Biaxially oriented polyester film for heat-sensitive transfer ribbon

A film free from the problem of the generation of abrasion powder on an inner part of a transporting system contacting with the surface of a ribbon in a heat-sensitive transfer printer in the case of using the film as a heat-sensitive transfer ribbon and giving a heat-sensitive transfer ribbon having remarkably improved windability is produced by using a biaxially oriented polyester film having a thickness of from 1.0 to 10.0 .mu.m and composed of a polyester composition containing two or more kinds of inert particles having different average particle diameters and each containing at least one kind of element selected from Al, Si, Ca and Mg, characterized in that the center-line average roughness (SRa) and the 10 points average roughness (SRz) of the film surface are 10 to 80 nm and 700 to 1,500 nm, respectively, the air-escaping rate between films is 20 to 120 mmHg/hr, and the end staggering width is 0 to 500 .mu.m when a film roll slit to 1/2 inch wide is wound at a speed of 250 m/min.

TEHCNICAL FIELD 
The present invention relates to a biaxially oriented polyester film for a 
transfer material (heat-sensitive transfer ribbon) for heat-sensitive 
transfer printer, more particularly it relates to a biaxially oriented 
polyester film giving little abrading action on mechanical parts in a 
printer and having extremely excellent windability not only in the winding 
of a roll in film manufacture but also in the slitting of the produced 
ribbon after the application of an ink layer and a back-coating layer. 
Especially, the present invention relates to a biaxially oriented 
polyester film applicable not only for a heat-sensitive transfer ribbon to 
perform the heat-transfer by the contact of an ink layer with an 
image-receptor but also for a sublimation-type heat-sensitive transfer 
ribbon to perform the heat-transfer printing in a non-contacting state of 
the ink layer and the image receptor. 
BACKGROUND ARTS 
Various printing systems were developed according to the progress of office 
automation. Heat-sensitive transfer recording system is attracting 
interest among these systems owing to its low noise-generation in printing 
and simple operation. In this system, an image-receiving member (e.g. 
common paper and plastic sheet) is placed as a transfer object at the side 
of hot-melt ink layer of a heat-sensitive transfer ribbon produced by 
placing a hot-melt ink layer on a base film, a thermal head is brought 
into contact with the heat-sensitive transfer ribbon at the side opposite 
to the ribbon, a thermal pulse is applied to the thermal head 
corresponding to a recording signal to melt the hot-melt ink layer at a 
specific position and the molten ink is transferred to the surface of the 
image-receiving member to record a letter or drawing. 
A polyester film industrially available as a thin film and having excellent 
mechanical strength has been used as the base film constituting the 
heat-sensitive transfer ribbon. 
Disclosed polyester films for heat-sensitive transfer ribbon include a film 
specifying the density of protrusions on the film surface (40 to 200/0.01 
mm.sup.2 for protrusions having a diameter of 1 .mu.m or larger and 
smaller than 5 .mu.m and 400 to 2,000/0.01 mm.sup.2 for protrusions having 
a diameter of 0.5 .mu.m or larger and smaller than 1 .mu.m) and a 
protrusion height (0.10 to 0.50 .mu.m) (JP-A 62-299389 (hereunder JP-A 
means "Japanese Unexamined Patent Publication")), a polyethylene 
naphthalate film having a Young's modulus of 600 kg/mm.sup.2 or above in 
machine direction (JP-B 6-30881 (hereunder JP-B means "Japanese Examined 
Patent Publication")) and a film having a thermal dimensional change of 5% 
or less in transversal direction (Japanese Patent 2581270). These films 
have improved film slipperiness and heat-resistance in the case of using 
as a heat-sensitive transfer ribbon. 
However, it has been clarified that the following two problems are inherent 
to the heat-sensitive transfer ribbons produced from these films. 
The first problem is the generation of abraded powder by the friction of 
the heat-sensitive transfer ribbon with a printer part contacting with the 
heat-sensitive transfer ribbon in high-speed printing to cause defective 
print. 
The second problem is the defective winding caused by the breakage and 
creasing of a heat-sensitive transfer ribbon in the slitting and winding 
of a broad raw film roll to the width of the product ribbon (hereunder 
called as slitting operation) in the process for the production of a 
heat-sensitive transfer ribbon. 
There was no actualization of these problems even by using the above 
conventional films since the printing speed of conventional printer was 
slow, the manufacturing quantity of heat-sensitive transfer ribbon was 
small to dispense with the high-speed slitting process and the windability 
was ensured to an extent by the improvement of the winding condition of a 
slitter and the back coating layer and the ink layer of the film. 
However, the solution of the above two problems became impossible by the 
use of conventional heat-sensitive transfer ribbon because of the 
requirement on the improvement of the productivity or the increase in the 
slitting speed to cope with the increase in the demand of the 
heat-sensitive transfer ribbon and the requirement on high-speed printing 
owing to the improvement of the performance of these printing apparatuses, 
according to the recent spread of facsimile, bar code printing, 
heat-sensitive photoprinter for amusement (Print Club (commercial name), 
etc.) and low-cost printer for computer allowing the printing on plain 
paper. 
JP-A 9-193241 discloses a film having a surface roughness of smaller than 
30 nm, a surface gas flow time of shorter than 2,900 seconds and improved 
windability in the form of film and usable mainly for capacitors. The use 
of the film for a heat-sensitive transfer ribbon, however, does not solve 
the above-mentioned abrasion resistance problem and gives insufficient 
windability as a heat-sensitive transfer ribbon. 
