U.S. patent application number 09/828786 was filed with the patent office on 2001-11-08 for heat-shrinkable polyester films.
Invention is credited to Anami, Tetsuya, Hashimoto, Masatoshi, Nagano, Hiroshi, Tabota, Norimi.
Application Number | 20010038920 09/828786 |
Document ID | / |
Family ID | 26589862 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038920 |
Kind Code |
A1 |
Hashimoto, Masatoshi ; et
al. |
November 8, 2001 |
Heat-shrinkable polyester films
Abstract
Heat-shrinkable polyester films which exhibit a total light
transmittance of 80% to 90% and a haze of 15% to 60%, both in a
thickness of 50 .mu.m and further exhibit a 45-degrees specular
gloss of 70% or lower, so that they have frosted glass appearances
without being printed or processed. Heat-shrinkable polyester films
which exhibit a light transmittance of 0% to 20% at a wavelength of
380 nm and of 0% to 60% at a wavelength of 400 nm and further
exhibit a haze of 15% or lower, so that they can prevent the
contents of a vessel fitted therewith from being deteriorated by
ultraviolet light and they have good shrinkage finish and
particularly cause only rare occurrence of wrinkles, shrinkage
spots, or other defects. These films are suitable for labels,
particularly for labels of great product value.
Inventors: |
Hashimoto, Masatoshi;
(Inuyama-shi, JP) ; Anami, Tetsuya; (Inuyama-shi,
JP) ; Tabota, Norimi; (Inuyama-shi, JP) ;
Nagano, Hiroshi; (Inuyama-shi, JP) |
Correspondence
Address: |
Barry E. Bretschneider
Morrison & Foerster LLP
Suite 5500
2000 Pennsylvania Avenue, N.W.
Washington
DC
20006-1888
US
|
Family ID: |
26589862 |
Appl. No.: |
09/828786 |
Filed: |
April 10, 2001 |
Current U.S.
Class: |
428/480 ;
528/272 |
Current CPC
Class: |
C08J 5/18 20130101; B32B
2519/00 20130101; B32B 27/18 20130101; Y10T 428/31786 20150401;
B32B 2307/42 20130101; B32B 2250/244 20130101; B32B 2307/71
20130101; Y10T 428/269 20150115; B32B 2307/412 20130101; Y10T
428/2813 20150115; Y10T 428/26 20150115; Y10T 428/2817 20150115;
Y10T 428/261 20150115; C08J 2367/02 20130101; Y10T 428/268
20150115; B32B 27/36 20130101; B32B 27/08 20130101 |
Class at
Publication: |
428/480 ;
528/272 |
International
Class: |
C08G 063/02; B32B
027/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2000 |
JP |
2000-109428 |
May 15, 2000 |
JP |
2000-142182 |
Claims
1. A heat-shrinkable polyester film, which exhibits a total light
transmittance of 80% to 90% and a haze of 15% to 60%, both in a
thickness of 50 .mu.m, and further exhibits a 45-degrees specular
gloss of 70% or lower.
2. The heat-shrinkable polyester film according to claim 1, which
exhibits surface roughness as determined both by a maximum height
(SR.sub.max) of 2.0 .mu.m or higher and by a center-plane average
roughness (SR.sub.a) of 0.20 .mu.m or higher.
3. The heat-shrinkable polyester film according to claim 1, which
has solvent bonding properties with 1,3-dioxolane.
4. The heat-shrinkable polyester film according to claim 1, which
has a heat shrinkability after treatment in hot water at 95.degree.
C. for 10 seconds, of 50% or higher in a main shrinkage direction
thereof and of 10% or lower in a direction perpendicular to the
main shrinkage direction.
5. A heat-shrinkable polyester film, which exhibits a light
transmittance of 0% to 20% at a wavelength of 380 nm and of 0% to
60% at a wavelength of 400 nm, and further exhibits a haze of 15%
or lower.
6. The heat-shrinkable polyester film according to claim 5, which
has a heat shrinkability after treatment in hot water 70.degree. C.
for 10 seconds, of 10% or higher in a main shrinkage direction
thereof, and a heat shrinkability after treatment in hot water at
85.degree. C. for 5 seconds, of 30% or higher in the main shrinkage
direction and of 10% or lower in a direction perpendicular to the
main shrinkage direction.
7. The heat-shrinkable polyester film according to claim 5, which
has a thickness distribution of 6% or lower.
8. The heat-shrinkable polyester film according to claim 5, which
comprises at least two layers of laminated films.
9. The heat-shrinkable polyester film according to claim 5, which
contains an ultraviolet light cut agent.
10. The heat-shrinkable polyester film according to claim 5, which
comprises at least three layers of laminated films and contains an
ultraviolet light cut agent in at least one internal layer not
coming to the surface thereof.
Description
FILED OF INVENTION
[0001] The present invention relates to heat-shrinkable polyester
films and more particularly to heat-shrinkable polyester films
which have frosted glass like appearances without being printed or
processed and to heat-shrinkable polyester films which can prevent
the contents of a vessel fitted therewith from being deteriorated
by ultraviolet light and have good shrinkage finish and
particularly cause only rare occurrence of wrinkles, shrinkage
spots, or other defects. These films are suitable for labels,
particularly for labels of great product value.
