Light diffusing film and its manufacture, a polarizing plate with a light diffusing layer, and a liquid crystal display apparatus

A light diffusing film is produced by preparing a paint by adding a light transmissive diffusing material comprising resin beads to a light transmissive resin, and coating the paint on one or both of the surfaces of transparent film substrate made of TAC, to produce a light diffusing layer. In the light diffusing film, the haze value on the surface of light diffusing layer is three or more, the difference between the haze value along the normal and that along the lines .+-.60.degree. apart from the normal is four or less, and the surface is practically smooth whose roughness is so adjusted as to give a surface roughness Ra of Ra.ltoreq.0.2 .mu.m. Application of such a light diffusing film onto a display panel inhibits scattering reflection which would otherwise cause the display to be whitish, reduces the variation of haze values which vary depending on the viewed angle, and thus improves display quality.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a light diffusing film and its manufacture, and a 
polarizing plate with a light diffusing layer, and a liquid crystal 
display apparatus which are suitably used for the display of a 
word-processor, computer, television set or the like, for a polarizing 
plate or an optical lens to be incorporated in a liquid crystal display 
apparatus, and as for a cover of various meters, and as the window-shield 
glass of an automobile or of a railway coach. 
2. Prior Art 
The display apparatus of a computer or the like as described above uses 
various light diffusing films to improve its visibility. 
Of such light diffusing films some depend on surface roughness to assume a 
light diffusing activity while others depend on a diffusing material 
contained in a resin film where the difference in refractive indices 
between the resin and the diffusing material is responsible for the light 
diffusing activity. 
When the light diffusing activity of a given film depends on its surface 
roughness, the light diffusing activity and the transparency of film vary 
according to from which angle it is seen, and thus the visibility thereof 
varies according to from which angle it is seen, which poses a problem. 
For example, with a display apparatus incorporating such a film, an image 
on display is quite visible when seen from front, but the same image 
becomes whitish when the visual angle becomes large. 
Such a light diffusing film containing a diffusing material in its resin 
substrate as described above is disclosed, to take as an example a film 
applied to a reflection type liquid crystal display apparatus, in Journal 
of Illumination Research Society MD-96-48 (1996) pp. 277-282. 
According to this disclosure, to obtain a reflection type liquid crystal 
display apparatus with a high contrast, it is important to design the 
apparatus such that the frontal light diffusing intensity is appropriately 
adjusted, and the backward light diffusing intensity is strongly 
suppressed, because such design is advantageous for the realization of a 
bright display and a high resolution, and further ensures the realization 
of a birefringent film which will compensate for the optical performance 
of liquid crystal which, in turn, will be beneficial for widening the 
effective view angle. 
The disclosure further asserts that, to achieve above object, it will be 
better to use a film where light diffusing occurs as a result of mismatch 
in refractive indices among film constituents, rather than a film where 
light diffusing occurs as a result of surface roughness, because with the 
latter film the backward light diffusing intensity will become so large as 
to lower the contrast. Namely, the disclosure recommends the use of a 
resin film which contains a diffusing material within, where light 
diffusing activity is invoked by the difference in refractive index among 
film constituents. 
The above-cited article in Journal of Illumination Research Society 
MD-96-48 states, utilizing the light diffusing theory offered by Mie and 
the theory by Hartel as a concept to support the design of an effective 
light diffusing film, it is possible to obtain a film with an optimum 
light diffusing activity, by appropriately adjusting the relative 
refractive index m between a diffusing material and a resin, and the size 
parameter .alpha. and particle density parameter Nd of diffusing material, 
and particularly it is useful for achievement of above purpose to keep the 
size parameter .alpha. at 10 or more. 
The size parameter .alpha. is .alpha.=2.pi.R/.lambda., and thus it depends 
on the diameter R of diffusing material (.lambda. represents the 
wavelength of light). 
Accordingly, if the size parameter .alpha. be 10 or more, inevitably the 
diffusing material will have a large particle size in association. If a 
diffusing material with such a large particle diameter consisting, for 
example, of spherical particles made of a plastics, is allowed to disperse 
in a transparent polymer (resin), the resultant film will become thick, 
and thus usable combinations of a diffusing material and resin for molding 
will be limited, or the film will develop a birefringence when molded by 
extrusion. These pose a problem when the film is put to practice. 
Further, when such a light diffusing film is applied to a liquid crystal 
display, it must be applied to the outside surface of liquid crystal 
panel, because, if it were applied to the inside surface of liquid crystal 
panel, it would interfere with the polarizing activity of the display 
unit. 
The alternative, conventional method whereby reflection of rays incident on 
the surface of a transparent substrate is prevented includes a method 
wherein an anti-reflection coat is applied on the surface of a glass or 
plastics substrate, a method wherein an ultra-thin film made of MgF.sub.2 
or other metals having a thickness of about 0.1 .mu.m is applied by vapor 
deposition on a transparent substrate made of glass or the like, a method 
wherein an ionizing-radiation setting resin is coated on the surface of a 
plastics acting as a plastics lens, and then another film made of 
SiO.sub.2 or MgF.sub.2 is plated by vapor deposition on the former, and a 
method wherein an ionizing-radiation setting resin is coated and on that 
hardened coat is applied a film with a low refractive index. 
However, for those conventional films to be given a light diffusing 
activity, only the outermost layer is available, and thus they can not 
have an anti-reflection layer if a light diffusing layer is prepared on 
the outermost layer. Hence, if such a light diffusing film is applied onto 
the surface of panel of a liquid crystal display apparatus, reflection of 
rays incident on the surface is not sufficiently prevented. 
Further, with a conventional reflex type liquid crystal apparatus, it is 
generally a custom to place polarizing plates on both surfaces of a liquid 
crystal cell, and to add to one of them a diffuse reflection plate having 
a roughened surface. 
However, when the diffuse reflection plate is placed on the outside surface 
of liquid crystal cell, a ghost display called parallax develops depending 
on the thickness of glass of liquid crystal cell, which greatly impairs 
the visibility of the display. 
To prevent the development of parallax, a method has been developed wherein 
only a single polarizing plate is used, and a metal electrode in the 
liquid crystal cell is allowed to act also as a light reflection agent. 
