JP2005114649A - Cover glass for timepiece - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cover glass for a timepiece having high hardness, excellent abrasion resistance, and anti-reflection function hardly damaged even if carried for a long period. <P>SOLUTION: In this cover glass for the time piece equipped with an anti-reflection coating whose outermost surface layer is made of SiO<SB>2</SB>, the hardness of the anti-reflection coating surface is raised and the abrasion resistance thereof is remarkably raised by including 0.1-10.0 atom%, more preferably, 0.2-5.0 atom% of nitrogen, in the SiO<SB>2</SB>coating of the outermost surface layer at least on the surface. Resultantly, the cover glass for the time piece has the anti-reflection function not having, even if carried for a long period, the problem wherein the surface is clouded and a pointer or a dial become difficult to be viewed because the surface of the anti-reflection coating is finely damaged or exfoliated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a watch cover glass, and more particularly, to a watch cover glass having an excellent antireflection function and scratch resistance over a long period of time.

  Blue glass (soda glass), white glass, sapphire glass, and the like are used for the watch cover glass. All of these cover glasses have a high reflectance in the visible light region, and the visibility of the pointer and dial is not sufficient. For this reason, in the watch that checks the time in various environments such as indoors, outdoors, and day and night, the external light and illumination change, so the external light is reflected on the surface of the cover glass and the time display is difficult to see. .

  As a solution for that, it has already been disclosed to coat an antireflection film on both sides or at least one side of a cover glass. (For example, refer to Patent Document 1).

  In general, an antireflection film is designed and combined with a metal or inorganic oxide film, nitride film, fluoride film, or sulfide film having an appropriate refractive index so as to have a desired reflectance in a limited wavelength region. Composed.

Japanese Patent Laid-Open No. 2002-202401 (FIGS. 1 and 2)

However, these antireflection films are inferior in scratch resistance and the like. For example, if a wristwatch equipped with a cover glass coated with an antireflection film having magnesium fluoride as the outermost layer is carried for a long time, the surface of the antireflection film There is a problem that the surface becomes cloudy due to fine scratches or peeling, and the pointer and dial are difficult to see. Further, even when SiO ₂ which is said to have high hardness instead of magnesium fluoride is used, the above problem cannot be solved.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a watch cover glass having an anti-reflection function that is excellent in wear resistance and hardly scratches even when carried for a long time.

In order to achieve the above object, the watch cover glass of the present invention employs the following configuration.
The watch cover glass of the present invention is a watch cover glass having an antireflection film made of a laminated film of SiO ₂ and SiNx on both surfaces of a glass substrate having a front surface and a back surface. The nitrogen content in the outermost SiO ₂ film of the top surface is characterized by containing 0.1 to 10.0 atomic% of nitrogen.

The watch cover glass of the present invention is a watch cover glass comprising an antireflection film having a laminated film of SiO ₂ and SiNx on both surfaces of a glass substrate having a front surface and a back surface. It is preferable that the content of nitrogen in the outermost surface SiO ₂ film is in the range of 0.2 atomic% to 5.0 atomic%.

In the watch cover glass of the present invention, the antireflection film is preferably produced by a reactive sputtering method.

In the watch cover glass of the present invention, the thickness of the outermost SiO ₂ film is preferably 80 nm or more.

(Function)
As a result of earnest and examination of the antireflection film in the watch cover glass, the inventor is a glass substrate provided with an antireflection film in which the outermost layers on the front surface and the back surface are SiO ₂ films. By containing nitrogen atoms bonded to Si (hereinafter referred to as N) in the outermost layer of SiO _{2 on the} front surface, it has excellent anti-abrasion and anti-reflection function that prevents scratches even when carried for a long time. It was possible to provide a watch cover glass having the same. Here, the front surface refers to the surface of the watch cover glass exposed to the outside air. In order to combine and contain N with Si in the outermost layer SiO ₂ , a reactive sputtering method that can form SiO ₂ and SiN x only by exchanging gas with Si as a target is suitable, together with O ₂ gas and Ar gas. by introducing a gas containing N at least the outermost layer of the SiO ₂ film formation, it is preferred to incorporate N in the SiO _2. As a result, the oxygen in the SiO ₂ film is easily replaced with N during film formation, and a nitride having a large internal stress composed of N combined with Si is formed, thereby improving the wear resistance and hardness of the film. I guess that has occurred. Furthermore, the amount of water contained in the under normal N ₂ gas atmosphere minimize this for SiO ₂ weak porous strength when there is water will be formed, but the proportion of water, such as N ₂ gas atmosphere One factor is that the SiO ₂ film formed in a small environment is likely to have a dense and strong amorphous structure. In this way, it is possible to form a SiO ₂ film which is not colored and has excellent wear resistance.

