JP2005201994A - Optical window and underwater photographing enclosure using optical window - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an optical window of equipment from fogging by forming a coating which is hard to fog on the optical window of the equipment used underwater. <P>SOLUTION: This is an optical window of the equipment used underwater and has a polyurethane film at least on one surface of the window base. The contact angle of the waterdrops is made 40°or less to this film when it has no absorbed water, and the water absorption is made 15 % or more but 30 % or less in weight when it is saturated with the absorbed water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technique for preventing fogging of an optical window used for a device used underwater, particularly, an underwater photographing housing for housing a camera or a video camera.

  In order to perform underwater camera or video shooting, a camera, a video camera, or the like is housed in a waterproof underwater shooting housing and shooting is performed. In the water, the optical window in contact with the water of the underwater photographing housing is cooled with water, and the temperature in the housing rises when the camera or the like is turned on. Thus, water droplets adhere to the inner side of the optical window in contact with water due to water vapor, resulting in cloudiness. This is particularly noticeable when a digital camera or a digital video camera is used.

In order to prevent the adverse effects of fogging, Patent Document 1 discloses an underwater photography housing in which a water-absorbing anti-fogging film made of polyethylene oxide, acrylic acid, metal alkoxide, or the like is formed inside an optical window. . Since a water-absorbing film is used for the antifogging film, it is said that the influence on the image quality can be almost eliminated. However, the antifogging property of the antifogging film is not sufficient, and further improvement is necessary.
JP 2000-47311 A

  In view of the above problems, an object of the present invention is to provide an optical window in which a coating that hardly causes fogging is formed in an optical window of equipment used in water that is likely to cause fogging.

  In order to prevent fogging of the optical window while reducing distortion of the fluoroscopic image, it is effective to provide the optical window with a film that exhibits antifogging properties due to water absorption. This is because the optical film tends to be easily distorted by the water film formed on the film only by developing the anti-fogging property only by the hydrophilic property, and the distortion of the fluoroscopic image tends to increase. On the other hand, when anti-fogging properties are manifested by water absorption, water is taken into the film when water droplets adhere to the film, so that the distortion of the fluoroscopic image is reduced.

  In order to make the expression of antifogging effective at the time of exhibiting antifogging property due to water absorption, it is necessary to instantaneously take the waterdrop into the coating when the waterdrop adheres to the coating. In the case of developing anti-fogging property only by water absorption, it takes time for water droplets to be absorbed into the coating when water vapor contacts the coating, and thus it takes time to develop anti-fogging.

  If the film has a water-absorbing function and a hydrophilic function, water and the film come into contact with each other over a wider area when water droplets contact the surface of the film, facilitating water absorption into the film. Is done. As a result, when water vapor comes into contact with the coating, the anti-fogging property immediately appears, and it is effective to eliminate the influence of fogging on the observation of the fluoroscopic image. Further, even when the film is saturated with water, a water film is formed on the surface of the film, so that fogging of the window can be prevented at a minimum.

  The phenomenon when the anti-fogging property is exhibited is illustrated in FIGS. 1 (a) and 1 (b). The optical window 11, the water droplet 113, the water droplet 114 in contact with the coating film, and the water film 115 in FIG. 1 each represent a cross section, and the straight arrows in FIG. 1 indicate when the water droplet is absorbed by the coating film or the water film. It represents a trajectory. FIG. 1 (a) illustrates the mechanism of antifogging expression under conditions until the coating reaches an absorption saturation state, and FIG. 1 (b) illustrates antifogging properties under conditions when the coating is in an absorption saturation state. Explains the mechanism of the expression of.

  The present invention is based on the above technical idea, and the optical window of the present invention is provided with a coating made of polyurethane on at least one side of a base material, and the contact angle of water droplets on the coating is such that the coating absorbs water. The water absorption at the time of water absorption saturation of the film is 15% by weight or more and 30% by weight or less. The film provided on the substrate here is a film that does not peel off by an artificial operation such as scratching, and the film itself or a component in the film does not elute over time. In addition, the water absorption rate in the present invention indicates the weight ratio of water present in the coating film based on the weight of the coating film in the state of not absorbing water.

