H I G ~I SOL I D S CB~
FXEI.D OF T_IE INVENTION
The present in~ention relates to a process for the production of a high solids content, aqueous~
microcapsule-containing, printing ink and to the printing inks so produced. More particularly, the present invention relates to the production of high solids content, aqueous, CB printing inks which may be press-applied in the production of carbonless copy paper.
~ACKG~O~LD OF THE INVENTION
In the manufacture of pressure-sensitive recording papers r better known as carbonless copy papers, a layer of pressure-rupturable microcapsules containing a solution of colorless dyestuff precursor is normally coated on the back side of the front sheet of paper of a carbonless copy paper set. This coated backside is known as the CB coating. In order to develop an image or copy, the CB coating must be mated with a paper containing a coating of ~ suitable color developer, also known as dyestuff acceptor, on its front. This coated front color developer coating is called the CF coating. The color developer is a material, usually acidic, capable of forming the color of the dyestuff by reaction with the dyestuff precursor.
Marking of the pressure-sensitive recording papers is effected by rupturing the capsules in the CB
coating by means of pressure to cause the dyestuff precursor solution to be exuded onto the front of the mated sheet below it. The colorless or slightly colored dyestu~f, or dyestuff precursor, thell reacts with the color developer in the areas at which pressure was applied, thereby effecting the colored marking. Such mechanism for the technique of producing pressure-sensitive recording papers is well known.
Among the well known color developers used on CF
record sheets are phenolic~type resins, such as acetylated phenolic resins, salicylic acid modified phenolics and, particularly, novolac type phenolic resins.
Among the well known basic, reactive, colorless chromogenic dye precursors useful for developing colored marks when and where applied to a receiving sheet coated with such color developers are Crystal Violet Lactone ~CVL), the p-toluenesulfonate salt of Michler's Hydrol or 4,4'-bis(diethylamino)benzhydrol, Benzoyl Leuco Methylene Blue (BLMB), Indolyl Red, Malachite Green Lactone, 8'-methoxybenzoindoline spiropyran, Rhodamine Lactone, and mi~tures thereof.
Microencapsulatioll has been used in the production of carbonless copy papers for some time. One of the major techniques involves phase separation from an aqueous solution. The complex coacervation process (U.S.
Patent 2,800,457 and others) ~alls into this category. In such a process, a phase separation into a liquid condensed colloid phase and a dilute colloid phase results from two oppositely charged condensed colloids neutralizing each other. Under appropriate conditions, the condensed colloid phase can be induced to first surround and envelope the oil droplets, and then be hardened to form the microcapsules.
Z~ 7~
Another method of producinq CB microcapsules involves polymerization or interfacial crosslinking.
Typically a film forming substance, sueh as an epoxy compound, a polyvalent isocyanate, or a polyacyl halide reactant is dissolved in a hydrophobic oily solution phase and a coreactant such as a polyfunctional amine or a polyvalent hydroxy compound is dissolv~d in a hydrophilic aqueous solution phase. An emulsion is formed from the two phases, the reactant and coreactant combine in the emulsion, and a wall is formed by interfacial polymerization or interfacial crosslinking around droplets of the oily solution phase (internal phase~ to form the microcapsules. See, for example, Kan patent No. 3,432,327 wherein a large number of reactants a~d coreactants are designated. Generally, the fragile capsules produced by the simple interfacial polymerization/crosslinking are inadequate for the processing procedures needed for preparing car~onless papers, namely, filtration and dispersion into ink vehicles.
A method to improve the strength of capsule walls is shown in U.S. Patent 4,404,251, which discloses printing ink containing microcapsules containing dye precursors. The microcapsules are made by polyaddition of a polyisocyanate and a polyamine, and the aqueous phase may contain protective colloids and emulsifiers.
Reference is also made to U.S. Patent No.
