Note: Descriptions are shown in the official language in which they were submitted.
- 13392~g
HEAT-SENSITIVE RECORD MATERIAL AND MICROCAPSULE
Background of the Invention
l. Field of the Invention
This invention relates to thermally-responsive recol~cl
material. It relates to such record material in the form of sheets
coated with color-forming systems comprising chromogenic material,
lo and acidic color developer. This invention particularly concerns
a thermally-responsive record material containing crosslin~ed
internal phase capsules. More particularly this invention relates
to thermally responsive record materials containing novel
microcapsules, said microcapsules having a spongelike cross-linked
networked structure extending from the wall material into the core
of the capsules.
2. Description of Related Art
Capsule-containing thermal record systems are known in the
art. Patents such as Usami et al., U.S. 4,628,194 describes a heat-
sensitive record material containing microcapsules containing a
leuco dye and an organic solvent in a core thereof, wherein the
microcapsules are of a polymer having a glass transition point (Tg)
of about 60 to 200~C.
13392~
Brief Description of Drawing
Figures 1, 2 and 3 are photographs of cross-sectioned
microcapsules according to the invention at 37.5 x, 27 x and 27 x
magnification respectively. The photographs show the sponge-like
networked core structure extending from the wall material
substantially into the interior of the capsule.
In Fig 1 the integral outer wall or shell of the
microcapsule is evident on the horizon of the half sphere of the
capsule shown.
The Fig 2 cross-section shows the spongelike core
filling the interior of a microcapsule.
The Fig 3 cross-section shows the spongelike core
extending substantially into but not filling the entire interior
of the microcapsule.
Summary
One aspect of the invention relates to a microcapsule
comprising an integral outer wall material and an open-pore
sponge-like networked core extending from the wall material into
the microcapsule and defined by a plurality of substantially
discrete but extensively interconnected void spaces, and a core
material filling the void spaces, the microcapsule being a
reaction product of an excess, compared to a stoichiometric amount
for effecting encapsulation, of a polyisocyanate having a
functionality greater than two with an active hydrogen-containing
compound.
1~39248
Another aspect of the invention relates to a heat-
sensitive recording material including the above-mentioned
microcapsule.
The record material comprises a support and a recording
layer. The recording layer comprises, in one or more layers,
microcapsules containing a chromogenic material and an organic
solvent in the core of the microcapsules. A color developer is
included outside of the microcapsules in the recording layer or as
a separate layer. The color developer may be an acidic material or
electron pair acceptor. The color developer reacts with the
chromogenic material to form a mark. The microcapsules of the
invention have wall material which is the reaction product of an
excess of an aliphatic polyisocyanate with an active hydrogen
containing compound. Additionally, the microcapsules have a
thickened wall in that they have a cross-linked network structure
extending from, and of the wall material, extending substantially
into the core of the microcapsules. This
13392~8
results in the microcapsules having a spongelike internal core. The
spongelike internal core is an open core network structure
extending from or of the wall material. Like a chain of
interconnected lakes, the networked or spongelike core is defined
by a plurality of substantially discrete but extensively
interconnected void spaces.
Capsules according to the invention can be made by interfacial
polymerization. The capsules can be made using an internal phase
of chromogen, (preferably up to about 3.38 parts of a fluoran
lo compound); solvent, (preferably up to about 8 parts diphenyl
methane and up to about 18.63 parts secondary butyl biphenyl), and
an aliphatic polyisocyanate wall-forming material (preferably about
4.00 parts polyisocyanate). A catalyst (preferably up to about 0.5
parts dimethyl tin dilaurate) can optionally be employed.
The aliphatic polyisocyanate is preferably selected to be a
trimer isocyanate.
