THERMALLY RESPONSIVE RECORD MATERIAL

Abstract: A high sensitivity thermal paper resistant to image erasure has a colour forming composition comprising a chromogenic material, an acidic developer material, a water insoluble hydrocarbon resin selected from poly-­ α-methylstyrene or α-methylstyrene/vinyltoluene copolymer, a thermal modifier and a binder. Preferably the thermal modifier is acetoacet-o-toluidine, diphenoxyethane, phenyl 1-hydroxy-2-naphthoate, diheptadecyl ketone or octadecanamide. The disclosed composition when thermally imaged is surprisingly resistant to image erasure and smearing attributable to fingerprint oils.

Description: This invention relates to thermally responsive record material. In particular it relates to such record material in the form of sheets coated with colour forming systems comprising chromogenic material and acidic colour developer material, including other components to give record material having improved resistance to fingerprinting and smearing upon being handled. Thermally responsive record material systems are well known in the art and are described in many patents, for example U.S. Patents Nos. 3539375, 3674535, 3746675, 4151748, 4181771, 4246318 and 4470057. In these systems, basic chromogenic material and acidic developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a coloured mark. Thermally responsive record materials have been progressively improved in sensitivity over the years in keeping with the requirements imposed by faster and faster facsimile equipment transmission and operating rates. High sensitivity thermal paper must promptly and efficiently form a high density mark upon thermal heating. As sensitivities have increased with the use of thermal modifiers (also sometimes described as "sensitizers"), a vexing problem has emerged with high sensitivity thermal papers of image erasure and smearing from fingerprint oils upon being handled following image formation. A need has arisen with high sensitivity thermal papers for coated composition which resists image erasure due to fingerprint oils. U.S. Patent 4134847 discloses the manufacture of a developer composition by fusing an aromatic carboxylic acid, an oxide or carbonate of a polyvalent metal and a water insoluble polymeric material such as poly- - methylstyrene, and grinding the fused material after cooling. U.S. Patent 4470057 discloses thermally responsive record materials which can include a latex binder such as polystyrene latex to protect the coated materials from brushing and handling forces. The present invention is based on our finding that the inclusion of poly-α-methylstyrene and/or α-methylstyrene/vinyltoluene copolymer in thermally reactive coatings including colour former, co-reactant, thermal modifier and binder can give superior resistance to image erasure or smearing on contact with fingerprint oils and/or commonly used skin lotions. Accordingly, the present invention provides thermally responsive record material resistant to image smearing comprising a support member bearing a thermally sensitive colour forming composition, the thermally sensitive colour forming composition comprising: a chromogenic mterial, and in contiguous relationship, an acidic developer material whereby the melting or sublimation of either material or another component of the coating produces a change in colour by reaction between the two; a water insoluble hydrocarbon resin which is poly-α-methylstyrene, α-methylstyrene/vinyltoluene copolymer or a mixture therof; and in combination therewith a thermal modifier selected from acetoacet-o-toluidine, diphenoxyethane, phenyl-1-hydroxy-2-naphthoate, diheptadecyl ketone, octadecanamide, and mixtures thereof; and a binder therefor. Apart from the inclusion of the hydrocarbon resin, the thermally reactive coating is substantially that of a conventional high sensitivity thermally responsive record material. In addition to the components referrred to above, the coating can include fillers such as silica, clay, talc, aluminium hydroxide, calcined kaolin clay and calcium carbonate; synthetic pigments, such as ureaformaldehyde resin pigments; natural waxes such as Carnuba wax; and synthetic waxes. The hydrocarbon resin used is poly-α-methylstyrene and/or α-methylstyrene/vinyltoluene copolymer. We do not know why these materials work to give enhanced fingerprint oil resistance to the thermal image. We have noted that using polystyrene instead appears to offer no substantial benefit in fingerprint oil resistance. Typically, the hydrocarbon resins will be present in the thermally reactive coating as finely divided solid particles e.g. obtained by