When the metal electrode assumes a light reflecting property by acting as 
a mirror, the visual angle becomes narrow, and brightness along the normal 
decreases. When the metal electrode assumes a light diffuse reflection 
property by having a roughened surface, it becomes difficult to control 
the orientation of liquid crystal, and the production processes become 
complicated. This poses a new problem. 
SUMMARY OF THE INVENTION 
The present invention has been performed in consideration of the 
above-mentioned existing problems, and an object of the invention is to 
provide: a light diffusing film which is thin, does not impose any 
restrictions on the selection of diffusing materials and resins, does not 
develop a birefringence, and is also applied in the interior of display 
panel, and its manufacture; and a polarizing plate and a display apparatus 
each with a light diffusing layer attached thereto. 
A further object of the present invention is to provide a light diffusing 
film which further includes an anti-reflection layer to sufficiently 
prevent the occurrence of reflection rays out of incident rays coming from 
outside, and its manufacture; and a polarizing plate and a liquid crystal 
display apparatus each with a light diffusing layer. 
The present invention attains the above-mentioned object by means of a 
light diffusing film which has, on at least one of the surfaces of a 
transparent film substrate, a light diffusing layer laminated which 
comprises a light transmissive resin containing a light transmissive 
diffusing material being different from the light transmissive resin in 
refractive index, wherein the haze value on the surface of light diffusing 
layer is three or more, the difference between the haze value along the 
normal and that along the lines having angles .+-.60.degree. apart from 
the normal is four or less, and Ra representative of the surface roughness 
is 0.2 .mu.m or less. 
The difference .DELTA.n in refractive index between the light transmissive 
resin and the light transmissive diffusing material of the light diffusing 
layer may be chosen so as to satisfy the inequality 
0.01.ltoreq..DELTA.n.ltoreq.0.5, and the average particle diameter of 
light transmissive diffusing material may be chosen so as to satisfy the 
inequality 0.1 .mu.m.ltoreq.d.ltoreq.5 .mu.m. 
The present invention attains the above-mentioned object by means of a 
light diffusing film which has, on at least one of the surfaces of a 
transparent film substrate, a light diffusing layer laminated which 
comprises a light transmissive resin containing a light transmissive 
diffusing material, wherein, between the light transmissive diffusing 
material and the light transmissive resin of the light diffusing layer, or 
on at least part of that interface, is inserted a layer having a lower 
refractive index than those of the light transmissive diffusing material 
and resin. 
The layer with a lower refractive index may be formed of air. 
The layer with a lower refractive index may be a coat applied on the 
perimeter of light transmissive diffusing material. 
Further, the haze value on the surface of light diffusing layer may be 
three or more, and the difference between the haze value along the normal 
to the surface and that along the lines .+-.60.degree. apart from the 
normal may be four or less. 
Still further, the transparent film substrate may be made of either 
triacetate cellulose or polyethylene terephthalate. 
The transmissive resin may have an bonding activity or adhesive activity. 
Still further, the light transmissive resin may be a ultra violet setting 
resin, and the light transmissive diffusing material may comprise melamine 
beads. 
Still further, the light diffusing layer may have, on at least one of the 
front and back surfaces, an anti-reflection layer including an optical 
thin film. 
To achieve above object, this invention provides a manufacture of the light 
diffusing film as above described which comprises the steps of choosing 
melamine beads as a light transmissive diffusing material and a UV setting 
resin as a light transmissive resin, applying the liquid light diffusing 
layer onto a transparent film substrate, and radiating UV rays thereupon 
to harden the light transmissive resin. 
To achieve above object, this invention provides a manufacture of the light 
diffusing film as above described which comprises the steps of converting 
the light transmissive diffusing material into beads, coating their 
perimeter with a material which, while the light transmissive resin is 
hardening, will become gas or adsorptive to the light transmissive resin, 
and applying that matter together with the liquid light transmissive resin 
onto a transparent film substrate to harden thereupon. 
Still further, to achieve above object, this invention provides a 
manufacture of the light diffusing film as above described which comprises 
the steps of coating the liquid light diffusing layer onto a transparent 
film substrate, overlaying a molding film thereupon whose surface has been 
so finely modified as to have a surface roughness of 0.2 .mu.m or less, 
and peeling off the molding film, after allowing the initially-coated 
layer to harden. 
Still further, to achieve above object, this invention provides a 
manufacture of the light diffusing film as above described which comprises 
the steps of applying a polarizing plate with laminated polarizing layers 
onto at least one of the surfaces of transparent film substrate, and 
applying a light diffusing layer on the other surface of transparent film 
substrate. 
An anti-reflection layer including an optical thin film may be laminated on 
either the polarizing layer or the light diffusing layer. 
Further, to achieve above object, this invention provides a liquid crystal 
display apparatus which has a liquid crystal panel, and a polarizing plate 
with a coat of light diffusing layer applied on the display surface of 
liquid crystal panel. 
The liquid crystal panel may be of reflex type which has, on its rear 
surface, a reflective member with a mirror-like reflective activity. 
This invention is based on a finding that, assumed that a light diffusing 
film includes a light diffusing layer consisting of a light transmissive 
resin containing a light transmissive diffusing material with a different 
refractive index, preparing the light diffusing layer such that the haze 
value of the surface be three or more, the difference between the haze 
value along the normal and that along the lines .+-.60.degree. apart from 
the normal be four or less, and the surface roughness Ra be 0.2 .mu.m or 
less, will make it possible to render the particle size of light 
transmissive diffusing material sufficiently small, and the display 
quality of, for example, liquid crystal display surface good to excellent, 
and to introduce the resulting light diffusing film in the interior of 
liquid crystal panel if required. 
This invention is based on another finding that, when between the light 
transmissive diffusing material and the light transmissive resin is 
inserted a layer which has a refractive index lower than those of the 
former two, the relative refractive index m between the light transmissive 
diffusing material and the light transmissive resin becomes large, which 
will make it possible to reduce the necessary add amount of light 
transmissive diffusing material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of this invention will be described in detail below with 
reference to attached figures. 
As shown in FIG. 1, the light diffusing film 10 representing Embodiment 1 
of this invention has, on one (upper one in the figure) of the surfaces of 
transparent film substrate 12, a light diffusing layer 18 comprising a 
light transmissive resin 16 containing a light transmissive diffusing 
material 14 wherein the haze value on the surface of light diffusing layer 
18 is three or more, the difference between the haze value along the 
normal and those along the lines .+-.60.degree. apart from the normal is 
0.7 or less, and the surface roughness Ra of light diffusing layer 18 is 
0.2 .mu.m or less. 