The above-described internal phase is emulsified in an
emulsifying aid, a protective colloid such as a mixture of low and
high viscosity polyvinyl alcohol (preferably up to about 2.5 parts)
low viscosity polyvinyl alcohol (20% solids), and (preferably up
to 3 parts) high viscosity polyvinyl alcohol (10% solids), and
distilled water (about 30 parts). In a preferred embodiment, when
the capsule diameter reaches approximately 10 ~m,
pentaethylenehexamine (PEHA) (about 3 parts 100% solids) is added
along with 50 parts distilled water. Stirring is continued for 24
hours at 50~C. In place of PEHA, multifunctional amines (about 3
parts at 100% solids) can be optionally employed and include the
/Page 3
1339248
following: tetraethylenepentamine;bis(hexamethylene)triamine;or
N,N~-bis(3-aminopropyl)ethylenediamine, or polyethylenimine at 50%
solids. Pentaethylenehexamine is preferred.
Detailed Description
The invention describes a heat-sensitive record system
comprising a novel microcapsule having a spongelike-in-appearance
networked polymeric structure extending substantially into the
interior of the microcapsule. The microcapsules of the invention
lo exhibit core thickening (i.e. wall thickening via a spongelike
network) from the isocyanate crosslinking. Thermal record materials
using such capsules have improved smudge resistance.
The capsules of the invention are a reaction product of a
polyisocyanate having a functionality greater than two, with an
active hydrogen-containing compound. The active hydrogen-containing
compound can include alcohols, amines, or water. Typically such
compounds include polyethylenimine or polyvinylalcohol. The
polyisocyanate is used in excess of the quantity of polymeric
reactant conventionally employed to form capsules for carbonless
paper which typically is less than 5% of the total capsule mass.
In a departure from the past, in capsules of the invention, the
polyisocyanate is employed and is deliberately selected to be used
in excess of the stoichiometric amount needed for encapsulation,
more particularly is used in excess in a concentration of 10-30~,
preferably 15~ by weight of the total capsule mass.
/Page 4
133924~
The isocyanates used in excess can participate in several
reaction pathways with active hydrogen containing compounds
including:
with alcohols:
R-N=C=O + RlOH ~R-HN-C-OR
o
with amines
R-N=C=O + R1-NH2 ~ R-HN-C-NH-R
o
with water
R-N=C=O + H20 ~R-NH-C-OH
O
~ degrades
R NH2+C02
+ R1-N=C=O
R-HN-C-NH-R
O
The isocyanates useful in the invention, more particularly are
aliphatic polyisocyanates having a functionality of more than one,
preferably a functionality of three. A functionality of two
optionally can be employed if for example the other monomer is
selected to have a functionality of three. A diisocyanate with a
functionality of two, for example, can give rise to extension of
the three dimensional network once branching with a trifunctional
monomer has initiated. Monomers with functionality of two can be
utilized to propagate network structures into the interior of the
/Page 5
- 13392~
capsule core, though further cross-linking of course would then not
be promoted through such monomer.
The microcapsules of the invention have a networked polymeric
structure extending substantially into the interior of the
microcapsules. This network core is a spongelike thickening of the
wall material in appearance defined by a plurality of discrete
extensively interconnected void spaces. This thickening of the wall
material is visually observable when cross-sections are made,
particularly of the larger microcapsules. Thermal record materials
lo made using these capsules are resistant to smudge. The polymeric
structure extending from the wall material substantially into the
core of the microcapsules is indirectly observable by the core
contents exhibiting higher viscosity. A cross-sectioned capsule
observed under magnification when poked with a blunt instrument
deforms and exudes core contents (internal phase solvent) through
cracks in the crosslinked IP (internal phase) material but
immediately receding into the microcapsule upon release of the
applied pressure.
The aliphatic polyisocyanates used in excess to form the wall
material of the capsules of the thermal record material of the
invention are aliphatic polyisocyanates selected from the formula
OCNRNCO or dimers or trimers thereof wherein R is a substituted or
an unsubstituted aliphatic group of 1 to 12 carbons. A convenient
formula for these isocyanates is (OCNRNCO)y wherein y is 1 to 3, R
as above defined, it being understood dimerization or trimerization
taking place via the reactive carbons and/or nitrogens. Oligomers
of the aliphatic polyisocyanates can also be advantageously
employed. By oligomer it is understood to include polymeric chains
of the trimer or dimer or isocyanate up to 10 units thereof, i.e.
