JPS584946B2 - Internal anti-reflection paint for optical glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating used to prevent harmful effects caused by reflection of light on the inner surface of optical components such as lenses and prisms made of optical glass.

Here, we will discuss internal reflection of a camera lens as an optical component.

FIG. 1 schematically shows a cross section of a camera lens.

In the figure, a represents a lens barrel, b represents an aperture, and C represents a lens.

Now, when external light 1 enters from the front surface of the lens, the end surface of the lens is roughened and has relatively large irregularities, making it look like ground glass, so the light is diffusely reflected as shown in 2, 3, and 4. .

Of these, for example, 2 travels toward the rear of the lens and causes so-called ghosts in the originally expected photographic image, or flare, which reduces the contrast of the image.

Further, the light passing through the optical path 4 enters the observer's eye from the front of the lens, causing the end face of the lens to shine and be recognized, which significantly reduces the commercial value of the photographic lens.

The internal reflection of optical glass, which is a problem in the present invention, refers to the phenomenon of generating reflected light as described in 2 and 3.4 herein.

The internal anti-reflection paint is a black paint applied to the end face of such a lens, and an enlarged sectional view of its application form is shown in FIG.

1 is external light, and 5 is an anti-reflection paint, which has the role of absorbing external light 1 and causing internal reflection.

Conventionally, ink or commercially available black paint has been used as this anti-reflection paint, but these have been extremely unsatisfactory in terms of internal reflection prevention performance.

In order to fully perform this function, it is desirable that the refractive index of the coating material be the same as that of the glass of the underlying lens, and that the coating material should contain the light absorber therein sufficiently densely.

However, the refractive index of optical glass ranges from less than 1.5 to 1.
While it is widely distributed to the point where it exceeds 8,
Since the paint component is an organic substance, the refractive index of the paint is in the range of 1.5 to 166 at most. Therefore, especially with high refractive index glass, light cannot be sufficiently guided to the inner anti-reflection paint layer, and the inner surface There was a problem that the reflection did not decrease as expected.

An object of the present invention is to provide a coating material with excellent internal reflection prevention performance.

Yet another object is to provide a coating with a high refractive index or a coating densely containing light absorbers.

Furthermore, it is an object of the present invention to provide a paint in which the spectral intensity of a small amount of internally reflected light remaining is averaged within the visible light range.

Still another object is to provide an internal antireflection coating that has excellent physical properties such as mechanical strength, adhesion, hardness, durability, and uniformity, and is inexpensive to manufacture.

Another object of the present invention is to provide a paint having a vehicle that is compatible with coal tar or coal tar pitch.

It is characterized by an internal antireflection coating for optical glass containing coal tar or coal tar pitch and a vinylidene chloride copolymer, which is a copolymer of vinyl ester or acrylonitrile.

A group including the present inventors has long taken up this problem of preventing internal reflection and has been researching countermeasures.

The first countermeasure considered is a method of absorbing so-called light seepage, which is based on the physical-optical interpretation of light reflection.

Figure 3 shows a schematic diagram of reflection. Light 1 entering the interface from glass C with paint 5 becomes reflected light 2 according to the law of reflection considered in geometrical optics, bounces off glass C layer, and is reflected internally. At this time, a part of the light seeps into the interior of the paint layer 5 as shown by the dotted line in the figure.

This seepage depth is considered to be about 1/5 of the wavelength of the light, considering the intensity distribution of the light.

Therefore, in order to sufficiently absorb this seeping light,
If light absorbers are arranged densely enough within the seepage depth, the seep light will be absorbed by them and the reflected light will be weakened. Conventionally, relatively large particles such as carbon black were used as light absorbers. In contrast, the group of the present inventors has invented a method of using dyes and pigments as light absorbers, which are sufficiently soluble in the paint vehicle and therefore dispersed down to the molecular order, and have developed a special method. Publication No. 47-32418, Special Publication No. 47-3 24. 1. It was disclosed as No. 9.

This method has made it possible to achieve an antireflection effect even if the refractive index of the antireflection paint vehicle is not sufficiently high.

By the way, the second method is to increase the refractive index of the paint.

As already mentioned, the refractive index of organic materials is generally at most 1.
．． 6, and it has been extremely difficult to find a material that exceeds this limit and still maintains practical physical and mechanical properties as a paint.

However, the inventors' group continued their intensive search and found that it has a refractive index of about 1.8, and is highly light-absorbing and is finely dispersed on the order of molecules so that it can absorb the light that seeps out in black color. We have found that coal tar or coal tar pitch as a material is extremely effective for our purposes.

However, coal tar or coal tar pitch does not necessarily have sufficient mechanical properties when used as a paint vehicle, and it is difficult to expect sufficient practical performance.