grinding of the bulk material. The record material includes a substrate or support material which is generally in sheet form. In the present context, the term "sheet" denotes articles having two large surface dimensions anda comparatively small thickness dimension, such as webs, ribbons, tapes, belts, films, cards and the like. The substrate or support material can be opaque, transparent or translucent and can, itself, be coloured or uncoloured. The material can be fibrous including, for example, paper and filamentous synthetic materials. It can be a film including, for example, cellulose film (cellophane) and synthetic polymeric sheets cast, extruded, or otherwise formed. Suitable chromogenic compounds, include well known colour forming compounds such as phthalides, leucauramines and fluorans. Examples of such compounds include Crystal Violet Lactone (3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, U.S. Patent No. Re. 23024); phenyl-, indol-, pyrrol-, and carbazol-substituted phthalides (e.g. U.S. Nos. 3491111, 3491112, 3491116, 3509174); nitro-, amino-, amido-, sulfonamido-, amino-benzylidene-, halo- and anilino-substituted fluorans (e.g. U.S. Nos. 3624107, 3627787, 3641011, 3642828, 3681390); spirodipyrans (U.S. No. 3971808); and pyridine and pyrazine compounds (e.g. U.S. Nos. 3775424 and 3853869). Specifically suitable chromogenic compounds include 3-diethylamino-6-methyl-7-anilinofluoran (U.S. No. 3681390); 7-(1-ethyl-2-methylindol-3-yl)-7-(4-diethyl-amino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one (U.S. No. 4246318); 3-diethylamino-7-(2-chloroanilino)-fluoran (U.S. No. 3920510); 3-(N-methylcyclohexylamino)-6-methyl-7-anilinofluoran (U.S. No. 3959571); 7-(1-octyl-2-methyl-indol-3-yl)-7-(4-diethylamino-2-ethoxyphenyl)-5,7-dihydrofuro[3,4-b]pyridin-5-one; 3-diethylamino-7,8-benzofluoran; 3,3-bis-(1-ethyl-2-methylindol-3-yl)-phthalide; 3-diethylamino-7-anilinofluoran; 3-diethyl-amino-7-benzylaminofluoran; and 3′-phenyl-7-dibenzylamino-2,2′-spiro-di-(2H-1-benzopyran). Examples of suitable acidic developer material include the compounds listed in U.S. Patent No. 3539375 as phenolic reactive material, particularly the monophenols and the diphenols. The following compounds can also be used as the acidic developer material individually or in mixtures: 4,4′-isopropylidinediphenol(Bisphenol A); p-hydroxybenzaldehyde; p-hydroxybenzophenone; p-hydroxypropiophenone; 2,4-dihydroxybenzophenone; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-bis(4-hydroxyphenyl)cyclohexane; salicylanilide; 4-hydroxy-2-methylacetophenone; 2-acetylbenzoic acid; m-hydroxyacetanilide; p-hydroxyacetanilide; 2,4-dihydroxyacetophenone; 4-hydroxy-4'-methylbenzophenone; 4,4'-dihydroxybenzophenone; 2,2-bis-(4-hydroxyphenyl)-4-methylpentane; benzyl 4-hydroxyphenyl ketone; 2,2-bis(4-hydroxphenyl)-5-methylhexane; ethyl 4,4-bis(hydroxyphenyl)pentanoate; n-propyl 4,4-bis-(4-hydroxyphenyl)pentanoate; isopropyl 4,4-bis-(4-hydroxyphenyl)pentanoate; methyl 4,4-bis-(4-hydroxyphenyl)pentanoate; 3,3-bis(4-hydroxyphenyl)pentane; 4,4-bis(4-hydroxyphenyl)heptane; 2,2-bis(4-hydroxyphenyl)-1-phenylpropane; 2,2-bis(4-hydroxyphenyl)butane; 2,2′-methylene-bis(4-ethyl-6-tertiarybutyl)phenol; 4-hydroxycoumarin; 7-hydroxy-4-methyl-coumarin; 2,2′-methylene-bis(4-octyl-phenol); 4,4′-sulfonyldiphenol; 4,4′-thiobis-(6-tertiarybutyl-m-cresol); methyl p-hydroxybenzoate; n-propyl p-hydroxybenzoate; and benzyl p-hydroxybenzoate. Preferred among these are the phenolic developer compounds, in particular 4,4′-isopropylindinediphenol and 2,2-bis(4-hydroxyphenyl)-4-methylpentane. Acidic compounds of other kinds and types can also be suitable such as phenolic novolak resins which are the product of reaction between, for example, formaldehyde and a phenol such as an alkylphenol, e.g. p-octylphenol, or other phenols such as p-phenylphenol, and the like; and acidic mineral materials including collodial silica, kaolin, bentonite, attapulgite, hallosyte, and the like. Some of the polymers and minerals do not melt but undergo colour reaction on fusion of the chromogen. The binder used in the thermally reactive coating will usually be a polymeric material. Most commonly, water soluble binders such as polyvinyl alcohol, hydroxy-ethylcellulose, methylcellulose methyl-hydroxypropyl-cellulose, starch, modified starches and gelatin can be used. However, latex binders such as polyacrylates, polyvinylacetates and styrene-butadiene copolymers can be used in some instances. The polymeric binder serves to bind the coating and adhere it to the substrate and acts to protect the coating from brushing and handling forces during storage and use of the thermally