WO2020117256A1

WO2020117256A1 - Imaging kits

Info

Publication number: WO2020117256A1
Application number: PCT/US2018/064360
Authority: WO
Inventors: Jayprakash C. Bhatt; Michael W. Cumbie; Juan Carlos Vives
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2018-12-06
Filing date: 2018-12-06
Publication date: 2020-06-11

Abstract

The present disclosure is drawn to imaging kits, imaging systems, and methods of forming images. In one example, an imaging kit includes an imaging medium and a film-promoting fluid. The imaging medium includes a substrate, a color layer on the substrate, and an opaque concealing layer over the color layer. The color layer includes a pattern of color regions, wherein individual color regions include multiple adjacently-applied colors. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The film-promoting fluid includes a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles after contact therewith.

Description

IMAGING KITS

BACKGROUND

[0001] There are several reasons that inkjet printing has become a popular way of recording images on various media surfaces. Some of these reasons include low printer noise, variable content recording, capability of high speed recording, and multi-color recording. Additionally, these features can be obtained at a relatively low price to consumers. Consumer demand can create pressure to develop inkjet printing systems and inks that can print on a wide variety of media quickly and with good image quality. Various types of specialty media have been developed for use with inkjet printing to provide better performance or features in certain printing applications.

BRIEF DESCRIPTION OF THE DRAWING

[0002] FIG. 1 is a cross-sectional view illustrating an example imaging kit in accordance with examples of the present disclosure;

[0003] FIG. 2 is a top down view of an example color layer of an imaging medium in accordance with examples of the present disclosure;

[0004] FIG. 3 is a top down view of another example color layer of an imaging medium in accordance with examples of the present disclosure;

[0005] FIG. 4 is a top down view of yet another example color layer of an imaging medium in accordance with examples of the present disclosure;

[0006] FIG. 5 is a top down view of another example color layer of an imaging medium in accordance with examples of the present disclosure;

[0007] FIG. 6 is a top down view of still another example color layer of an imaging medium in accordance with examples of the present disclosure; [0008] FIGs. 7A-7C show a cross-sectional view of an example imaging medium being printed with a film-promoting fluid in accordance with examples of the present disclosure;

[0009] FIG. 8 is a schematic view of an example imaging system in accordance with examples of the present disclosure; and

[0010] FIG. 9 is a flowchart illustration an example method of forming an image in accordance with examples of the present disclosure.

DETAILED DESCRIPTION

[001 1] The present disclosure describes imaging kits, imaging systems, and methods of forming images. In one example, an imaging kit includes an imaging medium and a film-promoting fluid. The imaging medium includes a substrate, a color layer on the substrate, and an opaque concealing layer over the color layer. The color layer includes a pattern of color regions, where individual color regions include multiple adjacently-applied colors. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The film-promoting fluid includes a

film-promoting additive that reduces the glass transition temperature of the transparent polymer particles after contact therewith. In some examples, the transparent polymer particles can include an acrylic latex, a methacrylic latex, a styrene acrylic latex, a styrene methacrylic latex, or a combination thereof. In additional examples, the pattern can be a repeating pattern of color regions, wherein the color regions include: three or more adjacent stripes of different colors; four or more spots including a two by two grid configuration of different colors; or nine or more spots including a three by three grid configuration of different colors. In further examples, the multiple adjacently-applied colors can include cyan, magenta, and yellow. In still further examples, the multiple adjacently-applied colors can be individually applied at a width from 15 pm to 100 pm. In other examples, the imaging medium can include a machine-readable colorless registration mark on the concealing layer. In still other examples, the film-promoting additive can be a diol, a glycol, or a combination thereof. In certain examples, the film-promoting additive can be 1 ,2-hexanediol, 1 ,6-hexanediol, tetramethyl-5-decyne-4,7-diol, ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,2,4-trimethyl-1 ,3-pentanediol monoisobutyrate, or a combination thereof. In additional examples, the multiple adjacently-applied colors may not include black, and the imaging kit can further include a black ink.

[0012] The present disclosure also extends to imaging systems. In one example, an imaging system includes an imaging medium and an inkjet printhead in fluid communication with a film-promoting fluid positioned to jet the

film-promoting fluid onto the imaging medium. The imaging medium includes a substrate, a color layer on the substrate, and an opaque concealing layer over the color layer. The color layer includes a pattern of color regions, wherein individual color regions include multiple adjacently-applied colors. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The inkjet printhead jets the film-promoting fluid onto the imaging medium to contact the opaque concealing layer. The film-promoting fluid includes a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles of the opaque concealing layer. In further examples, the imaging system can also include a heater positioned to heat the imaging medium after the film-promoting fluid has been jetted onto the imaging medium to a temperature that causes transparent polymer particles contacted with the film-promoting additive to coalesce, wherein transparent polymer particles not contacted by the film-promoting additive do not coalesce. In still further examples, the imaging system can include a second inkjet printhead in fluid communication with a reservoir of black ink positioned to jet the black ink onto the imaging medium.

[0013] The present disclosure also extends to methods of forming images. In one example, a method of forming an image includes jetting a film-promoting fluid onto an imaging medium. The imaging medium includes a substrate, a color layer on the substrate, and an opaque concealing layer over the color layer. The color layer includes a pattern of color regions, where individual color regions include multiple adjacently-applied colors. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The film promoting fluid includes a film-promoting additive that reduces the glass transition temperature of transparent polymer particles after contact therewith. The method also includes selectively reducing the glass transition temperature of the transparent polymer particles in a first area of the opaque concealing layer where the film-promoting fluid is jetted, which contributes to or causes the first area of the opaque concealing layer to form a film and becoming transparent or translucent while a second area is more opaque outside the first area. In further examples, the method can include heating the imaging medium to a temperature above the glass transition temperature of the transparent polymer particles in the first area, but below the glass transition temperature in the second area to contribute to the first area forming the film and becoming transparent or translucent while the second area is more opaque outside the first area. In still further examples, the method can include jetting a black ink onto the imaging medium, where the multiple adjacently-applied colors do not include black as one of the colors.