BACKGROUND OF THE INVENTION
[0002] Frosted glass bottles have been mainly used as sake bottles
for gifts, but their use has been unavoidably reduced in the recent
movement toward the recycling of bottles. Frosted glass bottles
have been therefore replaced by transparent glass bottles fitted
with labels made of heat-shrinkable films. For these labels,
heat-shrinkable films made of thermoplastic resins such as
polyvinyl chloride and polystyrene have been mainly used; in recent
years, however, serious problems have been indicated that, for
example, chlorine-containing gases will be evolved in the
incineration of polyvinyl chloride for disposal and printing is
difficult on polystyrene. Therefore, heat-shrinkable polyester
films have attracted considerable attention. The conventional
heat-shrinkable polyester films have been finished to have frosted
glass like appearances by printing or processing, which are,
however, unfavorable to industrial use because of their high cost
and long delivery time.
[0003] For heat-shrinkable films used as labels, particularly on
the barrel of bottles, those films made of thermoplastic resins
such as polyvinyl chloride and polystyrene have been mainly used;
however, as described above, serious problems have been indicated
that, for example, chlorine-containing gases will be evolved in the
incineration of polyvinyl chloride for disposal and printing is
difficult on polystyrene. Further, in the recycling of PET bottles,
labels made of thermoplastic resins other than PET should be
separated from the PET bottles. Therefore, heat-shrinkable
polyester films have also attracted considerable attention as those
which can solve such problem.
[0004] In recent years, the case has been increasing where
heat-shrinkable labels are used for the purpose of protecting the
content of a vessel fitted therewith from being deteriorated by
ultraviolet light. The ultraviolet light cut type heat-shrinkable
films made of polyvinyl chloride have been used so far; however,
for the above reason, there has been a great demand for
ultra-violet light cut type heat-shrinkable films made of other
materials. The specific cut properties may vary depending upon the
contents of a vessel fitted with these films. In the case of food
or beverage, cut properties in the long wavelength region,
particularly at 380 nm and at 400 nm, are important because the
contents will cause a change in quality or will become colored by
ultraviolet light in the long wavelength region, ie., at
wavelengths of 360 to 400 nm.
[0005] The conventional heat-shrinkable polyester films, however,
have no ultraviolet light cut properties in the above long
wavelength region.
SUMMARY OF THE INVENTION
[0006] Under these circumstances, the present inventors have
intensively studied to solve the above-described problems in the
prior art and to develop heat-shrinkable polyester films having
frosted glass like appearances and heat-shrinkable polyester films
having ultraviolet light cut properties in the long wavelength
region. As a result, they have found that this purpose can be
attained by the control of total light transmittance, haze and
45-degrees specular gloss, and by the control of light
transmittance at specific wave-lengths and haze, respectively,
thereby completing the present invention.
[0007] Thus the present invention provides a heat-shrinkable
polyester film, which exhibits a total light transmittance of 80%
to 90% and a haze of 15% to 60%, both in a thickness of 50 .mu.m,
and further exhibits a 45-degrees specular gloss of 70% or lower
(also referred to hereinafter as the first heat-shrinkable
polyester film(s) of the present invention).
[0008] The present invention further provides a heat-shrinkable
polyester film, which exhibits a light transmittance of 0% to 20%
at a wavelength of 380 nm and of 0% to 60% at a wavelength of 400
nm, and further exhibits a haze of 15% or lower (also referred to
hereinafter as the second heat-shrinkable polyester film(s) of the
present invention).
DETAILED DESCRIPTION OF THE INVENTION
[0009] The following will describe the first heat-shrinkable
polyester films of the present invention, which have frosted glass
like appearances without being printed or processed.
[0010] The first heat-shrinkable polyester films of the present
invention may preferably be prepared from polyester compositions
containing polyesters, which are composed of dicarboxylic acid
components and diol components, and polyester elastomers.
[0011] For the dicarboxylic acid components in the polyesters,
conventional dicarboxylic acids can be used alone or in
combination, including aromatic dicarboxylic acids such as
terephthalic acid, isophthalic acid and naphtha-lenedicarboxylic
acid; aliphatic dicarboxylic acids such as adipic acid, sebacic
acid and decanedicarboxylic acid; and alicyclic dicarboxylic acids.
For the diol components in the polyesters, conventional diols can
be used alone or in combination, including ethylene glycol,
propylene glycol, triethylene glycol, butylene glycol, diethylene
glycol, neopentyl glycol, 1,4-cylcohexanedimethanol, and ethylene
oxide adducts of tetramethylene glycol.
[0012] The polyester elastomers used in the present invention refer
to polyester block copolymers composed of high melting point
crystalline polyester segments (hard segments) and low melting
point soft polymer segments (soft segments) having molecular
weights of 400 or higher. Polyester elastomers containing
polylactones (e.g., poly-.epsilon.-caprolactone) as the soft
segments are particularly preferred.
[0013] The polyester compositions as the base material may further
contain, if necessary, additives such as stabilizers, colorants,
antioxidants and anti-static agents.
[0014] The present inventors have found that frosted glass like
appearances can be rendered to films by the formation of undulation
or large projections on their surface. More particularly, the gloss
of films can be removed by the formation of projections on their
surface, which are in size equal to or larger than a certain
constant value depending upon the kind of lubricating fine
particles. For example, the gloss of films can be controlled by
adjusting the size of projections on their surface with lubricating
fine particles made of an inorganic or organic compound, having an
average particle diameter of 2 to 15 .mu.m, in an amount of 0.1 to
10 wt %, preferably 0.5 to 5 wt %.
[0015] The present inventors have also found that the transparency
of films can be obtained by optimizing the size and shape of
lubricating fine particles. More particularly, lubricating fine
particles larger in average particle diameter have a tendency to
make a further improvement in the transparency of films containing
the same amount of lubricating fine particles, although the reason
for such tendency is not clear.
