Process for producing easily adherable polyester film

A process for producing an easily adherable biaxially stretched polyester film, which comprises coating a primer composition consisting of (A) and aqueous dispersion of polyurethane and (B) a montan wax salt and optionally a nonionic or anionic surface-active agent on the surface of a polyester film which has not yet been stretched completely, drying the coating, completing the stretching of the coated film, and then heat-setting it thereby to form a primer coated layer on the film surface.

This invention relates to an easily adherable polyester film. More 
specifically, this invention relates to an easily adherable polyester film 
which is free from various troubles during coating or unwinding and also 
from blocking during storage. 
It is known to form a film by melt-extruding a polyester prepared by 
polymerizing an aromatic dibasic acid or its ester-forming derivative and 
a diol or its ester-forming derivative, such as polyethylene terephthalate 
or its copolymers, a polyalkylene naphthalate, or a blend of this polymer 
with a minor proportion of another resin. A biaxially oriented heat-set 
polyester film is superior to films of other resins in heat resistance, 
gas-barrier property, electrical properties and chemical resistance, but 
has the defect that its surface has poor receptivity to paints, adhesives 
and inks because the surface is highly crystallized and oriented and has 
high cohesiveness. 
Accordingly, in providing a synthetic resin layer on the surface of a 
polyester film, it is common practice to activate its surface in advance 
by corona discharge treatment, ultraviolet irradiating treatment, plasma 
treatment or flame treatment. [Journal of the Adhesion Society of Japan, 
Vol. 15, No. 12, pages 581-588 (1979)]. These surface activating means, 
however, are not entirely satisfactory because the adhesion strength 
obtained thereby is not on a satisfactory level, and the activity obtained 
decreases with time. 
In order to increase receptivity of the surface of a polyester film 
substrate, an etching method was proposed in which the surface is swollen 
or partially dissolved with various chemicals. The gist of this method is 
that the surface of the film is etched with a chemical such as an acid, an 
alkali, an aqueous solution of an amine, trichloroacetic acid or a phenol 
to break down, dissolve or relax the crystalline orientation of the film 
near the surface and simultaneously decrease the cohesiveness of the 
surface, whereby the adhesion of the polyester film to binder resins is 
increased. This effect is most certain, and the adhesion between the 
substrate and a synthetic resin coated layer on it becomes firm. Since 
some of the chemicals used in this method are dangerous in handling or are 
likely to release hazardous vapors into the atmosphere, they should be 
carefully handled so as to avoid pollution of the working environment. 
Furthermore, the apparatus may undergo corrosion during coating and 
impregnation of these chemicals. Another disadvantage is that the treating 
chemicals remain in the treated substrate film, and exude with the lapse 
of time to adversely affect the upper coated layer. 
As a means similar to this method, there was proposed a process which 
comprises forming on the surface of a substrate a primer coated layer 
different in kind from the substrate, and then coating the desired 
synthetic resin layer on it (Japanese Patent Publication No. 26580/1979) 
The formation of the primer coated layer is carried out in a separate step 
from the film-forming process, and the film is likely to gather dirt, 
dust, foreign matter, etc. during the treating step. Meticulously 
processed films which must maintain a high level of quality, such as audio 
and video magnetic tapes, magnetic tapes for computers, radiographic 
films, photographic films for printing, and diazo microfilms, will be 
useless if they gather such dirt and dust during the step of providing a 
good adhesive surface. In any case, it is disadvantageous both 
economically and technologically to provide a step of primer coating in 
the process of finishing a base film into the desired product. 
It is desired therefore to perform in-line primer coating in the process of 
forming a polyester film which is carried out in an atmosphere 
substantially free from dust and dirt. In the prior art, the primer 
treatment for providing an easily adherable surface layer on a polyester 
film is carried out in many cases by coating the surface of the film with 
a composition dissolved in an organic solvent. When this technique is 
performed during the film formation, the organic solvent which dissipates 
may pollute the environment and bring about a situation which is 
undesirable both in regard to safety and santitation. This also adversely 
affects the film-forming process. The use of organic solvents, therefore, 
should be minimized, and in the in-line primer coating treatment in the 
film-forming process, the use of a composition dissolved in water as a 
solvent is preferred economically and in view of the process steps and 
safety. 
Many primer compositions containing water as a solvent have been known. In 
the in-line primer coating treatment, however, they are very effective 
only for limited top coating compositions, and no primer composition has 
been developed which imparts surface receptivity satisfactory with respect 
to a wide range of top coating compositions. 
When the in-line primer coating treatment is carried out in the 
film-forming process using resin emulsions or primers of the 
ethyleneimine-type, amine-type or epoxy-type which have been well known 
heretofore, the formation of a primer film is insufficient. Consequently, 
blocking occurs to reduce handlability, and many troubles in the 
properties and appearance of the film, such as stretching unevenness, 
coloration or discoloration are caused. 
