invention is a copolyester having terephthalic acid and ethylene glycol as main components. As the acid component, other than terephthalic acid, for example, adipic acid, sebacic acid, azelaic acid and other aliphatic dibasic acids: isophthalic acid,
Aromatic dibasic acids such as diphenyldicarboxylic acid, 5-tertiary butylisophthalic acid, 2,2,6,6-tetramethylbiphenyl-4,4-dicarboxylic acid: 2,6-naphthalenedicarboxylic acid, 1,1 , 3-Trimethyl-3-phenylindene-4,
Aromatic dibasic acids such as 5-dicarboxylic acids can be copolymerized.

Similarly, as the glycol component, in addition to ethylene glycol, an aliphatic diol such as neopentyl glycol, diethylene glycol, propylene glycol, butanediol, hexanediol, 1,4-cyclohexanedimethanol, xylylene glycol, bis ( 4-β-hydroxyphenyl) sulfone, 2,2- (4
Alicyclic or aromatic diols such as -hydroxyphenyl) propane derivative can be copolymerized.

In addition to terephthalic acid and ethylene glycol, the amount of the above-mentioned copolymerizable component that can be used is 3 in the total composition.
It is preferably in the range of ˜40 mol%. Particularly preferred is 5 to 25 mol%. When the content of the copolymerization component is less than 3 mol%, the retention time of the internal residual stress of the film is shortened during the heat shrinkage treatment. For example, when the film is coated on a bottle, the shoulder portion becomes loose due to shrinkage and subsequent sterilization treatment. Easy to cause undesired phenomenon. On the other hand, the copolymerization component is 4
If it exceeds 0 mol%, the effect of improving the residual stress retention time at the time of heat treatment is saturated, and even if the later-described requirements of the method of the present invention are satisfied, there are drawbacks such as progress of amorphousness and deterioration of carrying resistance. Come on.

The copolymerized polyester itself used in the method of the present invention can be manufactured by a conventional polyester manufacturing method. For example, a method of directly esterifying ethylene glycol or the like with terephthalic acid or the like, or a transesterification method of reacting dimethyl terephthalate or the like with ethylene glycol or the like is shown. Further, the copolyester composition that can be used in the method of the present invention can be produced by blending with the copolyester or homopolyester within the range and out of the range shown above, or with another copolyester, and by controlling these. A more preferable film can be obtained. That is, it was discovered that not only the retention property of the residual shrinkage stress according to the method of the present invention can be improved, but also the shrinkage unevenness originally generated during shrinkage can be reduced because the temperature sensitivity during shrinkage can be adjusted to control the shrinkage rate.

If necessary, a lubricant such as titanium dioxide, fine particle silica, kaolin or calcium carbonate may be added to the copolyester composition used in the method of the present invention. Further, an antistatic agent and an antiaging agent may be added. Further, it is also possible to add an ultraviolet protective agent and a coloring agent (dye etc.). The preferred intrinsic viscosity for forming a film substrate is 0.55 to 1.3 dl / g, preferably 0.58 to 1.2 dl / g, and particularly preferably 0.63 to
It is 1.2 dl / g.

The method of the present invention is for producing a film suitable for high-speed shrinking work, and it is necessary to stretch the film so that the shrinkage ratio at the intersection becomes 5% or more. The shrinkage rate at the intersection is obtained as shown in FIG. 1, and is an internal residual stress curve when an arbitrary shrinkage rate is given to the film and the shrinkage rate after the shrinkage rate is made larger than the shrinkage rate. It is defined as the contraction rate corresponding to the intersection with the curve of the tensile force required to return by tension to the contraction amount corresponding to the contraction rate. Therefore, below this intersection shrinkage ratio, even if the film has color spots or shrinkage spots due to local shrinkage, the internal shrinkage stress is larger than the force for stretching the locally shrunk portion, and the local shrinkage portion temporarily shrinks. Even so, the force to return it always acts,
It is based on the discovery of a very new fact that spots are resolved.

