Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article
Reexamination Certificate
2000-07-19
2002-09-24
Silbaugh, Jam H. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Light polarizing article or holographic article
C264S002500, C264S225000, C264S496000, C425S174600, C425S542000, C425S346000, C425S385000, C425S403000, C425S470000, C425S810000, C249S114100, C249S134000
Reexamination Certificate
active
06454970
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a method of producing a matrix that can be used in a compression moulding, embossing, injection moulding and/or other plastic element-producing machine. In particularly the present invention relates to a matrix having a surface, or a part of said surface, which is provided with a negative microstructure that can be replicated as a positive microstructure, on a surface of a plastic element, such as a compact disc (CD) formed in such a machine.
The invention also relates to a matrix manufactured by said method, the use of said matrix to form a plastic element and the plastic element so formed.
DEFINITIONS
In the following, the expression “positive surface structure” shall be understood to mean the surface structure (including topographic surface features such as microstructures or plane surfaces or parts of surfaces) that appears on a plastic element produced in a plastic element-producing machine, and that by “negative surface structure” is meant the inverse of the positive surface structure, i.e. the surface structure exhibited by a matrix used in such a machine.
By plastic composite is meant a curable mixture of polymeric material and a filling material, where the filler is normally present in surplus.
There is defined in the following description a matrix first wear surface that is formed on a first wear layer, and a matrix second wear surface that is formed on a second wear layer.
The first wear surface is the surface of the matrix that carries a microstructure and that faces towards the manufactured plastic element, while the second wear surface is the surface of the matrix, also referred to as the rear side, which is preferably planar and lies in abutment with the corresponding planar support surface of a mould half. It will be understood that these latter two surfaces need not necessarily be planar but that they shall connect with one another so as to be able to take-up forces generated during the moulding or casting process e.g. they can have complementary shapes.
DESCRIPTION OF THE BACKGROUND ART
In respect of replicating microstructures on plastic elements produced in a machine of the kind defined in the introduction, it is known to produce first an original master in some suitable way, and then to produce a matrix for use in said machine on the basis of this master. Matrices of this kind can be produced by coating a master or an original that has a positive microstructure on one surface with a metal layer or a metallic coating and removing the negative-microstructured metal layer from the master to thereby obtain a metal plate that can serve as a matrix in the compression moulding, embossing and/or injection moulding press. Normally each mould half can have its own matrix and a flowing, hot (approximately 400° C.) plastic mass is pressed under high pressure into a delimited mould cavity formed by cavities in brought together mould halves. The flowing hot plastic mass is then allowed to solidify (at approximately 140° C.) between the brought together mould halves before the mould halves are opened and the solidified element can be pressed out.
Lithographic processes, in particular lithographic processes that have been developed primarily for use in the micro-electrical field, are an example of known methods for producing a master. One of these methods is based on etching a semiconductor surface and/or depositing material thereon. Other methods are based on the removal of parts of material with the aid of a laser, so-called laser ablation, with the aid of traditional NC-machines, with the aid of precision-controlled, high-speed diamond millers, with the aid of electric discharge machining (EDM), wire EDM and/or some other suitable method.
Such originals or masters are normally produced from a material that is chosen to be suitable with respect to a given machining process.
In the case of lithographic processes, the material is most often a sheet of silicon, glass or quartz, whereas in the case of laser ablation the material most often used is a sheet of plastic composite and/or a polymeric material.
In the case of metal processing methods, plastics and soft metals may both be suitable.
It is well known that the requirements of a given replication process on a given material in the matrix and the plastic element are not the same as the requirements that must be met with respect to the original or the master. For instance, with respect to injection moulding of such plastic elements where one or more surface parts shall present a microstructure, one or both of the mould halves of the machine and the matrix used therein must be made of a stable material that can withstand the high pressures that occur during the course of manufacture, and which will not be worn down unnecessarily quickly by the thermal and mechanical wear-and-tear to which the mould halves and the matrix are subjected during the casting or moulding process.
It is known to produce such matrices, and primarily matrices for use with microstructure, by transferring the shape and surface structure of a master to a metal plate which can then serve as a matrix.
One manufacturing method is based on first producing a master on a surface of a glass plate, a semiconductor plate or a metal plate, coating the surface with a light-sensitive layer and exposing selected surface sections of this light-sensitive layer through the medium of a laser or the like, and washing and cleaning the selected surface sections. A metal layer is applied to the exposed and cleaned surface of the master, through the medium of a sputtering process, a vapour deposition process, and/or through the medium of a plating or cladding process, for the length of time required to form a metal plate. The metal plate can then be removed from the master. The metal plate has a first surface which exhibits a negative microstructure which is intended to face towards the inside of a mould cavity. The metal plate can be used as a matrix after further machining, i.e. smoothing, of a second surface that faces towards the mould half in the machine.
It is this method that is presently used in the manufacture of a matrix used in an injection moulding press for the production of optical discs, e.g. CD discs.
Other ways of producing a matrix or a master include:
an electrically insulating microstructured disc serving as a master or matrix can be coated with a thin metal layer by means of a sputtering process and/or by vapour deposition;
an electrically conductive microstructured disc or layer that functions as a master or matrix can be coated with a much thicker metal layer by means of a plating or cladding process;
a disc intended to function as a matrix can be coated with a thin electrically conductive layer, such as a nickel, silver, or gold layer or some like metal layer, by means of a plating or cladding process.
It is also known to connect a metal layer electrically and to submerge a disc in a solution that comprises among other things, metal ions, and to pass an electric current through the solution onto the disc or master unit and therewith cause metal ions to precipitate as pure metal onto the surface of the disc. In this way a structure can be produced in metal that has the inverse function of the microstructure on the master.
It has been found that the above method can be readily applied in respect of flatter structures, particularly when the depth of the microstructure is limited to, or smaller than, about 0.2 &mgr;m.
It has been found that in forming a matrix the metal build-up on the microstructure-carrying surface of a master results in minor defects or irregularities on the rear side of the matrix, which irregularities are caused by the microstructure, and that it is necessary to subsequently smooth said rear side in order for it to lie in effective abutment, e.g., flat, on a flat surface on the mould half that supports it in the pressing machine used.
Practical applications have shown that in the case of deeper structures in the master microstructure, the master pattern will be embossed on the re
Lundbladh Lars Rune
Öhman Per Ove
AMIC AB and Gyros AB
Del Sole Joseph S.
Jenkens & Gilchrist
Silbaugh Jam H.
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