United States Patent [191
`Ohtake et al.
`
`US005384658A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,384,658
`Jan. 24, 1995
`
`[54] PLASTIC OPTICAL MEMBER AND
`LIGHT -QUANTITY CONTROLLING
`MEMBER EACH HAVING A
`LIGHT-DIFFUSING LAYER ON ITS
`SURFACE
`I
`
`[75] Inventors: Genji Ohtake, Yokohama; Hisao
`Morohashi, Kawasaki; Souichi
`Hasegawa, Yokohama, all of Japan
`
`[73] Assignee: Ohno Research & Development
`Laboratories Co. Ltd., Yokohama,
`Japan
`849,398
`Sep. 3, 1991
`
`[21] Appl. No.:
`[22] PCT Filed:
`
`[86] PCT No.:
`§ 371 Date:
`§ 102(e) Date:
`
`PCT/JP91/01177
`Apr. 27, 1992
`Apr. 27, 1992
`
`[87] PCT Pub. No.: W092/044-00
`PCT Pub. Date: Mar. 19, 1992
`Foreign Application Priority Data
`[30]
`Sep. 4, 1990 [JP]
`Japan ................................ .. 2-233978
`Oct. 30, 1990 [JP]
`Japan ................................ .. 2-292991
`
`[51] Int. c1.<5 ...................... .. G02B 13/20; 6023 5/02;
`A61G 13/00
`[52] US. Cl. ....... .; ......................... .. 359/707; 359/599;
`362/33
`[58] Field of Search ............. .. 359/599, 707, 893, 894, -
`359/619; 362/26, 31, 33
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`3,671,101 6/1972 Finch ................................ .. 359/599
`3,850,667 11/1974 Tani et a1.
`1l7/36.7
`4,114,983 9/1978 Maf?tt et al. .
`359/599
`
`4,310,219 l/1982 Jaccard . . . . . . . . .
`
`. . . .. 359/599
`
`4,427,265 l/l984 Suzuki et a1. ..
`4,529,563 7/1985
`4,573,766 3/ 1986
`4,989,933 2/1991
`
`359/599
`
`' FOREIGN PATENT DOCUMENTS
`
`2054433 5/1972
`349167 ll/1959
`498711 2/ 1974
`57-128383 8/1982
`58-155947 9/1983
`59-8809 2/ 1984
`61-276831 12/1986
`2126501 5/ 1990
`
`Germany .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`Japan .
`
`OTHER PUBLICATIONS
`English language translation of claim of JP-A-34-9 167.
`English language translation of claim of J P-A-49-871 1.
`English language translation of claim of J P-B—59—8809.
`English language translation of claims of JP—A-5
`7-128383.
`English language Abstract of JP reference No.
`2-126501.
`English language translation of Claims of JP-A-S
`8-155947.
`English language Abstract of JP Reference No.
`61-276831.
`Derwent Publications Ltd. London, GB; AN
`89-183663 & JP 1 123 201 May 16, 1989.
`Derwent Publications Ltd. London, GB AN 86-058934
`& JP 61 010499 Jan. 17, 1986.
`Primary Examiner-Scott J. Sugarman
`Assistant Examiner-Thong Nguyen
`Attorney, Agent, or Firm-Ladas & Parry
`[57]
`ABSTRACT
`There is provided a plastics optical member having on
`its surface a light-diffusing layer composed of a layer of
`micro-joints formed by immersing a plastics material
`successively in a good solvent and a poor solvent, and a
`plastics light-quantity-controlling member having on its
`surface a white pattern composed of the micro-joints.
`The superiority in light diffuse reflection, transmission
`and ' light-quantity-controlling property permit their
`incorporation into various optical systems such as
`screens for projection, various displays, light-source
`directly-under-an-illumination-surface type light boxes,
`edge light type light boxes, etc.
