Mirror with chromium nitride layer

THE REPUBLIC OF POLAND (12) TRANSLATION OF THE EUROPEAN PATENT (19) PL (11) PL / EP 1797465

<img file="PL1797465T3_D0001.tif" />

Patent Office of the Republic of Poland (96) Date and number of the European patent application:

27.09.2005 05800106.6 (97) The granting of the European patent was announced: 07.11.2012 European Patent Bulletin 2012/45 EP 1797465 B1 (13) T3 (51) Int.CI.

G02B 5/08 (2006.01)

G02B 7/182 (2006.01) (54) Title of the invention:

A mirror with a layer of chromium nitride (3 °) r,

Priority:

October 7, 2004 US 959321 (43) Application announced:

On June 20, 2007 in the European Patent Bulletin No. 2007/25 (45) The following was announced about the submission of the translation of the patent:

30.04.2013 News of the Patent Office 2013/04 (73) The holder of the patent:

GUARDIAN INDUSTRIES CORP., Auburn Hills, US

Center Luxembourgeois de Recherches pour le Verre et la Ceramique SA, Dudelange, LU (72) Inventor (s):

FRANCIS WUILLAUME, Plymouth, US ANTON DIETRICH, Fontnas, CH BRENT BOYCE, Novi, US GREGORY SCOTT, Shelby, US 10 (74) Agent:

&lt;0 item, pat. Ewa Wojasinska

POLSERVICE

OFFICES 'OFFICE

Τ 'PATENTOWYCH SP. Z OO

Q_ iii ul. Bluszczańska 73

Ie 00-712 Warsaw

ABOUT.

Attention:

Within nine months of the publication of the information on the grant of the European patent, any person may file an objection to the European Patent Office against the European patent granted. The objection must be submitted in the form of a written statement of reasons. It is considered brought only when the opposition fee has been paid (Art. 99 (1) of the Convention on the Grant of European Patents).

The description of EP 1 797 465 B1

[0001] The application relates to a first surface mirror having a layer containing chromium nitride (CrN_x). In particular embodiments, the mirroring layer comprises chromium nitride and is nitrided to the extent that undesirable pinholes are reduced and / or adhesion is improved. In a particular example of unlimited incarnations, such a first surface mirror may be used in the context of projection television (PTV) equipment, in car mirrors, or in any other suitable application.

BACKGROUND OF THE INVENTION

[0002] Mirrors for various users are known in the art. For an example, see U.S. Patents Nos. 5,923,464 and 4,309,075. Mirrors are also known for use in projection television and other relevant applications. Projection TV context, for example, see US Patents Nos. 6,275,272, 5,669,681, and 5,896,236.

[0003] One type of mirror is with a second or back surface (the most known), while another type of mirror is a mirror with a first or front surface (less known). Rear-face mirrors typically include a glass substrate with a reflective coating on its rear face (ie, not the front face which comes in contact with the incident light first). Incident light passes through the glass backing before it is reflected by the coating on the other surface of the mirror. Hence, the reflected light passes through the glass backing twice in mirrors with a second or rear face; once before the reflection and the second time after the reflection, returning to the observer. In special cases, passing twice through the glass substrate may result in ambiguity in the directional reflection and may result in imperfections in the reflection. Mirrors such as bathroom mirrors, bedroom mirrors, and construction mirrors are customarily second or back surface mirrors so that a glass backing can be used to protect the reflective coating on the rear surface of the mirror.

[0004] In applications where there is a need for a more accurate reflection, front (or first) surface (FSM) mirrors are the most used. In first / front surface mirrors, a reflective coating is disposed on the front surface of the glass substrate so that incident light is reflected by the coating before passing through the glass substrate. When the reflected light does not have to pass through the glass backing of the mirror with the first surface (as opposed to mirrors with the back face), the mirror with the first face generally has a higher reflectance than the mirrors with the back face and causes no or less of a double reflected image. Examples of front face mirrors (or first face mirrors) are disclosed in US Pat. Nos. 6,783,253, 5,923,464, and 4,780,372.

