Primers with improved reflective and thermal insulation properties for microcapsule imaging systems

Abstract

The present disclosure provides a primer layer (104) with improved reflectance and thermal insulation properties for microencapsulation of a thermographic sheet (100). A primer layer having from about 3% to about 60% by weight of a polymeric binder, white particulates, a primer substrate (102), and hollow particulate particles relative to the total weight of the primer layer improves reflectance, color development, color density, and thermal insulation of microcapsule (108) imaging sheets including the primer layer. A black backside coating (105) applied to the substrate on a side opposite the primer layer further enhances the Dmax and E10 of the microcapsule imaging sheet and prevents premature exposure of the microcapsule imaging sheet in the stacked media.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 17 / 833,735, filed on June 6, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to the field of microcapsule imaging systems, and more particularly to primers for use in such microcapsule imaging systems. Background Art

[0004] Since the 1980s, monolithic, self-contained, full-color microcapsule imaging systems (e.g., Cycolor) have been developed. In these imaging systems, an imaging sheet comprising a microcapsule layer containing a photohardenable or photosoftenable composition and a leuco dye in an internal phase is image-wise exposed to actinic radiation. Typically, the photosensitive composition comprises a photopolymerizable multifunctional acrylate, a photoinitiator, and a color former. Typically, the microcapsules are image-wise hardened by actinic radiation, and when the exposed imaging sheet passes through a pressure roller, the microcapsules can be image-wise ruptured to release the internal phase encapsulated therein. The leuco dye thus released migrates to the developer material and reacts to form a continuous-tone full-color image whose color density (or grayscale) 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 for lightweight, portable, high-speed printing applications. Summary of the invention

[0005] Typical microcapsule imaging systems have several disadvantages. For example, very high pressure is required to rupture the microcapsules, resulting in low dye release efficiency, poor color density (Dmax), and slow color development. Although these problems can be partially solved by using larger microcapsules, image resolution and ease of operation decrease dramatically as the size of the microcapsules increases.

[0006] Additionally, a white substrate is often used to improve the color density of the image area (and improve the whiteness of the non-imaged area). However, the reflectivity of most commercially available white substrates, especially thin (≤50 μm) substrates, is not satisfactory. Significant light loss (e.g., leakage) through the substrate results in undesirably low color density and saturation. For example, commercially available white PET (e.g., 339 (manufactured by Dupont Teijin Films LP (Chester, VA)), 50 μm) has a reflectivity (%) of only about 85%. That is, about 15% of the incident light or color will leak through the substrate and will not be reflected back to the viewer's eye. Relatedly, substrates with low reflectivity tend to have low hiding power. When an imaging sheeting with low hiding power is placed on top of a highly colored background, the image in the viewer's eye appears to be "contaminated" by the background color or pattern. An imaging sheeting with high reflectivity and hiding power is particularly beneficial to image quality when a black annihilation layer on the opposite side of the substrate (relative to the microcapsule imaging layer) is used to improve resolution and ensure that there is no light leakage, which would prematurely expose the second imaging sheeting immediately below in the media stack.

[0007] Further, to alleviate the slow color development discussed above, some technologies require a heating step after crushing the microcapsules under pressure to increase the color development rate. The heating step consumes a lot of energy (or battery power), which is exacerbated by the waste of heat dissipated through the substrate, especially when thick stickers and release liners are attached to the back of the image sheet.

[0008] In addition, in order to improve the adhesion of microcapsules to substrates, some technologies use a primer coating between the substrate and the microcapsule layer. However, the primer coating is usually soft or sticky and sticks to the facing roller of the coater or to the back of the substrate during the rewinding process. This results in poor coating quality and low yield. Release coatings or intermediate layers on the back of the substrate can be used to prevent these problems, but these solutions mean additional processing steps, materials and costs. In addition, the release coating on the back of the substrate may cause the label (if present) to debond from the image sheet.

[0009] In this context, there is great commercial interest in primer layers that solve some or all of the aforementioned problems. The primer layers according to the present disclosure provide significant improvements in Dmax, color development rate (fresh Dmax), Dmin stability, energy consumption, printing speed, hiding power, anti-blistering and anti-blocking, ease of handling, ease of processing, cost, and yield of the primer coating without compromising the quality of adhesion between the image sheet and the label.

[0010] In one aspect that may be combined with any other aspect or embodiment, the present disclosure relates to a primer layer for a microcapsule imaging sheet, the primer layer comprising: a polymer binder; one or more microparticles (e.g., white microparticles), the one or more microparticles accounting for about 3 wt % to about 60 wt % of the total weight of the primer layer; and a substrate. In some embodiments, the primer layer further comprises about 1 wt % to about 30 wt % of polymer hollow particles accounting for the total weight of the primer layer.

[0011] In some embodiments, the white particles have a refractive index of about 1.5 to about 3.0. In some embodiments, the particles are selected from the group consisting of TiO2, BaSO4, CaSO4, CaCO3, BN, Al2O3, Ca3(PO4)2. In some embodiments, the white particles are TiO2. In some embodiments, the white particles have an average particle size of about 50nm to about 2000nm. In some embodiments, the white particles have an average particle size of about 100nm to about 300nm. In some embodiments, the concentration of the white particles is about 10% by weight to about 50% by weight relative to the gross weight of the primer layer. In some embodiments, the white particles include TiO2 and alkaline particles. In some embodiments, the alkaline particles are selected from CaCO3, Al2O3 or Ca3(PO4)2.

[0012] In some embodiments, the polymer binder comprises a latex polymer having a glass transition temperature (Tg) of about -70°C to about 40°C. In some embodiments, the polymer binder comprises a latex polymer having a Tg of about -20°C to about 20°C. In some embodiments, the polymer binder 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, polyvinyl pyrrolidone, and blends or copolymers thereof.

[0013] In some embodiments, the polymer hollow particles include a polymer shell and an air core. In some embodiments, the polymer hollow particles include a polymer shell, which includes a polymer selected from the group consisting of polyacrylate, polymethacrylate, polystyrene, polyvinyl acetate, polyolefin, polyamide, polyester, polyurea, polyurethane, melamine formaldehyde, phenolic resin and their blends or copolymers. In some embodiments, the polymer shell of the hollow particles is cross-linked or filled with an inorganic filler (such as silica).

[0014] In some embodiments, the polymer hollow particles have an average particle size of about 200nm to about 2000nm or about 500nm to about 2000nm. In some embodiments, the polymer hollow particles have an average particle size of about 100nm to about 1000nm or about 300nm to about 1000nm. In some embodiments, the air core has an average diameter of about 50nm to about 1000nm. In some embodiments, the air core has an average diameter of about 100nm to about 400nm. In some embodiments, the polymer hollow particles have an average particle size of about 0.1g / cm 3 To about 0.7g / cm 3In some embodiments, the polymer hollow particles are present in a concentration of about 5 wt % to about 30 wt % relative to the total weight of the primer layer.

[0015] In some embodiments, the polymeric hollow particles include a blend of first polymeric hollow particles having a first average particle size and second polymeric hollow particles having a second average particle size.

[0016] 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.

[0017] In another aspect that may be combined with any other aspect or embodiment, the present disclosure is directed to a microcapsule imaging sheet, the microcapsule imaging sheet comprising: a primer layer according to any one of the above embodiments; and a photosensitive microcapsule layer, the photosensitive microcapsule layer being in contact with the primer layer. In some embodiments, the microcapsule imaging sheet comprises: a first substrate; a primer layer according to any one of the above embodiments, the primer layer being in contact with a first surface of the first substrate; and a photosensitive microcapsule layer, the photosensitive microcapsule layer comprising photosensitive microcapsules in contact with the first substrate, the primer layer, or both the primer layer and the first substrate.

[0018] In another aspect that may be combined with any other aspect or embodiment, the present disclosure relates to a microcapsule imaging sheet material, the microcapsule imaging sheet material comprising a primer layer on a first surface of a substrate and a back coating 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 comprises hollow particles and reflective particles substantially identical to those in the primer layer. 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 is blackened by a black dye or pigment (such as carbon black) to further improve resolution and eliminate the risk of light leaking through the imaging sheet material and causing premature exposure of the imaging sheet material below in the stack.

[0019] In some embodiments, the microcapsule imaging sheet is a full-color imaging sheet containing photosensitive microcapsules, and the photosensitive microcapsules include red-sensitive microcapsules, green-sensitive microcapsules, and blue-sensitive microcapsules.