`
`8 Claims, 6 Drawing Sheets
`
`a "" T/
`‘3515-3113457
`
`2
`
`2
`
`7
`
`VIZIO EX. 1017
`K.J. Pretech Ex. 1017
`
`VIIO EX. 1017
`K.J. Pretech Ex. 1017
`
`Pretech_000724
`
`

`
`US. Patent
`
`Jan. 24, 1995
`
`Sheet 1 of 6
`
`5,384,658
`
`FIG.
`
`FIG. 2
`
`Pretech_000725
`
`

`
`US. Patent
`
`Jan. 24,
`
`5,384,658
`
`FIG. 3
`
`Pretech_000726
`
`

`
`US. Patent
`
`Jan. 24, 1995
`
`Sheet 3 of 6
`
`5,384,658
`
`FIG. 4
`
`Pretech_000727
`
`

`
`US. Patent
`
`Jan. 24, 1995
`
`Sheet 4 of 6
`
`5,384,658
`
`FIG. 5
`
`II I/ I l 7 I I
`
`6
`
`Q
`
`V/////// //////'//F//
`
`l
`5
`
`FIG.T’_
`6
`
`8
`
`Z
`
`9
`
`U/ ,/ //
`\JWQ 5’ PE
`
`Pretech_000728
`
`

`
`US. Patent
`
`Jan. 24, 1995
`
`Sheet 5 of 6
`
`5,384,658
`
`FIG. 8
`
`I3
`4
`(
`7l/////,)///////////I
`W"
`W;?»T\\\\\\\\\\\\\\\l
`
`2
`
`l2
`
`I4
`
`2
`
`Pretech_000729
`
`

`
`US. Patent ~
`
`Jan. 24, 1995‘
`
`Sheet 6 of6
`
`' 5,384,658
`
`FIG. ll
`
`l//////////////////7///////I
`
`4
`
`I?
`2
`
`I8
`
`Pretech_000730
`
`

`
`1
`
`PLASTIC OPTICAL IVIEMBER AND
`LIGHT-QUANTITY-CONTROLLING MEMBER
`EACH HAVING A LIGHT-DIFFUSING LAYER ON
`ITS SURFACE
`
`15
`
`TECHNICAL FIELD
`The present invention is a technique utilizing light
`diffusion, and relates to a plastic optical member having
`a speci?c micro-joints layer on its surface, and a light
`quantity-controlling member having a white pattern of
`the aforementioned micro-joints on its surface.
`Here, the term “optical member” refers to an optical
`member used in any part of various optical systems in
`which light is desired to be subjected to diffuse re?ec
`tion or diffuse transmission. Speci?c examples thereof
`are optical members used in planar light sources, pro
`jection screens, window materials for building, various
`displays, office automation appliances, and precision
`optical instruments. The term “light-quantity-controll
`ing member” refers to a speci?c optical member used
`for controlling the quantity of light. Speci?c examples
`thereof are optical members for homogenizing the light
`ness of the illumination surface in the so-called “thin
`light box” such as a backlight used in liquid crystal
`displays of personal computers, a schaukasten for medi
`cal treatment, an electrically illuminated display, etc., to
`render the brightness uniform. The optical member and
`the light-quantity-controlling member commonly uti
`lize the light-diffusing properties imparted by the provi
`sion of the aforementioned speci?c micro-joints layer
`on the whole or a part of their surfaces.
`
`5,384,658
`2
`When a light-diffusing white coating material is ap
`plied on a plastic material, the spectral absorption char
`acteristics of the coated material tend to be imbalanced
`because the light-diffusing white coating material is
`composed of a white pigment, a binder, various addi
`tives, etc. The reason is that in the case of such a coating
`material, coating properties should be given priority. It
`is dif?cult to make the content of the white pigment in
`the coating material much higher than that of the binder
`from the viewpoint of the ?lm-forming properties of the
`coating material. In addition, in this case, it is the
`boundary surface between the binder and the white
`pigment that scatters light. A small difference between
`their refractive indexes results in a small light-scattering
`effect. Therefore, if a large light diffuse re?ection effect
`is desired, it is necessary to thicken the coating of the
`light-diffusing white coating material, so that a thin
`light diffuse re?ective layer cannot be realized. More
`over, the light-diffusing white coating material is diffi
`cult to be applied on a curved surface.
