JPS595538B2 - Photochromic gradient lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photochromic eyeglass lens (absorption color change property: referred to as photochromic property in the industry, but photochromic property is mainly used herein) and a method for manufacturing the same.

In particular, the present invention relates to lenses with a continuous gradient of photochromic properties and methods of making the same.

Description of prior art Eyeglass lenses basically have three purposes: (1) Correction of visual defects; (2) Eye hazard protection; (3) protection against radiation; has.

This first objective is achieved by a lens-type transparent article with suitable refractive power.

The second objective is accomplished by (1) using impact resistant materials as the lens structure or (2) vortexing the glass lens to provide additional strength.

This method of increasing strength is known, for example, when glass is heated to a strain point (5tr).
This is a method in which the material is heated to a temperature higher than 100% and then rapidly cooled with an air stream or liquid.

An example of this method is described in US Pat. No. 3,768,992.

Another method of increasing strength is to create compressive stress across the lens surface.

An example of this is described in US Pat. No. 3,790,260.

Protection against ultraviolet, strong visible or infrared radiation is achieved by adding colorants to the glass batch, ie to the glass raw material.

Examples of this colorant are W and A. Weyl, Soc, Glas
s Technol,, 5heffield, Eng.
Book published by land1967, C0LOURED GL
It is described in ASSES (colored glass).

In the case of eyeglass lenses made of high molecular weight polymers, colorants are added to the raw material, similar to certain types of sunglasses that have been commercially available for many years.

It is also possible to color a colorless plastic lens by a surface coloring method.

This type of lens is commercially available from American Optical Company under the trade name "Tintolite."

Transparent glass lenses can also be manufactured using the so-called staining method, many examples of which are described in the above-mentioned books.
It can also be colored by ``cess''.

Various permanently colored lenses used for eyeglass lenses are manufactured by American Optical Company under the trade name "Truecolor".
"Crusite", "Cosmetan"
It is sold under `` and ' Calobar ''.

Permanently tinted or permanently dyed spectacle lenses have the disadvantage of low light transmission when used at low illumination levels, ie, in somewhat dark environments.

For example, it is of course dangerous to wear sunglasses while driving a car at night.

This drawback can be overcome to some extent by various commercially available glass or plastic lenses with photochromic properties.

Photochromic eyeglass lenses are, for example, U.S. Patent No. 319
No. 7296.

Although this lens is transparent to visible light, it becomes dark when exposed to actinic radiation, and its visible light transmittance drops to about 45% of its original value.

The decrease in transmittance of this lens is reversible and the half color time (hal
f-fading time) is 5 minutes or less.

Another conventional ophthalmic lens is that described in U.S. Pat. No. 3,197,296, which, expressed in weight percent, is 48-58 SiO2,6-10AA203°15-22B203.0.8-2.0Na20 , 2.4
-3.1 Li20, 20 on O-4, Li
The sum of 20+Na2O+ is 3.2-7.2, 4.
5-5.3 Pb0, 3-9BaO, 0-7,2Zr0
2.0.15-0.6Ag.

0.01-0.02CuO, 0,3-1°2C1,0-
1, OBr, 0-1. It utilizes OI and O-1,2F glass compositions, and in addition, for example, US Pat. No. 3,208,860; No. 3,548,060:
No. 594198; No. 3617316; No. 370338
No. 8; No. 3765913; No. 3795523; No. 3
No. 833511; No. 3834912; British Patent No. 12
75019, DE 2230506; and DE 2256775.

In addition to the above patent documents regarding photochromic glass, a glass containing uniformly dispersed silver halide is available from Chance-Pelkington, England, under the trade name "Reactolite".
There is a photochromic phosphosilicate glass commercially available from Cal GlassCo.

No patent documents regarding the detailed composition and manufacturing method of this glass have been published to date.