[0016] The lubricating fine particles used for rendering frosted
glass like appearances may include conventional inert foreign
particles such as those made of kaolin, clay, calcium carbonate,
silicon dioxide, calcium terephthalate, aluminum oxide, titanium
oxide, calcium phosphate or carbon black; and internal particles
made of high melting point organic compounds insoluble in the film
formation from molten polyester resins, or cross-linked polymers,
or formed in the polyesters by metal compound catalysts used in the
polyester polymerization. In particular, spherical particles of
cross-linked polymers may preferably be used because the gloss and
transparency of films can be obtained at the same time.
[0017] The present inventors have employed the total light
transmittance, haze, and 45-degrees specular gloss of films as the
indices of their gloss and transparency, and examined a
relationship between these indices and frosted glass like
appearances. As a result, the present inventors have found that
frosted glass like appearances can be obtained when heat-shrinkable
polyester films exhibit a total light transmittance of 80% to 90%
and a haze of 15% to 60%, both in a thickness of 50 .mu.m, and
further exhibit a 45-degrees specular gloss of 70% or lower.
[0018] In other words the first heat-shrinkable polyester films of
the present invention should exhibit a total light transmittance of
80% to 90% and a haze of 15% to 60%, both in a thickness of 50
.mu.m, and further exhibit a 45-degrees specular gloss of 70% or
lower.
[0019] The first heat-shrinkable polyester films of the present
invention may preferably exhibit surface roughness as determined
both by a maximum height (SR.sub.max) of 2.0 .mu.m or higher and by
a center-plane average roughness (SR.sub.a) of 0.20 .mu.m or
higher.
[0020] The first heat-shrinkable polyester films of the present
invention may preferably have a heat shrinkability of 50% or
higher, more preferably 50% to 75%, in the main shrinkage direction
of the film after treatment in hot water at 95.degree. C. for 10
seconds. If the films have a heat shrinkability of lower than 50%,
labels made of such films cause insufficient shrinkage at the necks
of bottles. In contrast, if the films have a heat shrinkability of
higher than 75%, labels made of such films cause jumping when
passing through a shrink tunnel because of their high heat
shrinkability.
[0021] The first heat-shrinkable polyester films of the present
invention may preferably have a heat shrinkability of 0% to 10%,
more preferably 1% to 7%, in a direction perpendicular to the main
shrinkage direction of the film after treatment in hot water at
95.degree. C. for 10 seconds. If the films have a heat
shrinkability of lower than 0%, the films can elongates in that
direction, and labels made of such films are difficult to remove
transverse wrinkles which have been formed during the shrinkage. In
contrast, if the films have a heat shrinkability of higher than
10%, labels made of such films cause larger longitudinal shrinkage
to make an increase in the amount of films used, resulting in the
occurrence of an economical problem.
[0022] The first heat-shrinkable polyester films of the present
invention may preferably have a glass transition temperature (Tg)
of 50.degree. C. to 90.degree. C., more preferably 55.degree. C. to
85.degree. C., and most preferably 55.degree. C. to 80.degree. C.
If the films have a glass transition temperature of higher than
90.degree. C., labels made of such films exhibit insufficient
shrinkage at low temperatures for satisfactory shrinkage finish. In
contrast, if the films have a glass transition temperature of lower
than 50.degree. C., labels made of such films exhibit large
spontaneous shrinkage unsuitable for practical use.
[0023] The first heat-shrinkable polyester films of the present
invention may preferably have solvent bonding properties with
1,3-dioxolane.
[0024] The first heat-shrinkable polyester films of the present
invention can be prepared, for example, by the following
method.
[0025] A polyester composition containing the appropriate amounts
of polyester(s) and polyester elastomer(s), and if necessary,
lubricating fine particles and other additive(s) is dried with a
hopper dryer, paddle dryer, vacuum dryer, or any other conventional
dryer, and then extruded at a temperature of 200.degree. C. to
320.degree. C. In the extrusion, any of the conventional methods
may be used, including T-die method and tubular method.
[0026] The extrusion and the subsequent rapid cooling give an
unstretched film. In the T-die method, the use of what is called
the electrostatic contact method is preferred for the rapid cooling
because it gives a film which is less uneven in thickness.
[0027] The unstretched film thus obtained is subjected to uni- or
bi-axial stretching so that the film finally obtained meets the
claimed requirements of the present invention.
[0028] The method of stretching may include uniaxial stretching
with rolls only in the machine direction (MD), uniaxial stretching
with a tenter only in the transverse direction (TD), and
conventional biaxial stretching at stretch ratios set higher in the
machine or transverse direction and set as low in the other
direction as possible. If necessary, the film thus stretched may be
subjected to further stretching.
[0029] In the above step of stretching, the film is stretched at a
stretch ratio of at least 2.0, preferably at least 2.5, in the main
shrinkage direction, and if necessary, further stretched in a
direction perpendicular to the main shrinkage direction, followed
by heat treatment.
[0030] The heat treatment is usually carried out in a fixed state
under tension, during which relaxation or tentering at 20% or lower
can also be carried out at the same time. The method of heat
treatment can be any of the conventional methods including bringing
the film into contact with heated rolls and holding the film with
clips in a tenter.
[0031] Before, during, or after the above step of stretching, the
film can also be subjected to corona discharge treatment on either
or both sides to improve the bonding properties of the film against
the print and/or adhesive layers.
[0032] Before, during, or after the above step of stretching, the
film can also be coated with an additive(s) on either or both sides
to improve the bonding, release, antistatic, self-lubricating,
shading, or other properties.
[0033] The first heat-shrinkable polyester films of the present
invention may preferably be 15 to 300 .mu.m, more preferably 25 to
200 .mu.m, in thickness.
[0034] The following will describe the second heat-shrinkable
polyester films of the present invention, which can prevent the
contents of a vessel fitted therewith from being deteriorated by
ultraviolet light and have good shrinkage finish and particularly
cause only rare occurrence of wrinkles, shrinkage spots, or other
defects.