9jl93,889 which discloses microcapsules and a process for the production of microcapsules, the walls of which consist of polycondensates of a ilm-forming aliphatic polyisocyanate containing at least one biuret group, or polyaddition products thereof, with a chain e~tending agent. The chain extending agent is preferably either water, a polyol or a polyamine. It is stated in that patent that the so-produced microcapsules have improved toughness, show adequate crosslinking density, and, therefore, are only slightly permeable to easily volatile encapsulated substances.
Another method for dealing with the problems of fragile microcapsules is disclosed in U.S. Patent 4,435,340, wherein an isocyanate is used in the hydrophobic phase and a polyamine, such as a low molecular weight polyamine, is used in the hydrophilic phase.
Microcapsules are formed by inter~acial polymeri7.ation.
U.S. Patent 4,356,108 also discloses an encapsulation process by interfacial r~action of an isocyanate and a low molecular weight polyamine.
Finally, an improvement on the interfacial polymerization method of encapsulation is found in U.S.
Patnet No. 4,729,792 issued March 8, 1988.
(Docket STD 156 PA), iled on an even date herewith. That improvement involves reacting a crosslinking agent, such as a polyisocyanate, dissolved in the oily solution phase with a polysalt made up of a high molecular weight polyanion, such as casein, and a low molecular weight polycationic polyamine, dissolved in the aqueous solution phase. That process results in microcapsules which are thicker and stronyer than microcapsules produced by ordinary interfacial polymerization.
Whichever encapsulation method is used, a problem remains in terms of the ink vehicle and CB coating method. According to the oldest prior art concerning the technology oE CB coating, such coatiny was carried out 2~
with an aqueous coating composition o~er the entir0 surface of the substrate, as shown in German Offenlegungsschrifts Nos. 1,934,437 and 1,955,542. The process described in these patents has the disadvantage that, following application of the coating co~position, the water is evaporated and this requires a considerable input of energy. Additionally, the need for drying requires the use of a comple~ and expensive apparatus for an aqueous coating composition. Another problem concerns removal of the polluted water which emanates from production and from the puriflcation of the aqueous coating composition.
If volatile organic solvents are used in the production of the coatings, the excess solvent also has to be evaporated in order to dry the coating. This results in the formation of solvent vapors which are particularly dangerous.
There are also numerous known processes for applying coating compositions to a paper substrate.
According to the prior art, aqueous or solvent-containing coatings may be applied to a paper substrate by rotogravure or fle~oprinting, as shown in U.S. Patents 3,016,308 or 3,914,511. These processes also have the disa~vantage that the coatings must be subseguently dried. For these reasons, it was proposed, as shown in U.S. Patents 3,079,351 and 3,684,549, to take up the microcapsules in wa~es and to coat the paper substrate with hot melt systems o~ this type. See also, U.S.
Patents 4,112,138 and 4,097,619 which disclose processes for the application o~ microcapsules to paper by means o a non--aqueous solvent~~ree hot melt system, or by means of 7~
a radiation-curable system. In U.S. Patent 4,161,570 microcapsules are added to a radiation-curable substance without irst spray-drying. Although thes~ proposed measures avoid removal of the solvents, the wa~-like coating changes the character of the paper bec~use relative large quantities of wax must be applied.
Additionally, the rnelt systems are applied by means of hot carbon printing machines which, although enabling printing, coating with waxes, and finishing to be combined in an online system, always require a separate installation for each process step~
Accordingly, it remains more desirable to use an aqueous-based CB ink if the solids content of that ink is high enough to avoid the problems found with typical aqueous-based CB inks. The major problem with aqueous CB
inks is the large drying capacity required. For example, a 45% solids content CB printing ink has a 55% water content which dictates the use of a large amount of energy to dry the coating~ In a typical CB coating at 1.25 lbs/ream dry weight (which contains 1.0 lbs/ream capsules), the coating must be applied at 2.78 lbs/ream wet (i.e. 1.25 lbs/ream divided by .45). That means that around 1.5 lbs~ream of water must be removed~ In addition, when this much water is added to a sheet, numerous controls rnust be added to the coater to prevent shee~ distortions like curl or cockle. Special grades of paper are also required to avoid excessive penetration and web hreaks on the coal;er. The result is a coater and accompanying facilities that are very expensive to build and operate. The centralization of production, due to high capitalization costs, also produces cost J8~7~
~7--inefficiencies in the form o~ high scrap levels and transportation costs. All of these factors add to the cost of the CB coated sheet.
