CA1246370A

CA1246370A - Method of producing an optical component, and components formed thereby

Info

Publication number: CA1246370A
Application number: CA000445714A
Authority: CA
Inventors: Dennis W. Robinson
Original assignee: Spafax Holdings PLC
Current assignee: Spafax Holdings PLC
Priority date: 1983-01-26
Filing date: 1984-01-20
Publication date: 1988-12-13
Also published as: NO843782L; IT8419314A0; CH665488A5; DK458684D0; DE3490033T1; AU2495584A; IE55013B1; NL8420019A; IT8419314A1; PT78009B; ES529203A0; DK458684A; IE840138L; PH23007A; DK161754C; DK161754B; FR2539881B1; SE8500918D0; FR2539881A1; WO1984002875A1

Abstract

A method of making an optical component having specular reflective properties from plastics material comprising applying to the plastics material a face layer of hard glass or a substance having hard glasslike properties and subsequently applying to the face layer a coating of specular reflective material.

Description

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A METHOD OF PRODUCING AN OPTICAT. COMPONENT, AND COMPONENTS
FORMED THEREBY _-This invention relates to a method of producing an optical component and components produced thereby.
It is known to use synthetic plastics materials for optical components and these have several advantages over traditional glass and crystalline materials, such as resis-tancelto~thermal and mechanical shocks, lower production costs, reduced weight and greater design flexibility. Such plastics optical components are however, vulnerable to sur-face damage by abrasion, scratching and environmental con-ditions which often impair their function.
It is knownthat transparent scratch resistant layers may be deposited on to plastics material surfaces by dip-coating, ultra violet polymerisation and varnishing. Addi-tional processing and end product problems are created, such as lack of thickness uniformity, variable adhesion to the plastic sub-strate gel formation on curing the coating and it is also generally expensive to produce at commercia ly acceptable efficiencies. The coating can be very speci-fic to a particular plastic and deposition directly over metallic reflective finishes on the plastics material can present many problems.
Thereare many optical applications where it is re-quired to produce an abrasion-resistant specular reflective finish onpl~stics material substrates.
This can be achieved in a number of ways including electro-chemical deposition of a hard reflective metal such as chromium or nickel onto the front surface of a clear or ~ -2~ 37~

opaque plastics material, usually acrylonitrile-butadiene-styrene copolymers. This method is very costly and prone to production problems. It also produces a mirror-like product of lower reflectivity than is achieved by conventional silver or aluminum surfaces. Despite the use of a relatively inert plastics base material for the mirror the multi-metal layer electroplating process can also give rise to troublesome electrolytic corrosion problems when the mirror is exposed to adverse environmental conditions. A further technique involves thermal evaporation of - aluminum on to the rear surface of an already coated transparent plastics material, the coating of which is abrasion resistan-t to a degree and previously deposited by a separate and costly wet chemical process. Articles produced by this technique are limited by the size, shape and configuration of the basic coated plastics materials, usually in flat-sheet form, and are expensive by virtue of the multi-stage production methods involved.
Vacuum assisted metal deposition onto untreated plastics material followed by a wet chemical coating process to confer abrasion resistance is also known but this is again costly and prone to optical faults.
It is an object of the present invention to overcome the above drawbacks.
In one broad aspect the present invention relates to a method of making an optical component having specular reflective properties from plastics material comprising subjecting the plastics material to a degreasing operation by vapour degreasing in a fluorocarbon solvent and then transferring the material to an ultrasonically vibrated heated solution of the same solvent, 4_ ~L24637~3 " --3~-performing a molecular cleaning operation, applying a face layer having hard glass like properties, said layer being applied in a vacuum vessel in an atmosphere of oxygen and argon, and being applied to a thickness of between 0.5 and l.0 microns, and subsequently applying a coating of specular reflective material, said coating being between 0.5 and 5.0 microns thick.
The plastics material is preferably subject to a degreasing opera-tion prior to applying the face layer, and the degreasing operation may be carried out by subjecting the plastics material to vapour degreasing in a fluorocarbon solvent and the material is then transferred to an ultrasonica]ly vibrated solution of the same solvent.
Preferably also a molecular cleaning operation is performed in a vacuum vessel after the degreasing operation.
Subsequently the face layer may be formed by applying a key coat layer of oxides of the material used for the specular reflective material. The key coat layer may be applied by means of a magnetron sputtering operation in a vacuum vessel in an atmosphere of oxygen and argon at a pressure in the region of 2 x lO 3 rnbar.
Immediately after the mo]ecular cleaning operation the vacuum vessel may be reduced to l x 10-5 mbar pressure and argon gas is introduced until the pressure reaches 5 x 10-4 mbar, oxygen then being added until the pressure has risen to 2 x 10-3 mbar.
The key coat is immediately applied by means of a magnetron sputtering operation using a target of the metal to be deposited on the key coat layer. The key coat layer is preferably of the order of 0.5 - l.0 microns thick.
A

