U.S. patent application number 11/250259 was filed with the patent office on 2006-03-02 for opaque, white film with low transparency made from a crystallizable thermoplastic.
Invention is credited to Ulrich Kern, Ursula Murschall, Klaus Oberlaender.
Application Number | 20060046041 11/250259 |
Document ID | / |
Family ID | 7631624 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060046041 |
Kind Code |
A1 |
Murschall; Ursula ; et
al. |
March 2, 2006 |
Opaque, white film with low transparency made from a crystallizable
thermoplastic
Abstract
The invention relates to an opaque, white film with a thickness
of from 10 to 500 .mu.m whose principal constituent is a
crystallizable thermoplastic. The film comprises barium sulfate and
an optional optical brightener. Optionally, at least one surface of
the film bears a functional coating with a thickness of from 5 to
100 nm, in order to confer on the film surface an additional
function such as sealability, printability, metallizability,
sterilizability, antistatic properties, aroma barrier properties or
improved adhesion to materials which would not adhere to the film
surface without the coating, for example photographic
emulsions.
Inventors: |
Murschall; Ursula;
(Nierstein, DE) ; Kern; Ulrich; (Ingelheim,
DE) ; Oberlaender; Klaus; (Wiesbaden, DE) |
Correspondence
Address: |
PROPAT, L.L.C.
425-C SOUTH SHARON AMITY ROAD
CHARLOTTE
NC
28211-2841
US
|
Family ID: |
7631624 |
Appl. No.: |
11/250259 |
Filed: |
October 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09779156 |
Feb 8, 2001 |
|
|
|
11250259 |
Oct 14, 2005 |
|
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Current U.S.
Class: |
428/220 |
Current CPC
Class: |
Y10T 428/24802 20150115;
B32B 27/36 20130101; Y10T 428/31786 20150401; C08K 2003/3045
20130101; C08K 5/0041 20130101; C08J 2367/02 20130101; Y10T
428/2495 20150115; C08K 5/0041 20130101; C08K 3/30 20130101; C08J
5/18 20130101; C08L 67/02 20130101; Y10T 428/31855 20150401 |
Class at
Publication: |
428/220 |
International
Class: |
B32B 27/32 20060101
B32B027/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2000 |
DE |
100 07 719.6 |
Claims
1. An opaque, white film with a thickness of from 10 to 500 .mu.m,
said film comprising thermoplastic and a pigment, said
thermoplastic consisting entirely of polyester and said pigment
comprising barium sulfate, said film further exhibiting a modulus
of elasticity in the transverse direction of greater than or equal
to 4200 N/mm.sup.2.
2. The film as claimed in claim 1, wherein the thermoplastic has
been selected from the group consisting of polyethylene
terephthalate, polybutylene terephthalate and polyethylene
naphthalate.
3. The film as claimed in claim 1, wherein from 0.2 to 40% by
weight of barium sulfate is present as pigment in the film, based
on the weight of the thermoplastic.
4. The film as claimed in claim 1, said film further comprises
optical brightener, said optical brightener present in an amount of
from 10 to 50,000 ppm based on the weight of the thermoplastic.
5. The film as claimed in claim 4, wherein the optical brightener
has been selected from the group consisting of bisbenzoxazoles,
phenylcoumarins and bisstearylbiphenyls.
6. The film as claimed in claim 4, wherein, in addition to the
optical brightener, a polyester-soluble blue dye selected from the
group consisting of cobalt blue, ultramarine blue, anthraquinone
dyes or combinations of these, is also present in the film, and
wherein the amount of blue dye present in the film is from 10 to
10,000 ppm, based on the weight of the thermoplastic.
7. The film as claimed in claim 1, wherein the barium sulfate is
present as precipitated barium sulfate in the film in an amount of
from 0.5 to 30% by weight, based on the weight of the
thermoplastic, and wherein the average grain size of the barium
sulfate is from 0.1 to 5 .mu.m (Sedigraph method).
