Note: Descriptions are shown in the official language in which they were submitted.
WO 95/07187 PCT/GB94J01921
z17o740
Title:- "Pressure-sensitive record materials"
Description of invention
This invention relates to pressure-sensitive record materials of the kind
comprising a base sheet, typically of paper, coated with a rupturable material
confining droplets of a solution of colour-forming substances, which when
released
by rupture of the material undergo a colour-forming reaction to produce an
image
either on the base sheet itself or on a further, receptor sheet in face-to-
face
contact with the coated face of the base sheet.
In particular, but without limitation, the invention is applicable to so-
called "carbon-less" copy papers which rely on two coatings formed
respectively
on the contiguous fares of superimposed sheets of paper, namely a coating
containing the colour-forming substance in the micro-capsules, on the back of
the
uppermost sheet (usually known as a CB coating) and a coating of a receptor
layer on the front of the lowermost sheet (usually known as a CF coating).
Colour-forming chemicals are typically dissolved in an oily solvent and
encapsulated by well known techniques, and when such capsules are ruptured by
mechanical pressure, as by impact of a type bar of a typewriter, the chemicals
are
released and react to form a visible mark on the CF coating of the adjacent
sheet.
Alternatively, the droplets may be dispersed throughout a continuous
phase coating of the rupturable material.
Conveniently, paper for use in such copying systems is of three types,
distinguished by their coatings, namely CB sheets having a CB coating on the
underside to form the top sheet of the set, CF sheets having a CF coating on
the
upper side to form the bottom sheet of a set, and optionally CFB sheets having
a CF coating on the upper side and a CB coating on the underside to form one
or more intermediate sheets of a set where required. Such coatings are
normally
applied by a continuous process to cover the entire area of the appropriate
face
of the sheet.
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WO 95/07187 PCT/GB94/01921
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Conventionally colour-formers, e.g. various chromogenic materials,
have normally been dissolved in a range of organic solvents, often aromatic
solvents, which afford adequate solubility for such colour-formers and enable
a
good image to be produced.
Other proposals have been made with regard to the use of alternative
solvents, which have environmental advantages, for the colour-formers, but so
far
no wholly acceptable alternative solvent has been found.
Whilst the use of animal or vegetable oils as solvents for colour-
formers is suggested in the patent literature, it is generally acknowledged
that they
do give rise to solubility problems. For example, British Patent 1429578
includes
various vegetable oils in a list of suitable solvents for conventional colour-
formers
and admits that some of the listed solvents have low solubility for the colour-
formers, but they can be used because the invention requires different
concentrations of colour-former solution at different positions within the
coating,
so that the relatively poor solvents can be used for the more dilute colour-
former
solutions required by that invention.
US patent 4859650 also proposes the use of plant, animal or paraffin
oils as solvents, and also admits that these are relatively poor solvents for
conventional colour-formers, but proposes to overcome this difficulty by the
use
of a special type of triphenylmethane leuco-dye which is more soluble in such
oils,
preferably together with the addition of up to 20% of a conventional synthetic
solvent. The use of such special leuco-dyes may be more costly than more
conventional colour-formers and since the addition of synthetic solvents is
required in practice to achieve an acceptable result, the full environmental
advantages of natural solvents are muted.
Indeed many different systems of colour-formers and solvents have ,
been proposed, including some which employ, at least in part, animal or
vegetable
oils as solvents. European Patent specification 0520639 A1 published 30th
December 1992 contains a lucid summary of such proposals which are directed
to various improvements in the performance of the copy paper in various
respects,
,~ WO 95/07187 . PCTIGB94/01921
3
but generally where the use of animal or vegetable oils as solvents is
proposed
either it is found necessary to use a synthetic oil as a co-solvent, or
systems using
animal or vegetable oils as solvents have been evaluated only as control
examples
to verify the superior performance of other solvent/colour-former systems, for
example as in European Patent specification 0520639 itself.
Against this background, the present invention arises from a discovery
that natural vegetable and animal oils can successfully be employed, without
necessarily employing any conventional synthetic solvent, for a group of
colour-
formers in conventional micro-capsules, and more particularly that
sufficiently
concentrated solutions of this group of colour-formers in such vegetable or
animal
oils can be achieved to provide good imaging, and good shelf-life
characteristics.
In accordance with one aspect of the present invention we provide a
composition, for use as the internal phase of a coating of rupturable material
for
application to a base sheet to form pressure-sensitive record material, the
composition comprising one or more colour-formers of which at least 90% are
monoamino and/or diamino fluoran derivatives, dissolved in a solvent
comprising
80% to 100% of one or more vegetable and/or animal oils.
It has been found that whilst such oils do not afford sufficiently good
solubility for most colour-formers in current use, they can be used for colour-
formers based on amino fluorans.