/Page 6
13392~8
[(OCNRI~CO)y]X wherein x is an integer from one to 10. Typical of
such aliphatic polyisocyanates are trimethylene diisocyanate;
tetramethylene diisocyanate, propylene-1,2-diisocyanate, butylene-
1,2-diisocyanate, ethylidene diisocyanate, cyclohexyl-1,4-
diisocyanate, hexamethylene-1,6-diisocyanate, and include
isocyanurate modified polyisocyanates such as whose preparation is
described in U.S. 4,324,879. Useful isocyanates however also
include aromatic isocyanates such as 1,4-xylene diisocyanate and
m-xylene diisocyanate.
lo Useful aliphatic polyisocyanates include aliphatic
polyisocyanate resins. An example would be
CH~ NCO
~ CH3 ~ C
CH2 OC NH _ f '\~ \CH3
CH3 . CH~ NCO
/
1~l fH3 ~< C \CH3
CH3 CH2 C CH2 OC- NH
CH3
CH3NCO
C~12 0 NH f _ ~ C\H3
CH3
/Page 7
I3392~
Useful aliphatie polyisoeyanates include dimers and trimers
of all of the foregoing. Partieularly useful are trimers of
alkyldiisoeyanates such as RNCO
I
~o~N\ =o
ONCR~N~ /N~RNco
wherein R is an aliphatie group of 1 to 12 earbons.
lo More preferable are trimers of hexamethylene diisoeyanate such
as (CH2)6NC0
o~C,N~C ~o
OCN(CH2)5 ~ll~ (CH2)6Nc
In a preferred process of the invention, eapsules are formed
by interfacial polymerization. The resulting condensation polymer
is formed by the reaction of a film forming aliphatic
polyisocyanate used in exeess with a polyvinylalcohol and
polyethylenehexamine the presence of a catalyst. While catalyst is
not always neeessary, eonventional isoeyanate reaction promoting
or urethanation eatalyst can be advantageously employed. Dimethyl
tin dilaurate catalyst is preferred.
The film forming aliphatie polyisoeyanates employed in the
present invention are known in the art and available commercially.
Eligible polyisocyanates include those marketed by Bayer under
tradenames Desmodur TT, L, N, R and M; by Mobay Chemical Company
as Desmodur N-100, N-3200, N-3300, by Rhone-Poulenc as HDT, HDB,
'Page 8
' 133g24g
and HDTLV. Polyisocyanates having a molecular weight above about
500 are more desirable.
The material encapsulated, or in other words, contained within
the capsule walls formed in accordance with this invention, i.e.,
the capsular internal phase or core material of the capsule can be
any material which is substantially water-insoluble. A few of the
materials which can be utilized as capsule internal phases include,
among a multitude of others: water-insoluble or substantially
water-insoluble liquids, such as conventional carbonless
lo microcapsule internal phase solvents, oils, mineral oil, xylene,
toluene, kerosene, diphenylmethane, sec-butylbiphenyl, chlorinated
biphenyl, methyl salicylate, along with color formers or dyes such
as leuco or fluoran dyes.
Solvents such as diphenylmethane and sec-butylbiphenyl are
preferred. The solvent employed in the microcapsules of the
invention can be any material which has sufficient solubility for
the color former material, and which does not suppress or otherwise
adversely affect the color-forming reaction. Examples of eligible
solvents include, but are not limited to, those solvents
conventionally used for carbonless copy paper, including
ethyldiphenylmethane (U.S. Patent No. 3,996,405); benzyxylenes
(U.S. Patent No. 4,130,299); alkylbiphenyls such as propylbiphenyl
(U.S. Patent Nos. 3,627,581) and butylbiphenyl (U.S. Patent No.
