JPH0798358B2 - 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 abbreviated as containers) or for bundling, in particular, covering some or all of these caps, shoulders, torso, 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 integrated packaging such as boxes, bottles, plates, sticks, notebooks, etc., where it is closely adhered to the object to be packaged such as skin packs, etc. It is expected to develop applications that utilize stress.

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

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

In applications that require printing, printing pinholes (fine irregularities due to fisheye due to additives in the film and gel of polymer) may occur due to poor ink transfer, or even if printing is successful, Also, there is a problem that the print pitch changes in size even if the film shrinks (shrinkage at room temperature). On the other hand, a tube using a polyester heat-shrinkable film has been manufactured in practice so far, but it is not possible to sufficiently increase the heat shrinkage ratio in the desired direction, or There is a problem that the heat shrinkage in the direction orthogonal to the above cannot be reduced, and it was 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) Absence of near-uniaxial shrinkage The above conventional film is completely unsuitable for applications where it is ideal that it has a large shrinkage in one direction, but does not shrink at all in the direction perpendicular to it. . 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 easily fibrillate, 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 conventional films described above 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 that can withstand boil treatment and retort treatment.

(C) Poor printability With respect to the generation of pinholes due to halftone printing and the adhesiveness with a wide range of various inks, the above-mentioned conventional films have their own drawbacks. For example, in the case of polyvinyl chloride, an ink pinhole due to a gel-like material is likely to occur, and in continuous tube processing, a pinhole exists 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 is 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 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 in the part and the front and back due to the influence of the seam, 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 control 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) Occurrence of craze Polystyrene 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 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 shrinkability of the above-mentioned conventional film tends to lack homogeneity. Once 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 becomes uneven and uneven. Therefore, it is desired to provide a heat-shrinkable film that does not cause shrinkage spots.

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 copolymerized polyester containing terephthalic acid and ethylene glycol as main components and a bisphenol derivative compound represented by the following formula (1) as a copolymerization component. System film, the heat shrinkage in hot air at 100 ℃ is 30% in at least one of the film longitudinal direction and width direction.
The heat-shrinkable polyester film is characterized by the above.

[In the formula, -X- is -CH ₂ -, _{-S -, - SO 2 -,} - represent either O-, l = 0
Or 1, and R represents a C _{1 to} C ₅ alkyl group or a halogen group. R ₁ and R _{2 each} represent a hydrogen atom, an alkyl having 4 or less carbon atoms, or an alkyl derivative. Further, m and n each represent an integer of 1 to 5, and O and P are 0 to
Represents an integer of 4. The bisphenol derivative compound may be used alone or in combination of two or more kinds. The copolymerization amount of the bisphenol derivative compound is preferably in the range of 1 mol% to 50 mol%. When the content of the bisphenol derivative compound is less than 1 mol%, the retention time of residual stress when heat-treated at 100 ° C. becomes short, and for example, when it is coated on 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 upon heat treatment is saturated, and the amorphous property is promoted, and the heat resistance is lost. It is preferably 5 to 40 mol% copolymer.

The polyester copolymer of the present invention can be produced by a conventional polyester production method. For example, a method by a direct esterification method using terephthalic acid, ethylene glycol and a bisphenol derivative may be used, or a method by a transesterification method between dimethyl terephthalate, a bisphenol derivative and ethylene glycol may be used.

Further, the polyester copolymer in the present invention may be one produced by blending the copolymer within the scope or outside the scope of the present invention with polyethylene terephthalate or other copolymerized polyester, and the bisphenol derivative compound is 1 to 50. It may be produced by any method within the range of mol%.

