WO2018110018A1

WO2018110018A1 - Optical element

Info

Publication number: WO2018110018A1
Application number: PCT/JP2017/033842
Authority: WO
Inventors: 松坂慶二; 能勢正章; 中村勝也; 青木洋輔; 今関秀和; 水町靖; 野村康之; 濱敬二
Original assignee: コニカミノルタ株式会社
Priority date: 2016-12-14
Filing date: 2017-09-20
Publication date: 2018-06-21
Also published as: JP2020024238A

Abstract

An optical element is provided which has a multilayer film with excellent acid resistance and scratch resistance and which can exhibit a photocatalytic effect. This optical element has a glass substrate on which a multilayer film of three or more layers is formed, wherein the multilayer film comprises at least one low refractive index layer and at least one high refractive index layer, the top layer furthest from the glass substrate is a low refractive index layer, a high refractive index layer adjacent to the top layer is a functional layer having a metal oxide with a photocatalytic function as the main component, and at least one of the high refractive index layers is formed from a specific material having any of Ta, Hf, Zr and Nb as the main component, and satisfies the following conditional expressions: 220nm ≤ Tcat ≤ 600nm (1) 100nm ≤ TH (2) Here, Tcat is the film thickness of the functional layer, and TH is the total film thickness of the high refractive index layers formed from the specific material.

Description

Optical element

The present invention relates to an optical element formed with a multilayer film.

For example, in-vehicle cameras are mounted on vehicles for driving support of vehicles. More specifically, a camera that captures the back and sides of the vehicle is mounted on the body of the automobile, and the image captured by the camera is displayed at a position where the driver can visually recognize it. Contributes to safe driving.

By the way, in-vehicle cameras are often mounted outside the vehicle, and dirt such as water droplets or mud often adheres on the lens. Depending on the degree of water drops and dirt adhering to the lens, the image captured by the camera may become unclear. In view of this, a technique has been developed in which a photocatalytic substance is applied to the object side surface of a lens to clean organic substances adhering to the surface by ultraviolet irradiation. For example, Patent Document 1 discloses a technique for obtaining a photocatalytic effect by applying Ti nanoparticles to a surface using spray coating or the like for spectacle lenses or building materials. It is also conceivable to apply Ti nanoparticles to the object side surface of an imaging lens mounted on a vehicle-mounted camera using such technology.

By the way, since an imaging lens or the like mounted on a vehicle-mounted camera is used in a harsh environment, sufficient environmental resistance is required. More specifically, there is a possibility that the exposed optical surface of the imaging lens may be damaged or eroded by impacts, wind pressure, and sand dust splashed by traveling. Furthermore, there is a risk of surface deterioration and alteration due to acid rain and chemicals such as detergents and waxes used during car washing. In particular, if oil, grease, dust, or the like adheres to the optical surface of the imaging lens, the optical surface may become clouded over time, and if the optical surface is in contact with dirt for a long time, the optical surface itself May be altered.

Therefore, when the Ti nanoparticles are applied to the side surface of an object such as an imaging lens used in a harsh environment such as an in-vehicle application using the technology disclosed in Patent Document 1, the glass substrate is acid-resistant. In addition, the material must be limited to a material having a high scratch resistance, which causes a problem that the degree of design freedom for controlling the optical characteristics is greatly impaired.

On the other hand, Patent Document 2 discloses a conductive optical member having excellent acid resistance. However, the technique of Patent Document 2 uses a material with low photocatalytic activity, and it is difficult to obtain a sufficient photocatalytic effect. Further, since the optical member is a film, there is a problem that scratch resistance cannot be secured. Similar problems may occur in communication optical elements used outdoors.

International Publication No. 1996/029375 JP 2013-174787 A

An object of the present invention is to provide an optical element having a multilayer film excellent in acid resistance and scratch resistance and capable of exhibiting a photocatalytic effect.