According to the present inventor, the optimum N content of a sample into which a gas containing N is introduced has been confirmed by XPS (X-ray photoelectron spectroscopy) analysis, and the optimum amount is about 0.1 atomic% to about 10. It has been confirmed by the present inventors that it is in the range of 0 atomic%, and more preferably in the range of 0.2 atomic% to 5.0 atomic% from the viewpoint of wear resistance and hardness. In order to include such N content, the value of N ₂ / (N ₂ + O ₂ ), which is the ratio of the N ₂ flow rate to the sum of the gas flow rates of O ₂ and N ₂ , is preferably 50% or more. . Further, even if the gas flow ratio N ₂ / (N ₂ + O ₂ ) is introduced up to 90%, in the present invention, the value of 1.47 which is the refractive index value of the SiO ₂ film hardly changes, and it is specific to the substance. Although it was almost the same as the value, when it exceeded 90%, the refractive index increased rapidly, and it was found that the refractive index tends to approach the refractive index of SiNx.

FIG. 4 shows an N1s orbital photoelectron spectrum by XPS according to the present invention. As is clear from this figure, it was confirmed that the film containing nitrogen atoms bonded to Si in the SiO ₂ of the present invention and the SiNx film are clearly different.

When N is contained in the outermost layer SiO ₂ , if the target used for sputtering is SiO ₂ , there is no effect even if a gas containing N ₂ is introduced, and it is unique to reactive sputtering when using a Si target. This phenomenon has also been confirmed by the present inventors. This is presumably because the sputtering of the Si target promotes the reaction because the plasma space and the deposited film surface are more activated than the sputtering using the SiO ₂ target. In addition, the film formation rate is much faster when the Si target is used, and improvement in productivity can be expected.

The thickness of the outermost layer SiO ₂ is suitably 80 nm or more. This is because the hardness and wear resistance are inferior due to the influence of the substrate below 80 nm.

It is desirable that the substrate temperature be 70 ° C. or higher during sputtering. This is presumably because an increase in the substrate temperature leads to active migration of sputtered particles on the substrate, resulting in a denser film. In this way, the outermost layer SiO ₂ has high hardness and excellent wear resistance, and it is possible to provide a watch cover glass having transparency and an antireflection function.

As described above, the watch cover glass of the present invention is a Si the outermost layer a watch cover glass having the antireflection film and SiO ₂ film, in the outermost layer of the SiO ₂ film of at least the surface By containing the bonded N, the hardness of the antireflection film surface is increased, and the wear resistance is remarkably increased. As a result, the anti-reflection film has an anti-reflection function that does not cause the problem that the anti-reflection film may be finely scratched or peeled off even if it is carried for a long time and the surface becomes cloudy, making it difficult to see the pointer and dial. It became possible to provide a cover glass for a watch. In addition, according to the present invention, since the antireflection function is not deteriorated, there is an effect that the decorativeness of the dial is not impaired by a change with time. Further, in the case of a timepiece in which a solar cell is mounted on the dial plate and receives electromotive force for driving the timepiece by receiving light that has passed through the cover glass, the antireflection function does not deteriorate in the present invention. Therefore, there is an effect of further improving the power generation efficiency of the solar cell.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing the structure of a watch cover glass of the present invention. The front and back surfaces of the sapphire glass 10 are coated with antireflection films 110 and 210 made of a laminate of a nitride film of SiO ₂ or SiNx (x is an arbitrary number greater than 0). The outermost surface layer of the antireflection film 110 on the front surface is covered with the SiO ₂ film 1, and this film is made of SiO ₂ partially bonded with N. FIG. 2 is a schematic sectional view of a sputtering apparatus for laminating an antireflection film. In the present invention, a DC reactive sputtering apparatus is used. The target is Si, and an inert gas such as Ar, He or Ne, O ₂ , N ₂ gas, etc. is introduced from the gas inlet 32 and a voltage is applied to the Si target to perform sputtering, and the sapphire glass 10 is laminated. To do. At this time, a Si target doped with boron may be used in order to give conductivity to the Si target and perform stable sputtering. The film produced by the sputtering method of the Si target is a SiO ₂ film or a nitride film expressed by SiNx, or SiOxNy, which can be formed by switching between O ₂ and N ₂ gases which are reactive gases. is there.