In order to overcome these problems there have been various proposals for production of high solids content, aqueous CB printing in~. For e~ample, in Jabs U.S. Patent No. 4,428,978 there is disclosed a process for the production of aqueous suspensions containing from 35 to 60% by weight of microcapsules prepared by interfacial polyaddition from polyisocyanates and H-active compounds, wherein a)an isocyanaurate-modified aliphatic polyisocyanate is used as the polyisocyanate, and b) the suspension is adjusted to a pH value of i 7 after the polyaddition reaction. It is disclosed that the suspensions may be converted into agglomerated~free capsule powders, for example by spray drying, or the suspensions may be used directly for the production of aqueous flexograph pastes and concommittently the production of completely or partly coated carbonless copy papers by flexograph proc~ss printing. The preferred aqueous solution phase as shown in the examples in Jabs is a polyamine dissolved in water, to which an aqueous acid is added after the polyaddition reaction takes place.
Another patent which discusses high solids content, aqueous-based, CB printing inks is Vassilliades U.S. Patent No. 4,138,362. Vassilliades discloses producing microcapsules by admixing a water-immiscible, oily material containing an oil-soluble, non-polyrneric polyunctional isocyanate cross-linking agent, and an aqueous solution o~ a polymeric emulsi~ying agent in the ~orrn of a water-soluble pol~mer containing recurring-NH2 ~ 3~3'7~
or = NH groups or a water-soluble natural gum containing recurring hydroxy groups. A water-in-oil emulsion is formed and a solid capsule wall is formed by the cross-linking of the emulsifying agent by the isocyanat~.
When the emulsion contains a natural po1ymeric emulsifying agent, a viscosity lowering agent in the form of a urea-formaldebyde or alkali metal periodate may be added in order to obtain a higher solids coat weight while at an efficient coating viscosity. The preferred aqueous solution phase as shown in the examples in Vassilliades is an aqueous chitosan or gelatin-mixed solution containing a water-soluble urea-formaldehyde prepolymer. In the case of casein, the capsules produced by the Vassilliades method are e~tremely poor. The capsules are very fragile, due to a very thin wall, and exhibit poor aging as a result of a steady release of the solutions they contain.
Despite these teachings, processes for printing microcapsules in coating compositions on offset printing machines or even book printing machines were heretofore regarded as unworkable because both in the production of the printing ink and in the distributor rollers of the printing machine and during the printing process, shearing and compressive forces woul~ destroy most of the microcapsules. A process for producing printing inks which may be press applied is described in U.S. Patent 4,404,251, referred to previously, in which formed microcapsules are formulated into the printing ink composition either by stirring the agueous dispersion of microcapsules directly in the binder and subsequently removing the water in vacuo (the so-called flushing proc~ss), or by spray-dr~ing the microcapsules and then 2~
adding to the binder. These processes require special equipment and are not entirely satisfactory. In the former process, the hydrophilic nature of the microcapsules may make direct incorporation into the binder very difficult. The spray-drying technique is very costly. Furthermore, during spray-drying some capsules inevitably aggregate which results in a larg~ particle size distribution. The aggregates can easily reach 100 microns or more, and once formed are virtually impossible to break up non-destructively to the capsule. Such large particles are quite unsuitable for inks.
Accordingly, the need remains for an improved process for the production of high solids content, aqueous, CB printing inks and for high solids content, aqueous, CB printing inks which contain microcapsules which are sufficiently strong to be press applied.
Summary of the Invention That need is met ~y the present invention which provides a process for making a high solids content, aqueolls, microcapsule-containing printing ink by preparing a dispersion of microcapeules (microcapsule slurry) in the ink vehicle itself. The result is a complete CB printing ink with a solids content preferably in the range of approximately 60-70% by weight.