In order to achieve at least one of the objects described above, an optical element reflecting one aspect of the present invention is an optical element having a glass substrate on which a multilayer film of three or more layers is formed. It has one low refractive index layer and at least one high refractive index layer, the uppermost layer farthest from the glass substrate is the low refractive index layer, and the high refractive index layer adjacent to the uppermost layer is A functional layer mainly composed of a metal oxide having a photocatalytic function, wherein at least one of the high refractive index layers is formed from a specific material mainly composed of Ta, Hf, Zr, or Nb; The following conditional expression is satisfied.
150 nm ≦ Tcat ≦ 700 nm (1)
100 nm ≦ TH (2)
here,
Tcat: film thickness of functional layer TH: total film thickness of high refractive index layer formed from specific material

It is a figure which shows typically the cross section of the optical element concerning this embodiment. It is a figure which shows the spectral characteristics of the multilayer film of the test numbers 1-6 which are an Example. It is a figure which shows the spectral characteristic of the multilayer film of the test number 2-3 which is an Example. It is a figure which shows the spectral characteristics of the multilayer film of the test number 2-4 which is an Example. It is a figure which shows the spectral characteristics of the multilayer film of the test number 2-5 which is an Example. It is a figure which shows the spectral characteristics of the multilayer film of test number 2-6 which is an Example. It is a figure which shows the spectral characteristics of the multilayer film of test number 2-7 which is an Example

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a cross section of an optical element according to the present embodiment. An optical element 100 shown in FIG. 1 has a multilayer film MC having a structure in which low refractive index layers L and high refractive index layers H are alternately laminated on a glass substrate (glass substrate) GL. However, the high refractive index layer H may be in contact with the glass substrate GL. Such an optical element 100 can be used as an in-vehicle lens or a communication lens. In FIG. 1, the layer located between the glass substrate GL and the functional layer 20 may be replaced with an equivalent film of an intermediate refractive index layer instead of a high refractive index layer or a low refractive index layer.

In FIG. 1, the uppermost layer 10 farthest from the glass substrate GL is a low refractive index layer L, and the high refractive index layer H adjacent to the uppermost layer 10 is a functional layer 20 of a metal oxide having a photocatalytic function. By using the low refractive index layer L having a relatively high strength as the uppermost layer 10, scratch resistance can be improved. Moreover, since the functional layer 20 exhibits a photocatalytic function using active oxygen excited by UV light through or through the uppermost layer 10, the functional layer 20 is preferably placed as close as possible to the uppermost layer 10. By providing the functional layer 20 adjacent to the uppermost layer 10, for example, a photocatalytic function can be effectively exhibited. Further, it is desirable that the functional layer 20 has a thickness exceeding 100 nm adjacent to the uppermost layer 10. Furthermore, it is preferable to use a metal oxide having a photocatalytic effect and a photoactive effect as the functional layer 20 because the surface organic substances can be removed and the hydrophilicity of the uppermost layer 10 can be maintained. The functional layer 20 using TiO ₂ is preferably formed using IAD (Ion Assisted Deposition (hereinafter referred to as IAD)) because the photocatalytic effect is enhanced.

“Photocatalytic function” means that strong oxidative power is generated when sunlight or artificial light is incident, effectively removes harmful organic compounds and bacteria, etc. that come in contact with water. In addition, the self-cleaning function such as washing with water or the like without fixing oily stains, for example, is a function of titanium dioxide. Note that “adjacent to the uppermost layer” means that the function is not hindered between the uppermost layer 10 and the functional layer 20 in addition to the case where the uppermost layer 10 and the functional layer 20 are in close contact with each other. This includes the case where a layer (for example, a layer of 20 nm or less) is provided.

Further, at least one of the high refractive index layers H is formed of a specific material mainly containing any one of Ta, Hf, Zr, and Nb. Examples of substances that are effective in improving acid resistance include Ta, Hf, Zr, and Nb oxides. “Main component” means that the content of the element is 51% by weight or more, preferably 70% by weight or more, more preferably 90% by weight, and still more preferably 100% by weight.

Furthermore, the optical element 100 of the present embodiment satisfies the following conditional expression.
150 nm ≦ Tcat ≦ 700 nm (1)
100 nm ≦ TH (2)
here,
Tcat: film thickness TH of the high-refractive index layer H or functional layer 20 adjacent to the uppermost layer 10: total film thickness of the high-refractive index layer H formed from a specific material

Since the film thickness of the functional layer 20 can be ensured that the value of the formula (1) is equal to or greater than the lower limit, a sufficient photocatalytic effect can be expected. On the other hand, as the thickness of the functional layer 20 increases, the photocatalytic effect can be expected. However, since it becomes difficult to obtain desired characteristics required for the multilayer film, the value of the expression (1) should be less than the upper limit. Is desirable. In addition, Preferably, it is satisfy | filling the following formula | equation.
220 nm ≦ Tcat ≦ 600 nm (1 ′)
More preferably, it is satisfy | filling the following formula | equation.
250 nm ≦ Tcat ≦ 600 nm (1 ″)