responsive record material. The amount of binder used will normally be sufficient to fulfil these requirements without being so great as to interfere with thermal imaging performance of the record material. In the thermally reactive coating the components of the coating, particularly the colour forming components, the chromogenic material and acidic colour developer, are generally in a contiguous relationship of substantially homogenously distributed finely divided solid particles. Typically, the particles of colour forming system components have an average particle size from about 0.1 to 10 µm and most commonly about 3 µm. The amount of the thermally reactive coating (the coatweight) wil usually be from about 3 to about 14 g m⁻², and more usually about 5 to about 6 g m⁻². In any particular case the amount of colour forming materials will be determined by economic considerations and the desired functional performance and handling characteristics of the thermally responsive record material. Typically in the thermally reactive coating the following proportions will be used (by weight on the coating): chromogenic material 3 to 12% hydrocarbon resin 2 to 20% acidic developer material 10 to 30% thermal modifier 10 to 30% binder 10 to 20%. When present, fillers and pigments can comprise up to 50%, but occasionally more, of the coating. The thermally responsive record material of the invention will usually be made by coating a coating mix onto the substrate, drying and calendering. Most commonly, the coating mix will comprise a dispersion of the solid components of the system in a vehicle, which is usually water, including dissolved (or dispersed) therein the binder and any process aids such as surfactants, dispersants, defoamers etc. The coating method is not particularly critical to the invention and conventional coating techniques can be used such as wire wound rod coating, roll e.g. 3-roll coating etc. The coating can be a single layer coating or a multi-layer, particularly a two-layer coating. Usually, in a two-layer coating, the hydrocarbon resin will be made up into a first coating mix in an aqueous vehicle, including binder, and optionally filler, wax, optical brightness etc, coated onto the substrate and dried to give the first coating layer. The second coating layer is provided over the top of this, by coating a coating mix, usually including chromogenic material, acidic colour developer, binder and other optional materials such as fillers, waxes, optical brighteners and process aids as desired, followed by drying and calendering. The coating mixes will usually be made up from separate dispersions of the materials used. In particular, the chromogenic material and acidic developer material will be ground and dispersed separately to avoid discolouration arising from reactions in the coating mix. The following Examples illustrate the invention. All parts and percentages are by weight unless otherwise stated. Examples 1 to 12 Examples 1C, 6C and 11C are identical controls and are, thus, suffixed "C". Examples 2 to 5 show the improved image stability when poly-α-methylstyrene is incorporated into the coating, Example 1C being the control coating prepared without the hydrocarbon resin. All of Examples 2 to 5 include the thermal modifier acetoacet-o-toluidine. Examples 7 to 10 show the improved image stability when α-methylstyrene/vinyultoluene copolymer is incorporated together with acetoacet-o-toluidine into the coating. Example 12 shows the improved image stability when poly-α-methylstyrene is included in a subcoat over which is placed the thermal sensitive layer. Example 11C serves as the control (not subcoated) coating. An outline of the coating composition (dry weight basis) for Example 1 to 12 is set out in Table 3 below. The following dispersions A to F were separately made up. Dispersion A : Chromogenic material Parts Chromogenic Material 32.0 Binder, 20% Solution of Polyvinyl Alcohol in Water 27.4 Defoaming and Dispersion Agents 0.4 Water 40.2 Dispersion A-a : the chromogenic Material used is 3-diethylamino-6-methyl-7-anilinofluoran Dispersion B : Acidic colour developer material Parts Acidic Material 42.5 Binder, 20% Solution of Polyvinyl Alcohol in Water 21.2 Defoaming and Dispersing Agents 0.2 Water 36.1 Dispersion B-a : The acidic colour developer material used is 2,2-bis(4-hydroxyphenyl)-4-methylpentane Dispersion C : Thermal Response Modifier Parts Thermal Modifier 42.5 Binder, 20% Solution of Polyvinyl Alcohol in Water 21.2 Defoaming and Dispersing Agents 0.2 Water 36.1 Dispersion C-a : The thermal modifier used is acetoacet-o-toluidine Dispersion D : Lubricant Dispersion