The necessity to solve the above problems by the surface properties of a 
base film has been further increased especially by the tendency of the 
thinning of the back coating layer and the ink layer for the cost 
reduction of a heat-sensitive transfer ribbon. 
Problems to be Solved by the Invention 
The object of the present invention is to provide a biaxially oriented 
polyester film for heat-sensitive transfer ribbon having excellent 
abrasion resistance and windability in the case of using as a 
heat-sensitive transfer ribbon. More particularly, the object of the 
present invention is to provide a biaxially oriented polyester film for 
heat-sensitive transfer ribbon free from generation of abraded powder in a 
printing apparatus, showing stable windability even by slitting a 
heat-sensitive transfer ribbon at a high speed and exhibiting stable 
windability as a base film in high-speed winding. 
Means for Solving the Problems 
The present invention has the following constitution for achieving the 
above object. Namely, the constitution of the present invention is a 
biaxially oriented polyester film for heat-sensitive transfer ribbon 
having a thickness of from 1.0 to 10.0 .mu.m and composed of a polyester 
composition containing two or more kinds of inert particles having 
different average particle diameters, characterized in that each of said 
inert particles contains at least one kind of element selected from Al, 
Si, Ca and Mg, the center-line average roughness (SRa) and the 10 points 
average roughness (SRz) of the film surface are 10 to 80 nm and 700 to 
1,500 nm, respectively, the air-escaping rate between films is 20 to 120 
mmHg/hr, and the end staggering width is 0 to 500 .mu.m when a film roll 
slit to 1/2 inch wide is wound at a speed of 250 m/min. 
The polyester constituting the film of the present invention is a polyester 
containing an aromatic dicarboxylic acid as a main acid component and an 
aliphatic glycol as a main glycol component. Such polyester is an 
essentially linear polymer and has a film-forming property, especially 
film-forming property by melt-molding. The aromatic dicarboxylic acid is, 
for example, terephthalic acid, isophthalic acid, naphthalenedicarboxylic 
acid, diphenyoxyethanedicarboxylic acid, diphenyldicarboxylic acid, 
diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, 
diphenyl ketone dicarboxylic acid and anthracenedicarboxylic acid. The 
aliphatic glycol is, for example, a polymethylene glycol having a carbon 
number of from 2 to 10, such as ethylene glycol, diethylene glycol, 
trimethylene glycol, tetramethylene glycol, pentamethylene glycol, 
hexamethylene glycol and decamethylene glycol or an alicyclic diol such as 
cyclohexanedimethanol. 
In the present invention, the polyester preferably contains an alkylene 
terephthalate and/or an alkylene naphthalate as a main constituent 
component. 
Especially preferable polyesters are polyethylene terephthalate, 
polyethylene-2,6-naphthalate or a copolymer containing terephthalic acid 
and/or 2,6-naphthalenedicarboxylic acid accounting for not less than 80 
mol % of the total dicarboxylic acid component and ethylene glycol 
accounting for not less than 80 mol % of the total glycol component. In 
this case, not more than 20 mol % of the total acid component may be the 
above-mentioned aromatic dicarboxylic acid other than terephthalic acid 
and 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acid such as 
adipic acid or sebacic acid or alicyclic dicarboxylic acid, etc., such as 
cyclohexane-1,4-dicarboxylic acid. Not more than 20 mol % of the total 
glycol component may be the above-mentioned glycols other than ethylene 
glycol, for example, an aromatic diol such as hydroquinone, resorcinol and 
2,2-bis(4-hydroxyphenyl)propane, a polyalkylene glycol (polyoxyalkylene 
glycol) such as polyethylene glycol, polypropylene glycol and 
polytetramethylene glycol, etc. 
The polyester of the present invention includes a polymer copolymerized or 
bonded with not more than 20 mol % of a component originated from an 
oxycarboxylic acid, e.g. an aromatic oxy-acid such as hydroxybenzoic acid 
or an aliphatic oxy-acid such as .omega.-hydroxycaproic acid based on the 
sum of the dicarboxylic acid component and the oxycarboxylic acid 
component. 
The polyester of the present invention includes a polymer copolymerized 
with a tri- or higher functional polycarboxylic acid or polyhydroxy 
compound such as trimellitic acid or pentaerythritol in an amount to give 
an essentially linear polymer, for example, not more than 2 mol % based on 
the total acid component. 
The above-mentioned polyester is known as it is and producible by 
conventional methods. The intrinsic viscosity of the polyester is 
preferably between 0.4 and 0.9 measured as an o-chlorophenol solution at 
35.degree. C. 
The generation of abrasion powder caused by the contact of a film with a 
machine part in a printer can be suppressed and a surface property capable 
of simultaneously improving the windability of the film in the form of a 
roll and the windability of the produced ribbon can be attained by adding 
two or more kinds of inert particles having different average particle 
diameters to the polyester for the film of the present invention. 
Two or more kinds of inert particles to be added to the polyester may be 
natural material obtained simply by crushing or pulverizing rocks or 
synthetic material obtained by adjusting the particle diameter of a 
mineral synthesized in molten state, and a synthetic material is 
preferable from the viewpoint of the quality stabilization of the film. 
There is no particular restriction on the method for the synthesis of the 
synthetic material, and any synthetic method achieving the object of the 
present invention can be used. An example of the melt synthesis comprises 
the compounding of natural feldspar, silica rock and borax at proper 
ratios, thorough mixing of the mixture with a mixer to get a mixture 
having further improved uniformity of each component, melting of the 
obtained mixture in a conjunction furnace or a tank furnace, cooling and 
drying of the product to obtain a synthetic raw stone, crushing of the raw 
stone with a sand grinder, etc., and the decanter treatment as an optional 
step to obtain fine particles having desired particle diameter and 
particle diameter distribution. The crushing of the synthetic raw stone 
can be performed by dry-crushing, wet-crushing or the combination of both 
methods, and particles having desired particle diameter and particle shape 
can be produced by any method. 
