Direct thermal recording media using diaryl urea combinations for oil resistance

Abstract

Non-phenolic direct thermal recording media have a thermally responsive layer containing a leuco dye and a plurality of diaryl urea acidic color developers selected to improve the quality and readability of images produced in such media, particularly after contact with oils such as vegetable oils. The diaryl urea color developers preferably comprise, consist essentially of, or consist of N,N'-diphenyl urea ("DPU") and derivatives of DPU. An exemplary combination is DPU with the color developer commercially known as TGMD.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 63 / 396,893, filed August 10, 2022, entitled "Direct Thermal Recording Media Using Diaryl Urea Combinations for Oil Resistance."

[0002] (Technical field) The present invention relates to direct thermal recording media, particularly to media that are substantially phenol-free and incorporate leuco dyes and acidic color developers to provide a heat-activated printing mechanism. The present invention also relates to related methods, systems, and articles. [Background technology]

[0003] In direct thermal recording, an image is created by passing a recording material (sometimes called coated thermochromic paper, thermal paper, thermal recording material or medium, or thermally responsive recording material) under or across a thermal print head, selectively heating the recording material at selected locations. The recording material includes a coating of a thermally responsive layer, and the image is provided by a heat-induced change in color of the thermally responsive layer. Common applications of direct thermal recording include, but are not limited to, cash register receipts, labels for food or other merchandise, or event tickets.

[0004] Numerous types of direct thermal recording media are known. See, for example, U.S. Pat. No. 3,539,375 (Baum); U.S. Pat. No. 3,674,535 (Blose et al.); U.S. Pat. No. 3,746,675 (Blose et al.); U.S. Pat. No. 4,151,748 (Baum); U.S. Pat. No. 4,181,771 (Hanson et al.); U.S. Pat. No. 4,246,318 (Baum); and U.S. Pat. No. 4,470,057 (Glanz). In these cases, a coating on a substrate contains a basic colorless or light-colored color-forming material, such as a leuco dye, and an acidic color-developing material, which, when heated to an appropriate temperature, melts or softens, allowing the materials to react and thereby produce a colored mark or image. It is desirable for a thermally responsive recording material to have a characteristic thermal response and produce a colored image of sufficient intensity upon selective heat exposure.

[0005] We have recently made many advances in this field regarding the use of specific chemicals or chemical groups in the thermally responsive layer of a recording medium to achieve desirable performance characteristics. For example, in U.S. Patent No. 2022 / 0184986 (Fisher), we disclose, among other things, the use of a combination of color developers in the thermally responsive layer to provide a phenol-free recording medium that can withstand multiple different types of environmental conditions or factors, such as exposure to water, contact with polyvinyl chloride meat packaging film, boiling water, heat, sunlight, and contact with hand sanitizer. The color developers in this case include a combination of N,N'-diphenylurea (DPU) and urea urethane (UU). In U.S. Patent No. 2022 / 0184985 (Fisher), we disclose, among other things, the use of specific color developers in the thermally responsive layer of a recording medium having a water-soluble or water-dispersible paper substrate rather than a conventional paper substrate, thereby providing a phenol-free, water-dispersible recording medium that can avoid image fading or image formation problems associated with high-temperature, high-humidity environmental storage conditions. In this case, the developer includes a derivative of DPU or a combination of DPU and UU. Summary of the Invention

[0006] We have made several further discoveries in this general area. These discoveries relate to the problem of image fading when direct thermal recording media are exposed to oil. As mentioned above, direct thermal recording materials are commonly used for food labels and cash register receipts. In these applications, the recording material may come into contact with oily or greasy fingers or may be splashed with cooking oils or other contaminants. Such oil contact often occurs after an image has been formed on the recording media to provide a bar code, indicia, or other printed information. Depending on the details of the recording material's structure, including the chemicals used in the thermally responsive layer, such oils may cause the printed image to fade or become more or less illegible.

[0007] The challenge of addressing this issue becomes even more acute when it is required that the recording material must be substantially free of phenolic chemicals, i.e., phenol-free, which limits the choice of chemicals to be used as acidic developers in the thermally responsive layer.

[0008] We have found that acceptable or improved image retention (reduced image fading after contact with oil) can be achieved by using certain combinations of non-phenolic color developers in the thermally responsive layer. Surprisingly, some of these combinations include two non-phenolic color developers that, when used individually in the thermally responsive layer, result in completely unacceptable image retention after contact with oil. Particularly interesting combinations are non-phenolic color developers that are both diaryl urea materials (e.g., DPU and a derivative of DPU). Of particular note is the combination of DPU and an N,N'-diaryl urea derivative known in the industry as TGMD (available from Nippon Kayaku Co., Ltd.), which has the following chemical formula: [ka] .

[0009] We have developed a family of new direct thermal recording materials or media that can address the problem of image fading caused by direct contact with oil, especially oil heated to temperatures above room temperature. The disclosed direct thermal recording media are desirably characterized as being non-phenolic, i.e., free of commercially significant concentrations or amounts of phenolic materials.

[0010] Accordingly, disclosed herein, among other things, is a substantially phenol-free direct thermal recording media comprising a substrate and a thermally responsive layer carried by the substrate. Dispersed throughout the thermally responsive layer are a leuco dye and a plurality of developers, the developers including N,N'-diphenylurea ("DPU") and derivatives of DPU. The DPU derivatives include: [ka] In an exemplary embodiment, the derivative of DPU is TGMD, and the DPU and TGMD are present in the thermally responsive layer in a relative weight ratio of DPU / TGMD in the range of 30 / 70 to 60 / 40, or in the range of 40 / 60 to 50 / 50, or less than 50 / 50.