[0014] In some examples, the imaging media, systems, and methods described herein can be used to record full-color images using a single inkjet ink. This can be useful in certain printing applications where printing with a single ink can be simpler, easier, or cheaper than printing multiple colored inks. In certain examples, a film-promoting fluid can be printed on the imaging media described herein to reduce the glass transition temperature of transparent polymer particles in the opaque concealing layer on the imaging media. This reduction in glass temperature can cause the transparent polymer particles to coalesce and form a film, either at the printing temperature or with moderate heating. The surrounding parts of the opaque concealing layer that were not printed with the film-promoting fluid can remain opaque as before, while the film formed in the area where the film-promoting fluid was printed can be more transparent. The transparent area can selectively reveal colors in the color layer beneath the opaque concealing layer. By selectively revealing certain colors in locations across the surface of the imaging medium, a full-color image can be formed. Printing the film-promoting fluid from a single printhead can be useful in label printing, packaging workflows, and other applications where using a single printhead is more efficient than using multiple printheads.

[0015] Generally, the opaque concealing layer can hide the color layer beneath because of light scattering effects of the transparent polymer particles in the opaque concealing layer. The opaque concealing layer can include transparent particles having a relatively high refractive index. In some examples, spaces between the transparent polymer particles can be occupied by air, which has a lower refractive index. The difference in refractive index between the particles and the air can create a strong scattering effect on light passing through the layer. Most light can be scattered and reflected back off the opaque concealing layer, which can cause the layer to appear opaque and white.

However, when the transparent polymer particles are heated to a temperature sufficient to make the particles coalesce and form a film, the film can appear much more transparent or translucent because the film does not have as many polymer/air interfaces to scatter light.

[0016] In order to selectively make the opaque concealing layer more transparent in specific locations to reveal specific colors of the color layer below, the film-promoting fluid can be applied to the opaque concealing layer in the specific locations. The film-promoting fluid includes a film-promoting additive that lowers the glass transition temperature of the transparent polymer particles. In certain examples, the film-promoting additive can be a diol or glycol, although other additives may also be effective to reduce the glass transition temperature of the transparent polymer particles. After the transparent polymer particles in a particular area of the opaque concealing layer have been contacted with the film-promoting additive, the particles can coalesce to form a film. In some cases, the temperature of the imaging medium during printing can be sufficient to cause the transparent polymer particles to coalesce. In other cases, the entire imaging medium can be heated to a temperature that is above the glass transition of the particles that were contacted with the film-promoting additive, but below the glass transition temperature of the particles that were not contacted with the film-promoting additive. In this way, a film can be selectively formed in the areas where the film-promoting fluid is printed. [0017] In some examples, the film-promoting fluid can be printed using an inkjet printhead, which can print at high resolutions such as 1/300^th inch, 1/600^th inch, or 1 /1200^th inch, for example. In certain examples, the colored layer can include multiple colors printed in a pattern such as stripes or a grid with the individual colors having a width corresponding to the print resolution. Thus, high resolution full-color images can be formed by selectively printing film-promoting fluid on the media to reveal particular colors beneath the opaque concealing layer.

[0018] To further illustrate the imaging kits described herein, FIG. 1 shows a cross sectional schematic view of an example imaging kit 100 in accordance with examples of the present disclosure. The imaging kit includes an imaging medium 102 and a film-promoting fluid 104. The imaging medium includes a substrate 1 10, a color layer 120 on the substrate, and an opaque concealing layer 130 over the color layer. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The color layer in this example includes a pattern of color regions, where the color regions include three different colors 122, 124, 126 applied adjacent one to another. The film-promoting fluid in this example is jetted from a printhead 140.

[0019] In some examples, the imaging kit can include the imaging medium and the film-promoting fluid packaged together as a material set for use with an imaging system. For example, the film-promoting fluid can be packaged in an ink cartridge or reservoir and the imaging medium can be in the form of sheets or a media roll. In other examples, the imaging medium and the film-promoting fluid can be incorporated into an imaging system. For example, the film-promoting fluid can be loaded in a printhead of an inkjet printer and the imaging medium can be loaded in the printer so that the film-promoting fluid can be printed onto the imaging medium.

[0020] The substrate of the imaging medium can include any type of print media substrate, such as base paper, coated paper, polymer films, self-adhesive labels, cardboard, and so on. In certain examples, the substrate can include cellulose fibers and/or non-cellulose fibers, such as synthetic fibers. In some cases, the substrate can also include a polymeric binder. The polymeric binder can be included, for example, when either cellulose or synthetic fibers are used. The cellulose fibers can be made from hardwood or softwood species. The synthetic fibers can be made from polymerization of organic monomers. The substrate can be formed with a pilot paper machine with a pulp, or the like. The substrate can also include other additives, such as a pigment dispersant, a thickener, a flow modifier, a defoamer, an antifoamer, a releasing agent, a foaming agent, a penetrant, a coloring dye, a coloring pigment, an optical brightener, an ultraviolet absorber, an antioxidant, a preservative, a fungicide, an insolubilizer, a wet paper strengthening agent, a dry paper strengthening agent, a sizing agent, or a combination thereof.

[0021] Although the thickness of the substrate is not particularly limited, in some examples the substrate can have a thickness of from about 50 pm to about 300 pm, and for example, from about 80 pm to about 250 pm. The form factor of the substrate can be any desired form factor, such as a sheet in a standard (e.g., A4 size, 8.5 inch by 1 1 inch size, etc.) or nonstandard size, a roll, a printable label, a printable packaging article, and so on.

[0022] In further examples, the color layer can be applied on the substrate by a printing process. The color layer can include multiple colors printed adjacently in a pattern. The colors can be formed by printing colored inks using any desired printing method. For example, the colors can be printed using a digital printing method such as inkjet printing, electrophotographic printing, and so on. In other examples, the colors can be printed using an analog printed method such as gravure printing, flexographic printing, lithographic printing, and so on.