[0035] The second heat-shrinkable polyester films may preferably be
prepared from polyesters having glass transition temperatures (Tg)
adjusted to 60.degree. C. to 75.degree. C. by the incorporation of
at least one C.sub.3-C.sub.6 diol (e.g., propanediol, butanediol,
hexanediol).
[0036] The polyesters should neither contain C8 or higher diols
(e.g., octane-idiol), nor polyhydric diols (e.g.,
trimethylolpropane, trimethylolethane, glycerin, diglycerin), nor
polycarboxlic acids (e.g., trimellitic acid, pyromellitic acid,
their anhydrides). For heat-shrinkable polyester films obtained by
the use of polyesters containing these diols or carboxylic acids,
the desired high shrinkability cannot be attained.
[0037] When the polyesters contain aliphatic carboxylic acids
(e.g., adipic acid, sebacic acid, decanedicarboxylic acid), their
amounts in the polyesters may preferably be lower than 3 mol %. For
heat-shrinkable polyester films obtained by the use of polyesters
containing these aliphatic carboxylic acids in amounts of 3 mol %
or greater, their film stiffness in the high-speed fitting is
insufficient, which is not preferred.
[0038] The acid components, which are contained in the polyesters
used in the present invention, may include terephthalic acid,
isophthalic acid, and naphthalene dicarboxylic acid. The diol
components may include, in addition to the above essential diols,
ethylene glycol, neopentyl glycol, and 1,4-cylcohexanedimethanol.
No incorporation of diethylene glycol, triethylene glycol, or
polyethylene glycol in the polyesters is preferred. In particular,
diethylene glycol may easily be formed as a by-product component in
the polymerization of polyesters. The polyesters used in the
present invention may preferably contain diethylene glycol in
amounts of smaller than 4 mol %.
[0039] When two or more polyesters are used in admixture, the
amounts of acid components and the amounts of diol components are
relative to the total amount of all acid components and the total
amount of all diol components, both of which are contained in these
polyesters, independently of whether or not transesterification has
been carried out after the mixing.
[0040] For the purpose of obtaining heat-shrinkable polyester films
having particularly excellent shrinkage finish, neopentyl glycol
may preferably be used as one of the diol components, more
preferably in an amount of 16 wt % or greater.
[0041] The second heat-shrinkable polyester films of the present
invention should exhibit a light transmittance of 0% to 20% at a
wavelength of 380 nm and of 0% to 60% at a wavelength of 400 nm,
and further exhibit a haze of 15% or lower.
[0042] The second heat-shrinkable polyester films of the present
invention can be rendered ultraviolet light cut properties, for
example, by the incorporation, application, or impregnation of an
ultraviolet light cut agent. To attain a high degree of ultraviolet
light cut properties, an ultraviolet light cut agent may preferably
be incorporated in a film because the film can have a thick cut
layer. The second heat-shrinkable polyester films of the present
invention may preferably have at least two layers of laminated
films. To prepare a label by bonding both ends of a film together
with a solvent, the presence of an ultraviolet light cut agent in a
great amount on the surface of the film is not preferred, and an
ultraviolet light cut agent may preferably be contained only in the
inner part of the film. For example, the second heat-shrinkable
polyester films of the present invention may have at least three
layers of laminated films and may contain an ultraviolet light cut
agent in at least one internal layer not coming to the surface
thereof.
[0043] The ultraviolet light cut agent may include those of the
organic type, which can absorb ultraviolet light, and those of the
inorganic type, which can block ultraviolet light. The ultraviolet
light cut agent of the organic type is exemplified by low molecular
weight organic compounds, including those of the indole,
benzotriazole, benzophenone, cyanoacrylate, or phenyl salycilate
type. The amount of ultraviolet light cut agent to be used may
preferably be in the range of 0.1 to 30 wt %.
[0044] The second heat-shrinkable polyester films of the present
invention may be in the form of a single layer; however, when a low
molecular weight organic compound is used as the ultraviolet light
cut agent, there may occur the deterioration or sublimation of the
ultraviolet light cut agent because of poor heat resistance or high
temperature in the molten state of the polyester, so that
sufficient ultraviolet light cut properties cannot be obtained.
[0045] To avoid this problem, the second heat-shrinkable polyester
films of the present invention may preferably take the form of at
least three layers of laminated films by co-extrusion, in which a
layer containing no ultraviolet light cut agent is provided on each
film surface. From the viewpoint of heat resistance as described
above, ultraviolet light cut agents of the polymer type are
preferred, specific examples of which may include Novapex U110
available from MITSUBISHI CHEMICAL CORPORATION. On the other hand,
the ultraviolet light cut agents of the inorganic type may include
inorganic particles having a average particle diameter below the
wavelength range of visible light, specific examples of which may
include fine particles of titanium oxide having an average particle
diameter of 0.04 .mu.m or smaller.
[0046] In the preparation of a polyester composition as the base
material, one must come up with some ideas. For example, when an
ultraviolet light cut agent is added to a polyester mixture and the
polyester composition thus obtained is dried, one must pay
attention to the drying temperature so that the ultraviolet light
cut agent causes no sublimation. In the case where the polyester
resin used as the base resin has a low glass transition
temperature, drying at an ordinary temperature, e.g., at
120.degree. C., causes sublimation of the ultraviolet light cut
agent.
[0047] To improve the self-lubricating properties of the second
heat-shrinkable polyester films of the present invention, inorganic
or organic lubricants may preferably be added. The second
heat-shrinkable polyester films of the present invention may
further contain, when so required, additives such as stabilizers,
colorants, antioxidants, defoamers, antistatic agents and
ultra-violet light absorbers.
