US 3914511 A
Copy sheets are provided having a localized coating of microcapsules by passing an uncoated paper web through a roll nip formed from a first roll and a raised portion of a second roll, wherein the first roll is an impression roll and the second roll is a printing roll having only a portion of its surface provided with a resilient material to provide a raised, resilient printing head on the second roll. A suspension of microcapsules containing a chromogenic material is coated onto the paper web as it passes between the first and second rolls in a configuration corresponding to the resilient printing head. The coated paper web is then passed to a drying zone where the microcapsular coating is dried. The same technique is used to provide a local coating of an electron-accepting material, such as acidic clay, on a receiving sheet, which may be used in combination with a local microcapsule coating which may be superimposed over the clay coating. Upon rupture of the microcapsules, the chromogenic material is released therefrom and reacts with the acidic clay to provide a localized image. In this manner a minimum of microcapsules and clay are required to produce a transfer copy system.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 Vassiliades Oct. 21, 1975 SPOT PRINTING OF COLOR-FORMING MICROCAPSULES AND CO-REACTANT THEREFOR Anthony E. Vassiliades, Deerfield, 111.
 Assignee: Champion International Corporation, New York, NY.
22 Filed: Oct. 18, 1973 211 App1,No.:407,654
 1 References Cited UNITED STATES PATENTS 3,016,308 1/1962 Macaulay 117/36.l 3,086,879 4/1963 Lassiter 117/38 3,230,106 1/1966 West 117/38 3,418,250 12/1968 Vassiliades 252/316 3,466,184 9/1969 Bowler et a1 117/36.2
3,732,141 5/1973 Brockett et al. 117/36.8 3,793,066 2/1974 Frenken et al 117/1 1111 Primary ExaminerThomas J. Herbert, Jr. Attorney, Agent, or Firm-Roylance, Abrams, Berdo & Kaul 5 7 ABSTRACT Copy sheets are provided having a localized coating of microcapsules by passing an uncoated paper web through a roll nip formed from a first roll and a raised portion of a second roll, wherein the first roll is an impression roll and the second roll is a printing roll having only a portion of its surface provided with a resilient material to provide a raised, resilient printing head on the second roll. A suspension of microcapsules containing a chromogenic material is coated onto the paper web as it passes between the first and second rolls in a configuration corresponding to the resilient printing head. The coated paper web is then passed to a drying zone where the microcapsular coating is dried. The same technique is used to provide a local coating of an electron-accepting material, such as acidic clay, on a receiving sheet, which may be used in combination with a local microcapsule coating which may be superimposed over the clay coating. Upon rupture of the microcapsules, the chromogenic material is released therefrom and reacts with the acidic clay to provide a localized image. In this manner a minimum of microcapsules and clay are required to produce a transfer copy system.
16 Claims, 4 Drawing Figures US. Patent Oct. 21, 1975 ow mm SPOT PRINTING OF COLOR-FORMING MICROCAPSULES AND CO-REACTANT THEREFOR This invention relates to the realized application of color-forming reactants to a substrate. More particularly, this invention relates to spot printing of an aqueous microcapsular dispersion, wherein the microcapsules contain a chromogenic material, and an electronaccepting co-reactant for said chromogenic materials onto a paper substrate by means of an offset printing procedure.
Carbonless copy paper and particularly the transfer copy systems have found a widespread commercial acceptance. A popular form of transfer copy system involves the use of microcapsules which contain a colorless dye intermediate material, such as crystal violet lactone, which is dispersed or dissolvedin an oil. The microcapsules are coated onto a transfer sheet, and upon rupture of the microcapsules under the localized application of a stylus, the dye intermediate material or chromogenic compound is released and transferred to an underlying copy sheet having an acidified, adsorbent coating comprising a material that will react with the dye intermediate causing a visible, colored mark at points where the microcapsules have been ruptured and the dye transferred.
