Polyester shrinkable film containing benzotriazole

Disclosed herein is a polyester shrinkable film. The film according to the present invention can provide extremely excellent durability and long-time storability of contents of a container in labelling and shrink packaging use.

BACKGROUND OF THE INVENTION 
The present invention relates to a shrinkable film excellent in durability 
upon transportation of containers, long-time storability of contents in 
the containers, etc. 
In recent years, shrinkable films have generally been used for labeling for 
containers such as PET bottles, glass bottles, etc. or shrink packaging 
applications. However, shrinkable films in the prior art involve problems 
in view of the durability and the long-time storability when they are used 
for labeling or shrink packaging application. That is, in containers 
labeled or applied with close packaging by means of shrinkable films such 
as of polyvinyl chloride or polystyrene, the films have often been broken 
due to the contact of the containers with each other upon long-distance 
transportation of the containers to bring about a problem in view of the 
appearance. 
On the other hand, in the case of applying shrink packaging to those 
containers filled with brewages such as Japanese sake, beer or wine, since 
both of the container and the shrinkable film are highly transparent, when 
the containers are exposed to direct sunlight they inevitably suffer from 
degradation in the quality of the filled drinks, particularly, due to 
ultraviolet rays. 
With the reason as described above, there has been strongly demanded for a 
shrinkable film excellent in the durability upon transportation of 
containers and also excellent in long-time storability of the content. 
In view of the foregoing problems, the present inventors have made an 
earnest study and have accomplished the present invention based on the 
finding that the durability and the long-time storability can be improved 
by using a polyester shrinkable film having specified shrinking 
characteristic and ultraviolet ray-absorbing characteristic. 
SUMMARY OF THE INVENTION 
In an aspect of the present invention, there is provided a polyester 
shrinkable film containing from 0.1 to 20% by weight of a ultraviolet ray 
absorber having a shrinkage of not less than 20% in one of longitudinal 
and transverse directions and not greater than 15% in the other direction 
of a film after treatment for five minutes at 100.degree. C. in air oven, 
and light transmittance of the film at a wave length of 390 nm of not 
greater than 20%.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a polyester shrinkable film having a 
shrinkage of not less than 20% in one of longitudinal or transverse 
directions and not greater than 15% in the other direction of the film 
after the treatment for five minutes at 120.degree. C. in air oven, and 
light transmittance of the film at a wave length of 30 nm not greater than 
20%. 
The polyester used in the present invention may be any of homopolyesters or 
copolyesters comprising, as the carboxylic acid component, one or more of 
known dicarboxylic acids such as terephthalic acid, oxalic acid, malonic 
acid, succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic 
acid, isophthalic acid, naphthalene dicarboxylic acid and diphenylether 
dicarboxylic acid and, as the diol component, one or more of known diol 
such as ethylene glycol, neopentyl glycol, propylene glycol, trimethylene 
glycol, tetramethylene glycol, hexamethylene glycol, diethylene glycol, 
polyalkylene glycol and 1,4-cyclohexane dimethanol. 
As the copolyester, those obtained by using two or more of dicarboxylic 
acids and/or diols as the dicarboxylic acid component and/or diol 
component. Also, polyester prepared by using other ingredients, for 
example, hydroxycarboxylic acid such as p-hydroxybenzoic acid and 
p-hydroxyethoxybenzoic acid, mono-functional compound such as benzoic 
acid, benzoyl benzoic acid, methoxypolyalkylene glycol, polyfunctional 
compound such as glycerin, penthaerythritol, trimethyrol and trimethylene 
propane within such a range that the product can be substantially a linear 
high molecular can also be used. 
As the polyester usable in the present invention, those copolyesters in 
which the dicarboxylic acid component mainly comprises terephthalic acid, 
the diol component mainly comprises ethylene glycol, and the copolymer 
ingredient comprises isophthalic acid and phthalic acid as the 
dicarboxylic acid component and neopentyl glycol, diethylene glycol, 
polyalkylene glycol and, if required, 1,4-cyclohexane dimethanol as the 
diol component are preferred since they are available industrially at a 
reduced cost and show satisfactory shrinking property for the resultant 
film. 