A melt synthesis product or a melt sintered product is preferable to 
natural material also in the case that the inert particle is double oxide 
particle to stabilize the qualities such as particle diameter and particle 
size distribution. The synthesis and sintering in the above case are 
carried out generally by sintering in an oven, however, the process is not 
restricted to the oven sintering process. 
Each of two or more kinds of inert particles in the present invention is 
required to contain at least one kind of element selected from Al, Si, Ca 
and Mg. The inert particle is preferably the oxide and/or carbonate of the 
above metal elements to enable the mass production at a low cost. Concrete 
examples of preferable inert particles are silicon dioxide (including 
hydrate, silica sand, quartz, etc.), alumina having various crystal forms, 
silicate containing not less than 30% by weight of SiO.sub.2 (for example 
amorphous or crystalline clay minerals), an aluminosilicate (including 
calcined product and hydrate), chrysotile, zircon, fly ash, etc., Ca and 
Mg carbonates, a spinel-type oxide such as MgAl.sub.2 O.sub.4 and a 
modified spinel-type oxide composed of alumina and other oxide. More 
preferable examples are inert inorganic oxide particles composed of Si 
and/or Al, such as SiO.sub.2, Al.sub.2 O.sub.3 and SiO.sub.2 --Al.sub.2 
O.sub.3. Among the above substances, SiO.sub.2, porous silica and/or their 
agglomerated particles and kaolin consisting of an aluminosilicate are 
especially preferable to ensure the impartment of the preferable film 
properties at reduced film production cost. 
It is also preferable in the present invention that two kinds (A,B) of 
inert particles are used in the invention, the average particle diameter 
of the inert particle A is 0.3 to 1.0 .mu.m, preferably 0.5 to 1.0 .mu.m, 
especially 0.7 to 1.0 .mu.m and the other inert particle B has an average 
particle diameter of 0.5 to 5.0 .mu.m, preferably 1.0 to 3.0 .mu.m, 
especially 1.5 to 2.8 .mu.m and that the average particle diameter 
(d.sub.A) of the inert particle A and the average particle diameter 
(d.sub.B) of the inert particle B satisfy the relationship of d.sub.A 
&lt;d.sub.B. 
The inert particle A having relatively small average diameter is effective 
for forming surface protrusions on the film and suppressing the generation 
of abraded particles especially in a printer. 
The abrasion resistance of film is lowered when the average particle 
diameter of the inert particle A is smaller than 0.3 .mu.m, and the 
printability with a printer is lowered when the average particle diameter 
exceeds 1.0 .mu.m. 
The addition amount of the inert particle A to the polyester is preferably 
between 0.05 and 1.0% by weight. The amount is further preferably between 
0.1 and 0.7% by weight, especially between 0.2 and 0.5% by weight. When 
the amount of the inert particle A is less than 0.05% by weight, the 
surface of the film becomes extremely flat to hinder the escape of air 
between the films, the abrasion resistance is lowered to cause the scratch 
and the generation of white powder during the transport of the produced 
ribbon in a printer and sometimes the produced ribbon is rated as 
defective product. On the other hand, the addition of more than 1.0% by 
weight of the inert particle causes excessive roughening of the film 
surface and high energy is necessary in the case of printing with the 
produced ribbon. The high energy induces the breakage of the film and 
increases the printing defects caused by the falling-off of the inert 
particles near the film surface and the deposition of the powder on the 
tip end of a printer head. 
The inert particle B mainly has the effect of developing the windability of 
the film. 
The inert particle B preferably has high Vickers hardness to decrease the 
damage on the protrusions formed on the polyester film in the case of 
transporting the produced ribbon in the printer, and the Vickers hardness 
is preferably higher than that of the inert particle A. 
The Vickers hardness is measured in conformity to the method A described in 
ASTM D2240. 
The inert particle B preferably has an average particle diameter of from 
0.5 to 5.0 .mu.m. When the average particle diameter is smaller than 0.5 
.mu.m, the air-escape speed abruptly decreases to disable the stable 
winding, and when the average particle diameter of the inert particle B 
exceeds 5.0 .mu.m, the protrusion on the film surface breaks through the 
back-coating layer or the ink layer to cause the defective printing. 
The addition amount of the inert particle B is preferably between 0.005 and 
0.5% by weight based on the polyester. The windability of the film becomes 
poor when the addition amount is smaller than 0.005% by weight and the 
printability of the produced ribbon is lowered at the addition amount 
exceeding 0.5% by weight. 
The average particle diameters of the inert particles A and B were measured 
by using a Centrifugal Particle Size Analyzer, Type CP-50 manufactured by 
Shimadzu Corp. In the case of using an agglomerated particle such as 
agglomerated silica as the inert particle, the average particle diameter 
means the average diameter of secondary particles. 
As mentioned above, the average particle diameter of the inert particle B 
is preferably larger than that of the inert particle A to realize the 
effect of each particle. 