  The characteristics of the antireflection film are greatly dependent on the number of oxide films and nitride films to be stacked, the order of arrangement, the refractive index and thickness of each film, and the reflectance characteristics that satisfy the specifications are calculated by simulation. Can be optimized. Further, the refractive indexes of the oxide film and the nitride film can be changed depending on the film formation conditions.

  Further, the antireflection film for a watch preferably has a reflectance of 5% or less as shown in FIG. 3 in the visible light region having a wavelength of 400 nm to 700 nm. For this purpose, the sapphire glass 10 is used as shown in FIG. It is essential to form antireflection films on the front and back surfaces.

Hereinafter, specific embodiments of the present invention will be described with reference to FIGS.
(Example 1)
In the watch cover glass in this embodiment, as shown in FIG. 1, the front surface of the sapphire glass 10 is coated with an antireflection film 110 and the back surface is coated with an antireflection film 210. The film configurations of the antireflection film 110 and the antireflection film 210 are the same. In this embodiment, SiO ₂ and SiNx are used to form a four-layer structure in which the layers are alternately stacked. The order is from the outermost layer (fourth layer) to SiO ₂ , SiNx, SiO ₂ , SiNx, and the film thickness is 100 nm, 70 nm, 20 from the outermost layer (fourth layer).
nm, 40 nm. The refractive index of SiNx is 1.97. Further, the refractive indexes of the SiO ₂ film and the SiNx film can be changed depending on the sputtering conditions.

  FIG. 2 shows a conceptual diagram of a DC reactive sputtering apparatus which is a method for producing an antireflection film in this example.

  The Si target 30 is disposed in the vacuum chamber 31 and a DC voltage is applied to the Si target 30. The sapphire glass 10 is installed so as to face the Si target 30. A DC power source 34 is connected to the Si target 30.

The inside of the vacuum chamber 31 is exhausted to 1 × 10 ⁻⁵ Torr by a vacuum pump (not shown), and the sapphire glass 10 is heated to about 200 ° C. by a heater (not shown). Then, a mixed gas was introduced from the gas inlet 32, DC reactive sputtering was performed under the following conditions, and the antireflection film 110 was laminated. The film formation of SiO ₂ and SiNx is possible by switching the gas type and gas flow ratio. The film forming conditions for each layer are shown below.
First layer (11)
Ar flow rate 20sccm
N ₂ flow rate 40sccm
DC output 2000W (300V)
Gas pressure 3 × 10 ^-3 Torr

Second layer (12)
Ar flow rate 20sccm
O ₂ flow rate 40sccm
DC output 1500W (200V)
Gas pressure 3 × 10 ^-3 Torr

Third layer (13)
Ar flow rate 20sccm
N ₂ flow rate 40sccm
DC output 2000W (150V)
Gas pressure 3 × 10 ^-3 Torr

Fourth layer (1)
Ar flow rate 20sccm
N ₂ flow rate 15sccm
O ₂ flow rate 15sccm
DC output 2000W (300V)
Gas pressure 8 × 10 ^-3 Torr

The antireflection film 110 was laminated on the front surface of the sapphire glass 10 as described above. At this time, the surface layer (fourth layer) O ₂ and N ₂ gas N ₂ gas flow rate ratio of to the sum of the time produced (hereinafter, the gas flow rate) to 50% the value of N ₂ / (N ₂ + O ₂₎ It mixed and introduced so that it might become. As a result, 0.1 atomic% of N was introduced into the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 so that the antireflection film 210 was laminated. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, the outermost layer (fourth layer) is followed by the SiO ₂ film 24, the SiNx film 23, the SiO ₂ film 22, and the SiNx film 21, and the film thicknesses are 100 nm, 70 nm, 20 nm, and 40 nm from the outermost layer (fourth layer). It has become.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 2)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost surface layer (fourth layer) on the front surface was mixed and introduced so that the gas flow ratio N ₂ / (N ₂ + O ₂ ) was 54%. As a result, 0.2 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 3)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost surface layer (fourth layer) on the front surface was mixed and introduced so that the gas flow ratio N ₂ / (N ₂ + O ₂ ) was 56%. As a result, 1.2 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

Example 4
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) was 58%. As a result, 2.2 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 5)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow ratio N ₂ / (N ₂ + O ₂ ) was 62%. As a result, 4.8 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.
As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 6)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) was 68%. As a result, 5.4 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 7)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow ratio N ₂ / (N ₂ + O ₂ ) was 76%. As a result, 6.2 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

(Example 8)
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow ratio N ₂ / (N ₂ + O ₂ ) was 82%. As a result, 7.5 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, a watch cover glass having an antireflection function containing N in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. 1 is completed. did.

Example 9
Next, as in Example 1, the front surface of the sapphire glass 10 was coated with an antireflection film 110 and the back surface was coated with an antireflection film 210. At this time, the outermost layer (fourth layer) on the front surface was mixed and introduced so that the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) was 88%. As a result, 9.8 atomic% of N bonded to Si was introduced into the outermost layer (fourth layer) SiO ₂ . Thereafter, the sapphire glass 10 was turned over, and the same operation as that on the front surface was performed to laminate the antireflection film 210.

As described above, according to the present embodiment, for a watch having an antireflection function containing N bonded to Si in the SiO ₂ film 1 on the outermost surface of the sapphire glass 10 as shown in FIG. The cover glass was completed.

(Comparative Example 1)
Next, as Comparative Example 1, an example in which N is not contained in the outermost SiO ₂ film 1 on the front surface will be described. The production method was the same as in Example 1, and an antireflection film 110 was laminated on the front surface of the sapphire glass 10. At this time, the conditions from the first layer to the third layer were exactly the same as those in Example 1, but the outermost layer, the fourth layer, was formed without flowing N ₂ gas under the following conditions.
Fourth layer (1) Ar flow rate 20 sccm
O ₂ flow rate 40sccm
DC output 2000W (300V)
Gas pressure 8 × 10 ^-3 Torr
That is, when the outermost layer (fourth layer) was manufactured, the gas flow ratio N ₂ / (N ₂ + O ₂ ) between O ₂ and N ₂ was introduced so that the value was 0%. As a result, a film made of SiO ₂ containing no N bonded to Si was formed on the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 to laminate the antireflection film 210. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, the outermost layer (fourth layer) is followed by the SiO ₂ film 24, the SiNx film 23, the SiO ₂ film 22, and the SiNx film 21, and the film thicknesses are 100 nm, 70 nm, 20 nm, and 40 nm from the outermost layer (fourth layer). It has become. As described above, the antireflection film 110 was laminated on the front surface of the sapphire glass 10 and 210 was laminated on the back surface. As a result, a film made of an SiO ₂ film containing no N was formed on the outermost layer (fourth layer).

(Comparative Example 2)
Next, an example in which the content of N in the present invention is less in the outermost SiO ₂ film 1 on the front surface will be shown as Comparative Example 2. The production method was the same as in Example 1, and an antireflection film 110 was laminated on the front surface of the sapphire glass 10. At this time, the conditions from the first layer to the third layer are exactly the same as in Example 1, but the value of the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) is 10% in the outermost layer, the fourth layer. Mixed and introduced. As a result, an SiO ₂ film containing 0.02 atomic% of N was formed on the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 to laminate the antireflection film 210. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, from the outermost layer (fourth layer) to the SiO ₂ film 24, SiNx film 23, SiO ₂ film 22, and Si ₃ N ₄ film 21, the film thickness is 100 nm, 70 nm from the outermost layer (fourth layer), 20 nm and 40 nm. The antireflection films 110 and 210 were laminated on the front and back surfaces of the sapphire glass 10 as described above.