[0011] We disclose a number of related methods, systems, and articles.

[0012] These and other aspects of the present disclosure will become apparent from the following detailed description, however, in no event should the above summary be construed as a limitation on the claimed subject matter, which subject matter is defined solely by the appended claims, as may be amended during prosecution. The articles, systems, and methods of the present invention are described in further detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a schematic perspective view of a roll of direct thermal recording material or media. [Figure 2] 1 is an enlarged schematic front view and a schematic cross-sectional view of a direct thermal recording material. [Figure 3] 1 is a graph of barcode readability measured under various conditions for printed images of a direct thermal recording material sample, in which the only acidic developer used in the thermally responsive layer is N,N'-diphenylurea ("DPU"). [Figure 4] This is a graph similar to that of FIG. 3, but the only acidic developer used in the thermally responsive layer is TGMD. [Figure 5] Graphs similar to FIGS. 3 and 4, but using a 50 / 50 mixture of DPU and TGMD as the acid developer in the thermoresponsive layer. [Figure 6] 1 is a chart showing the design details of a large group of direct thermal recording material samples that have been prepared and tested, and the test results of the direct thermal images formed in such samples. [Figure 7] Included is a photograph (grayscale image) of a portion of the test sample from one of the heating oil tests, which also includes a map or key for sample identification. [Figure 8] 1 is a graph of barcode readability measured under various conditions for printed images of two direct thermal recording material samples, one in which only D8 was used as the acidic developer in the thermally responsive layer, and the other in which a 50 / 50 mixture of D8 and DPU was used as the acidic developer. [Figure 9] Similar graph to FIG. 8, except that in one sample, only TGSH was used as the acid developer, and in the other sample, a 50 / 50 mixture of TGSH and DPU was used as the developer. [Figure 10] Similar graph to FIG. 8, except that in one sample, only tolbutamide was used as the acid developer, and in the other sample, a 50 / 50 mixture of tolbutamide and DPU was used as the developer. [Figure 11]Similar graph to Figure 8, except that in one sample, only NKK-1304 was used as the acid developer, and in the other sample, a 50 / 50 mixture of NKK-1304 and DPU was used as the developer. [Figure 12] Similar graph to Figure 8, except that in one sample, only S-176 was used as the acid developer, and in the other sample, a 50 / 50 mixture of S-176 and DPU was used as the developer. [Figure 13A] 8-12, but showing the test results of five direct thermal recording material samples, the relative weight ratios of DPU / TGMD of the samples being 30 / 70, 40 / 60, 50 / 50, 60 / 40, and 70 / 30, respectively. [Figure 13B] 13B is a graph replotting the data from FIG. 13A with the horizontal axis representing the weight ratio of DPU / TGMD. In the drawings, like reference numerals refer to like elements. DETAILED DESCRIPTION OF THE INVENTION

[0014] As described above, we have discovered unique phenol-free developer chemistries for use in direct thermal recording materials. These new chemistries consist of a combination of two developers that, when used with an appropriate leuco dye, can produce a versatile direct thermal recording material. When in contact with oils, such as vegetable oils, the resulting thermal images are significantly less susceptible to fading and degradation than those produced by using either of these developers individually (in an otherwise identical thermal recording material). In fact, recording materials using only one of these developers may produce images that, after contact with oil, do not even meet the minimum machine-readability standards for barcode images. Two such exemplary developers are 1,3-diphenylurea ("DPU") and TGMD.

[0015] Direct thermal recording materials are often manufactured in large rolls on industrial-sized coating machines using a continuous web of paper or other flexible substrate material. Such a roll 100 of direct thermal recording material 104 is shown schematically in FIG. 1. After manufacture, the roll 100 can be converted into individual sheets, labels, or smaller rolls by slitting, cutting, or other standard operations. An enlarged side or cross-sectional view of the recording material 104 is shown schematically in FIG. 2 to illustrate a typical substructure made up of constituent layers or coatings.

[0016] The recording material 104 can be created by applying several different coatings to at least one side or major surface 110a of the substrate 110. The major surface 110a can be referred to as the front surface of the substrate, and the exposed major surface 104a can be the front surface of the recording material 104. The opposite major surface 104b can be the back surface of the recording material. Briefly, the substrate 110 is coated to carry a base coat layer 112, a thermally responsive layer 114, and a top coat layer 116. The coatings are preferably applied in the order shown, with layer 114 positioned between layers 112 and 116 and layer 112 positioned between layer 114 and the substrate 110. In some cases, the base coat 112 may be omitted, the top coat 116 may be omitted, or both the base coat and the top coat may be omitted. The coatings can be formed by any suitable coating technique, including roll coating, knife coating, rod coating, gravure coating, curtain coating, spot coating, etc. Additionally, additional layers and coatings may be added to or included on the front and / or back side of the recording material. For example, one or more coatings may be applied to the opposite side, or major surface 110b, of the substrate, as described further below. However, the other elements of the direct thermal recording material 104 will now be described in more detail.

[0017] The substrate 110 can be any material onto which other layers can be coated or applied and then carried. The type or variety of substrate material is not critical. Generally, the substrate 110 is in the form of a sheet or roll and can be or include a support such as a web, ribbon, tape, belt, film, card, or the like. In this regard, a sheet refers to an article having two major (major) surface dimensions and a relatively small thickness dimension; in some cases, the sheet may be wound to form a roll. In that regard, the substrate 110 is typically thin and flexible, yet strong enough to withstand the forces and tensions experienced in a coating machine without undue breakage. The substrate 110 can be opaque, transparent, or translucent, and can be pigmented or unpigmented. The substrate material can be fibrous, including, for example, paper and fibrous synthetic materials. It can be film, including, for example, cellophane and synthetic polymer sheets that are cast, extruded, or otherwise formed. Suitable plastic films include polypropylene (including oriented polypropylene (OPP) and biaxially oriented polypropylene (BOPP)), polyethylene (PE), and polyethylene terephthalate (PET) films. Thus, the substrate material can be non-cellulose.