The film of the present invention is necessary to have a center-line 
average roughness (SRa) and a 10 points average roughness (SRz) of 10 to 
80 nm and 700 to 1,500 nm, respectively. The windability of the film is 
undesirably lowered when the center-line average roughness (SRa) is 
smaller than 10 nm or the 10 points average roughness (SRz) is smaller 
than 700 nm and, on the other hand, the abrasion resistance is lowered to 
an undesirable level when the center-line average roughness (SRa) exceeds 
80 nm or the 10 points average roughness (SRz) exceeds 1,500 nm. 
The center-line average roughness (SRa) and the 10 points average roughness 
(SRz) of the film surface can be adjusted within the above ranges by 
selecting the average particle diameter and the addition amount of the 
inert particles to be added to the polyester, concretely as mentioned 
above, by using two kinds of inert particles (A,B) wherein the average 
particle diameter (d.sub.A) and the addition amount of the inert particle 
A is 0.3 to 1.0 .mu.m and 0.05 to 1.0% by weight, respectively, the 
average particle diameter (d.sub.B) and the addition amount of the inert 
particle B is 0.5 to 5.0 .mu.m and 0.005 to 0.5% by weight, respectively, 
and the particles satisfy the relationship of d.sub.A &lt;d.sub.B. 
The center-line average roughness (SRa) and the 10 points average roughness 
(SRz) are defined by JIS-B0601 and JIS-B0602, respectively. 
The film of the present invention has an air-escaping rate between films of 
20 to 120 mmHg/hr, preferably 40 to 120 mmHg/hr, and the end staggering 
width of a film roll slit to 1/2 inch wide is 0 to 500 .mu.m, preferably 0 
to 250 .mu.m at a winding speed of 250 m/min. 
When the air-escaping rate between films is lower than 20 mmHg/hr, the 
windability is lowered to undesirable level and, on the other hand, when 
the rate exceeds 120 mmHg/hr, crease is generated on the film after 
winding. 
The requirement on the ranges of the air-escaping rate between films and 
the end staggering width can be satisfied by selecting the average 
particle diameters and/or addition amounts of two or more kinds of inert 
particles. Concretely, the air-escaping rate between films can be 
increased by increasing the average particle diameter of the particles 
having larger average particle diameter among two or more kinds of inert 
particles and the end staggering width can be decreased by increasing the 
addition amount of the particle having smaller average particle diameter 
among two or more kinds of inert particles. 
The air-escaping rate between films is determined by stacking twenty film 
sheets cut to 8 cm.times.5 cm, opening an equilateral triangular hole 
having a side length of 2 mm at the center of each of the lower nineteen 
sheets and measuring the lowering of the pressure (mmHg) per unit time 
using a digital Bekk smoothness tester (product of Toyo Seiki Industries 
Co., Ltd.). The end staggering width is measured by winding a polyester 
film of 400 m long slit to 1/2 inch on an aluminum core having a diameter 
of 8 cm and a winding part width of 2 cm in an atmosphere conditioned to 
25.degree. C. and 40% humidity at a winding speed of 30 m/min under a 
tension of 50 g while preventing the creasing of the film, rewinding 300 m 
of the wound film on the same aluminum core placed parallel to the wound 
film at a center-to-center distance of 300 mm at a speed of 250 m/min 
under a tension of 50 g, measuring the end staggering width of the film by 
a laser length measuring machine manufactured by KEYENCE Corp. during 
winding, repeating the measurements 10 times, selecting 8 data omitting 
the maximum and the minimum values and using the average value of the 8 
data as the end staggering width. 
A biaxially oriented polyester film for heat-sensitive transfer ribbon 
satisfying both of abrasion resistance and windability can be produced by 
adjusting all of the center-line average roughness (SRa), the 10 points 
average roughness (SRz), the air-escaping rate between films and the end 
staggering width to satisfy the above ranges. 
The film of the present invention preferably has a dimensional change of 
between -8 and +8%, more preferably -5 and 30 5% in transversal direction 
at 200.degree. C. The dimensional change at 200.degree. C. is defined as 
the dimensional change measured by heating a film from 0.degree. C. to 
200.degree. C. at a heating rate of 5.degree. C./min. 
The film of the present invention can be manufactured by conventional 
methods such as successive biaxial drawing method and simultaneous biaxial 
drawing method. It can be manufactured especially by a successive biaxial 
drawing method under the following conditions. 
The film is manufactured by drying a polyester composition, melting at 
280.degree. C. or above, preferably at 280 to 300.degree. C., extruding 
through a die (e.g. T-die or I-die) on a chilling drum, cooling the 
extrudate to obtain an undrawn film, drawing the undrawn film in one 
direction (for example, machine direction or transversal direction) at 70 
to 150.degree. C., preferably at 80 to 130.degree. C. at a draw ratio of 2 
to 7, preferably 3 to 5, successively drawing the uniaxially drawn film in 
the direction perpendicular to the former drawing direction at 90 to 
150.degree. C., preferably 100 to 140.degree. C. at a draw ratio of 2 to 
7, preferably 3 to 5, and heat-setting the product at 200 to 250.degree. 
C. for 0.1 to 30 seconds. A concrete example of an especially preferable 
production process is the production of an undrawn film from a polyester 
composition at a melting temperature of 290.degree. C., the successive 
drawing of the undrawn film in machine direction at 90.degree. C. at a 
draw ratio of 3.6, the drawing in transversal direction at 120.degree. C. 
at a draw ratio of 3.9 and the heat-setting of the biaxially drawn film at 
220.degree. C. for 3 seconds. 
The polyester composition constituting the film of the present invention 
may be a polyester composition containing reclaimed and recycled polyester 
composition as a part or total of the composition. The reclaimed and 
recycled polyester composition means a polyester composition composed of a 
film or a polyester polymer unsuitable for finished product and generated 
in a polyester film manufacturing process or a polyester film fabrication 
process such as a heat-sensitive transfer ribbon manufacturing process. 
