Patent Application
20070279467
In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
As noted above, ink jet printing suffers from certain limitations due to image spreading and excess liquid contents. This is substantially due to the requirement that the ink be of low enough viscosity to prevent clogging of the ink jet nozzles. It has been discovered that a certain category of inks has a high viscosity (i.e., low liquid level), but is capable of being used successfully in ink jet apparatus to take advantage of ink jet apparatus operational characteristics. Such inks for high speed/high quality printing are high solid concentration inks and exhibit shear-thinning behavior. A shear-thinning fluid is one in which the measured viscosity decreases with increasing shear rate.
It has been unexpectedly found that certain high-solids inks that exhibit shear-thinning behavior are jettable from an ink jet printhead. In view of this phenomenon, this invention is directed to ink jet printing with certain high-solids shear-thinning inks through a continuous ink jet printhead. Additionally this invention could be applied to ink jet printing through a drop-on-demand printhead if the ink is maintained in a shear-thinning state. Maintaining the shear-thinning state may be accomplished by mechanical methods. Examples of methods of agitation to maintain a shear-thinning state may include continuous ink circulation through the drop-on-demand head manifold and ultrasonic agitation of the ink in the drop on demand head manifold. This is necessary to provide the low ink viscosity required for drop ejection and fast chamber refill to support high printing speeds. Shear-thinning refers to a decrease in fluid viscosity as a fluid flows in response to an external stimuli, such as; an imposed volumetric flow rate or an applied pressure head.
Viscosity describes a material's resistance to flow; specifically it is defined as the ratio of the stress to the strain rate. In the laminar flow of fluid through a pipe or slot, the viscosity is related to the pressure drop across the bounding volume divided by the volumetric flow rate. It is useful to distinguish between fluids whose viscosity is independent of strain rate (Newtonian), and those that exhibit a viscosity that varies with strain rate (non-Newtonian). For shear deformations, the strain rate is often referred to as the shear rate and thus non-Newtonian fluids whose viscosity decreases as the shear rate increases are termed as shear-thinning fluids. Standard rheology and fluid dynamics text books, such as R. L. Mott, Applied Fluid Mechanics, (2nd Edition, Charles E. Merrill Company, Columbus, Ohio, 1972) or C. W. Macosko, Rheology, (1st Edition, Wiley-VCH, New York, 1994), detail how viscosity is related to stress and strain under different deformation conditions in shear and extension.
The phenomenon of shear-thinning is complex and manifests itself differently for different materials. Some fluids exhibit a viscosity plateau at low shear rates, followed by a region of viscosity decrease and then another plateau at high shear rates. Other materials shear thin continuously at low and moderate rates and reach a plateau at high shear rates, often termed the second Newtonian plateau. The details of the specific rheological response depend on the constituents of the fluids and their interactions.
Mathematically, these effects may be captured with an expression such as the Cross model (see Macosko, page 86):
where η is the viscosity, at a shear rate {dot over (γ)}, ηo is the viscosity at the low shear rate plateau, η∞ is the viscosity at the higher shear rate plateau, {dot over (γ)}c is the shear rate at the onset of shear-thinning, and the power law index n is the slope of the shear-thinning response. In the case where there is no observable low viscosity plateau, an expression of the following form is useful:
where {dot over (γ)}o is a material dependent shear rate and the other symbols have the same meaning as defined immediately above.
Using equation (2), the shear-thinning properties of high solids inks may be represented as shown for the ink in
The specific parameter values describing the ink rheology are:
η∞=14 mPa-s
{dot over (γ)}o=0.81/s
n=0.35
(n−1)=−0.65
Mathematically, one can calculate the slope ranges required to meet shear-thinning target lines representing the power law slopes for different n values are shown in
According to the fluids in this invention, the onset of shear-thinning occurs when the viscosity is within the range of 1 to 40 mPa-s at 1,000/s. The limiting cases are n=0 for plug flow when (n−1)=−1 and n=1 for Newtonian flow when (n−1)=0.