4,287,074); dialkyl phthalates in which the alkyl groups thereof
have from 4 to 13 carbon atoms, e.g. dibutyl phthalate,
dioctylphthalate, dinonyl phthalate and ditridecylphthalate; 2,24-
trimethyl-1,3-pentanediol diisobutyrate (U.S. patent No.
4,027,065); C~o-C~4 alkyl benzenes such as dodecyl benzene; alkyl or
aralkyl benzoates such as benzyl benzoate; alkylated naphthalenes
/Page 9
133~2ll~
such as dipropylnaphthalene (U.S. patent No. 3,806,463); partially
hydrogenated terphenyls; high-boiling straight or branched chain
hydrocarbons; and mixtures of the above. The solvents can be solid
or liquid. Solids can be encapsulated as melted liquids if desired.
The isocyanate is first dissolved in the core material of what
will subsequently become the capsule and the resulting organic
phase emulsified in the continuous aqueous phase containing
protective colloid and, optionally, emulsifiers. An aqueous active
hydrogen containing compound such as a polyamine solution is added
lo to the resulting emulsion in a stoichiometric quantity sufficient
to effect encapsulation, based on the normal amount for
encapsulation polyisocyanate in the organic phase. The
polyisocyanate is kept in excess of the stoichiometric amount
needed for encapsulation. The active hydrogen containing compound
can be selected from water, polyvinyl alcohol or an aliphatic
multifunctional amine.
The core material can be a synthetic or natural solvent or oil
along with the color former which is a chromogenic material.
Additional examples of oils or solvent which dissolve the
chromogenic material include chlorinated biphenyl, chlorinated
paraffin, cottonseed oil, peanut oil, silicone oil, phthalate
esters, phosphate esters, sulphonate esters, monochlorobenzene,
also partially hydrogenated terphenyls, alkylated diphenyls,
alkylated naphthalenes, aryl ethers, aryl alkyl esters, higher-
alkylated benzene and others which may be used either individually
or in combination.
Diluents such as, for example, kerosene, n-paraffins and
isoparaffins are frequently added to the solvents.
/Page 10
1339248
To produce the microcapsules by polycondensation, the
isocyanate present in excess may be dissolved in the hydrophobic
core materials mentioned above and the resulting organic phase
emulsif ied in the continuous aqueous phase which contains
5 protective colloid and, optionally, emulsifiers. An aqueous or
water soluble polyamine solution may be added to the resulting
emulsion in the organic phase.
Active hydrogen containing compounds suitable for reaction
with the isocyanates mentioned above are multifunctional amines,
lo namely, aliphatic, primary or secondary polyamines, such as for
example polyethylenimine, pentaethylenehexamine,
tetraethylenepentamine, bis (hexa methylene) triamine, N,N'-bis (3-
aminopropyl ) ethylenediamine, 1, 2 -ethylene diamine, bis- ( 3 -
aminopropyl ) -amine, hydraz ine, hydraz ine-2 -ethanol, bis- ( 2 -
15 methylaminoethyl) -methylamine, 1, 4-diaminocyclohexane, 3-amino-l-
methyl-aminopropane, N-hydroxyethyl ethylene diamine, N-methyl-bis-
( 3 -aminopropyl) -amine, 1, 4-diamino-n-butane, 1, 6-diamino-n-hexane,
1, 2-ethylene diamine-N-ethyl sulphonic acid (in the form of an
alkali salt); l-aminoethyl-1,2-ethylene diamine and bis-(N,N'-
20 aminoethyl)-1,2-ethylene diamine. Hydrazine and its salts are also
regarded as diamines in the present context.
To emulsify and stabilize the emulsion formed, protective
colloids and emulsification aids can be added to the aqueous phase.
Example of such products acting as protective colloids are
2 5 carboxymethyl cellulose, gelatin and polyvinyl alcohol . Examples
of emulsifiers are ethoxylated 3-benzyl hydroxy biphenyl, reaction
products of nonyl phenol with different quantities of ethylene
oxide and sorbitan fatty acid esters.