`On the other hand, conventional thin light boxes
`requiring a uniform illumination surface includes the
`following two types of light boxes: the so-called edge
`light type (see, for example, J P-A-57-128383 and JP-A
`2-126501) which comprises a light-source provided at a
`side end of an illumination surface, and a light-quantity
`controlling member with a light guide panel having a
`re?ective pattern formed thereon, which member dif
`fuses light from the light source uniformly on the illumi
`nation surface; and the so-called lighting curtain type
`(see, for example, J P-B-59-8809) which comprises a ?at
`housing with an illumination surface on its open side, a
`light source provided in the ?at housing and a light
`quantity-controlling member provided right above the
`light source and containing a translucent reflector
`called “lighting curtain” which has a re?ecting pattern,
`so as to allow light from the light source to re?ect
`repeatedly between the inner surface of the housing and
`the light-quantity controlling member to achieve uni
`form illumination.
`The edge light type light box is disadvantageously
`heavy because it is used together with a light guide
`panel made of transparent plastic, glass or the like. The
`edge light type light box is disadvantageous in that the
`area of light guide portion cannot be increased in pro
`portion to the enlargement of the illumination surface
`since light is introduced through the end face of the
`light guide panel, so that the light box is dark.
`The lighting curtain type light box is advantageous in
`that the light box is lightweight and very light because
`no light guide panel is used therein. However, its assem
`bling is complicated because the positional relationship
`between the illumination surface and the re?ective sur
`face at the inner surface of the housing must be strictly
`set to obtain a uniform illumination.
`In both the edge light type light box and the lighting
`curtain type light box, a regularly re?ecting pattern
`such as a conventional aluminum-deposited pattern as
`well as a printed pattern with a white pigment is con
`ventionally used as the re?ecting pattern on the light
`quantity-controlling member. However, the regularly
`re?ecting pattern has the shortcoming that parallax is
`caused on the illumination surface, depending on the
`angle from which the illumination surface is looked at,
`due to its directivity, although the regularly re?ecting
`pattern has a high re?ectance. The printed pattern with
`a white pigment is disadvantageous in that the re?ection
`wavelength characteristics of the pigment are shifted by
`
`65
`
`35
`
`55
`
`BACKGROUND ART
`Using conventional such as surface chemical treat
`ment, sandblasting method (see JP-B-49-87ll), coating
`with a light-diffusing white coating material (see, for
`example, JP-B-34-9168), etc., it is difficult to obtain on
`the surface of a plastic material a thin light-diffusing
`layer which can be formed partly or in the shape of a
`pattern, permits adjustment of light diffuse re?ection
`properties and light diffuse transmission properties, and
`can be formed not only on planar surfaces but also on
`any curved surfaces. The reason for the dif?culty is
`45
`explained below for each method.
`In the surface chemical treatment, a violent reaction
`is carried out using a strong acid, a strong base, etc., so
`that the spectral absorption characteristics of the sur
`face of the resulting light~diffusing layer are changed by
`the chemical reaction. In other words, coloring and the
`like are caused. Moreover, the chemical treatment
`merely forms depressions and protuberances in the sur
`face and hence does not impart signi?cant light diffuse
`re?ection properties or light diffuse transmission prop
`erties to the surface. Furthermore, when the treatment
`is carried out so as to form a pattern, it is difficult to
`prepare a resist which is resistant to the above-men
`tioned violent chemical reaction.
`In the sandblasting method, sand grains are caused to
`collide with a plastic material at high speeds. For the
`collision of the grains, high energy is required. In addi
`tion, the ?ner the sand grains, the greater the air resis
`tance, so that the fineness of the plastic material surface
`achieved by the treatment has its own limit and it can
`notbe expected to impart very high light diffuse re?ec
`tion properties or light di?'use transmission properties
`to the surface of the plastic material.