The microencapsulation method is preferably an interfacial polymerization or interfacial crosslinking one wherein a reactant, preferably a crosslinking agent such as a polyisocyanate, is dissolved in an oily solution which will serve as the internal phase of the microcapsu]es. Thus, for a CB ink, the oily solution will contain an oily solvent and a dye precursor capable of reacting with a color developer in order to form a color.
The crosslinking agent is dissolved in that oily solution.
The oily solution having the reactant dissolved therein is, thenl dispersed into an aqueous solution to form an emulsion. A coreactant may be adcled either before or after emulsification. In any event, aæ i~ known, the reactant and coreactant react in the emulsion by an interfacial polymerization or interfacial crosslinking mechanism to form a hard thick capsule wall around droplets of the oily solution and produce microcapsules.
Preferably, the coreactant is a polysalt which includes a high molecular weight polyanion, such as casein, and a polycationic polyamine having a molecular weight of less than 1200 and having a functionality of at least three, such as diethylene triamine.
A key to production of the high solids content printing ink of the present invention is the use of a non-volatile diluent in the aqueous solution as a co-solvent along with water. The non-volatile diluent should be soluble in water (i.e. greater than about 33 solubility in water), immiscible in the oily solution, non-reactive with the reactant and coreactant capsule wall materials, and have a low viscosity (i.e. less than appro~ima~ely 50 cps). Preferably, the non-volatile diluent should also be relatively non-hygroscopic, be a non-plasticizer ~or the capsule wall, have a vapor pressure of less than about 0.1 mm Hg, and be essentially tack free when dried. The preferred non-volatile diluents are non-reducing sugars such as methyl glucoside, but other materials such as dimethyl urea, dimethyl hydantoin .
. .
s formaldehyde resin, and sorbitol, erythritol, and polyoxyethylene polyols such as Carbowax 4000 can also be used.
Another important, but optional, feature of the present invention is the inclusion of a high concentration of a blend of protective colloids and/or binders (hereinafter referred to alternatively and collectively as "protective colloid hlend") in the printing ink in order to obtain good transfer properties required to apply the printing ink at low coat weights. Normally a high concentration of protective colloid or binder reduces the intensity of color formed with the CB dye precursor. Xn the present invention that reduction is a~oided through the use of blends of hard, brittle, poor-film-forming polymers or resins with soft, pliable, film-forming ones.
The protective colloid blend is preferably a rnixture of ~wo or more of the following materials: styrene-maleic anhydride copolymers, methyl vinyl ether-maleic anhydride copolymers, styrene-maleic ester copolymers, methyl vinyl ether-maleic ester copolymers, carboxymethyl-cellulose, casein, polyvinyl pyrrolidone, acrylic resins, and styrenated acrylic resins. As a further optional feature, a binder emulsion such as a styrene~acrylic or a styrene/butadiene late~ or alkali (usually ammonia~
soluble resin such as an acid modified rosin resin or a low molecular weight acrylic resin or styrene maleic anhydride resin may be added to the ink at the end of process to improve the moisture resistance and drying rate of the printing ink.
In the preferred process the oily solution contains an oil~ solvent present in an amount of 23-~3 '~5~ 5 (all percentages being based on the total weight o the printing ink) and 4.5-6 5% of the dye precursor. The reactant dissolved in the oily solution preferably is present in an amount ranging from 1 to 3.5%. In the aqueous solution preferably th~re is Eound 24-40% water and 12-25% (most preferably 13-20%~ non-volatile diluent.
The coreactant which may be dissolved in the aqu~ous solution and added before emulsification or added after emulsification, preferably is present in an amount ranging from 0.3 to 1.5%. If used, the optional protective colloid blend may be present in an amount ranging from 4-8% and if used the optional binder emulsion or alkali soluble resin may be present in an amount ranging from 0.001 to 20.0%.