EP 0 632 294 A1 discloses first or second surface mirrors comprising, in the following order, a primer, a first metal precoating layer, a metal reflecting layer, a second metal precoating layer and a protective layer, characterized in that the first initial coating layer comprises nickel and chromium or chromium nitride, and the second pre-metal coating layer comprises nickel and chromium or chromium nitride.

[0006] US 2004/0190141 A1 discloses a heavy duty non-planar optical element coated with a thin layer of silver to replace gold as a material for making such devices.

[0007] US 6,078,425 discloses a strong thin-film multi-layer coating for reflecting mirrors over a broad spectrum of infrared, visible and ultraviolet light. The coating comprises at least five layers: an aluminum layer, an adhesion layer, a silver layer, a passivation layer and a strength layer. The adhesion and passivation layers are composed of nickel, chromium, nickel-chromium alloy, nickel or chromium nitrides or nickel and chromium nitrides (NiCrN_x). [0008] US 6,524,714 B1 discloses heat treated, coated articles having a solar management, infrared (IR) reflecting or the like layer which is sandwiched between a substrate and an overlying dielectric layer. In particular embodiments, the solar management layer may include NiCrN_x while the dielectric layer (s) may contain nitrides such as silicone nitrides. The described coated articles can be used in the context of insulating glass (IG) in window units, vehicle windows or the like.

[0009] It has been proposed to use chromium (Cr) metal in the mirroring layer of the first surface. In particular, mirrors containing a layer of metallic Cr placed directly on and in contact with the glass substrate have been proposed. Unfortunately, such a first surface mirror with a glass / Cr structure is sensitive to the problem of puncture emergence. In particular, the structure of such a mirror is prone to pinholes in the Cr metal layer, especially when the Cr layer thickness increases in applications where low transmission (e.g. 0.5% visible transmission) is desired. Light leaks through such punctures, making their high abundance particularly unfavorable in applications where the reflectance (not transmission) of light is desired.

[0010] It is evident in view of the above that there is a need in the art for first / front surface mirrors or other types of mirrors that are less prone to forming a significant number of punctures.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0011] According to the invention, there is provided a mirror as defined in claim 1. 1 and the manufacturing method of a mirror as defined in claim 1 10.

[0012] In particular embodiments of the present invention, the mirror may be a mirror with a front surface. In particular embodiment examples, the CrN layer_x it can be the main mirror reflecting layer.

[0013] Surprisingly and unexpectedly, it has been found that adding nitrogen to chromium to form CrN_x reduces the formation of punctures in the obtained layer, without significantly affecting the reflective properties of the mirrors. In particular embodiments, the greater amount of nitrogen introduced into the layer reduces the number and / or size of punctures in the Cr layer. In particular embodiments, it has also been found that the addition of nitrogen to Cr can increase the strength of the mirror.

[0014] In a particular embodiment of the present invention, a first surface mirror incorporating such a layer can be used in projection television, copiers, scanners, barcode readers, graphoscopes, car mirrors (e.g., rearview, interior and exterior mirrors), and / or other relevant applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Fig. 1 is a cross-sectional view of a first surface mirror according to an exemplary embodiment.

[0016] Fig. 2 is a graph showing the decrease in the number of punctures in a CrN layer_x with increasing nitrogen content in the CrN layer_x in the mirror.

[0017] Fig. 3 is a graph depicting the decrease in the adhesion strength of the protective strip to the mirror Cr layer as the nitrogen content of the layer increases, indicating that the strength of the exposed CrN layer_x increases with increasing nitrogen content because the protective tape is likely to peel off fewer layer particles when the tape is removed.

[0018] Fig. 4 is a cross-sectional view of a first surface mirror according to another exemplary embodiment.