[0023] The colored inks used to form the color layer can vary in composition depending on the type of printing used to form the color layer.

Generally, the colored inks can include a colorant and a binder. In some examples, the colorant can be a pigment, a dye, or a combination thereof. The colorant can include a cyan colorant, a magenta colorant, a yellow colorant, a black colorant, or other colorants. In further examples, the binder can include a polymer such as polyvinyl alcohol, a latex, polyurethane, or others. Other ingredients in the colored inks can include a liquid vehicle, a surfactant, additives to inhibit the growth of microorganisms, viscosity modifiers, materials for pH adjustment, sequestering agents, anti-kogation agents, preservatives, and the like. In some examples, the liquid vehicle can be an aqueous liquid vehicle that includes water and optionally a co-solvent.

[0024] The color layer includes a pattern of color regions, wherein individual color regions include multiple adjacently-applied colors. FIG. 2 shows a top-down view of an example color layer 200 in accordance with examples of the present disclosure. In this example, the color layer includes a pattern of color regions 210. One of the color regions is marked inside a dashed box in the figure. The color region includes three color stripes 220, 230, 240. These three stripes are repeated across the entire color layer to form a repeating pattern. It should be noted that the color layer shown in FIG. 2 is not drawn to scale, and in practice a color layer in accordance with the present disclosure can have a much greater number of color strips than are shown in the figure. In some examples, the color stripes can have a small width corresponding to the printing resolution of an inkjet printer used to print film-promoting fluid onto the media. In certain examples, the color stripes can have a width of 1 /150^th inch, 1/300^th inch, 1/600^th inch, or 1/1200^th inch, for example. In further examples, the color stripes can have a width from 15 pm to 100 pm. Thus, a large of number of such color stripes can be printed in the pattern shown in FIG. 2, repeated across an entire imaging medium. In this example, the three colors used can be cyan, magenta, and yellow. In other examples, other colors can be used. In a particular example, a similar pattern of stripes can be formed with four different colors repeated, and the four colors can include cyan, magenta, yellow, and black.

[0025] FIG. 3 shows a different example color layer 300. This example includes color regions 310 that include four colored spots 320, 330, 340, 350 in a two by two grid configuration. In this example, two of the colored spots 320, 350 are the same color. In a certain example, the two colored spots that are the same color can be yellow, while the other two colored spots can be cyan and magenta. The two by two grid pattern is repeated across the entire imaging medium.

[0026] FIG. 4 shows a similar example color layer 400 with color regions 410 that have a two by two grid pattern. In this example, the four colored spots 420, 430, 440, 450 include four different colors. In a particular example, the four colors can include cyan, magenta, yellow, and black. Including black with the other colors can allow the printed images on the imaging medium to have a wider range of values while printing with a single film-promoting fluid.

[0027] FIG. 5 shows yet another example color layer 500. This color layer includes color regions 510 that include nine colored spots in a three by three grid configuration. The colored spots include three different colors 520, 530, 540 in a pattern. In this example, the three colors can include cyan, magenta, and yellow.

[0028] FIG. 6 shows another example color layer 600. This color layer also includes color regions 610 with a three by three grid configuration. However, in this example the colored spots are in the form of ovals instead of squares. The colored spots include three colors 620, 630, 640, which can be cyan, magenta, and yellow.

[0029] The example color layers shown in the figures are merely a few specific examples of the color patterns that can be used in the color layer. A variety of other patterns can be used in addition to the stripe and grid patterns shown in the figures.

[0030] In various examples, the color layer can include multiple colors printed adjacently. As used herein,“adjacently” refers to two colors printed next to one another. This can include printed colors in areas that contact one another along an edge, or areas that overlap somewhat, or areas that are separated by a gap. In certain examples, two adjacent colors can overlap by up to 10% of the width of the colored areas. Thus, two stripes of different colors printed adjacently can overlap by up to 10% of the width of an individual stripe. In further examples, two adjacent colors can have a gap with a gap width up to 25% of the widths of the colored areas. Thus, two stripes printed adjacently can be separated by a gap of up to 25% the width of an individual stripe. An imaging medium made with a white substrate can thus have a relatively small amount of white space between the adjacent colored areas.

[0031] In certain examples, the multiple adjacently-applied colors in the color layer can include cyan, magenta, and yellow. In further examples, the colors can include cyan, magenta, yellow, and black. The width of the applied colors, whether in the form of strips, spots, or other shapes, can be from 15 pm to 100 pm. In other examples, the width can be from 20 pm to 50 pm. In various examples, the color regions in the color layer can include three or more adjacent stripes of different colors, four or more spots including a two by two grid configuration of different colors, or nine or more spots including a three by three grid configuration of different colors.

[0032] The opaque concealing layer is applied over the color layer on the imaging medium. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to 120 °C. In some examples, the layer can include void spaces between the transparent polymer particles. These void spaces can be occupied by air, a binder, or a combination thereof. Because of differences between the refractive index of the transparent particles and the air or other material between the particles, the opaque concealing layer can have a strong light scattering effect, which makes the layer appear opaque. In contrast, when the transparent polymer particles coalesce and form a film, the film can appear much more transparent because the polymer is no longer in the form of many small individual particles that scatter light.

[0033] The opaque concealing layer can be applied at a coat weight that is sufficiently thick to make the layer appear opaque and conceal the colors of the color layer underneath. In some examples, the opaque concealing layer can be applied at a coat weight of 2 gsm (grams per square meter) to 10 gsm. In further examples, the coat weight can be from 3 gsm to 8 gsm.

