Process for coating and printing substrates

Details Process for coating and printing substrates Process for coating and printing substrates

1997-05-23

1998-08-25

Cameron, Erma

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

4273855, 2522995, C09K 1954, B05D 302, B05D 306

Patent

active

057981477

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a process for coating or printing substrates with a coating or printing composition, which comprises applying a polymerizable material containing liquid-crystalline, polymerizable monomers which carry the coating composition or the printing composition comprises into the polymeric binder by polymerization, or, in the case of emulsion coatings and printing inks, a dispersion auxiliary d), into the polymeric binder by polymerization, or, in the case of emulsion coatings and printing inks, a dispersion auxiliary d), and
The present invention furthermore relates to mixtures containing these polymerizable, liquid-crystalline compounds which are suitable as reaction-drying surface coatings, emulsion paints or printing pastes, to the use of these compounds in surface-coating systems, printing inks and writing inks, and to a process for the preparation of pigments from these compounds.
2. Description of the Background
Surface-coated materials whose color impression depends on the observation angle open up interesting potential applications.
DE-A 35 35 547 describes a process in which a mixture of cholesterol-containing monoacrylates can be converted into cholesteric layers by photocrosslinking. However, a material of this type, as a linear polymer with the mesogenic moieties in the side chain, is not very mechanically stable.
DE-A 42 40 743 describes pigments whose color is dependent on the observation angle and which comprise aligned, three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase and, if desired, further dyes and pigments. These pigments are suitable for coloring paints, plastics, fiber raw materials, cosmetics or printing inks of all types, for example screen printing inks.
However, the preparation of these pigments requires that three-dimensionally crosslinkable liquid-crystalline substances having a chiral phase are applied to a substrate, crosslinked on this substrate to give a brittle layer, and detached from the substrate after crosslinking. The pigments, obtained by grinding, are then incorporated into surface-coating systems or printing inks.
When used for coating substrates, these materials frequently prove disadvantageous owing to the uneven surface.
Further disadvantages are the process temperatures, which are significantly above room temperature, and the multistep procedure with application to an intermediate substrate, comminution to give pigments, preparation of semifinished products, known as pigment pastes, and incorporation into the color mixture.


SUMMARY OF THE INVENTION

It is an object of the present invention to overcome these disadvantages of the prior art.
We have found that this object is achieved by the process described at the outset for coating substrates.


DETAILED DESCRIPTION OF THE INVENTION

The novel coatings can be brittle or non-brittle after curing. For the purposes of the present invention, non-brittle is taken to mean, in contrast to DE-A 42 40 743, that the cured coatings cannot be detached from the substrate by mechanical means, for example by passing the coated substrate over a deflection roll of small diameter, without damage. Non-brittle coatings are particularly advantageous as paint-like coatings.
The color impression of the novel coatings is based on the formation of cholesteric liquid-crystalline phases.
In a cholesteric phase, the liquid crystals form a helical superstructure which is perpendicular to the long axes of the molecules (H. Baessler, Festkorperprobleme XI, 1971).
The cholesteric phase has remarkable optical properties: high optical rotation and pronounced circular dichroism caused by selective reflection of circular-polarized light within the cholesteric layer. The colors, which appear different depending on the viewing angle, depend on the pitch of the helical superstructure, which in turn depends on the twisting power of the chiral component. The pitch can be varied, in particular, by changing the concentration of a c

REFERENCES:
patent: 4614619 (1986-09-01), Shannon
patent: 4637896 (1987-01-01), Shannon
patent: 4780383 (1988-10-01), Garrett et al.
patent: 5362315 (1994-11-01), Muller-Rees et al.
Liquid Crystals,Heinz Baessler,Festkoerperprobleme X1 (1971), pp. 99-133.
Densely Crosslinked Cholesteric Polymer Networks, D.J. Broer, I. Heynderickx, J, Lub, Philips Research Abstr. II, 921 (1992).
Preparation of Ordered, Crosslinked and Thermally Stable Liquid Crystalline Poly (Vinyl Ether) Films H. Anderson, et al, Polymer, 1992, vol. 33, No. 19, pp. 4014-4019.
Anisotropic Networks Obtained by In Situ Cationic Polymerization of Liquid-Crystalline Divinyl Ethers, R.A. M. Hikmet et al, Polymer, 1993, vol. 1993, vol. 34, No. 8, pp. 1736-1740.
Translation of DE 4418075, Nov. 1995.
Translation of FR 2537976, Jun. 1984.
Translation of DE 4342280, Jun. 1995.

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