Polyester film

The present invention is directed to a polyester film comprising at least at its surface portion oriented sulfonic acid groups and/or salts thereof with an orientation degree of 5-100, which has an excellent adhesiveness, especially excellent anti-alkaline adhesiveness. The present invention also makes it possible to provide a polyester film having, in addition to the excellent adhesiveness, an excellent transparency, antistatic property and waterproof property.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates to a polyester film with good adhesion. 
II. Description of Related Art 
Polyester films are widely used as, for example, as wrapping material, base 
film for photosensitive materials, base film for magnetic recording 
materials, printing materials, and so on in a wide variety of fields. In 
these uses, the polyester films are often adhered to other materials such 
as photosensitive materials, magnetic recording materials, inks and other 
films, etc. In these cases it is preferred that the polyester film have 
good adhesion or receptive properties for the material to which the film 
is adhered. 
Conventional techniques for creating good adhesion for a polyester film 
include surface activation methods (e.g., U.S. Pat. Nos. 3,018,189, 
4,072,769 and U.S. Pat. No. 3,364,056) in which the surface of the 
polyester film is activated by corona discharge treatment, ultraviolet 
irradiation treatment, plasma treatment, flame treatment or the like; 
surface etching methods (e.g., U.S. Pat. No. 3,186,883) in which the 
surface of the polyester film is treated with a chemical such as an acid, 
alkali, aqueous amine solution, trichloroacetate or the like; and methods 
(e.g., U.S. Pat. No.4,224,270 and U.S. Pat. No. 3,136,655) in which a 
primer layer made of a polyester, acrylic resin, polyurethane or the like 
is formed on the surface of the polyester film. 
However, most of the above-mentioned conventional methods cannot give the 
polyester film sufficient adhesion. Further, even in cases where the 
polyester film exhibits good adhesion to a material having similar 
chemical structure to the polyester, if the composite film comprising the 
polyester film is immersed in aqueous ammonia solution or in boiling 
water, the material is often peeled off from the polyester film or the 
polyester film often hazes. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a polyester 
film having excellent adhesion, especially alkaliproof adhesion to various 
materials. 
Another object of the present invention is to provide a polyester film 
having, in addition to the excellent adhesion, excellent antistatic 
property and waterproof property. 
The present invention provides a polyester film comprising at least in its 
surface portion oriented sulfonic acid groups and/or salts thereof with an 
orientation degree of 5-100. 
Since the polyester film of the present invention has a good adhesion to 
various materials such as photosensitive materials, magnetic recording 
materials, inks and the like, it can be used as an excellent base film for 
these materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The polyester which is the major component of the polyester film of the 
present invention is a macromolecule having polyester bonds in the 
principal chain, which is obtained by polycondensation of a dicarboxylic 
acid and a diol. Representative examples of the polyester which may be 
employed in the present invention include polyethyleneterephthalate, 
polybutyleneterephthalate, polyethylenenaphthalate, and polyethylene 
.alpha., .beta.-bis(2-chlorophenoxy)ethane-4,4'-dicarboxylate, as well as 
copolymers thereof and those containing ether bonds in the main chain. In 
many cases, the advantageous effects of the present invention is greater 
when the polyester are homopolymer rather than copolymer. Although the 
polyester film of the present invention may preferably be those oriented 
and crystallized by biaxial stretching and heatsetting, uniaxially 
stretched and heatset film may also be used. The polyester film of the 
present invention may contain conventional additives such as stabilizers, 
viscosity-adjusting agents, antioxidants, fillers, lubricants, slip 
agents, antistatic agents, antiblocking agents and so on. The thickness of 
the polyester film is not important and may be, for example, 0.5 to 1000 
.mu.m. 
As mentioned above, the polyester film of the present invention comprises 
oriented sulfonic acid groups and/or salts thereof with prescribed 
orientation degree at least in the surface portion thereof. Thus, the 
polyester film of the present invention may comprise the oriented sulfonic 
acid groups and/or salts thereof in the entire mass of the film. 
Alternatively, the polyester film may be a composite film which comprises 
a polyester-based base film and a surface layer laminated on at least one 
surface of the base film, which surface layer contains sulfonic acid 
groups and/or salts thereof with the prescribed orientation degree. 
The sulfonic groups and/or salts thereof may be provided by incorporating a 
polymer or a copolymer (hereinafter referred to as "polymer (A)") 
containing the sulfonic groups and/or salts thereof in the entire 
polyester film or in the surface layer. The content of the polymer (A) in 
the surface portion of the film may preferably be 3% to 95%, more 
preferably 10% to 60%, still more preferably 15% to 30%. 
