JPS63161030A - Heat-shrinkable polyester film - Google Patents

Abstract

PURPOSE:To provide the titled film composed of a copolymerized polyester produced by the copolymerization of terephthalic acid, ethylene glycol and a naphthalenedicarboxylic acid derivative, and having a specific heat-shrinkage and excellent impact resistance, durability, heat-resistance and printability. CONSTITUTION:A polymerized polyester produced by using terephthalic acid and ethylene glycol as main components and copolymerizing a naphthalenedicarboxylic acid derivative (preferably 1,5-naphthalenedicarboxylic acid) (preferably at a ratio of 5-40mol%) is drawn preferably 3.0-6.0 times along a direction and 1.1-1.8 times perpendicular to the first direction to obtain the objective film having longitudinal and/or transversal heat-shrinkages of >=30% in hot air of 100 deg.C, suitable as a packaging material and giving a beautiful and durable package.

Description

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

(Prior art) A tube-shaped body made of heat-shrinkable plastic film is 1, for example, a container, a bottle (plastic pot)/
&) 1 can rod-shaped objects (pipes, rods.

For covering or bundling wood, various rod-shaped bodies), etc. (hereinafter referred to as containers), especially for covering part or all of their caps, shoulders, bodies, etc., for marking, protecting, and bundling. , boxes, bottles, boards, rods, etc. used for the purpose of improving product value, etc.
It is widely used in the fields of integrated packaging such as notebooks and wrapping of items such as skin bags.

It is expected that it will be used in applications that take advantage of its shrinkage and retention stress.

Traditionally, polyvinyl chloride/L/, polystyrene,
Using heat absorbing film such as polyethylene or hydrochloric acid rubber,
This was made into a tube-shaped body, which was then placed over the containers or packaged 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, printing pinholes (fine 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, However, there was also a problem in that the film subsequently suffered from condensation (at room temperature H), resulting in a dimensional change in the printing pitch. On the other hand, tubes using polyester heat harvesting films have been made on a trial basis, 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 the thermal contraction in the direction orthogonal to the direction, and it has been difficult to develop the above-mentioned applications.

(Problems to be Solved by the Invention) The above-mentioned conventional technology using a general-purpose heat-absorbing film made of polyvinyl chloride, polystyrene, polyethylene, etc. has the following problems.

(a) Absence of near-perfect uniaxial shrinkage band The conventional film described above is completely unsuitable for applications where it is ideal to have large N-accommodating properties in one direction, but no shrinkage at all in the direction perpendicular to this. be. For example, let's consider a case where the bottle is shrunk in the horizontal direction and a shrink lape/I/ is placed on the surface of the bottle.

Shrinking in the vertical direction of the lapay, ie, in the vertical direction of /l/, means that the flap does not come to a predetermined position and the label rises up, resulting in poor appearance. To prevent this, K must reduce shrinkage in the vertical direction, but if the film is simply oriented only in the horizontal direction for this purpose, then
As can be easily understood from the common knowledge of the properties of polymeric chemical substances, it is easy to tear, and the strength is also weakened because it is easy to become figgy. Considering that strength in the longitudinal direction is important for preventing bottle breakage, particularly when B)/l/ falls, simple unidirectional stretching cannot be said to be a good method. Furthermore, there are many cases in which the material cannot be used in other applications unless it has r# impact resistance.

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 treatment.

(C) Poor printability, occurrence of pinholes due to halftone printing, and compatibility with a wide variety of inks! & Regarding adhesion, each of the above conventional films has its own drawbacks.

For example, in polyvinyl chloride, ink pinholes are likely to occur due to gel-like substances, and in continuous tube processing, pinholes may exist in the middle of a long film. If this is supplied to an automatic lapping machine, pinho/I/
Since the product is manufactured with some parts remaining, all products must be inspected at the end, and the labor and reprocessing by sampling, etc., significantly reduce the actual operating rate.

