JP2011169961A - Hydrophilic antireflection structure and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrophilic antireflection structure which has a fine structure, having both of a light antireflection performance and hydrophilicity, is superior in durability, as well, and is capable of maintaining a stainproof performance excelling in the easiness of wiping off stains and the antireflection function over a long period; and to provide an article provided with such a hydrophilic antireflection structure, an automobile component, for instance. <P>SOLUTION: For a surface shape, on at least a part of a surface having a first irregularity 1, having periodicity shorter than the wavelength of a visible light beam, a second irregularity 2, whose irregularity interval and height difference are smaller than that of the first irregularity 1 is provided, and hence the contact angle with respect to water is set to 80° or smaller. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention has hydrophilicity and antifouling performance, that is, excellent adhesion to dirt and ease of wiping when adhered, and a hydrophilic reflection having a fine uneven surface that exhibits an antireflection function for light. The present invention relates to a prevention structure and a method for producing such a hydrophilic antireflection structure.

When scenery or lighting outside the vehicle, shadows of passengers, or the like are reflected on the surface of a display device such as a meter or a navigation display in a transport device such as an automobile, the visibility of displayed information may be significantly reduced.
In addition, when a shadow such as outside light or indoor lighting is reflected on various display devices such as a liquid crystal display and a CRT display, for example, a screen of a home television, the visibility of the original image may be significantly lowered.

  As a structure for preventing such reflection of light, a multilayer antireflection film composed of a plurality of thin films having different refractive indexes is known, but the reflectance is further lowered than such a multilayer antireflection film. An antireflection structure using a fine concavo-convex structure is known (see, for example, Patent Document 1).

When dirt such as fingerprints adheres to the surface of the concavo-convex fine structure as described above, even if an attempt is made to wipe it off with a cloth, the cloth fiber may not reach the bottom of the fine structure, so that the dirt may be difficult to remove.
As a technique for improving the wiping property of dirt, it is conceivable to make the surface hydrophilic so that the dirt is lifted up when wiping with water to facilitate wiping.

  In order to make the surface of the antireflection structure composed of such fine irregularities hydrophilic, it has been proposed to use a hydrophilic material as the material of such an antireflection structure (see, for example, Patent Document 2).

JP 2002-256815 A JP 2008-158293 A

However, although the antireflection structure described in Patent Document 1 is composed of innumerable fine irregularities arranged at a pitch equal to or less than the wavelength of light, the hydrophilicity of the surface is hardly taken into consideration and the antifouling structure is not considered. The performance is not met.
On the other hand, in the hydrophilic antireflection structure described in Patent Document 2, it is possible to make the surface hydrophilic with a hydrophilic material, but the fine irregularities made of such a material have durability against wiping with a cloth or the like. There was a problem of being low.

The present invention has been made to solve the above-mentioned problems in the antireflection structure for light and the hydrophilic fine structure.
And the purpose is to maintain both anti-fouling performance and light anti-reflection function for a long period of time, having both anti-reflection performance of light and hydrophilicity, excellent durability and easy wiping of dirt. It is an object of the present invention to provide a hydrophilic antireflection structure capable of achieving the above and an article provided with such a hydrophilic antireflection structure, for example, an automotive part.

  As a result of intensive investigations to achieve the above object, the present inventors have further formed a second unevenness smaller than that on the surface provided with the first unevenness having an antireflection function. The inventors have found that the above object can be achieved and have completed the present invention.

  That is, the present invention is based on the above knowledge, and the hydrophilic antireflection structure of the present invention has irregularities on at least a part of the surface having the first irregularities having a periodicity shorter than the wavelength of visible light. It is characterized by having second irregularities whose spacing and height difference are smaller than the first irregularities, and having a contact angle with water of 80 ° or less.

  The hydrophilic antireflection structure of the present invention is characterized in that the above-described hydrophilic antireflection structure is provided on at least one surface of a substrate, and together with the article of the present invention, the automotive part of the present invention comprises: The above-mentioned hydrophilic antireflection structure is provided.