The resulting printing ink thus will have as the preferred ingredients: 38% water, 16% non-volatile diluent, 36% oil-containing microcapsules, 6% protective colloid blend, 1.5% binder emulsion or alkali soluble resin, and 2.5% miscellaneous ingredients such as defoamers, slip agents, and preservatives. It has been found that a CB printing ink so formulated has both a high solids content and superior transfer properties that enable it to be coated at a low coat weight ~i.e. about 0.5 lbs./ream of 17" x 22" paper).
The combination of these two features--high solids content and low coat weight--enables one to coat the present CB printing ink with only minimal amounts of water added to the sheet. For example, at a 0.5 lbs./ream dry coat weight of CB printing ink having a 65% solids content, a 0.77 lbs./ream wet coating is applied (0.5 d 0.65 ~ 0.77). Therefore onl~ 0.27 lbs./ream (0.77 - 0.5 , ~:6~
0.27) of water is applied to the sheet along with the microcapsules. This represents over an 80% reduction in water content as compared to ordinary aqueous flexograph inks. The reduction is achieved thro~lgh the formulation of the present invention, not through expensive drying or flushing processes. The small amount of water that is added to the sheet is insufficient to cause the sheet distortions that plague normal aqueous coatings. Only modest efforts are required to dry the C~ coating of the present invention to a tack-free condition. A heated roll~ air bar, or mini-box dryer is adequate to assist drying. As a result the CB printing ink o~ thP present invention can be run on a simple fle~o or offset gravure unit which can fit easily into an e~isting press line.
While a printing ink containing CB microcapsules as described above is the preferr~d form of present invention, the oil-containing microcapsules of the present invention may include substances other than dye precursors. For example, fragrances, insecticides, liquid crystals and other frequently encapsulated substances may also be used.
Accordingly, it is an object of the present invention to provide an improved process for the production of high solids, aqueous, microcapsule-containing printing ink and a printing ink so produced These and other objects, features and attendant advantages o~ the present invention will become apparent to those skil}ecl in the art from a reading of the following detailed description o the preferred embodiments and the appended claims.
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~iLQd Descrie~iQn~ ~Q ~E~QL~ Embodim~s In the preferred embodiment, the printing ink of the present in~ention may be used to prepare CB coated carbonless copy papers using simple flexographic or offset gravure techniques. Since the preferred microcapsules are relatively strong they can withstand the pressur~s involved in such printing techniques without undue premature rupture.
The preferred microencapsulation method is an interfacial polymerization one of the type disclosed in U.S. Patent No. 4,729,792 issued March 8, 1988; although, as mentioned previously, other interfacial polymerization or interfacial crosslinking methods may also be used. As disclosed in my copending application, an oily solution of a dye precursor in an oily solvent and containing a crosslinking agent is emulsified into an aqueous solution of casein or other polyanion that has been dissolved using a weak base. A polyamine preferably with a functionality of 3 or more, and preferably having a molecular weight of less than 1200, is added either before or after emulsification.
The preferred polyamine also preferably has at least one active hydrogen available on at least two of the three amino groups. Examples of suitable polyamines are diethylenetriamine, triethylenetetramine, iminobispropylamine, bis(hexamethylene)triamine, polyo%ypropylenetriamines, polyoxypropylenepolyamines, and amine epoxy adducts (hydro%yaLkyl substituted polamines).
The polyanion and polyamine form a complex or polysalt which serves as a coreactant for the crosslinking agent. The crosslinking agent, then, is the reactant .. - .
-15- f~ 8~5 which reacts with both segments of the polyamine-polyanion comple~ simultaneously, or with the polyamine segment causing the polyanion segment to precipitate concurrently, or by both mechanisms. Examples of appropriate crosslinking agent reactants are polyisocyanates, polyacid chlorides, polyanhydrides, polyepoxides, polychloroformates, or polyaldehydes. It has been found that the crosslinking agent works best in the system of the present invention when it contains a functionality of at least three.
