U.S. patent application number 11/297493 was filed with the patent office on 2006-04-27 for transparent plastic optical components and abrasion resistant polymer substrates and methods for making the same.
Invention is credited to David A. Richard.
Application Number | 20060087755 11/297493 |
Document ID | / |
Family ID | 33552894 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060087755 |
Kind Code |
A1 |
Richard; David A. |
April 27, 2006 |
Transparent plastic optical components and abrasion resistant
polymer substrates and methods for making the same
Abstract
A polymer-based component formed from a synthetic thermoplastic
or thermoset resin substrate, such as polymethyl methacrylate,
which is resistant to warping and distortion from moisture. A
composite multi-layer surface-hardening coating is formed on at
least the anterior surface of the resin substrate. The component
can include a composite multi-layer reflective coating to form a
mirror. A protective back-coat layer is deposited on a posterior
surface of the mirror. A multi-layer weather-resistant coating may
optionally be applied to the anterior surface of the polymer-based
mirror in order to increase the weatherability and durability of
the mirror. The various layers coating the synthetic resin
substrate have their moisture permeabilities selected so that
substantially equal amounts of moisture permeate through to both
the anterior and posterior side of the synthetic resin substrate. A
sol-gel coating can be used to deposit the multi-layers in a single
step by providing gradient zones of zirconia/silica while enabling
a hydrophobic or a hydrophilic exterior surface.
Inventors: |
Richard; David A.;
(Shingles, CA) |
Correspondence
Address: |
SNELL & WILMER LLP
600 ANTON BOULEVARD
SUITE 1400
COSTA MESA
CA
92626
US
|
Family ID: |
33552894 |
Appl. No.: |
11/297493 |
Filed: |
December 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10633972 |
Aug 4, 2003 |
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11297493 |
Dec 8, 2005 |
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10177614 |
Jun 24, 2002 |
6601960 |
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10633972 |
Aug 4, 2003 |
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09916777 |
Jul 27, 2001 |
6409354 |
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10177614 |
Jun 24, 2002 |
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60227194 |
Aug 23, 2000 |
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Current U.S.
Class: |
359/883 |
Current CPC
Class: |
G02B 5/0883 20130101;
G02B 5/0841 20130101; B32B 27/08 20130101; G02B 5/0866
20130101 |
Class at
Publication: |
359/883 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Claims
1-26. (canceled)
27. A method of forming a coating on a plastic component comprising
the steps of: providing a synthetic resin substrate of a
predetermined configuration; preparing a liquid sol-gel having a
predetermined precursor concentration of colloid particles;
applying the liquid sol-gel having a predetermined precursor
concentration of colloid particles to the synthetic resin substrate
until a predetermined thickness is provided; permitting the colloid
particles to migrate and orientate in the liquid sol-gel over a
predetermined time period by a zeta potential to enable a
subsequent formation of an abrasion resistant exterior coating and
a tie-bond layer on the surface of the synthetic resin substrate
having respective different concentrations of colloid particles;
and curing the liquid sol-gel to form a solid abrasion resistant
exterior coating.
28. The method of claim 27 wherein the liquid sol-gel includes a
polysiloxane carrier.
29. The method of claim 28 wherein the precursor includes metal
oxide colloid particles that form a majority by weight
concentration adjacent an exterior surface as a first layer.
30. The method of claim 29 wherein a second layer of metal oxide
colloid particles form an approximately 10% concentration by weight
adjacent the first layer.
31. The method of claim 30 wherein a third layer of metal oxide
colloid particles form an approximately 15% concentration by weight
between the second layer and the synthetic resin substrate.
32. The method of claim 31 wherein the metal oxide colloid
particles are zirconia/silica.
33. The method of claim 31 wherein a cathodic chemabsorbed
zirconia/silica layer is formed between the third layer and the
synthetic resin substrate.
34. The method of claim 32 further including applying a
predetermined pH liquid solution to the exterior coating to form
one of a hydrophobic and a hydrophilic surface by causing the
zirconia/silica colloid particles to be one of cathodic and
anodic.
35. The method of claim 27 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing a partial hydrolysis of tetraethoxysilane with a solution
including ZrO.sub.2 percursor to consume all of the water to
provide a ZrO.sub.2 doped SiO.sub.2 solution; and dispersing the
ZrO.sub.2 doped SiO.sub.2 solution in a polysiloxane liquid
carrier.
36. The method of claim 27 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing a full hydrolysis of tetramethoxysilane oligomer in water
with a solution including a ZrO.sub.2 percursor in a polar solvent
to provide an anatose-type ZrO.sub.2; and dispersing the
anatase-type ZrO.sub.2 solution in a polysiloxane liquid
carrier.
37. The method of claim 27 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing sodium metasalicate with water at a balanced pH of 1; adding
zirconyl chloride while stirring; emulsifying the mixture in
ethanol; adding hexamethylenetetramine and urea; filter and wash
with ethanol to form an anatase ZrO.sub.2 sol-gel; and dispersing
the anatase ZrO.sub.2 sol-gel in a polysiloxane liquid carrier.
38. The method of claim 27 further including the steps of applying
a reflective layer to one side of the coated synthetic resin
substrate; and sealing the reflective layer.
39. A method of forming a plastic component with a transparent
abrasion resistant coating comprising the steps of: providing a
synthetic resin substrate of a pre-determined configuration;
preparing a liquid sol-gel having a predetermined precursor
concentration of colloid particles; applying a liquid sol-gel
having a predetermined precursor concentration of colloid particles
to the synthetic resin substrate until a pre-determined thickness
is provided; permitting the colloid particles to migrate and
orientate in the liquid sol-gel by a zeta potential to enable a
subsequent formation of an abrasion resistant coating layer having
a majority by weight of colloid particles adjacent the exterior
coating surface and a lesser weight of colloid particles adjacent
the synthetic resin substrate; and curing the liquid sol-gel to
form a solid abrasion resistant coating.
40. The method of claim 39 wherein the liquid sol-gel includes a
polysiloxane carrier.
41. The method of claim 39 wherein the precursor colloid particles
forms an approximately 75% concentration by weight adjacent an
exterior surface as a first layer.
42. The method of claim 41 wherein a second layer of colloid
particles forms an approximately 10% concentration by weight
adjacent the first layer.
43. The method of claim 42 wherein a third layer of colloid
particles forms an approximately 15% concentration by weight
between the second layer and the synthetic resin substrate.
44. The method of claim 43 wherein a cathodic chemabsorbed colloid
particle layer is formed between the third layer and the synthetic
resin substrate.
45. The method of claim 39 further including applying a
predetermined pH liquid solution to the exterior coating to form
one of a hydrophobic and a hydrophilic surface by causing the
colloid particles to be one of cathodic and anodic.
46. The method of claim 45 further including applying an aqueous
solution of approximately 20 percent by weight NaOH to the exterior
coating to form a hydrophilic surface.
47. The method of claim 39 wherein the colloid particles include a
metal oxide.
48. The method of claim 47 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing a partial hydrolysis of tetraethoxysilane with a solution
including ZrO.sub.2 percursor to consume all of the water to
provide a ZrO.sub.2 doped SiO.sub.2 solution; and dispersing the
ZrO.sub.2 doped SiO.sub.2 solution in a polysiloxane liquid
carrier.
49. The method of claim 47 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing a full hydrolysis of tetramethoxysilane oligomer in water
with a solution including a ZrO.sub.2 percursor in a polar solvent
to provide an anatose-type ZrO.sub.2 and dispersing the
anatase-type ZrO.sub.2 solution in a polysiloxane liquid
carrier.
50. The method of claim 47 wherein in the step of preparing a
liquid sol-gel, the following sub-steps are performed comprising:
mixing sodium metasalicate with water at a balanced pH of 1; adding
zirconyl chloride while stirring; emulsifying the mixture in
ethanol; adding hexamethylenetetramine and urea; filter and wash
with ethanol to form an anatase ZrO.sub.2 sol-gel; and dispersing
the anatase ZrO.sub.2 sol-gel in a polysiloxane liquid carrier.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/177,614, filed on Jun. 24, 2002, now issued
as U.S. Pat. No. 6,601,960, which is a continuation-in-part of U.S.
patent application Ser. No. 09/916,777, filed Jul. 27, 2001, now
issued as U.S. Pat. No. 6,409,354, which is a conversion of U.S.
Provisional Patent Application Ser. No. 60/227,194, filed Aug. 23,
2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to coated plastic
substrates such as polymer-based optical components including
window panes and mirrors, and specifically to lightweight and
durable synthetic resin optical components resistant to abrasion
and warpage and methods for the manufacture thereof.
[0004] 2. Description of Related Art
[0005] Coated plastic substrates and optical components are
commonly used in various applications. The use of lightweight
plastic substrates are frequently desirable but have presented
problems for long-term use.
[0006] Mirrors typically have a multilaminate configuration. In
particular, mirrors are typically formed by selectively depositing
a series of compounds on a glass substrate material. These layers
generally include a reflective layer and a protective back-coat
layer covering-the reflective layer. The reflective layer is
commonly formed from a thin film of aluminum, chromium, rhodium, or
silver. In industrial applications, aluminum is typically used in
place of silver due to its high reflectivity and low cost. The
protective back-coat layer serves a multiplicity of functions, such
as protecting the reflective layer from humidity. This function is
required as the reflective layer, especially if it is formed from
aluminum, is easily corroded by moisture. Since the substrate
material upon which the reflective layer is deposited is often
permeable to moisture, it is important that the protective
back-coat layer be substantially impermeable to moisture in order
to provide an effective encasement for the reflective layer. The
back-coat layer also serves as a mechanical barrier to, for
example, impact damage from airborne particulate matter. A properly
configured and applied back-coat layer thus assists to provide a
durable mirror.
