Primers with improved reflective and thermally insulative properties for microcapsule imaging system

Abstract

A primer layer with improved reflectivity and thermal insulation properties is provided for microencapsulated thermal imaging films. The primer layer comprises approximately 3% to approximately 60% by weight of polymer binder, white microparticles, a primer substrate, and hollow microparticles relative to the total weight of the primer layer. This primer layer improves, among other things, the reflectivity, color rendering, color density, and thermal insulation of the microencapsulated imaging film. A black back coating applied to the substrate on the side opposite to the primer layer further enhances the Dmax and E;10 of the microencapsulated imaging film and prevents premature exposure of the microencapsulated imaging film in the stacking medium.

Description

Technical Field

[0001] This disclosure is generally related to the field of microcapsule imaging systems, and more specifically, to primers used in microcapsule imaging systems. Prior Technology

[0002] Since the 1980s, monolithic, self-contained full-color microcapsule imaging systems (such as Cycolor) have been developed. In these imaging systems, an imaging sheet comprising a layer of microcapsules containing a photocurable or photosoftening composition and a leuco dye in an inner phase is exposed to photochemical radiation in an imaging manner. Typically, the photosensitive composition contains a photopolymerizable polyfunctional acrylate, a photoinitiator, and a colorant. Generally, the microcapsules are cured by photochemical radiation in an imaging manner, and after the exposed imaging sheet is passed through a pressure roller, the microcapsules can be broken up in an imaging manner to release the inner phase encapsulated within. The released leuco dye then migrates to the developer material and reacts to form a full-color image with continuous tones, the color density (or grayscale) of which is modulated by the exposure energy (time or pulse width), intensity (pulse amplitude), and / or pulse frequency. Such self-contained monolithic imaging systems can be used in lightweight, portable, high-speed printing applications. Summary of the Invention

[0003] Typical microcapsule imaging systems have several drawbacks. For example, the rupture of microcapsules requires extremely high pressure, leading to inefficient dye release, poor color density (Dmax), and slow color development rates. While these problems can be partially solved by using larger microcapsules, image resolution and ease of operation decrease significantly with increasing microcapsule size.

[0004] In addition, white substrates are often used to improve the color density of image areas (and improve the whiteness of non-image areas). However, the reflectivity of most commercially available white substrates, especially thin (≤ 50 μm) substrates, is unsatisfactory. Significant light loss through the substrate (e.g., light leakage) results in undesirable color density and saturation. For example, the reflectivity (%) of commercially available white PET (e.g., MELINEX®339 (manufactured by Dupont Teijin Films LP (Chester, VA)), 50 μm) is only about 85%. That is, approximately 15% of the incident light or color leaks through the substrate and is not reflected back to the viewer's eyes. Correspondingly, substrates with low reflectivity tend to have low opacity. When an image with low opacity is placed on top of a highly colored background, the image in the viewer's eyes appears "contaminated" by the background color or pattern. When a black annihilation layer is used on the opposite side of the substrate (relative to the microcapsule imaging layer) to improve resolution and ensure that no light leakage occurs, prematurely exposing the second imaging sheet below in the media stack, the image sheet with high reflectivity and opacity is particularly beneficial to image quality.

[0005] Furthermore, to alleviate the slow color development discussed above, some technologies require a heating step to increase the color development rate after crushing the microcapsules under pressure. The heating step requires considerable energy consumption (or battery power), and waste heat is dissipated through the substrate, exacerbating this, especially when thick stickers and release liner are attached to the back of the image film.

[0006] Furthermore, to improve the adhesion between microcapsules and the substrate, some technologies use a primer coating between the substrate and the microcapsule layer. However, the primer coating is often soft or sticky and adheres to the opposing rollers of the coating machine or the back of the substrate during rewinding. This results in poor coating quality and low yield. Release coatings or inserts on the back of the substrate can prevent these problems, but these solutions mean additional processing steps, materials, and costs. In addition, release coatings on the back of the substrate can cause stickers (if present) to detach from the image film.

[0007] Against this backdrop, there is significant commercial interest in primers that address some or all of the aforementioned issues. The primer disclosed herein significantly improves Dmax, color development rate (new Dmax), Dmin stability, energy consumption, printing speed, hiding power, anti-bubbling and anti-adhesion properties, ease of use, ease of processing, cost, and primer coating yield, without compromising the adhesion quality between the image film and the sticker.

[0008] In one of the categories that can be combined with any other category or embodiment, this disclosure relates to a primer layer for a microcapsule imaging sheet, comprising: a polymer binder; one or more microparticles (e.g., white microparticles) comprising about 3% to about 60% by weight of the total weight of the primer layer; and a substrate. In some embodiments, the primer layer further comprises about 1% to about 30% by weight of polymer hollow particles comprising the total weight of the primer layer.

[0009] In some embodiments, the white microparticles have a refractive index of about 1.5 to about 3.0. In some embodiments, the microparticles are selected from the group consisting of: TiO2, BaSO4, CaSO4, CaCO3, BN, Al2O3, and Ca3(PO4)2. In some embodiments, the white microparticles are TiO2. In some embodiments, the white microparticles have an average particle size of about 50 nm to about 2000 nm. In some embodiments, the white microparticles have an average particle size of about 100 nm to about 300 nm. In some embodiments, the concentration of the white microparticles relative to the total weight of the primer layer is about 10% by weight to about 50% by weight. In some embodiments, the white microparticles comprise TiO2 and alkaline microparticles. In some embodiments, the alkaline microparticles are selected from CaCO3, Al2O3, or Ca3(PO4)2.

[0010] In some embodiments, the polymeric adhesive comprises a latex polymer having a glass transition temperature (Tg) of about -70°C to about 40°C. In some embodiments, the polymeric adhesive comprises a latex polymer having a Tg of about -20°C to about 20°C. In some embodiments, the polymeric adhesive is selected from the group consisting of: acrylic polymers or copolymers, styrene copolymers, butadiene copolymers, vinyl chloride copolymers, vinylidene chloride copolymers, epoxy copolymers, ethylene copolymers, propylene copolymers, vinyl acetate copolymers, polyesters, polyurethanes, polylactones, polyamides, polyvinylpyrrolidone, and blends or copolymers thereof.

[0011] In some embodiments, the polymer hollow particles comprise a polymer shell and an air core. In some embodiments, the polymer hollow particles comprise a polymer selected from the group consisting of: polyacrylate, polymethacrylate, polystyrene, polyvinyl acetate, polyolefin, polyamide, polyester, polyurea, polyurethane, melamine-formaldehyde, phenolic resin, and blends or copolymers thereof. In some embodiments, the polymer shell of the hollow particles is crosslinked with or filled with an inorganic filler (such as silica).

[0012] In some embodiments, the polymer hollow particles have an average particle size of about 200 nm to about 2000 nm or about 500 nm to about 2000 nm. In some embodiments, the polymer hollow particles have an average particle size of about 100 nm to about 1000 nm or about 300 nm to about 1000 nm. In some embodiments, the air core has an average diameter of about 50 nm to about 1000 nm. In some embodiments, the air core has an average diameter of about 100 nm to about 400 nm. In some embodiments, the polymer hollow particles have a dry specific gravity of about 0.1 g / cm³ to about 0.7 g / cm³. In some embodiments, the polymer hollow particles are present at a concentration of about 5% by weight to about 30% by weight relative to the total weight of the primer layer.

[0013] In some embodiments, the polymer hollow particles comprise a blend of a first polymer hollow particle having a first average particle size and a second polymer hollow particle having a second average particle size.

[0014] In some embodiments, the primer layer has a thickness of about 1 µm to 10 µm. In some embodiments, the primer layer has a thickness of about 2 µm to about 5 µm.

[0015] In another category, which can be combined with any other category or embodiment, this disclosure relates to a microcapsule imaging sheet comprising: a primer layer according to any of the embodiments discussed above; and a photosensitive microcapsule layer in contact with the primer layer. In some embodiments, the microcapsule imaging sheet comprises: a first substrate; a primer layer according to any of the embodiments discussed above, in contact with a first surface of the first substrate; and a photosensitive microcapsule layer comprising photosensitive microcapsules, in contact with the first substrate, the primer layer, or both the primer layer and the first substrate.

[0016] In another category, which can be combined with any other category or embodiment, this disclosure relates to a microcapsule imaging sheet comprising a primer layer on a first surface of a substrate and a back coating layer on a second surface of the substrate to improve image resolution and energy efficiency. In some embodiments, the microcapsule layer is coated on the primer layer. In some embodiments, the back coating layer comprises hollow particles and reflective microparticles substantially identical to those in the primer layer. In some embodiments, the back coating layer is deposited on the second surface of the substrate by vapor deposition, sputtering, spraying, or wet coating. In some embodiments, the back coating layer is blackened with a black dye or pigment such as carbon black to further improve resolution and eliminate the risk of light leakage through the imaging sheet and premature exposure of the underlying imaging sheet in the stack.

[0017] In some embodiments, the microcapsule imaging sheet is a panchromatic imaging sheet, which contains photosensitive microcapsules including red-sensitive, green-sensitive, and blue-sensitive microcapsules.

[0018] In some embodiments, the photosensitive microcapsule comprises a polymer shell and a core comprising a leuco dye, a photoinitiator, and a polymerizable or crosslinkable monomer or oligomer. In some embodiments, the leuco dye is one or more of cyan, magenta, yellow, or black leuco dyes. In some embodiments, the photoinitiator is a red-sensitive, green-sensitive, or blue-sensitive photoinitiator or sensitizer, such as anthocyanin borate or hemicyanin borate. In some embodiments, the photoinitiator comprises a UV-sensitive or near-IR-sensitive photoinitiator or sensitizer, such as ketocoumarin or isopropyl 9-oxosulfuron. (ITX) and aryl cyanine dyes are basically composed of or composed of them.

[0019] In some embodiments, the microcapsule imaging sheet further comprises a developer layer that contacts (i) the microcapsule layer and / or a primer layer and (ii) a developer substrate. In some embodiments, the microcapsules are blended with a developer composition and coated as a monolayer on the primer layer.

[0020] In some embodiments, the back coating comprises a black pigment or dye and a polymer binder. In some embodiments, the back coating comprises 1-30 wt.% of a black pigment or dye relative to the total weight of the back coating. In some embodiments, the back coating comprises 3-20 wt.% of a black pigment or dye relative to the total weight of the back coating. In some embodiments, the black pigment is carbon black.

[0021] In some embodiments, the back coating further comprises hollow polymer particles. In some embodiments, the back coating further comprises one or more microparticles (e.g., white microparticles) selected from the group consisting of: TiO2, BaSO4, CaSO4, BN, CaCO3, Al2O3, Ca3(PO4)2.

[0022] In another category which may be combined with any other category or embodiment, this disclosure relates to a method of preparing an imaging sheet, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any embodiment disclosed herein to produce a primer-coated first substrate; (ii) contacting the primer layer of the primer-coated first substrate with a microcapsule layer to produce a microcapsule-coated first substrate; (iii) contacting the microcapsule-coated first substrate with a developer layer to produce a developer-coated first substrate; and (iv) contacting the developer layer of the developer-coated first substrate with a second substrate to produce an imaging sheet.