When the light diffusing layer 18 has a surface roughness Ra of 0.2 .mu.m 
or less as described above, it has a flatter surface than the conventional 
homologue which has a roughened surface, and thus it can greatly suppress 
diffuse reflections which may cause display to whiten. This will 
contribute to the realization of a clear display. 
Generally, the lower the haze value of light diffusing layer 18, the less 
blurred the display, that is, the clearer the display. However, unless the 
haze value were three or more, effects brought about by light diffusing 
would not be manifest, and a uniform display independent of visual angles 
would be impossible. Further, unless the difference between the haze value 
along the normal and that along the lines .+-.60.degree. apart from the 
normal were below four, the display would look blurred when viewed from an 
oblique angle, which is not desirable. 
To obtain a display which is clear, uniform independent of visual angles 
and less blurred when viewed from an oblique angle, with the present 
embodiment, the difference .DELTA.n between the refractive index of light 
transmissive resin 16 and that of light transmissive diffusing material 14 
both serving as the constituents of the light diffusing layer 18 was made 
to satisfy the inequality 0.01.ltoreq..DELTA.n.ltoreq.0.5, and the average 
particle diameter d of diffusing material to satisfy the inequality 0.1 
.mu.m.ltoreq.d.ltoreq.5 .mu.m. 
The reason why the difference .DELTA.n in refractive index was placed in 
above range is as follows. If the difference in question were made below 
0.1, it would be necessary for the light diffusing layer 18 to contain a 
greater amount of diffusing material in the light transmissive resin to 
develop a sufficient light diffusing activity, and then adherence of the 
light diffusing layer 18 to the transparent film substrate 12 would be 
impaired, and thus easiness with which the diffusing material can be 
coated would be damaged. On the contrary, if .DELTA.n were made over 0.5 
.mu.m, the content of light transmissive diffusing material 14 in the 
light transmissive resin 16 would become too meager to realize a uniform 
light diffusing layer 18. 
The reason why the average particle size d of light transmissive diffusing 
material 14 was placed in above range is as follows. If d were made below 
0.1 .mu.m, dispersion of the light transmissive diffusing material 14 into 
the light transmissive resin 16 would become so difficult that clumping of 
particles might result, and thus the formation of a uniform light 
diffusing layer would be impossible. On the contrary, if d were made d&lt;5 
.mu.m, the light transmissive diffusing material 14 would protrude from 
the surface, and ruin the uniform flatness thereof. 
The reason why the difference between the haze value along the normal to 
the surface of light diffusing layer 18 and the haze value along the lines 
.+-.60.degree. apart from the normal was made four or less is based on 
knowledge the inventors has obtained through experiments (see Examples and 
Tables described later). 
The preferred material of the transparent film substrate 12 includes 
transparent resin films, transparent resin plates, transparent resin 
sheets, and transparent glass. 
The transparent resin film may include triacetate cellulose (TAC) films, 
polyethylene terephthalate (PET) films, diacetyl cellulose films, 
acetatebutylate cellulose films, polyether sulfon films, polyacryl-based 
resin films, polyurethane-based resin films, polyester films, 
polycarbonate films, polysulfon films, polyether films, polymethylpentane 
films, polyetherketone films, (metha) acrylnitrile films, etc. Ordinarily, 
it may have a thickness of 25-1000 .mu.m. 
As a material of the transparent film substrate 12, TAC with no 
birefringence is particularly preferred, because it is possible with it to 
laminate a light diffusing film with a polarizing element coated 
thereupon, thereby to produce a polarizing plate with a light diffusing 
layer (described later), and further to obtain therewith a liquid crystal 
display apparatus excellent in display quality. 
In another aspect, as a material of the transparent film substrate 12, PET 
is particularly preferred, especially in cases where formation of the 
light diffusing layer 18 requires coating of many layers, and for this 
purpose the film substrate must have a sufficient resistance to heat, a 
mechanical strength, and a responsiveness to mechanical processing. 
The preferred light transmissive resin 16 serving as a constituent of light 
diffusing layer 18 may include following three kinds of resins: resins 
which will be set when exposed mainly to UV rays/electron beams, that is, 
ionizing-radiation setting resins; mixtures of an ionizing-radiation 
setting resin with a thermoplastic resin and a solvent; and thermosetting 
resins. 
The coat forming component of an ionizing-radiation setting resin 
composition may preferably include compounds with an acrylate functional 
group, such as comparatively low molecular weight polyester resins, 
polyether resins, acryl resins, epoxy resins, urethane resins, alkyd 
resins, spiroacetal resins, polybutadiene resins, polythiolpolyen resins, 
and olygomers or prepolymers of (metha) allylate homologues of compounds 
having multiple functional groups such as polyatomic alcohols, etc. The 
reactive diluent may include diluents containing a comparatively large 
amount of monomers with a single functional group such as ethyl (metha) 
acrylate, ethylhexyl (metha) acrylate, styrene, methyl styrene, N-vinyl 
pyrrolidone, etc., and of monomers with multiple functional groups such as 
polymethylolpropanetri (metha) acrylate, hexanediol (metha) acrylate, 
tripropyleneglicoldi (metha) acrylate, diethyleneglycoldi(metha) acrylate, 
pentaerythritoltri (metha) acrylate, dipentaerythritolhexa (metha) 
acrylate, 1,6-hexanedioldi (metha) acrylate, neopentylglycoldi (metha) 
acrylate, etc. 
Further, to make the ionizing-radiation setting resin composition into a UV 
ray setting resin composition, it may be added, as an initiator of 
photically induced polymerization, acetophenons, benzophenons, Michler's 
benzoyl benzoate, .alpha.-amyloximester, tetramethylthiurum monosulfide, 
thioxantones, and as a photo-multiplying agent n-butylamine, 
triethylamine, poly-n-bytylphosphine, etc. Particularly, with this 
invention it is preferred to add urethane acrylate as an olygomer and 
dipentaerythritolhexa (metha) acrylate, etc. as a monomer for mixture. 