[0007] Due to the high production costs related to glass mirrors,
significant research has been undertaken to develop a durable,
low-cost plastic mirror employing a synthetic resin substrate
material. Furthermore, due to the shatter-proof nature of synthetic
resin mirrors, their use is preferred in automobiles over
conventional glass mirrors in order to improve the safety of the
automobile. The primary focus of this research has been in
connection with dynamically stable and substantially optically
clear thermoplastic or thermoset resins, such as polymethyl
methacrylate (PMMA). As a result of these efforts, a method for
sequentially depositing an aluminum reflective material and an
impermeable back-coat layer on a resin substrate material has been
developed.
[0008] The main problem associated with synthetic resin mirrors is
their significantly limited operational service life resulting from
warpage or distortion of the mirrors due to the hygroscopic
properties of thermoplastics or thermoset resins. Unlike their
glass counterparts, mirrors formed with a thermoplastic or a
thermoset resin as their substrate material gradually absorb
moisture from the surrounding atmosphere. Over time, the moisture
so absorbed corrodes the reflective layer. Further, the absorption
of moisture, coupled with variations in other climatic conditions,
causes the thermoplastic or thermoset resin to expand and contract.
Compounding these problems is the fact that the back-coat layer is,
typically, not affected by humidity or other climatic conditions.
The back-coat layer thus acts to prevent the smooth linear
expansion and contraction of the thermoplastic or thermoset resin
substrate. Furthermore, the moisture permeability of the various
coatings applied to both sides of the synthetic resin substrate
often lead to different amounts of moisture being absorbed by the
opposing surfaces of the synthetic resin substrate, thus resulting
in uneven expansion and contraction on both sides of the substrate.
These conditions all interact to produce distortion to the image
produced by the reflective layer of the plastic mirror and a
related loss of optical clarity. As the mirror ages, this
degradation only becomes more acute.
[0009] In order to reduce the susceptibility of synthetic resins to
hygroscopic effects, it has been proposed that a hardening material
be applied to the thermoplastic or thermoset resin substrate before
deposition of the reflective layer. Currently organosilicon
polymers are the preferred hardening material. These polymers are
preferred due to their ability to provide protection against impact
damage and their high optical clarity when fully cured. Although
organosilicon polymers are the best available material for this
purpose, these polymers are not totally impermeable to water. Thus,
although partially effective, these polymers do not provide a
complete remedy to all of those issues related to the use of a
thermoplastic or thermoset resin substrate material in connection
with a mirror apparatus.
[0010] A need exists for a mirror apparatus and other optical
components that do not suffer from the foregoing disadvantages and
limitations. In particular, a need exists for a mirror apparatus
formed using a thermoplastic or thermoset resin substrate that will
remain substantially unaffected by ambient environmental
conditions.
SUMMARY OF THE INVENTION
[0011] The foregoing shortcomings and disadvantages of the prior
art are alleviated by the present invention that provides a
polymer-based optical component that is resistant to abrasion and
mechanical distortion resulting from climatic and hydrodynamic
conditions, such as a polymer-based mirror which includes a
substrate or transparent element formed from a synthetic
thermoplastic or thermoset resin, such as polymethyl methacrylate
or the like. The resin substrate has an anterior surface and a
posterior surface. In certain embodiments, a tie-bond layer is
typically applied to all of the exposed surfaces of the resin
substrate.
[0012] Following deposition of the tie-bond layer, a
surface-hardening layer is coated on at least the anterior surface
of the resin substrate. This layer may consist of one or more
layers of various materials which form a surface-hardening layer
substantially impermeable to water. A surface-hardening layer
formed of the following layers has been found to provide a desired
level of moisture permeability for the anterior surface of the
synthetic resin substrate: 500 to 1200 angstroms of SiO, preferably
750 angstrom; 300 to 1200 angstroms of SiO.sub.2, preferably 550
angstrom; and, 600 to 1400 angstroms of Z.sub.v(iPv).sub.2,
preferably 725 angstrom. A surface-hardening layer may also be
applied to the posterior surface of the synthetic resin substrate,
where the posterior surface-hardening layer preferably comprises
300 to 1200 angstroms of SiO.sub.2, preferably 550 angstrom; and,
600 to 1400 angstroms of Z.sub.v(iPv).sub.2 preferably 725
angstrom.
[0013] A reflective layer of a composition substantially resistant
to moisture is deposited on the posterior side of the resin
element. The reflective layer comprises a series of materials
sequentially deposited onto the posterior surface of the treated
resin substrate. A reflective layer formed from the following
layers exhibits the desired reflectance, moisture permeability, and
durability for the polymer-based mirror of the present invention:
500 to 1200 angstroms of SiO, preferably 750 angstroms; 700 to 1500
angstroms of aluminum, preferably 1200 angstroms; 500 to 1200
angstroms of SiO, preferably 750 angstroms; 600 to 1400 angstroms
of Z.sub.v(iPv).sub.2, preferably 725 angstroms; and 300 to 1200
angstroms of SiO.sub.2, preferably 550 angstroms. The reflective
layer of the invention is preferably formed on the synthetic resin
substrate via a vacuum deposition technique. A protective back-coat
layer is then deposited over the reflective layer to encase the
outer surface of the reflective film layer. When the
surface-hardening layer is also applied to the posterior surface of
the resin substrate, the back-coat layer can also encase the
surface-hardening layer as well as the reflective layer. A
weather-resistant coating is further applied to the anterior
surface of the polymer-based mirror in order to increase the
weatherability and durability of the mirror.
[0014] Overall, the polymer-based mirror of the present invention
has a multilaminate configuration including sequentially deposited
layers of organic and inorganic materials. The polymer-based mirror
of the present invention exhibits superior moisture resistance as
compared to conventional aluminum, chromium, and rhodium coated
mirrors. The present invention further provides a mirror that is
easily and economically produced.
[0015] Another embodiment of the present invention provides an
improved resin substrate component such as a mirror or window for
the automotive industry or any application of a resin substrate
component with superior abrasion resistant properties that can be
made in an economical manner. A gradient coating of a
zirconia/silica colloid particles can be provided directly on a
synthetic resin substrate by a sol gel method of coating the
substrate and permitting a controlled orientation and migration of
the zirconia/silica colloid particles within a polysiloxane carrier
before curing. As a result, the resin substrate is provided with
layers or gradient zones having varying amounts of zirconia/silica
colloid particles. In one embodiment, the exterior surface of the
final product will have a high concentration of zirconia/silica
particles to provide an abrasion resistant and moisture stable
product that can accommodate thermal expansion cycles during normal
use. The present invention further includes the method of making
such a product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The features of the present invention, which are believed to
be novel, are set forth with particularity in the appended claims.
The present invention, both as to its organization and manner of
operation, together with further advantages, may best be understood
by reference to the following description, taken in connection with
the accompanying drawings in which the reference numerals designate
like parts throughout the figures thereof and wherein:
[0017] FIG. 1 is a cross-sectional view of a preferred embodiment
of the polymer-based mirror of the present invention;
[0018] FIG. 2 is a cross-sectional view of another preferred
embodiment of the polymer based mirror of the present
invention;
[0019] FIG. 3 is a cross-sectional view of yet another preferred
embodiment of the polymer-based mirror of the present
invention;
[0020] FIG. 4 is a graphical representation of the results of a
reflectivity test of six mirrors made in accordance with the
present invention having a first coating;
[0021] FIG. 5 is a graphical representation of the results of a
reflectivity test of six mirrors made in accordance with the
present invention having a second coating;
[0022] FIG. 6 is a graphical representation of the results of a
reflectivity test of six mirrors made in accordance with the
present invention having a third coating;
[0023] FIG. 7 is a cross-sectional view of another preferred
embodiment of the polymer based mirror of the present
invention;
[0024] FIG. 8 is a cross-sectional view of another preferred
embodiment of the polymer based mirror of the present
invention.
[0025] FIG. 9 is a partial schematic cross-sectional view of still
another preferred embodiment of a coated resin substrate component
with abrasion resistant properties;
[0026] FIG. 10 is a schematic cross-sectional view of a polymer
based mirror; and
[0027] FIG. 11 is a flow chart of production steps to create a
pre-form product.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The following description is provided to enable any person
skilled in the art to make and use the invention and sets forth the
best modes contemplated by the inventors of carrying out their
invention. Various modifications, however, will remain readily
apparent to those skilled in the art, since the general principles
of the present invention have been defined herein specifically to
provide a coated resin substrate and method of making.
[0029] The present invention is directed to a coated resin
substrate such as optical components including polymer-based
mirrors which may possess any variety of configurations. For
example, as discussed with regard to the several FIGURES, the
polymer-based mirror of the present invention can have a
wedge-like, curved, toric, planar, or other configuration. The
polymer-based mirror can be utilized as an interior or exterior
rearview mirror for an automobile. However, it is understood that
the polymer-based mirror of the present invention is not limited to
automotive usage and may be utilized for other mirror applications
as well.
[0030] The polymer-based mirror of the invention is comparable to a
glass mirror in quality and appearance, but is advantageous over
glass due to its lightweight and durable design. The polymer-based
mirror of the present invention has been designed so as to not
exhibit significant moisture absorption. As a result, the
polymer-based mirror of the present invention does not exhibit
noticeable warping or other mechanical distortion. In varied
climatic conditions, the polymer-based mirror of the invention
remains dynamically stable. The mirror of the invention is also
very durable. The surface-hardening layers noted below impart
significant resistance to mechanical damage from, for example,
airborne particles. As a result, the mirror of the invention
exhibits sufficient stability so as to comply with automobile
industry test standards related to, for example, internally and
externally mounted rearview mirrors.
