Patent Application
20170368861
There are several reasons that inkjet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, variable content recording, capability of high speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers. However, though there has been great improvement in inkjet printing, accompanying this improvement are increased demands by consumers in this area, e.g., higher speeds, higher resolution, full color image formation, increased stability, etc. Additionally, inkjet printing technology is becoming more prevalent in high speed commercial printing markets. Regardless of the platform, achieving or maintaining a high image quality can be challenging. Coated media typically used for inkjet printing can perform acceptably with certain printing devices, but there is much more specialty media used for specific types of printers than in the past, and there is still room for improvement as it relates to image quality. As such, research and development of media continue to be sought.
Before the present disclosure is described, it is to be understood that this disclosure is not limited to the particular process steps and materials disclosed herein because such process steps and materials may vary somewhat. It is also to be understood that the terminology used herein is used for the purpose of describing particular examples only. The terms are not intended to be limiting because the scope of the present disclosure is intended to be limited only by the appended claims and equivalents thereof.
Obtaining high print quality for various inks on uncoated paper can sometimes be a challenge. In accordance with the present disclosure, coatings can be applied to various media substrates, including paper, that provide acceptable image quality, including optical density increase, image gloss increase, durability improvement, and/or color gamut improvement. More specifically, low glass transition temperature (Tg) polymeric binder (below 50° C.), high Tg cationic latex (50° C. to 130° C.), multivalent cationic salt, and high density polyethylene wax can be used to prepare a coating that, particularly when calendered under heat and pressure, provides image gloss, print quality and durability improvement.
In accordance with this, the present disclosure is drawn to a print medium including a substrate and a coating applied to the substrate, either on one side or on both sides of the substrate. The coating can include, by dry weight, 5 wt % to 60 wt % of a polymeric binder having a Tg below 50° C., 10 wt % to 60 wt % of cationic latex having a Tg from 50° C. to 130° C., 5 wt % to 30 wt % of a multivalent cationic salt, and 2 wt % to 25 wt % of a high density polyethylene wax. In one example, the coating can further be modified with the application of an ink, and the ink and coating can be heat and pressure fused at from 150° C. to 250° C. and from 1000 psi to 3000 psi.
In another example, a method of preparing a coated print medium can include applying a coating composition to a media substrate, the coating composition including water, polymeric binder having a Tg below 50° C., cationic latex having a Tg from 50° C. to 130° C., multivalent cationic salt, and high density polyethylene wax. Another step can include applying heat and pressure to the coating composition applied to the media substrate to yield a 0.5 to 10 gsm dry coating on the media substrate, comprising, by dry weight, 5 wt % to 60 wt % of the polymeric binder, 10 wt % to 60 wt % of the cationic latex, 5 wt % to 30 wt % of the multivalent cationic salt, and 2 wt % to 25 wt % of the high density polyethylene wax.
In another example, a printing system can include an ink, a coated print medium, and a calendering device. The coated print medium can include a substrate and a coating applied to the substrate. The coating can include, by dry weight, 5 wt % to 60 wt % of a polymeric binder having a Tg below 50° C., 10 wt % to 60 wt % of cationic latex having a Tg from 50° C. to 130° C., 5 wt % to 30 wt % of a multivalent cationic salt, and 2 wt % to 25 wt % of a. The system can also include a calendering device for applying heat and pressure to the coated print medium after the ink is printed on the coated print medium.
In these examples, it is noted that when discussing the coated print medium, the method of making the same, or the printing system, each of these descriptions can be considered applicable to all of these examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing details about the coated print medium per se, applicable discussion also refers to the methods or systems described herein, and vice versa.
Turning now to
The substrate is typically a base or foundational material or coated medium, e.g., in the form of a sheet, roll, etc., that is coated in accordance with examples of the present disclosure. The substrate can be, without limitation, a polymer substrate, a conventional paper substrate, a photobase substrate, an offset coated media substrate, or the like. As mentioned, in one aspect of the present disclosure, the coatings herein can be applied to substrates that are already pre-coated with another material, such as offset coated media. To illustrate, the substrate can be a raw, pre-coated base having an offset coating applied at from 2 gsm to 40 gsm. Exemplary offset or other coatings that can be present on offset media include media with clay carbonate coatings, precipitated calcium carbonate coatings, calcined clay coatings, silica pigment-based coatings, combinations thereof, or the like.
As a point of clarification, it is noted that certain coatings (or pre-coatings) described herein may already be present as part of a substrates, and these coatings are not the same as formulation coatings primarily discussed in the context of the present disclosure. Offset media or photobase, for example, already include coatings on one or both side of a substrate material (and thus are considered to be part of the “substrate”). The coating formulations of the present disclosure, conversely, are those which are overcoated with respect to the pre-applied coatings, or alternatively, to substrates that are not already pre-coated. Such coatings, i.e. the pre-coating and/or the coating formulation of the present disclosure, can be present on either one side of a media substrate or both.