If the intersection shrinkage ratio is less than 5%, internal residual stress is released even by a slight shrinkage.
It does not create the forces mentioned above that modify other contractions. Or, since the internal residual stress that relieves it is lost due to the remarkable shrinkage unevenness, the unevenness once generated cannot be removed. Therefore, the appearance is remarkably lost.

Further, it suffices if only the intersection shrinkage is high, and the object of the method of the present invention cannot be achieved by that alone. This is because the cross-point shrinkage is high in a film having a high degree of rigidity that does not cause heat shrinkage, and the heat shrinkage in hot air at 100 ° C is 30% or more in at least one of the film longitudinal direction and the width direction. It is necessary to manufacture a film that also satisfies the above-mentioned condition of heat shrinkage. On the other hand, in the case of a non-oriented film and a low-oriented film, which generally have low rigidity, the reduction of residual stress is small, and the way of increasing the tensile force with respect to the recovery is low, so that the shrinkage rate at the intersection becomes high. Therefore, it is necessary to manufacture a film satisfying the above-mentioned heat shrinkage, and for that reason, the following stretching method is recommended in the method of the present invention.

In order for the film to exhibit the above-mentioned preferable properties, not only the stretching ratio described below, but also preheating at a temperature not lower than the average glass transition temperature (Tg) of the polymer composition and not higher than Tg + 80 ° C., It is desirable that 9/10 or less of the total stretching step region is stretched at Tg + 75 ° C. or lower lower than the preheating temperature, and the remaining 1/10 or more is stretched at Tg + 60 ° C. or lower lower than the stretching temperature, more preferably Tg + 50 ° C. or lower. This stretching method is suitable for obtaining a unique shrinkage behavior that satisfies the above-mentioned intersection shrinkage and thermal shrinkage. In addition, the treatment temperature in the main-direction stretching (main shrinkage direction) suppresses the heat shrinkage rate in the direction orthogonal to the direction,
Moreover, it is extremely important to bring the minimum value to the temperature range of 80 ± 25 ° C. Further, after the stretching, the film is cooled while applying a stress to the film while keeping the film in a stretched or tensioned state, or further cooled, so that the shrinkage property becomes better and stable.

Regarding the stretching ratio, a film obtained by any method such as an extrusion method or a calendering method using the above-mentioned copolymerized polyester is stretched in one direction from 4 times to 10 times, preferably from 4.6 times to 7.0 times, It is preferable to stretch 1 to 2 times or less, preferably 1.1 to 1.8 times in the direction perpendicular to the direction. It does not matter which order of stretching is first. Stretching in the direction orthogonal to the main stretching direction is effective for further improving the impact resistance and tear resistance of the film obtained by the method of the present invention. However, if it is stretched to more than 2 times, the heat shrinkage in the direction orthogonal to the main shrinkage direction becomes too large, and the finish becomes wavy. To suppress this waviness, the heat shrinkage in the direction perpendicular to the main shrinkage direction should be 15%.
It is recommended that the shrinkage should be within 8-9%, preferably within 8-9%, and most preferably within 5%, or within 5%.

As a stretching method, an ordinary apparatus is used,
Methods such as roll drawing, long gap drawing, tenter drawing, and tuber drawing are applied, and the shape may be flat, tube or the like. Stretching is performed by successive biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, a combination of these, or the like. Further, the film of the present invention is stretched uniaxially in the longitudinal direction, uniaxially in the lateral direction, biaxially in the longitudinal direction and the lateral direction, but particularly 2
Regarding axial stretching, sequential biaxial stretching in which one of the longitudinal and lateral directions is performed first is effective, and the order may be either first. When performing simultaneous biaxial stretching, the stretching order is
Both vertical and horizontal, vertical leading, and horizontal leading may be used. The heat setting in these stretching is carried out according to the purpose, but in order to prevent the dimensional change under high temperature in summer, 30 ° C to 1 ° C.
It is recommended to pass a heating zone of 50 ° C. for about 1 to 60 seconds. Further, before or after such a treatment, a maximum of 70% may be stretched. In particular, it is preferable to extend in the main direction and relax in the non-contraction direction (direction perpendicular to the main contraction direction), and it is better not to extend in the perpendicular direction.

