Patent Application
20080100677
This description relates to printing devices, and to related devices and methods.
Some radiation-curable, e.g., UV-curable, jetting inks are liquid at room temperature. To ensure correct jetting viscosity, those liquid radiation-curable inks are often jetted above room temperature, e.g., 30° C. or more, e.g., 40° C. Such inks can be jetted onto substantially non-porous substances, e.g., plastic pen barrels or circuit boards, or porous substrates. When such liquid radiation-curable inks are jetted onto a substrate, e.g., paper or plastic, to form an image, phenomena such as bleed-through, pinhole wetting and fisheyes due to the wetting characteristics of the liquid can result in inadequate ink coverage and overall poor print quality. One solution that is often used to reduce wicking is to treat the substrate to make it less porous. However, some inks do not perform well with such treatments. Another solution to minimizing wicking and bleed-through is to rapidly surface cure the ink, but often this does not completely eliminate wicking and bleed-through, and can require cumbersome and expensive equipment.
“Hybrid-F” radiation-curable jetting inks, i.e., those that polymerize by radical and/or cationic mechanisms to give polymer networks, are often described as “semi-solid inks,” and are more viscous at room temperature than at jetting temperature. Hybrid-F inks are available from Aellora™, e.g., under the tradename VistaSpec™ HB. Typically, these inks are jetted at elevated temperatures, e.g., above 60° C. or above 65° C., to lower ink viscosity to an appropriate jetting viscosity. After jetting hybrid-F ink, e.g., through a piezoelectric drop-on-demand inkjet printhead, ink viscosity rapidly increases as the ink cools on contact with the substrate. Once cooled to about room temperature, the hybrid-F ink does not flow without shear, allowing “wet-on-wet” printing without intermediate curing stages. Since the hybrid-F ink does not substantially flow at room temperature, wetting defects can be reduced, often reducing or eliminating the need for substrate surface treatments.
Liquid and hybrid-F radiation-curable inks typically contain inhibitors, e.g., hydroquinone (HQ) or hydroquinone monomethyl ether (MEHQ), which help to stabilize the ink, e.g., inhibit premature polymerization of the ink. Premature polymerization is problematic since it can clog small and delicate ink flow pathways and/or jetting nozzles within a print engine. While many inhibitors require the presence of oxygen to be effective, anaerobic inhibitors are also available that do not require the presence of oxygen to be effective.
Regarding the use of such inks in printing, inkjet printers are among the most common type of printers in use. Inkjet printing is a non-impact method of printing, wherein the ink is emitted from nozzles on a printhead as the printhead passes over a substrate. Typically, the printhead scans the substrate in one direction as the substrate is fed in a direction perpendicular to the movement of the printhead, whereby a strip of an image is printed as an array of individual pixels, which are deposited with each pass of the printhead.
Generally, for creating color, inkjets printers closely position different amounts of key primary colors on a substrate, which, from extended distances, merge to form any color under a process known as dithering. More specifically, inkjets printers typically employ inks made of what are referred to as the primary substractive colors, i.e., cyan, yellow, magenta and black (CYMK). The primary colors are dithered to form the entire color spectrum. Dithering breaks a color pixel into an array of dots so that each dot is made up of one of the basic colors (or otherwise left blank).
In binary color printing, perhaps the simplest type of color printing, the cyan, yellow, magenta, and black dots are either printed or not printed, with no intermediate choices. Thus, if the printed ink dots are mixed together (i.e., deposited adjacent or within close proximity to each other) to make intermediate colors, a binary CYMK printer can only produce eight possible color variations (cyan, yellow, magenta, red, green, blue, black, and white).
An alternative to binary color printing is halftone color printing, in which a printhead's dot resolution (measured in dots per inch) is divided into a grid of halftone cells, each cell including a varying number of dots. By controlling the combination of cells containing different proportions of CYMK dots, halftone printing fools the human eye into seeing a palette of millions of colors.
Another emerging method of color printing is six-color process printing which adds orange and green to the traditional CYMK. This six-color process offers finer color graduations than standard CYMK schemes. However, it should be noted that color printing is not limited to the traditional four and six-color processes discussed above, i.e. other combinations of colors may be used, e.g., three-color printing with primary subtractive colors: cyan, magenta and yellow (CMY).