` -3a- ~246370 The coating of reflective material may then be applied directly -to the key coat layer and in this case the reflective material may be applied by a DC magnetron sputtering operation.

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In one arrangement the coating of specular reflective material is chromium, and in whlch case the key coat layer is preferably a thin layer of oxides of chromium of between 0.5 to 1.0 microns thick.
In an alternative arrangement the coating of specular reflective material is aluminium, in which case the key coat layer ls pre~erably a thin layer of oxides of aluminium of `~between 0.5 and 1.0 microns thick. In the latter case a hard abrasive resistant coat may also be applied to the 10 alumlnium, and in this case a top coat may be applied by means of a layer of dielectric oxide of between 0.5 and 5.0 microns thick.
In another alternative according to the invention the face layer may be formed by an in situ glass making opera-15 tion by co-reacting under plasma activated conditions typi-cal glass ma]cing chemicals such as a calcium carbonate, sodium carbonate and oxides of silicon. Such chemicals may be brought into a reactive state by bombardment with a high energy beam of elec-trons.
The invention also includes within its scope an op-tical component formed by the method set forth.
According to another aspect of the invention an opti-cal component having specular reflective properties comprises a platics material having a face layer thereon of glass or 25 a substance having glass like properties and a specular layer o~ reflective material coated thereon.
The invention may be performed in various ways and one specific emodi~ent will now be described by way of example.

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_ 5 --In this example the plastics base material comprises a polycondensate polymer prepared by the interactlon of a polyhydroxy compound with a carbonic acid derivative, typi-cally the reaction product of bis-phenol-A with either 5 phosgene or diphenyl carbonate which is available commercial-ly under the Trade Name "Lexan" polycarbonate and manufact-,ured by the General Electric Co. U.S.A. An appropriate shape r and size may be obtained either by a conventional thermo-plastics injection process or by cutting to a given, desired profile from precision manufactured extruded sheet.
The base material is vapour degreased in a fluoro-carbon solvent, typically "Arklon" P (ICI) for three minutes, then transferred to an ultrasonically vibra-ted heated solu-tion of the same solvent for a further three minutes for cleaning. A final vapour degreasing of three minutes dura-tion may be given. The plastics material is then transferred to an appropriate location jig in a process vacuum vessel, this operation being carried out under strictconditions of cleanliness.
The vacuum vessel is sealed and pumped out to a pressure of 1 x 10 5 mbar. Argon is then introduced until the pressure rises to 1 ~ 10 1 mbar. A voltage of 1.5 kilovolts AC is then applied to electrodes situated within the vacuum vessel and in close proximinity to the base plas-tics material surface which is to be processed. The glow discharge so initiated is held for a period of up to 20 minutes during which the plastics surface receives a'~ole-cular cleaning" and which treatment in effect although termed ~2~637~

cleaning provides a surface treatment which makes it more receptive,to xeceive the coatinglayer as described below.
After the molecular cleaing a reactive oxidation process to provide a key coat face layer is carried out as 5 follows. The vessel is re-pumped to 1 x 10 5 rnbar pressure and argon gas is introduced until the pressure reaches S x 10 4 ~ mbar. Oxygen is then added until the pressure has risen to 2 x 10- mbar.
A magnetron sputtering operation using a chromium 10 target i5 then initiated within the vacuum chamher and the charged chromium atoms interact reactively with oxygen so as to deposit thekey coat layer of chromium oxides onto the surface of the adjacent polycarbonate. This layer consists of one or more Gxides of chromium and possibly also the 15 metal itself. The layer i~s preferab]y 0.5 - 1.0 microns thick.
The oxygen supply is then discontinued and a coven-tional DC magnetron sputtering of chromium initiated at target power density levels which gradually increase from 20 ~ W/cm to 12 W/cm2. This gradual deposition of chromium onto the chromium oxide key coat layer ensures thata stress-free film is deposited. It is known in the art that thin layers of chrornium are prone to either compressive or tensile stresses and care is necessary at this stage. Typically a 25 reflective layer thickness of from 0.5 to 5.0 microns is applied.
Although the invention has been described with ref-erence to chromium oxides and a chromium multi-layer system 37(~

