CA1111692A

CA1111692A - Infrared reflecting articles

Info

Publication number: CA1111692A
Application number: CA324,585A
Authority: CA
Inventors: Leei Chang
Original assignee: Leei Chang; American Optical Corporation; Sola International, Inc.
Current assignee: Sola International Inc
Priority date: 1978-04-03
Filing date: 1979-04-02
Publication date: 1981-11-03
Also published as: DE2912943A1; GB2017965A; GB2017965B; US4179181A; FR2422181A1; FR2422181B1; JPS54133507A

Abstract

INFRARED REFLECTING ARTICLES
Abstract of the Disclosure Articles having an interference coating which reflects infrared energy are disclosed. The coating has a period of three layers in which the first and third layers are a refractory dielectric material and the intermediate, or second layer, is silver. If the period is repeated once, the cut-off between transmission and reflection is sharper than the coating having a single period.

Description

Back~round of the Invention The present inVention relates to infrared reflecting articles and more particularly to in-terference coatings which reflect in~rared energy.
Infrared reflective coatings are generally known.
However, the prior art reflective coatings are either expensive because of the materials used or because many layers are required to obtain the necessary transmission-reflection cut-off. The most common single-layer infrared-reflecting coating is gold.
Gold is undesirable as a single layer coating for two reasons.
The first reason is the high cost and the second reason is that gold also reflects a large amount of the yellow-red portion o the visible 5pectrum. Therefore, articles having a gold, single-layer, infrared-reflecting coating transmit little of the visible spectrum. Multi-layer, band-pass filters are efficient and ` flexible in meeting design requirements of a sharp cut-off point and good transmission in the visible range with low transmission in the infrared range. However, the multi-layer band pass filters of the prior art usually require over 10 and up to 30 layers in the coating and neither the band-width of transmitted light or the hand-width of reflected light is very wide. Spurious leaks are also a problem with prior art multi-layer, interference films as well as the difficulty of manufacture and expense associated with producing many superimposed coatings.

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Brief Description of the Present Invention sroadly speaking the present invention provides an inter~erence-coated, infrared reflectin~ article compris-~ ve~
,~ ing, in~sequence, ~a) a substrate having a surface, (b) afirst layer of a refractory dielectr~c (c) a layer of silver having a thickness between about 110 and 250 ~, (d) a second layer of the refractory dielectric.
The above article may be produced by utilizing a method of treating a substrate to cause it to reflect in-~rared light which comprises, (1) coating the substrate witha refractory dielectric material, (2) coating the material of step 1 with about 110 to about 250 ~ oE silver, and t3) coating the silver of step 2 with the refractory dielectric of 1.
Thus, the present invention relates to an interfer-ence coating for re1ecting infrared light and selectively transmitting visible light. The infrared coating has a period o~ three layers~ The first and last layers of the period are a refractory dielectric material. The intermediate, or second coating, is silver metal. When a sharp cut-off between rè-flected and transmitted light is desired, the period may be do~bled to give a total of six layers in the interference coat-ing. Some plastics may require an intermediate layer of SiO
or SiO2 on top of the substrate to prove suitable bonding of the refractory dielectric to the substrate. Also for some articles such as ophthalmic lenses, welding goggles and the like, it may be desirable to have an abrasion-resistant coating on the final or top-most coating of the interference coating.

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Brief Des'cription o'f' th~ Drawings . _ ~ ' Fig. 1 lS a diagrammaticai representation o the preferred embodiment according to the pre.se~t inyention, and Fig. 2 is a graph showing representative transitions from transmissi.on to reflection according to the present in-ven~ion.
Detail'ed Des.cription of the Present'Invent_on Referring to Fig. 1 a substrate has an infrared re-~lecting interference coating with first and second periods~
While substrates are usually transparent, opaque substrates such as metal and opaque plastics arè also suitabie. ,Trans-parent, clear or dyed_strates whi~h may be used include '.` ~

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polycarbonate resins, poly(allyl diglycol carbonate);
polymethi~lmetharcylate; and glass~ The substrate may be in form of sheet, an ophthalmie lens, a safety lens, small plates, such as those used in welding helmets and solar refleetors. When synthetie resin substrates are used, it is usuallv desirable to coat the substrate with a thin layer of SiO to promote adhesion of the refraetory dielectrie if the dielectrie material is not SiOx. The adhesion promoting layer 1 is shown in Fig. 1 and when optionally used is applied in a thiekness of about S A. The silver layer of each ?eriod is sandwiched between a pair OI refractory dieleetrie layers 2. Some suitable refraetory dielectric materials are TiO2, CeO2, ZrO2, Nd203, 25gO, A1203, and SiOx `where x is from 1 to 2, and perferrably about 1.5. Frequently it is desirable to protect the final layer of the refraetory dielectric with an abrasion-resistant coating 3. The abrasion-resistant coating is an optional coating which does not form a part of the present invention. One example of a suitable abrasion-~esis.ant coating is that taught by ~. S. Patent No. 3,986,997 issued to Clark. When Siox is used as the refrac~o-y dielectric, it is eonvenient to use SiO2 as the abrasion-resistant coating. Abrasion-resistant coatings are usually in the oxder of 4 to 10 microns thicX. Although not shown in Fig. 1, the band of ~ ~layer to a SiOx dielectric layer may be improved by an intermediate layer of palladium metal about 5 A thicko , .