However, to achieve the required solubility it may be necessary to
perform the step of dissolving such colour-formers at a temperature above that
normally employed, for example in the range 100°C to 135°C and
in accordance
with another aspect of the invention we provide a method of manufacturing a
pressure-sensitive record material of the kind comprising a base sheet coated
with
one or more colour-formers characterised in that at least 90% of said colour
formers are monoamino and/or diamino fluoran derivatives, and said colour-
formers are dissolved in a solvent comprising 80% to 100% of an animal or
vegetable oil, dissolution of said colour-formers being carried out at a
temperature above 100°C, and typically at up to 135°C.
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Once such a solution has been formed at such an elevated
temperature, it can subsequently be cooled and processed in generally
conventional manner to form the required rupturable coating to provide a
product
which has a good shelf life and good image forming properties in a manner
which
could not be achieved by dissolving other colour-forming substances, such as
triphenylmethane leuco-dye stuffs, in the same solvents at the-temperatures,
generally below 100°C, normally employed.
In this way, we have found it possible to use a solvent which is up to
100% animal and/or vegetable oil.
The oils which may be used include rape seed oil, cotton seed oil, olive
oil, corn oil, wheat oil, soy oil, castor oil, thistle oil, ground nut oil,
sunflower oil,
grape seed oil, coconut oil, sesame oil, whale oil, sperm oil, fish oil cod-
liver oil
or any mixtures of one or more of these.
The colour-forming substances which may be employed in accordance
with the invention include chromogenic materials such as particularly, but not
exclusively,
2'-(octylamino)-6'-(diethylamino) fluoran,
2'-anilino-3'-methyl-6'(diethylamino) fluoran,
6'(diethylamino)-2'-(1,1-dimethylethyl) fluoran,
6'-(dibutylamino)-3'-methyl-2'-(phenylamino)-spiro[isobenzofuran-
1(3H),9'-[9HJxanthen)-3-one,
which are fluoran derivatives, as distinct from triphenalmethane leuco-dye
stuffs.
One or more such chromogenic materials can be totally dissolved in
a solvent consisting of up to 100% vegetable and/or animal oils to provide an
internal phase for use in pressure-sensitive copying systems. It will however
be
understood that the solution may contain other additives to modify the
characteristics or performance of the copying systems.
According to a further aspect of the invention we provide a pressure-
sensitive record material comprising a base sheet coated with a rupturable
~.,n;,ENp=D SHEET
CA 02170740 2002-02-11
material confining droplets of an internal phase comprising a solution made in
accordance with the above-specified method.
In accordance with a still further aspect of the invention we provide
a method of forming micro-capsules containing a solution of colour-formers in
an
organic solvent by coacervation, characterised in that at least 90°~0
of said colour-
formers comprise monoamino and/or diamino fluoran derivatives, dissolved at a
temperature in excess of 1()0°C in a solvent comprising 80% to 100% of
one or
nu>re vegetahle and/or animal oils to form an internal phase solution which is
subsequently subject to coacervation at a temperature helow 70°C.
Apart from the preparation and composition of the internal phase or
core material, the micro-capsules in accordance with the invention and used
for
the pressure-sensitive copying paper are prepared by conventional methods and
as such do not require an in depth description.
Using as internal phase the solution of chromogenic materials
dissolved in animal and/or vegetable oil, micro-capsules can be prepared by
the
coacervation of gelatine and one or more other polymers such as carboxymethy)
cellulose, gum arahic etc., in conventional manner.
The micro-capsules produced may be blended with other additives
including a binder, such as starch or polyvinyl alcohol or a mixture of both,
and
undissolved buffer or "stilt" material such as calibrated wheat starch or
finely
ground cellulose floc (or a mixture of both) to prevent premature rupture of
the
coating composition during processing and suhsequent handling.
The shove coating composition may be applied to a range of paper
substrates (40-ISOg/rn-') by use of standard coating techniques designed to
apply
a closely monitored wet film weight e.g. air knife, offset gravure, metering
roll.
In order to effect total dissolution of the chromogenic materials at the
required concentration it is necessary to raise the temperature of the animal
and/or vegetable oils to temperatures well above those required for
conventional
WO 95107187 PCTIGB94/01921
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6
internal phase solvents such as alkylated naphthalene, chlorinated paraffins
and
hydrogenated terphenyls.
Experiment has shown that in order to affect total dissolution of the
chromogenic materials it is necessary to raise the temperature of the oil to
100°C-
135°C as compared with the temperatures required for conventional
internal
phase solvents which are generally below 100°C.