  By setting the contact angle of water droplets to the coating to be 40 ° or less as described above, a sufficient contact area of the water droplets to the coating can be secured, so that water absorption into the coating is promoted and instant antifogging can be realized. . The smaller the contact angle is, the better the antifogging property is. However, if the contact angle is set to be small, the durability of the coating film may be deteriorated. From a practical viewpoint, the contact angle is preferably 10 ° or more. More preferably, the angle is preferably 25 ° or more and 35 ° or less. Here, the contact angle of water droplets on the coating is the contact angle when 2 μl of water is dropped on the surface of the coating that is not absorbing water.

  Also, the water absorption rate to the coating at the time of water absorption saturation is set in the above range. If it is less than 15% by weight, the antifogging effect due to the water absorption function is not effective, and if it exceeds 30% by weight, the coating durability This is because it must be made worse. By setting the water absorption rate of the coating at the time of water absorption saturation to 15 wt% or more and 30 wt% or less, it is possible to secure sufficient water absorption for the development of antifogging properties while ensuring the durability of the coating. Even if the film is saturated with water, the film becomes super hydrophilic (the contact angle of water droplets is 10 ° or less), so that the antifogging property is maintained, and as a result, the visibility is ensured. (This phenomenon is illustrated in FIG. 1B).

  In order to obtain a sufficient water-absorbing function, the film thickness is preferably 5 μm or more. As the film thickness is increased, the water absorption capacity of the film is increased. However, if the film is too thick, optical distortion tends to occur and productivity is reduced.

  In addition, considering the effects on shooting when using an optical window in an underwater shooting housing, the optical properties of the coating are the visible light transmittance of the coating without water absorption and the visible light transmittance of the water absorption saturation state. Is preferably set within 2%, more preferably within 1%, and the center line average roughness of the coating is preferably set in the range of 0.05 nm to 1.5 nm.

  The water absorbing function can be efficiently performed by introducing an oxyalkylene chain, preferably an oxyethylene chain, into the polyurethane. The oxyethylene chain has a function of absorbing water as bound water and makes it possible to develop antifogging properties due to water absorption. Water absorption by the oxyethylene chain is particularly preferable for application to a housing for underwater photography because it reduces the change in visible light transmittance due to water absorption.

  Since the water absorbed by the coating forms hydrogen bonds with oxygen in the oxyethylene chain, when water is absorbed by the coating, a hydroxyl group is generated at the chain. When the water absorption in the film reaches saturation, the hydroxyl groups appear on the surface of the film, so that the formation of a water film on the film is promoted, so that the antifogging property is maintained, and as a result, visibility is minimized. Therefore, it is preferable.

  The optical window of the device used underwater of the present invention is particularly effective when used in an underwater photography housing in which a camera or a video camera is housed because it has excellent anti-fogging properties and light transmission characteristics when the anti-fogging properties are exhibited. Demonstrate.

  The optical window of the device used in the water of the present invention is provided with a film made of polyurethane on at least one side of the substrate. The base material includes soda lime silicate glass plate, alkali borosilicate glass plate, lead-free glass plate, crystal glass plate and other inorganic glass plates, sapphire crystal plates, polycarbonate, polyethylene terephthalate, etc. Plastic glass etc. can be used.

  This is because polyurethane has elasticity unique to urethane and is therefore superior in wear resistance compared to other resins. In consideration of economy, the coating is preferably made of a resin alone. Polyurethane is obtained by reacting an isocyanate prepolymer (chemical species having an isocyanate group) with a polyol, and the function of the film can be set by appropriately selecting the polyol. The isocyanate prepolymer, polyol, and other chemical species, And a coating film is obtained by apply | coating and applying the coating agent which has those reaction materials to a base material by well-known coating means, such as a spin coat method, a dip coat method, a flow coat method. At this time, it is preferable to adjust the number of isocyanate groups and isocyanate-reactive groups in the vicinity of the stoichiometry. In order to further improve the durability of the coating, a treatment for improving the adhesive strength between the substrate and the coating may be performed on the substrate in advance.

