THERMOSENSITIVE SHEET MATERIAL

Abstract: A thermosensitive sheet material including a substrate (10, 30, 40) and a thermosensitive coating (12, 32, 42) thereon in which the color-forming components or the thermally printed matter is protected from adverse environmental conditions by a cross-linked polymeric binder (32, 44, 54) or a protective layer (14, 24) including a fluorocarbon sizing material. The binder of the thermosensitive coating may be directly cross-linked (32) or the cross-linking agent may be included in a binder forming on top coating (44, 52) over the thermosensitive coating. In the embodiment in which the fluorocarbon sizing material is included in the protective layer, both color-forming components may be included in the thermosensitive coating (13) or one may be included in this coating (22) and the other in the protective layer (24).

Description: THERMOSENSITIVE SHEET MATERIAL Technical Field The present invention relates to thermosensitive sheets or labels and, more particularly, to means for protecting the color- forming components or the printed matter from exposure to elements present in an adverse environment. The printed sheets formed in the manner of labels may be provided for those products normally contained in wrapped packages. Background Art In the field of product labeling, it has been common practice to apply the appropriate parameters such as content, weight, price and the like to the labels by means of printing apparatus utilizing ink or ink ribbons. It is further common practice to print machine readable indicia such as the bar code (now in use on the vast majority of products) on the product label by means of conventional ink printing apparatus. Meanwhile, the use of thermal printing on product label-s has greatly increased in the manner of providing clear and well-defined printed characters and/or images. The machine readable and human readable printing by use of thermal elements also has been expanded into the area of perishable goods which may be packaged in soft packages and stored in an adverse atmosphere that may affect the printing on the package. The wrapped products may include meat, poultry, fish, produce or the like which are subject to an environment containing water or water vapor (condensation) animal fat, oil, vinegar, blood, and alcohol, and it is commonly known that the printing on the labels for these products must be protected from exposure to such environmental elements to enable fast and correct reading of the printed matter. Disclosure of Invention It is an object of the present invention to provide a thermosensitive sheet in which the color forming components or the printed matter on the sheet is protected from adverse elements or material in the surrounding atmosphere in order to maintain the printing in clear and well-defined condition to enable machine and human reading of such printed matter. Thus, according to the invention there is provided a thermosensitive sheet material including a substrate and a coating thereon which includes at least one component of a heat responsive color-forming system, characterized in that the color-forming components are protected from adverse environmental conditions by a cross-linked polymeric binder or a protective layer including a fluorocarbon sizing material. The thermosensitive sheet of the present invention may include a thermally reactive coating or layer, and a top coat containing a fluorocarbon sizing material for providing protection against intrusion of adverse material or elements into the reactive coating. The thermally reactive coating usually includes a color forming dye, a color developer, a wax, and a binder. In one formulation, the sizing agent is mixed with a binder and an anti-stick material. This mixture is applied on top of the thermally reactive layer and provides a protection therefor in a manner wherein any adverse material or element is caused to bead on the surface of the mixture. A second formulation provides for mixing the sizing agent with a binder, an anti-stick material, and a color-forming dye. This mixture is applied on top of the thermally reactive material containing the color developer. A further embodiment provides for cross-linking the binder of the thermally reactive dye coating or the top coating by a chrome complex or glyoxal. A preferred base coating composition consists of a color developer formulation and a dye formulation, the first formulation including a bisphenol, a wax, a clay and a binder, and the dye formulation including a binder and a black dye. Another arrangement for the protection includes a two coat system including a thermally reactive layer and a top coating having a cross-linking agent in a binder. Brief