Isocyanates suitable for this purpose are polyisocyanates and polyisocyanate prepolymers. The term "polyisocyanate" includes polyisocyanates and polyisothiocyanates. Examples of suitable oleophilic polyisocyanates include diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyanate, 2,6-tolylenediisocyanate, 2,4-tolylenediisocyanate, naphthalene~l,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-biphenyldiioscyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, xylylene-1,3-diioscyanate, 4,4'-diphenylpropanediisocyanate, trimethylenediisocyanate, hexamethylenediisocyanate, propylene--1,2-diisocyanate, butylene-1,2-diisocyanate, ethylidynediisocyanate, cyclohe~ylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate, xylylene-1,4-diisothiocyanate, ethylidynediisothiocyanate, hexamethylenediisocyanate, etc.; triisocyanates such as 4,4',4'l-triphenylmethanetri-isocyanate, toluene-2,4,6-triisocyanate, etc; and tetraisocyanates such as 4,4'-dimethyldiphenylmethane, 2,2',5,5'-tetraisocyanate, etc. Particularly preferred are the addition product of hexamethylene diisocyanate and -16- Z~ a hexane triol, the addition product of 2,4-toluene diisocyanate with pyrocatechol, the addition product of toluene diisocyanate with hexane triol, the addition product of toluene diisocyanate with trimethylol propane, the addition product of tetramethylxylene diisocyanate with trimathylol propane, the addition product of hexamethylene diisocyanate with trimethylol propane, or suitable polyisocyanates analogous to the compounds mentioned, or methylene (polyphenyl isocyanate).
Other usable modi~ied isocyanates are those based on hexamethylene-1,6-diisocyanate, m-xylylene diisocyanate, 4,4'-diisocyanato-dicyclohexyl methane and isophorone diisocyanate which contain at least two functional isocyanate groups per molecule. Polyisocyanates based on derivatives of hexamethylene-1,6-diisocyanate having a biuret structure, as disclosed in U.S. Patent 4,051,16S, or having an isocyanurate structure are also comprehended.
The oily solution into which the reactant is dissolved preferably contains an oily solvent such as any of the dye precursor solvents normally used in CB systems.
Suitable materials include alkylated naphthalenes, alkylated biphenyls, chlorinated diphenyls, diphenyl methanes and ethanes, alkyl phthalates, and the like.
Additional oily solvent materials which may be employecl include the aliphatic and aromatic hydrocarbon oils such as kerosene, mineral spirits, naphtha, xylene, toluene, and the like.
Likewise, with a CB printing ink typical dye precursors may be used. These include triphenyl methane and diphenyl methane compounds including the well known leuco dyes, ~anthene compounds, thiaæine compounds, spiropyran compounds, and the like.
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The aqueous solution which serves as both the aqueous emulsion phase for the microencapsulation process and the aqueous ink vehicle for the CB printing ink preferably ~ontains water and optionally a weak base such as sodium hydroxide, sodium tetraborate (borax), and the like, as is typical. However, unlike typical aqueous solutions used in interfacial polym~rization or interfacial crosslinking, the aqueous solution of the present invention also contains a non-volatile diluent.
The non-volatile diluent is used as a co-solvent with water to provide the liquid media for the encapsulation reaction. The properties it should possess include:
(i) Its solubility in water should be k 33%.
~ ii) The viscosity of its aqueous solution should be low, i.e. j 50 cps. This effectively restricts the non-volatile diluent to low molecular species.
(iii3 The relative chemical reactivity towards the capsule wall precursors ~i.e. reactant and coreactant) should be be negligible, that is, similar to water in that it does not participate in the wall forming reaction.
(iv) The non-volatile diluent cannot be miscible or soluble in the oily solution.
The ahove properties are important in terms of the substitution of non-volatile diluent for some of the water in the encapsulation process. In order for the final ink matrix of the CB printing ink to function adequately (in drying, imaging, and aging) additional desirable features include:
(v) The material should be non-hygroscopic (or only slightly). Otherwise, the non-volatile diluent will slow the water loss to such an extent as to cause tracking (incompletely drying~.