[0048] The second heat-shrinkable polyester films of the present
invention may preferably have a heat shrinkability of 10% or
higher, more preferably 10% to 50%, in the main shrinkage direction
of the film after treatment in hot water 70.degree. C. for 10
seconds. If the films have a heat shrinkability of lower than 10%,
labels made of such films exhibit insufficient shrinkage at low
temperatures, requiring the rise in temperature for shrinkage,
which is not preferred. In contrast, if the films have a heat
shrinkability of higher than 50%, labels made of such films cause
jumping, which is also not preferred.
[0049] The second heat-shrinkable polyester films of the present
invention may preferably have a heat shrinkability of 30% or
higher, more preferably 75% to 95%, in the main shrinkage direction
of the film after treatment in hot water at 85.degree. C. for 5
seconds. If the films have a heat shrinkability of lower than 75%,
labels made of such films cause insufficient shrinkage at the necks
of bottles, which is not preferred. In contrast, if the films have
a heat shrinkability of higher than 95%, labels made of such films
have a possibility of causing jumping because of their still having
shrinkability after the shrinkage, which is also not preferred.
[0050] The second heat-shrinkable polyester films of the present
invention may preferably have a heat shrinkability of 10% or lower
in a direction perpendicular to the main shrinkage direction of the
film after treatment in hot water at 85.degree. C. for 5
seconds.
[0051] It is important that the second heat-shrinkable polyester
films of the present invention have a shrinkage stress of 1.0
kg/mm.sup.2 or greater at 90.degree. C. If the shrinkage stress is
smaller than 1.0 lg/mm.sup.2, the speed of shrinkage is too slow
that labels made of such films cause possible occurrence of
insufficient shrinkage at the necks of bottles. The second
heat-shrinkable polyester films of the present invention may
preferably have a shrinkage stress of 3.0 kg/mm.sup.2 or smaller.
If the shrinkage stress is greater than this value, such films
cause possible deterioration of transparency by formation of voids
around the ultraviolet light cut agents (and lubricants, if used)
contained in the films.
[0052] It is also important that the second heat-shrinkable
polyester films of the present invention have a compressive
strength of 300 g or higher in the form of a label. The compressive
strength, although it may be affected by the thickness of films,
should be 300 g or higher from the viewpoint of suitability for
high-speed machines. If the compressive strength is lower than 300
g, labels made of such films particularly cause possible occurrence
of a failure in fitting on the bottles by label fitting
machines.
[0053] The second heat-shrinkable polyester films of the present
invention may preferably be, but are not particularly limited to,
10 to 200 .mu.m, more preferably 20 to 100 .mu.m, in thickness as
the heat-shrinkable films for labels.
[0054] The second heat-shrinkable polyester films of the present
invention may preferably have a thickness distribution of 6% or
lower. If the films have a thickness distribution of higher than
6%, they cause the deviation of patterns in the superposition of
many colors when processed in the multi-color printing, which is
not preferred.
[0055] The second heat-shrinkable polyester films of the present
invention can be prepared, for example, by the following
method.
[0056] A polyester composition containing the appropriate amounts
of polyester(s), and if necessary, ultraviolet light cut agents and
other additive(s) is dried with a hopper dryer, paddle dryer,
vacuum dryer, or any other conventional dryer, and melt extruded
into a film shape at a temperature of 200.degree. C. to 300.degree.
C. In the extrusion, any of the conventional methods may be used,
including T-die method and tubular method.
[0057] The extrusion and the subsequent rapid cooling give an
unstretched film. In the case of a laminated film, polymers for the
respective layers are formed one on top of another by lamination,
or polymers for the respective layers are melted and co-extruded
using separate extruders and then rapidly cooled by casting from
the nozzles onto the rotating drum, to give an unstretched
film.
[0058] The unstretched film thus obtained is subjected to
stretching so that the film finally obtained meets the claimed
requirements of the present invention. For attaining the purpose of
the present invention, the transverse direction (ie., the direction
perpendicular to the direction of extrusion) is practical as the
main shrinkage direction of the film; therefore, the following
explanation is for an example of the film formation when the main
shrinkage direction of the film is taken as the transverse
direction. However, the film formation in which the main shrinkage
direction of the film is taken as the machine direction (ie., the
direction of extrusion) can also be carried out substantially in
the same manner as described below, except that the direction of
stretching is turned 90 degrees around the line perpendicular to
the film surface.
[0059] In the present invention, the unstretched film should be
stretched at a temperature of (Tg-5.degree. C.) or higher but lower
than (Tg+15.degree. C.) where Tg is the glass transition
temperature of the unstretched film. If the unstretched film is
stretched at a temperature of lower than (Tg-5.degree. C.), the
second heat-shrinkable polyester film thus obtained is difficult to
have heat shrinkability such as one of the claimed requirements of
the present invention and it has deteriorated transparency, which
is not preferred. If the unstretched film is stretched at a
temperature of (Tg+15.degree. C.) or higher, the second
heat-shrinkable polyester film thus obtained exhibits insufficient
film stiffness in the high-speed fitting and it has a remarkably
deteriorated thickness distribution, which is also not
preferred.
[0060] The method of stretching may include uniaxial stretching
only in the transverse direction (TD) with a tenter, in which case
the film can also be slightly stretched in the machine direction
(MD). In such biaxial stretching, any of the sequential or
simultaneous biaxial stretching method can be employed, and the
film may further be stretched, if necessary, in the machine or
transverse direction.