Preferred examples of the polymer (A) may include copolymers of 
styrenesulfonic acid represented by the formula [I] with one or more 
comonomers selected from the group consisting of acrylic acid, acrylic 
acid esters, methacrylic acid, methacrylic acid esters and styrene; as 
well as styrenesulfonic acid homopolymer. 
##STR1## 
(wherein X represents a cation) Preferred "X" in the formula [I] includes 
H.sup.+, Na.sup.+, Li.sup.+, NH.sub.4.sup.+ and Ca.sup.+. Among these, 
most preferred are NH.sub.4.sup.+ and H.sup.+. 
Among the above-described preferred polymer (A), especially preferred are 
sulfonated polystyrene and/or salts thereof in view of the waterproof 
property and alkaliproof property. 
The polymer A preferably has a weight average molecular weight of 1000 to 
5,000,000, more preferably 2000 to 1,000,000. In cases where the polymer 
(A) is a copolymer, the copolymerization ratio of the monomer containing 
the sulfonic acid group or a salt thereof may preferably be 40-100 mol% in 
view of the waterproof and alkaliproof adhesion. 
Although the polymer (A) alone may be blended in the entire polyester film 
or may be coated as the surface layer, it is preferred that the polymer 
(A) be blended in the entire film or coated as the surface layer in the 
form of a mixture with another polymer or copolymer (hereinafter referred 
to as "polymer (B)"). Preferred examples of the polymer (B) may include 
water-soluble or water-dispersible polymers and copolymers such as 
polyester resins, acrylic resins, polyamide resins, urethane resins, vinyl 
resins, butadiene resins, epoxy resins, silicone resins and mixtures 
thereof. Among these, in view of the adhesiveness and transparency, 
polyurethanes, polyesters and acrylic resins are especially preferred. It 
should be noted that in cases where the polymer (B) is a polyester and the 
polymers (A) and (B) are coated as the surface layer, the resulting film 
is a composite film having the above-mentioned polyester-based base film 
and a polyester-based surface layer containing the sulfonic acid groups 
and/or salts thereof. 
Preferred examples of the polymer (B) will now be described in more detail. 
Preferred examples of the polyurethanes may include those containing at 
least one of carboxylic acid base, sulfonic acid base and sulfuric acid 
semiester base, especially in the form of ammonium salt. 
Preferred examples of the polyester as the polymer (B) may include 
polyester copolymers in which 0.5-20 mol% of 5-sulfosodium isophthalic 
acid or 1-30 mol% of polyethyleneglycol or ethyleneoxidepropyleneoxide is 
copolymerized. Among these, polyesters containing as the acid component at 
least one of terephthalic acid, isophthalic acid, naphthalenedicarboxylic 
acid, diphenyldicarboxylic acid and as the diol component at least one of 
hexane glycol, 1,4-butanediol, diethyleneglycol, neopentylglycol, 
tetramethyleneglycol and polyethyleneglycol, which polyesters have a 
viscosity of 3-6 cps when diluted with water to a concentration of 5% by 
weight, are especially preferred since they are excellent not only in 
adhesiveness and antistatic property, but also in smoothness and gloss. 
Preferred acrylic resins as the polymer (B) are those containing as the 
major constituent alkylacrylate, alkylmethacrylate or alkylbutyrate 
especially those containing 30-99.9 mol% of alkylacrylate, 
alkylmethacrylate or alkylbutyrate and 70-0.01 mol% of one or more vinyl 
monomers copolymerizable with the alkyl(meth)acrylate and one or more 
functional groups, which are water-soluble or water-dispersible and have 
an average number molecular weight of 200,000 to 1,000,000. 
The content of the alkylacrylate, alkylmethacrylate or the alkylbutyrate in 
the above-mentioned preferred acrylic resins is 30 mol% or more because 
the coating layer is easily applied to the base film and the strength and 
antiblocking property are good. The reason why the content of the 
alkylacrylate, alkylmethacrylate or the alkylbutyrate in the 
above-mentioned preferred acrylic resins is 99.9 mol% or less is that 
incorporating a monomer with a functional group as a copolymerization 
component makes it possible to promote water-solubility or 
water-dispersibility of the resin and to stabilize the aqueous solution or 
dispersion for a long time, as well as to promote the adhesion between the 
polyester base film and the surface layer, to promote the strength, 
waterproof property and chemical resistance of the surface layer by the 
reaction in the surface layer, and to promote the adhesion between the 
film of the present invention and other materials. 