(vi) The dried non-volatile diluent material should be essentially tack free.
(vii) The non-volatile diluent should not plasticize the protective colloid blend or the capsule wall. Unacceptable amounts of smudge (inadvertent discoloration) can occur from the CB material if this requirement is ignored.
(viii) The vapor pressure of the non-volatile diluent should be less than 0.1 mm Hg to avoid environmental restrictions and assure worker safety.
Preferred as the non-volatile diluent is a non-reducing sugar such as methyl glucoside. Other materials which may be used include selected polyols, amides, and ureas such as dimethyl urea, dimethyl hydantoin formaldehyde resin, sorbitol, erythritol, and polyo~yethylene polyols such as Carbowax*4000.
In terms of the preferred CB printing ink, it is also desirable to add to the microcapsule slurry a relatively high concentration of a protective colloid blend. The use of a relatively high level of a protective colloid blend insureis the desired microcapsule particle size, which is that 95% of the capsules should be 5 microns or less for a 0.5 lbs./ream coating. The protective colloid blend also provides desirable barrier and mechanical properties for the CB coated sheet during hanclling and storage. FinalLy, as rnentioned, the protective coLloid blend is preferably a blend of hard, *Trademark , .j .
2~0~8'~a brittle, poor~film forming polymers or resins such as casein, styrene-maleic anhydride, styrene-ma:Leic anhydride ester copolymers, styrenated acryl:ics and carboxymethyl cellulose with soft, pliable, film forming ones such as polyvinyl pyrrolidone, acrylic, methyl vinyl maleic anhydride copolymers, polyvirlyl alcohol, and methyl vinyl ether-maleic ester copolymers. In this manner the mechanical hardness properties of the CB coated sheet can be adjusted to allow for fracture under the appropriate stress.
As a further modification a binder emulsion such as a styrene~acrylic or styrene/butadiene latex or an alkali (usually ammonia) ammonia soluble resin such as an acid modified rosin resin or a low molecular weight acrylic resin or styrene maleic anhydride resin may be added to the microcapsule slurry to improve the properties of the CB
printing ink.
Generally, the total encapsulation mixture which will form the CB printing ink contains by weight approximately:
In~redient Weiqht%
Oily solvent 23-43 Dye precursor(s) 4.5-6.5 Reactant/Coreactant 1.0-5.0 Protective Colloid 4-8 Blend toptional) Water 24-40 Non-volatile diluent 12-25 Base (optional) 7-27 Binder Emulsion 0.001 to 20 or alkali soluble re~in (optional) The resulting CB printing ink will have as its preferred ingredients in the approximate amounts by weight of:
38~ water 16% non-volatile diluent 36% oil-containing microcapsules 6% protective colloid blend 1.5% binder emulsion or alkali so:Luble resin 2.5% miscellaneous ingredients The following examples will more clearly define the invention:
Example I
a) Oily Solution In a 2L beaker 33.25g Pergascript*I-GD Green, a dye precursor from Ciba-Geigy of Greensboro, N.C., 20.85g Copikem*XX Red, a dye precursor from Hilton-Davis of Cincinnati, Ohio, 8.5g Copikem I Blue, also from Hilton-Davis, and 81.2Sg Pergascript I-BR Black, also from Ciba Geigy, were dissolved in 707.5g diisopropyl naphthalene. The mixture was heated to 110C to effectively dissolve the dye precursors. After the dyes were dissolved, 93.75g Morpar*13 Special, an aliphatic oily solvent from Exxon of Baytown, Texas, was added and the hot solution cooled to 25C. At that point 45g Desmo~ur*N-3200, a biuret containing polyisocyanate from *Trademark 0.
'' f~
:. . .
.
,. :
.