In view of the fact that the function of polyester films is considered as 
important in the field of high-grade and high-performance products, it is 
very significant to modity the surface of a polyester film to make it 
convenient for use in the production of film products without impairing 
its excellent properties, such as mechanical strength, thermal stability, 
transparency and chemical resistance. 
Previously, the present inventors found that a polyester film having a 
fairly satisfactory easily-adherable surface can be obtained by coating a 
specified aqueous dispersion of polyurethane and a nonionic or anionic 
surface-active agent on a polyester film before it has been crystallized 
and oriented, and thereafter stretching the coated film (Japanese 
Laid-Open Patent Publication No. 15825/1980). The polyester film treated 
by the method of Japanese Laid-Open Patent Publication No. 15825/1980 has 
fairly satisfactory adhesion to cellophane ink, magnetic coating agents, 
gelatin compositions, offset inks, electrophotographic toner compositions, 
chemical mat paints, diazo paints, heat-sealability imparting 
compositions, inorganic film-forming substances, and metal evaporant 
materials. During the process of forming the aforesaid easily adherable 
coated polyester film, the primer coated layer should be heat-treated at a 
temperature of at least 180.degree. C. for at least 4 seconds, and heating 
under milder conditions does not sufficiently induce formation of the 
primer coated layer, and the polyester film may sometimes have 
insufficient adhesion to the primer coated layer. 
Furthermore, since the surface of the easily adherable film obtained by the 
process of Japanese Laid-Open Patent Publication No. 15825/1980 has high 
chemical activity, when it is wound up in roll form and stored, the film 
surface and the treated surface adhere to each other by the influences of 
temperature, humidity, pressure, etc. and at the time of unwinding, 
various troubles are caused by static charge buildup. Static buildup at 
the time of unwinding not only gives a shock to the human body as a result 
of discharging, but also generates coating unevenness during the coating 
step and may cause exposition and fire by spark discharge. When the 
surface of the film is very adhesive, the film adheres to itself to cause 
a so-called blocking phenomenon. This not only reduces handlability, but 
also breaks the film. 
It is a primary object of this invention therefore to provide an easily 
adherable polyethylene terephthalate film free from the aforesaid defects. 
The present inventors, in order to achieve the above object, extensively 
investigated from various angles into a method which can provide an easily 
adherable surface and a sufficient adhesion strength between a polyester 
film and a primer layer and inhibit the adhesion of the film surface to 
the treated surface, under all conditions in the process of producing a 
biaxially oriented polyester film. These investigations have led to the 
present invention. 
According to this invention, there is provided a process for producing an 
easily adherable biaxially stretched polyester film, which comprises 
coating a primer composition consisting of (A) an aqueous dispersion of 
polyurethane and (B) a montan wax salt and optionally a nonionic or 
anionic surface-active agent on the surface of a polyester film which has 
not yet been stretched completely, drying the coating, completing the 
stretching of the coated film, and then heat-setting it thereby to form a 
primer coated layer on the film surface. 
The polyester, as referred to in this invention, is a linear saturated 
polyester prepared from an aromatic dibasic acid or its ester-forming 
derivative and a diol or its ester-forming derivative. Examples of the 
polyester are polymers such as polyethylene terephthalate, polyethylene 
isophthalate, polybutylene terephthalate and 
polyethylene-2,6-naphtahalate, copolymers composed of the monomers 
constituting these polymers and blends of these polymers or copolymers 
with a minor proportion of other resins. The polyester film, as referred 
to in this invention, is obtained by melt-extruding the linear saturated 
polyester resin, formed into a film form in a customary manner, and then 
crystallized by orientation and heat-treatment. This polyester film is 
crystallized and oriented to such a degree that its crystal melting heat 
measured in a nitrogen stream by a scanning calorimeter at a temperature 
raising rate of 10.degree. C./min. is usually at least 4 cal/g. 
The polyester film which exists before the completion of crystallization 
and orientation in this invention includes an unstretched cast film 
obtained by melting the polymer and forming it into a film; a monoaxially 
stretched film obtained by orienting the unstretched film either 
longitudnally or transversely; and an incompletely biaxially oriented film 
which has been stretched longitudinally and/or transversely only at low 
stretch ratios and has not yet been finally stretched logitudinally and 
transversely. If the primer coating treatment is applied to a film which 
has been biaxially stretched and heat-set to complete crystallization and 
orientation, the adhesion between the primer coated layer and the base 
film does not become sufficient. 