[0023] In another category which may be combined with any other category or embodiment, this disclosure relates to a method of preparing an imaging sheet, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any embodiment disclosed herein to produce a primer-coated first substrate; (ii) contacting the primer layer of the primer-coated first substrate with a microcapsule layer to produce a microcapsule-coated first substrate; (iii) contacting a second substrate with a developer layer to produce a developer-coated second substrate; and (iv) contacting the developer layer of the developer-coated second substrate with a microcapsule layer of the microcapsule-coated first substrate to produce an imaging sheet.

[0024] In some embodiments, the second primer layer is disposed between the second substrate and the developer layer.

[0025] In some embodiments, the method further includes (v) contacting a second surface of the first substrate with a back coating, wherein the second surface of the first substrate is opposite to a first surface of the first substrate. In some embodiments, the contact in (v) is performed by physical vapor deposition, sputtering, chemical vapor deposition, lamination, or spin coating.

[0026] In another category which may be combined with any other category or embodiment, this disclosure relates to an imaging or printing method comprising exposing an imaging sheet comprising a primer layer according to any embodiment disclosed herein and a microcapsule layer comprising microcapsules to heat, pressure, or radiation; wherein the microcapsules comprise a polymer shell and an inner phase comprising a leuco dye, to heat, pressure, or radiation; and wherein the exposure is sufficient to release the leuco dye from the microcapsules in the microcapsule layer, thereby producing an image.

[0027] Further scope and / or embodiments of the invention will be provided (not limited to) in the detailed description of the invention techniques set forth below. The following detailed description is exemplary and illustrative, but not intended to be limiting. Simple Explanation of the Diagram

[0028] The various objectives, scope, features and advantages of this disclosure will become more apparent and better understood through a detailed description with reference to the accompanying drawings.

[0029] Figure 1A is a schematic diagram of one embodiment of a microcapsule imaging sheet according to the present disclosure, having a primer coating between the microcapsule layer and the substrate. Figure 1B is a schematic diagram of another microcapsule imaging sheet according to the present disclosure, having a primer coating between the microcapsule layer and the substrate. Figure 1C is a schematic diagram of a microcapsule imaging sheet according to the present disclosure, having a primer coating between the microcapsule layer and the substrate and a back coating on the other side of the substrate.

[0030] Figure 2A is a schematic diagram of a clamping device with a thermocouple used to measure the static temperature drop through the primer layer according to this disclosure.

[0031] Figure 2B shows a curve illustrating the temperature difference between the top of the primer layer and the bottom of the primer layer substrate as a function of heating time.

[0032] Figures 3A, 3B, 3C, 3D, 3E and 3F show the actual temperature difference between the top of the primer layer and the bottom of the primer layer substrate as a function of heating time and as a function of the primer layer composition for an imaging film containing a primer layer according to this disclosure.

[0033] Figure 4A shows a curve comparing the color density (Dmax) of a magenta microcapsule layer coated on a primer layer containing approximately 10% NTR-50 hollow particles with the fixture temperature.

[0034] Figure 4B shows a curve comparing the color development (recent Dmax) of a magenta microcapsule layer coated on a primer layer with different ratios of NTR-50 hollow particles (approximately 0.25 µm in diameter) and NTR-100 hollow particles (approximately 0.9 µm in diameter) with the composition of the primer layer.

[0035] Figure 5A shows the optical image of the film immediately after development (Dmax (new)) as the composition of the primer layer changes. Figure 5B shows the test results of color density (Dmax) and color development as the composition of the primer layer changes immediately after development (Dmax (new)), 4 hours after development (Dmax, 4 hours), and 12 hours after development (Dmax, 12 hours).

[0036] Figure 6 shows the optical density contrast exposure energy (mJ / cm²) curves of microcapsule imaging sheets according to this disclosure with no back coating (control) and with back shells containing different concentrations of carbon black (%K). Implementation

[0037] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Certain exemplary embodiments of the present invention may be practiced without some or all of these specific details. In other instances, certain process operations have not been described in detail, but will be understood by those skilled in the art. [Photosensitive microcapsule layer]

[0038] Referring to Figures 1A and 1B, in some embodiments, the microcapsule imaging sheet 100 according to this disclosure includes a photosensitive microcapsule layer 106. The photosensitive microcapsule 108 may comprise a polymer shell and a core within the polymer shell, the core containing a photosensitizer or photoinitiator, a photocurable monomer or oligomer, and a dye precursor (e.g., a leuco dye). This dye precursor, after being released under pressure and subsequently exposed to heat, certain pH conditions, reactive chemicals (e.g., Lewis acid), or a developer, imparts color to the microcapsule imaging sheet. The shell can act as an oxygen barrier to ensure high photosensitivity of the photosensitive core and prevent any premature mixing of the photoinitiator and various colored dye precursors, thereby ensuring successful color separation and reproduction. In some embodiments, the photocurable monomer may be replaced with a photosoftening or photodegradable composition.

[0039] For example, the developer may be present in the developing layer 110a in contact with the developer substrate 114, configured to be separately placed in contact with the microcapsule layer 106, or present as a developer particle layer 110b in discrete developer particles 112. In some embodiments, the developer may be mixed with the microcapsules and coated in a single layer (not shown). After release from the microcapsule 108, the dye precursor (e.g., a leuco dye) undergoes a chemical transformation from a colorless state to a colored state (e.g., magenta, cyan, yellow, or black). Suitable developers include, but are not limited to, acidic clays, salicylic acid derivatives, phenolic resins and phenolic varnish resins (especially those grafted or copolymerized with salicylic acid derivatives) and their zinc complexes.

[0040] The photosensitive microcapsule layer may contain one or more types of microcapsules. For example, a positive panchromatic microcapsule imaging film may contain three types of microcapsules: red-sensitive microcapsules containing a red-sensitive photoinitiator and a cyan leuco dye; green-sensitive microcapsules containing a green-sensitive photoinitiator and a magenta leuco dye; and blue-sensitive microcapsules containing a blue-sensitive photoinitiator and a yellow leuco dye. For example, in a positive imaging film, after exposure to white light, all three types of microcapsules harden and no color is formed after the color development step. After full exposure to red light, the red-sensitive microcapsules harden, so the cyan leuco dye is not released during the development step. Therefore, red is reproduced in the exposed areas. In contrast, after full exposure to a combination of blue and green light (cyan light), the corresponding magenta and yellow leuco dyes are not released, and cyan is reproduced in the exposed areas. Mid-tone colors of various color densities can also be reproduced in areas exposed to various energies and / or intensities of light.

[0041] In some embodiments, the dye precursor is a cyan, magenta, yellow, or black leuco dye. By way of non-limiting examples, representative leuco dyes may include, but are not limited to, PERGASCRIPT® Red I6B, Blue I-2G, or Blue-63 from BASF; Blue 220, Blue 203, Red 500, Red 40, or Black 305 from Yamada; JYDY-1, JYDR-2, JYDR-3, JYDB-1, or JYDB-2 from WuXi Jiayida New Materials; Red-16, O-C6, or O-C8 from Synmedia Chemicals; or ODB-2 from Anyang General Chemicals.

[0042] In some embodiments, the photoinitiator is anthocyanin boronic acid ester, hemicyanin boronic acid ester, or ketocoumarin, which are sensitive to blue, green, or red. Red, green, and blue photoinitiators with narrow spectral sensitivity bandwidths of less than 100 nm are preferred for panchromatic imaging systems. In some embodiments, the photoinitiator comprises a UV-sensitive or near-IR-sensitive photoinitiator or sensitizer, such as ketocoumarin or isopropyl 9-oxosulfuron. (ITX) and aryl cyanine dyes, substantially composed of or composed of these. In some embodiments, a UV initiator or an infrared initiator is used in a false-color imaging system. In some embodiments, the photosensitive microcapsule 108 may comprise a polymer shell that can be softened by photochemical radiation and a core containing a dye precursor (e.g., a leuco dye). In this context, the core may also be photosoftening or biodegradable. In this case, a negative image is obtained, wherein the exposed area / capsule is colored after development with a developer. In some embodiments, the microcapsule further comprises monomers or oligomers selected from the group consisting of (e.g., polymerizable or crosslinkable monomers or oligomers): polyfunctional acrylates and methacrylates, polyfunctional vinyl ethers, polyfunctional allyl or vinylbenzene and their oligomers, dendritic polymers, or blends. Polyfunctional acrylates are particularly suitable due to their excellent photosensitivity, compatibility with leuco dyes and developers, and outdoor weather resistance. Examples of multifunctional acrylates include, but are not limited to, neopentyl terephthalate triacrylate (PETA-3), neopentyl terephthalate tetraacrylate (PETA-4), dinepentyl terephthalate hexaacrylate (DPHA), dinepentyl terephthalate pentaacrylate (DPPA), trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), and neopentyl glycol diacrylate (NPGDA). [Substrate]

[0043] According to this disclosure, a primer layer 104 is applied onto a substrate 102. The substrate can be any suitable material having sufficient thickness, flexibility, reflectivity (e.g., opacity), and durability to record printed media (e.g., images). In some embodiments, the substrate is white or transparent. By way of non-limiting examples, in some embodiments, the substrate is polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate, polyolefin, cyclic olefin copolymer (COC), cellulose acetate or copolymers, blends, or composites thereof. A range of PET substrates are readily available (e.g., white PET films MELINEX® 329, 339, 394, 331, 534 and transparent PET film MYLAR® from DuPont Teijin Films LP (Chester, VA), and HOSTAPHAN® from Mitsubishi).

[0044] The substrate may have any suitable thickness. In some embodiments, the substrate has a thickness of about 3.5 µm to about 150 µm, about 12.5 µm to about 100 µm, or about 25 µm to about 75 µm. In some embodiments, the substrate may be surface-treated, for example, by corona, plasma, or sublayer to improve adhesion between the substrate and the primer or back coating. In some embodiments, one side of the substrate may be pretreated with an antistatic layer to reduce unwanted static charge buildup during coating or printing. In some embodiments, one side of the substrate may be pretreated with a release layer, such as a polysiloxane or wax layer, to improve media transport during printing and / or improve media anti-blocking properties during conversion and packaging. [Primer coat]

[0045] In various embodiments, the microcapsule imaging sheet according to this disclosure includes a primer layer 104. The primer layer is disposed between a substrate and the microcapsule layer to improve performance characteristics, including adhesion, image resolution, capsule breakage efficiency, or a recent Dmax (maximum optical density), energy efficiency, and photosensitivity achievable immediately after pressure development. In some embodiments, the thickness of the primer layer is about 0.5 μm to about 10 μm, about 1 μm to about 8 μm, or about 2 μm to about 5 μm. In some embodiments, the primer layer may include a polymeric binder, white microparticles, and a substrate. In some embodiments, the primer layer may further include hollow polymer particles. In some embodiments, the primer layer may further include alkaline microparticles. polymer adhesives

[0046] The primer layer according to this disclosure comprises one or more polymeric adhesives. The one or more polymeric adhesives may be any suitable polymeric material, present at any suitable concentration and having any suitable molecular weight, to impart favorable adhesion, flexibility, anti-blocking properties, and film quality (e.g., uniform thickness) to the primer layer.