[0034] In general, the transparent polymer particles are made of a polymer having a glass transition temperature from about 20 °C to about 120 °C. In further examples, the glass transition temperature can be from about 60 °C to about 100 °C or from about 80 °C to about 120 °C. Non-limiting examples of transparent polymers that can be used include an acrylic latex, a methacrylic latex, a styrene acrylic latex, a styrene methacrylic latex, a styrene-butadiene latex, or a combination thereof. Specific examples of latex particles that can be used include ROPAQUE® latex particles such as ROPAQUE® OP-62, ROPAQUE®OP-96, ROPAQUE®Ultra, or ROPAQUE®Ultra-EF particles, which have an average particle size from 400 nm to 600 nm (Dow Chemical Company, Michigan).

Additional examples include ROVENE® latex particles, such as ROVENE® 41 1 (styrene-butadiene latex with a Tg of 69 °C), ROVENE® 4009, ROVENE® 61 1 1 (Tg of 100 °C), ROVENE® 61 12 (Tg of 20 °C), ROVENE® 61 15 (Tg of 105 °C), ROVENE® 6101 (Tg of 100 °C), ROVENE® 6102 (Tg of 20 °C), ROVENE® 6400 (styrene-acrylic latex with a Tg of 25 °C), and ROVENE® 4106

(styrene-butadiene latex with a Tg of 69 °C) (Mallard Creek Polymers, North Carolina).

[0035] In further examples, the transparent polymer particles of the opaque concealing layer can have an average particle size from 20 nm to 500 nm. In still further examples, the transparent polymer particles can have an average particle size from 100 nm to 300 nm. In certain examples, the transparent polymer particles can have a non-uniform particle size with a variety of different particle sizes mixed together. The non-uniform particle size can result in increased light scattering and higher opacity of the layer.

[0036] In further examples, the opaque concealing layer can have a sufficient porosity and pore size distribution to make the layer appear opaque due to light scattering at the interfaces between transparent polymer particles and air, binders, or other materials in the layer. When the particles coalesce to form a film, the porosity can be reduced so that the polymer takes the form of a more continuous film without so many interfaces that can scatter light. In some examples, the opaque concealing layer can have a porosity from 5% to 80%. In other examples, the porosity can be from 10% to 50% or from 30% to 80%. As used herein,“porosity” refers to the volume fraction of the geometric volume of the opaque concealing layer that is void space, i.e., occupied by air.

[0037] Besides the transparent polymer particles described above, the opaque concealing layer can also include a binder in some examples. The binder can be a polymer that holds the transparent polymer particles together and helps the particles adhere to the color layer beneath. In some examples, the binder can include water soluble or water-dispersible binders. Water-soluble binders can include but are not limited to polyvinyl alcohols, water-soluble polyvinyl alcohol-poly(ethylene oxide) copolymers, water-soluble copolymers of polyvinyl alcohol and polyvinylamine, cationic polyvinyl alcohols, acetoacetylated polyvinyl alcohols, silyl-modified polyvinyl alcohols, polyvinyl acetates,

polyvinylpyrrolidones, copolymers of polyvinylpyrrolidone and polyvinyl acetate, starches, modified starches (including oxidized starches and ethylated starches), water soluble cellulose derivatives (including carboxymethyl cellulose and hydroxyethyl cellulose), polyacrylamides, casein, gelatin, maleic anhydride resin, styrene-butadiene copolymer, acrylic polymers (including polymers and copolymers of acrylic and methacrylic acids), vinyl polymers (including ethylene-vinyl acetate copolymers) or combinations thereof. Examples of water dispersible binders can include acrylic polymers, acrylic copolymers,

styrene-acrylic polymers, vinyl acetate latex, polyesters, polyurethane, vinylidene chloride latex, styrene-butadiene copolymer latex, styrene/n-butyl acrylate copolymer (such as, e.g., ACRONAL® S728, available from BASF Corp., Ludwigshafen, Germany), and/or acrylonitrile-butadiene copolymer latex.. In some examples, the binder can be a transparent polymer. In further examples, the transparent polymer binder can have a refractive index close to the refractive index of the transparent polymer particles. In one example, the binder can be a transparent polymer with a refractive index within 0.1 from the refractive index of the transparent polymer particles.

[0038] In certain examples, the amount of binder in the opaque concealing layer can be from 1 wt% to 20 wt% based on the dry weight of the layer. In other examples, the amount of binder can be from 2 wt% to 15 wt% or from 3 wt% to 10 wt%. In a particular example, the opaque concealing layer can consist of the binder and the transparent polymer particles. In other examples, the layer may include additional additives such as dispersants, surfactants, and so on. In some examples, the total amount of additives in addition to the binder and the transparent polymer particles can be from 0.1 wt% to 5 wt%. In further examples, the amount of transparent polymer particles in the opaque layer can be from 75 wt% to 99 wt%, from 80 wt% to 99 wt%, or from 90 wt% to 99 wt%.

[0039] As used herein,“opaque” and“opacity,” when used with respect to the opaque concealing layer, refer to the hiding power or ability of the layer to conceal the colors of the color layer below. The opacity can be quantified by calculating the contrast ratio of the layer using ASTM test method D2805. In some examples, the opaque concealing layer can have a contrast ratio of 80% to 100% when the transparent polymer particles are separate and have not formed a film. After the film-promoting fluid is printed on the opaque concealing layer and the transparent polymer particles that were printed have coalesced and formed a film, the contrast ratio can be less because the film appears more transparent. In some examples, the contrast ratio of the layer after forming a film ink can be from 0% to 50%, from 0% to 35%, or from 0% to 25%. Accordingly, lower contrast ratios correspond to more transparency.