Transfer copy systems generally involve multipartforms including a CB sheet wherein the back of the sheet is coated with microcapsules containing the chromogenic compounds, a CFB sheet, which is a middle sheet having a coating on the front comprising an electron-accepting material of the Lewis acid type, such as an acid-treated clay, and a coating of the imageforming microcapsules on its underside or back side. The CB and CFB sheets are placed in register with a CF sheet which has a coating of the adsorbent clay on the front side thereof. Thus, when localized pressure is applied to the front of the CB sheet, the microcapsules coated on the back side thereof are ruptured to release the chromogenic material which reacts with the front of the CFB sheet to produce an image, while the very same localized pressure is transferred through the CFB sheet to the underside thereof in order to rupture microcapsules thereunder and thus release the chromogenic material for reaction with the front of the CF sheet to produce an image thereon.
The relatively fragile nature of the microcapsules has presented various problems involving the coating of aqueous suspensions or dispersions containing such microcapsules onto paper webs or substrates.
In the past, elaborate precautions have been taken in order to avoid rupture of the microcapsules during the coating of the paper substrates in the formation of the CF and CFB sheets. Thus, air-knife coating heads have been employed almost exclusively when applying the aqueous microcapsular suspensions to the surface of a paper web in order to avoid the destruction of the structural integrity of the microcapsules and thereby prematurely release the chromogenic compounds for reaction with the clay.
Multi-part forms involving'transfer copy systems as described above have been conventionally employed in various applications, such as for invoices for billing purposes, wherein it is desired to exclude data on certain copies while including it on others. Thus, for example, a customers copy of an order acknowledgement should not contain data which must be entered on copies to be used for internal purposes. Heretofore, the practice has been for the manufacturer of the carbonless copy paper to coat the entire surface of the CF and CB paper webs, for example, with the microcapsular suspension and the adsorbent clay suspension and ship sheets of such paper to the printer. The printer must then employ desensitizing inks in order to block out certain selected areas of the form on one or more copies. The desensitizing ink prevents the colorless dye, that is released from the CB coating, for example, from contacting the CF surface and thereby forming an image. Unfortunately, such a procedure is both uneconomic and wasteful, since it requires the general application of the microcapsules and its co-re'active clay coating to the entire surface of the paper web by the manufacturer, followed by a desensitization of large areas of the microcapsular coating by the printer. Additionally, such a procedure has commonly caused distortion of the areas that are rendered inactive.
It has now been found that aqueous, microcapsular dispersions may be applied in a localized manner by a coating system which involves passing a web, such as a paper web, continuously between a first roll and a second roll, said first and second rolls being partially in nip-defining relation, said first roll being an impression roll and said second roll being a printing roll, said printing roll being a roll having only a portion of its surface coated with a resilient material to provide a raised, resilient printing head on the second roll. A coating of the microcapsules, which contain a color-forming material, is formed on the paper web as it passes between the first and second rolls at the nip formed between the first roll and the raised surface portion of the second roll. The coating therefore corresponds to the configuration of the raised indicia on the second roll. The coated paper is thereafter passed to a drying zone wherein the microcapsular coating is dried.
Surprisingly, by employing a modified flexographictype roll, having a raised portion in the form of the desired microcapsular coating, which raised portion is formed of soft rubber or a similar synthetic, resilient material, the microcapsules may be locally applied to the paper and in any desired configuration. Thus, whereas in the past the printer had to employ a desensitizing material in order to desensitize and therefore block out large areas of the CB sheets that were coated over their entire surface with microcapsules, the printer, by employing the present invention, can apply the microcapsular dispersion in any desired configuration by merely changing the surface configuration of the raised, resilient portion of the second roll, i.e., the printing roll. Thus, the present invention eliminates the wasteful, generalized coating and desensitization of the CB sheets, and avoids the distortion caused by the use of desensitizing inks.
Although it is not intended to limit the present invention by any particular theory or mechanism, it appears that the use of a soft, resilient, polymeric, raised coating applicator on the second roll, as thecoating head, in combination with a microcapsular dispersion which has a relatively high viscosity as compared with the usual microcapsular coating dispersion, surprisingly permits the use of an offset printing technique for the localized or spot-printing of the microcapsular dispersion without rupturing the microcapsules and prematurely releasing the chromogenic material contained therein.