In the polyester used in the present invention, not less than 70 mol %, 
more preferably, not less than 75 mol % of the dicarboxylic acid component 
is a terephthalic acid unit, while not less than 70 mol %, more 
preferably, not less than 75 mol % of the diol component is an ethylene 
glycol unit. Those copolyesters with the terephthalic acid unit and/or 
ethylene glycol unit is less than 70 mol % are not preferred since the 
strength and the solvent resistance of the resultant film are poor. 
Further, those polymers other than the polyester may be admixed to the 
polyester described above so long as the amount added is not greater than 
30 mol % based on the entire amount of the mixture. 
Further, fine particles of organic and inorganic lubricants, etc. may 
preferably be incorporated in order to improve the slipperiness of the 
film. Further, additives such as stabilizer, colorant, antioxidant, 
defoamer, antistatic agent, etc. may also be incorporated as required. As 
fine particles for providing a good slipperiness, there can be mentioned 
those known inert external particles such as kaolin, clay, calcium 
carbonate, silicon oxide, potassium terephthalate, aluminum oxide, 
titanium oxide, calcium phosphate, lithium fluoride and carbon black and; 
high melting organic compounds not melted upon molten film formation of 
polyester resin; crosslinked polymer and internal particles formed at the 
inside of polyesters upon production thereof by metal catalyst, for 
example, alkali metal compound, alkaline earth metal compound, etc. used 
for the synthesis of the polyester. The fine particles contained in the 
shrinkable film is preferably from 0.005 to 5.0% by weight and the 
preferred average particle size is from 0.001 to 3.5 .mu.m. 
The light transmittance of the shrinkable film according to the present 
invention at a wave length of 390 nm is from 0.1 to 20%, preferably from 
0.1 to 10% and, more preferably from 0.1 to 5%. Those films having light 
transmittance over 20% are insufficient for the absorption capacity for 
the entire ultraviolet region and can not provide long-time storability 
for the contents of containers. In a case where they are applied to 
containers of brewages such as sake and wine, the contents are remarkably 
discolored due to oxidation. 
For providing the film with ultraviolet absorbing capacity, it is possible 
to dispose a coating layer on the film surface during or after the 
production of the film, ultraviolet absorbers are usually contained in the 
polyester. The ultraviolet absorber can be selected, for example, from 
benzophenones, benzotriazoles, salicylic acid derivatives, cyanoacrylates, 
oxalic acid anilide, etc. and, particularly, those ultraviolet absorbers 
having 10% weight loss temperature (T.sub.10) upon thermogravimetric 
analysis of not lower than 200.degree. C., preferably, not lower than 
220.degree. C. are preferred since the contaminations in each of the 
production steps can be reduced. If T.sub.10 is lower than 200.degree. C., 
sublimation or decomposition is undesirably caused to the ultraviolet 
absorbers. 
As the benzophenone type ultraviolet absorber, there can be mentioned, for 
example, 
2-hydroxybenzophenone, 
2,4-dihydroxybenzophenone, 
2-hydroxy-4-methoxybenzophenone, 
2-hydroxy-4-octoxybenzophenone, 
2-hydroxy-4-dodecyloxybenzophenone, 
2-hydroxy-4-octadecyloxybenzophenone, 
2-hydroxy-4-(2-hydroxy-3-methacryloxy)-propoxybenzophenone, 
2-hydroxy-4-chlorobenzophenone, 
2-hydroxy-4-methoxy-5-sulfobenzophenone, 
2-hydroxy-4-methoxy-2'-carboxybenzophenone, 
2,2'-dihydroxybenzophenone, 
2,2'-dihydroxy-4-methoxybenzophenone, 
2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 
2,2',4,4'-tetrahydroxybenzophenone and 
sodium 2,2'-dihycroxy-4,4'-methoxy-5'-sulfobenzophenone. 