[0019] Fig. 5 is a cross-sectional view of a first surface mirror according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

[0020] The present invention relates to a mirror that can be used in the context of projection television (PTV), copiers, scanners, bar code readers, graphoscopes, and / or other suitable applications. The mirror has a layer containing CrN_x. CrN layer_x it may be used as the sole or first mirror reflecting layer in particular embodiments of this invention. In a particular embodiment of the embodiment, the mirror is a mirror with a front surface (FSM). According to the invention, the CrN layer_x it is formed by sputtering.

[0021] In most cases known in the art, no nitrogen is added to the reflecting layer in the mirror because nitrogen degrades the reflective characteristics which are highly desirable in a mirror. However, surprisingly and unexpectedly, it was found that adding nitrogen to chromium to form CrN_x reduces the number of punctures formed in the obtained layer without significantly adversely affecting the reflective properties of the mirror. In particular embodiments, the greater the amount of nitrogen introduced into the layer results in a smaller size and / or number of punctures in the Cr-containing layer. In particular embodiments, it has also been found that adding nitrogen to Cr can increase the strength of the mirror.

[0022] It has also been found that the addition of nitrogen reduces the tension of the Cr-containing layer, thus bringing it close to zero (compared to the absence of nitrogen in a Cr-containing layer of the same thickness). Hence, the voltage in reflection layer 3 tends to lower values ​​when nitrogen is added (resulting in a CrN layer_x) so that the adhesive forces of layer 3 to the glass are less likely to overcome, which would cause delamination. The strength is improved in this context and can lead to a reduction in the occurrence of punctures due to improved adhesion.

[0023] The introduction of nitrogen during physical vapor deposition (e.g. sputtering) onto a mirror with a metal-based first surface or even a bulk backing or stepped backing has been found to significantly reduce the formation of stinging. Nitrogen can produce a variety of effects that reduce pinhole formation, such as lowering the tension in the Cr-containing layer, reducing the ability to stick to any possible protective tape applied to the Cr-containing layer, and / or increasing the adhesion of the Cr-containing layer to the underlying glass substrate. While nitrogen is conventionally considered to have a strong unfavorable reflective effect, it has surprisingly been found that it is possible to adjust nitrogen flow levels so as to reduce pinhole formation and / or improve strength while not sacrificing the desired reflective properties. For example, in specific examples, the Cr-containing layer is only partially nitrided and / or is only partially nitrided such as its lower part, thus a reduced number of punctures and / or improved strength can be achieved in combination with the satisfactory optical properties of the mirror such as reflection and / or color.

[0024] Fig. 1 is a cross-sectional view of a first surface mirror (FSM) according to an exemplary embodiment. The first face mirror of Fig. 1 comprises a glass backing 1 and a CrN-containing reflection layer 3_x. The glass backing 1 may be about 1-10 mm thick depending on the embodiment of the invention, it may be any suitable color (e.g. gray, transparent, green, blue, etc.). As a specific example, the glass (e.g., soda-lime type silicon glass) substrate 1 may be about 1-5 mm thick, more preferably from about 2 to 3 mm. If the substrate 1 is glass, it may have a refractive index value of from about 1.48 to 1.53 (more preferably about 1.51 to 1.52). In Fig. 1, the incident light is denoted by I and the reflected light by R.

[0025] The reflecting layer 3 is comprised of / or includes CrN_x. The layer 3 reflecting layer reflects most of the incident light before it reaches the glass backing 1 and directs it towards the observer from the glass backing, such as a mirror defined as the mirror having the first surface. In particular embodiments of this invention, the reflection layer 3 includes CrN_x can be produced on the glass substrate 1 by sputtering Cr on the target in an atmosphere containing argon (Ar) and nitrogen (N), however other methods may be used interchangeably in alternative embodiments. The nitrogen content of layer 3 may be provided uniformly in the layer or may be graded (e.g., see the discussion with reference to Fig. 5 below).