[0031] Referring now to FIG. 1, a cross-sectional view of a
preferred embodiment of the polymer-based mirror 10 designed as an
inside rearview mirror for a vehicle is illustrated. A transparent
mirror body 14 is typically made of a synthetic resin substrate
high in optical clarity, such as a thermoplastic or thermoset
resin. A preferable synthetic resin is polymethyl methacrylate
(PMMA) resin, while it is understood that other similar polymers
may also be utilized in forming the synthetic resin substrate 14,
such as polycarbonate (bisphenol-A), cyclic olefins, styrene,
acrylic/styrene, CR-39.RTM. manufactured by PPG Industries,
acetate, polyvinyl butyrate, or polyurethane. This synthetic resin
substrate 14 can readily be shaped by an injection or compression
molding process.
[0032] The PMMA resin substrate 14 is preferably formed by
polymerizing methyl methacrylate, where virtually all of the methyl
methacrylate reacts during the polymerization reaction to form
PMMA. Some unreacted monomers do remain on a front surface 12 and a
rear surface 16 of the resin substrate 14 as well as within the
core of the resin substrate 14. Those monomers within the resin
substrate 14 typically blush to the closest of either the front
surface 12 or rear surface 16 following the molding process. In
order to eliminate any detrimental effects which these monomers may
cause, all of the exposed surfaces of the resin substrate 14 are
treated with a thin and transparent surface preparation in the form
of an organic silicon material. This action renders the resin
substrate 14 virtually chemically inert.
[0033] This organic silicon material is sprayed, dipped, or
centrifugally coated onto the resin substrate 14 to form a tie-bond
layer 18 on the front surface 12 and the rear surface 16 of the
resin substrate 14. The tie-bond layer 18 is preferably an
organosilicon polymer with a thickness of between about 3 and about
10 microns. The tie-bond layer 18 also serves to provide the
substrate with a sufficient degree of scratch resistively. A
typical organosilicone is one prepared from triethoxymethyl silane
CH.sub.3Si(OC.sub.2H.sub.5).sub.3. The tie-bond layer 18 is,
generally, permeable to humidity, for example, the rate of moisture
absorption through the organosilicon silane is about 3g/m.sup.2 per
24 hours when tested in an atmosphere maintained at 50.degree. C.
with 98% room humidity. Thus, the tie-bond layer 18 requires an
additional coating to reduce this permeability.
[0034] Following application of the tie-bond layer 18, the front
(anterior) surface 12 of the resin substrate 14 is coated with a
surface-hardening layer 20. The surface-hardening layer 20 may
consist of one or more layers of various materials which form a
surface-hardening layer substantially impermeable to water. A
surface-hardening layer 20 formed of the following layers has been
found to provide a desired level of hardness and moisture
permeability for the synthetic resin substrate: 500 to 1200
angstroms of SiO, preferably 750 angstrom; 300 to 1200 angstroms of
SiO.sub.2 preferably 550 angstrom; and, 600 to 1400 angstroms of
Z.sub.v(iPv).sub.2, preferably 725 angstrom. If desired, the rear
(posterior) surface 16 can also be coated with a surface-hardening
layer 22 without detracting from the performance of a subsequent
reflective layer 24 and protective back-coat layer 26 applied to
the posterior surface 16. A surface hardening layer 22 formed of
the following layers has been found to provide a desired level of
hardness and moisture permeability for the synthetic resin
substrate: 300 to 1200 angstroms of SiO.sub.2, preferably 550
angstrom; and, 600 to 1400 angstroms of Z.sub.v(iPv).sub.2
preferably 725 angstrom.
[0035] To provide a mirror surface, the posterior surface 16, or
posterior surface-hardening layer 22 (if applied), of the resin
substrate body 14 is further coated with a thin composite
reflective layer 24. The reflective layer 24 is applied using
vacuum deposition techniques. The reflective layer 24 is formed by
sequentially depositing a series of organic and inorganic material.
A reflective layer 24 having the following sequential layers has
been found to provide the desired moisture permeability, level of
reflectivity, durability, and resistance to corrosion: 500 to 1200
angstroms of SiO, preferably 750 angstrom; 700 to 1500 angstroms of
aluminum, preferably 1200 angstrom; 500 to 1200 angstroms of SiO,
preferably 750 angstrom; 600 to 1400 angstroms of
Z.sub.v(iPv).sub.2, preferably 725 angstrom; and, 300 to 1200
angstroms of SiO.sub.2, preferably 550 angstrom. The reflective
layer 24 having this construction has been found to provide good
reflectivity and excellent resistance to erosion from the influence
of moisture. Furthermore, this alloy for the reflective layer 24 is
superior to the reflectivity of a standard aluminum thin film
reflective coatings. The reflective layer 24 possesses a luminous
transmission of approximately 94.5%.
[0036] As a mechanical protection for the thin reflective layer 24,
a protective back-coat layer 26 is formed so as to closely cover
the entire area of the outer major surface of the reflective layer
24. Various known materials and coating methods can be used to
form, and apply, the back-coat layer 26. For example, a back-coat
layer 26 of excellent properties can be obtained by applying a
resin based paint containing a relatively large amount of a powered
inorganic filler material such as calcium carbonate, barium
carbonate and/or aluminum silicate. As a particular example of this
type of coating method, it is possible to form a back-coat layer 26
sufficiently high in physical strength and appropriate in reduced
humidity permeability by the application of a paint which comprises
an alkyd resin binder and a calcium carbonate powder (between about
1 to about 5 microns in particle size) amounting to 75 to 80% by
weight of the alkyd resin so as to afford a thickness of between
about 10 to about 20 microns to the resultant back-coat layer 26.
The presence of the back-coat layer 26 further eliminates the need
to include the SiO layer, which is present in the anterior
surface-hardening layer 20, in the posterior surface-hardening
layer 22. As a primary feature of the invention, the permeability
of the back-coat layer 26 to moisture is selected to operate in
conjunction with the moisture permeability of the underlying
layers, i.e., reflective layer 24 and posterior surface-hardening
layer 22, and the anterior surface-hardening layer 20 so as to
ensure that substantially equal amounts of moisture permeate
through to both the anterior surface 12 and the posterior surface
16 of the resin substrate 14.
[0037] The polymer-based mirror illustrated in FIG. 1 has a
generally laterally elongated rectangular shape as well as
generally rectangular cross-sectional shape. In other preferred
embodiments of the present invention, the resin body 14 may be
formed as other than rectangular. For example, as shown in FIG. 2,
a polymer-based mirror 200 having a planoconvex resin substrate 202
is shown. In FIG. 3, a polymer-based mirror 300 having wedge shaped
resin substrate 302 is shown, where the anterior surface 12 and the
posterior surface 16 are not parallel to each other. The resin
substrate 302 is so shaped as to be wedge-like in cross-section in
order to avoid glare from the mirror 300 during night running of a
vehicle employing the mirror 300. In FIGS. 2 and 3, like reference
numbers refer to like elements described in connection with FIG. 1
and further discussion of these like elements will be omitted. It
is also possible for the polymer-based mirror to have other shapes
and configurations, including but not limited to toric, bi-convex,
plano-concave, and bi-concave.
[0038] From a practical viewpoint, the polymer-based mirror of the
present invention is comparable to a conventional mirror created by
a glass plate coated with an aluminum film owing to the high
transparency of the optically clear thermoplastic or thermoset
resin substrate 14 and good reflectivity of the reflective
SiO--Al--SiO-Z.sub.v(iPv).sub.2, SiO.sub.2 reflective layer 24.
Moreover, the polymer-based mirror 10 is advantageous in its
lightweight nature and durability of the resin substrate 14.
Furthermore, the possibility of shaping the cross-sectional resin
substrate 14 by a simple injection or compression molding without
the need of any machining operations leads to reduction of the
total cost of production compared with the production conventional
glass mirror of the same shape.
[0039] As one of the most remarkable effects of the invention, the
polymer-based mirror 10 of the present invention 10 is quite stable
and can withstand extended use in either dry or humid atmospheres.
The polymer-based mirror 10 has an anterior treated surface and a
posterior treated surface that exhibit substantially equivalent
reduced moisture permeability to prevent warpage or distortion of
the mirror 10. The reason for the substantially equivalent reduced
moisture permeability is that the composition and thicknesses of
the anterior surface hardening layer 20, posterior
surface-hardening layer 22, reflective layer 24, and back-coat
layer 26 are selected to have a moisture permeability providing the
anterior surface 12 of the resin substrate 14 with substantially
the same exposure to moisture as the posterior surface 16. The
resin substrate 14 absorbs low levels of moisture from its anterior
surface 12 and undergoes only slight swelling in the region
contiguous to the anterior surface 12 as a result. At the same
time, the same atmospheric moisture condition is applying itself to
the posterior surface 16 of the resin substrate 14. The moisture
permeability conditions of the posterior surface-hardening layer
22, reflective layer 24, and back-coat layer 26 are selected such
that the resin substrate 14 absorbs the same minimum levels of
moisture from the posterior surface 16 as its anterior surface 12
and tends to undergo only slight swelling on the posterior side of
the resin substrate 14 as well. For this reason, even when the
resin substrate 14 swells by absorption of moisture, the swelling
occurs on both anterior surface 12 and posterior surface 16 in an
almost balanced manner. Therefore, the swelling of the resin
substrate 14 does not result in distortion of the optical surface
figure of the mirror to a degree that it degrades the optical
performance of the mirror 10.
[0040] Experiments on the polymer-based mirror 10 formed in
accordance with the present invention were performed to determine
the advantageous characteristics and effects of the thin film
formula ranges described within the invention on mirror
reflectivity performance. In these experiments, the
surface-hardening layers 20 and 22 and the organosilicon silane
tie-bond layer 18 were not altered, where the composition of the
reflective layer 24 was altered to illustrate its effect on
reflectivity of the mirror 10.