Photochromic glasses sensitized with silver halide are described in the following documents: W, H, Arm1stead and S, D, 5to.
okey: ”Photochromic Sil
1cate Glasses 5ensitizedb
y S 11ver Hal 1des”, 5CIEN
CE, Vol.

144 (1964) pp, 150-154; G, Gl
iemeroth and K.H.Mader:
“PhototropicQlass”, Ange
w, Chem, International, Edit, ,
Vol, 9 (1970) pp, 434-445; A.V., Dotsenko et al.: “AS
study of the effect of Copp
er Ions on the Reaxation
Properties of Photochromi
c Glasses”, Sov.

J, Opt, Technol,, Vol, 41 (
1974) pp.

395-397; R, J, Araujo: ” Photochrom
ic Glasses”.

Chapter 8 of the book PHOT
OCHROMISMedited by G,H,Br
own, Will ley Interscience
.

New York (1971) pp, 667-686;
H, Bach and Gliemeroth: ”
Phase 5 separation in Photo
ropic S 11ver -Hat ide -C
ontainingGlasses”, J, Am
er, Cer, Soc, (1971) pp.

43-44 These conventional glasses are considered to have the following points in common: 1. The component that produces photochromic properties is silver halide uniformly dispersed in the glass matrix; and 2. The resulting products require strict heat treatment as they develop photochromic properties.

These glasses also appear to differ in the composition of the base glass that serves as a carrier for the photochromic center.

General photochromic glass articles are described in US Pat. No. 3,208,860.

The photochromic article of this patent is made of silicate glass containing at least a portion of microcrystals of at least one silver halide selected from the group consisting of silver chloride, silver bromide, and silver iodide. , the crystal concentration is at least 0.005 vol.

In addition to glass articles with silver halide crystals dispersed throughout (
It has also been proposed to manufacture photochromic glass lenses by diffusing silver ions into a surface layer of a base glass containing a certain amount of halide ions, and then subjecting this to a specific heat treatment.

This article and method of manufacture are described in US Pat. No. 3,419,370.

It has also been proposed to make photochromic articles by providing phototropic coatings on substrates such as glass or plastic.

Articles of this kind are disclosed, for example, in U.S. Pat.
75th Annual Meeting of Ceramic Society (19
Paper published on May 2, 1973 (Cincinnati, Ohio), this will be discussed later” Reversible 0ptic
al Density Change Compo
J, Amer, C under the title “Site Layers”
era.

Soc, (1974), pp 332-335
described in a paper published in.

Photochromic lenses such as those described above overcome to some extent the drawbacks of permanently colored lenses.

Because of the reversibility of the photochromic effect, these lenses exhibit low transmission when exposed to ultraviolet or blue light, but regain high transmission in environments with low levels of activating radiation.

Glass lenses are more scratch resistant than plastic photochromic lenses and do not lose their photochromic properties during long-term use due to deterioration of the active ingredients.

Currently known photochromic lenses have the disadvantage that recovery of high transmittance takes several minutes.

This causes discomfort to the user when driving a car where the interior lighting level is low and the exterior lighting level is high.

It is desirable to reduce the light intensity to the driver's eyes while the driver is viewing the road and traffic conditions, while still being able to clearly see the instrument displays on the instrument panel with low illumination levels.

In fact, failing to do this is dangerous.

Other examples of this problem are (1) sudden changes in the intensity of the light source, or (2) sudden changes in illumination level that occur when the eyeglass wearer moves from a high-light environment to a low-light environment.

Similar drawbacks have been observed in permanently tinted lens wearers.

Some of the above drawbacks are overcome by using a lens whose transmittance varies continuously from the top to the bottom of the lens.

Lenses of this type with a permanent gradient of tint are currently commercially available.

These lenses are made by either progressively tinting a plastic lens or applying a varying-density colored coating onto a glass lens by vacuum deposition of an absorbing material.

Color gradients in plastic lenses are obtained by continuously or progressively varying the dye concentration absorbed by the lens.