`
`Pretech_000731
`
`

`
`15
`
`25
`
`5,384,658
`3
`various additives added to an ink for printing in order to
`layers in the direction of the depth of the plastic mate
`maintain the printability, resulting in the so-called color
`rial. The cracks provide a very large boundary surface
`shift. Furthermore, in the case of a white pattern ob
`area between air and the constituent plastic of the plas
`tained by printing, the size of dots constituting the pat
`tic material. Since light is scattered at the boundary
`tern is restricted by printing techniques and cannot be
`surfaces, there are an extremely large number of por
`made very small. Therefore, the illumination surface
`tions from which light is scattered. Therefore, a large
`requires an additional light diffuser panel for hiding a
`light-diffusing effect can be obtained even by using a
`thin light-diffusing layer.
`dot image since printing of dots with an invisible size is
`difficult.
`When such a light-diffusing layer comprising micro
`10 joints as described above is formed on the surface of a
`plastic material by treatment with the solvents, the
`surface portion of the plastic material is at ?rst swollen
`by the immersion of the plastic material in a ?rst solvent
`which is a good solvent for the constituent plastic of the
`plastic material. The swelling is caused by the expansion
`of the surface portion of the plastic material. This ex
`pansion is caused by the intrusion of the molecules of
`the solvent between the molecules of the constituent
`plastic. When the plastic material in this state is im
`mersed in a second solvent which is a poor solvent for
`the plastic, the molecules of the ?rst solvent present
`between the molecules of the plastic are replaced by the
`molecules of the second solvent, so that the molecules
`of the plastic are rapidly shrunk and solidi?ed. There
`fore, a large number of cracks are formed and become
`micro-joints.
`In this case, unless the ?rst solvent and the second
`solvent are compatible with each other, the molecules
`of the ?rst solvent are not smoothly replaced by the
`molecules of the second solvent, and hence no uniform
`micro-joints are formed. Therefore, the ?rst solvent and
`the second solvent must be compatible with each other.
`Owing to this compatibility, the molecules of the ?rst
`solvent are gradually replaced by the molecules of the
`second solvent as the ratio of the former to the latter is
`changed, so that uniform micro-joints are formed.
`Thus, the micro-joints according to the present in
`vention have a structure composed of very small cracks
`and spaces integrated closely with high density. The
`appearance of the micro-joints slightly varies depending
`on the kind of the constituent plastic to be treated, the
`kinds of the ?rst and second solvents, immersion
`method, immersion temperature, immersion time, etc.
`For example, the micro-joints appear as assemblies of
`very small cracks or appear spongy or felt-like. How
`ever, the micro-joints serve as the light-diffusing layer
`of an optical member, irrespective of their appearance.
`The average thickness (depth) of the micro-joints
`layer obtained in the present invention is l to 30 nm. A
`micro-joints layer having an average thickness of 10 to
`20 pm is particularly preferable for a light-diffusing
`layer. The average distance between the cracks or
`spaces formed is 0.01 to 50 pm, and in particular, in an
`optical member is preferably 0.02 to 20 pm.
`The outstanding advantages of the micro-joints are as
`follows: the micro-joints provide a very high light dif
`fuse reflectance (a high whiteness degree of the sur
`face); they do not peel off because they are integral with
`the substrate (they have the same quality as that of the
`substrate) and provide a higher surface strength as com
`pared with the coating with a white pigment, etc. The
`micro-joints also have advantages in their production.
`For example, their characteristics can easily be chosen
`by changing the kinds of the solvents employed and the
`conditions of the treatment.
`As regards the plastic material used as the optical
`member or the light~quantity-controlling member of the
`present invention, the micro-joints layer can be formed
`
`SUMMARY OF THE INVENTION
`The present invention seeks to solve the various prob
`lems in the formation of a thin light-di?’using layer on
`the surface of a plastic as present material in the prior
`art, and provides a plastic optical member comprising a
`plastic material as present having on the surface a light
`diffusing layer which has adjustable diffuse re?ection
`properties or light diffuse transmission properties, can
`be formed partly or in the shape of a pattern, on any
`curved surfaces, and has a ?at spectral absorption distri
`20
`bution. In addition, the present invention is seek to solve
`the above-mentioned various problems in conventional
`light-quantity-controlling means in light-quantity-con
`trolling members for adjusting the quantity of transmit
`ted light and the quantity of re?ected light, and pro
`vides a light-quantity-controlling member which makes
`it possible to obtain a bright box that is lightweight,
`very light, and easy to construct and hardly causes
`parallax, and which member is free from color irregu
`larities and has a simple structure.