8. The film as claimed in claim 1, wherein the surface gloss of the
film, measured to DIN 67530 (measurement angle 20.degree.) is
.gtoreq.10, and wherein the luminous transmittance (transparency)
of the film, measured to ASTM-D 1003 is .ltoreq.30%.
9. The film as claimed in claim 1, wherein the film has one or more
layers, and the film having more than one layer comprises at least
one base layer and at least one outer layer.
10. The film as claimed in claim 1, wherein at least one of the
surfaces of the film bears a functional coating said coating
comprising substances or compositions selected from the group
consisting of acrylates, ethylvinyl alcohols, PVDC, waterglass
(Na.sub.2SiO.sub.4), hydrophilic polyesters, vinyl acetates,
polyvinyl acetates, polyurethanes, silanes, the alkali metal or
alkaline earth metal salts of C.sub.10-C.sub.18 fatty acids,
butadiene copolymers with acrylonitrile or methyl methacrylate,
methacrylic acid, acrylic acid or esters thereof and mixtures of
these.
11. The film as claimed in claim 10, wherein the coating comprises
from 0.05 to 5% by weight of additional additives.
12. An opaque white film with a thickness of from 10 to 500 .mu.m,
comprising (i) a single thermoplastic consisting of polyester and
(ii) barium sulfate, wherein the film exhibits tear strengths in
the transverse direction of greater than or equal to 170 N/mn?
13. The opaque white film as claimed in claim 12, wherein said
opaque white film further comprises regrind formed from said film
in amounts of up to 50 weight percent, said film having a thickness
of up to 50 microns and exhibiting a yellowness of up to 20.
14. The opaque white film as claimed in claim 12, wherein said
opaque white film further comprises regrind formed from said film
in amounts of up to 50 weight percent, said film having a thickness
of from 50 to 250 microns and exhibiting a yellowness of up to
45.
15. The opaque, white film as claimed in claim 1, wherein the
luminous transmittance of said film is 15 to 20% lower than the
luminous transmittance of a comparable film formed from said
thermoplastic having the same thickness as said film and lower
longitudinal orientation than said film.
16. An opaque, white film with a thickness of from 10 to 500 .mu.m,
comprising a crystallizable thermoplastic and barium sulfate
wherein said crystallizable thermoplastic consists entirely of
polyester, said film exhibiting an elongation at break of greater
than or equal to 120% in the machine direction.
Description
[0001] This application is a continuation of parent co-pending U.S.
application Ser. No. 09/779,156, filed Feb. 8, 2001. This
application further claims priority through its parent U.S.
application to German Application No. 100 07 719.6, filed Feb. 19,
2000. Both U.S. application Ser. No. 09/779,156 and German
Application No. 100 07 719.6 are hereby incorporated by reference
herein in their entirety.
[0002] The invention relates to an opaque, white biaxially oriented
film with low transparency made from a crystallizable thermoplastic
and having a thickness of from 10 to 500 .mu.m, where at least one
surface of the film has optionally been provided with an additional
functionality. The film comprises at least barium sulfate and an
optional optical brightener, and has good orientability, low
transparency, and also very good optical and mechanical properties.
The invention further relates to a process for producing this film
and to the use of the film.
BACKGROUND OF THE INVENTION
[0003] In many food and drink packaging applications, there is
demand for a high level of barrier action with respect to gases,
water vapor and flavors. For this reason, use is usually made of
polypropylene films which have been metallized or have been coated
with polyvinylidene chloride (PVDC). In the case of PVDC-coated
films--as with metallizing--the coating takes place in a second
operation, which makes the packaging markedly more expensive.
Ethylene-vinyl alcohol copolymers (EVOH) likewise exhibit strong
barrier action. However, films modified with EVOH are particularly
sensitive to moisture, and this limits their range of application.
In addition, due to their poor mechanical properties they have
relatively high thickness or have to be laminated with other
materials at high cost. The disposal of EVOH-modified films after
they have been used is also more complicated than that of other
films. In addition to this, some raw materials are not approved by
the authorities or are unsuitable for producing packaging for food
or drink.