In one aspect, a method of mixing inks includes conveying a predetermined volume of a first ink along a first conduit from a first ink supply to an ink pathway. A predetermined volume of a second ink is conveyed along a second conduit to the ink pathway. The first and second inks are conveyed through the ink pathway to a print head, and the first ink and the second ink are mixed together as they are conveyed through the ink pathway to form a mixed ink upstream of the print head (i.e., prior to jetting).
In another aspect, a method of mixing inks includes conveying a predetermined volume of a first ink along a first conduit from a first ink supply to a mixing station. A predetermined volume of a second is conveyed along a second conduit from a second ink supply to the mixing station. The first ink and the second ink are mixed at the mixing station to form a mixed ink prior to jetting, and the mixed ink is conveyed from the mixing station to a print head along an ink pathway.
According to another aspect, a method of mixing inks includes conveying a predetermined volume of a first ink along an ink pathway from a first ink supply to a print head. A predetermined volume of a second ink is conveyed along an ink conduit from a second ink supply to a first portion of the ink pathway upstream from the print head, and the first and second inks are mixed in the first portion of the ink pathway to form a mixed ink prior to jetting.
In yet another aspect, an ink supply includes a first ink supply module configured to store a first ink, a second ink supply module configured to store a second ink, and an ink pathway configured to transfer predetermined volumes of the first and second inks from the first and second ink supply modules to a print head. The ink pathway is configured to mix the predetermined volumes of the first and second inks as they are transferred to the print head to form a mixed ink prior to jetting.
Preferred implementations may include one or more of the following additional steps and/or features. The ink pathway can include a first portion configured to maintain the mixed ink below a first temperature. The ink pathway can include a second portion, downstream of the first portion, configured to heat the mixed ink above the first temperature as it is conveyed through the second portion. Methods of mixing ink can include heating the mixed ink as it is conveyed through the second portion such that substantially no thermal polymerization of the mixed ink occurs during the heating in the second portion. Methods of mixing ink can include heating the ink in the second portion, wherein a residence time of the mixed ink being conveyed through the second portion is less than 60 minutes. In some cases, the residence time of the ink being conveyed through the second portion is less than 30 minutes. The ink pathway can include a second portion, downstream from the first portion, configured to heat the mixed ink as the mixed ink is conveyed through the second portion such that substantially no thermal polymerization of the mixed ink occurs during the heating in the second portion. The first and/or second ink can be a solid granule powder, a semi-solid ink or a liquid ink. Methods of mixing inks can include heating the mixed ink in a second portion of the ink pathway downstream from the first portion. The first and/or second ink can include solid granules, and heating the mixed ink can include melting the solid granules of the first and/or second ink. The first ink can include solid granules including a first colorant, and the second ink can include solid granules including a second colorant different from the first colorant, and heating the mixed ink can include melting the solid granules of the first and second inks to achieve a blended color. The first and/or second ink can include a microwave energy absorbing material, and heating can be performed with microwave energy. Heating of inks can be performed with ultrasound. In some cases, the heating is performed with a thin-walled heat exchanger. Heating can be performed with microwave energy. Heating can be performed with a PTC thermistor. Heating can be performed by addition of a chemical material to the first and/or second ink. The ink can include an electrically conductive material, and the heating can be performed using an electrical current. Heating can be performed with a moving heat source. Heating can be performed with a resistive material. Heating can be performed with a fluid directed proximate the ink pathway. Heating can be performed by friction. The mixed ink can be heated to a second temperature that is greater than 50° C. The second temperature can be greater than 70° C. The heating of the mixed ink can be performed progressively such that a temperature of the ink increases as the ink travels through the second portion. The first ink can include a first colorant and the second ink can include a second colorant different from the first colorant, and mixing the first and second inks can include mixing the first and second inks in proportionate volumes to achieve a predetermined color. The first ink can be conveyed along the first conduit with vacuum pressure. The first and second inks can be conveyed through the ink pathway with vacuum pressure. The first and second inks can be conveyed through the ink pathway pneumatically. The first ink can be conveyed along the first conduit pneumatically. The first and/or second inks can be conveyed through the ink