Furthermore, since the total film thickness of the high refractive index layer H can be ensured that the value of the formula (2) is not less than the lower limit, sufficient acid resistance can be expected. Although there is no particular limitation on the upper limit of the formula (2), a common-sense total film thickness naturally becomes the upper limit in securing the optimum design of the optical element 100. In addition, Preferably, it is satisfy | filling the following formula | equation.
150 nm ≦ TH (2 ′)

The high refractive index layer H or the functional layer 20 adjacent to the uppermost layer 10 is preferably formed from an oxide (for example, TiO ₂ ) containing Ti as a main component. This is because Ti oxides such as TiO ₂ have a very high photocatalytic effect.

Preferably the top layer 10 is formed of SiO _2. UV light is hard to be incident at night or outdoors, and the hydrophilic effect is reduced with an oxide mainly composed of Ti. However, even in such a case, the hydrophilic effect can be exhibited by forming the top layer 10 from SiO ₂ and scratch resistance. Sex is also enhanced. When SiO ₂ is used for the uppermost layer 10, scratch resistance is improved by performing a heat treatment at 500 ° C. for 2 hours after film formation.

The uppermost layer 10 is preferably formed from a mixture of SiO ₂ and Al ₂ O ₃ (provided that the composition ratio of SiO ₂ is 90% by weight or more). Thereby, a hydrophilic effect can be exhibited at night or outdoors, and scratch resistance is further improved by using a mixture of SiO ₂ and Al ₂ O ₃ . When a mixture of SiO ₂ and Al ₂ O ₃ is used for the uppermost layer 10, scratch resistance is improved by performing a heat treatment at 500 ° C. for 2 hours after film formation. Note that it is preferable to use IAD when a part or all of the uppermost layer 10 is formed. Thereby, the scratch resistance is improved.

Each layer of the multilayer film MC is formed by a vapor deposition method, and any one of the layers is preferably formed by IAD. Scratch resistance can be further improved by film formation by IAD.

When the uppermost layer 10 is formed by the IAD method, it is preferable that the following conditional expression is satisfied.
12 nm ≦ D (iad) ≦ 30 nm (7)
here,
D (iad): Nano-indentation depth of the uppermost layer 10 formed by the IAD method

When the value of the expression (7) is below the upper limit, the ion assist power does not become too weak, the value D (iad) is stabilized, and the photocatalytic effect can be stabilized. On the other hand, if the value of the expression (7) is equal to or higher than the lower limit, the value D (iad) does not become too small even if the ion assist power is increased, and a high-density film is not formed and the photocatalytic effect is maintained. Can do.

When the uppermost layer 10 is formed by the IAD method, it is preferable that the following conditional expression is satisfied.
0.8 nm ≦ F (iad) ≦ 0.97 nm (8)
here,
F (iad): Filling rate of the uppermost layer 10 formed by the IAD method

Here, the filling rate indicates the proportion of atoms in the volume of the film. The calculation formula when the filling rate is F is shown below. A value F (noiad) described later is calculated in the same manner.
F = (nf1-nf2 + 0.33) /0.33
here,
nf1: Refractive index of the uppermost layer film after standing for 24 hours in an environment at a temperature of 25 ° C. and a humidity of 50% RH nf2: Refractive index of the uppermost layer film in a vacuum (during film formation)

When the value of the equation (8) is equal to or higher than the lower limit, the ion assist power is not weakened, the value F (iad) is stabilized, and the photocatalytic effect can be stabilized. On the other hand, if the value of the formula (8) is below the upper limit, the value F (iad) does not become too large even if the ion assist power is increased, and a high-density film is not formed and the photocatalytic effect is maintained. Can do.

In addition, when the uppermost layer 10 is formed without using the IAD method, it is preferable that the following conditional expression is satisfied.
25 nm ≦ D (noad) ≦ 50 nm (9)
here,
D (noiad): nano-indentation depth of the uppermost layer 10 formed without using the IAD method

If the value of formula (9) is equal to or greater than the lower limit, even if the amount of oxygen introduced during film formation is reduced, the value D (noad) does not become too small and a high-density film is not formed, and the photocatalytic effect is maintained. be able to. On the other hand, if the value of equation (9) is less than or equal to the upper limit, even if the amount of oxygen introduced is increased, the value (noad) does not become too large, and a film having a density that can withstand optical applications can be formed.