[0018] An exemplary substrate 110 may be or include a medium-sized base paper (e.g., a conventional paper that is neither water-soluble nor water-dispersible). The thickness of the substrate 110 may depend on its composition, but typical thicknesses (calipers) for cellulosic materials range from 1.9 to 12 mils (e.g., 50 to 300 μm), or other suitable thicknesses. Paper may range from 35 to 200 g / m 2The substrate 110 may have a basis weight in the range of 100 to 1500 mm, although other suitable basis weights may be used. The paper may also be treated with one or more agents, such as a surface sizing agent. Uncoated base papers (including unsized, conventional sized, and lightly treated base papers) may be used. The substrate 110 may be simple in structure and devoid of glossy coatings or other substantial functional coatings. The substrate 110 may be substantially uniform in composition throughout its thickness, rather than, for example, a multi-layer structure or material that has one or more separate functional coatings already applied. However, in some cases, it may be desirable to treat, prepare, or otherwise process the substrate 110 in preparation for coating one or more other layers shown thereon.

[0019] The base coat 112 can be applied directly to the surface 110a of the substrate 110 before other coatings are applied. The base coat 112 can be characterized or described as a thermal insulation layer, separator layer, heat-reflective layer, isolation layer, or prime coat, as the case may be. By tailoring the thermal conductivity of the layer 112 to be lower than both the thermal conductivity of the thermally responsive layer 114 and the thermal conductivity of the substrate 110, the base coat 112 provides a degree of thermal insulation between these other two layers. Such insulation promotes image quality, imaging speed, or both, by ensuring that heat transferred to the front surface 104a by a thermal printhead (not shown) is not substantially lost by thermal conduction through the thermally responsive layer 114 to the more massive substrate 110.

[0020] The base coat 112 may be composed of hollow sphere pigments (HSPs), such as product codes Ropaque™ TH-2000 or TH-500EF, available from The Dow Chemical Company, or other suitable materials. The HSPs help reduce the thermal conductivity of the base coat. The base coat 112 can be created by a process in which a dispersion is coated onto the surface 110a of the substrate and then dried. In some cases, the base coat 112 can be removed and omitted from the product structure. When included as part of the recording material, the thermal insulation layer may have a thickness ranging from 2 μm to 12 μm, or other suitable thickness.

[0021] The thermally responsive layer 114 may be coated over the base coat 112 or over the substrate 110 if the base coat is omitted. The layer 114 may alternatively be referred to as a thermally sensitive color-forming layer. This layer 114 contains a color-forming composition that is sensitive to heat (i.e., changes color upon sufficient heating). The color-forming composition has two main components: a color-forming dye (electron-donating dye precursor), also known as a leuco dye or color-forming material, and an acidic color developer. The leuco dye and acidic color developer are typically ground to individual particle sizes of 1 to 10 micrometers, dispersed in a binder, and distributed uniformly and in continuous relationship with one another throughout the layer 114. Upon sufficient heating at a given location, the acidic color developer particles react with the leuco dye particles, resulting in a color change at the heated location, typically from a lighter color to a darker color. Known systems and materials are described in U.S. Pat. No. 3,539,375 (Baum); U.S. Pat. No. 3,674,535 (Blose et al.); U.S. Pat. No. 3,746,675 (Blose et al.); U.S. Pat. No. 4,151,748 (Baum); U.S. Pat. No. 4,181,771 (Hanson et al.); U.S. Pat. No. 4,246,318 (Baum); U.S. Pat. No. 4,470,057 (Glanz); and U.S. Pat. No. 5,955,398 (Fisher et al.).

[0022] The acidic developer is preferably non-phenolic and, as already explained above, advantageously comprises a combination of two different non-phenolic diaryl urea developer materials, such as 1,3-diphenylurea ("DPU"), and a material that is a chemical derivative of DPU. DPU may alternatively be 1-3-diphenylurea or 1-3-diphenylurea; N,N'-diphenylurea; diphenylurea; urea, N,N'-diphenyl-; carbanilide; diphenylcarbamide; or C 13 H 12 It is also known as N2O. The chemical formula for DPU is: [ka] .

[0023] Exemplary DPU derivative developers are the materials designated herein as NKK-304, TGMD, and S-176, each having the following chemical formula: [ka] .

[0024] NKK-1304 is represented as N-[2-(3-phenylureido)phenyl]benzenesulfonamide and is available from Nippon Soda Co., Ltd. TGMD is available from Nippon Kayaku Co., Ltd. S-176 is available from Sanko Co., Ltd.

[0025] One rationale for using a non-phenolic developer in the thermally responsive layer 114 is to meet market demand for phenol-free receipts, labels, and the like. Thus, while it is often desirable that not only the thermally responsive layer 114 be phenol-free or substantially phenol-free, but that the entire direct thermal recording material 104 be phenol-free or substantially phenol-free, this is not necessary in all cases. The term substantially phenol-free is used to include both items that are absolutely and completely phenol-free and items that contain only trace amounts of phenolic materials below commercially acceptable thresholds.