[0040] To illustrate the process of printing the film-promoting fluid and coalescing the transparent polymer particles to allow the color underneath to show through, FIG. 7A shows a cross-sectional view of an imaging medium 700 with a film-promoting fluid 704 being printed on the medium. The medium includes a substrate 710, a color layer 720, and an opaque concealing layer 730 including transparent polymer particles 740. The color layer includes three color spots 722, 724, 726 of different colors printed adjacent one to another. The film-promoting fluid in this example is jetted from an inkjet printhead onto the area over color spot 724. Before the fluid is jetted onto the opaque concealing layer, the layer has an opaque appearance because of light scattering at the interfaces between the transparent polymer particles and air in the void spaces between the particles. FIG. 7B shows the imaging medium after the film-promoting fluid has been printed over the color spot 724. The film-promoting fluid interacts with the transparent polymer particles to effectively lower the glass transition temperature of the polymer making up the particles. FIG. 7C shows the imaging medium after the transparent polymer particles that were printed with the film-promoting fluid have coalesced to form a film 706. The film of the transparent polymer appears to be more transparent because the film does not scatter light as strongly as the individual particles before coalescing. Thus, the color of color spot 724 can be seen. The opaque concealing layer remains opaque over color spots 722 and 726, so that those colors are not visible.

[0041] In certain examples, registration marks can be added to the surface of the opaque concealing layer. The registration marks can be used to help an imaging system locate the correct areas for printing film-promoting fluid to produce a particular visible color. In some cases, the registration marks can be colorless machine-readable registration marks. These can be formed by printing with a machine-detectable ink such as infrared ink, ultraviolet ink, and so on.

[0042] The film-promoting fluid includes a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles after contact therewith. As explained above, the film-promoting fluid can be applied to an area of the opaque concealing layer to reduce the glass transition temperature of transparent polymer particles in that area. The film-promoting additive can reduce the glass transition temperature of the transparent polymer particles sufficiently so that the imaging medium can be heated to a temperature above the reduced glass transition temperature but below the original glass transition temperature of the particles, and thereby the particles in contact with the film-promoting agent can coalesce and form a film while the other particles do not coalesce. In certain examples, the film-promoting additive can reduces the glass transition temperature of the transparent polymer particles by 10 °C to 60 °C. In further examples, the film-promoting additive can reduce the glass transition temperature of the transparent polymer particles by 10 °C to 50 °C or 20 °C to 40 °C.

[0043] In further examples, the overall reduction in glass transition temperature can depend on the amount of the film-promoting additive that is applied to the transparent polymer particles. In some examples, the amount of film-promoting fluid that can be applied to the imaging medium can be from 50 ng to 150 ng per printed dot at a printing resolution of 300 dots per inch.

[0044] In some examples, the film-promoting additive can be a diol, a glycol, or a combination thereof. Non-limiting examples of film-promoting diols that can be used include 1 ,2-hexanediol, 1 ,6-hexanediol,

tetramethyl-5-decyne-4,7-diol, ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,2,4-trimethyl-1 ,3-pentanediol monoisobutyrate, or a combination thereof. Non-limiting examples of

film-promoting glycols that can be used include ethylene glycol, ethylene glycol n-butyl ether, ethylene glycol phenyl ether, diethylene glycol n-butyl ether, diethylene glycol methyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, propylene glycol n-propyl ether, propylene glycol n-butyl ether, propylene glycol phenyl ether, dipropylene glycol methyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol n-propyl ether, dipropylene glycol n-butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene glycol n-propyl ether, tripropylene glycol n-butyl ether, and combinations thereof. In another example, the film-promoting additive can be trimethylol propane. In further examples, the film-promoting additive can be a plasticizer that can reduce the glass transition temperature of the transparent polymer particles.

[0045] In certain examples, the film-promoting fluid can consist of or consist essentially of the film-promoting additive. In other examples, the film-promoting fluid can include other ingredients. In some cases, the

film-promoting additive can be mixed with a liquid vehicle. In particular examples, the concentration of the film-promoting additive in the film-promoting fluid can be from 5 wt% to 60 wt%, from 5 wt% to 40 wt%, or from 10 wt% to 40 wt%. In some examples, the liquid vehicle can include water or water mixed with co-solvents and/or additional additives. In certain examples, water can be present in the film-promoting fluid in an amount of 30 wt% or greater, 40 wt% or greater, 50 wt% or greater, or 60 wt% or greater. In further examples, water can be present in an amount of at most 95 wt%. In particular examples, water can be present in the film-promoting fluid in an amount of 30 wt% to 95 wt %, 40 wt% to 95 wt%, 50 wt% to 95 wt%, 60 wt% to 93 wt%, or 70 wt% to 90 wt%.

[0046] In further examples, the film-promoting fluid can include additional ingredients, such as additives to inhibit the growth of microorganisms, viscosity modifiers, materials for pH adjustment, sequestering agents, anti-kogation agents, preservatives, and the like. Such additives may be present in an amount of 0 to 5 wt % of the film-promoting fluid.

[0047] The film-promoting fluid can typically be colorless. Therefore, in some examples the film-promoting fluid can be devoid of colorants such as dyes or pigments. In other examples, the film-promoting fluid may include a small amount of colorant but the amount can be small enough to allow the colors from the color layer of the imaging medium to be seen through the printed

film-promoting fluid.

[0048] In some examples, the film-promoting fluid can be loaded within or fluidly coupled to an inkjet printhead to selectively print the film-promoting fluid onto the imaging medium. As used herein,“ink-jet” or“jet” refers to jetting architecture, such as ink-jet architecture. Ink-jet architecture can include thermal or piezo architecture. Additionally, such architecture can be configured to print varying drop sizes such as less than 10 picoliters, less than 20 picoliters, less than 30 picoliters, less than 40 picoliters, less than 50 picoliters, etc.

[0049] Imaging systems according to the present disclosure include an imaging medium and an inkjet printhead in fluid communication with a film-promoting fluid positioned to jet the film-promoting fluid onto the imaging medium. The imaging medium can have any of the features and components described above. Generally, the imaging medium includes a substrate, a color layer on the substrate, wherein the color layer includes a pattern of color regions, wherein individual regions include multiple adjacently-applied colors, and an opaque concealing layer over the color layer. The opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C. The film-promoting fluid includes a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles of the opaque concealing layer.