For proper jettability and drop breakup in a printer, the viscosity must be within a certain range, typically less than 10 mPa-s. The novelty of the present invention is that inks with low shear viscosities much larger than the cutoff dictated by the printing system may be used, if they shear thin into the proper viscosity range under the flow rates encountered during use. The shear-thinning properties of the high solids inks herein allow these materials to achieve this required viscosity condition at shear rates lower than those necessary for robust ink jet printer operation.
As known in the art, the shear-thinning behavior of a fluid can arise from particle-particle interactions, particle-liquid interactions, and interactions between soluble molecules in the fluid such as polymers. At low shear rates, the particles or molecules in the fluid associate with each other or other parts of the fluid and form a random network, resulting in a high viscosity. At higher shear rates, the shear field causes the particles or fluid molecules to disassociate and align or elongate in the direction of shear, resulting in a low viscosity.
Useful shear-thinning inks for jetting in this invention have a concentration in the range of about 20-70 wt. % solids, a viscosity between 50 and 200 mPa-s at a shear rate of about 0.1/s, and a viscosity less than 20 mPa-s at a shear rate of about 1,000/s. Preferably, the shear-thinning inks have a concentration in the range of about 30-40 wt. % solids, a viscosity between 60 and 100 mPa-s at a shear rate of about 0.1/s, and a viscosity less than 10 mPa-s at a shear rate of about 1,000/s. The following example of some shear-thinning additives is not exhaustive or meant to exclude other shear-thinning fluids that might be suitable for the ink according to this invention.
Typical examples of shear-thinning additives suitable in an ink are also particles such as organic and inorganic pigments and dyes, clays such as bentonite, hectorite, and montmorillonite, clays modified with ionic organic groups, and water-dispersible polymers.
In applications where pigments are used as the colorant in the ink, any known pigment, or combination of pigments, commonly used in an ink composition having an aqueous or non-aqueous, or solvent based carrier can be used. The pigments can be stabilized by a dispersant; for example, those pigments disclosed in U.S. Pat. Nos. 5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436 for aqueous inks; and U.S. Pat. Nos. 6,053,438; 6,133,341; 6,166,105; and U.S. Publication Nos. 2003/0192453 and 2004/0227799; for solvent based inks. Additionally, they can be either self-dispersible pigment, such as those described in U.S. Pat. No. 5,630,868, or encapsulated pigments. The exact choice of pigments will depend upon the specific application and performance requirements, such as color reproduction and image stability. Pigments suitable for use include, for example: azo pigments, monoazo pigments, diazo pigments, azo pigment lakes, β-Naphthol pigments, Naphthol AS pigments, benzimidazolone pigments, diazo condensation pigments, metal complex pigments, isoindolinone and isoindoline pigments, polycyclic pigments, phthalocyanine pigments, quinacridone pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, diketopyrrolo pyrrole pigments, titanium oxide, iron oxide, and carbon black. Typical examples of pigments, which may be used include: Color Index (C. I.) Pigment Yellow 1, 2, 3, 5, 6, 10, 12, 13, 14, 16, 17, 62, 65, 73, 74, 75, 81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100, 101, 104, 106, 108, 109, 110, 111, 113, 114, 116, 117, 120, 121, 123, 124, 126, 127, 128, 129, 130, 133, 136, 138, 139, 147, 148, 150, 151, 152, 153, 154, 155, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 183, 184, 185, 187, 188, 190, 191, 192, 193, 194; C. I. Pigment Orange 1, 2, 5, 6, 13, 15, 16, 17, 17:1, 19, 22, 24, 31, 34, 36, 38, 40, 43, 44, 46, 48, 49, 51, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69; C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22, 23, 31, 32, 38, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2, 49:3, 50:1, 51, 52:1, 52:2, 53:1, 57:1, 60:1, 63:1, 66, 67, 68, 81, 95, 112, 114, 119, 122, 136, 144, 146, 147, 148, 149, 150, 151, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 181, 184, 185, 187, 188, 190, 192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216, 220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252, 253, 254, 255, 256, 258, 261, 264; C.I. Pigment Violet 1, 2, 3, 5:1, 13, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50; C.I. Pigment Blue 1, 2, 9, 10, 14, 15:1, 15:2, 15:3, 15:4, 15:6, 15, 16, 18, 19, 24:1, 25, 56, 60, 61, 62, 63, 64, 66; C.I. Pigment Green 1, 2, 4, 7, 8, 10, 36, 45; C.I. Pigment Black 1, 7, 20, 31, 32; and C.I. Pigment Brown 1, 5, 22, 23, 25, 38, 41, 42. In one embodiment, the pigment is C.I. Pigment Blue 15:3, C.I. Pigment Red 122, C.I. Pigment Yellow 155, C.I. Pigment Yellow 74, bis(phthalocyanylalumino)tetraphenyldisiloxane or C.I. Pigment Black 7.