Examples of the bisphenol derivative compound are 2,2bis (carboxymethoxyphenyl) propane, 2,2bis (2carboxyethoxyphenyl) propane, 2,2bis (3carboxypropoxyphenyl) propane, 2,2bis (4carboxybutoxyphenyl). Propane, 2,2 bis [3,5 dimethyl (carboxymethoxy) phenyl] propane, 2,2
[Bis3,5dimethyl (2carboxyethoxy) phenyl] propane, 2,2bis [1methyl, 5ethyl (carboxymethoxy) phenyl] propane, bis (carboxymethoxyphenyl) sulfone, 2,2bis [3,5dibromo] (Carboxymethoxy) phenyl] propane, bis [3,
5 dibromo (carboxymethoxy) phenyl] sulfone, 2,2bis [3,5diethyl (carboxymethoxy) phenyl] propane, bis (carboxymethoxyphenyl)
Ether, bis (carboxymethoxyphenyl) thioether, (4carboxymethoxy) diphenyl, bis (carboxymethoxyphenyl) methane, bis [3,5dimethyl (4carboxymethoxy) phenyl] sulfone,
Examples include 2,2 bis [3,5 diethyl (4carboxymethoxy) phenyl] propane, bis [3,5diethyl (4carboxymethoxy) phenyl] sulfone, and their methyl esters, ethyl esters, propyl esters, It may be butyl ester or 2-hydroxyl ethyl ester.

The heat-shrinkable polyester of the present invention contains terephthalic acid as an acid component as a main component and a bisphenol derivative as a copolymerization component, but other acid components may be copolymerized within a range that does not significantly change their properties. For example, aliphatic dibasic acids such as adipic acid, sebacic acid, azelaic acid, isophthalic acid, diphenyldicarboxylic acid, 5-tert-butylisophthalic acid, 2,2,6,6 tetramethylbiphenyl 4,4 dicarboxylic acid , 2,6 naphthalenedicarboxylic acid, 1,1,3 trimethyl-3 phenylindene 4,5 dicarboxylic acid, and other aromatic dibasic acids. Similarly, the glycol component is mainly composed of ethylene glycol, but other components may be copolymerized within a range that does not significantly change their properties. For example, aliphatic diols such as diethylene glycol, propylene glycol, butanediol, hexanediol, and neopentyl glycol, 1,4 cyclohexanedimethanol, xylylene glycol, bis (4-beta-hydroxyphenyl) sulfone, 2,2 (4 Examples include oxyphenyl-propane derivative diols.

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 proper intrinsic viscosity as a film substrate is 0.5 to 1.3 dl / g.

A film obtained by any method such as extrusion or calendering using such a polymer is stretched in one direction from 2.5 times to 7.0 times, preferably from 3.0 times to 6.0 times, and 1.0 times to 2.0 in the direction perpendicular to the direction. It is stretched up to twice, 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 effective in resolving badness.

However, when it is stretched beyond 2.0 times, the thermal shrinkage in the direction perpendicular to the main shrinkage direction becomes too large and the finished product becomes wavy. In order to suppress this waviness, it is recommended that the heat shrinkage rate is 15% or less, preferably 8 to 9% or less, and more preferably 7% or less. The stretching means is not particularly limited, and roll stretching, long gap stretching, tenter stretching and the like are applied, and the shape may be flat, tubular or the like.

The stretching is performed by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. Further, in the present invention, the film is stretched uniaxially in the longitudinal direction, uniaxially in the lateral direction, biaxially in the longitudinal and transverse directions, etc. In particular, in the biaxial stretching, the stretching in the longitudinal and transverse directions is carried out first in either direction. 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 stretching is carried out according to the purpose, but in order to prevent the dimensional change under high temperature in summer, it is recommended to pass through a heating zone of 30 to 150 ° C. for about 1 to 30 seconds. Further, before or after such treatment, a maximum of 70% may be stretched before or after the treatment. Especially stretches in the main direction, non-contracting direction (direction perpendicular to the main contracting direction)
It is better to relax, and it is better not to extend in the perpendicular direction.