Concretely, it is a film generated in the polyester film manufacturing 
process and unsuitable for finished product because of failing in the 
satisfaction of physical quality standards such as thickness or a film 
scrap left after the slitting of a film to the width of the product. 
These polyester compositions were discarded as wastes heretofore, however, 
it is preferable to use these polyester compositions as the polyester 
composition constituting the film of the present invention because the use 
of the reclaimed composition is effective for reducing the production cost 
of the film and reducing the amount of waste. 
The composition of the recycled and reclaimed polyester composition and the 
mixing ratio of the composition in the case of using the composition by 
mixing with a new material (virgin material) are arbitrarily selectable 
provided that the film produced therefrom satisfies the essential 
requirements of the present invention. Above all, the reclaimed and 
recycled polyester composition is especially preferably derived from the 
film of the present invention. 
In the case of producing the film of the present invention exclusively from 
a polyester composition recycled and reclaimed from a film, the 
center-line average roughness (SRa(1)) of the surface of the film before 
recycling and the center-line average roughness (SRa(2)) of the surface of 
the film produced exclusively from the recovered film preferably satisfy 
the following formula. 
EQU 0.8.ltoreq.SRa(2)/SRa(1).ltoreq.1.2 
The thickness of the film of the present invention is preferably from 1.0 
to 10.0 .mu.m. When the thickness is thinner than 1 .mu.m, crease is 
generated during printing with a printer to disable smooth winding. 
Further, the film is undesirable because the breakage of ribbon occurs 
frequently during printing. On the other hand, a film having a thickness 
exceeding 10 .mu.m is also undesirable because high energy has to be 
applied to the head for printing. 
The film of the present invention is suitable for a heat-sensitive transfer 
ribbon. 
A heat-sensitive transfer ribbon can be produced by applying a 
heat-sensitive transfer ink layer to a surface of the film of the present 
invention and applying a back-coating layer to the reverse side of the 
film. The film of the present invention may be subjected as necessary to 
pretreatment such as corona discharge treatment and undercoating. 
There is no particular restriction on the heat-sensitive transfer ink 
constituting the heat-sensitive transfer ink layer to be formed on one 
surface of the film of the present invention, and conventional 
heat-contact ink and sublimation ink can be used as the transfer ink. 
A heat-contact ink layer is constructed concretely by using a binder 
component and a color component as main components and optionally a 
softener, a flexibilizer, a melting point modifier, a smoothing agent, a 
dispersing agent, etc., as additive components. These components are 
composed of a combination of properly selected conventional materials. 
Concrete examples of the binder component are waxes and various 
low-melting polymers such as paraffin wax, carnauba wax and ester wax, and 
concrete examples of the color component are carbon black and various 
organic or inorganic pigment or dye. 
A sublimable dye dispersed in a resin binder can be used as the 
heat-sublimation ink layer. A dye quickly sublimable within a relatively 
narrow temperature range near the transfer temperature is ideal as the 
sublimable dye. Most dyes usable for heat transfer printing have a 
molecular weight of from 230 to 370, and the dye having the molecular 
weight of the above range exhibits sublimation characteristics suitable 
for dyeing and has the molecular size easily diffusible in the dyeing 
object. The dye preferably has a structure free from ionic groups such as 
sulfonic acid group and carboxyl group and properly containing polar 
groups such as hydroxyl group, amino group, nitro group and sulfone group. 
The resin binder preferably has a property to enable easy sublimation of 
the dye molecule and homogeneous dispersion of the dye. Examples of such 
binder are cellulosic resin, acrylic resin, polyvinyl alcohol and 
polyamide, however, the binder is not limited to the examples. 
These heat-sensitive transfer ink layers can be applied to the film of the 
present invention by conventional methods such as a hot-melt coating 
method, a gravure coating method in a state added with a solvent, a 
reverse coating method, a slit die coating method, etc. 
It is preferable to apply a back-coating layer on the surface opposite to 
the face laminated with the heat-sensitive transfer ink layer of the film 
of the present invention. 
The back coating layer is effective for preventing the thermal sticking in 
case of contacting the film with a thermal head, and known components can 
be used as the constituent components of the back coating layer. 
Concretely, the layer is composed mainly of a lubricant such as waxes, 
higher fatty acid and its derivative, silicon compound and fluorine 
compound or a combination of the above lubricant with inorganic particles, 
crosslinked organic particles, fluororesin particles, etc. The application 
of the back coating layer to the film of the present invention can be 
carried out by coating the film with the back coating material in the form 
of aqueous solution or dispersion in the film-forming process and 
subjecting the coated film to drying, drawing and heat-setting treatments 
or by applying the back coating material in the form of aqueous system or 
organic solvent system to the film after completing the orientation and 
crystallization of the film and drying the applied material.

EXAMPLES 
The present invention is further explained in detail by the following 
examples. 
Various physical values and characteristics in the present invention are 
measured and defined as follows. 
(1) Average Diameter of Particles 
The average particle diameter was measured by using Centrifugal Size 
Analyzer Type CP-50 manufactured by Shimadzu Corp. The particle diameter 
corresponding to 50 mass % was read from a cumulative curve showing the 
relationship between the particle diameter and the residual amount of the 
particles calculated based on the obtained centrifugal precipitation 
curve, and the diameter was used as the average particle diameter (refer 
to the Book "Particle Size Measuring Technique" published by the Nikkan 
Kogyo Shimbun, Ltd., 1975, p.242-247). 