Before the orientation and crystallization of the film structure are 
completed, the aqueous dispersion of polyurethane (A) is coated on the 
surface of the film, and the coated film layer forms a primer layer 
adhering closely to the surface of the substrate film by going through the 
steps of stretching and heat-treating the substrate film. Desirably, the 
primer coated layer has good adhesion to various top coatings to be used 
in the subsequent processing step. 
The aqueous dispersion of polyurethane (A) which can be used in this 
invention is an aqueous dispersion of polyurethane not containing an 
emulsifier, which is obtained by reacting 
(i) a dihydroxy compound having a molecular weight of 750 to 3,000, 
(ii) a polyisocyanate compound, 
(iii) a water-soluble salt of an aliphatic sulfonic acid or an aliphatic 
aminocarboxylic acid having at least one hydrogen atom bonded to nitrogen, 
and 
(iv) a compound containing two hydrogen atoms reactive with the isocyanate 
groups, having a molecular weight of not more than 300, and being free 
from a salt group, as a chain extender, 
as dissolved or dispersed in a water-containing organic solvent, and 
finally removing the organic solvent. 
The polyurethane constituting the primer coated layer in accordance with 
this invention can be produced by known methods. This reaction is carried 
out in the presence or absence of an inert organic solvent. The reaction 
temperature is usually about 50.degree. to about 100.degree. C., and in 
the reaction, an organometallic compound (such as, stannous octylate and 
acetylacetonatoiron) or a tertiary amine (e.g., N-methylmorpholine) may be 
added. First, the dihydroxy compound (i) having a molecular weight of 750 
to 3,000 is dissolved in an inert organic solvent, and reacted with the 
polyisocyanate compound (ii) at a temperature of not more than 100.degree. 
C. The reaction product is then reacted with the chain extender (iv) free 
from a salt group to form a prepolymer having a terminal isocyanate group. 
Then, an aqueous solution of the aliphatic aminocarboxylic acid salt or 
aliphatic sulfonic acid salt (iii) is mixed, and water is further added. 
Finally, the low-boiling organic solvent is removed by steam distillation 
to obtain an aqueous dispersion (A) of polyurethane having a solids 
content of 30 to 50% by weight. 
Examples of the dihydroxy compound (i) having a molecular weight of 750 to 
3,000 include polyester diols, polyether diols, polythioether diols, 
polylactone diols and polyacetal diols. The polyester diols and polyether 
diols are preferred. 
Typical exampls of the polyester diols are linear polyesters having a 
hydroxyl group at both terminals, which are obtained by reacting diols 
such as ethylene glycol, propylene glycol, butylene glycol and diethylene 
glycol or mixtures thereof, with organic dicarboxylic acids, for example 
saturated aliphatic dicarboxylic acids (e.g. adipic acid or sebacic acid), 
unsaturated aliphatic dicarboxylic acids (e.g., maleic acid, or fumaric 
acid), aromatic dicarboxylic acids (e.g., isophthalic or phthalic acid) or 
the anhydrides or mixtures of these. There can be used polyesters obtained 
by ring-opening polymerization of lactones such as caprolactam or 
methylcaprolactone with diols. 
If the molecular weight of the dihydroxy compound is lower than 750, the 
strength and abrasion resistance of the primer coated layer tend to be 
insufficient. If it is higher than 3,000, the aqueous dispersion has poor 
stability, and the adhesion of the primer coated layer to the base film 
tends to be insufficient. 
Examples of the polyisocyanate compound (ii) include 1,4-tetramethylene 
diisocyanate, 1,6-hexamethylene diisocyanate, 1,8-octamethylene 
diisocynate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene 
diisocyanate, toluene diisocyanate, 1,3-phenylene diisocyanate, 
4,4'-methylenebis (cyclohexyl isocyanate), 4,4'-diphenylmethane 
diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and 
mixtures of these. 
In order to obtain a stable dispersion (A) and a tough coated film, it is 
preferred to use an aromatic diisocyanate and then an aliphatic 
diisocyanate, or both of them simultaneously. Of course, it is not 
impossible to perform polymerization using an aromatic or aliphatic 
diisocyanate singly. The use of the aromatic diisocyanate alone, however, 
gives a polymer which tends to sediment. When the aliphatic diisocyanate 
alone is used, the resulting coated film becomes too soft. In order to 
balance the various properties, it is preferred that the mole ratio of the 
former to the latter should be within the range of from 1:1 to 6:1. 
The water-soluble salt (iii) of an aliphatic aminocarboxylic acid or an 
aliphatic sulfonic acid includes, for example, an alkali salt of an 
unsaturated carboxylic acid to which ethylenediamine can add, preferably 
such as a sodium or potassium salt of methacrylic, crotonic or maleic 
acid. Preferably, the alkali salt is used in such an amount that 0.02 to 
1% by weight of --COO group or SO.sub.3 group will be contained in the 
resulting polyurethane. 
