Self-contained pressure-sensitive carbonless recording sheet having anti-scuff protective overcoating

Abstract: A protective overcoat is provided for a self-contained pressure-sensitive carbonless recording sheet. The sheet is initially coated with a blend of a microencapsulated color former and a color developer in a binder medium. The purpose of the overcoat is to prevent premature color formation through acci­ dental rupture of the microcapsules and reaction of the color former and color developer. The overcoat comprises essentially an aqueous-based film forming material; suitable materials include: synthetic latex, polyvinylalcohol and polyvinyl alcohol-acetate copolymers, cellulose gums and ethers, acrylic resins, polyethylene oxide ethers, polyvinylpyrrolidone and copolymers of styrene, ethylene and methylvinylether with maleic anhydride.

Description: Background of the Invention The present invention relates to providing a self-contained pressure sensitive carbonless recording sheet with a protective coating for improving the scuff-resistance and other handling qualities of the product. Pressure-sensitive carbon less recording sheets are generally available in several different types, in particular they are commercially available in two specific types, complementary and self-contained. Thus complementary types of recording sheet are described in Specifications US No. 2299693 and Japanese A-62121086 and a self-contained recording sheet is described in European Specification No. EP-A-171795. In manufacturing the complementary type, a first kind of coating is applied on the back of a sheet which will be used as an overlying sheet, and a second kind of coating is applied to a sheet which will be used as an underlying sheet. In use, these sheets are placed in an overlying/underlying relation. As the overlying sheet is written-upon or printed-upon using pressure, for instance by means of a ballpoint pen or impact-type of printer, some material in the coating on the back of the over lying sheet is transferred onto (or into) the coating on the front of the underlying sheet, causing a chemical and/or physical reaction at the situs of and in the pattern of the applied pressure, resulting in a visible mark being produced on the front of the underlying sheet in correspondance with the situs and pattern of pressure applied to the front of the overlying sheet. In manufacturing self-contained pressure-sensitive carbonless recording sheets, of the kind most frequently manufactured at Moore Business Forms Inc., the manufacturing process best known to the present inventors, quanta of the coating slurries conventionally used for respectively coating the backs and fronts of the coated back ("CB") and coated front ("CF") members of the complementary-type of pressure-sensitive carbonless recording sheets mentioned above, are blended together on the front of each sheet. Conventionally, the CB coating slurry comprises microencapsulated colour-former solution dispersed in an emulsifier/binder medium, and the CF coating slurry comprises a colour developer, such as zinc-modified novolac polymer particles dispersed in a binder medium. When this blend is coated onto a paper substrate, the resultant sheet will produce a visible mark in the area where the impact is applied to the sheet with no transfer of materials required. This has great utility in imaging systems where impact alone is used to impart information on the sheet without the benefit of transfer of any materials such as ink, carbon, toner, colour former or such. Such a system generally requires a high degree of sensitivity to imaging pressure. As a result, since the sheet is always active, it is prone to premature imaging caused by normal handling operations such as printing, winding, collating, filing, copying, the imaging process itself, distribution, collection, and scanning. Also a further pressure-sensitive recording sheet as described in British Specification No. 967390 comprises pressure-sensitive recording material comprising a coloured base sheet with a coating composition which is normally opaque but which becomes transparent when sufficient pressure is applied to it for example by writing implement or a typewriter type face. However because in certain circumstances the coating composition became offset from the base sheet an overcoating was supplied. Also US Specification No. 2949381 describes a sheet having a coating including a waxy substance including a colour former and also having an overlying protective layer. This sheet is suitable for use in a spirit duplicating process. Also US Specification No. 4098114 describes a recording sheet for measuring pressures containing a colour former and a colour developer and a protective layer of a transparent synthetic resin. There is considerable prior art disclosing using latexes, polyvinyl