JPH02202428A - Polyester shrinkable film - Google Patents

Abstract

PURPOSE:To enhance the shrinking characteristics by specifying shrinkage factor, glass transition temperature and birefringence rate in an air oven at the specified temperature and after treating for the specified time. CONSTITUTION:Shrinkage factor after treating for five minutes in a 100 deg.C air oven is required to be 30% or above in one direction of a film, preferably 40% or above, and more preferable, 50% or above. Shrinkage factor after treating for five minutes in a 100 deg.C air oven in the direction crossing at right angle with the main shinking direction should be 20% or below, preferably 15% or below, and more preferably 10% or below. When the shrinkage factor of the film is more than 20% in the direction crossing at right angle with the main shrinking direction, distortion or curls at the ends are generated at the time of shrinking and not practical. The glass transition temperature (Tg) of the film is in the range of 35-65 deg.C, preferably 40-65 deg.C, and more preferably 40-60 deg.C. The birefringence rate is in the range of 0.005-0.0050, preferably 0.005-0.040. When the birefringence rate of the film is more than 0.050, large distortion is generated and not preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technique of the Invention + RJ Field] The present invention relates to a polyester shrink film for labels, which has extremely few wrinkles, distortions, and shrinkage spots during shrinkage.

[Prior art and problems to be solved by the invention] In recent years,
Polyester-based shrink films are gaining popularity as a film that can solve the problem of combustibility during disposal or recyclability after being attached to PET bottles.

However, in conventional polyester-based shrink films, shrinkage occurs rapidly and residual shrinkage stress decreases significantly, resulting in wrinkles and distortions in the film after shrinkage, which poses a practical problem.

As a solution to the above problems, the present inventors have previously proposed various methods for improving shrinkage characteristics.

Although it has been possible to improve the shrinkage characteristics of the film to some extent by such improvement measures, it has not yet reached a level sufficient for practical use. In particular, when applied as a shrink label for PET bottles with special shapes that have recently come into use, such as rectangular PET bottles, wrinkles and distortions that occur on the level are noticeable. There was an urgent need for the development of a shrink film.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventors have conducted intensive studies and found that a polyester film having a specific shrinkage rate, glass transition temperature, and birefringence has satisfactory shrinkage characteristics as a shrinkage film for labels. The present invention has been completed based on the discovery that the present invention has the following properties.

That is, the gist of the present invention is that the shrinkage rate after treatment in a 100°C air oven for 5 minutes is 30% or more in one direction and 20% or less in a direction perpendicular to the said direction, and the glass transition temperature is 35 to 65°C. Yes, and the birefringence is 0.0
05 to 0.050.

The present invention will be explained in detail below.

The polyester in the present invention includes known dicarboxylic acid components such as terephthalic acid, oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, etc. Consisting of one or more acids, and diol components such as ethylene glycol, neopentyl glycol, propylene glycol, 1,4-butanediol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, polyalkylene glycol, 1. It is a polyester or copolymerized polyester consisting of one or more types of known diol components such as 4-cyclohexane dimetatool.

The copolymerized polyester includes a dicarboxylic acid component and/or
Alternatively, those obtained by substituting a part of the glycol component with other dicarboxylic acids or glycol components can be used, but other components such as p-oxybenzoic acid, p-
Oxycarboxylic acids such as oxyethoxybenzoic acid, benzoic acid, benzoylbenzoic acid, monofunctional compounds such as methoxypolyalkylene glycols, and polyfunctional compounds such as glycerin, pentaerythritol, trimethylol, trimethylenepropane. It can be used to the extent that the product can retain substantially linear macromolecules.

In the polyester of the present invention, a copolymerized polyester mainly containing terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component is preferably used, and the copolymerized polyester includes isophthalic acid, phthalic acid, adipic acid as the dicarboxylic acid component. , sebacic acid, 1.
A copolymerized polyester using 10-decanedicarboxylic acid, neopentyl glycol, diethylene glycol, polyalkylene glycol as a diol component, and optionally 1,4-cyclohexane dimetatool is industrially available at low cost and has good shrinkage properties. is also good and desirable.

In the copolymerized polyester used in the present invention, the use of a dicarboxylic acid component as one of the copolymerization components is as follows:
This is preferable in that it reduces the shrinkage stress of the film. especially,
Aliphatic dicarboxylic acid components such as adipic acid, sebacic acid, and 1,10-decanedicarboxylic acid lower the glass transition temperature and crystallinity of the film, increasing (lowering) the maximum shrinkage stress in the main shrinkage direction. Preferably. In the copolymerized polyester of the present invention, the content of the aliphatic dicarboxylic acid component is preferably 1 to 25 mof%, more preferably 2 to 20 mof%.