[0050] FIG. 8 shows an example imaging system 800. The system includes the imaging medium 802 with a substrate 810, color layer 820, and opaque concealing layer 830. The system also includes a film-promoting fluid 804 as mentioned above. In this example, the film-promoting fluid is printed from an inkjet printhead 840. This system also includes a black ink 860 printed from a second inkjet printhead 862. A heater 870 is also included in the system. The film-promoting fluid can be printed in specific locations on the imaging medium, and the heater can be used to heat the imaging medium so that the transparent polymer particles in the printed locations of the opaque concealing layer will coalesce and form a film. This can allow the colors of the color layer to show through. The black ink can be printed in any location where black coloring is desired.

[0051] In various examples, the imaging media described herein can be used with imaging systems that include a single printhead for printing a film-promoting fluid, or systems that include two printheads for printing a film-promoting fluid and a black ink. In some examples, the imaging medium can be designed for use with a single printhead that prints film promoting fluid. In some such examples, the color layer of the imaging medium can include black as one of the colors present in the color layer. For example, the color layer can include four colors: cyan, magenta, yellow, and black. In other examples, the imaging medium can be designed for use with a film-promoting fluid and a black ink. In some such examples, the color layer of the imaging medium can be devoid of black because black can be produced by printing the black ink. In certain examples, the color layer can include three colors: cyan, magenta, and yellow. The black ink can then be printed wherever black is desired in the image. These various systems, whether the systems include a single printhead or two printheads, can be simpler compared to full-color printing systems with separate printheads for every color.

[0052] In further examples, the imaging system can include a sensor for reading machine-readable registration marks on the imaging medium. Examples of the sensor can include a scanner, an electric eye, a contrast sensor, a luminescence sensor, and other types of photoelectric registration mark sensors.

[0053] As mentioned above, in some examples an imaging system can include a black ink in addition to the film-promoting fluid. In certain examples, the black ink can be loaded within or fluidly coupled to a second inkjet printhead to print the black ink onto the imaging medium. The second inkjet printhead for printing black ink can operate in the same way as the inkjet printhead for printing the film-promoting fluid.

[0054] The black ink can include a black colorant, such as a black dye, black pigment, or combination thereof. Examples of black colorants can include the following pigments available from Degussa Corp.: Color Black FWI, Color Black FW2, Color Black FW2V, Color Black 18, Color Black, FW200, Color Black 5150, Color Black S160, and Color Black 5170. The following black pigments are available from Cabot Corp.: REGAL® 400R, REGAL® 330R, REGAL® 660R, MOGUL® L, BLACK PEARLS® L, MONARCH® 1400, MONARCH® 1300, MONARCH® 1 100, MONARCH® 1000, MONARCH® 900, MONARCH® 880, MONARCH® 800, and MONARCH® 700. The following pigments are available from Orion Engineered Carbons GMBH: PRINTEX® U, PRINTEX® V,

PRINTEX® 140U, PRINTEX® 140V, PRINTEX® 35, Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW 1 , Color Black FW 18, Color Black S 160, Color Black S 170, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4. Other black pigments and dyes can also be included in the black ink.

[0055] The black ink can also include a liquid vehicle. In some examples, the liquid vehicle can include water or water mixed with co-solvents and/or additional additives. In certain examples, water can be present in the ink composition in an amount of 30 wt% or greater, 40 wt% or greater, 50 wt% or greater, or 60 wt% or greater. In further examples, water can be present in an amount of at most 99 wt% or at most 95 wt%. In particular examples, water can be present in the ink composition in an amount of 30 wt% to 99 wt %, 40 wt% to 98 wt%, 50 wt% to 95 wt%, 60 wt% to 93 wt%, or 70 wt% to 90 wt%.

[0056] Co-solvents that may be used can include organic co-solvents, including alcohols (e.g., aliphatic alcohols, aromatic alcohols, polyhydric alcohols (e.g., diols), polyhydric alcohol derivatives, long chain alcohols, etc.), glycol ethers, polyglycol ethers, a nitrogen-containing solvent (e.g., pyrrolidinones, caprolactams, formamides, acetamides, etc.), and a sulfur-containing solvent. Examples of such compounds include primary aliphatic alcohols, secondary aliphatic alcohols, 1 ,2-alcohols, 1 ,3-alcohols, 1 ,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higher homologs (C6-C12) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Still other examples of suitable co-solvents include propylene carbonate and ethylene carbonate. [0057] A single co-solvent may be used, or several co-solvents may be used in combination. When included, the co-solvent(s) can be present in total in an amount ranging from 0.1 wt% to 60 wt%, depending on the jetting architecture, though amounts outside of this range can also be used. In another example, the co-solvent(s) can be present in an amount from 1 wt% to 30 wt% or from 1 wt% to 20 wt% of the total weight of the ink

[0058] In further examples, the black ink can include additional ingredients, such as additives to inhibit the growth of microorganisms, viscosity modifiers, materials for pH adjustment, sequestering agents, anti-kogation agents, preservatives, and the like. Such additives may be present in an amount of 0 to 5 wt % of the ink.

[0059] The black ink may also include surfactants in some examples. Suitable surfactants may include non-ionic, cationic, and/or anionic surfactants. Examples include a silicone-free alkoxylated alcohol surfactant such as, for example, TEGO® Wet 510 (Evonik Tego Chemie GmbH, Germany) and/or a self-emulsifiable wetting agent based on acetylenic diol chemistry, such as, for example, SURFYNOL® SE-F (Air Products and Chemicals, Inc., Pennsylvania). Other suitable commercially available surfactants include SURFYNOL® 465 (ethoxylated acetylenic diol), SURFYNOL® CT 21 1 (non-ionic,

alkylphenylethoxylate and solvent free), and SURFYNOL® 104 (non-ionic wetting agent based on acetylenic diol chemistry), (all of which are from Air Products and Chemicals, Inc., Pennsylvania); ZONYL® FSO (a.k.a.