If this pinhole defect were to be inspected and removed after printing, it would be necessary to return the film to a continuous film after cutting and to connect it with V-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).

Moreover, it is difficult to manage as it constantly changes under the distribution temperature conditions. Therefore, refrigerated trucks, low-temperature warehouses, etc. are required for polyvinyl chloride-containing films. For this reason, it is desired to provide a heat-containing film that can be printed without pinhole defects and that does not change over time after printing.

(d) Generation of crazes Crazes occur in polystyrene. ib<, ##Poor chemical properties. 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 photovoltaic used has been rapidly increasing. When considering the recovery of this photo.

Especially the polyester bottle cover 1! If a different type of film such as polyvinyl chloride or polystyrene is used, there is a problem that it cannot be recovered and reused.

Furthermore, polyvinyl chloride is susceptible to corrosion due to chlorine gas, so a heat-absorbing FeJ film that does not cause waste pollution is desired.

(f) Shrinkage spots The heat absorption curve of the conventional film described above tends to lack homogeneity, and if heat is applied one after another to form separate areas with sufficient shrinkage and areas with insufficient shrinkage, heat may be applied once again. Even if given a certain amount, no further re-shrinkage occurs and one surface becomes uneven. Therefore, it is desired to provide a heat-shrinkable film that does not cause shrinkage spots. On the other hand, polyethylene terephthalate film suffers from high oriented crystallinity, which inhibits its low-temperature shrinkability, resulting in insufficient elasticity, resulting in 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 present invention is a film consisting of a copolyester containing terephthalic acid and ethylene glycol/I/gold as main components, and a naphthalene dicarboxylic acid derivative as a copolymerization component, which This is a heat-shrinkable polyester resin film characterized in that the film has a heat shrinkage rate in hot air of 100°C of 30% or more in at least one of the longitudinal direction and the width direction of the film.

The heat-shrinkable polyester of the present invention has terephthalic acid and ethylene glycol as main components and a lenaphthalene dicarboxylic acid derivative as a copolymerized component, and the naphthalene dicarboxylic acid derivative is in the range of 1 to 50 mo/I'%. preferable.

Particularly preferably 5 to 40 mo/L'%. If the naphthalene dicarboxylic acid content is less than 17%, the retention time of residual stress will be shortened when heat treated at 100°C.1 For example, when coating a bottle, the shoulders may become loose due to sterilization, which is undesirable. cause a phenomenon. On the contrary, 50mo/I'%
If the value exceeds 100%, the effect of improving the residual stress holding time during heat treatment becomes saturated, and the amorphous property progresses, resulting in loss of thermal properties.

Examples of naphthalene dicarboxylic acid derivatives include the following. 1,2 naphthalene dicarboxylic acid.

1.3 naphthalene dicarboxylic acid, 1,4 naphthalene dicarboxylic acid, 1,5su7thalene dicarboxylic acid, 1,6
naphthalene dicarboxylic acid, l, 7 naphthalene dicarboxylic acid, 1,8 naphthalene dicarboxylic acid, 2,3 naphthalene dicarboxylic acid, 2,4 naphthalene dicarboxylic acid, 2,5
Naphthalenedicarboxylic acid, 2.6-7thalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid.

2.8 Naphthalene dicarboxylic acid or its lower alkyl ester can be exemplified. Particularly preferred are 1,5 naphthalene dicarboxylic acid and 2,6 naphthalene dicarboxylic acid.

The polyester copolymer according to the second invention can be produced by a conventional polyester production method. For example, it may be a method of esterification using terephthalic acid, naphthalene dicarboxylic acid, and ethylene glycol, or a method of transesterification using dimethyl ester of dimethyl terephthalate, naphthalene dicarboxylic acid, and ethylene glycol. You can.