[0026] As shown in the test results below, when DPU is used alone with an appropriate leuco dye in the thermally responsive layer of a direct thermal recording material, the image initially produced by the direct thermal printer is completely acceptable—dark and clear enough to be easily readable by humans, and even easily machine-readable if the image is in the form of a barcode, QR code, or similar. However, if a vegetable oil or other substance is subsequently applied to the surface of the imaged recording material, the image quality dramatically changes from acceptable to completely unacceptable. In other words, when DPU is used alone, it offers virtually no protection against oil contamination compared to the visibility of the direct thermal image. Our testing has also shown that some DPU-derived materials, particularly TGMD and NKK-1304, offer little protection against oil contamination. Surprisingly, however, when the two developer materials are combined (using an appropriate leuco dye in the thermally responsive layer of a direct thermal recording material), the resulting product exhibits dramatically improved image retention in the presence of oil compared to either developer used alone.

[0027] In embodiments using a combination of DPU and TGMD or DPU and a developer such as NHK-1304, it is preferred that the developer and the selected leuco dye are each homogeneously and uniformly dispersed throughout the thermally responsive layer 114. This does not necessarily mean that these various materials are evenly loaded within the layer. In some cases, it may be desirable to have approximately equal loadings of DPU and the other developer, i.e., a relative weight ratio of approximately 1. However, other weight ratios can be used, as shown in the examples below. When DPU is used in combination with TGMD or a different derivative of DPU, it is preferred that only two developers are used as chemical developers in layer 114.

[0028] In addition to the DPU and second color developer, the thermally responsive layer 114 also includes, of course, at least one leuco dye adapted to react with the color developers at elevated temperatures to produce a mark or color change. The leuco dye(s) can be any known dye(s) capable of such a reaction. Examples include, but are not limited to: ·ODB-2 (CAS number: 89331-94-2, chemical name spiro(isobenzofuran-1(3H),9'-(9H)xanthene)-3-one, 6'-(ethyl(4-methylphenyl)amino)-3'-methyl-2'-(phenylamino)-); BK305 (CAS number: 129473-78-5, chemical name: spiro(isobenzofuran-1(3H),9'-(9H)xanthen-3-one,6'-(dipentylamino)-3'-methyl-2'-(phenylamino)-); and ETAC (CAS number: 59129-79-2, chemical name spiro(isobenzofuran-1(3H),9'-(9H)xanthene)-3-one, 6'-(ethyl(4-methylphenyl)amino)-3'-methyl-2'-(phenylamino)-).

[0029] The thermally responsive layer 114 also includes one or more suitable binders to help hold the particles within the layer together. Such binders may include poly(vinyl alcohol), hydroxyethyl cellulose, methyl cellulose, isopropyl cellulose, starch, modified starch, gelatin, and the like. Latex materials, including polyacrylates, polyvinyl acetates, polystyrene, and the like, may also be used. The binder helps maintain the mechanical integrity of the layer 114 in response to brushing or handling forces resulting from use or storage of the recording material 104. Enough binder should be present to provide such protection, but not so much that it prevents reactive contact between the color-forming reactive materials from being achieved. The binder may be present at 5-30% by weight of the dried coating.

[0030] In addition to the leuco dye, color developer, and binder, the color-forming composition of layer 114 may also include one or more materials called modifiers that aid in color formation. The modifiers can function by either (a) lowering the melting point of the dye / color developer and / or (b) acting as a type of solvent in which the dye and color developer dissolve or melt. Thus, the modifiers can enhance the reaction between the leuco dye and color developer to produce stronger thermal images, faster image formation, or both. See, for example, U.S. Patent Nos. 4,531,140 (Suzuki et al.), 4,794,102 (Petersen et al.), 5,098,882 (Teraji et al.), 6,835,691 (Mathiaparanam et al.), and 6,921,740 (Hizatate et al.).

[0031] Typically, the thermally responsive layer of a conventional direct thermal recording material has a coating weight of 1.5 to 6 lbs / 3,300 sq ft (2.2 to 8.9 g / m) for a finished dry thickness ranging from 1.2 to 4.8 μm or 1 to 5 μm. 2 ), more typically 2-4 lb / 3,300 sq ft (3.0-5.9 g / m 2 ) coat weight. The practical lower limit is about 1 lb / 33,000 cubic feet (about 1.48 g / m 2 The thermally responsive layer 114 of the recording material 104 of the present invention can also be applied at these same conventional coat weights and thicknesses, if desired.

[0032] Returning again to FIG. 2 , a topcoat layer 116 is shown overlying and in contact with the thermally responsive layer 114. In the illustrated embodiment, the outer major surface of the topcoat 116 is exposed to air and directly corresponds to the outer major surface 104a of the thermal recording material 104. The topcoat 116 is optional and can be omitted if desired. When included, the topcoat can protect the underlying layers of the recording material 104 from undesirable contaminants or substances. For example, some topcoats can be used as a barrier or seal against the infiltration of oil or other unwanted liquids, but their barrier effect against oil is limited, especially at elevated temperatures, and is secondary to their barrier effect against water.

[0033] The topcoat 116 may be any suitable topcoat of conventional design. The topcoat 116 may include, for example, a binder such as modified or unmodified polyvinyl alcohol, an acrylic binder, a crosslinker, a lubricant, and a filler such as aluminum trihydrate and / or silica. The topcoat 116 may have a thickness in the range of 0.5 to 2 μm, or other suitable thickness.

[0034] The disclosed recording materials may include additional layers and coatings beyond those described above. Such other layers or coatings include coating(s) that can be applied to the back surface 110b of the substrate 110. One such layer is shown in FIG. 2 and is labeled 118. This layer 118 can be an adhesive layer including a pressure-sensitive adhesive (PSA), a hot-melt adhesive, or other suitable adhesive. By providing this on the back side of the recording material 104, the recording material can function as a label, attached to a container, film, or other object with its front, thermally printed side visible to the user. A release liner (not shown) can also be included to cover the PSA layer until ready for use. For applications that do not require a liner, a release coating can also be applied to the surface.