CAPSTONE®, which is a water-soluble, ethoxylated non-ionic fluorosurfactant from Dupont, Delaware); TERGITOL™ TMN-3 and TERGITOL™ TMN-6 (both of which are branched secondary alcohol ethoxylate, non-ionic surfactants), and TERGITOL™ 15-S-3, TERGITOL™ 15-S-5, and TERGITOL™ 15-S-7 (each of which is a secondary alcohol ethoxylate, non-ionic surfactant) (all of the

TERGITOL™ surfactants are available from The Dow Chemical Co., Michigan). Fluorosurfactants may also be employed. When present, the surfactant can be present in the ink in an amount ranging from about 0.01 wt% to about 5 wt% based on the total wt% of the ink. [0060] In another example, the present disclosure can include a method of forming an image using the imaging systems described above. FIG. 9 is a flowchart illustrating an example method 900 of forming an image. The method includes: jetting 910 a film-promoting fluid onto an imaging medium, the imaging medium including: a substrate, a color layer on the substrate, wherein the color layer includes a pattern of color regions, wherein individual color regions include multiple adjacently-applied colors, and an opaque concealing layer over the color layer, wherein the opaque concealing layer includes transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C; the film-promoting fluid including a film-promoting additive that reduces the glass transition temperature of transparent polymer particles after contact therewith; and selectively reducing 920 the glass transition temperature of the transparent polymer particles in a first area of the opaque concealing layer where the film-promoting fluid is jetted, which contributes to or causes the first area of the opaque concealing layer to form a film and becoming transparent or translucent while a second area is more opaque outside the first area.

[0061] In other examples, the method of forming an image can also include heating the imaging medium to a temperature above the glass transition of the transparent polymer particles that are contacted with the film-promoting additive, but below the glass transition temperature of the transparent polymer particles that were not contacted with the film-promoting port.

[0062] As mentioned above, the color layer can be formed by printing the color regions using any suitable printing method. The opaque concealing layer can be applied using any suitable coating method. In some examples, the opaque concealing layer can be formed from a composition including the transparent particles, binder, and a solvent. The composition can be coated at the desired coat weight and dried to form the opaque concealing layer.

[0063] It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise.

[0064] The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 5% or other reasonable added range breadth of a stated value or of a stated limit of a range. The term“about” when modifying a numerical range is also understood to include the exact numerical value indicated, e.g., the range of about 1 wt% to about 5 wt% includes 1 wt% to 5 wt% as an explicitly supported sub-range.

[0065] As used herein,“average particle size” refers to a number average of the diameter of the particles for spherical particles, or a number average of the volume equivalent sphere diameter for non-spherical particles. The volume equivalent sphere diameter is the diameter of a sphere having the same volume as the particle. Average particle size can be measured using a particle analyzer such as the Nanotrac® Wave II particle size analyzer available from Microtrac Inc., Pennsylvania. The particle analyzer can measure particle size using laser diffraction. A laser beam can pass through a sample of particles and the angular variation in intensity of light scattered by the particles can be measured. Larger particles scatter light at smaller angles, while small particles scatter light at larger angles. The particle analyzer can then analyze the angular scattering data to calculate the size of the particles using the Mie theory of light scattering. The particle size can be reported as a volume equivalent sphere diameter.

[0066] As used herein,“liquid vehicle” or“ink vehicle” refers to a liquid fluid in an ink. A wide variety of ink vehicles may be used with the systems and methods of the present disclosure. Such ink vehicles may include a mixture of a variety of different agents, including, surfactants, solvents, co-solvents, anti-kogation agents, buffers, biocides, sequestering agents, viscosity modifiers, surface- active agents, water, etc.

[0067] As used herein,“colorant” can include dyes and/or pigments.

[0068] As used herein,“dye” refers to compounds or molecules that absorb electromagnetic radiation or certain wavelengths thereof. Dyes can impart a visible color to an ink if the dyes absorb wavelengths in the visible spectrum.

[0069] As used herein,“pigment” generally includes pigment colorants, magnetic particles, aluminas, silicas, and/or other ceramics, organo-metallics or other opaque particles, whether or not such particulates impart color. Thus, though the present description primarily exemplifies the use of pigment colorants, the term“pigment” can be used more generally to describe pigment colorants and other pigments such as organometallics, ferrites, ceramics, etc. In one specific example, however, the pigment is a pigment colorant.

[0070] As used herein,“glass transition temperature” and“Tg” refer to the temperature at which a polymer transitions from a hard, glassy state to a softer, rubbery state. Glass transition temperature can be measured using differential scanning calorimetry according to ASTM D6604: Standard Practice for Glass Transition Temperatures of Hydrocarbon Resins by Differential Scanning Calorimetry. Differential scanning calorimetry can be used to measure the heat capacity of the polymer across a range of temperatures. The heat capacity can jump over a range of temperatures around the glass transition temperature. The glass transition temperature itself can be defined as the temperature where the heat capacity is halfway between the initial heat capacity at the beginning of the jump and the final heat capacity at the end of the jump.

[0071] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though the individual members of the list are individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0072] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include the numerical values explicitly recited as the limits of the range, and also to include all the individual numerical values or sub-ranges

encompassed within that range as if induvial numerical values and sub-ranges are explicitly recited. For example, a layer thickness from about 0.1 pm to about 0.5 pm should be interpreted to include the explicitly recited limits of 0.1 pm to 0.5 pm, and to include thicknesses such as about 0.1 pm and about 0.5 pm, as well as subranges such as about 0.2 pm to about 0.4 pm, about 0.2 pm to about 0.5 pm, about 0.1 pm to about 0.4 pm etc. [0073] The following illustrates an example of the present disclosure. However, it is to be understood that the following is illustrative of the application of the principles of the present disclosure. Numerous modifications and alternative compositions, methods, and systems may be devised without departing from the spirit and scope of the present disclosure. The appended claims are intended to cover such modifications and arrangements.

