Ink jet dye discharge printing for fabrics

WO 2015/025310 A1
Dye discharge inkjet ink compositions
Kornit Digital Ltd.

Dye discharge printing is a method of forming a design on a dyed fabric by printing onto this surface a colour-destroying (dye discharging) agent to create a white or light pattern. This discharge ink can also include a colorant that is unaffected by the discharge chemistry, thereby allowing light, vibrant colours to be printed onto darkly dyed backgrounds, with perfect registration.

An alternative approach to dye discharge printing, often used for printing onto dark coloured T-shirts, is one in which a thick opaque white background ink is first applied to the fabric before the subsequent colours. Although this is a cost effective and relatively simple approach, the resultant fabric can have a compromised feel due to the quantity of materials deposited on the surface. In comparison, dye discharge printing “removes” colorants resulting in a fabric with a soft hand-feel in the printed areas and so is often used for more luxurious fabrics.

A common discharge agent is zinc formaldehyde sulfoxylate (ZFS) that, although effective, has a short pot life of around a working day. Solutions of this material tend to degrade into insoluble side products of zinc oxide and zinc sulphide which can go on to block ink jet printheads. A discharge ink suitable for ink jet printheads would have to be stable for months, and ideally a year, to be useful. This patent suggests that this can be achieved with the ZFS discharge agent if it is formatted with an excess of a complexing agent such as ethylene diamine tetra acetic acid (EDTA ).

Specifically the ratio of the ZFS:EDTA should be less than 0.6:1 to achieve lifetimes of greater than 1 month and, in some cases, up to one year. This combination was formulated into an ink jet ink formulation with 7 wt% ZFS, 18.9 wt% EDTA , 37.2 wt% various humectants, 0.2 wt% surfactants, enough acetic acid to neutralise/buffer and water to make up. This was loaded into a “Kornit Avalanche” T-shirt printer and used to print onto a black T-shirt at various levels from 30 to 100%. As the black T-shirt used was not pre-bleached before dying, the base colour of the cotton is a light brown colour, requiring a small amount of a white ink to bring the colour towards pure white.

The exemplified test print demonstrates that a good white can be achieved on black T-shirts at significantly lower pigmented white ink levels.

Ink jet wallpaper media from HP

WO 2014/120149 A1
Printable medium
Hewlett-packard Development Company L.P.

Wallpaper and other wall covering papers are used both for decorative and display purposes. One function of the paper will be to conceal cracks and other imperfections in the underlying surface, so it is important that it should have a high degree of opacity. This is achieved by using a laminated structure in which an adhesive is tinted with a dark-coloured opaque pigment or dye and is sandwiched between two sheets of paper. In fact, several layers can be laminated in this way if necessary. The laminated structure is shown in the diagram.

Aug-14At the core of the laminate is an opacity enhancing adhesive layer (110) that can be from 2-50 μm in thickness. On either side of this is a paper layer (104, 108). This part of the structure forms the basic substrate, which will have 150 to 400 μm thickness and a weight of 100-500 gsm. On the top or outer surface of the paper adjacent to paper 104 is a printable image receiving layer (106) while a glue layer (118) may be positioned on the reverse surface adjacent to paper 108.

The paper layers are composed of a mixture of wood pulp and synthetic fibres and may also contain fillers, which in themselves will impart a certain degree of opacity. The paper will be dimensionally stable with a machine direction to cross direction tensile stiffness that is less than 2.5 and with hydroexpansibility of less than 1%.

The light blocking adhesive layer will contain up to 3% of a light absorbing pigment or dye for which the lightness (L*) will be around 30, giving a dark colour. So light will consequently be blocked from passing through the paper, giving an opacity defined as i(x)/io ≤ 0.05 where i(x) is the light intensity at distance x from the surface of the substrate where the light intensity is io. Any black or dark coloured pigment or dye is suitable, for example direct black dyes such as Pergasol black BTB or carbon black pigments such as irgalite black 2BL. The adhesive itself, which can be cross-linkable for improved hardness, may be an aqueous polymer emulsion such as polybutadiene or styrene-butadiene or it may be a solution polymer in which case the solvent can be aqueous or organic.

Finally, the ink receiving layer is coated on the surface of the substrate and comprises pigments and a polymeric binder. Provision is also made for a latex ink film-forming agent, such as a citrate of a glycol polymer.

An exemplary paper showed superior physical properties (tear and tensile strength, hydroexpansion and taber stiffness) in comparison to HP PVC free wallpaper.

