JPH0618903B2 - Heat-shrinkable polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention exhibits a heat-shrinkable polyester film (including a sheet, the same applies hereinafter) which exhibits particularly suitable properties in the field of packaging materials such as coating and binding. It is about.

(Prior Art) A tube-shaped body formed of a heat-shrinkable plastic film is, for example, a container, a bottle (including a plastic bottle), a can-bar-shaped material (pipe, bar, wood, various bar-shaped materials).
Etc. (hereinafter referred to as "containers") for covering or bundling, especially covering some or all of these caps, shoulders, trunks, etc. for marking, protection, bundling, improvement of commercial value, etc. In addition to being used for the purpose, it is widely used in fields such as boxes, bottles, plates, sticks, notebooks, etc., such as integrated packaging or skin packs that are closely attached to objects to be packaged. It is expected that the application will be expanded by utilizing.

Conventionally, a heat-shrinkable film such as polyvinyl chloride, polystyrene, polyethylene, or rubber chloride has been used for the above-mentioned applications, and the heat-shrinkable film is made into a tube-shaped body and then covered with the above-mentioned containers or heat-shrinked by integrated packaging.

However, these films have poor heat resistance and have a drawback in that they cannot be maintained in a film-like state by melting or bursting when subjected to boil treatment or retort treatment.

Furthermore, in applications that require printing, printing pinholes (fine irregularities based on the texture due to additives in the film and gel of polymer) may be seen due to poor ink transfer, or even if printing is successful, There is also a problem that the film shrinks (shrinks at room temperature) and causes a dimensional change in the printing pitch. On the other hand, a tube using a polyester-based heat-shrinkable film has been made on a trial basis until now, but the heat-shrinkage rate in the desired direction cannot be sufficiently increased, and There is a problem that the heat shrinkage in the direction orthogonal to the above cannot be reduced, and it is difficult to develop the above-mentioned application.

(Problems to be Solved by the Invention) The above-mentioned conventional techniques using general-purpose heat-shrinkable films such as polyvinyl chloride, polystyrene, and polyethylene have the following problems.

(a) Deficiency of uniaxial shrinkage close to perfection While having a large shrinkage in one direction, it is ideally unsuitable for the above conventional film in applications where it is ideally not to shrink in the direction at right angles to this. . 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 contraction in the vertical direction, but if the film is simply oriented in the horizontal 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 is easily fibrillated, so the strength is weakened. Considering that 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 having a very small shrinkage in a specific temperature range, but a sufficiently large shrinkage in the direction perpendicular to the film.

(b) Insufficient heat resistance None of the above-mentioned 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 destroyed and burst during the treatment, and all the functions are lost. Therefore, it is desired to provide a heat-shrinkable film which can withstand the boil treatment and the retort treatment.

(c) Poor printability With respect to the generation of pinholes due to halftone printing, adhesion to various inks over a wide range, etc., the conventional films described above have their own drawbacks. For example, polyvinyl chloride tends to cause ink pinholes 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 items, and the labor and reworking due to sampling will significantly reduce the actual operation rate. 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 shape after cutting, and it will be necessary to join it with an adhesive tape. For this reason, a seam is inserted, and a defective product is generated due to the influence of the seam in the part and the front and back, and the defective package must be removed during the process. Further, in high-precision printing, the print pitch is reduced (shrinkage over time) due to the shrinkage of the film after printing, and furthermore, it is difficult to manage because it constantly changes under the flow temperature condition. 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 does not change with time after printing.

(d) Generation of craze Polystyrene is apt to cause craze and has poor chemical resistance.
Therefore, the printed surface is easily soiled by chemicals 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 recovered and reused especially when a different film such as polyvinyl chloride or polystyrene is used for coating the polyester bottle.

In addition, 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 unevenness The heat shrinkage of the conventional film described above tends to lack homogeneity. When heat is applied to form separate areas where sufficient shrinkage and insufficient shrinkage occur, heat is applied again. However, further re-contraction does not occur, and the surface has uneven unevenness. Therefore, it is desired to provide a heat-shrinkable film which does not cause shrinkage spots. On the other hand, polyethylene terephthalate film suffers from high oriented crystallinity and impairs low temperature shrinkability, resulting in insufficient shrinkage, which causes shrinkage unevenness.

The present invention has been made in view of such circumstances, and an object thereof is to provide a polyester film which does not have the defects as described in the above (a) to (f).

(Means for Solving the Problem) The present invention is a film comprising a copolyester having terephthalic acid and ethylene glycol as main components and a naphthalene dicarboxylic acid derivative as a copolymerization component. A heat-shrinkable polyester film characterized in that the heat shrinkage in hot air is 30% or more in at least one of the longitudinal direction and width direction of the film, and the heat shrinkage residual stress retention time is 2 minutes or more. is there.