Page 1 1
133924~
The microcapsules may be produced continuously or in batches.
Dispersion machines capable of generating a shear gradient are
generally used. Example of such machines are high-speed stirrers,
colloid mills, homogenisers, and ultrasonic dispersers. The
intensity of the turbulence generated during mixing is a
determining factor for the diameter of the microcapsules obtained.
The microcapsules of the invention have a void volume of 60
to 80% by volume. Void volume herein refers to the plurality of
void spaces in the spongelike network of the microcapsule interior.
The void spaces, of course it is understood will be filled with the
ingredients, solvent, chromogen etc., chosen to be encapsulated.
The void volume can be conveniently calculated by a variety
of conventional methods. For example, the formed microcapsules can
be weighed, the diameter measured and volume calculated. The
capsules then can be compressed to exude the contents, selected
to be a uniform solvent only. The microcapsules or contents can be
separately reweighed. Based on the weight and density of the
solvent, or weight and density of the wall material, the volume
occupied and therefore the void volume is readily ascertainable.
The microcapsules of the invention have a integral outer wall.
On visual observation this wall appears substantially continuous.
Of course it can be degraded, dissolved, or melted by the
environment in which the capsule is situated. Material selection
more so determines the mode of capsule disintegration as would be
apparent to those skilled in the art. It is from the wall inward
that the open pore network structure is substantially developed.
/Page 12
13392~
The capsules can be single oil drops or agglomerates and have
a narrow particle size distribution. The ratio by weight of core
material and sponge-like network to shell material is from 75-90
to 25-10.
In the process according to the invention, the formulations
for producing the microcapsules are adjusted in such a way that
suspensions containing from 10 to 60% by weight of capsules are
obtained.
The polymerization reaction is a polycondensation conducted
lo at a starting pH which is acidic, around pH of 5. As reaction
proceeds, alkalinity increases to about pH 7. With use of amines
the pH increases to above about 9. The time and temperature
requirements are variable to optimize the reaction. The pH need not
be specifically modified as reaction proceeds even under the
developing alkaline conditions.
After the reaction has progressed to the point where the
capsule walls have been solidified and, in that respect, the
capsule manufacture is completed, the capsules can be separated
from the manufacturing vehicle by filtering and then washed with
water. The capsule walls are dried by placing the capsules in a
forced air dryer. It should be understood, however, that the
capsules need not have dried walls or even be separated from the
liquid vehicle prior to their use. If it is desired or required
for some intended purpose, the capsule product of this invention
can be supplied as a slurry of capsules in a liquid carrier, either
with the manufacturing vehicle or not, such as for use in a paper
coating composition, or the like.
/Page 13
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Individual capsules prepared by the present invention are
substantially spherical and can be manufactured having diameters
of less than 1 micron to about 100 microns, the preferred size
range being from about 1 to about 10 microns, in diameter.
5The heat-sensitive record system includes a substrate or
support material which is generally in sheet form. For purposes of
this invention, sheets can be referred to as support members and
are understood to also mean webs, ribbons, tapes, belts, films,
cards and the like. Sheets denote articles having two large surface
lodimensions and a comparatively small thickness dimension. The
substrate or support material can be opaque, transparent or
translucent and could, itself, be colored or not. The material can
be fibrous including, for example, paper and filamentous synthetic
materials. It can be a film including, for example, cellophane and
15synthetic polymeric sheets cast, extruded, or otherwise formed.
Invention resides in the color-forming composition coated on the
substrate. The kind or type of substrate material is not critical.
The components of the color-forming system are in a proximate
relationship meaning, a substantially contiguous or near contiguous
20relationship, substantially homogeneously distributed throughout
the coated layer or layers of material deposited on the substrate.