[0026] In particular embodiments of this invention (e.g., the Figures 1-5 embodiment), the 3 CrN layer_x it may have a thickness from about 200 to 700 Å, more preferably from about 250 to 600 Å. The thickness of layer 3 may be controlled according to the desired reflection (and hence the inverse of transmission). By way of example only, when a visible light transmission of about 2.5% through a mirror is desired, a 3 CrN layer_x may be about 300 A thick. However, when a visible light transmission of about 0.5% through a mirror is desired, the 3 CrN layer_x it may be about 525 Å thick. Punctures in metallic Cr layers are particularly problematic at higher thicknesses. Hence, when a low visible transmission and therefore a higher thickness is desired, the addition of nitrogen to the Cr-containing reflecting layer is particularly advantageous. The use of nitrogen in the Cr-containing layer may be used at any thickness in various embodiments of this invention. However, with regard to the above, nitrogen is added to the Cr-containing reflecting layer to form a 3 CrN layer_x is particularly preferred, for example, in a layer 3 having a thickness of less than about 300 Ά, more preferably at least about 350 Ά, and particularly preferably at least about 400.

The mirror of the present invention (e.g., Figs. 1-5) has a visible light transmission of no more than 1.5% and possibly no more than 0.5% in the particular examples. Moreover, the mirror in particular embodiments of this invention (e.g., Figs. 1-5) has a light reflectance (e.g., from the surface of the film, measured by Hunter as Rf Y) of at least 50%, more preferably at least 60%.

[0028] Moreover, in particular embodiments of this invention (e.g. the embodiment in Figs. 1-5), the mirror has a * reflectance of color (film surface, measured by Hunter) from -2 to +2, more preferably from -1.5 to +1.5 and particularly preferably from -1 to +1. Additionally, in particular embodiments of this invention, the mirror has reflectivity b * color (film surface, measured by Hunter) from -3 to +2, more preferably from -3 to +1.5, and even more preferably from -1.5 to +1. 0.

[0029] While only layer 3 is provided on the backing 1 in the embodiment of Fig. 1, the present invention is not limited thereto. For example, and without limitation, other layer (s) may be applied between layer 3 and backing 1 in particular embodiments of the invention. For example, a dielectric layer may be deposited between the reflecting layer 3 and the glass backing 1. Moreover, other layer (s) such as dielectric layer (s) may be applied to the glass substrate 1 over the reflection layer 3.

As another alternative embodiment (s) of this invention, Cr may be replaced in reflecting layer 3 by Al, Ag, or any other reflective material whose surface tension is reduced by adding nitrogen, in any other embodiment of this invention.

Fig. 2, based on the example data, is a graph showing the number of punctures in a layer 3 per square foot (vertical axis of the graph) as a function of nitrogen flow when sputtering the 3 CrN layer._x for sputtering with Cr. Nitrogen flow% (horizontal axis of the graph) is the fraction of the total gas flow (only Ar and N were used₂) showing nitrogen. For example, if the gas flow used to sputter the 3 CrN layer_x was 162 sccm of nitrogen and 788 sccm of argon (ie 17% nitrogen and 83% argon), the amount of nitrogen in the gas flow is 17% (ie 162/950 = 17%).

