 |
Description  |
|
|
This invention relates to an imaged copy film, and in particular to an
electrostatically imaged copy film.
Transparencies for the projection of light images are known and can be
formed from a transparent film base and an image or print applied thereto
by an electrostatic copying process. Such applied images may lack
permanence, in the sense that they exhibit inferior resistance to abrasio
and erasure during repeated handling and use, unless special measures are
taken to develoop adequate adhesion between the film base and the image
layer. Similar problems are encountered with pigmented (white) or opaque
copy or drafting films suitable for use in xerographic laser printer
equipment or in wide format (841.times.1189 mm) copiers. This invention is
concerned with improving the adhesion to a film base of an image layer
derived from a copying toner powder and applied by an electrostatic
copying process.
Accordingly, the present invention provides an imaged copy film comprising
(a) a film substrate of a synthetic polymeric material having, on at least
one surface thereof,
(b) a receiving layer, and, on a surface of the receiving layer remote from
the substrate,
(c) an electrostatic copying toner image layer wherein the receiving layer
comprises a terpolymer of
(i) from 60 to 98 weight % of a vinyl halide,
(ii) from 1 to 20 weight % of a vinyl ester of a saturated aliphatic
carboxylic acid and the molecule of which contains from 2 to 6 carbon
atoms, and
(iii) from 1 to 20 weight % of a functional group-containing
ethylenically-unsaturated termonomer.
The invention also provides a method of producing an imaged copy film
comprising forming a receiving layer on at least one surface of a film
substrate of a synthetic polymeric material and electrostatically applying
to the receiving layer an image layer of a copying toner, wherein the
receiving layer comprises a terpolymer of
(i) from 60 to 98 weight % of a vinyl halide,
(ii) from 1 to 20 weight % of a vinyl ester of a saturated aliphatic
carboxylic acid the molecule of which contains from 2 to 6 carbon atoms,
and
(iii) from 1 to 20 weight % of a functional group-containing
ethylenically-unsaturated termonomer.
The substrate may comprise any suitable polymeric material, in the form of
a self supporting film or sheet. Suitable polymeric materials include
cellulose esters, such as cellulose acetate, polystyrene, polyamides,
polymers and copolymers of vinyl chloride, polymers and copolymers of
olefins, eg polypropylene, polysulphones and particularly linear
polyesters which may be obtained by condensing one or more dicarboxylic
acids or their lower alkyl (1-5 carbon atoms) diesters, eg terephthalic
acid, isophthalic acid, phthalic acid, 2,5-, 2,6- and 2,7-naphthalene
dicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid,
diphenyl dicarboxylic acid, and hexahydroterephthalic acid or
bis-p-carboxy phenoxy ethane, optionally with a mono-carboxylic acid, such
as pivalic acid, with one or more glycols, eg ethylene glycol,
1,3-propanediol, 1,4-butanediol, neopentyl glycol and
1,4-cyclohexane-dimethanol. A biaxially oriented and heat-set film of
polyethylene terephthalate is particularly useful for the production of a
copy film according to the invention and may be produced by any of the
processes known in the art, eg as described in British patent
specification GB-A-838,708.
A substrate intended for use as a projection film should be transparent to
permit relatively unrestricted transmission of light during image
projection operations. However an opaque or pigmented polymeric substrate
may be employed for plain paper copying operations. Thus, a substrate may
be pigmented by the application of a pigmented coating layer on a surface
thereof, or a substrate may be rendered opaque by incorporation into the
film-forming synthetic polymer of an effective amount of an opacifying
agent. In a further embodiment of the invention the opaque substrate is
voided by incorporating into the polymer an effective amount of an agent
which is capable of generating an opaque, voided substrate structure.
Suitable voiding agents, which also confer opacity, include an
incompatible resin, filler, a particulate inorganic filler or a mixture of
two or more such fillers.
Particulate inorganic fillers suitable for generating an opaque, voided
substrate include conventional inorganic pigments and fillers, and
particularly metal or metalloid oxides, such as alumina, silica and
titania, and alkaline earth metal salts, such as the carbonates and
sulphates of calcium and barium. Barium sulphate is a particularly
preferred filler which also functionas as a voiding agent.