[0047] In some embodiments, one or more polymeric adhesives may comprise, consist substantially of, or consist of one or more polymers selected from the group consisting of: acrylic polymers or copolymers, styrene copolymers, butadiene copolymers, vinyl chloride copolymers, vinylidene chloride copolymers, ethylene copolymers, propylene copolymers, vinyl acetate copolymers, epoxy copolymers, polyesters, polyurethanes, polylactones, polyamides, polyolefins, polyvinylpyrrolidone, and blends or copolymers thereof. In some embodiments, one or more polymeric adhesives are latex polymers or blends thereof.

[0048] In some embodiments, one or more polymeric adhesives may have a weight average molecular weight of about 5,000 g / mol to about 10,000,000 g / mol. In some embodiments, one or more polymeric adhesives comprise, are substantially composed of, or consist of, a latex adhesive with a molecular weight in the range of 100,000 g / mol to several million g / mol and a particle size in the range of about 0.05 µm to about 1.0 μm. In some embodiments, the applicable latex may have a minimum film-forming temperature (MFFT) or glass transition temperature (Tg) below 50°C, below 30°C, or below 20°C. In some embodiments, crosslinkable latexes may be used to improve the cohesive strength of the primer layer.

[0049] In some embodiments, the weight average molecular weight of one or more polymeric adhesives may be greater than or equal to about 5,000 g / mol, greater than or equal to about 10,000 g / mol, greater than or equal to about 5,000,000 g / mol, greater than or equal to about 10,000,000 g / mol, less than or equal to about 5,000,000 g / mol, less than or equal to about 5,000,000 g / mol, or less than or equal to about 5,000,000 g / mol.

[0050] In some embodiments, one or more polymeric adhesives, alone or in combination, may be present in the primer layer at a concentration of about 5 wt.% to about 80 wt.%, preferably about 10 wt.% to about 70 wt.%, more preferably about 20 wt.% to about 60 wt.%, and even more preferably about 30 wt.% to about 50 wt.%, expressed as wt.% of the total primer layer weight.

[0051] In some embodiments, one or more polymeric adhesives, alone or in combination, may be present in the primer layer at a concentration greater than or equal to about 5 wt.%, greater than or equal to about 10 wt.%, greater than or equal to about 80°C, greater than or equal to about 90°C, or greater than or equal to about 100°C, less than or equal to about 90°C, or less than or equal to about 80°C, expressed as a percentage of the total primer layer weight. In some embodiments, one or more polymeric adhesives may have a glass transition temperature (Tg) less than or equal to about -100°C to about 100°C, about -70°C to about 60°C, or about -30°C to about 30°C. In some embodiments using latex adhesives, the latex may have a minimum film-forming temperature (MFFT) below 60°C, for example, below 20°C, to ensure acceptable film properties after coating. particle

[0052] In some embodiments, the polymer adhesive layer according to this disclosure includes one or more microparticles, such as white microparticles, including white microparticles having a high refractive index or reflectivity. The white microparticles may be any suitable composition, size, and concentration for enhancing the reflectivity and / or hiding power of the primer layer.

[0053] In some embodiments, one or more particles may include one or more of TiO2, BaSO4, CaSO4, CaCO3, silicon dioxide, BN, Al2O3, Ca3(PO4)2, Ca(HPO4), ZrO2, ZnO, or any other suitable metal oxide, transition metal oxide, sulfate, carbonate, or phosphate material. In some embodiments, the white particles are one or more selected from the group consisting of TiO2, BaSO4, CaSO4, BN, Al2O3, CaCO3, and Ca3(PO4)2. In some embodiments, the white particles comprise, are substantially composed of, or are composed of TiO2.

[0054] In some embodiments, one or more particles may have an average particle size between about 0.1 µm and about 5 µm, between about 0.14 µm and about 2 µm, or between about 0.2 µm and about 1 µm.

[0055] In some embodiments, the average particle size of one or more particles may be greater than or equal to about 0.1 µm, greater than or equal to about 0.11 µm, greater than or equal to about 0.12 µm, greater than or equal to about 0.13 µm, greater than or equal to about 0.14 µm, greater than or equal to about 0.15 µm, greater than or equal to about 0.2 µm, greater than or equal to about 0.3 µm, greater than or equal to about 0.4 µm, greater than or equal to about 0.5 µm, greater than or equal to about 0.6 µm, greater than or equal to about 0.7 µm, greater than or equal to about 0.8 µm, greater than or equal to about 0.9 µm, or greater than or equal to about 1 µm.

[0056] In some embodiments, one or more particles may comprise a single white particle composition (e.g., TiO2) or two or more white particle compositions (e.g., TiO2 and Al2O3), substantially composed of or consisting of such compositions.

[0057] In some embodiments, one or more microparticles may further comprise one or more alkaline microparticles, including (but not limited to) Al₂O₃, CaCO₃, or Ca₃(PO₄)₂. In some embodiments, one or more alkaline microparticles are included as buffers in the primer layer to improve Dmin stability by neutralizing or absorbing any acidic chemicals that may diffuse or migrate from other layers (e.g., developer layers). In some embodiments, one or more alkaline microparticles are selected from the group consisting of CaCO₃, Al₂O₃, and Ca₃(PO₄)₂.

[0058] In some embodiments, one or more particles may have only one average diameter (e.g., a unimodal size distribution). In some embodiments, one or more particles may have a bimodal or trimodal size distribution (e.g., a white particle having an average diameter of about 0.1 µm to about 2 µm, and a white particle having an average diameter of about 0.2 µm to about 0.5 µm, although other differences in average diameter may be achieved, such as the difference between the average diameters of any two of the examples identified above).

[0059] In some embodiments, one or more filler particles of smaller particle size, such as silica or CaCO3, may be used to further increase the bulk density of the primer layer. Suitable particle sizes for filler particles may range from about 0.01 µm to about 1 µm, from about 0.02 µm to about 0.5 µm, and from about 0.05 µm to 0.2 µm.

[0060] In some embodiments, one or more microparticles, alone or in combination, may be present in the primer layer, expressed as wt.% relative to the total weight of the primer layer, with a concentration of about 10 wt.% to about 50 wt.%, about 15 wt.% to about 40 wt.%, or about 20 wt.% to about 35 wt.%.

[0061] In some embodiments, one or more microparticles, individually or in combination, may be present in the primer layer at a concentration expressed as wt.% relative to the total weight of the primer layer. In some embodiments, the refractive index of one or more microparticles is greater than or equal to about 1.5, preferably greater than or equal to about 2.0, more preferably greater than or equal to about 2.4, or any range or value between these values.

[0062] In some embodiments, the refractive index of one or more microparticles is from about 1.4 to about 3, from about 2 to about 3, or any range or value thereto. In some embodiments, low refractive index filler particles, such as silica and CaCO3, may be present in the primer layer at a concentration of from about 0.1 wt.% to about 15 wt.%, preferably from about 1 wt.% to about 10 wt.%, expressed as wt.% of the total primer layer weight. polymer hollow particles

[0063] In some embodiments, the primer layer according to this disclosure comprises one or more polymer hollow particles. The polymer hollow particles may have any suitable composition, size (average diameter) or specific gravity, and may be present at any suitable concentration to improve the thermal insulation properties of the primer layer relative to conventional primer layers that do not contain any polymer hollow particles, while providing acceptable reflectivity (e.g., hiding power), anti-blocking properties, adhesion, anti-foaming properties, and film quality.

[0064] In some embodiments, one or more polymer hollow particles may comprise, consist substantially of, or be composed of. In some embodiments, the core is an air core or a precursor thereof, such as a highly water-swellable gel, which forms an air core from itself during or after coating and after water removal.

[0065] In some embodiments, one or more hollow polymer particles comprise a polymer shell containing a polymer selected from the group consisting of: polyacrylates, polymethacrylates, polystyrene, polyesters, melamine-formaldehyde condensates, polyolefins, polyureas, polyurethanes, and blends or copolymers thereof. In some embodiments, the polymer shell is cross-linked. In some embodiments, the polymer shell may comprise an inorganic network, such as silica formed by, for example, a sol-gel process. Exemplary polymeric hollow particles can be prepared according to the disclosures found in the following: CJ McDonald et al., 99 Adv. Colloid & Interface Sci. 181-213 (2002) (DOI: 10.1016 / S0001-8686(02)00034-9) and W. Wichaita et al., 58 Indus. Eng' g Chem. Res. 20880-20901 (2019) (DOI: 10.1021 / acs.iecr.9b02330), the entire contents of which are incorporated herein by reference.

[0066] In some embodiments, one or more polymer hollow particles may have an average diameter or D50 of about 0.1 µm to about 2 µm, about 0.1 µm to about 1 µm, about 0.3 µm to about 5.0 µm, or about 0.5 µm to about 2 µm. In some embodiments, the air core of the polymer hollow particles has a diameter of about 0.1 µm to about 1.0 µm or about 0.15 µm to about 1 µm. The hollow particles or their cores preferably have a narrow particle size distribution. A range of polymer hollow particles are readily available from, for example, Dow Chemicals and Taiwan Hopax Chemicals.

[0067] In some embodiments, the average diameter or D50 of the hollow particles in one or more polymers may be greater than or equal to about 0.1 µm, greater than or equal to about 0.2 µm, greater than or equal to about 0.3 µm, greater than or equal to about 0.4 µm, greater than or equal to about 0.5 µm, greater than or equal to about 0.6 µm, greater than or equal to about 0.7 µm, greater than or equal to about 0.8 µm, greater than or equal to about 0.9 µm, greater than or equal to about 1 µm, greater than or equal to about 1.5 µm, greater than or equal to about 2 µm, greater than or equal to about 2.5 µm, greater than or equal to about 3 µm, greater than or equal to about 3.5 µm, greater than or equal to about 4 µm, greater than or equal to about 4.5 µm, greater than or equal to about 5 µm, greater than or equal to about 10 µm, or any range or value between these values.

[0068] In some embodiments, the average diameter D50 of the hollow particles in one or more polymers may be less than or equal to about 5 µm, less than or equal to about 4.5 µm, less than or equal to about 4 µm, less than or equal to about 3.5 µm, less than or equal to about 3 µm, less than or equal to about 2.5 µm, less than or equal to about 2 µm, less than or equal to about 1.5 µm, less than or equal to about 1 µm, less than or equal to about 0.9 µm, less than or equal to about 0.8 µm, less than or equal to about 0.7 µm, less than or equal to about 0.6 µm, less than or equal to about 0.5 µm, less than or equal to about 0.4 µm, less than or equal to about 0.3 µm, less than or equal to about 0.2 µm, or any range or value thereof.