[0031] Still referring to Fig. 2, it can be seen that adding nitrogen to the Cr-containing layer reduces the number of pinholes that can be formed therein. For example, as shown in Fig. 2, when nitrogen was not used in the layer (i.e., for the Cr metal layer, with a gas flow containing 100% argon), there were approximately 18 punctures per square foot in the 300 A Cr layer and 525 A per square foot. Cr there were approximately 23 punctures per square foot. However, once nitrogen was added to the sputtering gas in the sputtering chamber to form a 3 CrN layer_x, the number of punctures drops significantly. For example, with about 9% nitrogen flow into the 3 CrNx layer, with a layer thickness of about 300 A, there were about 11 punctures per square foot on the glass backing (less than about 18 punctures with 0% nitrogen flow per layer of similar thickness), and layer 3 CrN_x With a thickness of 525 Å, there were approximately 7 punctures (less than about 23 punctures with 0% nitrogen flow per layer of similar thickness) per square foot. In the other examples shown in Fig. 2, at about 17% nitrogen flow (i.e. 17% of the sputter gas in the sputtering chamber is nitrogen and the remaining gas is argon) per 3 CrN layer._x, for the layer with a thickness of about 300 Ά on the glass substrate, there were no punctures per square foot (less than about 18 punctures with 0% nitrogen flow per layer of similar thickness) and for the 3 CrN layer_x with a thickness of 525 µm, there were approximately 4 punctures (less than about 23 punctures with 0% nitrogen flow per layer of similar thickness) per square foot. Hence, it can be seen in Fig. 2 that adding nitrogen to the Cr-containing layer to form a 3 CrN layer_x it significantly reduces the number of punctures in the Cr-containing layer in an unexpectedly surprising manner. [0032] The protective tape is sometimes applied to the mirror surface during delivery, handling, and the like, and then removed after the mirror is mounted . Occasionally, punctures are formed in the mirror layer (s) upon removal of the tape. It is believed that this may be caused by pieces of the covering material peeling off with the strip. Hence, it may be advantageous to reduce the adhesive forces of the tape to the coating. In this regard, Fig. 3 is a graph based on example data showing that the adhesion strength of the protective tape to the Cr-containing layer in the mirror decreases with increasing nitrogen content in the layer, thus the strength of the exposed 3 CrN layer._x it may increase as nitrogen content increases, so that the protective tape has less chance of detaching the layer particles when it is removed. The vertical axis in Fig. 3 is the same as the vertical axis in Fig. 2. Hence, Fig. 3 shows that the mirror can become more durable if the amount of nitrogen in the 3 CrN layer is_xwill increase.

[0033] Fig. 4 shows another example of an embodiment of the invention. In the embodiment in Fig. 4, a first surface mirror having a glass backing 1, a layer 3 of CrN_x (discussed above) and a metal layer or substantially a Cr layer 7. Each of the layers 3 and 7 may function as a reflective layer in the embodiment in Fig. 4. In the embodiment in Fig. 4, the CrN layer 3_x helps to reduce the number of punctures in the coating, thus improving the mirror performance, and the metallic 7 Cr layer can provide excellent reflection performance. In the embodiment in Fig. 4, it is possible that the 3 CrN layer_x it can be relatively thinner than the layers discussed above.

[0034] Fig. 5 shows an exemplary embodiment of this invention. In the embodiment in Fig. 5, the 3 CrN layer_x it is nitrated gradually, which means that the nitrogen content in the individual portions differed. The use of N in layer 3 in Fig. 5 illustrates the nitrogen content. Hence, in the embodiment in Fig. 5, part of the 3 CrN layer_x closer to the glass substrate 1 contains more nitrogen than the part of the layer 3 remote from the glass substrate. Such grading may be continuous or staggered depending on the embodiment of the invention. In the embodiment in Fig. 5, part of the 3 CrN layer_x away from the substrate 1 has a lower nitrogen content (e.g. little or no nitrogen) than the part of the layer 3 closer to the glass substrate 1.

[0035] In particular embodiments of this invention, it has been found that adding nitrogen to the Cr-containing layer leads to unexpected results. In particular, as shown in Fig. 2, for example, if too little nitrogen (e.g., 0% or very little) is added to the Cr-containing layer, the problem of large numbers of pinholes may occur. Moreover, if too much nitrogen is added to the Cr-containing layer, the reflectance deteriorates and / or the reflective surface b * color becomes undesirable (e.g. b * becomes too large and significant yellow can be obtained). Hence, a particular amount of nitrogen is added in a specific non-limiting example of an embodiment of this invention. For example, in a particular embodiment, layer 3 comprises CrNx where x is from 0.01 to 0.5, more preferably from 0.01 to 0.4, also more preferably from 0.01 to 0.25, most preferably from 0.01 to 0 , 20, and still more preferably from 0.05 to 0.15 (based on the atomic percentage).