Furthermore, the polyester copolymer in the present invention may be produced by blending copolymers within and outside the scope of the present invention with homopolyester or other copolyester, and the polyester copolymer may contain 1 to 5 naphthalene dicarboxylic acids.
It may be manufactured by any method as long as the %o range is 0%.

The polyester ρ copolymer of the present invention has terephthalic acid as the main acid component and naphthalene sica acid as a copolymerized component, but other acid components may be copolymerized within the range that does not significantly change their properties. Good too. For example, aliphatic dibasic acids such as adipic acid and sepacic acid, isophthalic acid, diphenyl cicabonic acid, 5-tert-butyl isophthalic acid, 1.1.3) Rimethy/I/3-722μ Examples include aromatic dibasic acids such as indane-4,5-dicarboxylic acid.

Similarly, the glyco component is mainly ethylene glyco/l/i, but it may be copolymerized as long as the properties thereof are not changed. For example, diethylene glycol/L/.

Propylene glyco-, butanediol, aliphatic di-μ such as hexane di-μ, 1,4 cyclohexanedimethanol-/L/, xylylene glyco-/L/.

Examples include diols such as bis(4-hydroxypheny/L/)sulfone and 2,2(4-hydroxypheny/L/)furopane derivatives.

Furthermore, lubricants such as titanium dioxide, particulate silica, kaolin, calcium carbonate, etc. may be added as necessary, and furthermore, antistatic agents, anti-aging agents, ultraviolet ray inhibitors, dyes, etc. may be added as coloring agents. .

The preferable intrinsic viscosity of the film base material is 0.50.
~1.3 dll? It is.

A film obtained by any method such as an extrusion method or a calendar method using such a polymer is stretched in one direction by 2.5 times to 7.0 times, preferably 3.0 times to 6.0 times.

It is stretched 1.0 times to 2.0 times or less, preferably 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 a direction perpendicular to the first direction is performed.

This method is extremely effective in solving the problems of poor impact resistance and tear resistance of films initially stretched in one direction.

However, when stretched more than 2.0 times, the heat absorption coefficient 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 inches or less, more preferably 7
% or less is recommended. There are no particular restrictions on the stretching method.

Methods such as low μ stretching, long gap stretching, and tenter stretching are applied, and the shape does not matter whether it is flat or tubular.

The stretching may be carried out by sequential biaxial stretching, simultaneous biaxial stretching, uniaxial stretching, or a combination thereof. In addition, the film of the present invention is stretched in, for example, one axis in the longitudinal direction, one axis in the transverse direction, and two axes in the longitudinal and transverse directions. In particular, in biaxial abrasive stretching, stretching in the longitudinal and transverse directions is carried out sequentially in one direction and then in the other direction. Stretching is effective and the order of stretching may be either first. When carrying out the simultaneous biaxial stretching method, the stretching order may be either simultaneous in the longitudinal and lateral directions, first in the longitudinal direction, or first in the transverse direction. Heat setting in these stretching processes is carried out depending on the purpose, but in order to prevent dimensional changes under high temperatures in summer, a heating zone of 30 to 150°C is used.

It is recommended to run for about 1 second to 30 seconds. Further, the image may be expanded by up to 70 inches either before or after such processing, or both. especially stretching in the main direction.

It is better to relax in the non-contraction direction (perpendicular to the main contraction direction) and not to stretch in the perpendicular direction.

In order to exhibit the preferable characteristics of the present invention, it is necessary not only to adjust the above-mentioned stretching ratio but also to adjust the average glass transition temperature (
Preheating and stretching at a temperature higher than Tg (Tg), for example about Tg + 80° C., can also be cited as an effective means. In particular, the above-mentioned processing temperature in the main direction stretching (main shrinkage direction) suppresses the heat shrinkage rate in the direction perpendicular to the direction, and as mentioned above, the processing temperature is 80±
It is extremely important to bring the minimum value to 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 the film successively, the back and forth shrinkage characteristics become more beautiful and stable.

