阅读说明：本技术 多孔质膜、光学元件、光学系统、交换透镜、光学装置和多孔质膜的制造方法 (Porous film, optical element, optical system, exchange lens, optical device, and method for producing porous film ) 是由 铃木涼子 米山健司 逢坂昌宏 于 2020-03-27 设计创作，主要内容包括：多孔质膜是具有二氧化硅颗粒的多孔质膜,其折射率为1.1～1.25,对水的接触角为40°以上。(The porous film is a porous film having silica particles, and has a refractive index of 1.1 to 1.25 and a contact angle with water of 40 DEG or more.)

1. A porous membrane which is a porous membrane having silica particles, wherein,

the refractive index of the porous film is 1.1 to 1.25,

the contact angle to water is 40 DEG or more.

2. The porous membrane of claim 1 having trimethylsilyl groups on the surface.

3. A porous membrane which is a porous membrane having silica particles, wherein,

the refractive index of the porous film is 1.1 to 1.25,

has a trimethylsilyl group on the surface.

4. A porous membrane which is a porous membrane having silica particles, wherein,

the refractive index of the porous film is 1.1 to 1.25,

the surface is treated with a silane coupling agent.

5. The porous film according to any one of claims 1 to 4, wherein the scattering of the porous film at a wavelength of 350nm is 1000ppm or less.

6. An optical element comprising an antireflection film comprising a single-layer film on a substrate, wherein the single-layer film is the porous film according to any one of claims 1 to 5.

7. An optical element comprising an antireflection film comprising a plurality of layers on a substrate, wherein at least one layer of the plurality of layers is the porous film according to any one of claims 1 to 5.

8. The optical element according to claim 7, wherein an outermost layer in the multilayer film is the porous film.

9. The optical element according to any one of claims 6 to 8, wherein the substrate is a lens.

10. An optical system comprising the optical element of any one of claims 6 to 9.

11. An exchange lens having the optical system of claim 10.

12. An optical device having the optical system of claim 10.

13. A method for producing a porous membrane, comprising the steps of:

mixing a solvent containing a tertiary amine, water, and methoxypropanol (PGME) with a silicon compound to prepare a mixed solution;

stirring the mixed solution;

coating the mixed solution after stirring on a substrate to form a coating film; and

and a step of heating the coating film to form a porous film.

14. The method for producing a porous membrane according to claim 13, wherein in the step of stirring the mixed solution, the mixed solution is stirred at 15 to 30 ℃.

15. The method for producing a porous membrane according to claim 13 or 14, wherein in the step of stirring the mixed solution, the mixed solution is stirred for 12 to 100 hours.

16. The method for producing a porous membrane according to any one of claims 13 to 15, wherein in the step of forming a porous membrane, the coating film is heated to 140 ℃ to 180 ℃.

17. The method for producing a porous membrane according to any one of claims 13 to 16, wherein in the step of forming a porous membrane, the coating film is heated for 1 to 5 hours.

18. A porous membrane manufacturing method according to any one of claims 13 to 17, wherein the silicon compound is tetramethylorthosilicate.

19. The method for manufacturing a porous membrane according to any one of claims 13 to 18, wherein the tertiary amine is triethylamine.

20. The method for manufacturing a porous membrane according to any one of claims 13 to 19, wherein a surface of the porous membrane is subjected to a silane coupling agent treatment.

21. The method for manufacturing a porous membrane according to claim 20, wherein the silane coupling agent treatment is performed using Hexamethyldisilazane (HMDS).

22. The method for manufacturing a porous membrane according to claim 20 or 21, wherein the silane coupling agent treatment is a gas phase treatment, a liquid phase treatment, or a mist treatment.

Technical Field

The present invention relates to a porous film, an optical element, an optical system, an exchange lens, an optical device, and a method for producing a porous film.

Background

For example, patent document 1 discloses a low refractive index antireflection film having a refractive index of 1.28 to 1.38. Such a low anti-reflection film is required to have a low refractive index and excellent environmental resistance.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 8-122501

Disclosure of Invention

According to the 1 st aspect, the porous film is a porous film having silica particles, has a refractive index of 1.1 to 1.25, and has a contact angle with water of 40 ° or more.

According to the 2 nd aspect, the porous film is a porous film having silica particles, has a refractive index of 1.1 to 1.25, and has trimethylsilyl groups on the surface.