  According to the present invention, the first unevenness provided with innumerable fine unevenness arranged at a cycle shorter than the wavelength of light and the second unevenness smaller than this are provided on the first uneven surface. For this reason, the first unevenness exerts the light reflection preventing function. And the hydrophilicity is imparted without affecting the strength of the fine irregularities in the first irregularities, that is, the anti-wiping durability, by the second irregularities thereon, and the light antireflection property and hydrophilicity (antifouling performance) ) Can be exhibited over a long period of time.

It is sectional drawing which shows an example of the hydrophilic antireflection structure of this invention. It is a perspective view which shows the uneven | corrugated shape which consists of a fine convex part which makes cone shape as an example of the 1st unevenness | corrugation in the hydrophilic antireflection structure of this invention. Similarly, as another example of the first concavo-convex in the hydrophilic antireflection structure of the present invention, it is a perspective view showing a concavo-convex shape composed of fine convex portions having a quadrangular pyramid shape. Similarly, as another example of the first unevenness in the hydrophilic antireflection structure of the present invention, it is a perspective view showing an uneven shape composed of a conical fine convex portion and a fine concave portion. Similarly, as another example of the first unevenness in the hydrophilic antireflection structure of the present invention, it is a perspective view showing an uneven shape composed of fine convex portions and fine concave portions having a quadrangular pyramid shape. It is an electron micrograph which shows the surface shape of the structure obtained by the comparative example 2 as an example of the hydrophilic antireflection structure of this invention. It is an electron micrograph which shows the surface shape of the structure obtained by Example 2 as another example of the hydrophilic antireflection structure of this invention. It is an electron micrograph which shows the surface shape of the structure obtained by Example 3 as another example of the hydrophilic antireflection structure of this invention. It is an electron micrograph which shows the surface shape of the structure obtained by Example 4 as another example of the hydrophilic antireflection structure of this invention.

  Hereinafter, the hydrophilic antireflection structure of the present invention and the structure to which the hydrophilic antireflection structure is applied will be described in more detail along with the manufacturing method and embodiments thereof.

As described above, the hydrophilic antireflection structure of the present invention has the first unevenness in the interval between the unevenness and the height difference on at least a part of the surface having the first unevenness having a periodicity shorter than the wavelength of visible light. And a contact angle with water of 80 ° or less.
In other words, FIG. 1 is a cross-sectional view showing an example of the hydrophilic antireflection structure of the present invention, and this hydrophilic antireflection structure is formed on the surface of the first unevenness 1 in the first and second unevenness intervals and height differences. The second unevenness 2 smaller than the unevenness 1 is provided.

  Here, as long as the second unevenness 2 is smaller than the first unevenness 1, there is no shape limitation. In addition, it is not always necessary that the first unevenness 1 is densely arranged on the surface of the first unevenness 1 without a gap in the sense that the surface area of the first unevenness 1 is increased.

In the hydrophilic antireflection structure of the present invention, the surface area is increased due to the presence of the finer second irregularities 2 on the surface of the first irregularities 1, and the surface tension is apparently increased. As a result, the water adhering to the surface becomes more wet and spreads and becomes hydrophilic.
As a hydrophilicity index at this time, it is necessary that the contact angle of the surface provided with the first and second irregularities 1 and 2 with respect to water is 80 ° or less. Thereby, when the surface is wiped with water, the attached dirt can be lifted to facilitate wiping. The smaller the contact angle, the higher the affinity with water and the better the antifouling property. Therefore, the contact angle is more preferably 40 ° or less, and the load and the number of reciprocations when wiping can be reduced. .

When the fine irregularities are made of a hydrophilic material as in the prior art, the surface hardness of the fine irregularities tends to decrease due to the presence of many hydrophilic functional groups on the irregular surface. For this reason, while the operation of wiping off the attached dirt with a cloth or the like is repeated, it gradually wears from the vicinity of the apex of the fine unevenness, and the uneven shape tends to be destroyed.
In this invention, since hydrophilicity is expressed by providing the 2nd unevenness | corrugation instead of using a hydrophilic material, it does not affect the surface hardness of a fine unevenness | corrugation. For this reason, it becomes difficult to wear near the vertex of the 1st unevenness which cloth etc. contact at the time of wiping off. As a result, it becomes difficult for the cloth or the like to come into contact with the side surface or bottom of the first unevenness, and the uneven shape is easily held together with the applied second unevenness. Since the shape of the 2nd unevenness | corrugation is hold | maintained, the fall of hydrophilicity fall (aging deterioration) and the fall of the effect | action which raises dirt at the time of water wiping can be prevented.

