JP2000297160A - Heat shrinkable polyester based film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide heat shrinkable polyester based film having a sufficiently high shrinkability in the right-angle direction while having an extremely low shrinkability in a specific temperature range and, at the same time, a sufficient oxygen scavenging capacity. SOLUTION: Heat shrinkable polyester based films contain a composition having sufficient oxygen scavenging properties, and have a heat shrinkability in 80 deg.C hot air in at least one direction of the longer direction and the width direction of the films of not less than 30%. The composition having oxygen scavenging properties contains an oxidizable polymer and a metal catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polyester film (including a sheet; the same applies hereinafter) exhibiting particularly suitable characteristics in the field of packaging materials for coating or binding.

[0002]

2. Description of the Related Art Tubular bodies formed from a heat-shrinkable plastic film include, for example, containers, bottles (including plastic bottles), can-bars (pipes, rods, wood, various rods) (hereinafter referred to as containers). Abbreviated as a kind) for covering or bundling, in particular, covering part or all of these caps, shoulders, torso, etc. and used for the purpose of marking, protection, bundling, improving the commercial value, etc. Boxes, bottles, plates,
It is widely used in the field of packaging such as sticks, notebooks and the like or in close contact with an object to be packaged, such as a skin pack, and is expected to develop 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. The heat-shrinkable film is formed into a tube and then covered with the above-mentioned containers or packed and packaged to be heat-shrinked. Was.

However, these films have poor heat resistance, and have the drawback that when they are subjected to a boil treatment or a retort treatment, they are melted or ruptured, so that the film cannot be maintained.

[0005] Further, in applications requiring printing, printing pinholes due to poor ink transfer (fine irregularities due to fish eyes due to additives or polymer gels in the film)
There is also a problem that even if printing is successfully performed, the film shrinks (shrink at normal temperature) after that, causing 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, but the heat-shrinkage rate in a desired direction cannot be sufficiently increased. There is a problem that the heat shrinkage in the direction perpendicular to the direction cannot be reduced, and it has been difficult to develop the above-mentioned application.

[0006]

The above prior art using a general-purpose heat-shrinkable film such as polyvinyl chloride, polystyrene, and polyethylene has the following problems.

(A) Lack of near-perfect uniaxial shrinkage [0007] In applications where it is ideal that the film has large shrinkage in one direction but does not shrink at all in a direction perpendicular thereto, the conventional film described above is not used at all. Not suitable. 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 does not come to a predetermined position and the label shrinks. Causes poor appearance. In order to prevent this, the shrinkage in the vertical direction must be reduced, but if the film is simply oriented only in the horizontal direction for this purpose, it can be easily understood from the common sense in the properties of polymer chemicals In this way, it is easy to tear, and it becomes easy to fibrin, so the strength is weak. In particular, when the bottle falls, simple unidirectional stretching is not a good method considering that the strength in the longitudinal direction is important for preventing the bottle from breaking. Also, there are many cases in which it cannot be used without impact resistance even in other applications.

[0008] In view of the above, it is desired to develop a film having extremely small shrinkage in a specific temperature range, but having sufficiently large shrinkage in a direction perpendicular thereto.

(B) Insufficient heat resistance Any of the conventional films cannot withstand high-temperature boil treatment or retort treatment, and is unsuitable for sterilization treatment. For example, when a retort treatment is performed, the conventional film breaks or ruptures during embedding, and all functions are lost.

Therefore, it is desired to provide a heat-shrinkable film that can withstand boil processing and retort processing.

(C) Poor printability The above-mentioned conventional films have their own drawbacks with respect to the occurrence of pinholes due to halftone printing and the adhesion to a wide variety of inks. For example, in the case of polyvinyl chloride, an ink pinhole is easily generated by a gel-like material, 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.Therefore, the entire product must be inspected. I 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 formed, and a defective product is generated at that portion and before and after the seam due to the seam, and the defective package must be removed during the process. In high-precision printing, the print pitch decreases (shrinkage with time) due to film shrinkage after printing,
In addition, it encounters the difficulty of management that constantly changes under the conditions of the flow temperature. Therefore, in the case of a polyvinyl chloride shrink film or the like, an insulated truck, a low-temperature food storage, and the like are required. From such a situation, it is desired to provide a heat-shrinkable film capable of printing without pinhole defects and having no change with time after printing.

(D) Generation of craze Polystyrene is liable to generate craze and has poor chemical resistance.
Therefore, during use, the printed surface is easily damaged by the chemical solution, and the printed surface is also stained. Therefore, a film having excellent chemical resistance and durability is desired.