DESCRIPTION OF THE INVENTION
[0004] The object of the present invention was to provide an
opaque, white biaxially oriented film with a thickness of from 10
to 500 .mu.m and optionally having at least one additional
functionality and which, besides having good orientability, good
mechanical properties and good optical properties and a low
Yellowness Index, above all has a high level of whiteness and low
transparency and can be produced simply and cost-effectively and
does not cause any disposal problems.
[0005] The good optical properties include uniform, streak-free
coloration, low luminous transmittance/transparency (.ltoreq.30%),
acceptable surface gloss (.gtoreq.10), and also a low Yellowness
Index (dependent on thickness, .ltoreq.45 for 250 .mu.m films and
.ltoreq.20 for 50 .mu.m films).
[0006] The good mechanical properties include a high modulus of
elasticity (E.sub.MD.gtoreq.3300 N/mm.sup.2; E.sub.TD.gtoreq.4200
N/mm.sup.2), and also good tear strengths (in MD.gtoreq.120
N/mm.sup.2; in TD.gtoreq.170 N/mm.sup.2) and finally also good
longitudinal (MD) and transverse (TD) elongations at break (in
MD.gtoreq.120%; in TD.gtoreq.50%).
[0007] Good orientability includes excellent capabilities of the
film for orientation during its production, both longitudinally and
transversely, without break-offs.
[0008] The novel film should moreover be recyclable, that is to say
that any cut material arising during continuous film production can
be fed back into the production operation, in particular without
loss of optical or mechanical properties, so that the film can
still be used for interior applications and in constructing
exhibition stands, for example.
[0009] This object is achieved by an opaque white film with a
thickness of from 10 to 500 .mu.m whose principal constituent is a
crystallizable thermoplastic, and whose characterizing features are
that the film comprises at least barium sulfate and optionally at
least one optical brightener, that the barium sulfate and/or the
optional optical brightener have been incorporated directly into
the crystallizable thermoplastic or are fed as a masterbatch during
film production, and that at least one surface of the film bears an
optional functional coating with a thickness of from 5 to 100
nm.
[0010] The novel film comprises, as principal constituent, a
crystallizable thermoplastic. Examples of suitable crystallizable
or semicrystalline thermoplastics are polyethylene terephthalate,
polybutylene terephthalate and polyethylene naphthalate, and
preference is given to polyethylene terephthalate.
[0011] For the purposes of the present invention, a crystallizable
thermoplastic is
[0012] 1. a crystallizable homopolymer;
[0013] 2. a crystallizable copolymer;
[0014] 3. a crystallizable compound;
[0015] 4. a crystallizable recycled material, or
[0016] 5. another type of crystallizable thermoplastic.
[0017] The present invention also provides a process for producing
this film, comprising:
[0018] 6. production of a film from at least one base layer and, if
desired, (an) outer layer(s), by extrusion or, if desired,
coextrusion;
[0019] 7. biaxial orientation of the film;
[0020] 8. heat-setting of the oriented film; and
[0021] 9. optional functionalization of at least one surface of the
film prior to, during or after steps 2 and/or 3.
[0022] The novel film may have one layer, i.e. have only one base
layer and the optional functional coating, or else have two or more
layers, i.e. have one base layer, at least one outer layer on the
base layer and the optional functional coating, the combination of
base layer and outer layer expediently being produced by way of
coextrusion technology.
[0023] According to the invention, the film optionally comprises at
least barium sulfate as pigment, and the amount of pigment here is
preferably from 0.2 to 40% by weight, based on the weight of the
crystallizable thermoplastic. The barium sulfate is preferably fed
by way of what is known as masterbatch technology during film
production.