Preferred examples of the alkyl groups of the alkylacrylate, 
alkylmethacrylate or alkylbutyrate may include methyl group, ethyl group, 
n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl 
group, 2-ethylhexyl group, lauryl group, stearyl group and cyclohexyl 
group. 
Preferred functional groups contained in the vinyl monomer are those which 
improve hydrophilicity of the resin to promote the water-solubility or 
water-dispersibility of the resin, and those which improves the adhesion 
of the resin to the base film or to the other materials. Examples of the 
preferred functional groups may include carboxylic group and salts 
thereof, acid anhydride groups, sulfonic acid group and salts thereof, 
amide group and alkylolamide group, amino group (including substituted 
amino group) and alkylol amino group, and salts thereof, hydroxide group 
and epoxy groups. Among these, especially preferred are carboxylic group 
and salts thereof, acid anhydride groups and epoxy groups in view of the 
adhesiveness, water-solubility and water-dispersibility. Two or more of 
these functional groups may be contained in the resin. 
Preferred examples of the vinyl monomer containing carboxylic acid or a 
salt thereof, or acid anhydride may include acrylic acid, methacrylic 
acid, itaconic acid, maleic acid, fumaric acid and crotonic acid, as well 
as metal salts such as sodium salt thereof, ammonium salt thereof, and 
maleic anhydride. 
Preferred examples of the vinyl monomer containing sulfonic acid group or a 
salt thereof may include vinyl sulfonic acid, metal salts such as sodium 
salt thereof and ammonium salt thereof. 
Preferred examples of the vinyl monomer containing amide group or 
alkylolamide group may include acrylamide, methacrylamide, 
N-methylmethacrylamide, methylolacrylamide, methylolmethacrylamide, 
ureidovinyl ether, .beta.-ureidoisobutylvinyl ether and 
ureidoethylacrylate. 
Preferred examples of the amino group and alkylolamino group may include 
diethylaminoethylvinyl ether, 2-aminoethylvinyl ether, 3-aminopropylvinyl 
ether, 2-aminobutylvinyl ether, dimethylaminoethylmethacrylate and 
dimethylaminoethylvinyl ether, as well as derivatives thereof which has 
methylolamino group instead of amino group or of which amino group is 
converted to a quaternary salt by halogenated alkyl, dimethyl sulfate, 
sultone or the like. 
Preferred examples of the vinyl monomer containing hydroxide group may 
include .beta.-hydroxyethylacrylate, .beta.-hydroxyethylacrylate, 
.beta.-hydroxyethylmethacrylate, .beta.-hydroxyvinyl ether, 
5-hydroxypentylvinyl ether, 6-hydroxyhexylvinyl ether, 
polyethyleneglycolmonoacrylate, polyethyleneglycolmonomethacrylate, 
polypropyleneglycolmonoacrylate and polypropylelneglycolmonomethacrylate. 
Preferred examples of the vinyl monomer containing an epoxy group may 
include glycidylacrylate and glycidylmethacrylate. 
As the polymer (B), the following compounds, for example, may also be used: 
acrylonitrile, methacrylonitrile, styrenes, butylvinyl ether, mono- and 
di-alkyl maleate, mono- and di-alkyl fumarate, mono- and di-alkyl 
itaconate, methylvinyl ketone, vinyl chloride, vinylidene chloride, vinyl 
acetate, vinylpyridine, vinylpyrrolidone and vinyltrimethoxysilane. 
Although the acrylic resin used as the polymer (B) may contain a 
surfactant, low molecular weight surfactant contained in the acrylic resin 
may be coagulated in the film-forming process and may be accumulated at 
the interfaces among the particles or may be transferred to the interface 
of the surface layer to deteriorate the mechanical strength, waterproof 
property and adhesion between the surface layer and the base film. In such 
a case, acrylic resins which do not contain a surfactant obtained by so 
called soap-free polymerization may preferably be used. 
Among these acrylic resins, especially preferred are the water-dispersible 
acrylic resins containing as the principal chain a copolymer of methyl, 
ethyl or butylmethacrylate-methyl, ethyl or butylacrylate copolymer with a 
copolymerization ratio of 35/65-65/35 (molar ratio) and further contain 
-COOH and -CH.sub.2 OH in the amount of 1-5% by weight, respectively. 