When the uppermost layer 10 is formed without using the IAD method, it is preferable that the following conditional expression is satisfied.
0.7 ≦ F (noad) ≦ 0.87 (10)
here,
F (noad): Nano-indentation depth filling rate of the uppermost layer 10 formed without using the IAD method

If the value of equation (10) is below the upper limit, even if the amount of oxygen introduced during film formation is reduced, the value F (noad) does not become too large, and a high-density film is not formed, and the photocatalytic effect is maintained. can do. On the other hand, when the value of the expression (10) is equal to or higher than the lower limit, even if the amount of oxygen introduced is increased, the value F (noiad) does not become too small, and a film having a density that can withstand optical use can be formed.

The uppermost layer 10 preferably satisfies the following conditional expression.
60 nm ≦ TL ≦ 350 nm (3)
here,
TL: film thickness of the uppermost layer 10

When the value of the formula (3) is not more than the upper limit, the photocatalytic effect can be exhibited by exchanging active oxygen excited by UV light through the uppermost layer 10. On the other hand, when the value of the formula (3) is equal to or higher than the lower limit, the uppermost layer 10 can be made strong and sufficient scratch resistance can be secured. In addition, Preferably, it is satisfy | filling the following formula | equation.
60 nm ≦ TL ≦ 250 nm (3 ′)

It is preferable that the optical element 100 satisfies the following conditional expression.
1.3 ≦ NL ≦ 1.5 (4)
1.9 ≦ NH ≦ 2.45 (5)
here,
NL: Refractive index at the d-line of the material of the low refractive index layer L NH: Refractive index at the d-line of the specific material

By satisfying the expressions (4) and (5), the optical element 100 having desired optical characteristics can be obtained. Here, the d line means light having a wavelength of 587.56 nm. As a material for the low refractive index layer L, SiO ₂ having a refractive index of 1.48 at d-line or MgF ₂ having a refractive index of 1.385 at d-line can be used. Further, Ta, Hf, Zr, and Nb oxides can be suitably used as the specific material that satisfies the formula (5).

It is preferable that the optical element 100 satisfies the following conditional expression.
1.7 ≦ Ns ≦ 2.2 (6)
here,
Ns: Refractive index at d line of glass substrate GL

The optical performance of the optical element 100 can be enhanced with a compact configuration by satisfying the expression (6) as the refractive index at the d-line of the glass substrate GL in terms of optical design. By forming the multilayer film of the present invention on the glass substrate GL satisfying the formula (6), it can be used for a lens exposed to the outside world, and both excellent environmental resistance and optical performance are achieved. Is possible.

According to this embodiment, the film thickness, density, film formation recipe of the multilayer film uppermost layer SiO ₂ , and the TiO ₂ film thickness of the functional layer 20 adjacent to the uppermost layer 10 are optimized to maximize the photocatalytic effect and scratch resistance. In addition, it has sufficient acid resistance by providing an appropriate film thickness using a material mainly composed of Ta, Hf, Zr, and Nb for the multilayer film. A photocatalytic multilayer film that can be provided can be realized.

The optical element 100 has a multilayer film excellent in acid resistance and scratch resistance as described above, can exhibit a photocatalytic effect, and is suitably used for an in-vehicle lens, a communication lens, or a building material.

(Example)
Hereinafter, an example suitable for the above-described embodiment will be evaluated in comparison with a comparative example. In forming the multilayer films of the following examples and comparative examples, a film deposition apparatus BES-1300 manufactured by SYNCHRON Co., Ltd. was used, and NIS-175 was used as an ion source for IAD.