Furthermore, a solvent drying resin may be added in addition to the 
aforementioned ionizing-radiation setting resin as a component of the 
light transmissive resin 16 which forms a constituent of the light 
diffusing layer 18. Mainly the solvent drying resin may include 
thermoplastic resins. The solvent drying thermoplastic resin to be added 
to the ionizing-radiation setting resin may include those used for general 
applications, but when a cellulose resin such as TAC is used as a material 
of transparent substrate film 12, the appropriate solvent drying resin may 
include cellulose resins such as nitrocellulose, acetylcellulose, 
celluloseacetate propionate, ethylhydroxyethylcellulose, etc., because the 
resulting coat will have a good adhesive activity and transparency. 
The reason why above solvent drying resin is advantageous is as follows. 
Assume that toluene is used as a solvent for such a cellulose resin. 
Toluene is a solvent ineffective to polyacetyl cellulose, which is usually 
a constituent of a transparent film substrate 12. Nevertheless, a coat 
including the solvent drying resin in question dissolved in toluene will 
retain a good adhesive activity to the transparent film substrate 12. In 
addition, because toluene does not dissolve polyacetyl cellulose or the 
constituent of film substrate, the surface of transparent film substrate 
12 will not become whitish, and retain its transparency. 
Further, addition of a solvent drying resin to the ionizing-radiation 
setting resin composition will bring a benefit described below. 
Assume that the ionizing-radiation setting resin composition is coated on a 
transparent film substrate with a roll coater having a metalling roll. A 
liquid resin membrane remaining on the surface of metalling roll flows in 
the course of time to form streaks and indentations, which may be 
transferred to the surface of a coat which may result in the formation of 
similar streaks and indentations thereupon. However, addition of a solvent 
drying resin to the ionizing-radiation setting resin will eliminate the 
possibility of development of such flaws on the coat surface. 
The method for hardening the ionizing-radiation setting resin composition 
may include any common methods routinely employed for hardening 
ionizing-radiation setting resin compositions using electron beams or 
ultraviolet rays. 
Hardening via electron beams may take place, for example, by the use of 
electron beams having an output voltage in the range of 50-1000 KeV, or 
more preferably 100-300 KeV emanated from any kind of electron beam 
accelerator such as Cockcroft-Walton type, van-de-Graaff type, resonance 
transformer type, insulating core transformer type, linear type, 
dinamitron type, radio wave type, etc. Hardening via UV rays may take 
place using UV rays emanated from a ultra-high voltage mercury lamp, high 
voltage mercury lamp, low voltage mercury lamp, carbon arc, xenon arc, 
metal halide lamp, etc. 
The thermoplastic resin to be added to the ionizing-radiation setting resin 
may include senor resins, urea resins, diallylphtalate resins, melamine 
resins, guanamine resins, unsaturated polyester resins, polyurethane 
resins, epoxy resins, aminoalkyd resins, melamine-urea co-condensed 
polymer resins, silicone resins, polysiloxane resins, etc. They may be 
used as appropriate in combination with a cross-linking agent, a 
polymerization initiator, a polymerization stimulator, a solvent, a 
viscosity adjuster, etc. if need be. 
The light transmissive diffusing material 14 to be added to the light 
diffusing layer 18 preferably includes plastic beads: particularly those 
that give a high transparency, and present a refractive index which is so 
different from that of matrix resin (light transmissive resin 16) as to 
satisfy the above relation. 
The plastic bead may include melamine beads (refractive index being 1.57), 
acryl beads (refractive index being 1.49), acryl-styrene beads (refractive 
index being 1.54), polycarbonate beads, polyethylene beads, polystyrene 
beads, vinylchloride beads, etc. The average particle size of these beads 
should be so chosen as to fall in the above range of 0.1-5 .mu.m. 
When the light transmissive diffusing material 14 is added, it also acts as 
an organic filler, and the organic filler readily sinks when mixed with 
the resin composition (light transmissive resin 16). To prevent the light 
transmissive diffusing material from sinking readily to bottom, a silica, 
etc. as an inorganic filler may be added. What should be noted in this 
connection is this: addition of an inorganic filler will be effective for 
preventing the organic filler from precipitating, but may give adverse 
effects on the transparency of resulting coat. Therefore it is 
recommendable to add an inorganic filler having the particle size, 
preferably, of 0.5 .mu.m or less to the light transmissive resin 16 at a 
concentration not exceeding 0.1 weight % so that it can prevent the 
precipitation of diffusing material, without inflicting any adverse 
effects on the transparency of resulting coat. 
When an inorganic filler to prevent the precipitation of organic filler is 
not added, it is necessary to stir the coat material thoroughly to 
evenness before it is coated onto the surface of transparent film 
substrate 12, because otherwise the organic filler might accumulate on the 
bottom. 
Generally, the ionizing-radiation setting resin has a refractive index of 
about 1.5, or nearly the same with that of glass. But its refractive index 
should be adjusted when its refractive index is smaller than that of light 
transmissive diffusing material 14. Adjustment for upping the refractive 
index in question is achieved by adding appropriate particles made of a 
substance having a high refractive index such as TiO.sub.2 (refractive 
index being 2.3-2.7), Y.sub.2 O.sub.3 (refractive index being 1.87), 
La.sub.2 O.sub.3 (refractive index being 1.95), ZrO.sub.2 (refractive 
index being 2.05), Al.sub.2 O.sub.3 (refractive index being 1.63) at such 
an amount as to be compatible with the distensibility of resulting coat. 
In the embodiment represented by FIG. 1, a light diffusing layer 18 is 
formed on one surface of (upper surface in the figure) of transparent film 
substrate 12. But, as shown in Embodiment 2 of this invention represented 
by FIG. 2, the light diffusing layer may be formed on both surfaces of 
transparent film substrate 12. 
Next, description will be given of a light diffusing film 30 of Embodiment 
3 of this invention as represented by FIG. 3. 
Production of this light diffusing film 30 consists of forming an 
anti-reflection layer 32 on the outer surface of light diffusing layer 18 
of light diffusing film 10 shown in FIG. 1, and laminating an adhesive 
layer 34 and a separator 36 in this order on the surface of transparent 
film substrate 12 opposite to the surface upon which the anti-reflection 
layer has been formed. 
The anti-reflection layer 32 is formed mainly to prevent rays coming from 
outside from being reflected at the display surface. 