Moreover, the adsorbent clay coating can likewise be applied to the front side of a CF sheet in a configuration similar to that used for coating of the CB sheet by the process of this invention, and the resulting CF sheet can be used in combination with a CFB or CB sheet, thereby additionally reducing the wasteful coating of the acid-clay material in a generalized manner.
In the accompanying drawing, wherein an illustrative embodiment of the present invention is disclosed,
FIG. 1 is a schematic elevational view of a coating system embodying the features of the present invention;
FIG. 2 is a perspective showing a section of the printing roll of the present invention;
FIG. 3 is an enlarged section of a CB sheet produced in accordance with the practice of the present invention; and
FIG. 4 is an enlarged section of a two sheet unit manifold.
Referring now to FIG. 1, coating pan is provided with an aqueous, microcapsular dispersion 12. The chromogenic compound-containing microcapsules present in the dispersion may be provided by any suitable process, whether physical or chemical, so long as the microcapsules process sufficient structural integrity to withstand the coating pressures to which they are subjected by the apparatus hereinafter described.
The microcapsules to be coated onto the copy paper may have diameters ranging from 0.1 to several hundred microns. However, capsules having an average diameter in the range from 3 to 5 microns are preferred for transfer copy systems.
Preferably, the microcapsular dispersion 12 shown in FIG. 1 contains a suitable binder, such as carboxymethyl cellulose, methyl cellulose, starch, casein, polyvinyl alcohol, polyvinyl acetate latex, and styrenebutadiene latex. Alternatively, binders such as urea formaldehyde or melamine formaldehyde condensates may be employed.
An aqueous dispersion of the microcapsules may be used directly as formed in the coating dispersion 12. However, it is preferred to subject the microcapsular dispersion to a spray drying operation in order to additionally cure the capsule walls. The dry microcapsules obtained from the spray drying unit are redispersed into an aqueous medium including a suitable binder, such as carboxymethyl cellulose.
The lower portion of the pickup roll 14 dips into the aqueous suspension of the microcapsules to receive a layer of a microcapsular coating. A portion of this coating is transferred to form a layer on the peripheral surface of transfer roll 16. Pickup roll 14 may be suitably a steel surfaced roll, while transfer roll 16 is provided with a resilient blanket, fabricated from rubber or a synthetic resilient material. For example, the resilient blanket may have a three-ply fabric base on one surface of which is a skim coat of a suitable rubber compound 0.12 to 0.015 inch thick. The rubber blanket may be wrapped around the transfer roll and held under a tension of about 50 pounds per inch of width, for example.
The thickness of the ultimate coating of the microcapsules may be controlled by adjusting the gap between rolls 14 and 16. Thus, opening or closing the gap between rolls l4 and 16 can regulate the amount of microcapsular coating that is metered onto the transfer roll 16. The use of a rubber blanket 18 reduces the impact upon the microcapsules upon transfer of the microcapsular dispersion coating material from the blanket 18 to the printing cylinder 20. Printing cylinder 20 may be a metal roll having the desired raised, flexible, resilient printing head 22 adhered to the surface thereof. Printing head 22 may be made of resilient material which is similar to blanket l8 and thus would include a rubber plate, for example, formed of a resilient, synthetic material.
Referring now to FIG. 2, printing head 22 is shown as a rectangular rubber plate. Thus, for example, plate 22 may have a height of one-half inch or the like and have a width and length of 2-4 inches, for example. After picking up a microcapsular coating on its surface from blanket 18, plate 22 is transferred to paper web W by adjusting the desired nip pressure between the top surface of plate 22 and impression roll 24. Suitable nip pressures include between about 2 and about 200 preferably between and about pounds per square inch.