The mixing ratio of the polymer (A) to the polymer (B) may preferably be 
10-95% by weight, more preferably 15-30% by weight in view of obtaining 
adhesion, waterproof property, alkaliproof property, strength and 
antistatic property. 
To improve the blocking propensity, heat resistance, solvent resistance and 
mechanical strength of the surface layer, reactive compounds such as 
methylolurea resins, alkylolurea resins, melamine resins, acrylamide 
resins, polyamide resins, as well as epoxy compounds, aziridine compounds, 
block polyisocyanate and vinyl compounds may be incorporated in the 
surface layer as a cross-linking agent. Further, the surface layer may 
contain, if desired, defoaming agents, coating property improvers, 
viscosity-increasing agents, organic lubricants, antioxidants, ultraviolet 
absorbers, foaming agents, dyes, pigments and the like. Further, the 
surface layer may contain inorganic particles with a particle size of, for 
example, 1 .mu.m or less, preferably 0.5 .mu.m or less, more preferably 
0.2 .mu.m or less. Preferred examples of the materials constituting the 
particles include kaolin, silica, silica sol, calcium carbonate, titanium 
oxide, barium salt, alumina, molybdenum sulfide, carbon black and 
zirconium compounds. 
Incorporation of laminated silicate which exhibits swelling in the surface 
layer is also preferred in view of obtaining good adhesion and high 
strength of the surface layer. Examples of such laminated silicate may 
include montmorilonite, vermiculite, hectorite, taeniolite and 
tetrasilicic mica. 
Although the thickness of the surface layer is not restricted, it is 
usually 0.001-5 .mu.m, preferably 0.01-0.4 .mu.m, more preferably 0.04-0.2 
.mu.m in view of the good adhesion and antistatic property. 
The sulfonic acid groups and/or salts thereof must be aligned so as to have 
an orientation degree of 5-100 , preferably 20-80. By the alignment of the 
sulfonic acid groups and/or salts thereof, the adhesion to various 
materials, particularly diazo coatings, UV inks, gelatin compositions are 
largely improved, and the adhesion becomes resistant to water treatment 
and alkali treatment. More particularly, if the orientation degree is less 
than 5, the adhesion is largely weakened by processing such as alkali 
treatment, so that the film cannot have practically acceptable adhesion. 
On the other hand, if the orientation degree is more than 100, small 
cracks, projections and recesses may be formed in the surface portion to 
deteriorate the transparency and antistatic property. In addition, the 
adhesion is sharply weakened by boiling treatment or alkali treatment, so 
that it cannot be used in practice. Thus, unless the orientation degree of 
the sulfonic acid groups and/or salts thereof is in the range of 5-100, 
good adhesion which is waterproof and alkaliproof cannot be obtained. 
The specific alignment of the sulfonic acid groups and/or salts thereof 
cannot be attained by merely coating a mixture of the polymer (A) and 
polymer (B) on the base film or by merely blending a mixture of the 
polymer (A) and polymer (B) in the polyester film. Therefore, even if a 
mixture of 0.5-15 parts by weight of an electroconductive macromolecular 
electrolyte containing sulfonic acid salt and 100 parts by weight of 
acrylic copolymer is used as a plastic coating as disclosed in Japanese 
patent disclosure (Kokai) Nos. 86526/79 and 93025/79, although the 
antistatic property and heatsealability may be promoted, adhesion cannot 
be improved. 
The specific alignment of the sulfonic acid groups and/or salts thereof can 
only be attained by stretching the film under specific conditions 
hereinafter described in detail. The alignment of the sulfonic acid groups 
and/or salts thereof is such that not only the principal chains of the 
polymer to which the sulfonic acid groups and/or salts are attached are 
aligned in parallel to the surface plane of the base film, but also the 
sulfonic acid groups and/or salts thereof are aligned in parallel to the 
surface plane of the base film because of the strong polarity thereof. 
Unless the stretching is conducted under specific conditions, the sulfonic 
acid groups and/or salts thereof do not align not only in the plane, but 
also in the direction of thickness of the film (i.e., the sulfonic acid 
groups and/or salts thereof do not align in the direction of thickness of 
the film, i.e., perpendicularly to the film surface. 