According to the 3 rd aspect, the porous film is a porous film having silica particles, has a refractive index of 1.1 to 1.25, and has a surface treated with a silane coupling agent.

According to the 4 th aspect, the method for producing a porous membrane comprises the steps of: mixing a solvent containing a tertiary amine, water, and methoxypropanol (PGME) with a silicon compound to prepare a mixed solution; stirring the mixed solution; coating the stirred mixed solution on a substrate to form a coating film; and a step of heating the coating film to form a porous film.

Drawings

Fig. 1 is a flowchart illustrating a method for producing a porous membrane according to an embodiment.

Fig. 2 is a perspective view of an image pickup apparatus according to an embodiment.

Fig. 3 is a front view of another example of the image pickup apparatus in one embodiment.

Fig. 4 is a rear view of another example of the image pickup apparatus in one embodiment.

Fig. 5 is a graph showing the refractive index of the porous film in the comparative example and example.

Fig. 6 is a graph showing the scattering of light of 350nm wavelength and 544nm wavelength by the porous film in the comparative example and example.

Fig. 7 is a graph showing contact angles of the porous films with water in the comparative examples and examples.

FIG. 8 shows that IR measurement was performed on the porous membranes of comparative example and confirmed at 1259cm^-1Figure showing the results of the presence or absence of absorption bands in the vicinity.

Detailed Description

Embodiment-a porous membrane in one embodiment is explained with reference to the drawings. The porous membrane of the present embodiment is made of silica particles (SiO)₂Particles) and is a porous film having a low refractive index and excellent environmental resistance.

The porous membrane of the present embodiment has the following structure: it consists of a gel network of silica particles with a plurality of pores in the membrane of a size of a few nanometers. The refractive index of the porous film of the present embodiment is in the range of 1.1 to 1.25, and more preferably in the range of 1.17 to 1.23. The refractive index in this specification means a refractive index for light having a wavelength of 550 nm. The porous membrane of the present embodiment has a contact angle with water of 40 ° or more, and more preferably 45 ° or more. To achieve this contact angle, the porous membrane has trimethylsilyl groups on the surface. The porous membrane of the present embodiment has a scattering at a wavelength of 350nm of 1000ppm or less, more preferably 900ppm or less.

The following describes a method for producing the porous membrane.

The porous particles of the present embodiment can be formed by hydrolysis and dehydration condensation of a silicon compound under an alkali catalyst. Tetramethyl orthosilicate (TMOS) was used as the silicon compound. The tetramethyl orthosilicate is added to a solvent comprising tertiary amine, water and methoxypropanol (PGME) and stirred. Triethylamine, for example, can be used as the tertiary amine. For the purpose of prolonging the life of the solution, a specific amount of nitric acid may be added to the solvent in the container. The stirring was performed at room temperature. If the temperature at this time is too high, the reaction rate tends to be too high, and it tends to be difficult to control the refractive index of the porous film to be finally formed. On the other hand, if the temperature is too low, the reaction rate is too slow, and the porous film finally formed tends to become brittle. Therefore, the temperature during stirring is preferably 15 to 30 ℃, and more preferably 20 to 25 ℃. The stirring time in this case is also a condition that affects the refractive index of the porous film to be formed. The stirring time is suitably set according to the desired refractive index, and may be, for example, 12 to 100 hours. The longer the stirring time, the more the refractive index of the porous film tends to decrease. By stirring, the tetramethyl orthosilicate is hydrolyzed as follows, forming silica particles in solution.

Si(OMe)₄+2H₂O→SiO₂+4MeOH

The stirred solution is applied to a substrate, and a coating film is formed by a film forming process. The film formation process is performed using, for example, a spin coater. By appropriately setting the conditions set when the spin coater is used, the thickness of the coating film can be set to an arbitrary thickness. In the coating film obtained by the film formation, silica particles are linked to form a gel network. The coating film is heated to be cured. The heating conditions in this case may be a heating temperature in the range of 140 to 180 ℃ and a heating time in the range of 1 to 5 hours. Specifically, the heating temperature may be set to, for example, 160 ℃ and the heating time may be set to, for example, 3 hours. If the heating time is too long, the porous film finally formed becomes brittle, and therefore temperature control is important. By the heat treatment, the gel network undergoes dehydration condensation to form a porous membrane having a plurality of pores of several nanometers in size. After heating, the coating film is allowed to stand at normal temperature for a predetermined time and cooled, thereby completing the formation of a porous film.