The configuration of printing head 22 may be varied to meet the needs of the particular business form. Thus, a very narrow strip of the microcapsular coating may be applied over a very small portion of the paper web, and the configuration of the strip may be varied from rectangular to any geometrical shape and dimension as desired. The coating surface 23 of the printing head 22 preferably has the same contour as the surface of the roll to which it is attached. Furthermore, more than one printing head may be employed, if desired, in order to provide a series of closely spaced microcapsular coatings. Regardless of the configuration that is utilized for printing head 22, the process of the present invention permits the localized or spot printing of a microcapsular dispersion onto a paper web and avoids the wasteful and expensive application of a microcapsulardispersion over the entire width of a paper web or sheet. Thus, for example, rubber plate 22 may have a 2 inch by 4 inch surface with a one-half inch depth, and be placed in the center of the surface of the printing cylinder 20. This technique may be applied to the CB sheet or the CB portion of a CFB sheet. Similarly, as previously mentioned, this technique can be used concurrently to apply a clay dispersion to local areas of a CF sheet or the front portion of a CFB sheet.
The process of the present invention can be used to apply localized coatings of microcapsules to all multipart business forms, credit card forms, etc., i.e., in any application where it is desired to restrict the amount of information provided from one sheet to another.
Suitably, the pressures to which the microcapsules are subjected in the nip formed between plate 22 and roll 24 are in the range of between about 5 and about 50 psi, preferably between about 5 and about 10 psi. Accordingly, the microcapsules utilized in the present invention must have sufficient structural integrity to withstand pressures up to the nip pressure.
After the microcapsular dispersion has been applied to the underside of web W in the desired configuration, the web is passed to a drying zone 26 where the paper web having the coating thereon is subjected to any suitable temperature conditions in order to dry the microcapsular coating. Preferably, the drying zone 26 is a drying oven and is provided with infrared heaters 28 and hollow metal tubes 30. The metal tubes contain perforations, such as round holes, which permit the introduction of air into the drying zone which can impinge on the back or uncoated side of web W. Suitable air velocities include between about 2000 and about 10,000 cubic feet per minute, preferably 6000 cubic feet per minute at temperatures between about 100 and about 300 F, preferably 190F. Of course, the drying conditions will vary depending upon the particular press'speeds, i.e., the speed at which web W is passed through the drying oven. However, such conditions are suitable for press speeds in the range of 100 to 800 feet per minute.
After the web W exits the drying oven, it is passed to a wind-up roll 32 which is powered to wind the coated web onto the roll. Various guide rollers and tensioning rollers may be suitably employed as needed. However, their use is conventional and has not been illustrated in the drawing.
FIG. 3 illustrates a sectional view of a copy sheet 36 having a surface 40 with a microcapsular coating 38 printed thereon, wherein the remaining portions of the surface 40 is devoid of microcapsules. Suitable coat weights for the microcapsular coating include between about 1 and about 4 pounds per ream of paper (3300 square feet), preferably about 3 pounds per ream.
As previously mentioned, any suitable process can be used for forming the microcapsules for use in the present process. However, a preferred method for forming the microcapsules used in the coating process of the present invention involves providing an aqueous solution of a water-soluble, polymeric, film-forming, emulsifying agent, such as polyvinyl alcohol, which emulsifier possesses hydroxyl groups, and thereafter forming an emulsion by admixing a water-immiscible, oily material containing an oil-soluble, non-polymeric, crosslinking agent for the emulsifying agent selected from the group consisting of polyfunctional isocyanates and orthoesters of Group IV elements. The cross-linking agent interacts with the hydroxyl groups of the polymeric emulsifying agent to form a solid, cross-linked, resinous capsule wall. In addition to the cross-linking agent, the oily material contains suitable chromogenic material, such as a combination of crystal violet lactone and benzoyl leucomethylene blue.
Thus, in general, the process for providing the chromogenic-containing, pressure-rupturable microcapsules involves admixing:
A. a water-immiscible, oily material containing an oil-soluble, non-polymeric cross-linking agent selected from the group consisting of a polyfunctional isocyanate and an ortho ester of a Group IV element, and a chromogenic material; and
B. an aqueous solution of a hydroxyl groupcontaining, polymeric emulsifying agent; said admixing being conducted under conditions to form an oil-inwater emulsion wherein said oily material is dispersed in the form of microscopic emulsion droplets in an aqueous, continuous phase, reacting said cross-linking agent with said polymeric emulsifying agent and thereby surrounding each of the droplets with a solid, cross-linked capsule wall. Preferably, the polymeric emulsifying agent is the sole reactant for the crosslinking agent.