  As the isocyanate prepolymer, difunctional, preferably trifunctional polyisocyanate having a biuret and / or isocyanurate structure starting from hexamethylene diisocyanate can be used. The substance has weather resistance, chemical resistance and heat resistance, and is particularly effective for weather resistance. In addition to the above substances, diisophorone diisocyanate, diphenylmethane diisocyanate, bis (methylcyclohexyl) diisocyanate, toluene diisocyanate and the like can also be used.

  In order to give the coating water absorbability, an oligomeric water absorbable polyol can be used as the polyol. The water-absorbing polyol has the property of absorbing water and swells, and the hydroxyl group in the molecule reacts with the isocyanate group of the isocyanate prepolymer to form a urethane bond, thereby introducing the water-absorbing property to the polyurethane. Can do. The water-absorbing polyol may have water-soluble properties.

  The amount of water-absorbing polyol used is adjusted so that the water absorption rate in the coating at the time of water absorption saturation is 15% by weight or more, and the amount of water-absorbing component derived from the water-absorbing polyol in the coating is adjusted. The water-absorbing component may be derived from an oxyalkylene-based polyol, preferably has an oxyethylene chain, an oxypropylene chain, etc., and particularly preferably has an oxyethylene chain excellent in water absorption.

  The oxyalkylene polyol preferably has a number average molecular weight of 400 to 5,000. When the number average molecular weight is less than 400, the ability to absorb water as bound water becomes low, and when the average molecular weight exceeds 5000, the strength of the coating tends to decrease. In view of water absorption and film strength, the average molecular weight is more preferably 400-4500. As the polyol, an oxyethylene / oxypropylene copolymer polyol, polyethylene glycol, or the like can be used. When polyethylene glycol is used, the number average molecular weight is 400 to 2000 in view of water absorption and the strength of the resulting film. It is preferable to do.

  A typical chemical species that imparts hydrophilicity to the film is a surfactant. In order to prevent the surfactant from eluting from the coating, it is preferable that the surfactant is present in the coating in a state of being bonded to the resin crosslinking. In order to be in a state of being bonded to the resin crosslinking, it is necessary to use a surfactant containing a reactive group as a surfactant starting material. When the reactive group is a hydroxyl group, an amino group, a mercapto group or the like, the reactive group reacts with the isocyanate prepolymer, and the surfactant can be chemically bonded to the resin crosslinking. Further, an isocyanate group can be provided on the surfactant and reacted with a polyol.

  The chemical species that imparts hydrophilicity to the coating can be introduced into the coating such that the contact angle of water droplets in a state where the coating does not absorb water is 40 ° or less. However, since excessive introduction of chemical species weakens the strength of the coating and deteriorates durability, it is preferable to introduce the chemical species so that the contact angle is 10 ° or more.

  The above are the requirements necessary for obtaining a film having a water-absorbing function and a hydrophilic function by polyurethane. In addition to the above, the polyol includes a hydrophobic polyol and a short-chain polyol having a number average molecular weight of 60 to 200 Can be used.

  The hydrophobic polyol has both flexibility and scratch resistance, and it is difficult to reduce the water absorption function and hydrophilic function of the film, and as a result, the water resistance and abrasion resistance of the film can be improved. It is preferable that it is a polyester polyol having a number average molecular weight of 500 to 2,000. When the number average molecular weight is less than 500, the coating film becomes too dense and wear resistance decreases. On the other hand, if it exceeds 2000, the film formability of the coating solution deteriorates and it becomes difficult to form a coating film. In consideration of the denseness of the resulting film, the polyol preferably has 2 or 3 hydroxyl groups.

  As the polyester polyol, any of polycarbonate polyol, polycaprolactone polyol, and a mixture thereof can be used. The hydrophobic components derived from these hydrophobic polyols are introduced so that the water absorption rate and water droplet contact angle of the coating are in the above-mentioned ranges, and the pencil hardness of the coating obtained in accordance with “JIS K 5400” is preferably It is preferable to introduce HB to F at the time of water absorption saturation.

