JP2014211650A - Manufacturing method for light diffusion sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve the anisotropic diffusion capability of a light diffusion sheet of synthetic resin having an approximately wavy or approximately cylindrical rough pattern, in which crests are formed in series in one direction and a crest and a trough are repeated in a direction orthogonal to this direction.SOLUTION: A sheet having a series of crests in one direction and in which a crest and a trough are repeated in a direction orthogonal to the series of crests is used as an original fabric sheet. Fine particles are attached to the crest parts or trough parts of the original fabric sheet. In this condition, the entire surface of the original fabric sheet is subjected to a conducting process such a metal deposition. This is then electrically plated, thereby forming a mold of a surface shape in which a waving pattern and fine roughness are combined. By molding a resin sheet by this mold, a light diffusion sheet is obtained such that crests are formed in series in one direction, a crest and a trough are repeated in a direction orthogonal to this direction, and fine roughness is imparted to at least part of the surface. Thus, a manufacturing method for a light diffusion sheet is provided.

Description

The present invention relates to a light diffusing sheet that is used in displays, lighting fixtures, and the like and has a concavo-convex pattern on the surface. Specifically, the present invention relates to a light diffusing sheet having a substantially corrugated or substantially semi-cylindrical concavo-convex pattern in which peaks are continuous in one direction and peaks and valleys are repeated in a direction perpendicular thereto.

A concavo-convex pattern-forming sheet having a wavy concavo-convex pattern formed on the surface thereof has been conventionally used as a light diffuser, an antireflective body or the like.
For example, in Patent Document 1, a plurality of protrusions are formed on at least one surface of a light-transmitting substrate as a light diffusing body having a concavo-convex pattern, the height of the protrusion is 2 to 20 μm, and the apex of the protrusion is A material having an interval of 1 to 10 μm and an aspect ratio of protrusions of 1 or more is disclosed. Further, as a method for forming a protrusion, a method is disclosed in which the surface of a light-transmitting substrate is processed by irradiation with an energy beam such as a KrF excimer laser.

Patent Document 2 discloses a light diffuser in which an anisotropic diffusion pattern made of wavy irregularities is formed on one side. As a method of forming an anisotropic diffusion pattern, a photosensitive resin film is irradiated with a laser beam, exposed, developed, and a master hologram having irregularities formed on one side is formed, and the master hologram is formed into a mold. A method of transferring and molding a resin using the mold is disclosed.

Patent Documents 3 and 4 disclose a technique for forming a ridge-like (wave-like) unevenness on the surface by forming a thin film on the surface of the heat-shrinkable film and thermally shrinking. In these techniques, the wave peaks extend in one direction, and the degree of light diffusion differs between the direction and the direction perpendicular to the direction, and an anisotropic diffusion pattern is formed.
Patent Document 5 discloses an anisotropic diffusion sheet in which an irregular waveform is formed by molding with a mold or the like.

JP-A-10-123307 Japanese Patent Application Laid-Open No. 2006-261064 JP 2008-299072 A JP 2008-302591 A JP 2009-25438 A

In the case of a prism sheet for improving display brightness, unlike the light diffusion sheet, the interval (pitch) between the tops of the peaks exceeds approximately 10 μm, and many tops with angular shapes have been proposed. ing. Also, in fields such as solar cells and light-emitting diodes, pyramidal or conical irregularities are formed on the surface of semiconductors such as silicone and electrodes for various purposes such as light diffusion, light confinement, and light extraction efficiency. There is.
On the other hand, in the case of a light diffusing sheet formed of a synthetic resin film as in Patent Documents 2 to 5 and having an unevenness of about 1 to 10 μm, the surface of the light diffusion sheet is sharp because it takes a means of molding the synthetic resin. It does not become a shape. Therefore, the effect of anisotropic diffusion is limited. That is, in FIG. 1, light such as d that hits the corrugated slope is refracted and reflected and diffused in the X-axis direction, but light that does not diffuse as a to c at the gentle top of the corrugation. There are many.

Accordingly, the present invention provides a synthetic resinous light diffusion sheet having a substantially corrugated or substantially semi-cylindrical concavo-convex pattern in which peaks are continuous in one direction and peaks and valleys are repeated in a direction perpendicular thereto. The task is to further enhance the ability of sex diffusion.