As the benzotriazole type ultraviolet absorber, there can be mentioned, for 
example, 
2-(2'-hydroxyphenyl)benzotriazole, 
2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 
2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole, 
2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 
2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, 
2-(2'-hydroxy-3',5'-di-t-butylphenyl)benzotriazole 
2-(2'-hydroxy-3',5'-bis- 
.alpha.,.alpha.-dimethylbenzylphenyl)-2H-benzotriazole, 
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 
2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole. 
As the salicylic acid derivative type ultraviolet absorber, there can be 
mentioned, for example, phenyl salicylate, p-t-butylphenyl salicylate and 
p-octylphenyl salicylate. 
As the cyanoacrylate type ultraviolet absorber, there can be mentioned, for 
example, 
2-ethyl-2-cyano-3,3'-diphenyl acrylate and 
2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate 
As other ultraviolet absorbers, there can be mentioned, for example, 
dimethyl p-methoxybenzilidenemalonate, 
dibenzoylresorcinole, 
hexamethylphosphoric triamine, 
tetraphenylsuccinylate dinitrile, 
[2,2'-thiobis(4-t-octylphenolate)]-n-butylamine nickel (II) 
nickel-bis(octylphenyl)sulfide, 
nickel complex-3,5-di-t-butyl-4-hydroxybenzyl phosphoric acid monoethylate, 
nickel butyldithiocarbide, 
naphthalene tetracarboxylic acid diimide, 
bis-(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 
2,2'-p-phenylene-bis(3,1-benzooxazin-4-one). 
Among the compounds as described above, particularly preferred are: 
2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 
2-(2'-hydroxy5'-t-octylphenyl)benzotriazole, 
2-[2'-hydroxy-3',5'-bis(.alpha.,.alpha.-dimethylbenzyl)phenyl]-2H-benzotria 
zole, 
naphthalene tetracarboxylic acid diimide, 
bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane and 
2,2'-p-phenylene bis(3,1-benzooxazin-4-one). 
While the ultraviolet absorber may be incorporated into a film by adding 
during polymerization, adding before film-formation or by previously 
forming a master batch, the method of forming the master batch is 
preferred since the contaminations by the ultraviolet absorber in the step 
can be reduced. 
The content of the ultraviolet absorber in the shrinkable film is 
preferably from 0.1 to 20% by weight and, more preferably from 0.2 to 10% 
by weight. If the content is less than 0.1% by weight, the ultraviolet 
absorbing capacity is insufficient, whereas if it exceeds 20 wt %, 
sublimation products are formed and bleedout of the ultraviolet absorber 
to the film surface are caused and they are no more usable. 
The film according to the present invention has a shrinkage of from 20 to 
80%, preferably, from 30 to 80% in one of longitudinal and transverse 
directions (hereinafter referred to as the main shrinking direction), 
after treatment for 5 minutes in an air oven at 100.degree. C. In the 
shrinkable film according to the present invention, the shrinkage in the 
main shrinking direction of less than 20% is not preferred since the 
amount of shrinkage when shrunk as a label is insufficient and the film is 
not closely fit to the container. 
Further, the shrinkable film according to the present invention has a 
shrinkage from -10 to 15%, preferably from -5 to 10% and, more preferably 
from -5 to 5% in the other direction perpendicular to the main shrinking 
direction after treatment for 5 minutes in an air oven at 100.degree. C. 
A film having the shrinkage of larger than 15% is not preferred since the 
film when shrunk as a label remarkably shrinks along the longitudinal 
direction of the container to cause distortion of patterns, etc. 
For improving the durability of the shrinkable film, the strength at break 
in the main shrinking direction is, preferably, from 20 to 40 kg/mm.sup.2, 
more preferably, from 25 to 40 kg/mm.sup.2. 
The intrinsic viscosity [.eta.] of the shrinkable film according to the 
present invention is, preferably, from 0.50 to 1.20, more preferably, from 
0.60 to 1.20 and, particularly preferably, from 0.65 to 1.20. If the 
intrinsic viscosity of the film is less than 0.50, crystallinity becomes 
higher, failing to obtain sufficient shrinkage. 