  In addition, the component derived from the short-chain polyol has the effect of increasing the curability of the coating solution, increasing the strength of the coating film, and reducing the static friction coefficient of the coating surface. Optical windows are easily assumed to have a wide variety of deposits attached to the film surface during use, impairing the appearance and quality, and are usually wiped with a cloth to remove these deposits. Is done. At that time, if the static friction coefficient of the surface is large, problems such as an increase in removal time and poor appearance due to uneven wiping occur in the wiping operation. During the wiping operation, the deposits are rubbed against the film surface. If the coefficient of friction is large, the deposits are likely to be caught on the film surface, and many scratches may be generated, and the cloth used for the wiping operation may be reversed. Adverse effects such as sticking to the surface may occur. When the static friction coefficient on the film surface is small, the wear resistance and antifouling property of the film are improved, and the coefficient is a very important physical property from a practical viewpoint.

  The short chain polyol preferably has 2 or 3 hydroxyl groups. When the hydroxyl group is 1, the short-chain polyol does not become a skeleton component of the film, so that the film becomes fragile. When it exceeds 3, the reactivity is too active and the coating agent tends to be unstable.

  Short chain polyols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5 -Pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, glycerin, 2- And alkyl polyols such as ethyl-2- (hydroxymethyl) -1,3-propanediol, 1,2,6-hexanetriol, and 2,2′-thiodiethanol, and alkanolamines such as diethanolamine and triethanolamine. They can be used alone or as a mixture or Can be used copolymers that are not molecular weight greater than 200 and, component derived from short-chain polyols, water absorption of the film, and the water droplet contact angle is preferably introduced such that the ranges described above.

  Next, an example of an underwater photographing housing using the optical window of the present invention will be described. As one form of the underwater photographing housing, for example, the one shown in JP-A-2002-122929 is known. 2 is a perspective view showing the entire housing for underwater photography, FIG. 3A is a front view showing a state in which the front lid is removed from the housing for underwater photography, and FIG. 3B is a view of the front lid from the back side. It is a front view. The underwater photographing housing 1 includes a bottom portion 2, a left side wall 3, a right side wall 4, a back surface 5, and a mountain-shaped top surface 6. In FIG. 2, the underwater camera insertion / exit opening 7 on the front side is fully open. The front lid 8 is a front lid that is detachably attached to the camera insertion / removal port 7 of the underwater photographing housing 1, and has a through hole 9 in the center, and a mirror is horizontally directed from the through hole 9 toward the front side. A tube 10 is attached. The optical window 11 is watertightly attached to the distal end side in the lens barrel 10, and the optical window 11 is composed of the optical window of the present invention, and the coating is formed on the inner side.

  The grips 12 a and 12 b are grips attached to the left and right side walls 3 and 4 of the housing 1. The shutter button 13 is incorporated in the right grip 12a, and when the shutter button 13 is pushed in, the linear motion is converted into rotational motion by the gear mechanism 14, and this rotational motion is transmitted to the shutter of the camera 30 via the rotational shaft 15. Is done.

  The fixing bracket 16 is for detachably fixing the front lid 8 to the underwater shooting housing 1, which fixes the hook 17 to a required position on the underwater shooting housing 1 side, and a fixing claw. The 18 side is fixed to the front lid 8 and can be attached and detached with one touch.

  The mating ridge 19 is formed on the entire edge of the camera slot 7 of the underwater photography housing 1, and this is a recess in which an O-ring (seal material) 21 formed on the front lid 8 side is incorporated at the back. It fits into the groove 20 to ensure water tightness in the housing. The fixing means 22 is a fixing means for the underwater camera 30 provided at the inner bottom of the underwater photographing housing 1, and the camera 30 is fixed in the underwater photographing housing 1 using the fixing means 22. The fixing means 22 is configured to be adjustable depending on the model, size, etc. of the camera 30.

  The underwater photographing housing 1 is configured such that the camera 30 is inserted into the underwater photographing housing 1 from the camera insertion / removal port 7 and is fixed using the fixing means 22, and then the fixing bracket 16, the hook bracket 17, and the fixing claw 18 are attached. The underwater photographing housing 1 is watertight. During underwater photography, when the grips 12a and 12b are grasped with both hands and the shutter button 13 is pushed with the thumb, this linear motion is converted into rotational motion by the gear mechanism 14, and this rotation is transmitted from the rotational shaft 15 to the camera 30. Thereby, underwater photography can be performed. In the underwater photographing housing, since the optical window 11 is excellent in antifogging property, the optical window is not easily fogged, and photographing underwater is easy.

