Method of preparing volume type hologram film

A method of preparing a volume type phase hologram film comprises forming a volume type phase hologram in a polymer film formed on a substrate and comprises of a polymer of vinylcarbazoles, and separating the polymer film from the substrate. Preferably, the polymer film is separated from the substrate in a liquid inert to the hologram.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of preparing a volume type phase 
hologram film, and more particularly to a method of preparing a volume 
type phase hologram film having sufficient flexibility and further a 
superiority in high diffraction efficiency, high transparency and high 
moisture resistance, the method being capable of being used in various 
purposes. 
2. Related Background Art 
Holography is a unique technique of forming an optical image by which an 
object is irradiated by a well coherent wave such as a laser beem where 
the wave is modulated in amplitude and phase in accordance with the shape 
of the object, the modulated wave reflected upon or transmitted through 
the object is recorded (=hologram) and the hologram is irradiated again by 
the laser beam so as to reproduce an optical image of the original object. 
With the recent development of study on holography, it has been made clear 
to a certain extent what material is suitable for use in holography or 
what characteristics such a hologram recording material should have. 
Thus, there have already been proposed various materials such as bleached 
silver salt (U.S. Pat. No. 3,672,744), dichromate gelatine (U.S. Pat. No. 
3,617,274), photoresist, thermoplastic resin, inorganic glass materials 
and ferroelectric substances, and at present a further study on the 
properties of these materials is proceeding in the art. 
The properties which a hologram recording material (or sensitive material) 
should have may be summarized as follows: 
(1) to have a sensitivity to a laser beam, especially to a laser beam in 
the visible wavelength region and to have a high sensitivity at the same 
time; 
(2) to have a high resolving power; 
(3) to give a hologram of high diffraction efficiency; 
(4) to give a hologram of low noise level; 
(5) to give a stable hologram; and 
(6) to allow easy recording and reproducing operations. 
As will be seen from the above, the requirements for a hologram recording 
material are very severe ones. 
In view of practical purposes, very few known hologram recording materials 
can satisfy the above requirements completely or at least partially to the 
extent that its use may be practical. 
Among the above mentioned materials, bleached silver salt and dichromate 
gelatine may be considered to be practically usable. However, they have 
particular disadvantages. The former necessitates a bleaching treatment in 
adition to ordinary treatments and furthermore the hologram obtained from 
it is poor in light fastness. The latter has a difficulty regarding the 
preservation of hologram because the hologram obtained from this material 
lacks adequate stability against moisture. 
To overcome the disadvantages the conventional holograms have had, U.S. 
Pat. No. 4,287,277 discloses a hologram employing polyvinyl carbazole. 
This hologram employing polyvinyl carbazole is suitably used as it can 
satisfy the properties (1) to (6) mentioned above. 
In general, volume type phase holograms are holograms in which a Bragg's 
grating is formed in the inside of a polymer and diffraction light 
wavelength is controlled by the grating distance (or grating space), where 
the grating pattern comprising several thousand or more lines is formed in 
a thickness of several ten .mu.m with a grating space of 0.1 to 0.2 .mu.m. 
Therefore, at the time of manufacturing a volume type phase holograms 
(particularly at the time of exposure to laser beam), the exposure to 
laser beam must be carried out in a stationary state so that fluctuation 
may be suppressed within approximately 0.01 to 0.02 .mu.m. 
More specifically, at the time of the exposure to light, vibration, 
air-swirling caused by the passage of a laser beam, deformation of a 
holder of a sensitive material, thermal expansion, density gradient owing 
to temperature of air, etc. must be made sufficiently small. For the 
purpose a rigid and transparent material is used as a support for 
supporting the sensitive material, and in general usually used is glass. 
However, the holograms for which glass is used as the support can be 
applied only to uses of very limited scope, such as displays or the like. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to overcome such 
disadvantages in the prior art to provide a technique of making the volume 
type phase hologram into a film, and to provide a method of preparing a 
volume type phase hologram film that can be applied in various uses such 
as optical coupling devices used in head-up displays and protectors for 
protecting eyes from a laser beam. 
