High viscosity heat sensitive ink

[0001] The present invention relates to an ink containing heat-activated dyes.

BACKGROUND OF THE INVENTION [0002] Digital jet printing is commonly used for many applications. Thanks to better image quality compared to conventional analog technologies such as offset printing, screen printing, lithographic printing, digital stream printing technologies, the results are more convenient, more efficient and more environmentally friendly.

[0003] However, digital printing with aqueous ink on non-paper materials may be worse than other processes, due to the lack of color intensity and speed, which is due to some shortcomings of digital stream printing methods. These include the fact that water-based inks with low viscosity and low pigment content, and especially with small droplet size, require a much larger amount of ink to produce a comparable final image. This is a bigger problem when the dyes used in the inkjet ink are not soluble dyes, but pigments or other insoluble dyes. High color saturation and so-called color supersaturation may be difficult to achieve when using these inkjet inks.

[0004] One way of producing an aqueous ink is to add viscosity regulating agents that are high molecular weight real artificial polymers, water-soluble or water miscible glycols with higher viscosity, higher alcohols accompanied by a higher concentration of dyes. There are several problems associated with such a simple approach. The use of high molecular weight polymers can lead to an aqueous system that deviates from the physical properties required by the inkjet printer used for printing with the ink, such as the preservation of the Newtonian fluid. This ink therefore reacts improperly to the jet mechanism. A high molecular weight polymer combined with an increased content of dyes, especially of the insoluble type, can cause blockages in the nozzles of the print head,

[0005] Hot-activated dyes have been used in digital inkjet printers. The image quality depends on how effectively and efficiently the hot-activated dyes are transferred to the substrate or bound to it. Hale et al., US Patent No. 5,642,141, and Xu et al., US Patent No. 5,488,907, disclose methods for inkjet printing using finely divided hot activated solid pigments. These methods include an ink typically having a viscosity of about 2 to 4 mPa.s (cP) at ambient temperature. These patents do not specifically disclose how to produce an ink with high transfer efficiency and relatively high viscosity using hot-activated dyes.

[0006] High-viscosity inkjet inks can cause further problems for hot-activated inks when the dye concentration is high. Agents for regulating or modifying the physical properties of the ink may reduce the efficiency of activating the dye by heat, due to the high boiling points, affinity to the hot-activated dye at the activation temperature or the closure / encapsulation of the dye particle due to

EP 2837665 B1 long-chain polymeric structure of the reagent / agent. These problems may be more pronounced when the particle size of the dyes used in the inks will be very small. For example, a high concentration of glycerin may alter the efficiency of hot activation of a small pigment particle at normal temperature and at the normal duration of the hot activation. In addition, a thickener such as carboxymethylcellulose (CMC) can form a non-Newtonian system, at the same time also hindering the activation or sublimation of a heat activated dye.

[0007] Inkjet printheads, including drop-on-demand ("DOD") piezoelectric heads, have nozzles and openings of varying sizes. These nozzles and openings dictate the droplet size, printing speed and viscosity of the firepable ink, as well as the tolerance to insoluble dyes or polymeric particulates. A suitable particle size range with respect to the size of the nozzle or opening is important when formulating heat activated inks with increased viscosity.

Document US 6284004B1 discloses inks that use a dispersion dye. The disclosed inks are not suitable for producing high quality images in a modern large format inkjet printer head. Document WO 2008 / 103424A1 discloses inks that do not contain hot-activated dyes that require dissolution. Document US 2005 / 199152A2 discloses a carcass in which the particle size of the components is not disclosed.

[0008] There is a need for an increased viscosity mascara comprising hot-activated solid pigments for digital printing, including decal or direct print, which ink will not clog the print head, give high heat-activating efficiency and be environmentally safe, and which is suitable for high-viscosity inkjet printers, i.e. printers requiring a liquid ink with a viscosity of at least 5.0 mPa.s (centipoises, cP) at ambient temperature.

SUMMARY OF THE INVENTION [0009] The present invention provides an inkjet ink according to claim 1.

[0010] The present invention is a high inkjet ink which is useful for printing images with hot activation using image printers, such as drop-on-demand piezoelectric printers. The ink contains hot-activated dye particles that are not activated during the inkjet printing process, and are printed onto the image-containing substrate, which can be activated and transferred to the next or final substrate by applying heat and adhering to the two substrates. The ink may also be heat-activated on the substrate without further handling, by applying heat at a temperature suitable for activating the dye.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0011] The present invention is an inkjet liquid ink having a preferred viscosity of not less than 5 mPa.s (cP) and a viscosity of 6 to 100 mPa.s (cP) with a total water content not less than than 30% by weight the combined ink formulation. The preferred viscosity range is from 7 mPa.s (cP) to 30 mPa.s (cP). The hot-activated dye is present in the ink during printing in particulate form. A specific amount of dye (s) is provided to achieve at the time of hot activation

EP 2837665 B1 suitable intensity of color and image quality. The dye is preferably from 1% to 15% by weight. the combined ink formulation.

