Multipurpose phenol-free direct thermal recording medium

Abstract

To provide a non-phenolic direct thermal recording medium. [Solution] The non-phenolic direct thermal recording medium has a thermal response layer containing a leuco dye and a plurality of non-phenolic colorants, including 1,3-diphenylurea (DPU) and urea urethane (UU). This chemical enables a multi-purpose recording material that can withstand multiple different types of environmental conditions or chemicals, such as water immersion, contact with polyvinyl chloride meat packaging film, boiling water, dry and wet heat, sunlight, and contact with hand sanitizer. Due to the unique non-phenolic chemical, the coating weight of the thermal response layer of the product is 1.48 g / m². 2 It can be made extremely lightweight, weighing less than a certain amount.

Description

[Technical Field]

[0001] The present invention relates to a sheet-like recording material suitable for recording or printing by conventional direct thermal recording techniques. The present invention also relates to a direct thermal recording medium, and in particular to a medium incorporating a leuco dye and an acidic developer to provide a thermal activation printing mechanism. The present invention also relates to related methods, systems, and articles. [Background technology]

[0002] In direct thermal recording, an image is generated by selectively heating a recording material (sometimes called coated thermochromic paper, thermal paper, thermal recording material or medium, or thermally responsive recording material) at a selected location, either by passing the material under or across a thermal printhead. The recording material includes a thermally responsive coating, and the image is provided by a thermally induced change in the color of the thermally responsive layer. Common applications of direct thermal recording may include, but are not limited to, cash register receipts, labels for food or other merchandise, or event tickets.

[0003] Numerous types of direct thermal recording media are known. For example, see Patent Documents 1 to 7. In such cases, a basic colorless or pale color-developing material, such as a leuco dye, and an acidic color developer material are contained within a coating on the substrate. When heated to an appropriate temperature, the materials melt or soften, allowing them to react, thereby generating a colored mark or image at the location where heat is applied. It is desirable that the thermally responsive recording material has a characteristic thermal response and generates a colored image with sufficient intensity or contrast through selective thermal exposure.

[0004] Depending on how such recording materials are used, they may be exposed to certain contaminants or environmental conditions. For example, direct-to-thermal media used as labels in pharmaceutical applications may be exposed to hand sanitizer. Direct-to-thermal media used in other applications may be exposed to environmental factors or conditions specific to those applications, such as sweat (water), heat and / or humidity, sunlight, or meat packaging film. Ideally, barcodes or other images thermally printed on direct-to-thermal recording materials should remain visible and functional even when exposed to such chemicals. However, designing such functionality within direct-to-thermal products can be challenging and is not always possible or practical.

[0005] Apart from these issues, concerns about the presence of phenol-based chemicals in direct thermal recording materials were raised many years ago. Originally, phenolic materials were present in the thermal response layer of thermal recording materials, more specifically in the developer chemicals that react with leuco dyes within that layer to cause heat-induced color changes. To address these concerns, phenol-free alternative developer chemicals were developed. One group of such chemicals was introduced by Ciba Specialty Chemical Corp. about 20 years ago under the Pergafast® brand, which includes Pergafast 201 (3-(3-tosylureido)phenyl p-toluenesulfonate). This developer is still widely used today in the manufacture of phenol-free direct thermal recording materials. Other known phenol-free colorants include NKK 1304 (N-[2-(3-phenylureido)phenyl]benzenesulfonamide), tolbutamide (1-butyl-3-(4-methylphenyl)sulfonylurea), and dapsone (4,4'-diaminodiphenylsulfone), all sold by Nippon Soda Co., Ltd. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 3,539,375 [Patent Document 2] U.S. Patent No. 3,674,535 [Patent Document 3] U.S. Patent No. 3,746,675 [Patent Document 4] U.S. Patent No. 4,151,748 [Patent Document 5] U.S. Patent No. 4,181,771 [Patent Document 6] U.S. Patent No. 4,246,318 [Patent Document 7] U.S. Patent No. 4,470,057 [Overview of the project] [Problems that the invention aims to solve]

[0007] The inventors have discovered a unique color developer chemical for use in the thermal response layer of direct thermal recording materials. In addition to being non-phenolic, this unique chemical allows for the creation of direct thermal recording materials that can withstand multiple different types of environmental conditions or chemicals, and in this respect, these recording materials can be described as multipurpose. The unique chemical is a combination of two non-phenolic color developers, neither of which can produce a direct thermal recording material with such properties on its own (even in combination with a suitable leuco dye), but which, when combined, can produce surprisingly unexpected results. The two color developers are 1,3-diphenylurea ("DPU") and urea urethane ("UU"). Furthermore, the inventors have discovered that the unique chemical also makes it possible to make the coating weight of the thermal response layer of the product extremely light, i.e., extremely thin. This enables a reduction in product mass and many related benefits, including a reduction in the post-use waste flow associated with direct thermal recording materials, improving the environmental impact.