[0061] To make even thickness distribution in the second
heat-shrinkable polyester films of the present invention, the
unstretched film may preferably be heated to a prescribed film
temperature at a low air flow rate with a heat transmission
coefficient of 0.0013 cal/cm.sup.2.multidot.sec.multidot..degree.
C. (0.0054 J/cm.sup.2.multidot.sec.multidot.K) or lower in the step
of preheating to be carried out prior to the step of stretching
when the unstretched film is stretched in the transverse direction
with a tenter. The stretching in the transverse direction may
preferably be carried out at a stretched ratio of 3.0 or higher,
more preferably 3.5 or higher.
[0062] To prevent heat evolution in the films during stretching to
reduce the unevenness of film temperature in the width direction of
the films when the main shrinkage direction of the films (ie., the
direction of stretching) is taken as the transverse direction, the
step of stretching may preferably be carried out at an air flow
rate with a heat transmission coefficient of 0.0009
cal/cm.sup.2.multidot.sec.multidot..de- gree. C. (0.0038
J/cm.sup.2.multidot.sec.multidot.K) or higher, more preferably
0.0011 to 0.0017 cal/cm.sup.2.multidot.sec.multidot..degree. C.
(0.0046 to 0.0072 J/cm.sup.2.multidot.sec.multidot.K).
[0063] If the air flow rate employed in the step of preheating
corresponds to a heat transmission coefficient of higher than
0.0013 cal/cm.sup.2.multidot.sec.multidot..degree. C. (0.0054
J/cm.sup.2.multidot.sec.multidot.K) or if the air flow rate
employed in the step of stretching corresponds to a heat
transmission coefficient of lower than 0.0009
cal/cm.sup.2.multidot.sec.multidot..degree. C. (0.0038
J/cm.sup.2.multidot.sec.multidot.K), the film thus obtained is
difficult to have even thickness distribution, so that it causes
the deviation of patterns in the super-position of many colors when
processed in the multi-color printing, which is not preferred. More
particularly, films having a thickness distribution of 6% or lower
are easy to make superposition of many colors, for example, in the
three-color printing to be carried out in the evaluation of
shrinkage finish as described below. In contrast, films having a
thickness distribution of higher than 6% are not preferred in the
superposition of many colors.
[0064] The stretched film is then heat treated, if necessary, at a
temperature of 70.degree. C. to 100.degree. C. to give a second
heat-shrinkable polyester film of the present invention.
EXAMPLES
[0065] The present invention will hereinafter be further
illustrated by some examples; however, the present invention is not
limited to these examples.
[0066] The first heat-shrinkable polyester films of the present
invention are exemplified in Examples 1, 2 and Comparative Example
1, while the second heat-shrinkable polyester films of the present
invention are exemplified in Examples 3-9 and Comparative Examples
2-5.
[0067] The following will describe various testing methods for
evaluation of heat-shrinkable polyester films prepared in these
Examples and Comparative Examples.
[0068] (1) Total Light Transmittance and Haze
[0069] According to JIS K 7105, a film was measured for total light
transmittance and haze with a hazemeter (an integrating sphere type
light transmittance measuring apparatus), model NDH-1001DP,
available from NIP-PON DENSHOKU INDUSTRIES CO., LTD.
[0070] (2) Maximum Height and Center-Plane Average Roughness
[0071] Using a three-dimensional microfigure measuring instrument,
model ET-30HK, available from KOSAKA LABORATORY LTD, a film was
measured for maximum height and center-plane average roughness
under the conditions that the cut-off value was 80 .mu.m and the
driving speed was 100 .mu.m/sec. The values of maximum height
(SR.sub.max) and center-plane average roughness (SR.sub.a) were
obtained by direct reading from the above instrument.
[0072] The maximum height (SR.sub.max) is defined as the maximum
height from the standard line, which is an average of the center
lines (the area formed by the center line and the roughness curve
of a sample above the center line is equal to the area formed by
the center line and the roughness curve of the sample below the
center line) obtained by scanning a constant area on the surface of
a sample. The center-plane average roughness (SR.sub.a) is defined
as the three-dimensional average roughness for the center plane
(the volume formed by the center plane and the surface profile of a
sample above the center plane is equal to the volume formed by the
center plane and the surface profile of the sample below the center
plane) and expressed by the following formula: 1 SR a = 1 L x L y 0
Ly 0 Lx f ( x , y ) x y
[0073] wherein SR.sub.a is the center-plane average roughness, Lx
and Ly are measuring lengths in the direction of x-axis and y-axis,
respectively, on the surface of the sample, and f(x,y) is a
roughness curved surface for the center plane.
[0074] (3) Heat Shrinkability
[0075] A film was cut into a square of 10 cm.times.10 cm with two
sides parallel to the machine direction and to the transverse
direction, respectively. This sample was heat-shrunk by immersion
under no load in hot water at a prescribed temperature
.+-.0.5.degree. C. for a prescribed period of time and then
measured for side lengths in the machine direction and in the
transverse direction, respectively. The heat shrinkability was
calculated from the measured values of side lengths by the
following equation. The direction of either side corresponding to
the larger value of heat shrinkability was referred to as the main
shrinkage direction. 2 heat shrinkability = Side length before
shrinkage - Side length after shrinkage Side length before
shrinkage .times. 100 ( % )
[0076] (4) Solvent Bonding Properties
[0077] A film was formed into a tube shape by bonding with
1,3-dioxolane, the circumference being 273 mm along the main
shrinkage direction and the tube length being 100 mm along the
direction perpendicular thereto, and the tube was cut in 15 mm
width along the tube lengthwise direction. This sample was then
drawn to cause the peeling of its bonded part in the direction
perpendicular to the tube lengthwise direction, and evaluated to
have good solvent bonding properties, when exhibited sufficient
peeling resistance.