These materials have a low tendency to dissolve heat activated pigments or do not show them at all. In addition, these solvents, co-solvents or viscosity control agents will not substantially alter the behavior of the Newtonian (incompressible) water system fluid. This behavior can be expressed by the following equation:

<img file="PL2837665T3_D0001.tif" />

with a contributing stress strainer P (also designated as σ)

<img file="PL2837665T3_D0002.tif" />

where

Tj is the shear stress on the i-th surface of the liquid element in the direction j-th and i is the velocity in the direction i-th xj is the y-th coordinate direction.

[0013] Other materials that can be used to regulate viscosity are polypeptides such as an abietic soy polypeptide, an undecylenyl soy polypeptide, an alcohol / glycol soluble prolamine, a fatty alcohol ethoxylate, an oily fatty amine, acrylamide, homopolymers, copolymer and / or terpolymers 2- etylooksazoliny.

[0014] Depending on the specific viscosity requirements of the printer and / or the printhead, the viscosity-regulating solvents / co-solvents may weigh at least 20 times the number of hot activated dyes in the combined weight of the ink formulation, while maintaining high viscosity and firepower. The total content of the viscosity-regulating solvents / co-solvents may be between 15% and 60% by weight. the entire formulation.

[0015] Other components may be used to stabilize the dye and to accurately control the physical properties of the ink, such as surface tension, pH value, conductivity and density. Also,

Heat-stained dyes and other dyes may be used in combination with hot-dye / dyes to improve image quality and properties in certain applications. Self-dispersing dyes and / or pre-stabilized dyes may also be used.

[0016] Aqueous inkjet inks with the desired viscosity may have different stabilizing requirements due to changes in physical properties such as ink density, particle motion of the particulate matter and electrical conductivity. These changes have an effect on the particle size distribution profile, and in particular on the requirement for an upper limit of the particle size distribution. The following empirical equation can be used as an aid in choosing the upper limit of the particle size distribution if the particle size distribution does not differ significantly from the normal distribution model:

φ&gt; (SD)³1- / where

Φ indicates the narrowest ink path inside the print head, such as nozzle / hole diameter (in micrometers)

D is the particle size represented as 95% of the total particle size distribution (in micrometers) f is the mass fraction of the dye in the total weight of the formulation (&lt;1).

[0017] For example, a 35μm / micrometer nozzle printhead indicates a particle size (diameter), with a distribution of 95%, equal to or less than 0.62 μm (micrometer) if the dyes constitute 5% of the total weight. This pattern helps to obtain ink that does not seize a narrow path inside the print head.

[0018] Hot-using dyes suitable for use may contain various suspension dyes or sublimation dyes which are activated or sublimed by supplying heat to the substrate or transfer substrate to be heat-treated. Typically, the hot activation temperature does not exceed 505 K (450 ° F), and most preferably does not exceed 483 K (410 ° F). Examples of dyes, in various proportions, include, but are not limited to, Disperse Orange 13, 29, 31: 1, 33, 49, 54, 55, 66, 73, 119 and 163; CI Disperse Red 4, 11, 54, 60 72, 73, 86, 88, 91, 92, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167: 1, 177, 181, 204, 206, 207, 221, 258, 278, 283, 288, 311, 323, 343, 348 and 356; CI Disperse Violet 33; CI Disperse Blue 4, 13, 56, 73, 113, 128, 148, 154, 158, 165, 165: 1, 165: 2, 183, 197.201, 214, 224, 225, 257, 266, 267, 287, 358, 359, 360, 379, Disperse Brown 26, 27; and Disperse Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184: 1, 186, 198, 199, 204, 224 and 237. Dependent from a specific application, it is also possible to use other organic and inorganic pigments as well as soluble and insoluble pigments, such as direct dyes, acid dyes, reactive dyes, vat dyes, cationic dyes, alkaline dyes, luco dyes and thermochromic and photochromatic dyes.

[0019] For the dye to be activated hot or sublimated, it will remain in the form of solid particles. This is not a significant problem for water-insoluble dyes, such as sublimation dyes, in less viscous applications where little is used

The use of glycol or other viscosity-enhancing agent is not used at all. The difference between the boiling point of the water and the hot ink activation temperature, typically greater than 27.8 K (50 ° F), indicates that the activation or sublimation of the ink solids will occur after evaporation of the aqueous components such that activation or sublimation is not materially hindered these mascara ingredients.