[0008] Therefore, the inventors have developed a new system of phenol-free direct thermal recording materials or media. These materials are configured for direct thermal imaging, and the thermal images thus produced can be robust enough to withstand multiple different environmental conditions or factors. These materials use a combination of two non-phenolic colorants, neither of which can produce a direct thermal recording material with the desired multi-purpose functionality on its own. [Means for solving the problem]

[0009] Accordingly, the inventors disclose in this specification a recording medium comprising, in particular, a substrate and a thermally responsive layer supported by the substrate. The recording medium is substantially phenol-free, and the thermally responsive layer comprises a leuco dye and a plurality of color developers comprising 1,3-diphenylurea (DPU) and urea urethane (UU).

[0010] The recording medium may further include a base coat layer between the thermal response layer and the substrate, and a top coat supported by the substrate such that the thermal response layer is positioned between the top coat and the substrate. The thermal response layer has a density of 1.48 g / m². 2 (1lb / 3300ft 2 ) less than 0.9 g / m² 2 From 1.48 g / m 2 The coat weight may be in the range of less than . DPU and UU may be dispersed throughout the thermal response layer. Chromogenators other than DPU and UU may not be substantially present in the thermal response layer. DPU and UU may be present in the thermal response layer in a relative weight ratio ranging from 1 / 3 to 3, or 1 / 2 to 2, or a relative weight ratio that can be substantially 1.

[0011] 11.7 mJ / mm 2In the thermal printer energy setting of, the print quality of the recording medium when printing at a printing speed of 6 inches per second (ips), i.e., approximately 15 cm / second, can be characterized by an ANSI value of at least 1.5 (at a wavelength of 650 nm, or 670 nm, or both 650 nm and 670 nm). The print quality of the printed recording medium is any one, or several, or all of the following: after the printed recording medium is immersed in water for 24 hours and then taken out and dried; after the printed recording medium is immersed in water and then placed in contact with a polyvinyl chloride meat packaging film under a weight of 7 pounds (approximately 3.2 kg) for 24 hours and then taken out and dried; after the printed recording medium is immersed in boiling water for 20 minutes and then taken out and dried; after the printed recording medium is heated to 60 °C for 24 hours and then taken out and cooled; after the printed recording medium is exposed to air at 40 °C and a relative humidity of 90% for 24 hours and then taken out and cooled; after the printed recording medium is subjected to an accelerated sunlight test at 0.67 W / m 2 for 7 hours and then taken out; or even after a drop of a 70% ethyl alcohol-based hand disinfectant is dropped on the printed recording medium and dried, it can still be characterized by an ANSI value of at least 1.5.

[0012] The inventors also disclose a recording medium that includes a flexible substrate and a heat-responsive layer supported by the substrate, and the heat-responsive layer includes a leuco dye and a plurality of developers including DPU and UU and contains substantially no phenol. Both DPU and UU can be dispersed throughout the heat-responsive layer and can be present in the heat-responsive layer at a relative weight ratio that falls within the range of 1 / 3 to 3, or 1 / 2 to 2, or a relative weight ratio that is substantially 1. When printing at a printing speed of 6 inches per second (ips) with a thermal printer energy setting of 11.7 mJ / mm 2 the print quality of the recording medium can be characterized by an ANSI value of at least 1.5 (at a wavelength of 650 nm, or 670 nm, or both 650 nm and 670 nm).

[0013] The print quality of the printed recording medium can still be characterized by at least an ANSI value of 1.5 after performing any, some, or all of the following: submerging the printed recording medium in water and then placing it in contact with a polyvinyl chloride meat packaging film under a weight of 7 pounds for 24 hours and then removing and drying it; heating the printed recording medium to 60°C for 24 hours and then removing and cooling it; or exposing the printed recording medium to air at 40°C and 90% relative humidity for 24 hours and then removing and cooling it.

[0014] The inventors have disclosed a number of related methods, systems, and articles.

[0015] These and other aspects of the disclosure will become apparent from the following detailed description. However, in no case should the above summary be construed as a limitation on the claimed subject matter, which is defined only by the appended claims (which may be amended during the prosecution of the application).

[0016] The articles, systems, and methods of the present invention are described in further detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic perspective view of a roll of direct thermal recording material or medium. [Figure 2] It is an enlarged schematic front view and schematic cross-sectional view of direct thermal recording material.

[0018] In the drawings, like reference numerals indicate like elements.

Modes for Carrying Out the Invention

[0019] As described above, the inventors have discovered a unique phenol-free developer chemical for use in direct thermal recording materials. The new chemical consists of a combination of two developers, which, when used with a suitable leuco dye, can produce a multi-purpose direct thermal recording material that can pass multiple environmental exposure tests, but the same thermal recording material cannot pass the same environmental exposure tests when used individually. In fact, using one of the two developers alone with a suitable leuco dye produces a direct thermal recording material that, when an image is created with a thermal printer before environmental exposure testing is performed, produces an image that does not even meet the minimum standards of machine readability for barcodes. The two phenol-free developers in this unique combination are 1,3-diphenylurea ("DPU") and urea urethane ("UU").

