JP2793713B2 - Polyester shrink film with improved surface properties - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyester shrink film having excellent low-temperature heat shrinkage properties and excellent printability and used for shrink labels, packaging and the like.

<Conventional technology> Conventionally, films for shrink labels used for various containers including glass include polyvinyl chloride,
Alternatively, films made of polystyrene have been mainly used.

On the other hand, polyethylene terephthalate (hereinafter PET) is used mainly for food containers such as juice, sake, tea, soy sauce, oil, etc.
Abbreviations) Bottles have become widespread, and PET
Conventionally, heat-resistant PET bottles that withstand hot water disinfection have been the mainstream, but in recent years, hot water disinfection and disinfection steps have been omitted by adopting an aseptic filling method, reducing cost. The use of low heat-resistant PET bottles is being promoted.

However, since a non-heat-resistant PET bottle undergoes a volume change when a temperature of about 80 ° C. or higher is applied, use a film of the above-mentioned polyvinyl chloride or polystyrene, which exhibits a high shrinkage rate at 80 ° C. or higher. Therefore, a film that does not exhibit high shrinkage at a lower temperature is desired. Also, PET
Bottles are industrially and socially required to be recovered and reused.
Since a separation step is required, a polyester-based shrink film is desired for label use in order to reuse the bottle and the label without separating them.

To meet such demands, recently, by using an amorphous copolyester obtained by copolymerizing neopentyl glycol or isophthalic acid, it is possible to obtain a film having a large shrinkage and excellent heat sealability. And JP-A-63-156833, JP-A-63-202429, and JP-A-63-7573. However,
The film in which neopentyl glycol is copolymerized has a high Galus transition temperature of about 75 ° C., and as a result, the heat shrinkage behavior at 80 ° C. or higher exhibits a large shrinkage rate and excellent performance of uniformly shrinking, The heat shrinkage behavior at a temperature lower than 0 ° C. has a drawback that tarmi occurs due to insufficient shrinkage or the like.

In addition, the film obtained by copolymerizing isophthalic acid can lower the glass transfer temperature to around 60 ° C,
Even at a temperature lower than 80 ° C., a large shrinkage can be obtained. However, when this film is heated in a shrinking tunnel device, it shrinks instantaneously in the initial stage of heating, and exhibits a unique shrinking behavior that it hardly shrinks even with subsequent heating. A spot of shrinkage occurs, and wrinkles, waviness and the like occur.

Attempts to adjust the heat shrinkage, seal strength, heat shrinkage stress, etc. have been proposed to improve these problems, but it is extremely difficult to control these in the actual operation process, and slight fluctuations in conditions This also causes problems such as uneven shrinkage of the film, the upper end or lower end of the shrinked label being skewed, and frequent pattern distortion.

In addition, polyester film represented by PET,
The surface activity is low, there are restrictions on the printing inks that can be used,
Cellophane printing ink using nitrocellulose as a binder, which is inexpensive and has good coloring properties, cannot be used. For the purpose of improving the printability of this polyester-based film, a film composed of a mixture of PET, a polyester containing a metal salt of sulfonic acid, and a polyester containing a polyoxyalkylene glycol is disclosed in JP-A-56-16549. However, even if this film is stretched, it hardly shrinks at a low temperature of less than 80 ° C., and is insufficient as a shrink film.

<Problems to be Solved by the Invention> The inventors of the present invention have conducted intensive studies in order to achieve these problems, and as a result, by mixing a dicarboxylic acid component and a diol component having a specific composition in a specific ratio, low-temperature heat shrinkage has been achieved. The inventors have found that a polyester shrink film having excellent properties and printability can be obtained, and have reached the present invention. That is, an object of the present invention is to excel in low-temperature heat shrinkage properties,
An object of the present invention is to provide a polyester shrink film which has good adhesion to a T bottle or the like, does not cause shrinkage spots or wrinkles, and has improved printability for cellophane printing inks.