`Further in the present invention, these objects are
`achieved by forming a light-diffusing layer on the sur
`face of a plastic material. The light-diffusing layer com
`prises micro-joints formed on the surface of the plastic
`material.
`For forming such micro-joints, the plastic material is
`immersed in a good solvent (hereinafter referred to also
`as first solvent) for the constituent plastic of the plastic
`material, and then in a poor solvent (hereinafter re
`ferred to also as second solvent) for the constituent
`plastic which is compatible with the ?rst solvent. By
`this procedure, the light-diffusing layer is formed on the
`surface of the plastic material. Each solvent may be
`either a single solvent or a mixed solvent. In general,
`when an object is increased in volume by swelling,
`dissolution, melting, etc., and returns to its original
`state, it shrinks toward the centers of shrinkage scat
`tered in the object. Owing to the cracks or spaces
`formed by the shrinkage between the centers of shrink
`age, numerous laminated structures in a pillar shape, a
`string shape, a plate shape or a spherical shape are
`formed near the surface of the object, and they are
`called joints.
`In some cases, the joint structures become spongy or
`felt-like depending on the shrinkage rate and the ?exi
`bility and brittleness of the object. Their sizes reach
`several micrometers to several tens of centimeters in
`some cases.
`The present inventors found that by the above-men
`tioned immersion of the plastic material in the good
`solvent and then in the poor solvent, extremely minute
`joints are formed on the surface of the plastic material.
`These micro-joints are assemblies of very small
`cracks formed by expansion of a surface portion of the
`plastic material, followed by the rapid shrinkage
`thereof. The cracks are formed in a very small size with
`very high density in the surface portion of the plastic
`material. Furthermore, the cracks are formed in multi
`
`35
`
`45
`
`50
`
`55
`
`65
`
`Pretech_000732
`
`

`
`6
`The removal of the solvent on the surface and of the
`resist forms a sharp pattern composed of a micro-joints
`layer on the surface of the plastic material. The micro
`joints in the white pattern constitute a multiple voids
`layer having an average distance between the voids of
`0.01 to 50 um and an average layer thickness of l to 30
`pm.
`When the pattern comprising the micro-joints layer
`formed on the surface of the plastic material in the
`manner as described above is irradiated with light, the
`cast light carries out repeated re?ection and refraction
`due to the existence of a large number of the very small
`cracks which are densely and irregularly overlaid in the
`direction of the depth of the plastic material. Therefore,
`in spite of the thinness of the layer of the micro-joints,
`the pattern has a high whiteness and a very high non
`directional re?ectance.
`As described above, the white pattern comprising a
`micro-joints layer repeats re?ection and refraction very
`many times in three dimensions in the thin layer. There
`fore, the white pattern exhibits extremely excellent
`effective diffusion, per unit transmittance, than does an
`etched surface or a sandblasted surface, whose diffusion
`is mainly attributable to planar re?ection and refraction.
`Accordingly, the white pattern layer can be made thin
`ner, whereby light loss is reduced. Therefore, the light
`quantity-controlling member of the present invention
`having the white pattern comprising micro-joints effi
`ciently re?ects or refracts the light thereby to enable
`accurate and non-directional control of the light.
`The light-quantity-controlling member of the present
`invention does not contain any factor which changes
`the wavelength characteristics of the light at the time
`when the member re?ects or refracts the light. There
`fore, the member does not cause color shift.
`Embodiments of the present invention are explained
`below.
`~
`
`20
`
`35
`
`25
`
`5,384,658
`5
`on the surface of any kind of plastic so long as there is
`a good solvent for the plastic. Examples of plastic in
`clude homopolymers such as acrylic resin (e.g.