[0069] In some embodiments, one or more polymer hollow particles may comprise a single polymer hollow particle composition (e.g., NTR-50 (D 50 = about 0.16 µm)) or a composition of two or more polymer hollow particles (e.g., Hopax NTR-50 (D 50 = 0.16 µm), Hopax NTR-100 (D 50 = about 0.82 µm), Dow ROPAQUE™ ULTRA-E (D 50 = about 0.35 µm), and Dow ROPAQUE™ TH-1000 (D 50 = about 1.0 µm), etc.), substantially comprise or comprise of thereof.

[0070] In some embodiments, one or more polymer hollow particles, alone or in combination, may be present in the primer layer at a concentration of about 2 wt.% to about 30 wt.%, about 5 wt.% to about 25 wt.%, or more preferably about 10 wt.% to about 25 wt.%, expressed as wt.% of the total primer layer weight. Back coating

[0071] Referring to Figure 1C, in some embodiments, an opaque back coating 105 is applied to a second surface of a substrate 102, wherein a primer layer 104 is applied to the first surface. Such embodiments can improve image resolution, recent Dmax, and energy efficiency, and eliminate the risk of light leakage via the top image sheet, which would cause premature exposure of the underlying image sheet in a media stack. In some embodiments, the opaque back coating contains components substantially identical to those in the primer layer (e.g., white microparticles, filler microparticles, or hollow polymer particles), having any of the same composition or size disclosed above, or present at any of the concentrations disclosed above relative to the total weight of the back coating. For example, in some embodiments, the back coating contains hollow polymer particles. In some embodiments, the back coating further contains one or more microparticles (e.g., microparticles selected from the group consisting of: TiO2, silicon dioxide, BaSO4, CaSO4, BN, CaCO3, Al2O3, AlN, and Ca3(PO4)2). In some embodiments, the back coating contains an adhesive (e.g., a polymeric adhesive).

[0072] In some embodiments, the back coating further comprises an annihilation dye or pigment for initial light annihilation. In some embodiments, the annihilation dye or pigment is a black dye or pigment, such as carbon black. Commercially available examples of carbon black include, but are not limited to, NW-KAB85 ((D50 = 0.15 µm), from Taiwan Nanotechnology Co., Ltd.).

[0073] The back coating may have any thickness suitable for ensuring easy handling of the media sheet and acceptable annihilation of initial light. In some embodiments, the thickness of the back coating is from about 2 μm to about 30 μm, from about 3 μm to about 20 μm, or from about 5 μm to about 15 μm.

[0074] In some embodiments, the thickness of the back coating may be greater than or equal to about 1 µm, greater than or equal to about 1.5 µm, greater than or equal to about 2 µm, greater than or equal to about 2.5 µm, greater than or equal to about 3 µm, greater than or equal to about 3.5 µm, greater than or equal to about 4 µm, greater than or equal to about 4.5 µm, greater than or equal to about 5 µm, greater than or equal to about 6 µm, greater than or equal to about 7 µm, greater than or equal to about 8 µm, greater than or equal to about 9 µm, greater than or equal to about 10 µm, greater than or equal to about 15 µm, greater than or equal to about 20 µm, greater than or equal to about 25 µm, greater than or equal to about 30 µm, greater than or equal to about, or any range or value thereof.

[0075] In some embodiments, the thickness of the back coating may be less than or equal to about 50 µm, less than or equal to about 45 µm, less than or equal to about 40 µm, less than or equal to about 35 µm, less than or equal to about 30 µm, less than or equal to about 25 µm, less than or equal to about 20 µm, less than or equal to about 15 µm, less than or equal to about 10 µm, less than or equal to about 5 µm, or any range or value thereof.

[0076] In some embodiments, the back coating comprises a black pigment or dye at a concentration of about 0.1 wt.% to about 50 wt.%, about 1 wt.% to about 30 wt.%, or about 3 wt.% to about 20 wt.% or any range or value thereof relative to the total weight of the back coating.

[0077] In some embodiments, the back coating comprises a black pigment or dye at a concentration of greater than or equal to about 0.1 wt.%, greater than or equal to about 0.2 wt.%, greater than or equal to about 0.3 wt.%, greater than or equal to about 0.4 wt.%, greater than or equal to about 0.5 wt.%, greater than or equal to about 0.6 wt.%, greater than or equal to about 0.7 wt.%, greater than or equal to about 0.8 wt.%, greater than or equal to about 0.9 wt.%, greater than or equal to about 1 wt.%, greater than or equal to about 2 wt.%, greater than or equal to about 3 wt.%, greater than or equal to about 4 wt.%, greater than or equal to about 5 wt.%, greater than or equal to about 6 wt.%, greater than or equal to about 7 wt.%, greater than or equal to about 8 wt.%, greater than or equal to about 9 wt.%, greater than or equal to about 10 wt.%, greater than or equal to about 15 wt.%, greater than or equal to about 20 wt.%, greater than or equal to about 25 wt.%, or any range or value thereof relative to the total weight of the back coating.

[0078] In some embodiments, the back coating comprises a black pigment or dye at a concentration of less than or equal to about 60 wt.%, less than or equal to about 55 wt.%, less than or equal to about 50 wt.%, less than or equal to about 45 wt.%, less than or equal to about 40 wt.%, less than or equal to about 35 wt.%, less than or equal to about 30 wt.%, less than or equal to about 25 wt.%, less than or equal to about 20 wt.%, less than or equal to about 15 wt.%, less than or equal to about 10 wt.%, or any range or value thereof relative to the total weight of the back coating.

[0079] In some embodiments, the back coating is deposited on the second surface of the substrate by vapor deposition, sputtering, spraying, or wet coating. In some embodiments, the back coating may not contain a polymer binder. In some embodiments, the back coating may not contain a black pigment or dye. In some embodiments, the back coating may comprise a metal, metal nitride, metal oxide, metal carbide, or metal boride film (e.g., Al, Cr, Ag, Ni, Au, Cu, Ti, and combinations thereof) applied to the second surface of the substrate (e.g., a first substrate) by vapor coating or sputtering.

[0080] Although it is believed that those skilled in the art will fully understand the foregoing terms, the following definitions are set forth in order to explain the subject matter disclosed in this invention.

[0081] The term "a / an" can refer to one or more of the entities, that is, it can refer to multiple references. Therefore, the terms "a / an," "one or more," and "at least one" are used interchangeably in this document. Furthermore, referring to "one element" by the indefinite article "a / an" does not preclude the possibility of more than one element, unless the context explicitly requires the presence of exactly one element.

[0082] Throughout this specification, the terms "an embodiment," "an embodiment," "a category," or "a category" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of this disclosure. Therefore, the phrases "in an embodiment" or "in a category" appearing in various places throughout this specification do not necessarily refer to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0083] As used herein, the terms “about” or “approximately” when preceding a numerical value indicate a range of ±10% of that value.

[0084] Those skilled in this art will understand that, for any and all purposes, especially for the purpose of providing a written description, all scopes disclosed herein also encompass any and all possible subscopes and combinations thereof. Any listed scope can be readily identified by sufficient description and can be decomposed into at least two, three, four, five, ten, etc., identical scopes. As a non-limiting example, the scopes discussed herein can be readily decomposed into a lower third, a middle third, and an upper third, etc. Those skilled in this art will also understand that all terms such as “at most,” “at least,” “greater than,” “less than,” and similar terms include the listed numbers and refer to a scope that can subsequently be decomposed into subscopes as discussed above. Ultimately, those skilled in this art will understand that a scope includes its individual members.

[0085] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should be further understood that terms (such as those defined in common dictionaries) shall be interpreted as having the same meaning as they have in the context of this application and in the related art, and shall not be interpreted in an idealized or overly formal sense unless expressly defined herein. Even if such terms are not expressly defined below, they shall be interpreted according to their common meaning.

[0086] For the purposes of this disclosure, the terms "color density" or "color optical density" refer to the ability of a medium to reflect light, wherein the greater the reflection of certain colors of light by a dye, the higher the color optical density (i.e., the more saturated the color). The lower the light reflection of a dye, the lower the color density (i.e., the less saturated the color).

[0087] For the purposes of this disclosure, the term "maximum color density" (or "Dmax") refers to the maximum color density achieved by dye after a predetermined development time, as measured by a Konica Minolta FD-5 reflectance densitometer. For example, Dmax, recent or recent Dmax refers to the maximum color density of the developed image measured immediately after development, and Dmax, t refers to the maximum color density measured after the developed image has been adjusted for a period of time (t).

[0088] For the purposes of this disclosure, the term "leuco dye" refers to a chemical dye that can alternate between two chemical forms, one of which is colorless. The conversion from colorless to colored form can be reversible or irreversible and can be induced by changes in Lewis acid or alkali, or by temperature, pH, irradiation, or redox state. Suitable developers include, but are not limited to, phenols, phenolic resins, salicylic acid, oxalic acid, phthalic acid, organophosphonic acids, organosulfonic acids, and their zinc-oxidized derivatives. Zinc-oxidized salicylate derivatives and phenolic varnish resins are particularly suitable due to their high rate of color formation and the high color fastness of the dyes formed therefrom. [Methods for preparing imaging slides] []

[0089] In another category which may be combined with any other category or embodiment, this disclosure relates to a method of preparing an imaging film, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any embodiment disclosed herein to produce a primer-coated first substrate; (ii) contacting the primer layer of the primer-coated first substrate with a microcapsule layer to produce a microcapsule-coated first substrate; (iii) contacting the microcapsule-coated first substrate with a developer layer to produce a developer-coated first substrate; and (iv) contacting the developer layer of the developer-coated first substrate with a second substrate to produce an imaging film.

[0090] In some embodiments, this disclosure relates to a method for preparing an imaging film, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any embodiment disclosed herein to produce a primer-coated first substrate; (ii) contacting the primer layer of the primer-coated first substrate with a microcapsule layer to produce a microcapsule-coated first substrate; (iii) contacting a second substrate with a developer layer to produce a developer-coated second substrate; and (iv) contacting the developer layer of the developer-coated second substrate with a microcapsule layer of the microcapsule-coated first substrate to produce an imaging film.

[0091] In some embodiments, the second primer layer may be disposed between the second substrate and the developer layer.

[0092] In any of the above embodiments, the method of generating an image sheet may further include: (v) contacting a second surface of a first substrate with a back coating, wherein the second surface of the first substrate is opposite to a first surface of the first substrate. In some embodiments, the contact in (v) is performed by physical vapor deposition, sputtering, chemical vapor deposition, lamination, or spin coating. [Method for using a primer layer and an imaging film containing it] []

[0093] In another category, which may be combined with any other category or embodiment, this disclosure relates to a method of using a primer layer according to any of the embodiments described above. In another category, which may be combined with any other category or embodiment, this disclosure relates to a method of using an imaging sheet according to any of the embodiments described above.