In order to put this into practical use, it is necessary to add a better vehicle component, but this will again cause a decrease in the refractive index of the coating film.

Therefore, a material with a high refractive index and sufficient compatibility with coal tar pitch is required.

It was technically extremely difficult to find a material that could overcome this difficulty, but copolymers mainly composed of halogenated styrene, polycyclic vinyl compounds, etc. ) Our group has proposed polymers containing heavy metal salts of unsaturated aliphatic carboxylic acids (Japanese Unexamined Patent Publication No. 10935/1983).

The present invention is based on the discovery of a more suitable vehicle component in this second method.

In order for an internal antireflection paint to fully exhibit its performance, it needs to be composed of many components, among which the paint vehicle plays an important role along with the light absorber.

As already mentioned, it is desirable for the internal anti-reflection paint to have a refractive index as high as that of glass, so ideally each component that makes up the paint should have a high refractive index, but all It is difficult for the refractive index to be the only one that has a conveniently high refractive index.

Among these, the first feature of the paint of the present invention is that coal tar or coal tar pitch is selected as the vehicle and light absorber.

Coal tar or coal tar pitch has a very complex composition, consisting mainly of aromatic compounds, especially fused polycyclic compounds, including many compounds such as anthracene, naphthalene, carbazole, chrysene, pyrene, and fluorene. Contains.

These compounds exhibit a refractive index as high as 1.8 or more, and together with the free carbon and pigment components they contain, exhibit black light absorption.

As described above, although coal tar or coal tar pitch is optically very suitable for internal antireflection coatings, it does not necessarily have sufficient performance as a coating vehicle.

In other words, the vehicle in a paint holds coloring components or light absorbers, various fillers for improving the mechanical properties of the paint film, and provides sufficient mechanical strength as a paint film, adhesion to the base, and the ability to maintain the paint film's properties. It must have the role of guaranteeing hardness, durability, etc.

However, as is clear from the above-mentioned components, coal tar, coal tar pitch, etc. are all composed of low molecular weight components, so they have weak mechanical strength, heat resistance, etc., and cannot form coatings with sufficient physical properties. I can't.

Therefore, it is necessary to improve the physical properties of the coating film by blending a vehicle component with excellent coating film properties into coal tar or coal tar pitch.

The performance required of this vehicle component is firstly to have a high refractive index, to minimize the decrease in refractive index obtained by coal tar or coal tar pitch, and secondly to minimize the decrease in refractive index obtained by coal tar or coal tar pitch.
The coating must have excellent adhesion, mechanical strength, heat resistance, and durability.

Furthermore, compatibility with coal tar or coal tar pitch is a critical requirement.

Blending materials with poor compatibility causes partial gelation, separation, aggregation, etc. in the paint state, and the paint cannot exist as a stable paint.

Furthermore, when such a paint is applied and dried, the surface of the paint becomes severely rough, and in some cases, a uniform paint film may not be formed even if sufficient film strength is not obtained, making it unsuitable for use as an internal anti-reflection paint. The present inventors have continued to conduct intensive studies on various polymeric materials in search of materials that meet these requirements, and have found that vinylidene chloride copolymers are suitable.

In general, vinylidene chloride homopolymer has relatively high crystallinity, so it has poor solubility and is not very useful.However, copolymerized vinylidene chloride with other vinyl compounds has good solubility in appropriate solvents. Although it has been put to practical use as a coating agent for packaging materials and as a paint base, no example has been found to date of its use focusing on its refractive index.

The present inventors have found that products using vinyl esters such as acrylic esters as copolymerization components with vinylidene chloride, and products using acrylonitrile have excellent compatibility with coal tar and coal tar pitch, and have a refractive index. It has been found that the antireflection rate is also relatively high, making it an excellent vehicle for internal antireflection coatings.

The smaller the so-called copolymerization ratio of the copolymer component to vinylidene chloride, the higher the refractive index, but the lower the solubility, making it difficult to form a paint.

Therefore, the copolymerization ratio of vinyl ester and acrylonitrile must be at least 2% by weight or more, but from the viewpoint of the refractive index, it is desirable to keep it to about 20% by weight or less.

Commercially available vinylidene chloride copolymers include the following.

Vinylidene chloride-acrylic acid ester type is Aron CX-8-2 (Toagosei Kagaku brand name) Vinylidene chloride-acrylonitrile type is Saran F-310, F-2
16, R-200, R-202 (Asahi Dow brand name), etc.

The next important component of paint is the light absorber.

As already mentioned, it is desirable for the light absorber to be dispersed as small as possible and packed sufficiently densely in the light seepage layer in view of the mechanism by which the internal antireflection performance is exhibited. In the vehicle structure with good compatibility, pitch is dissolved in the coating film on the order of molecules.