Description of the Drawing Embodiments of the invention will now be described by way of example, with reference to the accompanying drawing, in which: Pig. 1 is a sectional view of a thermally coated sheet of the present invention; Fig. 2 is a sectional view of a base sheet having means protecting a coating on the sheet; Fig. 3 is a sectional view of a base sheet having thermally reactive material thereon which material includes a protective binding material; Fig. 4 is a sectional view of a base sheet having a reactive layer and a protective coating; and Fig. 5 is a sectional view of a modified arrangement from Fig. 4. Best Mode for Carrying Out the Invention Prior to discussing the several illustrations and examples disclosing the present invention, it should be noted that the protective coatings or layers are especially significant and important for use in business entities having meat and produce type environments. The labels which are placed on packaged meat or produce generally carry a company name and/or logo along with a bar code, and printed matter identifying the commodity, the unit weight, the price per unit, and the total price. The bar code and the identifying indicia are thermally printed and such thermal printing must be protected from any adverse environmental material or elements for a period of time so as to maintain a readable image of the printed matter. Referring now to the drawing. Fig. 1 illustrates a protective arrangement which comprises a base sheet 10 of paper or like material and which is preferably of quality grade coated two sides (C2S) paper. The paper 10 is weighted at a range of 15 to 25 kg per ream based on a 60 cm x 90 cm size and preferably at 20.5 kg per ream and is of a quality which displays intense and well-defined black images. The base sheet 10 supports a thermally reactive coating or layer 12 consisting essentially of a color- forming dye, a wax, and a binder. The color-forming dye may be one selected from the group of colorless or light colored dyes. The wax may be one selected from the group of those waxes that enable fast transfer of heat in the color-forming process and which remain wet or moist in a tacky condition for but a short period of time. A top coating or layer 14 includes a fluorocarbon sizing agent, hereinafter further described. The following examples disclose thermal paper coating systems including means for providing protective material layers or coatings and utilizing same to prevent intrusion of adverse material into the thermally active material and prepared for use on a thermally printed label. EXAMPLE I Example I is a composition, arranged as in Fig. 1, and a method of providing the protection required for thermosensitive or thermally reactive material. Material % Dry Range Cellulose Binder 73.0 70-95 Sizing Agent 5.0 1-10 Release Agent 5.0 1-10 Synthetic Wax 15.0 10-20 Anti-foam and Wetting Agents 2.0 1-3 100.0 The fluorocarbon sizing agent is mixed into the top coat or layer -14 consisting of the binder, the wax, the wetting agent and the anti-foam material, and the coating or layer is applied on top of the thermally reactive layer 12. The top coat or layer 14 containing the fluorocarbon sizing agent causes beading, illustrated as 16 in Fig. 1, of any damaging or adverse material or elements, such as oil, water, alcohol, etc., and prevents penetration of such material or elements into the thermally reactive layer 12 which, in a preferred thickness and range thereof, has a weight of 1.6 to 2 kg per ream based on a 62 cm X 95 cm size. EXAMPLE II Another example of the use of the fluorocarbon sizing agent for providing protection for thermosensitive material is described by way of the following example and illustrated in Fig. 2. Material % Dry Range Cellulose Binder 76.0 60-95 Sizing Agent 5.0 1-10 Black dye 15.0 10-20 Synthetic Wax 2.0 1-10 Anti-foam and Wetting Agents 2.0 1-3 100.0 The fluorocarbon sizing agent is mixed into a top coat or layer 24 consisting of the binder, the anti-foam and wetting materials, the wax, and the color-forming black dye. This mixture is applied on the surface of a reactive material layer 22 which consists of a reactive material, a wax and a binder on the top surface of a paper or like substrate 20. The fluorocarbon material in the top layer 24 causes any damaging or adverse material to bead on the surface, the beading formation being illustrated as 26 in Fig. 2, and the top layer prevents penetration of such adverse material into the thermally reactive material layer 22. EXAMPLE III Example III is another composition and a method of providing protection for the thermosensitive material in a single coat arrangement, as illustrated in Fig. 3. COLOR DEVELOPER FORMULATION