A large number of OH groups are present on the surface of the porous membrane formed as described above. Since OH groups on the surface of the porous film are condensed with each other in a high-temperature and high-humidity environment, and cause a change in the refractive index of the porous film or a change in the film thickness, the porous film is poor in environmental resistance in a state where a large amount of OH groups are present. Therefore, in the present embodiment, the surface of the porous membrane is treated with a silane coupling agent to reduce the amount of OH groups. The silane coupling agent treatment was performed using Hexamethyldisilazane (HMDS). The silane coupling agent treatment may employ any of gas phase treatment, liquid phase treatment, or mist treatment. In the case of the gas phase treatment, the substrate on which the porous film is formed is left to stand at normal temperature in an environment (in a closed container) in which hexamethyldisilazane is gasified for a certain period of time. Followed by heating at a specific temperature for a specific time. In the case of performing the liquid phase treatment, the substrate on which the porous film is formed is immersed in a solution of hexamethyldisilazane, left for a certain period of time in a state where ultrasonic waves are applied, and then heated at a certain temperature for a certain period of time. In the case of the mist treatment, the substrate on which the porous film is formed is placed in a container, and the container is filled with mist-like hexamethyldisilazane. After a predetermined time has elapsed, the substrate is taken out of the container, cleaned, and heated at a predetermined temperature for a predetermined time.

By the silane coupling agent treatment, OH groups on the surface of the porous membrane are bonded (coupled) to trimethylsilyl groups of the silane coupling agent. That is, a trimethylsilyl group is formed on the surface of the porous membrane. As a result, the contact angle of the porous film with water is relatively larger than that before the silane coupling agent treatment, and the value is as described above. That is, the amount of OH groups on the surface of the porous film is reduced by the silane coupling agent treatment, and the change in refractive index and the change in film thickness of the porous film derived from the OH groups in a high-temperature and high-humidity environment can be suppressed, so that the porous film has high environmental resistance.

The method for producing the porous membrane will be described with reference to the flowchart shown in fig. 1.

In step S1, tetramethyl orthosilicate (TMOS) is added to a solvent containing tertiary amine, water, and methoxypropanol (PGME), stirred at room temperature (stirring process), and the process proceeds to step S2. The time for stirring (reaction time) is determined based on the refractive index required in the porous film to be produced.

In step S2, the solution after stirring is applied to the substrate fixed to the spin table of the spin coater, and then the spin table is rotated to perform the film formation process for forming the coating film, and the process proceeds to step S3. In step S3, the formed coating film is heated and cured (heat curing treatment) at, for example, 160 ℃ for 3 hours to form a porous film, and the process proceeds to step S4. In step S4, the surface of the porous membrane is treated with a silane coupling agent to reduce the amount of OH groups on the surface of the porous membrane. The silane coupling agent treatment is performed by any one of gas phase treatment, liquid phase treatment, and mist treatment using Hexamethyldisilazane (HMDS). The porous membrane of the present embodiment is obtained as described above.

The porous film thus obtained can be suitably used as an antireflection film. The antireflection film may be a single layer film or a multilayer film. When the antireflection film is a multilayer film, it is known that the optical performance can be improved by increasing the refractive index of the film material used or by using a low refractive index film as the outermost layer, and the number of layers of the multilayer film can be reduced even with the same optical performance. In particular, it has been shown by simulations that the optical performance can be made extremely high by making only the outermost layer a low refractive index film having a refractive index of 1.30 or less. The porous film of the present embodiment has a low refractive index of 1.1 to 1.25, and therefore can be suitably used as a structure of an antireflection film, and particularly can be suitably used as an outermost layer of a multilayer film constituting an antireflection film. The outermost layer refers to a layer farthest from the substrate in the multilayer film.

The optical element provided with the antireflection film can be suitably used as, for example, a lens. Examples of the optical system including such a lens include an objective lens, a condenser lens, an imaging lens, and a camera replacement lens. Further, they can be used for imaging devices such as lens-interchangeable cameras and lens-non-interchangeable cameras, and optical devices such as microscopes. The optical device is not limited to the above-described imaging device and microscope, and includes a camera, a telescope, binoculars, a monocular, a laser range finder, a projector, and the like. An example of the imaging device will be described below.