In order to improve the adhesion, flexibility, toughness, etc. of 
polyurethane, the compound (iv) having a molecular weight of not more than 
300 and reactivity with the isocyanate groups and being free from a salt 
group is used as a chain extender. Examples of the chain extender (iv) 
include aliphatic diols such as ethylene glycol, diethylene glycol, 1,2- 
and 1,3-propylene glycols, 1,2-, 1,3-, and 1,4-butylene glycol, 
2,2-dimethyl-1,3-propylene glycol, 1,6-hexanediol, 
2,2,4-trimethyl-1,3-pentanediol, 2,2,4,4-tetramethylcyclobutanediol, 
1,3-cyclopentanediol, 1,4-cyclohexanediol and 
1,4-methylenebis(cyclohexanol); aromatic diols such as 
1,4-phenylenebis(.beta.-hydroxyethyl ether), 
1,4-phenylenebis(.beta.-hydroxyethyl ether), and 
isopropylidenebis-(.beta.-hydroxyethyl phenyl ether); and amino compounds 
such as ethylenediamine, hexamethylenediamine, diethylenetriamine, 
hydrazine, piperazine and diaminodiphenylmethane. 
In preparing the polyurethane aqueous dispersion (A), it is recommended to 
select the reactants such that the ratio of the number of isocyanate 
groups to that of all active hydrogens which can react with the isocyanate 
groups is generally from 0.90 to 1.10, i.e. nearly equimolar. 
In order that the resulting polyurethane may exhibit its good properties, 
the reactant ratio, i.e. the dihydroxy compound (i)/the isocyanate 
compound (ii)/the compound (iii) containing a salt group+the chain 
extender (iv), is from 1/4/3 to 1/10/9. 
Examples of the polyurethane aqueous dispersion (A) are those available 
under the tradenames HYDRAN W-140, VONDIC 1150 and 1150NS of Japan 
Reichhold Co., Ltd., IMPRANIL DLN and DLH of Bayer AG, and DESMOCOLL 
KA-8100 and 8066 of Sumitomo Bayer Co., Ltd. 
The montan wax salt (B) to be mixed with the aqueous polyurethane 
dispersion (A) denotes a metal salt of montan acid containing aliphatic 
monocarboxylic acids having 26 to 32 carbon atoms as main ingredients. 
Suitable montan wax salts (B) contain at least one metal of Groups I to 
III of the periodic table, such as lithium, sodium, potassium, barium, 
magnesium, calcium or aluminum, as a cation. The montan wax salt (B) is 
produced by reacting montan acid with 0.2 to 1.0 equivalent weight of a 
hydroxide or oxide of the above metal. Sodium montanate produced by the 
reaction of montan acid with an aqueous solution of sodium hydroxide is 
especially effective. 
The montan wax salt (B) embraces a mixture of a montan acid ester and a 
montan acid metal salt, which is obtained by partially esterifying montan 
acid with not more than 0.9 equivalent, particularly 0.5 to 0.8 
equivalent, of a dihydric alcohol having 2 to 4 carbon atoms in the 
alkylene group, and thereafter neutralizing the product with the aforesaid 
metal oxide or hydroxide. Examples of the diol used in esterification are 
ethylene glycol, 1,2- or 1,3-propanediol, and 1,3- or 1,4-butanediol. 
The montan wax salt (B) may be in the form of an aqueous dispersion 
prepared by using an emulsifier, etc., or in the form of a fine powder. 
The aqueous polyurethane dispersion (A) is mixed with the montan wax salt 
(B) to form a primer coating composition. The weight ratio of the 
polyurethane to the montan wax salt is from 90:10 to 99.99:0.01, 
preferably from 95:5 to 99.9:0.1. If this ratio is lower than 90:10, 
namely if the proportion of the montan wax salt (B) is too high, the 
adhesion between the primer coated layer and the substrate film and the 
adhesion between the primer coated layer and a top coated layer thereon 
are reduced. Furthermore, if the ratio is more than 99.99:0.01, namely if 
the proportion of the montan wax salt (B) is too low, the effect of the 
montan wax salt to prevent tackiness of the montan wax salt and impart 
slippage is reduced. The mixing of the two components may be effected by 
adding an aqueous dispersion of the montan wax salt (B) to the aqueous 
solution of polyurethane (A) and stirring the mixture; or by adding a 
powder of the montan wax salt (B) to the aqueous polyurethane dispersion 
(A) optionally together with an emulsifier and stirring the mixture. 