Production of a substrate having satisfactory degrees of opacity, voiding
and whiteness requires that the filler should be finely-divided, and the
average particle size thereof is desirably from 0.1 to 10 microns (.mu.m)
provided that the actual particle size of 99.9% by number of the particles
does not exceed 30 .mu.m. Preferably, the filler has an average particle
size of from 0.1 to 1.0 .mu.m, and particulaly preferably from 0.2 to 0.75
.mu.m.
The amount of filler, particularly of barium sulphate, incorporated into
the substrate polymer desirably should be not less than 5% nor exceed 50%
by weight, based on the weight of the polymer. Particularly satisfactory
levels of opacity and gloss are achieved when the concentration of filler
is from about 8 to 30%, and especially from 15 to 20%, by weight, based on
the weight of the substrate polymer.
The thickness of the film substrate is suitably from 25 to 500,
particularly from 50 to 300, and especially from 75 to 175 microns.
To promote adhesion of the receiving layer to the substrate, a surface of
the latter may first be treated with a priming medium. Creation of a
priming layer is conveniently effected by treating a surface of the
polymeric substrate with an agent known in the art to have a solvent or
swelling action on the substrate polymer. Examples of such agents, which
are particularly suitable for the treatment of a polyester substrate,
include a halogenated phenol such as p-chloro-m-cresol,
2,4-dichlorophenol, 2,4,5- or 2,4,6-trichlorophenol or 4-chlororesorcinol.
The agent may be applied as a solution in a common organic solvent, such
as acetone or methanol.
The primed substrate is conveniently dried by heating to a temperature of
from 60.degree. to 80.degree. C. for from 1 to 5 hours.
Alternatively, or additionally an agent known to have a solvent or swelling
action on the film substrate may be incorporated into the terpolymer resin
for application therewith.
Adhesion of the receiving layer to the substrate may also be improved by
first coating a surface of the substrate with a layer of an adhesive
film-forming polymer resin. Particularly suitable resins include
copolymers of acrylic acid and/or methacrylic acid and/or lower alkyl (up
to 6 carbon atoms) esters thereof, such as--copolymers of ethyl acrylate
and methyl methacrylate, copolymers of methyl methacrylate/butyl
acrylate/acrylic acid typically in the molar proportions 55/27/18% and
36/24/40%, and especially copolymers containing hydrophilic functional
groups, such as--copolymers of methyl methacrylate and methacrylic acid,
and cross-linkable copolymers, particularly terpolymers comprising ethyl
acrylate/methyl methacrylate/acrylamide or methacrylamide, conveniently in
the approximate molar proportions 46/46/8% respectively. The latter
polymer is particularly effective when thermoset--for example, in the
presence of a cross-linking agent--such as a methoxylated
melamine-formaldehyde resin, typically present in an amount of up to about
25% by weight of the terpolymer.
Formation of the adhesive layer may be effected by techniques known in the
art, the layer being conveniently applied to the substrate, particularly
as an inter-draw coating, from a coating composition comprising a solution
or dispersion of the resin in a volatile medium, particularly an aqueous
medium.
Adhesion of the image layer to the film substrate is promoted by the
intermediate receiving layer which comprises a functional terpolymer. The
vinyl halide component of the terpolymer conveniently comprises vinyl
chloride, and the vinyl ester component conveniently comprises vinyl
acetate.
Functionality in the termonomer component is conveniently conferred by the
presence of hydroxyl group(s), and the hydroxyl group-containing
ethylenically unsaturated termonomer suitably comprises a
hydroxyl-containing alkyl acrylate or methacrylate, particularly a lower
alkyl acrylate or methacrylate in which the alkyl group contains from 1 to
6 carbon atoms--especially a methyl, ethyl or propyl group.
Functionality may also be converred by the presence of a termonomer
comprising a carboxylic acid or anhydride group, especially maleic acid or
anhydride.
The functional group content of the terpolymer is relatively low, and when
a hydroxyl-containing termonomer is present, the total hydroxyl content,
based on the weight of the terpolymer, is desirably from 1.5 to 2.5 wt %,
particularly from 1.8 to 2.2, eg 2.0 wt %. Similar concentrations of
carboxylic acid or anhydride functional groups are of utility.