Hewlett Packard’s microwave-curable media coating

WO 2013/062510 A1
Inkjet recording medium, and method of using the same
Hewlett-Packard Development Company, L.P.

Over the years, much effort has been put into improving the image stability and gloss of photo prints.  Here, ink passes through a porous top coating which is subsequently made to be non-porous, so providing both image protection in the form of wet and dry rub resistance along with good levels of gloss and image distinctness.

The substrate can be any typical medium such as paper, olefin coated paper or polymer film.  It is first coated with an ink receiving coating that will absorb fluid from the ink.  This is a typical porous coating and primarily consists of a porous pigment and a binder.

Protection is given to the image by the particulate-based reactive coating applied above the porous coating.  This is in itself porous to the ink and so the ink will pass through it and be absorbed in the ink receiving coating.  After printing, barrier properties are created by exposure to microwave radiation which will cause cross-linking of some of the particles and coalescence of others.  This is shown in the figure in which ink (26) is shown absorbed in the ink absorbing layer (14), having almost entirely passed through the protective coating (16).

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The coating is applied as a latex in which both reactive and non reactive particles are dispersed.  Suitable reactive polymers include those with epoxy functionality, and those with fatty acid, alkoxy-silane, acetoacetoxy, hydroxyl, amine or carboxyl functional groups.  Self cross-linking polymers can be used or a cross-linking agent can be included.  The uncured particles (0.2 to 10 µm) should have good mechanical stability (Youngs Modulus 600 to 3000 MPa) at a temperature below 110C.

A polar microwave radiation cure promoter may also be included.  This acts to strengthen the dipole relaxation effect in which particles turn or rotate with some lag as the dipole direction changes at high frequency.  Heat is also generated which is helpful to both the curing and coalescence processes.  Suitable agents are calcium acetate monohydrate, calcium propionate and calcium propionate hydrate.  Exposure to microwaves also induces coalescence of the non reactive polymer particles which are generally hydrophobic polymers such as PTFE or hydrocarbon waxes.  It appears that much or all of the coalescence and cure processes will take place at temperatures exceeding 110C.

These media appear to be suitable for most types of aqueous, solvent or latex ink and can be applied using more or less any mode of ink jet.  Microwave exposure can be carried out either in-line or off-line at a frequency of 0.3 to 300 GHz.  Exposure time should be from around 10 seconds to 4 minutes, although the longer times would seem impractical.

Ink jet films for medical imaging

US 2012/0107528 A1
US 2012/0107529 A1
US 2012/0107532 A1
Transparent ink-jet recording films, compositions, and methods
Carestream Health, Inc.

In recent months, Carestream Health (formerly Eastman Kodak’s Health Group) has been particularly active in the field of high quality coatings for transparent film that are designed to give excellent resolution and to accommodate a wide range of optical densities, so making them suitable for medical imaging purposes. These three patents address the problem of detection of transparent media in printers such as the Epson Model 4900, that rely on optical detection of media in order to determine the area printed. As these printers are designed to produce borderless images, they use optical sensors to detect the location of the leading edge of the media sheet, relying on reflection from a white or opaque paper. The solution presented is to incorporate a small amount of a white or reflective pigment particulate material either in a back coating or in one or more layers of the front recording surface.

As previously described, the substrate is a polyester film such as PET and may be blue-tinted. It is coated on one side with a primer or under layer on top of which one or more polyvinyl alcoholbased ink receiving layers is deposited. These coatings may also contain the inorganic pigment boehmite alumina along with nitric acid as a deflocculant. The reverse side of the film is also coated.

Titanium dioxide is initially chosen as a suitable pigment. However, as incorporation of a titanium dioxide pigment in the image receiving layer causes flocculation of the boehmite alumina while a primer layer containing titanium dioxide is not detectable by a printer, the pigment must be incorporated in the reverse side coating. The pigment has a particle size of less than 40 nm and is incorporated into a gelatine coating at a dry loading of around 0.1 gsm within a coating weight up to about 2 gsm and must give rise to a level of haze of less than 53% with a minimum optical density of 0.25. Alternatively, rice starch, zirconium dioxide or zinc oxide pigments may be used. While these pigments can be incorporated in the gelatine-based reverse side coating it is also possible to incorporate them within the front side coatings and the level of haze exhibited is less than 41%.

Further improvements in performance may be achieved when the reverse side coating is a cross-linkable hydroxyl group-containing polymer such as polyvinyl alcohol rather than gelatine. In this case, as is shown in the table, detection using an Epson Model 4900 is achieved for media exhibiting a haze value of less than 28%.

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Dr Clare Conboy