In order to solve the above-mentioned problems, the present invention employs the following first to third inventions, that is, the configurations of the inventions [1] to [3].
[1] A sheet having a substantially corrugated pattern in which peaks and valleys are repeated in one direction and peaks and valleys are repeated in a direction perpendicular thereto is used as a raw sheet, and a peak or a valley of the raw sheet is formed. In this state, the entire surface of the original sheet is subjected to a conductive treatment such as metal vapor deposition, and electroplating is performed to produce a mold having a surface shape in which corrugated patterns and fine irregularities are combined. , By forming a resin sheet with the mold, the ridges are continuous in one direction, the ridges and valleys are repeated in the direction orthogonal to the direction, and light diffusion that forms fine irregularities on at least a part of the surface A method for producing a light diffusion sheet to obtain a sheet.
[2] In the method of attaching fine particles to the crests or troughs of the raw sheet, the particles are attached by applying an aqueous dispersion in which fine particles are dispersed to the original sheet and drying. The manufacturing method of the light-diffusion sheet | seat as described in [1].
[3] The light according to [1] or [2], wherein a part of the surface of the original sheet is made water-repellent before applying an aqueous dispersion in which fine particles are dispersed to the original sheet. A method for manufacturing a diffusion sheet.

According to the present invention, in a synthetic resinous light diffusing sheet having a substantially corrugated or substantially semi-cylindrical concavo-convex pattern in which peaks are continuous in one direction and peaks and valleys are repeated in a direction perpendicular thereto, light travels straight. The area to be reduced is reduced, and the ability of anisotropic diffusion is further enhanced.

Conceptual diagram showing the light diffusion effect Schematic diagram of an original fabric sheet having irregularities with a substantially semi-cylindrical cross section Schematic diagram of an original sheet having irregularities with a substantially wavy cross-sectional shape Cross-sectional schematic diagram cut along a plane perpendicular to the Y direction in FIG. Schematic diagram of the light diffusion sheet of the present invention having fine irregularities formed

Although the present invention relates to an anisotropic diffusion sheet, in this specification, one direction in which light is diffused is expressed as a diffusion direction, and a direction perpendicular to the direction is expressed as a non-diffusion direction. In FIG. 2, the X-axis direction is the diffusion direction and the Y-axis is the non-diffusion direction.
In the present invention, “a mountain is continuous in one direction” typically refers to a shape as shown in FIG. 2, but also includes a shape as shown in FIG. That is, in FIG. 3, it means that the mountains are continuous in the Y-axis direction as a whole, and there may be a state in which the top of the mountain undulates in the X-axis direction at a certain part.
In the present specification, the substantially waveform indicates a mountain having a substantially triangular cross section as shown in FIG. 3, but having a round top. This also applies to shapes whose cross section is a sine curve.
In addition, the substantially semi-cylindrical shape means that the cross-sectional shape of the mountain is almost a semicircular shape as shown in FIG. 2, and is a shape that is close to a half circle or shallower than a semicircle. May be. In addition, as shown in FIG. 1 or FIG.

4 is a cross-sectional view of the concavo-convex shape of FIG. 3 cut along a plane perpendicular to the Y-axis direction. In the present invention, the peak pitch means the length L shown in FIG. An average value of pitches is obtained by measuring 20 points at random in the X-axis direction and the Y-axis direction and averaging them.
In the present invention, the height of the mountain is an average height from the valley between the valleys between the valleys, and many values obtained by subtracting B2 from the average value of b1 and b2 in FIG. The average value of 20 locations.
In the present invention, for the purpose of diffusing light, the average value of the pitch is in the range of 0.4 to 10 μm, and the height may be arbitrary, but it is preferably in the range of 0.2 to 20 μm. The height is preferably about 0.5 to 2 times the pitch.

In the present invention, the synthetic resin constituting the light diffusion sheet is not particularly limited, and resins generally used for optical sheets can be used. The synthetic resin referred to here is a thermoplastic resin, a curable resin such as thermosetting or radiation curable, synthetic rubber, and the like, and includes a semi-synthetic product made from natural cellulose.
As the thermoplastic resin, various general-purpose resins such as polyolefin-based, polyester-based, polyamide-based, polyimide-based, polyacrylate ester-based, polyurethane-based resins, silicone resins, fluororesins, and the like can be used. Transparent resin is preferable when not only diffusion but also brightness improvement. Examples of the transparent resin include polymethyl methacrylate, polycarbonate, cycloolefin polymer, polyethylene terephthalate, polypropylene, polystyrene, and a copolymer of methyl methacrylate and styrene. Is mentioned.