The anti-reflection layer 32 contains an optical thin layer, production of 
which consists of applying a coat comprising an anti-reflection pigment, 
an ultra-thin film of MgF.sub.2 or the like with a thickness of about 0.1 
.mu.m, a metal plated film, or a SiO.sub.2 or MgF.sub.2 plated film 
prepared by vapor deposition. The thickness of film in question should be 
adjusted in the manner described below. 
Assume that incident light having a wavelength of .lambda..sub.0 
perpendicularly hits upon the thin film, the anti-reflection film has a 
refractive index of n.sub.0, and a thickness of h, and the substrate has a 
refractive index of n.sub.g. For the anti-reflection film to completely 
inhibit the reflection of the incident light, or, to completely transmit 
the incident light through itself, it is known that the anti-reflection 
film must satisfy the equations (1) and (2) described below (Science 
Library, Physics=9, "Optics," pp. 70-72, 1980, published by Science Co.). 
EQU n.sub.0 =.sqroot.n.sub.g (1) 
EQU n.sub.0 h=.lambda..sub.0 /4 (2) 
Namely, if refractives n.sub.0 and n.sub.g are larger than 1, n.sub.0 
&gt;n.sub.g never fails to stand. Accordingly, when an anti-reflection layer 
32 is added on the outside surface of light diffusing layer 18, it is 
necessary for the optical thin layer acting as the anti-reflection layer 
32 to have a refractive index n.sub.0 which is smaller than that of light 
diffusing layer 18. 
Generally, the light transmissive resin 16 constituting the light diffusing 
layer 18 has a refractive index of about 1.5, or the same with that of 
glass. To be compatible with the resin having such a refractive index, the 
optical thin layer acting as the anti-reflection layer 32 is preferably 
made of an inorganic material such as LiF (refractive index being 1.4), 
MgF.sub.2 (refractive index being 1.4), 3NaF.AlF.sub.3 (refractive index 
being 1.4), AlF.sub.3 (refractive index being 1.4), Na.sub.3 AlF.sub.6 
(cryolite; refractive index being 1.33), etc. 
As an alternative case, assume that the anti-reflection film is made of 
MgF.sub.2 having a refractive index of n.sub.0 =1.38, and incident light 
has a wavelength of .lambda..sub.0 =5500 .ANG. (reference). From equation 
(2), it is deduced that the best condition is obtained when the 
anti-reflection film has a thickness of about 0.1 .mu.m. 
If, for a given anti-reflection film 32, a light transmissive resin 16 
could not be obtained that would give a refractive index to satisfy 
equation (1) in relation to the refractive index of that anti-reflection 
film, it is necessary as described earlier to add fine particles made of a 
material having a high refractive index such as TiO.sub.2 to that resin, 
to raise therewith the refractive index of resulting mixture. 
Formation of the anti-reflection layer 32 is performed by choosing as 
appropriate one from general thin film forming techniques including, for 
example, vapor deposition in vacuum, sputtering, reaction sputtering, ion 
plating, electric plating, etc. 
The adhesive layer 34 implemented on the side of transparent film substrate 
12 opposite to the side upon which the anti-reflection layer 32 has been 
formed is used when the light diffusing film 30 is attached, for example, 
to a liquid crystal panel: the separator 36 is peeled off; the exposed 
adhesive surface of adhesive layer 34 is pressed against the liquid 
crystal panel; and then the light diffusing film 30 is fixed to the 
latter. 
The positional relation of the light diffusing layer 18 of light diffusing 
film 30 to the transparent film substrate 12 with respect to the 
anti-reflection layer 32 in FIG. 3 may be reversed as shown in the light 
diffusing film 30A in FIG. 4. 
Further, the light transmissive resin 16 may be made of an adhesive 
material, to make thereby the resulting the light transmissive resin 16 
also act as an adhesive layer. In such case, the adhesive layer 34 in FIG. 
4 may be dismissed. 
Next, description will be given of Embodiment 5 of this invention as shown 
in FIG. 5. 
Production of the light diffusing film 40 of Embodiment 5 consists of 
inserting, between the light transmissive resin 16 and the light 
transmissive diffusing material 14 constituting the light diffusing film 
10 of the aforementioned first embodiment represented in FIG. 1, a lower 
refractive layer 38 with a lower refractive index than those of the light 
transmissive diffusing material 14 and resin 16. 
Because other composition is the same with that of Embodiment 1, the same 
symbols are attached to corresponding parts, and further explanation will 
be omitted. 
When, between the light transmissive diffusing material 14 and the light 
transmissive resin 16, a low refractive layer 38 is inserted which has a 
lower refractive index than those of the former two, light passing through 
the light transmissive resin 16 enters the low refractive layer 38 and is 
then reflected from the surface of light transmissive diffusing material 
14, and thus a remarkable light diffusing effect is obtained. 
Further, in this particular embodiment, the light transmissive diffusing 
material 14 and the light transmissive resin 16 do not make direct contact 
with each other, and thus the difference in refractive index of the two 
does not pose a notable problem. 
The low refractive layer 38 may be formed of a gas, liquid or solid body, 
but when a gas such as air is employed, a remarkable light diffusing 
effect will be obtained because it has a low refractive index (refractive 
index being 1). 
When the light transmissive diffusing material 14 was made of melamine 
beads, and the light transmissive resin 16 of a UV setting resin, and the 
cross-section of light diffusing layer 18 was observed after hardening of 
the resin, it was found, although the reason remains unclear, that a space 
(low refractive layer) with a thickness of about 0.1 .mu.m exists between 
each of spherical melamine beads with a diameter of 1.5 .mu.m and hardened 
light transmissive resin 16. 
Alternatively, the light transmissive resin 16 may be made of a resin which 
will expand when being transferred from a liquid state to a solid state, 
such that, after hardening of the resin, a space comes into being around 
each of particles acting as the light transmissive diffusing material 14. 
As a further variation, the light transmissive diffusing material 14 may 
have its outer surface coated with a material which absorbs the hardening 
or hardened light transmissive resin 16. 
As a still further variation, the light transmissive diffusing material 14 
may have its outer surface coated with a material which has a smaller 
refractive index than those of light transmissive diffusing material 14 
and light transmissive resin 16 in advance such that the coat may act as a 
low refractive layer 38 later. 