The heat-shrinkable polyester of the present invention contains terephthalic acid and ethylene glycol as main components and a naphthalene dicarboxylic acid derivative as a copolymerization component, and the naphthalene dicarboxylic acid derivative is preferably in the range of 1 to 50 mol%. It is particularly preferably 5 to 40 mol%. If the naphthalene dicarboxylic acid content is less than 1 mol%, the retention time of residual stress when heat-treated at 100 ° C. becomes short, and, for example, when coating a bottle, unfavorable phenomena such as loosening of shoulder due to sterilization treatment. Cause. On the other hand, if it exceeds 50 mol%, the effect of improving the residual stress retention time at the time of heat treatment is saturated, and the amorphous property is promoted, and the heat resistance is lost.

The following are mentioned as a naphthalene dicarboxylic acid derivative. 1,2 naphthalene dicarboxylic acid, 1,3 naphthalene dicarboxylic acid, 1,4 naphthalene dicarboxylic acid, 1,5 naphthalene dicarboxylic acid, 1,6 naphthalene dicarboxylic acid, 1,7 naphthalene dicarboxylic acid, 1,8 naphthalene dicarboxylic acid,
2,3 naphthalene dicarboxylic acid, 2,4 naphthalene dicarboxylic acid, 2,5 naphthalene dicarboxylic acid, 2,6 naphthalene dicarboxylic acid, 2,7 naphthalene dicarboxylic acid, 2,8 naphthalene dicarboxylic acid, or lower alkyl ester thereof can be exemplified. . Particularly preferred are 1,5 naphthalenedicarboxylic acid and 2,6 naphthalenedicarboxylic acid.

The polyester copolymer of the present invention can be produced by a conventional polyester production method. For example, the method may be a direct esterification method using terephthalic acid, naphthalene dicarboxylic acid and ethylene glycol, or a method for producing by a transesterification method of dimethyl terephthalate and naphthalene dicarboxylic acid dimethyl ester and ethylene glycol. Good.

Further, the polyester copolymer in the present invention may be one produced by blending a copolymer within the scope of the present invention and a copolymer outside the scope of the present invention with a homopolyester or another copolyester, wherein the naphthalene dicarboxylic acid is 1 to 5
It may be produced by any method within the range of 0 mol%.

The polyester copolymer in the present invention contains terephthalic acid as an acid component as a main component and naphthalenedicarboxylic acid as a copolymerization component, but other acid components may be copolymerized within a range that does not significantly change the properties thereof. For example, aliphatic dibasic acids such as adipic acid and sebacic acid, and aromatic compounds such as isophthalic acid, diphenyldicarboxylic acid, 5-tertiarybutylisophthalic acid, and 1,1,3 trimethyl 3-phenylindane 4,5dicarboxylic acid. The dibasic acid can be exemplified. Similarly, the glycol component contains ethylene glycol as a main component, but may be copolymerized within a range that does not change their properties.
For example, diethylene glycol, propylene glycol,
Aliphatic diols such as butanediol, hexanediol, 1,4 cyclohexanedimethanol, xylylene glycol, bis (4-beta-hydroxyphenyl) sulfone, 2,2 (4-hydroxyoxyphenyl) propane derivatives, etc. A diol can be illustrated.

If necessary, a lubricant such as titanium dioxide, fine particle silica, kaolin or calcium carbonate may be added, and an antistatic agent, an antiaging agent, an ultraviolet ray inhibitor, a dye or the like as a colorant may be added. . The intrinsic viscosity of the film base material is preferably 0.50 to 1.3 dl / g.

A film obtained by any method such as an extrusion method or a calendering method using such a polymer is stretched in one direction from 2.5 times to 7.0 times, preferably 3.0 times to 6.0 times, And 1.0 to 2.0 times or less, preferably 1.1 to 1.8 times. Stretching in the first direction is carried out to obtain a high heat shrinkage ratio, and stretching in the direction orthogonal to the first direction is effective in terms of impact resistance and tear resistance of the film stretched in the first direction. It is extremely effective in resolving badness.

However, if it is stretched over 2.0 times, the thermal shrinkage in the direction perpendicular to the main shrinkage direction becomes too large, and the finished product becomes wavy. To suppress this waviness, the heat shrinkage rate should be 15
% Or less, preferably 8 to 9% or less, more preferably 7
% Or less is recommended. The stretching means is not particularly limited, and roll stretching, long gap stretching, tenter stretching and the like can be applied, and the shape can be flat, tube or the like.