In a film in which the content exceeds 25 mo1%, the Tg decreases significantly, causing natural shrinkage of the film, which is not preferable.

Further, a film having the content of less than 1mo42% is not preferable because a sufficient reduction in Tg cannot be obtained.

In the copolymerized polyester used in the present invention, preferably 70 mol% or more of the dicarboxylic acid component, more preferably 75 mol% or more, is terephthalic acid units, and preferably 70 mol% or more, more preferably 75 mol% or more of the diol component. More than mol% is ethylene glycol units. A copolyester containing less than 70 mol % of terephthalic acid and/or ethylene glycol units is not preferred because the strength and solvent resistance of the film are poor when formed into a film.

In addition, the above polyester may contain 30%
-L% or less, other polymers may be added or mixed.

Furthermore, in order to improve the slipperiness of the film, it is also preferable to contain fine particles of an organic lubricant, an inorganic lubricant, or the like.

Moreover, additives such as stabilizers, colorants, antioxidants, antifoaming agents, and antistatic agents may be contained as necessary. Fine particles that impart slipperiness include known inert external particles such as kaolin, clay, calcium carbonate, silicon oxide, calcium terephthalate, aluminum oxide, titanium oxide, calcium phosphate, lithium fluoride, and carbon black, and melted polyester resin. Examples include internal particles formed inside the polymer during polyester production by insoluble high-melting point organic compounds during film formation, crosslinked polymers, and metal compound catalysts used during polyester synthesis, such as alkali metal compounds and alkaline earth metal compounds. can. The content of fine particles contained in the film is usually 5 to 0.9% by weight of O, OO, and the average particle size of the fine particles is usually in the range of 0.001 to 3.5 μm.

In the present invention, the heat of fusion of the film is preferably 1 to 8 c.
af/g, more preferably 2 to 6 cal/g. If the heat of fusion of the film is less than 1 caf/g, it will be difficult to use the drying method normally used for polyethylene terephthalate in the drying step before extrusion film formation, which is not preferred. Further, a film having a heat of fusion exceeding 8 cal/g is not preferred because a sufficient shrinkage rate cannot be obtained.

The intrinsic viscosity of the film of the present invention is preferably 0.50 or more, more preferably 0.60 or more, particularly preferably 0.6
It is 5 or more. If the intrinsic viscosity of the film is less than 0.50, crystallinity becomes high and sufficient shrinkage cannot be obtained, which is not preferable. In the film of the present invention, 100°C
It is necessary that the shrinkage rate after treatment in an air oven for 5 minutes is 30% or more in one direction of the film, preferably 40% or more, and more preferably 50% or more.

Hereinafter, this direction of shrinkage will be referred to as the main shrinkage direction of the film. Usually, the main shrinkage direction is the lengthwise or crosswise direction of the film. In the present invention, if the shrinkage rate of the film in the main shrinkage direction is less than 30%, when it is shrunk as a label, the amount of shrinkage will be insufficient and the film will not adhere sufficiently to the container, which is undesirable.

The film of the present invention has a shrinkage rate of 2 after being treated in an air oven at 100°C for 5 minutes in a direction perpendicular to the main shrinkage direction.
It needs to be 0% or less, preferably 15% or less, more preferably 10% or less. A film with a shrinkage rate of more than 20% in the direction perpendicular to the main shrinkage direction is not practical because distortions, curls at the edges, etc. occur during shrinkage.

In the film of the present invention, 70°C in the main shrinkage direction
The shrinkage rate after treatment in an air oven for 5 minutes is preferably 20% or more, more preferably 30%, particularly preferably 4
It is 0% or more. A film having such a shrinkage rate of less than 20% is undesirable because it causes uneven shrinkage in some parts (for example, in the creases after bag making) at the initial stage of shrinkage of the film.

In the film of the present invention, the glass transition temperature (Tg) of the film is in the range of 35 to 65°C.

Preferably 40-65℃1 More preferably 40-60℃
It is. For films with a Tg higher than 65°C, when passing through a shrink tunnel at a relatively low temperature (for example, PET
(for bottles), the amount of heat necessary for shrinking the film is not given sufficiently, so wrinkles in the film that occur at the beginning of shrinkage cannot be completely removed by the end of shrinkage, which is undesirable as it causes shrinkage spots. In addition, if the film has a Tg of less than 35° C., large natural shrinkage will occur during long-term storage in a warehouse or the like before shrinkage processing, making it impossible to attach the film to a container, which is undesirable.