[0094] For example, in some embodiments, the imaging or printing method includes exposing an imaging sheet comprising a primer layer according to any of the embodiments disclosed herein and a microcapsule layer according to any of the embodiments disclosed herein to heat, pressure, or radiation, wherein the exposure is sufficient to release a leuco dye from the microcapsules in the microcapsule layer, thereby producing an image.

[0095] In some embodiments, this disclosure relates to a method for improving one or more properties of an imaging film, comprising including (or adding) a primer layer according to any embodiment disclosed herein in the imaging film. In some embodiments, one or more properties include one or more of the following: Dmax; recent Dmax; Dmax, t; Dmin; image resolution; opacity; anti-adhesion; adhesion; reflected light density; and thermal insulation performance.

[0096] Unless otherwise expressly indicated, all specified embodiments, features, and terms are intended to include the said embodiments, features, or terms and their equivalents.

[0097] Reference will now be made to the various specific embodiments covered in this disclosure. While various embodiments are described herein, it should be understood that the invention is not intended to be limited to the described embodiments. Rather, it is intended to cover alternatives, modifications, and equivalents that may be included within the spirit and scope of the technology as defined by the appended claims. Example [Materials and Methods] [] [surface] [1.] Materials used in exemplary embodiments [] [Material] [describe] Versa TL502 Sulfonated polystyrene from Nouryon CYMEL® 385 Allnex's methylated high-imino melamine resin with a lower degree of alkylation NW-YOT05 Yellow (Pigment Yellow 155) water-based ink dispersion (D50 0.14 µm) from Taiwan Nanotechnology Co., Ltd. NW-MEA12 Magenta (Pigment Purple 19) water-based ink dispersion (D50 0.14 µm) from Taiwan Nanotechnology Co., Ltd. DESMODUR® N-100 Aliphatic polyisocyanates from Covestro AEROSOL™ OT Sodium bis(2-ethylhexyl)sulfosuccinate surfactant from Cytec TRITON™ X-114 Nonionic surfactants from Dow Company IRGANOX® 1035 Key phenolic antioxidants and heat stabilizers from BASF GSB1202 Spacer particles from Guidewin CELLOSIZE™ QP-52000H Hydroxyethyl cellulose from Dow METHOCEL™ K15M Hydroxypropyl methylcellulose from DuPont SILWET® L-7001 Polysiloxane surfactants from Momentive Performance Materials SILWET® L-7604 Polysiloxane surfactants from Momentive Performance Materials JONCRYL® FLX 5040 Latex adhesives from BASF M-35 Latex adhesive (D50 0.12 μm) from TOA Resin. TAMOL™ 731 DP Hydrophobic copolymer dispersants from Dow Chemical TAMOL™ 165A Hydrophobic copolymer dispersants from Dow Chemical PVA2488 Polyvinyl alcohol from Sinochem PVA205 Polyvinyl alcohol from Sinochem CAB-O-SPERSE® 1015A Aqueous dispersion of CAB-O-SIL® L-90 (fumigated silica) from Cabot Corporation CAB-O-SPERSE® 2012A Aqueous dispersion of CAB-O-SIL® M-5 (fumigated silica) from Cabot Corporation Eastman AQ™ 55S Water-dispersible polyester resin from Eastman TIPURE™ 6341 Titanium dioxide aqueous dispersion from DuPont NW-WNQ11 Rutile titanium dioxide aqueous dispersion (D50=0.34 µm) from Taiwan Nanotechnology. NTR-50 Hollow polymer particles (D50=0.13 µm) from HOPAX. NTR-100 Hollow polymer particles (D50 = 0.30 µm) from HOPAX. ROPAQUE™ ULTRA-E opaque polymer Hollow particles (D 50 = 0.38 µm) of polymer opacifier from Dow Chemical Company MK-WD42515 Aqueous dispersion of calcium carbonate from Taiwan Nanotechnology (D 50 = 0.11 µm) NW-KAB85 Carbon black water-based pigment dispersion (D 50 = 0.15 µm) from Taiwan Nanotechnology Co., Ltd. FOAMSTAR® ST 2410 Star-shaped defoamer from BASF PRIMAL™ AC-261T Acrylic latex from Dow Chemical [surface] [2.] The internal phase of photosensitive microcapsules Green photosensitive capsule dry portion TMPTA (trimethylolpropane triacrylate) 90.00 TPGDA (tripropylene glycol diacrylate) 10.00 THEED(N,N,N',N'-Tetra(2-hydroxyethyl)ethylenediamine) 0.20 DIDMA (2,6-diisopropyl-N,N-dimethylaniline) 3.00 Magenta leuco dye (CAS: 50292-95-0, from Synmedia-chem) 20.00 (MTBS) mercaptobenzothiazole disulfide 0.50 Green-sensitive light initiator (1-hepta-2-[3-(1-hepta-3,3-dimethyl-1,3-dihydro-2H-indole-2-ylidene)-propenyl]-3,3-dimethyl-3H-indole isobutyltriphenylboronic acid ester) 0.075 DESMODUR® N-100 8.00 DBTDL (Dibutyltin Dilaurate) 0.05 Preparation of photosensitive microcapsules

[0098] Photosensitive microcapsules were prepared using the materials listed in Table 2 and the process described below: 1. Add 220 parts water and 8 parts Versa TL502 sulfonated polystyrene (dry) to a 1000 ml stainless steel beaker and mix thoroughly. 2. Slowly sieve 10 parts of pectin (polygalacturonic acid methyl ester) into the mixture and stir overnight at room temperature (500-1000 rpm). 3. Adjust the pH to 7.5 with 10% sodium carbonate and increase the mixing speed to 1750 rpm. 4. Add the internal phase as shown in Table 2 over a period of 15-30 seconds, stir the resulting mixture for 30 minutes, add 11 parts of 9.1% (pH adjusted to 7.0) aqueous solution of DETA (diethylenetriamine), and allow it to react at 25°C for 30 minutes, followed by reaction at 40°C for one hour. 5. Add a solution containing 19.9 parts CYMEL® 385 and 40 g of water (pH adjusted to 6.0), and allow the mixture to react at 70°C for another 2 hours. 6. Add 15.23 parts of 34.3% sodium sulfate aqueous solution, stir for 10 minutes, then add 1.97 parts of CYMEL® 385 and 10 parts of water, and allow the mixture to react at 70°C for another hour. 7. Reduce the mixing speed to 600 rpm, adjust the pH to 9.5 using 20% ​​NaOH solution, and stir the resulting reaction mixture overnight at room temperature.

[0099] The microcapsules prepared in this manner were thoroughly washed with water and centrifuged to remove excess water-soluble polymers and additives present in the aqueous phase. The particle size (D 50) of the purified / washed microcapsules was approximately 6 μm, as measured by a HORIBA LA-960 particle size analyzer. [, , ] Preparation of control microcapsule tablets - microcapsule coating on PET (MELINEX® 339) without primer or back coating. [surface] [3.] Composition of microcapsule fluids Element Dry portion Green Sensitive Microcapsules (45% Solid) 100.00 Calcium carbonate (33% solid) (particle size, D 50==0.12 μm) 5.00 CELLOSIZE™ QP-52000H 0.51 AEROSOL™ OT 0.05 TRITON™ X-114 0.20 SILWET® L*-7001 0.20 SILWET® L*-7604 0.20 TAMOL™ 731 DP 2.00 Joncryl FLX 5040 10.00 Eastman AQ™ 55S 8.00

[0100] The coating fluid shown in Table 3 was adjusted to 33 wt.% by adding water and thoroughly dispersed using a low-shear mixer. It was then coated onto a 2-mil white PET substrate (MELINEX® 339) using a Myrad rod and dried in an oven at 80°C for 10 minutes. The dry coating thickness was approximately 8 µm, as measured by a Mitutoyo thickness gauge. Preparation of color developer coating

[0101] To prepare the color developer coating, the composition shown in Table 4 was coated onto a 1-mil transparent PET film using a Myrad rod and dried in an oven at 80°C for 10 minutes, with a target dry coating thickness of approximately 13 μm. [surface] [4.] Composition of developer coating [] Element Dry portion Richful (China) resin developer RD9870A 98.00 CAB-O-SPERSE® 1015A from Cabot (USA) 0.86 PVA1799 from Sinochem (China) 1.14 Preparation of control image films to image films without primer or back coating

[0102] The microcapsule membranes and developer membranes prepared as described above were laminated together using a Tamerica TCC2700 roller laminator. The temperature, pressure, and speed were set to 100°C, 3.621 Kgf / 170 mm, and 0.368 m / min, respectively, to form various photosensitive imaging films, as described in the following examples. [Example] [1.] [The role of the primer coating in resisting adhesion, reflectivity, hiding power, tack, and bubbling] []

[0103] To test the relative effects of hollow particles in the primer layer, the primer formulation contained 30 wt.% TiO2 particles (from DuPont's TIPURE™ 6431), 5 wt.% PVA 205, 0-10 wt.% hollow particles NTR-50 (D 50 = 0.25 μm, from Hopax Chemicals), and 55-60 wt.% M35 latex as a buffer. The primer formulation was applied to a MELINEX® 339 substrate using a Myrad rod. For comparison, a primer layer containing 5 wt.% (dry) silicon dioxide CAB-O-SIL® 1015 was also prepared. The thicknesses of each coating ranged from 6.3 µm to 6.7 µm. []

[0104] For the adhesion test, each sample was pressed against the back of the MELINEX® 339 substrate at 10 kg / 100 cm² for 24 hours at 40°C and 85% relative humidity, and the percentage of test areas with observable damage marks was recorded. []

[0105] To test the hiding power, primer layers with various concentrations of hollow particle NTR-50 were applied to the top surface of MELINEX® 339, and the gloss density was measured relative to a black surface. The lower the reflected gloss density, the higher the hiding power; for color to be hidden against a black background, the gloss density is approximately 2.0. []

[0106] As shown in Table 5, compared to the control group without any primer coating, all samples with primer coatings showed a significant increase in hiding power or a decrease in reflected light density (black OD 0.0-0.02 or reflectivity 95.5-100%). It is also evident that, compared to primer coatings containing only silica particles (an additive commonly used to improve the anti-blocking properties of coatings), after the adhesion test, all samples coated with primer coatings containing 5-10 wt.% NTR-50 showed significantly improved anti-blocking properties or a reduction in the percentage of areas with observable damage markings. [] [surface] [5, . Covering power and anti-adhesion properties of hollow particle concentration (Example 1) Example 1 (6.5 + 0.2 μm) Reflected light density Adhesion test Anti-adhesion (area %)* Cyan (C) Magenta (M) Yellow (Y) Black (K) Comparison MELINEX® 339 only 0.08 0.06 0.02 0.07 NA NA Example 1-1** 5 wt.% CAB-O-SPHERSE® 1015A 0 0 0 0 pass >90% Example 1-2** 5.0 wt.% NTR-50 0.02 0.01 0.01 0.02 pass <30% Examples 1-3** 7.5 wt.% NTR-50 0 0 0 0 pass 30-35% Examples 1-4** 10.0 wt.% NTR-50 0.01 0 0.01 0 pass 30-35% * % of areas with observable damage after adhesion test (weight: 10 kg / 100 cm², 85% RH / 40°C for 24 hours) ** MELINEX® 339, coated with a primer layer containing 30 wt.% TiO2 (TIPURE™ 6431) and 5.0-10.0 wt.% NTR-50.