[0035] As mentioned above, direct thermal recording materials have the potential to be used in a variety of applications. Some of these applications involve the use of oil, and in some cases, hot oil may be splashed, deposited, or otherwise applied to the imaged recording material. One of the goals of our research was to identify chemicals, particularly non-phenolic chemicals, that can be used to maintain high-quality direct thermal images even when in contact with or contaminated by such oils. [Example]

[0036] Examples and Comparative Examples A number of direct thermal recording media samples were prepared and tested in accordance with the teachings above.

[0037] Each sample (Example or Comparative Example) was prepared in the following manner unless otherwise specified: The first step was to coat a base coat (e.g., see layer 112 in FIG. 2) on one side or main surface of a substrate (e.g., see substrate 110 in FIG. 2). The substrate used was 63 g / m 2 (gsm) highly refined paper sheets. This paper was neither soluble nor dispersible in water. The basecoat was thermally insulating and contained a mixture of calcined clay, such as BASF Corporation's Ansilex 93, and The Dow Chemical Company's Ropaque™-TH-2000 hollow sphere pigment (HSP), and an SBR binder, at 4.5 g / m. 2 After drying, a thermally responsive layer (see, for example, layer 114 in Figure 2) was coated on top of the base coat. The coat weight of the thermally responsive layer was 1.5 g / m 2 After this coating dried, a topcoat (see, for example, topcoat 116 in FIG. 2) was coated on the surface of the thermally responsive layer. The topcoat consisted of exfoliated clay, PVOH, a crosslinker, and a lubricant such as zinc stearate, and was applied at a thickness of 1.5 g / m. 2 After the topcoat had dried, no other coatings were applied to the samples and they were ready for thermal printing and testing.

[0038] Details of the coating compositions used for the thermally responsive layer are now provided: A number of dispersion formulations were prepared.

[0039] One dispersion, designated Dispersion A, was made for the chromogenic material (leuco dye), and had the following formulation: where all parts or percentages are understood to be by weight:

[0040] [Table 1]

[0041] Another dispersion, designated Dispersion B1, was made for DPU (described in detail above), an acidic developer material, N,N'-diurea. The formulation of this dispersion was as follows:

[0042] [Table 2]

[0043] Another dispersion, designated Dispersion B2, was made for another developer material, the N,N'-diurea derivative TGMD (described in detail above), and the formulation was the same as B1, except that DPU was replaced with TGMD.

[0044] Another dispersion, designated Dispersion B3, was made for another developer material, D8, which has the chemical formula 4-hydroxyphenyl-4-isopropoxyphenyl sulfone and has the following structure: [ka] This formulation was the same as B1 except that DPU was replaced with D-8.

[0045] Another dispersion, designated Dispersion B4, was made for another developer material, TGSH, which has the chemical formula 2,2'-diallyl-4,4'sulfonyldiphenol and has the following structure: [ka] This formulation was the same as B1 except that DPU was replaced with TGSH.

[0046] Another dispersion, designated Dispersion B5, was made for another developer material, tolbutamide, which has the chemical formula 1-butyl-3-(4-methylphenyl)sulfonylurea and has the following structure: [ka] This formulation was the same as B1 except that DPU was replaced with tolbutamide.

[0047] Another dispersion, designated Dispersion B6, was made for another developer material, NKK-1304, an N,N'-diurea derivative, which has the chemical formula N-[2-(3-phenylureido)phenyl]benzenesulfonamide and the following structure: [ka] This formulation was the same as B1 except that DPU was replaced with NKK-1304.

[0048] Another dispersion, designated Dispersion B7, was made for another developer material, S-176, an N,N'-diurea derivative, available from Sanko Co., Ltd., and having the following structure: [ka] This formulation was the same as B1 except that DPU was replaced with S-176.

[0049] Different of these dispersion formulations were mixed with other ingredients to make the coating formulations used to form the thermally responsive layer of a given sample. Unless otherwise stated, the coating formulations were as follows:

[0050] [Table 3]

[0051] The first sample, "CE1" (Comparative Example 1), was made using Dispersion B1 as the developer component in the coating formulation of Table 3. This sample therefore contained only one developer (DPU) in the thermally responsive layer.

[0052] Another sample, "CE2" (Comparative Example 2), was made using Dispersion B2 as the developer component in the coating formulation of Table 3. Thus, this sample contained only one developer (TGMD) in the thermally responsive layer.

[0053] Another sample, "Example 2" (or simply "2"), was made using a mixture of equal amounts (by weight) of Dispersion B1 and Dispersion B2 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B2. This sample therefore contained two developers (DPU and TGMD; 50 / 50 ratio) in the thermally responsive layer.

[0054] Another sample, "CE3" (Comparative Example 3), was made using Dispersion B3 as the developer component in the coating formulation of Table 3. Thus, this sample contained only one developer (D-8) in the thermally responsive layer.

[0055] Another sample, "Example 3" (or simply "3"), was made using a mixture of equal parts (by weight) of Dispersion B1 and Dispersion B3 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B3. This sample therefore contained two developers (DPU and D-8; 50 / 50 ratio) in the thermally responsive layer.

[0056] Another sample, "CE4" (Comparative Example 4), was made using Dispersion B4 as the developer component in the coating formulation of Table 3. Thus, this sample contained only one developer (TGSH) in the thermally responsive layer.