A further object of the present invention is to provide a method of 
preparing a volume type phase hologram film having a superiority in high 
diffraction efficiency, high moisture resistance and high transparency. 
The above objects can be achieved by the invention described below. 
According to one aspect of present invention, there is provided a method of 
preparing a volume type phase hologram film, comprising forming a volume 
type phase hologram in a polymer film formed on a substrate and comprised 
of a polymer of vinylcarbazoles, and separating said polymer film from 
said substrate. 
According to another aspect of the present invention, there is provided a 
method of preparing a volume type phase hologram film, comprising forming 
a volume type phase hologram in a polymer film formed on a substrate and 
comprised on a polymer of vinylcarbazoles, and separating said polymer 
film from said substrate in a liquid inert to said hologram. 
According to a further aspect of the present invention, there is provided a 
method of preparing a volume type phase hologram member, comprising 
forming a volume type phase hologram in a polymer film formed on a 
substrate and comprised of a polymer of vinylcarbazoles, thereafter 
separating said polymer film from said substrate, and bringing the polymer 
separated film to be supported on another substrate. 
According to a still further aspect of the present invention, there is 
provided a method of preparing a volume type phase hologram member, 
comprising forming a volume type phase hologram in a polymer film formed 
on a substrate and comprised of a polymer of vinylcarbazoles, thereafter 
separating said polymer film from said substrate in a liquid inert to said 
hologram, and bringing the separated polymer film to be supported on 
another substrate. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A typical embodiment of the present invention will be described below along 
the process. 
First, a sensitive material layer comprised of a polymer of vinylcarbazoles 
as a principal component is formed on a light-transmissive substrate. 
Utilizable as this light-transmissive substrate are substrates having the 
rigidity that may cause no vibration to occur owing to the irradiation of 
a laser beam, and having no remarkable absorption at the visible light 
region. 
Particularly in regard to the light transmission properties, it is 
preferable to use a substrate having a light transmittance of 30% or more, 
preferably 50% or more, at 400 nm and also a light transmittance of 40% or 
more, preferably 80% or more, at 450 to 800 nm when the light 
transmittance is measured according to the method described in ASTM 
D-1003. 
To exemplify the light-transmissive substrates used in the present 
invention, they may include a substrate made of glass, poly(4-methyl) 
pentene, polyvinyl chloride or the like, and, if necessary, the substrate 
having been made transparent by effecting drawing in the biaxial direction 
at the time of forming to cause orientation crystallization; and a 
substrate comprising an amorphous polymer such as polymethyl methacrylate, 
polycarbonate, polyallylate polyether ether ketone, polysulfone, a 
styrene/methyl methacrylate copolymer or acrylic acid polyhydric alcohol 
esters (CR-39). 
It is also possible to use water soluble substrates in the case that the 
substrate is dissolved and removed in a solvent as described later. 
For example, the water soluble substrates are formed from water soluble 
alkali halides as exemplified by sodium chloride, sodium bromide, 
potassium chloride, potassium bromide, etc. There is no particular 
limitation in the shape of the substrate comprised of these alkali 
halides, but it may preferably be in the shape of a flat sheet of 
approximately from 2 mm to 10 mm in thickness. The surface of the 
substrate on which the sensitive material layer is formed may be smooth or 
of any form including curved or uneven form, where a sensitive material 
layer of the form corresponding to its surface is formed. 
In instances in which the exposure to light at the time of forming a 
hologram is carried out from the substrate side, the above substrates are 
required to be substantially transparent, but in instances in which the 
exposure to light is carried out from the sensitive material layer side, 
they may not necessarily be required to be transparent. 
The surface of the photosensitive material layer formed on the transparent 
substrate and comprised of a polymer of vinylcarbazoles, may further be 
subjected to surface treatment as exemplified by an electrical discharge 
treatment using corona, plasma or the like, a physical treatment such as a 
flame treatment, a chemical treatment by use of sulfuric acid, nitric 
acid, fluoride compounds, alkalis, silane compounds, etc. for the purpose 
of enhancing the affinity for the photosensitive material layer so long as 
the peeling step described later in detail may not be hindered. It is 
necessary to carry out these treatments so as not to impair the required 
optical properties 
The photosensitive material layer formed on the transparent substrate and 
comprised of a polymer of vinylcarbazoles is used in the present invention 
as being superior in the overall aspects of moisture resistance, storage 
stability, diffraction efficiency, etc. of the resulting hologram itself. 
This polymer of vinylcarbazoles polymer refers to polyvinyl carbazole, 
alkyl-substituted polyvinyl carbazoles, halogen-substituted polyvinyl 
carbazoles, and polymers comprised of these, and one or more of these can 
be used as desired. Specifically, there can be utilized, for example, 
polyvinyl carbazole, a 3-chlorovinyl carbazole polymer, a 3-bromovinyl 
carbazole polymer, a 3-iodoovinyl carbazole polymer, a 3-methylvinyl 
carbazole polymer, a 3-ethylvinyl carbazole polymer, chlorinated polyvinyl 
carbazole, brominated polyvinyl carbazole, etc. 
In particular, suited for practical use is the unsubstituted polyvinyl 
carbazole, as being readily available and yet as being particularly 
superior in the performances of the resulting holograms. 
The polymer of vinylcarbazoles may also be optionally copolymerized with 
other monomers for the purpose of controlling the properties such as 
strength or softness when formed into a film. Other monomers usable in 
such purpose may include, for example, in addition to the above vinyl 
carbazoles, vinyl monomers copolymerizable by radical polymerization, 
including vinyl esters such as vinyl acetate, esters of acrylic acid and 
methacrylic acid, styrene and styrene derivatives, etc. Other polymers as 
exemplified by polystyrene, a styrene/butadiene copolymer, a 
styrene/hydrogenated butadiene copolymer can also be used by blending so 
long as a hologram diffraction grating can be recorded. 
These are used by selecting the proportion of addition so that the desired 
properties can be obtained. 
In forming a hologram, the polymer of vinylcarbazoles is used in such a 
state that the polymer can be activated with radiation in the presence of 
an iodine compound. 
Used as this iodine compound are compounds capable of coexisting in a 
polymer component to constitute a sensitive material layer having a 
sufficient sensitivity to the visible light wavelength, as exemplified by 
carbon tetraiodide, iodoform, ethylene tetraiodide, triiodoethane, 
tetraiodoethane, pentaiodoethane, hexaiodoethane, etc. 
The formation of the photosensitive material layer comprised of the polymer 
of vinylcarbazoles on the transparent substrate may be carried out 
according to the coating method disclosed in U.S. Pat. No. 4,287,277. 
Next, the photosensitive material layer is subjected to exposure to light 
and development processing to form the volume type phase hologram. The 
exposure to light may be in accordance with any of known photosensitive 
method, which may be appropriately selected depending on the type of 
objects, uses of holograms, etc. The exposure and development may be 
carried out, for example, according to the method disclosed in U.S. Pat. 
No. 4,287,277, etc. 
More specifically, for example, an interference pattern is formed by 
exposure to two coherent laser beams, comprising the object beam and the 
reference beam, with use of an argon laser beam of (488 nm), and 
thereafter subjected to a development step comprising swelling and 
shrinking by using solvents. 
The hologram obtained by such procedures may preferably have a thickness 
ranging from 4 to 20 .mu.m. The thickness less than 4 .mu.m may result in 
a lowering of the strength as a film, and the thickness otherwise more 
than 20 .mu.m tends to cause cracking. The hologram may more preferably 
have a thickness ranging from 6 to 15 .mu.m. 
Next, the hologram obtained as above is dipped in a liquid inert to the 
hologram, so that a hologram layer in which the hologram diffraction 
grating has been recorded can be peeled from the substrate. This procedure 
makes it possible to obtain a hologram film without any destruction of the 
diffraction grating and further without causing any change in the optical 
properties possessed before treatment. 