For example, one method is to increase the concentration in the upper part of the lens and lower it in the lower part.

US Pat. No. 3,419,370 describes that a photochromic gradient across a glass body can be obtained by varying the time and/or temperature at which each portion of the glass body is exposed to an ion exchange medium.

According to this patented invention, the ion exchange column contains silver ions in all instances (see Table 2 of the patent specification).

This photochromic gradient is obtained by varying the concentration of silver ions diffusing into the glass.

It appears that the glasses according to this patent cannot be rendered photochromic without being subjected to a diffusion treatment in a silver-containing ion exchange bath prior to the heat treatment necessary to generate photochromic properties.

This glass paste composition does not contain silver ions.

There is no specific discussion in this patent regarding photochromic gradients in spectacle lenses.

In the opinion of the present inventors, the manufacturing method of spectacle lenses having photochromic properties as a whole can be summarized as follows: 1. Glass having the composition listed in Table 1 below is melted by the following known method. do.

2. A lens material, ie a lens blank, is made from the above glass by methods such as embossing or casting.

3. Apply controlled heat treatment to the lens product, 5〈dd
Silver halide grains with a diameter d in the range <50 mμ are produced.

The lower end of this range is necessary to produce photochromic properties, and the upper end is necessary to avoid undesirable light scattering in eyewear products.

The total concentration of silver halide grains homogeneously dispersed in the glass article must be at least 0.005% by volume.

In the opinion of the inventors, the method for producing glass products with a gradient in photochromic properties, such as those obtained by the method of US Pat. No. 3,419,370, can be summarized as follows: 1. General system, i.e. alkaline oxide- Person 1203-B
A batch of 203S t O2 with added halide is melted under conditions that retain the halide.

2. Make a lens blank from this glass by known methods such as embossing or casting.

3. Make a completed lens from this blank by grinding and polishing.

4. Contacting the finished lens with a source of silver ions at an elevated temperature, particularly those parts of the lens that require a high degree of photochromicity, are contacted with a higher silver concentration than those that require a lower degree of this property.

5. Carefully heat-treat the above-treated lens to grow silver halide crystals to a size not exceeding 50 mμ to avoid light scattering, which is necessary for photochromic properties but is inappropriate for eyeglass lenses.

SUMMARY OF THE INVENTION Non-photochromic ophthalmic lenses are made by embossing from glass containing all the components necessary to produce photochromic properties.

This glass is referred to as ``unnuclea''.
ted) Sometimes called photochromic glass.

This terminology is used solely for ease of explanation.

Of course, the submicroscopic nuclei necessary to generate silver halide grains are already present in the non-photochromic state of the glass.

In other words, the nucleus is so small that it cannot be seen with an optical microscope because it does not reflect light.

In numerical terms, the maximum dimension of this nucleus, that is, the maximum particle size, is 5 m.
It is less than μ.

In fact, as is known in the industry, these core particles are so small that they do not interact with visible light.

Although the inventors did not measure this particle size, it can be easily measured using an electron microscope, and a value of 5 mμ is adopted as a value meaningful to those skilled in the art.

The embossed material has not been subjected to the heat treatment necessary to produce photochromic properties.

A photochromic gradient is imparted by processing the embossed object or lens blank and exposing the lens blank to a temperature varying environment.

This exposure involves heating a portion of the blank to a temperature above the strain point of the glass but below its softening point, while other portions of the blank remote from said portion are maintained at a temperature below the strain point.

It has also been discovered that ophthalmic lenses made from non-nucleating glass embossments that have not been subjected to the special heat treatment required to produce photochromic properties can be processed into semi-finished or finished lenses with photochromic gradients across their surfaces. It was done.

