EP 2 871 062 A1
Production method of recording material, and recording material
Seiko Epson Corporation
This extensive patent (84 pages) is, like the following one, concerned with the production of a glossy or mirror-finished surface, however in this context it is applied to the production of hard surfaced décor panels and similar articles. The method can be used as an alternative to metallic plating or foil stamping and is beneficial in that it can be applied to a curved surface, and also that patterning and gradation in the metal tone can be achieved.
In essence, two UV curable layers are sequentially printed on the substrate surface. The first layer is cured prior to printing the second layer so that it creates a regular dimpled texture with a surface roughness of 3 to100 μm; the metal-powder-containing upper layer has a planarising effect. Thus the time elapsing between the landing of any drop and curing is critical. In the case of the first layer (2), it is cured within a second of printing while a longer time (5-60 seconds) can elapse between deposition and cure of the top layer (3). The elapsed time can have significant influence on the appearance of the printed material.
While the substrate 1 can be more or less anything and may be absorbing or non-absorbing, a non-absorbing polyester-based substrate for which the contact angle of the ink droplets is at least 10 degrees is preferred and plastics such as PET are particularly suitable.
The first layer is formed from an ink comprising 50-88% of at least one monomer with an alicyclic structure, as this gives good adhesion to the polymer substrate. If at least some (15-75%) of this content is a monofunctional monomer with a heteroatom in the alicyclic structure, such as tris (2-(meth)acryloxyethyl) isocyanurate, then curing shrinkage can be minimised and furthermore, the long term jetting stability is good. The remainder of the monomer content need not have an alicyclic structure and can enhance some aspects of the film, for example inclusion of 2-(vinyloxyethoxy) ethyl acrylic acid improves the cure speed while inclusion of phenoxyethyl acrylate gives rise to a relatively flexible film. Inclusion of a colourant or metal powder in this layer can influence the colour tone or the opacity of the finished article.
The second, and metallic ink, will be deposited at a volume of 80 to 200% of the deposition volume of the first ink, in order to ensure full coverage and a glossy mirror finish. The greater print to cure interval also enables a smooth surface. More or less any metal powder (31) can be dispersed in this ink at a content up to 10% w/w. Ideally, the powder is formed by CVD and subsequently pulverised to give a flake structure which may additionally take the form of curved flakes for additional effects. The thickness of the flakes is preferably in the 20 to 80 nm range while the diameter is between 500 nm to 3 μm. Treatment of the flakes with a fluorinated compound, such as a silane, disperses the particles in the ink and enhances its storage stability, as well as improving the abrasion resistance and gloss of the printed film. In common with the first ink, the bulk of this ink is also made up of alicyclic monomers which will result in good inter-film adhesion, while the inclusion of minor quantities of other monomers will improve dispersion stability of the metal flakes, enhance cure rate and endow the final article with specific properties such as hardness and flexibility.