[0020] In some embodiments, the photosensitive microcapsule comprises a polymer shell and a core, the core comprising a leuco dye, a photoinitiator, and a polymerizable or cross-linkable monomer or oligomer. In some embodiments, the leuco dye is one or more of a cyan dye, a magenta dye, a yellow dye, or a black leuco dye. In some embodiments, the photoinitiator is a red-sensitive, green-sensitive, or blue-sensitive photoinitiator or sensitizer, such as a cyanine borate or a hemicyanine borate. In some embodiments, the photoinitiator comprises, consists essentially of, or consists of a UV-sensitive or near-IR-sensitive photoinitiator or sensitizer (such as ketocoumarins, isopropylthioxanthone (ITX), and squarylium dyes.

[0021] In some embodiments, the microcapsule imaging sheet further comprises a developer layer in contact with: (i) the microcapsule layer and / or the primer layer and (ii) the developer substrate. In some embodiments, the microcapsules are blended with the developer composition and coated as a monolayer on the primer layer.

[0022] In certain embodiments, the back coating comprises a black pigment or dye and a polymer binder. In certain embodiments, the back coating comprises a black pigment or dye of 1 wt % to 30 wt % relative to the gross weight of the back coating. In certain embodiments, the back coating comprises a black pigment or dye of 3 wt % to 20 wt % relative to the gross weight of the back coating. In certain embodiments, the black pigment is carbon black.

[0023] 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.

[0024] In another aspect that may be combined with any other aspect or embodiment, the present disclosure is directed to a method of preparing an imaging sheeting, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any of the embodiments 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 sheeting.

[0025] In another aspect that may be combined with any other aspect or embodiment, the present disclosure is directed to a method of making an imaging sheeting, 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 the microcapsule layer of the microcapsule-coated first substrate to produce an imaging sheeting.

[0026] In some embodiments, the second primer layer is located between the second substrate and the developer layer.

[0027] In some embodiments, the method further comprises: (v) contacting the second surface of the first substrate with a back coating, wherein the second surface of the first substrate is opposite to the 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.

[0028] In another aspect that may be combined with any other aspect or embodiment, the present disclosure is directed to a method of imaging or printing, the method comprising: exposing an imaging sheeting to heat, pressure, or radiation, the imaging sheeting comprising a primer layer according to any embodiment disclosed herein and a microcapsule layer comprising microcapsules; wherein the microcapsules comprise a polymer shell and an inner phase comprising a leuco dye, exposed to heat, pressure, or radiation; and wherein the exposure is sufficient to release the leuco dye from the microcapsules in the microcapsule layer to produce an image.

[0029] Additional aspects and / or embodiments of the present invention will be provided in the detailed description of the present technology set forth below, but are not limited thereto. The following detailed description is exemplary and explanatory, but is not intended to be limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various objects, aspects, features and advantages of the present disclosure will become more apparent and better understood by referring to the detailed description taken in conjunction with the accompanying drawings.

[0031] Figure 1A is a schematic diagram of one embodiment of a microcapsule imaging sheeting having a primer coating between the microcapsule layer and the substrate according to the present disclosure. Figure 1B is a schematic diagram of another microcapsule imaging sheet having a primer coating between the microcapsule layer and the substrate according to the present disclosure. Figure 1C is a schematic diagram of a microcapsule imaging sheeting according to the present disclosure, with a primer coating between the microcapsule layer and the substrate, and a backside coating on the other side of the substrate.

[0032] Figure 2A is a schematic diagram of a fixture setup with a thermocouple for measuring the static temperature drop across a primer layer in accordance with the present disclosure.

[0033] Figure 2B A plot showing the temperature difference between the top of the primer layer and the bottom of the primer layer substrate as a function of heating time is shown.

[0034] Figure 3A , Figure 3B , Figure 3C , Figure 3D , Figure 3E and Figure 3F The actual temperature difference between the top of the primer layer and the bottom of the primer layer substrate for an imaged sheeting including a primer layer according to the present disclosure is shown as a function of heating time and as a function of primer layer composition.

[0035] Figure 4A A plot of color density (Dmax) versus fixture temperature is shown for a magenta microcapsule layer coated on a primer layer having about 10% NTR-50 hollow particles.

[0036] Figure 4B A plot of the color development (fresh Dmax) of a magenta microcapsule layer coated on a primer layer having different ratios of NTR-50 hollow particles (about 0.25 μm in diameter) and NTR-100 hollow particles (about 0.9 μm in thickness) versus the primer layer composition is shown.

[0037] Figure 5A The optical images of the imaged sheets immediately after development (Dmax(fresh)) are shown as a function of primer layer composition. Figure 5B Test results for color density (Dmax) and color development immediately after development (Dmax(fresh)), 4 hours after development (Dmax, 4 hours), and 12 hours after development (Dmax, 12 hours) as a function of primer layer composition are shown.

[0038] Figure 6 The optical density of microcapsule imaging sheets according to the present disclosure without backside coating (control) and with backside coatings containing different concentrations of carbon black (%K) is shown versus exposure energy (mJ / cm 2 )’s drawing. DETAILED DESCRIPTION

[0039] In the following description, many specific details are set forth in order to provide a thorough understanding of the present technology. Specific exemplary embodiments of the present technology can be implemented without some or all of these specific details. In other cases, some process operations have not been described in detail, but those skilled in the art will understand.

[0040] Photosensitive microcapsule layer

[0041] refer to Figure 1A and Figure 1B In some embodiments, the microcapsule imaging sheet 100 according to the present disclosure includes a photosensitive microcapsule layer 106. The photosensitive microcapsule 108 may include a polymer shell and a core within the polymer shell, the core containing a photosensitizer or photoinitiator, a photohardenable monomer or oligomer, and a dye precursor (e.g., a leuco dye), which imparts color to the microcapsule imaging sheet when released under pressure and subsequently exposed to heat, certain pH conditions, reactive chemicals (e.g., Lewis acids), or a developer. The shell can act as an oxygen barrier to ensure the high photosensitivity of the photosensitive core and avoid any premature intermixing of the photoinitiator and the dye precursors of various colors, thereby ensuring successful color separation and reproduction. In some embodiments, the photohardenable monomer can be replaced with a photosoftenable or photodegradable composition.

[0042] The developer may be present, for example, in a developer layer 110a in contact with a developer substrate 114, configured to be placed in contact with the microcapsule layer 106 alone, or as a developer particle layer 110b in discrete developer particles 112. In some embodiments, the developer may be mixed with the microcapsules and applied as a single layer (not shown). When released from the microcapsules 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). Useful developers include, but are not limited to, acidic clays, salicylic acid derivatives, phenolic resins, and novolac resins, particularly those grafted or copolymerized with salicylic acid derivatives, and their zinc complexes.

[0043] The photosensitive microcapsule layer can contain one or more types of microcapsules. For example, a positive full-color microcapsule imaging sheet can contain three types of microcapsules: red-sensitive microcapsules containing red-sensitive photoinitiators and cyan-leuco dyes, green-sensitive microcapsules containing green-sensitive photoinitiators and magenta-leuco dyes, and blue-sensitive microcapsules containing blue-sensitive photoinitiators and yellow-leuco dyes. For example, in a positive imaging sheet, when exposed to white light, all three types of microcapsules harden, and no color is formed after the color development step. When fully exposed to red light, the red-sensitive microcapsules harden, so the cyan-leuco dye will not be released in the development step. Therefore, red will be reproduced in the exposed area. On the contrary, when fully exposed to a combination of blue light and green light (cyan light), the corresponding magenta and yellow-leuco dyes will not be released, and cyan will be reproduced in the exposed area. Intermediate tone colors of various color densities can also be reproduced in areas exposed to various lights of various energies and / or intensities.

[0044] In some embodiments, the dye precursor is a cyan dye, a magenta dye, a yellow dye, or a black leuco dye. As a non-limiting example, representative leuco dyes may include, but are not limited to, RedI6B, Blue I-2G or Blue-63; Blue 220, Blue 203, Red 500, Red 40 or Black305 purchased from Yamada; JYDY-1, JYDR-2, JYDR-3, JYDB-1 or JYDB-2 purchased from WuXi Jiayida New Materials; Red-16, O-C6 or O-C8 purchased from Synmedia Chemicals; or ODB-2 purchased from Anyang General Chemicals.