[0020] Unique chemicals make it possible to make the thermal response layer of a product extremely lightweight, or even extremely thin. Lower coating weight reduces material and manufacturing costs, and decreases the overall weight or mass of the product. The reduction in product mass also reduces the flow of post-use waste associated with direct thermal recording materials, improving the environmental impact.

[0021] Direct thermal recording materials are often manufactured in the form of large rolls using an industrial-sized coating machine, using a continuous web of paper or other flexible substrate material. A roll 100 of such a direct thermal recording material 104 is schematically shown in Figure 1. After manufacturing, 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 schematically shown in Figure 2, showing a typical substructure consisting of constituent layers or coatings.

[0022] The recording material 104 can be made by applying several different coatings to at least one side or main surface 110a of the substrate 110. The main surface 110a can be called the front surface of the substrate, and the exposed main surface 104a can be the front surface of the recording material 104. The opposite main surface 104b can be the back surface of the recording material. In short, the substrate 110 is coated to support a base coat layer 112, a thermal response layer 114, and a top coat layer 116. The coatings are preferably applied in the order shown in the illustration such that layer 114 is located between layers 112 and 116, and layer 112 is located 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. Furthermore, additional layers and coatings can be added to or incorporated into the recording material on the front and / or back sides. For example, one or more coatings can be applied to the opposite side of the substrate, i.e., the main surface 110b, as will be further described below. However, first, we will describe in more detail the other elements of the direct thermal recording material 104.

[0023] The base material 110 can be any material on which other layers can be coated or applied and then supported. The type or kind of base material is not important. Generally, the base material 110 is in the form of a sheet or roll and can be, or may contain, a support member for, for example, a web, ribbon, tape, belt, film, card, etc. In this regard, a sheet refers to an article having two large (main) surface dimensions and a relatively small thickness dimension, and in some cases the sheet may be wound to form a roll. In this regard, the base material 110 is typically thin and flexible but strong enough to withstand the forces and tensions it receives in the coating machine without causing excessive damage. The base material 110 may be opaque, transparent, or translucent, and may be colored or uncolored. The base material can be fibrous, for example, paper and fibrous synthetic materials. It can be a film, for example, cellophane and synthetic polymer sheets formed by casting, extrusion, or other methods. Suitable plastic films include polypropylene (including stretched polypropylene (OPP) and biaxially oriented polypropylene (BOPP)), polyethylene (PE), and polyethylene terephthalate (PET) films. Therefore, the base material can be non-cellulose-based.

[0024] The exemplary substrate 110 may be or may contain intermediate-sized base paper. The thickness of the substrate 110 may depend on its composition, but a typical thickness (caliper) range for cellulosic materials is 1.9 to 12 mils (e.g., 50 to 300 μm), or other suitable thicknesses. The paper is 35 to 200 g / m². 2The basis weight can be in the range shown, but other suitable basis weights can also be used. The paper may also be treated with one or more agents, such as a surface sizing agent. Uncoated base papers can be used, including unsizing base papers, conventionally sized base papers, and lightly treated base papers. The base material 110 may have a simple structure and may not have a glossy coating or other substantially functional coating. The base material 110 may not be a multilayer structure or material with, for example, one or more distinct functional coatings already applied, and may have a substantially uniform composition throughout its thickness. However, in some cases, it may be desirable to treat, prepare, or otherwise process the base material 110 in preparation for coating thereon one or more layers as shown in the figure.

[0025] The base coat 112 may be applied directly to the surface 110a of the substrate 110 before any other coatings are applied. The base coat 112 may, in some cases, be characterized or described as an insulating layer, a separator layer, a heat reflecting layer, an isolation layer, or a primer. By adjusting layer 112 to have a lower thermal conductivity than both the thermal responsive layer 114 and the thermal conductivity of the substrate 110, the base coat 112 provides some degree of insulation between these two other layers. Such insulation improves image quality, image forming speed, or both by ensuring that the heat transferred to the surface 104a by the thermal print head (not shown) is not substantially lost by heat conduction to the larger substrate 110 through the thermal responsive layer 114.

[0026] The base coat 112 may include hollow sphere pigments (HSPs) such as product code Ropaque (trademark) 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 produced by a process of coating a dispersion on the surface 110a of the substrate and then drying it. In some cases, the base coat 112 can also be removed and omitted from the product structure. When included as part of the recording material, the heat insulating layer can have a thickness in the range of 2 μm to 12 μm, or other suitable thickness.