The heat of fusion of the shrinkable film according to the present 
invention is preferably of not greater than 8 cal/g, more preferably, not 
greater than 6 cal/g and, particularly preferably, from 2 to 6 cal/g. A 
film with the heat of fusion of excess of 8 cal/g is not preferred since 
the shrinking characteristic is reduced. It is considered that the 
reduction is due to the progress of crystallization when the film is 
heated in a shrink tunnel to cause an uneven shrinkage. 
Further, the maximum shrinkage (neck-in ratio) of the shrinkable film 
according to the present invention in the direction in perpendicular to 
the main shrinking direction after treatment for 5 sec in water at 
75.degree. C. while fixing both ends of the film in the main shrinking 
direction is, preferably, from 1 to 20% and, more preferably, from 2 to 
15%. A film having the neck-in ratio in excess of 20% is not preferred 
since distortion or oblique buckling are caused frequently upon shrinking 
as a label. 
The double refraction index of the shrinkable film according to the present 
invention is, preferably, from 0.040 to 0.120 and, more preferably, from 
0.040 to 0.090. 
A film with a double refraction index of lower than 0.040 is not preferred 
since it is poor in warm water proofness, solvent resistance, etc as a 
label. Further, a film with a double refractive index in excess of 0.120 
is not preferred since the shrinking stress occurring along the main 
shrinking direction is increased to reduce the shrinking characteristic. 
In the shrinkable film according to the present invention, it is also 
possible to provide a cushioning effect and improve breaking strength of 
bottle after the packaging of glass bottles, etc. by printing a foaming 
ink layer or laminating a thermoplastic resin film or sheet having fine 
cells inside thereof on one or both surfaces of the film. As the 
thermoplastic resin, any of known thermoplastic resins such as polyvinyl 
chloride, polyethylene, polypropylene, acrylic polymer, polystyrene and 
polyester resins may be used. 
There is no particular restriction for the thickness of the shrinkable film 
according to the present invention but the thickness, when used a 
shrinkable film for labelling use is, preferably, from 10 to 300 .mu.m 
and, more preferably, from 20 to 200 .mu.m. 
Description is to be made specifically for the method of producing the film 
according to the present invention but the method is not particularly 
limited to the following production methods. 
After drying a polyester containing an appropriate amount of a ultraviolet 
absorber and inorganic particles as the lubricant, etc. as required by a 
usual drier such as a hopper drier or a paddle drier or by using a vacuum 
drier, it was extruded at a temperature of 200.degree. to 320.degree. C. 
As the extruding means, any of known methods such as a T-die method or 
tubular method may be employed. A non-stretched film obtained by rapid 
cooling after extrusion is stretched in at least one of longitudinal and 
transverse directions by, preferably, from 2.5 to 6.0 times and more 
preferably, from 3.0 to 5.0 times. During the stretching step, it is 
preferred that the film is uniformly heated in such a way that the surface 
temperature T.sub.1 of the film is from Tg -10.degree. C. to Tg+40.degree. 
C. (Tg means glass transition temperature of the polyester) at the start 
of the stretching and is stretched under such a condition that the surface 
temperature of the film reaches to T.sub.1 -50.degree. C. to T.sub.1 
+5.degree. C., preferably, from T.sub.1 -50.degree. C. to T.sub.1 at the 
end of the stretching. This stretching method is preferred to reduce 
uneven thickness of the film and increase shrinkage at a lower 
temperature. 
For the stretching method, longitudinal mono-axial stretching by means of 
rolls, transverse mono-axial stretching by means of tenter and usual 
biaxial stretching are used. It is also possible to stretch at a high 
ratio in one of the longitudinal and transverse directions, while 
stretching at a ratio as low as possible in the other direction. As the 
biaxial stretching method, known sequential biaxial stretching or 
simultaneous stretching may be used. Further, re-stretching may also be 
applied. 