As the curable resin, epoxy resin, epoxy / acrylic resin, urethane resin, urethane / acrylic resin, melamine resin, phenol resin, unsaturated polyester resin, and the like can be used.
Examples of the semi-synthetic material using cellulose as a raw material include cellulose acetate and rayon.
The thickness of the light diffusion sheet is about 30 μm to 3 mm.

The size of the fine irregularities is determined by the diameter in the largest direction when viewed from a micrograph viewed from the plane of the sheet. If the irregularities are spherical, it means the diameter.
The size of the fine irregularities is preferably less than a half wavelength of visible light so as not to impair the uniformity of the entire light transmittance, and in the case of a spherical shape, the diameter is preferably 200 nm or less. In the case of being elongated like a fiber, the length is preferably 200 nm or less. In addition, it is preferable that the fine irregularities are present by agglomerating some particles from the viewpoint of light diffusibility, and it is particularly preferable that the aggregates are present at intervals.
The amount of fine irregularities is 0.1 to 10% when the sheet is photographed from above with an electron microscope, and the ratio of the fine irregularities to the area of the photographed portion is defined as the area occupation ratio. It is preferable. As for the area occupancy rate, arbitrarily measure 10 points and take an average value, and shooting at one place takes a 10 μm square field of view at 10,000 times.
If the area occupancy is less than 0.1%, the effect of improving anisotropic diffusion is poor, and if it exceeds 10%, there is a risk that large unevenness will occur unevenly. For the same reason, the area occupation ratio is most preferably 0.5 to 5%.

Next, the manufacturing method will be described by taking as an example the case where the surface shape is substantially corrugated.
The light diffusing sheet of the present invention is an original sheet of “a synthetic resin sheet having a substantially corrugated concavo-convex pattern in which a mountain is continuous in one direction and a mountain and a valley are repeated in a direction orthogonal thereto” Manufactured as. Subsequently, the fine particles are attached to the peaks or valleys of the original sheet, and in this state, the entire surface of the original sheet is subjected to a conductive treatment such as metal vapor deposition, and electroplating is performed thereon, thereby forming a waveform. A mold with a surface shape that combines a pattern and fine irregularities is manufactured. The light diffusion sheet of the present invention is completed by molding a resin sheet using this mold.

First, manufacture of a raw fabric sheet is demonstrated.
The original fabric sheet can be manufactured by the method described in Patent Document 4 by the present applicant.
A hard layer with a smooth surface and a thickness of about 0.05 to 5 μm is formed on one side of a uniaxially heat-shrinkable film base material to form a laminated sheet. The hard layer is folded by heat shrinking the laminated sheet. As a result, the corrugated irregularities are generated on the surface.
The film base is manufactured by using a general-purpose resin such as polyethylene resin, polypropylene resin, polyester resin, polyamide resin, etc., and stretched so that the thermal shrinkage rate in the uniaxial direction is increased by the T-die method or the inflation method. To do.
The thickness of the film substrate is preferably 0.3 to 500 μm. If the thickness of the film substrate is 0.3 μm or more, the concavo-convex pattern forming sheet is hardly broken, and if it is 500 μm, the strength is sufficient, and if it is less than this, handling is easy.

When the substance forming the hard layer is a resin, the resin preferably has a glass transition temperature higher by 10 ° C. or more than the resin constituting the film substrate. The hard layer may be a metal or metal oxide vapor deposition layer. As the resin forming the hard layer, polyvinyl alcohol, polystyrene, acrylic resin, styrene-acrylic copolymer, styrene-acrylonitrile copolymer, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethersulfone, fluorine resin Etc.
The thickness of the hard layer is more than 0.05 μm and 5.0 μm or less, preferably 0.1 to 1.0 μm. By setting the hard layer thickness within the above range, the most frequent pitch of the concavo-convex pattern can be controlled to 0.4 to 10 μm.

Below, the method of forming fine unevenness | corrugation in the said original fabric sheet is demonstrated concretely. Here, a method for adhering fine particles to the original fabric will be described. However, after a metal plate as a mold is prepared from the original fabric, another method may be used in which processing such as laser beam or etching is performed on the metal plate. Is possible.
<Example 1>
The prepared raw fabric sheet is coated with an aqueous dispersion in which fine particles are dispersed, and dried to adhere the particles to the corrugated valleys. By adjusting the particle concentration and the amount of liquid coating in the aqueous dispersion, fine particles can be attached only at the valleys with an appropriate interval.
At this time, it is necessary to make the surface in the vicinity of the top water-repellent so that the fine particles do not adhere to the top of the unevenness or the slope of the mountain.
The size of the fine particles is preferably about the same as the size of the fine irregularities described above. However, if the particles are very small, the size of the aggregated particles is reduced to the size of the fine irregularities even if they are coated to some extent. It is possible.