In manufacturing the record material, a coating composition is
prepared which includes a fine dispersion of the components of the
color-forming system, binder material typically a polymeric
25material, surface active agents and other additives in an aqueous
coating medium. The composition can additionally contain inert
pigments, such as clay, talc, aluminum hydroxide, calcined kaolin
clay and calcium carbonate; synthetic pigments, such as urea-
formaldehyde resin pigments; natural waxes such as Carnuba wax;
~Page 14
1339248
synthetic waxes; lubricants such as zinc stearate; wetting agents;
defoamers, and antioxidants. Clearly the components of the color-
forming system can be assembled in one layer or with individual
components partially or full segregated into multiple layers, such
configuration being readily apparent to the skilled worker in the
field.
The color-forming system components are substantially
insoluble in the dispersion vehicle (preferably water) and except
for the microcapsules are ground to an individual average particle
size of between about 0.3 micron to about 10 microns, preferably
about 1-3 microns. A binder can be included. The binder can be a
polymeric material and is substantially vehicle soluble although
latexes are also eligible in some instances. Preferred water
soluble binders include polyvinyl alcohol, hydroxy ethylcellulose,
methylcellulose, methyl-hydroxypropylcellulose, starch, styrene
maleic anhydride salts, modified starches, gelatin and the like.
Eligible latex materials include polyacrylates, styrene-butadiene-
rubber latexes, polyvinylacetates, polystyrene, and the like. The
polymeric binder is used to protect the coated materials from
brushing and handling forces occasioned by storage and use of
thermal sheets. Binder should be present in an amount to afford
such protection and in an amount less than will interfere with
achieving reactive contact between color-forming reactive
materials.
Coating weights can effectively be about 3 to about 9 grams
per square meter (gsm) and preferably about 5 to about 6 gsm. The
practical amount of color-forming materials is controlled by
economic considerations, functional parameters and desired handling
characteristics of the coated sheets.
~Page 15
13392~
Eligible chromogenic compounds, such as the phthalide,
leucauramine and fluoran compounds, for use in the color-forming
system are well known color-forming compounds. Examples of the
compounds include Crystal Violet Lactone (3,3-bis(4-
5 dimethylaminophenyl)-6-dimethylaminophthalide, U.S. Patent No. Re.
23,024); phenyl-, indol-, pyrrol-, and carbazol-substituted
phthalides (for example, in U.S. Patent Nos. 3,491,111; 3,491,112;
3,491,116; 3,509,174); nitro-, amino-, amido-, sulfonamido-,
aminobenzylidene-, halo-, anilino-substituted fluorans (for
example, in U.S. Patent Nos. 3,624,107; 3,627,787; 3,641,011;
3,642,828; 3,681,390); spirodipyrans (U.S. Patent No. 3,971,808);
and pyridine and pyrazine compounds (for example, in U.S. Patent
Nos. 3,775,424 and 3,853,869). Other specifically elegible
chromogenic compounds, not limiting the invention in any way, are:
3-diethylamino-6-methyl-7-anilino-fluoran (U.S. Patent No,
3,681,390); 2-anilino-3-methyl-6-dibutylamino-fluoran (U.S. Patent
4,510,513) also known as 3-dibutylamino-6-methyl-7-anilino-fluoran;
3-dibutylamino-7-(2-chloroanilino) fluoran; 3-(N-ethyl-N-
tetrahydro f urf uryl amino ) - 6 -methy l - 7 - 3, 5 ' 6 -
tris(dimethylamino)spiro[9H-fluorene-9,1'(3'H)-isobenzofuran]-3'-
one; 7-(1-ethyl-2-methylindol-3-yl) -7-(4-diethylamino-2-
ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one (U.S. Patent No.