In the film of the present invention, the shrinkage stress generation start temperature in the main shrinkage direction is preferably in the range of 40 to 60°C, more preferably 45 to 60°C, and particularly preferably 45 to 55°C. If the starting temperature exceeds 60° C., the heat required for shrinkage cannot be obtained in the shrink tunnel, and shrinkage spots and wrinkles remain on the film after shrinkage, which is undesirable. Further, in a film at such a temperature of less than 40'C, the above-mentioned natural shrinkage becomes large, which is not preferable.

As mentioned above, the present inventors have found that the wrinkles of the film after shrinkage are considerably improved by controlling the shrinkage rate, Tg, etc. of the film within a specific range.

However, the distortion of the film during shrinkage was still insufficient in the above studies, and further improvements were required for practical use.

As a result of further intensive studies, the present inventors have discovered that by extremely reducing the birefringence of the film, the distortion of the film during shrinkage can be significantly reduced.

That is, in the film of the present invention, the birefringence is O
, OO5 to 0.050. Preferably O, O
It is in the range of O5 to 0.040. A film with a birefringence index exceeding 0.050 is undesirable because it causes a large amount of distortion during shrinkage. The reason for this is not clear, but the inventors estimate that the birefringence is 0.0.
This is believed to be because films with a diameter exceeding 50 have a large shrinkage stress in the main shrinkage direction, resulting in a high shrinkage speed at the start of film shrinkage, resulting in non-uniform shrinkage.

On the other hand, a film having a birefringence index of less than O, OO5 has poor solvent resistance, thickness unevenness, etc., and is unfavorable from the viewpoint of printing suitability.

Furthermore, in the film of the present invention, the degree of plane orientation of the film is preferably in the range of 0.005 to 0.040, more preferably in the range of 0.0 O5 to 0.035.

Films with a degree of plane orientation of less than O, OO5 have low solvent resistance and hot water resistance and are not practical. On the other hand, a film with a degree of plane orientation exceeding 0.040 is not preferable because the maximum shrinkage stress in the direction orthogonal to the main shrinkage direction of the film becomes high and the shrinkage characteristics deteriorate.

In the film of the present invention, the maximum shrinkage stress of the film in the main shrinkage direction is preferably 1000 g/mm! The maximum shrinkage stress is preferably 700 g/mm" or less, particularly preferably 500 g/mm2 or less. A film having a maximum shrinkage stress of more than 100057 mm" is undesirable because the film will be greatly distorted during shrinkage.

Further, in the film of the present invention, the maximum shrinkage stress at 40 to 100° C. in a direction perpendicular to the main shrinkage direction of the film is preferably 50 g/mm” or less, more preferably 30 g/s” or less.

When a film having a maximum shrinkage stress in this direction exceeds 50 g/mm' is shrunk as a label, many curls and wrinkles occur, particularly near the upper end of the label, which is not preferable.

In addition, in the film of the present invention, the initial value of shrinkage stress in the main shrinkage direction in silicone oil at 75° C.
(g/mm”) and 2 in silicone oil at 75°C.
It is desirable that the relationship of shrinkage stress F2° (g/m+a'') at the elapse of 0 seconds preferably satisfies F20≧F0-100 g/mm'', more preferably F20≧F0. If F2° is less than (FO-100) 57 mm, it is undesirable because it becomes difficult to correct or eliminate wrinkles that occur at the beginning of shrinkage of the film at the end of shrinkage or after the shrinkage is completed.

Furthermore, on one or both sides of the film of the present invention, a foaming ink layer is printed, or a thermoplastic resin film or sheet with bubbles inside is laminated to provide cushioning properties, and the glass bottle is broken after packaging. It is also possible to improve the effects. As such a thermoplastic resin, any known thermoplastic resin such as polyvinyl chloride, polyethylene, polypropylene, polyacrylic, polystyrene, polyester, etc. may be used.

The thickness of the film obtained as described above is not particularly limited, but the thickness preferably used as a shrink film for labels is 10 to 300 μm, particularly preferably 1
It is 5 to 200 μm.

Next, the method for manufacturing the film of the present invention will be specifically explained.
The manufacturing method described below is not particularly limited.

Polyester or copolymer polyester having the composition of the present invention containing an appropriate amount of inorganic particles as a lubricant, if necessary.
After drying using a conventional hopper dryer, paddle dryer, vacuum dryer, etc., extrusion is carried out at a temperature of 200 to 320''C.

For extrusion, any existing method such as the T-die method or the tubular method may be used.

After extrusion, the film is rapidly cooled to obtain an unstretched film. When using the T-die method, it is preferable to use the so-called electrostatic application adhesion method during the rapid cooling because a film with uniform thickness can be obtained.