(2) Average Diameter of Particles in a Film 
When the added inert particle is a secondary particle consisting of 
agglomerated primary particles, the following method was adopted because 
the particle diameter obtained by the average diameter measurement shown 
in the item (1) sometimes became smaller than the actual average particle 
diameter. 
The film containing the particles was sliced in the direction of 
cross-section to ultra-thin slices having a thickness of 100 nm and the 
agglomerated particles (secondary particles) were observed and 
photographed by using a transmission electron microscope (JEM-1200EX 
manufactured by JEOL, Ltd.) at a magnification of about 10,000. The 
diameter of a circle having an area equal to that of the particle was 
determined on 1,000 particles by using an image analyzer and the 
number-average diameter was used as the average secondary diameter. The 
material of the particle can be determined e.g. by the quantitative 
analysis of metallic element using SEM-XMA, ICP, etc. The average primary 
particle diameter was measured in conformity to the method for the 
measurement of the average secondary particle diameter except for the use 
of the magnification of 100,000 to 1,000,000 in photographing with a 
transmission electron microscope. 
(3) Addition Amount of Each Kind of Inert Particles 
The addition amount of particles was determined by burning 100 grams of 
polyester film before recovery in a platinum crucible in an oven heated at 
about 1000.degree. C. for 3 hours or longer, mixing the burnt residue in 
the crucible with terephthalic acid (powder) to form a tablet-formed plate 
of 50 grams weight, subjecting the tablet to wavelength dispersive 
fluorescent X-ray spectroscopy, and converting the obtained count of each 
element into the addition amount by using a calibration curve prepared 
beforehand. The X-ray tube for the measurement of fluorescent X-ray is 
preferably a Cr tube, and an Rh tube is also usable. The X-ray output was 
set to 4 KW and the analyzing crystal was changed for each element to be 
analyzed. 
When different inert particles contained the same element, the relative 
addition amount was determined from the particle image obtained by the 
transmission electron microscope. The total addition amount of inert 
particles to be used as a base for the above estimation was measured by 
the following method (4). 
(4) Total Addition Amount of Inert Particles 
The total addition amount of particles was determined by burning 100 grams 
of a polyester film in a platinum crucible in an oven heated at about 
1000.degree. C. for 3 hours or longer, mixing the burnt residue in the 
crucible with terephthalic acid (powder) to form a tablet-formed plate of 
50 grams weight, subjecting the tablet to wavelength dispsersive 
fluorescent X-ray spectroscopy, and converting the obtained count of each 
element into the addition amount by using a calibration curve prepared 
beforehand. The X-ray tube for the measurement of fluorescent X-ray is 
preferably a Cr tube, and an Rh tube is also usable. The X-ray output was 
set to 4 KW and the analyzing crystal was changed for each element to be 
analyzed. 
(5) Surface Roughness of Film (SRa, SRz) 
The center-line average roughness (SRa) is a value defined in JIS-B0601, 
and the 10 points average roughness (SRz) is a value defined in JIS-B0602. 
Both values were measured in the present invention by using a tracer-type 
surface roughness tester (SURFCORDER SE-30C) manufactured by Kosaka 
Laboratory Ltd. The measurement conditions were as follows. 
(a) Stylus tip radius: 2 .mu.m 
(b) Measurement pressure: 30 .mu.mg 
(c) Cut-off: 0.25 mm 
(d) Measurement length: 2.5 mm 
(e) Rearrangement of data: Measurements were repeated six times on the same 
specimen, the highest one was omitted and the average of the remaining 5 
data was used as the average roughness. 
(6) Air-Escaping Rate of Film 
The windability of a film was expressed by the air-escaping rate in stacked 
state and the end staggering width of wound film roll. The air-escaping 
rate was determined by stacking twenty film sheets cut to 8 cm.times.5 cm 
before recovery, opening an equilateral triangular hole having a side 
length of 2 mm at the center of each of the lower nineteen sheets and 
measuring the lowering of the pressure (mmHg) per unit time using a 
digital Bekk smoothness tester (product of Toyo Seiki Industries Co., 
Ltd.). 
(7) End Staggering Width of Film 
The end staggering width was measured by winding a polyester film of 400 m 
long slit to 1/2 inch on an aluminum core having a diameter of 8 cm and a 
winding part width of 2 cm in an atmosphere conditioned to 25.degree. C. 
and 40% humidity at a speed of 30 m/min under a tension of 50 g while 
preventing the creasing of the film, rewinding 300 m of the wound film on 
the same aluminum core placed parallel to the wound film at a 
center-to-center distance of 300 mm at a speed of 250 m/min under a 
tension of 50 g, measuring the end staggering width of the film by a laser 
length measuring machine manufactured by KEYENCE Corp. during winding, 
repeating the measurements 10 times and using the average value of 8 data 
omitting the maximum and the minimum values as the end staggering width 
(.mu.m). 
(8) Abrasion Resistance of Film (White Powder, Scratch) 
A film slit to 1/2 inch wide was brought into contact with a fixed guide 
pin formed by bending a sintered SUS plate in cylindrical form and having 
insufficient surface finish (center-line surface roughness (Ra); 0.15 nm) 
at a contact angle of 60.degree. in an atmosphere of 20.degree. C. and 60% 
humidity and transported (rubbed) at a speed of 250 m/min under an inlet 
tension of 50 grams. After transporting 200 m of the film, the amount of 
abraded powder (white powder) deposited on the fixed guide pin and the 
number of scratches on the transported film were evaluated by the 
following criterion. 