In this case, the coating material may take any state chosen from liquid, 
gel and solid states when the light transmissive resin 16 has hardened. 
When, between the light transmissive diffusing material 14 and the light 
transmissive resin 16, is inserted a low refractive layer which has a 
smaller refractive index than those of the former two in the manner as 
stated above, the low refractive layer exerts such a remarkable light 
diffusing effect that the necessary amount of light transmissive diffusing 
material will become smaller than otherwise is possible. Through this 
device, it is possible to prevent the display from becoming whitish, 
suffering decolorization, and exhibiting a disturbed polarization which 
would otherwise occur as a result of the existence of excess diffusing 
material, and thus to ensure a clear display. 
Embodiment 5 represented in FIG. 5 as described earlier consists of the 
light diffusing layer 18 formed on one surface of transparent film 
substrate 12, and in the same manner as in Embodiments 2 to 4 represented 
in FIGS. 2 to 4, it may have a low refractive layer 38 inserted between 
the light transmissive diffusing material 14 and the light transmissive 
resin 16, and the resulting light diffusing film incorporating those three 
elements can take any composition out of 50, 60 or 60A of FIGS. 6A to 6C. 
Next, description will be given of Embodiment 1 of a polarizing plate with 
a light diffusing layer of this invention as represented in FIG. 7. 
As shown in FIG. 7, this embodiment concerns with a polarizing plate with a 
light diffusing layer 70 wherein an anti-reflection layer 44 is formed on 
one surface (upper surface in FIG. 4) of a polarizing layer 42 and a light 
diffusing layer 18 having the same constitution as above is formed on the 
other surface. 
The polarizing layer 42 has a three layered structure which contains a film 
between two transparent film substrates 45A and 45B made of TAC. The first 
and third layers are films made of polyvinyl alcohol (PVA) supplemented 
with iodine, and the second layer between the two is a film made of PVA. 
The anti-reflection layer 44 has the same constitution as the 
aforementioned anti-reflection layer 32 formed on the light diffusing film 
30. 
As TAC composing the transparent substrates placed on both outer surfaces 
of polarizing layer 42 has no birefringence, and thus does not interfere 
with the polarizing activity, TAC substrates do not interfere with the 
polarizing activity of films made of PVA and of PVA plus iodine even when 
they are overlapped with the latter. Hence it is possible by the use of 
such a polarizing plate with a light diffusing layer 70 to obtain a liquid 
crystal display apparatus which gives a high quality display. 
The polarizing element composing the polarizing layer 42 to be inserted 
into the polarizing plate with a light diffusing layer 70 may be, besides 
the PVA film described above, polyvinylformal film, polyvinylacetal film, 
ethylene-vinylacetate copolymerized saponized film or etc. 
When individual films are placed one over another to form the polarizing 
layer 42, it is better to saponize TAC films in advance because such 
treatment will improve the adhesive activity of those films, and reduce 
accumulation of static electricity thereupon. 
Next, description will be given of the process necessary for the formation 
of light diffusing layer 18 with reference to FIG. 8. 
On a transparent film substrate 12 shown in (A) of FIG. 8, is applied a 
light transmissive resin 16 supplemented with a light transmissive 
diffusing material 14 as shown in (B) of FIG. 8; on the top of coat is 
laminated a finely roughened molding film 46 which has a surface roughness 
of Ra=0.2 .mu.m or less such that the film comes into a close contact with 
the underlying coat (see (C) of FIG. 8); next, when the light transmissive 
resin 16 is made of an electron-beam or UV ray setting resin, an electron 
beam or UV rays as appropriate is radiated onto the resin through the 
molding film 46; or when the resin is a dissolved, dried type resin, it is 
heated to harden; and the molding film 46 is peeled off from the hardened 
light diffusing layer 18. 
Adoption of this process allows the formation of a light diffusing layer 18 
which, even though generally having smooth surfaces, has one surface so 
finely modified as to assume a surface roughness of Ra=0.2 .mu.m or less 
which corresponds to the surface roughness of molding film 46. 
Hence, the light transmissive resin layer formed through above process on 
the light diffusing layer 18 will have a smoother surface than the same 
would have if it were simply coated on the latter without resorting to 
above process. 
The light diffusing layer 18 may be placed above the polarizing layer 42, 
as shown by a polarizing plate with a light diffusing layer 80 in FIG. 9, 
that is, just inside of the anti-reflection layer 44. 
Further, as indicated by a polarizing plate 82 with a light diffusing layer 
in FIG. 10, a third TAC film 45C may be placed inside of the 
anti-reflection layer 44; just inside of this TAC film 45C may be 
introduced a light diffusing layer 18; and the light diffusing layer 18 
may be further laid, through the bonding activity of adhesive layer 34 
inserted in between, onto TAC film 45A. 
Furthermore, as indicated by a polarizing plate 84 with a light diffusing 
layer of FIG. 11, a phase difference layer 86, an adhesive layer 34 and 
TAC film 45C in this order when counted from the side of TAC film 45B, may 
be inserted between TAC film 45B and the light diffusing layer 18 of the 
polarizing plate 70 with a light diffusing layer 70 in FIG. 7. 
With regard to the polarizing plate with a light diffusing layer as 
represented by Embodiments of FIG. 7 and FIGS. 9 to 11, the light 
transmissive diffusing material 14 which constitutes a part of light 
diffusing layer 18 may have a low refractive layer inserted between the 
light transmissive diffusing material 14 and the light transmissive resin 
16 as shown by Embodiments of FIGS. 5 and 6. 
Polarizing plates with a light diffusing layer 88, 90, 92 and 94 
corresponding with the polarizing plates with a light diffusing layer 70, 
80, 82 and 84 of FIG. 7 and FIGS. 9 to 11 are shown in FIGS. 12A and 12B, 
and FIGS. 13A and 13B. 
Because other composition is the same with that of polarizing plates with a 
light diffusing layer shown in FIG. 7 and FIGS. 9 to 11, the same symbols 
are attached to corresponding parts, and further explanation will be 
omitted. 
Next, explanation will be given of embodiments embodying liquid crystal 
display apparatuses of this invention as represented by FIGS. 14 to 16. 