[0045] In some embodiments, the photoinitiator is a blue-sensitive, green-sensitive or red-sensitive cyanine borate, a hemicyanine borate or a ketocoumarin. For full-color imaging systems, red, green and blue photoinitiators with narrow spectral sensitivity bandwidths of less than 100 nm are preferred. In some embodiments, the photoinitiator includes, consists essentially of or consists of a UV-sensitive or near-IR-sensitive photoinitiator or sensitizer (such as ketocoumarin, isopropylthioxanthone (ITX) and squarylium dyes). In some embodiments, UV initiators or infrared initiators are used for false color imaging systems. In some embodiments, the photosensitive microcapsule 108 may include a polymer shell and a core, the polymer shell may be softened by actinic radiation, and the core contains a dye precursor (e.g., a leuco dye). In this scenario, the core may also be light-softenable or degradable. In this case, a negative working image is obtained, in which the exposed area / capsule is colored after development with a developer. In some embodiments, the microcapsule further comprises a monomer or oligomer (e.g., a polymerizable or crosslinkable monomer or oligomer) selected from multifunctional acrylates and methacrylates, multifunctional vinyl ethers, multifunctional allyl or vinyl benzenes, and oligomers, dendrimers, or blends thereof. Multifunctional acrylates are particularly useful for their excellent photospeed, compatibility with leuco dyes and developers, and outdoor weatherability. Examples of multifunctional acrylates include, but are not limited to, pentaerythritol triacrylate (PETA-3), pentaerythritol tetraacrylate (PETA-4), dipentaerythritol hexaacrylate (DPHA), dipentaerythritol pentaacrylate (DPPA), trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), and neopentyl glycol diacrylate (NPGDA).

[0046] Base

[0047] A primer layer 104 according to the present disclosure is coated on a substrate 102. The substrate can be any suitable material having sufficient thickness, flexibility, reflectivity (e.g., hiding power), and durability for recording printed media (e.g., images). In some embodiments, the substrate is white or transparent. As a non-limiting example, 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 on the market (e.g., white PET films purchased from DuPont Teijin Films LP (Chester, VA)). 329, 339, 394, 331, 534 and transparent PET film and purchased from Mitsubishi ).

[0048] The substrate can have any suitable thickness. In certain 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 certain embodiments, the substrate can be surface treated by, for example, corona, plasma, or sublayers to improve the adhesion between the substrate and the primer or back coating. In certain embodiments, one side of the substrate can be pre-treated with an antistatic layer to reduce undesirable static charge accumulation during coating or printing. In certain embodiments, one side of the substrate can be pre-treated with a peeling layer such as a polysiloxane or wax layer to improve the media transmission during printing and / or improve the media anti-blocking during conversion and packaging.

[0049] Primer layer

[0050] In various specific implementations, the microcapsule imaging sheet according to the present disclosure includes a primer layer 104. The primer layer is disposed between the substrate and the microcapsule layer to improve performance characteristics, including adhesion, image resolution, capsule rupture efficiency or fresh Dmax (maximum optical density) that can be achieved immediately after pressure development, energy efficiency, and photosensitive speed. 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 polymer binder, white particles, and a substrate. In some embodiments, the primer layer may further include polymer hollow particles. In some embodiments, the primer layer may further include alkaline particles.

[0051] Polymer Binder

[0052] The primer layer according to the present disclosure comprises one or more polymer binders. The one or more polymer binders can be any suitable polymer material, present in any suitable concentration and having any suitable molecular weight, for imparting favorable adhesion, flexibility, anti-blocking and film quality (e.g., uniform thickness) to the primer layer.

[0053] In some embodiments, the one or more polymeric binders may include, consist essentially 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, polyvinyl pyrrolidone, and blends or copolymers thereof. In some embodiments, the one or more polymeric binders are latex polymers or blends thereof.

[0054] In some embodiments, the one or more polymer binders may have a weight average molecular weight of about 5,000 g / mol to about 10,000,000 g / mol. In some embodiments, the one or more polymer binders include, consist essentially of, or consist of a latex binder having 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, useful latexes may have a minimum film forming temperature (MFFT) or glass transition temperature (Tg) of less than 50°C, less than 30°C, or less than 20°C. In some embodiments, crosslinkable latexes may be used to improve the cohesive strength of the primer layer.

[0055] In some embodiments, the one or more polymer binders may have a weight average molecular weight of 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

[0056] In some embodiments, the one or more polymeric binders (alone or in combination) may be present in the primer layer at a concentration expressed in weight % relative to the weight of the total primer layer 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 %, even more preferably about 30 wt % to about 50 wt %.

[0057] In some embodiments, the one or more polymeric binders (alone or in combination) may be present in the primer layer at a concentration expressed as wt % relative to the weight of the total primer layer of 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., 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. In some embodiments, the one or more polymeric binders may have a glass transition temperature (Tg) of 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 a latex binder, the latex may have a minimum film forming temperature (MFFT) of less than 60° C. (e.g., less than 20° C.) to ensure acceptable film properties after coating.

[0058] particle

[0059] In some embodiments, the polymer binder layer according to the present disclosure includes one or more particles, such as white particles, such as white particles with high refractive index or reflectivity. The white particles can be any suitable composition, size and concentration for enhancing the reflectivity and / or hiding power of the primer layer.

[0060] In some embodiments, the one or more particles may include one or more of the following: TiO2, BaSO4, CaSO4, CaCO3, silica, 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, consist essentially of, or consist of TiO2.

[0061] In some embodiments, the one or more microparticles may have an average particle size of about 0.1 μm to about 5 μm, about 0.14 μm to about 2 μm, or about 0.2 μm to about 1 μm.

[0062] In some embodiments, the one or more microparticles may have an average particle size of 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.

[0063] In some embodiments, the one or more particles may comprise, consist essentially of, or consist of a single white particle composition (e.g., TiO2) or two or more white particle compositions (e.g., TiO2 and Al2O3).

[0064] In some embodiments, the one or more particles may further include one or more alkaline particles, including but not limited to Al2O3, CaCO3 or Ca3(PO4)2. In some embodiments, the one or more alkaline particles are included in the primer layer as a buffer to improve Dmin stability by neutralizing or absorbing any acidic chemicals that may diffuse or migrate from other layers (e.g., developer layer). In some embodiments, the one or more alkaline particles are selected from the group consisting of CaCO3, Al2O3, Ca3(PO4)2.

[0065] In some embodiments, the one or more microparticles may have only one average diameter (e.g., a unimodal size distribution). In some embodiments, the one or more microparticles may have a bimodal or trimodal size distribution (e.g., one white microparticle has an average diameter of about 0.1 μm to about 2 μm and one white microparticle has an average diameter of about 0.2 μm to about 0.5 μm, although other differences in average diameters may be achieved, such as the difference between any two of the example average diameters described above).

[0066] In some embodiments, one or more smaller filler particles (such as silica or CaCO3) can be used to further improve the packing density of the primer layer. The useful particle size range of the filler particles can be about 0.01 μm to about 1 μm, about 0.02 μm to about 0.5 μm, about 0.05 μm to about 0.2 μm.

[0067] In some embodiments, the one or more microparticles (alone or in combination) may be present in the primer layer at a concentration, expressed as weight %, of about 10 wt % to about 50 wt %, about 15 wt % to about 40 wt %, or about 20 wt % to about 35 wt %, relative to the weight of the total primer layer.

[0068] In some embodiments, the one or more microparticles (alone or in combination) may be present in the primer layer at a concentration expressed as wt % relative to the weight of the total primer layer. In some embodiments, the one or more microparticles have a refractive index 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 therebetween.

[0069] In some embodiments, the one or more particles have a refractive index of about 1.4 to about 3, about 2 to about 3, or any range or value therein. In some embodiments, low refractive index filler particles (such as silica and CaCO3) may be present in the primer layer at a concentration of about 0.1 wt% to about 15 wt%, preferably about 1 wt% to about 10 wt%, expressed in wt% relative to the weight of the total primer layer.

[0070] Polymer hollow particles

[0071] In some embodiments, the primer layer according to the present disclosure includes one or more polymer hollow particles. The polymer hollow particles can have any suitable composition, size (average diameter) or specific gravity, and can be present in any suitable concentration to improve the heat insulation of the primer layer relative to a conventional primer layer without any polymer hollow particles, while providing acceptable reflectivity (e.g., hiding power), anti-blocking, adhesion, anti-blistering and film quality.

[0072] In some embodiments, the one or more polymer hollow particles may include, consist essentially of, or consist of a polymer shell and a core. In some embodiments, the core is an air core or a precursor thereof, such as a highly water-swelling gel, from which the air core is formed when water is removed during or after coating.