The obtained unstretched film is mainly uniaxially stretched in one or more stages so that the finally obtained film satisfies the constituent requirements of the present invention.

l-axis stretching methods include stretching only in one vertical axis with rolls, stretching only in one horizontal axis with a tenter, and stretching strongly in either the vertical or horizontal direction during known biaxial stretching. , it is also possible to stretch the other one as small as possible.

As such a biaxial stretching method, a known sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, and further stretching can be performed again.

In the above stretching, by stretching in the main shrinkage direction at a stretching ratio of at least 2.5 times or more, preferably 3.0 times or more, and satisfying the birefringence range of the film of the present invention, it is possible to A film can be obtained which has a low birefringence and is excellent in solvent resistance, thickness unevenness, etc.

After stretching, the stretched film is heated at 60°C or higher for 1
It is also a preferable method to perform heat treatment at 00° C. or lower for 0.01 seconds or more and 60 seconds or less, particularly preferably 0.01 seconds or more and 30 seconds or less, in order to obtain uniform shrinkage of the film. Heat treatment is usually carried out under tension fixation, but at the same time 20%
It is also possible to carry out the following relaxation or widening. As the heat treatment method, known methods such as a method in which the material is brought into contact with a heating roll or a method in which the material is gripped by a clip in a tenter can be used. Further, it is also possible to perform re-stretching after heat treatment.

It is also possible to perform a corona discharge treatment on one or both sides of the film during, before, or after the stretching process to improve the adhesion of the film to the printed layer or the like.

It is also possible to improve the adhesion, antistatic properties, slipperiness, light-shielding properties, etc. of the film by coating one or both sides of the film during, before, or after the stretching process.

The film thus obtained is wound up to form a product.

As described above, by satisfying the constituent requirements of the present invention, it is possible to obtain a polyester-based shrink film having excellent shrinkage properties with extremely few film distortions, wrinkles, shrinkage spots, etc. during shrinkage.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

In addition, the evaluation method of the film is shown below.

(1) Intrinsic viscosity of film [η] 200 mg of sample was mixed with phenol/tetrachloroethane
In addition to 20 ml of mixed solvent of 50150, 1
After heating for a period of time, measurements were taken at 30°C.

(2) Shrinkage rate 1cm width Locm long strip of film 70'
The product was held in a guarded oven at a temperature of C+2°C and 100+2°C for 5 minutes without any load, and the shrinkage rate was determined according to the following formula.

[2: Length after shrinkage (am) 3 (3) Glass transition temperature of the film The Tg film was melted by heating at 300″C in a nitrogen atmosphere for 5 minutes, rapidly cooled to an amorphous state, and then sold to Seiko Electronics Co., Ltd. Temperature increase rate 4℃/m using Kogyo's differential calorimeter 5SC580DSC20 type
Tg was measured at in. Tg was defined as the arithmetic mean value of the temperature T at which the baseline began to diverge to the endothermic side and the temperature T2 at which the baseline settled to the new baseline.

(4) Birefringence Δn Retardation was measured using a polarizing microscope manufactured by Carl Zeiss, and birefringence (Δn) was determined using the following formula.

Δn=R/d (5) Degree of Planar Orientation ΔP The refractive index of the film was measured using an Ache refractometer manufactured by Akugo Co., Ltd. (l@) and using a sodium lamp as the light source.

The maximum refractive index ny in the plane of the film, the refractive index nβ in the direction perpendicular thereto, and the refractive index nα in the thickness direction were determined, and the degree of plane orientation ΔP was determined using the following formula.

ΔP=-(nT+nβ)-nα (6) Maximum shrinkage stress, shrinkage stress onset temperature (main shrinkage direction) Using Intesco 2001 model manufactured by Intesco ■, use a sample cut out with a chuck distance of 10 cm and a width of 1 cm. The temperature was measured at a heating rate of 10° (:/min).

The maximum shrinkage stress is 40 to 10 in the main shrinkage direction.
The maximum shrinkage stress at 0°C was determined. The temperature at which shrinkage stress starts to occur is set to a temperature at which shrinkage stress is substantially generated (for example, 5 g/mm 2 or more) in the main shrinkage direction.

(7) Shrinkage characteristics of the film The film was printed and made into a bag as a shrink label, made into a cylindrical shape, and then placed over a PET bottle and passed through a shrink tunnel set at 140° C. for 6 seconds to shrink. The shrinkage finish of the obtained label was visually judged as O1Δ, × in terms of wrinkles, distortion, and print shading due to shrinkage spots. O indicates that almost no defects are observed, Δ indicates that some defects are present but can be put to practical use, and × indicates that many defects are observed and cannot be used. In addition, considering the above three evaluation items comprehensively, the overall shrinkage characteristics are ○,
A rating of × was given.