[0107] All coatings also demonstrated excellent water resistance (bubbling test) and adhesion to PET 339 (tape test). [] [Example] [2.] [Reduced thickness of the primer layer] []

[0108] Except for reducing the coating thickness to 2.9 ± 0.3 μm, the same primer layer as described in Example 1 was prepared. To achieve high color density images, the leuco dye released from the microcapsules must diffuse as much as possible into the developer layer to convert the leuco dye from its leuco form into a color form. A thin, impermeable primer layer is ideal because it reduces the risk of unwanted dye diffusion or absorption into the primer layer, and it is positioned opposite the microcapsule layer in the following imaging film structure: PET / primer layer / microcapsule layer / developer layer / PET. Thin primer layer compositions were prepared, containing 0.4-1.1 wt.% hydroxypropyl methylcellulose (HPMC) (DuPont METHOCEL™ K15M) as a thickener to improve coating quality, and various concentrations of M35 latex as a buffer (to bring the composition to 100 wt.%). The thin primer layer compositions were then coated onto MELINEX® 339. The samples underwent the above tests for adhesion, covering force, and bonding (see Example 1). []

[0109] As shown in Table 6, all films prepared from the HPMC-containing primer formulations exhibited excellent coating quality, adhesion, anti-foaming properties, and hiding power (measured against a black background with a gloss level >2.0, with reflected black gloss level ≤0.01 or reflectance ≥97.7%), even after the primer layer thickness was reduced to 2.9 ± 0.3 μm. All four primer layers in Example 2 also showed significantly improved anti-blocking properties, with the percentage of areas showing observable damage markings after the adhesion test significantly decreasing from <30% (see Examples 1-2) to <10%. [] [surface] [6.] Hiding power of primer layers containing thickeners (Example 2) [] Example 2 (2.9 ± 0.3 μm) Reflected light density Adhesion test Anti-adhesion (area %)* Cyan (C) Magenta (M) Yellow (Y) Black (K) Comparison MELINEX® 339 only 0.08 0.06 0.02 0.07 N / A N / A Example 2-1** 0.4 wt.% HPMC 0.02 0 0.01 0.01 pass <10% Example 2-2** 0.6 wt.% HPMC 0.02 0.01 0.01 0.01 pass <10% Example 2-3** 0.8 wt.% HPMC 0.02 0.01 0.01 0.01 pass <10% Example 2-4** 1.1 wt.% HPMC 0.02 0.01 0.01 0.01 pass <10% * % of areas with observable damage after adhesion test (weight: 10 kg / 100 cm², 85% RH / 40°C for 24 hours) ** MELINEX® 339 with a primer layer containing 30 wt.% TIPURE™ 6431, 5.0 wt.% NTR-50, and 0.4-1.1 wt.% HPMC-K15M [Example] [3.] [Having various particle concentrations () [30-37 wt.%] [) Primer layer []

[0110] Except that the concentration of TiO2 (TIPURE™ 6431) was increased from 30 wt.% to 37 wt.% and the concentration of M35 latex as a buffer was changed (to bring the composition to 100 wt.%), the same primer layer described in Example 2 was prepared. The coating thickness on MELINEX® 339 ranged from 2.5 µm to 3.2 µm. The samples were subjected to the same hiding power, anti-blocking, tack, and anti-foaming tests as discussed above (see Examples 1 and 2). []

[0111] As shown in Table 7, all primer layers prepared in this manner exhibited excellent hiding power (reflective black density ≤0.01 or reflectance ≥97.7% compared to 0.07 or 85.1% reflectance of bare PET MELINEX® 339), indicating that higher concentrations of TiO2 particles can produce highly reflective primer layers with a thickness as low as 2.5 μm. Higher reflectance means higher photosensitivity, as reflected light acts as an additional light source to expose the microcapsules. The color intensity of the developed image was also improved because more light of appropriate color was reflected back to the observer's eye during image evaluation. [surface] [7.] Primer layers with various TIPURE™ 6431 concentrations offer excellent hiding power and anti-blocking properties (Example 3). Example 3 (2.85 ± 0.35 μm) Reflected light density Adhesion test Anti-adhesion (area %)* Cyan (C) Magenta (M) Yellow (Y) Black (K) Comparison MELINEX® 339 only 0.08 0.06 0.02 0.07 N / A N / A Example 3-1 30.0 wt.% TiO2 0.02 0 0.01 0.01 pass <5% Example 3-2 32.5 wt.% TiO2 0.02 0 0.01 0.01 pass <5% Example 3-3 35.0 wt.% TiO2 0.01 0 0.01 0.01 pass <5% Example 3-4 37.0 wt.% TiO2 0.01 0 0.01 0.01 pass <5% * % of areas with observable damage after adhesion test (weight: 10 kg / 100 cm², 85% RH / 40°C for 24 hours) ** MELINEX® 339 is coated with a primer layer containing 5.0 wt.% NTR-50, 0.6 wt.% HPMC-K15M, 30-37 wt.% TiO2 and M35 as a buffer adhesive.

[0112] Referring to Table 7, the anti-adhesion test showed that all primer layers exhibited good anti-adhesion properties, with very light markings observed in areas with less than 5% load. Primer layers with ≥32.5 wt.% TiO2 without release liner or coating showed slightly less tendency to adhere to the edges of the PET 339 substrate, with only slight blurring at the edges under load. All primer layers showed acceptable tack (i.e., passed the tack test), regardless of TiO2 concentration. All primer layers also showed good anti-foaming properties in the presence of two different test liquids: deionized water and water containing 0.01 wt.% each of AEROSOL OT™ (sodium dioctyl sulfosuccinate) and TRITON™ X-114 nonionic detergent (Sigma-Aldrich, Saint Louis, MO). [] [Example] [4.] [The Role of Hollow Particle Concentration and Size] []

[0113] To test the effect of hollow particle size and concentration on film performance, five primer layers with varying hollow particles (different sizes and concentrations) were prepared as described in Example 3, in addition to using the hollow particle types and concentrations shown in Table 8. Table 8 also shows their hiding power, indicated by reflected light density measured relative to a black substrate (OD = 2.0, black). [] [surface] [8.] Hiding power and anti-blocking properties of primers with different hollow particle sizes and concentrations (Example 4) Example 4 (2.6-4.0 μm) Reflected light density Adhesion test Anti-adhesion (area %)* Cyan (C) Magenta (M) Yellow (Y) Black (K) Comparison MELINEX® 339 only 0.08 0.06 0.02 0.07 N / A N / A Example 4-1 10.0 wt.% NTR-50 0.02 0.01 0.01 0.01 pass Approximately 10% Example 4-2 12.2 wt.%NTR-50 0.02 0.01 0.01 0.01 pass Approximately 10% Example 4-3 14.3 wt.% NTR-50 0.01 0.01 0.01 0.01 pass Approximately 10% Example 4-4 10.0 wt.% NTR-100 0.01 0.00 0.01 0.01 pass <5% Example 4-5** 14.3 wt.% NTR-100 0.02 0.00 0.00 0.01 pass <5% * % of areas with observable damage after adhesion test (weight: 10 kg / 100 cm², 85% RH / 40°C for 24 hours) ** Only MELINEX® 339 is coated with a primer layer containing 30 wt.% TIPURE™ 6431 and 55-59.3 wt% M35 adhesive.

[0114] As shown in Table 8, regardless of the size or concentration of hollow particles, primer layers with hollow NTR-50 and NTR-100 particles (D 50 = 0.9 μm) exhibited excellent hiding power compared to bare MELINEX® 339 substrates, as evidenced by low reflectance density (or high reflectivity, 97.7%). Furthermore, all primer layers demonstrated acceptable anti-blocking properties. Primer layers containing 10 wt.% or 14.3 wt.% NTR-100 showed slightly better anti-blocking properties than similar primer layers containing NTR-50 particles. []

[0115] Regardless of the size or concentration of hollow particles, all films passed the dry tack test, demonstrating acceptable adhesion of the primer layer to the MELINEX® 339 substrate. However, at the same concentration, the primer layer containing NTR-50 hollow particles showed slightly better film quality after visual observation compared to a similar primer layer containing NTR-100 hollow particles. [] [Example] [5.] [The effect of mixed hollow particle size on primer quality and performance] [] Anti-blocking properties, hiding power, adhesion and anti-foaming properties

[0116] To test the effects of hollow particles with a bimodal size distribution on the hiding power, anti-blocking, adhesion, and anti-foaming properties of the primer layer, primer formulations were prepared according to Table 9. Each primer layer contained NTR-50 (D 50 = 0.25 µm). [and] NTR-100 (D 50 = 0.9 µm), with a combined concentration of 10.0 wt.% but with a different NTR-50:NTR-100 ratio. All primer coatings in Example 5 contained 0.8 wt.% HPMC-K15M and were applied to MELINEX® 339 with a target dry thickness of approximately 2.8 µm, following the same procedure described in Example 4.

[0117] As shown in Table 9, all primer coatings in Example 5 exhibited good adhesion to the PET substrate, and the sample with hollow particles showed improved anti-blocking properties and hiding power compared to the sample without any hollow particles (see Example 5-0). While all primer coatings showed acceptable coating quality, one coating with a higher concentration of larger particles (NTR-100) showed slightly poorer coating uniformity. [surface] [9.] Primer formulations with a bimodal hollow particle size distribution [] Example 5 (2.8 ± 0.3 μm) Primer composition (wt.%, dry) Adhesion test Anti-adhesion (area %)* Reflection OD(K)** NTR-50 NTR-100 TIPURE™ 6431 M35 Example 5-0 0 0 36.46 62.55 pass > 20% 0.02 Example 5-1 10 0 32.8 56.3 pass < 5% 0.01 Example 5-2 9 1 32.8 56.3 pass < 5% 0.01 Example 5-3 8 2 32.8 56.3 pass < 5% 0.01 Example 5-4 7 3 32.8 56.3 pass < 5% 0.01 Example 5-5 5 5 32.8 56.3 pass < 5% 0.01 * % of areas with observable damage after adhesion test (weight: 10 kg / 100 cm², 85% RH / 40°C for 24 hours) ** Measurement against a black background with an OD(K) of approximately 2.0

[0118] Judging from the size of the watermarks observed after exposure to deionized water and aqueous solutions containing 0.5 wt.% AEROSOL OT™ and TRITON™ X-114 respectively, all primer formulations also showed good anti-foaming properties. Primer formulations containing blends of hollow particles of different sizes (e.g., Examples 5-3 and 5-4, NTR-50 / NTR-100 = 8 / 2 to 7 / 3) appeared to exhibit the desired coating quality and anti-blocking properties, while also demonstrating excellent reflectivity, film quality, and anti-foaming properties. [] Thermal insulation performance