Experiment Number One
[0041] Six (6) sample mirrors of the present invention were
subjected to the test. All samples were subjected to film
deposition. The reflective coating 24 deposited was: 500 Angstrom
of SiO, 700 Angstrom of Al, 500 Angstrom of SiO, 600 Angstrom of
Zv(iPv).sub.2, and 300 Angstrom of SiO.sub.2. An adequate
background of O.sub.2 gas was introduced for reaction of the
coating media. Evaporation was performed at 5.times.10.sup.-5 TORR.
This pressure has been found to allow reactive evaporation and is
low enough to produce dense coatings. Upon completion of the
coating process, the mirrors were subjected to reflectivity testing
and aesthetic observation. The outcome of the reflectivity test
was: TABLE-US-00001 Wavelength % Reflectivity Color 750 94.993 dark
blue 700 94.948 dark blue 650 71.360 dark blue 600 63.169 dark blue
550 72.609 dark blue 500 87.223 dark blue 450 92.197 dark blue 400
64.793 dark blue 380 4.292 dark blue 300 2.089 dark blue
[0042] A graphical representation of the results of the foregoing
reflectivity test is shown in FIG. 4.
Experiment Number Two
[0043] Six (6) sample mirrors of the present invention were
subjected to the test. All samples were subjected to film
deposition. The reflective coating 24 deposited was: 750 Angstrom
of SiO, 1200 Angstrom of Al, 750 Angstrom of SiO, 725 angstrom of
Z.sub.v(iPv).sub.2, and 500 Angstrom of SiO.sub.2. An adequate
background of O.sub.2 gas was introduced for reaction of the
coating media. Evaporation was performed at 5.times.10.sup.-5 TORR.
This pressure has been found to allow reactive evaporation and is
low enough to produce dense coatings. Upon completion of the
coating process, the mirrors were subjected to reflectivity testing
and aesthetic observation. The outcome of the reflectivity test
was: TABLE-US-00002 Wavelength % Reflectivity Color 750 95.220
silver 700 95.131 silver 650 95.133 silver 600 94.959 silver 550
94.339 silver 500 95.220 silver 450 95.025 silver 400 95.503 silver
380 5.146 silver 300 4.399 silver
[0044] A graphical representation of the results of the foregoing
reflectivity test is shown in FIG. 5.
Experiment Number Three
[0045] Six (6) sample mirrors of the present invention were
subjected to the test. All samples were subjected to film
deposition. The reflective coating 24 deposited was: The coating
description was: 1200 Angstrom of SiO, 1500 Angstrom of Al, 1200
Angstrom of SiO, 1400 Angstrom of Z.sub.v(iPv).sub.2, and 1200
Angstrom of SiO.sub.2. An adequate background of O.sub.2 gas was
introduced for reaction of the coating media. Evaporation was
performed at 5.times.10.sup.-5 TORR. This pressure has been found
to allow reactive evaporation and is low enough to produce dense
coatings. Upon completion of the coating process, the mirrors were
subjected to reflectivity testing and aesthetic observation. The
outcome of the reflectivity test was: TABLE-US-00003 Wavelength %
Reflectivity Color 750 95.306 gold 700 95.054 gold 650 95.259 gold
600 94.998 gold 550 95.434 gold 500 95.139 gold 450 95.139 gold 400
94.653 gold 380 12.153 gold 300 7.589 gold
[0046] A graphical representation of the results of the foregoing
reflectivity test is shown in FIG. 6.
Experiment Number Four
[0047] An experiment was carried out to determine the resistance
and stability of the polymer-based mirror formed in accordance with
the present invention when exposed to a high moisture and salt
environment according to the ASTM B117-95 standard. Each reflective
film was fabricated according to the description presented. There
were three (3) mirrors subjected to the test. Two (2) of the
mirrors of the present invention samples were of an aspheric
anterior surface figure and one (1) was of a plano anterior surface
figure. All three samples of the invention were subjected to a
concentrated salt solution of 5.+-.1% water with sodium chloride.
The specific gravity of the condensate was 1.036. The pH of the
condensate was 6.8. The volume of the concentrate was 1.3 ml/hr/80
cm.sup.2. The test chamber temperature was 35.+-.1.degree. C. The
invention specimens were positioned at an incline to the spray of
15.degree. from the vertical. All invention samples were exposed to
the test for 96 hours of continuous spray. None of the samples of
the invention were subjected to any pre-cleaning. After the
conclusion of the test, the sample mirrors were water rinsed and
air-dried. Observations at the conclusion of the test were that
there were no visual or mechanical defects on any of the three (3)
sample mirrors. Additionally, an examination of the reflectivity
concluded that there had been no deterioration of the pre-test
reflectivity results. Additionally, examination of the optical
imagery of the sample mirrors showed no post-test distortion.
[0048] The mirror of the invention also includes modification of
the anterior surface geometry so as to both increase the viewing
angle of the device and allow for the correction of image
aberrations. By incorporating aspheric formulae such as: z
.function. ( x ) = cx 2 1 + 1 - c 2 .function. ( k + 1 ) .times. x
2 + a 1 .times. x 4 + a 2 .times. x 6 + a 3 .times. x 8 + a 4 10
##EQU1## where: c, k, a.sub.n=spherical, conic, and aspheric
coefficients [0049] x=distance (radius) from the center of the lens
[0050] z=depth or as NERBS in a CAD/CAM design the mirror of the
invention can be given an anterior configuration configured to
correct magnification errors and distortions typically observed in
glass interior and exterior rearview mirrors.
[0051] Referring now to FIG. 7, a cross-sectional view of a
polymer-based mirror 400 formed in accordance with another
preferred embodiment of the present invention is illustrated in
which the polymer-based mirror 10 described in FIG. 1 further
includes a weather-resistant coating 402 on the anterior side of
the mirror 400. The elements of FIG. 7 which are similarly numbered
as those elements in FIG. 1 are equivalent, and a further
description of these elements already described in connection with
FIG. 1 will be omitted from the description of the polymer-based
mirror 400 of FIG. 7. The elements of the polymer-based mirror 400
which are similarly numbered as those elements are The
weather-resistant coating 402 includes a hydrophilic stack of
layers 404 having its outer surface covered with a hydrophobic
layer 406, where the hydrophilic stack 404 is formed over the
anterior surface-hardening layer 20. The hydrophilic stack 404
preferably comprises alternating layers of zirconia (ZrO.sub.2) and
silicon dioxide, where a stack 404 of the following construction
has been found by the inventors to provide optimal levels of
reflectivity and transmission while maintaining an absence of color
in the stack 404: 2616 angstrom of SiO.sub.2, 246 angstrom of
ZrO.sub.2, 174 angstrom of SiO.sub.2, 765 angstrom of ZrO.sub.2,
907 angstrom of SiO.sub.2. The hydrophobic layer 406 is preferably
a hydrophobic acting perfluoroalkylsilane which forms a strongly
adherent fluorised siloxane coating on the outer surface of the
hydrophilic stack 404. The optimal coating thickness for the
perfluoroalkylsilane layer 406 is approximately 5-20 nm.
[0052] By utilizing alternating layers of SiO.sub.2 and ZrO.sub.2
in the hydrophilic stack 404 in combination with the hydrophobic
perfluoroalkylsilane layer 406, a weather-resistant coating 402 is
provided which increases the weatherability and durability of the
mirror 400 by affording a more weather resistant barrier to water
infusion. The layers of the hydrophilic stack 404 and the
hydrophobic layer 406 are both dry coatings which are vacuum coated
onto the surface of the anterior surface-hardening layer 20.
Furthermore, the compositions of the hydrophilic stack 404 and the
hydrophobic layer 406 are selected to have matching thermal
coefficients of expansion, so that the various layers within the
weather-resistant coating 402 expand and contract in a
substantially uniform manner under all conditions to which the
mirror 400 is exposed. The thermal coefficient of expansion of the
weather-resistant coating 402 is further matched against the other
layers of the polymer-based mirror 400, so that all of the various
layers expand and contract in a substantially uniform manner. By
matching the thermal coefficients of expansion of the various
layers, the bonds formed between the layers will also be maintained
in a more secure manner to prevent the leakage of moisture there
through. The above-described stack composition of the
weather-resistant coating 402 has been found to provide the optimal
balance between warpage, reflectivity, and weatherability of the
polymer-based mirror 400.
[0053] Referring now to FIG. 8, a cross-sectional view of a
polymer-based mirror 500 formed in accordance with an alternative
embodiment of the present invention is illustrated in which the
reflective layer 24 is positioned on the anterior side of the resin
substrate 14. The elements of FIG. 8 which are similarly numbered
as those elements in FIG. 1 are equivalent, and a further
description of the composition of these elements already described
in connection with FIG. 1 will be omitted from the description of
the polymer-based mirror 500 of FIG. 8. The core of the
polymer-based mirror comprises a resin substrate 14 having tie-bond
layers 18 respectively formed on its front surface 12 and its rear
surface 16. The posterior surface-hardening layer 22 and back-coat
layer 26 would then be respectively formed over the tie-bond layer
18 on the posterior side of the resin substrate 14. Prior to
forming the reflective layer 24 on the anterior side of the resin
substrate, a layer of SiO material 502 between 500 to 1200
angstroms, preferably 750 angstrom, is formed over the tie-bond
layer 18. The reflective layer 24 is then formed over the SiO layer
502. An anterior surface-hardening layer 504 is then formed to coat
the reflective layer, where the anterior surface-hardening layer
504 has the same composition as posterior surface hardening layer
22. The weather-resistant coating 402 is then formed over the
anterior surface-hardening layer 504. In this embodiment of the
polymer-based mirror 500, the reflective surface of the mirror 500
is located on the anterior side of the resin substrate 14 so that
light is reflected from the mirror without actually passing through
the resin substrate 14. However, the polymer-based mirror may still
be subjected to the same warpage and distortion problems from
moisture as the other embodiments of the present invention. Thus,
each of the various layers of polymer-based mirror 500 are also
selected to have a moisture permeability providing the anterior
surface 12 of the resin substrate 14 with substantially the same
exposure to moisture as the posterior surface 16.