(E) The problem of industrial waste In recent years, the amount of plastic bottles used has been rapidly increasing. Considering the recovery of this bottle, there is a problem that it cannot be recovered and reused especially when a different kind of 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 pollution of waste is desired.

(F) Spots of shrinkage The heat shrinkability of the conventional film tends to lack homogeneity, and once heat is applied to form sufficient and insufficient shrinkage separately, then heat is applied again. , No further re-shrinkage occurs and the surface becomes uneven. Accordingly, 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 has as its object to provide a polyester film free from defects as described in the above (a) to (f). is there.

Another object of the present invention is to provide a polyester film having a sufficient oxygen-scavenging ability.

[0019]

The heat-shrinkable polyester film of the present invention is a polyester film, wherein the polyester contains a composition having an oxygen-scavenging property. The heat shrinkage rate in the film is 30% or more in at least one of the longitudinal direction and the width direction of the film, thereby achieving the above object.

[0020] In one embodiment, the composition having oxygen scavenging properties contains an oxidizable polymer and a metal catalyst.

[0021] In one embodiment, the oxidizable polymer is a polyamide.

[0022] In one embodiment, the metal catalyst is a cobalt catalyst or a rhodium catalyst.

In one embodiment, the oxidizable polymer is contained in an amount of 1 to 20% by weight based on the polyester.

In one embodiment, the metal catalyst is contained in an amount of 10 to 10000 ppm based on the polyester.

In one embodiment, a polyester film comprising a copolyester containing terephthalic acid and ethylene glycol as main components and neopentyl glycol and / or 1,4-butanediol as a copolymer component, The neopentyl glycol and / or
Alternatively, the copolymerization amount of 1,4-butanediol is 5 to 45 mol% based on the dicarboxylic acid component constituting the polyester.
It is blended in the range.

[0026]

DETAILED DESCRIPTION OF THE INVENTION The heat-shrinkable polyester of the present invention contains terephthalic acid and ethylene glycol as main components and neopentyl glycol and / or 1,4-butanediol as a copolymer component. And / or the copolymerization amount of 1,4-butanediol is 5-45 to the dicarboxylic acid component constituting the polyester.
A mole% range is preferred. Especially preferably, it is 10 to 40 mol%. The molar ratio of neopentyl glycol to 1,4-butanediol is not particularly limited.

Neopentyl glycol and / or 1,4
-When butanediol is less than 5 mol%, the retention time of the residual stress when heat-treated at 80 ° C in hot air is shortened,
For example, when coated on a bottle, undesired phenomena such as loosening of the shoulder due to sterilization are caused. On the other hand, if the content of neopentyl glycol and / or 1,4-butanediol exceeds 45 mol%, the amorphousness increases and the heat resistance is lost.

The polyester copolymer in the present invention can be produced by a conventional method for producing polyester. For example, a method by direct esterification of terephthalic acid and ethylene glycol, neopentyl glycol and / or 1,4-butanediol, or dimethyl terephthalate and ethylene glycol, neopentyl glycol and / or 1,4-butanediol
The production method may be a transesterification method of butanediol.

Further, the polyester copolymer in the present invention may be prepared by blending a copolymer within or outside the scope of the present invention with a homopolyester or another copolymerized polyester. And / or 1,4-butanediol may be produced by any method as long as it is in the range of 5 to 45 mol%.

Although the heat-shrinkable polyester of the present invention contains terephthalic acid as a main component as an acid component, other acid components may be copolymerized as long as their properties are not significantly changed. For example, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and azelaic acid, isophthalic acid, diphenyldicarboxylic acid, 5-tertbutylisophthalic acid, 2,2,6
6-tetramethylbiphenyl-4,4-dicarboxylic acid,
Examples thereof include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 1,1,3-trimethyl-3-phenylindene-4,5-dicarboxylic acid.

As the glycol component, ethylene glycol is used as a main component, and neopentyl glycol and / or 1,4-butanediol are used as copolymer components. Other components are copolymerized as long as their properties are not significantly changed. You may. For example, aliphatic diols such as diethylene glycol, propylene glycol, and hexanediol, 1,4-cyclohexanedimethanol, xylylene glycol, bis (4-βhydroxyphenyl) sulfone, and 2,2 (4-oxyphenyl) propane Derivative diols can be exemplified.

The heat-shrinkable polyester in the present invention must contain a composition having oxygen-scavenging properties. Here, the composition having oxygen-scavenging properties is characterized by capturing oxygen by metal-catalyzed oxidation of an oxidizable organic component, and the oxidizable organic component mainly means an oxidizable polymer. .