Mobay Chemical Corp. of Pittsburgh, Pennsylvania, was added and the mixture stirred until a c]ear solution was obtained.
b) Aqueous Solution In a 4L beaker containing 785g of water, 87.5g casein was added followed by 3.7g of a 50% sodium hydroxide solution, and 3.2g Borax. The mixture was heat~d to 60C
and maintained Eor 30 minutes. The heat was turned off and 537.5g Sta-Meg*104, a methyl glucoside non-volatile diluent from Horizon Chemical Corp. of Decatur, Illinois, was added. After stirring for 15 minutes, 87.5g polyvinyl pyrrolidone (PVP R-30, molecular weight 40,000) was added. The solution was then cooled to 30C.
c? Encapsulation/Compounding Process The aqueous solution ~b) was placed in a Waring blender connected to a Variac. With the blender set on low and the Variac at 60%, the oily solution ~a) was poured into the vortex within a period of 30 seconds.
After the addition was complete, the Variac was set to 90%, and the blender was allowed to run for an additional 30 seconds. The emulsion was then transferred to the 4L
beaker, and stirred moderately to produce a slight vortex. Then 10.9g diethylene triamine in 10.9g water was added to the emulsion. The mixture is heated to 60C and held at that temperature for 2 hours. After cooling to room temperature, 62.5g Neptune*l~Nl, a microni~ed polyethylene wax slip agent from Shamrock Chemical Corp.
*Trademark i :~
, ~..
of Newark, New Jersey, was added. The ink at 69% solids was diluted with water (around 225g H20) to 62.5~
solids. The viscosity was 600 cps at 24C, pH = 8.4.
Defoamer, such as 50g of SWS-213 silicone emulsion from SWS Company, may be added if needed. The capsule size is 3 microns. The CB printing ink will contain 60% capsules by weight. When coated at 0.5#/R (17 x 22), the CB
coating is capable of producing an intense black image upon rupture of the microcapsules and contact of the dye precursor with a dye developer.
Example II
a) Oily Solution An oily solution is made as in Example I e~cept 60.5 g of Coronate*EH, an isocyanurate-modified aliphatic polyisocyanate from Nippon Polyurethane Kogyo K.K. is used in place of the Desmodur N-3200.
b) Aqueous Solution Ihe aqueous solution is prepared as in Example I.
c) Encapsulation/Compound Process The process is exactly as in Example I.
*Trademark ,1' '~ ~
Exam~le III
a) Oily Solution In a 2L beaker dissolve 36g of Pergascript I-2GN
Green 18.159 of of Pergascript I-6B Red, and 81.5g of Pergascript I-BR Black (all available from Ciba-Geigy~ in 726g diisopropyl naphthalene. At room temperature, add a solution of 100g of Cythane*3160, an addition product of tetramethylxylene with trimethylol propane from American Cyanamide, in 100g diisopropyl naphthalene.
b) Aqueous Solution In a 4L beaker, add 87.5g casein to 850g water.
Heat to 80-85C and hold for 30 minutes. Cool to 60C, and then add 28.5g Jeffamin~ J-403, a polyfunctional amine from Jefferson Chemical, and 3.2g of Borax. Stir until casein dissolves. Add 450g of Sta-Meg*104, a methyl glucoside non-volatile diluent from Horizon Chemical Corp., and 87.59 of polyvinyl-pyrrolidone ~40,000 molecular weight~. Cool the solution to room temperature.
c) Encapsulation/Compounding Process The process is the same as in Example I except that no diethylene triamine is added.
*Trademark 2~0~,Bi75 Example IV
aj Oily Solution The oily solution is prepar~d as in Example I, except that 91.6g of Huls adduct EXP-121 9, an adduct of hexamethylene diisocyanate with trimethylol propane from Huls Chemische Werke, is used in place of the Desmodur N-3200.
b) Aqueous Solution The aqueous solution is prepared as in Exampla III except that 10.9g of diethylene triamine is used instead of the Jeffamine T-~03.
c) Encapsulation~Compounding Process The process is the same as in Example I except that no diethylene triamine is added at this stag~.
It will be obvious to those skilled in the art that vari.ous changes may be made without departing from the scope of the invention which is not to be considered limited to what is described in the specification.
What is claimed is: