Patent Application
20140302292
Inkjet technologies have been used to form circuitry. These inkjet technologies include a variety of methods. Some involve ink jetting of a precursor material which aids in deposition of conductive metals. Other methods involve printing of conductive inks onto a substrate.
The present application relates to a printed electronic device and a coating composition for forming an inkjet recording medium for making a printed electronic device by application of an electrically conductive ink to a recording medium. More specifically, the resulting recording medium is particularly useful as a recording medium carrying an electrically conductive circuit.
Printed electronics are typically made by printing the electronic circuit or other component or device on a substrate using an electrically conductive metal-containing ink. The inks typically contain silver particles, and occasionally copper particles, other metallic particles, and/or conductive polymers.
This application describes a printed electronic device and a coating composition for forming a printed electronic device. In accordance with one aspect of the present invention, a inkjet recording medium is disclosed to which an electrically conductive ink is applied in the form of an electric circuit. The recording medium comprises an inkjet-receptive coating on a paper substrate. The inkjet-receptive coating contains a synergistic combination of pigments, binder and optionally, in one embodiment, a multivalent salt. In another embodiment, the coating does not contain a multivalent salt.
In accordance with certain embodiments, the paper coating includes a combination of a primary pigment and a secondary pigment. In one embodiment the primary pigment includes anionic particles having a particle size distribution where at least 96% of the particles by weight have a particle size less than 2 microns. In one embodiment, the primary pigment can be precipitated calcium carbonate or a fine ground calcium carbonate. The secondary pigment may be a cationic, grit-free pigment having an average particle size of 3 microns or less. The coating also includes up to 17 weight % of a hydrophilic styrene-butadiene latex binder based on the weight of the dry pigments and a co-binder. One such composition that does not contain a multivalent salt and is particularly useful with conductive ink is described in U.S. Pat. No. 7,803,224 to Schliesman which is herein incorporated by reference in its entirety. The coating optionally includes a co-binder. In another embodiment, a multi-valent salt, a calcium stable binder, and a dispersant may also be included in the coating composition as disclosed in U.S. Pat. No. 8,431,193 and Published Application 2012/0212555 which are incorporated herein by reference.
Aragonite is a particularly useful precipitated calcium carbonate that differs from other forms of calcium carbonate in both particle shape and size distribution. It is particularly useful as the primary pigment. Aragonite has a needle-like structure and a narrow particle size distribution making it particularly suitable as the primary pigment. While not wishing to be bound by theory, it is believed that the structure discourages tight particle packing of the pigment and provides the porosity needed for good ink absorption from different printing techniques. Use of the aragonite form produces a surface on the treated paper having a controlled porosity that allows it to perform well with any printing process. U.S. Pat. No. 8,431,193 to Romano is incorporated herein by reference for aragonite coating compositions useful herein.
Another embodiment is a process for forming an electronic device which comprises the steps of applying a pattern of a conductive ink by means of an ink jet printing head to the surface of an ink jet recording layer or medium as described herein to form an electric circuit.
U.S. Published Application 2013/0033810 is incorporated herein by reference in its entirety for its disclosure of printed electronics and electrically conductive inks applied by inkjet printing.
In one embodiment, the present invention provides a method of forming a conductive path or circuit on a substrate comprising the steps of providing conductive particulates, a liquid vehicle, and a substrate including an ink receptive coating; forming a suspension comprising the liquid vehicle and the particulate conductive material; jetting from an inkjet a predetermined pattern of the suspension onto the ink-receptive coating; and heating the substrate with the suspension ink jetted thereon to a temperature wherein the conductive particulates are bound and adhere to the substrate and provide the conductive path.
The coating for producing the ink receptive coating typically includes at least two pigments, a primary pigment and a secondary pigment. The primary pigment may be a narrow particle size distribution, precipitated (or finely ground), anionic pigment. The secondary pigment may be a cationic pigment such as a medium or coarse aground calcium carbonate. The pigments typically are inorganic pigments. Further, the coating typically includes a binder and, optionally, a co-binder. Pigments typically comprise the largest portion of the coating composition on a dry weight basis. Unless otherwise noted, amounts of component materials are expressed in terms of component parts per 100 parts of total pigment on a weight basis.