The liquid inert to the hologram, which is used to peel (or separate) the 
hologram layer from the substrate, refers to a liquid that may not 
dissolve the hologram layer, and that may penetrate into the interface 
between the both without impairing at all the optical properties of the 
hologram to bring them to peel from each other owing to a surface tension 
of the liquid, or to dissolve the substrate without exerting any action to 
the hologram layer. 
The liquid used in such a step may be any of those that have the above 
properties and also may not substantially adversely affect the 
hologram-constituting component (especially the polymer of vinylcarbazoles 
polymer), but, in particular, water, alcohols and saturated hydrocarbons 
can be particularly suitably used, which may be appropriately selected 
depending on the material of the substrate used. 
Preferable examples thereof are water and a mixed solvent of water with an 
organic low-boiling solvent, and the organic low-boiling solvent may 
include alkane or cycloalkanes such as n-heptane, n-hexane, Diflon (trade 
name; available from Daikin Kogyo), n-pentane, n-octane, iso-octane and 
cyclohexane, alcohols such as methyl alcohol, ethyl alcohol, propyl 
alcohol, isopropyl alcohol and n-butyl alcohol, ethers such as dimethyl 
ether and methyl ether, etc. 
Application of a physical stimulation such as a moderate heating and 
ultrasonic treatment to water or a low-boiling solvent generally brings 
about an effective action for proceeding the peeling, showing a preferable 
tendency. 
The peeled hologram film floats in the medium or on the medium, and can be 
readily taken out. 
If in this peeling step it is predicted that practice of peeling by using 
the solvent is difficult (for example, if the hologram film may eventually 
have a small thickness and a low strength), it is preferably recommended 
that a peel layer first is laminated on the substrate in the first step 
and then the photosensitive material layer is laminated. 
The peel layer mentioned in the present invention is used to make it easier 
to effect the peeling of the hologram film by use of the solvent. 
Usable as the peel layer used for such a purpose is, for example, a layer 
comprised, for example, of a polymer, having a surface tension larger or 
smaller enough for obtaining a good peeling state than the surface tension 
of the hologram film 2 (30 to 40 dyne/cm when the polymer of 
vinylcarbazoles is used), or a layer comprised of a low-molecular surface 
improver called a silane coupling agent or titanium coupling agent. 
Materials that can constitute the peel layer may specifically include, for 
example, polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, 
polyethylene fluoride-propylene and polyorganosiloxane; silane coupling 
agents such as gamma-glycidoxypropyl trimethoxysilane and vinyl 
trimethoxysilane; titanium coupling agents such as 
isopropyltristearoyltitanate and isopropyltrioctyltitanate; etc. 
The peel layer can be provided by laminating, for example, a layer 
comprising the above polymers on the substrate, or by treating the surface 
of the substrate with a solution containing the silane coupling agent or 
titanium coupling agent. 
When peeled, the peel layer, if it is transparent, may remain on any of the 
substrate side and the hologram film side. when the peel layer remains on 
the hologram film side, it may be constituted of a material that functions 
as a protective layer of the hologram film, or various additives capable 
of imparting a protective function to the peel layer may be added. 
Materials for forming the peel layer and capable of functioning also as the 
protective layer may include, for example, polyethylene terephthalate, 
polyether ether ketone, polyperfluoroethylene-propylene, polyvinylidene 
fluoride, polyvinyl alcohol, etc. 
The additives that can be added to impart the function as the protective 
layer may include, for example, as an ultra-violet ray aboving agent, 
triazole derivatives such as 2-(hydroxyphenyl)benzotriazole, triazine 
derivatives such as 1,3,5-tris(2'-hydroxyphenyl)triazine, benzophenone 
derivatives such as resorcylmonobenzoate, etc. 
If opaque, the peel layer may preferably be made to remain on the substrate 
side by suitably selecting the solvents. 
In the case that the hologram itself has no supporting function, it is 
required to apply a flexible support. Then the hologram film taken out as 
mentioned above is scooped up with the flexible substrate (as exemplified 
by a polymer film). 