A preferred receiving layer comprises a terpolymer containing from 75 to 85
weight % of vinyl chloride, from 2 to 8 weight % of vinyl acetate and the
balance (to 100 weight %) of an unsaturated functional termonomer (such as
hydroxy-ethyl methacrylate).
The terpolymer resin is a relatively low molecular weight material, and the
average molecular weight (number average) thereof is suitably within a
range of from 1,000 to 100,000, more preferably from 4,000 to 16,000, and
especially from 6,000 to 10,000.
The receiving layer may be of any appropriate thickness, but, for
convenience, the dry coat thickness is suitably from 0.01 to 5 microns,
and especially from 0.02 to 2 microns.
Formation of the receiving layer is conveniently effected by application to
the film substrate of a receiving medium comprising a solution of the
terpolymer in an organic solvent, such as acetone, methanol, diacetone
alcohol or a mixture of two or more thereof. The solution conveniently
comprises from 0.1 to 20%, and preferably from 0.5 to 5%, by weight of the
terpolymer by volume of the solvent.
Application of the receiving medium to the film substrate may be effected
by a conventional coating technique--for example, by a slot-, roller-, or
bead-coating technique. The coating operation may be effected during or
after production of the film substrate. Thus, in the production of a
biaxially oriented film substrate by sequential stretching in two mutually
perpendicular directions, the receiving medium may be applied before
stretching commences, or between the two stages of the stretching
operation. Alternatively, the medium may be applied to the biaxially
oriented film on completion of the stretching operation.
Drying of the applied medium may be effected by a conventional drying
technique--for example, by suspending the coated substrate for several
(conveniently up to 10) minutes in a hot air oven maintained at an
appropriate temperature. A drying temperature of from 70.degree. to
130.degree. C., preferably from 80.degree. to 115.degree. C., is usually
suitable for a polyester substrate. Differential drying, at different
temperatures, optionally for different durations, may be practised to
control the rheology of the receiving layer.
An image layer may be formed on the receiving layer by a conventional
electrostatic copying technique using a thermally fusible (thermoplastics)
toner powder. Available toner powders include those based on
styrene-acrylate copolymers, and blends thereof.
Electrostatic copying machines are well known and generally available for
use in office copying operations. Such machines, particularly those which
are commercially available under the registered trade mark "Xerox" may be
used for the application of an image to a transparent film substrate in
accordance with the invention. Machines of this nature generally operate
by initially depositing a uniform positive electrostatic charge from a
corona discharge electrode onto a drum having a photoconductive surface,
eg a selenium coated drum, maintained in a dark environment. The charged
surface is then exposed to a light image of the original document or
representation to be copied, whereby the charge is dissipated and flows to
earth from those areas of the drum struck by the light. The charge is not
affected in the dark areas masked by the original document or
representation. The image is then formed by passing negatively charged
coloured thermoplastic toner powder over the light-exposed drum so that
the powder is electrostatically attracted to the residual charged areas on
the drum surface. The thus-formed toner powder image may be transferred to
the film substrate of the invention by placing the receiving layer of the
substrate over the toner image and positively charging the substrate by
corona discharge so that the toner powder is attracted to the substrate by
the residual negative charge on the toner powder. Finally the substrate
may be heated to fuse the toner powder and bond it to the receiving layer
surface of the film substrate as an image layer.
Thermal bonding of fusible toner powder to a film substrate is generally
effected at relatively high fusion temperatures, for example--at about
200.degree. C., in known electrostatic copying processes, and is commonly
achieved by infra-red heating. However, somewhat lower temperatures, in
the region of 120.degree. C., applied by heated rollers or ultra-violet
lamps, may also be used. It has been found that the adhesion of the toner
powder to the film substrate in accordance with the invention is
satisfactory at both high and low bonding temperatures.
A receiving layer may be provided on one or each surface of a film
substrate, and an image may thus be generated on one or each receiving
layer. The invention is of particular utility in the production of paper
backed copying film where the non-image surface of the film substrate is
laminated along one edge to a backing paper (usually of 40 to 100 gsm
gauge) using an adhesive element, such as a thin longitudinal deposit of
adhesive (pressure-sensitive or non pressure-sensitive) or tape. The
presence of a paper layer in the laminated copy film assembly tends to
inhibit transfer of heat to the receiving layer during the thermal bonding
stage of the copying process, and therefore effectively impairs toner
adhesion. The present receiving medium enables a satisfactorily high level
of toner adhesion to be achieved even when a paper backing layer is
employed in association with a copying film in accordance with the
invention.