In one embodiment, the primary component of the coating may be an anionic pigment having a narrow particle size distribution where 96% of the particles are less than 2 microns in diameter. Preferably, at least 80% by weight of the particles should be less than 1 micron and fall within the range of 0.1-1μ. In another embodiment, the distribution has at least 85% of the particles less than 1 micron and fall in the range of 0.1-1 microns. In another embodiment, 98% of the particles are less than 2 microns in diameter. In another embodiment, the inkjet-receptive coating comprises a primary pigment having an average particle size of less than 1 micron; a secondary pigment having an average particle size of 3 to 5 microns; and a binder wherein said binder is present in an amount from about 2 to 15 parts by weight based on 100 parts total pigments. In another embodiment the composition additionally contains a multivalent metal salt. This embodiment is disclosed in U.S. Published Application 2012/0212555 which is incorporated herein in its entirety by reference. Yet another embodiment the recording coating uses a calcium carbonate wherein about 98% of the particles fall in the range of 0.1-1.0 microns. In accordance with certain embodiments, the primary pigment is from about 35 to about 85 parts, more particularly from about 60 to about 76 parts, of the total pigment by weight.
Calcium carbonate is useful as the primary pigment in any form, including aragonite, calcite or mixtures thereof. Calcium carbonate, when present as the primary pigment, typically makes up 35-85 parts of the coating pigment on a dry weight basis. In certain embodiments, the calcium carbonate may be from about 60 to 76 parts of the pigment weight. Aragonite is a particularly useful calcium carbonate. An advantage to using aragonite as the primary pigment is that the porous structure of the coating better withstands calendering to give it a gloss finish. When other forms of calcium carbonate are used in coatings, surface pores can be compacted so that some absorbency can be lost before a significant amount of gloss is achieved. A particularly useful aragonite is Specialty Minerals OPACARB A40 pigment (Specialty Minerals, Inc., Bethlehem, Pa.). A40 has a particle size distribution where 99% of the particles have a diameter of from about 0.1 to about 1.1 microns.
For the primary pigment, an alternate calcium carbonate having a narrow particle size distribution such as OMYA CoverCarb 85, OMYA CoverCarb 90, or OMYA CoverCarb HP ground calcite calcium carbonate (OMYA AG, Oftringen, Switzerland) may be used. It provides the porous structure for successful ink absorption but less paper gloss development. This calcium carbonate, in accordance with certain embodiments, has a particle size distribution where 99% of the particles have a diameter less than 2 microns.
The secondary pigment typically is a cationic pigment. It is added to the coating which, when fully assembled, typically has an overall anionic nature. Attractive forces between the anionic coating and cationic pigment are believed to open up surface pores in the coating, increasing the porosity and the ink absorption rate. Ink drying times are also reduced. Additionally, since the ionic interaction is on a very small scale, the improved porosity is uniform over the coating surface.
The particle size distribution of the secondary pigment typically has an average particle size less than 3.0 microns and typically is grit-free. The term “grit-free” is intended to mean there are substantially no particles on a 325 mesh screen. In some embodiments, substantially all of the particles in the secondary pigment are sized at less than 1 micron. Amounts of the secondary pigment are typically less than 20 parts based on 100 parts by weight of the total pigment. Use of excessive cationic component may lead to undesirable ionic interaction and chemical reactions that can change the nature of the coating. The secondary pigment may be present in amounts greater than 5 parts cationic pigment per 100 total parts pigment. The secondary pigment may be present in amounts from about 0-50 parts, more particularly from about 8-16 parts. Examples of secondary pigments include carbonates, silicates, silicas, titanium dioxide, aluminum oxides and aluminum trihydrates. Particularly useful secondary pigments include cationic OMYAJET B and 5010 pigments (OMYA AG, Oftringen, Switzerland) and Carbital 35 calcium carbonate (Imerys, Roswell, Ga.).
Supplemental pigments are optional and may include anionic pigments used in the formulation as needed to improve gloss, whiteness or other coating properties. In one embodiment up to an additional 50 parts by weight (or in another embodiment up to 30 parts by weight) of the dry coating pigment may be an anionic supplemental pigment. Up to 35 parts, more particularly less than 25 parts, of the pigment may be a coarse ground calcium carbonate, another carbonate, plastic pigment, TiO2, or mixtures thereof. An example of a ground calcium carbonate is Carbital 35 calcium carbonate (Imerys, Roswell, Ga.). Another supplemental pigment is anionic titanium dioxide, such as that available from Itochu Chemicals America (White Plains, N.Y.). Hollow spheres are particularly useful plastic pigments for paper glossing. Examples of hollow sphere pigments include ROPAQUE 1353 and ROPAQUE AF-1055 (Rohm & Haas, Philadelphia, Pa.). Higher gloss papers are obtainable when fine pigments are used that have a small particle size. The relative amounts of the supplemental pigments are varied depending on the whiteness and desired gloss levels.
A primary binder is added to the coating for adhesion. When a multivalent salt is present, the primary binder is compatible with the incorporation of the multivalent salt and the pigments in the coating formulation and typically is non-ionic. In accordance with certain embodiments, the binder may be a biopolymer such as a starch or protein. In accordance with particularly useful embodiments, the polymer may comprise biopolymer particles, more particularly biopolymer microparticles and in accordance with certain embodiments, biopolymer nanoparticles. In accordance with particularly useful aspects, the biopolymer particles comprise starch particles and, more particularly, starch nanoparticles having an average particle size of less than 400 nm. Compositions containing a biopolymer latex conjugate comprising a biopolymer-additive complex reacted with a crosslinking agent as described in WO 2010/065750 are particularly useful. Biopolymer-based binders and, in particular, those binders containing biopolymer particles have been found to be compatible with the inclusion of a multivalent salt in the coating formulation and facilitate coating production and processing. For example, in some cases coating compositions can be prepared at high solids while maintaining acceptable viscosity for the coating composition. Biopolymer binders that may find use in the present application are disclosed in U.S. Pat. Nos. 6,677,386; 6,825,252; 6,921,430; 7,285,586; and 7,452,592, and WO 2010/065750, the relevant disclosure in each of these documents is hereby incorporated by reference. One example of a suitable binder containing biopolymer nanoparticles is Ecosphere®2240 available from Ecosynthetix Inc.
The binder may also be a synthetic polymeric binder. In accordance with certain embodiments, the binder may be a non-ionic synthetic latex such as an acrylate or an acrylate copolymer. In accordance with other embodiments, the binder may be a calcium stable vinyl acetate or a styrene butadiene latex.
The binder may also be a synthetic polymeric binder such as polyvinyl alcohol, polyvinyl pyrrolidone, polyethlyene oxide, acrylates, polyurethanes, etc.
The total amount of primary binder in one embodiment is up to about 17% per 100 parts of total pigments. In another embodiment the binder is present in an amount from about 2 to about 15, more particularly about 5 to about 12, parts per 100 parts of total pigments. In accordance with certain embodiments, a binder containing biopolymer particles may be the only binder in the coating composition. In one embodiment, the binder is styrene butadiene latex. This coating is disclosed in more detail in U.S. Pat. No. 7,803,224. In another embodiment it is a stabilized anionic synthetic styrene butadiene latex binder as disclosed in U.S. Publication 2012/0212555.
In another embodiment, the coating may also include a co-binder that is used in addition to the primary binder. Examples of useful co-binders include polyvinyl alcohol and protein binders. The co-binder, when present, typically is used in amounts of about 1 to about 8 parts co-binder per 100 parts of pigment on a dry weight basis, more particularly from about 2 to 5 parts co-binder per 100 parts dry pigment. Another co-binder that is useful in some embodiments is starch. Both cationic and anionic starches may be used as a co-binder. ADM Clineo 716 starch is an ethylated cornstarch (Archer Daniels Midland, Clinton, Iowa). Penford PG 260 is an example of another starch co-binder that can be used. If a cationic co-binder is used, the amount used typically is limited so that the overall anionic nature of the coating is maintained. The binder levels should be carefully controlled. If too little binder is used, the coating structure may lack physical integrity, while if too much binder is used, the coating may become less porous resulting in longer ink drying times.
