Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating predominantly nonmetal substrate
Reexamination Certificate
1998-07-09
2001-05-22
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating predominantly nonmetal substrate
C205S162000, C205S164000, C205S210000, C427S096400, C427S122000, C427S123000, C427S197000, C427S203000, C252S500000
Reexamination Certificate
active
06235182
ABSTRACT:
SPECIFICATION
The invention relates to a solution for the pretreatment of electrically non-conductive surfaces and a method for coating surfaces with solid matter particles, for example carbon black, graphite, silicon dioxide, aluminium oxides, transition metal chalcogenides and titanium dioxide. Furthermore, the invention relates to a production method for the solution also.
It is known to coat electrically non-conductive surfaces especially with carbon black or graphite or mixtures of these materials; the materials being present in the form of particles, for example with a particle diameter of less than approx., 3 &mgr;m (for example EPO 200 398 B1).
An improvement relative to the previously mentioned invention is represented by a method with substrate-induced coagulation of the dispersion (WO-A 93/11881 and WO-A 92/19092). In a first step in this procedure water-soluble polymers, preferably polyelectrolytic compounds are adsorbed on the substrate surfaces. In the subsequent second step the adsorbed polymer compounds initiate the substrate-induced coagulation of the substrate, the substrate being plunged into the dispersion. As examples of polymer of this type, gelatine, polyvinylpyrrolidones, salts of carboxymethylcellulose, polyacrylic acid and polyvinyl alcohol are mentioned.
This method has the advantage that the carbon particles coagulate predominantly on the surfaces which are brought into contact with the polyelectrolytic solution and form an adhesive carbon coating. This coating in contrast to the coating produced according to EP O 200 398 B1 cannot be removed again even when rinsed with water. Because of this, it is possible to rinse off completely any dispersion residue adhering to the surfaces, so that the danger of contamination from areas of the surface which are not to be coated, for example copper surfaces on circuit boards, is reduced. Altogether, after a further electrolytic metal deposition a sufficiently adhesive bond of the metal layers is achieved.
In the named publications it is described how cationic polyelectrolytic compounds with the relatively low charge density of below 0.5 milliequivalents per gram of compounds represent good coagulation initiators.
In addition it is shown in detail that the composition of a coagulatable dispersion is also important for the adsorption of solid material particles. The dispersion is formed by using stabilising surfactants and salts in the dispersion which destabilise the dispersion. The concentration of salts should be about 0.05 mol/liter.
A typical example of a polyelectrolytic compound with a relatively low charge density is gelatine. This denatured protein consists of a combination of numbers of amino acids in irregular sequence. In particular, glycine, prolin, alanine, hydroxyprolin, glutamine acid and other amino acids are contained in gelatine (I. Tomka,
Chimia,
37, (2) (1983), Pages 33 to 40).
M. S. Celik as well as J. C. Abram and M. C. Bennet have described in
J. Colloid and Interface Science,
129 (2) (1989) Pages 428 to 440 and 27 (1) (1968) Pages 1, to 6, respectively the adsorption of surface-active agents on carbon black particles in aqueous dispersion. In this case, the dispersion of carbon black particles was stabilised by a repellent surface charge barrier or by steric interactions of the adsorbed surfactant molecules. In most cases adsorption isotherms were observed with Langmuir characteristic with a wide plateau region for most types of carbon black.
In EP O 583 426 B1, a method for the electroplating of the surfaces of a non-conductive material, in which the surfaces are brought into contact with a liquid carbon black dispersion, which contains carbon black particles, a surfactant for dispersing the carbon black and a dispersing medium and in which the surfaces are dried subsequently and after that brought into contact with a graphite dispersion. The dispersion contains a surfactant and a dispersing medium besides the graphite particles. After that, the electrically conductive layers are coated electrolytically with metal. By coating the surfaces first with carbon black, an adhesive graphite and metal coating can be obtained.
A part of the described methods has the disadvantage that a reliable and irreversible coating with solid matter particles is not possible. For adhesive coating therefore, the additional pretreatment of the surfaces with polyelectrolytic compounds is proposed so that the solid matter particles from the dispersion are coagulated irreversibly on the surfaces. Because of this, coating of the substrates in selected areas is also made possible, since the polyelectrolytic compounds (coagulation initiators) can be selected such that they are adsorbed either preferably on hydrophobic or hyrophilic surfaces or those capable of forming hydrogen bonds. In this way, the non-conductive surfaces on circuit boards can be covered with a stronger carbon black layer than the copper surfaces.
The particle coating which is performed by means of substrate-induced coagulation has the disadvantage however, that optimal accommodation of the polyelectrolytic compounds onto various substrate surfaces is only possible in a qualified manner, since only a limited number of compounds of this type is available. For example it has emerged that coating of polypropylene surfaces with carbon black according to known methods is simply inadequate.
Therefore the problem underlying the present invention is to avoid the disadvantages of the known treatment solutions and methods and to find in particular a suitable solution for the pretreatment of electrically non-conductive surfaces and a method for coating varying surfaces with solid matter particles. Above all, the method should be carried out without problems, and it should also be possible to be able to coat surfaces of highly hydrophobic character with no difficulty.
This problem is solved by the solution according to the present invention.
The solution according to the invention serves for pretreating electrically non-conductive surfaces, preferably for pretreating polymers. Said solution contains a solvent, preferably water, also at least one polyelectrolytic compound as a coagulation trigger and additionally at least one charged surfactant which is of opposite polarity relative to the polyelectrolytic compound and by means of which the charge of the polyelectrolytic compounds can be at least partly compensated for or overcompensated.
For coating these surfaces with solid material particles, the procedure is carried out using the following procedure steps:
a) treatment of the surfaces with the pretreatment solution;
b) coating with the solid material particles by bringing the surfaces into contact with a dispersion containing the solid material particles, a second surfactant stabilising the dispersion against coagulation of the particles and a salt destabilising the dispersion.
In the first procedure step, the coagulant initiator is adsorbed on the surfaces of substrates, made of for example polytetrafluorethylene, glass, metals, polyethylene, epoxy resins and cellulose. In the second procedure step the solid material particles, for example for the group of carbon black, graphite, silicon dioxide, aluminium oxides, transition metal chalcogenides, for example molybdenum disulphide and titanium dioxide, are coagulated on the pretreated surfaces. The charge density of the polyelectrolytic compounds in the pretreatment solution is controlled by using the amount of additionally contained charged surfactants for controlling the net charge density on the polyelectrolytic compounds.
Furthermore, in the second procedure step a coagulatable dispersion with a defined coagulation behaviour is brought into contact with the pretreated substrate, so that a maximum quantity of solid matter particles are coagulated on the substrate.
For pretreating the non-conductive surfaces, special polyelectrolytic compounds are used, which are soluble in the solvent and which must fulfill a range of predetermined criteria: in the first place the compounds must be adsorbed on the su
Bele Marjan
Besenhard Jurgen Otto
Meyer Heinrich
Pejovnik Stane
Atotech Deutschland GmbH
Paul & Paul
Wong Edna
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