Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2001-01-24
2002-09-10
Pianalto, Bernard (Department: 1762)
Coating processes
Measuring, testing, or indicating
C118S300000, C118S612000, C118S665000, C118S666000, C118S688000, C118S689000, C118S708000, C118S712000, C118S713000, C427S385500, C427S402000, C427S407100, C427S489000, C427S494000, C427S496000, C427S508000, C427S532000, C427S552000, C427S553000, C427S557000, C427S558000, C427S559000, C427S595000
Reexamination Certificate
active
06447836
ABSTRACT:
The present invention relates to a method of and to a device for optimizing coating materials, especially radiation-curable coating materials.
coating materials, especially radiation-curable coating materials, generally have a highly complex composition. Key components of a radiation-curable coating material include reactive diluents, oligomers, prepolymers, synergists, photoinitiators, light stabilizers, such as UV absorbers or sterically hindered amines, for example, pigments, dulling agents, flow agents and other additives. This results in a great diversity of possible coating compositions. To date, the coating materials have been formulated in practice by the trial and error principle and with many years of experience have been optimized in laborious series of tests, which have to be analyzed manually. Despite this costly and time-consuming procedure, the large number of possible coating compositions throws up only random hits of adequately satisfactory quality but does not lead to high-quality coatings determined systematically and in a targeted manner, since targeted investigation of the abovementioned sphere of parameters, conducted in parallel, is impossible owing to the massive effort it would entail. Predicting the properties of a certain composition for a coating material is possible only to a limited extent, since various components, such as photoinitiators and UV stabilizers, for example, have effects on one another which are nonlinear.
It is an object of the present invention to provide a method and a device for optimizing coating materials, said method and device allowing targeted and systematic variation in the key components of a coating material, especially of a radiation-curable coating material, in order to be able to arrive objectively at an optimum composition of the various components of the coating material.
We have found that this object is achieved by the method of the invention, as claimed in claim
1
, and by the corresponding devices, as claimed in claims
5
,
9
and
10
and the dependent subclaims. The method of the invention constitutes a method of optimizing at least one coating material at at least one point of a substrate surface to which the coating material is applied. In accordance with the invention, at least the following steps of the method are conducted in a device provided for that purpose:
a) applying said at least one coating material to said at least one point of said substrate surface.
Preferably, two or more different coating compositions are applied simultaneously at different points of the substrate surface, which together form a grid. The different compositions are suitably applied to the corresponding points of a desired substrate surface, such as a wood or metal or paper surface, for example, with the aid, for example, of metering pipettes, microdoctors or microspray heads, preferably under computer control.
The points of the substrate surface at which each of the different coating compositions is applied are preferably chosen to be very small, so as to enable application of many different coating compositions to a single substrate surface. The points of the substrate surface at which the coating compositions are applied preferably form a kind of matrix, corresponding to an arrangement of m rows each having n columns, n and m each being less than 1000. The size of an individual point of the substrate surface to which one of the different coating compositions is applied depends primarily on how the coating material is later to be characterized. Using current techniques it is possible to investigate up to 10,000 different coating compositions on 10 cm
2
of a substrate surface.
Thereafter, the coating compositions are optionally dried in order, for example, to allow evaporation of the solvent which is required in certain cases for optimum mixing.
b) Curing said at least one coating material at said at least one point of said substrate surface.
Preferably, the coating material, or the different coating compositions applied at different points of the substrate surface, which together form a grid, are radiation-cured. In the course of radiation curing, described for example in J.-P. Fouassier,
Photoinitiation, Photopolymerization and Photocuring
, Hanser Publishers, Munich, 1995, the mixture of the individual components of a coating composition is converted by exposure, preferably UV exposure, into a three-dimensional, mechanically stable polymer network. Advantages of this technology lie in the high speed, low energy consumption, virtually complete absence of environmentally harmful reaction products on curing, and low costs. Curing is preferably performed simultaneously for all corresponding points of the substrate surface, preferably by means of exposure over a large area with UV light or with electron beams. This results in three-dimensionally cured coating films at the corresponding points of the substrate surface. Exposure over a large area is very economic in time and energy terms and, furthermore, provides the required uniform processing of all coating films applied to the substrate surface. Preferably, the coating material, or the different coating compositions applied at different points of the substrate surface, which together form a grid, is or are heated in the course of curing. In this way it is possible first to accelerate the reaction—i.e., the formation of the three-dimensional network—and, second, to ensure that the reaction proceeds completely by itself.
c) Determining the condition, especially the curing and/or yellowing and/or gloss, of said at least one coating material at said at least one point of said substrate surface, possessed by said coating material as a consequence of steps a) and b).
As set out above, it is possible according to the invention to determine and/or analyze individually each of the parameters describing the condition, such as curing, yellowing and gloss, for example, or else all of the parameters are determined and/or analyzed, preference being given to the determination/analysis of all parameters since it gives virtually a complete picture of the condition of the coating material.
The cured coating material, or the different cured coating compositions applied to the substrate surface, is or are preferably characterized by means of a spectroscopic technique which has a high lateral local resolution and, if required, a sufficient depth resolution. In this way it can be ensured that in each case only one coating composition is characterized at one of the relevant points of the substrate surface, without any interaction with coating compositions that have been applied at adjacent points on the substrate surface. It is preferable here to use the method of confocal Raman spectroscopy. In this method, the coating network which forms in the course of curing is detected on the basis of the disappearance of reactive groups; in other words, the reaction conversion which takes place in the course of curing is determined directly (W. Schrof, L. HäuBling, Tiefenauflösung der Trocknungsvorgänge in Lackfilmen, in “
Farbe und Lack
”, 103, 1997, 22-27). In this case, by using highly sensitive spectrometers which operate primarily in backscattered light, the measurement times can be shortened to the order of seconds. For the state of the art in the field of Raman spectroscopy and, respectively, confocal imaging, reference may be made to Schrader B.,
Infrared and Raman Spectroscopy
, VCH, Weinheim, 1995 and Markwort L., Kip B., Da Silva E., Roussel B.,
Appl. Spectrosc
. 49 (1995) 1411-30. In addition to confocal Raman spectroscopy it is also possible to use IR spectroscopy or fluorescence spectroscopy. Fluorescence methods (O. Wolfbei&bgr;,
Fluorescence Spectroscopy: New Methods and Applications
, Springer, Berlin, 1993) analyze the structure of the coating network formed as a result of curing, analysis being carried out on the basis of the decrease in local mobility or translation diffusion of fluorescence probes. All of these optical methods can be carried out with high local resolution, in combi
Horn Dieter
Meisenburg Uwe
Pfau Andreas
Schrof Wolfgang
Schwalm Reinhold
BASF - Aktiengesellschaft
Keil & Weinkauf
Pianalto Bernard
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