[0027] The heat-responsive layer 114 may be coated on top of the base coat 112 or, if the base coat is omitted, on the substrate 110. Layer 114 may alternatively be referred to as a thermosensitive color-forming layer. This layer 114 contains a thermosensitive (i.e., color-changing upon sufficient heating) color-forming composition. The color-forming composition has two main components: a leuco dye or a color-forming dye (electron-donating dye precursor), also known as a color former, and an acidic developer. The leuco dye and the acidic developer are typically ground to individual particle sizes of 1 to 10 micrometers, dispersed in a binder, and distributed uniformly and in a continuous relationship with each other throughout layer 114. When heated sufficiently at any location, the particles of the acidic developer react with the particles of the leuco dye, and as a result, the color at the heated site can change from a light color to a dark color. Known systems and materials are described in Patent Documents 1 to 7 and U.S. Patent No. 5,955,398.

[0028] The acidic developer is preferably non-phenolic and, as already explained above, advantageously includes a combination of two different non-phenolic developer materials, particularly 1,3-diphenylurea ("DPU") and urethane urea ("UU"). DPU may alternatively be 1-3-diphenylurea or 1-3-diphenylurea; N,N'-diphenylurea; diphenylurea; urea, N,N'-diphenyl-; carbanylamide; diphenylcarbamide; or C 13 H12 It is sometimes referred to by names such as N2O. UU is instead called urethane urea, urethane-urea copolymer, polyurethane urea, or poly(urethane urea); polyurethane urea elastomer, or poly(urethane urea) elastomer; polyurea-urethane; poly(urea)urethane; poly(urea-urethane) polymer; poly(urea-urethane) thermosetting resin; poly(ether urethane urea); poly(ester urethane urea); poly(ester urethane) urea elastomer; or C4H 11 It is sometimes referred to by names such as N3O3.

[0029] One rationale for using a non-phenolic color developer in the thermal response layer 114 is to meet the market demand for phenol-free receipts, labels, etc. Therefore, while it is often desirable, but not always necessary, that the entire direct thermal recording material 104, as well as the thermal response layer 114, be phenol-free or substantially phenol-free, this is not always required. 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 material below a threshold.

[0030] Neither DPU nor UU are particularly noteworthy when used alone in combination with appropriate leuco dyes. In fact, when UU is used alone in combination with appropriate leuco dyes in the thermal response layer, without other colorants, the resulting direct thermal recording material produces an initial image that, when imaged with a direct thermal printer, does not even meet the minimum requirements for machine readability of a barcode. On the other hand, when the UU in such a product is completely replaced by DPU, i.e., when DPU is used alone as the sole colorant in layer 114, the image initially produced by the direct thermal printer meets the minimum requirements for machine readability of a barcode, but, as will be further explained below, after the printed sample has been exposed to any of the numerous environmental exposure tests, it no longer meets those minimum requirements for machine readability. Remarkably, when DPU and UU are used in combination, and naturally in conjunction with appropriate leuco dyes, the resulting direct thermal recording material not only provides a thermally generated image that meets the minimum requirements for machine readability of barcodes, but also maintains its image quality after the printed sample undergoes environmental exposure testing that would not be passed by otherwise identical recording materials containing only DPU or only UU as developer.

[0031] In embodiments using a combination of DPU and UU, it is preferable that the DPU, UU, and selected leuco dye are homogeneously and uniformly dispersed throughout the thermally responsive layer 114. This does not necessarily mean that these various materials have equal loads within the layer. However, it has been found that in most cases, it is desirable that the loads of DPU and UU are approximately equal, i.e., that the relative weight ratio of DPU / UU is approximately 1. However, other weight ratios of DPU / UU are also usable, as shown in the following examples. The weight ratio of DPU / UU may be in the range of, for example, 1 / 3 to 3, or 1 / 2 to 2, or it may be about 1. When DPU and UU are used in combination, it is preferable that they are the only chemical developers used in layer 114. However, if necessary, one or more other chemical developers may be added in addition to DPU and UU. If this is done, it is preferable that such other developers(s) are present individually and collectively in layer 114 at weight percentages lower than the weight percentage of DPU and lower than the weight percentage of UU.

[0032] In addition to the DPU and UU, the thermally responsive layer 114 also naturally includes at least one leuco dye, which is formulated to react with multiple color developers at high temperatures to produce a mark or a change in color. One or more leuco dyes can be any known dye(s) capable of such a reaction. Examples include, but are not limited to, the following: 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)xanthene-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)-).

[0033] The thermally responsive layer 114 also includes one or more suitable binders that help to hold the particles within the layer together. Such binders may include poly(vinyl alcohol), hydroxyethylcellulose, methylcellulose, isopropylcellulose, starch, modified starch, gelatin, etc. Latex materials including polyacrylate, polyvinyl acetate, polystyrene, etc. can also be used. The binder helps to maintain the mechanical integrity of the layer 114 in response to the brushing or handling forces resulting from the use or storage of the recording material 104. There should be enough binder to provide such protection, but not so much that it hinders the achievement of reactive contact between the color-reactive materials. The binder may be present in 5 to 30% by weight of the dry coating.