It is preferred for such stretched film to apply heat treatment at 
60.degree. to 100.degree. C. for 0.1 sec to 5 min, more preferably, from 
0.1 sec to 60 sec in order to obtain a desired neck-in ratio. The heat 
treatment can be conducted under fixing with stress, relaxation of not 
more than 20% or tentering, for which known method can be used such as 
contact with heating rolls, gripping by a clip in a tenter, etc. 
Re-stretching may also be applied after heat treatment. 
It is also possible to apply corona discharging treatment on one or both of 
the film surfaces during, before or after the stretching to improve the 
adhesion of the film to the printing layer, etc. 
Further, it is also possible to improve the ultraviolet absorbing property, 
adhesion, antistatic property, slipperiness, light screening property, 
etc. of the film by applying coating to one or both of the film surfaces 
during, before or after the stretching. 
The thus obtained film is taken up into a product. 
Shrinkable films used for labels of extremely excellent durability upon 
transportation of containers and long-time storability of contents in 
containers can be obtained by satisfying the above requirements of the 
present invention. 
The present invention is to be described more specifically referring to 
examples, but the invention is not restricted only to these examples 
unless it goes beyond the scope of the invention. 
The method of evaluating the film is shown below. 
(1) Shrinkage factor 
A film specimen in a strip form of 1 cm width was subjected to heat 
shrinking treatment for 5 min in a geared oven at a temperature of 
100.+-.2.degree. C. without load and the shrinkage was determined in 
accordance with the following equation: 
##EQU1## 
L.sub.o : original length (10 cm) L: length after shrinking (cm) 
(2) Light Transmittance 
Transmittance at a wavelength of 390 nm was measured by using a 
self-recording photospectrometer Model 340 manufactured by Hitachi 
Limited. 
(3) Intrinsic Viscosity of Film [.eta.] 
200 mg of specimen was dissolved in 20 ml of a mixed solvent comprising 
phenol/tetrachloroethane at 50/50 ratio by heating at about 110.degree. C. 
for 1 hour, and the viscosity was measured at 30.degree. C. 
(4) 10% Weight Loss Temperature (T.sub.10) of Ultraviolet Absorber 
Thermogravimetric analysis was conducted at a temperature increasing rate 
of 10.degree. C./min by using SSC 580/TG-DTA 20 manufactured by Seiko 
Denshi Kogyo Co. and the temperature at which the weight loss reached 10% 
was measured. 
(5) Strength at Break (main shrinking direction) 
A film of 15 mm width and inter-chuck length of 50 mm was stretched at 
20.degree. C., 65% RH by 50 mm/min using a TENSILON (UTN-III) manufactured 
by TOYO-BALDWIN CO., and the strength of the film upon break was divided 
by the initial cross sectional area, which was expressed by kg/mm.sup.2. 
(6) Film Durability 
After making a film into a cylindrical label, it was fitted over a PET 
bottle and caused to shrink by passing through a shrink tunnel. 
The upper surface of the label was rubbed with a pencil of H hardness and 
evaluation was made as X for those easily broken and as O for those 
showing no substantial change. 
(7) Storability of Contents 
In the same procedures as in (6) above, SAKE was filled in a transparent 
PET bottle and the film was shrunk. In this case, the film was shrunk so 
as to cover more than 95% of the side of the bottle. 
After capping the PET bottle and left for three days outdoor, change of the 
SAKE contents was observed. Evaluation was made as X for those causing 
yellow discoloration and deterioration in the quality and as O for those 
showing no changes in view of the appearance. 
EXAMPLE 1 
Polyethylene terephthalate with [.eta.]=0.66 was blended with 20% by weight 
of a ultraviolet absorber: 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole 
(Cyasorb UV5411; registered trade mark of products from Cyanamid 
Co.)(T.sub.10 =232.degree. C.), and then kneaded by using a two shaft 
extruder of 30 mm.phi., to obtain a master batch polyester (A). 
Further, a copolyester (B) with [.eta.]=0.70 comprising 80 mol % of 
terephthalic acid unit and 20 mol % of isophthalic acid unit as the acid 
component, 97 mol % of ethylene glycol unit and 3 mol % of diethylene 
glycol unit as the glycol component and containing 400 ppm of amorphous 
silica of 1.2 .mu.m of average particle size was prepared. The master 
batch polyester (A) and the copolyester (B) were blended at 30/70 weight % 
ratio. 