Plane orientation of the film thus obtained
The coefficient is 40 × 10^-3~ 120 × 10^-3The following is preferred
Yes. Plane orientation coefficient is 40 × 10^-3If less than
Incomplete shrinkage, wrinkles, color spots,
Various defects such as slack due to secondary heating are recognized. Further
Not only this, but when or after heat shrink
When subjected to heat treatment such as illness, retort treatment, hot water sterilization, etc.
It becomes cloudy and the appearance deteriorates significantly. On the other hand, 120 × 10^-3Beyond
If this happens, the bottle-breaking prevention effect will be reduced and it will be easier to break,
It is also easy to tear due to external injury. On the other hand, the birefringence is 20 ×
Ten^-3~ 175 × 10 ^-3Is preferred, and the birefringence is 20 × 10^-3
If less than the above, it is difficult to obtain the above-mentioned contraction shrinkage, and wrinkles and metal
The color spots and the like seen in the black ink are not preferable. Again 17
5 x 10^-3If it exceeds, the contraction speed will be too fast and the temperature during heating will be too high.
Unevenness, such as the temperature difference between near and far from the heat source,
Due to the temperature difference between where hot air is likely to hit and where it is not
Due to the coming temperature unevenness, shrinkage unevenness is extremely likely to occur.

The film obtained by the method of the present invention will be described below from the viewpoint of use. Boiling and retorting are used in packaging applications, especially in packaging of foods and beverages.
No existing heat-shrinkable film can withstand these treatments sufficiently. The film of the present invention can withstand heat sterilization by boil treatment or retort treatment, and furthermore, a crater-shaped shrinkage portion due to shrinkage spots that may occur, and color spots of metallic ink are also corrected during heating. It has succeeded in imparting various properties, has a higher heat shrinkage stress than a polyvinyl chloride film, and is excellent in cohesion. Therefore, even in containers having a large diameter ratio, a coated state having uniform adhesion can be obtained, and the same applies to deformed containers. In addition to polyester bottles, it is also possible to shrink plastic bottles such as polyethylene, polypropylene, polyvinyl chloride, and styrene containers at low temperatures so as not to cause thermal deformation, and the film shrinks before the bottle reaches the deformation temperature. Has been completed.

In addition to the above, it is possible to carry out a strong coating or bundling wrapping that does not collapse the load even on heavy objects and deformed molded articles, and at the heat shrinkage rate level of 50 to 70% required for wrapping, the main shrinking direction. Since it has a broad heat shrinkage property that the heat shrinkage ratio in the direction perpendicular to that shows the lowest value, the process from the initial heat shrinkage to the completion of shrink wrapping is performed in the temperature range (80 ± 25 ° C) showing the minimum shrinkage amount. Will be contracted.
As a result, the feature that the error of the finished size becomes small was obtained.

In a package utilizing heat shrinkability, heating is continued after completion of heat shrinkage (a state in which the product is in close contact with the object to be packaged and has the ability to shrink further, but does not shrink further). Has become a common procedure, which plays an important role in dealing with numerous product variations and achieving full shrinkage. The same applies to boil and retort processing. At this time, if the shrinkage capacity of the film has reached saturation and not only this but also the tensile force of the adjacent high shrinkage portion is higher than this residual shrinkage stress, shrinkage spots and color spots that have already occurred are continuous. There is a problem in that the film is not corrected even by heating for a long time, and the film is linearly expanded in the opposite direction, and the film is slackly contracted even though it is contracted tightly. In the method of the present invention, in order to prevent such a situation, not only the contraction stress is simply increased, but also the residual retention level of the contraction stress is increased, and the adjacent high contraction portions are stretched from the contraction stress. The heat-shrinkable film completed could be manufactured by setting the holding level to be sufficient.