[0073] In certain embodiments, the one or more polymer hollow particles include a polymer shell, which includes a polymer selected from the group consisting of polyacrylate, polymethacrylate, polystyrene, polyester, melamine formaldehyde condensate, polyolefin, polyurea, polyurethane and blends or copolymers thereof. In certain embodiments, the polymer shell is crosslinked. In certain embodiments, the polymer shell may include an inorganic network, such as silica formed by, for example, a sol-gel process. Exemplary polymer hollow particles can be prepared according to the disclosures found in the following documents: 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.

[0074] In some embodiments, the one or more polymer hollow particles may have an average diameter or D 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. 50 In some embodiments, the air core of the polymer hollow particle has a diameter of about 0.1 μm to about 1.0 μm, or about 0.15 μm to about 1 μm. Preferably, the hollow particle or its core has a narrow particle size distribution. A series of polymer hollow particles can be easily purchased from, for example, Dow Chemicals and Taiwan Hopax Chemicals.

[0075] In some embodiments, the one or more polymer hollow particles may have an average diameter or D of about 0.1 μm or more, about 0.2 μm or more, about 0.3 μm or more, about 0.4 μm or more, about 0.5 μm or more, about 0.6 μm or more, about 0.7 μm or more, about 0.8 μm or more, about 0.9 μm or more, about 1 μm or more, about 1.5 μm or more, about 2 μm or more, about 2.5 μm or more, about 3 μm or more, about 3.5 μm or more, about 4 μm or more, about 4.5 μm or more, about 5 μm or more, about 10 μm or more, or any range or value therebetween. 50 .

[0076] In some embodiments, the one or more polymer hollow particles may have an average diameter D of 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. 50 .

[0077] In some embodiments, the one or more polymer hollow particles may comprise a single polymer hollow particle composition (eg, NTR-50 (D 50 = about 0.16 μm)) or two or more polymer hollow particle compositions (e.g., HopaxNTR-50 (D 50 =0.16μm)、Hopax NTR-100(D 50 = about 0.82 μm), Dow ROPAQUE TM ULTRA-E(D 50 = about 0.35 μm) and Dow ROPAQUE TM TH-1000(D 50 = about 1.0 μm), etc.), or essentially consisting of or consisting of.

[0078] In some embodiments, the 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 %, and more preferably about 10 wt % to about 25 wt %, expressed as wt % relative to the weight of the total primer layer.

[0079] Back coating

[0080] refer to Figure 1CIn some embodiments, an opaque back coating 105 is applied to the second surface of the substrate 102, wherein the first surface is coated with a primer layer 104. Such embodiments can improve image resolution, fresh Dmax and energy efficiency, and eliminate the risk of light leakage through the top imaging sheet, which can lead to premature exposure of the image sheet below in the media stack. In some embodiments, the opaque back coating comprises substantially the same ingredients as in the primer layer (e.g., white particles, filler particles or hollow polymer particles) relative to the gross weight of the back coating, having any of the same compositions or sizes disclosed above, or existing in any concentration in the concentrations disclosed above. For example, in some embodiments, the back coating comprises hollow polymer particles. In some embodiments, the back coating further comprises one or more particles (e.g., particles selected from the group consisting of TiO2, silica, BaSO4, CaSO4, BN, CaCO3, Al2O3, AlN and Ca3(PO4)2). In some embodiments, the back coating comprises a binder (e.g., a polymer binder).

[0081] In some embodiments, the back coating further comprises an annihilation dye or pigment for the initial light. 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), purchased from Taiwan Nanotechnology Corp.).

[0082] The back coating can have any thickness suitable to ensure easy handling of the dielectric sheet and acceptable annihilation of the initial light. In some embodiments, the back coating has a thickness of about 2 μm to about 30 μm, about 3 μm to about 20 μm, or about 5 μm to about 15 μm.

[0083] In some embodiments, the back coating may have a thickness of 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 therein.

[0084] In some embodiments, the back coating may have a thickness of 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 therein.

[0085] In some embodiments, the backside 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 therein, relative to the total weight of the backside coating.

[0086] In some embodiments, the backside 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 therein, relative to the total weight of the backside coating.

[0087] In some embodiments, the backside coating comprises a black pigment or dye in 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 therein, relative to the total weight of the backside coating.

[0088] 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 include a polymer binder. In some embodiments, the back coating may not include a black pigment or dye. In some embodiments, the back coating may include a metal, metal nitride, metal oxide, metal carbide or metal boride film (e.g., Al, Cr, Ag, Ni, Au, Cu, Ti and combinations thereof, etc.) that is vapor coated or sputtered onto the second surface of the substrate (e.g., the first substrate).

[0089] While the foregoing terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

[0090] The term "a" or "an" may refer to one or more of the entity, i.e., may refer to multiple referents. Thus, the terms "a" or "an", "one or more" and "at least one" are used interchangeably herein. In addition, reference to "an element" with the indefinite article "a" or "an" does not exclude the possibility that more than one element is present, unless the context clearly requires the presence of one and only one element.

[0091] References throughout this specification to "one embodiment," "an embodiment," "one aspect," or "aspect" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present disclosure. Thus, the phrases "in one embodiment" or "in an embodiment" appearing in various places in this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0092] As used herein, the term "about" or "approximately" when preceding a numerical value means a range of plus or minus 10% of the value.

[0093] As will be understood by those skilled in the art, for any and all purposes, particularly with respect to providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily considered to fully describe and enable the same range to be decomposed into at least equal halves, thirds, quarters, fifths, tenths, etc. As non-limiting examples, each range discussed herein can be easily decomposed into lower thirds, middle thirds, and upper thirds, etc. It will also be understood by those skilled in the art that all language, such as "up to," "at least," "greater than," "less than," etc., includes the cited numbers and refers to the range that can subsequently be decomposed into subranges as described above. Finally, as will be understood by those skilled in the art, a range includes each individual member.

[0094] Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as those commonly understood by those of ordinary skill in the art to which the present invention belongs. It should be further understood that terms such as those defined in common dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the present application and related fields, and unless explicitly defined as such herein, should not be interpreted in an idealized or overly formal sense. Although not explicitly defined below, such terms should be interpreted according to their usual meanings.

[0095] For the purposes of this disclosure, the term "color density" or "color optical density" refers to the ability of a medium to reflect light, wherein the greater the light reflectance of a dye in certain colors, the higher the color optical density (i.e., the more intense the color). The lower the light reflectance of a dye, the lower the color density (i.e., the lighter the color).

[0096] For the purposes of this disclosure, the term "maximum color density" (or "Dmax") refers to the maximum color density achieved by a dye after a given development time, as measured by a reflectance spectrodensitometer FD-5 available from Konica Minolta. For example, Dmax ,新鲜 Or fresh Dmax refers to the maximum color density of the developed image sheet as measured immediately after development, while Dmax,t refers to the maximum color density as measured after conditioning the developed image sheet for a period of time (t).

[0097] 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 transition from colorless to colored form can be reversible or irreversible, and can be induced by Lewis acids or bases, or changes in temperature, pH, radiation, or redox state. Useful developers include, but are not limited to, phenol, phenolic resins, salicylic acid, oxalic acid, phthalic acid, organic phosphonic acids, organic sulfonic acids, and zincated derivatives thereof. Zincated salicylate derivatives and novolac resins are particularly useful because of their high color formation and the color fastness of the dyes formed therefrom.

[0098] Method for preparing imaging sheeting

[0099] In another aspect that may be combined with any other aspect or embodiment, the present disclosure is directed to a method of preparing an imaging sheeting, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any of the embodiments 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 sheeting.

[0100] In some embodiments, the present disclosure is directed to a method of preparing an imaging sheeting, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any of the embodiments 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 the microcapsule layer of the microcapsule-coated first substrate to produce an imaging sheeting.

[0101] In some embodiments, a second primer layer may be located between the second substrate and the developer layer.

[0102] In any of the above embodiments, the method of producing an image sheet may further include: (v) contacting the second surface of the first substrate with a back coating, wherein the second surface of the first substrate is opposite to the 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.

[0103] Methods of using primer layers and imaging sheets including the same

[0104] In another aspect that may be combined with any other aspect or embodiment, the present disclosure relates to a method of using the primer layer according to any of the above embodiments. In another aspect that may be combined with any other aspect or embodiment, the present disclosure relates to a method of using the imaging sheeting according to any of the above embodiments.

[0105] For example, in some embodiments, a method of imaging or printing includes exposing an imaging sheeting including 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 to produce an image.

[0106] In some embodiments, the present disclosure is directed to a method of improving one or more properties of an imaging sheeting, the method comprising including (adding to) an imaging sheeting according to any embodiment disclosed herein a primer layer. In some embodiments, the one or more properties include one or more of the following: Dmax; fresh Dmax; Dmax,t; Dmin; image resolution; hiding power, anti-blocking; adhesion; reflected optical density; and thermal insulation performance.