[0034] In addition to the leuco dye, developer, and binder, the color composition of layer 114 may contain one or more substances called modifiers that aid in color formation. Modifiers may function by either (a) lowering the melting point of the dye / developer, and (b) acting as a kind of solvent through which the dye and developer dissolve or melt, or both. Thus, modifiers may accelerate the reaction between the leuco dye and the developer to produce a stronger thermal image, faster image formation, or both. See, for example, U.S. Patent No. 4,531,140 (Suzuki et al.), No. 4,794,102 (Petersen et al.), No. 5,098,882 (Teraji et al.), No. 6,835,691 (Mathiaparanam et al.), and No. 6,921,740 (Hizatate et al.).

[0035] Typically, the thermal response layer of conventional direct thermal recording materials has a finished dry thickness ranging from 1.2 to 4.8 μm or 1 to 5 μm, with a weight of 1.5 to 6 pounds / 3,300 square feet (2.2 to 8.9 g / m²). 2 ), more typically 2-4 pounds / 3,300 square feet (3.0-5.9 g / m²) 2 It will be applied to a thickness equivalent to the court weight. The actual lower limit is approximately 1 pound / 33,000 cubic feet (approximately 1.48 g / m²) of court weight. 2 The thermal response layer 114 of the recording material 104 of the present invention can be applied with the same conventional coat weight and thickness as these, if necessary. However, another advantage of the disclosed color developer DPU / UU combination has been found to be that the layer 114 can be fabricated much thinner while still providing acceptable thermal image quality. In particular, the layer 114 can be made 1 pound / 3,300 square feet (1.48 g / m²). 2 It can be manufactured with a coat weight of less than 0.9 g / m². The inventors have determined that the coat weight of layer 114 (containing DPU and UU developer) is 0.9 g / m². 2 This demonstrated acceptable product performance even at such a low level. Therefore, the coating weight of layer 114 is, for example, 0.9~8.9g / m². 2 , or 0.9~5.9g / m 2 , or 0.9~2.2g / m 2 , or 0.9~1.48 g / m 2 , or 0.9~1.48 g / m 2 The range can be less than

[0036] The ability to make the thermal response layer 114 extremely thin offers many advantages, including reduced product weight / mass, reduced product cost, and reduced environmental impact related to waste flow after use.

[0037] Returning to Figure 2, the topcoat layer 116 is shown in contact with the thermal response layer 114. In the illustrated embodiment, the outer main surface of the topcoat 116 is exposed to air and directly corresponds to the outer main surface 104a of the thermal recording material 104. The topcoat 116 is optional and can be omitted if necessary. If included, it can protect the layer beneath 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.

[0038] The topcoat 116 may be any suitable topcoat of the conventional design. The topcoat 116 may contain, for example, a binder such as modified or unmodified polyvinyl alcohol, an acrylic binder, a crosslinking agent, 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 thicknesses.

[0039] The disclosed recording material may include additional layers and coatings other than those discussed above. Such other layers or coatings may include coatings that can be applied to the back surface 110b of the substrate 110. One such layer is shown in Figure 2, and the label is 118. This layer 118 may be an adhesive layer containing a pressure-sensitive adhesive (PSA), a hot-melt adhesive, or other suitable adhesive. By being provided on the back surface of the recording material 104, the recording material can function as a label and be attached to a container, film, or other object with its front, heat-printed surface visible to the user. A release liner (not shown) may also be included to cover the PSA layer until ready for use. In applications where a liner is not required, a release coating may be applied to the surface.

[0040] Because direct thermal recording materials can be used in a potentially diverse range of environments, they may be exposed to a variety of environmental factors, contaminants, and conditions. Images formed on such materials by direct thermal printing are known to degrade when exposed to at least some of these conditions. A given recording material may degrade to a greater or lesser extent to these conditions depending on the structural details, including the chemicals used in the thermal response layer. Naturally, the more environmental conditions a recording material can withstand without significant image degradation, the more environments and applications it can be used in.

[0041] Dry Heat: One environmental condition of interest is the thermal exposure of the imaged material, i.e., its thermal stability. Naturally, if the imaged recording material is heated to a sufficiently high temperature (e.g., approaching the printhead temperature of at least about 200°C), the leuco dyes react with the developer throughout the thermal response layer, discoloring the entire front surface of the recording material and erasing the previously formed image on it. Here instead, we consider a heating environment around 60°C, significantly above ambient room temperature, which the imaged recording material might experience if it were attached as a label to a cup or container of coffee or other hot beverage, or attached to packaging of food intended for heating or cooking in a microwave oven.