A more specific description will be given below. (a) Unidirectional shrinkage: One of the roles of the shrink film is to prevent the package from being broken or the load from falling, but for that purpose it has high impact resistance and large shrinkage in the main direction. It is necessary to get a rate. In that respect, the film obtained by the method of the present invention has a high shrinkage ratio and a high impact resistance, so that a beautiful packaging can be obtained and, in addition, it exhibits excellent durability in terms of protection of the article to be packaged. This tendency is evidenced by drop tests on containers. Also, near-unidirectional shrinkage is extremely reliable by stretching in the main stretching direction 4 times or more, and even in containers having a large dimensional ratio, the finished dimensional stability after shrink-wrapping is good.

(B) Heat resistance: None of the conventional general-purpose films can withstand high temperature boil treatment or retort treatment, and are not suitable for high temperature sterilization treatment. For example, film tearing, tearing, clouding, etc. occur. Furthermore, it has the property that shrinkage plaques are corrected during the process. On the other hand, the film obtained by the method of the present invention exhibits excellent usefulness as a heat-shrinkable film which can be boiled or retorted.

(C) Printability: Conventional films have inherent disadvantages such as pinhole formation due to halftone printing and adhesion to ink, but the polyester film obtained by the method of the present invention has chemical resistance. The printability was improved because the adhesiveness was improved by using a copolymer.

(D) Industrial waste problem: In recent years, the use of plastic bottles has been rapidly spreading. Considering the recovery of such a bottle, homogeneity is preferable for stabilizing the quality of the recycled product, and it is advantageous in this respect to apply the film obtained by the method of the present invention to the packaging of a polyester bottle.

(E) Shrinkage unevenness: The film obtained by the method of the present invention has a large shrinkage ratio and a high shrinkage stress, and if continuously heated even in the secondary heating, the shrinkage stress of the excessive shrinkage part is lower than that of the shrinkage part. Since it has a characteristic of being stretch-corrected by, the shrinkage unevenness is not corrected, and therefore the color unevenness of the metallic ink is also eliminated.

[0033]

EXAMPLES Examples will be described below, and the measuring methods used in the examples are as follows. (1) Haze It was measured based on JIS-K 6714. (2) Heat shrinkage rate (%) The distance between sample marked lines is set to 200 mm and the film width is 15 mm.
It cut | disconnected and it measured at each temperature. 80 ℃ and 10 for heating
Each was heated for 1 minute using hot air of 0 ° C.

(3) Cross-point contraction rate (%) A tensilon is used to obtain the heat contraction stress, and the width is 20 m.
Take a sample of m and 150 mm in length and put it on the film 1
The sample piece was attached to the upper and lower chucks with a marked line of 00 mm, which was set to an arbitrary size (L ₁ ) smaller than 100 mm and larger than 50 mm, and treated in hot air at 100 ° C. to shrink the film. The shrinkage force at this time was calculated and the residual shrinkage stress was calculated by the following formula. Shrinkage force / cross-sectional area = residual shrinkage stress The shrinkage ratio at that time was calculated by the following formula. Shrinkage rate = 100 × (100−L ₁ ) / 100 (%)

On the other hand, the tensile stress is 50% after the heat shrinkage in the measurement of the residual shrinkage stress, and the chuck distance is 50%.
Any inter-chair distance L greater than 100 mm and less than 100 mm
_The tensile force required to return to ₂ was calculated, and the tensile stress was calculated by the following formula. Tensile force / cross-sectional area = tensile stress Reexpansion rate = 100 × (L ₂ −50) / 50 (%) A graph showing both the above-mentioned residual shrinkage stress and shrinkage rate, and tensile stress and reexpansion rate (FIG. 1). The contraction rate corresponding to the intersection point obtained from () is defined as the intersection point contraction rate.