Stretching is performed by successive biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. The film of the present invention is stretched uniaxially in the longitudinal direction, uniaxially in the transverse direction, biaxially in the longitudinal and transverse directions, and particularly in the biaxial stretching, the longitudinal or transverse stretching is carried out either one by one, the successive biaxial stretching. Is effective, and either order may come first. When the simultaneous biaxial stretching method is performed, the stretching order may be vertical-horizontal simultaneous, vertical-first, or horizontal-first. The heat setting in these stretchings is carried out according to the purpose, but it is recommended to pass a heating zone of 30 to 150 ° C for about 1 to 30 seconds in order to prevent dimensional change under high temperature in summer. Further, before or after such a treatment, one or both of them may be stretched up to 70%. 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.

In order to exhibit the preferred characteristics of the present invention, not only the above draw ratio but also the average glass transition temperature of the polymer composition
Preheating and stretching at a temperature of (Tg) or higher, for example, Tg + 80 ° C. are also effective means. In particular, the treatment temperature in the main-direction stretching (main shrinkage direction) suppresses the heat shrinkage ratio in the direction perpendicular to the direction, and as described above, 80%.
It is extremely important to have the minimum value in the temperature range of ± 25 ° C. Further, after stretching, the film is cooled while applying tension to the film while keeping it stretched or tensioned, or further cooled, so that the pre- and post-treatment properties become better and more stable.

The plane orientation coefficient of the film thus obtained is 100 × 1.
It is preferably 0 ^-3 or less. Plane orientation coefficient is 100 × 10
^If it exceeds ^-3 , it tends to be destroyed by an external shock,
This is because even a small amount of injury makes it easy to tear. On the other hand, the birefringence is preferably 15 × 10 ^{−3 to} 160 × 10 ⁻³ , and if the birefringence is less than 15 × 10 ⁻³ , the longitudinal thermal shrinkage and shrinkage stress are insufficient, and 160 × 10 ⁻³ is set. If it exceeds the range, the scratch resistance and impact strength will decrease, and the usefulness will decrease in practice even if the film is not used.

The thickness of the film of the present invention is practically in the range of 6 to 250 μm.

The film of the present invention needs to retain residual stress for 2 minutes or more when heat-treated at 100 ° C. in hot air after being relaxed by 50%. More preferably, it is held for 4 minutes or more. If the retention time of the residual stress is short, secondary tarmi occurs, and for example, when the bottle is coated, a phenomenon such as loosening of the shoulder portion due to sterilization occurs, which is not preferable.

The film of the present invention will be described below from the viewpoint of use. Packaging applications,
In particular, boil processing and retort processing are performed 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, has a good appearance of the original film, and has a good finish due to heat shrinkage, and has a heat shrinkage stress higher than that of PVC, It has excellent properties.

Therefore, it is possible to carry out a strong covering or bundling wrapping that does not cause the heavy load or the deformed molded product to be overloaded. In addition, at the heat shrinkage level of 50 to 70% required for packaging, the heat shrinkage in the direction perpendicular to the main shrinkage direction exhibits a minimum value, so that the heat shrinkable package shrinks from the initial stage of heat shrinkage. The process until completion is the temperature range (80
Heat shrinkage will occur at ± 25 ° C. As a result, the feature that the error of the finished size becomes small was obtained.

In the case of packaging that uses heat shrinkability, it is common to continue heating after completion of heat shrinkage (even if it has a capability of shrinking even more even if it adheres well to the object to be packaged). This is an important step in dealing with numerous product variations and achieving full shrinkage. At this time, if the shrinkage capacity of the film has reached saturation, the film is linearly expanded in the opposite direction due to the heating that is being performed continuously, and despite the fact that the film is contracted tightly, There is a problem that loosening will occur.
In the present invention, in order to prevent such a situation, it is recommended to increase the shrinkage stress and, as described above, further stretch after stretching. At this point, the meaning of orientation in the present invention exists.

The details will be described below.

(a) Unidirectional shrinkage One of the roles of the shrinkable 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 of the present invention has a high shrinkage ratio and a high impact resistance, so that a beautiful package can be obtained, and further, it has excellent durability in terms of protection of an article to be packaged. This tendency is proved by the drop bag test. Also, due to the near-unidirectional shrinkage, 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 sterilization treatment is inappropriate, and the film is destroyed during the treatment and loses its function. The film exhibits excellent usefulness as a heat shrinkable film that can be subjected to boil or retort treatment.

(c) Printability Conventional films have inherent drawbacks with respect to the generation of pinholes and adhesiveness with ink due to halftone printing, but the polyester film has chemical resistance and adhesiveness when made into a copolymer. And the printability was improved.

(d) Industrial waste problem In recent years, the use of plastic bottles is rapidly spreading.
When considering the recovery of such a bottle, it is preferable that the bottle is formed of the same material, and it is advantageous to apply the film of the present invention to the packaging of the polyester bottle.

(e) Shrinkage unevenness The film of the present invention has a large shrinkage ratio and a high shrinkage stress,
Even in the secondary heating, if it is heated continuously, it tends to shrink, so that shrinkage unevenness does not occur.