<Means for Solving the Problems> The object of the present invention is to provide a polyester for forming a film,
As a dicarboxylic acid component, 95 to 70 mol of terephthalic acid
%, 0.1 to 10 mol% of 5-sulfoisophthalic acid metal salt, and a total of 5 to 30 mol% with 5-sulfoisophthalic acid metal salt.
1% of isophthalic acid, and 94 to 40 mol% of ethylene glycol, 5 to 30 mol% of diethylene glycol, and 1 of neopentyl glycol as diol components.
3030 mol%, and in a 75 ° C. glycerin bath of the film.
This is achieved by a polyester-based shrink film characterized in that the heat shrinkage in 0 second is 40% or more in one direction in either the machine direction or the transverse direction.

 Hereinafter, the present invention will be described in detail.

The composition ratio of each component of the polyester constituting the polyester shrink film of the present invention is one of the important requirements in the present invention. As the dicarboxylic acid component, terephthalic acid is 95 to 70 mol%, preferably 90 to 80 mol%. , 5-
0.1 to 10 mol% of the metal sulfoisophthalate, preferably
0.5 to 5 mol%, and further contains 5 to 30 mol%, preferably 10 to 20 mol% of isophthalic acid in total with 5-sulfoisophthalic acid metal salt, and 94 to 40 mol%, preferably, ethylene glycol as a diol component, preferably Is 88 to 60 mol%, diethylene glycol is 5 to 30 mol%, preferably 8 to 20 m
It is important to contain 1 to 30 mol%, preferably 4 to 20 mol% of neopentyl glycol.

If the amount of the 5-sulfoisophthalic acid metal salt is less than 0.1 mol%, the printability is not improved, and if it exceeds 10 mol%, the mechanical strength is reduced, and the film-forming property and the stretchability are deteriorated. If the sum of the metal 5-sulfoisophthalate and isophthalic acid is less than 5 mol%, the shrinkage is small, while if it exceeds 30 mol%, the mechanical strength and solvent resistance are undesirably reduced.
The metal of the 5-sulfoisophthalic acid metal salt is preferably an alkali metal such as lithium, sodium, potassium and calcium or an alkaline earth metal.

For the diol component, diethylene glycol is 5m
If the amount is less than 80%, the heat shrinkage property at a low temperature of 80 ° C. or less becomes poor.
The effect of improving shrinkage spots is insufficient. Further, when the content of diethylene glycol or neopentyl glycol exceeds 30 mol%, the strength and stretchability are remarkably reduced.

A film made of polyester having the above composition ratio is excellent in low-temperature heat shrinkage property, unlike a conventional polyester shrink film having another composition, when the film is shrunk by being passed through a shrink tunnel device after being attached to a bottle. It is suitable as a shrink film for labels, free from wrinkles and sagging. The reason is that the composition having the above composition ratio tends to take a more uniform copolymerization form than that of the other composition, and therefore retains the excellent mechanical performance inherent in polyester, and furthermore, the other components. It can be said that the structure is easy to maximize the advantages of. That is, depending on the metal salt of 5-sulfoisophthalic acid and isophthalic acid, orientation crystallization when the film is stretched is suppressed, and a uniform and large heat shrinkage rate is given, and depending on diethylene glycol, the glass transition temperature is lowered. In addition, the temperature at which the film starts shrinking decreases, and it is possible to use the film sufficiently even in a low temperature range of less than 80 ° C. It is thought that it is effective to have an appropriate contraction speed so as not to cause contraction spots. In addition, generally, when the glass transition temperature is lowered, the films tend to adhere to each other and tend to lack thermal stability such that the color tends to be yellowish, but the composition of the present invention has It will also exhibit excellent effects.

Furthermore, the shrink film of the present invention is compared with a conventional polyester shrink film having another composition.
The printability is improved, and it is possible to use a cellophane printing ink using nitrocellulose as a binder inexpensively and with good coloring properties. One of the reasons is that the activity of the film surface is increased by the sulfonic acid metal base and the diethylene glycol component contained in the polyester. Printing on the shrink film of the present invention can be performed by gravure printing or any other method.

The polyester constituting the polyester film of the present invention may contain a copolymer component other than the above components as long as the properties of the film are not changed. As the components other than the above components, dicarboxylic acid components include oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, 5-tert-butylisophthalic acid, naphthalenedicarboxylic acid, and diphenylether dicarboxylic acid And diol components such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, polyalkylene glycol, 1,4-cyclohexanedimethanol, and the like.