In the hydrophilic antireflection structure of the present invention, as the first unevenness 1, for example, as shown in FIG. 2, the fine convex portion 1 a having a conical shape has a cycle shorter than the wavelength of visible light in the XY direction (that is, It is possible to adopt a structure arranged at a pitch P) (square arrangement).
The pitch P here is specifically defined as the distance between the vertices of the fine protrusions 1a or the distance between the centers of gravity of the bottom surfaces, which is equal to or greater than the wavelength of visible light, specifically, the minimum value of visible light of 380 nm or greater. Then, since diffracted light is generated and the antireflection performance is lowered, it is required to be less than 380 nm, particularly preferably 250 nm or less.

  Needless to say, the periodic arrangement of the fine protrusions 1a is not limited to a square arrangement, and may be a hexagonal arrangement. At this time, when the pitch P is different depending on the direction as in the square arrangement, the larger value is defined as the pitch P.

  Thus, in the 1st unevenness | corrugation 1 which arrange | positions the fine convex part 1a like a cone regularly with the pitch P shorter than the wavelength of visible light, the occupation area of the material in each cross section of the thickness direction The refractive index in the thickness direction determined by ## EQU1 ## changes smoothly from the refractive index 1.0 of air to the refractive index of the material without abrupt changes. Therefore, the light incident on such fine irregularities 1 travels straight with almost no diffraction or reflection, and the reflectance of light on the incident surface can be greatly reduced.

The shape of the fine convex portion 1a is not particularly limited as long as it is a tapered shape whose cross-sectional area gradually decreases from the proximal end side toward the distal end, and is a pyramid shape as shown in FIG. In addition, the shape of a vertebra, a shell, a bell, a semi-spindle, and a pyramid having a two-dimensional curved surface may be used. Moreover, it is good also as a truncated cone shape and a truncated pyramid shape which flattened the top part.
Furthermore, it is possible to use a concave portion instead of the convex portion, or to arrange the fine convex portion 1a and the fine concave portion 1b regularly as shown in FIGS. Moreover, it can also be set as an uneven surface where a sinusoidal curved surface continues three-dimensionally.

In the first unevenness 1 in the hydrophilic antireflection structure of the present invention, it is desirable that the aspect ratio defined by the ratio H / P of the height H and the pitch P of the fine protrusions 1a is 1 or more. The light reflectance can be more reliably lowered.
Note that in the case of a concavo-convex structure including fine concave portions 1b instead of the fine convex portions 1a, the aspect ratio is set to H ′ / P using the depth H ′ of the concave portions 1b corresponding to the height H. 4 and 5, when the fine convex portion 1a and the fine concave portion 1b are mixed, the difference between the highest portion and the lowest portion, that is, H + H 'is used, and (H + H') / P is defined as the aspect ratio. Define.

On the other hand, as shown in FIG. 1, the second unevenness 2 is not limited in shape as long as it is smaller than the first unevenness 1 in the unevenness interval and height difference.
That is, the surface area is increased due to the presence of the finer second irregularities 2 on the surface of the first irregularities 1, and the surface tension is apparently increased.

And in order to make the contact angle with respect to the water of the uneven | corrugated surface in the hydrophilic antireflection structure of this invention 80 degrees or less as mentioned above, the contact angle with respect to the water of the material which comprises the said uneven | corrugated surface is 90 degrees. It is desirable to use less than the material.
That is, when the material constituting the uneven surface is a material whose surface tension against water is smaller than the surface tension against air, that is, a material whose contact angle with water is less than 90 °, the surface area increases so that the water spreads more wetly. Thus, the water contact angle becomes 80 ° or less.