Judgement of Abraded Powder (White Powder) 
.circleincircle.: Absolutely no abraded powder was visible. 
.largecircle.: Abraded powder was faintly visible. 
.DELTA.: The presence of abraded powder was recognizable at a glance. 
.times.: Abraded powder was thickly deposited. 
Judgement of Scratch 
.circleincircle.: Absolutely no scratch was visible. 
.largecircle.: One to five scratches were visible. 
.DELTA.: Six to fifteen scratches were visible. 
.times.: The number of scratches was 16 or more. 
(9) Windability of Produced Ribbon in Slitting 
One thousand (1,000) meters of a heat-sensitive transfer ribbon slit to 3 
cm wide was wound on an aluminum core having an outer circumference of 3 
inches and provided with a winding part having a width of 4 cm and a 
thickness of 3 mm under a tension of 100 g while increasing the winding 
speed from 20 m/min at an interval of 20 m/min, the maximum speed capable 
of winding 1,000 m of the heat-sensitive transfer ribbon without causing 
the end staggering was determined and the windability was evaluated by the 
following criterion. 
.times.: Less than 100 m/min 
.DELTA.: 100 m/min or more and less than 200 m/min 
.largecircle.: 200 m/min or more and less than 300 m/min 
.circleincircle.: 300 m/min or more 
(10) Vickers Hardness 
Vickers hardness was measured by the method A described in ASTM D2240. 
The measurement was repeated five times using the Type MD-1 hardness tester 
manufactured by Kobunshi Keiki Co., Ltd., and the average of the five data 
was used as the Vickers hardness value. 
Examples 1 to 9 and Comparative Examples 1 to 8 
A polyethylene terephthalate having an intrinsic viscosity of 0.56 (in 
o-chlorophenol at 35.degree. C.) was produced by polymerizing dimethyl 
terephthalate and ethylene glycol by conventional method adding manganese 
acetate as a transesterification catalyst, antimony trioxide as a 
polymerization catalyst, phosphorous acid as a stabilizer and particles 
shown in the Tables 1 to 4 as lubricants. The pellets of the polyethylene 
terephthalate were dried at 170.degree. C. for 3 hours, supplied to the 
hopper of an extruder, melted at 280 to 300.degree. C., and extruded 
through a single-layer die on a rotary chilling drum having a surface 
finish of about 0.3 s and surface temperature of 20.degree. C. to obtain 
an undrawn film having a thickness of about 65 .mu.m. The produced undrawn 
film was preheated to 75.degree. C., drawn 3.6 times between a low-speed 
roll and a high-speed roll under heating with a single IR heater placed 15 
mm above the film and having a surface temperature of 800.degree. C., 
quenched, supplied to a stenter and drawn 3.9 times in transversal 
direction at 120.degree. C. The biaxially oriented film produced by this 
process was heat-set for 5 seconds at 205.degree. C. to obtain a heat-set 
biaxially oriented polyester film having a thickness of 4.6 .mu.m. The 
film thickness was controlled by varying the rotational speed of the 
extruder to change the thickness of the undrawn sheet. Characteristics of 
these biaxially oriented polyester films are shown in the Tables 1 to 4. 
A transfer ink layer was formed on a surface of the film by applying a 
heat-sensitive transfer ink coating agent having the following composition 
to the surface by hot-melt coating process with a hot roll in an amount to 
get a coating film thickness of 5 .mu.m. The windability data of the 
obtained product ribbon in slitting are shown in the Tables 1 to 4. 
Composition of Heat Transfer Ink 
______________________________________ 
Magenta dye (MS Red G) 
3.5% by weight 
Polyvinyl acetoacetal resin 
3.5% by weight 
Methyl ethyl ketone 46.5% by weight 
Toluene 46.5% by weight 
______________________________________ 
Effect of the Invention 
The present invention enables the production of a biaxially oriented 
polyester film having high abrasion resistance and giving a product ribbon 
having good windability in slitting and has high industrial value. 
TABLE 1 
__________________________________________________________________________ 
Example 1 
Example 2 
Example 3 
Example 4 
__________________________________________________________________________ 
Inert 
Kind Kaolin 
Kaolin 
Kaolin 
ag-po-Si 
particle 
Constitution 
Si, Al 
Si, Al 
Si, Al 
Si 
(A) element 
Vickers 
-- 80 80 80 170 
hardness 
Addition 
wt. % 
0.3 0.15 0.15 0.2 
amount 
Average 
.mu.m 
0.66 0.66 0.66 0.18 
diameter dA 
Average 
.mu.m 
-- -- -- 0.012 
primary 
diameter 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
method 
Inert 
Kind po-Si po-Si po-Si po-Si 
particle 
Constitution 
Si Si Si Si 
(B) element 
Vickers 
-- 275 275 275 275 
hardness 
Addition 
wt. % 
0.05 0.01 0.05 0.05 
amount 
Average 
.mu.m 
2.3 2.3 2.3 2.3 
diameter dB 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
process 
Film thickness 
.mu.m 
4.6 4.6 4.6 4.6 
SRa nm 32 22 25 35 
SRz nm 1200 1350 1420 1370 
Air escaping rate 
mmHg/ 
hr 85 55 40 68 
End staggering width 
.mu.m 
40 65 54 57 
Abrasion 
White powder 
.circleincircle. 
.largecircle. 
.largecircle. 
.largecircle. 
resistance 
Scratch .circleincircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Windability of product ribbon in 
.circleincircle. 
.largecircle. 
.circleincircle. 