,c ., Fig. 2 illustrates the more rapid cut-off provided when a two period interference coating is used. Rèferring to Fig. 2 the solid line shows the high transmission in the visible range with very low transmission in the infrared range for two-period coating. The transmission properties of a single period interference coating are represented by the curve having the dotted line which has substantiall~- the same cut-off point but is less efficient in reflecting infrared energy than is a two-period interference coating.
Example I
~ sing an electron beam evaporator in a chamber evacua~ed to 9 X 10 Torr, Ti~03 was deposited on a polycarbonate lens at room temperature using an 2 partial pressure of 7 X 10 5. After the Ti~o2 deposit reached a thickness of 160 A, the beam was turned off and residual 2 was removed from the chamber. An Ag source was then evaporated at room temperature until an Ag deposit of 180 A was obtained. 2 was reintroduced into the chamber and a second Ti~C2 layer was deposited on the Ag layer also having a thickness of 160 A. The transmission tT) and reflection (R) properties of the coated lens are shown in Table I. In preparing the interference coatings of the invention, temperatures sigr.ificantly above room temperature adversely affect the transmission of visible wavelengths and should be avoldedO
Example II
A polycarbonate lens was treated at roo`m temperature to provide a two period coating following the procedure of ` ' , , ,, .
, Example I by repeating each deposition to obtain a six layer coating with each layer having the same thickness as ~he respective layer in Example I. This lens had a sharper as shown by the transmission values in Table I.
EXAMPLE III
A polycarbonate lens was coated with single period and a lens with double period coatings using ZrO2 as the re'ractory dielectric material by conventional vapor deposition procedures at room temperature. The refractory dielectric layer thicknesses were each 250 A thick and the silver layers were each 110 A
thick. The transmission (T) and reflectance (R) values at various wavelengths (2) are given in Table I.
EXAMPLE IV
Two polycarbonate lenses were coated uing conventional, room-temperature, vapor deposition procedures and one lens had a single period coating and one a double period coating.
The SiOl 5 layers each had a thickness of 200 A and the silver thickness of each layer was 130 A, the transmission (T) and reflectance (Rj values at various wavelengths are given in Table I.

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Claims

WHAT IS CLAIMED IS:

1. An interference-coated, infrared reflecting article comprising, in overlying sequence, a) a substrate having a surface, b) a first layer of a refractory dielectric c) a layer of silver having a thickness between about 110 and 250 .ANG., d) a second layer of the refractory dielectric.

2. The article according to claim 1 wherein b), c) and d) are repeated in sequence.

3. The article according to Claim 1 wherein said substrate is glass and the refractory dielectric has an index of refraction at least 1.6.

4. The article in claim 1 wherein said substrate is a transparent plastic having a layer of SiO on the surface and the refractory dielectric has an index of refraction of at least 1.6.

5. The article according to claim 1 wherein said dielectric is selected from the group consisting of TiO2, CeO2, ZrO2, Nd2O3, MgO, A12O3 and SiOx where x is 1 to 2.

6. The article according to claim 1 wherein c) is about 140 to about 220 .ANG. thick.

7. The article according to claim 1 further including a final coating of an abrasion resistant material.

8. The article according to claim 1 further including an adhesion promoting material under one of the layers

9. The article according to claim 2 wherein b) and d) are SiOx.

10. The article according to claim 2 wherein a) is a synthetic resin selected from the group consisting of polycarbonate, poly (allyl diglycol carbonate), and polymethyl methacrylate, b) and d) are a material selected from the group consisting of SiO, SiO1.5, SiO2 and mixtures thereof and have a thickness of about 110 to about 250 .ANG., and b), c) and d) are repeated once to provide the order a) b) c) d) b) c) d).

11. The article according to claim 10 wherein the surface of a) is coated with SiO

12. The article of claim 10 wherein the surfaces of b) and c) are coated with palladium before coating with c) and d) respectively.

13. The article according to claim 10 further including a final coating of an abrasion-resistant material.

14. The article according to claim 10 wherein each b) and d) layer is about 180 .ANG. thick.

l5. A method of treating a substrate to cause it to reflect infrared light which comprises, 1 coating the substrate with a refractory dielectric material, 2 coating the material of step 1 with about 110 to about 250 .ANG. of silver, and 3 coating the silver of step 2 with the refractory dielectric of 1.

16. The method of claim 15 wherein steps 1, 2, and 3 are repeated.