The invention is illustrated by the following non-limiting specific
examples. All formulations are expressed by weight unless otherwise stated,
and
the specific colour formers employed in these examples are as follows:-
A) 2'-(Octylamino)-6'-(diethylamino)fluoran:
NH-(CH 2 ) 7- Me
(A)
0
B) 2'-Anilino-3'-methyl-6'(diethylamino)fluoran:
Et N Me
NHPh
(B)
"~ WO 95/07187 PCT/GB94/01921
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7
C) b'-(diethylamino)-2'-(l,l-dimethylethyl)-spiro(isobenzofuran-1(3H),9'-
[9H)xanthen]-3-one,
Et2N -
E3u-t
(C)
0
D) 6'-(dibutylamino)-3'-methyl-2'-(phenylamino)- Spiro[isobenzofuran-
1 (3f1 );9'-[9H)xanthen]-3-one,
~n-Bu ~ ZN Me
NH Ph
(D)
'o
where - Me = methyl (CH;~-)
Et = ethyl (CH3-CH,-)
Bu-t = tert-butyl ((CHI),-CH-Cfl,-)
Ph = phenyl (C~,H~,-)
The above-identified colour-formers were used in the following
combinations as set out in Table 1.
WO 95/07187 PCT/GB94/01921
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TABLE 1
COLOUR EXAMPLE EXAMPLE
FORMER 1 2
A 65.0 65.0
B 20.0 20.0
C 15.0 7.5
D - 7.5
100 100
EXAMPLE 1:
(i) Preparation of internal Phase Solution
The three selected chromogenic materials used in this
example (A,B,C) were mixed in the proportions indicated in Table I such that
an
intense black print is subsequently obtained in use.
The mixture of chromogenic materials was dispersed into
deodorised refined rape seed oil and the temperature raised to 115°C.
In order to ensure total dissolution the temperature was held
for 30 minutes. The concentration of the chromogenic materials dispersed in
rape
seed oil was 6.9%.
The dissolution characteristics of the solvent system during
the temperature rise and fall were determined by turbidimetry with the
following
results:-
Temperature C Dissolution %
65 19
81 41
99 87
11~ 98
56 97
35 96
27 97
showing that substantially complete solution was attained and maintained.
9
The above solution was then allowed to cool at 60°C and maintained
at this temperature.
(ii) Preparation of Emulsion
The internal phase solution was emulsified in a mixture of gelatine and
carboxymethyl cellulose (CMC) at 55~ 5°C to a mean capsule size of
approximately S ~cm as measured using a Coulter Counter.
(iii) Coacervation Process
The emulsion (ii above) was diluted by the addition of soft water and
the pH adjusted by the addition of 20% Sodium Hydroxide to a pH value 9.0 -
9.5.
Dilute acetic acid was added to reduce the pH of the gelatine below
the isoelectric point resulting in a change in charge of the gelatine and, on
further
acidification, the formation of liquid coacervates results from the phase
separation
and inter-relation with the negatively charged C.M.C. in conventional manner.
On further acidification the liquid coacervates are attracted to the
nucleus or core material (i.e. the internal phase solution produced at (i)
above)
and coalesce to form a liquid wall.
When further acidification resulted in the desired degree of clustering
acidification was stopped.
(iv) Cooling
The dispersion was cooled at 8°C - 10°C in order to gel the
liquid walls
of the coacervates.
At 8°C - 10°C the liquid walls were cross linked by the
addition of an
aldehyde (e.g. formaldehyde) and followed by an increase in pH by the further
addition of 20% sodium hydroxide to pH 9Ø
(v) Ageing,/1=inishing
The cross linked dispersion was returned to amhient temperature and
allowed to homogenise and condition (e.g. age) for a predetermined period (1-3
hours).
After ageing the resultant capsule dispersion was blended with a
suitable binder (e.g. starch or starch/P.V.A. mixture) and a suitable "stilt
buffew'
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WO 95/07187 PCT/GB94/01921
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to
(e.g. cellulose floc or calibrated wheat starch) to produce a mixture suitable
for
coating onto a sheet material by conventional means.
The pressure-sensitive record material thus produced has been found
to have a good shelf life and to provide intense colour-forming.
EXAMPLE 2:
The four selected chromogenic materials (A,B,C,D) were mixed in the
proportions indicated in Table I such that an intense black print is
subsequently
obtained in use. In this example these four chromogenic materials were
initially
dispersed in a solvent comprising deodorised refined rape-seed oil at a
concentration of 6.9% at ambient temperature and the temperature was increased
to 115°C and then decreased.
The subsequent preparation of the emulsion the co-acervation process,
cooling and ageing/finishing proceeded as in Example 1.
Laboratory scale encapsulations have also been made and tested with
similar good results, utilising other vegetable oils such as sunflower oil and
animal
oils such as cod liver oil and beef dripping, and various mixtures of such
oils.
Whilst in the above-described Examples the colour-formers used are
all fluoran derivatives and the solvents are 100°lc animal or vegetable
oil, it is to
be understood that additional non-fluoran colour-formers may be included at up
to 10% of the colour-former formulation, and that other non-animal or
vegetable
oil solvents may be included in the solvent at up to 20°lc of the
solvent if required,
although the use of 100% fluoran colour-formers and 100% animal or vegetable
oils as solvents is entirely satisfactory.