[0024] According to the invention, the film comprises at least one
optical brightener, and the amount of the optical brightener used
here is from 10 to 50,000 ppm, in particular from 20 to 30,000 ppm,
particularly preferably from 50 to 25,000 ppm, based on the weight
of the crystallizable thermoplastic. It is preferable for the
optical brightener, too, to be fed by way of what is known as
masterbatch technology during film production.
[0025] The optical brighteners according to the invention are
capable of absorbing UV radiation in the region from 360 to 380 nm
and of re-emitting this as longer-wavelength, visible blue-violet
light.
[0026] Suitable optical brighteners are bisbenzoxazoles,
phenylcoumarins and bisstearylbiphenyls, in particular
phenylcoumarin, and particularly preferably triazine
phenylcoumarin, which is obtainable as the product TINOPAL.RTM.
(Ciba-Geigy, Basle, Switzerland), or else HOSTALUX.RTM. KS
(Clariant, Germany), or EASTOBRITE.RTM. OB-1 (Eastman).
[0027] Besides the optional optical brightener, blue dyes soluble
in polyester may also be added if this is useful. Dyes which have
proven successful are cobalt blue, ultramarine blue and
anthraquinone dyes, in particular Sudan Blue 2 (BASF, Ludwigshafen,
Germany).
[0028] The amounts of the blue dyes used are from 10 to 10,000 ppm,
in particular from 20 to 5000 ppm, particularly preferably from 50
to 1000 ppm, based on the weight of the crystallizable
thermoplastic.
[0029] It was highly surprising that the use of the abovementioned
combination of barium sulfate and optional optical brightener and,
if present, blue dyes in the films in conjunction with the
increased longitudinal stretching ratio during film production gave
the desired result.
[0030] It is also very surprising that the cut material produced
while film production is running can also be reused as regrind for
the production process without any adverse effect on the Yellowness
Index of the film.
[0031] A preferred embodiment of the invention uses precipitated
grades of barium sulfate. Precipitated barium sulfate is obtained
as a fine-particle colorless powder from barium salts and sulfates
or sulfuric acid, and the particle size of the powder can readily
be controlled via the conditions of precipitation. Precipitated
barium sulfate may be prepared by the usual processes, which are
described in Kunststoff-Journal 8, No. 10, 30-36 and No. 11, 36-31
(1974).
[0032] According to the invention, the amount of barium sulfate is
from 0.2 to 40% by weight, preferably from 0.5 to 30% by weight,
particularly preferably from 1 to 25% by weight, based on the
weight of the crystallizable thermoplastic.
[0033] The average grain size of the barium sulfate is relatively
small and is preferably from 0.1 to 5 .mu.m, particularly
preferably from 0.2 to 3 .mu.m (Sedigraph method). The density of
the barium sulfate used is from 4 to 5 g/cm.sup.3.
[0034] In one particularly preferred embodiment, the novel film
comprises, as principal constituent, a crystallizable polyethylene
terephthalate, and also from 1 to 25% by weight of precipitated
barium sulfate, appropriately with a particle diameter of from 0.4
to 1 .mu.m, particularly preferably BLANC FIXE.RTM. XR-HX or BLANC
FIXE.RTM. HXH from Sachtleben Chemie, Germany.
[0035] The surface gloss of the novel film, measured to DIN 67530
(measurement angle 20.degree.) is greater than or equal to 10,
preferably greater than or equal to 15.
[0036] The luminous transmittance (transparency) of the novel film,
measured to ASTM-D 1003, is less than or equal to 30%, preferably
less than or equal to 25%. The coloration is uniform and
streak-free over the entire running length and the entire width of
the film.
[0037] As a result of the synergistic action of the additives
barium sulfate, optional optical brightener, and, if present, blue
dye in conjunction with an optimized longitudinal stretching ratio,
the novel film is whiter, that is to say has less yellow tinge, and
has lower light transmittance, that is to say has lower
transparency than a film provided only with barium sulfate as
pigment.