[0042] Plasticizers: Another environmental condition of interest is contact with plasticizing films, particularly polyvinyl chloride (PVC) films used to wrap meat in grocery stores. Direct thermal recording materials can be used as labels affixed to such packaged meat. Direct thermal images printed on the front of the label may come into contact with PVC films from other packages.

[0043] Water: Another environmental condition of interest is immersion in water. This can occur if a printed receipt or ticket is left in a clothing pocket and accidentally sent into a washing machine cycle. The mildest version of this environmental condition is when the water is at room temperature, or even lukewarm.

[0044] Boiling water: This environmental condition of interest is similar to immersion water conditions, but the water is at its boiling point.

[0045] Humidity: Another humid environmental condition of interest is exposure to hot and humid conditions that may be experienced in tropical regions. This could include, for example, temperatures of around 40°C and 90% relative humidity.

[0046] Sunlight: Another environmental condition of interest is exposure to sunlight.

[0047] Disinfectants: Another environmental condition of interest is contact with alcohol-based hand sanitizers.

[0048] Examples and Comparative Examples In accordance with the above instructions, numerous examples and comparative examples of direct thermal recording media were manufactured and tested.

[0049] In preparation for sample preparation, numerous dispersion formulations were prepared. There were two types: dispersion formulations for leuco dyes and dispersion formulations for acidic color developers. It is understood that all parts or percentages are in parts by weight, as follows: the leuco dye formulations were prepared according to the first recipe "A", and the color developer formulations according to the second recipe "B".

[0050] [Table 1]

[0051] [Table 2]

[0052] The formulation called dispersion A1 followed recipe "A," using ODB-2, or 2-anilino-3-methyl-6-dibutylaminofluorane, as the coloring agent.

[0053] The formulation called dispersion A2 followed recipe "A," using BK-305, or 2-anilino-3-methyl-6-dipentylaminofluorane, as the coloring agent.

[0054] The formulation called dispersion B1 followed recipe "B," using DPU, or 1,3-diphenylurea, as the color developer.

[0055] The formulation called dispersion B2 followed recipe "B," using UU, i.e., urethane urea (specifically, the urea urethane compound sold by Chemipro Chemicals Co., Ltd., CAS number: 321860-75-7), as the color developer material.

[0056] The formulation called dispersion B3 followed recipe "B," using D-8, or 4-hydroxyphenyl-4-isopropoxyphenyl sulfone, as the color developer.

[0057] The formulation called dispersion B4 followed recipe "B," using BPS, or 4-hydroxyphenylsulfone, as the color developer.

[0058] The formulation called dispersion B5 followed recipe "B," using BPS-MBE, or 4-benzyloxyphenyl-4'-hydroxyphenyl sulfone, as the color developer.

[0059] The formulation called dispersion B6 followed recipe "B," using tolbutamide, or 1-butyl-3-(4-methylphenyl)sulfonylurea, as the color developer.

[0060] The formulation called dispersion B7 followed recipe "B," using dapsone, or 4,4'-diaminodiphenylsulfone, as the color developer.

[0061] The formulation called dispersion B8 followed recipe "B," using Pergafast (trademark) 201, sold by Solenis LLC, specifically N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, as the color developer.

[0062] The formulation called dispersion B9 followed recipe "B," using NKK-1304, i.e., N-[2-(3-phenylureido)phenyl]benzenesulfonamide sold by Nippon Soda Co., Ltd., as the color developer.

[0063] Different versions of these dispersion formulations were mixed with other components to prepare coating formulations used to form a thermally responsive layer on a given sample. Unless otherwise specified, the coating formulations were as follows:

[0064] [Table 3]

[0065] Each sample (example or comparative example) was prepared by the following method unless otherwise specified. The first step was to coat one side or the main surface of the substrate (see, for example, substrate 110 in Figure 2) with a base coat (see, for example, layer 112 in Figure 2). The substrate used was 63 g / m². 2 It was a highly refined paper sheet of (gsm). The base coat was thermally insulating and contained a mixture of calcined clay such as BASF Corporation's Ansilex 93 and The Dow Chemical Company's Ropaque (trademark)-TH-2000 hollow sphere pigment (HSP), along with an SBR binder, at 4.5 g / m². 2 The coating was applied with a coat weight of . After drying, a thermal response layer (see, for example, layer 114 in Figure 2) was coated on top of the base coat. Unless otherwise specified, the coat weight of the thermal response layer is 1.3 g / m². 2After this coating dried, a topcoat (see, for example, topcoat 116 in Figure 2) was applied to the surface of the thermally responsive layer. The topcoat consisted of exfoliated clay, PVOH, a crosslinking agent, and a lubricant such as zinc stearate, at a concentration of 1.5 g / m². 2 The sample was applied with a coat weight of [weight]. After the topcoat dried, no other coatings were applied to the sample, and the sample was ready for thermal printing and testing.

[0066] The following table shows the names given to the various samples that were fabricated and tested (Examples 1-6 and Comparative Examples 1-12), along with details of their respective thermal response layers.