Particle materials include metals such as Al, Au, Ti, Pt, Ag, Cu, Cr, Fe, Ni, Si, metal oxides such as SiO2, Al2O3, TiO2, MgO2, and CaO2, polystyrene, polymethyl methacrylate, etc. In addition to these organic polymers, one or more of semiconductor materials, inorganic polymers, and the like can be employed.
Specifically, for example, anionic colloidal silica sol and cationic alumina sol can be used. As colloidal silica, for example, Snowtex series ST-XS (average particle size 4-6 nm), ST-20 (average particle size 10-20 nm), ST-20L (average particle size 40-50 nm) manufactured by Nissan Chemical Industries, Ltd. ST-YL (average particle size 50-80 nm), ST-ZL (average particle size 70-100 nm), and the like. Examples of the alumina sol include alumina sol 520 (average particle size of 10 to 20 nm) and alumina sol 100 (average particle size of 10 × 100 nm) manufactured by Nissan Chemical Industries, Ltd.
The fine particles may be fine fibers.

After applying fine particles and drying,
With the fine particles attached, the entire uneven surface of the raw sheet is subjected to a conductive treatment such as metal vapor deposition, and electroplating is performed to produce a mold with a surface shape that combines corrugated patterns and fine unevenness. To do.
In the conductive treatment, a metal is vacuum-deposited or sputtered on the surface. Alternatively, the CVD method may be used. The vapor deposition metal may be used for a normal electrode film such as copper, zinc, and aluminum, and a film thickness of about 20 to 100 nm is sufficient.

Next, metal plating is performed on the conductively processed surface by electroplating. The thickness of the plating may be a thickness that does not deform the plated portion as a metal plate and can withstand the subsequent forming process, and may be a sheet of about 0.1 to 1 mm. However, when used alone as a stamper, the thickness of the plating layer needs to be 1 mm or more, preferably about 2 to 5 mm. The metal to be plated is not particularly limited, and copper, silver, iron, lead, zinc, tin, nickel, chromium, molybdenum, or an appropriate alloy thereof can be used.
Thereafter, the original sheet and the metal plate manufactured by the plating method are separated, and the deposited metal is washed and removed as necessary to complete the mold.
The fine particles used in the above procedure were spherical, but in the process of vapor deposition and plating, the spheres of the fine particles and the vicinity of the contact points of the valleys were buried, and as a result, the protrusions due to the fine particles became substantially hemispherical. .

<Example 2>
When molding is performed by pouring a resin into the above mold, the finished molding resin has a shape in which a fine concave portion exists at the top of the mountain. On the other hand, when it is desired to provide fine convex portions on the tops of the ridges of the molded resin, another manufacturing method is required. Here, an example of the method is shown below.
First, a fine particle particle layer is formed on the plate by a coating method, and a small amount of adhesive is applied to the top of the uneven crest of the original fabric sheet, and the particle can be transferred from the particle layer to the top of the mountain. is there.

It is preferable that a small amount of adhesive be applied by the following transfer method.
First, a sheet in which an adhesive having a thickness of about 10 to 50 nm is applied in a stripe shape or a polka dot pattern is prepared, and the adhesive layer is transferred from the sheet to the top of the original sheet. Separately, a sheet coated with fine particles is prepared, and the original sheet on which the pressure-sensitive adhesive layer is transferred is pressed to transfer the fine particles to the pressure-sensitive adhesive layer.
By this method, the agglomerated fine particles can be intermittently disposed on the tops of the uneven peaks. The stripe interval or polka dot pattern can also be used for product identification. Also in this method, the mold is manufactured by the plating method as in the first embodiment.
Again, the fine particles used were spherical, but in the bonding, vapor deposition, and plating processes, the spherical shape of the fine particles and the vicinity of the contact point of the ridges were buried, and as a result, the projections due to the fine particles were approximately hemispherical. become.