Turning now more specifically to the coating formulations of the present disclosure, as mentioned, such coatings include, by solids content (dry weight), 5 wt % to 60 wt % of a polymeric binder having a Tg below 50° C., 10 wt % to 60 wt % of cationic latex having a Tg from 50° C. to 130° C., 5 wt % to 30 wt % of a multivalent cationic salt, and 2 wt % to 25 wt % of a high density polyethylene wax. The solids are typically prepared in a liquid vehicle which is evaporated or dried off to leave the coating solids behinds as a dry coating on the substrate. The liquid vehicle, which is usually primarily water or can be only water, typically includes from 25 wt % to 60
wt % of the initial coating formulation. That being stated, the weight percentages listed for the coating composition recite the weights after the liquid vehicle has been dried or evaporated from the coating composition.
Turning now to specific ingredient that can be present in the coating applied to the media substrate, polymeric binder having a glass transition temperature (Tg) less than 50° C., can be present and used to bind the materials of the coating together, but can also provide other print quality advantages, e.g., provide improved bleed control. In one specific aspect of the present disclosure, the polymeric binder can be a water soluble polymer binder, though this is not required. To illustrate, the polymeric binder can be any hydrophilic or hydrophilic/hydrophobic blend of polymer material that can be used to bind particulates together in accordance with examples of the present disclosure. By “water soluble,” it is noted that the polymer binder is typically at least partially water soluble, mostly water soluble (at least 50%), or in some examples, completely water soluble (at least 99%) in the coating composition. Polyvinyl alcohol, polyvinyl pyrrolidone, starch, low Tg latex having a glass transition temperature (Tg) ranging from −20° C. to 20° C., and protein are examples of acceptable water soluble polymer binders that can be used. Examples of starch binders that can be used include Penford® Gums, such as Penford® 280 (hydroxyethylated starch), available from Penford Corporation. Examples of a low Tg latexes that can be used as a binder are the Neocar® latexes, such as Neocar® 2300 (vinyl versatate-containing latex), among others. Examples of a polyvinyl alcohol binders that can be used include Mowiol® PVOH binders, e.g., Mowiol® 4-98 available from Kuraray.
In some aspects, in combination with the polymeric binder, a crosslinker or crosslinking agent can be included in the coating formulations of the present disclosure. Crosslinkers include materials that have crosslinking properties specifically with respect to the water soluble polymer binder used in a given coating composition. Suitable crosslinkers include boric acid, ammonium zirconium carbonate (AZC), potassium zirconum carbonate (KZC), and OCHCHO (glyoxal). More specifically, in some examples, boric acid is an acceptable crosslinker for polyvinyl alcohol, and in other examples, AZC, KZC, and glyoxal are acceptable crosslinkers for proteins and starches. In one example, non-acidic crosslinkers, such as a blocked glyoxal-based insolubilizer (e.g., Curesan® 200 from BASF) can be used to crosslink the water soluble binder, and these are particularly useful when the anionic non-film forming polymer particulates are also being used. Crosslinkers, if present, are usually present at relatively small concentrations in the coating composition, e.g., from 0.01 wt % to 5 wt % of the formulation, and in many instances, the crosslinkers are more typically present at a ratio of 1:100 to 1:4 crosslinker to binder by weight, though these concentrations and ratios are not intended to be limiting.
The cationic latex, which can be in the form of plastic pigment particles, can range in glass transition temperature from 50° C. to 130° C. in one example, and in another example, the cationic latex can be a high Tg cationic latex ranging from 70° C. to 120° C. Such materials can include materials such as Raycat® 82 from Specialty Polymers, Inc. (acrylic emulsion polymer, solids 40 wt %, pH 4.5, and glass transition temperature 25° C.), Raycat® 29033 (styrene/acrylic copolymer, solids 40 wt %, pH 5.0, and glass transition temperature 77° C.), or Raycat® 78 (polyacrylic emulsion polymer, solids 40 wt %, pH 5.5, and glass transition temperature 115° C.). More generally and in accordance with another example, the cationic latex can be an acrylic emulsion polymer, a styrene acrylic copolymer, a styrene methacrylic copolymer, a polyacrylic emulsion polymer, ethylene acrylic copolymer, ethylene methacrylic copolymer, or combinations thereof. These exemplary cationic latexes are examples of suitable materials that can be used herein, but it is noted that other materials currently available or available in the future that meet the criteria of being a cationic latex can also be used.