Parts Zinc Stearate 10.2 Behenyl Alcohol 7.9 Binder, 20% Solution of Polyvinyl Alcohol in Water 8.7 Defoaming and Dispersing Agents 0.2 Water 73.0 Dispersion E : Pigment Dispersion Parts Fumed Silica 8.7 Urea-Formaldehyde Resin 4.1 Binder, 10% Solution of Polyvinyl Alcohol in Water 23.8 Defoaming and Dispersing Agents 0.8 Water 62.6 Dispersion F : Hydrocarbon Resin Dispersion Parts Hydrocarbon Resin 17.0 Binder, 10% Solution of Polyvinyl Alcohol in Water 30.0 Defoaming and Dispersing Agents 0.2 Water 52.8 Dispersion F-a : The hydrocarbon resin used is poly-α-methylstyrene commercially available as Kristalex 1120. Dispersion F-b : The hydrocarbon resin used is α-methylstyrene/vinyltoluene copolymer commercially available as Piccotex 100. The above dispersions A to F may be prepared with water soluble binders other than polyvinyl alcohol. Nopco NDW (a sulphonated castor oil produced by Nopco Chemical Co.) and Surfynol 104 (a di-tertiary acetylene glycol surface active agent produced by Air Products and Chemicals, Inc.) were used as the defoamer and dispersing agent in the above dispersions. Resito Coat 135 (a paraffin wax emulsion) was added as a lubricant in the pigment dispersion (E). A combined dispersion was made up from Dispersions A to D (plus water and further binder) as follows: Parts Dispersion A 10.3 Dispersion B 20.6 Dispersion C 25.9 Dispersion D 21.7 Binder, 10% PVA in Water 21.5 The combined dispersion was used to make up coating compositions (mixes) I to IV as follows: Coating Formulation I Control Parts Combined Dispersion 45.6 Dispersion E 33.1 Water 21.3 Coating Formulation II Hydrocarbon Resin (Level 1) Parts Combined Dispersion 45.6 Dispersion E 30.1 Dispersion F 2.4 Water 21.9 Coating Formulation III Hydrocarbon Resin (Level 2) Parts Combined Dispersion 45.6 Dispersion E 25.5 Dispersion F 5.9 Water 23.0 Coating Formulation IV Hydrocarbon Resin (Level 3) Parts Combined Dispersion 45.6 Dispersion E 20.9 Dispersion F 9.4 Water 24.1 Coating Formulation V Hydrocarbon Resin (Level 4) Parts Combined Dispersion 45.6 Dispersion E 17.8 Dispersion F 11.8 Water 24.8 The thermal papers of Examples 1 to 12 were made by coating base paper with formulations as summarised below: Example 1C : This (control) Example uses coating formulation I containing no poly-α-methylstyrene or α-methylstyrene/vinyltoluene copolymer. Example 2 : This Example uses coating formulation II, containing poly-α-methylstyrene as the water insoluble hydrocarbon resin and acetoacet-o-toluidine as thermal modifier. Examples 3 to 5 use increasing amounts of poly-α-methylstyrene as the water insoluble hydrocarbon resin. Example 3 : This Example uses coating formulation III including Dispersion F-a. Example 4 : This Example uses coating formulation IV including Dispersion F-a. Example 5 : This Example uses coating formulation V including Dispersion F-a. Example 6C : This (control) Example uses coating formulation I which contains no poly-α-methylstyrene or α-methylstyrene/vinyltoluene copolymer. Acetoacet-o-toluidine thermal modifier is included. Example 7 : This Example uses coating formulation II including Dispersion F-b to provide α-methylstyrene/vinyltoluene copolymer as the hydrocarbon resin. The thermal modifier is acetoacet-o-toluidine. Examples 8-10 include increasing amounts of α-methylstyrene/vinyltoluene copolymer as the hydrocarbon resin. Example 8 : This Example uses coating formulation III including Dispersion F-b. Example 9 : This Example uses coating formulation IV including Dispersion F-b. Example 10 : This Example uses coating formulation V including Dispersion F-b. Example 11C : This (control) Example uses coating formulation I. Example 12 : This Example illustrates two layer coating using Dispersion F-a (including poly-α-methylstyrene) as subcoat and formulation I as topcoat. The thermal response of the sheet was tested by producing an image with a Group III facsimile printer (HIFAX 3M EMT 2700) using a solid block test pattern. The resulting image was measured using a Macbeth RD 514 reflection densitometer through a Wratten 106 filter. The instrument was calibrated such that a value of 0.04 indicated pure white and 1.78 a fully saturated black. The results of these tests are set out in Table 1 below. Fingerprint resistance was determined by applying a hand lotion (SBS 40 Medicated Skin Cream manufactured by Sugar Beet Products Co.) to a freshly imaged area of the thermal sensitive paper with a finger. The lotion remained in contact with the image throughout the experiment. The image intensity was monitored as a function of time and when forty percent of the original image intensity was lost