Fig. 2 is a perspective view of an imaging device having an optical system provided with an antireflection film (the antireflection film includes the porous film of the present embodiment). The imaging device 1 is a so-called digital single-lens reflex camera (lens exchange camera), and the imaging lens 103 (optical system) has a lens provided with an antireflection film (the antireflection film includes the porous film of the present embodiment). The lens barrel 102 is detachably mounted on a lens mount (not shown) of the camera body 101. The light transmitted through the imaging lens 103 of the lens barrel 102 forms an image on a sensor chip (solid-state image pickup device) 104 of a multi-chip module 106 disposed on the rear surface side of the camera body 101. The sensor Chip 104 is a bare Chip such as a so-called CMOS image sensor, and the multi-Chip module 106 is, for example, a COG (Chip On Glass) type module in which the sensor Chip 104 is mounted as a bare Chip On a Glass substrate 105.

Fig. 3 is a front view of another example of an imaging device having an optical element provided with an antireflection film (the antireflection film includes the porous film according to the present embodiment), and fig. 4 is a rear view of the imaging device shown in fig. 3. The imaging device CAM is a so-called digital still camera (lens non-interchangeable camera), and the imaging lens WL (optical system) has a lens provided with an antireflection film (including the porous film of the present embodiment).

In the imaging device CAM, when a power button (not shown) is pressed, a shutter (not shown) of the imaging lens WL is opened, and light from an object (object) is converged by the imaging lens WL to form an image on an imaging element disposed on an image plane. The subject image formed on the image pickup device is displayed on a liquid crystal monitor LM disposed behind the image pickup device CAM. The photographer specifies the composition of the subject image while viewing the liquid crystal monitor LM, then presses the release button B1, and takes a subject image with the image pickup device, and records and stores it in a memory (not shown). The imaging device CAM is provided with an auxiliary light emitting portion EF (which emits auxiliary light when the subject image is dark), a function button B2 (for setting various conditions of the imaging device CAM), and the like.

In an optical system used in such a camera or the like, a higher antireflection performance is required. In order to achieve this performance, it is effective to use the porous film of the present embodiment for an antireflection film.

Examples of the porous membrane according to the above embodiment will be described.

Examples

In this example, a porous membrane was formed in the following order. To a resin bottle was added 54.43 g of 1-methoxy-2-Propanol (PGME) (fuji film and guokang). Then, 36.1. mu.L of triethylamine (manufactured by Tokyo chemical Co., Ltd.) and 1.731mL of pure water were measured out by a micropipette, and the solution was added to a resin bottle, and stirred by rotating a magnetic stirrer at a rotation speed of 600rpm for 5 minutes to form an alkali solvent.

To the alkali solvent, 7.31 g of tetramethyl orthosilicate (TMOS) (formed by tokyo chemical reaction) was added, and the mixture was stirred at room temperature for a predetermined time. Further, 27.2 g of 1-methoxy-2-Propanol (PGME) was added thereto, and the mixture was diluted so that the content of PGME became 70 wt%, thereby obtaining a coating solution. In the case where nitric acid is added to extend the solution life of the coating solution, 11. mu.L of nitric acid (1.42) (Fuji film and Wako pure chemical industries) may be added dropwise. The coating solution was stored in a syringe and dropped onto a substrate through a syringe filter having a mesh opening of 5.0 μm. The substrate to which the coating liquid was added was fixed to a rotary table of a spin coater, and the rotary table was accelerated to 3000rpm for 5 seconds, rotated for 30 seconds in this state, and then decelerated for 5 seconds to stop. The rotation of the rotary table is controlled according to a preset program. The coating film formed on the substrate by the spin coater was heated in an oven at a heating temperature of 160 ℃ for 3 hours. After heating, the mixture was left to stand at normal temperature for 24 hours. The porous film is formed on the substrate through the above process. In the following description, this state is referred to as a sample.

The porous film of the sample was treated with a silane coupling agent. As described above, as methods for performing the silane coupling agent treatment, there are gas phase treatment, liquid phase treatment, and mist treatment. The respective processing conditions are described below.