  The optical window of the present invention is effective not only in the above-described underwater photographing housing but also in underwater goggles and underwater lights.

  Hereinafter, the present invention will be described specifically by way of examples. In addition, quality evaluation was performed by the method shown below about the optical window with which the film which exhibits the water absorption and hydrophilic property obtained by the present Example and the comparative example was comprised.

  [Appearance evaluation]: Appearance, permeability, and presence / absence of cracks of the film were visually evaluated. Those having no problem were evaluated as acceptable (◯), and those having problems were regarded as unacceptable (x).

  [Water absorption rate when the film is saturated with water absorption]: The weight (a) of the optical window when held for 12 hours in an environment of 50% humidity and a temperature of 55 ° C. Measure, and bring the coating film into contact with saturated water vapor at 43 ° C. for 5 minutes. Then, immediately wipe off the water film on the coating surface, and then measure the weight (b) of the optical window, and [b−a] / [a− (mirror body Weight)] × 100 (%) was obtained as the water absorption rate at the time of water absorption saturation. The value (a) here corresponds to that in a state in which the film does not absorb water.

  [Contact angle of water droplets on the coating]: The contact angle of water droplets on the coating was measured in accordance with “JIS R 3257“ Test method for wettability of substrate glass surface ”. After maintaining for 12 hours in an environment of 55 ° C., the test piece was in a state where the film was not absorbed by holding the same humidity for 12 hours in an environment of 25 ° C. The sample was a contact angle meter made by Kyowa Interface Chemical. (CA-2 type), 2 μl of water was dropped on the coating, the contact angle of the water droplet was measured, and 43 ° C. saturated water vapor was contacted with the coating of the test piece for 5 minutes to absorb the coating. After being saturated, the test piece was placed on the contact angle meter, 2 μl of water was dropped on the coating, and the contact angle of the water droplet was measured.

  [Anti-fogging property]: After being kept in a freezer set at −20 ° C. for 30 minutes, the appearance, cloudiness, and cloudiness due to expiration are observed when taken out at room temperature (23 ° C., humidity 63%). This operation was carried out 10 times as 1 cycle, and the film appearance with no abnormality and no clouding occurred was judged as acceptable (O), and the film with clouding was judged as unacceptable (X). A sample that passes this evaluation item exhibits a remarkable effect in developing anti-fogging properties when used in an optical window of a housing for underwater photography.

  [Measurement of transmittance] According to “JIS R 3106” (Testing method of transmittance, reflectance, and solar heat gain rate of plate glass), the visible light spectrophotometer (U-4000, Hitachi, Ltd.) is used to absorb the coating. The visible light transmittance was measured with respect to the optical window in the absence and saturated state of water absorption.

  [Water resistance]: What is immersed in water at 23 ± 2 ° C. for 1 hour, has no abnormal appearance after immersion, has not been clouded by exhalation, and has a pencil hardness reduction of within one rank. (◯) A product that deteriorated by 2 ranks or more was regarded as rejected (x).

Example 1
Hexamethylene diisocyanate burette type polyisocyanate (trade name “N3200”, manufactured by Sumitomo Bayer Urethane Co., Ltd.) was prepared as an isocyanate prepolymer, and this was used as coating agent A.

  12.5 g of ricinoleamidopropylethyldimonium ethosulphate (trade name “Lipoquat®” manufactured by Lipochemicals Inc) as a surfactant having an isocyanate-reactive group, 17.5 g of polyethylene glycol having an average molecular weight of 1000 as a water-absorbing polyol 20.5 g of polycaprolactone diol having an average molecular weight of 1250 (trade name “Placcel L212AL”, manufactured by Daicel Chemical Industries) as a hydrophobic polyol, and 5 g of 1,4 butanediol as a short-chain polyol are mixed together, and this is used as coating agent B. It was.