pathway peristaltically, e.g., with a peristaltic pump. The first ink and/or second ink can be conveyed by gravity. In some cases, the first and/or second ink is conveyed thermally, e.g., by a thermal gradient and/or by thermal expansion of the ink. In such cases, conveyance of the first ink and/or second ink can be at least partially controlled with a check valve. Mixing of inks can be performed with an auger. Mixing of the inks can be performed with a static mixer. The first ink can be conveyed along the first conduit with a recirculating ball-chain. The first and/or second inks can be conveyed through the ink pathway with a recirculating ball-chain. The first and/or second ink can include a radiation-curable material. The radiation that cures the radiation-curable material can be ultra-violet light. A wavelength of the ultraviolet light that cures the radiation-curable material can be between about 200 nm and about 400 nm. The radiation that cures the radiation curable material can be visible light. The radiation that cures the radiation-curable material can be provided by an electron beam device. The radiation-curable material can include a cross-linkable material, such as a cross-linkable monomer and/or oligomer. The cross-linkable monomer can include diacrylates, diarylates, or mixtures thereof. The cross-linkable monomer can include (2-hydroxyethyl)-isocyanurate triacrylate, dipentaerythritol pentaacrylate, ethoxylated trimethylolpropane, triacrylates, propoxy glyceryl triacrylate, propoxylated pentaerythritol tetraacrylate, or mixtures thereof. The first and/or second ink can include wax or resin. The first and/or second ink can include a polymerization inhibitor, such as hydroquinone. The first temperature can be less than about 25° C. The first temperature can less than about 0° C. The ink pathway can be permeable to air. The first portion can be chilled below room temperature with a chiller.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Generally, devices and methods are described that utilize ink handling systems in which in the systems can mix two or more inks prior to jetting.
Referring to
During conveyance of the mixed ink through the second portion P2, little thermal polymerization of polymerizable ink components occurs during heating. In some implementations, substantially no thermal polymerization of polymerizable components of the ink occurs during conveyance of the ink through the second portion P2, e.g., less than 0.05 percent by weight, e.g., less than 0.01, less than 0.005, less than 0.001, or less than 0.0001 percent by weight. Any thermal polymerization during conveyance of the ink can block ink flow pathways, nozzles, valves and/or filters, leading to a reduction in print quality.
Generally, the first temperature T1 is chosen, e.g., such that little or no thermal polymerization occurs in the first portion P1 while the ink passes through the first portion.
Ink pathway 18 can be formed of a permeable material to allow for oxygenation of the mixed inks. In particular implementations, ink pathway 18 can include disks 41 (
In the embodiment of
Various means of conveyance are available, for example, the inks can be conveyed; pneumatically, e.g., a positive displacement pump can be employed to deliver the first and second inks from the first and second ink supply modules (as shown in
In some instances, as described in greater detail above, the ink can be pre-heated along the ink pathway 18 prior to entering the reservoir 40, such that an ink temperature exiting the ink pathway 18 is within 15°°C. of ink residing in the reservoir 40. This minimizes the possibility that the ink in reservoir 40 is thermally shocked by the ink entering from the ink pathway 18. The ink then travels along flow path 42 to printhead 44. Controller 46 controls the jetting of ink onto substrate 12, which is traveling below the printhead 44.
Ink drop ejection is controlled by pressurizing ink with an actuator, which may be, for example, a piezoelectric actuator, a thermal bubble jet generator, an electrostatically deflected element, or a valve mechanism. Typically, printhead 44 has an array of ink paths with corresponding nozzle openings and associated actuators, such that drop ejection from each nozzle opening can be independently controlled. U.S. Pat. No. 5,265,315 describes a printhead that has a semiconductor body and a piezoelectric actuator. Piezoelectric inkjet printheads are described in U.S. Pat. Nos. 4,825,227, 4,937,598, 5,659,346, 5,757,391, and in U.S. Patent Application No. 2004/0004649. Ink on substrate 12, e.g., in the form of text or graphics, is cured with a radiation source 47, e.g., ultra-violet light or e-beam radiation. If UV radiation is used to cure the radiation-curable material, a wavelength of the light that cures the radiation-curable material is between about 200 nm and about 400 nm, e.g., a typical output from a medium pressure, metal-doped lamp, e.g., an iron-mercury lamp.
With renewed reference to
Referring now to FIGS, 5, 6 and 7, a more detailed description of the operation of a piezoelectric printhead 44 is provided. Piezoelectric inkjet printhead 44 includes jetting modules 50 and an orifice plate 52 with an array of orifice openings 53. The orifice plate 52 is mounted on a manifold 54, attached to a collar 56. The inkjet printhead 44 is controlled by electrical signals conveyed by flexprint elements 60 that are in electrical communication with controller 46 of print module 14.