The hologram comprising polyvinyl carbazole has a surface tension of 36 
dyne/cm when measured according to the wetting test method described in 
JIS K6768. When the surface tension of the polymer film with which the 
hologram thrown into water and peeled and separated from the substrate is 
scooped up is found according to the above method, the hologram wrinkles 
or peels from the polymer film to curl in the case of the polymer film 
having the same surface tension as polyvinyl carbazole when it is scooped 
up and dried. On the other hand, when the polymer film having a value of 
38 dyne/cm or more, more preferably 40 dyne/cm or more, is used, the 
adherence thereof to the hologram is so good that there is seen no wrinkle 
or curl of the hologram. The polymer film may be any of film showing no 
swell or dissolution in water or an organic low-boiling solvent, and the 
change in interfacial tension may not be required to be brought about by 
the change of the polymer film itself, but may be brought about by 
applying a physical treatment using corona, plasma, etc. or a chemical 
treatment using organic siloxane, epoxy, etc. to the surface of the 
polymer film. 
There is a difference in the diffraction efficiencies measured respectively 
from the free surface (the surface having not come into contact with the 
substrate) of the hologram separated from the substrate in the liquid and 
from the surface having come into contact with the substrate. Accordingly, 
in order to obtain a hologram film having a higher diffraction efficiency, 
the polymer film should be supported so that it may come into contact with 
the free surface of the hologram. 
Thickness of the hologram film thus obtained may preferably be in the range 
of from 10 .mu.m to 200 .mu.m, and suitably in the range of from 10 .mu.m 
to 100 .mu.m.

EXAMPLES 
The present invention will be specifically described below by giving 
Examples. 
EXAMPLE 1 
On a washed glass substrate, a solution obtained by dissolving 2.5 g of 
N-polyvinyl carbazole and 0.2 g of carbon tetrachloride in 30 g of 
monochlorobenzene was applied in a dark place by means of a spinner 
(Mikasa Spinner, 1H-2), followed by drying to obtain a hologram-forming 
sensitive material layer of 8.9 .mu.m in layer thickness. 
Using an argon laser (488.0 nm), this sensitive material layer were 
irradiated with parallel beams from the opposite two directions of the 
sensitive material layer to effect exposure to light. 
Thereafter the sensitive material layer was successively subjected to 
development processing according to the following steps (1) to (3), 
followed by drying to obtain a volume type phase hologram. 
(1) Dipped in toluene for 2 minutes, 25.degree. C. 
(2) Dipped in xylene for 3 minutes, 25.degree. C. 
(3) Dipped in heptan for 3 minutes, 25.degree. C. 
The resulting hologram was left in water for 30 minutes to bring the 
hologram to peel from the glass substrate. 
Subsequently, a polyester film (thickness: 50 .mu.m) having a surface 
tension of 40 dyne/cm according to JIS K6768 was dipped in water to scoop 
up the hologram in such a manner that the hologram surface which had come 
into contact with the glass substrate may face the polyester film, 
followed by drying. 
The volume phase hologram film thus obtained had a diffraction peak at 520 
nm, a diffraction light half width of 18 nm, and a maximum diffraction 
efficiency of 95%. Also the transmittance at 600 nm showed 85%. 
On the other hand, the hologram was scooped up in such a manner that the 
hologram surface which had not faced the glass substrate may face the 
polyester film, followed by drying. 
The diffraction efficiency of the hologram film thus obtained reached 97% 
at its maximum, and thus the diffraction efficiency was higher than that 
of the hologram film previously obtained. There was seen no change in 
other properties of the holograms. 
In any of the cases, the resulting films showed sufficient flexibility, had 
superior adherence between the hologram and the polyester film, and had 
superior film properties without causing the hologram to naturally peel 
from the polyester films or wrinkle. 
EXAMPLE 2 
Example 1 was repeated to prepare a hologram film, except that a biaxially 
oriented polypropylene film (thickness: 45 .mu.m) having a surface tension 
of 42 dyne/cm was used in place of the polyester film used in Example 1. 