  Examples of such materials include polyethylene, polypropylene, polyvinyl alcohol, polyvinylidene chloride, polyethylene terephthalate, polyvinyl chloride, polystyrene, AS resin, acrylic resin, polyamide, polyacetal, polybutylene terephthalate, glass reinforced polyethylene terephthalate, polycarbonate, Modified resins such as polyphenylene ether, polyphenylene sulfide, polyether ether ketone, polyarate, polysulfone, polyethersulfone, polyamideimide, polyetherimide, thermoplastic polyimide, phenol resin, melamine resin, urea resin, epoxy resin, Thermosetting resins such as saturated polyester resins, alkyd resins, diallyl phthalate resins, or two or more of these Rend material, more can be mentioned glass, oxide silicate, a transparent inorganic material such as aluminum oxide.

  In order to obtain the hydrophilic antireflection structure of the present invention, a mold having innumerable concave portions and convex portions obtained by inverting the fine convex portions 1a and the fine concave portions 1b constituting the first concave and convex portions 1 is prepared. The first unevenness 1 as described above is first formed on the surface of the base material by relatively pressing one or both of the molding die and the base material made of the above material in a heated state.

And in order to give the 2nd unevenness | corrugation 2 on the surface provided with the 1st unevenness | corrugation 1, the 1st uneven | corrugated surface obtained by the above is exposed to corona discharge, a plasma arc, an ultraviolet-ray etc., for example Can be adopted.
Further, the first and second surfaces can be etched using a method of forming the second unevenness 2 by etching the surface of the first unevenness 1 or using a mold capable of transferring the shape of the second unevenness 2. A method of simultaneously forming irregularities can also be employed, and is not particularly limited.

By forming the hydrophilic antireflection structure of the present invention on one side, preferably both sides of a transparent substrate, a hydrophilic antireflection structure can be obtained. Such a hydrophilic antireflection structure can be applied to, for example, panels and covers of various display devices, touch panels, mirrors, windshield glass, show windows, show cases, and the like.
As a result, reflection of external light and indoor lighting can be reduced, reflection of reflected images can be effectively prevented, and visibility of images, displays, and internal exhibits can be improved. Dirt can be easily wiped off, and such an effect can be maintained over a long period of time.

  Hereinafter, the present invention will be described more specifically based on examples. However, it is needless to say that the present invention is not limited to these examples.

Example 1
Using a mold produced by a commercially available electron beam drawing apparatus, fine projections having a cone shape having a three-dimensional sinusoidal ridgeline with a height H = 390 nm as shown in FIG. 6 have a pitch P = 300 nm. An acrylic film (contact angle with respect to water: 80 °) having first irregularities formed on a hexagonal close-packed surface on one side was prepared.
The obtained acrylic film was placed between the electrodes of the corona discharger (300 W) so that the uneven surface side became the treated surface, and moved between the electrodes at a speed of 2.14 m / min, thereby providing the first unevenness. On the surface, second irregularities were formed to obtain a hydrophilic antireflection structure having the first irregularities and the second irregularities.

The uneven shape of the hydrophilic antireflection structure thus obtained is shown in Table 1 together with the treatment conditions.
Further, the structure after 14 days from the treatment where the corona discharge treatment is stabilized was evaluated for hydrophilic performance, antireflection performance, wear resistance performance (durability), and antifouling performance in the following manner. These results are shown in Table 2.

(Measurement of contact angle)
As an evaluation method of hydrophilic performance, using a contact angle meter (Kyowa Interface Science Co., Ltd .: CA-X), 5 μL of water was allowed to stand from the syringe on the obtained hydrophilic antireflection structure. The contact angle was measured. The measurement was performed 5 times, and the average value was used as the contact angle of each sample.