For attaining the specific alignment of the sulfonic acid groups and/or 
salts thereof, in cases where the surface layer containing the sulfonic 
acid groups and/or salts thereof is formed on the base film, a coating 
solution containing the polymer (A) (and preferably polymer (B)) is 
applied on the base film and then the base film is stretched at least in 
one direction. In cases where a biaxially stretched film is to be 
produced, it is preferred that the coating solution be applied on the base 
film after stretching the film in one direction and before stretching the 
film in another direction. At the time of stretching the film after 
coating the solution, it is preferred that the coated solution do not 
contain water. That is, the coated solution is preferably dried completely 
before the stretching. To accomplish this, it is effective to prolong the 
preheating time, to raise the stretching temperature and to increase the 
stretching velocity in the range of not causing film breakage or necking 
stretching. Specifically, the concentration of the polymer(s) in the 
coating solution may preferably be 3-20% by weight, more preferably 5-10% 
by weight, and the stretching temperature may preferably be 
98.degree.-180.degree. C., more preferably 110.degree.-150.degree. C. The 
stretching velocity should be selected depending on the stretching 
temperature and may be, for example, 10,000%/min. to 400,000%/min. 
To attain the specific alignment of the sulfonic acid groups and/or salts 
thereof, it is important that water exist in the atomosphere in which the 
stretching of the film is conducted. This can be attained by conducting 
the stretching in pressurized water or in the presence of pressurized 
steam. The relative humidity at the surface of the film to be stretched 
should be not less than 10%, preferably not less than 25%. Thus, the fact 
that the coated solution does not contain water (i.e., dried) but water is 
supplied only to the surface portion of the coated layer (or only to the 
surface portion of the polyester film in cases where the polymer (A) is 
blended in the entire polyester film) from the atomosphere makes it 
possible to strongly align the sulfonic acid groups and/or salts thereof 
to attain the orientation degree defined in the present invention. 
A typical manufacturing process of the polyester film of the present 
invention which has a base film and the surface layer will now be 
described in more concretely. It should be noted, however, the 
manufacturing process is not restricted to the method. 
Well dried pellets of polyester are supplied to a conventional extruder 
which preferably has a compression ratio of not less than 3.8. The pellets 
are then melted in the extruder at a temperature lower than the 
decomposition temperature of the polyester and the molten polyester is 
extruded through a slit-shaped die to form a sheet. The sheet is cooled 
and solidified to obtain a non-stretched sheet. The non-stretched sheet is 
then stretched in the longitudinal direction at 80.degree.-80.degree. C. 
with a draw ratio of 3-8 times the original length. Then the coating 
composition containing at least the polymer (A) is then applied to the 
film. The film is then subjected to a preheating step to dry the coated 
solution and the resulting film is then stretched in the transverse 
direction at a draw ratio of 3-6 times the original length while 
humidifying the film by pressurized steam with a temperature of 
98.degree.-180.degree. C. If desired, the resulting film may be heatset at 
150.degree.-250.degree. C. for 0.1-10 seconds while relaxing by 0-10 % in 
the transverse direction Further, if desired, the resulting film may be 
stretched again in the longitudinal direction at a draw ratio of 1.1-1.7 
times the original length. 
In the manufacturing process just mentioned above, the coating composition 
may be applied by any of the conventional methods including gravure 
coating, reverse coating, spray coating, kiss coating, die coating and 
metering rod coating. It should be noted, however, the surface layer 
containing the polymer (A) may also be formed by employing extrusion 
lamination method and melt coating method, although application of the 
coating composition is a better method for forming a thin surface layer. 
Although not required, to further promote the coating property of the 
surface layer and the adhesion between the base film and the surface 
layer, the base film may be subjected to a chemical treatment, anchor 
treatment using a conventional anchor-coating agent such as urethane resin 
and epoxy resin or to discharging treatment such as corona discharging 
treatment, as conventional. 
The polyester film of the present invention which contains sulfonic acid 
groups and/or salts thereof in the entire film may also be produced in the 
same manner as described above except that the polymer (A) is blended in 
the starting material instead of applying the coating composition. 
In cases where the polyester film of the present invention is a composite 
film comprising the polyester-based base film and the surface layer 
containing the sulfonic acid groups and/or salts thereof, the base film 
may also contain a polymer or a copolymer having sulfonic acid groups 
and/or salts thereof. In this case, the adhesion between the base film and 
the surface layer may be further improved. The content of the polymer or 
the copolymer having sulfonic acid groups and/or salts thereof may 
preferably be 5 ppm to 20% by weight. 
