JPH0459333A - Polyester shrink film for label - Google Patents

Abstract

PURPOSE:To obtain a film which possesses high-shrink properties unidirectionally and is hard to tear in the direction meeting at right angles with that direction and superior in strength, by a method wherein shrinkage factors of a lateral and longitudinal directions are specified and breaking extension of the longitudinal direction of the film is specified. CONSTITUTION:Shrinkage factors of a film after treatment of the film for 5 minutes in an air oven having a temperature of 100 deg.C are at least 40% in a lateral direction and 20% or lower in a longitudinal direction and breaking extension of the longitudinal direction of the film is at least 250%. Terephthalic acid and copolymeric polyester consisting mainly of ethylene glycol are used preferably respectively as a dicarboxylic acid component and diol component, in polyester. It is preferable from the view point of reduction of shrinkage factor of the film to make use of dicarboxylic acid component as one of copolymeric components. Especially, an aliphatic dicarboxylic acid component such as adipic acid or sebacic acid lowers the glass transition temperature and deteriorates crystallinity and the maximum shrinkage stress of a main shrinkage direction can be deteriorated greatly. Content of the above-mentioned aliphatic dicarboxylic acid component is preferably 1-25mol%, further preferably 2-20mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyester shrink film for labels having excellent shrink properties and strength.

[Prior art and problems to be solved by the invention] In recent years, polyester-based shrink film for labels has attracted attention as a film that can solve the problems of flammability during disposal and recyclability after being attached to PET bottles. are collecting.

One of the properties particularly required for shrink film for labels is to have high shrinkability in one direction,
Another reason is that there is almost no contraction in the direction perpendicular to this. However, in order to obtain a film that has high shrinkability in only one direction, for example, if the film is simply strongly oriented only in the transverse direction, the film will be easily torn and its strength will be weakened in the longitudinal direction.

Label films are manufactured through printing, bag making, and cutting processes, but if a film with low strength is used because it easily tears in the vertical direction, the film will frequently break during the above processing steps, resulting in extremely low productivity. decreases to

Therefore, a shrink film for labels that has high shrinkability in one direction, is difficult to tear in a direction perpendicular to that direction, and has excellent strength has been desired.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventors have conducted extensive studies and found that a polyester film having certain shrinkage characteristics and strength is extremely useful as a shrink film for labels, and have completed the present invention. .

That is, the gist of the present invention is that the shrinkage rate of the film after being treated in an air open environment at 100°C for 5 minutes is 40% in the transverse direction.
% or more, and 20% or less in the machine direction, and the elongation at break in the machine direction of the film is 250% or more.

The present invention will be explained in detail below.

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,
Copolyesters using 10-decanedicarboxylic acid, neopentyl glycol, diethylene glycol, polyalkylene glycol, and 1,4-cyclohexane dimetatool as diol components are industrially available at low cost and have good shrinkage properties. preferable.

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 are preferred because they can lower the glass transition temperature and crystallinity of the film and greatly reduce the maximum shrinkage stress in the main shrinkage direction. 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 mo1%.

For films with such content exceeding 25 mof%, Tg
This is not preferable because it causes a significant decrease in the film temperature and induces natural shrinkage of the film. In addition, in a film with a content of less than 1 wof%,
This 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%
-t% 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.
Al! /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 preferable. Also, the heat of fusion is 8caI! .

If the weight exceeds 7 g, a sufficient shrinkage rate cannot be obtained, which is not preferable.

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.
It is 65 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.

The film of the present invention has a shrinkage rate in the lateral direction (main shrinkage direction) of the film after being treated in an air oven at 100°C for 5 minutes.
The shrinkage rate is preferably 45% or more, more preferably 50% or more. A film having a transverse shrinkage rate of less than 40% cannot be used for labels because the amount of shrinkage is insufficient.

The film of the present invention is
The shrinkage rate after the minute treatment is 20% or less in the longitudinal direction of the film, that is, the direction perpendicular to the main shrinkage direction, and the shrinkage rate is preferably 15% or less, more preferably 10% or less.

If the shrinkage rate in the longitudinal direction exceeds 20%, distortion or curling of the edges will occur during shrinkage, resulting in poor appearance of the label and cannot be put to practical use.

The film of the present invention generally has a shrinkage rate in the transverse direction of the film after being treated in 75° C. hot water for 5 seconds, preferably 30% or more, preferably 35% or more, and more preferably 40% or more. The shrinkage rate of the film in the longitudinal direction under the same conditions is preferably 10% or less, more preferably 5% or less.

Shrink tunnels used for non-heat resistant PET bottles have a low set temperature in the shrink zone of less than 80°C, so a film with a shrinkage rate of less than 30% in the main shrinkage direction under the above conditions will not adhere well to the container. It is not possible and not desirable. In addition, the shrinkage rate in the direction perpendicular to the main shrinkage direction is 10%.
If the film exceeds this value, the design of the film will be distorted after shrinkage, making it undesirable as a shrink film for labels.