it is not limited thereto.
For example a more highly reflective alumium mirror can be produced in a similar manner with a reactively sput-tered aluminium layer which would be similar to the chrom-ium layer and consist of alumium oxides and possible alu-minium metal itself, followed by a layer of alumium metal.
In the case of a softer metal such as this, it may be neces-;~ sary to apply a hard abrasion resistant top coat of a die-, '~ lectric oxide such as an oxide of si:licon either by sputter-lo~ ~ing with the assistance of an RF field or by an electron beam evaporation. Both techniques are well known to those `~ ~ skllled in the art. A typical thickness range for this top coa;t would be 0.5 to 5.0 microns.
; Alternatively the glass or glass-like top coat layers ~lS `may~be formed in a variety of ways such as by means of an in situ glass making operation by co-reacting under plasma acti-vation`conditions typical gla5s making chemicals such as calcium carbonate, sodium carbonate and oxides of silicon.
By this method conventional calcium/sodium/silicon glass may be formed on the surface of the plastics material. Alterna-tively alumino/silicon glass films and lead glass films can ` also be made in a similar way. Another method for depositing a gl~ass layer is by the direct in vacuo vaporization of an alr~adyl~formed glass material e.g. borosilicate glass using ~25 èlectron beàms or conventional electrical heating devices .~ .
to induce vaporization.
It is also possible to use so called filled plastics material such as glass-filled, talc and chalk-Eilled, or : ~, " ;j, .

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other mineral filled polypropy.lene materials. Although these `fillers are primaril~ designed t~ reduce cost and improve properties, the filler component can be co-reacted with - substances in a vacuum chamber to improve bonding of the glass anchor coating.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making an optical component having specular reflective properties from plastics material comprising subjecting the plastics material to a degreasing operation by vapour degreasing in a fluorocarbon solvent and then transferring the material to an ultrasonically vibrated heated solution of the same solvent, performing a molecular cleaning operation, applying a face layer having hard glass like properties, said layer being applied in a vacuum vessel in an atmosphere of oxygen and argon, and being applied to a thickness of between 0.5 and 1.0 microns, and subsequently applying a coating of specular reflective material, said coating being between 0.5 and 5.0 microns thick.

2. A method as claimed in claim 1 in which the face layer is formed by applying a key coat layer of oxides of the material used to form the specular reflective properties.

3. A method as claimed in claim 2 in which the layer of oxide is applied by means of a magnetron sputtering operation in a vacuum vessel in an atmosphere of oxygen and argon at a pressure in the region of 2 x 10-3 mbar.

4. A method as claimed in claim 3 in which immediately after the molecular cleaning the vacuum vessel is reduced to 1 x 10-5 mbar pressure and argon gas is introduced until the pressure reached 5 x 10-4 mbar oxygen then being added until the pressure has risen to 2 x 10-3 mbar.

5. A method as claimed in claim 4 in which the layer of oxide is built up to the said thickness of between 0.5 and 1.0 microns by means of a magnetron sputtering operation using a target of the metal to be deposited to form the said layer.

6. A method as claimed in claim 5 in which the coating of reflective material is applied directly to the said layer.

7. A method as claimed in claim 6 in which the reflective material is applied by a DC magnetron sputtering operation using target power density levels increased gradually from 4W/cm2 to 12W/cm2 until the layer thickness of 0.5 to 5.0 microns is achieved.

8. A method as claimed in claim 7 in which the coating of a specular reflective material is chromium to a thickness of 0.5 to 5.0 microns.

9. A method as claimed in claim 7 in which the coating of specular reflective material is aluminum.

10. A method as claimed in claim 9 in which a hard abrasion resistant top coat is applied to the aluminum by sputtering with the assistance of a R.F. field.

11. A method as claimed in claim 9 in which a hard abrasion resistant top coat is applied to the aluminum by electron beam welding.

12. A method as claimed in claim 10 in which the top coat comprises a layer of dielectric oxide of between 0.5 and 5.0 microns thick.

13. A method as claimed in claim 1 in which the layer having hard glass like properties is applied in a vacuum vessel by means of electron beam vaporation.