Turning now to the multivalent cationic salt, various types of salts can be used in the media coatings of the present disclosure. Often, the salt can be, for example, calcium chloride, magnesium chloride, calcium bromide, magnesium bromide, calcium nitrate, magnesium nitrate, magnesium sulfate, or aluminum chlorohydrate. These salts can act as crashing agent for pigment-based inkjet inks. Thus this additive can provide versatility to the coated media in that other ingredients can assist in providing improved image quality for dye-based inks, whereas the presence of the multivalent salt can assist with image quality when a pigmented inkjet ink is used.
High density polyethylene wax (HDPE) can also be included. Commercially available waxes that can be used include Michemshield® 29235 from Michelman, Inc., and Ultralube® E846 or D806 from Keim Additec Surface GmbH, for example. In certain examples, the HDPE can have an average particle size from 500 nm to 30 μm or from 1 μm to 10 μm, a density from 0.9 g/cc to 1.0 g/cc or from 0.93 g/cc to 0.97 g/cc, and/or a melting point from 110° C. to 150° C. or 125° C. to 135° C. HDPE is useful for the coatings of the present technology because of its strength-to-density ratio, due in part to its very low branching and higher density and crystallinity. These properties provide strong intermolecular forces and tensile strength, more so than low density polyethylene (LDPE).
Other additives can also be present, such as cationic or anionic inorganic pigments. For example, the inorganic pigments can be added at from 0.1 wt % to 35 wt %, by solids content (dry weight). Examples of such inorganic pigments include anionic calcium carbonate, cationic calcium carbonate, or clay. More specific examples of calcium carbonates that can be used include Hydrocarb® 60, from Omya North America, which is an anionic calcium carbonate; or Micronasize® CAT, from Specialty Products, Inc., which is a cationic calcium carbonate. Optical brighteners can also be included at from 0.01 wt % to 15 wt %, by solids content (dry weight). Slip aids can also be included that contribute to abrasion resistance and coefficient of friction (COF) reduction. Lubricants, thickeners, biocides, defoamers, buffering agents, CMS, and surfactants can also be added in minor amounts as well, e.g., from 0.01 wt % to 5 wt % if present. Fillers can also be included in minor amounts, e.g., from 0.01 wt % to 5 wt %, including materials such as clays, barium sulfate, titanium dioxide, silica, aluminum trihydrate, aluminum oxide, boehmite, and combinations thereof. Again, these materials are optional and considered fillers, and if added, should not detract from the functional characteristics of the coating formulation as a whole.
Once the formulation is prepared, the coating can be applied to the substrate by any of a number of coating methods. Thus, turning now to
In
In accordance with examples of the present disclosure, the substrate can be coated using the coating applicator as described above. The coating applicator can be set up for spray coating, dip coating, cascade coating, roll coating, gravure coating, curtain coating, air knife coating, cast coating, Mayer rod coating, blade coating, film coating, metered size press coating, puddle size press coating, calender stack, and/or by using other known coating techniques. The thickness selected for each coated layer can depend upon the particular desired property or application. However, an advantage of the formulations of the present disclosure is that they can be applied relatively thinly compared to many other commercially available coating compositions. To illustrate, in one example, the coating can be applied at a coat weight from 0.5 gsm to 10 gsm. In another example, the coating can be applied to the substrate at a coat weight from 1 gsm to 6 gsm. More typical coat weights for comparative media that does not include the components of the present disclosure are usually in the order of about 15 gsm or greater, so a thinner coating with provide acceptable image quality and smudge resistance can be particularly advantageous.
Any drying device (or in some cases, ambient drying can be used without the use of a dryer device) can be used to dry the coating once applied to the substrate. Suitable drying devices can include forced air dryers, heated dryers, IR heaters, or combinations thereof.
Any printing device that applies ink to the coated print medium can be used, such as a thermal inkjet printer, a piezo inkjet printer, or the like. In one specific example, the printer can be a web press printer, such as HP T200 series, T300 series, or T400 series Color Inkjet Web Presses. Web Press devices print very rapidly and thus, the coating applications described herein can be prepared so that they are suitable for very fast coating, drying, printing, and/or calendering. These coating layers can, for example, deliver acceptable image quality at high printing speed greater than 400 feet/min (fpm) with HP Web Presses.
Once dried and printed, in one example, the coated print medium can be passed between a pair of heated rollers as part of a calendering process. As mentioned, calendering can be carried out in-line or with a larger system, or off-line in a separate device. The calendering device can be a separate super-calendering machine, an on-line, soft-nip calendering machine, an off-line, soft-nip calendering machine, or the like.
Using this process, prints can be prepared that have a desirable image gloss and gloss uniformity. For example, the cationic latex, or plastic pigment, under heat and pressure can form a continuous film. The printed ink can thus be integrated into the film resulting in a very smooth surface with good gloss uniformity, e.g., high gloss for unprinted areas and printed areas alike. Durability of the printed image can also be enhanced with dry smear resistance and wet rubbing resistance improvements. Also, in accordance with the present disclosure, the ink colorant can become anchored to the coating layer after printing, and then become encapsulated by calendering due to the heat and pressure applied thereto.