In order to exert the preferable characteristics of the present invention, it is effective to perform not only the above-mentioned stretching ratio but also preheating and stretching at a temperature equal to or higher than the average glass transition temperature (Tg) of the polymer composition, for example, about Tg + 80 ° C. It can be mentioned as a means. In particular, the above treatment temperature in the main-direction stretching (main shrinkage direction) is extremely effective in suppressing the heat shrinkage ratio in the direction perpendicular to the direction and bringing the minimum value in the temperature range of 80 ± 25 ° C as described above. is important. Further, after 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 front-rear shrinkage property becomes better and stable.

The plane orientation coefficient of the film thus obtained is 100 × 10
^-3 or less is preferable. This is because if the surface orientation coefficient exceeds 100 × 10 ⁻³ , it will be easily broken by an impact external force, and will be easily broken even by a small amount of external damage. On the other hand, the birefringence is preferably 15 × 10 ^-3 ~ 160 × 10 ^-3 , the birefringence is 15 × 10
^If it is less than ^-3 , the thermal shrinkage and shrinkage stress in the longitudinal direction are insufficient, and 16
When it exceeds 0 × 10 ⁻³ , scratch resistance and impact strength are reduced, and even if it becomes a film, the usefulness is reduced in practice.

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 must have a heat shrinkage ratio at 100 ° C. of 30% or more. If it is less than 30%, it cannot be sufficiently attached to the surface of the irregularly shaped package when it is contracted. 90% is appropriate for the upper limit.

The film of the present invention is required to retain residual stress for 2 minutes or more when heat-treated in hot air at 100 ° C. 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, and the original film appearance, further good finish by heat shrinkage, also has a higher heat shrinkage stress than PVC, binding It has excellent properties.

Therefore, it is possible to carry out a strong covering or bundling wrapping that does not cause the load of heavy objects or deformed molded articles to slip. Also, at the 50-70% heat shrinkage level required for packaging, it has a broad heat shrinkage that the heat shrinkage in the direction perpendicular to the main shrinkage direction shows the lowest value, so shrink packaging from the initial heat shrinkage The process until completion is the temperature range (80 ± 25
It will be heat-shrinked at (° 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 procedure in dealing with numerous product variations and achieving complete shrinkage. At this time, if the shrinkage of the film has reached saturation, the film will linearly expand in the opposite direction due to the subsequent heating, and the film will loosen even though it has been contracted tightly. There is a problem. 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 shrink film is to prevent the packaged items from being broken or the load to collapse, 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 property, so that a beautiful package can be obtained, and further, it has excellent durability in terms of protection of the object 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 the sterilization treatment is inappropriate, and the film is destroyed during the treatment and loses its function. The film can be boiled or retort treated. It exhibits excellent usefulness as a heat shrink film.

(B) Printability The conventional film has inherent drawbacks with respect to the generation of pinholes and adhesion to ink by halftone printing, but the polyester film has chemical resistance and adhesiveness when made into a copolymer. And the printability was improved.

(B) 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 measurements used in the examples are as follows.

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

2.Heat shrinkage residual stress retention time (at 50% relaxation) Using Tensilon, create a sample piece with a width of 20 mm and a length of 150 mm, mark a 100 mm mark on the film of the sample piece, and set it accurately on the upper and lower chucks set to 50 mm. Was fitted with a 100 mm marked line, treated in hot air at 100 ° C., and the time until the shrinkage stress became 0 was measured.

4. The refractive index was measured in the longitudinal, lateral, and thickness directions using a refractometer with a plane orientation coefficient and a birefringence Abbe.

The abbreviations described in this example indicate the following compounds.