alcohols, or cellulose gums and ethers in carbonless systems, either as binders for the capsules or as an inherent carry-over material from the capsule-making process. Summary of the Invention A protective overcoat is provided for a self-contained pressure-sensitive carbonless recording sheet. The sheet is initially coated with a blend of a microencapsulated colour former and a colour developer in a binder medium. The purpose of the overcoat is to prevent premature colour formation through accidental rupture of the microcapsules and reaction of the colour former and colour developer. The overcoat comprises a film forming material dissolved, dispersed or otherwise distributed in an essentially aqueous medium. These materials can be prepared in an aqueous medium from the dry state prior to use or supplied in a pre-dissolved or dispersed state by a manufacturer. It is an object of this invention to provide a method for improvement of the general handling qualities of a self-contained sheet by overcoating the self-contained coated sheet with a barrier comprised of a film forming material in an essentially aqueous medium. That the film former be carried in an essentially aqueous medium is relatively important for several reasons. The first deals with the microcapsules contained in the self-contained coating. The majority of microcapsule shells are composed of materials which are permeable to organic solvents, particularly polar ones, to various degrees and allow removal of the core material. If an amount of core material is extracted by application of an organic solvent, premature colour formation will occur when the core colour former contacts the colour developing material. Another reason deals primarily with the phenolic or zinc-modified phenolic polymer based systems. These materials all exhibit various degress of solubility in organic solvents, polar and non-polar. Under application of such they can lose significant amounts of their colour developing capability. Neither of these problems occur when a substantially water based system is employed. Since many industrially prepared emulsions, solutions and dispersions of film forming materials can contain additives or in themselves hold properties which may be harmful in some way to the imaging characteristics of a carbon less self-contained system without the user's knowledge, it is necessary to screen them by application to the self-contained coated sheet as an overcoat followed by testing to determine acceptability. Suitable materials which have been found include synthetic latexes, polyvinylalcohols (PVA) and polyvinylalcohol-acetate copolymers (PVAc), cellulose gums and ethers, acrylic resins, polyethylene oxide ethers, polyvinylpyrrolidone (PVP) and copolymers of styrene, ethylene and methylvinylether with maleic anhydride. Other materials conventionally used for binding, film forming may also be suitable for use and can easily be identified by the methods shown in this application. The principles of the invention will be further discussed with reference to the drawing wherein a preferred embodiment is shown. The specifics illustrated in the drawing are intended to exemplify, rather than limit, aspects of the invention as defined in the claims. Brief Description of the Drawing In the Drawing The figure is an enlarged fragmentary cross-sectional view of a sheet of paper, coated with a scuff-protected self-contained pressure-sensitive carbonless recording material provided in accordance with the principles of the present invention, this sheet being covered with an overlying sheet which is shown as it is about to be impacted by an impact printer member for causing a visible mark to be intentionally made on the underlying sheet. In practicing a best mode of the invention for laboratory test purposes, a self-contained carbonless coating composition comprised of a blend of microcapsules containing color former solution designed to provide a black image, zinc modified novolac phenol polymer particles, filler pigments and binders are coated on the front surface of a white bond paper such as Boise Summit Bond, with a basis weight of 45 g/m² (12 lbs per 500 sheets, 17 x 22 inches), by means of a wire wound rod to achieve a dry coating weight in the range of 5.0 to 10.0 grams/m², or approximately 1.33 to 2.66 pounds/17 x 22 in. per 500 sheets. Thereafter, this stock of conventional SC product was divided into nine lots. The first lot was left plain (non-overcoated) for comparison, and the other eight lots were overcoated with eight different notionally-potential overcoating compositions in the research laboratory by flowing a solution of the respective composition onto a respective SC-coated sheet, and using a smooth rod to spread the coating to a generally uniform level of thickness. The coated sheets and control sheets were then