Referring particularly to
Generally, suitable inks include colorants, polymerizable materials, e.g., monomers and/or oligomers, and photoinitiating systems. The polymerizable materials can be cross-linkable.
Colorants include pigments, dyes, or combinations thereof. In some implementations, inks include less than about 10 percent by weight colorant, e.g., less than 7.5 percent, less than 5 percent, less than 2.5 percent or less than 0.1 percent.
The pigment can be black, cyan, magenta, yellow, red, blue, green, brown, or a mixture these colors. Examples of suitable pigments include carbon black, graphite and titanium dioxide. Additional examples are disclosed in, e.g., U.S. Pat. No. 5,389,133.
Alternatively or in addition to the pigment, the inks can contain a dye. Suitable dyes include, e.g., Orasol Pink 5BLG, Black RLI, Blue 2GLN, Red G, Yellow 2GLN, Blue GN, Blue BLN, Black CN, and Brown CR, each being available from Ciba-Geigy. Additional suitable dyes include Morfast Blue 100, Red 101, Red 104, Yellow 102, Black 101, and Black 108, each being available from Morton Chemical Company. Other examples include, e.g., those disclosed in U.S. Pat. No. 5,389,133.
Mixtures of colorants may be employed.
Generally, the inks contain a polymerizable material, e.g., one or more polymerizable monomers. The polymerizable monomers can be mono-functional, di-functional, tri-functional or higher functional, e.g., penta-functional. The mono-, di- and tri-functional monomers have, respectively, one, two, or three functional groups, e.g., unsaturated carbon-carbon groups, which are polymerizable by irradiating in the presence of photoinitiators. In some implementations, the inks include at least about 40 percent, e.g., at least about 50 percent, at least about 60 percent, or at least about 80 percent by weight polymerizable material. Mixtures of polymerizable materials can be utilized, e.g., a mixture containing mono-functional and tri-functional monomers. The polymerizable material can optionally include diluents.
Examples of mono-functional monomers include long chain aliphatic acrylates or methacrylates, e.g., lauryl acrylate or stearyl acrylate, and acrylates of alkoxylated alcohols, e.g., 2-(2-ethoxyethoxy)-ethyl acrylate.
The di-functional material can be, e.g., a diacrylate of a glycol or a polyglycol. Examples of the diacrylates include the diarylates of diethylene glycol, hexanediol, dipropylene glycol, tripropylene glycol, cyclohexane dimethanol (Sartomer CD406), and polyethylene glycols.
Examples of tri- or higher functional materials include tris(2-hydroxyethyl)-isocyanurate triacrylate (Sartomer SR386), dipentaerythritol pentaacrylate (Sartomer SR399), and alkoxylated acrylates, e.g., ethoxylated trimethylolpropane triacrylates (Sartomer SR454), propoxylated glyceryl triacrylate, and propoxylated pentaerythritol tetraacrylate.
The inks may also contain one or more oligomers or polymers, e.g., multi-functional oligomers or polymers.
In some instances, the viscosity of the ink is between about 1 centipoise and about 50 centipoise, e.g., from about 5 centipoise to about 45 centipoise, or from about 7 centipoise to about 35 centipoise, at a temperature ranging from about 20° C. to about 150° C.
A photoinitiating system, e.g., a blend, in the inks is capable of initiating polymerization reactions upon irradiation, e.g., ultraviolet light irradiation.
The photoinitiating system can include, e.g., an aromatic ketone photoinitiator, an amine synergist, an alpha-cleavage type photoinitiator, and/or a photosensitizer. Each component is fully soluble in the monomers and/or diluents described above. Specific examples of the aromatic ketones include, e.g., 4-phenylbenzophenone, dimethyl benzophenone, trimethyl benzophenone (Esacure TZT), and methyl O-benzoyl benzoate.
An amine synergist can be utilized. For example, the amino synergist can be a tertiary amine. Specific examples of the amine synergists include, e.g., 2-(dimethylamino)-ethyl benzoate, ethyl-4-(dimethylamino) benzoate, and amine functional acrylate synergists, e.g., Sartomer CN384, CN373.
An alpha-cleavage type photoinitiator can be an aliphatic or aromatic ketone. Examples of the alpha-cleavage type photoinitiators include, e.g., 2,2-dimethoxy-2-phenyl acetophenone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-methyl-1-[4-(methylthio)phenyl-2-morpholino propan-1-one (Irgacure 907).