Therefore, the particle size is incomparable to carbon black, which has a particle size of several microns to several tens of microns, and is probably several hundred A0 or smaller, so it comes close enough to the light reflecting surface and the light seeps out. can be coordinated to

Furthermore, the absorber concentration can be further increased by adding, for example, an organic solvent such as an oil-soluble dye, a dye that is sufficiently soluble in the film, or another light absorber dissolved in the paint.

In particular, coal tar or coal tar pitch cannot be said to have sufficient performance, but since it has the function of a vehicle component, it acts as both a light absorber and a vehicle, increasing the density of the light absorber and creating a paint with high absorption efficiency. It can be seen that it is an extremely excellent material for

As is clear from the disclosure of the invention previously made by the inventors' group, the thickness of light seeping out is considered to be about 1/5 of the wavelength, so naturally, long wavelength light seeping out over a long distance. As it becomes larger and easier to absorb, the reflected light shifts to shorter wavelengths and takes on a bluish tinge.

Therefore, it is desirable to increase the blending ratio of a dye that absorbs bluish light in the composition of the absorber in the internal antireflection coating.

Specifically, for example, oil-soluble dye Oil Scarlet 308 (absorbs blue tinge) manufactured by Orient Chemical Co., Ltd., Oil Black HBB (black), Ouzor Black (black manufactured by Ciba Geigy), Neo Pomelo Black RE (manufactured by BASF), etc. can be used.

These vehicles and light absorbers are dissolved in an organic solvent to make a paint, but this solvent must also ensure the compatibility of the vehicle mentioned above and sufficiently dissolve the light absorber, which is the dye. Needless to say.

In particular, pinylidene chloride resins with low copolymerization ratios have poor solubility, and only limited solvents such as tetrahydrofuran and cyclohexanone can be used as solvents, but these solvents cannot be used as one component for copolymers of several percent or more. It also becomes soluble in mixed solvents, especially mixed solvents with ketone ester solvents.

However, coal tar or coal tar pitch is also relatively difficult to dissolve, and a wide variety of polycyclic compounds precipitate during dissolution or dilution, making it difficult to make into paints.

Therefore, the solvent for coal tar or coal tar pitch is often selected from among chlorinated solvents such as pyridine and methylene chloride. Fortunately, tetrahydrofuran and cyclohexanone, which are good solvents for vinylidene chloride resins, are often selected from coal tar or coal tar pitch. It was also found to be a good solvent for tar and coal tar pitch.

Therefore, it is preferable to use these common good solvents as essential components and to appropriately select a solvent for mixing from common solvents in consideration of the drying speed, cost, toxicity, etc. of the paint.

Internal anti-reflection paint is used in areas as shown in Figure 2, and its purpose is to prevent light reflection on the surface that is in close contact with the underlying lens, so the performance of the paint surface is of secondary importance, as with regular paints. Although it only has a meaning, the reflection of light on the upper surface of the lens barrel located within the lens barrel can also become a problem in some cases.

Therefore, it is necessary to reduce surface reflection as much as possible.
For this purpose, it is necessary to mix a so-called matting agent such as Aerosil (manufactured by Nippon Aerosil Co., Ltd.), which is a finely powdered silica gel, to form fine irregularities on the surface of the coating film to make the surface matte.

Other paint components such as antifungal agents for preventing mold from forming on the lens surface and inside the lens barrel may also be mixed, but this does not prevent the present invention from being realized.

The above-mentioned paint has the following weight composition in the solid content excluding the solvent.

The vinylidene chloride copolymer is 10 to 45%, the coal tar or coal tar pitch is 15 to 70%, and the light absorber is 3 to 40%.

Furthermore, the present invention does not place any restrictions on the method of manufacturing paint, and any method that is commonly applied to manufacturing paint can be applied.

That is, it can be manufactured by a commonly used method such as a ball mill, paint mill, or attritor.

The method of use will vary depending on the size of the object to be coated, but any of the methods used for regular paint application, such as brush application, roller application, or spray application with a spray gun, can be applied. be.

It is also within the range of common sense in the field of ordinary paints and coatings that it is necessary to slightly adjust the viscosity, paint solid content, solvent drying speed, etc. according to each application form, and this internal anti-reflection paint is no exception. do not have.

Regarding the performance and evaluation method of this internal antireflection paint and its coating film, methods already established in the technical field related to paints can be applied.

Among them, we particularly consider viscosity, drying time, surface reflectance,
We perform performance evaluations with particular attention to coating film adhesion, coating film hardness, temperature/humidity resistance, light resistance, etc., but given our original purpose, we pay particular attention to internal spectral reflectance. .