In accordance with some embodiments, the coating is substantially free (for example, no more than 0.2 parts) of any SBR latex binder that is not calcium stable.
In one embodiment the coating composition may also include a multivalent salt. In certain embodiments of the invention, the multivalent metal is a divalent or trivalent cation. More particularly, the multivalent metal salt may be a cation selected from Mg+2, Ca+2, Ba+2, Zn+2, and Al+3, in combination with suitable counter ions. Divalent cations such as Ca+2 and Mg+2 are particularly useful. Combinations of cations may also be used.
Specific examples of the salt used in the coating include (but are not limited to) calcium chloride, calcium acetate, calcium nitrate, magnesium chloride, magnesium acetate, magnesium nitrate, magnesium sulfate, barium chloride, barium nitrate, zinc chloride, zinc nitrate, aluminum chloride, aluminum hydroxychloride, and aluminum nitrate. Similar salts will be appreciated by the skilled artisan. Particularly useful salts include CCaCl2, MgCl2, MgSO4, Ca(NO3)2, and Mg(NO3)2, including hydrated versions of these salts. Combinations of the salts may also be used. The salt may be present in the coating in an amount of about 2.5 to 25 parts, more particularly about 4 to 12.5 parts by weight based per 100 total parts of pigment.
A water retention aid may also be included in the coating to improve water retention. Coatings containing multivalent ions can lack sufficient water holding capability for commercial applications. In addition to increasing water retention, a secondary advantage is that it unexpectedly enhances the binding strength of the biopolymer. Tape pulls indicate better strength in coating formulations including a retention aid. Examples of water retention aids for use herein include, but are not limited to, polyethylene oxide, hydroxyethyl cellulose, polyvinyl alcohol, starches, and other commercially available products sold for such applications. One specific example of a suitable retention aid is Natrasol GR (Aqualon). In accordance with certain embodiments, the water retention aid is present in an amount of about 0.1 to 2 parts, more particularly about 0.2 to 1 part per 100 parts of total pigments.
In accordance with some aspects, the coating composition may contain a dispersant that enables the composition to be formulated at a high solids content and yet maintain an acceptable viscosity. However, due to the particular components utilized to prepare the high solids coatings, typically used dispersants may not be suitable because they may lead to unacceptable viscosities. Examples of dispersants include Topsperse JXA (Polyether polycarboxylate, sodium salt in aqueous solution), Topsperse TSA, Rheocarb 100 (Acrylic copolymer in aqueous solution), polyoxyalkylene sodium salt (Carbosperse™ K-XP228 polymer), XP1838 (Polyether polycarboxylate, sodium salt in aqueous solution) and XP-1722 (Polyether polycarboxylate, sodium salt in aqueous solution) from Coatex, BYK-190 (Solution of a high molecular weight block copolymer with pigment affinic groups) and BYK-2010 (Acrylate copolymer with pigment affinic groups) from BYK Chemie, Polystep TD-507 (Tridecyl alcohol ethoxylate) from Stepan Chemicals, and Cartosperse K-XP228 (Polyoxyalkylene sodium salt) from Lubrizol.
In accordance with certain embodiments, the dispersant may be present in an amount of about 0.5 to 2.5 part, more particularly about 0.75 to 2 parts per 100 parts of total pigments. One class of dispersants that have been found to be suitable in certain embodiments include dispersants containing polymers with pigment affinic groups, polyether polycarboxylate salts and polyoxyalkylene salts. Additional examples include, without limitation, the following:
Other optional additives may be used to vary properties of the coating. Brightening agents, such as Clariant T26 Optical Brightening Agent, (Clariant Corporation, McHenry, Ill.) can be used. Insolubilizers or cross-linkers may be useful. A particularly useful cross-linker is Sequarez 755 (RohmNova, Akron, Ohio). A lubricant is optionally added to reduce drag when the coating is applied with a blade coater. Diglyceride lubricants are particularly useful in accordance with certain embodiments. These optional additives, when present, are typically present in an amount of about 0.1 to 5 parts, more particularly about 0.2 to 2 parts per 100 parts of total pigments.