EXAMPLES

Example 1 - Making an Imaging Medium

[0074] An example imaging medium is prepared as follows:

1 ) An inkjet printer is used to print a series of colored stripes on a paper substrate. The colored stripes include a first cyan stripe, a second magenta stripe adjacent to the cyan stripe, and a third yellow stripe adjacent to the magenta stripe. This pattern is repeated across the width of the paper substrate. Each individual stripe has a width of 1 /300^th inch (about 85 pm).

2) After printing the colored stripes, an opaque concealing layer is coated over the colored stripes at a coat weight of 5 gsm. The opaque concealing layer includes particles of acrylic latex having a glass transition temperature of 60 °C and an average particle size of 150 nm in an amount of 90 wt% with respect to the dry weight of the layer. The opaque concealing layer also includes MOWIOL® 8-88 polyvinyl alcohol (Kuraray America Inc., Texas) as a binder in an amount of 10 wt% with respect to the dry weight of the layer.

3) Machine readable registration marks are printed at locations spaced across the imaging medium using a colorless infrared ink.

Example 2 - Forming an Image on the Imaging Medium

[0075] An image is formed on the imaging medium of Example 1 as follows:

1 ) A film-promoting fluid is loaded in an inkjet printhead. The film-promoting fluid includes 1 ,2-hexanediol as the film-promoting additive mixed in a liquid ink vehicle. The liquid ink vehicle includes water, 2-pyrrolidone as a cosolvent, DOWFAX™ 2A1 surfactant (Dow Chemical Company, Michigan), SURFYNOL® CT -1 1 1 surfactant (Evonik Industries, Germany), and ZONYL® FSA surfactant (DuPont, Delaware).

2) The imaging medium is fed into a printer having a sensor for detecting the machine-readable registration marks. Based on the

machine-readable registration marks, the printer determines the locations of the individual colored stripes in the color layer of the imaging medium.

3) The printer jets the film-promoting fluid on specific locations to reveal the cyan, magenta, or yellow stripes below the opaque concealing layer in order to form the appropriate colors of a full-color image. 4) The printer jets a black ink from a second printhead in specific locations to provide black where appropriate in the full-color image.

Claims

What is claimed is: 1. An imaging kit, comprising:

an imaging medium, comprising:

a substrate,

a color layer on the substrate, wherein the color layer comprises a pattern of color regions, wherein individual color regions include multiple adjacently-applied colors, and

an opaque concealing layer over the color layer, wherein the

opaque concealing layer comprises transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C; and

a film-promoting fluid comprising a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles after contact therewith.

2. The imaging kit of claim 1 , wherein the transparent polymer particles comprise an acrylic latex, a methacrylic latex, a styrene acrylic latex, a styrene methacrylic latex, or a combination thereof.

3. The imaging kit of claim 1 , wherein the pattern is a repeating pattern of color regions, wherein the color regions include: three or more adjacent stripes of different colors; four or more spots including a two by two grid configuration of different colors; or nine or more spots including a three by three grid configuration of different colors.

4. The imaging kit of claim 1 , wherein the multiple adjacently-applied colors include cyan, magenta, and yellow.

5. The imaging kit of claim 1 , wherein the multiple adjacently-applied colors are individually applied at a width from 15 pm to 100 pm.

6. The imaging kit of claim 1 , further comprising a machine-readable colorless registration mark on the concealing layer.

7. The imaging kit of claim 1 , wherein the film-promoting additive is a diol, a glycol, or a combination thereof.

8. The imaging kit of claim 1 , wherein the film-promoting additive is 1 ,2-hexanediol, 1 ,6-hexanediol, tetramethyl-5-decyne-4,7-diol, ethoxylated 2,4,7,9-tetramethyl-5-decyn-4,7-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,2,4-trimethyl-1 ,3-pentanediol monoisobutyrate, or a combination thereof.

9. The imaging kit of claim 1 , wherein the multiple adjacently-applied colors do not include black, and wherein the imaging kit further includes a black ink.

10. An imaging system, comprising:

an imaging medium, comprising:

a substrate,

an opaque concealing layer over the color layer, wherein the

an inkjet printhead in fluid communication with a film-promoting fluid positioned to jet the film-promoting fluid onto the imaging medium to contact the opaque concealing layer, the film-promoting fluid comprising a film-promoting additive that reduces the glass transition temperature of the transparent polymer particles of the opaque concealing layer.

1 1. The imaging system of claim 10, further comprising a heater positioned to heat the imaging medium after the film-promoting fluid has been jetted onto the imaging medium to a temperature that causes transparent polymer particles contacted with the film-promoting additive to coalesce, wherein transparent polymer particles not contacted by the film-promoting additive do not coalesce.

12. The imaging system of claim 10, further comprising a second inkjet printhead in fluid communication with a reservoir of black ink positioned to jet the black ink onto the imaging medium.

13. A method of forming an image, comprising:

jetting a film-promoting fluid onto an imaging medium,

the imaging medium comprising:

a substrate,

a color layer on the substrate, wherein the color layer

comprises a pattern of color regions, wherein individual color regions include multiple

adjacently-applied colors, and

an opaque concealing layer over the color layer, wherein the opaque concealing layer comprises transparent polymer particles having a glass transition temperature from about 20 °C to about 120 °C; the film-promoting fluid comprising a film-promoting additive that reduces the glass transition temperature of transparent polymer particles after contact therewith; and

selectively reducing the glass transition temperature of the transparent polymer particles in a first area of the opaque concealing layer where the film-promoting fluid is jetted, which contributes to or causes the first area of the opaque concealing layer to form a film and becoming transparent or translucent while a second area is more opaque outside the first area.

14. The method of claim 13, further comprising heating the imaging medium to a temperature above the glass transition temperature of the transparent polymer particles in the first area, but below the glass transition temperature in the second area to contribute to the first area forming the film and becoming transparent or translucent while the second area is more opaque outside the first area.

15. The method of claim 13, further comprising jetting a black ink onto the imaging medium, wherein the multiple adjacently-applied colors does not include black as one of the colors.