[0038] The longitudinal modulus of elasticity (ISO 527-1-2) of the
novel film is greater than or equal to 3300 N/mm.sup.2, preferably
greater than or equal to 3500 N/mm.sup.2. Its transverse modulus of
elasticity (ISO 527-1-2) is greater than or equal to 4200
N/mm.sup.2, preferably greater than or equal to 4400
N/mm.sup.2.
[0039] The standard viscosity SV (DCA) of the polyethylene
terephthalate preferably used for the novel film, measured in
dichloroacetic acid to DIN 53728, is from 600 to 1100, preferably
from 700 to 1000.
[0040] The intrinsic viscosity IV (DCA) is calculated from the
standard viscosity SV (DCA) as follows:
IV(DCA)=6.6710.sup.-4SV(DCA)+0.118
[0041] The opaque white polyethylene terephthalate film which
comprises at least barium sulfate, an optional optical brightener
and, if desired, blue dyes may have either one layer or else two or
more layers.
[0042] In the embodiment having two or more layers, the film has a
structure of at least one base layer and at least one outer layer,
and particular preference is given here to a three-layer A-B-A or
A-B-C structure.
[0043] For the embodiment having two or more layers, it is
appropriate for the polyethylene terephthalate of the base layer to
have a standard viscosity similar to that of the polyethylene
terephthalate of the outer layer(s) directly adjacent to the base
layer.
[0044] In one particular embodiment, the outer layers may also be
composed of a polyethylene naphthalate homopolymer or of a
polyethylene terephthalate-polyethylene naphthalate copolymer, or
of a compound. In this particular embodiment, the thermoplastics of
the outer layers likewise have a standard viscosity similar to that
of the polyethylene terephthalate of the base layer.
[0045] In the embodiment having two or more layers, the barium
sulfate, and also the optional optical brightener and, if present,
the blue dye are preferably present in the base layer. However,
modification of the outer layers is also possible, if required.
[0046] Unlike in the single-layer embodiment, in the film having
two or more layers the amounts given for the additives are based on
the weight of the thermoplastics in the layer provided with the
additive(s).
[0047] There may also, if required, be provision of a
scratch-resistant coating on one or more sides of the novel
film.
[0048] In addition, the novel film is easy to recycle without
pollution of the environment and without loss of mechanical
properties, making it suitable, for example, for use as short-lived
promotional placards, labels or other promotional requisites.
[0049] An example of a production process for producing the novel
film is extrusion on an extrusion line.
[0050] According to the invention, the barium sulfate, the optional
optical brightener and, if present, the blue dye may be
incorporated into the thermoplastic as early as when the
thermoplastic polymer is prepared, or else fed into the extruder by
way of masterbatch technology during film production.
[0051] It is particularly preferable for the barium sulfate, the
optional optical brightener and, if present, the blue dye to be
added by way of masterbatch technology. The additives here are
fully dispersed in a solid carrier material. Carrier materials
which may be used are the thermoplastic itself, e.g. the
polyethylene terephthalate, or else other polymers sufficiently
compatible with the thermoplastic.
[0052] It is important that the particle size and the bulk density
of the masterbatch(es) are similar to the particle size and the
bulk density of the thermoplastic, so that uniform dispersion is
achieved, and with this a uniform level of whiteness and thus also
uniform opacity.
[0053] The polyester films may be produced by known processes from
a polyester with, if desired, other polymers, and also with the
optional optical brightener, the barium sulfate, if desired with
the blue dye, and/or with a usual amount of from 0.1 to a maximum
of 10% by weight of other customary additives, either in the form
of monofilms or else in the form of, if desired, coextruded films
having two or more layers and with identical or differently
constructed surfaces, where one surface may have provision of
pigment, but no pigment is present in the other surface. In
addition, known processes can be used to provide one or both
surfaces of the film with an optional functional coating.
[0054] Optionally, at least one of the surfaces of the film is
coated, so that on the finished film a coating of from 5 to 100 nm,
preferably from 20 to 70 nm, in particular from 30 to 50 nm is
present. The coating is preferably applied in-line, i.e. during the
film-production process, appropriately prior to the transverse
stretching. Particular preference is given to application by
reverse gravure-roll coating, which is capable of applying the
coatings extremely uniformly with the layer thicknesses mentioned.