[0057] Another sample, "Example 4" (or simply "4"), was made using a mixture of equal parts (by weight) of Dispersion B1 and Dispersion B4 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B4. This sample therefore contained two developers (DPU and TGSH; 50 / 50 ratio) in the thermally responsive layer.

[0058] Another sample, "CE5" (Comparative Example 5), was made using Dispersion B5 as the developer component in the coating formulation of Table 3. This sample therefore contained only one developer (tolbutamide) in the thermally responsive layer.

[0059] Another sample, "Example 5" (or simply "5"), was made using a mixture of equal parts (by weight) of Dispersion B1 and Dispersion B5 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B5. This sample therefore contained two developers (DPU and tolbutamide; 50 / 50 ratio) in the thermally responsive layer.

[0060] Another sample, "CE6" (Comparative Example 6), was made using Dispersion B6 as the developer component in the coating formulation of Table 3. Thus, this sample contained only one developer (NKK-1304) in the thermally responsive layer.

[0061] Another sample, "Example 6" (or simply "6"), was made using a mixture of equal amounts (by weight) of Dispersion B1 and Dispersion B6 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B6. Thus, this sample contained two developers (DPU and NKK-1304; 50 / 50 ratio) in the thermally responsive layer.

[0062] Another sample, "CE7" (Comparative Example 7), was made using Dispersion B7 as the developer component in the coating formulation of Table 3. Thus, this sample contained only one developer (S-176) in the thermally responsive layer.

[0063] Another sample, "Example 7" (or simply "7"), was made using a mixture of equal parts (by weight) of Dispersion B1 and Dispersion B7 as the developer component in the coating formulation of Table 3. Thus, this coating formulation used 19 parts Dispersion B1 and 19 parts Dispersion B7. Thus, this sample contained two developers (DPU and S-176; 50 / 50 ratio) in the thermally responsive layer.

[0064] All of these samples were thin and flexible, with a uniformly white or light-colored front surface. Each sample was then tested for its ability to form an image by direct thermal printing, the print quality of the image, and the print quality of the image after the sample was exposed to vegetable oil for 24 hours.

[0065] Direct thermal printing was performed using a Zebra™ thermal printer, model 140-401, at a speed of 6 inches per second (ips) with the printhead's default energy setting (11.7 mJ / mm 2) was used to measure each sample. The printed images in each case were a barcode pattern and a rectangular block. Print quality, or image quality, was tested using two methods. First, the quality (machine readability) of the barcode pattern was measured using a TruCheck™ Barcode Verifier (Model TC-843) operating at a wavelength of 650 nm. The verifier was calibrated to the ANSI (American National Standards Institute) Barcode Print Quality Guideline X3.182, published in 1990. The verifier provides ANSI values ​​for the measurement of the barcode image. From best quality (best readability) to worst quality (worst readability), the measurements range from A (3.5-4.0), B (2.5-3.4), C (1.5-2.4), D (0.5-1.4), and F (0-0.4). Thus, a measurement of "A" indicates the best readability of the barcode, and "F" indicates the worst readability of the barcode. For many applications, values ​​of C or greater (at least 1.5) are acceptable or passing, and values ​​below 1.5 are failing.

[0066] In the second technique, the quality of the direct thermal image was tested by measuring the optical density (darkness) of a rectangular block of the image. This measurement was performed using a Techkon™ SpectroDens densitometer. The measured optical density (OD) values ​​are logarithmic, meaning that an OD of 2.0 is 10 times darker than an OD of 1.0.

[0067] For each sample, the initial print quality of the printed image was measured using the two techniques described above to obtain (1) an ANSI value (A, B, C, etc.) and (2) an OD value. Three substantially identical samples were then exposed to oil at various temperatures for 24 hours: (1) Crisco™ vegetable oil was brushed onto the front surface of the first sample (after thermal imaging) and allowed to stand at room temperature (RT) for 24 hours, after which the image quality was measured; (2) the same oil was brushed onto the front surface of the second sample (after thermal imaging) and allowed to stand at 40°C for 24 hours, after which the sample was removed from the oven and the image quality was measured; and (3) the same oil was brushed onto the front surface of the third sample (after thermal imaging) and allowed to stand at 60°C for 24 hours, after which the sample was removed from the oven and the image quality was measured. The high-temperature exposure was included to more realistically assess the actual usage conditions of these products, as hot oil is known to be present in some user environments.

[0068] The results of this testing are summarized in the table in Figure 6. This table includes a column labeled "% Loss" for each oil exposure test. This number is obtained by comparing the OD measured after the oil test with the initial OD value. Specifically, the difference between those OD values ​​is divided by the initial OD value, and the result is expressed as a percentage. The remaining columns, letters, and numbers are self-explanatory from the above discussion.

[0069] A wide range of responses was observed. Figure 7 includes a photograph of an array of 13 samples mounted on a rigid backing for placement in a 40°C oil testing oven. The samples remained in the oven for several hours, then were temporarily removed for photographing and then returned to the oven for the duration of the test. The map or key portion of Figure 7 can be used to identify each sample in the photograph: (I) corresponds to CE1, (II) corresponds to CE7, (III) corresponds to Example 7, (IV) corresponds to CE2, (V) corresponds to Example 2, (VI) corresponds to CE3, (VII) corresponds to Example 3, (VIII) corresponds to CE4, (IX) corresponds to Example 4, (X) corresponds to CE5, (XI) corresponds to Example 5, (XII) corresponds to CE6, and (XIII) corresponds to Example 6.

[0070] The data in the table in Figure 6 can be used to create some insightful graphs. Three particularly relevant graphs are shown in Figures 3, 4, and 5.