Example 1 Terephthalic acid unit 80 moβ% as dicarboxylic acid component
, isophthalic acid unit 15mof%, sebacic acid unit 5
91 mo1% of ethylene glycol units and 3 diethylene glycol units as diol components.
copolymerized polyester ([η
) = 0.67) by a conventional method, and then extruded to 280"
C and extruded through a T-die, followed by rapid cooling and solidification to obtain an unstretched film. The resulting unstretched film was directly introduced into a tenter, stretched 2.8 times in the transverse direction at 120°C, and then further stretched 7 times.
The film was laterally stretched 1°3 times at 0°C, then heat treated at 83°C for 7 seconds, and cooled to obtain a film with an average thickness of 45 μm.

Example 2 82 mo1 terephthalic acid units were used as the dicarboxylic acid component.
%, isophthalic acid units 10 moi%, 1,10-decanedicarboxylic acid units 8 moi%, and the diol component consists of ethylene glycol units, average particle size 1.
A copolymerized polyester ([η)=0.71) containing 400 ppm of 2 μm amorphous silica was pre-crystallized at 120° C. for 54 hours, dried at 180° C. for 4 hours, and then dried at 290° C. using an extruder. The film was melted and extruded through a T-die, and rapidly solidified to obtain an unstretched film. The obtained unstretched film was stretched 1.05 times in the machine direction at 90°C, then introduced into a tenter, stretched 3.0 times in the transverse direction at 110°C, and then stretched 6 times in the transverse direction at 110°C.
It was laterally stretched 163 times at 5°C. The obtained stretched film was once wound up, then unwound again and heat treated at a'o'c for 10 seconds to obtain a film with an average thickness of 60 μm.

Example 3 Terephthalic acid unit 85 moβ% as dicarboxylic acid component
, a copolymerized polyester consisting of 15 moff% of adipic acid units, 87.5 mof% of ethylene glycol units and 12.5 mof% of neopentyl glycol units as diol components, and polyethylene terephthalate containing 2000 ppm of amorphous silica with an average particle size of 1.2 μm. 8
After blending at a ratio of 0/20 (weight ratio), an unstretched film ([η)=0.69) was obtained in exactly the same manner as in Example 2. The obtained film was heated with a heating roll at 110°C for 2
．． After 6 times fiiT stretching, 1
．． The film was longitudinally stretched 25 times, and then heat-treated by contacting it with a heating roll at 85° C. for 0.6 seconds. The average thickness of the film obtained by cooling after heat treatment was 30 μm.

Comparative Example 1 The lateral stretching conditions in Example 1 were changed to 2°8 at 120'C.
A film having an average thickness of 45 μm was obtained in the same manner as in Example 1, except that after the double stretching, the film was laterally stretched 1.8 times at 70'C.

Comparative Example 2 82 moI of terephthalic acid units as dicarboxylic acid component!
, %, 18 mof% of isophthalic acid units, and ethylene glycol units as the diol component. Drying, extrusion, and rapid solidification were carried out in exactly the same manner as above to obtain an unstretched film. The obtained unstretched film was stretched and heat treated in the same manner as in Example 1, cooled, and rolled to an average thickness of 45 μm.
obtained the film.

The evaluation results of the films obtained above are summarized in Table 1.

In the film of Comparative Example 1, Δn was large, and as a result, a lot of distortion occurred in the film during shrinkage, which was not preferable.

Since the film of Comparative Example 2 had a high Tg, many wrinkles remained on the film after shrinkage, and the printing was unfavorable.

In contrast to the above Comparative Examples, the films of Examples 1 to 3 show almost no wrinkles, printing shading, distortion, etc. after shrinkage, and have extremely excellent properties as shrink films for labels.

[Effects of the Invention] The film of the present invention is a film with extremely excellent shrinkage characteristics, with very few film wrinkles, printing shading, distortion, etc. when shrinking, and has extremely high industrial value, especially as a shrink film for labels. It's a film.

Applicant: Diafoil Co., Ltd. Representative Patent Attorney Hase 1 other person

Claims (1)

[Claims] (1) The shrinkage rate after treatment for 5 minutes in an air open environment at 100°C is 30% or more in one direction and 20% or less in a direction perpendicular to the said direction, and the glass transition temperature is 35 to 6.
A polyester shrink film having a temperature of 5° C. and a birefringence of 0.005 to 0.050.