4,246,318); 3-diethylamino-7-(2-chloroanilino)fluoran (U.S. Patent
No. 3,920,510); 3-(N-methylcyclohexylamino)-6-methyl-7-
anilinofluoran (U.S. Patent No. 3,959,571); 7-(1-octyl-2-
methylindol-3-yl) -7- (4-diethylamino-2-ethoxyphenyl) -5,7-
dihydrofuro-3,4-b]pyridin-5-one; 3-diethylamino-7,8-benzofluoran;
/Page 16
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3,3-bis(l-ethyl-2-methylindol-3-yl)phthalide; 3-diethylamino-7-
anilinofluoran; 3-diethylamino-7-benzylaminofluoran; 3'-phenyl-7-
dibenzylamino-2,2'-spirodi-[2H-l-benzopyran] and mixtures of any
of the foregoing.
Examples of eligible acidic developer material include the
compounds listed in U.S. Patent No. 3,539,375 as phenolic reactive
material, particularly the monophenols and diphenols. Eligible
acidic developer material also includes, without being considered
as limiting, the following compounds which may be used individually
lo or in mixtures: 4,4'-isopropylidinediphenol (Bisphenol A); p-
hydroxybenzaldehyde; p-hydroxybenzophenone; p-hydroxypropiophenone;
2,4-dihydroxybenzophenone; l,l-bis(4-hydroxyphenyl)cyclohexane;
salicyanilide; 4-hydroxy-2-methylacetophenone; 2-acetylbenzoic
acid; m-hydroxyacetanilide; p-hydroxyacetanilide; 2,4-di-
hydroxyacetophenone; 4-hydroxy-4'-methylbenzophenone; 4,4'-
dihydroxybenzophenone; bis(3-allyl-4-hydroxyphenyl)sulfone, 2,2-
bis(4-hydroxyphenyl)-4-methylpentane; benzyl 4-hydroxyphenyl
ketone; 2,2-bis(4-hydroxyphenyl)-5-methylhexane; ethyl-4,4-bis(4-
hydroxyphenyl)-pentanoate; isopropyl-4,4-bis(4-
hydroxyphenyl)pentanoate; methyl-4,4-bis(4-hydroxy-
phenyl)pentanoate; allyl-4,4-bis(4-hydroxyphenyl)pentanoate; 3,3-
bis(4-hydroxyphenyl)-pentane; 4,4-bis(4-hydroxyphenyl)-heptane;
2,2-bis(4-hydroxyphenyl)-l-phenylpropane; 2,2-bis(4-
hydroxyphenyl)butane; 2,2'-methylene-bist4-ethyl-6-
tertiarybutylphenol); 4-hydroxycoumarin; 7-hydroxy-4-
methylcoumarin; 2,2'-methylene-bis(4-octyl phenol); 4,4'-
sulfonyldiphenol; 4,4'-thiobis(6-tertiarybutyl-m-cresol); methyl-
p-hydroxybenzoate; n-propyl-p-hydroxybenzoate; benzyl-p-hydroxy-
benzoate; 4-(4-(1-methylethoxy)phenyl) sulphonyl phenol. Preferred
/Page 17
133~2~8
among these are the phenolic developer compounds. More preferred
among the phenol compounds are 4,4'-isopropylindinediphenol, ethyl-
4,4-bis(4-hydroxyphenyl)-pentanoate, n-propyl-4,4-bis(4-
hydroxyphenyl)pentanoate, isopropyl-4,4-bis(4-
hydroxyphenyl)pentanoate, methyl-4,4-bis(4-hydroxy-
phenyl)pentanoate, 2,2-bis(4-hydroxyphenyl)-4-methylpentane, p-
hydroxybenzophenone, 2,4-dihydroxybenzophenone, l,l-bis(4-
hydroxyphenyl)cyclohexane, and benzyl-p-hydroxybenzoate; 4-(4-(1-
methylethoxy)phenyl) sulphonylphenoland4,4'-[1,3-phenylenebis(l-
lo methylethylene]bisphenol. Acid compounds of other kind and types
are eligible. Examples of such other compounds are phenolic novolak
resins which are the product of reaction between, for example,
formaldehyde and a phenol such as an alkylphenol, e.g., p-
octylphenol, or other phenols such as p-phenylphenol, and the like;
and acid mineral materials including colloidal silica, kaolin,
bentonite, attapulgite, hallosyte, and the like. Some of the
polymers and minerals do not melt but undergo color reaction on
fusion of the chromogen. Of the foregoing particularly the phenol
type of compounds are more preferable acidic developer materials.