Here, the evaluation method of the internal spectral reflectance that we use will be explained with reference to FIGS. 4a and 4b.

Figures a and b are a plan view and a front view, respectively, schematically showing a Beckman spectrophotometer for measuring internal spectral reflectance.

In the figure, 11 is a light source.

12 is a spectrometer. Reference numeral 13 is a right-angled isosceles sample rhythm with a sand-sanded bottom surface, and the bottom surface is coated with internal anti-reflection paint 19.

14 is a reference prism whose bottom surface is not painted.

15 is a detector. 16 is a recorder.

17a is a half mirror. 17b is a mirror. 18 is a slit.

Measurements are made with this device as follows.

The light that exits the light source and becomes monochromatic light in the spectrometer is sent to half mirror 1.
At 7a, the light is split into both the sample and the reference, and the reflected light is guided again to the detector by a half mirror.

Although not shown in the figure, the intensity ratio of the reflected light from the sample is recorded on a recorder using a chopper mechanism and electrical processing.

The optical path is 70° relative to the normal to the paint surface, as shown in Figure 4b.
The detector detects the incident light at 100°.

In this way, the internal spectral reflectance is evaluated by measuring the percentage of the intensity of the reflection from the paint-coated surface to the reflection from the surface not coated with the paint for each wavelength of light.

The coordinates are shown as a chart with the measurement wavelength on the horizontal axis and the reflectance on the vertical axis, but in order to express numerical values more simply, 410 nm, 450 nm, 500 nm, 55
The reflectance at 5 nm, 600 nm, and 660 nm is read from the chart, and the average value is calculated and evaluated as the average internal reflectance.

A detailed explanation will be given below using examples.

EXAMPLE The materials shown in Table 1 were placed in a ball mill and mixed and dispersed for approximately 24 hours to prepare a paint.

In Table 1, Aron CX-8-2, Krehalon SOA,
Eslet C and Ryuron QJ-1 are approximately 30~
It was a solution with a solid content of 45%, and all other resins were in the form of solid powders.

The resulting paint was coated with optical glass LAK-01 as described above.
(Refractive index of 1.64) was coated on a prism and the average internal reflectance was measured.

Other coating film properties are measured values obtained by applying and curing the coating on a glass plate at room temperature and then curing for 1 hour at about 80°C.

A cross-cut tester was used for the cross-cut test, and a drawing tester was used for the drawing test, and both were judged according to the criteria of the Paint Inspection Association and evaluated on a 10-point scale.

Pencil hardness was measured using a pencil hardness tester according to JIS-K-5400 - General Test Methods for Paints.

Storage stability as a paint was evaluated as good if it did not cause any deterioration such as precipitation or separation during storage.

Note that Krehalon SOA used as a comparative example in this formulation is a vinylidene chloride/vinyl chloride copolymer manufactured by Kureha Chemical Industries.

S-LEC C is a vinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical.

Ryuron QJ-1 is a vinyl chloride/vinyl propionate copolymer manufactured by Tekkosha.

Furthermore, the paints of Examples 3 and 4 were applied to optical glasses having various refractive indexes along with conventionally available black paints, and the spectral average internal reflectances were measured. The results are shown in Figure 5. show.

In the figure, N1 is the paint of Example 4.

N2 is the paint of Example 5. N3 is an oil-based marker ink.

N4 is ink. N5 is a commercially available black epoxy paint.

N6 is a commercially available acrylic black paint.

The optical glass used in the measurement was BK-7 (refractive index 1.5 2
), LAK-0 1 (1.64), SF-4
(1.76), LaSF-03 (1.8 1)
It is.

As is clear from Table 1 and FIG. 5, the coating material according to the present invention had excellent internal reflection prevention performance and coating film properties.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a camera lens for explaining internal reflection. FIG. 2 is an enlarged sectional view of the end face of the lens. FIG. 3 is a schematic diagram of reflection showing the seepage of light. FIGS. 4a and 4b are a plan view and a front view, respectively, schematically showing a Beckmann spectrophotometer for measuring internal spectral reflectance. FIG. 5 is a graph showing the internal reflectance measurement results. 1...Incoming light. 2, 3, 4, 19...Inner reflected light. 5--・Internal anti-reflection paint. 13. One song sample prism. 14. Reference prism. a゜゜゜・・・lens barrel.

Claims (1)

[Scope of Claims] 1. An internal antireflection coating for optical glass, characterized in that it contains coal tar or coal tar pitch, and a vinylidene chloride copolymer that is a copolymer with vinyl ester or acrylonitrile. 2. The paint according to claim 1, wherein the solvent is tetrahydrofuran or cyclohexanone.