When multiple copies are to be produced in a high speed electrostatic
copying machine, a finely divided particulate material, such as silica
particles, may be incorporated as an anti-blocking agent into the
receiving medium. If desired, an antistatic coating medium may be applied
to the surface of the film support remote from the image receiving layer.
The static friction of the film base can be reduced by applying a wax--for
example a natural wax, such as carnauba wax, or a synthetic wax, to one or
both surfaces of the film support, the wax coating on that surface
carrying the receiving layer being applied over that layer. These
precautions facilitate the feeding of single sheets froma stack of sheets
in a high speed copying machine.
The presence of an anti-friction medium, such as wax, on the receiving
layer is particularly desirable in the case of paper backed laminate copy
sheets to be fed in succession from a stack of sheets. Thus, in a stack
feed assembly, the image surface of one copy laminate sheet is in contact,
in the supply magazine, with the surface of the paper backing sheet of an
adjacent copy laminate, and the frictional characteristics of these
relatively incompatible surfaces must be controlled so that one laminate
slides readily over the other when fed to the copier by the usual belt or
suction mechanism. Surprisingly, we have observed that the presence of a
wax on the receiving layer does not significantly impair the toner
adhesion characteristics of the specified terpolymer medium.
The invention is illustrated by reference to the following Examples.
EXAMPLES 1a-1g
A conventional transparent 100 micron thick biaxially oriented and heat set
film of polyethylene terephthalate was pretreated by bead coating on one
surface with a solution of 2 g p-chloro-m-cresol in 100 ml of methanol to
yield a wet coat weight of 100 mg/dm.sup.2. The pretreated surface was
dried by heating in an air oven for 2 minutes at 80.degree. C.
The pretreated surface was then bead coated with a solution of 1 g of a
terpolymer of vinyl chloride (81 wt %), vinyl acetate (4 wt %) and a
hydroxyl-containing propyl acrylate (15 wt %) with a total hydroxyl
content of 2.0% by weight of the terpolymer, and an average molecular
weight (number average) of 8,000, in a solvent mixture of 81 ml acetone,
14 ml methanol and 5 ml diacetone alcohol to yield a wet coat weight of
100 mg/dm.sup.2. The coating was dried by heating in an air oven at
80.degree. C. for 3 minutes and then at 115.degree. C. for 2 minutes to
yield a receiving layer having a dry thickness of about 0.2 micron.
A solution of 0.10 g of `Pluriol` E9000 wax in 100 ml methanol was then
applied to the dried receiving layer, and the wax coating was dried in an
air oven at 90.degree. C. for 2 minutes.
The waxed film was cut into A4 sheets and to the non-image surface of each
sheet was laminated an A4 sheet of white paper (70 gsm Garnett Poster
Paper) by means of a thin layer of pressure sensitive adhesive along one
long edge, to yield a paperbacked composite.
Respective composite sheets were imaged in a variety of plain paper
copiers, using conventional "Xerox" thermoplastics toner powder, operated
at the specification pre-set powder fusin temperature.
Parallel control experiments were performed using similar composite
sheets--identical to those of the invention save that the receiving layer
comprised a copolymer of n-butyl methacrylate and methyl methacrylate
(70:30 molar) of the kind disclosed in the specification of British patent
GB-A-1447272.
The respective imaged sheets were assessed by two tests:
(1) by scraping the image layer with a finger nail and
(2) by crease folding the image layer.
Results are recorded in the accompanying Table, and show that adhesion of
the image to the copy film formed according to the invention was good, and
better than that of control films formed in accordance with GB-A-1447272.