Both ends of the film of the present invention in the main shrinkage direction are fixed, and
The maximum shrinkage rate in the direction perpendicular to the main shrinkage direction after treatment in °C warm water for 5 seconds (hereinafter referred to as "nequin ratio") is usually 20% or less, preferably 18% or less, more preferably It is 15% or less.

In the present invention, the neck-in rate is 13c in the main contraction direction.
m, measured on a rectangular sample with a direction perpendicular to this direction of 10 cm, and this size is the average value of the folded diameter length and medium length of commonly used shrink labels. be. The shrinkage rate is closely related to shrinkage spots such as diagonal overlapping of the film and distortion of the film after passing through the shrink tunnel. That is, a film with a neck-in rate exceeding 20% frequently suffers from shrinkage spots, which is extremely undesirable from a practical standpoint.

The reason why shrinkage spots are more likely to occur when the neck-in rate is large is not clear, but the inventors' considerations are as follows.

It is considered that in a film with a high neck-in ratio, when the main shrinkage direction is fixed, a considerable proportion of the shrinkage stress that should act in the main shrinkage direction acts in a direction perpendicular to the main shrinkage direction. When this type of film is actually used as a shrink film for labels and is shrunk after being attached to a container, especially a bottle, immediately after the film comes into close contact with the largest external part of the bottle along the main shrink direction, there is a large amount of shrinkage in the direction perpendicular to the main shrink direction. Shrinkage stress is generated, and the shrinkage behavior of the film portion that is shrinking in the main shrinkage direction becomes extremely unstable, and as a result, it is thought that shrinkage spots such as diagonal overlapping and distortion of the film occur.

In addition to the above-mentioned shrinkage properties, particularly the shrinkage properties after being treated in an air open environment at 100° C. for 5 minutes, the film of the present invention is required to have a longitudinal elongation at break of 250% or more. The elongation at break as used in the present invention is 15 mm width, 25
It refers to the elongation at break when a mm-long sample is pulled at a tensile speed of 50 Qan/min.

Regarding the elongation at break, longitudinal tearing of the film is closely related to development, and films with an elongation at break of less than 250% frequently break when processed for labels. The elongation at break is preferably 300% or more, more preferably 350% or more,
Particularly preferably, it is 400% or more.

The birefringence of the film of the present invention is usually 0.005 or more, preferably in the range of 0.030 to 0.150. A film with a birefringence index of less than 0.005 has poor welding resistance, which poses a problem when printing for labels.

Furthermore, a film with a birefringence index exceeding 0.150 tends to be distorted during shrinkage.

Next, the manufacturing method of the film of the present invention will be specifically explained, but the method is not particularly limited to the following manufacturing method as long as it does not go beyond the gist of the present invention.

A polyester or copolyester containing an appropriate amount of inorganic particles as a lubricant, if necessary, is dried using a conventional hopper dryer, paddle dryer vacuum dryer, etc., and then extruded 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 employ the so-called electrostatic application adhesion method during the rapid cooling, since a film with uniform thickness can be obtained.

The obtained unstretched film is stretched one step in the longitudinal direction using a heated longitudinal stretching roll so that the birefringence index (ΔnI) is in the range of 0.005 to 0.050, preferably in the range of O,OO5 to 0.030. Or, it is stretched 1.1 to 2.0 times in two or more stages. Next, the longitudinally uniaxially stretched film was adjusted to have a birefringence index (△n2) of 0.
040 or less, preferably 0.030 or less,
Relax in the machine direction by 0.70 to 0.98 times in the machine direction. It is preferable to perform longitudinal relaxation between rolls, especially after longitudinal stretching.
A method of continuous longitudinal relaxation without cooling is preferred. Further, the ratio Δn+/Δn2 of the birefringence index Δn after longitudinal stretching and the birefringence index Δn2 after longitudinal relaxation is preferably 0.95 or less. When Δn1/Δn2 exceeds 0.95, the shrinkage rate of the film in the longitudinal direction becomes too large, which is not preferable.

The film stretched and relaxed in the machine direction is stretched horizontally using a tenter at a stretching ratio of 3.0 times or more, but before stretching, the film is heated to 100 to 140°C to further reduce the shrinkage rate in the machine direction. Relaxation is also preferred.

After transverse stretching, the film is heated at 60-100°C to 0.01-6
The shrinkage characteristics of the film can be improved by performing heat treatment for 0 seconds, particularly preferably from 0.01 to 30 seconds. Heat treatment is usually carried out under tension fixation, but at the same time it is also possible to perform relaxation or widening of up to 20%. As the heat treatment method, known methods such as a method of contacting with a heating roll or a method of holding the material with 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.

Furthermore, during the above-mentioned stretching process, it is also possible to coat one or both sides of the film before or after stretching to improve the film's adhesion, antistatic properties, slipperiness, light-shielding properties, etc.