Prior to coating the primer composition consisting of the aqueous 
polyurethane dispersion (A) and the montan wax salt (B) on the surface of 
a polyester film which is in the process of being oriented and 
crystallized, the film surface may be subjected to an electrical discharge 
treatment in advance as an auxiliary means of rendering the coating 
operation smooth. Instead of employing such an auxiliary means, there may 
be used a primer composition obtained by adding preferably not more than 
15 parts by weight, per 100 parts by weight of polyurethane, of a 
surface-active agent to the mixture of the aqueous polyurethane dispersion 
(A) and the montan wax salt (B). Effective surface-active agents are those 
which promote wetting of a polyester film by decreasing the surface 
tension of the primer composition to below 40 dynes/cm. Many known 
surface-active agents can be used which are not chemically reactive with 
the polyurethane. Examples of the surfactants include polyoxyethylene 
alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty 
acid esters, glycerin fatty acid esters, fatty acid metal soaps, 
alkylsulfates, alkylsulfonates, alkylsulfosuccinates, quaternary ammonium 
chloride, and alkylamine hydrochlorides. 
In coating the primer composition composed of the aqueous polyurethane 
dispersion and the montan wax salt and optionally a surfactant on a 
polyester film which has not yet been completely oriented and 
crystallized, the suitable solids concentration of the primer composition 
is usually not more than 20% by weights, preferably not more than 15% by 
weight. The amount of the primer composition coated may be that required 
to cover the surface of the polyester film completely with the coated 
film. There is no need to coat it excessively. It is sufficient to form a 
coated film layer which is generally considered to be a primer layer in 
the art. 
It is essential in the process of this invention to form a primer coated 
layer before the crystallization and orientation of the polyester film are 
completed. Application of the primer composition to a film which has been 
biaxially oriented and heat-set is scarcely effective. No clear reason can 
be assigned to it, but it may be theorized as follows: A very small amount 
of the montan wax salt exhibits an effect of markedly increasing the speed 
of crystallization of a polyester. This effect is not at all observed with 
other paraffin waxes and their salts. In the course of stretching, 
heat-treatment, etc. of the polyester film to which the primer composition 
containing the montan wax salt having such a property has been coated, the 
montan wax salt contacts the polyester film, and through a complex 
crystallization step, a strong adhesion will be generated between the 
polyester film and the primer coated layer. 
Presumably, the montan wax salt also contributes to the antiblocking 
property of the easily adherable polyester film of the invention during 
storage. The montan wax salt is present in the finely dispersed or 
dissolved state in the primer coated layer, and when the easily adherable 
polyester film undergoes heating and humidification, the montan wax salt 
precipitates on the surface of the primer coated layer, and thus prevents 
sticking of the film. 
The primer composition of this invention may contain other resins and other 
functional materials so long as its effect is not lost. In order to 
perform rapid drying and increase solubility, alcohol, ester and ether 
solvents may be added in amounts which do not markedly pollute the 
environment in the film-making process. 
Any known coating methods can be used to coat the polyurethane on the 
surface of a polyester film before stretching-orientation. For example, 
there can be used roll coating, gravure coating, roll brush coating, spray 
coating, air knife coating, dip coating, and curtain coating either singly 
or in combination. 
Usually, the primer composition is applied to the surface of an unstretched 
film which has just been cast from a molten polymer, or a monoaxially 
stretched film which has just been stretched longitudinally or 
transversely. In order to form the desired primer coated layer, it is 
preferred to dry the coated primer composition and then heat it for at 
least 2 seconds at a temperature of at least 120.degree. C., immediately 
before the film is heat-set. It is also possible to coat the primer 
composition on the unstretched film or the monoaxially stretched film out 
of the film-forming line and subsequently biaxially or monoaxially 
stretching the coated film and then heat-set it within the film-forming 
line. From the standpoint of the treating time and economy, it is 
preferred to perform all of the steps within the film-forming line. 
The easily adherable film of this invention exhibits excellent adhesion to 
cellophane ink, magnetic coating agents, gelatin compositions, linseed 
oil-type offset ink, electrophotographic toner compositions, chemical 
matte paints, diazo paints, heat-sealability imparting compositions, 
inorganic film-forming substances and metal evaporant materials.

The following Examples illustrate the present invention more specifically. 
All parts in these examples are by weight, and the various properties 
given therein were measured by the following methods. 
1. Adhesion 
A top coating composition was coated under predetermined conditions on a 
primer coated layer applied to the surface of a polyester film. A Scotch 
tape (MMM Co., Ltd.), 19.4 mm in width and 8 cm in length, was adhered to 
the coated layer with care being taken not to include air bubbles. A 
manually operable load roll described in JIS C2701 (1975) was rolled over 
the tape to level it. Then, the adhered portion measuring 5 cm in length 
was peeled off in T-shape with the tape side downward at a head speed of 
300 mm/min. using Tensilon UM-III made by Toyo-Baldwin Co., Ltd., and the 
peel strength was measured. The peel strength was devided by the width of 
the tape and the quotient is defined as adhesion (g/cm). 