[0067] [Table 4]

[0068] All of these samples were thin, flexible, phenol-free, and had a uniformly white or light-colored front surface. Next, each sample was tested for its image formation ability by direct thermal printing, the print quality of the resulting image, and the print quality of the image after being subjected to numerous different environmental tests.

[0069] 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 / mm²). 2The process was performed on each sample using the TruCheck® barcode authentication device (model TC-843) operating at a wavelength of 650 nm. Pass results corresponded to an ANSI value of 1.5 or higher, and fail results corresponded to an ANSI value of less than 1.5. In some cases, the print quality of the same image was also evaluated at 670 nm using the TruCheck® barcode authentication device model TC-854. Again, pass scores corresponded to an ANSI value of 1.5 or higher, and fail scores corresponded to an ANSI value of less than 1.5.

[0070] After measuring the initial print quality of the printed recording media, each sample specimen was subjected to one of the seven environmental tests outlined above (i.e., dry heat, plasticizer, water, boiling water, humidity, sunlight, and disinfectant).

[0071] In the dry heat test, printed test pieces were exposed to 60°C (dry) heat for 24 hours and then removed from the heat. After this test, the quality of the printed image was tested at both 650nm and 670nm.

[0072] In the plasticizer test, printed test specimens were immersed in water at room temperature, then removed and placed in contact with polyvinyl chloride meat packaging film under a 7-pound weight for 24 hours, after which they were removed and dried. Following this test, the quality of the printed image was tested at 650 nm.

[0073] In the water test, printed test pieces were immersed in room temperature water for 24 hours, then removed and dried. After this test, the quality of the printed image was tested at 650 nm.

[0074] In the boiling water test, printed test pieces were attached to a plastic sample, immersed in boiling water for 20 minutes, and then removed and dried. After this test, the quality of the printed image was tested at 650 nm.

[0075] In the heat and humidity test, printed test pieces were exposed to a heat of 40°C and 90% relative humidity for 24 hours. After this test, the quality of the printed image was tested at both 650nm and 670nm.

[0076] In the solar testing, printed test specimens were placed in an accelerated solar power testing chamber (Q-Sun (trademark) xenon testing chamber sold by Q-Lab Corporation in Westlake, Ohio) at an irradiance of 0.67 W / m². 2 The samples were left for 7 hours and then removed. After this test, the quality of the printed images was tested at both 650nm and 670nm.

[0077] In the disinfectant test, one drop of Purell (trademark) hand sanitizer, sold by Gojo Industries, was placed on a printed test piece and allowed to dry. After this test, the quality of the printed image was tested at both 650nm and 670nm.

[0078] Table 5 reports the results of some of these sample runs, initial print quality tests, and print quality tests after each of the environmental tests described above.

[0079] [Table 5]

[0080] In this table, a "Pass" result means that the ANSI value at 650nm (and 670nm, if applicable) is at least 1.5, a "Pass*" result means that the ANSI value at 650nm is at least 1.5 but the ANSI value at 670nm is less than 1.5, and a "Fail" result means that the ANSI value at 650nm (and 670nm, if applicable) is less than 1.5.

[0081] The comparison between Comparative Examples 1-4 and Examples 1-6 in the table demonstrates that the novel combination of DPU and UU developer chemicals can produce a multi-purpose direct thermal recording material that can pass multiple environmental exposure tests. However, using the same thermal recording material individually does not result in passing the same environmental exposure tests. The comparative example using UU alone produces a direct thermal recording material that generates images that do not even meet the minimum standards for machine readability of barcodes.

[0082] The results in Table 5 indicate that the relative weight ratio of DPU to UU in the thermal response layer does not need to be 1, but can be in the range of at least 1 / 3 to 3, or even a narrower range such as 1 / 2 to 2. Furthermore, the results in Table 5 indicate that when DPU and UU are used in combination, the coating weight of the thermal response layer is 0.9 g / m². 2 This demonstrates that, even at a lower level, it is still possible to produce direct thermal images with acceptable print quality.

[0083] The results for the remaining comparative examples are shown in Table 6. Here, "Pass," "Pass*," and "Fail" have the same meanings as in Table 5.

[0084] [Table 6]

[0085] Unless otherwise specified, all numerical values ​​used in this specification and the claims, representing quantities, measured characteristics, etc., should be understood as being modified by the term “approximately.” Therefore, unless otherwise noted, the numerical parameters described in the specification and the claims are approximations that may vary depending on the desired characteristics sought by those skilled in the art using the teachings of this application. Without limiting the application of the doctrine of equivalents to the claims, each numerical parameter should be interpreted by applying common rounding techniques, taking into account at least the reported number of significant figures. Although the numerical ranges and parameters representing the broad scope of the present invention are approximations, wherever numerical values ​​are described in the specific examples described herein, they are reported as accurately as reasonably possible. However, any numerical value may contain considerable error related to the limitations of the test or measurement.