During the formation of the microcapsules, the reaction of the cross-linking agent with the polymeric emulsifying agent, i.e., the curing step, may be conducted at any suitable temperature, for example, between ambient temperature and about 100C, for periods of time between 1 and 24 hours. The upper temperature at which the curing step may be conducted is only limited by the temperature at which the emulsion will break, i.e., the stability limit of the emulsion. Preferably, the cross-linking reaction is conducted at a temperature at a range of between 40 and C, for a period of 1 to 3 hours. Suitable ratios of emulsifier to cross-linking agent in the formation of such microcapsules include at least one part by weight of emulsifying agent per part of cross-linking agent up to about parts by weight of emulsifier per part of cross-linking agent, preferably between about 4 and about 20 parts by weight of emulsifier per part of cross-linking agent.
Suitable oil soluble polyfunctional isocyanates that may be employed for production of the microcapsules include, for example, 4,4-diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, triphenylmethane triisocyanate, mixtures of such isocyanates, and adducts of such isocyanates with polyhydric alcohols, such as trimethylolpropane.
The ortho esters of Group IV elements which may be employed as cross-linking agents include the aliphatic and aromatic ortho esters of Group IV(a) and IV(b) elements, preferably the lower alkyl and aryl ortho esters of Group IV elements, such as tetraethyl orthosilicate, tetrapropyl orthosilicate, tetraphenyl orthosilicate, tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate, tetraphenyl titanate, tetraethyl germanate, tetrapropyl orthocarbonate, and thelike.
Suitable polyhydroxyl polymers useful as emulsifying agents include polyvinyl alcohol, methyl cellulose, starch and the like.
Polyvinyl alcohol is especially preferred, and such material may be employed in any of the available water-soluble grades, either fully or partially hydrolyzed, high or low molecular weight. The especially preferred polyvinyl alcohols suitable for use in the present invention are those grades known as the 88 percent (nominal) hydrolyzed, high molecular weight products (e.g., commercially available as Covol 97-40 from CPI, or Elvanol 50-42 from du Pont).
Substituted starches are the preferred form of starch for use as an emulsifier, and such material may be provided by any suitable process. For example, they may be provided by etherification of the starch in granular form under non-gelatinizing conditions with a monofunctional etherifying agent which provides the starch with etherlinked hydrophobic groups. Thus, the starch granule will become more oleophilic due to the presence of a high percentage of hydrophobic groups. The hydrophobic groups may be, for example, alkyl groups having at least three carbon atoms, ayralkyl groups containing at least 7 carbon atoms, and the like. The term substituted starch as employed herein refers to a starch that has been rendered more eleophilic due to an increase in hydrophobic groups. A preferred substituted starch is an ether-linked benzol starch. The starches are described in US. Pat. No. 3,707,514 to Vassiliades et al, which is hereby incorporated by reference.
The polyfunctional isocyanate or ortho ester crosslinking agent is utilized in amounts sufficient to result in the formation of microcapsules. The relative amounts will vary with the particular system and may be easily determined in each case. The polymeric emulsifying agent may be provided in relatively substantial amounts of, for example, at least 1 part by weight of emulsifier per part of cross-linking agent, with between about 4 and about 20 parts emulsifier per part by weight of the oil-soluble cross-linking agent being preferred. An especially preferred range of cross-linking agent based upon the oil is between about I and 40 weight percent of cross-linking agent, preferably between about 2 and 10 weight percent.
The emulsification may be conducted at any suitable temperature. For example, temperatures in the range of between and 100C are preferred, although temperatures outside of this range may also be utilized. Subsequent to emulsification, the microcapsular dispersion may be heated to a temperature, for example, in the range of between about 40 and 80 for a period of between 1 and 4 hours under conditions of mild agitation in order to accelerate the cross-linking reaction. The cross-linking reaction may be otherwise conducted at ambient temperatures for longer periods of time, e.g., 24 hours, while obtaining similar results.