[0107] Unless expressly stated otherwise, all specified embodiments, features, and terms are intended to include the described embodiments, features, or terms and their equivalents.

[0108] Reference will now be made in detail to various specific embodiments contemplated by the present disclosure. Although various embodiments are described herein, it should be understood that it is not intended to limit the present technology to the described embodiments. On the contrary, the present invention is intended to cover alternatives, modifications and equivalents as may be included in the spirit and scope of the technology defined by the appended claims.

[0109] Examples

[0110] Materials and Methods

[0111] Table 1. Materials used in exemplary embodiments

[0112]

[0113]

[0114] Table 2. Internal phase of photosensitive microcapsules

[0115]

[0116] Preparation of photosensitive microcapsules

[0117] Photosensitive microcapsules were prepared using the materials listed in Table 2 and the following method:

[0118] 1. Add 220 parts of water and 8 parts of Versa TL502 sulfonated polystyrene (dry) to a 1000 ml stainless steel beaker and mix thoroughly.

[0119] 2. Slowly sift 10 parts of pectin (methyl polygalacturonate) into the mixture and stir overnight at room temperature (500 to 1000 rpm).

[0120] 3. Adjust pH to 7.5 with 10% sodium carbonate and increase mixing speed to 1750 rpm.

[0121] 4. The internal phase shown in Table 2 was added over a period of 15 to 30 seconds, the resulting mixture was stirred for 30 minutes, and 11 parts of a 9.1% aqueous solution of DETA (diethylenetriamine) (pH adjusted to 7.0) was added and reacted at 25°C for 30 minutes and then at 40°C for one hour.

[0122] 5. Add 19.9 parts 385 and 40 g of water (pH adjusted to 6.0), and the mixture was reacted at 70°C for a further 2 hours.

[0123] 6. Add 15.23 parts of 34.3% sodium sulfate aqueous solution, stir for 10 minutes, then add 1.97 parts 385 and 10 parts of water, and the mixture was reacted at 70°C for another hour.

[0124] 7. The mixing speed was reduced to 600 rpm, the pH was adjusted to 9.5 using 20% ​​NaOH solution, and the resulting reaction mixture was stirred at room temperature overnight.

[0125] The thus prepared microcapsules were washed thoroughly with water and centrifuged to remove excess water-soluble polymer and additives in the aqueous phase. The particle size (D 50 ) is about 6μm.

[0126] Preparation of control microcapsule sheets - PET ( 339) without primer or back coating

[0127] Table 3. Composition of microcapsule fluid

[0128]

[0129] The coating fluids shown in Table 3 were adjusted to 33 wt% solids by adding water and dispersed thoroughly using a low shear mixer and then coated onto a 2 mil white PET substrate ( 339) and dried in an oven at 80°C for 10 minutes. The dry coating thickness was about 8 μm as measured by a Mitutoyo thickness gauge.

[0130] Preparation of developer coating

[0131] To prepare the developer coating, the composition shown in Table 4 was coated onto 1 mil clear PET film using a Myrad rod and dried in an 80°C oven for 10 minutes with a target dry coating thickness of about 13 μm.

[0132] Table 4. Composition of developer coating

[0133]

[0134] Preparation of Control Image Sheeting - Image Sheeting without Primer or Backside Coating

[0135] The microcapsule film and developer film prepared above were laminated together using a Tamerica roll laminator TCC2700 with the temperature, pressure and speed settings being 100°C, 3.621 Kgf / 170 mm and 0.368 m / min, respectively, to form various photosensitive imaging sheets, as described in the following examples.

[0136] Example 1. Effect of primer coating on blocking resistance, reflectivity, hiding power, adhesion and blistering

[0137] To test the relative impact of hollow particles present in the primer layer, the primer formulation contained 30 wt % TiO2 particles (TIPURE TM 6431, available from DuPont), 5 wt% PVA 205, 0 wt% to 10 wt% hollow particle NTR-50 (D 50 = 0.25 μm, purchased from Hopax Chemicals) and 55 to 60 wt % of M35 latex as a buffer. The primer formulation was applied to the 339 substrate. As a comparison, a (dry) silica containing 5 wt % was also prepared. A primer layer of 1015. The thickness of each coating is between 6.3 μm and 6.7 μm.

[0138] For the blocking test, each sample was heated at 40°C and 85% relative humidity at 10 kg / 100 cm 2 Pressed 339 substrate for 24 hours and record the percentage of the test area with observable signs of damage.

[0139] To test the hiding power, a primer layer with various concentrations of hollow particles NTR-50 was applied to 339, and measure the optical density on a black surface. The lower the reflected optical density, the higher the hiding power, so that the color of the black background is covered with an optical density of about 2.0.

[0140] As shown in Table 5, all samples coated with the primer coating showed a significant increase in hiding power or a decrease in reflected optical density (black OD of 0.0 to 0.02, or reflectivity of 95.5% to 100%) compared to the control without any primer coating. It is also obvious that all samples coated with the primer coating containing 5 wt% to 10 wt% of NTR-50 showed a significant improvement in blocking resistance or a decrease in the area percentage of observable damage marks after the blocking test compared to the samples containing only silica particles (an additive commonly used to improve the blocking resistance of the coating).

[0141] Table 5 .Hiddenness and anti-adhesion concentration of hollow particles (Example 1)

[0142]

[0143] All coatings also exhibited excellent water resistance (blister test) and adhesion to PET 339 (tape test).

[0144] Example 2. Reduced thickness primer layer

[0145] A primer layer was prepared identical to that described in Example 1, except that the coating thickness was reduced to 2.9±0.3 μm. In order to obtain an image with high color density, the leuco dye released from the microcapsules must diffuse as much as possible into the developer layer to convert the leuco dye from the leuco form to the color form. A thin, impermeable primer layer is highly preferred because it reduces the risk of undesired dye diffusion or absorption into the primer layer, which is located on the opposite side of the microcapsule layer in an imaging sheet having the following structure: PET / primer layer / microcapsule layer / developer layer / PET. A thin primer layer composition was prepared comprising 0.4 wt % to 1.1 wt % hydroxypropyl methylcellulose (HPMC) (DuPont METHOCEL TM K15M) as a thickener to improve the coating quality, and various concentrations of M35 latex as a buffer (to make the composition up to 100% by weight). A thin primer layer composition is then applied to the 339 on. The samples were subjected to the above-mentioned adhesion, hiding and blocking tests (see Example 1).

[0146] As shown in Table 6, all films prepared from the primer formulations containing HPMC exhibited excellent coating quality, adhesion, anti-blistering, and hiding power (reflected black optical density ≤ 0.01 or reflectance ≥ 97.7%, as measured against a black background with an optical density > 2.0), even after the thickness of the primer layer was reduced to 2.9 ± 0.3 μm. All four primer layers in Example 2 also showed significant improvement in blocking resistance, with the percentage of area with observable damage marks after blocking testing significantly reduced from < 30% (see Examples 1-2) to < 10%.

[0147] Table 6. Hiding power of primer layer containing thickener (Example 2)

[0148]

[0149] Example 3. Primer layers with different particle concentrations (30 wt % to 37 wt %)

[0150] Prepare the same primer layer as described in Example 2, except that TiO2 (TIPURE TM 6431) concentration was increased from 30 wt% to 37 wt%, and the M35 latex concentration was varied with buffer (to bring the composition to 100 wt%). The coating thickness on 339 was 2.5 μm to 3.2 μm. The samples were subjected to the same hiding power, blocking resistance, adhesion and blistering resistance tests as above (see Examples 1 and 2).

[0151] As shown in Table 7, all the primer layers prepared in this way showed excellent hiding power (reflection black optical density ≤ 0.01 or reflectivity ≥ 97.7%, compared with the non-hiding PET 339 has a reflective black optical density of 0.07 or a reflectance of 85.1%), indicating that higher concentrations of TiO2 particles are able to produce highly reflective primer layers as thin as 2.5μm. This higher reflectivity means higher photospeed because the reflected light acts as an additional light source to expose the microcapsules. The color intensity of the developed image is also improved because more light of the appropriate color will be reflected back to the viewer's eye during image evaluation.