`PMMA), polyester resin (e.g. PET), polycarbonate,
`polyole?n (e.g. polyethylene), polystyrene, polyamide,
`polyoxymethylene, polyvinyl chloride and the like, and
`copolymers such as ABS, AS and the like. These plastic
`can be used even when they are not particularly trans
`parent.
`As a method for allowing the ?rst solvent and the
`second solvent to act on the plastic, any methods can be
`employed, such as immersion in each of the solvents,
`exposure to the vapor of each of the solvents, spraying
`each of the solvents onto the surface, coating of the
`surface with each of the solvents, etc. Since the second
`solvent replaces the ?rst solvent which has already
`swollen the surface portion of the plastic, it is necessary
`to supply a large amount of the second solvent to the
`surface.
`As described above, the plastic material having a
`light-diffusing layer comprising the micro-joints as a
`white surface for carrying out light diffuse re?ection
`provides highly ef?cient and dense diffuse-re?ected
`light. The plastic material can be employed for the
`production of a diffuse re?ector used in various illumi
`nators, a material constituting the inner surface of a
`light box, a projection screen, etc. Particularly when
`the material is utilized as a projection screen, a light and
`highly clear projected image can be obtained owing to
`the thin light-diffusing layer and the dense surface
`thereof.
`The light-quantity-controlling member of the present
`invention for adjusting the quantity of transmitted light
`and for adjusting the quantity of re?ected light has a
`light-quantity-controlling means comprising a white
`pattern comprising micro-joints formed on the surface
`of a plastic material. Such a light-quantity-controlling
`means can be formed as follows. Before forming the
`white pattern comprising the micro-joints, the surface
`of the plastic material is masked with a resist such as
`photoresist which is insoluble in both the ?rst and sec
`ond solvents, wherein the ?rst solvent is a good solvent
`for the constituent plastic, and the second solvent is a
`poor solvent for the constituent plastic and is compati
`ble with the ?rst solvent. The plastic material thus
`45
`treated is immersed successively in the ?rst solvent and
`then in the second solvent.
`i
`In the present invention, the surface of the plastic
`material in which the white pattern is to be formed is
`masked with a resist insoluble in both the ?rst solvent (a
`good solvent for the plastic material) and the second
`solvent (a poor solvent for the plastic material), while
`leaving a portion to be patterned. Then, the plastic
`material thus treated is immersed in the ?rst solvent. At
`this time, a portion not masked with the resist is allowed
`55
`to swell and increase in volume.
`The immersion of the plastic material in the second
`solvent causes rapid replacement of the ?rst solvent by
`the second solvent due to the compatibility between
`these solvents, and results in the rapid shrinkage and
`60
`solidi?cation of the swollen portion, which lead to the
`formation of numerous extremely minute cracks. Since
`the plastic material has low crystallinity, the cracks
`constitute a layer of the so-called micro-joints which
`are irregularly placed one upon another in a large num
`65
`ber- in the direction of the depth of the plastic material,
`as can be seen from FIG. 2 and FIG. 3 given hereinaf
`ter.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic view of one example of the
`surface of a light-diffusing layer comprising the micro
`joints of the present invention observed under a micro
`scope;
`FIG. 2 is a schematic view of one example of a sec
`tion of the light-diffusing layer comprising the micro
`joints;
`FIG. 3 is a schematic illustration of the micro-joints
`of the present invention at a magni?cation of 5,000;
`FIG. 4 is a partial perspective view of the light-quan
`tity-controlling member of the present invention;
`FIG. 5 shows another example of the light-quantity
`controlling member of the present invention. FIG. 6,
`FIG. 7, FIG. 8, FIG. 9, FIG. 10 and FIG. 11 are sec
`tional side views of other examples of the present inven
`tion.
`The symbols employed in these ?gures denote as
`follows.