The coatings are preferably applied as solutions, suspensions or
dispersions, particularly preferably as an aqueous solution,
suspension or dispersion. The coatings mentioned give the surface
of the film an additional function, making the film sealable,
printable, metallizable, sterilizable or antistatic, for example,
or improving the flavor barrier, for example, or permitting
adhesion to materials (e.g. photographic emulsions) which would not
adhere to the surface of the film without the coating. Examples of
substances/compositions which give additional functionality
are:
[0055] acrylates, for example as described in WO 94/13476,
ethylvinyl alcohols, PVDC, waterglass (Na.sub.2SiO.sub.4),
hydrophilic polyesters, such as PET/IPA polyesters containing the
sodium salt of 5-sulfoisophthalic acid, as described in EP-A-0 144
878 or U.S. Pat. No. 4,252,885, for example, or in EP-A-0 296 620,
vinyl acetates, as described in WO 94/13481, for example, polyvinyl
acetates, polyurethanes, silanes, the alkali metal or alkaline
earth metal salts of C.sub.10-C.sub.18 fatty acids, butadiene
copolymers with acrylonitrile or methyl methacrylate, methacrylic
acid, acrylic acid or esters thereof.
[0056] The substances/compositions which give the additional
functionality may comprise from 0.05 to 5% by weight, preferably
from 0.1 to 3% by weight, of the customary additives, e.g.
antiblocking agents or pH stabilizers.
[0057] The substances/compositions mentioned are applied as dilute
solution, emulsion or dispersion, preferably as aqueous solution,
emulsion or dispersion, to one or both surfaces of the film, and
the solvent is then evaporated. If the coatings are applied in-line
prior to the transverse stretching, it is usual for the heat
treatment during the transverse stretching and subsequent
heat-setting to suffice for evaporating the solvent and drying the
coating. The dried coatings then have layer thicknesses of from 5
to 100 nm, preferably from 20 to 70 nm, in particular from 30 to 50
nm.
[0058] In the preferred extrusion process for producing the
polyester film, the polyester material melted in the extruder is
extruded through a slot die and quenched on a chill roll, as a
substantially amorphous prefilm. This prefilm is then reheated and
stretched longitudinally and transversely, or transversely and
longitudinally, or longitudinally, transversely and again
longitudinally and/or transversely. According to the invention, the
stretching temperatures are from T.sub.g+10 K to T.sub.g+60 K
(T.sub.g is the glass transition temperature), the longitudinal
stretching ratio according to the invention is from 2 to 5, in
particular from 2.5 to 4.5, and the transverse stretching ratio is
from 2 to 5, in particular from 3 to 4.5, and the ratio for any
second longitudinal stretching carried out is from 1.1 to 3. The
first longitudinal stretching may, if desired, be carried out
simultaneously with the transverse stretching (simultaneous
stretching). Stretching is followed by the heat-setting of the film
at oven temperatures of from 200 to 260.degree. C., in particular
from 220 to 250.degree. C. Following the heat-setting, the film is
cooled and wound up.
[0059] An entirely unexpected finding was that the process
parameters for the longitudinal stretching are a variable which
significantly affects the optical properties (transparency) of the
film. The longitudinal process parameters include in particular the
longitudinal stretching ratio and the longitudinal stretching
temperature. It was highly surprising that the transparency could
be markedly affected by varying the longitudinal stretching ratio.
If, for example, a film plant produces a film whose transparency is
above the values according to the invention, novel films with a
lower transparency can be produced by increasing the longitudinal
stretching ratio during the longitudinal stretching procedure. A
relative increase of 7% in the longitudinal stretching ratio gave a
relative reduction of from 15 to 20% in transparency.