< gas phase treatment > 0.614. mu.L of a sample and Hexamethyldisilazane (HMDS) (Tokyo chemical conversion) were charged into a closed vessel having a capacity of about 1L, and the vessel was allowed to stand at room temperature for 24 hours. Thereafter, the sample taken out of the closed vessel was heat-treated at a heating temperature of 60 ℃ for a heating time of 30 minutes.

< liquid phase treatment > Hexamethyldisilazane (HMDS) was diluted to 30 wt% with methanol to prepare a HMDS dilution. The sample was immersed in the HMDS diluted solution, and treated for 20 minutes while applying ultrasonic waves. The treated sample was subjected to ultrasonic cleaning in methanol for 1 minute, and then to heat treatment at a heating temperature of 60 ℃ for a heating time of 30 minutes.

< fog treatment > the sample was heat-treated at a heating temperature of 70 ℃ for a heating time of 30 minutes. After the heat treatment, the sample was placed in a container, and the container was filled with a mist of Hexamethyldisilazane (HMDS) using a nebulizer. Mist was generated by a nebulizer for 5 minutes, and then 5 minutes passed with generation of mist stopped, and thereafter a sample was taken out from the container. The sample taken out was heat-treated at a heating temperature of 70 ℃ for 30 minutes. The heat-treated sample was immersed in methanol and subjected to ultrasonic cleaning for 2 minutes. Thereafter, the sample was washed with pure water, and then heat-treated at a heating temperature of 70 ℃ for 30 minutes.

Fig. 5 is a graph showing the refractive index of each example and each comparative example of the porous membrane manufactured by the above-described manufacturing method.

FIG. 5(a) shows the refractive indices of comparative examples 1 to 6. Comparative examples 1 to 6 are porous films whose surfaces were not treated with a silane coupling agent. In comparative example 1, the stirring time of the mixed solution of the alkali solvent and tetramethyl orthosilicate (TMOS) in the production of the porous film was 15 hours. Comparative examples 2 to 6 are porous films with stirring times of 18 hours, 21 hours, 24 hours, 48 hours, and 96 hours, respectively.

FIG. 5(b) shows refractive indices of examples 1 to 6. In examples 1 to 6, the surfaces of the porous films formed under the same conditions as in comparative examples 1 to 6 were treated with a silane coupling agent by vapor phase treatment. That is, examples 1 to 6 were porous membranes with stirring times of 15 hours, 18 hours, 21 hours, 24 hours, 48 hours, and 96 hours, respectively.

FIG. 5(c) shows the refractive indices of examples 7 to 12. In examples 7 to 12, the surfaces of the porous films formed under the same conditions as in comparative examples 1 to 6 were treated with a silane coupling agent by liquid phase treatment. That is, examples 7 to 12 were porous membranes with stirring times of 15 hours, 18 hours, 21 hours, 24 hours, 48 hours, and 96 hours, respectively. FIG. 5(d) shows refractive indices of examples 13 to 18. In examples 13 to 18, the surfaces of the porous films formed under the same conditions as in comparative examples 1 to 6 were treated with a silane coupling agent by a mist treatment. That is, examples 13 to 18 were porous membranes with stirring times of 15 hours, 18 hours, 21 hours, 24 hours, 48 hours, and 96 hours, respectively.

As shown in fig. 5, the longer the stirring time of the alkali solution and tetramethyl orthosilicate (TMOS) in the production, the smaller the refractive index of the porous film. In addition, by performing the silane coupling agent treatment on the surface, the refractive index of the porous film is larger than that before the silane coupling agent treatment. As shown in fig. 5, the refractive index was less than 1.25 regardless of the presence or absence of the silane coupling agent treatment. Although not shown in fig. 5, when the reaction time is 96 hours or more, the refractive index of the porous film formed is less than 1.1.

Fig. 6 is a graph showing the relationship between the porous films of the above-described examples and comparative examples and the scattering of light with respect to the wavelength of 350nm and the wavelength of 544 nm. FIG. 6(a) shows the scattering of comparative examples 1 to 6, FIG. 6(b) shows the scattering of examples 1 to 6, FIG. 6(c) shows the scattering of examples 7 to 12, and FIG. 6(d) shows the scattering of examples 13 to 18. The scattering values shown in fig. 6 represent the proportion of scattered light with respect to incident light incident on the porous membrane. The scattered light is a combination of forward scattering and backward scattering detected using an integrating sphere. The scattering values of the porous films of the examples were all set to values of 1000ppm or less, and it was found that the scattering of the porous film produced by the production method of the present example was sufficiently small. That is, the porous membrane of the present example has a smooth surface and a fine internal structure. Thus, the porous film of the present example can be used as a thin film for an optical member in the visible light region.