[0119] To test the thermal insulation properties of primer layers containing hollow particles, primer formulations of Examples 5-0 (without hollow particles), 5-1 (10 wt.% NTR-50), and 5-5 (5 wt.% NTR-50 and 5 wt.% NTR-100) were used. Using the apparatus shown in Figure 2A, the temperature difference between the top and bottom of an imaging film containing the primer layer was measured as a function of heating time at a preset fixture temperature of 70°C, with thermal probes placed at the top and bottom of the imaging film. []

[0120] Referring to Figure 2B, the temperature difference between the top and bottom of the primer layer increases significantly with the addition of hollow particles and further with the addition of hollow particle dopants. Compared to the difference of approximately 3.5°C after 26 seconds and 5.4°C after 29 seconds for the primer layer without hollow particles and the bare MELINEX® 339 substrate, respectively, the primer layer containing hollow particles reaches a maximum temperature difference of approximately 17°C after approximately 20 seconds. As indicated by Figure 2B, the presence of hollow particles greatly increases the rate of temperature increase and equilibrium temperature on the top surface of the primer layer (or the bottom of the image layer if the image layer is applied over the primer). []

[0121] The actual temperature difference between the top and bottom probes for each sample is shown in Figures 3A-3F. The slight cyclic deviation in temperature at the top probe is caused by the relay control (which shuts off the heater at 70°C) looping the heater. Consistent with the results shown in Figure 2B, the primer layer with NTR-50 / NTR-100 hollow particles exhibits the largest equilibrium temperature difference between the top and bottom probes (Example 5-5, 8.3°C, Figure 3F), followed by the primer layer with only NTR-50 hollow particles (Example 5-1, 6.7°C, Figure 3E), which is significantly higher than the temperature differences observed for formulations without hollow particles (Example 5-0, 2.5°C, Figure 3D) or without a primer layer (2.7°C, Figure 3C). Figures 3A and 3B are overlay plots comparing the temperature over time for all top probe readings and all bottom probe readings, respectively. []

[0122] Therefore, the presence of hollow particles in the primer layer effectively minimizes heat loss from the primer layer (e.g., leakage into the substrate). Furthermore, primer layers with blends of different hollow particle sizes appear to have better insulation and heating efficiency than primer layers with a single hollow particle size. [] [Example] [6.] [The effect of clamp temperature and hollow particle composition on color development] []

[0123] To test the effects of processing parameters (e.g., fixture temperature) and hollow particle composition (e.g., the ratio of NTR-50 to NTR-100) on color development, microcapsule imaging sheets were prepared by coating a magenta capsule layer (8 µm thick; 15 phm PERGASCRIPT® Red I6B in microcapsules, D 50 5-6 µm) with a primer layer (2-3 µm, once corona treated) according to Examples 5-1 and 5-4. These primer layers contained 10 wt.% hollow particles, with NTR-50:NTR-100 ratios of 10 / 0 and 7 / 3, respectively. A control experiment (Example 6-0) was prepared using a primer layer from Example 5-0 without any hollow particles. The resulting microcapsule imaging sheets were laminated together with a developer sheet (1 mil clear PET with 15 µm developer RD9870 / 15% phenolic varnish 586) under low pressure at room temperature. The prepared media were developed using a developing fixture at various preset temperatures (60°C, 70°C, and 80°C). []

[0124] Referring now to Figure 4A, the recent Dmax of the medium with primer 5-1 (containing 10% NTR-50) increases from approximately 2.25 to approximately 2.35 as the fixture temperature increases (60°C to 80°C). After cooling to room temperature, the Dmax continues to increase for approximately 1 hour, eventually reaching a Dmax value of approximately 2.43 (80°C) from 2.35 (60°C). Assuming that the Dmax after 1 hour of fixture development represents the maximum conversion of the leuco dye, the dye conversion immediately following fixture development is calculated to be 93.6% (60°C) to 94.7% (80°C). []

[0125] Referring to Figure 4B, the primer particle composition further improves the initial dye conversion and yields a higher recent Dmax. Figure 4B shows that the Dmax of the control medium without hollow particles in the primer is approximately 2.2, while the media with primer layers according to Example 5-1 (NTR-50 only) and Example 5-4 (NTR-50:NTR-100 approximately 7:3) show a significantly increased recent Dmax (approximately 2.37 and 2.48, respectively). Without being constrained by any particular theory, it is believed that the approximately 10% increase in Dmax is due to the improved thermal insulation achieved by the hollow particles, which prevents heat loss from the reactive dye development zone. [] [Example] [7.] [The effect of primer composition on color density and color rendering] []

[0126] To test the effect of primer composition on color development and color density, microcapsule imaging layers containing magenta leuco dyes as shown in Table 1 were coated onto primer layers containing compositions of various concentrations of NTR-50, NTR-100, and TIPURE™ 6431 (as shown in Table 10). Microcapsule sheets were laminated together with developer sheets having compositions according to Table 4. The fixture temperature was maintained at 60°C for color development, and maximum color density was measured immediately after pressure development (Dmax, recent), 4 hours after development (Dmax, 4 hours), and 12 hours after development (Dmax, 12 hours). The results are shown in Table 10 and Figures 5A-5B. [surface] [10.] The effect of primer composition on Dmax [] Example 7 (2.8 ± 0.3 μm) Primer composition (parts, dry) Dmax, recently Dmax, 4 hours Dmax, 12 hours NTR-50 NTR-10 TIPURE™ 6431 M35 Comparison, no primer 0 0 0 0 1.6 1.95 2.12 Example 7-0 0 0 0 99.1 1.53 1.88 1.96 Example 7-1 0 0 30 69.1 1.68 2.02 2.15 Example 7-2 16 4 22.8 56.3 1.82 2.13 2.19

[0127] Figure 5A shows the optical image of a freshly developed film, corresponding to the Dmax, recent value, shown in Table 10 and Figure 5B. Meanwhile, Figure 5B shows the color development (optical density) immediately after development (Dmax (fresh)) and 4 hours and 12 hours after development (Dmax, 4 hours) and 12 hours after development (Dmax, 12 hours). As shown in Figures 5A-5B and Table 10, compared to microcapsule layers directly coated onto the substrate (MELINEX® 339) or coated onto a primer layer containing only M35 or M35+TiO2, a primer layer containing 22.8 wt.% TiO2, 16.0 wt.% NTR-50, and 4.0 wt.% NTR-100 yields higher Dmax (fresh), Dmax (4 hours), and Dmax (12 hours). Therefore, TiO2... The addition of hollow particles significantly improves both the recent and final Dmax values. Without being constrained by any specific theory, it is believed that the presence of 22-23 wt.% TiO2 (Example 7-1) in the primer layer results in: (1) higher reflectivity, allowing the viewer's eye to detect more colors; and / or (2) higher capsule rupture efficiency, due to increased media modulus or stress concentration at the microcapsule-primer interface. The addition of hollow particles NTR-50 and NTR-100 (Example 7-2) further significantly improves Dmax, especially the recently developed Dmax. Without being constrained by any specific theory, it is believed that even at clamp temperatures as low as 60°C, the presence of hollow particles significantly improves the thermal efficiency of the media, thereby increasing Dmax. [] [Example] [8.] [The effect of the black back coating on premature exposure of the second imaging element in media stacking] []

[0128] A primer coating comprising 30 (dry) parts of NW-WNQ11 TiO2 dispersion (54.73% solids), 11.05 (dry) parts of MK-WD42515 CaCO3 dispersion (33.16% solids), 37.80 (dry) parts of M35 latex, 20.0 (dry) parts of ROPAQUE™ ULTRA-E hollow particles (29.89% solids), 0.15 (dry) parts of TAMOL™ 165A, 0.75 (dry) parts of CELLOSIZE™ QP-52000H, 0.05 (dry) parts of SILWET® L-7604, and 0.1 (dry) parts of FOAMSTAR® ST2410 was applied to a first surface of MELINEX® 339 with a dry thickness of 2.4 ± 0.1 µm.

[0129] On the second surface of MELINEX® 339 (the side opposite the substrate with primer coating), a mixture comprising 30.0 (dry) parts of NW-WNQ11 TiO2 dispersion (54.73% solids), 3 (dry) parts of CAB-O-SPERSE® 1015A fumed silica dispersion (11.9% solids), 0-10 (dry) parts of NW-KAB85 carbon black dispersion (27% solids), 35.55-41.55 (dry) parts of PRIMAL™ AC-261T (51.24% solids), 20.0 (dry) parts of ROPAQUE™ ULTRA-E hollow particles (29.89% solids), 0.15 (dry) parts of TAMOL™ 165A, and 1.0 (dry) part of CELLOSIZE™ A back coating of QP-52000H, 0.05 (dry) parts of SILWET® L-7604, and 0.1 (dry) parts of FOAMSTAR® ST2410 is applied to the first surface of MELINEX® 339 with a dry thickness of 5.0 + 0.1 µm.

[0130] As described in Example 7, a microcapsule imaging layer was coated onto a primer layer, and the resulting microcapsule sheets were laminated together with a developer sheet to obtain an imaging media sheet. Next, two imaging sheets were stacked together with a developer sheet facing upwards. Then, starting from the top media sheet, the stack was exposed to a 14.3 mW / cm² green LED via a neutral density stepped light wedge for 1–30 seconds. The bottom media sheet was then developed using a pressure fixture, and the optical density at each step was recorded as shown in Figure 6 and Table 11. Referring to Figure 6 and Table 11, the control media without any back coating was prematurely exposed via the top media, with an E10 (the exposure energy required to cause a 10% loss of optical density in the bottom media) of approximately 0.3 mJ / cm² for a 1-second exposure time. In reality, the bottom media was completely overexposed for 30 seconds. With a back coating containing 30 wt.% TiO₂ (Example 8-1), the E10 of the bottom media increased slightly to approximately 0.4 mJ / cm², but it was still prone to premature exposure via the top media. With a back coating containing 30 wt.% TiO₂ and 4 wt.% black pigment (NW-KAB85), the E10 increased significantly to 154 mJ / cm² for a 30-second exposure time. With a back coating containing 30 wt.% TiO2 and 10 wt.% black pigment (NW-KAB85), E10 further increased significantly to >271 mJ / cm2 at an exposure time of 30 seconds. During the exposure of the top media sheet, when a back coating containing more than 4-7 wt.% back pigment and 30 wt.% TiO2 was applied to the second surface of the substrate, the bottom media sheet showed virtually no premature light exposure. As shown in Table 11, the Dmax of the media sheet containing the black back coating increased with increasing black pigment concentration. [, , ] [surface] [11.] The effect of the back coating composition on premature exposure of the second imaging film. Example 8 (5.1±0.1μm) Composition (wt%, dry) Dmax E 10(mJ / cm 2) * 1 second E 10(mJ / cm 2) * 30 seconds NW-WNQ11 NW-KAB85 AC261T Comparison (No back coating) - - - 1.82 Approximately 0.3 - Example 8-0 30.0 0.0 45.55 1.84 Approximately 0.4 - Example 8-1 30.0 4.0 41.55 1.88 N / A** 154 Example 8-2 30.0 7.0 38.55 1.90 N / A** > 271 Example 8-3 30.0 10.0 35.55 1.91 N / A** > 271 * Energy required to cause a 10% Dmax loss in the second media at 1 second and 30 seconds at 14.3 mW / cm² ** No signs of premature exposure or Dmax loss were observed in the second media film. [Example] [9.] [The effect of primer and back coating on the resolution of imaging film]

[0131] To test the effect of the primer and back coating on the resolution of the imaging film, the same primer and back coating as those shown in Example 8 were used, except that: in the back coating, 35.8 (dry) parts of M35 latex (instead of PRIMAL™ AC-261T) were used as the adhesive, and 20 (dry) parts of carbon black and 20 (dry) parts of TiO2 were used as the back coating. The same green-sensitive microcapsule layer used in Example 8 was applied to bare MELINEX® 339 (capsule 9-1), MELINEX® 339 with primer (capsule 9-2), and MELINEX® 339 with both primer and back coating (capsule 9-3). The obtained microcapsule tablets were laminated together with the same developer tablets from Example 8 using a Tamera TCC2700 roller laminator at 90°C, 3.621 Kgf / 170 mm and 0.368 m / min to form media tablets of Examples 9-1, 9-2 and 9-3 (corresponding to capsule tablets 9-1, 9-2 and 9-3, respectively).