Material % Dry Range Bisphenol 22.7 20-40 Amide Wax 20.0 15-25 Clay 41.1 35-45 Polyvinyl Alcohol Binder 15.0 10-20 Anti-foam and Wetting Agents 1.1 1-3 99.9 Water is added to the formulation for dilution as necessary depending upon the coating technique. DYE FORMULATION Material % Dry Range Polyvinyl Alcohol Binder 10.0 8-15 Anti-foam and Wetting Agents 0.3 0.2-1.0 Black dye 89.7 85-92 100.0 Water is added to the formulation for dilution as necessary depending upon the coating technique. A preferred base coating composition, for protecting against adverse material or elements in certain environments, consists of the above formulations each of which are mixed and dispersed by means of an attritor or like dispersion apparatus. The formulated mixtures are then mixed together with a Quilon solution prior to coating on the paper 30. The Quilon "S" solution is mixed in an equal* ' amount on a 1 to 1 ratio based on the total polyvinyl alcohol (PVA) solids. The combined formulations of color developer and dye including the Quilon "S" solution are mixed directly into the thermally reactive coating 32 and this overall mixture is coated on a base sheet 30. The combined formulated coating 32 material allows any adverse material to spread on the surface in a thin film-like condition, as illustrated at 34 in Fig. 3, but prevents entry of such adverse material into the thermally reactive material of the coating. The single coating 32 utilizes the effective crosslinking of the polyvinyl alcohol binder by the Quilon chrome complex to provide or render a thermally active dye coating that has good to excellent protection against oil, lard, water and/or alcohol solutions and allows such adverse materials to spread in a film-like condition, illustrated as 34 on the surface of coating 32. The addition of the Quilon solution to the base coating formulation causes a light green surface color on the finished thermal paper. EXAMPLE IV Another two coat system for protecting thermal activated reactants from adverse materials is described as follows and illustrated in Fig. 4. A paper or like substrate 40 has coated thereon a base layer or coat 42 with a protective top coat 44 on the base coat. The base coat 42 composition is made up of the color developing formulation and the dye formulation of Example III, and glyoxal (HCOCHO) is the cross linking agent for the polyvinyl alcohol binder incorporated into both the thermally reactive base coat 42 and into the top coat 44. The amount of glyoxal is in the range of 5 to 12 percent and preferably is 10 percent based on the total solids in " the base coat 42. The top coat 44 consists of the polyvinyl alcohol binder, glyoxal in a range of 5 to 15 percent and preferably 10 percent based on the PVA solids, a wetting agent, and water for dilution as necessary. The two coat system provides good protection to thermally printed matter from oil, lard, water and aqueous alcohol solutions, and sustains any such adverse matter in the spread or film-like condition, illustrated as 46 on the surface of the top coat 44. EXAMPLE V This example is similar to Example IV in utilizing glyoxal as a cross linking agent for the polyvinyl alcohol binder incorporated into the thermally reactive base coat 42 and into the top coat 44, as seen in Fig. 4. The formulation for the top coating 44 includes oxidized starch as a substitute for the polyvinyl alcohol binder, glyoxal in a range of 5 to 15 percent and preferably 10 percent based on the oxidized starch solids, a wetting agent, and water for dilution as necessary. EXAMPLE VI A further example includes the use of Casein in the top coating 54 formulation (Fig. 5) along with a wetting agent and water for dilution. The base coating 52 on the paper or like substrate 50 is the same as described for Example III, except for the combined materials therein. The casein provides good to excellent protection to thermally developed printing or images from the presence of oil, lard, water and alcohol solution, which materials appear as and form a spread or film-like condition, illustrated as 56 in Fig. 5. The various ingredients utilized in the above ' examples are hereafter further identified and are available from the noted sources. The cellulose binder is CMC-7 carboxymethyl cellulose from Hercules Inc., the sizing agent is FC-807 Fluorocarbon from 3M . Company, and the black dye is Pergascript I-BR from Ciba-Geigy Corporation. One wax as listed is Acrawax C which is a synthetic wax available from Glyco Inc. The bisphenol A is defined as 4, 4 iso- propylidenediphenol, the amide wax is Armid HT from Armour Chemical Company, Engelhard Corporation manufactures the Ansilex clay, and Air Products Corporation provides the polyvinyl alcohol