The oxidizable polymer used in the present invention includes polyamide. Among them, - arylene -CH ₂ -NH-CO-, especially -NH-CH ₂ - polyamides containing arylene -CH ₂ -NH-CO- alkylene -CO- unit groups.

Particularly suitable arylene groups include phenylene groups, especially m-phenylene groups, which may be substituted by alkyl groups and / or other unsubstituted or alkyl-substituted aromatic rings. May be condensed. The alkylene and alkyl groups have from 1 to 10 carbon atoms and are preferably straight-chain or branched.
A particularly suitable alkylene group is an n-butylene group. m-
Copolymer of xylylenediamine and adipic acid (MXD
6) is very suitable. Advantageously, the relative viscosities of these polyamides are in the range from 1.5 to 4.5, in particular from 2.0 to 3.5.

Metal catalysts particularly suitable for polyamides include cobalt and rhodium catalysts. As the cobalt catalyst, divalent and trivalent catalysts are preferable. Among them, cobalt carboxylate represented by cobalt acetate is preferable. Of course, a white alcohol solution of cobalt carboxylate, such as cobalt Siccatol (Akzo Chimie), is also preferable. The rhodium catalyst is preferably divalent.
Particularly, rhodium carboxylate represented by rhodium acetate is particularly preferred.

The oxidizable polymer contained in the heat-shrinkable polyester of the present invention is 1 to 20% by weight, preferably 1 to 10% by weight, more preferably 1 to 10% by weight based on the polyester.
5% by weight. When the content of the oxidizable polymer is large, sufficient oxygen scavenging ability can be exhibited even when high oxygen contamination is assumed, but there is a problem that the mechanical properties and thermal properties of the obtained heat shrinkable film are deteriorated. If the content of the oxidizable polymer is too small, it does not show sufficient oxygen scavenging ability.

The metal catalyst contained in the heat-shrinkable polyester of the present invention is 10 to 10,000 pp with respect to the polyester.
m, preferably 50 to 2000 ppm, particularly preferably 100 to 500 ppm. If the content of the metal catalyst is too high, undesirable side reactions such as depolymerization of the polyester occur. If the content of the metal catalyst is too small, sufficient oxygen scavenging ability is not exhibited.

If necessary, a lubricant such as titanium dioxide, fine particle silica, kaolin, calcium carbonate, etc. may be added. Further, an antistatic agent, an antioxidant, an ultraviolet ray inhibitor and a dye as a coloring agent may be added. It can also be added. In addition,
Preferred intrinsic viscosity as a film substrate is 0.50 to 0.50.
1.3 dl / g.

A film obtained by using such a polymer by an arbitrary method such as an extrusion method or a calendering method is stretched in one direction by 2.5 times to 7.0 times, preferably 3.0 times to 6.0 times. Then, it is stretched in a direction perpendicular to the direction by a factor of 1.0 to 2.0 or less, preferably from 1.1 to 1.8. Stretching in the first direction is performed in order to obtain a high heat shrinkage, and stretching in the direction perpendicular to the first direction is performed in the direction of impact resistance and tear resistance of the film stretched in the first direction. It is extremely effective in solving badness.

However, when the film is stretched beyond 2.0 times, the heat shrinkage in the direction perpendicular to the main shrinkage direction becomes too large,
The finish is wavy. To suppress this undulation,
It is recommended that the heat shrinkage be 15% or less, preferably 8 to 9% or less, more preferably 7% or less.

The stretching means is not particularly limited, and methods such as roll stretching, long gap stretching and tenter stretching are applied, and the shape thereof may be flat or tubular.

The stretching is carried out by stretching or successive biaxial stretching, simultaneous biaxial stretching, monoaxial stretching or a combination thereof.
For the film of the present invention, for example, one axis vertically, one axis horizontally,
Stretching in the longitudinal and transverse directions is performed. In particular, in the case of the biaxial stretching, stretching in the longitudinal and transverse directions, or sequential biaxial stretching in which one of the directions is performed first, is effective. In addition, when performing the simultaneous biaxial stretching method, the stretching order, the vertical and horizontal simultaneous,
It may be either vertical or horizontal. The heat setting in these stretchings is carried out according to the purpose, but it is recommended to pass through a heating zone at 30 to 150 ° C. for about 1 to 30 seconds in order to prevent dimensional change under high temperature in summer.

The stretching may be up to 70% before and / or after such treatment. In particular, it is preferable to stretch in the main direction and relax in the non-contracting direction (the direction perpendicular to the main contracting direction), and it is better not to perform the expansion in the perpendicular direction.