Preferred polymers or copolymers to be blended in the base film are those 
containing as the monomer unit a metal salt such as Li, Na, Mg, Zn and Mn 
salt of sulfoisophthalic acid unit, sulfoterephthalic acid unit, 
sulfonaphthalene dicarboxylic acid unit and ester-forming derivatives 
thereof. Among these, polyester compounds comprising as the acid component 
terephthalic acid, isophthalic acid or the like containing 5-sodium 
sulfoisophthalic acid and 5-sodium sulfodimethylisophthalic and comprising 
as the diol component ethyleneglycol, butanediol, polyethyleneglycol, 
polytetramethyleneglycol or the like are especially preferred. The content 
of the polyester compounds may preferably be 1-20% by weight in view of 
the heat stability and adhesion. 
The base film containing the sulfonic acid groups and/or salts thereof may 
be one containing the above-described coating composition. In this case, 
the amount of the coating composition added may preferably be 5 ppm to 2% 
by weight in view of obtaining good adhesion and surface smoothness. 
The polyester film of the present invention may suitably be used as, for 
example, wrapping materials such as those for IC, photosensitive materials 
such as microfilms, magnetic recording base, various plates for printing, 
tracing films, films for electronphotograph, films for overhead projector, 
base films for offset printing inks, ultraviolet-set inks and for 
cellophane inks. 
The method of measuring the characteristics and criteria for evaluation 
thereof will now be described in summary. 
(1) Adhesiveness 
The coating material (a), (b) or (c) described later was coated on a sample 
film and a plurality of cross-shaped cuts were formed (100 cuts/cm.sup.2) 
in the resulting coating such that the crosses align in the same 
direction. To the cross-cut surface, a cellophane tape (Cello-Tape CT-24, 
manufactured by Nichiban Co., Ltd.) was sticked such that the direction of 
the tape forms an angle of 45.degree. to the cuts. The tape was pressed 
with a hand roller with a force of about 5 kg, which hand roller was moved 
back and forth 10 times, to pressure-stick the cellophane tape. The tape 
was then peeled off by hand and the peeling of the coating was observed 
and evaluated. The criteria of evaluation were as follows: 
Mark .circle.O Good (Peeled area was less than 5%) 
Mark .DELTA.: Somewhat Inferior (Peeled area was not less than 5% and less 
than 20%) 
Mark .times.: Bad (Peeled area was not less than 20%) 
Coating (a): 
Ultraviolet-set type ink (UV ink) "FDO (black)" (manufactured by Toyo Ink 
Co., Ltd.) was coated with a gravure roll coater to a thickness of about 5 
.mu.m and the coated ink was treated with an UV lamp having a irradiation 
power of 80W/cm with an irradiation distance of 10 cm for 8 seconds. 
Coating (b): 
Polyvinyl alcohol with a degree of polymerization of 1500 and a degree of 
saponification of 90 mol% was dissolved in water and the resulting 
solution was coated on the film so as to form a coating with a dry 
thickness of about 5 .mu.m. After the coating, the coated solution was 
dried at 130.degree. C. for 2 minutes. 
Coating (c): 
Commercially available cellulose ("CBA381-05", manufactured by Nagase 
Sangyo Co., Ltd.) for diazo binders was dissolved in ethyl acetate to a 
concentration of 10% by weight and the resulting solution was coated with 
a bar coater. The resulting coating was then dried at 110.degree. C. for 
1.5 minutes to form a coating layer with a thickness of 5.0 .mu.m. 
(2) Transparency 
The haze measured using "SEP-H-2" type turbidimeter (manufactured by Nippon 
Seimitsu Kogaku Co., Ltd.) in accordance with the method defined in 
JIS-K-6714-58. 
(3) Antistatic Property 
Specific surface resistivity was measured under an applied voltage of 100 V 
at 20.degree. C., 60% RH by the use of ultra insulation resistance tester 
MODEL-VE-40 (manufactured by Kawaguchi Denki Kogyo Co., Ltd.). 
(4) Waterproof Property 
The sample film was immersed in warm water at 50.degree. C. for 30 minutes 
and then a plurality of cross-shaped cuts were formed (100 cuts/cm.sup.2) 
in the coating layer. Peeling of the coating layer was observed and 
measured in the same manner as in (1). In cases where abnormity 
(cloudiness) was found in the surface, even if the evaluation for 
adhesiveness by the peeling test was good ( .circle.O , the sample was 
evaluated bad (X). 
(5) Alkaliproof Property 
A film having the above-mentioned coating (c) was immersed in an aqueous 
ammonia solution with a concentration of 30% by weight for 20 hours and 
the peeling of the coating was observed and evaluated as in (1). 