(4) Retention time of heat shrinkage residual stress (at the time of 50% relaxation) Using Tensilon, a sample piece was prepared in the same manner as the heat shrinkage stress, a 100 mm marked line was marked on the film of the sample piece, and 50 mm
Accurately fit a 100 mm marked line to the upper and lower chucks set to, and process in hot air at 170 ° C., and determine the residual stress after the time until the shrinkage stress becomes 0 or after 10 minutes. 1
When the stress is retained after 0 minutes, it is calculated in the same manner as the heat shrinkage stress.

Example 1 Using a stainless steel autoclave, 100 mol% of terephthalic acid as a dibasic acid component, 85 mol% of ethylene glycol as a glycol component and 15 mol% of neopentyl glycol as a glycol component, and antimony trioxide as a catalyst. Polycondensation was carried out by the direct esterification method with 0.05 mol (based on the acid component). This copolymer had an intrinsic viscosity of 0.75 dl / g. This polyester was melt extruded at 300 ° C. to obtain an unstretched film having a thickness of 180 μm.

Since the film is stretched in the transverse direction, 130
Preheat at 8 ℃ for 8 seconds, then 88 ℃ half of the total stretching section
The remaining 1/2 area was heated to 80 ° C. and stretched 5.2 times. After the stretching, it was cooled to 40 ° C. while applying a lateral stretching of about 3%. The obtained film is a heat-shrinkable film with a thickness of 40 μm, and has a birefringence index and a plane orientation coefficient of 105 ×, respectively.
It was 10 ^-3 and 68 x 10 ^-3 . The physical properties of this film are shown in Table 1.

Examples 2 and 3 and Comparative Examples 1 and 2 In the same manner as in Example 1, a polyester having the composition shown in Table 1 was added to polyethylene terephthalate (an intrinsic viscosity of 0.8 dl).
/ g) so that the former is 60% by weight and the latter is 40% by weight to prepare a mixed polyester composition. Comparative Example 1 is polyethylene terephthalate having an intrinsic viscosity of 0.6.
Comparative Example 2 is polyvinyl chloride. For Examples 2 and 3, stretching was performed in the same manner as in Example 1. The plane orientation coefficient of the obtained film was 71 × 10 ⁻³ in Example 2 and 6 in Example 3.
0 × 10 ^-3 , the birefringence of the former is 107 × 10 ^-3 , and the latter is 10
It was 4 × 10 ^-3 . In Comparative Example 1, the film was stretched in the transverse direction at 95 ° C to 4.2 times and cooled to 40 ° C. Plane orientation coefficient is 45 × 10 ^-3 ,
The birefringence was 72 × 10 ^-3 . The physical property values are also shown in Table 1. Example 4 and Comparative Example 3 The same raw material composition as in Example 3 was used, and the stretching ratio shown in Table 1 was used, and the other stretching conditions were the same as those in Example 1.
The film of Comparative Example 3 was formed. Table 1 shows the physical properties and the results of the practical test. The surface orientation coefficient is 7 in Example 4.
9 × 10 ⁻³ , Comparative Example 3 had 34 × 10 ⁻³ , and the birefringence was 116 × 10 ⁻³ for the former and 33 × 10 ⁻³ for the latter.

Comparative Example 4 A copolymerized polyester using 100 mol% of terephthalic acid as a dibasic acid component and ethylene glycol (55 mol%) and neopentyl glycol (45 mol%) as a glycol component was used as in Example 1. The film was formed by the method, but the heat resistance of the polyester was low, and the clip was broken in the tenter, so that stable film formation was not possible.