`1 - - - housing,
`
`2 - - - light source,
`
`3 - - - light-quantity-controlling member,
`4 - - - light di?user panel,
`
`5 - - - re?ective surface,
`
`6 - - - white pattern,
`
`7 - - - light-quantity-controlling member,
`8 - - - white layer,
`
`9 - - - transparent member,
`
`10 - - - light-quantity-controlling member,
`11 - - - light diffuse transmission member,
`
`Pretech_000733
`
`

`
`5,384,658
`8
`amorphous structure of the polymethyl methacrylate
`plate.
`For comparison, the same polymethyl methacrylate
`plate is sandblasted on one side and the above-men
`tioned re?ection optical density was measured. The
`re?ection optical density was 0.62. When visually ob
`served, the sandblasted surface was not so white and
`was rough.
`Next, a white coating material comprising titanium
`oxide as a white pigment was applied on one side of a
`polymethyl methacrylate plate to a thickness of 20 pm.
`The thickness was the same as that of the aforesaid
`light-diffusing layer composed of the micro-joints
`formed by the method of the present example. In this
`case, the re?ection optical density was 0.08. For further
`reducing the re?ection optical density, the coating
`thickness or the titanium oxide content in the white
`coating material may be increased. However, even
`when either of these factors is increased, the application
`of the white coating material becomes difficult and the
`formation of a dense layer on the surface of the poly
`methyl methacrylate plate becomes impossible.
`In the present example, the transparent polymethyl
`methacrylate plate was used merely for showing the
`result of evaluation of the formed light-diffusing layer
`composed of the micro-joints in terms of the re?ection
`optical density. As mentioned above, the plastic mate
`rial used in the present invention is not limited to trans
`parent plastic plates.
`In the method of the present example, it is sufficient
`to immerse the plastic material successively in the ?rst
`solvent and then in the second solvent. Therefore,
`whatever shape the plastic material may have, the light
`diffusing layer can be formed on the surface of the
`plastic material in the same manner as described above.
`
`15
`
`20
`
`25
`
`35
`
`7
`
`12 - - - re?ective sheet,
`13 - - - light guide member,
`14 - - - re?ecting pattern,
`I
`15 and 15' - - - white pattern comprising a micro
`joints layer,
`16 - - - light-quantity-controlling member,
`17 - - - light-quantity-controlling member,
`18 - - - housing.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`The present invention is further illustrated below
`with examples.
`
`EXAMPLE 1
`A 30 mm X 80 mm transparent polymethyl methacry
`late plate was immersed in dichloromethane (a ?rst
`solvent) for 30 seconds and then in n-hexane (a second
`solvent) for 60 seconds, and dried to form a white light
`diffusing layer on the surface of the polymethyl methac
`rylate plate. In the formation of the light-diffusing layer,
`one side of the polymethyl methacrylate plate was cov
`ered with an adhesive tape made of polyester so that the
`light-diffusing layer was formed only on the other side
`of the polymethyl methacrylate plate which was ex
`posed to the solvents. After the formation of the light
`diffusing layer, the adhesive tape was peeled off.
`The re?ection optical density of the light-diffusing
`layer thus formed on the surface of the polymethyl
`methacrylate plate was measured with a photographic
`densitometer (Model P-2, mfd. by Fuji Photo Film Co.,
`Ltd.) [the re?ection optical density is expressed by the
`equation D=log (IQ/I) (log: common logarithm)
`wherein D is the value of the re?ection optical density,
`I0 is the intensity of an incident light, and I is the inten
`sity of a re?ected light]. A sheet of black felt was
`brought into close contact with the reverse side of a
`sample to be measured, whereby the light transmitted
`through the light-di?using layer was absorbed.
`The re?ection optical density of the light-diffusing
`layer formed on the surface of the polymethyl methac
`rylate plate was 0.03, and the value corresponds to a
`re?ectance of 93%. Thus, the light-diffusing layer has
`suf?cient light diffuse re?ection properties and hiding
`power as a white layer.
`Observation of the light-diffusing layer formed on the
`surface of the polymethyl methacrylate plate under a
`microscope demonstrated that there were micro-joints
`composed of numerous extremely minute and irregular
`cracks on the surface of the polymethyl methacrylate
`plate. As mentioned above, the micro-joints observed
`under the microscope are schematically shown in FIG.
`1.
`Microscopic observation of a section of the poly
`methyl methacrylate plate having the light-diffusing
`layer on the surface revealed that the thickness of the
`light-diffusing layer was about 20 pm. The section ob
`served under a microscope is schematically shown in
`FIG. 2. Each of FIG. 1 and FIG. 2 merely shows an
`example, and the size and shape of the micro-joints vary
`depending on the conditions at the formation of the
`light-di?using layer.
`When visually observed, the light-diffusing layer
`formed on the surface of the polymethyl methacrylate
`plate was pure-white, had a very dense surface shape,
`and showed no directional property of surface pro?le at
`all. This is considered to be due to the non-crystalline,
`
`40
`
`50
`
`55
`
`60
`
`65
`
`EXAMPLE 2
`A light diffuse re?ective layer of micro-joints was
`formed on the surface of each of 3 kinds of plastic plates
`in the same manner as in Example 1, except for replac
`ing the ?rst solvent and the second solvent. The re?ec
`tion optical density was measured in the same manner as
`in Example 1.
`For choosing solvents as the ?rst solvent and the
`second solvent, respectively, the value of solubility
`parameter can be used.
`The de?nition of solubility parameter is shown be
`low:
`
`SP: solubility parameter,
`AH: latent heat of vaporization,
`R: gas constant (cal/mole),
`’
`C: density (g/cc),
`M: gram-molecular weight (g/mol),
`T: absolute temperature.
`When a polymethyl methacrylate plate is used as a
`transparent plastic plate, the value of solubility parame
`ter (hereinafter referred to as SP value) of the ?rst sol
`vent, i.e. the good solvent, is preferably between 9.0 and
`9.8, more preferably between 9.3 and 9.7. It is suf?cient
`that the SP value of the second solvent, i.e. the poor
`solvent, is 9.9 or more, or 8.8 or less. As the second
`solvent, there can be exempli?ed alcohols, glycols,
`chain hydrocarbons and cyclic hydrocarbons.
`
`Pretech_000734
`
`

`
`5,384,658
`9
`Table 1 shows examples of the formation of a light
`diffuse re?ective layer of micro-joints in the surface of
`a polymethyl methacrylate plate by immersion of the
`polymethyl methacrylate plate in each of the ?rst sol-
`vents having different solubility parameters for 30 sec- 5
`onds and then in ethanol (SP value: 12.7) as the second
`solvent for 60 seconds. For the layers of micro-joints
`which remained transparent, the symbol T 18 written in
`the table instead of measuring the re?ection optical
`density.
`
`10
`?rst solvents for 30 seconds and then in n-hexane as the
`second solvent for 60 seconds.
`
`Xylene
`
`t
`l
`F. t
`_
`us so yen
`Cam“ mmhbndc
`Benzene
`chloroform
`Dichloromethane
`Dioxaue
`Acetone
`
`TABLE 4
`SP 31
`v “6
`8'5
`92
`9.3
`9.7
`9.9
`10.0
`
`8.8
`
`_
`?zg?m‘lt
`op m y
`T
`Nonunifom
`Nonuniform
`Nonuniform
`0.24
`T
`
`0.02
`
`10
`
`.
`
`.
`
`.
`
`.
`
`.
`
`Fm solvent
`£31112;
`chloroform
`Chlorobenzene
`nichlomm?h?ne
`Dmme
`
`TABLE 1
`
`SP value
`3';
`93
`9.5
`9-7
`9'9
`
`Re?ection
`optical dens“),
`($3
`0:32
`0.28
`034
`T
`
`In the case where a light diffuse re?ective layer of
`15 micro-joints is formed on the polycarbonate plate, a ?rst
`solvent having an SP value of from 8.6 to 9.9 is used for
`forming the light diffuse re?ective layer of micro-joints.
`When a ?rst solvent having an SP value of from 9.1 to
`9.7 is used, the surface portion of the polycarbonate
`20 plate is dissolve