(6) Solvent Resistance 
The coating was rubbed 5 times (back and forth) with an applicator in which 
an organic solvent, i.e., ethyl acetate, toluene, methylethyl ketone, 
acetone or isopropanol, was impregnated. The change of the state of the 
rubbed surface was observed by gross examination or by using a magnifier 
or a differential interference microscope. The change was compared to a 
non-treated control. The criteria for evaluation were as follows: 
Mark .circleincircle.O : did not change at all 
Mark .circle.O : slightly dissolved 
Mark .DELTA.: considerably dissolved but the coating layer remained 
Mark .times.: dissolved and removed almost completely 
(7) Concentration of Sulfonic Acid Grpoups and/or Salts Thereof 
The concentration of the sulfonic acid and/or salt thereof was expressed in 
terms of the ratio of the relative intensities of C.sub.1S to S.sub.2p in 
the uppermost surface of 10 nm thickness, which intensities were measured 
in the following conditions using an X-ray photoelectron spectrophotometer 
"ESCA750" (manufactured by Shimazu Corporation): 
Excitation X-ray: MgK.alpha..sub.1,2 Ray (1253.6 eV) 
X-ray Power: 8 kV, 30 mA 
Temperature: 20.degree. C. 
Degree of Vacuum: 10.sup.-5 Pa 
(8) Degree of Orientation of Sulfonic Acid Groups and/or Salts Thereof 
The orientation degree of the sulfonic acid groups and/or salt thereof is 
expressed in terms of the value obtained by multiplying the difference 
spectrum of the absorbance by 1000, which difference spectrum was measured 
in the longitudinal and transverse directions in the film plane in 
accordance with FT-IR-ATR method. More particularly, a Ge plate with an 
internal reflection number of 25 employed as a high index of refraction 
medium was set in a Wilks' ATR apparatus, and the difference spectrum was 
measured by the FT-IR-ATR method such that the difference of the 
absorbance of the longitudinal and transverse directions at 1450cm.sup.-1 
was set to 0. The film sample was a rectangule measuring 20 mm .times.45 
mm and was sticked with pressure to the Ge plate, and the spectrum was 
measured using a polarized light perpendicular to the incident plane. The 
base line was obtained by drawing a straight line between the absorbances 
at 1450 cm.sup.-1 and 1000 cm.sup.-1. As the absorbance of the 
orientation, the band of 1155 cm.sup.-1 was used. The equipment and 
conditions employed in the FT-IR-ATR measurement were as follows: 
Apparatus: IFS-85 (FT-IR manufactured by Bruker) 
Light Source: Clover (SiC) 
Detector: Deutrium Triglycine Sulfate (DTGS) 
Beam Splitter: Ge coat/KBr 
Measuring Conditions 
Resolving Power: 4 cm.sup.-1 
Number of Integration: 1024 
Apodization: Triangle 
Phase Compensation: Mertz method 
Zero Filling: 2 
Accessories: 
Accessories for ATR Measurement (Model-9, manufactured by Wilks) 
IRE Ge (52.5 .times.20 .times.2 mm) 
Polarizer Wire Grid Type (manufactured by Specac) 
EXAMPLES 
The present invention will now be described by way of examples. The 
examples are presented for the illustration purpose only and should not be 
interpreted in any restrictive way. 
EXAMPLE 1 
Polyethyleneterephthalate with an intrinsic viscosity of 0.62 was 
melt-extruded at about 280.degree. C., and then cooled on a quenching drum 
with a temperature of about 35.degree. C. to obtain an amorphous sheet. 
During this process, an electrostatic charge was deposited on the surface 
of the sheet. The sheet was stretched in the longitudinal direction at a 
draw ratio of 3.5 times the original length at about 90.degree. C. Then 
the coating composition containing the following (A) and (B) was applied: 
Sulfonated Polystyrene and/or Salt Thereof (A): Sulfonated polystyrene 
with a molecular weight of about 70,000 which has H.sup.30 as the X.sup.+ 
ion of SO.sub.2 O.sup.- X.sup.+. Acrylic Polymer (B): Acrylic polymer 
(average molecular weight of 500,000) based on 
methylmethacrylate/ethylacrylate (50/50 mol%) in which carboxylic group 
and methylol group are introduced in the amount of 2.5% by weight, 
respectively. 
The mixture of (B)/(A) with a weight ratio of 20/80 was diluted with water 
to a concentration of 6% by weight, and 0.3% by weight, with respect to 
the solid content, of colloidal silica with an average particle size of 
0.12 .mu.m was added thereto to obtain a coating composition. 