[0054] While it is understood that polymer-based mirror of the
present invention may be formed in any number of ways known to
shape thermoplastic or thermoset resin objects, the resin substrate
14 in the various embodiments of the polymer-based mirror of the
present invention is preferably formed using an improved
injection/compression molding technique. Once the resin substrate
14 has been formed using this technique, it is removed from the
mold where the various coatings of the present invention are then
applied to form the polymer-based mirror. The injection/compression
molding process of the preferred invention consists of enjoining a
compression action within an injection mold (not shown) with the
activity of a conventional injection molding process. The
injection/compression molding process can be described as a
cyclical process which encompasses the following steps: heating and
melting of a thermoplastic resin material; mixing and homogenizing
the now liquid material (the melt); injecting the melted
thermoplastic material into the mold cavity; initiating the
injection/compression cycle of the present invention; cooling and
curing or solidifying the melted thermoplastic resin in the mold
cavity, and ejecting the finished resin substrate 14 from the mold.
The injection/compression molding process requires that the
thermoplastic material undergo two phase changes during the cycle.
The solid thermoplastic resin is first heated to form a viscous
liquid melt for injection into the mold after which the melt is
converted back into a solid state by cooling in the mold under
secondary compression.
[0055] In selecting PMMA as the preferred optical grade material
for the present invention, it is understood that all plastics are
governed by the thermodynamic principles which are basic to the
chemical structure of each. In the melting of various
thermoplastics, the quantity of heat required per unit weight may
vary significantly depending on the differences in heat capacity of
the various thermoplastics. This characteristic also defines the
control the process and mold design have over molecular orientation
in the processing of plastic mirrors.
[0056] The present invention overcomes the problems of poor mold
surface replication and residual part stresses by the molded
thermoplastic article, and more specifically to maximize
micro-replication of the finest surface detail and figure onto an
optical grade thermoplastic injection molded product such as a
plastic mirror. Such fidelity of the injection molded part to the
molding surfaces is achieved by dynamically moving, under hydraulic
pressure, the surfaces of the mold toward one another during a
particular phase of the injection cycle. As the injection portion
of the molding cycle is underway, at a predetermined point of
change over from a first stage of injection, the pre-determined,
volumetrically metered filling of the mold cavity is stopped and
the injection cycle goes into a second stage holding time phase.
Synchronous with the point of first stage to second stage cycle
phase change over, the mold starts to compress the contents of its
cavity simultaneously with cessation of the injection of
thermoplastic material. Prior to the thermoplastic material
temperature declining below its glass transition temperature, the
mold has compressed the cavity contents to a pre-adjusted position.
Uniform compression is exerted over the entire surface of the resin
substrate 14. As a result of the uniform compression, all stresses
are distributed uniformly over the entire area of the parts
surface, significantly negating stress induced birefringence.
Furthermore, the process also creates a processing environment that
renders uniformity to part-to-part density thus controlling the
parts optical clarity and weight.
[0057] The injection/compression technique of the present invention
incorporates unique characteristics that differ considerably from
that of conventional injection mold techniques. While conventional
injection mold techniques utilize stationary molds the use of
injection packing pressures to complete the fill cycle of the
thermoplastic material injection process, the present invention
incorporates dynamic components that allow for the reduction of
injection pressures during the molding process while integrating
exceptional control over the part volume and the ability to
molecularly replicate the resin substrate surfaces. In another
preferred embodiment of the present invention, an annealing
procedure may be added to the formation of the polymer-based mirror
10 to further enhance its compliance with weatherability
requirements for both interior and exterior vehicular applications.
The annealing process is done to release internal stress within the
synthetic resin substrate 14. The annealing process consists of
heating the polymer-based mirror 10 (in an oven for example) to
about 130.degree. to 150.degree. F. for about 5-6 hours. The piece
is then cooled slowly to room temperature, 70.degree. F., and must
at least be cooled to 110.degree. F. In performing the annealing
process, forced-air circulation ovens designed for the annealing
and heating of synthetic polymers are recommended. Good forced air
circulation ensures uniform temperatures essential to the annealing
process. The oven's air velocity should be between 150-250 feet per
minute and should be controllable to within .+-.10.degree. F.
(.+-.6.degree. C.) to avoid uneven or excessive heating.
Temperature control selection effects oven performance. Controllers
monitoring oven temperature and maintaining constant voltage into
the heating elements are considered to work best, but conventional
controllers can be used, such as percentage timer controls which
regulate the percent of time heaters are on, but may not provide
the best uniform heat the better controllers offer for this
process. Proportional time controls with step switches to vary heat
output have shown to produce uneven temperatures when evaluated
under this process.
[0058] Before the annealing process begins, the polymer-based
mirror must be clean and dry. Spray masking, protective tape, paper
masking, and other material must be removed to prevent it from
baking onto the material. Plastic masking may remain in place. To
anneal synthetic polymers, heat to 180.degree. F. (80.degree. C.),
just below the deflection temperature, and cool slowly. Heat one
hour per millimeter of thickness. For thin sheet, a minimum of two
hours has been found to be preferable. While cooling times are
generally shorter than heating times, thermal stresses may occur if
cooled too quickly. A minimum cooling time of two hours should be
used.
[0059] Experiments showed that for thicknesses above 8 mm, the
hours required to cool equal the thickness in millimeters divided
by four. It is important that the items are not removed until the
oven temperature falls below 140.degree. F. (60.degree. C.).
Removing the mirror too soon can offset annealing's positive
effects. It is important to ensure that the mirror is adequately
supported during annealing. Raised sections may need independent
support to prevent sagging. Lack of proper support can also inhibit
relaxation. TABLE-US-00004 Heating Cooling Cooling Thickness Time
Time Time (in.) (min.) (hours) (hours) (.degree. F./hr.) .080 2.0 2
2 28 .098 2.5 2 2 28 .118 3.0 3 2 28
[0060] The character of the mirror substrate 14 can be further
enhanced through the application of light path and reflectivity
enhancing organic or inorganic coatings or additives. Such coatings
or additives may be applied through a variety of methods, such as
but not limited to dipping, spraying, vacuum deposition and/or
compounding into the synthetic substrate. Such coatings and/or
additives may be utilized to enhance the weatherability of the
mirror assembly through the application of anti-abrasion and
antireflective surface coatings and/or through the addition of
Hindered Amine Light Stabilizers (HALS), Antioxidants, Quenchers,
and Ultraviolet absorbers or inhibitors to the substrate
material.
[0061] The synthetic substrate 14 further may be UV (ultra-violet)
stabilized with a UV inhibitor or UV absorber in order to prevent
color or synthetic substrate degradation over time as well as
enhancing the light energy absorbing characteristics of the
synthetic substrate. UV absorbers work by absorbing ultraviolet
radiation and converting it into thermal energy through
tautomerism. To counteract the damaging effect of UV light and
improve the weatherability of the synthetic substrate 14, UV
stabilizers may be used to solve the degradation problems
associated with exposure to sunlight. UV stabilizers can be
categorized by two general classifications for an ultraviolet light
absorber (UV A), either benzopheneone or benzotriazole based
systems. The preferred substrate 14 additives for the present
invention being the type based on benzotriazole and hindered amine
light stabilizers (HALS).
[0062] Typical UV inhibitors or stabilizers which may be utilized
in the present invention are: Cyagard.RTM. 1164L, Cyagard.RTM.
3638, Cyagard.RTM. UV 531, Cyagard.RTM. UV 5411, Cyagard.RTM. UV 9,
Cyasorb.RTM. 1084, Cyasorb.RTM. 1164, Cyasorb.RTM. 284,
Cyasorb.RTM. UV 1988, Cyasorb.RTM. UV 2098, Cyasorb.RTM. UV 2126,
Cyasorb.RTM. UV 24, Cyasorb.RTM. UV 2908, Eastman Inhibitor RMB,
Givsorb.RTM. UV-1, Givsorb.RTM. UV-2, Givsorb.RTM. UV-13,
Givsorb.RTM. UV-14, Givsorb.RTM. UV-15, Givsorb.RTM. UV-16, Mark
1535, Mark 446, Maxgard.RTM. 200, Maxgard.RTM. 800, Norbloc.RTM.
6000, Norbloc.RTM. 7966, Quercetin, Sanduvor.RTM. 3206,
Sanduvor.RTM. EPU, Sanduvor.RTM. VSU, Seesorb 201, Syntase 1200,
THPE BZT, Tinuvin.RTM. 99, Tinuvin.RTM. 109, Tinuvin.RTM. 1130,
Tinuvin.RTM. 120, Tinuvin.RTM. 1545, Tinuvin.RTM. 1577FF,
Tinuvin.RTM. 320, Tinuvin.RTM. 326, Tinuvin.RTM. 327, Tinuvin.RTM.
328, Tinuvin.RTM. 384, Tinuvin.RTM. 400, Tinuvin.RTM. 571,
Tinuvin.RTM. 840, Tinuvin.RTM. 900, Tinuvin.RTM. 928, Tinuvin.RTM.
P, Uvinul.RTM. 3035, Uvinul.RTM. 3039, Uvinul.RTM. 3048,
Uvinul.RTM. 400, Uvinul.RTM. D 49, Uvinul.RTM. D 50, Uvinul.RTM. P
25, Uvinul.RTM. T-150.