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

1. Haze Measured according to JIS-K 6714.

2. Heat shrinkage The distance between sample marked lines is set to 200 mm and the film width is 15 mm.
The sample was cut into pieces and measured at each temperature. For heating, hot air of 100 ° C. was used for heating for 1 minute.

3. Heat shrinkage stress (kg / mm ² ) Using Tensilon, take a sample piece with a width of 20 mm and a length of 150 mm, and mark a 100 mm mark on the film.
Attach the sample piece to the upper and lower chucks set to mm and
Was treated in hot air, and the maximum shrinkage stress during that time was calculated, and the shrinkage stress was calculated according to the following equation.

Maximum shrinkage force / cross-sectional area = heat shrinkage stress 4. Heat shrinkage residual stress retention time (at the time of 50% relaxation) Using Tensilon, create a sample piece in the same way as the heat shrinkage stress, and mark 100 mm on the film of the sample piece. Then, the upper and lower chucks set to 50 mm are accurately fitted with the marked lines of 100 mm, and treated in hot air at 100 ° C. to find the residual stress after the time until the shrinkage stress becomes 0 or after 10 minutes. 10
When the post-minute stress is retained, it is calculated in the same manner as the heat shrinkage stress.

Example 1 Using a stainless steel autoclave, 60 mol% of terephthalic acid and 40 mol% of 2,6 naphthalenedicarboxylic acid were used as dibasic acid components, 210 mol% of ethylene glycol was used as a glycol component, and antimony trioxide of 0.1% was used as a catalyst. Polycondensation was carried out by the direct esterification method using 025 mol (relative to the acid component). This copolymer has an intrinsic viscosity of 0.
It was 71 dl / g. This polyester was melt extruded at 290 ° C. to obtain an unstretched film having a thickness of 180 μm.
The film was stretched 1.2 times in the machine direction and then 4.1 times in the cross direction, and then cooled under elongation in the cross direction by about 20% to obtain a heat-shrinkable film having a thickness of 40 μm. The birefringence index and the plane orientation coefficient of the obtained film are 75 ×, respectively.
It was 10 ⁻³ and 52 × 10 ⁻³ . The physical properties of this film are shown in Table 1. As shown in Table 1, a high shrinkage rate was obtained, and a result that the heat shrinkage residual stress retention time was sufficiently long was obtained, and a good result was obtained in a practical test.

Examples 2 to 5 In the same manner as in Example 1, heat-shrinkable films made of polyester having the composition shown in Table 1 were obtained. The characteristic values of the heat shrinkable film thus obtained are shown in Table 1. Both of the heat-shrinkable films were satisfactory in both the heat shrinkage rate and the heat shrinkage residual stress retention time, and good results were obtained in the practical test.

Comparative Examples 1 to 3 Polyester films having the compositions shown in Table 1 were obtained in the same manner as in Examples. Comparative Example 1 is a film obtained from ordinary polyethylene terephthalate. Comparative Example 2 is a copolyester obtained by copolymerizing 10 mol% of isophthalic acid as a dibasic acid component. Comparative Example 3 is a copolyester obtained by copolymerizing 80 mol% of naphthalene dicarboxylic acid as a dibasic acid component. The heat-shrinkable films obtained in Comparative Examples 1 and 2 have a high shrinkage ratio in the transverse direction and are practically sufficient, but the residual stress retention time is short, and secondary talmi occurs due to boil treatment or retort treatment. Because of this, it could not be put to practical use. Also, the heat shrinkage in the vertical direction was high, and the finish was poor in practical tests.

The heat-shrinkable film of Comparative Example 3 could not obtain a sufficient heat-shrinkage rate.

(Effect of the invention) Since the film of the present invention is configured as described above, stable heat shrinkability in a specific direction is exhibited, and a beautiful and strong packaging state can be provided in a coated packaging,
It has various effects such as stability and heat resistance improvement of printing pitch, and can exhibit excellent utility value in a wide range of fields.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location // B29K 67:00 B29L 7:00 4F C08L 67:00 (72) Inventor Osamu Makimura Tsuruga, Fukui Prefecture Masami Kobayashi (56) Reference Examiner, Tsuruga Branch, Toyobo Co., Ltd. Research Institute, Toyobo Co., Ltd. (56) Reference JP-A-63-27235 (JP, A)

Claims (2)

[Claims] 1. A film comprising a copolyester having terephthalic acid and ethylene glycol as main components, and a naphthalene dicarboxylic acid derivative as a copolymerization component, wherein the polyester film has a heat shrinkage ratio in hot air of 100 ° C. Is 30% or more in at least one of the longitudinal direction and the width direction of the film, and the heat-shrinkable residual stress retention time is 2 minutes or more. 2. The naphthalenedicarboxylic acid derivative is 1 to 50.
The heat-shrinkable polyester film according to claim 1, which is a copolyester consisting of mol%.