[0020] A relatively high concentration of glycols, polyol and other high boiling viscosity regulating components can produce a high boiling system that will make the activation or sublimation of the dyes very difficult. The boiling point may be close to or even higher than the heat activating temperature of the dye, such as within 11.1 K (20 ° F) of the hot activation temperature. Particles with smaller diameters may temporarily or even permanently bind to this component and fail to activate, due to hydrogen bonding, closure or forming a co-boiling system at very high boiling points. The ability to dissolve the non-polar part of these components can also contribute to the binding of the dye, especially the external part of the dye solids at a temperature close to the boiling point of these solvents or agents. Only internal parts of the dye particles that are not in contact with the &amp; quot; bulk &amp; quot; ink components can be activated or sublimated.

[0021] In a certain embodiment of the invention, the particle size of the hot-activated dyes is limited in that a sufficient number of dye molecules can be activated or sublimated. The following model indicates the size of the dye particles:

<img file="PL2837665T3_D0003.tif" />

where d is the minimum diameter of the particle (in micrometers), ensuring the efficiency of hot activation K

K means the efficiency of hot activation (K &lt;1)

Ts is the size of the hot-dye dye molecule in the longest dimension (in nanometers, usually Ts = 1.25) and denotes the dissolution-binding parameter, in the case of high viscosity inks, and&gt; 1.

In the case of relatively high viscosity carcasses containing more than 20% by weight high viscosity solvent a = 3, means that about three layers of dye molecules can be bound. Thus, the relationship between the size of the particle and the efficiency of hot activation can be expressed as:

<img file="PL2837665T3_D0004.tif" />

where d is the minimum diameter of the particle (in micrometers), ensuring the efficiency of hot activation K

K means the efficiency of hot activation (K &lt;1).

[0022] An embodiment of the invention has a heat-activating effect for particulate dyes greater than 65% (K). Essentially, all dye particles with a diameter of less than 50 nanometers are excluded from the ink. The low transfer efficiency to these solid particles due to the high concentration of solvents regulating viscosity is therefore largely eliminated.

[0023] The present invention can be used with inkjet inks in continuous ink jet printing systems, thermal or dot drop printing, "drop on demand" piezoelectric printing, ultrasonic or mechanical inkjet printing. The physical properties of the ink can be adjusted according to the requirements of the particular print head. A preferred inkjet printer according to the invention is an RICOH GELSPRINTER® inkjet printer, designed for printing with OEM inks having a viscosity of around 7. This printer is known in the industry as a high viscosity inkjet printer. Inkjet printers designed for inks with a viscosity of 5.0 mPa are preferred^.s or more.

[0024] Hot activation is carried out in accordance with known processes for activating hot dyes. For activating or carrying inks containing sublimation dyes, for example, a heat press can be used, according to Hale's instructions, US Patent No. 5,488,907. [0025] The following examples illustrate the general composition of the high viscosity hot-activated viscosity ink.

Example 1:

[0026] Ink with a viscosity of approximately 7.5 mPa.s (cP) for use in the Ricoh GelSprinter® inkjet printer, nozzle size 35 μm (micrometres):

<td>Component</td><td>wt%</td>

<td colspan="2">Blue suspension dye (pre-stabilized) 3.5%</td>

<td>Glycerine</td><td>40%</td>

<td>Poly (2-ethyl-oxazoline)</td><td>2%</td>

<td>Non-ionic surfactant</td><td>3.5%</td>

<td>Proxel® GXL</td><td>0.1%</td>

<td>Other means</td><td>2.0%</td>

<td>Demineralized water</td><td>rest</td>

[0027] The ink of this example is made with an upper limit (95%) of particles 0.3 μm (micrometer) and a lower limit of 0.05 μm (micrometer). The image decal printed in ink on a polyester fabric using a temperature of 478 K (400 ° F), with hot activation for 35 seconds, gives an optical density (blue-green) of 1.25 or more as measured by an X-Rite densitometer.

Example 2:

Ink with a viscosity of about 15cP for use in a Spectra Skywalker inkjet printer, nozzle size 45 micrometres:

EP 2837665 B1

Ingredient% wt.

Mixture of disperse dyes (pre-stabilized) 5.6% CAB-O-JET® aqueous suspension of black pigment 1.5%

Diethylene glycol 20% ε-caprolactam 15%

Non-ionic surfactant 3.5%

Proxel® GXL 0.1%

Other measures 2.0%

Demineralised water residue [0029] This ink has an upper limit of particles (95%) of 0.6 μ ^ιη (micrometers) and a lower limit of 0.05 μ ^ιη (micrometers). Direct printing on a polyester / cotton blend (50/50) with hot dye activation at 483K (410 ° F) for 30 seconds, gives an image with an optical density of 1.30 or more as measured by an X-Rite densitometer.

EP 2837665 B1