The water-immiscible oily materials include liophilic materials which are preferably liquid, such as oils, which will not mix with water and which are inert with regard to the components of the particular system.
Oils are the preferred nucleus materials, and preferred oily materials include the aliphatic and aromatic hydrocarbon oils, such as kerosene, mineral spirits, naptha, xylene, toluene and the like. Also for example terpenes, such as terpentine; esters, such as dimethylpthalate, dioctylphthalate, dimethylazelate, methyl-2- ethylhexanoate, 2-ethylhexyl acetate and the like may be employed. The amount of emulsifying agent relative to the oily nucleus material employed will vary over a wide range depending upon the particular system. However, suitable amounts include between 5 and 100 parts by weight of emulsifying agent per 100 parts by weight of oil, preferably between 10 and 50 parts of emulsifying agent per 100 parts by weight oil.
Suitable chromogenic materials are wholly conventional in this art. Examples of the colorless dye intermediates which may be employed in the formation of the microcapsules include the leuco dyes, such as crystal violet lactone, and derivatives of bis(p-dialkyl amino aryl) methane such as disclosed in US. Pat. Nos. 2,981,733 and 2,981,738, which dye intermediates are colorless in an alkaline or neutral medium and react to form a visible color in an acidic medium. Thus, when the capsule containing such compound is ruptured and the compound is discharged onto an adsorbent, acidic electron-acceptor material, such as a paper web coated with an organic or inorganic acid material, a visible color appears on the adsorbent material at the point of contact.
Inhibitors may optionally be dispersed in the oily material along with the dye intermediates. Such materials are helpful in preventing light and heat degradation of the intermediates during the encapsulation procedure, especially when elevated temperatures are required. Inhibitors are also considered to aid in the stabilization of the colored marking on the copy sheet against the effects of the atmosphere. A small amount (generally 1 to 10 percent by weight of the dye) of an inhibitor, such as N-phenol 2-naphthlamine, may be used. The leuco dye intermediates which are mentioned above are, in general, oil soluble. Oils that are inert with respect to the dye and in which the dye has appreciable solubility, e.g., above 0.5 g of dye per 100 g of oil, are preferable.
As previously mentioned, the microcapsules are preferably spray dried and redispersed, rather than utilized directly as produced.
The spray drying of the microcapsules may be accomplished by injecting the chromogenic materialcontaining microcapsules into a spray drier chamber of tower nozzle spray drier at a feed rate of, for example, 50 to 52 milliliters per minute while employing an inlet temperature of about 150F. The outlet temperature is lower, e.g., about 106F. The capsular solution is injected into the spray drying chamber from a two-fluid type atomizer at a pressure of psig. The dry capsular material is then collected and redispersed in an aqueous coating medium. Alternatively, the capsular suspension as produced may be injected into a conical spray drier at an atomizing pressure of, for example, psig. Inlet temperatures and outlet temperatures for the spray drying operation may be varied, but preferably inlet temperatures are from about 150 to 250F, while the outlet temperatures are from to F. Similarly, the feed rate may be varied depending upon the particular material undergoing the spray drying operation, and may be varied from 20 to 75 milliliters per minute.
Regardless of whether the microcapsular coating dispersion 12 is formed from microcapsules as made directly, or subsequent to being spray dried and redispersed, the viscosity is thereafter adjusted to the desired degree. The solids content of the microcapsules in water is generally higher in the coating dispersons of the present invention than that employed in the conventional coating operations previously employed for microcapsules. The solids content of the microcapsular dispersion is suggested to be between about 5 and about 30 percent, preferably between about 18 and about 25 percent, e.g., 22 percent by weight solids, and thereafter a suitable binder, such as carboxymethyl cellulose is added to increase the viscosity of the dispersion to the desired extent. A suitable viscosity range for purposes of the present invention includes between about 10 and about 300 centipoises, preferably between about 50 and about 100 centipoises.