The plane orientation coefficient of the film thus obtained was 100XI
Those of O-3 or less are preferable. Planar orientation coefficient is 100xl
This is because if it exceeds O-3f, it becomes easy to break due to an impactful external force and becomes easy to tear even with the slightest external trauma.

On the other hand, the birefringence is preferably between 15X10-3 and 160x10-a.If the birefringence is less than 15X10-3, the thermal shrinkage rate and shrinkage stress in the longitudinal direction will be insufficient, and if it exceeds 160XIQ-3, the scratch resistance and impact strength will be insufficient. However, even if it is made into a film, its usefulness in practical use is reduced.

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

The film of the present invention must maintain residual stress for 2 minutes or more when it is relaxed by 50% and heat treated in hot air at 100°C. It is more preferable to hold the temperature for 4 minutes or more. If the retention time of the residual stress is short, secondary microscopic distortion occurs, and for example, when a bottle is coated, phenomena such as loosening of the shoulders due to sterilization treatment occur, which is not preferable.

The film of the present invention will be explained below from the viewpoint of its use. packaging applications,
In particular, boiling and retort processing are used for food and beverage packaging. None of the existing heat-shrinkable films can withstand these treatments sufficiently. The film of the present invention can withstand heat sterilization by boiling and retort processing, has a good original film appearance, and also has a good finish due to heat shrinkage, and has a higher heat shrinkage stress than PVC, and can be bound The quality is also excellent.

Therefore, it is possible to strongly cover or bind and package heavy items or deformed molded items without causing them to collapse. In addition, in the heat shrinkage rate of 50 to 70% required for packaging, the heat shrinkage rate in the direction perpendicular to the main shrinkage direction shows the lowest value. The process up to completion of shrink wrapping is carried out in the temperature range (80°C) showing the minimum yield a.
It will be heat-shrinked at ±25°C). As a result, we were able to obtain the characteristic that the error in finished dimensions was reduced. After that, it becomes impossible to shorten it any further).

Subsequent heating has become a common procedure and plays an important role in accommodating numerous product variations and achieving complete 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 K has been carefully contracted, it will instead become loose. There is a problem. In order to prevent such problems, 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) One of the roles of a unidirectional astringent shrink film is to prevent the packaged items from being destroyed or deformed, 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, the film of the present invention has a high shrinkage rate and high impact resistance, so that beautiful packaging can be obtained, and moreover, it exhibits excellent durability in terms of protecting the packaged items. This trend is confirmed by the drop bag test. Also, the nearly perfect one-way convergence guarantees excellent dimensional stability after shrink wrapping.

(b) Heat resistance All conventional general-purpose films are boiled at high temperatures)
/L') The film is unsuitable for sterilization because it cannot withstand treatment, and it breaks during treatment, resulting in a! However, the film of the present invention exhibits excellent utility as a heat-shrinkable film that can be subjected to boiling and retort processing.

(C) Printability Conventional films have inherent drawbacks such as generation of binho due to halftone printing and adhesion with ink, but this polyester film has chemical resistance and adhesive properties due to copolymerization. The printability was improved due to the improvement.

(d) Industrial waste issues In recent years, the use of plastic photoμ has spread rapidly.

When considering the recovery of such photos, it is preferable to use a homogeneous material.It is advantageous in this respect to apply the film of the present invention to the packaging of polyester bottoms.

Ce) Yield spots The film of the present invention has a large shrinkage rate and high shrinkage stress,
Even in the secondary heating, if the material is heated continuously, it will show a tendency to shrink, so no shrinkage spots will occur.

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

1. Heads Measured based on JIS-K 6714K.

2. Heat shrinkage rate Sump/I/Between the marked lines is 200 silk, and the film has a width of 1
It was cut into 5fl pieces and measured at each temperature. 100 for heating
It was heated for 1 minute using hot air at ℃.