TPA: terephthalic acid IPA: isophthalic acid EG: ethylene glycol BIS-CMPP: 2,2 bis (carboxymethoxyphenyl) propane BIS-CMPS: bis (carboxymethoxyphenyl) sulfone BIS-DMCMPP: 2,2 bis [3,5 dimethyl (4 Carboxymethoxyphenyl)] Propane Example 1 Using a stainless steel autoclave, 70 mol of terephthalic acid, 30 mol of bis (carboxymethoxyphenyl) propane and 220 mol of ethylene glycol as dibasic acid components, and antimony trioxide as catalyst. Polycondensation was carried out by the direct esterification method with 0.05 mol (based on the acid component).
The composition of this copolyester is such that the acid component is 70 mol% terephthalic acid, bis (carboxymethoxyphenyl) propane is 30 mol%, and the glycol component is ethylene glycol 10 mol%.
It was 0 mol% and the intrinsic viscosity was 0.72 dl / g. This polyester was dried and melt-extruded at 290 ° C. to obtain an unstretched film having a thickness of 180 μm. The film vertically 1.1
Stretched twice, then stretched transversely 4.6 times, then about 20%
Allowed to cool laterally under stretching. The birefringence and plane orientation coefficient of the obtained film are 80 × 10 ^-3 and 59 × 10 respectively.
It was ^-3 . A stretched film having a thickness of 45 μm was obtained, and the physical properties thereof are shown in Table 1. The films shown in Table 1 have sufficient heat shrinkage characteristics, and even in a practical test used for shrink labels for bottles, shrinkage unevenness did not occur and a product having an excellent aesthetic appearance was obtained.

Comparative Examples 1 and 2 In the same manner as in Example 1, polyester films having the compositions shown in Table 1 were obtained. Comparative Example 1 is ordinary polyethylene terephthalate. Comparative Example 2 is a copolyester obtained by copolymerizing 10 mol% of isophthalic acid as a dibasic acid component. The film obtained in this comparative example has a good heat shrinkage ratio, but the heat shrinkage residual stress retention time is short, and secondary talumi is generated by the boil treatment or the retort treatment, so that it cannot be put to practical use. In addition, the heat shrinkage in the vertical direction was high, and it was unpleasant in a practical test.

Examples 2 to 8 In the same manner as in Example 1, heat-shrinkable films made of polyester having the composition shown in Table 1 were obtained. The properties of the heat-shrinkable film thus obtained are shown in Table 1. Both films had satisfactory results in both the heat shrinkage rate and the heat shrinkage residual stress retention time, and also obtained sufficient results in the practical test.

Comparative Examples 3 to 4 In the same manner as in Example 1, polyester films having the compositions shown in Table 1 were obtained. Comparative Example 3 is obtained by copolymerizing 70 mol% of bis (carboxymethoxyphenyl) sulfone.
In Comparative Example 4, 70 mol% of 2,2 bis (carboxymethoxyphenyl) propane was copolymerized. Comparative Examples 3 and 4
In both cases, the heat shrinkage residual stress was good, and the heat shrinkage ratio in the transverse direction was sufficient, but the shrinkage ratio in the longitudinal direction showed elongation, which was unpleasant for practical use.

(Effect of the invention) The film of the present invention exhibits stable heat shrinkability in a specific direction, can provide a beautiful and strong packaging state in coated packaging, has various effects such as improved heat resistance, and has a wide range of fields. Can exhibit excellent utility value.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29L 7:00 (72) Inventor Osamu Makimura 2-8 Dojimahama, Kita-ku, Osaka-shi, Osaka Toyo Spinning Co., Ltd. Head Office Examiner Akihiro Wataya

Claims (2)

[Claims] 1. A film comprising a copolyester containing terephthalic acid and ethylene glycol as main components and a bisphenol derivative compound represented by the following formula (1) as a copolymerization component, wherein the polyester film has a temperature of 100 ° C. The heat shrinkage in hot air is at least one of the longitudinal direction and width direction of the film.
A heat-shrinkable polyester film characterized by 30% or more. [In the formula, -X- is -CH ₂ -, _{-S -, - SO 2 -,} - represent either O-, l = 0
Or 1, and R represents a C _{1 to} C ₅ alkyl group or a halogen group. R ₁ and R _{2 each} represent a hydrogen atom, an alkyl having 4 or less carbon atoms, or an alkyl derivative. Further, m and n each represent an integer of 1 to 5, and O and P are 0 to
Represents an integer of 4. ] 2. A heat-shrinkable polyester film according to claim 1, which is a copolyester comprising 1 to 50 mol% of a bisphenol derivative.