The coating was applied to the film using a gravure roll coater to a 
thickness after biaxial stretching of 0.07 .mu.m, and the film was 
preheated at 110 to sufficiently eliminate water. Then the atmosphere was 
heated to 145.degree. C. and moistured by raw steam, and the film was 
stretched in the transverse direction in a tenter at a draw ratio of 4.5 
times the original length. Then the film was heatset at 210.degree. C. to 
obtain a film comprising a base film of 50 .mu.m thickness and a coating 
of 0.07 .mu.m thickness. 
The characteristics of the thus prepared film are shown in Table 1. 
TABLE 1 
______________________________________ 
ITEM RESULTS 
______________________________________ 
Orientation Degree Sulfonic Acid Groups 
25 
Solvent Resistance .circleincircle. 
Adhesiveness 
UV Ink .circle. 
PVA .circle. 
CAB 
Non-treated .circle. 
Waterproof Testing Treatment 
.circle. 
Alkaliproof Testing Treatment 
.circle. 
Specific Surface Resistivity (.OMEGA./.quadrature.) 
10.sup.9 
Haze (%) 1.5 
______________________________________ 
COMATIVE EXAMPLE 1 
The same procedure as in Example 1 was repeated except that the conditions 
of preheating and stretching in the transverse direction were changed as 
shown in Table 2 such that stretching in the transverse direction was 
conducted before the coated composition is completely dried. 
As can be seen from Table 2, unless the sulfonic acid is appropriately 
aligned in the surface layer, the adhesiveness, especially the 
adhesiveness after alkali treatment is degraded, so that cannot be 
practically used. 
TABLE 2 
______________________________________ 
Comp. 
Ex. 1 Ex. 1 
______________________________________ 
Conditions of Stretching in 
Transverse Direction 
Preheating Temp. (.degree.C.) 
110 80 
Stretching Temp. (.degree.C.) 
145 105 
Relative Humidity of 30 0 
Environment of 
Stretching 
Method of Moisturing Steaming None 
Orientation of Sulfonic Acid Groups 
Exists Exists 
Orientation Degree of Sulfonic Acid Groups 
25 120 
Adhesiveness with CAB 
Non-treated .circle. .circle. 
Waterproof Testing Treatment 
.circle. X 
Alkaliproof Testing Treatment 
.circle. X 
Specific Surface Resistivity (.OMEGA./.quadrature.) 
10.sup.9 10.sup.13 
Haze (%) 1.5 4.0 
______________________________________ 
COMATIVE EXAMPLE 2 
The coating employed in Example 1 was applied to a commercially available 
biaxially stretched polyester film and dried to obtain a polyester film 
with a coating layer of 0.07 .mu.m thickness. 
The coated surface of the thus obtained film was evaluated as in Example 1 
and the results are shown in Table 3. As is apparent from Table 3, no 
excellent effect such as improved adhesion was brought about. 
TABLE 3 
______________________________________ 
ITEM RESULTS 
______________________________________ 
Orientation Degree of Sulfonic Acid Groups 
0 
Adhesiveness 
UV Ink .DELTA. 
PVA X 
CAB 
Non-treated .DELTA. 
Waterproof Testing Treatment 
X 
Alkaliproof Testing Treatment 
X 
Specific Surface Resistivity (.OMEGA./.quadrature.) 
10.sup.11 
Haze (%) 1.8 
______________________________________ 
EXAMPLE 2 
The same procedure as in Example 1 was repeated except that a polyester 
consisting of 85 mol% of terephthalic acid and 15 mol% of 5-sodium 
sulfoisophthalic acid as the acid components and ethyleneglycol as the 
diol component was used in place of polyethyleneterephthalate to obtain a 
film with a thickness of 50 .mu.m. The adhesiveness of the thus obtained 
film was evaluated. The results are shown in Table 4. 
As can be seen from Table 4, the adhesiveness and transparency are even 
further improved if the base film contains sulfonic acid salt. 
TABLE 4 
______________________________________ 
ITEM RESULTS 
______________________________________ 
Orientation Degree of Sulfonic Acid Groups 
35 
Solvent Resistance .circleincircle. 
Adhesiveness 
UV Ink .circleincircle. 
PVA .circle. 
CBA 
Waterproof Testing Treatment 
.circleincircle. 
Alkaliproof Testing Treatment 
.circle. 
Haze (%) 0.8 
______________________________________