Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD OF MAKING AN OPTICAL COMPONENT HAVING SPECULAR
REFLECTIVE PROPERTIES AND AN OPTICAL COMPONENT FORMED
THEREBY.
The present invention relates to a method of making
an optical component having specular reflective properties
and an optical component formed thereby.
The invention is more particularly concerned with
producing a shatterproof mirror which is particularly
suitable for use on vehicles which exhibits high
reflectivity, good optical clarity and will meet EC
directives.
According to one aspect of the present invention a
method of making an optical component having specular
reflective properties comprises forming a membrane by
applying to an optical grade plastics material a coating of
reflective material, applying a protective coating to the
reflective material, bonding the membrane so formed to a
correspondingly formed surface on a base member with the
reflective material adjacent to the base member.
The plastics material is preferably polycarbonate
film and the reflective material is preferably aluminium
and may be applied by evaporation under high vacuum.
The membrane preferably has an abrasion resistant
coating on its surface opposite that to which the
reflective material is applied.
The membrane is preferably in the region of 500
microns thick.
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The aluminium is preferably deposited to a thickness
of approximately 500 Angstroms and protected against
atmospheric corrosion by means of a protective
layer such as a silicon oxide coating.
The membrane is conveniently bonded to the base
member by use of a transfer adhesive to form the complete
optical component .
The membrane may conveniently be coated with the
transfer adhesive and also a backing member, the backing
member being removed when the membrane is to be applied to
the moulding. The membrane may be applied to the surface
by means of pressure pads.
Preferably the surface to which the membrane is
applied is recessed in the moulding and the membrane is
dimensioned so as to project slightly above the recess so
that even pressure can be applied by the pressure pads
which also can shape the membrane to the shape of the
surface which may for example be convex.
The thickness of the membrane is such that the
optical quality of the mirror is not affected by the slight
distortion caused by applying a flat membrane to a curved
surface.
The invention also includes an optical component
having specular reflective properties and made by the
method set forth.
According to another aspect of the invention an
optical component having specular reflective properties
comprises a membrane formed by a layer of polycarbonate,
applied to which is a layer of aluminium, protected by a
protective coating and which is adhered to a base member.
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-- 3
Preferably the layer of polycarbonate is protected
on its side remote from the aluminium coating by an
abrasion resistant layer.
The membrane is preferably located in a recess in
the base member and projects slightly above the recess.
The membrane preferably has a gap between it and the
walls of the recess and a silicon sealant is applied to
prevent the ingress of moisture etc.
The invention may be performed in various ways and
one specific embodiment will now be described by way of
example with reference to the accompanying drawings in
which:
j Figure 1 is a schematic view of a membrane for
application to a base member and:
Figure 2 is a cross-section of a membrane applied to
a base member.
The membrane shown in Figure 1 is formed as
follows:-
A sheet of optical grade polycarbonate approximately500 microns thick is put into a vacuum chamber. This sheet
has previously been coated on one side with an abrasion
resistant coating, and the unprotected side is to be
coated. The vacuum in the chamber is then lowered to
approximately 10-~ millibars and pure aluminium is
evaporated in the chamber to form a layer on the exposed
side of the sheet of approximately 500 Angstroms. The
deposition of aluminium is then stopped and a silicon oxide
protective coating is also applied by evaporation onto the
layer of aluminium.
'~162335
The membrane so formed is then removed from the
chamber and is coated with a transfer adhesive. This is
applied by passing it under a roller where a strip of
transfer adhesive applied to a backing member is rolled on
to it so that the layer of silicon oxide has the transfer
adhesive applied to it.
The membrane so formed is shown in Figure 1 and the
layers are shown as follows, 10 is the abrasion resistant
coating, 11 is the polycarbonate layer, 12 is the aluminium
layer, 13 is the silicon oxide layer, 14 is the transfer
adhesive and 15 is the backing strip.
Before application to the base moulding, the strip
with the transfer adhesive is cut into appropriate lengths,
and widths if necessary, to fit into a base member. The
base member is in the form of a moulding manufactured from
shatterproof materials such as polycarbonate, ABS or
polypropylene.
The base moulding is in the shape of for example the
rear view mirror for a vehicle, with one surface of
suitable optical form to which the reflective membrane may
be applied. The other surfaces may be aerodynamically and
aesthetically shaped to give the required appearance, and
the moulding may be suitably formed with means by which it
can be attached to a vehicle.
The base moulding is shown diagrammatically in
Figure 2. In this-base moulding is shown at 16 and has a
surface 17 of optical quality to which the membrane is
applied. This is achieved by removing the backing strip
and applying the exposed transfer adhesive 14 to the
surface 17. The surface 17 is recessed below the rim of
the mirror so that there is a peripheral wall 18 around the
edge of the moulding.
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The membrane is dimensioned so that when it is
inserted its peripheral edge is spaced from the wall 18 by
a small gap of approximately 0.8 mm. The depth of the
recess is also slightly less than the thickness of the
membrane so that the membrane projects very slightly above
the top surface 19 of the wall 18. In practice the depth
of the recess is 0.4 mm and the thickness of the membrane
is 0.5 mm so that there will be projection of the order of
0.1 mm.
The projection ensures that when the membrane is
applied a continuous pressure point can be applied across
the surface. The bonding of the membrane to moulding is
effected by inverting the moulding and applying to it the
exposed transfer adhesive which faces upwards and is
located by suitable means e.g. suction pads. The membrane
is then smoothed by pressure pads and moulded to the
membrane by the pressure. The gap allows for tolerances
and the silicon sealant seals the membrane against ingress
of moisture etc.
A mirror made in accordance with the above method
placed in a concentrated saline solution for a period of
six months showed no penetration at all.