Fig. 7 is a graph showing the contact angle of the porous film against water in each of the examples and comparative examples. Fig. 7(a) shows contact angles of the porous films of comparative examples 1 to 6 with water, fig. 7(b) shows contact angles of the porous films of examples 1 to 6 with water, fig. 7(c) shows contact angles of the porous films of examples 7 to 12 with water, and fig. 7(d) shows contact angles of the porous films of examples 13 to 18 with water. As shown in fig. 7(a), the porous films of comparative examples 1 to 6 had a small contact angle of 7.3 ° to 14.7 ° because they were not treated with a silane coupling agent. On the other hand, as shown in fig. 7(b) to (d), it is understood that the contact angles of the porous films of examples 1 to 18, the surfaces of which were treated with the silane coupling agent, with water were all larger than 40 °, and much larger than those of the porous films of comparative examples 1 to 6. In this case, it is assumed that the contact angle with water increases, that is, the amount of OH groups on the surface of the porous film decreases, by forming trimethylsilyl groups on the surface of the porous film by the silane coupling agent treatment.

The presence or absence of trimethylsilyl groups on the surface of the porous membrane can be determined by IR (infrared absorption spectroscopy) measurement. That is, in the IR measurement, 1259cm was observed due to the Si-C bond peculiar to the trimethylsilyl group^-1In the case of the nearby absorption, the presence of trimethylsilyl groups was confirmed.

FIG. 8 shows the results of IR measurements of the above examples and comparative examples, which were confirmed to be 1259cm^-1The result is the presence or absence of an absorption band in the vicinity. FIG. 8(a) shows the results of IR measurements on the porous membranes of comparative examples 1 to 6, FIG. 8(b) shows the results of IR measurements on the porous membranes of examples 1 to 6, FIG. 8(c) shows the results of IR measurements on the porous membranes of examples 7 to 12, and FIG. 8(d) shows the results of IR measurements on the porous membranes of examples 13 to 18. In comparative examples 1 to 6, the thickness was 1259cm^-1No absorption band was observed in the vicinity, but in examples 1 to 18, all of them were 1259cm^-1Absorption bands were confirmed nearby. That is, it was found that trimethylsilyl groups were present on the surfaces of the porous films of examples 1 to 18. It is presumed that this case shows a large contact angle with water.

The following operational effects are obtained according to the above embodiment. (1) The porous film has silica particles, a refractive index of 1.1 to 1.25, and a contact angle with water of 40 DEG or more. Thus, the porous film has a low refractive index and high environmental resistance, and therefore can be used for applications such as a thin film of an optical member.

(2) In the porous film, OH groups on the surface are treated with a silane coupling agent and have trimethylsilyl groups. This increases the contact angle of the porous film. That is, since the amount of OH groups on the surface of the porous film is reduced, it is possible to suppress a change in refractive index and a change in film thickness of the porous film due to OH groups in a high-temperature and high-humidity environment.

(3) The porous membrane scatters less than 1000ppm at a wavelength of 350 nm. Thus, the porous film is a low-scattering film, and therefore can be used for applications such as an antireflection film for an optical member.

(4) A solvent containing tertiary amine, water and methoxypropanol (PGME) is mixed with a silicon compound to prepare a mixed solution, the mixed solution is stirred, the stirred mixed solution is coated on a substrate to form a coating film, and the coating film is heated to form a porous film. Thus, a porous film having a low refractive index can be safely produced by a simple process without using hydrofluoric acid or the like.

The present invention is not limited to the above-described embodiments as long as the features of the present invention are not impaired, and other embodiments that can be considered within the scope of the technical idea of the present invention are also included in the scope of the present invention.

The disclosures of the following priority base applications are incorporated by reference into this application.

Japanese Special application No. 2019-63714 (submitted in 2019 on 3 and 28 months)

Description of the symbols

1. CAM … imaging device 103, WL … shooting lens