A modifier (also known as a sensitizer) such as a 1,2-
diphenoxyethane can be included. However, the capsule solvent acts
as a modifier. A modifier typically does not impart any image on
its own but facilitates reaction between the mark-forming
components. Modifiers are described in U.S. patent No. 4,531,140.
Other modifiers for example include acetoacet-o-toluidine, phenyl-
1-hydroxy-2-naphthoate, dibenzyloxalate, diphenoxy ethane and para-
benzylbiphenyl. The person of ordinary skill in this art
appreciates the modifier or the solvent can be a low melting point
solid.
/Page 18
~ 1339248
The following examples are given to illustrate some of the
features of the present invention and should not be considered as
limiting. In these examples all parts or proportions are by weight
and all measurements are in the metric system, unless otherwise
stated.
In all examples illustrating the present invention a
dispersion of a particular system component (unencapsulated) was
prepared by milling the component in an aqueous solution of the
binder until a particle size of between about 1 micron and 10
lo microns was achieved. The milling was accomplished in an attritor
or other suitable milling device. The desired average particle size
was about 1-3 microns in each dispersion.
Example
Interfacial capsules were made using an internal phase of 3.38
parts fluoran based color forming agent, 8.00 parts diphenyl
methane, 18.63 parts secondary butyl biphenyl, 4.00 parts aliphatic
polyisocyanate (HDT or N-3300) and 0.50 parts dimethyl tin
dilaurate catalyst. This internal phase was emulsified in a mixture
of 2.50 parts low viscosity polyvinyl alcohol (20% solids), 3.00
parts high viscosity polyvinyl alcohol (10% solids), and 30.00
parts distilled water until the capsule size was under 10 um, then
3.00 parts PEHA (100% solids) was slowly mixed into the emulsion.
Fifty (50) parts distilled water was added to the emulsion which
was then stirred for 24 hours at 50~C.
The thermally-sensitive coating consisted of 2.91 parts
capsules, 2.30 parts medium viscosity polyvinyl alcohol (10%
solids), 1.17 parts small media milled coreactant, 0.20 parts zinc
stearate, 0.50 parts filler material and 17.93 parts distilled
/Page 19
13392~8
water. The coating was applied to 34 lb./ream base stock paper to
get an 8 lb. coating/ream layer. Test results showed Macbeth image
intensities of 1.30 in combination with opacimeter readings of 91.3
for frictional smudge, 100.0 for static smudge and 86.6 for
background brightness.
A CB coating was made that consisted of 2.91 parts capsule,
5.00 parts starch binder tl~% solids), 0.75 parts stilt starch,
0.48 parts clay filler and 16.97 parts distilled water. This
coating was applied to 34.5 lb./ream base stock paper to get a 6.0
lb. coating/ream layer. Test results showed an opacimeter measured
typewriter intensity of 95.0, frictional smudge of 91.0 and static
smudge of 100.0 against a standard CF. Based on past experience
this combination of functionalities would be indicative of a high
viscosity (i.e. thickened) internal phase capsule.
When large 3-4mm sized capsules were made, a sponge-like
network, defined by a plurality of discrete extensively
interconnected void spaces, from the wall material extending into
the capsules was visibly evident upon cross-sectional examination.
The principles, preferred embodiments, and modes of operation
of the present invention have been described in the foregoing
specification. The invention which is intended to be protected
herein, however, is not to be construed as limited to the
particular forms disclosed, since these are to be regarded as
illustrative rather than restrictive. Variations and changes can
be made by those skilled in the art without departing from the
spirit and scope of the invention.
/Page 20