(Comparative Example 3)
Next, an example in which the content of N is slightly higher than Comparative Example 2 as Comparative Example 3 will be shown. The production method was the same as in Example 1, and an antireflection film 110 was laminated on the front surface of the sapphire glass 10. At this time, the conditions from the first layer to the third layer are exactly the same as in Example 1, but the value of the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) is 20% in the outermost layer, the fourth layer. Mixed and introduced. As a result, an SiO ₂ film containing 0.05 atomic% of N was formed on the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 to laminate the antireflection film 210. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, from the outermost layer (fourth layer) to the SiO ₂ film 24, SiNx film 23, SiO ₂ film 22, and Si ₃ N ₄ film 21, the film thickness is 100 nm, 70 nm from the outermost layer (fourth layer), 20 nm and 40 nm. As described above, the antireflection films 110 and 210 were laminated on the front surface and the back surface of the sapphire glass 10.

(Comparative Example 4)
Next, as Comparative Example 4, as in Comparative Example 2, an example in which the content of N in the present invention is less in the outermost SiO ₂ film 1 on the front surface will be shown. The production method is the same as in Example 1, and sapphire glass 1
An antireflection film 110 was laminated on the front surface of zero. At this time, the conditions from the first layer to the third layer are exactly the same as in Example 1, but the value of the gas flow ratio N ₂ / (N ₂ + O ₂ ) is 30% in the outermost fourth layer. Mixed and introduced. As a result, a SiO ₂ film containing 0.08 atomic% N was formed on the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 to laminate the antireflection film 210. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, from the outermost layer (fourth layer) to the SiO ₂ film 24, SiNx film 23, SiO ₂ film 22, and Si ₃ N ₄ film 21, the film thickness is 100 nm, 70 nm from the outermost layer (fourth layer), 20 nm and 40 nm. As described above, the antireflection films 110 and 210 were laminated on the front surface and the back surface of the sapphire glass 10.

(Comparative Example 5)
Next, as Comparative Example 5, an example in which 10.0 atomic% or more of N is contained in the outermost SiO ₂ film 1 on the front surface will be described. The production method was the same as in Example 1, and an antireflection film 110 was laminated on the front surface of the sapphire glass 10. At this time, the conditions from the first layer to the third layer are exactly the same as in Example 1, but the value of the gas flow rate ratio N ₂ / (N ₂ + O ₂ ) is 95% in the outermost layer, the fourth layer. Mixed and introduced. As a result, a SiO ₂ film containing 11.2 atomic% of N was formed on the outermost layer (fourth layer). Thereafter, the sapphire glass 10 was turned over, and the same operation as that of the front surface was performed on the back surface of the sapphire glass 10 to laminate the antireflection film 210. The antireflection film 210 on the back surface has the same film formation conditions as the antireflection film 110 on the front surface, and the film configuration is also the same. That is, from the outermost layer (fourth layer) to the SiO ₂ film 24, SiNx film 23, SiO ₂ film 22, and Si ₃ N ₄ film 21, the film thickness is 100 nm, 70 nm from the outermost layer (fourth layer), 20 nm and 40 nm. The antireflection films 110 and 210 were laminated on the front and back surfaces of the sapphire glass 10 as described above.

For Examples 1 to 9 and Comparative Examples 1 to 5 obtained as described above, alumina particles having a particle diameter of 10 μm were dispersed in order to evaluate the effect of the outermost SiO ₂ film containing N. The watch cover glass of each of these Examples and Comparative Examples coated with a wrapping film and an antireflection film was brought into contact with a contact load of 500 g, and the surface of the cover glass was reciprocated several times to start scratching the cover glass. A sliding wear test was performed to evaluate the number of reciprocations. In this evaluation, if scratches do not occur after sliding 100 times or more, the hardness and wear resistance are practically sufficient, and scars and peeling hardly occur even when actually carried and used for a long time. As a result, it has already been confirmed by the present inventor that the surface does not become cloudy and the pointer and the dial are not difficult to see. Furthermore, the hardness of the surface was measured with a nanoindenter (ultrafine area hardness meter). The results are shown in Table 1. Moreover, in order to evaluate the superiority or inferiority of the antireflection effect, the transmittance at a wavelength of 550 nm obtained from the measurement of the reflectance characteristics before the sliding wear test is also shown.