2. Surface Slippage 
The coefficient of friction between that surface of a polyester film to 
which the primer coated layer was formed and that surface which did not 
have the primer coated layer was measured at a temperature of 20.degree. 
C. and a relative humidity of 60% by using a slippage measuring tester of 
Toyo Tester Co., Ltd. 
3. Antiblocking Property 
Two polyester films (15 cm.times.10 cm) each having a primer coated layer 
formed on one surface were superimposed so that the primer-coated surface 
contacted the uncoated surface. A pressure of 2 kg/cm was applied to the 
superimposed assembly for 24 hours in an atmospher kept at 60.degree. C. 
and 75% RH. In accordance with ASTM-D1893, two fully smoothened chrome 
plated rods having a diameter of 5 mm were interposed between the two 
films, and the two films were stripped off at a speed of 100 mm/min. The 
stripping force at this time was measured (if this value exceeds 100 g/10 
cm, troubles occur in the processing of the film at an increased 
frequency). 
4. Haze 
The total transmittance (T) and the diffusion transmittance (Td) of the 
film sample were measured by using an integral spherical light 
transmittance measuring device (NDH-2, made by Nippon Senshoku Kogei 
Kabushiki Kaisha). The haze value is calculated as follows: 
EQU Haze=Td/T.times.100 
The various top coating compositions used in evaluating adhesion were 
prepared by the following methods. 
PREATION OF TOP COATING COMPOSITIONS 
(1) Magnetic Paint 
Nitrocellulose RS-1/2" (flakes containing 25% of isopropanol; a product of 
Dicell Co., Ltd.) was dissolved in a concentration of 40% by weight in a 
lacquer thinner. Then 439 parts of the resulting solution, 325 parts of a 
polyester resin (Desmophen #1700, a product of Bayer AG), 200 g of 
magnetic chromium dioxide powder, 1 part of soybean fatty acid (Lecion P, 
a product of Riken Vitamin Co., Ltd.) as a dispersant or wetting agent, 
0.5 part of a cationic surfactant (Cation AB, a product of Nippon Oils and 
Fats Co., Ltd.) and 0.8 part of squalene (in shark liver oil) were put in 
a ball mill, and 2.82 parts of a mixture of methyl ethyl ketone (MEK for 
short), cyclohexanone and toluene in a weight ratio of 3:4:3 was further 
added. They were milled to prepare a matrix paint (45% by weight). To 50 
parts of the matrix paint was added a solution of 4.8 parts of an addition 
reaction product of trimethylolpropane and tolylene diisocyanate (CORONATE 
L, a product of Nippon Polyurethane Kogyo Co., Ltd.; solids content 75% by 
weight) in 6.25 parts of n-butyl acetate to obtain a magnetic paint having 
a solids content of 42.75% by weight. 
(2) Gravure Printing Ink 
Two parts of a commercially available cellophane printing ink containing 
nitrocellulose and rosin-type resin as main binders (CLS-709; a product of 
Dainippon Ink and Chemicals Co., Ltd.) was diluted with 1 part of a mixed 
solvent consisting of toluene, ethyl acetate and methyl ethyl ketone in a 
ratio of 1:1:1 to form a paint. 
(3) Gelatin Coating Composition 
Ten parts of gelatin for photography (Nitta gelatin), 1 part of saponin and 
539 parts of distilled water were mixed to prepare a gelatin coating 
composition having a solids content of 2%. 
Each of the three paints described above was coated in the following manner 
on the primer coated layer of the polyester film which has been biaxially 
oriented and crystallized. 
The magnetic paint (1) is roll-coated so that a coating having a thickness 
of 5 microns on an average will be obtained when the coating is dried at 
80.degree. C. for 1 minute and then aged at 60.degree. C. for 24 hours. 
The gravure printing ink (2) is gravure-coated so that a coating having a 
thickness of 1.2 microns on an average will be obtained when the coating 
is dried at 80.degree. C. for 1.4 minutes. 
The gelatin coating composition (3) is roll-coated so that a coating having 
a thickness of 0.6 micron on an average will be obtained when the coating 
is dried at 110.degree. C. for 2 minutes. 
The adhesions of these top coating paints were measured, and the results 
are shown in Table 1. 