[0071] In Figure 3, we can see that the barcode readability (measured with a barcode verifier device) of a sample using only DPU as the acid developer in the thermally responsive layer starts out excellent. However, upon exposure to oil, even at room temperature, the image deteriorates from the highest ANSI score of "A" to the lowest score of "F." Figure 4 shows similar behavior for a sample using only TGMD (a derivative of DPU) as the acid developer. Surprisingly, when these two developers are used in combination (equal amounts, 50 / 50), the resulting recording medium exhibits dramatically improved image retention when exposed to oil, even when exposed to hot oil at 40°C and 60°C, as shown in Figure 5.

[0072] Figure 8 compares recording media using only D8 as the developer with recording media using a 50 / 50 combination of D8 and DPU, showing that the addition of DPU had no measurable effect on the initial image quality, but did degrade image quality in the room temperature oil test.

[0073] Figure 9 compares recording media using only TGSH as the developer with a 50 / 50 combination of TGSH and DPU, showing that the addition of DPU had no measurable effect on any of the ANSI measurements.

[0074] Figure 10 compares recording media using only tolbutamide as the developer with a 50 / 50 combination of tolbutamide and DPU, showing that adding DPU degrades the initial ANSI image quality without any measurable effect on any of the oil-related measurements.

[0075] Figure 11 compares recording media using only NKK-1304 as the developer with a 50 / 50 combination of NKK-1304 and DPU, showing that the addition of DPU had no measurable effect on the initial ANSI image quality, but did improve image quality / retention in all oil-related measurements.

[0076] Figure 12 compares recording media using only S-176 as the developer with a 50 / 50 combination of S-176 and DPU, showing that the addition of DPU had no measurable effect on the initial ANSI image quality, but did improve image quality / retention in all oil-related measurements.

[0077] For embodiments using multiple color developers, the effect of using weight ratios other than 50 / 50 was also investigated. In that regard, direct thermal recording media samples similar to Example 2 (a 50 / 50 combination of DPU and TGMD) were prepared using different ratios of these materials. For example, the sample designated "Example 2A" or simply "2A" was prepared using the coating formulation in Table 3, but the 38 parts developer dispersion consisted of 30% (approximately 11.4 parts) Dispersion B1 (containing DPU) and 70% (approximately 26.6 parts) Dispersion B2 (containing TGMD). Similarly, Example 2B ("2B") was prepared using a 40 / 60 weight ratio of DPU / TGMD, Example 2D ("2D") was prepared using a 60 / 40 ratio, and Example 2E ("2E") was prepared using a 70 / 30 ratio. Example 2C is simply Example 2 relabeled to reflect the 50 / 50 weight ratio. Details of the samples and measurements made on these samples were performed in the same manner as described above in relation to Figure 6 and are shown in Table 4 below.

[0078] [Table 4]

[0079] Figures 13A and 13B plot a portion of the data from Table 4. Figure 13A has a layout similar to Figures 3 through 5, showing the ANSI values ​​for barcode readability on the vertical axis and various measurement conditions (initial read, room temperature oil, 40°C oil, and 60°C oil) on the horizontal axis. Figure 13B plots the same data, but with the DPU / TGMD weight ratio on the horizontal axis. Both figures show that the benefit of mixing the two developers generally decreases when the ratio deviates from 50 / 50. However, Figure 13B shows an asymmetric effect. That is, the 40 / 60 sample provides the same ANSI image quality results as the 50 / 50 sample under all conditions, while the 30 / 70 sample shows improvement compared to the 70 / 30 sample. Therefore, to the extent that manufacturing variations in density from the target ratio can occur, there may be an advantage to using a target ratio less than 50 / 50.

[0080] Further explanation regarding the various scopes of disclosure follows.

[0081] A. Recording Medium. The recording medium comprises a substrate and a thermally responsive layer. The thermally responsive layer is carried by the substrate. The thermally responsive layer includes a leuco dye and a plurality of color developers. The recording medium is substantially free of phenol. The plurality of color developers include N,N'-diphenylurea ("DPU") and derivatives of DPU.

[0082] B. Any of the media disclosed above, further comprising a base coat between the thermally responsive layer and the substrate.

[0083] C. Any of the media disclosed above further comprising a base coat containing hollow sphere pigments.

[0084] D. Any of the media disclosed above, further comprising a topcoat carried by the substrate, the thermally responsive layer being disposed between the topcoat and the substrate.

[0085] E. Any of the media disclosed above, wherein the DPU and derivatives of DPU are dispersed throughout the thermally responsive layer.

[0086] F. Any of the media disclosed above, wherein the thermally responsive layer is substantially free of color developers other than DPU and derivatives of DPU.

[0087] G. DPU derivatives are [ka] The medium of any of the preceding disclosures, selected from one of:

[0088] H. Any of the media disclosed above, wherein the derivative of DPU is TGMD.

[0089] I. Any of the media disclosed above, wherein the derivative of DPU is TGMD, and the DPU and TGMD are present in the thermally responsive layer in a relative weight ratio of DPU / TGMD ranging from 30 / 70 to 60 / 40.

[0090] J. Any of the media disclosed above, wherein the derivative of DPU is TGMD, and the DPU and TGMD are present in the thermally responsive layer in a relative weight ratio of DPU / TGMD ranging from 40 / 60 to 50 / 50.

[0091] K. Any of the media disclosed above, wherein the derivative of DPU is TGMD, and the DPU and TGMD are present in the thermally responsive layer in a relative weight ratio of DPU / TGMD of less than 50 / 50.

[0092] L. Any of the media disclosed above, wherein the recording medium is phenol-free.

[0093] M. Any of the media disclosed above, wherein the plurality of color developers consists essentially of DPU and derivatives of DPU.