Example 5 1% polyethylene terephthalate was added to the copolymer of Comparative Example 4.
When the composition mixed with 5% by weight was used, the composition could be stretched under the same conditions as in Example 1 and exhibited practically effective characteristics. The plane orientation coefficient is 69 × 10 ^-3 , and the birefringence is 118 × 10 ^-3.
Met. The physical property values are shown in Table 1.

Example 6 Copolyester using 90 mol% of terephthalic acid and 10 mol% of adipic acid as dibasic acid components and 96 mol% of ethylene glycol and 4 mol% of diethylene glycol as glycol components (intrinsic viscosity 0.73 dl / g) was melt extruded to obtain an unstretched film having a thickness of 180 μm. To stretch the film in the transverse direction, preheat at 120 ° C. for 5 seconds,
Then, set the 1/3 zone of the entire stretching section to 85 ° C and leave the remaining 2/3
The zone was brought to 75 ° C. and stretched 5.2 times. After stretching, it was cooled to 35 ° C. with a transverse stretching of about 2%. The obtained film was a heat-shrinkable film having a thickness of 40 μm. The physical properties of this film are shown in Table 1.

Example 7 In Example 6, the composition of the polyester was 100 mol% of terephthalic acid as the dibasic acid component, 60 mol% of ethylene glycol as the glycol component, 20 mol% of 1,4-cyclohexanedimethanol and 20 mol of butanediol. %
A film was obtained in the same manner as in Example 6 except for the above, and the physical properties are shown in Table 1.

[0044]

[Table 1]

As is clear from Table 1, the film obtained by the method of the present invention has a high shrinkage ratio at the intersections, a good residual stress retention property, a low thermal shrinkage ratio in the longitudinal direction and a wrinkle in the high shrinkage portion. And there was no color spot due to metallic ink. The jagged undulations seen in the comparative example were not observed at all on the top and bottom of the label, and there was no vertical tilt or large undulations, and it was possible to cover the shape of the polyester bottle used without any deviation. It was

On the other hand, since Comparative Example 1 has a low intersection shrinkage,
The residual stress retention property was insufficient and could not be put to practical use. Comparative Example 2 is vinyl chloride and is inferior in heat resistance. In Comparative Example 3, the cross-point shrinkage rate is satisfied, but the vertical heat shrinkage rate is high. In a practical test, wrinkles, color spots, and upper and lower wrinkles are observed at the high shrinkage portion in the small diameter portion (neck portion) at the top of the bottle. The product had a poor appearance and could not be used for products.

[0047]

Since the production method of the present invention is constructed as described above, it is possible to produce a film having stable heat shrinkability in a specific direction. Therefore, the obtained film can give a beautiful and strong packaging state in covered packaging and bundling packaging, has various effects such as stability of printing pitch and improvement of heat resistance, and is excellent in a wide range of fields. The utility value can be demonstrated.

[Brief description of drawings]

FIG. 1 is a graph for explaining an intersection shrinkage rate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location B29L 7:00 4F C08L 67:00 (72) Inventor Katsuro Kuse 10-24 Toyo-cho, Tsuruga City, Fukui Prefecture No. Toyobo Co., Ltd. Research Institute, Tsuruga Branch Office

Claims (2)

[Claims] 1. A polyester film comprising a copolymerized polyester-containing composition containing terephthalic acid and ethylene glycol as main components, wherein the heat shrinkage in hot air at 100 ° C. is at least one of the longitudinal direction and the width direction of the film. A method for producing a heat-shrinkable polyester-based film, which comprises stretching so as to have a shrinkage ratio of 30% or more in a direction and an intersection shrinkage ratio of 5% or more. 2. The stretching is performed by preheating at a temperature not lower than Tg and not higher than Tg + 80 ° C. of the copolymerized polyester-containing composition, and then 9/10 or less of the entire stretching process area is maintained at Tg + 75 ° C. lower than the preheating temperature. The manufacturing method according to claim 1, wherein the remaining 1/10 or more is Tg + 60 ° C which is lower than the stretching temperature and is stretched more than 4 times.