The procedure illustrated in FIG. 1 can be employed for the application of a localized coating of an electronaccepting material in the manner described for local application of microcapsules. Although any electronaccepting material may be applied to the web W by means of printing head 22, the preferred electronaccepting material is an acidic solid, such as bentonite, kaolin, montmorillonite, other acidic clays, talc, aluminum silicate, calcium citrate, metal chlorides, or the like. The electron-accepting acidic clays are especially preferred. Accordingly, a coating suspension 12 of acidic clay, for example, is provided in vessel 10 and pickup roll 14 dips into an aqueous suspension of the clay and transfers a portion of the clay to transfer roll 16 and printing head 22 as previously described. The viscosity of the coating suspension is adjusted by the addition of water to obtain a consistency similar to that of ofiset printing ink.
The aqueous clay coating is applied to the web and dried in oven 26 as described previously in connection with the application of microcapsular coating suspensions. The same printing heads may be used for the clay and the resulting web W will have the configuration shown in FIG. 4 as described in connection with the microcapsular coating. The same printing head may be used for applying the microcapsular dispersion in forming a CB and/or CFB sheet and for applying an acidic clay coating in order to form a CF and/or CFB sheet.
The resulting sheets can be then utilized together in register with a minimum waste of coating materials.
In FIG. 4, the clay coated web W is provided with the local or spot clay coating 144 on surface 146 of the sheet 142. Superimposed over sheet 142 is sheet 136 having a microcapsule coating 138 on its surface 140. The coating 138 has the same configuration as does coating 144 and is placed in register therewith. In actual use, the coatings are placed in physical contact, and the localized pressure of a writing instrument on the upper or uncoated surface of sheet 136 directly above the coating 138 ruptures the capsules in the coating 138 and releases chromogenic material for reaction with the clay coating 144 upon which a colored image is produced. Although FIG. 4 illustrates a two sheet couplet, the invention can be utilized with a multisheet system having CFB sheets sanwiched in between other CFB sheets, if desired, with the top sheet being a CB sheet and the bottom sheet being a CF sheet. Also, any modifications may be utilized. For example, sheet 36 of FIG. 3 may be used with a CF sheet having its entire surface coated with an electron-accepting material, rather than merely a local coating thereof. Conversely, sheet 142 of FIG. 4 may be used with a CB sheet having a microcapsule coating over its entire back surface. Similarly, although FIG. 4 shows a single local coating of microcapsules and clay, the sheets may be provided with numerous such coatings as needed.
The following examples illustrate the present invention.
EXAMPLE 1 diameter is obtained. The emulsion is then heated while under mild agitation at a temperature of 60C for 2 hours. The microcapsular dispersion is then injected into a spray drier chamber at a feed rate of about 50 milliliters a minute at an inlet temperature of about 150F and an outlet temperature of about 100F. The
resulting microcapsules are collected as a dry powder and are redispersed in water to obtain a solids content of about 24 percent by weight. Carboxymethyl cellulose and a'load bearing agent, e.g., starch or the like, are added to the dispersion to form a viscosity of 50 centipoises.
EXAMPLE 2 Employing the apparatus shown in FIG. 1, coating pan is provided with the microcapsular dispersion obtained in Example 1. The dispersion is picked up by roll 14 and transferred to roll 16 which meters the microcapsular coating to plate 22 so as to provide a coat weight of about 2 to 4 pounds per 3,300 square feet of surface area to web W. The dispersion is coated onto paper web W which is moving at a speed of 400 feet per minute. After the web W receives the coating, the web is passed to drying oven 26 containing the infrared heaters and receives heated air on the upper side thereof at a velocity of 600 cubic feet per minute and at a temperature of F. The web W is collected on winder 34.
The resulting localized coating of microcapsules is placed in register with a CB sheet and tested. When a ballpoint pen is applied to the front side of the CB sheet, a sharp blue mark is provided on the CF sheet adjacent the microcapsular coating.
EXAMPLE 3 The apparatus of FIG. 1 is employed to apply spot coatings of an aqueous coating of active bentonite clay to a paper web to form a CF sheet. The clay slurry is diluted with water until it has the consistency of offset printing ink. The clay is applied by plate 22 at a coat weight of 2 to 4 pounds per 3,300 square feet of paper. The coatings are dried in drying oven 26 employing the conditions used in Example 2. A sample of a CF sheet as produced herein is placed in register with a sample of the CB paper produced in Example 2. Upon the application of localized pressure by means of a ballpoint pen, an instantaneous blue image results on the localized area.