The liquid crystal display apparatus 100 shown in FIG. 14 is a transmission 
type liquid crystal display apparatus which consists of a polarizing plate 
with a light diffusing layer 102, a liquid crystal panel 104 and a 
polarizing plate 106 placed one over another in this order, and further 
contains a back light 108 on the rear surface of polarizing plate 106. 
FIG. 15 shows a reflection type liquid crystal display apparatus 110 which 
is applied from outside to a relevant system. With this liquid crystal 
display apparatus 110, instead of the back light as used in said liquid 
crystal display apparatus 100, a reflection plate 112 is placed in close 
contact with the polarizing plate 106. 
FIG. 16 shows a reflection type liquid crystal display apparatus 120 
containing an internal reflection electrode incorporating the method of 
this invention. This liquid crystal display apparatus 120 contains a 
reflection electrode 116 within a liquid crystal cell 114 of a liquid 
crystal panel 104, which also acts as an electrode of reflection plate. 
The polarizing plate 106 and reflection plate 112 of liquid crystal 
display apparatus in FIG. 15 are omitted in this embodiment. 
The mode how liquid crystal exists in the liquid crystal panel 104 of 
liquid crystal display apparatuses 100, 110 and 120 may take any one 
chosen from twist nematic type (TN), super twist nematic type (STN), 
guest-host type (GH), phase conversion type (PC), polymer dispersing type 
(PDLC), etc. 
Further, the driving mode of liquid crystal may be of simple matrix type or 
of active matrix type, and when it is of active matrix type, the driving 
occurs in TFT or MIM mode. 
Furthermore, the liquid crystal panel 104 may of color type or of 
monochromatic type. 
EXAMPLES 
Next, Examples of this invention will be described below. 
Table 1 list the results obtained from Examples 1 to 11 representing light 
diffusing films prepared according to this invention in comparison with 
comparative examples 1 to 3 representing similar light diffusing films 
prepared according to conventional techniques: the test films were 
attached to a liquid crystal display so that one can evaluate whether 
their attachment may improve the quality of display when the display is 
visually inspected from a distance 30 cm apart from the display surface. 
TABLE 1 
______________________________________ 
Trans- 
Production Ra Haze; parency; 
Display 
method; (.mu.m) 
0.degree. 
60.degree. 
0.degree. 
60.degree. 
quality 
______________________________________ 
Example 1; 
A 0.038 12.2 12.4 98.6 98.9 Good 
Example 2; 
A 0.051 36.0 37.2 94.4 94.9 Good 
Example 3; 
A 0.062 60.6 64.2 87.4 87.9 Slightly 
whitish 
Example 4; 
A 0.048 16.7 17.3 97.4 97.8 Good 
Example 5; 
A 0.042 17.8 18.3 98.1 98.6 Good 
Example 6; 
A 0.052 19.2 19.7 97.8 98.3 Good 
Example 7; 
B 0.048 24.1 24.6 96.2 96.7 Good 
Example 8; 
A 0.041 18.9 19.2 98.1 98.6 Good 
Example 9; 
A 0.052 23.3 23.8 96.8 97.1 Good 
Example 10; 
A 0.049 35.2 36.0 95.6 95.9 Slightly 
uneven 
coloration 
Example 11; 
A 0.055 36.9 37.6 93.9 94.5 The best 
Comparative 
A 0.497 42.3 72.1 47.2 25.9 Whitish 
example 1; display 
Comparative 
A 0.042 2.7 2.8 99.1 99.2 Inadequate 
example 2; light 
diffusing 
Comparative 
A 1.320 65.4 86.3 33.8 17.6 Whitish 
example 3; display 
______________________________________ 
From Table 1, it is obvious that, when the light diffusing layer has a 
surface roughness of Ra=2 .mu.m or less, and its haze value is three or 
more, and haze value along the normal to the surface of light diffusing 
layer differs by 0.7 or less from that of the lines .+-.60.degree. apart 
from the normal, the resulting panel gives a display good or excellent in 
quality, and that, if a panel giving a slightly whitish display is 
tolerated, the face plate with a light diffusing film whose haze value is 
0.7 or less will also fall within the tolerable limit. 
The manner how above evaluation was performed was as follows. 
Production of Examples 1 to 9 proceeded as follows: TAC film was used as a 
material of transparent film substrate; and on this film was coated a 
paint containing melamine beads, acryl beads or acrylstyrene beads as 
shown in Tables 2 to 4 as a light diffusing material, and a resin 
composition described below. 
TABLE 2 
______________________________________ 
Melamine beads, weight parts. 
Average particle diameter: 1.2.mu. 
______________________________________ 
Example 1 1.11 
Example 2 3.89 
Example 3 7.41 
Comparative example 1 
0.20 
______________________________________ 
TABLE 3 
______________________________________ 
Melamine beads; 
Average particle size; (.mu.m) 
Weight parts 
______________________________________ 
Example 4 0.1 1.62 
Example 5 0.3 1.85 
Example 6 0.6 1.79 
Example 7 5.0 3.21 
______________________________________ 
TABLE 4 
______________________________________ 
Diffusing Refractive 
Average particle 
Weight 
material; index; size (.mu.m); 
parts 
______________________________________ 
Example 8 
Acryl beads 
1.49 2.0 30.0 
Example 9 
Acryl styrene 
1.54 2.0 36.0 
beads 
______________________________________ 
UV setting resin: pentaerythrytolacrylate, 100 weight parts; 
Photo-polymerization initiator: 3 weight parts; 
Cellulose propionate: 1.25 weight part; 
Leveling agent: silicone, 0.1 weight part; and 
Organic solvent: toluene, 130 weight parts. 
The UV setting resin has a refractive index of 1.50. 
For Example 10, PET was used instead of TAC as a material of transparent 
film substrate, and other conditions were the same with those of Example 
2. 
Production of Example 11 proceeded as follows: on the top of light 
diffusing layer of light diffusing film of Example 2 was deposited 
MgF.sub.2 (refractive index being 1.38) by vapor deposition to form a thin 
film of magnesium fluoride having a thickness of 900 .ANG., and therewith 
a light diffusing film having an anti-reflection layer in the same manner 
as the embodiment of FIG. 3 was obtained. 
Examples 1 to 11 were produced by either method A or B as shown in Table 1. 