In order to exhibit the preferable characteristics of the present invention, not only the above-mentioned stretching ratio but also preheating and stretching at a temperature higher than the average glass transition temperature (Tg) of the polymer composition, for example, at about Tg + 80 ° C. This is also an effective means. In particular, the processing temperature in the main direction stretching (main shrinkage direction) is extremely low in order to suppress the heat shrinkage in the direction perpendicular to the direction and bring the minimum value to the temperature range of 80 ± 25 ° C. as described above. is important. Further, after stretching, the film is cooled while applying stress to the film while being stretched or tensioned, or by further cooling, the front-back shrinkage characteristics become better and more stable.

The surface orientation coefficient of the thus obtained film is preferably 100 × 10 ⁻³ or less. If the plane orientation coefficient exceeds 100 × 10 ⁻³ , it is easy to be broken by an impact external force, and it is easily broken even by a slight damage. 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 heat shrinkage and shrinkage stress in the longitudinal direction are insufficient, and 160 × 10 ^−3. If it exceeds, the scratch resistance and the impact strength are reduced, and even if the film is formed, its usefulness is reduced in practical use.

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

The film of the present invention has a 10%
It is necessary to keep the residual stress for 2 minutes or more when heat-treated in hot air at 0 ° C. More preferably, it is held for 4 minutes or more. If the retention time of the residual stress is short, secondary thickening occurs. For example, when the bottle is covered with a bottle, a phenomenon such as loosening of the shoulder due to sterilization treatment occurs, which is not preferable.

Hereinafter, the film of the present invention will be described in terms of application.

In packaging applications, particularly for packaging of foods and beverages, boiled embedding and retorting are performed. 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 also has good original film appearance and good finish due to heat shrinkage, and has higher heat shrinkage stress than PVC, and The nature is also excellent.

Therefore, it is possible to provide a strong covering or bundling package that does not cause the load to be dislodged even with a heavy or deformed molded product. In addition, at a heat shrinkage level of 50 to 70% required for packaging, the heat shrinkage in the direction perpendicular to the main shrinkage direction has the lowest value. The process until the completion is to perform the heat shrink in the temperature region (80 ± 25 ° C.) showing the minimum shrinkage.
As a result, the feature that the error of the finished dimension is reduced was obtained.

In the packaging utilizing heat shrinkability,
After the completion of heat shrinkage (it must be in a state where it does not shrink any more even if it has the ability to shrink even more closely to the packaged material), it is a general procedure to continue heating, and this is a number of products. And plays an important role in achieving complete contraction in response to variations in At this time, if the shrinking ability of the film has reached saturation, the subsequent heating causes the film to expand in the opposite direction, and although the film has been shrunk tightly, loosening occurs instead. There is a problem. In the present invention, in order to prevent such a situation from occurring, it is recommended that the contraction stress is increased and, as described above, the stretching is further performed after the stretching. In this respect, the meaning of the orientation in the present invention exists.

This will be described more specifically below. (A) One-way shrinkage: One of the roles of the shrink film is to prevent breakage of the packaged object and collapse of the load. For this purpose, the shrink film has high impact resistance and a large shrinkage in the main direction. It is necessary to get In that respect, the film of the present invention has high shrinkage and high impact resistance, so that beautiful packaging can be obtained,
Moreover, it shows excellent durability in terms of protection of the packaged object.
This trend is evidenced by the dropping bag test. In addition, due to the unidirectional shrinkability which is almost perfect, the finished dimensional stability after shrink wrapping is good. (B) Heat resistance: All conventional general-purpose films cannot withstand high-temperature boil processing or retort processing and are unsuitable for sterilization processing. They break during processing and lose their functions. The film of the present invention exhibits excellent utility as a heat shrinkable film that can be boiled or retorted. (C) Printability: Conventional films have inherent drawbacks with respect to the occurrence of pinholes and adhesion to ink due to halftone printing. However, the polyester film has a chemical resistance and a copolymer. The printability was improved due to the improved adhesiveness. (D) Problems with industrial waste: In recent years, the use of plastic bottles has been rapidly spreading. In consideration of such recovery of the bottle, it is preferable that the bottle is formed of the same substance, and it is advantageous in this respect to apply the film of the present invention to the packaging of a polyester bottle. (E) Irregular shrinkage: The film of the present invention has a large shrinkage ratio and a high shrinkage stress. Even if it is heated in the secondary heating, it shows a tendency to shrink if heated continuously.