This invention has been described in considerable detail with particular reference to preferred embodiments, but it will be understood that variations and modifications can be effected within the spirt and scope of the invention as described in the appended claims.
1. A process for the production of a pressure sensitive sheet having a local coating of microcapsules thereon, which comprises passing a web continuously between a first roll and a second roll, said first and second rolls being partially in nip-defining relation, said first roll being an impression roll and said second roll being a printing roll, said printing roll being a roll having only a portion of its surface coated with a resilient material to provide a raised, resilient printing head on said second roll, said nip being formed between said first roll and the coating surface of said raised, resilient printing head, said coating surface of said printing head being provided with a coating of microcapsules prior to passage of said printing head through said nip, and thereby forming a coating of microcapsules on said web as it passes through said nip in a configuration corresponding to said printing surface of said printing head, said microcapsules containing a chromogenic material and being capable of withstanding pressures of up to 50 psi without rupturing, and passing said coated web to a drying zone wherein said microcapsular coating is dried.
2. The process of claim 1 wherein said raised printing head is provided with a microcapsular coating by means of a transfer roll, said transfer roll having a resilient surface.
3. The process of claim 2 wherein said transfer roll receives microcapsules from a pickup roll, which, in turn, picks up microcapsules from an aqueous dispersion of microcapsules.
4. The process of claim 1 wherein said microcapsules have walls comprising polyvinyl alcohol cross-linked by a polyisocyanate.
5. The process of claim 1 wherein said printing head comprises a rubber plate having a rectangular shape.
6. The process of claim 5 wherein said printing head has a surface which is between about 1 and about 8 inches in width, between about 1 and about 12 inches in length.
7. The process of claim 1 wherein said drying zone is provided with infrared drying means.
8. The process of claim 7 wherein the web is paper and is additionally subjected to heated air which directly contacts the uncoated side of said paper web.
9. The process of claim 1 wherein said chromogenic material is a combination of crystal violet lactone and benzoyl leuco methylene blue.
10. A process for the production of a copy sheet having a local coating of an electron-accepting material of the Lewis acid type thereon, which comprises passing a web continuously between a first roll and a second roll, said first and second rolls being partially in nipdefining relation, said first roll being an impression roll and said second roll being a printing roll being a roll having only a portion of its surface coated with a resilient material to provide a raised, resilient printing head on said second roll, said nip being formed between said first roll and the coating surface of said printing head being provided with an aqueous coating of clay prior to passage of said printing head through said nip, and thereby forming a coating of said clay on said web as it passes through said nip in a configuration corresponding to said printing surface of said printing head and passing said coating paper web having a local coating of clay thereon to a drying zone wherein said clay coating is dried.
11. The process of claim 10 wherein said raised printing head is provided with an aqueous clay coating by means of a transfer roll, said transfer roll having a resilient surface.
12. A pressure sensitive copy system comprising a transfer sheet having a surface thereof provided with a local coating consisting essentially of pressurerupturable microcapsules in a predetermined configuration on only a portion of said surface, said microcapsules containing a chromogenic material and being capable of withstanding pressures of up to 50 psi without rupturing.
13. The copy system of claim 12 wherein said transfer sheet is superimposed over a receiving sheet, said receiving sheet having a surface thereof provided with a local coating consisting essentially of an electronaccepting clay in a predetermined configuration on only a portion of a surface of said receiving sheet, said microcapsule coating and said clay coating being positioned in physical contact with each other.
14. The copy system of claim 13 wherein the configuration of said microcapsule coating and that of said clay coating is substantially identical, and said coatings are positioned in substantial register with one another.
15. The copy system of claim 12 wherein said microcapsule coating covers only a minor portion of said surface.
16. The copy system of claim 12 wherein said microcapsules have walls comprising polyvinyl alcohol crosslinked by a polyisocyanate.