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