[0053]

EXAMPLES Examples will be described below, and the measuring method used in the examples is as follows. 1. Gas barrier property evaluation (sensory evaluation) 500 processed into a cylinder so that the main shrinkage direction is the circumferential direction of the bottle, the lower end of the film is adhered, and oren juice (Ehime mandarin orange “POM juice”) is filled in advance.
ml PET bottle with the plug part facing upward, 90 ° C
Was shrunk through a steam tunnel to produce a PET bottle in which all surfaces except the upper part of the plug were covered with a film, and a sensory evaluation was performed. After the elapse of the predetermined period, those with impaired original flavor were evaluated as x, those with the preserved flavor as ○, and those with intermediate flavor as △.

2. Heat shrinkage The distance between the sample marks was set to 200 mm and the film was set to a width of 15 mm.
mm. Heating was performed using hot air at 80 ° C. for 1 minute.

Example 1 Using a stainless steel autoclave, 100 mol% of terephthalic acid as a dicarboxylic acid component, 90 mol% of ethylene glycol and 10 mol% of neopentyl glycol as glycol components, and antimony trioxide as an acid catalyst were used. A polycondensation reaction was carried out by a direct esterification method using 0.025 mol% of the components. The intrinsic viscosity of the obtained polymer was 0.75 dl / g.

When the polyester was melt-extruded at 300 ° C., MXD6 (Toyobo Nylon T-600) was added
0.06% by weight of cobalt acetate (200 ppm as cobalt atom) was added to obtain an unstretched film having a thickness of 180 μm.

The obtained film was stretched 2.0 times in the longitudinal direction and then 4.1 times in the transverse direction, and then cooled under stretching in the transverse direction by about 20% to obtain a heat-shrinkable film having a thickness of 40 μm. Table 1 shows the physical property values of the obtained film. The result of the sensory evaluation was ○, indicating that sufficient gas barrier properties were exhibited.

Examples 2 to 5 and Comparative Examples 1 to 5 Polyesters having the compositions shown in Table 1 were obtained in the same manner as in Example 1. MXD6 and cobalt atoms in the proportions shown in Table 1 were added to each polyester during film formation.

[0059]

[Table 1]

From Table 1 it can be seen that the proper amount of MX for the polyester
It is understood that a heat-shrinkable film having excellent gas barrier properties can be obtained by containing D6 and a cobalt atom.

[0061]

According to the present invention, a heat-shrinkable polyester film having the following characteristics can be obtained. (A) While having a very small shrinkage in a specific temperature range, it has a sufficiently large shrinkage in a direction perpendicular thereto. (B) It can withstand boil processing and retort processing. (C) Printing without pinhole defects is possible, and there is no change over time after printing. (D) It has excellent chemical resistance and durability. (E) Does not cause waste pollution. (F) No contraction spots are generated. (G) It has sufficient oxygen scavenging ability.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) C08L 77:10) B29K 67:00 105: 02 B29L 7:00 F term (reference) 4F071 AA43 AA45 AA46 AA54 AC09 AE22 AF61Y AH04 4F210 AA24 AA29 AB01 AB16 AE01 AG01 RA03 RC02 RG02 RG04 RG30 RG43 4J002 CF061 CL012 CL032 EG046 FD170 FD202 FD206 GG02

Claims (7)

[Claims] 1. A polyester film, wherein the polyester contains a composition having oxygen-scavenging properties, and the polyester film has a heat shrinkage in hot air of 80 ° C. at least in the longitudinal direction and width direction of the film. A heat-shrinkable polyester film characterized by being at least 30% in any one direction. 2. The heat-shrinkable polyester film according to claim 1, wherein the composition having an oxygen-scavenging property contains an oxidizable polymer and a metal catalyst. 3. The heat-shrinkable polyester film according to claim 2, wherein the oxidizable polymer is a polyamide. 4. The heat-shrinkable polyester film according to claim 2, wherein the metal catalyst is a cobalt catalyst or a rhodium catalyst. 5. The heat-shrinkable polyester film according to claim 2, wherein the oxidizable polymer is contained in an amount of 1 to 20% by weight based on polyester. 6. The method according to claim 1, wherein the metal catalyst is 1 to polyester.
The heat-shrinkable polyester film according to any one of claims 2 to 5, which is contained in an amount of 0 to 10000 ppm. 7. A composition comprising terephthalic acid and ethylene glycol as main components, neopentyl glycol and / or
Or a polyester film comprising a copolymerized polyester containing 1,4-butanediol as a copolymer component, wherein the amount of neopentyl glycol and / or 1,4-butanediol to be copolymerized is a dicarboxylic acid constituting the polyester. The heat-shrinkable polyester film according to claim 1, which is blended in an amount of 5 to 45 mol% based on the components.