[0152] Table 7. Various TIPURE TM Hiding power and anti-blocking properties of primer layer with a concentration of 6431 (Example 3)

[0153]

[0154]

[0155] Referring to Table 7, the anti-blocking tests show that each primer layer exhibited good blocking resistance, with very light marks showing in areas less than 5% loading. Primer layers with a TiO2 content of ≥ 32.5 wt% had a slightly less tendency to stick to the edge of the PET 339 substrate in the absence of a release liner or coating, with only slight blurring of the film at the edge of the loaded weight. All primer layers exhibited acceptable adhesion (i.e., passed the adhesion test) regardless of TiO2 concentration. All primer layers also exhibited good resistance to blistering in the presence of two different test liquids: deionized water and a 0.01 wt% AEROSOL OT TM (Dioctyl sodium sulfosuccinate) and TRITON TM X-114 nonionic detergent (Sigma-Aldrich Inc., Saint Louis, MO).

[0156] Example 4. Effect of Hollow Particle Concentration and Size

[0157] To test the effect of hollow particle size and concentration on film performance, five primer layers with different hollow particles (different sizes and concentrations) were prepared as described in Example 3, except that the types and concentrations of hollow particles shown in Table 8 were used. Their hiding power, as shown by the reflected optical density measured relative to a black substrate (OD = 2.0, black), is also shown in Table 8.

[0158] Table 8. Hiding power and anti-blocking properties of primers with various hollow particle sizes and concentrations (Example 4)

[0159]

[0160] As shown in Table 8, Compared with the 339 substrate, the hollow particles NTR-50 and NTR-100 (D 50 =0.9 μm) showed excellent hiding power, as evidenced by the low reflected optical density (or high reflectivity, 97.7%), regardless of hollow particle size or concentration. In addition, all primer layers showed acceptable blocking resistance. Primer layers containing 10 wt % or 14.3 wt % NTR-100 showed slightly better blocking resistance than similar primer layers containing NTR-50 particles.

[0161] All films passed the dry adhesion test, indicating that the primer layer Adhesion to the 339 substrate was acceptable regardless of hollow particle size or concentration. However, at the same concentration, the primer layer containing NTR-50 hollow particles exhibited slightly better film quality by visual inspection compared to a similar primer layer containing NTR-100 hollow particles.

[0162] Example 5. Effect of mixed hollow particle size on primer quality and performance

[0163] Anti-blocking, hiding, adhesion and anti-blistering

[0164] In order to test the effect of hollow particles with bimodal size distribution on the hiding power, anti-blocking, adhesion and anti-blistering of the primer layer, the primer layer formulations were prepared according to Table 9, wherein each primer layer contained NTR-50 (D 50 =0.25μm) and NTR-100 (D 50 =0.9 μm), the combined concentration was 10.0 wt%, but the ratio of NTR-50:NTR-100 was different. All primer coatings of Example 5 contained 0.8 wt% HPMC-K15M and were prepared according to the same procedure as described in Example 4. 339 was coated with a target dry thickness of about 2.8 μm.

[0165] As shown in Table 9, all primer coatings of Example 5 exhibited good adhesion to the PET substrate, and the samples with hollow particles exhibited improved anti-blocking and hiding power compared to the samples without any hollow particles (see Example 5-0). Although all primer coatings exhibited acceptable coating quality, a coating with a higher concentration and larger size particles (NTR-100) exhibited slightly poor coating uniformity.

[0166] Table 9. Primer formulation with bimodal hollow particle size distribution

[0167]

[0168] It was also observed that all primer formulations exhibited good blister resistance as measured by exposure to deionized water and 0.5 wt. % AEROSOL OT TM and TRITON TM The primer formulations containing blends of hollow particles of different sizes (e.g., Example 5-3 and Example 5-4, NTR-50 / NTR-100=8 / 2 to 7 / 3) appear to exhibit ideal coating quality and anti-blocking properties, while exhibiting excellent reflectivity, film quality, and anti-blistering properties, as judged by the size of the water spots observed after the aqueous solution of X-114.

[0169] Thermal insulation performance

[0170] In order to test the heat insulation of the primer layer containing hollow particles, the primer formulations of Example 5-0 (no hollow particles), Example 5-1 (10 wt % NTR-50) and Example 5-5 (5 wt % NTR-50 and 5 wt % NTR-100) were used. Figure 2A The apparatus shown, in which heat probes are placed at the top and bottom of the imaged sheeting, measures the temperature difference between the top and bottom of the imaged sheeting including the primer layer as a function of heating time at a preset fixture temperature of 70°C.

[0171] refer to Figure 2B The temperature difference between the top and bottom of the primer layer increased significantly with the addition of hollow particles and further increased with the addition of the hollow particle blend. For the primer layer containing hollow particles, the temperature difference reached a maximum value of about 17°C after about 20 seconds, while for the primer layer without hollow particles and without masking, the temperature difference reached a maximum value of about 17°C after about 20 seconds. 339 substrate, the temperature difference was about 3.5°C after 26 seconds and 5.4°C after 29 seconds. Figure 2B As shown, the presence of hollow particles greatly increases both the rate of temperature rise and the equilibrium temperature on the top surface of the primer layer (or the bottom of the image layer if the image layer is coated on top of the primer).

[0172] The actual temperature difference between the top and bottom probes for each sample is displayed on FIG. 3A to FIG. 3F The slight periodic deviation in the temperature at the top probe is due to the relay-controlled heater cycling (which turns the heater off at 70°C). Figure 2B The results shown are consistent, the equilibrium temperature difference between the top probe and the bottom probe is the best for the primer layer with NTR-50 / NTR-100 hollow particle blend (Example 5-5, 8.3°C, Figure 3F ) is the largest, followed by the primer layer with only NTR-50 hollow particles (Example 5-1, 6.7°C, Figure 3E ), which is much higher than that without hollow particles (Example 5-0, 2.5°C, Figure 3D ) or without primer layer (2.7℃, Figure 3C )’s temperature difference. Figure 3A and Figure 3B Overlaid are temperature versus time plots for all top probe readings and all bottom probe readings, respectively.

[0173] Therefore, the presence of hollow particles in the primer layer effectively minimizes the loss of heat energy from the primer layer (e.g., leakage into the substrate). Further, the primer layer having a blend of different hollow particle sizes appears to provide better insulation and heating efficiency than the primer layer having a single hollow particle size.

[0174] Example 6.Effects of fixture temperature and hollow particle composition on color development

[0175] In order to test the effect of processing parameters (e.g., fixture temperature) and hollow particle composition (e.g., ratio of NTR-50 to NTR-100) on color development, a magenta capsule layer (8 μm thick; D) was coated with a primer layer (2 μm to 3 μm, after 1 corona treatment) according to Example 5-1 and Example 5-4. 50 15 phm in 5 μm to 6 μm microcapsules The microcapsule imaging sheet was prepared by using a primer layer (NTR-50:NTR-100) with a ratio of 10 / 0 and 7 / 3 respectively. The primer layer of Example 5-0 without any hollow particles was used to prepare a control experiment (Example 6-0). The obtained microcapsule imaging sheet was laminated with a developer sheet (15 μm developer RD9870 / 15% Novolac 586 on 1 mil clear PET) under low pressure at room temperature. The prepared media was developed using a developing fixture at various preset temperatures (60°C, 70°C and 80°C).

[0176] Reference now Figure 4A , the fresh Dmax of the media with Primer 5-1 (10% NTR-50 in the primer) increased from about 2.25 to about 2.35 as the jig temperature increased (60°C to 80°C). After cooling to room temperature, Dmax continued to increase for about 1 hour and reached a final Dmax value of 2.35 (60°C) to about 2.43 (80°C). Assuming that the Dmax after 1 hour of jig development represents the maximum conversion of the leuco dye, the dye conversion immediately after jig development was calculated to be 93.6% (60°C) to 94.7% (80°C).

[0177] refer to Figure 4B , the primer particle composition can further improve the initial dye conversion rate and provide a higher fresh Dmax. Figure 4B It is shown that the Dmax for the control medium with a primer without hollow particles is about 2.2, while the medium with the primer layer according to Example 5-1 (NTR-50 only) and Example 5-4 (NTR-50:NTR-100 is about 7:3) shows a significant improvement in fresh Dmax (about 2.37 and 2.48, respectively). Without being bound by any particular theory, the approximately 10% increase in Dmax is believed to be due to the improvement in thermal insulation achieved by the hollow particles, thereby preventing the loss of thermal energy in the active dye development area.

[0178] Example 7. Effect of primer composition on color density and color development

[0179] To test the effect of primer layer composition on color development and color density, a microcapsule imaging layer containing magenta leuco dye as shown in Table 1 was coated on a substrate containing various concentrations of NTR-50, NTR-100 and TIPURE TM 6431, as shown in Table 10. The microcapsule sheet was laminated together with a developer sheet having a composition according to Table 4. The jig temperature was maintained at 60°C for color development, and the maximum color density was measured immediately after pressure development (Dmax, fresh), 4 hours after development (Dmax, 4 hours), and 12 hours after development (Dmax, 12 hours). The results are shown in Table 10 and FIG. 5A to FIG. 5B middle.