TABLE 1 
______________________________________ 
Substrate 
Biaxially oriented poly- 
ester film after completion 
of crystallization and 
Paints orientation 
______________________________________ 
Magnetic paint 
3.3 (g/cm) 
Cellophane ink 
4.1 (g/cm) 
Gelatin coating 
1.0 (g/cm) 
composition 
______________________________________ 
EXAMPLE 1 
(a) Preparation of an Aqueous Polyurethane Dispersion 
203 Parts of a commercially available polyester (Desmophen, a product of 
Bayer AG) having an OH value of 55 and derived from adipic acid, 
hexanediol and neopentyl glycol was stirred in a glass vessel, and at 20 
mmHg, it was dehydrated for 30 minutes. After cooling, 200 parts of 
acetone was added. The solution was then fully mixed with butanediol-1,4. 
Then, 69.7 parts of tolylene diisocyanate (isomer ratio 24/26=80/20), 33.6 
parts of hexamethylene diisocyanate and 0.02 part of dibutyltin laurate 
were added, and they were stirred at 60.degree. C. for 3 hours. The 
mixture was diluted with 300 parts of acetone, and gradually cooled to 
room temperature. Into the resulting product was introduced 193 parts of a 
40% by weight aqueous solution of an equimolar adduct of sodium acrylate 
and ethylenediamine, and the mixture was further stirred well. Thirty-two 
minutes later, 709 parts of water was added dropwise, and subsequently, 
under reduced pressure, acetone was distilled off by steam distillation. 
Finally, a white dispersion having a polymer solid concentration of 47% 
was obtained. 
(b) Preparation of a Primer Composition 
180 Parts of the aqueous polyurethane dispersion obtained in (a) above, 5.5 
parts of sodium montanate (m.p. 178.degree. C.) and 10 parts of 
polyoxyethylene nonyl phenyl ether (a nonionic surfactant, HLB 12.3) were 
mixed, and treated for 30 minutes by a high-speed mixer. To the resulting 
dispersion was added 1.660 parts of deionized water was added to prepare a 
primer composition having a solids content of 5.4% by weight. 
(c) Preparation of an Easily Adherable Film 
Polyethylene terephthalate having an intrinsic viscosity, measured in 
o-chlorophenol at 25.degree. C., of 0.65 was melt-extruded into a film 
having a thickness of 152 microns on a rotating drum kept at about 
20.degree. C., and stretched to 3.5 times in the machine direction on a 
metallic roll heated at 93.degree. C. The primer coating composition 
prepared in (b) above was coated on one surface of the film by a kiss 
coating technique so that the average amount content of solids coated was 
100 mg/m.sup.2. The coated film was dried by passing it through a 
preheating zone at 98.degree. C., and stretched transversely to 3.9 times 
at 105.degree. C. Subsequently, the stretched film was heat-treated at 
200.degree. C. for 4.2 seconds to give an easily adherable polyester film 
having a primer coated layer with a thickness of 121 microns. The adhesion 
of the primer coated layer and the surface slippage, antiblocking property 
and haze of the film were measured. The results are shown in Table 2. 
Comparative Example 1 
An easily adherable polyester film having a primer coated layer was 
produced in the same way as in Example 1 except that a primer composition 
having a solids content of 5.4% obtained by diluting 223 parts of the 
aqueous polyurethane dispersion obtained in (a) of Example 1 and 10.4 
parts of polyoxyethylene nonyl phenyl ether (HLB 12.3) with 1900 parts of 
deionized water was used instead of the primer composition prepared in (b) 
of Example 1. 
The adhesion of the primer coated layer and the surface slippage, 
antiblocking property and haze of the resulting film were measured. The 
results are shown in Table 2. 
It is seen from Table 1 that the film of Comparative Example 1 has an 
antiblocking property exceeding 100 g/10 cm which is the critical limit 
leading to processing troubles, but the film of Example 1 has a lower 
antiblocking value (0.5 g/10 cm) and thus has excellent processability. 
TABLE 2 
______________________________________ 
Film 
Comparative 
Items of evaluation 
Example 1 Example 1 
______________________________________ 
(1) Magnetic paint 
158 145 
Adhesion 
(2) Gravure ink &gt;300 &gt;300 
(g/cm) (3) Gelatin coating 
&gt;300 &gt;300 
composition 
Coefficient of static 
0.34 0.48 
friction 
Surface 
slippage 
Coefficient of dynamic 
0.33 0.46 
friction 
Antiblocking property (g/10 cm) 
0.5 150 
Haze (%) 3.4 3.5 
______________________________________ 
EXAMPLE 2 
194 Parts of the aqueous polyurethane dispersion obtained in (a) of Example 
1, 0.8 part of sodium montanate (m.p. 172.degree. C.) and 8.2 parts of 
Penerol NP-9 (a nonionic surfactant made by Matsumoto Yushi Seiyaku 
Kabushiki Kaisha) were mixed, and treated for 15 minutes in a homogenizer. 