Further, other copolymerization components, for example, monofunctional compounds such as oxycarboxylic acids such as p-oxybenzoic acid, p-oxyethoxybenzoic acid, benzoic acid, benzoylbenzoic acid, and methoxypolyalkylene glycol, glycerin, pentaerythritol Polyfunctional compounds such as trimethylolethane, trimethylolpropane, and the like, may also be used as long as the product can retain a substantially linear polymer.

The polyester of the present invention may be produced using a usual direct esterification method or transesterification method.

Further, other polyesters, other polymers or various additives may be added to and mixed with the polyester constituting the film of the present invention as long as the gist of the present invention is not changed. For example, known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, etc. as inorganic lubricants and organic lubricants for improving the lubricity of the film. Is formed inside the polymer during the production of polyester, such as an insoluble high-melting organic compound, a cross-linked polymer, a metal compound catalyst used in the production of a polyester such as an alkali metal compound or an alkaline earth metal compound, etc., which is blended in the melt film formation of the polyester resin. Internal particles. Further, if necessary, a stabilizer, a coloring agent, an antioxidant, an antifoaming agent and the like may be contained. The fine particles contained in the film are usually 0.005 to 0.5% by weight.

The intrinsic viscosity of the film of the present invention is preferably 0.1.
It is 50 or more, more preferably 0.60 or more. If the intrinsic viscosity of the film is less than 0.50, the film formation, stretchability, and mechanical strength tend to decrease.

The film of the present invention is required to have a shrinkage ratio of 30% or more in a glycerin bath at 75 ° C. in one direction of either the length or width of the film of 40% or more, preferably 45% or more.
Or more, more preferably 50% or more. A film having a shrinkage ratio of less than 40% is not preferable because a shrink tunnel used for a non-heat-resistant PET bottle has a low setting temperature of a shrinkage zone of less than 80 ° C. and thus cannot sufficiently adhere to a container.

The glass transition temperature of the polyester constituting the film of the present invention is preferably 50 ° C. or more and 70 ° C. or less, more preferably 65 ° C. or less. When the temperature exceeds 70 ° C., it becomes difficult to lower the shrinkage starting temperature of the film, and therefore, even when passing through a shrink tunnel of less than 80 ° C., it is difficult to sufficiently adhere to the container due to insufficient shrinkage. , And sag easily occurs. On the other hand, if the glass transition temperature is lower than 50 ° C., there is a tendency that problems occur in storage and handling of the shrink film in the non-shrink film.

Next, the film production method of the present invention will be described. Using a polyester having the composition of the present invention, a film obtained by any method such as an extrusion method or a calendar method, for example, is stretched in one direction to 2.0 times or more and 5.0 times or less, preferably 2.5 times or less to 4.5 times or less. The film is stretched 1.0 to 2.0 times, preferably 1.1 to 1.8 times in a direction perpendicular to the direction. The first stretching is performed to obtain a high shrinkage, and the stretching in the direction perpendicular to the direction is performed in order to solve the poor impact resistance and tear resistance of the film stretched in the direction. Done. There is no special restriction on the stretching means,
Methods such as roll stretching and tenter stretching 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. For the film of the present invention, for example, one axis in the longitudinal direction, one axis in the horizontal direction, and two axes in the vertical and horizontal directions. In the biaxial stretching, in particular, in the longitudinal and transverse directions, successive biaxial stretching in which one of them is performed first is effective. The heat setting in these stretchings is carried out according to the purpose, and it is recommended to pass through a heating zone at 90 ° C. or lower for 1 second to 30 seconds. The thickness of the film thus obtained is not particularly limited, but a range of 5 to 250 μm is practical.

<Effects of the Invention> As described above, a polyester film satisfying the constitutional requirements of the present invention has good heat shrinkage properties at low temperatures, excellent adhesion to a PET bottle, and causes shrinkage spots and whitening. Without this, it has good printability, is very excellent in appearance, and is extremely useful in industry.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

 The measurement and evaluation methods are described below.