Moreover, in a particular embodiment of this invention the nitrogen gas percentage (of the total amount of gas used to coat the 3 CrN layer)_x) used for sputtering is about 1-21%, more preferably about 3-19% and most preferably about 5-18%.

EXAMPLES

[0037] The following examples of first surface mirrors have been made and tested, but are not intended to be limited thereto. Example 1 has glass / Cr layers, all of which in the other examples all have glass / CrN layers_x as shown in Fig. 1. The glass substrate 1 is approximately 2.3 mm thick. The examples were made by sputtering a Cr-containing layer on an undercoat using a Cr sputtering target in a gas atmosphere using the following process parameters. Lower line speeds have been used to create thinner layers and hence with less visible transmission if desired .___________________________________________

<td></td><td>At-</td><td>At-</td><td>At-</td><td>At-</td><td>At-</td><td>At-</td><td>At-</td>

<td></td><td>example 1</td><td>case 2</td><td>case 3</td><td>case 4</td><td>case 5</td><td>case 6</td><td>case 7</td>

<td>Flow n₂(sccm):</td><td> 0</td><td> 92</td><td> 131</td><td> 131</td><td> 160</td><td> 198</td><td> 94</td>

<td>Flow Ar (sccm):</td><td> 970</td><td> 878</td><td> 825</td><td> 825</td><td> 790</td><td> 747</td><td> 878</td>

<td>Totally- you gas (sccm):</td><td> 970</td><td> 970</td><td> 956</td><td> 956</td><td> 950</td><td> 945</td><td> 972</td>

<td>% N in flow:</td><td> 0</td><td> 9%</td><td> 14%</td><td> 14%</td><td> 17%</td><td> 21%</td><td> 10%</td>

<td>Linear speed (ipm):</td><td> 160</td><td> 160</td><td> 142</td><td> 150</td><td> 142</td><td> 85</td><td> 90</td>

<td>Pressure- no (mTorr):</td><td> 2, 6</td><td> 2,5</td><td> 2,4</td><td> 2,4</td><td> 2,3</td><td> 2,2</td><td> 2,5</td>

[0038] The mirrors of Examples 2-6 (which have nitrogen in layer 3 containing Cr) were found to have significantly fewer punctures than the mirror of Example 1 (which had a metallic layer 3 Cr - no nitrogen). Some of these examples, and others, were used to collect the data shown in Figs. 2-3, indicating unexpected results that relate to fewer punctures and improved strength.

[0039] Moreover, Examples 1-6 have the following optical characteristics (optical data was measured with

Hunter Ultrascan XE in action; reflectance / color index was measured on the reflective surface side):

<td></td><td>Example 1</td><td>Example 2</td><td>Example 3</td><td>Example 4</td><td>Example 5</td><td>Example 6</td><td>Example 7</td>

<td>Reflectivity (Rf Y%):</td><td> 65, 88</td><td> 64,96</td><td> 64,24</td><td> 63, 97</td><td> 63, 64</td><td> 62, 68</td><td> 65, 13</td>

<td>a *:</td><td> -1, 05</td><td> -0,52</td><td> -0, 15</td><td> -0, 12</td><td> + 0, 12</td><td> 0,55</td><td> -0, 15</td>

<td>b *:</td><td> -1, 02</td><td> 0,31</td><td> 0, 67</td><td> 0,7</td><td> 1, 08</td><td> 1, 64</td><td> 0,43</td>

<td>Visible transmission (TY%):</td><td> 2,55</td><td> 2,53</td><td> 2,28</td><td> 2,52</td><td> 2,53</td><td> 0, 69</td><td> 0,43</td>

[0040] It can be seen that Examples 6-7 have a lower visible transmission at lower line speeds and hence a thicker layer used. Moreover, it can be seen from the above that a higher nitrogen flow increases the b * value towards yellow, which may be undesirable in the particular example of unrestricted lifetimes.