When a pigment dispersant is added to the ink composition, the pigment dispersant(s) can include water-soluble resins, surface-active agents, and the like. Examples of water-soluble resins include natural resins, semi-synthetic resins, synthetic resins, etc. Examples of synthetic resins include alkali-water-soluble resins such as polyacrylic acid resins, polymaleic acid resins, styrene-acrylic acid co-polymers and styrene-maleic acid co-polymers, water-soluble styrene resins, polyvinyl pyrrolidone, polyvinyl alcohol, water-soluble urethane resins, etc. Examples of surface-active agents include anionic surface-active agents, cationic surface-active agents, non-ionic surface-active agents, ampholytic surface-active agents, etc.
In the case of organic pigments, the ink may contain up to approximately 20% pigment by weight, but will generally be in the range of approximately 0.1 to 10%, preferably approximately 0.1 to 5%, by weight of the total ink composition for most ink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of pigment than with comparable inks employing organic pigments.
Instead of pigment, dye can also be used as the ink colorant. The dye can be either water-soluble or water-insoluble. The water-insoluble dye can be directly dissolved in the non-aqueous liquid carrier, or dispersed, or encapsulated into water-dispersible particles as disclosed in U.S. Pat. No. 6,867,251. A broad range of water-insoluble dyes may be used such as an oil dye, a disperse dye, or a solvent dye, such as Ciba-Geigy Orasol Red G, Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, and Ciba-Geigy Orasol Yellow. Preferred water-insoluble dyes can be xanthene dyes, methine dyes, polymethine dyes, anthroquinone dyes, merocyanine dyes, azamethine dyes, azine dyes, quinophthalone dyes, thiazine dyes, oxazine dyes, phthalocyanine dyes, mono or poly azo dyes, and metal complex dyes. More preferably, the water-insoluble dyes can be an azo dye such as a water insoluble analog of the pyrazoleazoindole dye disclosed in U.S. Pat. No. 6,468,338, and the arylazoisothiazole dye disclosed in U.S. Pat. No. 4,698,651, or a metal-complex dye, such as the water-insoluble analogues of the dyes described in U.S. Pat. Nos. 5,997,622 and 6,001,161; i.e., a transition metal complex of an 8-heterocyclylazo-5-hydroxyquinoline. The solubility of the water insoluble dye can be less than 1 g/L in water, and more preferably less than 0.5 g/L in water.
