Patent Application
20080049090
The present invention will be further explained by means of the following non-limitative illustrative figures and examples, wherein:
Example 1 describes a process of making a recording medium for use in the method according to the present invention.
Example 2 describes a result that can be achieved with the method according to the present invention.
Roller 1 is internally provided with a radiation heater 12, which heater is configured to heat the receiving medium 2 by heating the roller circumference which gives off its heat to the medium that contacts the roller 1. In this way, the recording medium can be treated to allow the hot melt ink to pass into the medium immediately after the corresponding ink droplets have hit the surface of the recording medium. The heater 12 is controlled by a piece of control software that is incorporated in controller 10. In this embodiment, the software makes use of a memory which comprises numerous combinations of inks that can be used in the printer and recording media that can be used according to the present invention. Each combination is linked to a dedicated setting of the temperature of the roller, which setting is the parameter to be directly controlled in the embodied system. That is, the temperature of the roller surface is measured using a contact sensor (not shown) and compared to the pre-programmed temperature setting. Depending on the difference between the pre-programmed temperature and the measured temperature, the heater is controlled to make this difference as small as necessary.
The fusible layer is a film of thermoplastic polymer particles (polyester resin; Mn=900, Tg=55° C.). These particles have an average size between 2 to 5 μm and are rod-coated on the support starting with an aqueous dispersion of the particles (10 weight % of resin in water) to provide a film of about 20 μm in thickness. On top of the fusible layer 17 lies a layer of solid phase change ink droplets 20 that has been jetted onto the surface of the recording medium.
Example 1 describes a process of making a recording medium for use in the method according to the present invention. A resin is chosen, typically having a Tg (glass transition temperature) between 50 and 70° C. As an example, the polyester resin exemplified as resin number 3 in table 2 of international patent application PCT/EP2006/062614 is chosen. A 10% resin dispersion (10 weight percent of resin) in water is created such that the resin particles have an average size below 1 micron (which can be easily verified with a light scattering particle size measurement apparatus). The viscosity of this dispersion is in almost the same as that of the water itself and the dispersion has a milk-like appearance.
A clean screen that is commonly used in a screen printer is placed on top of a suitable substrate, in this case Kodak Instant Dry Glossy photo paper, 190 g. It is ensured that there is good contact between the screen and the substrate by supporting the substrate and putting adequate pressure on the framework of the screen. The screen in this case is made out of mono-filaments of an inert fabric, which filaments are 40 micron wide leaving openings of 20×20 micrometers.
The resin dispersion is applied on the side of the screen facing away from the substrate, making sure that it is not able to wet the substrate yet. With a rubber squegee the dispersion is applied over the whole screen in one movement. It is important that the squegee does not run dry because this will cause imperfections in the coated layer. Any surplus dispersion is removed from the screen because this can interact with the substrate causing cockling or too thick layers of coating. After the coating step, the screen and substrate are left in place to allow drying. This can be done under ambient conditions. After drying the screen is removed. This method results in a recording medium having on the substrate as a support, a fusible layer consisting of dots of the polyester resin of about 40×40 micrometers wide and a height of about 15 to 20 micrometers in a regular pattern and a open space of a few micron in between the dots. The thickness of the dots can be varied, for example by changing the amount of resin in the dispersion.
Other coating techniques for obtaining a fusible layer can also be successfully applied. For example, it is recognised that rod-coating techniques or cast coating techniques, both when starting from aqueous or non-aqueous media as a carrier for the fusible material, can be applied to obtain a recording media for use in the present invention. The present invention can also be applied to parts of recording media. For example, if an overcoat is only desired for a certain smaller image of a complete image (for example, a company name above a letter, which name should appear in high gloss), a medium could be made having the fusible layer only at the location corresponding to the company name.
In this example a result is described that can be achieved with the method according to the present invention. With the screen print method described here-above (“example 1”) four recording media are produced. For the fusible layer, four different kinds of resin are chosen, namely resin number 3 in table 2 of international patent application PCT/EP2006/062614, resin number 1 in the same table of that patent application, a polyester-amide resin having a Mn (number averaged molecular weight) of 900 and a Tg of 65° C., and a semi-crystalline polyolefin resin (available from Dow Chemical Corporation under the trade name “Engage”).
These four materials are each printed with three different hot melt inks of a constitution as given in Table 1. Each of these ink compositions contains a crystalline material (K), an amorphous material (A) and a gelling agent (G). The ink compositions are provided with a dye (KI), Macrolex Rot (Bayer) in the case of the ink compositions I and III, Orasol Blau (Ciba-Geigy) in the case of composition II. In addition, the three ink compositions are provided with wetting agent (V) BYK 307 (Byk Chemie). The chemical formulae of the crystalline base material (K), the amorphous binder (A) and the gelling agent (G) are given in tables 2, 3a and 1 respectively of EP 1 067 157.
The inks are jetted at a temperature of 130° C. to the recording media which is maintained at a temperature of 35° C. Here-after, the recording media are transferred to an oven which is maintained at 90° C. After 30 seconds the inks have passed into the media, and they are transferred to an oven kept at 110° C. Here they stay for 90 seconds which is sufficient to fuse an ink free upper layer of the recording media. Then they are brought to ambient conditions.
To test the durability under thermal load, the printed and now “sealed” recording media are brought over to an oven at a temperature of 45° C. The image quality is inspected every 24 hours. A first relevant feature of the image quality is the gloss level (which can be measured for example using a Hunter 75° glossmeter according to TAPPI procedure T 480OM-92). Another feature is the appearance of white spots, possibly a crystallisation effect of the crystalline material in the ink vehicle. It appears that during the first few days a slight deterioration of the gloss level occurs (typically from 70 to 60%). However, this decrease in gloss can hardly be noticed with the naked human eye. After that, the gloss level remains substantially constant, up to even 800 hours of thermal load. No white spots can be noticed with the naked human eye.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06119292.8 | Aug 2006 | EP | regional |