subjected to drying in an oven at a temperature of 110 degrees Centigrade for a period of one minute, removed, permited to regain ambient temperature and humidity and then weighed, and tested for scuff resistance as reported below in connection with the results tabulated in table I. LOT TRADE NAME TYPE OF MATERIAL % SOLIDS DEPOSIT IMAGE SCUFF IMM. 20 MIN. 1 S/C-no overcoat - - - 55.7 43.6 67.3/71.4 2 Dow 620 SBR latex 48 1.1 51.3 43.5 96.7/96.2 3 Vinol 325 PVA 10 .7 52.3 42.1 94.9/96.4 4 Techniflex 5200 Acrylic OPV 40 .9 54.2 48.3 98.5/98.4 5 EMA 1103 EMA resin 10 .7 53.2 42.9 88.7/90.1 6 Scriptset 540 Styrene MA resin 10 .5 45.8 39.7 90.8/90.8 7 Future Acrylic floor coating 20 .8 48.2 40.6 93.4/94.5 8 Rhoplex B-15 Cationic latex 45 1.0 67.9 58.7 - 9 Joncryl 678 Acrylic resin in solvent 20 .7 70.3 60.2 - In the DEPOSIT column, the amount recorded is the weight of over-coating, subsequent to drying, given as a value of pounds per 500 sheets of 17 x 22 inch paper. These values divided by 0.266 give the corresponding values in g/m². As for the coating materials, Dow 620 is a styrene-butadiene rubber, Vinol 325 is polyvinyl alcohol, Techniflex 5200 is an acrylic overprint varnish, EMA 1103 is ethylene-maleic anhydride, Scriptset 540 is styrene-maleic anhydride, Future is an acrylic floor coating sold in grocery stores for household use, Rhoplex B-15 is a cationic latex, and, as a further control, Joncryl 678 is an acrylic resin, which was dissolved in ethanol/methyl carbitol, rather than being applied as an aqueous emulsion as were lots 2-8. Referring briefly to the drawing figure, in each instance, the sheet of paper (10) with its SC coating (12), overcoated with an overcoating composition and dried to provide an overcoat (14), was covered with a sheet of 45 g/m² (12-pound) bond paper (16), and typed-on using an IBM Selectric typewriter. The IMAGE column in Table I tabulates the results of such testing in terms of a darkness of intentionally-created image in comparison to background. As is conventional for such testing, results are tabulated both from immediate (IMM.) readings, and ones made 20 minutes after impact printing. The testing was conducted using a Bausch & Lomb opacimeter further described below. Scuff resistance was measured by scuffing the coated side of each sheet using a Scott C-fold paper towel No. 150, under a pressure of 20.7-27.6 kPa (3-4 psi), with scuffing being performed both with and crosswise of the coating application direction. In the SCUFF column, the two numbers separated by the slash indicates the direction of the scuff. The first number, before the slash, in the scuff column is the reading for scuffs with the web, and the second number, after the slash, is for scuffs across the web. These two readings were taken because a doctor blade or similar device spreads the coating material over the paper surface as the paper is drawn through the coater. Because of irregularities in the particle sizes, in the blade, or in the paper, striations occur in the coating. When the scuff occurs with the striations, it may give one reading which might be biased. Accordingly, to effect a more true reading, two scuffs at right angles to each other are made, and a reading of each is made. In Table I, the numbers in the SCUFF column are separated by a slash, e.g. the first entry is 67.3/71.4. These are readings from a Bausch & Lomb opacimeter. The opacimeter reads reflectance, and the opacimeter is calibrated by setting the reflectance of the substrate at 100. The substrate is usually white paper. Thus, the first reading of 67.3/71.4 indicates poor reflectance (color resulting from broken capsules representing a mark absorbed some of the light). The second reading of 96.7/96.2 indicates good reflectance (very little color from broken capsules), i.e. just a few points below the white substrate reading of 100. No scuff value was generated for lots 8 and 9 due to poor imaging intensity results. Further interpreting the test results which are tabulated in Table I, the present inventors have concluded that in many instances, paper having a self-contained pressure-sensitive carbonless recording coating can be improved by having that coating overcoated using an aqueous-based film-forming material so as to dramatically improve scuff resistance, without significantly deteriorating the image-providing capability in comparison with the non-overcoated control (Lot 1). The application of an overcoat film-forming material dissolved in a non-aqueous solvent was seen to have a significant detrimental effect, as did the cationic latex overcoat. Aqueous based overcoats can be applied during the coating phase of manufacture of the conventional self-contained pressure-sensitive carbonless recording sheet product by a coating fountain of various available types, or during the finishing phase by a