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.
“Substrate” or “media substrate” includes any base material that can be coated in accordance with examples of the present disclosure, such as film base substrates, polymer substrates, conventional paper substrates, photobase substrates, offset media substrates, and the like. Further, pre-coated and film coated substrates can be considered a “substrate” that can be further coated in accordance with examples of the present disclosure.
As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.
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 each member of the list is 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.
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 not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a weight ratio range of about 1 wt % to about 20 wt % should be interpreted to include not only the explicitly recited limits of 1 wt % and about 20 wt %, but also to include individual weights such as 2 wt %, 11 wt %, 14 wt %, and sub-ranges such as 10 wt % to 20 wt %, 5 wt % to 15 wt %, etc.
The following examples illustrate some of the coated media substrates, systems, and methods that are presently known. However, it is to be understood that the following are only exemplary or illustrative of the application of the principles of the present compositions, systems, and methods. Numerous modifications and alternative compositions, systems, and methods may be devised by those skilled in the art without departing from the spirit and scope of the present disclosure. The appended claims are intended to cover such modifications and arrangements. Thus, while the examples have been described above with particularity, the following provide further detail in connection with what are presently deemed to be the acceptable examples.
Several coating formulations were prepared in accordance with Table 1 (expressed in parts by weight, dry):
These coating formulations can be prepared using various preparative methods, with various liquid vehicles, and adding ingredients using various orders of addition. To illustrate, in one example, the order of addition of ingredients can be water (which is not shown above because dry wt % is provided above after removal of water), cationic latex polymer, multivalent cationic salt, polymeric binder (polyvinyl alcohol, starch, or low Tg latex in these examples), and high density polyethylene wax, for example. Other orders of addition can be used as well.
Each of the coatings of Example 1 (Formulations 1-4) can be applied to one side or both sides of a media substrate, such as paper, and dried so that the solvent or liquid vehicle components are removed. It is noted the liquid vehicle in Tables 1 is not listed because Formulas 1-4 are provided in dry weight. That being stated, the liquid vehicle which is removed by drying can be primarily water with or without other small amounts of other volatile ingredients that can be readily removed upon drying. The remaining dry weight can typically be from 0.5 gsm to 10 gsm. In the present example, coating formulations of Tables 1 were overcoated on single side of a plain paper print media substrate using a blade coater to produce a dry coating weight of about 1 gsm.
In accordance with this, four media sample types were prepared and printed on using a dye-based inkjet ink set, and some samples were calendered at 100° C. and 1500 psi. Additionally, for comparison purposes, AC Utopia book paper 45# media was tested as well. Each of the samples were specifically tested for sheet gloss (gloss of unprinted portion) and image gloss (gloss of printed portion) to give a delta gloss (or gloss difference). Lower gloss difference is typically considered better because the gloss is more uniform over the entire page. Also tested was color gamut, black optical density (KOD), L*min, and print durability. Coating 1 (C1) represents Formula 1 coated at 1 gsm on single side of a paper media substrate; coating 2 (C2) represents Formula 2 coated at 1 gsm on single side of a paper media substrate; and so forth. AC is AC Utopic Book Paper 45# without any of the formulation coatings (C1-C4) applied thereto. With color gamut and black optical density, a larger number is better indicating more color gamut and more optical density for the inkjet inks printed thereon. Additionally, a lower value for L*min is a better value, as it indicates high black color density. The durability values were collected visually after various rubbing tests, including rubbing printed image samples with a Sutherland 2000 Rub Tester with the ASTM F1571-95 standard test method. A scale of 1 to 5 was used, with 5 being the highest durability value, and thus the best durability. A value of less than 4 is considered less desirable, whereas 4 or better has excellent durability. In these examples, HP A50 color pigmented inkjet ink, which is a water-based inkjet ink, was printed on the various coated media and either dried, or dried and calendered. All of these data points are assembled in Tables 2A and 2B below.
As can be seen from Tables 2A and 2B, the presence of cationic salt, high density polyethylene wax, and binder provides acceptable print results in some categories (see calendered coating 4), but by adding the high Tg cationic latex, as in coatings 1-3, the calendered coating increases in durability to greater than 4. Additionally, it is noted that calendered image gloss for coatings 1-3 is also superior to the calendered image gloss of coating 4. Each of coatings 1-3 also provide improved image quality and durability generally compared to the comparative AC Utopia media.
While the disclosure has been described with reference to certain examples, those skilled in the art will appreciate that various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the disclosure. It is intended, therefore, that the disclosure be limited only by the scope of the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US15/12719 | 1/23/2015 | WO | 00 |