[0063] The addition of UV absorbers alone to a substrate often have
limited effectiveness because their performance is a function of
Beer's (Lambert) law, which specifies that the amount of UV
radiation absorbed is a function of both sample thickness and
stabilizer concentration. This means that UV absorbers need to be
used in high concentrations and require relatively long path
lengths in order to absorb enough UV light to be effective. Thus,
the protection of the substrate 14 of the present invention is
enhanced with a HALS (Hindered Amine Light Stabilizer), where the
present invention preferably utilizes a combination of CIBA
Chemicals Tinuvin.RTM. P and Tinuvin.RTM. 770 to provide the
aforementioned UV light stabilization.
[0064] HALS are extremely efficient stabilizers against
light-induced degradation of most polymers. They do not absorb UV
radiation, but act to inhibit degradation of the polymer.
Significant levels of stabilization are achieved at relatively low
concentrations. HALS' high efficiency and longevity are due to a
cyclic process wherein the HALS are regenerated rather than
consumed during the stabilization process. HALS additives found to
perform well with the UV inhibitor/absorber constituents chosen for
the present invention are: CHIMASSORB.RTM. 119FL, CHIMASSORB.RTM.
2020, CHIMASSORB.RTM. 944, TINUVIN.RTM. 123, TINUVIN.RTM. 123S,
TINUVIN.RTM. 622, TINUVIN.RTM. 765, TINUVIN.RTM. 770, TINUVIN.RTM.
783, AND TINUVIN.RTM. 791, all manufactured by CIBA Specialty
Chemicals, Inc. The preferred HALS additive, TINUVIN 770 is a low
molecular weight hindered amine light stabilizer that provides
excellent stability for thick section synthetic polymer substrates.
The range of the TINUVIN 770 additive concentration used in the
present invention is from approximately 0.1% to 0.5% by weight,
with a preferred amount of approximately 0.2%.
[0065] It is further possible to add a certain amount of dyes or
tint color to the substrate 14 in order to enhance the optical
performance of the mirror without reducing its reflectance below
the acceptable standards of the international automotive
industries. Several tints have been found to increase the contrast
ratio of the image viewed through or from the mirror of the present
invention, where these tints fall primarily in the spectrum range
of 320 to 700 nm wavelengths. The tint colors being blue, red,
green and yellow. Although the red, green and yellow tints helped
to reduce the glare of the present invention, the rate of reduction
was most dramatic through the introduction of a blue tint. The
tints added to the substrate were generally found to only absorb
about 1/3 of the visible light spectrum, while allowing the
residual 2/3 to be reflected back.
[0066] In the automotive industry, the glare from light reflected
back from automotive mirrors to a viewer is commonly known as the
dazzle effect. This dazzle effect results from the reflected blue
light, and not the remaining green, yellow, red and infrared light
rays. Infrared light is for the most part removed by the water
particles found in Earth's lower atmosphere. With the exception of
blue light, the other colors have long wavelengths which pass
through the atmosphere without being scattered and diffused.
Conversely, the short wavelength blue light is diffused very
rapidly. These blue light rays are then chaotically bounced around
by water particles in the upper strata and lower down, continue to
be thrown in all directions by any reflective surface on the ground
so as to radiate in any and all directions. As these blue light
rays enter the eye, they result in a haze effect, thus bleaching
out the other colors and creating the effect known as glare. The
tendency of blue light to scatter creates the effect of competing
with all the other colors of the spectrum, thus causing the image
that forms on the retina at the back of the eye to suffer from a
certain amount of "bleaching" or glare.
[0067] Blue light is a higher energy light. By reducing or
filtering it through absorption, we first allow all the remaining
colors of the spectrum to show through more clearly and vividly as
the blue light is no longer there to dominate. Secondly, the visual
acuity (sharpness of vision) is enhanced by reducing the bleaching
effect which causes the outline of objects to be hazed and
indistinct. And, thirdly, there is a quantum improvement in the
individuals' comfort by way reduced light sensitivity.
[0068] The preferred blue tint additive for the substrate 14 for
both cosmetic and light absorption reasons was found to be NIBIOLA
Ultra Marine Blue, a sodium aluminum sulfosilicate. The typical
chemical analysis of a medium Ultra Marine Blue gives us: SiO2 . .
. 37%, Al2O3 . . . 28%, S . . . 14%, and Na2O . . . 19%. The
NIBIOLA Ultra Marine Blue chemical formula can be expressed as:
Na.sub.688 (Al.sub.5.65Si.sub.6.35)O.sub.24S.sub.4.24. While the
best results were observed from the use of NIBIOLA Ultra Marine
Blue, it is understood that other blue tint additives could
similarly be utilized. For example, the following blue tint
additives were found to be compatible with the synthetic polymer
base material comprising the substrate 14 of the present invention:
heliogen pigments made by BASF, which are phthalocyanines, KRONOS
2073, Ti-Pure R-103 by Dupont, Tronox Chloride 470 and 435 as well
as Tronox Sulfate R-KB-2 and CR-840. These blue tint additives
performed well in reducing glare and dazzle in the reflective image
from the mirror of the present invention. It is the full intention
of the inventor of the present invention not to limit the tint
additives to the above-described blue tint additives, where it is
understood that any color tint additive could be utilized without
departing from the teachings of the present invention.
[0069] The synthetic resin substrate 14 making up the base of the
mirror of the present invention is a polymer, where most polymers
are manufactured by processes involving chain polymerization,
polyaddition, or polycondensation reactions. These processes are
generally controlled to produce individual polymer molecules with
the following defined variables: molecular weight (or molecular
weight distribution), degree of branching, and composition. Once
the initial product of these processes is exposed to further shear
stress, heat, light, air, water, radiation or mechanical loading,
chemical reactions start in the polymer which have the net result
of changing the chemical composition and the molecular weight of
the polymer.
[0070] These reactions, in turn, lead to a change in the physical
and optical properties of the polymer. In practice, any change of
the polymer properties relative to the initial, desirable
properties is called degradation. In this sense, "degradation" is a
generic term for any number of reactions which are possible in a
polymer. The important aspect of this scheme is that once oxidation
starts, which it always will, it sets off a circular chain reaction
which accelerates degradation unless stabilizers are used to
interrupt the oxidation cycle. Exposure to sunlight and some
artificial lights can have adverse effects on the useful life of
plastic products. UV radiation can break down the chemical bonds in
a polymer. This process is called photo degradation and ultimately
causes cracking, chalking, color changes and the loss of physical
properties.
[0071] For the present invention to possess such image clarifying
characteristics is was required to overcome several obstacles
associated with synthetic polymers in general. By combining the
aforementioned constituency of ultraviolet absorbers, antioxidants,
quenchers, and hindered amine light stabilizers and compatible tint
chromospheres, the polymer mirror of the present invention has been
able to maintain the transmissivity and stability of the mirror
device as well as to maintain its compatibility with the
aforementioned coatings.
[0072] It has been found that the combined use of a HALS component
clearly improves the performance of a PMMA substrate's resistance
to environmental degradation and the UV inhibitor additive augments
the resistance to chemical bond breakdown. While any combination of
a HALS component and a UV inhibitor could be utilized with the
present invention, the preferred combination has been found to be
that of Tinuvin.RTM. P with Tinuvin.RTM. 770 to provide the desired
UV light stabilization.
[0073] The performance of the synthetic resin substrate 14 of the
present invention was tested using variances of the aforementioned
additives. The additives addressed were HALS, antioxidants, thermal
stabilizers, and UV absorbers. These tests evaluated stabilizer
performance and the effect of combined enhancement additives on
overall performance of the substrate 14. The preferred combination
of tints and resins were compared with a wide range of individual
stabilizers. It has been found that lifetime effects of single
stabilizers ranged from 0.03 to 6.1 times the lifetime of
unaltered, unstabilized synthetic substrates for the various resins
of the present invention that were tested. The known top performing
single stabilizers were combined to optimize the UV and
antioxidation stabilization concentrations and combinations of each
of the single UV stabilizers and anti-oxidants. Each of the single
UV stabilizers and anti-oxidants loadings were varied in the
synthetic resin raw materials used to manufacture the substrate 14
test plaques. The stability of each test plaque variant was
observed. The process was repeated as necessary to optimize the
relationship between the individual additive components.
[0074] The tint additive, UV absorber, and anti-oxidant
concentrations were held constant, while concentrations of HALS and
thermal stabilizers were optimized at different quencher
concentrations. All other processing variables were held to within
a processing window of plus or minus 5% by weight of the best
recommended process window as derived from proprietary molding test
protocols. In the present invention, it was observed that as the
quencher light stabilizers were varied, the concentrations of HALS
and thermal stabilizers required to achieve the maximum substrate
service life also changed.
[0075] The results of the combined optimizations within the
described new invention greatly expands the expected lifetime of
the present inventions synthetic polymer based mirror substrates
when compared to substrates not treated with the preferred
additives described herein. In an evaluation of the stability of
the described preferred tint additive, Ultramarine blue dye from
NIBIOLA, the preferred tint of the present invention, lasted three
times longer with accompanying additives than normal untreated
synthetic substrates. The blue tint additive, KRONOS 2073 lasted
more than 2.5 times longer in the substrate 14 of present invention
with accompanying additives than normal untreated synthetic
substrates. For example, the visual observations shown in the
following chart illustrate that, after 24 hours, ULTRAMARINE Blue
dye from NIBIOLA exhibited the following matrix interaction effects
and reflectivity. TABLE-US-00005 Stability (2000 Hrs) Accelerated
Resin Reflectivity Color Testing PMMA (Acrylic) 72% Cobalt Blue
Excellent Polycarbonate 56% Intense Royal Blue Good CR-39 70% Dark
Blue Excellent
[0076] The present invention solves the difficult task of
stabilizing synthetic resins having optical characteristics from
the effects of weathering and ultra-violet radiation. The required
stabilization is complicated by the multiple interactive effects
observed between the available stabilizers, tint dyes, and
synthetic resins. However, the additives to the resin substrate 14
of the present invention have been found to extend the expected
lifetime of the substrate 14 over that of non-stabilized synthetic
resins by a factor of 20.