The ink jet inks of the invention can be prepared by any process suitable for preparing liquid-carrier based inks. The pigmented ink is prepared by pre-mixing the selected pigment(s) and dispersant in the liquid carrier. In the case of dyes, some of the same factors apply except that there is no dispersant present and no need for pigment de-aggregation. The dye-based ink is prepared in a well-agitated vessel rather than in dispersing equipment. Co-solvents may be present during the dispersion. The dispersing step may be accomplished in a horizontal mini mill, a ball mill, an attritor, or by passing the mixture through a plurality of nozzles within a liquid jet interaction chamber at a liquid pressure of at least 1,000 psi to produce a uniform dispersion of the pigment particles in the liquid carrier medium. The pigment dispersion will also have a small enough particle size so as not to result in clogging of typical commercial ink jet heads or nozzles. A smaller particle size is preferred since this will reduce the chance of forming aggregates that could potentially plug the ink jet printing head or nozzle. Typical pigmented inks of the invention have, a median particle size, less than about 100 nanometers. If the pigment dispersion is made in liquid carrier, it is diluted with the appropriate liquid carrier to obtain the appropriate concentration in the ink jet ink. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density, and print area coverage for the particular application.
Typical examples of shear-thinning liquid-dispersible or liquid-soluble polymers include high molecular weight homo-polymers and co-polymers of acrylic acid crosslinked with polyalkenyl polyether sold under the trade name Carbopol®, synthetic hydrophobically-modified acrylate polymers sold under the trade name Acusol®, polyurethane elastomers, homo-polymers, and co-polymers of styrene, α-methylstyrene, 2-ethylhexylacrylate, acrylic or methacrylic acid, polystyrene, high-density polyethylene (HDPE), linear low density polyethylene (LLDPE), polyethylene oxide (PEO), polyvinyl pyrrolidone, polyvinyl acetate, and polyvinyl alcohol. Other examples of shear-thinning fluids known in the art are liquid-soluble or liquid-dispersible polysaccharides, whose structure includes repeating sugar units. Examples of such polysaccharides are xanthan gum and its derivatives, guar gum and its derivatives, hydroxyethylcellulose, carboxymethyl cellulose, and alginic acid salts. Shear-thinning water-dispersible gums or resins can be either natural or synthetic. Natural gums include seaweed extracts, plant exudates, seed or root gums, and microbiologically fermented gums. Synthetic gums, such as modified versions of cellulose or starch, include propylene glycol alginate, carboxymethyl locust bean gum and carboxymethyl guar. The ink compositions useful in this invention are based upon the use of polar solvents (preferably water) that are 50%-95% by weight of the ink. Although water is preferred, other polar solvents may be used in place of up to 50% of the water.
Suitable shear-thinning additives are miscible or dispersible in the polar solvent along with the dispersed pigment particles.
For maximum compatibility with a variety of printing receivers and superior water resistance, solvent based inks can be used. Liquid carriers for solvent-based inks include both non-polar and polar solvents. Examples of non-polar solvents include straight chain or branched chain aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, and halogen-substituted products thereof. Specific examples of the solvent carrier liquid include octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, Isopar E, Isopar G, Isopar H, Isopar L (Isopar: trade name of Exxon Co.), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell Oil Co.), Amsco OME and Amsco 460 (Amsco: trade name of Spirits Co.), and mixtures thereof. Examples of non-polar solvents include fatty acids, esters, alcohols, and ethers. Examples of fatty acids include isopalmitic acid, oleic acid, and isostearic acid. Examples of esters include methyl laurate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, methyl linoleate, isobutyl linoleate, ethyl linoleate, isopropyl isostearate, soybean oil methyl ester, soybean oil isobutyl ester, tall oil methyl ester, tall oil isobutyl ester, diisopropyl adipate, diisopropyl sebacate, diethyl sebacate, propylene glycol monocapric ester, trimethylolpropane tri-2-ethylhexanoic ester, and glycerol tri-2-ethylhexanoic ester. Examples of alcohols include isopalmityl alcohol, isostearyl alcohol, and oleyl alcohol. Examples of ethers include glycol ether-based solvents, such as diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and propylene glycol dibutyl ether.