[Measurement of average reflectance]
As an evaluation method of the antireflection function, the reflectivity at an incident angle of 0 ° is measured with a variable angle spectrophotometer (manufactured by Otsuka Electronics: visible / near infrared automatic variable angle measuring device) for each wavelength of 380 to 780 nm. The average reflectance was calculated from the measured value.
The reflectance is measured after lapse of 14 days (initial performance) after the treatment is stabilized, and a surface of the cloth subjected to a load of 100 gf / □ 5 cm (100 gf per 5 cm square surface) at a speed of 100 mm / s 5000 times. The test was conducted after the abrasion resistance test for reciprocation, and the difference ΔR was used as an index of durability. That is, as the reflectance difference ΔR is smaller, the uneven shape is not destroyed by the abrasion resistance test, and the durability is excellent.

[Evaluation of antifouling performance]
After attaching the fingerprint by touching the uneven surface of the obtained hydrophilic antireflection structure with a hand, wipe it off with a towel soaked in water, visually observing the remaining state of the fingerprint, the following three steps Evaluation based on the criteria of.
3: Can be wiped away 2: There is unwiped residue 1: Not wiped off

  The contact angle of the surface of the hydrophilic antireflection structure produced in Example 1 is 68 °, the average reflectance is 0.12%, the increase in reflectance by the wear resistance test is 0.26%, and the antifouling performance is 3 The rating was “2”.

(Example 2)
On the surface of the first uneven surface by repeating the same treatment two more times and conveniently three times on the same surface on the surface subjected to the corona discharge treatment by the same method as in Example 1 above. Second unevenness was formed on the surface to obtain the hydrophilic antireflection structure of Example 2. FIG. 7 shows an electron micrograph of the uneven shape on the surface of the obtained structure.
And the same evaluation was performed about the said performance. As a result, the contact angle of the structure surface is 33 °, the average reflectance is 0.09%, the increase in reflectance by the abrasion resistance test is 0.28%, and the antifouling performance is “2”, which is evaluated in three stages. Met. These results are also shown in Table 1.

(Example 3)
The same treatment is repeated four times on the surface subjected to the corona discharge treatment by the same method as in the first embodiment, and the corona discharge treatment is repeated five times on the same surface. Second unevenness was formed on the surface to obtain a hydrophilic antireflection structure of Example 3. FIG. 8 shows an electron micrograph of the uneven shape on the surface of the obtained structure.
As a result of performing the same evaluation on the above performance, the contact angle of the surface of the structure is 6 °, the average reflectance is 0.14%, the increase in reflectance by the wear resistance test is 0.22%, The soiling performance was “3” with a three-level rating. These results are also shown in Table 1.

Example 4
Except that the output of the corona discharger was 600 W, the same method as in Example 3 was repeated to form second irregularities on the first irregular surface, and the hydrophilic antireflection structure of Example 4 Got the body. FIG. 9 shows an electron micrograph of the concavo-convex shape on the surface of the obtained structure.
As a result of the same evaluation test, the contact angle of the surface of the structure was 8 °, the average reflectance was 0.14%, the increase in reflectance by the wear resistance test was 0.65%, and the antifouling performance Was 3 on a three-point scale. These results are also shown in Table 1.

(Example 5)
Except that the output of the corona discharge treatment was 600 W, the same method as in Example 3 was repeated to form second irregularities on the first irregular surface, and the hydrophilic antireflection of Example 5 concerned A structure was obtained.
As a result of the same evaluation test, the contact angle of the surface of the structure was 9 °, the average reflectance was 0.14%, the increase in reflectance by the wear resistance test was 1.04%, and the antifouling performance Was 3 on a three-point scale. These results are also shown in Table 1.

(Example 6)
Except that the output of the corona discharger was set to 450 W, the same method as in Example 2 was repeated to form second irregularities on the first irregular surface, and the hydrophilic antireflection of Example 6 concerned A structure was obtained.
As a result of the same evaluation test, the contact angle of the surface of the structure was 34 °, the average reflectance was 0.12%, the increase in reflectance by the abrasion resistance test was 0.77%, and the antifouling performance Was "2" with a three-level rating. These results are also shown in Table 1.