3. Heat shrinkage stress (kf/-) Using Tensilon, take a sample piece with a width of 20 wII and a length of 150 ff, mark the 100 cod mark on the film,
Attach the sample piece to the upper and lower chucks set at 100+W,
Treated in hot air at 100°C.

The maximum condensation stress during that period was determined, and the contraction stress was calculated according to the following formula.

Maximum shrinkage force/cross-sectional area = heat shrinkage stress 4, heat shrinkage residual stress retention time (at 50% relaxation) Using Denjiron, prepare a sample piece in the same manner as for heat shrinkage stress, and mark the film of the sample piece with 100 fin marks. Mark the line and attach it to the upper and lower chucks set at 50ff, accurately aligning the 10On+ marked line, process in hot air at 100'C, and determine the time until the shrinkage stress becomes 0 or the residual stress in 10 minutes. If the stress is to be maintained after 10 minutes, it is calculated in the same way as the heat shrinkage stress.

Example 1 Using a stainless steel autoclave, 60 mol% of terephthalic acid and 40 mol% of 2,6 naphthalene dicarboxylic acid were used as the dibasic acid component. *210 mol% of ethylene glyco-1v1 was used as the glyco-μ component. stomach.

Polycondensation was carried out by a direct esterification method using 0.025 mo/v of antimony dioxide (for m components) as a catalyst. This copolymer has an intrinsic viscosity of 0.71 dl/f. This polyester /I/ was melt-extruded at 290"C to obtain an unstretched film with a thickness of 180 μm. The film was stretched 1.2 times in the machine direction, then 4.1 times in the transverse direction, and then Cooled under about 20% lateral elongation to a thickness of 4
A heat-absorbing lIJ film of 0 μm was obtained. The birefringence and planar orientation coefficient of the obtained film were 75X10-
3 and 52xlO-8. The physical properties of this film are shown in Table 1. As shown in Table 1, the results showed a high shrinkage rate and a sufficiently long heat shrinkage residual stress retention time.
Good results were also obtained in practical tests.

Examples 2 to 5 In the same manner as in Example 1, heat-shrinkable films made of polyester having the compositions shown in Table 1 were obtained. Table 1 shows the characteristic values of the heat-shrinkable film obtained.

All of the heat-shrinkable films had sufficiently satisfactory results in terms of heat shrinkage rate and heat yielding residual stress holding time, and excellent results were obtained in practical tests.

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 copolymerized polyester obtained by copolymerizing 10 moles of isophthalic acid as a dibasic acid component. Comparative Example 3 is a copolymerized polyester obtained by copolymerizing 80 mol'v% of naphthalene cyponic acid as a dibasic acid component. The heat-shrinkable films obtained in Comparative Examples 1 and 2 have a high shrinkage rate in the transverse direction and are sufficiently practical, but the residual stress retention time is short and secondary talumining is difficult to achieve through boiling or retro-μ treatment. could not be put to practical use because of the occurrence of In addition, the heat shrinkage rate in the longitudinal direction was high and the finish was poor in the practical test.The heat shrinkable film of Comparative Example 3 could not obtain a sufficient heat shrinkage rate.

Margins below (Effects of the Invention) Since the film of the present invention is constructed as described above, it exhibits stable heat shrinkability in a specific direction, and can provide a beautiful and strong packaging state in covered packaging.
It has various effects such as improving printing pitch stability and heat resistance, and can exhibit excellent utility value in a wide range of fields.

Claims (2)

[Claims] (1) A film made of a copolyester containing terephthalic acid and ethylene glycol as main components and a naphthalene dicarboxylic acid derivative as a copolymer component,
A heat-shrinkable polyester film, characterized in that the polyester film has a heat shrinkage rate of 30% or more in at least one of the longitudinal direction and the width direction of the film in hot air at 100°C. (2) 1 to 50 mol% of naphthalene dicarboxylic acid derivatives
Claim 1, which is a copolymerized polyester consisting of
The heat-shrinkable polyester film described in Section 1.