As a result, there were obtained the same results as in Example 1. 
EXAMPLE 3 
On a washed glass substrate, an N-polyvinyl carbazole sensitive material 
layer was formed in the same manner as in Example 1 except that the peel 
layer was provided by coating with an aqueous 7% solution of polyvinyl 
alcohol to a thickness of 2 .mu.m by means of a spinner, followed by 
exposure to light and development processing. 
The resulting laminated body was left in water for 10 minutes to bring the 
hologram to peel from the glass plate. 
The two resulting holograms thus obtained were placed on the same polyester 
films as used in Example 1 to obtain two volume type phase hologram films. 
In one volume type phase hologram film, its hologram surface which had 
faced the glass substrate faced the surfaces of the polyester film, and in 
the other, its hologram surface which had not faced the glass surface 
faced the surface of the polyester film. 
The holograms thus obtained had a diffraction peak half width of 18 nm and 
a transmittance of 81%. The diffraction efficiency was 82% for film on 
which the hologram was placed in such a manner that hologram surface which 
had faced the glass substrate may face the polyester film, and 89% for the 
other film. 
There were also shown superior film properties like those in Example 1. 
EXAMPLE 4 
Trimethoxyvinylsilane (available from Shin-Etsu Chemical Co., Ltd.) was 
dissolved in ethyl alcohol to give a concentration of 5%, and a glass 
plate was dipped in the resulting solution for 1 hour, and thereafter 
allowed to stand in an oven of 80.degree. C. for 4 hours. 
On this glass substrate, the photosensitive material used in Example 1 was 
applied by means of a spinner to form a sensitive material layer of 20 
.mu.m thick. 
Subsequently, using an argon laser (488 nm), irradiation of convergent 
light was carried out from one side of the sensitive material layer, and 
irradiation of parallel light was made from the other side opposite 
thereto to record a diffraction grating having a function of a convex 
lens. 
Thereafter, this sensitive material layer was subjected to the development 
processing in the same manner as in Example 1 to obtain a volume type 
phase hologram. 
The hologram obtained was left in methanol for 30 minutes to bring the 
hologram to peel from the glass plate, thus obtaining a volume type phase 
hologram film. 
The resulting hologram film had a diffraction peak at 515 nm, and showed a 
maximum diffraction efficiency of 78%, a diffraction peak half width of 6 
nm and a transmittance of 72%. 
EXAMPLE 5 
Example 4 was repeated to prepare a volume type phase hologram film, except 
that irradiations of argon laser beams (488 nm) were effected as parallel 
beams from the opposite two directions of the sensitive material layer to 
conduct exposure to light. 
The hologram free surface and the hologram surface which had faced the 
glass substrate had diffraction efficiencies of 76% and 80%, respectively, 
and the hologram surface which had faced the glass substrate showed high 
diffraction efficiency at any of plural measurement points. 
The width of the diffraction efficiency was found to be 5.9 nm, and the 
transmittance, 72%, being same in each hologram surface. 
EXAMPLE 6 
Bisphenol allylate resin substrate (TS-26, available from Tokuyama Soda 
Co., Ltd.) of 2 mm thick was washed with methanol, and the photosensitive 
material used in Example 1 was applied by means of a spinner to form a 
sensitive material layer of 7.6 .mu.m thick. 
Using an argon laser (488 nm), irradiation of convergent light was effected 
from one side of the sensitive material layer, and irradiation of parallel 
light was effected from the other side opposite thereto to record a 
diffraction grating having a function of a concave lens. This was 
subjected to the development and the substrate-peeling treatment in the 
same manner as in Example 1. 
Thereafter the polyester film same as in Example 1 was dipped in water, and 
the hologram was scooped up in such a manner that the surface which had 
come into contact with the substrate may come into contact with the 
polyester film, followed by drying. 
The volume type phase hologram film thus obtained had a diffraction peak at 
520 nm and showed a half width of 19 nm, a diffraction efficiency of 96% 
and a transmittance of 86% at 600 nm, having the function of a concave 
lens. 