flexo print deck on the printing press or collator. This produces a self-contained sheet with the advantages of high imaging sensitivity and extended form life during use. Overcoats also offer the opportunity to include additives for better performance which may not be as useful or compatible with the blended self-contained system itself. For instance, a U.V. absorber can be include in the overcoat to give resistance to U.V. exposure. A surface-modifying agent may be included to give an overcoat with a more receptive surface for printing or scanning, or to produce a glossy or matte finish. Suitable aqueous-based film-forming material found for use as the overcoat of the present invention include emulsions, dispersions or solutions of synthetic latexes, polyvinylalcohols and polyvinylalcohol-acetate copolymers, cellulose gums and ethers, acrylic resins, polyethylene oxide ethers, polyvinylpyrrolidone, copolymers of styrene, ethylene and methylvinylether with maleic anhydride, and other materials variously conventionally used for binding, film-forming and the like. Self-contained carbonless coatings with protective overcoating could be used in many products and applications where improved scuff resistance and reduced discoloration are required. These overcoats provide improved protection of the image against weather and abrasion. Enhanced security aspects, indelibility, and alteration resistance of the image is obtained with these overcoatings. Some examples of products which may benefit from overcoatings are business forms, airline tickets, lottery tickets, shipping labels, and other similar items. Generally, any document having carbonless microcapsules, or more particularly, self-contained carbonless coatings will be improved by an overcoat according to the present invention. It should now be apparent that the self-contained pressure-sensitive carbonless recording sheet having anti-scuff protective overcoating as described hereinabove, possesses each of the attributes set forth in the specification under the heading "Summary of the Invention" hereinbefore.

Claims: A pressure-sensitive carbonless recording sheet, comprising; a sheet (10) of paper or paper-like recording material bearing on one side a pressure-sensitive recording coating (12), which if impacted by local application of pressure at a site produces an optically sensible mark corresponding in locality to the site; and an overcoating (14) characterised in that the pressure-sensitive coating (12) contains a self-contained carbon less microencapsulated colour former and a colour developer and the overcoating comprises dried in-situ, aqueous-based film-forming material forming a film on the self-contained pressure-sensitive carbonless microencapsulated coating. The pressure-sensitive carbonless recording sheet as claimed in Claim 1, characterised in that the overcoating film is made of at least one material selected from the group consisting of synthetic latex, polyvinylalcohol and polyvinylalcohol-acetate copolymers, cellulose gums and ethers, acrylic resins, polyethylene oxide ethers, polyvinylpyrrolidone and copolymers of styrene, ethylene, and methylvinylether with maleic anhydride. The pressure-sensitive carbonless recording sheet as claimed in Claims 1 or 2 characterised in that the colour developer is zinc-modified novolac polymer particles dispersed in a binder medium. A method for providing a pressure-sensitive recording sheet, comprising; applying an overcoating (14) to the coated side of a sheet (10) of paper or paper-like recording material bearing on said coated side a pressure-sensitive recording coating (12), which if impacted by local application of pressure at a site produces an optically sensible mark corresponding in locality to the site and drying said overcoating (14) to provide an overcoating film on the pressure-sensitive recording coating; characterised in that pressure-sensitive coating (12) contains a self-contained carbonless microencapsulated colour former and a colour developer and said overcoating comprises dried in-situ, aqueous-based film-forming material forming a film on the self-contained pressure-sensitive carbonless microencapsulated recording coating. The method according to Claim 3, characterised in that the overcoating film is made of at least one material selected from the group consisting of synthetic latex, polyvinylalcohol and polyvinylalcohol-acetate copolymers, cellulose gums and ethers, acrylic resins, polyethylene oxide ethers, polyvinylpyrrolidone and copolymers of styrene, ethylene and methylvinylether with maleic anhydride.

Inventors: BRUNEA ROBERT W, MAALOUF GEORGE E, SWIERCZ WILLIAM D, BRUNEA, ROBERT W., MAALOUF, GEORGE E., SWIERCZ, WILLIAM D.
Applicants: MOORE BUSINESS FORMS INC, MOORE BUSINESS FORMS, INC.
Application year: 1988
Main classification: B41M5
IPC codes: B41M5