Transparent photochromic article including an...

Details Transparent photochromic article including an... Transparent photochromic article including an...

1998-11-10

2001-01-16

Nguyen, Thong (Department: 2872)

Optical: systems and elements

Light interference

Produced by coating or lamina

C359S580000, C359S581000, C359S588000, C359S359000

Reexamination Certificate

active

06175450

ABSTRACT:

The present invention relates to transparent photochromic articles having anti-reflection surface coatings.
The transparent articles according to the present invention are preferably employed in the preparation of articles such as optical lenses, including spectacle lenses, ophthalmic or not, visors, shields, glass sheets, protective screens, and the like.
A well known difficulty of long standing in the art and in particular in the production of spectacle lenses, has been the dilemma of trying to achieve very good light transmission in the visible region (wavelength (&lgr;)=400 to 700 nm), whilst adequately protecting the eye from harmful light transmission, in particular from ultraviolet (UV) rays.
The prior art suggests that the characteristics of transmission of light through an article are improved by applying an anti-reflection coating, generally including a plurality of thin layers of suitable materials, respectively of a low and high index of refraction, which increase the transmission in the range of the visible radiation whilst simultaneously reducing the quantity of light reflected from the substrate.
To adequately protect the eye from solar radiation, the prior art suggests instead incorporating into the substrate, either internally or on the surface, one or more so-called photochromic compounds which are able to “darken” the substrate to reduce the transmission whenever they are activated from solar radiation in the UV range (350 to 400 nm approx.).
In fact, in their “activated” state such compounds pass from colourless to coloured effectively filtering light at a wavelength corresponding to visible light (approximately 400 to 700 nm).
All the attempts carried out in the prior art to obtain a photochromic substrate having an anti-reflection surface coating, have however, up to now, inevitably encountered the unavoidable effect of reflecting or absorbing light impinging upon the article in the UV range (the photochromic activity region) and thus causing the article not to darken as much as normally required.
Accordingly, it remains a deficiency of the prior art to provide a transparent article which includes an anti-reflection surface coating that simultaneously provides adequate transmission of visible light and adequate characteristics of photochromaticity when it becomes illuminated by sun light.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art.
In accordance with the present invention, it has been found that these desired characteristics may be simultaneously achieved by suitably combining the optical thickness of the layers forming the anti-reflection coating.
Accordingly, in a first aspect of the present invention there is provided a transparent photochromic article including
a transparent substrate including a photochromic material; and
an anti-reflection surface coating produced with a plurality of overlapping layers incorporating, alternatively a first and a second material having respectively higher and lower refractive indices, the anti-reflection coating including
a first layer including said first material having an optical thickness of approximately 20 to 45 nm;
a second layer including said second material having an optical thickness of approximately 25 to 45 nm;
a third layer including said first material having an optical thickness of approximately 220 to 250 nm; and
a fourth layer including said second material having an optical thickness of approximately 95 to 115 nm.
As used herein, by the term “transparent substrate”, we mean any form of transparent substrate, whether it be of glass or of plastic material.
As used herein, by the term “photochromic material” we mean a material that is able to reduce the quantity of the light transmitted by the substrate when exposed to solar radiation.
As used herein, by the term “optical thickness” we mean the thickness obtained by multiplying the physical thickness of the layer by the refractive index “n”, of the material forming the same layer, measured at a wavelength (&lgr;) of 500 nm.
After repeated tests, the Applicants have found that when the layers of the anti-reflection coating have an optical thickness which falls within the above mentioned ranges, the reflection of the incident radiation on the substrate is minimal in the wavelength range required to activate the photochromic mixtures incorporated in, or deposited on, the substrate (approximately 350 to 400 nm) and sufficiently reduced in the visible range (approximately 400 to 700 nm), so as to simultaneously provide adequate transmission and photochromaticity for the substrate.
In fact, in contradistinction to what has been taught in the prior art the Applicants have found that the mean reflectance at the external surface of the article in the UV range as a function of wavelength is not limited to greater than 4% of the incident radiation, and may be noticeably reduced and preferably is less than approximately 1% of the incident radiation.
As a consequence, the layers described in the present invention not only perform an efficient photoprotection action when exposed to solar radiation, but also present excellent characteristics of transmission of the light in non-activating radiation surroundings, i.e. in surroundings in which the article will tend to resume its unactivated state characteristics.
In accordance with the present invention, it has also been found that the same type of positive results may be achieved by varying the number of layers of the anti-reflection coating (and, that is, with a different optical structure), provided that the total optical thickness is maintained in the range of +/− approximately 10% of the four coating layers described above.
Accordingly, in a second aspect, the present invention provides a transparent photochromic substrate of the type mentioned above, wherein said anti-reflection coating includes
a first layer including said first material having an optical thickness of approximately 20 to 40 nm;
a second layer including said second material having an optical thickness of approximately 40 to 55 nm;
a third layer including said first material having an optical thickness of approximately 65 to 85 nm;
a fourth layer including said second material having an optical thickness of approximately 30 to 45 nm;
a fifth layer including said first material having an optical thickness of approximately 50 to 65 nm; and
a sixth layer including said second material having an optical thickness of approximately 110 to 135 nm.
The photochromic materials according to these aspects of the present invention may be selected from one or more of the group consisting of silver halides including mixed silver halides, anthraquinones, phthalocyanines, spiro-oxazines, chromenes, pyrans including spiro-pyrans and fulgides. The photochromic materials may be incorporated into the monomer formulation used to produce a polymer substrate layer or in the glass formulation used to produce a glass substrate or in coatings applied to substrates prior to the application of abrasion resistant or anti-reflective coatings.
Examples of preferred photochromic dyes may be selected from one or more of the group consisting of
1,3-dihydrospiro[2H-anthra[2,3-d]imidazole-2,1′-cyclohexane]-5,10-dione
1,3-dihydrospiro[2H-anthra[2,3-d]imidazole-2,1′-cyclohexane]-6,11-dione
1,3-dihydro-4-(phenylthio)spiro[2H-anthra′1,2-diimidazole-2,1′-cyclohexane]-6,11-dione
1,3-dihydrospiro[2-H-anthra[1,2-d]imidazole-2,1′-cycloheptane]-6,11-dione
1,3,3-trimethylspiro′indole-2,3′-[3H]naphtho[2,1-b]-1,4-oxazine]
2-methyl-3,3′-spiro-bi-[3H-naphtho[2,1-b]pyran] (2-Me)
2-phenyl-3-methyl-7-methoxy-8′-nitrospiro[4H-1-benzopyran-4,3′-[3H]naphtho][2,1-b]pyran
Spiro[2H-1-benzopyran-2,9′-xanthene]
8-methoxy-1′,3′-dimethylspiro(2H-1-benzopyran-2,2&

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