(1) Evaluation on presence / absence of IAD and amount of oxygen introduced The inventors of the present invention formed a multi-layer film of 9 layers by a vapor deposition method on a glass substrate while changing the film formation formulation of the uppermost layer and used for the test. did. More specifically, as shown in Table 1, the glass substrate TAF3: the (HOYA Co. refractive index 1.80) on the low refractive index layer with SiO _2, OA600 (manufactured by Canon Optron Inc. A high refractive index layer using a material and a functional layer using TiO ₂ were stacked in the order shown in Table 1 to form a film. As the uppermost layer, SiO ₂ was used. Here, each film thickness (d (nm)) was made constant, and the film formation rate RATE (Å / SEC) of each film was also made constant. Table 1 shows the film configuration (the first layer is the layer in contact with the glass substrate (glass substrate), the same applies hereinafter), the film formation prescription, and the evaluation results. In Table 1, “Layer” indicates a layer number, “Air” indicates a layer material, and “d” indicates a layer thickness (the same applies to the following tables).

OA600 in the table is a mixture of Ta ₂ O ₅ , TiO and Ti ₂ O ₅ , and the specific composition thereof is mainly composed of tantalum oxide as shown in Table 2.

The refractive index n (λ) in Table 1 was determined by the following equation. In this specification, the refractive index is measured by d-line (wavelength: 587.56 nm).
n (λ) = A ₀ + A ₁ / (λ−A ₂ )
Here, λ is the wavelength of the d-line, and A ₀ , A ₁ , and A ₂ of the materials used in the examples and comparative examples are the following values, respectively.
TAF3: A ₀ = 1.768, A ₁ = 14.724 (nm), A ₂ = 181.535 (nm)
_{_{OA600: A 0 = 2.014, A}} 1 = 31.680 (nm), A 2 = 233.891 (nm)
SiO ₂ : A ₀ = 1.460, A ₁ = 0 (nm), A ₂ = 0 (nm)
TiO ₂ : A ₀ = 2.013, A ₁ = 36.149 (nm), A ₂ = 284.651 (nm)

The film formation prescription is as shown in Table 1. Regarding the film formation of the uppermost layer, the presence or absence of oxygen gas and the amount of introduction when it is introduced, the presence and extent of IAD used for the film formation of SiO ₂ are determined. 4 examples (test numbers 1-5 to 1-8) and 6 comparative examples (test numbers 1-1 to 1-4, 1-9, 1-10) were prepared, It used for the following tests. The heating temperature was 340 ° C., and the starting vacuum was 3.00E-03 Pa (3.00 × 10 ⁻³ Pa).

“Factor” in Table 1 means that the oxygen gas introduction amount and the IAD conditions were changed. Here, “APC” means that the partial pressure is adjusted by an abbreviation of Auto Pressure Control, and “SCCM” is an abbreviation of standard cc / min, 1 atm (atmospheric pressure 1013 hPa), 1 at 0 ° C. This is a unit indicating how many cc per minute.

In Table 1, IAD (H) indicates that the IAD power is set to (acceleration voltage 500 V, acceleration current 300 mA, oxygen introduction amount 50 SCCM), and IAD (M) indicates the IAD power (acceleration voltage 400 kV). , Acceleration current 400 mA, oxygen introduction amount 50 SCCM), and IAD (L) indicates that the IAD power is set to acceleration voltage 300 V, acceleration current 300 mA, oxygen introduction amount 50 SCCM.

In the “acid resistance test”, the test sample is immersed in a solution adjusted to PH 1.7 by adding nitric acid to 5% strength saline solution, and the size and number of white spots are measured with a stereomicroscope (× 58 times). Counting was evaluated as x when the white spot was visually observed to such an extent that it could not be practically used, and evaluated as o when the white spot was not visually observed. The “scratch resistance test” is evaluated as ▲ when a test piece is rubbed 250 times with a tortoise scourer under a load of 2.0 kg and a scratch affecting the photographed image is attached when used as a camera lens, or When such a flaw did not adhere, it was set as evaluation o.

“Photocatalytic effect measurement” is performed by irradiating a test sample with a black light (model number BL20) of YAZAWA at a distance of 30 mm from the test sample for 5 minutes, and then using “visualiser Pen” of inkintelient. Changes were evaluated in stages. Here, when the color change is minimal, the photocatalytic effect is absent (evaluation x), when the color change is small, the photocatalytic effect is almost absent (evaluation ▲), and when the color change is medium, the photocatalytic effect is excessive None (evaluation Δ), and those having a large degree of color change had a photocatalytic effect (evaluation ○).

(Consideration of evaluation results)
All of the test numbers 1-1 to 1-10 were good with no evaluation x for acid resistance and scratch resistance. However, there were variations in the evaluation results for the photocatalytic effect. Specifically, the evaluation of the photocatalytic effect of test numbers 1-1 and 1-2 was evaluated as x. This is because use of IAD improves the film density of the uppermost layer (SiO ₂ ) (strengthening the scratch resistance), but it is difficult for active oxygen excited by UV light to pass through. Further, the evaluation of the photocatalytic effect of Test No. 1-3 was x. This is because without the introduction of oxygen gas, the uppermost layer (SiO ₂ ) becomes insufficiently oxidized, so that it becomes difficult for active oxygen excited by UV light to pass through. Further, the evaluation of the photocatalytic effect of Test No. 1-4 was ▲. This is because, even if oxygen gas is introduced, if the amount of introduction is insufficient, SiO ₂ becomes insufficiently oxidized, making it difficult for active oxygen excited by UV light to pass. On the other hand, in the test numbers 1-5 to 1-10 in which the power of IAD was lowered or the oxygen introduction amount was made appropriate without using IAD, the photocatalytic effect was evaluated as “good”.

On the other hand, the evaluation of the scratch resistance of test numbers 1-9 and 1-10 was ▲. This is because the greater the amount of oxygen gas introduced, the higher the photocatalytic effect, but the lower the film density, the weaker the scratch resistance of the film. On the other hand, the scratch resistance was ○ for test numbers 1-1 to 1-8 in which IAD was used or the oxygen introduction amount was appropriate. From the above results, it was found that the prescriptions of test numbers 1-5 to 1-8 are preferable in order to achieve both the photocatalytic effect and the scratch resistance.

FIG. 2 is a graph showing the spectral characteristics of the multilayer film of test numbers 1-6, which is an example. The vertical axis represents reflectance (unit:%), and the horizontal axis represents wavelength (unit: nm). (The same applies to the following figures). It can be seen that the multilayer film shown in FIG. 2 has antireflection characteristics in the visible range of approximately 400 to 700 nm. Since the layer configuration is the same, the other multilayer films shown in Table 1 have similar spectral characteristics.

(2) Evaluation on the component and film thickness of the uppermost layer and the total film thickness of the high refractive index layer The inventors of the present invention have the following components on the glass substrate: A 9-layer or 7-layer multilayer film was formed by a vapor deposition method while changing the above and was used for the test. More specifically, as shown in Table 3, on glass substrate TAF3 (made by HOYA Co., Ltd .: refractive index 1.804), SiO ₂ or a mixture of SiO ₂ and Al ₂ O ₃ (SiO ₂ A low refractive index layer using a composition ratio of 90% by weight or more), a high refractive index layer using OA600 (material manufactured by Canon Optron Co., Ltd.), and a functional layer using TiO ₂ are laminated in the order shown in Table 3. To form a film. As the uppermost layer, SiO ₂ or a mixture of SiO ₂ and Al ₂ O ₃ was used, and the power of IAD at that time was set to (acceleration voltage 300 V, acceleration current 300 mA, oxygen introduction amount 50 SCCM). Here, the deposition rate RATE (Å / SEC) of each film was constant. The film forming conditions not specifically shown are the same as those described above. Table 3 shows the film configuration, film formation recipe, and evaluation results.

The multilayer films with test numbers 2-1 to 2-7 use SiO ₂ as the uppermost layer, and the multilayer films with test numbers 2-8 to 2-10 have SiO ₂ and Al ₂ O _{3 as the} uppermost layers. A mixture with is used. Further, the film thickness of the high refractive index layer mainly composed of Ta in each multilayer film is changed as shown in Table 3. Only the multilayer film of test number 2-6 has 7 layers, and the others have 9 layers. Only for the multilayer film of test number 2-6, the film thickness of the uppermost layer is 220 nm or more, and the film thickness of the other multilayer film is 90 nm or less. OA600 was used for all high refractive index layers. The evaluation content of each test is the same as described above.

(Consideration of evaluation results)
The multilayer film of test number 2-1 using SiO ₂ as the uppermost layer and the multilayer film of test number 2-8 using a mixture of SiO ₂ and Al ₂ O ₃ as the uppermost layer are high refractive index layers. The total film thickness was 90.3 nm, but the acid resistance test was evaluated as x. The other multilayer films were evaluated as “good” in the acid resistance test. Moreover, in all the multilayer films shown in Table 3, the scratch resistance test and the evaluation of the photocatalytic effect measurement were good.

Considering the above evaluation results, it can be seen that the high refractive index layer has sufficient acid resistance when the total thickness of the high refractive index layer is 100 nm or more, regardless of the component of the uppermost layer. Further, it can be seen that when the film thickness of the uppermost layer is in the range of 80 to 230 nm, the acid resistance and scratch resistance are satisfied, and a sufficient photocatalytic effect can be obtained.

FIG. 3 is a diagram showing the spectral characteristics of the multilayer film with test number 2-3 as an example, and FIG. 4 is a diagram showing the spectral characteristics of the multilayer film with test number 2-4 as an example. FIG. 5 is a diagram showing the spectral characteristics of the multilayer film of test number 2-5 as an example, and FIG. 6 shows the spectral characteristics of the multilayer film of test number 2-6 as an example. FIG. 7 is a diagram showing the spectral characteristics of the multilayer film of test number 2-7 as an example, and the vertical axis represents the reflectance and the horizontal axis represents the wavelength.

It can be seen that the multilayer films shown in FIGS. 3 to 5 have antireflection characteristics in the visible range of approximately 400 nm to 700 nm. It can be seen that the multilayer film shown in FIG. 6 has antireflection characteristics in the infrared region of approximately 1150 nm to 1800 nm. It can be seen that the multilayer film shown in FIG. 7 has antireflection characteristics in the visible range of approximately 400 nm to 700 nm.

(3) Evaluation of the top layer component and the high refractive index layer component The inventors of the present invention applied a vapor deposition method while changing the top layer component and the high refractive index layer component on the glass substrate. A multilayer film of layers was formed and used for the test. More specifically, as shown in Table 4, when a multilayer film is formed on a glass substrate TAF3 (manufactured by HOYA Co., Ltd .: refractive index 1.80), the uppermost layer is SiO ₂ (in the d-line). When the refractive index is 1.46, the IAD is set to (acceleration voltage 300 V, acceleration current 300 mA, oxygen introduction amount 50 SCCM), or a mixture of SiO ₂ and Al ₂ O ₃ as the uppermost layer (refractive in d-line) IAD at the time of using (rate 1.475) was set to (acceleration voltage 300 V, acceleration current 250 mA, oxygen introduction amount 50 SCCM). TiO ₂ was used as a functional layer adjacent to the uppermost layer. Here, the deposition rate RATE (Å / SEC) of each film was constant. The film forming conditions not specifically shown are the same as those described above. Table 4 shows the film configuration, film formation recipe, and evaluation results.

The multilayer films with test numbers 3-1 to 3-7 use SiO ₂ as the uppermost layer, and the multilayer films with test numbers 3-8 to 3-14 have SiO ₂ and Al ₂ O _{3 as the} uppermost layers. A mixture with is used. The multilayer films of test numbers 3-1 and 3-8 use Ta ₂ O ₅ for the high refractive index layer (also referred to as a high material), and the multilayer films of test numbers 3-2 and 3-9. HfO ₂ is used for the high refractive index layer, and the multilayer films of test numbers 3-3 and 3-10 use ZrO ₂ for the high refractive index layer, and the test numbers 3-4, 3- The multilayer film No. 11 uses Nb ₂ O ₅ for the high refractive index layer, and the multilayer films Nos. 3-5 and 3-12 use OA600 for the high refractive index layer. The multilayer films of −6 and 3-13 use TiO ₂ for the high refractive index layer, and the multilayer films of test numbers 3-7 and 3-14 have a compound of TiO ₂ and La ( Lanthanum titanate (LaTiOx) manufactured by MERCK is used. The refractive index of the high refractive index layer is as shown in Table 4.

(Consideration of evaluation results)
Test numbers 3-6 and 3-13 using TiO ₂ for the high refractive index layer, and test numbers 3-7 and 3-14 using a mixture of TiO ₂ and La for the high refractive index layer In the multilayer film, the acid resistance test was evaluated as x. The other multilayer films were evaluated as “good” in the acid resistance test. Moreover, in all the multilayer films shown in Table 4, the scratch resistance test and the evaluation of the photocatalytic effect measurement were good. From the above, at least one of the high refractive index layers satisfies the acid resistance and scratch resistance by using a specific material mainly containing any one of Ta, Hf, Zr, and Nb, and provides a sufficient photocatalytic effect. I understand that.

(4) Summary The above evaluation results are shown in Table 5 separately for Examples and Comparative Examples. here,
Tcat: film thickness (nm) of the high refractive index layer or functional layer adjacent to the uppermost layer
TH: Total film thickness (nm) of the high refractive index layer formed from a specific material
TL: film thickness of the top layer (nm)
NL: Refractive index at d line of material of low refractive index layer NH: Refractive index at d line of specific material Ns: Refractive index at d line of glass substrate

The “nanoindentation indentation depth” in the table indicates that a single layer film having a thickness of 200 nm is formed on a glass plate, and the nanoindentation measuring device is a minimal indentation hardness tester ENT manufactured by Elionix. -100 was fitted with a 115 ° triangular pyramid diamond indenter and pressed against the membrane for measurement. In the measurement, the indenter gives a load at a load speed of 0.2 mgf / sec, holds the maximum load of 0.98 mN for 1 second, then unloads at the same load speed, and determines the indenter indentation depth obtained from a series of operations. The indentation depth when the maximum load was reached was obtained from the load curve. In Table 5, “indentation depth range” indicates conditional expression (7) or (9), and “filling rate range” indicates conditional expression (8) or (10).

Claims

In an optical element having a glass substrate on which a multilayer film of three or more layers is formed,
The multilayer film has at least one low refractive index layer and at least one high refractive index layer,
The uppermost layer farthest from the glass substrate is the low refractive index layer,
The high refractive index layer adjacent to the uppermost layer is a functional layer mainly composed of a metal oxide having a photocatalytic function,
At least one of the high refractive index layers is formed of a specific material mainly containing any one of Ta, Hf, Zr, and Nb.
An optical element that satisfies the following conditional expression.
150 nm ≦ Tcat ≦ 700 nm (1)
100 nm ≦ TH (2)
here,
Tcat: film thickness TH of the functional layer TH: total film thickness of the high refractive index layer formed from the specific material
The optical element according to claim 1, wherein the functional layer is formed of an oxide containing Ti as a main component.
The optical element according to claim 1, wherein the uppermost layer is made of SiO 2 .
The optical element according to claim 1, wherein the uppermost layer is formed of a mixture of SiO 2 and Al 2 O 3 .
5. The optical element according to claim 1, wherein each layer of the multilayer film is formed by an evaporation method, and any one of the layers is formed by ion-assisted deposition.
The optical element according to any one of claims 1 to 5, which satisfies the following conditional expression.
60 nm ≦ TL ≦ 350 nm (3)
here,
TL: film thickness of the uppermost layer
The optical product according to any one of claims 1 to 6, wherein the uppermost layer is formed by ion-assisted deposition and satisfies the following conditional expression.
12 nm ≦ D (iad) ≦ 30 nm (7)
here,
D (iad): Nano-indentation depth of the uppermost layer formed by ion-assisted deposition
The optical product according to any one of claims 1 to 7, wherein the uppermost layer is formed by ion-assisted deposition and satisfies the following conditional expression.
0.8 nm ≦ F (iad) ≦ 0.97 nm (8)
here,
F (iad): Filling rate of the uppermost layer formed by the ion-assisted deposition
The optical product according to any one of claims 1 to 6, wherein the uppermost layer is formed without using ion-assisted deposition and satisfies the following conditional expression.
25 nm ≦ D (noad) ≦ 50 nm (9)
here,
D (noad): Nano-indentation depth of the uppermost layer formed without using the ion-assisted deposition
The optical product according to any one of claims 1 to 6 and 9, wherein the uppermost layer is formed without using ion-assisted deposition and satisfies the following conditional expression.
0.7 ≦ F (noad) ≦ 0.87 (10)
here,
F (noad): Filling rate of the uppermost layer formed without using the ion assist deposition
The optical element according to any one of claims 1 to 10, which satisfies the following conditional expression.
1.3 ≦ NL ≦ 1.5 (4)
1.9 ≦ NH ≦ 2.45 (5)
here,
NL: refractive index at the d-line in the material of the low refractive index layer NH: refractive index at the d-line of the specific material
The optical element according to any one of claims 1 to 11, which satisfies the following conditional expression.
1.7 ≦ Ns ≦ 2.2 (6)
here,
Ns: Refractive index at d-line of the glass substrate