[0077] As can be seen from the foregoing, a polymer-based mirror
formed in accordance with the present invention provides a
lightweight and durable synthetic resin mirror that is resistant to
mechanical distortion resulting from moisture absorption. Further,
the polymer-based mirror of the present invention possesses
increased weatherability and durability by providing a more weather
resistant barrier to water infusion.
[0078] An alternative embodiment of the present invention provides
at least equivalent or better performance characteristics to a
polymer substrate coated with dry layers of zirconia and silicon
dioxide by creating a gradient coating of a zirconia/silica colloid
in a polysiloxane liquid carrier through a sol gel coating step
that not only provides an appropriate sealing of a synthetic
substrate but also provides an anti-abrasive coating and the
ability to inherently create a hydrophobic surface with a high
concentration of zirconia/silica. The resulting coating can further
be processed to provide a hydrophilic coating depending upon a
desired application.
[0079] As can be appreciated, FIG. 9 is a schematic view for
purposes of illustration only to assist in understanding the
features of the present invention.
[0080] Referring to FIG. 9, a schematic cross-sectional view of the
resulting sol gel layer on a synthetic substrate is disclosed. As
will be subsequently described, by an appropriate preparation of a
sol gel solution, it is possible to create a layered configuration
of various concentrations of zirconia/silica colloid particles with
a preferred exterior surface of primarily a zirconia/silica
containing coating composition while dispensing with the necessity
of separate deposition production steps in creating the multiple
layers that may be required in other embodiments.
[0081] As mentioned above, a synthetic resin substrate with
appropriate optical clarity such as polymethyl methacrylate (PMMA)
resin can be used, although other similar polymers are also
applicable such as described with regards to the embodiment shown
in FIG. 1. The synthetic resin substrate 602 can be appropriately
formed into a desired shape and can include appropriate tints,
ultraviolet absorbers, light stabilizers and other inhibiters,
depending on the particular desired end use of the product.
[0082] The synthetic substrate 602 which is only shown in partial
view, with only one surface illustrating schematically the coating
arrangement, can be appropriately prepared or cleaned depending on
the specific synthetic resin, before its submersion into a prepared
sol gel solution. The resulting sol gel coating or layer 604 is
shown schematically broken into roughly three separate zones or
layers. The first exterior layer 606 represents an approximately
75% concentration of a zirconia/silica colloid concentration within
the polysiloxane carrier. The next zone or layer 608 comprises
approximately a 10% zirconia/silica colloid concentration, while
the remaining zone or layer 610 adjacent to the surface of the
synthetic substrate 602 has a dispersed layering of a final
approximately 15% of zirconia/silica colloid suspension in the
polysiloxane carrier. The thickness of the accumulative respective
layers 606, 608 and 610 can usually be 10 microns and below, such
as between 3 and 6 microns although other ranges of thickness are
possible depending on the specific end product 600. As can be
appreciated, the sol-gel coating can cover all or just one surface
of the substrate depending on the manner of application and the
desired end product.
[0083] In the schematic shown in FIG. 9, there is a ZETA potential
influenced interspersed elements of an anodic and cathodic
zirconia/silica colloid. Initially, the final resulting coating 604
will be hydrophobic, with an abrasion or scratch-resistant exterior
surface having a high concentration of zirconia/silica colloid
without requiring an additional coating step. Likewise, the surface
of the synthetic substrate 602 will have a chemabsorbed cathodic
element layer 612 of zirconia/silica that provides an equivalent
tie bond coating without requiring an extra coating step in the
production procedure. The representative circles with negative
charges in FIG. 9 indicate cathodic zirconia/silica colloid
particles while the plus circles indicate anodic zirconia/silica
colloid particles.
[0084] The amount of concentration of zirconia/silica colloid
particles with the same potential in the specific layers or zones
can be controlled by regulating post-applied conditions after the
sol gel coating has been deposited on the synthetic substrate 602.
Initially, the entire layer 604 as applied will have a homogenous
dispersion of the charged zirconia/silica colloid particles.
Subsequently, the particles will migrate and orientate as they are
drawn to the surface and will continue to do so until they reach a
balance state in the uncured sol gel coating. As can be appreciated
by persons of ordinary skill in this field, the amount of solid
zirconia/silica colloid precursor added to the polysiloxane liquid
carrier will have an effect on the balanced or gradient state of
concentration of the zirconia/silica particles. Additionally,
depending upon the design characteristics of the end product, it is
possible to intentionally cure the sol gel layer before the
zirconia/silica colloid particles have completely migrated and
orientated to a final balanced position. Such curing can be done
thermally while respecting the glass transition temperature of the
underlying substrate. Other curing procedures are possible such as
but not limited to the inclusion of UV activators in the
polysiloxane liquid carrier that when treated with ultraviolet
light, will assist in a cross-linking of the polysiloxane.
[0085] The sol gel coating of the present invention can be applied
by most conventional methods of applying liquid coatings, i.e.,
spray, dip, spin, flow or even vapor deposition coating techniques.
One of the preferred application methods for a vehicle window or
mirror is the use of a dip coating method to provide a high degree
of control over the resulting thickness of the coating by
controlling the rate of removal of the substrate from a tank of the
sol gel solution with the sol gel coating in a liquid state so that
a desired thickness is achieved by virtue of the surface tension
and attraction between the substrate and the sol gel coating. This
pre-form product is then placed in a stationary or a static
position in an environmentally controlled enclosure for a desired
period of time. For example, with a thickness in the range of 3 to
6 microns, for an optical product for use in the auto industry, the
time period can be between 3 to 10 minutes with 6 minutes being
preferred. This holding period, however, may change depending upon
the part geometry and the particular end use and design purpose of
the product. Generally, the enclosed environment should be at a
normal ambient temperature at a 50% to 70% humidity. This holding
period allows the ZETA potential of the colloid suspension to
orientate itself and also allows the excess moisture and volatile
organic compounds to escape from the sol gel coating prior to
undergoing cure.
[0086] While the exact scientific understanding for achieving the
desired finished product is not necessary, if the method teachings
of the present invention are followed, it is believed that the
following explanation may be applicable.
[0087] It is known that Van Der Waals force is constant at a given
separation distance between particles and is strongest at the
equilibrium separation distance in the dispersed state. Colloidal
particles usually absorb ions to the surface. This primary
absorption layer gives rise to a substantial surface charge or
electrical potential to the surface that may facilitate the
interspersing or layering of the zirconia/silica. First it causes a
repulsion to exist between two particles when they approach each
other preventing the nanoparticles from sticking together. And,
secondly, attracts counter ions into the vicinity of the
nanoparticle giving the layered construction of the suspension.
[0088] The electrostatic force may be varied from zero to a high
value by surface potential control. In the present invention, both
pH and magnetic attraction could be used to manipulate the density
and overlap of the zirconia/silica precursor. By altering the ionic
strength by way of exposing the dispersion to altered pH and ZETA
potential, the linear relationship between nanoparticles can be
adjusted or the potentials and densities over layered. The exposure
of the sol-gel to atmosphere exposes it to anionic potential and
draws a significant amount of the zirconia precursor to this
surface and while the substrate offers a lesser amount of anionic
charge, it does facilitate the adhesive qualities of the coating to
the synthetics substrate.
[0089] The sol-gel colloid solution for forming the sol gel layer
604 is preferably formed according to a multi-step process. Three
examples of coating formulas A, B and C are set forth and each
formula is designed to prevent any premature coagulation or gelling
of the constituents of the sol gel layer 604 due to uncontrolled
thermal reactivity. The use of well defined precursors allows
relationships to be established between the precursor and the final
coating material. The formation of the sol gel involves the
evolution of inorganic networks through the formation of a
colloidal suspension (sol) and gelation of the sol to form a
network in a continuous liquid phase (gel). The precursors for
synthesizing these colloids consist of a metal or metalloid element
surrounded by various reactive ligands. The metal alkoxides react
readily with pure water. The metal alkoxides used in the present
invention are alkoxysilanes, such as tetramethoxysilane (TMOS).
However, other alkoxides such as aluminates, titanates, and borates
are also commonly used in the sol-gel formation process, often
mixed with tetraethoxysilane (TEOS).
[0090] The sol-gel colloid solution for coating the substrate 602
includes the preparation of basically three stages, a hydrolysis,
an alcohol condensation and water condensation stage. Within the
context of these stages, many factors affect the resulting silica
network,-such as pH, temperature and time of reaction, reagent
concentrations, catalyst nature and concentration, H2O/Si molar
ratio (R), aging temperature and time. However, the characteristics
and properties of the present sol-gel inorganic network are related
to a number of factors that affect the rate of hydrolysis and
condensation reactions, such as pH, temperature and time of
reaction, reagent concentrations, catalyst nature and
concentration, H2O/Si molar ratio (R), aging temperature and time,
and drying. Of the factors listed above, pH, nature and
concentration of catalyst H2O/Si molar ratio (R), and temperature
can be controlled to vary the structure and properties of the
sol-gel-derived inorganic network over a wide range.
[0091] The actual sol-gel polymerization occurs in three
stages:
[0092] 1. Polymerization of monomers to form particles
[0093] 2. Growth of particles
[0094] 3. Linking of particles into chains, then networks that
extend throughout the liquid medium, thickening into a gel.