the sample was considered to have failed. The results of these tests are included in Table 1 below. Examples 13 - 24 Examples 13C, 15C, 17C, 19C, 21C, and 23C are controls (coating formulation I) where none of the hydrocarbon resin used in the invention is present and baseline fade data for each of the various modifiers is established (these are thus suffixed "C"). In Examples 14, 16, 18, 20 and 22 (coating formulation IV) dispersion F-b (α-methylstyrene/vinyltoluene copolymer resin) is used with the various modifiers to retard "fingerprinting". Example 24 is for comparison purposes and includes polystyrene rather than the poly-α-methylstyrene or α-methylstyrene/vinyltoluene copolymer used in the invention. The coating formulations used in Examples 13 to 24 are summarised (dry weight basis) in Table 4 below. Examples 13C and 14 These Examples use acetoacet-o-toluidine (AAOT) as thermal modifier. Examples 15C and 16 These Examples use diphenoxyethane (DPE) as thermal modifier: Examples 17C and 18 These Examples use phenyl 1-hydroxy-2-naphthoate (PHNT) as thermal modifier: Examples 19C and 20 These Examples use Stearone Wax, the principle constituent of which is diheptadecyl ketone as the thermal modifier: (Stearone Wax is a trade mark product of Argus Chemical Division of Witco.) Examples 21C and 22 These Examples use Kemamide B Wax, the principal constituent of which is octadecanamide as the thermal modifier. (Kemamide B is a trademark product of Humko Sheffield.) Examples 23C and 24 These Examples use acetoacet-o-toluidine as thermal modifier. Example 23C is a control using coating formulation I and Example 24 (coating formulation IV) uses a water dispersable polystyrene latex (reported in the prior art in thermal formulations) in place of the α-methylstyrene/vinyltoluene copolymer to show that it has little if any effect on "fingerprinting". The latex used was purchased from Dow Chemical Company as Dow Plastic Pigment 722. The results of testing the product of Examples 13 to 24 are set out in Table 2 below. Fingerprint Resistance Data Image Erasure Over Time Example Original Macbeth Image Density Length of exposure (days) 0 1 6 11 15 21 26 31 1C 1.36 + + + - - - - - 2 1.36 + + + + + + + + 3 1.34 + + + + + + + + 4 1.30 + + + + + + + + 5 1.30 + + + + + + + + 0 1 4 6 8 18 6C 1.31 + + + - - - 7 1.31 + + + + + + 8 1.30 + + + + + + 9 1.25 + + + + + + 10 1.21 + + + + + + 0 1 3 7 21 24 11C 1.31 + + + - - - 12 1.31 + + + + + + "-" indicates the loss of at least 40% of the original image density "+" indicates the loss of less than 40% of the original image density

Claims: Thermally responsive record material resistant to image smearing comprising a support member bearing a thermally sensitive colour forming composition, the thermally sensitive colour forming composition comprising: a chromogenic material, and in contiguous relationship, an acidic developer material whereby the melting or sublimation of either material or another component of the coating produces a change in colour by reaction between the two; a water insoluble hydrocarbon resin, which is poly-α-methylstyrene or α-methylstyrene/vinyltoluene copolymer or a mixture thereof, and in combination therewith; a thermal modifier selected from acetoacet-o-toluidine, diphenoxyethane, phenyl-1-hydroxy-2-naphthoate, diheptadecyl ketone, octadecanamide, and mixtures thereof; and a binder therefor. Record material as claimed in claim 1, wherein the thermal modifier comprises 10 to 30% by weight of the thermally sensitive colour forming composition. Record material as claimed in claim 1 or claim 2 , wherein the water insoluble hydrocarbon resin comprises 2 to 20% by weight of the thermally sensitive colour forming composition. Record material as claimed in any preceding claim, wherein the acidic developer material is a phenol compound. record material as claimed in claim 4, wherein the phenol compound is 4,4'-isopropylindinediphenol, 2,2-bis (4-hydroxyphenyl)-4-methylpentane, 2,2-bis(4-hydroxyphenyl)5-methylhexane, or a mixture thereof. Record material as claimed in any preceding claim, wherein the chromogenic material is 3-diethylamino-6-methyl-7-aninilinfluoran; 3-diethylamino-7-(2-chloroanilino) fluoran; 3-(N-methylcyclohexylamino)-6-methyl-7-anilinofluoran, or a mixture thereof. Record material as claimed in any preceding claim, wherein the binder is selected from the group consisting of polyvinyl alcohol, methylcellulose, methyl-hydroxypropylcellulose, starch, and hydroxyethylcellulose.

Inventors: DALEBROUX, DEAN G., PETERSEN, THOMAS C.
Applicants: APPLETON PAPERS INC.
Application year: 1988
Main classification: B41M5
IPC codes: B41M5