binder. The anti-foam and wetting agents used in the above Examples are Nopco NDW from Diamond Shamrock Corp., Zonyl FSO from E.I. du Pont de Nemours and Company, Niaproof 08, further identified as sodium 2-ethylhexyl sulfate, from Niacet Corporation, and Calgon is hexametaphosphate from Calgon Corporation. Quilon "S" is octadecanotao chromic chloride hydroxide from du Pont, glyoxal (HCOCHO) from Aldrich Chemical Company, Stayco G starch is available from A.E. Staley Company, and casein is made by National Casein. A testing operation was set up to test surface resistance of the protected thermosensitive coatings to oil, lard, water and aqueous alcohol. The testing procedure and equipment included the use of a heat gradient step wedge instrument (Precision Gage & Tool Co.) to develop black color on the surfaces of the thermosensitive coatings at seven different temperatures ranging from 93 degrees C to 154 degrees C, and a DNL-2 opacimeter (Technidyne Corporation) to read light reflectance from the surfaces of the test areas. Test sample preparation for oil and lard testing included the developing of black color areas by using the step wedge instrument and then spreading a 3 to 10 micron layer of oil and lard across all seven developed black areas. The test samples ' were then allowed to stand at laboratory ambient temperature for one, two, and four hour testing periods. After such test periods, the samples were wiped clean with an absorbent paper towel and the light reflectance of each test surface was measured with the DNL-2 opacimeter. For the water and 20% aqueous ethanol testing, the black color areas which were developed at 127 degrees C and 138 degrees C were subjected to 5 square cm absorbent paper pads soaked with the water or the 20% aqueous ethanol and weighted with a 100 gram weight across the paper pad to assure intimate contact between the soaked pads and the test surfaces. After standing for one hour at laboratory ambient temperature, the soaked pads were removed, the wet paper was allowed to dry, and the test surface light reflectance was measured with the opacimeter. The test samples included Examples III, IV, V, and VI and a control sample which comprised a 1 ! coating of the thermally reactive, materials without topcoating or binder cross linking agents. It was found that whenever oil, lard, water, or an aqueous alcohol solution penetrated the protected coatings, the black, heat developed color was destroyed and the color returned to white. The reflectance readings obtained from the opacimeter were low readings when the black areas were read, solid black approaching 0 percent reflectance, and the readings were high readings as the color turns to white, a solid white color approaching 100 percent reflectance. The test data is presented in Tables 1 to 4. Table 1 presents readings taken for resistance to oil with a control sample and with the protective coating as set out in above Examples III, IV, V and VI. Table 2 presents readings taken for resistance to lard with samples from above Examples III, IV, V and. VI. Table 3 illustrates test results for water resistance at two temperatures and at an initial time and at one hour later, and Table 4 shows the results for 20 percent aqueous ethanol resistance. TABLE 1 OIL RESISTANCE (Planters Oil) IMAGE CONTROL DEV. 13538- -67B TEMP. 0 1 hr. 2 hr. 4 hr. 93°C 9.4 78.2 82. .8 65.9 104°C 5.6 64.4 -74. .5 60.2 110°C 6.3 66.6 77. .0 61.0 116°C 5.7 64.3 73, .0 61.5 127°C 5.4 59.7 74, .9 58.3 138°C 5.1 57.2 69. .3 60.8 154°C 4.9 49.3 52. .9 46.7 EXAMPLE 3 EXAMPLE 4 13539-14B 13539-22C 0 1 hr. 2 hr. 4 hr. 0 1 hr. . 2 hr. 4 hr. 10.3 42.2 37.9 43.4 13.0 12.4 12.8 14.5 7.5 29.3 26.8 33.1 9.2 8.6 8.2 8.7 6.2 19.4 21.4 26.1 8.9 8.3 8.9 10.0 5.3 17.5 19.0 21.7 7.6 7.4 8.3 9.3 5.1 13.0 14.0 16.5 6.9 6.8 7.5 8.4 4.7 12.2 10.9 12.4 6.2 6.0 6.6 7.1 4.5 9.7 9.1 10.4 6.2 5.8 6.3 6.3 EXAMPLE 5 EXAMPLE 6 13539-22D 13539-28 0 1 hr. 2 hr. 4 hr. 0 1 hr. . 2 hr. 4 hr. 11.5 11.7 12.4 14.9 8.2 9.7 10.5 11.7 7.8 12.7 12.8 15.4 7.7 8.2 11.4 20.4 7.5 16.1 15.2 19.4 6.6 8.1 10.3 18.4 6.9 17.9 17.4 25.4 6.5 7.3 10.3 12.8 6.3 14.9 19.5 25.4 6.1 7.0 9.5 10.6 5.7 14.0 11.1 13.8 6.2 10.0 11.6 16.4 . TABLE 2 LARD RESISTANCE (Bob Evans Lard) IMAGE CONTROL DEV. 13538 -67B 93°C 9.4 62.6 70. 8 70.8 104°C 5.6 41.6 60. 0 57.3 110°C 6.3 50.1 64. ,7 60.8 116°C 5.7 60.4 63. ,5 62.9 127°C 5.4 37.8 63. ,8 52.7 138°C 5.1 29.1 43. ,3 41.4 154°C 4.9 19.5 25. ,8 36.8 EXAMPLE 3 EXAMPLE 4 13539-14B 13539-22C 0 1 hr. 2 hr. 4 hr. 0 1 hr. , 2 hr. 4 hr. 10.3 29.8 24.5 24.0 13.0 13.6 12.2 14.4 7.5 20.1 17.5 14.2 9.2 9.9 7.6 8.3 6.2 16.0 13.8 10.7 8.9 9.1 8.5 9.8 5.3 10.8 11.6 9.8 7.6 8.1 7.7 8.8 5.1 9.8 9.9 8.8 6.9 7.3 7.1 7.7 4.7 7.6 8.2 8.1 6.2 6.4 6.4 6.8 4.5 6.6 7.8 7.2 6.2 6.4 6.3 6.4 EXAMPLE 5 EXAMPLE 6 13539-22D 13539-28 0 1 hr. 2 hr. 4 hr. 0 1 hr, . 