  44.5 g of coating agent A adjusted to have an isocyanate group / isocyanate reactive group ratio of 1.2 was added to and mixed with coating agent B to obtain a mixture of coating agent A and coating agent B. .

  Diacetone alcohol was added as a diluent solvent so that the concentration of the total amount of isocyanate prepolymer, polyol, and surfactant was 35% by weight, and dibutyltin dilaurate as a curing catalyst was added to the total amount of urethane components. A coating agent for forming an antifogging film was prepared by adding 0.005% by weight.

  As the optical window, a soda-lime silicate glass plate by a float method having a thickness of 3 mm and a size of 60 mmφ was used. The optical window and the coating agent were applied by spin coating. The optical window coated with the coating agent was heated at 150 ° C. for 30 minutes to obtain an optical window having a coating having a thickness of 28 μm.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that the film was suitable for use in an underwater photographing housing.

Example 2
Example 1 except that the hydrophobic polyol was 15 g of polycaprolactone diol having an average molecular weight of 500 (trade name “Placcel L205AL” manufactured by Daicel Chemical Industries), and the amount of coating agent A added to coating agent B was 50 g. Thus, an optical window provided with a film having a film thickness of 7 μm was obtained.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that the film was suitable for use in an underwater photographing housing.

Example 3
20.0 g of ricinoleamidopropylethyldimonium ethosulphate for the surfactant having an isocyanate reactive group, 20.0 g of polyethylene glycol with an average molecular weight of 1000 for water-absorbing polyol, and 5.6 g for the average molecular weight of hydrophobic polyol 1250 polycaprolactone diol and short-chain polyol were changed to 5 g ethylene glycol, and the amount of coating agent A added to coating agent B was 49.4 g so that the isocyanate group / isocyanate reactive group ratio was 1.1. Except for the above, the same operation as in Example 1 was performed to obtain an optical window having a coating film with a film thickness of 22 μm.

  The obtained optical window has the water absorption rate of the coating and the contact angle of water droplets as shown in Table 1. It has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that it was suitable for use in an underwater photography housing.

Example 4
20.0 g of ricinoleamidopropylethyldimonium ethosulphate surfactant having an isocyanate-reactive group, 19.5 g of polycaprolactone diol having an average molecular weight of 1250, and 2.5 g of glycerol The same procedure as in Example 3 was carried out except that the amount of the coating agent A added to the coating agent B was 38 g so that the isocyanate group / isocyanate-reactive group number ratio was 1.1, and the film thickness was 22 μm. An optical window with a coating was obtained.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that the film was suitable for use in an underwater photographing housing.

Example 5
Example 4 except that 5.1 g of a polycarbonate polyol having an average molecular weight of 1250, 5 g of ethylene glycol was used as the hydrophobic polyol, and 49.9 g of the additive A was added to the coating agent B. Thus, an optical window provided with a film having a film thickness of 13 μm was obtained.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that it was suitable for use in an underwater photography housing.

Example 6
The hydrophobic polyol is 8.3 g of polycaprolactone triol having an average molecular weight of 500 (trade name “Placcel 305” manufactured by Daicel Chemical Industries), the short-chain polyol is 5 g of 1,4 butanediol, and the coating agent A is applied to the coating agent B. The same operation as in Example 3 was performed except that the amount of the added mixture was changed to 46.7 g, to obtain an optical window having a coating film with a film thickness of 29 μm.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that the film was suitable for use in an underwater photographing housing.

Example 7
The surfactant having an isocyanate-reactive group is 17.5 g of ricinoleamidopropylethyldimonium ethosulphate, the water-absorbing polyol is 15.0 g of polyethylene glycol having an average molecular weight of 1000, and 10 g of ethylene oxide is 50%. Addition of coating agent A to coating agent B with propylene oxide / ethylene oxide random triol having an average molecular weight of 2800, 13.2 g of a hydrophobic polyol, polycaprolactone diol having an average molecular weight of 500, and 2.5 g of glycerin as a short-chain polyol The same procedure as in Example 1 was carried out except that the mixing amount was 41.9 g so that the isocyanate group / isocyanate-reactive group number ratio was 1.2, and an optical window provided with a film having a film thickness of 19 μm was obtained. It was.