A photosensitizer can be a substance that either increases the rate of a photoinitiated polymerization reaction or shifts the wavelength at which the polymerization reaction occurs. Examples of photosensitizers include, e.g., isopropylthioxanthone (ITX), diethylthioxanthone and 2-chlorothioxanthone.
The inks may contain an adjuvant such as a vehicle (e.g., a wax or resin), a stabilizer, an oil, a flexibilizer, or a plasticizer. The stabilizer can, e.g., inhibit oxidation of the ink. The oil, flexibilizer, and plasticizer can reduce the viscosity of the ink.
Examples of waxes include, e.g., stearic acid, succinic acid, beeswax, candelilla wax, carnauba wax, alkylene oxide adducts of alkyl alcohols, phosphate esters of alkyl alcohols, alpha alkyl omega hydroxy poly (oxyethylene), allyl nonanoate, allyl octanoate, allyl sorbate, allyl tiglate, bran wax, paraffin wax, microcrystalline wax, synthetic paraffin wax, petroleum wax, cocoa butter, diacetyl tartaric acid esters of mono and diglycerides, alpha butyl omega hydroxypoly(oxyethylene)poly(oxypropylene), calcium pantothenate, fatty acids, organic esters of fatty acids, amides of fatty acids (e.g., stearamide, stearyl stearamide, crucyl stearamide (e.g., Kemamide S-221 from Crompton-Knowles/Witco), calcium salts of fatty acids, mono & diesters of fatty acids, lanolin, polyhydric alcohol diesters oleic acids, palmitic acid, d-pantothenamide, polyethylene glycol (400) dioleate, polyethylene glycol (MW 200-9,500), polyethylene (MW 200-21,000); oxidized polyethylene; polyglycerol esters of fatty acids, polyglyceryl phthalate ester of coconut oil fatty acids, shellac wax, hydroxylated soybean oil fatty acids, stearyl alcohol, and tallow and its derivatives.
Examples of resins include, e.g., acacia (gum arabic), gum ghatti, guar gum, locust (carob) bean gum, karaya gum (sterculia gum), gum tragacanth, chicle, highly stabilized rosin ester, tall oil, manila copais, corn gluten, coumarone-indene resins, crown gum, damar gum, dimethylstyrene, ethylene oxide polymers, ethylene oxide/propylene oxide copolymer, heptyl paraben, cellulose resins, e.g., methyl and hydroxypropyl; hydroxypropyl methylcellulose resins, isobutylene-isoprene copolymer, polyacrylamide, functionalized or modified polyacrylamide resin, polyisobutylene, polymaleic acid, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone, rosin, pentaerythritol ester, purified shellac, styrene terpolymers, styrene copolymers, terpene resins, turpentine gum, zanthun gum and zein.
Examples of stabilizers, oils, flexibilizers and plasticizers include, e.g., methylether hydroquinone (MEHQ), hydroquinone (HQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate, tert-butyl hydroquinone (TBHQ), ethylenediaminetetraacetic acid (EDTA), methyl paraben, propyl paraben, benzoic acid, glycerin, lecithin and modified lecithins, agar-agar, dextrin, diacetyl, enzyme modified fats, glucono delta-lactone, carrot oil, pectins, propylene glycol, peanut oil, sorbitol, brominated vegetable oil, polyoxyethylene 60 sorbitan monostearate, olestra, castor oil; 1,3-butylene glycol, coconut oil and its derivatives, corn oil, substituted benzoates, substituted butyrates, substituted citrates, substituted formats, substituted hexanoates, substituted isovalerates, substituted lactates, substituted propionates, substituted isobutyrates, substituted octanoates, substituted palmitates, substituted myristates, substituted oleates, substituted stearates, distearates and tristearates, substituted gluconates, substituted undecanoates, substituted succinates, substituted gallates, substituted phenylacetates, substituted cinnamates, substituted 2-methylbutyrates, substituted tiglates, paraffinic petroleum hydrocarbons, glycerin, mono- and diglycerides and their derivatives, polysorbates 20, 60, 65, 80, propylene glycol mono- and diesters of fats and fatty acids, epoxidized soybean oil and hydrogenated soybean oil.
Additional inks have been described by Woudenberg in Published U.S. Patent Application No. 2004/0132862.
Referring to
A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, while embodiments described above with respect to
