Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-12-18
2001-07-03
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S472200, C428S432000, C428S469000, C428S697000
Reexamination Certificate
active
06255007
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a laminate system based on aluminum, zirconium and nitrogen, a process for the production of that laminate system by a deposit procedure, and the use of the laminate system.
BACKGROUND OF THE INVENTION
It is known for titanium nitride coatings to be applied to injection molding tools for the injection molding of plastic materials, in order to reduce the level of coating deposit thereon, to improve the ease with which moldings can be removed from the molding tools, and to reduce the amount of tool wear. It has been found however that those titanium nitride coatings are often not satisfactory in regard to their properties.
Coatings which are found to be an improvement in comparison with such titanium nitride coatings, in terms of the surface properties thereof, are those which contain chromium nitride as an essential constituent thereof. Chromium nitride-bearing coatings however suffer from the disadvantage that the most important properties thereof tend to partially vary during the service life of the molding tools, for example when assembling or vulcanizing rubber parts in which the chromium nitride coatings lose their adhesion-inhibiting effect after a short period of operation.
It is also known that zirconium nitride coatings can be applied to articles in some cases as decorative coatings, by virtue of their brass colorations. Those coatings admittedly in themselves form a hard surface and are chemically resistant to lyes, but they have in particular metal bonds.
Reference may be made to EP-A-0 603 486 describing a multi-stage process for coating cutting and shaping tools with ternary hard-material layer assemblies or laminate structures such as titanium aluminum nitride, zirconium aluminum nitride or chromium aluminum nitride. Although those layer materials are admittedly suitable for tools for metal machining, they cannot however be used to real effect for reducing contact adhesion and for enhancing the chemical resistance of sensitive surfaces such as for example plastic material extrusion tools which are polished to a high state of shine.
With those materials the solid laminate components involve predominantly metal bonds, in which respect thorough and extensive scientific tests have demonstrated that all materials involving a predominantly metal bonding effect have a tendency to suffer from contact adhesion to a greater or lesser degree.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a laminate system which can at least markedly reduce the tendency to adhesion thereof and the degree of deposit coating formation.
Another object of the present invention is to provide a layer or laminate system which can afford a high level of corrosion resistance and an enhanced degree of resistance to abrasion wear.
A further object of the present invention is to provide a laminate system which enjoys an enhanced surface quality in terms of reliability of manufacture, productivity and use-friendliness.
Yet another object of the present invention is to provide a laminate system which enjoys a low level of surface friction and an improved release effect for example for the release of a molding from the surface thereof.
Still a further object of the present invention is a process for the production of a laminate system which is simple to implement and reliable in terms of the production results.
Still another object of the present invention is to provide for the use of a laminate system on a workpiece such as to impart improved qualities and properties thereto.
In accordance with the principles of the present invention, in a first aspect, the foregoing and other objects are attained by a layer or laminate system based on aluminum, zirconium and nitrogen, wherein at least one layer of the system has covalent bonds of aluminum nitride or aluminum nitride and zirconium nitride.
It has been found in that respect that in accordance with the invention the addition of zirconium nitride affords stabilization in respect of the covalent aluminum nitride bond, whereby it is possible to achieve a high level of chemical resistance. The choice of the chemical composition adopted and the further alloying elements is effected depending on the respective properties required, in particular for example in terms of minimizing adhesive forces upon coming into contact with materials which have a tendency to adhere, more especially plastic materials such as thermosetting materials, thermoplastic materials, elastomers, resins, adhesives, rubber, caoutchouc, glass or aluminum.
The improved properties of a minimal tendency to adhesion, chemical resistance in relation to lyes, the low coefficient of friction and the high level of resistance to wear afford components and members such as molds which are provided with such coatings or laminate systems significantly higher levels of surface quality in regard to manufacturing reliability, productivity and user-friendliness.
A preferred feature in accordance with the invention is for the atomic ratio between aluminum and zirconium to be set at 1 or smaller, as that can greatly enhance the adhesive qualities of the coating according to the invention.
In a preferred aspect of that feature the ratio between aluminum and zirconium is between 0.5 and 0.7, whereby the adhesion-inhibiting properties of the system according to the invention, in relation to coating deposits thereon, can be greatly enhanced.
An advantage of the laminate coating system according to the invention in that respect is that it is optically transparent or at least partially translucent and/or electrically non-conductive or at least has a high specific electrical resistance.
In accordance with a further embodiment the layer includes bonds of the aluminum nitride and zirconium nitride type, wherein desirably the atomic ratio between aluminum and zirconium is 1 or less. Preferably the atomic ratio between aluminum and zirconium is 0.5 or less, in particular between 0.25 and 0.45, whereby the level of wear resistance can be substantially enhanced and in particular it is possible to afford a high level of chemical resistance on the part of a coating produced in that way.
In accordance with a preferred feature the coatings afforded by the laminate system according to the invention are of a thickness of at least 50 nm. In accordance with a preferred embodiment the coating is at least between 200 nm and 2 &mgr;m thick for for example optical uses and to satisfy the high demands in terms of surface quality or between 2 &mgr;m and 6 &mgr;m for example for uses in plastic material processing, to avoid unwanted adhesion and coating deposit formation. Even a thickness of over 6 &mgr;m with an additional abrasive loading on the coated surface is possible.
In accordance with the invention it is possible to adjust the ohmic resistance of the coating according to the invention by suitable selection of the nitrogen component. Layers with a high proportion of nitrogen have a high level of such resistance and thus a low level of conductivity, whereas layers with a lower level of resistance have a nitrogen content which is lower than the proportion of aluminum. In a preferred embodiment with a very low level of ohmic resistance the layer or layers essentially comprise or comprises pure aluminum or contains or contain at least practically no nitrogen. Conversely, in the case of coatings with a high level of ohmic resistance, the layer or layers at least predominantly comprises or comprise covalent bonds of aluminum nitride and zirconium nitride.
In accordance with the invention, for the purposes of increasing resistance to wear or chemical resistance, it can be provided that at least two coatings are respectively arranged alternately, with layers with a high proportion of nitrogen and layers with a low proportion of nitrogen being deposited one upon the other. An advantage of such a configuration is the combination of different ones of the above-mentioned properties in a laminate or layer system.
In that respect, the layer with a low level of ohmic resi
Hartec Gesellschaft fur Haststoffe Und Dunnschichttechnik mbH &
Jones Deborah
McNeil Jennifer
Morgan & Finnegan , LLP
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