Then, 9800 parts of deionized water was added to give a primer composition 
having a solids content of 1.0%. The primer composition was coated in the 
same way as in Example 1 on one surface of an unstretched film having a 
thickness of 152 microns immediately after melt-extrusion. It was dried 
and biaxially stretched and heat-set under the same conditions as in 
Example 1 to give an easily adherable polyester film having a primer 
coated layer. The adhesion of the primer coated layer, and the surface 
slippage, antiblocking property and haze of the film were measured. The 
results are shown in Table 3. 
EXAMPLES 3 AND 4 
In the same way as in Example 2, the same primer composition as used in 
Example 2 was coated on an unstretched cast polyester film, and dried. The 
film was then longitudinally stretched to 3.5 times at 93.degree. C. and 
then transversely to 3.9 times at 105.degree. C. Thereafter, the stretched 
film was heat-treated at 200.degree. C. for 2.4 seconds (Example 3) or for 
3.0 seconds at 178.degree. C. (Example 4). The properties of the resulting 
easily adherable films are shown in Table 3. 
Comparative Example 2 
A polyester film having a primer coated layer was produced in the same way 
as in Example 3 by using the same primer composition as used in 
Comparative Example 1 but diluted to a solids content of 1.0% by weight. 
The properties of the film were measured, and the results are shown in 
Table 3. 
Comparative Example 3 
A polyester film having a primer coated layer was produced in the same way 
as in Example 4 by using the same primer composition as used in 
Comparative Example 2. The properties of the film were measured, and the 
results are shown in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Com- 
Com- 
para- 
para- 
tive 
tive 
Ex- Ex- Ex- Ex- Ex- 
ample 
ample 
ample 
ample 
ample 
2 3 4 2 3 
__________________________________________________________________________ 
Heat- Temperature (.degree.C.) 
200 200 178 200 178 
treating 
conditions 
for the 
Time (seconds) 
4.2 2.4 3.0 2.4 3.0 
film 
Adhesion 
(1) Magnetic paint 
105 99 95 49 58 
(g/cm) 
(2) Gravure ink 
&gt;300 
&gt;300 
&gt;300 
170 244 
(3) Gelatin coating 
&gt;300 
&gt;300 
&gt;300 
183 190 
composition 
Surface 
Coefficient of static 
0.33 
0.41 
0.37 
0.49 
0.51 
slippage 
friction 
Coefficient of dynamic 
0.36 
0.42 
0.35 
0.48 
0.49 
friction 
Antiblocking property (g/10 cm) 
2 5 8 115 145 
Haze (%) 3.1 3.2 3.0 3.3 3.2 
__________________________________________________________________________ 
EXAMPLES 5 TO 10 
Each of the commercially available polyurethane dispersions shown in Table 
4 was mixed with sodium montanate in each of the ratios indicated, and a 
surface-active agent (Nonion NS 208.5; a product of Nippon Oils and Fats 
Co., Ltd.) and deionized water were added to the mixture to prepare a 
primer composition. The primer composition was coated on one surface of a 
polyester film in the same way as in Example 1 to form a primer coated 
layer. The properties of the resulting easily adherable polyester film 
were measured, and the results are shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Example 5 
Example 6 
Example 7 
Example 8 
Example 9 
Example 10 
__________________________________________________________________________ 
Commercially available 
Desmocoll 
Impranil 
Impranil 
Hydran 
Vondic 
UE-296 
aqueous polyurethane 
KA-8100 
DLH DLN W-140 1150 (Kao Soap 
dispersion (manufacturer) 
(Sumitomo- 
(Bayer AG) 
(Bayer AG) 
(Japan 
(Japan 
Co., Ltd.) 
Bayer) Reichhold) 
Reichhold) 
Weight ratio of poly- 
98:2 99:1 92:8 90:10 99.8:0.2 
95:5 
urethane to montan wax 
salt 
Solids concentration (%) 
5 5 12 15 2 10 
Adhesion 
(1) Magnetic 
182 175 201 210 144 193 
(g/cm) 
paint 
(2) Gravure ink 
&gt;300 &gt;300 &gt;300 &gt;300 &gt;300 &gt;300 
(3) Gelatin 
&gt;300 &gt;300 &gt;300 &gt;300 &gt;300 &gt;300 
coating 
composition 
Surface 
Coefficient of 
0.41 0.39 0.52 0.52 0.32 0.49 
slippage 
static friction 
Coefficient of 
0.43 0.41 0.50 0.53 0.31 0.47 
dynamic friction 
Antiblocking property 
18 12 54 43 2 31 
(g/10 cm) 
Haze (%) 3.5 3.4 4.1 4.0 3.3 3.7 
__________________________________________________________________________