EXAMPLE 7 
Diethylene glycol bisacrylate resin substrate (TS-16, available from 
Tokuyama Soda Co., Ltd.) of 2 mm thick was washed with ethanol, and the 
solution of polyvinyl carbazole photosensitive material used in Example 1 
was applied to the substrate by means of a spinner to form a sensitive 
material layer of 8.1 .mu.m thick. 
Irradiations of parallel beams from an argon laser (488 nm) were effected 
on the opposite two directions of this sensitive material layer to conduct 
exposure to light. 
Subsequently, the resulting sensitive material layer was developed in the 
same manner as in Example 5, and thereafter dipped in a mixed solvent of 
water/methanol=7/3 to bring the hologram to peel from the resin substrate, 
and the hologram was scooped up with a polyester film having a surface 
tension of 45 dyne/cm, followed by drying. 
Reflective diffraction efficiencies measured, when light was made incident 
from the respective surfaces of the hologram free surface at the time of 
exposure to light and the surface having come into contact with the resin 
substrate at the time of the exposure to light, were found to be 92% for 
the free surface and 97% for the surface having come into contact with the 
resin substrate. 
As other properties of the hologram, the half width was found to be 19 nm, 
and the transmittance at 600 nm, 86%, being same in the above both 
surfaces. 
EXAMPLE 8 
On a sodium chloride crystal substrate (available from Nippon Bunko K.K.) 
of 5 mm thick, 30 mm diameter smooth on its surface, a solution obtained 
by dissolving 2.5 g of poly(N-vinyl carbazole) and 0.2 g of carbon 
tetrachloride in 30 g of monochlorobenzene was applied in a dark place by 
means of a spinner (Mikasa Spinner, 1H-2), followed by drying to obtain a 
hologram-forming sensitive material layer of 5.0 .mu.m in layer thickness. 
On this sensitive material layer, an image corresponding to a desired 
object was recorded according to the Denisyuk's method using an argon 
laser (488 nm) and under the condition of the offset angle of 70.degree. 
and the light intensity ratio of 1:1 (the sum of light intensities of the 
both beams was 3 mW/cm.sup.2 right before incidence of light). 
After exposure to light, the sensitive material layer was successively 
processed according to the following steps (1) to (3) to obtain a 
hologram. 
(1) Dipped in toluene of 20.degree. C. for 2 minutes. 
(2) Dipped in xylene of 30.degree. C. for 3 minutes. 
(3) Dipped in n-heptan of 25.degree. C. for 3 minutes, followed by drying. 
After development, the hologram plate was dipped in hot water of 80.degree. 
C. for 60 minutes to dissolve the sodium chloride substrate in part, a 
hologram film was floated on water surface, and this was scooped up on a 
polyethylene terephthalate film having a surface tension of 40 dyne/cm, 
followed by washing with water and drying to obtain a volume type phase 
hologram film of the present invention. 
EXAMPLE 9 
On the substrate used in Example 8, the photosensitive material solution 
same as in Example 1 was applied to form a sensitve material layer of 8.0 
.mu.m thick, and irradiations of parallel beams from an argon laser (488 
nm) were effected from the opposite two directions of the sensitive 
material layer to conduct exposure to light. 
Development was carried out in the same manner as in Example 1, and the 
hologram was brought to peel from the substrate in the same manner as in 
Example 6. 
Subsequently, on the polypropylene film (substrate) used in Example 2, the 
two holograms as obtained above were scooped up in such a manner that in 
one hologram its hologram free surface at the time of exposure to light 
and in the other hologram its surface having come into contact with the 
substrate may each face the substrate surface, followed by drying. 
Light was made incident to each of the hologram free surface and the 
surface having come into contact with the sodium chloride substrate to 
measure the reflective diffraction efficiency to reveal that the 
reflective diffraction efficiency was 90% for the free surface and 92% for 
the sodium chloride substrate. The transmittance (600 nm) was found to be 
83%.