In addition, so-called "integrated multifocal" glass lenses or "protruding step multifocal" glass lenses having desired properties, and variable power (
The design of glass lenses (with progressively varying magnification) is particularly suited to the practice of the present invention as these lenses can be given photochromic properties, thus imparting photochromic properties in the far-sighted part of the lens and photochromic properties in the near-sighted part. It has been discovered that it is also possible to avoid giving this property.

The present invention can be applied to all glass lens blanks or lenses.

In this lens and lens blank, the components necessary to produce photochromic properties are almost uniformly dispersed, but the silver halide is in an unnucleated state, meaning that the size of the particles is large enough to produce photochromic properties. Color everything that is smaller than the required thickness gold.

It is appropriate to use glass with a coefficient of thermal expansion of 60.70-7° C. to prevent thermal destruction of the lens or blank during heat treatment in a temperature gradient environment.

However, the invention is not limited to this type of glass.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The products and methods of manufacture according to the present invention will be better understood from the following description.

The transmittance T of the glass lens is 1 T = exp (- 1 ZO) is represented here = extinction coefficient, Zo1o - Lens thickness at the position measured in the light emitting line.

K is a function of the wavelength of the light, and is usually a constant for a constant wavelength due to the glass that makes up the lens.

Lens thickness Z.

are the two coordinates X and y in a plane perpendicular to the optical axis of the lens
is a variable.

The rate of change in Zo changes depending on the Rx (prescription) value of the lens.

Z for negative lenses.

is larger at the periphery than at the center, and is Z for positive lenses.

The center is thicker than the periphery. Therefore, the transmittance changes locally.

A strongly negative lens, for example a lens made of tinted glass, will be darker at the periphery than at the center.

The rate of change in T in this case is determined entirely by the shape of the lens required to achieve a particular prescription.

Generally Z. -Zo(X.y).

In the case of photochromic lenses, the extinction coefficient is time dependent and varies with wavelength and activating radiation intensity.

To simplify the explanation, we assume monochromatic activating radiation of constant intensity.

If t is the exposure time of this radiation, 1 increases with time, that is, it changes to some extent in precise measurements, but becomes constant after about 1/2 hour.

Therefore, the above equation (1) is - to 1(t)・Z.

T1(t)=e That is, the transmittance decreases with increasing time.

The saturation value of T, (t) after about 30 minutes is 30 to 45%, depending on the glass material and lens thickness.

The transmittance before exposure to activating radiation is usually 90% or more.

When the activating radiation is removed, the lens gradually returns to its original transmittance.

This process results in a time-dependent second extinction coefficient of 2 (t)
By introducing , it can be expressed as .

Therefore, the change in transmittance T2 with respect to time t is expressed by the following formula 7%: Therefore, the transmittance of a photochromic lens is generally: T (
t, x, y) −exp (−to 1(t)・Zo(X
, y)) where K i (t) − to 1 (t) between activating radiation exposure and K 1(t) = to 2 (t) after activating radiation removal Zo(X, y) is the vision correction determined by the prescription values required for each.

In order to obtain a photochromic gradient across the plane of the lens, the extinction coefficient must be a function of the spatial coordinates X and yl and time t: thus = K(t, x, y).

The transmittance through the lens at point (X, y) is: ]T(
t, x, y)-exp(-K(t, x, y) Zo(x
+y)), and in the case of a plan lens, it becomes simple as follows: T(t, x, y)-exp(-K(t, x, y)・Zo
) Zo=constant In order to obtain the extinction coefficient which depends on the coordinate position, i.e. the plane spatial position, as described above, US Pat.
The '370 invention utilizes a corresponding change in silver concentration to produce the silver halide crystals necessary to impart photochromic properties.

As mentioned above, this method can only be applied to finished lenses.

This method is also difficult to control and requires an additional step, ie, introduction of silver ions by diffusion.

Additionally, the method involves melting the glass in special conditions that retain sufficient halogen to form silver halide grains.

is necessary.

Prior researchers did not realize that all highly photochromic glass articles that utilize silver halide grains to obtain photochromic properties could be used to make articles with a gradient of this property.