Method A consists of preparing a light diffusing paint from a resin 
component and a light diffusing material as described above, coating the 
paint on a film substrate by the gravure reverse method such that the 
resulting coat has a thickness of 20 .mu.m/dry, maintaining the film at 
70.degree. C. for two minutes to evaporate the solvent to dryness, and 
passing the film under a UV radiation unit with an output of 240W at a 
rate of 20 m/min, thereby allowing the resin to harden. 
Method B consists of coating a light diffusing paint on a film substrate by 
the gravure reverse method such that the resulting coat has a thickness of 
20 .mu.m/dry, maintaining the film at 70.degree. C. for two minutes to 
evaporate the solvent to dryness to produce a coated film, laminating a 
PET molding film with smooth surfaces (whose surface roughness Ra is 
Ra.ltoreq.2 .mu.m) onto the coated film such that the finely roughened 
surface of molding film gets in close contact with the coat, passing the 
film assembly under the UV radiation unit with an output of 240W at a rate 
of 20 m/min, and then peeling off the molding film to produce a light 
diffusing film with a light diffusing layer whose surface is smooth. 
Production of Comparative example 1 consisted of preparing a light 
diffusing paint by mixing a resin component described below and melamine 
beads listed in Table 2, and coating the paint on a TAC film serving as a 
transparent film substrate. 
UV setting resin: urethaneacrylate, 100 weight parts; 
Photo-polymerization initiator: 3 weight parts; and 
Organic solvent: toluene, 130 weight parts. 
Method C by which Comparative example 1 was produced was as follows. 
A light diffusing paint was coated on a film substrate by gravure reverse 
method such that the resulting coat has a thickness of 20 .mu.m/dry; a PET 
molding film whose surfaces had been finely roughened was laminated onto 
the coated film such that the finely roughened surface of molding film got 
in close contact with the coat; the film assembly was passed under the UV 
radiation unit with an output of 240W at a rate of 20 m/min; and then the 
molding film was peeled off to produce a light diffusing film with a light 
diffusing layer whose surface is finely roughened. 
Comparative example 2 was a light diffusing film obtained under the same 
conditions as in Examples 1 to 9 except that it incorporated a diffusing 
material as listed in Table 2. 
Comparative example 3 was a light diffusing film obtained under the same 
conditions as in Example 7 except that it was produced by method A. 
Results of surface roughness as listed in Table 1 were obtained after the 
profile along the middle line of a given light diffusing film had been 
traced with a meter (Surfcoder AY-31, Kosaka Research Institute), and 
surface roughness were averaged to give an average surface roughness Ra. 
Acquisition of haze values and transparency values consisted of using a 
meter (Haze card plus, Toyo Fine Machination Co.) according to the 
"Standard testing method for determination of haze and light transmission 
of transparent plastics," ASTMD1003. 
Next, light diffusing films each having a low refractive layer 38 between a 
light transmissive diffusing material 14 and a light transmissive resin 16 
were attached to a liquid crystal display in the same manner as described 
above; the display quality was visually evaluated from a distance 30 cm 
apart from the display surface; and the evaluation results are listed in 
Table 5. 
TABLE 5 
__________________________________________________________________________ 
Diffusing material, 
Anti- 
Diameter, Weight 
reflection 
Reflection Contrast 
Haze 
Refractive index 
parts; 
layer 
(%); Color ratio; 
0.degree. 
60.degree. 
Display 
__________________________________________________________________________ 
quality 
Example 
1 Melamine; 
1.11 
Absent; 
14 OK 79 12.2 
12.4 
Slightly dark 
1.2 .mu.m 1.57 
2 Melamine; 
3.89 
Absent; 
33 OK 62 36.0 
37.2 
Good 
1.2 .mu.m 1.57 
3 Melamine; 
7.41 
Absent; 
61 Slightly yellowish, 
55 60.6 
64.2 
Slightly low 
1.2 .mu.m 1.57 contrast 
4 Melamine; 
3.89 
present; 
30 Slightly bluish, 
67 36.9 
37.6 
Good 
1.2 .mu.m 1.57 but acceptable; 
Comparative 
example 
1 Melamine; 
0.20 
Absent; 
1.6 OK 91 2.7 
2.8 
Dark, inadequate 
1.2 .mu.m 1.57 light 
2 Acryl; 7.69 
Absent; 
2.2 OK 88 2.5 
2.6 
Dark, inadequate 
1.2 .mu.m 1.49 light 
3 Acryl; 36.0 
Absent; 
19 Slightly yellowish, 
43 17.3 
17.7 
Low contrast 
1.2 .mu.m 1.49 
__________________________________________________________________________ 
Substrate: TAC 
Determination of contrast ratio as listed in Table 5 was achieved, for a 
white/black display, by measuring brightness changes with a brightness 
meter (BM-7, Topcon) and by calculating the ratio of brightness of white 
display against brightness of black display, that is, by utilizing the 
equation: (brightness of white display)/(brightness of black 
display)=contrast ratio. 
The liquid crystal display used for the measurement was a reflection type 
liquid crystal display having a reflection plate acting as a mirror. 
Determination of the reflection of a given film consisted of, as shown in 
FIG. 17, placing a light source 1 such that light therefrom is incident on 
the surface of liquid crystal display apparatus 110 or 120 at an angle of 
30.degree. apart from the normal to the surface, measuring light reflected 
back along the normal with a brightness meter 2, comparing its intensity 
with that from a standard white reflection plate serving as a reference, 
and calculating the percent reflection. For colors, the sensory test 
dependent on vision was performed. 
In another run, Examples 1 to 4 and comparative examples 1 to 3 were cut 
with a microtom to produce cross-sections, which were then observed with 
an electron microscope (Nippon Electronic Co.). It was found through this 
observation that, when melamine beads were used in combination with a 
light transmissive resin comprising a UV setting resin, the resulting film 
gave a profile as shown in FIG. 18 where at each interface between the two 
exists a low refractive layer with a thickness of several tenths .mu.m or 
a space (probably filled with air). If the film contains acryl beads or 
does not contain a UV setting resin, it will not have such low refractive 
layer formed in its substance. 
When a given film has such low refractive layer in its substance, light 
passing through the light transmissive resin temporarily enters into this 
low refractive layer, but is reflected back by the surface of light 
transmissive diffusing material. Thus, such film will have a good light 
diffusing activity.