As can be seen from Table 1, in the results of the sliding wear test for evaluating wear resistance in Examples 1 to 9, that is, when N bonded to Si is 0.1 atomic% to about 10.0 atomic%, No scratches were generated even after sliding more than once, good wear resistance was obtained, and in particular, Examples 2 to 5 corresponding to N content of 0.2 atomic% to 5.0 atomic% were nanoin A high value was also obtained in the surface hardness measurement by a denter. These reflectance characteristics remain as shown in FIG. 3 even after the sliding wear test, and it was confirmed that the transmittance at 550 nm was 96% or more.

  On the other hand, in Comparative Examples 1 to 5, scratches occurred and the surface was clouded before reaching 100 times in the sliding wear test. As a result, the reflectance also changed greatly from the curve shown in FIG. 3, and a wavelength region where the reflectance exceeded 5% was generated, resulting in a problem that the dial was difficult to see. As shown in Table 1, the surface hardness measurement with a nanoindenter showed a value much lower than that of the example. In addition, the refractive index was almost constant at 1.47 until the N content was 10.0% in particular. However, when it exceeds 10.0%, the refractive index becomes larger and it is easy to design an antireflection film. It was confirmed that

FIG. 4 shows N1s orbital photoelectron spectra by XPS in Example 3 and Comparative Example 3 of the present invention. As is clear from this figure, it was confirmed that the film containing nitrogen atoms bonded to Si in the SiO ₂ of the present invention and the SiNx film are clearly different. This difference is presumed to be the result of N being adsorbed and replaced by vacancies and grain boundaries in the SiO ₂ film, increasing the internal stress and causing a chemical shift.

  As described above, according to the present invention, it is possible to provide a timepiece cover glass having a high surface hardness, excellent wear resistance, and having an antireflection function that is difficult to be damaged even when carried for a long period of time.

In the above embodiment, N ₂ gas is used, but it has been confirmed by the present inventor that the same effect can be obtained with NH ₃ gas. In the present embodiment, an example in which four antireflection films are laminated on one side is shown, but there are many antireflection films and combinations thereof, and the present invention is not limited to this. In the above embodiment, the front surface and the back surface have exactly the same film structure, but at least the content of nitrogen in the outermost SiO ₂ film of only the front surface is 0.1 atomic% to 10%. It may be in the range of 0.0 atomic%. Moreover, although the example of the sapphire glass was shown in the said Example also in the said Example, it is not limited to this, Soda glass, blue plate glass, white plate glass, or plastic glass may be sufficient.

It is a cross-sectional schematic diagram which shows the structure of the watch cover glass of this invention which coat | covered the antireflection film. It is a cross-sectional schematic diagram of the sputtering device for laminating | stacking an antireflection film. It is a reflectance characteristic spectrum figure which shows the characteristic of the reflectance of the cover glass for timepieces of this invention which coat | covered the antireflection film. A N1s orbital photoelectron spectrum diagram by XPS (X-ray photoelectron spectrometer) of SiO ₂ and SiNx which N contains Si bound of the present invention.

Explanation of symbols

1 SiO ₂ film 10 Sapphire glass 11, 13, 21, 23 Si ₃ N ₄ film 12, 22, 24 SiO ₂ film 110, 210 Antireflection film 30 Si target 31 Vacuum chamber 32 Gas inlet 34 DC power supply 50 SiNx film N1s orbital photoelectron spectrum 51 N1s photoelectron spectrum of SiO ₂ film containing N

Claims (4)

A watch cover glass having the antireflection film having a multilayer film of the SiO ₂ film and the SiNx film on both surfaces of a glass substrate having a front surface and a back surface, the outermost layer of at least the front surface SiO ₂ A watch cover glass having a nitrogen content in the range of 0.1 atomic% to 10.0 atomic%. _2. The watch cover glass according to claim 1, wherein the content of nitrogen in the outermost SiO ₂ film is in the range of 0.2 atomic% to 5.0 atomic%. The timepiece cover glass according to claim 1 or 2, wherein the antireflection film is produced by a reactive sputtering method. 4. The timepiece cover glass according to claim 1, wherein a thickness of the outermost SiO ₂ film is 80 nm or more. 5.

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