The ink may form a permanent image upon irradiation of UV light, and contain polymerizable oligomers, stabilizers, photoinitiators, colorants, and other ink jet components that are commonly known in the art for formulating UV curable inks. UV curable urethane resins, acrylic resins, polyester resins, and epoxy resins suitable for use in the invention are known in the art. Examples of suitable UV curable resins include, but are not limited to, those urethane resins described in U.S. Pat. Nos. 5,596,065 and 5,990,192; which are incorporated by reference herein in their entirety, and polyester resins described in U.S. Pat. No. 6,265,461, which is incorporated by reference herein in its entirety. The UV curable ink composition may contain up to 100% solids. The UV curable ink can contain less than 100% solids, in which case the components are dispersed in the liquid carrier. The dispersible UV curable resins will also have a small enough particle size so as not to result in clogging of typical commercial ink jet beads or nozzles. A smaller particle size is preferred since this will reduce the chance of forming aggregates that could potentially plug the ink jet printing head or nozzle. Typical UV curable resins of the invention have a median particle size, less than about 100 nanometers. Curing of the image formed from the ink jet ink composition can be initiated via a source of UV light. That is, while curing can be initiated by naturally occurring UV light, normally, a man-made source of UV is employed; e.g., to crosslink the polymeric matrix.
Agents to control pH may also be included in the ink, if desired. Examples of such pH controlling agents suitable for inks of the present invention include, but are not limited to: acids; bases, including hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide and potassium hydroxide; phosphate salts; carbonate salts; carboxylate salts; sulfite salts; amine salts; amines such as diethanolamine and triethanolamine; and mixtures thereof and the like.
Additionally, the ink may contain additives such as organic solvent material capable of penetrating into the receiver to act as a drying agent, defoamers, corrosion inhibitors, surfactants to tune the surface tension, viscosity modifiers, biocides, sequesterants, and humectants, all commonly known in the art for formulating inks. It is understood that the optimal composition of such an ink is dependent upon the jetting method used and on the nature of the receiver to be printed on.
The ink is applied to a suitable receiver in an image-wise fashion. Application of the ink to the receiver can be by any suitable ink jet process compatible with the ink composition, such as CIJ and DOD ink jet printing as discussed above.
The ink composition of the present invention is suited for printing on a variety of receivers of both absorbing and non-absorbing types. A wide variety of receivers can be used in the practice of the present invention; e.g., papers, fabrics, polymeric films, cellulosic films, glasses, metals, sintered metals, woods, carbon-based materials, ceramics, and the like. Many ink receiving elements commonly used in ink jet printing can be used. The support for the ink receiving element can be paper or resin-coated paper, plastics such as a polyolefin-type resin or a polyester-type resin such as poly(ethylene terephthalate), polycarbonate resins, polysulfone resins, methacrylic resins, cellophane, acetate plastics, cellulose diacetate, cellulose triacetate, vinyl chloride resins, poly(ethylene naphthalate), polyester diacetate, various glass materials, etc., or an open pore structure such as those made from polyolefins or polyesters. Exemplary papers contemplated for use in the practice of the present invention include ragbond papers, coated papers (e.g., matte papers, semi-gloss papers, clear film papers, high-gloss photographic papers, semi-gloss photographic papers, latex papers, color ink jet papers, presentation papers, and the like), heavy coated papers, opaque bond papers, translucent bond papers, vellum, papers treated for ink, dye or colorant receptivity, and the like. Of course the ink composition is also suitable for printing on any well-known intermediate member for subsequent transfer to a receiver (see U.S. Pat. No. 6,409,331).
Fabrics contemplated for use in the practice of the present invention include any fabric prepared from fibers which (naturally or by post-treatment) contain free hydroxyl and/or free carboxyl groups. Exemplary fibers from which suitable fabrics can be prepared include 100% cotton, cotton/polyester blends, polyesters, silks, rayons, wools, polyamides, nylons, aramids, acrylics, modacrylics, polyolefins, spandex, saran, linens, hemps, jutes, sisals, latexes, butyl rubbers, vinyls, polyamide fibers, aluminum, stainless steel, fabrics treated for ink, dye or colorant receptivity, and the like, as well as combinations of any two or more thereof. The non-absorbing receivers that may be used in the present invention include any receiver that is essentially non-porous. They are usually not specially treated for additional liquid absorption. Therefore, these materials have very low or no liquid absorbing capacity. Examples of such non-absorbing receivers are plastics such as vinyl, polycarbonate, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polystyrene, cellulose; and other receivers such as ceramics, glass and metals such as aluminum, copper, stainless steel and metallic alloys.