[0086] For example, the use of relational terms such as “top,” “bottom,” “upper,” “lower,” “above,” and “below” to describe various embodiments is merely for convenience to facilitate the description of some embodiments herein. Despite the use of such terminology, this disclosure should not be interpreted as being limited to any 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.

[0087] Without departing from the spirit and scope of the present invention, various modifications and changes to the present invention will be apparent to those skilled in the art and are not limited to the exemplary embodiments described herein. Unless otherwise specified, readers should assume that the configuration of one disclosed embodiment is applicable to all other disclosed embodiments.

Claims

1. A recording medium, Substrate and A thermally responsive layer comprising a leuco dye and a plurality of colorants, supported by the aforementioned substrate, Equipped with, The recording medium substantially does not contain phenol, The recording medium comprises the aforementioned plurality of color developers, 1,3-diphenylurea (DPU) and urea urethane (UU).

2. The medium according to claim 1, further comprising a base coat layer between the thermal response layer and the substrate.

3. The medium according to claim 1, further comprising a top coat supported by the substrate, wherein the thermal response layer is disposed between the top coat and the substrate.

4. The thermal response layer has a density of 1.48 g / m². ２ The medium according to claim 1, having a coat weight of less than 100%.

5. The coating weight of the thermal response layer is at least 0.9 g / m². ２ The medium according to claim 4.

6. The medium according to claim 1, wherein the DPU and the UU are dispersed throughout the entire thermal response layer.

7. The medium according to claim 1, wherein the thermal response layer is substantially free of colorants other than DPU and UU.

8. The medium according to claim 1, wherein the DPU and the UU are present in the thermal response layer in a relative weight ratio in the range of 1 / 3 to 3.

9. The medium according to claim 8, wherein the relative weight ratio is in the range of 1 / 2 to 2.

10. The medium according to claim 9, wherein the relative weight ratio is 1.

11. 11.7 mJ / mm ２ The medium according to claim 1, wherein the print quality of the recording medium when printed at a print speed of 6 inches per second (ips) with the thermal printer energy setting is characterized by an ANSI value of at least 1.

5.

12. The medium according to claim 11, wherein the print quality of the printed recording medium is still characterized by an ANSI value of at least 1.5 even after the printed recording medium has been immersed in water for 24 hours and then removed and dried.

13. The print quality of the printed recording medium is characterized by an ANSI value of at least 1.5 even after immersing the printed recording medium in water, then placing it in contact with a polyvinyl chloride meat packaging film under a weight of 7 pounds for 24 hours, and then removing and drying it, according to claim 11.

14. The print quality of the printed recording medium is characterized by an ANSI value of at least 1.5 even after the printed recording medium has been immersed in boiling water for 20 minutes and then removed and dried, according to claim 11.

15. The medium according to claim 11, wherein the print quality of the printed recording medium is still characterized by an ANSI value of at least 1.5 even after the printed recording medium is heated to 60°C for 24 hours and then removed and cooled.

16. The medium according to claim 11, wherein the print quality of the printed recording medium is still characterized by an ANSI value of at least 1.5 even after the printed recording medium has been exposed to air at 40°C and 90% relative humidity for 24 hours and then removed and cooled.

17. The print quality of the printed recording medium is such that the printed recording medium has a print quality of 0.67 W / m². ２ The medium according to claim 11, which undergoes a 7-hour accelerated sunlight test and is still characterized by an ANSI value of at least 1.5 after being removed thereafter.

18. The medium according to claim 11, wherein the print quality of the printed recording medium is still characterized by an ANSI value of at least 1.5 even after a drop of a 70% ethyl alcohol-based hand sanitizer is dropped onto the printed recording medium and dried.

19. The aforementioned medium is substantially free of phenol, The aforementioned substrate is flexible, Both the DPU and the UU are dispersed throughout the thermal response layer. The DPU and UU are present in the thermal response layer in a relative weight ratio in the range of 1 / 3 to 3. 11.7 mJ / mm ２ The medium according to claim 1, wherein the print quality of the recording medium when printed at a print speed of 6 inches per second (ips) with the thermal printer energy setting is characterized by an ANSI value of at least 1.

5.

20. The print quality of the printed recording medium is characterized by an ANSI value of at least 1.5 even after immersing the printed recording medium in water, then placing it in contact with a polyvinyl chloride meat packaging film under a weight of 7 pounds for 24 hours, and then removing and drying it. The print quality of the printed recording medium is characterized by an ANSI value of at least 1.5 even after the printed recording medium is heated to 60°C for 24 hours, then removed and cooled. The medium according to claim 19, wherein the print quality of the printed recording medium is still characterized by an ANSI value of at least 1.5 even after the printed recording medium has been exposed to air at 40°C and 90% relative humidity for 24 hours and then removed and cooled.

Images