.largecircle. 
slitting 
__________________________________________________________________________ 
Note: Kinds of the inert particles: poSi; porous silica, agpo-Si; 
agglomerated porous silica 
TABLE 2 
__________________________________________________________________________ 
Example 
Example 
Example 
Example 
Example 
5 6 7 8 9 
__________________________________________________________________________ 
Inert 
Kind Kaolin 
Kaolin 
Kaolin 
Kaolin 
Kaolin 
particle 
Constitution 
Si, Al 
Si, Al 
Si, Al 
Si, Al 
Si, Al 
(A) element 
Vickers 
-- 80 80 80 80 80 
hardness 
Addition 
wt. % 
0.07 0.5 0.95 0.5 0.5 
amount 
Average 
.mu.m 
0.66 0.66 0.66 0.66 0.66 
diameter 
dA 
Average 
.mu.m 
-- -- -- -- -- 
primary 
diameter 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
method 
Inert 
Kind CaCO3 
po-Si 
po-Si 
po-Si 
po-Si 
particle- 
Constitution 
Ca Si Si Si Si 
(B) element 
Vickers 
-- 128 275 275 275 275 
hardenss 
Addition 
wt. % 
0.26 0.09 0.05 0.05 0.05 
amount 
Average 
.mu.m 
1.2 2.3 2.3 2.3 2.3 
diameter 
dB 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
process 
Film thickness 
.mu.m 
4.6 4.6 4.6 1.2 9.8 
SRa nm 21 74 67 29 43 
SRz nm 1210 1480 1400 1315 1325 
Air escaping rate 
mmHg/ 
31 85 85 83 92 
hr 
End staggering width 
.mu.m 
72 105 308 230 330 
Abrasion 
White powder 
.circleincircle. 
.largecircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
resistance 
Scratch .circleincircle. 
.largecircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Windability of product ribbon 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
slitting 
__________________________________________________________________________ 
Note: Kinds of the inert particles: poSi; porous silica, CaCO3; Calcium 
carbonate 
TABLE 3 
__________________________________________________________________________ 
Compara. 
Compara. 
Compara. 
Compara. 
Example 1 
Example 2 
Example 3 
Example 4 
__________________________________________________________________________ 
Inert 
Kind Kaolin 
ag-po-Si 
Kaolin 
Kaolin 
particle 
Constitution 
Si, Al 
Si Si, Al 
Si, Al 
(A) element 
Vickers 
-- 80 170 80 80 
hardness 
Addition 
wt. % 
0.500 0.150 0.500 0.500 
amount 
Average 
.mu.m 
0.66 1.70 0.66 0.66 
diameter dA 
Average 
.mu.m 
-- 0.012 -- -- 
primary 
diameter 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
method 
Inert 
Kind None None po-Si po-Si 
particle 
Constitution 
-- -- Si Si 
(B) element 
Vickers 
-- -- -- 275 275 
hardness 
Addition 
wt. % 
-- -- 0.005 0.100 
amount 
Average 
.mu.m 
-- -- 2.3 2.3 
diameter dB 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
process 
Film thickness 
.mu.m 
4.6 4.6 4.6 4.6 
SRa nm 30 31 32 71 
SRz nm 920 1050 710 1510 
Air escaping rate 
mmHg/ 
42 61 45 140 
hr 
End staggering width 
.mu.m 
401 109 740 710 
Abrasion 
White powder 
X X .DELTA. 
.largecircle. 
resistance 
Scratch .DELTA. 
.DELTA. 
.DELTA. 
.DELTA. 
Windability of product ribbon in 
.DELTA. 
.DELTA. 
X X 
slitting 
__________________________________________________________________________ 
Note: Kinds of the inert particles: poSi; porous silica, agpo-Si; 
agglomerated porous silica 
TABLE 4 
__________________________________________________________________________ 
Compara. 
Compara. 
Compara. 
Compara. 
Example 5 
Example 6 
Example 7 
Example 8 
__________________________________________________________________________ 
Inert 
Kind Kaolin 
Kaolin 
Kaolin 
Kaolin 
particle 
Constitution 
Si, Al 
Si, Al 
Si, Al 
Si, Al 
(A) element 
Vickers 
-- 80 80 80 80 
hardness 
Addition 
wt. % 
0.05 1.50 0.50 0.50 
amount 
Average 
.mu.m 
0.66 0.66 0.66 0.66 
diameter dA 
Average 
.mu.m 
-- -- -- -- 
primary 
diameter 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
method 
Inert 
Kind po-Si po-Si po-Si po-Si 
particle 
Constitution 
Si Si Si Si 
(B) element 
Vickers 
-- 275 275 275 275 
hardness 
Addition 
wt. % 
0.050 0.050 0.050 0.050 
amount 
Average 
.mu.m 
2.3 2.3 2.3 2.3 
diameter dB 
Production 
Synthesis 
Synthesis 
Synthesis 
Synthesis 
process 
Film thickness 
.mu.m 
4.6 4.6 0.5 12.0 
SRa nm 20 84 24 36 
SRz nm 615 1240 1210 1080 
Air escaping rate 
mmHg/ 
9 125 19 140 
hr 
End staggering width 
.mu.m 
1095 940 895 629 
Abrasion 
White powder 
X .DELTA. 
.largecircle. 
.largecircle. 
resistance 
Scratch X .DELTA. 
.largecircle. 
.largecircle. 
Windability of product ribbon in 
X X X X 
__________________________________________________________________________ 
slitting 
__________________________________________________________________________ 
Notes: Kinds of the inert particles: poSi; porous silica,