[0078] (6) Glass Transition Temperature (Tg)
[0079] Using a differential scanning calorimeter, model DSC220,
available from SEIKO INSTRUMENTS & ELECTRONICS LIMITED, an
unstretched film of 10 mg in weight was heated from -40.degree. C.
to 120.degree. C. at a heating rate of 20.degree. C./min. to draw a
heat absorption curve, from which the glass transition temperature
(Tg) was determined. Two tangent lines were drawn before and after
the inflection point on the heat absorption curve, and the point of
their intersection was regarded as the glass transition temperature
(Tg).
[0080] (7) Ultraviolet Light Transmittance
[0081] A film was cut in a size of 38 mm.times.13 mm, and this
sample was then measured for ultraviolet light transmittance at
prescribed wavelengths with a double beam spectrophotometer, model
U-2001, available from HITACHI, LTD.
[0082] (8) Thickness Distribution
[0083] A film was cut in a size of 5 cm.times.50 cm along the
machine direction and along the transverse direction, respectively.
This sample was measured for thickness (the number of measured
points =20) with a contact thickness meter, model KG60/A, available
from ANRITSU CORPORATION. For each sample, the thickness
distribution (ie., scattering of thickness) was calculated by the
following formula. The measurement was repeated for fifty samples
of each film and, the average value of thickness distribution was
determined and evaluated on the following criteria: 3 Thickness
distribution = Maximum thickness - Minimum thickness Agerage
thickness .times. 100 ( % )
[0084] Good: average value was 6% or lower;
[0085] Fair: average value was between 6% and 10%;
[0086] Poor: average value was 10% or higher.
[0087] The polyesters used in the examples and comparative examples
were as follows:
[0088] Polyester A: polyethylene terephthalate (IV=0.75);
[0089] Polyester B: a polyester consisting of 100 mol %
terephthalic acid, 70 mol % ethylene glycol and 30 mol % neopentyl
glycol (IV=0.72);
[0090] Polyester C: a polyester elastomer consisting of 70 wt %
polybutylene terephthalate and 30 wt % .epsilon.-caprolactone
(reduced viscosity (.eta..sub.sp/c)=1.30);
[0091] Polyester D: polybutylene terephthalate (IV=1.20)
[0092] The lubricating fine particles used in Examples 1,2 and
Comparative Example 1 were as follows:
[0093] Lubricating Fine Particles A: EPOSTAR MA1010 (average
particle diameter, 10 .mu.m) available from NIPPON SHOKUBAI CO.,
LTD.
[0094] Lubricating Fine Particles B: EPOSTAR MA1006 (average
particle diameter, 6 .mu.m) available from NIPPON SHOKUBAI CO.,
LTD.
[0095] Lubricating Fine Particles C: Amorphous SYLOID (average
particle diameter, 1.5 .mu.m) available from FUJI SYLYSIA CHEMICAL
LTD.
[0096] In the following Examples 1, 2 and Comparative Example 1,
there will be illustrated some examples of the first
heat-shrinkable polyester films of the present invention.
Example 1
[0097] A polyester composition containing 30 wt % polyester A, 49
wt % polyester B, 20 wt % polyester C, and 1 wt % polyester A was
melt extruded from a T-die at 280.degree. C. and rapidly cooled on
chill rolls to give an unstretched film having a glass transition
temperature (Tg) of 60.degree. C.
[0098] The unstretched film was stretched in a tenter at a film
temperature of 70.degree. C. at a stretch ratio of 4.0 in the
transverse direction to give a heat-shrinkable polyester film of 50
.mu.m in thickness. The main shrinkage direction of the film was
corresponding to the transverse direction.
Example 2 and Comparative Example 1
[0099] Heat-shrinkable polyester films of 50 .mu.m in thickness
were obtained in the same manner as described in Example 1, except
that the kind and mixing ratio of lubricating fine particles were
changed as shown in Table 1.
[0100] The heat-shrinkable polyester films prepared in Examples 1,
2 and Comparative Example 1 were evaluated by some of the testing
methods as described above. The results are shown in Table 1.
1 TABLE 1 Base material Lubricating Heat Total light Surface
Polyesters fine particles shrinkability trans- roughness Solvent
(wt %) (wt %) 95.degree. C., 10 sec. mittance Haze Gloss (.mu.m)
bonding A B C A B C MD TD (%) (%) (%) SR.sub.max SR.sub.a
properties Example 1 30 49 20 1 0 0 2.5 59.0 84 36 70 8.1 0.29 good
Example 2 30 49 20 0 1 0 3.0 63.0 85 40 68 5.1 0.26 good Comp. Ex.
1 31 49 20 0 0 0.04 3.0 63.0 95 4.5 161 0.6 0.05 good Polyester A:
TPA//EG = 100//100 (mol %) Polyester B: TPA//EG/NPG = 100//70/30
(mol %) Polyester C: a copolyester of (TPA//BD =
100//100)/.epsilon.-caprolactone = 70/30 (wt %) Lubricating fine
particle A: EPOSTAR MA1010 Lubricating fine particle B: EPOSTAR
1006 Lubricating fine particle C: Amorphous SYLOID TPA:
Terephthalic acid EG: Ethylene glycol NPG: Neopentyl glycol BD:
Butanediol
[0101] As can be seen from Table 1, the heat-shrinkable polyester
films of Examples 1 and 2 had good frosted glass like appearances.
This indicates that the first heat-shrinkable polyester films of
the present invention have high quality and high practical
availability, and they are particularly suitable for
heat-shrinkable labels having frosted glass like appearances.
[0102] In contrast, the heat-shrinkable polyester film of
Comparative Example 1 had poor frosted glass like appearances, and
it therefore had low quality and low practical availability.