The following examples illustrate the utility of the present invention.
Formation of stable drops in an ink jet apparatus using a high percent solids, shear-thinning ink.
A gravure ink from Flint Group, called Arrowvure 5 Cyan Blue® was used in the jetting experiment. The ink contained 34.44% solids, a surface tension of 31.7 dynes/cm, a pH of 9.46 and a median particle size of 0.105 microns as measured by light scattering using a Microtrac® UPA 150 instrument. The rheology of the ink was measured with an Advanced Rheometric Expansion System (ARES®) rheometer by Rheometric Scientific. This instrument controls strain (rotational velocity in a given geometry) and measures stress (torque). The testing geometry used to analyze the sample was a large Couette (concentric cylindrical bob in cup) with a cup diameter of 34 mm, a bob diameter of 32 mm, a bob length of 33.4 mm, and bob height above cup bottom of 4.0 mm. Steady shear rate sweeps were performed at the desired test temperatures of 25° C. and 50° C. For the 50° C. runs, the sample was rapidly preheated to approximately 50° C. prior to loading into the temperature-equilibrated geometry. To remove any residual structure in the fluid, a pre-shear sweep of 100/s to 400/s was used, with a 3 second delay at each rate followed by a 3 second measurement in both rotational directions. The subsequent rate sweep was performed under the same measurement and delay conditions progressing from 0.1/s to 1,000/s. The auto-range option for the transducer was enabled to change the sensitivity from 10 g-cm to 100 g-cm of torque during the measurement as needed. Table 1 gives the viscosity of the ink equilibrated at 25° C. and 50° C. before testing at shear rates from 0.1/s-1,000/s. The data in Table 1 shows that the ink is shear-thinning at both temperatures. As shown in Table 1, increasing temperature reduces the ink viscosity. This temperature effect can be used in combination with the shear-thinning effect, upon equilibrating the ink, to adjust (control) the desired ink viscosity. The data from Table 1 is graphically represented in
A continuous ink jet apparatus similar to a device utilizing nozzles 1 (one shown) and circuit diagram 21 shown respectively in
The ink was pre-filtered through a 6.0 μm Pall® cylindrical filter before jetting through the ink jet head device. The pressure on supply vessel was set to 35 psi. A Hewlett Packard waveform generator provided heater pulses, and a Fluke Multimeter was used to measure heater resistance. A test stand for the continuous ink jet device was fitted with a camera, strobe, and video system. A strobe light was adjusted to view drops on a video monitor. The frequency was set to 100 KHz with a duty cycle set to 10% (pulse width near 1.0 μm). The voltage pulses were applied to the ink jet head device heaters to form drops and the drop formation from the single nozzle device was observed. With the voltage set to 7.0 volt peak, the vessel pressure was adjusted to 30-70 psi until the straight jets were observed. The voltage, frequency, and pressure were varied to determine the effect of these variables on the device range.
Table 2 shows the effect of frequency on ink drop volume at an operating pressure of 65 psi.
In the jetting test, drops were formed from the fluid when frequencies of 50 kHz, 150 kHz, and 200 kHz were applied. These frequencies provided enough difference in drop size for the ink jet head device to deflect unwanted small drops and to print with the large drops. The velocity of the drops was approximately 15 m/s at 65 psi. Each jet delivered 1.025 g/min. at an operating pressure of 65 psi. The voltage necessary for stable drop formation was 6.8 volts. The jetting test in this Example 1 continued to jet for more than 40 minutes without clogging the nozzles.
Formation of prints on various receivers from an ink jet apparatus using high-percent solids, shear-thinning ink.