  The obtained optical window has the water absorption rate of the film and the contact angle of water droplets as shown in Table 1, has excellent antifogging performance and water resistance, and the visible light transmittance is almost the same as that of the substrate. Further, the change in transmittance due to water absorption of the film was small, and it was confirmed that the film was suitable for use in a housing for underwater photography.

Comparative Example 1
The same operation as in Example 1 was performed except that the hydrophobic polyol was not added and the water-absorbing polyol was changed to 38 g of polyethylene glycol having an average molecular weight of 1000 to obtain an optical window having a coating having a film thickness of 27 μm.

  The obtained optical window had a water absorption rate of the coating and a contact angle of water droplets as shown in Table 1, and had excellent antifogging performance, but had a poor appearance and poor water resistance. It was unsuitable for use in a photography housing.

Comparative Example 2
Example 1 except that a surfactant having an isocyanate-reactive group was not added, the water-absorbing polyol was changed to 27 g of polyethylene glycol having an average molecular weight of 1000, and the hydrophobic polyol was changed to 26.5 g of polycaprolactone diol having an average molecular weight of 1250. The same operation was performed to obtain an optical window provided with a film having a film thickness of 27 μm.

  As shown in Table 1, the obtained optical window has a low water droplet contact angle in a state in which the film does not absorb water, so that the antifogging property does not immediately appear, and the antifogging performance is inferior. It was unsuitable for use in a housing.

Comparative Example 3
A coating film having a film thickness of 28 μm in the same manner as in Example 1, except that the surfactant is 22 g of sodium alkyl ether sulfate having no isocyanate-reactive group and the amount of coating agent A is 40 g. An optical window equipped with was obtained.

  The obtained optical window gradually decreased in antifogging property during the antifogging test, and after the test, the contact angle of water droplets in a state where the film did not absorb water was 8 ° after the water resistance test. It changed to 44 ° and was unsuitable for use in a housing for underwater photography.

Comparative Example 4
The water-absorbing polyol was 17.5 g of polypropylene glycol having an average molecular weight of 2000, and the concentration of the total amount of isocyanate prepolymer, polyol, and surfactant in adjusting the coating agent was adjusted to 40% by weight. The same operation as in Example 1 was performed to obtain an optical window provided with a film having a film thickness of 33 μm.

  Optical distortion was observed in the appearance of the obtained optical window. In addition, the water absorption rate was low, the anti-fogging test was rejected, and it was not suitable for use in an underwater photography housing.

The figure explaining the mechanism of the antifogging expression of the optical window of the present invention, and the figure explaining the mechanism of the antifogging expression under the conditions until the film is saturated with water and the film is saturated with water It is the figure (b) explaining the mechanism of anti-fogging expression under the conditions. It is a perspective view which shows one form of the housing for underwater photography using the optical window of this invention. It is the front view (a) of the state which removed the front cover of the housing for underwater photography shown in FIG. 2, and the front view (b) when the front cover is seen from the back side part.

Explanation of symbols

1. 7. Underwater photography housing Front lid 9. Through hole 10. Lens barrel 11. Optical window 111. Substrate 112. Coating 22. Camera fixing means 30. Camera to be stored 113. Water droplets present in the air 114. Water droplets in contact with the coating 115. Water film formed on the film

Claims (5)

An optical window for equipment used in water, wherein the optical window is provided with a coating made of polyurethane on at least one side of a substrate, and the contact angle of water droplets on the coating is such that the coating does not absorb water An optical window having a water absorption rate of 15 wt% or more and 30 wt% or less when the film is saturated with water absorption at 40 ° or less. 2. The optical window according to claim 1, wherein a difference between the visible light transmittance of the coating in a state of not absorbing water and the visible light transmittance in a saturated water absorption state is within 2%. The optical window according to claim 1 or 2, wherein water absorption by the coating is performed by an oxyalkylene chain in the polyurethane. The optical window according to any one of claims 1 to 3, wherein the thickness of the coating is 5 µm or more and 30 µm or less. 5. A housing for underwater photography in which a camera or a video camera using the optical window according to claim 1 is accommodated.