[0180] Table 10. Effect of primer composition on Dmax

[0181]

[0182] Figure 5A Optical images of freshly developed imaged sheets are shown, corresponding to Tables 10 and Figure 5B Dmax, fresh value, is shown. Figure 5B The color development (optical density) immediately after development (Dmax(fresh)), 4 hours (Dmax, 4 hours) and 12 hours (Dmax, 12 hours) are shown. FIG. 5A to FIG. 5B As shown in Table 10, the primer layer containing 22.8 wt % TiO2, 16.0 wt % NTR-50 and 4.0 wt % NTR-100 was significantly lower than that directly applied to the substrate ( 339) or on a primer layer containing only M35 or M35+TiO2 has higher Dmax (fresh), Dmax (4 hours) and Dmax (12 hours). Therefore, the addition of TiO2 and hollow particles significantly improves the fresh Dmax and final Dmax values. Without being bound by any particular theory, it is believed that the presence of 22 wt % to 23 wt % TiO2 in the primer layer (Example 7-1) provides: (1) higher reflectivity, thereby allowing the observer's eye to detect more colors; and / or (2) higher capsule rupture efficiency due to an increase in the modulus of the medium 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 freshly developed Dmax. Without being bound by any particular theory, it is believed that the presence of hollow particles significantly improves the thermal efficiency of the medium, and in turn improves Dmax, even at fixture temperatures as low as 60°C.

[0183] Example 8. Effect of Black Backside Coating on Premature Exposure of Second Imaged Sheet in Media Stack

[0184] In the dry thickness of 2.4μm+0.1μm A primer coating was applied to the first surface of 339, the primer coating consisting of 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 TM ULTRA-E hollow particles (29.89% solids), 0.15 (dry) parts of TAMOL TM 165A, 0.75 (dry) parts of CELLOSIZE TM QP-52000H, 0.05 (dry) L-7604 and 0.1 (dry) parts ST2410 composition.

[0185] exist On the second surface of 339 (the other side of the primer-coated substrate), a layer of 5.0 μm + 0.1 μm in dry thickness was formed. A backside coating is applied to the first surface of 339, the backside coating comprising 30.0 (dry) parts of NW-WNQ11 TiO2 dispersion (54.73% solids), 3 (dry) parts of 1015A fumed silica dispersion (11.9% solids), 0 to 10 (dry) parts of NW-KAB85 carbon black dispersion (27% solids), 35.55 to 41.55 (dry) parts of PRIMAL TM AC-261T (51.24% solids), 20.0 (dry) parts of ROPAQUE TM ULTRA-E hollow particles (29.89% solids), 0.15 (dry) parts of TAMOL TM 165A, 1.0 (dry) part of CELLOSIZE TM QP-52000H, 0.05 (dry) L-7604 and 0.1 (dry) parts ST2410.

[0186] The microcapsule imaging layer was coated onto the primer layer, and the resulting microcapsule sheet was laminated with a developer sheet as described in Example 7 to obtain an imaging media sheet. The two imaging sheets were then stacked together with the developer sheet facing up and then exposed to light with a neutral density step wedge at 14.3 mW / cm 2The stack is exposed to light from the top dielectric sheet for 1 second to 30 seconds using a green LED. The bottom dielectric sheet is then developed using a pressure fixture and the optical density at each step is recorded, as Figure 6 As shown in Table 11.

[0187] refer to Figure 6 As shown in Table 11, the control media sheet without any backside coating was prematurely exposed through the top media sheet, E 10 The exposure energy required to lose 10% of the optical density of the bottom dielectric sheet is about 0.3 mJ / cm 2 The exposure time was 1 second. In fact, the bottom dielectric sheet was actually completely overexposed, with an exposure time of 30 seconds. Using a back coating containing 30 wt. % TiO2 (Example 8-1), the E of the bottom dielectric sheet 10 Slightly increased to about 0.4 mJ / cm 2 , but is still susceptible to premature exposure through the top dielectric sheet. Using a backside coating containing 30 wt% TiO2 and 4 wt% black pigment (NW-KAB85), E 10 Significantly increased to 154mJ / cm 2 , the exposure time is 30 seconds. Using a back coating containing 30 wt% TiO2 and 10 wt% black pigment (NW-KAB85), E 10 Further increased significantly to >271mJ / cm 2 , with an exposure time of 30 seconds. When a backside coating comprising more than 4 wt % to 7 wt % backside pigment and 30 wt % TiO2 is applied on the second surface of the substrate, the bottom dielectric sheet is substantially free of any premature light exposure during the exposure of the top dielectric sheet. As shown in Table 11, the Dmax of the dielectric sheet comprising a black backside coating increases with increasing black pigment concentration.

[0188] Table 11. Effect of Backside Coating Composition on Premature Exposure of Second Imaged Sheeting

[0189]

[0190] Example 9. Effect of Primer and Backside Coating on Resolution of Imaged Sheets

[0191] To test the effect of primer and backside coating on the resolution of imaged sheets, the same primer and backside coatings as described in Example 8 were used, except that 35.8 (dry) parts of M35 latex (instead of PRIMAL TM AC-261T) was used as a binder, and 20 (dry) parts of carbon black and 20 (dry) parts of TiO2 were used as a back coating. The same green sensitive microcapsule layer as used in Example 8 was coated on an uncovered 339 (capsule sheet 9-1), with primer 339 (capsule sheet 9-2) and having both a primer and a back coating The obtained microcapsule sheet was laminated with the same developer sheet of Example 8 using a Tamerica roll laminator TCC2700 at 90°C, 3.621Kgf / 170mm and 0.368m / min to form the media sheets of Examples 9-1, 9-2 and 9-3 (corresponding to capsule sheets 9-1, 9-2 and 9-3, respectively).

[0192] Use a collimated light unit (ESPCOL60-W) at 0.8 mW / cm 2 The green photosensitive dielectric sheet was exposed for 1.7 seconds to 4.0 seconds through a black and white line PET photomask with line widths varying from 20 μm to 1000 μm. The exposed dielectric sheet was developed as in the previous example, and the widths of the developed lines are shown in Tables 12A and 12B.

[0193] Table 12A. Effect of primer and back coating on black line width

[0194]

[0195] Table 12B Effect of primer and back coating on white line width

[0196]

[0197] As is apparent from Table 12A, while the presence of the primer layer exhibits significant improvements in many aspects of media performance, as shown in Examples 1 to 7, it makes printing of thin black lines more difficult (Example 9-2). Adding a black backside coating (Example 9-3) helps correct the shortcomings caused by the primer layer. In fact, the thin black line printing performance of the media sheet containing both the primer and the black backside coating is significantly improved down to 28 μm (Example 9-3) compared to 36.0 μm and 40 μm of the control (Example 9-1) and the media sheet with only the primer coating (Example 9-2).

[0198] The effects of primer and black back coating on white fine line printing performance are shown in Table 12B. It can be clearly seen that while the sample with only a primer layer (Example 9-2) exhibits the narrowest white line printability, the addition of a black back coating (Example 9-3) exhibits the best overall white line printing line width control because it can best reproduce the line width of the photomask over a wider line width range.

[0199] The compositions and methods illustratively described herein may be appropriately practiced in the absence of any one or more elements, one or more limitations not specifically disclosed herein. Thus, for example, the terms "comprise", "include", "contain", etc. should be understood expansively and without limitation. In addition, the terms and expressions employed herein have been used as terms of description rather than limitation, and when such terms and expressions are used, it is not intended to exclude any equivalents of the features shown and described or parts thereof. It should be recognized that various modifications are possible within the scope of the disclosure claimed. Therefore, it should be understood that although the present disclosure has been specifically disclosed by preferred embodiments and optional features, modifications and variations of the present disclosure implemented therein disclosed herein may be adopted by those skilled in the art, and such modifications and variations are considered to be within the scope of the present disclosure.

[0200] Unless the context indicates otherwise, it is expressly intended that the various features of the invention described herein may be used in any combination. In addition, the present disclosure also contemplates that, in some embodiments, any feature or combination of features set forth herein may be excluded or omitted. For example, if the specification states that a composite comprises components A, B, and C, it is expressly intended that any one or combination of A, B, or C may be omitted and abandoned, either alone or in any combination.