After drying the blend as described above by means of a usual method, it 
was extruded at 280.degree. C. from an extruder and rapidly cooled and 
solidified to obtain a non-stretched film. The resultant not-stretched 
film was introduced into a tenter in which it was stretched transversely 
by 4.0 times at a stretching temperature of 80.degree. C. and applied with 
heat treatment at 85.degree. C. for 8 sec, cooled and then taken up. 
During the heat treatment, 2% relaxation was applied in the longitudinal 
direction. The average thickness of the resultant film was about 40 .mu.m. 
EXAMPLE 2 
A master batch polyester (C) was obtained by using 
2-(2'-hydroxy-5'-methylphenyl)benzotriazole (Tinuvin P;trade mark of 
products manufactured by Ciba-Geigy, Ltd.) (T.sub.10 =198.degree. C.) as 
the ultraviolet absorber to be kneaded in the polyester (A) of Example 1. 
The resultant polyester (C) and the polyester (B) were blended at 20/80 
weight % ratio, extruded and made into a film in the same manner as in 
Example 1 to obtain a film of about 40 .mu.m of average thickness. 
COMATIVE EXAMPLE 1 
Using the polyester (B), a film of about 40 .mu.m average thickness was 
obtained by applying extrusion and film-formation in the same way as in 
Example 1. 
COMATIVE EXAMPLE 2 
A polyvinyl chloride shrinkable film (average thickness of 40 .mu.m) 
containing 2.0% by weight of the same ultraviolet absorber, 
2-(2'-hydroxy-5'-methylphenyl)benzotriazole as in Example 2 was used as 
the Comparative Example 2. 
EXAMPLE 3 
After drying a copolyester (D) with [.eta.]=0.72 comprising a terephthalic 
acid unit as the acid component and 88 mol % of ethylene glycol unit and 
12 mol % of neopentyl glycol unit as the glycol component, 20 wt % by 
weight of 2-[2'-hydroxy-3', 
5'-bis(.alpha.,.alpha.-dimethylbenzyl)phenyl]-2H-benzotriazole (Tinuvin 
234, registered trade mark of products manufactured by Ciba-Geigy, Ltd.) 
(T.sub.10 =305.degree. C.) was kneaded therewith to obtain a master batch 
polyester (E). 
The polyester (D) and the polyester (E) was blended at 80/20 weight % 
ratio, extruded at 280.degree. C. and rapidly cooled and solidified to 
obtain a non-stretched film. The resultant non-stretched film was 
stretched by 3.5 times at 85.degree. C. in the longitudinal direction by 
the difference in the circumferential speeds between a heating roll and a 
cooling roll and, heat treatment was applied to the film by contacting the 
film with a heating roll at 92.degree. C. for 0.2 sec. The average 
thickness of the resultant film was 50 .mu.m. 
EXAMPLE 4 
A copolyester (F) with [.eta.]=0.79 comprising terephthalic acid unit as 
the acid component and 80 mol % of ethylene glycol unit and 20 mol % of 
1,4-cyclohexane dimethanol unit as the glycol component was blended with 
the polyester (E) at 80/20 weight % ratio. The blend was extruded and 
formed into a film in the same manner as in Example 3 to obtain a film of 
50 .mu.m of average thickness. 
The properties of the resultant films are collectively shown in Table 1. 
TABLE 1 
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Shrinkage Light 
(%) transmittance at 
Strength at 
longitudinal 
transverse 
390 nm Break Film Storability of 
direction 
direction 
(%) (kg/mm.sup.2) 
Durability 
contens 
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Example 
1 3 48 4.5 31.2 O O 
2 2 51 4.8 30.7 O O 
3 52 0 3.7 28.7 O O 
4 54 -1 3.7 27.6 O O 
Comparative 
2 54 76.0 30.3 O X 
Example 1 
Comparative 
6 57 4.8 13.0 X O 
Example 2 
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