Formula A
Formula A
Preparation procedure:
[0095] Si(OC2H5) TEOS Molecular Weight: 208.33
[0096] SiO.sub.2 Molecular Weight.: 60.09
[0097] Zr(poropyloxide).sub.4, TPT Molecular Weight.: 284.26
ZrO.sub.2 Molecular Weight.: 79.9 Silicone tetraethoxide is
partially hydrolyzed with water
[0098] Formula A is the preferred formulation and is formed by
combining a solution A (a partial hydrolysis of TEOS) with a
solution B (a zirconia precursor). Solution A is formed by
combining a mixture of 186.6 grams of Si (OET).sub.4, 53.8 grams of
SiO.sub.2, and 322.4 grams of 95% ethanol (including 5% water: 16.1
gram). To this mixture, 0.3 grams of concentrated HCl, having a
solid content of 12.5%, are dropped. The mixture is then reflux at
the boiling point of ethanol for 2 hours to consume all of the
water in the ethanol solvent. A check of the rate of evaporation
should be used to verify full consumption of the water content. The
solution is then cooled to room temperature, and Solution A is thus
formed having a solid content of approximately 12.5%.
[0099] Solution B is the ZrO.sub.2 precursor and is formed by
initially adding 33.7 gram of TPT (triphenyltin) and ZrO.sub.2 9.5
grams with IPA. ETOH is then added very slowly to dilute Solution
B. Solution B is then slowly added to Solution A. The mixed
solution temperature will rise about 2-3 degrees C. After continued
stirring and cooling to room temperature, 27.9 grams of 0.1 N HCl
aqueous is added into the mixed solution. The solution is then
stirred for approximately 30 to 45 minutes to generate Formula A as
a ZrO.sub.2 doped SiO.sub.2 solution.
Formula B
[0100] Formula B is prepared by combining two solutions: Solution C
(a full hydrolysis of TMOS oligomer in water) and Solution D (a
ZrO.sub.2 precursor prepared in polar solvent). Solution C is
prepared by initially dropping 28.0 grams of 0.1 N HCl aqueous into
100 grams of TMOS Oligomer (having SiO.sub.2: 53.06 gram). The
solution initially is a phase separation, and it will change into a
transparent liquid in about 10 minutes. The temperature should be
controlled so that it does not exceed 25 degrees C. At least 225
grams of water is slowly added while stirring the solution to
dilute the solution into solid content of 15% to form Solution
C.
[0101] Solution D is prepared by dissolving 22.2 grams of ZrO.sub.2
in 240 ml of DMAC (dimethylammonium acetate) at about 10 degrees C.
The solution should be heated slowly during this process. To this
solution, 4.2 grain of water is added by drops so as not to raise
the temperature of the solution. Solution C is then slowly added
into solution D, and the combined solution is heated at 100 degrees
C. for not more than 1 hour to fully hydrolyze the ZrCl.sub.4. The
resultant sol becomes a dichloride by using a cation ion-exchanger
to provide a hydrophilic sol solution. When the reflux is complete,
an anatase-type ZrO.sub.2 solution of Formula B is generated.
Formula C
[0102] Formula C is prepared by distilling 400 grams of sodium
metasalicate in 40 ml of water. The pH is adjusted to 1 by adding
HCL. The resultant mixture is stirred at 22.degree. C. while adding
64 grams of zirconyl chloride to create a reactive sol. The
reactive sol is emulsified in 500 ml of ethanol by stirring at 1800
RPH for 10 minutes. Subsequently, 40 grams HMTA
(hexamethylenetetramine) and 40 grams of urea are added and the
resultant mixture is stirred for approximately 50 hours. The
mixture is then cooled, filtered, and washed with ethanol. The
resulting solution is then redispersed to form an anatase ZrO.sub.2
base of 100%. The anatase ZrO.sub.2 sol-gel is transparent.
[0103] Each of the formulas A, B and C are mixed or dispersed in a
carrier fluid such as a polysiloxane liquid medium that can be
conventionally purchased such as Dow Corning's SYL-OFF.RTM. series
polysiloxane. The zirconia/silica sol-gel can be dispersed in a
polysiloxane liquid medium in four different ways: a) in solution
form; (b) in sol or micelle form; c) attached to the surface of the
inorganic particles, forming a shell or partial shell around the
inorganic particles; and d) combinations of a), b), and c). Once
the components are mixed together, uniform dispersion of all
components can be facilitated, if necessary, by subjecting
compositions of the present invention to sonification, utilizing
equipment such as VibraCell 700 Watt ultrasonic horn (available
from Sonics and Materials), or shear mixing.
[0104] Dispersions of several hundred milliliters to several
gallons with concentrations of up to 75 weight percent of the
respective formulas can be practically prepared by dispensing into
a rapidly agitated carrier fluid. The preferred percent of
precursor solids is approximately 50 weight percent. Surface
wetting and dispersion is best achieved with moderate rate
agitation of approximately 800-1200 rpm. Motorized mixers such as
the Eppenbach, Colframo, Arde-Barinco, Janke and Kunkel or
Lightnin' Mixers with a conventional open-blade impeller (pitched
marine or saw tooth propeller) are most appropriate. Extremely
high-shear mixers such as Waring blenders or rotor-stator
homogenizers should be avoided. The mixing intensity generated by
this type of mixer can shear the opened (hydrated) polymers
resulting in permanent viscosity loss. Conventional impellers, such
as propellers or turbines, do not impart excessively high shear
rates. They can be used to mix mucilages for extended periods with
virtually no decrease in formula efficiency.
[0105] The thickness, crystalline phase, grain size, and surface
hydroxyl amount of the sol gel layer 604 are optimized using the
above-described manufacturing process. After application of the sol
gel, the sol gel is cured to form the sol gel layer 604. The
zirconia coated silica sol gel can be cured thermally or through
the addition of an ultraviolet sensitive photo-initiator to be
included in the formulation in order to start the polymerization
reaction, as radiation-cured coatings are typically superior to
those of other systems. Photosensitive radiation curing can be
accomplished in a short time period, thus making radiation curing a
particularly economic technique. The resulting cured sol gel layer
604 is hard and abrasion resistant and further resistant to
degradation from chemicals and other external elements.
[0106] As shown in FIG. 9, the exterior layer 606 surface is
charged to a cathodic response as a result of the method of coating
to provide a hydrophobic surface state to repel water. A secondary
treatment procedure is available to convert the 606 surface layer
to a hydrophilic surface state to attract or wet the surface with
water. The optical product 600 can be immersed in a water solution
having 20% by weight Sodium Hydroxide (NaOH) at an ambient
temperature of 72.degree. F. for 3 to 5 minutes to create a phase
change in polarity of the surface from a cathodic response to an
anodic response. The resultant optical product is rinsed with pure
water and dried.
[0107] The sol gel coating method enables a surface coating layer
of either a hydrophobic or hydrophilic state without requiring
separate deposition steps, therefore saving cost while increasing
design options for the end product.
[0108] The sol gel coating method of the present embodiment can be
advantageously utilized with a large number of different products
having a synthetic substrate. For example, plastic resin windows
and plastic resin mirrors can be utilized in the automobile
industry. Plastic resin substrates of various configurations,
however, are also possible wherein the substrate is protected from
environmental conditions and is further provided with an abrasion
resistant exterior surface. The sol gel method of applying the
gradient coating layer to such a synthetic resin substrate is
particularly economical in lowering the production cost of such
parts.
[0109] Referring to FIGS. 9 and 10, one example of a sol gel coated
optical product can be a polymer-based mirror 700 having a
synthetic resin substrate 702 encapsulated with a multi-layered
gradient coating of polysiloxane with a variable concentration of
zirconia/silica colloid particles in each layer. The surface will
have a tie-bond concentration of cathodic chemabsorbed
zirconia/silica. An exterior surface as shown in FIG. 9, will have
a high concentration of zirconia/silica colloid particles to
provide a highly abrasion resistant surface. On the rear surface of
the substrate 702, a reflective coating 706 or multi-layered
coatings can be deposited as previously described in the other
embodiments. Finally, a barrier coating or paint 708 can also be
applied to seal the reflective layer 706. As should be appreciated,
FIG. 10 represents only a schematic view and is not drawn to
proportion relative to the size of the substrate 702 and the
respective coating, reflective and barrier layers.
[0110] To create a pre-form or sol coated substrate for the mirror
of FIG. 10, the following production steps are utilized. Referring
to FIG. 11, a sol-gel solution as described herein is prepared. A
resin substrate of a desired geometry and configuration is
appropriately cleaned with water, solvent or other material
appropriate to the particular resin in step 804. The pre-formed
substrate is appropriately mounted and then dipped into the sol-gel
solution in step 806. The coated pre-form is then removed under a
controlled speed from the tank of sol-gel solution so that an
appropriate thickness is provided on the substrate in step 808. The
coated substrate is then placed into a controlled environment to
permit the desired migration and orientation of colloid particles
as water and solvents are evaporated to produce the desired
gradient layers to the coating in step 810. Finally, the coated
substrate is appropriately cured in step 812.
[0111] Subsequently, the reflective coating and the barrier coating
can be added.
[0112] In each of the above embodiments, the different structures
of the polymer-based mirror are described separately in each of the
embodiments. However, it is the full intention of the inventor of
the present invention that the separate aspects of each embodiment
described herein may be combined with the other embodiments
described herein. Those skilled in the art will appreciate that
various adaptations and modifications of the just-described
preferred embodiment can be configured without departing from the
scope and spirit of the invention. Therefore, it is to be
understood that, within the scope of the appended claims, the
invention may be practiced other than as specifically described
herein.
* * * * *