Conventional mixing techniques may be used in making this coating. If starch is used, it typically is cooked prior to preparing the coating using a starch cooker. In accordance with certain embodiments, the starch may be made down to approximately 35% solids. Separately, all of the pigments, including the primary pigment, secondary and any supplemental pigments, may be mixed for several minutes to ensure no settling has occurred. In the laboratory, the pigments may be mixed on a drill press mixer using a paddle mixer. The primary binder is then added to the mixer, followed by the co-binder 1-2 minutes later. If starch is used, it is typically added to the mixer while it is still warm from the cooker, approximately 190° F. The final coating is made by dispersion of the mixed components in water. Solids content of the dispersion typically is from about 35% to about 60% by weight. More particularly, the solids may be about 45% to about 55% of the dispersion by weight.
Yet another embodiment relates to an improved printing paper for applying an electrically conductive ink having a paper substrate to which the coating has been applied on at least one surface. Any coating method or apparatus may be used, including, but not limited to, roll coaters, jet coaters, blade coaters or rod coaters. The coating weight is typically about 2 to about 10, more particularly about 5 to about 8, pounds per 3300 ft.2 per side, to size press, pre-coated or unsized base papers. Coated papers would typically range from about 30 lb. to about 250 lb./3300 ft.2 of paper surface. The coated paper is then optionally finished using conventional methods to the desired gloss.
The substrate or base sheet may be a conventional base sheet. Examples of useful base sheets include, Newpage 45 lb, Pub Matte, NewPage 45 lb New Era, NewPage 60 lb. Web Offset base paper, Orion, and NewPage 105 lb. Satin Return Card Base Stock, both from NewPage Corporation (Wisconsin Rapids, Wis.).
The finished coated paper is useful for application of electrically conductive inks Ink is applied to the coating to create a circuit. In one embodiment, depending on the nature of the ink, after application, the ink vehicle penetrates the coating and is absorbed therein. The number and uniformity of the coating pores result in even and rapid ink absorption, even when multiple layers of ink are applied. This coated paper may also be well suited for multifunctional printing, whereby an image on a coated paper media is created from combinations of dyes or pigmented inks from ink jet printers, toner from laser printers and inks from gravure or flexo presses.
The following non-limiting examples illustrate specific aspects of the present invention.
Coatings were prepared from the components of Table I. A40 is an anionic, precipitated aragonite, Opacarb A40 by Specialty Minerals, and serves as the primary pigment. The secondary pigment is OMYAJET B. AF 1055 refers to the plastic pigment by RohmNova, Akron, Ohio. C35 is an anionic, course CaCO3 available from Imerys Minerals Ltd., Cornwall, England. It is a supplemental pigment. The three latex polymer binders tested are Genflo 5915 styrene/butadiene latex (“5915 SBR”), Gencryl 9750 acrylonitrile latex (“9750 ACN”) and Genflo 5086 styrene/butadiene (“5086 SBR”) latex discussed above. The type and amount of latex tested is shown in Table I. ADM 716 refers to Clineo 716 (“ADM 716”) cornstarch by Archer Daniels Midland, a co-binder. Sequarez 755 is a crosslinker available from RohmNova, Akron, Ohio. Clariant T 26 OBA (“T26 OBA”) is an optical brightener by Clariant Corporation, McHenry, Ill. The ADM 716 starch was cooked and the coating prepared as described above.
OMYAJET B pigment is normally sold as cationic. Upon request, a sample was prepared by the manufacturer exactly like OMYAJET B pigment, except in an anionic form. Coatings were made from both the anionic and cationic forms of OMYAJET B pigment to determine if the ionic charge had a significant effect on the coating performance. The coating formulations are shown in Table 2. The coating weight is shown in Table 3.
Representative coating compositions include those shown in Table 4 below.
0-12.5
Having described the invention in detail and by reference to specific embodiments thereof, numerous variations and modifications are possible without departing from the spirit and scope of the following claims.
This application is a continuation-in-part of U.S. application Ser. No. 13/326,915 filed Dec. 15, 2011, which claims the benefit of U.S. Provisional Application Ser. No. 61/423,408 filed Dec. 15, 2010, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61423408 | Dec 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13326915 | Dec 2011 | US |
| Child | 14309201 | US |