In order to obtain the extinction coefficient of K(t, x, y) by a local change of 1 degree of silver, previous researchers melted the glass under special conditions and then applied the silver diffusion method.

On the other hand, the present inventors have proposed that silver halide particles with an appropriate particle size distribution be placed under strict control in an unnucleated glass that initially contains all the silver and halogen atoms uniformly distributed in the glass article. We succeeded in producing locally varying absorbance by generating

This desirable silver halide grain distribution is obtained by carefully exposing the glass article to a locally varying temperature environment.

This is possible with both lens blanks and finished lenses.

These lenses are made of a glass designated as ``advanced photochromic glass.''

When practicing the present invention, care must be taken to avoid thermal destruction of the lens or lens blank when exposed to locally varying temperature environments.

Glasses with low coefficients of thermal expansion, such as certain borosilicate glasses, are more suitable for the present invention than glasses with higher coefficients of thermal expansion, such as phosphosilicate glasses.

The coefficient of thermal expansion of borosilicate glass is approximately 30 to 60
It is in the range of 10-7/'C.

Other glasses commercially available as carriers or matrices for photochromic centers have coefficients of thermal expansion of 90 x 10-
7°C or higher.

The higher the coefficient of thermal expansion, the greater the thermal stress in the glass article when the article is exposed to a temperature gradient environment.

Example 1 A disk-shaped glass-embossed object of 8.5 mm in thickness and 6571!711 in diameter, that is, a lens blank, made of unnucleated photochromic glass having composition A shown in Table 1 below, was heated in the furnace shown in Fig. 1 of the attached drawings. and exposed to the temperature gradient shown in FIG. 2 for about 90 minutes.

The lens blank was removed from the oven and cooled to room temperature by inserting it between preheated insulating asbestos cloth.

This blank showed a photochromic gradient in sunlight.

This property returned to its original high-speed transmittance after being left at room temperature for about 2 hours after cessation of ultraviolet radiation (ie, sunlight).

A plan lens with a center thickness of 2.2 mm was made from this blank, and both sides were polished in the usual manner.

After edging this, it was fitted into the left eye frame of a metal frame sold by American Optical under the trade name "Quasar."

Another plan lens was made in the same manner and fitted to the right eye frame.

Both lenses were surface-strengthened by ion exchange, ie, placed in a sodium-potassium nitrate bath at 400°C, and then treated in a conventional manner.

These lenses were subjected to an impact test in accordance with FAD (United States Food and Drug Administration) recommendations and then mounted on frames.

The spectacle lens produced in this manner exhibited the desired photochromic properties that varied from the top to the bottom of the lens.

Example 2 The lens blank of Example 1 was made using the same process and ground to produce a -5.62 diopter unfinished lens.

This lens was framed and fitted into the left eye frame of the same type of frame.

Another lens was made in the same manner, ground to form a -4.75 diopter unfinished lens, and then edged to fit into the right eye frame of the same frame.

Both lenses were surface-reinforced and impact tested before being installed in the frame.

Practical use of these prescription ophthalmic lenses has demonstrated the advantages described in the Summary of the Invention above.

Example 3 Six blanks were made according to the method of Example 1 and processed in the laboratory furnace of FIG.

These blanks were ground and polished using commercial manufacturing equipment to create bifocal lenses with raised steps.

The Rx (prescription) values of these lenses were the prescription most commonly used for early presbyopia, ie, 0 diopter for hyperopia and +1 diopter for myopia.

These unfinished lenses exhibited the advantages described in the "Summary of the Invention" above, ie, the desired photochromic gradient.

Example 4 A plan lens with a single field of view and a center thickness of 3.4 mm was made from a photochromic glass blank having composition A in Table 1 below.

This lens is often used in a safety mounting frame.
Edged to 8imFV7 type.