The ink used was the same ink as described in Example 1, except 2 wt. % Dapro DF-1760 defoamer (from Elementis Corp.) and 5 wt. % glycerol were added. The final ink contained 30.17 wt. % solids, a surface tension of 32.0 dynes/cm, a pH of 9.38 and a median particle size of 0.0964 microns. Table 3 gives the viscosity of the ink equilibrated at 25° C. at shear rates from 0.1/s-1,000/s. The data in Table 3 show that the ink is shear-thinning at a temperature of 25° C.
The receivers shown in Table 4 were used upon which to print the ink in Example 2:
The ink was pre-filtered through a 1.2 μm Pall® cylindrical filter before jetting though the ink jet head device. A continuous ink jet apparatus similar to the device described above, utilizing the printing system with nozzles 52′ and printhead 30, shown in
The transport system shown in
Ink is contained in an ink reservoir 40 under pressure. In the non-printing state, continuous ink jet drop streams are unable to reach receiver 32 due to an ink gutter 42 that blocks the stream and which may allow at least a portion of the ink to be recycled by an ink-recycling unit 44. The ink-recycling unit 44 reconditions the ink and feeds it back to ink reservoir 40. Such ink recycling units 44 are well known in the art.
The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir 40 under the control of ink pressure regulator 46. The ink is distributed to the back surface of printhead 30 by an ink channel device 48. The ink preferably flows through slots and/or holes etched through a silicon receiver of printhead 30 to its front surface, where a plurality of nozzles and heaters (such as one shown in
At least one nozzle 52′ (two shown in
A heater 66′ is at least partially formed, or positioned, on printhead 30′ around a corresponding nozzle 52′. Although heater 66′ may be disposed radially away from an edge of the corresponding nozzle, the heater is preferably disposed close to edge of corresponding nozzle in a concentric manner. In a preferred embodiment, heater 66′ is formed in a substantially circular or ring shape. However, it is specifically contemplated, and therefore within the scope of this disclosure, that heater 66′ may be formed in a partial ring, square, or other suitable shape. Heater 66′ includes an electric resistive heating element electrically connected to contact 68 via conductor 70. Conductor 70 and contact 68 may be at least partially formed or positioned on printhead 30′ and provide an electrical connection between controller 38′ and heater 66′. Alternatively, the electrical connection between controller 38′ and heater 66′ may be accomplished in any well-known manner. Additionally, controller 38′ may be a relatively simple device (a power supply for heaters, for example) or a relatively complex device (logic controller, programmable microprocessor, for example) operable to control many components in a desired manner.
Referring to
Gas source 74 of droplet deflector system 50′ includes a gas pressure generator 76 coupled to a plenum 78 having at least one baffle 80 (a plurality shown) to facilitate laminar flow of gas through plenum 78. An end of plenum 78 is positioned proximate path X. A recovery plenum 82 is disposed opposite plenum 78 and includes at least one baffle 84 (a plurality shown). Additionally, baffle 84 includes catcher surface 86 defined on a surface thereof proximate path X. Alternatively, a surface of recovery plenum 82 may define a catcher surface thereon. An ink recovery conduit 88 communicates with recovery plenum 82 to facilitate recovery of non-printed ink droplets by an ink recycling unit 44′ for subsequent use. Additionally, a vacuum conduit 90, coupled to a negative pressure source 92, can communicate with recovery plenum 82 to create a negative pressure in recovery plenum 82, improving ink droplet separation and ink droplet removal. In operation, a print media W (receiver), or intermediate image-receiving web, is transported in a direction transverse to path X by a drive roller 94 and idle rollers 96 in a known manner. Transport of print media W is coordinated with operation printhead 30′ to produce a desired image thereon. This can be accomplished using controller 38′ (
The ink in this example was printed with the above described ink jet printing apparatus on each of the four receivers described in Table 4. After printing, all receivers contained images that exhibited excellent adhesion, excellent durability to dry, rub resistance, and excellent image quality.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