2 hr. 4 hr. 11.5 11.7 12.6 13.8 8.2 9.8 11.4 12.2 7.8 11.3 13.6 17.7 7.7 7.4 8.6 10.9 7.5 12.8 13.7 16.4 6.6 7.2 8.4 9.2 6.9 13.0 13.8 21.1 6.5 6.7 7.8 9.3 6.3 10.8 10.4 19.2 6.1 6.5 8.1 9.3 5.7 10.0 8.1 14.2 6.2 6.9 8.4 11.4 TABLE 3 WATER RESISTANCE IMAGE 13538-67B EXAMPLE 3 DEV. CONTROL 13538-67B TEMP. 0 1 HR. 0 1 HR. 127°C 5.2 9.4 4.4 5.7 138°C 4.8 6.3 4.3 5.0 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 13539- -22C 13539-22D 13539-28 0 1 HR. 0 1 HR. 0 1 HR. 7.0 9.1 6.5 8.0 6.8 9.4 6.3 7.7 5.9 7.1 6.3 8.3 TABLE 4 20% AQUEOUS ETHANOL RESISTANCE IMAGE 13538-67B EXAMPLE 3 DEV. CONTROL 13539-14B TEMP. 0 1 HR. 0 1 HR. 127°C 5.2 21.4 4.6 11.3 138°C 4.9 18.6 4.3 10.6 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 13539- -22C 13539-22D 13539-28 0 1 HR. 0 1 HR. 0 1 HR. 6.8 16.9 6.2 15.9 6.3 29.9 6.2 14.3 5.7 12.4 6.7 22.5 An analysis of the data presented in Tables 1 to 4 demonstrates the protective nature of the composition or formulation described in Examples III, IV, V, and VI when compared with their respective control samples (non-protected coatings) . For example, in Table 1, it is seen that the control sample changed appreciably in reflectance after being in contact with oil after one hour of time, 4.9% reflectance (very black) to 49.3% reflectance (light gray) at 154 degrees C color development temperature. Contrasting with such test result is the reflectance value of Example IV in Table 1 which shows practically no change after being in contact with oil for 4 hours, 6.2% to 6.3% reflectance. The test data in Tables 1 and 2 demonstrates that all four Examples, III to VI, provide appreciable protection from oil and lard contact. The test data in Tables 3 and 4 show the % reflectance difference between time 0 and at 1 hour thereafter when subjected to water and 20% aqueous ethanol contact. The difference between time 0 and at 1 hour of the control samples is compared to the same time interval of Examples III to VI. It is discovered that the step wedge heat developed black color areas vary in depth of blackness with the development temperature, and it is seen that the black area developed at 154 degrees C was much darker than the black area developed at 93 degrees C. The data collected at 127, 138, and 154 degrees C development temperatures are most significant since they more closely represent thermal printing temperatures.

Claims: CLAIMS 1. A thermosensitive sheet material including a substrate (10, 30, 40) and a coating thereon (12, 32, 42) which includes at least one component of a heat responsive color-forming system, characterized in that the color-forming components are protected from adverse environmental conditions by a cross-linked polymeric binder (44) or a protective layer (14) including a fluorocarbon sizing material. 2. Thermosensitive sheet material according to claim 1, characterized in that said protective layer (14) contains a second component of said color- forming system. 3. Thermosensitive sheet material according to either claim 1 or claim 2, characterized in that said protective layer (14) also contains a wax, a wetting agent and an anti-foam agent in a binder. -- 4. Thermosensitive sheet material according to claim 3, characterized in that said binder is carboxymethyl cellulose. 5. Thermosensitive sheet material according to claim 1, characterized in that said coating (32) includes said color-forming components, a binder and a cross-linking agent therefor. 6. Thermosensitive sheet material according to claim 1, characterized in that said coating (42) containing the color-forming components is covered by an overcoating (44) including a binder and a cross- linking agent therefor. 7. Thermosensitive sheet material according to either claim 5 or 6, characterized in that said binder is polyvinyl alcohol and said cross-linking agent therefor is octadecanotao chromic chloride hydroxide. 8. Thermosensitive sheet material according to either claim 5 or 6 characterized in that said binder is polyvinyl alcohol and said cross-linking agent therefor is glyoxal. 9. Thermosensitive sheet material according to either claim 5 or 6, characterized in that said binder is oxydized starch and said cross-linking agent is glyoxal. 10. Thermosensitive sheet material according to claim 1, characterized in that the weight of said coating (12, 32, 42) is 1.6 to 2 kg per ream of paper 62 cm x 95 cm/500.

Inventors: LAKES STEPHEN D, LEWIS MAURICE W, MARINELLI NICOLA, SEITZ PAUL W, LAKES, STEPHEN, D., LEWIS, MAURICE, W., MARINELLI, NICOLA, SEITZ, PAUL, W.
Applicants: NCR CO, NCR CORPORATION
Application year: 1986
Main classification: B41M5
IPC codes: B41M5, G09F3