[0201] The present disclosure has been described broadly and generally herein. Each of the narrower species and sub-species groups falling within the general disclosure also forms part of the composition or method. This includes a general description of the composition or method, with a proviso or negative limitation that removes any subject matter from the genus, regardless of whether the excised material is specifically described herein. The technology of the present invention is not limited to the specific embodiments described in this application, which are intended to be representative illustrations of a single aspect of the technology of the present invention. Without departing from the spirit and scope of the technology of the present invention, many modifications and changes can be made to the technology of the present invention, which will be obvious to those skilled in the art. According to the above description, in addition to those compositions, methods and devices listed herein, functionally equivalent compositions, methods and devices within the scope of the technology of the present invention will be obvious to those skilled in the art. Such modifications and changes are intended to fall within the scope of the technology of the present invention. It should be understood that the technology of the present invention is not limited to specific methods, reagents, compounds or compositions, which can of course vary. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not intended to be restrictive.

[0202] It will be readily appreciated by those skilled in the art that the present disclosure is well suited to achieving the stated objectives and obtaining the stated purposes and advantages, as well as those inherent therein. Modifications and other uses thereof will occur to those skilled in the art. Such modifications are encompassed within the spirit of the present disclosure and are limited by the scope of the claims, which set forth non-limiting embodiments of the present disclosure.

[0203] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Claims

1. A primer layer for a microcapsule imaging sheet, the primer layer comprising: polymer binder; White particles, the white particles accounting for about 3 wt % to about 60 wt % of the total weight of the primer layer; and Base. 2 . The primer layer according to claim 1 , further comprising polymer hollow particles accounting for about 1 wt % to about 30 wt % of the total weight of the primer layer.

3. The primer layer according to claim 1 or claim 2, wherein the white particles have a refractive index of about 1.5 to about 3.

0.

4. The primer layer according to any one of claims 1 to 3, wherein the white particles are selected from the group consisting of TiO2, BaSO4, CaSO4, CaCO3, Al2O3 and Ca3(PO4)2.

5. The primer layer according to any one of claims 1 to 4, wherein the white particles are TiO2.

6. The primer layer according to any one of claims 1 to 5, wherein the white particles comprise TiO2 and basic particles.

7. The primer layer according to claim 6, wherein the basic particles are CaCO3, Al2O3 or Ca3(PO4)2. 8 . The primer layer according to claim 1 , wherein the white particles have an average particle size of about 50 nm to about 2000 nm. 9 . The primer layer according to claim 1 , wherein the white particles have an average particle size of about 100 nm to about 300 nm. 10 . The primer layer according to claim 1 , wherein a concentration of the white particles is about 10 wt % to about 50 wt % relative to the total weight of the primer layer.

11. The primer layer of any one of claims 1 to 10, wherein the polymer binder comprises a latex polymer having a glass transition temperature of about -70°C to about 40°C.

12. The primer layer of any one of claims 1 to 11, wherein the polymer binder comprises a latex polymer having a glass transition temperature of about -20°C to about 20°C.

13. The primer layer according to any one of claims 1 to 12, wherein the polymer binder 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, polyvinyl pyrrolidone, and blends or copolymers thereof. The primer layer according to claim 2 , wherein the polymer hollow particles comprise a polymer shell and an air core.

15. The primer layer according to claim 2, wherein the polymer hollow particles include a polymer shell comprising 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. 16 . The primer layer according to claim 2 , wherein the polymer hollow particles have an average particle diameter of about 200 nm to about 2000 nm.

17. The primer layer of claim 14, wherein the air core has a diameter of about 50 nm to about 1000 nm.

18. The primer layer of claim 14, wherein the air core has a diameter of about 100 nm to about 400 nm.

19. The primer layer according to claim 2, wherein the polymer hollow particles have a particle size of about 0.1 g / cm 3 To about 0.7g / cm 3 Dry specific gravity. 20 . The primer layer according to claim 2 , wherein the polymer hollow particles are present in a concentration of about 5 wt % to about 30 wt % relative to the total weight of the primer layer. 21 . The primer layer according to claim 14 , wherein the polymer hollow particles comprise a blend of first polymer hollow particles having a first average particle size and second polymer hollow particles having a second average particle size.

22. The primer layer according to any one of claims 1 to 21, wherein the primer layer has a thickness of about 1 μm to about 10 μm.

23. The primer layer according to any one of claims 1 to 22, wherein the primer layer has a thickness of about 2 μm to about 5 μm.

24. A microcapsule imaging sheet, comprising: first base; The primer layer according to any one of claims 1 to 23, the primer layer being in contact with the first surface of the first substrate; and A photosensitive microcapsule layer comprises photosensitive microcapsules in contact with the primer layer.

25. The microcapsule imaging sheet according to claim 24, wherein the microcapsule imaging sheet is a full-color imaging sheet comprising photosensitive microcapsules, and the photosensitive microcapsules include red-sensitive microcapsules, green-sensitive microcapsules and blue-sensitive microcapsules.

26. The microcapsule imaging sheet according to claim 24 or claim 25, wherein the photosensitive microcapsules comprise: Polymer housing; and A core comprising a leuco dye, a photoinitiator and a polymerizable or cross-linkable monomer or oligomer.

27. The microcapsule imaging sheet according to claim 26, wherein the leuco dye is one or more of a cyan leuco dye, a magenta leuco dye, a yellow leuco dye or a black leuco dye.

28. The microcapsule imaging sheet according to claim 26 or claim 27, wherein the photoinitiator is a red-sensitive cyanine borate or a hemicyanine borate, a green-sensitive cyanine borate or a hemicyanine borate, or a blue-sensitive cyanine borate or a hemicyanine borate.

29. The microcapsule imaging sheet according to any one of claims 24 to 28, further comprising a developer layer in contact with: (i) the microcapsule layer and / or the primer layer; and (ii) a developer base.

30. The microcapsule imaging sheet according to any one of claims 24 to 29, further comprising a back coating layer on the second surface of the first substrate, wherein the first surface of the first substrate is coated with the primer layer.

31. The microcapsule imaging sheet of claim 30, wherein the backside coating comprises a black pigment or dye and a polymer binder.

32. The microcapsule imaging sheet according to claim 30 or claim 31, wherein the back coating comprises 1 wt% to 30 wt% of a black pigment or dye relative to the total weight of the back coating.

33. The microcapsule imaging sheet according to claim 32, wherein the back coating comprises 3 wt% to 20 wt% of the black pigment or dye relative to the total weight of the back coating.

34. The microcapsule imaging sheet according to any one of claims 31 to 33, wherein the black pigment is carbon black.

35. The microcapsule imaging sheet according to any one of claims 31 to 34, wherein the backside coating further comprises hollow polymer particles.

36. The microcapsule imaging sheet according to any one of claims 30 to 35, wherein the back coating further comprises microparticles selected from the group consisting of TiO2, silica, BaSO4, CaSO4, BN, CaCO3, Al2O3, AlN and Ca3(PO4)2.

37. A method of preparing an imaged sheeting, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any one of claims 1 to 23 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; as well as (iv) contacting the developer layer of the developer-coated first substrate with a second substrate to produce an imaged sheet.

38. A method of preparing an imaged sheeting, the method comprising: (i) coating a first surface of a first substrate with a primer layer according to any one of claims 1 to 23 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 second substrate with the developer layer to produce a developer-coated second substrate; as well as (iv) contacting the developer layer of the developer-coated second substrate with the microcapsule layer of the microcapsule-coated first substrate to produce an imaged sheet.

39. A method according to claim 37 or claim 38, wherein a second primer layer is located between the second substrate and the developer layer.

40. The method according to any one of claims 37 to 39, further comprising: (v) contacting a second surface of the first substrate with a backside coating, wherein the second surface of the first substrate is opposite to the first surface of the first substrate.

41. The method of claim 40, wherein the contacting in (v) is performed by physical vapor deposition, sputtering, chemical vapor deposition, lamination, or spin coating.

42. A method of imaging or printing, the method comprising: exposing an imaged sheet comprising a primer layer according to any one of claims 1 to 23 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, are exposed to heat, pressure or radiation, and wherein the exposing is sufficient to release the leuco dye from the microcapsules in the microcapsule layer to produce an image.

43. A method of improving one or more properties of an imaged sheeting, the method comprising: adding a primer layer according to any one of claims 1 to 23 to the imaged sheet, The one or more characteristics include one or more of the following: Dmax; fresh Dmax; Dmax, t; Dmin; image resolution; hiding power, anti-blocking; adhesion; reflected optical density; and thermal insulation performance.

Images