[0060] A major advantage is that the production costs for the novel
film are only insignificantly higher than those for a film made
from standard polyesters. The other processing properties and use
properties of the novel film remain essentially unchanged or indeed
show improvement. In addition, the method of film production
ensures that the regrind can be used again in a proportion of up to
50% by weight, preferably from 10 to 50% by weight, based in each
case on the total weight of the film, without any appreciable
adverse resultant effect on the physical properties of the
film.
[0061] The surprising combination of excellent properties makes the
novel film highly suitable for a variety of different applications,
such as interior decoration, for constructing exhibition stands,
for exhibition requisites, for displays, for placards, for labels,
for protective glazing of machines or of vehicles, in the lighting
sector, in the fitting out of shops or of stores, as a promotional
requisite or a laminating material, in applications associated with
food or drink or, depending on the functionality of one or both
surfaces, as a photographic film, as a graphic film, a laminatable
film, a metallizable film or a printable film.
[0062] The examples below illustrate the invention in more
detail.
[0063] The following standards and methods are used here when
testing individual properties.
Test Methods
Surface Gloss
[0064] Surface gloss is measured with a measurement angle of
20.degree. to DIN 67530.
Luminous Transmittance/Transparency
[0065] For the purposes of the present invention, the luminous
transmittance/transparency is the ratio of total light transmitted
to the amount of incident light.
[0066] Luminous transmittance is measured using "Hazegard plus"
test equipment to ASTM D 1003.
Surface Defects and Uniform Coloration
[0067] Surface defects and uniform coloration are determined
visually.
Mechanical Properties
[0068] The modulus of elasticity, tear strength and elongation at
break are measured longitudinally and transversely to ISO
527-1-2.
SV (DCA) and IV (DCA)
[0069] The standard viscosity SV (DCA) is measured by a method
based on DIN 53726 in dichloroacetic acid.
[0070] The intrinsic viscosity (IV) is calculated as follows from
the standard viscosity (SV) IV(DCA)=6.6710.sup.-4SV(DCA)+0.118
Yellowness Index
[0071] The Yellowness Index YID is the deviation from the colorless
condition in the "yellow" direction and is measured to DIN
6167.
Whiteness
[0072] The whiteness is determined according to Berger, generally
using more than 20 mutually superposed layers of film, and with the
aid of the ELREPHO.RTM. electrical reflectance photometer from
Zeiss, Oberkochem, Germany, with standard aluminant C and a
2.degree. standard observer. The whiteness is defined as
W=RY+3RZ-3RX. W=whiteness, and RY, RZ and RX=corresponding
reflection factors using the Y, Z and X color measurement filter.
The whiteness standard used is a barium sulfate pressing (DIN 5033,
Part 9). A detailed description is found in Hansl Loos
"Farbmessung" [Color measurement], Verlag Beruf and Schule, Itzehoe
(1989), for example.
[0073] In the examples and comparative examples below, each of the
films is a single-layer opaque white film, produced on the
extrusion line described.
EXAMPLE 1
[0074] An opaque white film of 50 .mu.m thickness was produced and
comprised polyethylene terephthalate (RT32, KoSa, Germany) as
principal constituent, 18% by weight of barium sulfate (BLANC
FIX.RTM. XR-HX, Sachtleben Chemie), 200 ppm of optical brightener
(TINOPAL.RTM., Ciba-Geigy, Basle) and 40 ppm of blue dye (SUDAN
BLUE.RTM. 2, BASF, Ludwigshafen). The additives barium sulfate,
optical brightener and blue dye were added as masterbatches.
[0075] The polyethylene terephthalate used to prepare the
masterbatches had a standard viscosity SV (DCA) of from 900 to
1100.
[0076] The masterbatch (1) was composed of clear polymer, 50% by
weight of barium sulfate and 600 ppm of optical brightener. The
masterbatch (2) comprised 2000 ppm of blue dye, besides clear
polymer.