[0094] N. Any of the media disclosed above, wherein the thermally responsive layer has a coat weight of 1.5 to 6 pounds per 3,300 square feet.

[0095] O. Alternative recording medium. The recording medium comprises a substrate and a thermally responsive layer. The thermally responsive layer is carried by the substrate. The thermally responsive layer includes a leuco dye and a plurality of color developers. The plurality of color developers consists essentially of N,N'-diphenylurea ("DPU") and a derivative of DPU, with the relative weight ratio of DPU / DPU derivative being within the range of 30 / 70 to 60 / 40. The recording medium is substantially phenol-free.

[0096] P. DPU derivatives are [ka] any medium of the foregoing alternative medium disclosure selected from one of:

[0097] Q. Any of the media of the preceding alternative media disclosures wherein the derivative of DPU is TGMD.

[0098] R. Any of the media disclosed above, wherein the DPU and derivatives of DPU are dispersed throughout the thermally responsive layer.

[0099] S. The medium of any of the preceding alternative medium disclosures, wherein the DPU derivative is TGMD and the relative weight ratio of DPU / TGMD is from 40 / 60 to 50 / 50.

[0100] T. The medium of any of the preceding alternative medium disclosures, wherein the plurality of color developers consists of DPU and TGMD.

[0101] Unless otherwise noted, all numerical values ​​expressing quantities, measured properties, and the like used in the specification and claims are understood to be modified by the term "about." Accordingly, unless otherwise indicated, the numerical parameters set forth in the specification and claims are approximations that may vary depending on the desired properties one of ordinary skill in the art would obtain using the teachings of the present application. The doctrine of equivalents is not intended to be limiting to the scope of the claims, and each numerical parameter should be construed in light of, at least, the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, to the extent that numerical values ​​are set forth in the specific examples set forth herein, they are reported as precisely as reasonably possible. However, any numerical value can contain substantial errors associated with the limitations of testing or measurement.

[0102] The use of relative terms such as "top," "bottom," "upper," "lower," "above," "below," and the like to describe various embodiments is for convenience to facilitate the description of some embodiments herein. Despite the use of such terms, the present disclosure should not be construed as limited to a particular orientation or relative position, but rather should be understood to encompass embodiments having any orientation and relative position in addition to those described above.

[0103] Various modifications and alterations of the present invention will be apparent to those skilled in the art without departing from the spirit and scope of the present invention, which is not limited to the exemplary embodiments described herein. The reader should assume that features of one disclosed embodiment are applicable to all other disclosed embodiments unless otherwise specified. All U.S. patents, patent application publications, and other patent and non-patent literature referenced herein are incorporated by reference to the extent they do not contradict the foregoing disclosure.

Claims

1. A recording medium, Substrate and A thermally responsive layer supported by a substrate, Between the thermal response layer and the substrate is a base coat layer, Equipped with, The thermal response layer contains a leuco dye and multiple color developers. The recording medium is substantially phenol-free. Multiple color developers include N,N'-diphenylurea ("DPU") and derivatives of DPU, the derivatives of DPU are 【Chemistry 1】 It has a structure, DPU and DPU derivatives are present in the thermal response layer, with a relative weight ratio of DPU / DPU derivatives ranging from 30 / 70 to 60 / 40. The above recording medium.

2. The medium according to claim 1, wherein the base coat further comprises a hollow spherical pigment.

3. The medium according to claim 1, further comprising a topcoat supported by a substrate, wherein a thermally responsive layer is disposed between the topcoat and the substrate.

4. The medium according to claim 1, wherein DPU and a derivative of DPU are dispersed throughout the entire thermal response layer.

5. The medium according to claim 1, wherein the thermal response layer substantially contains no colorants other than DPU and DPU derivatives.

6. The medium according to claim 1, wherein the relative weight ratio is in the range of 40 / 60 to 50 / 50.

7. The medium according to claim 1, wherein the relative weight ratio is less than 50 / 50.

8. The medium according to claim 1, wherein the recording medium does not contain phenol.

9. The medium according to claim 1, wherein the multiple color developers essentially consist of DPU and derivatives of DPU.

10. The medium according to claim 1, wherein the thermally responsive layer has a coat weight of 1.5 to 6 pounds / 3,300 square feet.

11. A recording medium, Substrate and A thermally responsive layer supported by a substrate, Between the thermal response layer and the substrate is a base coat layer, Equipped with, The thermally responsive layer comprises a leuco dye and several color developers essentially consisting of N,N'-diphenylurea ("DPU") and derivatives of DPU, wherein the relative weight ratio of DPU / DPU derivatives is in the range of 30 / 70 to 60 / 40. The recording medium is substantially phenol-free. DPU derivatives are 【Chemistry 2】 Having a structure The above recording medium.

12. The medium according to claim 11, wherein DPU and a derivative of DPU are dispersed throughout the entire thermal response layer.

13. The medium according to claim 12, wherein the relative weight ratio of DPU / TGMD is 40 / 60 to 50 / 50.

14. The medium according to claim 13, wherein the multiple color developers consist of DPU and TGMD.

15. The medium according to claim 1, wherein the color developer comprises DPU and a derivative of DPU.

16. The medium according to claim 11, wherein the base coat further comprises a hollow spherical pigment.

17. The medium according to claim 1, wherein the relative weight ratio of DPU / DPU derivatives is 40 / 60 to 50 / 50, and the plurality of color developers consist of DPU and DPU derivatives.

18. The medium according to claim 11, wherein the relative weight ratio of DPU / DPU derivatives is 40 / 60 to 50 / 50, and the plurality of color developers consist of DPU and DPU derivatives.

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