(Comparative Example 1)
70% by mass of dipentaerythritol hexaacrylate (Toagosei Co., Ltd., M-400), 25% by mass of polyethylene glycol diacrylate, and 5% by mass of 1-hydroxycyclohexyl phenyl ketone (Ciba Specialty Chemicals, Irgacure 184) The resin composition mixed in the above was applied onto an acrylic resin film, and after pressing the resin composition using the mold used in the above examples, an ultraviolet ray with an integrated light amount of 3200 mJ / cm ² was irradiated from the film side. Curing was performed. This produced the film which provided the unevenness | corrugation similar to the 1st unevenness | corrugation of the said Example on the single side | surface side. And the same evaluation test was implemented by making this film into the structure of the comparative example 1 as it is, without giving a corona discharge process.
As a result, the contact angle of the structure surface is 8 °, the average reflectance is 0.15%, the increase in reflectance by the abrasion resistance test is 1.80%, and the antifouling performance is “3”, which is evaluated in three stages. Met. These results are also shown in Table 1.

(Comparative Example 2)
A corona discharge treatment is performed on the acrylic film provided with the first irregularities on one side, which are formed in a hexagonal close-packed arrangement of fine convex portions having a conical shape with a height of H = 390 nm, and used in each of the above examples. The structure of Comparative Example 2 was subjected to the same evaluation test as it was. FIG. 6 shows an electron micrograph of the uneven shape on the surface of the obtained structure.
As a result, the contact angle of the structure surface was 78 °, the average reflectance was 0.13%, the increase in reflectance by the abrasion resistance test was 0.67%, and the antifouling performance was “1”, which was evaluated in three stages. Met. These results are also shown in Table 1.

  As is apparent from the results shown in Tables 1 and 2, according to the embodiment of the present invention having the second unevenness smaller than the first unevenness on the surface exhibiting the light reflection preventing function. It was confirmed that the structure was excellent in antireflection performance, durability, and antifouling property (hydrophilicity).

On the other hand, it was found that the structure of the comparative example not provided with the second unevenness was inferior in durability or antifouling property.
In other words, Comparative Example 2 made of the same material as the above example has unevenness (first unevenness) having the same shape and dimensions, but has no second unevenness, and thus has low hydrophilicity and is prevented. It turns out that it is inferior to soiling. Further, in Comparative Example 1 in which the hydrophilicity of the material itself is increased by the addition of the hydrophilic material, even if only the first unevenness shows high hydrophilicity and excellent antifouling property, there is a difficulty in durability. It was confirmed that there was.

  On the other hand, in the examples, particularly in the hydrophilic antireflection structures according to Examples 2, 3, 4, and 6, it was confirmed that the balance between antifouling property and durability was excellent and these performances were compatible.

By increasing the number of corona discharge treatments from 1 to 5 (Examples 1 to 3), the height and pitch of the second unevenness increased and the surface area increased, thereby reducing the water contact angle. . Further, by increasing the power of corona discharge treatment (Examples 2 and 6, Examples 3 to 5), the water contact angle was similarly reduced, but reflection before and after the wear resistance test, which is an evaluation of durability. The rate change has increased.
The mechanism of this phenomenon is unclear, but by increasing the electric power of the discharge treatment, it is provided near the top of the first concavo-convex (the part where the friction cloth contacts in the wear resistance test) among the second concavo-convex. It is presumed that the shape of the product was locally increased, the structural strength was reduced, and the wearability was reduced.

1 1st unevenness 2 2nd unevenness

Claims (6)

  At least part of the surface having the first unevenness having a periodicity shorter than the wavelength of visible light is provided with second unevenness in which the interval and height difference between the unevenness is smaller than the first unevenness, and the contact angle with water is A hydrophilic antireflection structure characterized by being 80 ° or less.   The hydrophilic antireflection structure according to claim 1, wherein the uneven pitch on the first uneven surface has a pitch of less than 380 nm and an aspect ratio of 1.0 or more.   The hydrophilic antireflection structure according to claim 1, wherein a contact angle of the material constituting the uneven surface with respect to water is less than 90 °.   A hydrophilic antireflection structure comprising the hydrophilic antireflection structure according to any one of claims 1 to 3 on at least one surface of a substrate.   An article comprising the hydrophilic antireflection structure according to any one of claims 1 to 3.   The article according to claim 5, wherein the article is an automotive part.

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