This plan lens was subjected to the heat treatment of Example 1. This is then subjected to an air-cooling strengthening method commonly used in the safety eyewear industry.
After conducting an impact test according to ANSIZ-87, it was mounted on a plastic safety frame.

I made another lens using the same method and attached it to the same frame.

This safety eyewear exhibits the advantages described in the ``Summary of the Invention'' above.

Table 1 Composition by weight of non-nucleated glass used in the present invention ABCD E Si0 53.021.458.857.3 0.0
A720310.537.722.9 9.1 8.3
Zr022.00.00.0 0.0 1.3Li0
2.10.04.5 0.0 0.0Ba0
6.0 5.5 0.0 0.0 3.3Sr0
0.20.00.0 0.0 0.0Na20 0
．． 63.81.5 6.516.2NaF 1.
01,04.7 3.1 0.0NaC11,01,0
1,82,61,0Ag20 0.40.50.4
0.5 0.6Pb0 5.10.00.0 1.0
0.0Cu0 0.10.10.020.020.
02P OO,015,60,00,07,55 ABCD E B20318.04.82.518.661.8 20
0.08.60.0 0.0 0.0NaBr
O,00,00,81,30,0Mg0 0
．． 0 0.0 2.1 0.0 0.0 Colorants known in the industry may also be included.

These colorants are essentially neutral, ie, non-reactive with other glass components.

These are for example transition metal oxides such as Fe2O3, Cr2O3, CoO; and Nd203, Pr20
This includes certain rare earth oxides such as No. 3.

Example 5 Glasses B, C, D and E from the table above can also be used in the practice of this invention.

Although lenses were not actually made in the laboratory using the method of the present invention, these glasses are also encompassed by the present invention.

Lenses or lens blanks are made from these glasses as in Examples 1-4 above.

Paying attention to the strain point and softening point of each glass, heat insulators are placed to provide an appropriate temperature gradient in the longitudinal direction of the furnace.

Because of this temperature gradient, silver halide crystals grow in a controlled manner with a greater degree of freedom for nucleation in the upper part of the lens than in the lower part.

This is accomplished, for example, by heating the leading edge of the lens to a temperature above the strain point and below the softening point, and the opposite or trailing edge to a lower temperature.

After heating, the lens is cooled in an annealing furnace or wrapped in asbestos cloth to prevent thermal damage.

It is then attached to the frame by grinding, polishing, edging and fitting in the usual manner.

Harden to meet U.S. government standards by appropriate surface hardening methods.

Table ■ Examples of conventional silver halide-containing glasses that require heat treatment to impart photochromic properties Base glass system (main component) Basis Silicates U.S. Patent No. 3,208,860 Alumino-borosilicate No. 3,197,296 Bo-alumina -Alkaline earth No. 354806
Potassium silica No. 0 porium oxide No. 3594
No. 198 Borate No. 36173
No. 16 Lanthanum-Borate No. 37033
No. 88 Lanthanum-Alumina-Borosilicate No. 3765913 Alumina-Borosilicate No. 3795523 Base glass system (main component) Basis Alumina Potassium oxide-Borosilicate No. 3833511 Lead-Zinc-Alumina-Borate No. 3834912 No. Alumina-borophosphate British Patent No. 1275019 Alumina-borosilicate Reactolite
Analysis: The glasses of these documents can be used in the practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a suitable heat resistant support structure 10 for a laboratory furnace used in the practice of the present invention.

An elongated curved furnace body 12 is supported on the upper surface of the structure.

The rear end 13 of this furnace body is closed with bricks 20, forming a box with one side open.

This opposite end 14 can be freely closed with a fireproof shield 15.

An electric heating element (not shown) is arranged in a groove 16 formed on the inner surface of the furnace body 12.

This electric heating element is Heavy Duty Elec.
A model 808-104°850 watt manufactured by Tric Co., Ltd. was used.

Above the furnace body is a series of refractory bricks.