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 give it cushioning properties. It is also possible to improve the bottle-breaking effect, etc. As such 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.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples unless it exceeds the gist thereof.

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

(1) Intrinsic viscosity of the film [η] Sample 200μ is phenol/tetrachloroethane = 50
It was added to a mixed solvent of 150 and 20°C, heated at about 110°C for 1 hour, and then measured at 30°C.

(2) Shrinkage rate The shrinkage rate was measured under the following heat treatment conditions (a) and et al.

(a) 100℃ air oven 1cI1 width 10C11 length strip of film 10
The sample was held in a guarded oven with no load for 5 minutes at a temperature of 0±2° C., and the shrinkage rate was determined according to the following formula.

[! : Length after shrinkage (am)) b) A 75°C hot water film is made into a 10cm x 10cm square, and the length is 75±0.
．． After heat-shrinking the film by holding it in 5° C. hot water for 5 seconds under no load, the longitudinal and transverse directions of the film were determined according to the following formula.

(3) Neck-in rate film with a length of 13C111 or more in the horizontal direction and a width of 10cm
Cut out a rectangle, fix both ends of the film in the horizontal direction to metal fittings with internal dimensions of 13cm long x 10cm wide, and then process it in hot water at 75±0.5°C to find the maximum shrinkage rate in the vertical direction. It was taken as the neck-in rate.

(4) Glass transition temperature of the film The Tg film was heated and melted at 300°C for 5 minutes in a nitrogen atmosphere, cooled to an amorphous state, and then measured using a differential calorimeter 5SC580DSC20 model manufactured by Seiko Electronics Co., Ltd. Heating rate 4° (:/
'rg was measured at min. 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.

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

Δn=R/d (6) Degree of Planar Orientation ΔP The refractive index of the film was measured using an Atsube refractometer manufactured by Atago Co., Ltd. and a sodium lamp as the light source.

The maximum refractive index nr in the film plane, 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 P was determined using the following formula.

ΔP=(nT-nβ)-nα (7) Breaking elongation in the longitudinal direction of the film Using Tensilon manufactured by Toyo Baldwin Co., Ltd., 20°C1
The tensile speed was 500 mn/win at 65% RH,
Samples with a width of 15+m were fixed with chucks at intervals of 25 mm, and the elongation at break was measured for the five samples, and the average value was taken as the elongation at break in the longitudinal direction of the film.

(8) Evaluation of tear resistance The film is used as a label film and is continuously processed through printing, bag making, and cutting. During the processing process, there is no tearing and there is no problem at all. Items with practical problems were marked as ×.

(9) Evaluation of shrinkage characteristics After making the film into a cylindrical shape and covering it over a cylindrical bottle,
The shrink properties of the film were evaluated by passing it through a shrink tunnel and attaching it to a bottle. Labels with no distortion of the design, excellent adhesion, and a beautiful finish were rated ◎, labels with slightly inferior appearance but no problem in practical use were rated ○, and labels that did not reach a practical level were rated ×.

Practical example 1 80 mof% terephthalic acid unit as dicarboxylic acid component
, a copolymerized polyester ([
η)=0.70, Tg=66°C) was pre-crystallized using a paddle dryer, then main drying was performed, extruded from an extruder at 260°C, and rapidly solidified to obtain an unstretched film.

The obtained film was stretched 1.
The film was stretched 4 times, and the longitudinal edges were loosened by 0.90 times in the machine direction between a stretching roll and a cooling roll continuously without cooling. The film was then introduced into a tenter, heat treated at 120°C, stretched 4.5 times in the transverse direction at 85°C, and then stretched at 80°C.
After heat treatment, the film was cooled to obtain a film with an average thickness of 40 μm.

Example 2 A film with an average thickness of 40 μm was obtained in the same manner as in Example 1, except that the heat treatment at 120° C. was not performed.

Comparative Example 1 The unstretched film of Example 1 was directly introduced into a tenter, and was laterally stretched and heat treated in the same manner as in Example 1 to obtain a film with an average thickness of 40 μm.

Comparative Example 2 The unstretched film of Example 1 was stretched 1.4 times in the longitudinal direction using a stretching roll and a cooling roll at 80°C.

The film was then introduced into a tenter, heated at 120'C in exactly the same manner as in Example 1, and then stretched and heat-treated in the transverse direction to obtain a film with an average thickness of 40 μm.

The results obtained above are summarized in Table 1 below.

[Effects of the Invention] The shrink film for labels of the present invention has excellent shrink characteristics and strength, and has high industrial value.

Claims (1)

[Claims] (1) The shrinkage rate of the film after being treated in an air open environment at 100°C for 5 minutes is 40% or more in the transverse direction and 20% or less in the longitudinal direction, and the elongation at break in the longitudinal direction of the film is 250%. A polyester shrink film for labels characterized by the above characteristics.