[0132] A green photosensitive medium was exposed for 1.7–4.0 seconds using a collimated light unit (model ESPCOL60-W) at 0.8 mW / cm² via a PET black-and-white line mask with a linewidth varying from 20 µm to 1000 μm. The exposed medium was then developed as described in the previous examples, and the widths of the developed lines are shown in Tables 12A and 12B. [surface] [12A.] The effect of primer and back coat on the width of black lines The black linewidth (μm) of the photomask used. 20 30 40 50 60 80 100 250 500 1,000 The corresponding black line width of the developing medium at 0.8 mW / cm² for 1.7 seconds. Example 9-1 In comparison, only MELINEX® 339 X* X* 36.0 44.5 58.5 79.7 100.2 243.3 496.2 990.3 Example 9-2 Primer only X* X* X* 40 53 74 87 241 497 988 Example 9-3 Primer + Black back coating X* 28.0 34.1 49.2 59.7 80.2 97.5 246.2 495.8 1001.3 * Damaged or unidentifiable thread [surface] [12B.] The effect of primer and back coat on white line width White line width (μm) of the photomask used 20 30 40 50 60 80 100 250 500 1000 The corresponding white line width of the developing medium at 0.8 mW / cm² for 4.0 seconds. Example 9-1 In comparison, only MELINEX® 339 X* 21.1 32.3 46.1 64.4 83.5 117.3 270.1 529.2 1026.5 Example 9-2 Primer only 20.2 26.4 35.7 49.9 66.0 85.4 121.0 273.9 530.5 1026.5 Example 9-3 Primer + Black Back Coating X* 26.0 30.0 43.7 52.0 79.9 99.8 255.3 501.0 1009.1 * Damaged or unidentifiable thread

[0133] As is evident from Table 12A, while the presence of the primer layer shows significant improvements in many areas of media performance, as illustrated in Examples 1-7, it also makes printing fine black lines more difficult (Example 9-2). The addition of a black back coating (Example 9-3) helps to correct this drawback caused by the primer layer. In fact, compared to 36.0 μm for the control (Example 9-1) and 40 μm for the media sheet with only a primer coating (Example 9-2), the media sheet containing both primer and black back coating shows a significant improvement in the printability of fine black lines, down to 28 μm (Example 9-3).

[0134] Table 12B shows the effect of the primer and black backing coating on the printability of white fine lines. It can be clearly seen that although the sample with only the primer layer (Example 9-2) shows the narrowest white line printability, the addition of the black backing coating (Example 9-3) shows the best overall white line printing linewidth control, because it can best reproduce the linewidth of the photomask over a wider linewidth range.

[0135] The compositions and methods described herein can be suitably practiced without the presence of any one or more elements or limitations not specifically disclosed herein. Therefore, terms such as "comprising," "including," and "containing" should be interpreted broadly and non-limitingly. Furthermore, the terms and expressions used herein are descriptive rather than limiting, and their use is not intended to exclude any equivalents of the shown and described features or portions thereof. It should be recognized that various modifications are possible within the scope of this disclosure. Therefore, it should be understood that although this disclosure has been specifically disclosed by way of preferred embodiments and features as appropriate, those skilled in the art may employ modifications and variations embodied in this disclosure, and consider such modifications and variations to be within the scope of this disclosure.

[0136] Unless the context otherwise indicates, it is particularly intended that the various features of the invention described herein may be used in any combination. Furthermore, this disclosure also covers some embodiments in which any feature or combination of features set forth herein may be excluded or omitted. For illustration, if this specification states that a complex comprises components A, B, and C, it is particularly intended that any one of A, B, or C, or any combination thereof, may be omitted or discarded individually or in any combination.

[0137] This disclosure has been described extensively and generally herein. Smaller species and subgenus groups within the general scope of this disclosure also form part of the composition or method. This includes a general description of the composition or method, from which any limiting or negative limitations may be removed, regardless of whether the removed material is specifically described herein. The invention is not limited to the specific embodiments described in this application, which are intended to be representative of a particular category of the invention. Many modifications and variations can be made without departing from the spirit and scope of the invention, as will be apparent to those skilled in the art. In addition to the compositions, methods, and apparatuses listed herein, functionally equivalent compositions, methods, and apparatuses within the scope of the invention will be apparent from the foregoing description. Such modifications and variations are intended to fall within the scope of the invention. It should be understood that the invention is not limited to specific methods, reagents, compounds, or compositions; of course, variations are possible. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be restrictive.

[0138] Those skilled in the art will readily understand that this disclosure is highly suitable for carrying out the objectives and achieving the stated purposes and advantages, as well as the inherent purposes and advantages therein. Those skilled in the art will recognize the modifications and other uses therein. These modifications are covered within the spirit of this disclosure and defined by the scope of the claims, illustrating non-limiting embodiments of this disclosure.

[0139] Furthermore, in describing the features or scope of this disclosure in accordance with the Markush group, those skilled in the art will recognize that this disclosure is also described in accordance with any individual member or subgroup of the Markush group.

[0140] 100: Microcapsule Imaging Sheet 102:Substrate 104: Primer layer 105: Opaque back coating 106: Photosensitive microcapsule layer 108: Photosensitive microcapsules 110 a: Developing layer 110 b: Developer particle layer 112: Discrete developer particles 114: Developer substrate

Claims

1. A primer-coated substrate for use in microcapsule imaging sheets, the primer-coated substrate comprising a substrate and a primer layer on the substrate, the primer layer comprising: a polymeric adhesive; 1 to 25% by weight of hollow polymer particles relative to the total weight of the primer layer, wherein the hollow polymer particles comprise a mixture of first hollow polymer particles and second hollow polymer particles; and 3 to 60% by weight of white microparticles relative to the total weight of the primer layer.

2. The substrate with primer coating as claimed in claim 1, wherein the white particles are selected from the group consisting of: TiO2, BaSO4, CaSO4, CaCO3, Al2O3, Ca3(PO4)2 and combinations thereof.

3. The substrate with primer coating as claimed in claim 2, wherein the white particles comprise TiO2 and alkaline particles.

4. A substrate coated with a primer as described in any of claims 1 to 3, wherein the white particles have an average particle size of about 50 nm to about 2000 nm.

5. A substrate coated with a primer as described in any of claims 1 to 3, wherein the concentration of the white particles is about 10% by weight to about 50% by weight relative to the total weight of the primer layer.

6. A substrate with a primer coating as claimed in any of claims 1 to 3, wherein the polymer adhesive comprises a latex polymer having a glass transition temperature of about -70°C to about 40°C.

7. A substrate with a primer coating as claimed in any of claims 1 to 3, wherein the polymeric adhesive is selected from the group consisting of: acrylic polymers or copolymers, styrene copolymers, butadiene copolymers, vinyl chloride copolymers, vinylidene chloride copolymers, epoxy copolymers, ethylene copolymers, propylene copolymers, vinyl acetate copolymers, polyesters, polyurethanes, polylactones, polyamides, polyvinylpyrrolidone, and blends or copolymers thereof.

8. A substrate with a primer coating as described in any of claims 1 to 3, wherein: The hollow polymer particles comprise a polymer shell and an air core; and the polymer shell comprises a polymer selected from the group consisting of: polyacrylate, polymethacrylate, polystyrene, polyvinyl acetate, polyolefin, polyamide, polyester, polyurea, polyurethane, melamine-formaldehyde, phenolic resin and blends or copolymers thereof.

9. A substrate with a primer coating as described in any of claims 1 to 3, wherein: The first polymer hollow particles have an average particle size of about 200 nm to about 2000 nm; or the second polymer hollow particles have an average particle size of about 500 nm to about 2000 nm.

10. A substrate with a primer coating as claimed in any of claims 1 to 3, wherein the hollow polymer particles are present at a concentration of about 5% by weight to about 10% by weight relative to the total weight of the primer layer.

11. A microcapsule imaging sheet comprising: a first substrate; a primer layer in contact with a first surface of the first substrate, wherein the primer layer comprises: a polymeric adhesive; 1 to 25% by weight of hollow polymer particles relative to the total weight of the primer layer, wherein the hollow polymer particles comprise a mixture of first hollow polymer particles and second hollow polymer particles; and 3 to 60% by weight of white microparticles relative to the total weight of the primer layer; and a photosensitive microcapsule layer comprising photosensitive microcapsules in contact with the primer layer.

12. The microcapsule imaging sheet of claim 11, wherein the photosensitive microcapsules comprise: a polymer shell; and a core comprising a leuco dye, a photoinitiator, and polymerizable or crosslinkable monomers or oligomers.

13. The microcapsule imaging sheet of claim 11 or 12, wherein the white microparticles comprise TiO2 and alkaline microparticles.

14. The microcapsule imaging sheet of claim 11 or 12, further comprising a developer layer and a developer substrate, wherein the developer layer is in contact with: (i) the microcapsule layer on the primer layer; and (ii) the developer substrate.

15. A method of preparing an imaging film, the method comprising: (i) coating a first surface of a first substrate with a primer layer to produce a primer-coated first substrate, wherein the primer layer comprises: a polymer binder; 1 to 25% by weight of hollow polymer particles relative to the total weight of the primer layer, wherein the hollow polymer particles comprise a mixture of first hollow polymer particles and second hollow polymer particles; and 3 to 60% by weight of white microparticles relative to the total weight of the primer layer; (ii) contacting the primer layer of the primer-coated first substrate with a microcapsule layer; (iii) contacting the microcapsule layer with a developer layer; and (iv) contacting the developer layer with a second substrate or a layer comprising a polymer to produce the imaging film.

Images