In the laboratory furnace described above, these bricks are 9 inch regular bricks, two of which have curved openings cut into the long sides.

These bricks are designed to provide a temperature gradient and are made by cutting openings of different diameters into bricks of the same shape.

Therefore, the second brick 21 is tightly attached to the back surface of the furnace body 12.

The second brick 21 is provided with a curved opening 22, and the third brick 23 is provided with a deeper curved opening 24.

The bricks 21 and 23 are therefore spaced at different distances from the furnace body 12.

As this distance gradually increases, the air flow rate changes and therefore the cooling effect of convection and radiation increases.

In this way a gradual change in temperature is obtained.

Of course, finer or larger temperature changes can be achieved by using thinner bricks and by reducing the step change in the air flow space.

This technique is well known in the refractory and ceramic industries.

In fact, many similar technologies are used to construct and operate tunnel kilns.

A tunnel kiln is a suitable facility for practicing the present invention, in which a conveyor carrying unprocessed lenses enters the kiln at one end and finished lenses are continuously discharged from the other end.

This lens movement path is perpendicular to the temperature gradient.

For example, a kiln or lehr is useful for mass production of lenses and lens blanks according to the present invention.

There is a relationship between the belt speed (■) and the heating zone where a temperature gradient exists.

The belt speed will vary depending on the desired photochromic gradient and the type of raw glass used.

Referring again to FIG. 1, the lens 30 is supported on a refractory brick 31 that serves as a support.

Since this drawing is drawn approximately to scale, one skilled in the art will be able to readily reproduce this laboratory furnace using the dimensions described below.

Table 1 below lists the parts for the furnace of FIG. 1 used to perform the repeated operations in Examples 1-4 above.

The support structure 10 has a length of 15" (38 crfL) and a width of 4
“(10c*) placed on the support table.

Legs are 2-! −/′×2−! The thickness 4 of the structure 10 using -''×1 small-sized bricks has two thicknesses.

This refractory brick is of standard type, 9" x 4" x 2 boxes.

The curved furnace body 12 has a length of 6" (15 crfL) and is made of bricks 23.
It protrudes 1" (2,5cffL) from.

The inner diameter of the exposed surface of the strut or beam forming the channel in which the heating element is disposed is 1".
1" = 21. The radius of curvature on the outside of the furnace body is ¥7, and the front brick is 24
The radius of each curved notch is 1.

The shield 15 is made of seven-point angle steel and has a rear extension leg of length 21.

Generally, the articles made with the present invention are lenses or lens blanks that have a gradual change in photochromic properties from top to bottom with the lens being fitted into a frame.

The oxide glass from which the lens or blank is made has a distribution of silver halide grains corresponding to at least 0.005 volumes of the glass.

The silver halide is selected from the group consisting of silver chloride, silver bromide and silver iodide.

The size of the silver halide grains in the finished lens is less than 5 mμ in at least part of the article and between 5 mμ and 50 mμ in the remainder.

Therefore, the particles in the upper part of the lens, commonly called the hyperopic part, are relatively large and gradually decrease towards the bottom, reaching about 5 mμ at the bottom.

As mentioned above, FIG. 2 is a diagram showing the temperature distribution in the furnace used for manufacturing the lenses of Examples to Example 4.

FIG. 3A shows the transmittance of the transparent lens having non-nucleation characteristics before the treatment in the furnace of FIG. 1, and FIG. 3B shows the transmittance after the treatment.

A preferred embodiment of the present invention is to prepare glass A of Table 1 in the furnace of FIG.
The temperature distribution used is the distribution shown in Figure 2.

The above describes changes in the grain size of silver halide grains.

Of course, the particle sizes described above, ie the gradual increase from 5 mμ to 50 mμ, are average particle sizes.

"Average par" here means that particles with a specific particle size are preferentially present.

