Anti-reflection film and process for preparation thereof

Details Anti-reflection film and process for preparation thereof Anti-reflection film and process for preparation thereof

1998-01-15

2001-03-27

Dixon, Merrick (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

C428S213000, C428S142000

Reexamination Certificate

active

06207263

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a film having optical functions such as anti-glare properties. More specifically, the invention relates to a film with excellent optical characteristics which is suitable as an anti-reflection film on the surface of various displays of word processors, computers and TV sets, polarizing plates for use in liquid crystal display devices, lenses of sunglasses composed of transparent plastics, lenses of vision-correcting eyeglasses, optical lenses such as camera finder lenses, covers for various gauges, and window glasses of automobiles and electric trains.
Transparent base plates of glass, plastic or the like are used for displays of curve mirrors, rear view mirrors, goggles, window glasses, displays for personal computers and word processors, and various other displays for commercial use. One may see objects or recognizes visual information, such as characters or graphics, through these transparent base plates, or may observe images from a reflection layer through the transparent base plate of the mirror. In so doing, one may feel it difficult to discern the necessary visual information located in the transparent base plate, because the surface of the transparent base plate reflects light.
Techniques for preventing the reflection of light include a method of coating an anti-reflection coating on the surface of a glass or plastic material, a method of providing a super thin film of MgF
2
or the like or a vacuum deposited metal film about 0.1 &mgr;m thick on the surface of a transparent base plate of glass or the like, a method of coating an ionizing radiation curing resin on the surface of a plastic lens and forming a film of SiO
x
or MgF
2
on the coating by vacuum deposition, and a method of further forming a coating with a low refractive index on a cured film of an ionizing radiation curing resin.
The above-mentioned thin film of MgF
2
about 0.1 &mgr;m thick formed on glass will be described in further detail. This thin film as an anti-reflection film is required to prevent reflection of light completely and allow 100% transmission of light when incident light falls vertically on the thin film in the air. With a specific wavelength designated as &lgr;
0
, the refractive index of the anti-reflection film for this wavelength as n
0
, the thickness of the anti-reflection film as h, and the refractive index of the base plate as n
2,
the relations of the following Equations 1 and 2 must hold to fulfill the above requirements, as have been already known (Science Library, Physics=9 “Optics”, pp. 70-72, 1980, Science Ltd.):
n
0
=(n
2
)
½
  (Equation 1)
n
0
h={fraction (&lgr;
0
+L /
4
)}  (Equation 2)
The refractive index of glass n
2
=1.5, the refractive index of MgF
2
n
0
=1.38, and the wavelength of incident light &lgr;
0
=5500 Å (reference) are known. Substituting these values into Equation 2 yields about 0.1 &mgr;m as the optimal thickness h of the anti-reflection film.
Equation 1 tells that an effective way of preventing reflection of light 100% is to select a material in which the refractive index of a coating on the upper layer side is close to the square root of the refractive index of the lower layer laid under the coating.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an anti-reflection film for use in a display in which the surface of a transparent base plate prevents the reflection of light and transmits necessary visual information inside the transparent base plate, and enables an observer to clearly discern the visual information, when seeing objects or visual information, such as characters or graphics, through the transparent base plate, or observing an image from a reflection layer through the transparent base plate of a mirror.
The invention for attaining this object, as shown in
FIG. 1
or
2
, resides in an anti-reflection film
10
having an intermediate refractive index layer
3
, a high refractive index layer
2
and a low refractive index layer
1
formed in this sequence on a transparent base film
5
via a hard coat layer
4
, the anti-reflection film
10
comprising:
the low refractive index layer
1
comprising an SiO
x
layer;
the intermediate refractive index layer
3
constituted by a coating of a composition comprising a binder and ultrafine particles having a refractive index of 1.5 or more; and
the high refractive index layer
2
having electric conductivity; and
the anti-reflection film
10
having:
the relationship: 2.20>refractive index of the high refractive index layer>refractive index of the intermediate refractive index layer>refractive index of the low refractive index layer>1.40;
the thickness of each refractive index layer being 80 to 110 nm for the low refractive index layer, 30 to 110 nm for the high refractive index layer, and 50 to 100 nm for the intermediate refractive index layer; and
an optical film thickness D not larger than the wavelength of visible light (D=n·d where n is the refractive index of the intermediate refractive index layer and d is the thickness of the intermediate refractive index layer).
In the present invention, it is preferred that the anti-reflection film
10
is such that the hard coat layer
4
has irregularities on its surface in contact with the intermediate refractive index layer
3
, and the hard coat layer
4
is provided on the transparent base film
5
directly or via a primer layer
7
and/or an adhesive layer
9
, as illustrated in FIG.
6
.
Preferably, the anti-reflection film
10
is such that the intermediate refractive index layer is composed of 0.1 to 20 parts by weight of a mat material based on one part by weight of a thermosetting resin and/or an ionizing radiation curing resin, the mat material being selected from fine particles of one or more kinds selected from the group consisting of ultrafine particles of ZnO, TiO
2
, CeO
2
, Sb
2
O
5
, SnO
2
, ITO, Y
2
O
3
, La
2
O
3
, Al
2
O
3
, Hf
2
O
3
and ZrO
2
.
Preferably, the anti-reflection film
10
is such that the high refractive index layer and the low refractive index layer are each a layer provided by vacuum coating.
Preferably, the anti-reflection film
10
is such that the low refractive index layer is formed by plasma CVD involving the discharge of the starting gas of an organosiloxane, and the undecomposed organosiloxane remains in an amount of 0.1 to 0.2 part based on the SiO
X
.
Furthermore, an antifouling layer may be formed on the low refractive index layer.
A first process for preparation of the anti-reflection film of the present invention is as follows:
As shown in
FIG. 3
, an uncured hard coat layer
46
of the curing reaction type is provided on a transparent base film
5
. Then, an uncured intermediate refractive index layer
36
comprising a composition containing a binder and fine particles having a higher refractive index than the refractive index of the binder is coated on the transparent base film.
A laminate having a finely irregular, matted shaped film
6
laminated and shaped on the uncured hard coat layer and intermediate refractive index layer (see
FIG. 3A
) is heat-treated and/or ionizing radiation treated to cure the hard coat layer and intermediate refractive index layer.
From the cured laminate, the shaped film
6
H is stripped off to form an intermediate refractive index layer
3
having irregularities on the surface of a hard coat layer
4
as illustrated in FIG.
3
B.
On the cured intermediate refractive index layer
3
having irregularities, a high refractive index layer
2
is formed by vacuum deposition or sputtering. Further, a low refractive index layer
1
comprising an SiO
x
layer is formed by vacuum deposition, sputtering or plasma CVD to constitute an anti-reflection film
10
. This is shown in FIG.
3
C.
A second process for preparation of the anti-reflection film of the invention is as follows:
A matted shaped film
6
having irregularities on the surface is coated with an uncured intermediate refractive ind

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