[0077] Prior to extrusion, 36% by weight of the masterbatch (1), 2%
by weight of the masterbatch (2) and 62% by weight of clear polymer
were dried at a temperature of 150.degree. C. and then melted in
the extruder. The melt was extruded through a flat-film die, cooled
by a chill roll and then further processed.
[0078] The longitudinal stretching ratio set during film production
was 3.1. After longitudinal stretching, both sides of the film were
coated with an aqueous dispersion, using reverse gravure-roll
coating. The dispersion comprised, besides water, 4.2% by weight of
hydrophilic polyester (PET/IPA polyester containing the sodium salt
of 5-sulfoisophthalic acid, SP41.RTM., Ticona, USA), 0.15% by
weight of colloidal silicon dioxide (NALCO.RTM. 1060, Deutsche
Nalco Chemie, Germany) as antiblocking agent, and also 0.15% by
weight of ammonium carbonate (Merck, Germany) as pH buffer. The wet
application weight was 2 g/m.sup.2 for each side coated. After
transverse stretching, the calculated thickness of the coating was
40 nm.
EXAMPLE 2
[0079] Example 1 was repeated, except that the film had no blue
dye.
EXAMPLE 3
[0080] The mixing specification of the film of Example 3 and its
coating corresponded to those of the film of Example 2, but the
longitudinal stretching ratio was increased to 3.3, while the
longitudinal stretching temperatures remained unchanged.
EXAMPLE 4
[0081] A coextruded, opaque white ABA film of thickness 75 .mu.m
was produced, where A are the outer layers and B is the base layer.
The mixing specification for the base layer of 71 .mu.m thickness
corresponded to the mixing specification of Example 2. The outer
layers of 2 .mu.m thickness comprised 93% by weight of clear
polymer, and also 7% by weight of a masterbatch which comprised,
besides clear polymer, 10,000 ppm of silicon dioxide
(SYLOBLOC.RTM., Grace, Germany). This film has high surface gloss.
The longitudinal stretching ratio was 3.3. The film was coated in a
manner similar to that of Example 1, but only on one side.
COMPARATIVE EXAMPLE 1
[0082] Example 3 was repeated. The longitudinal stretching ratio
was reduced to 2.8, while the longitudinal stretching temperatures
remained unchanged. The film was not coated after longitudinal
stretching.
COMPARATIVE EXAMPLE 2
[0083] Comparative Example 1 was repeated, but the film was not
provided with optical brightener. The film comprised only 18% by
weight of barium sulfate, and this was incorporated directly during
preparation of the polymer. The standard viscosity of the barium
sulfate-containing polymer was 810. The film was not coated after
longitudinal stretching.
[0084] The opaque white PET films produced in Examples 1 to 4 and
the films produced according to Comparative Examples 1 and 2 had
the property profiles shown in the table below: TABLE-US-00001
TABLE Properties Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. Ex. 1 Comp. Ex. 2
Thickness [.mu.m] 50 50 50 75 50 50 Surface gloss 20 20 20 165 20
20 side 1 (Measurement angle 20.degree.) 20 20 20 165 20 20 side 2
Luminous transmittance/ 20 20 16 12 25 24 transparency [%]
Yellowness Index (YID) 12 14 14 18 15 24 Whiteness by the Berger 93
91 91 90 91 84 Method [%] Longitudinal modulus of 3600 3600 3650
3650 3350 3500 elasticity [N/mm.sup.2] Transverse modulus of 5200
5300 5200 5300 5300 5300 elasticity [N/mm.sup.2] Longitudinal tear
strength 150 155 155 150 150 150 [N/mm.sup.2] Transverse tear
strength 240 240 235 240 250 250 [N/mm.sup.2] Longitudinal
elongation at 175 180 175 170 180 175 break [%] Transverse
elongation at 70 75 75 75 70 80 break [%] Coloration brilliant
brilliant brilliant brilliant brilliant white tinged yellow white
white white white Adhesion with respect to 1 1 1 on one 2 2
printing inks and side 1 photographic emulsions 1 = excellent; 2 =
poor
* * * * *