Therefore, because the chemical reactions that cause particle growth cannot be precisely controlled, some particles within a given area will be larger than the average, while others will be smaller.

Further, although silver chloride, silver bromide and silver iodide have been explained, a mixture thereof may also be used.

In its broadest sense, the invention provides a localized change in photochromic properties from one edge of the lens to the other.

For example, when a lens is glued to a frame, in the case of a bifocal lens, the area adjacent to the upper edge will have a lower transmittance and the area adjacent to the lower edge will have a higher transmittance.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of a laboratory furnace used to process lens blanks at the temperature gradients required for the practice of the invention; FIG. Figure 1 shows the temperature distribution in the furnace used to produce photochromic properties in the nucleation glass, and Figure 3 shows the appearance of the plan lens,
The visible light transmittance of the cross-section of the lens before and after exposure to activating radiation (sunlight) for about 30 minutes is shown. 12... Furnace body, 15... Shield, 2
0,2L23... Firebrick, 30...
·lens.

Claims (1)

[Scope of Claims] 1. At least one silver halide selected from the group consisting of silver chloride, silver bromide, silver iodide, and mixtures thereof, containing at least 0.005 volume fraction in the total volume. A lens made of oxide glass, at least a part of which exhibits photochromic properties due to the presence of the above-mentioned silver halide particles, and the average particle size of the particles corresponds to changes in photochromic properties. The average grain size of the silver halide grains is small (about 5 mμ or less in some parts of the lens, and the average grain size gradually increases to about 50 mμ in the rest of the lens). , a photochromic gradient lens characterized in that it has a localized change in photochromicity progressively from one edge of the lens towards the remaining area.2 Claim 1, which is a type of lens blank for spectacles. 3. The lens according to claim 1, which is a type of spectacle lens selected from the group consisting of a safety lens, a variable magnification lens, a protruding focal lens, and a single vision lens. 4. The lens according to claim 2, which is a type of lens blank for spectacles in which only the upper part, that is, the far-sighted part exhibits photochromic properties. 6. The spectacle lens according to claim 4, which is a variable power lens type spectacle lens. 7. The spectacle lens according to claim 4, which is a spectacle lens of the variable power lens type. 7. The spectacle lens according to claim 4, which is a spectacle lens of the variable power lens type. A method for producing a glass spectacle lens exhibiting local changes in photochromic properties; at least one silver halide selected from the group consisting of silver chloride, silver bromide, silver iodide and mixtures thereof; making an oxide glass lens containing 0.005% by volume in the total volume; and providing the lens with a temperature above the strain point but below the softening point of the glass in an area adjacent one edge of the lens. The silver halide grains are heated for a sufficient time to grow to an average grain size of about 50 mμ, and in other areas, the average grain size of the silver halide grains is increased toward the area away from the edge. The process includes a step of locally changing the photochromic property by applying a heat treatment that gradually changes the temperature so that the 8 Based on oxide analysis standards: (wt%) Si02 53.0 A120310.5 Zr022.0 Li2O2,1 Ba0 6.0 8r0 0.2 Na20 0.6 N a F 1.0 NaCl 1. O Ag20 0.4 Pb0 5. I Cu 0 0.1 P2O30,0 B203 18.0 to 2O0,O N a B r 0. 8. A method according to claim 7 for producing glass lenses from a batch consisting of O M g 0 0.0. 9. The manufacturing method according to claim 7, comprising a heating step of exposing the lens to a temperature gradient environment of about 400° C. to 700° C. for about 90 minutes from about ICrrL to about 12CrfL at the front surface of the heating furnace. 10--A method according to claim 9, in which the temperature in the area remote from the edge does not exceed the strain point of the glass. 11. The lens is selected from the group consisting of silicates, borosilicate, and phosphosilicate, and at least one type of silver halide selected from the group consisting of silver chloride, silver bromide, and silver iodide. , at least 0.005 volumes of Ti as particles in the glass matrix.