TABLE
______________________________________
Toner Adhesion
Crease/Fold
Example
Copier Type Nail/Scratch*
(mm)**
______________________________________
1a XEROX 1045 f 1.0
Control
XEROX 1045 s 3.0
1b XEROX 1048 m/g 0.5
Control
XEROX 1048 s/f 1.5
1c XEROX 1075 f/m 1.0
Control
XEROX 1075 s/f 1.0
1d XEROX 2830 f 1.0
Control
XEROX 2830 s 1.5
1e XEROX CBA 9400 g 1.0
Control
XEROX CBA 9400 g 1.5
1f XEROX CBA 9500 m/g 1.0
Control
XEROX CBA 9500 p 2.5
1g CANON NP 300 m/g <0.5
Control m <0.5
______________________________________
*Toner adhesion: g = good, m = moderate, f = fair, s = slight, p = poor
**To effect the crease/fold test a square sample (10 .times. 10 mm) of th
imaged film, after cooling to ambient temperature, was placed on a flat
support with the imaged surface uppermost and sharply folded along a
diagonal. The sample was then unfolded and gently wiped with a paper
tissue along the resultant diagonal crease line to remove loose toner
powder. With the aid of an optical magnifier, the width of the zone from
which toner had been removed was measured perpendicular to, and at severa
locations along, the crease line. The average of these width measurements
is the measurement recorded in the Table.
EXAMPLE 2
The procedure of Example 1 was repeated save that (a) the terpolymer
receiving medium, and associated wax layer, was applied to both surfaces
of the polyethylene terephthalate supporting film, and (b) the copy film
was not provided with a paper backing layer. Parallel control films having
both surfaces coated with the n-butyl methacrylate--methyl methacrylate
copolymer were prepared.
After imaging ina XEROX 1048 plain paper copier, the films according to the
invention were shown to exhibit superior toner adhesion relative to the
control films, when assessed by the aforementioned tests.
EXAMPLE 3
The procedure of Example 1 was repeated save that the terpolymer was
applied at a concentration to yield a receiving layer having a dry
thickness of about 0.4 .mu.m.
Imaged sheets, prepared as in Example 1, again exhibited superior toner
adhesion relative to comparable control films.
EXAMPLE 4
The procedure of Example 1 was repeated save that the terpolymer was
applied at a concentration to yield a receiving layer having a dry
thickness of about 0.6 .mu.m.
Imaged sheets, prepared as in Example 1 again exhibited superior toner
adhesion relative to comparable control films.
EXAMPLE 5
The procedure of Example 1 was repeated save that the terpolymer
(vinylchloride/vinyl acetate/hydroxylated propyl acrylate:81/41/15), which
was applied to yield a receiving layer having a dry thickness of about 0.2
.mu.m, had an average molecular weight (number average) of about 4,000.
Imaged sheets prepared as in Example 1, exhibited improved toner adhesion
of the same order as that of the products of that Example.
EXAMPLE 6
The procedure of Example 1 was repeated save that the terpolymer which was
applied to yield a receiving layer having a dry thickness of about 0.2
.mu.m comprised vinyl chloride, vinyl acetate and maleic acid in a weight
ratio of 81:17:2.
Films imaged in accordance with Example 1 again exhibited superior toner
adhesion relative to control films according to GB-A-1447272.
EXAMPLE 7
The procedure of Example 1 was repeated save that the base film comprised a
biaxially oriented and heat-set film of polyethylene terephthalate of 125
.mu.m thickness having on one surface thereof a layer of a thermoset
acrylic resin comprising methyl methacrylate/ethylacrylate/methacrylamide
ina molar ratio of 46:46:8 and containing 25 mole % of methoxylated
melamine formaldehyde, the thermoset resin having been applied from an
aqueous latex between the longitudinal and transverse film drawing stages
and dried to yield a thermoset coating of about 0.03 .mu.m thickness.
The terpolymer coating medium of Example 1 was applied directly to the
acrylic surface of the film without prior treatment with a swelling agent,
and when tested by the procedure of Example 1 was observed to exhibit
excellent adhesion and abrasion-resistance.
EXAMPLE 8
The procedure of Example 1 was repeated save that the base film comprised
an opaque, voided biaxially oriented film of polyethylene terephthalate
containing 18% by weight of a finely-divided particulate barium sulphate
filler having an average particle size of 0.5 .mu.m.
When tested by the procedure of Example 1 the applied terpolymer coating
was again observed to exhibit excellent adhesion and abrasion-resistance.
* * * * *
|
|
 |
|
 |
Description |
|