(1) Shrinkage The film was thermally shrunk in a glycerin bath at 75 ° C. ± 0.5 ° C. for 30 seconds with no load, and determined according to the following equation.

(2) Intrinsic viscosity [η] A 200 mg sample was phenol / tetrachloroethane = 50/50
Was added to 20 ml of a mixed solvent, and dissolved by heating at about 110 ° C. for 1 hour, and then measured at 30 ° C.

(3) Glass transition temperature / Tg (° C) Temperature rise rate 4 ° C / mi using DSC-1B manufactured by PerkinElmer
Measured at n.

(4) Evaluation of heat shrinkage characteristics of shrink film After sticking the film in a tubular shape to form a label, cover it over a PET bottle, leave it in a hot air dryer at a set temperature of 75 ° C for 5 minutes, and check whether the film is sufficiently adhered. Was visually evaluated, and good samples were evaluated as ○, and poor samples were evaluated as ×. The film was visually evaluated for wrinkles or distortions, and was evaluated as "O" when there was no shrinkage spot, and as "X" when it did.

(5) Evaluation of printability Using a cellophane printing ink, the film was subjected to gravure printing, and then sufficiently dried at room temperature. Thereafter, a peeling test was carried out using a cellophane tape, and those where the printing ink did not peel were evaluated as ○, and those which peeled were evaluated as x.

(6) Evaluation of Strength Tensile strength in the longitudinal and transverse directions of the film was measured. A film having a strength of 200 g / cm ² or more in both directions was evaluated as ○, and a film having at least one of less than 200 g / cm ² was evaluated as ×.

<Example 1> Dimethyl terephthalate, dimethyl isophthalate, ethylene glycol, diethylene glycol, and neopentyl glycol were blended in the proportions shown in Table 1, and 0.05 mol of calcium acetate-water salt was taken as a catalyst in a stainless steel autoclave and placed under a nitrogen stream. The transesterification reaction was performed at 150 to 240 ° C. Next, metal ester of 5-sulfoisophthalic acid, 400 ppm of antimony trioxide (based on polymer) and 100 ppm of trimethyl phosphate (based on polymer) were further added to carry out esterification. After completion of the esterification, the temperature was raised to 280 ° C., and polymerization was carried out under reduced pressure to obtain a copolymerized polyester.

This polyester was extruded from a T-die at 270 ° C. to obtain an unstretched film having a thickness of 185 μm. The film was further stretched 1.1 times in the machine direction and then 4.0 times in the transverse direction to obtain a shrink film having a thickness of 42 μm. As shown in Table 2, the evaluation of this shrink film was high in both heat shrinkage characteristics and printability.

<Examples 2 to 5> In the same manner as in Example 1, a shrink film was prepared from a polyester in which the components described in Table 1 were blended.
Was obtained. All were suitable as shrink films.

<Comparative Examples 1 to 9> A stretched film was prepared from the polyester having the composition shown in Table 1 in the same manner as in the Example, and the results shown in Table 2 were obtained. Comparative Example 1
Is low in both heat shrinkage properties at low temperature and printability. Comparative Examples 2, 3, 5,
Sample No. 7 had poor heat shrinkage characteristics at low temperatures, Comparative Example 4 did not sufficiently improve printability, and Comparative Examples 3, 6, 8, and 9 had significantly reduced mechanical strength.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08L 67:02

Claims (1)

(57) [Claims] The composition of the polyester constituting the film is such that the terephthalic acid is 95 to 70 mol as a dicarboxylic acid component.
%, 0.1 to 10 mol% of 5-sulfoisophthalic acid metal salt, and a total of 5 to 30 mol% with 5-sulfoisophthalic acid metal salt.
1% of isophthalic acid, and 94 to 40 mol% of ethylene glycol, 5 to 30 mol% of diethylene glycol, and 1 of neopentyl glycol as diol components.
3030 mol%, and in a 75 ° C. glycerin bath of the film.
A polyester shrink film characterized in that the heat shrinkage for 0 second is 40% or more in one of the longitudinal direction and the transverse direction.