[0103] According to the present invention, heat-shrinkable
polyester films can be obtained, which have frosted glass like
appearances without being printed or processed and further have
sufficient solvent bonding properties, and they are therefore
extremely useful as heat-shrinkable polyester films for labels,
particularly for labels of great product value.
[0104] In the following Examples 3-9 and Comparative Examples 2-5,
there will be illustrated some examples of the second
heat-shrinkable polyester films of the present invention.
Example 3
[0105] A polyester composition was prepared by mixing 26 wt %
polyester A, 50 wt % polyester B and 24 wt % polyester D, and
adding 1 part by weight of an ultraviolet light cut agent
(available from CIBA SPECIALTY CHEMICALS K.K.; trade name, Tinuvin
326), relative to 99 parts by weight of the polyester mixture. The
polyester composition was subjected to melt co-extrusion from a
T-die at 280.degree. C., at which time a core layer and a skin
layer were laminated together so that the ratio of skin/core layer
thickness after stretching came to 25 .mu.m/25 .mu.m, followed by
rapid cooling, to give an unstretched film having a glass
transition temperature (Tg) of 70.degree. C.
[0106] The unstretched film was then preheated until the film
temperature came to 88.degree. C. with a heat transmission
coefficient of 0.0010 cal/cm.sup.2.multidot.sec.multidot..degree.
C. (0.0042 J/cm.sup.2.multidot.sec.multidot.K), and stretched in a
tenter at 78.degree. C. at a stretch ratio of 3.9 in the transverse
direction with a heat transmission coefficient of 0.0014
cal/cm.sup.2.multidot.sec.multi- dot..degree. C. (0.0059
J/cm.sup.2.multidot.sec.multidot.K), and heat treated at 76.degree.
C. for 10 seconds to give a heat-shrinkable polyester film of 50
.mu.m in thickness. The main shrinkage direction of the film was
corresponding to the transverse direction.
[0107] Examples 4-9 and Comparative Examples 2-5 Heat-shrinkable
polyester films of 50 .mu.m in thickness were obtained in the same
manner as described in Example 3, except that the kind and amount
of ultraviolet light cut agent contained in the core layer and/or
the skin layer were changed as shown in Table 2.
[0108] The heat-shrinkable polyester films prepared in Examples 4-9
and Comparative Examples 2-5 were evaluated by some of the testing
methods as described above. The results are shown in Table 2.
2 TABLE 2 Co-extrusion Ultraviolet light cut agent (ultraviolet
light cut Ultraviolet light Heat shrinkability Thick- Total amount
agent contd. or not) transmittance (%) ness in the film skin (%)
70.degree. C. 70.degree. C. 85.degree. C. 85.degree. C. distri-
Haze Product name*) (wt %) core layer layer 380 nm 400 nm MD TD MD
TD bution (%) Example 3 Tinuvin 326 1.0 contd. contd. 2 30 1.0 30.0
3.0 60.0 good 5.0 Example 4 Tinuvin 326 0.5 contd. contd. 13 51 1.0
31.0 2.0 61.0 good 5.0 Example 5 Bonasorb UA-3901 0.5 contd. contd.
1.3 0.5 1.5 32.0 2.5 61.0 good 4.9 Example 6 Novapex U110 30 contd.
contd. 0 52 1.0 30.0 1.5 49.0 good 5.5 Example 7 Tinuvin 326 1.3
contd. not contd. 0 20 1.0 28.0 2.0 58.0 good 5.0 Example 8
Bonasorb UA-3901 0.5 contd. not contd. 1 0.5 0.5 29.0 3.0 60.0 good
5.2 Example 9 Tinuvin 326/ 0.5/0.1 contd. contd. 6.3 18 1.0 30.0
2.0 61.0 good 5.2 Bonasorb UA-3901 Comp. Ex. 2 -- -- -- -- 81 82
1.0 31.0 2.0 62.0 good 5.0 Comp. Ex. 3 Tinuvin 326 0.1 contd.
contd. 63 78 1.0 31.0 2.5 61.0 good 5.0 Comp. Ex. 4 LA31 0.5 contd.
contd. 27 78 1.5 30.0 3.0 59.0 good 5.2 Comp. Ex. 5 TiO.sub.2 5
contd. contd. 0 0 1.0 30.0 2.5 59.0 good 89.5 *)Tinuvin 326 is
available from CIBA SPECIALTY CHEMICALS K.K.; Bonasorb UA-3901 from
ORIENT CHEMICAL INDUSTRIES LTD.; Novapex U110 from MITSUBISHI
CHEMICAL CORPORATION; LA31 from ASAHI DENKA KOGYO K.K.; and
TiO.sub.2 is in the form of fine particles having an average
particle diameter of 0.25 .mu.m.
[0109] As can be seen from Table 2, the heat-shrinkable polyester
films of Examples 3-7 had good ultraviolet light cut properties,
good shrinkage finish, and good thickness distribution. This
indicates that the second heat-shrinkable polyester films of the
present invention have high quality and high practical
availability, and they are particularly suitable for shrinkable
labels.
[0110] In contrast, the heat-shrinkable polyester films of
Comparative Examples 2-5 had insufficient ultraviolet light cut
properties, and they therefore had low quality and low practical
availability.
[0111] According to the present invention, heat-shrinkable
polyester films can be obtained, which can prevent the contents of
a vessel fitted therewith from being deteriorated by ultraviolet
light and have good shrinkage finish and particularly cause only
rare occurrence of wrinkles, shrinkage spots, or other defects, and
they are therefore extremely useful as heat-shrinkable polyester
films for labels, particularly for labels of great product
value.
* * * * *