<Example 3>
Specific examples of the method for producing the light diffusion sheet of the present invention using the mold include the following methods (a) to (d).
(A) After applying the uncured ionizing radiation curable resin to the surface on which the concave / convex pattern of the mold is formed, and irradiating ionizing radiation such as ultraviolet rays and electron beams to cure the curable resin And a step of peeling the cured coating film from the mold.
(B) a step of applying an uncured liquid thermosetting resin to the surface of the mold having the concavo-convex pattern formed thereon; and heating and curing the liquid thermosetting resin; And a step of peeling from the substrate.
(C) A step of bringing a sheet-like thermoplastic resin into contact with the surface of the mold on which the concavo-convex pattern is formed, and a step of cooling the sheet-like thermoplastic resin while heating it against the mold and then cooling it And a step of peeling the cooled sheet-like thermoplastic resin from the mold.
(D) A method in which a molten thermoplastic resin is poured onto the surface of the mold on which the concavo-convex pattern is formed to cool and solidify.

<Comparative Example 1>
Create the original sheet:
Polymethylmethacrylate (Polymer Source Co., Ltd.) diluted with toluene on one side of a polyethylene terephthalate heat-shrinkable film (Mitsubishi Resin HXIPET LX-60S, glass transition temperature 70 ° C.) having a thickness of 50 μm that thermally shrinks in a uniaxial direction (P4831-MMA manufactured by Glass Manufacturing Co., Ltd., glass transition temperature 100 ° C.) was applied by a bar coater so as to have a thickness of 1 μm, and a functional layer was formed to obtain a laminated sheet. Next, the laminated sheet is heated at 80 ° C. for 50 seconds to cause heat shrinkage to 60% of the length before heating (ie, deformation at a deformation rate of 40%), and on the functional layer forming surface in the shrinking direction. Thus, an original sheet having a wavy uneven pattern along the orthogonal direction was obtained. By using this raw sheet, an optical element was obtained as follows.

Transfer from the original sheet:
That is, the surface of the original sheet on which the concave / convex pattern was formed was subjected to nickel plating, and the nickel plating was peeled off to obtain a mold having a thickness of 200 μm. An uncured ultraviolet curable resin composition containing an epoxy acrylate prepolymer, 2-ethylhexyl acrylate and a benzophenone photopolymerization initiator was applied to the surface of the mold on which the concavo-convex pattern was formed.
Next, a 50 μm thick triacetyl cellulose film was superimposed on the surface of the uncured ultraviolet curable resin composition coating film not in contact with the original sheet, and pressed.
Subsequently, an anisotropic diffusion sheet was obtained by irradiating ultraviolet rays from above the triacetylcellulose film to cure the uncured ultraviolet curable resin composition and peeling the cured product from the mold.
The performance of the obtained anisotropic diffusion sheet as a light diffuser was evaluated as follows. That is, the diffusion angle was measured using GENESISA GonioFar Field Profiler (manufactured by Genesia). As a result, the diffusion angle in the contraction direction, that is, the maximum value of the diffusion angle was 27 degrees.

Here, the diffusion angle means that the measurement light is incident along the normal direction of the sheet surface from the surface where the uneven pattern of the anisotropic diffusion sheet is not formed, and from the surface where the uneven pattern is formed. When emitting and measuring the illuminance, the ± (plus or minus) angle that makes the relative illuminance 0.5 or more when the relative illuminance is 1 in the normal direction of the sheet surface (this direction is the light emission angle 0 degree) It is a range. For example, when the light emission angle is in the range of ± 15 degrees and the relative illuminance is 0.5 or more, the diffusion angle is 30 degrees. The maximum value of the diffusion angle is the maximum diffusion angle when the diffusion angle is measured in all directions within the sheet surface.

<Example 4>
An acrylic adhesive stripe film having a thickness of about 50 nm was formed on a polypropylene film with a width of 1 mm and a spacing of 1 mm, and this stripe pattern was transferred to the uneven surface of the original fabric sheet of Comparative Example 1. Next, the particle layer obtained by applying and drying colloidal silica having an average particle diameter of about 100 nm by the method of Example 2 is transferred to the transferred stripe film, and with fine particles having the same shape as in FIG. A raw sheet was prepared. Subsequently, thereafter, an anisotropic diffusion sheet was produced in the same manner as in Comparative Example 1. With respect to this anisotropic diffusion sheet, the maximum diffusion angle was measured in the same manner as in Comparative Example 1. As a result, it was 32 degrees, an improvement of 18% compared with Comparative Example 1.

It can be used as an anisotropic light diffusing sheet that diffuses light emitted from fluorescent lamps, light emitting diodes, organic EL, etc. in a desired direction and hides the shape of the light source in a display or a lighting fixture.

Claims (3)

Crests are continuous in one direction, and crests and troughs are repeated in a direction perpendicular thereto, and a sheet having a substantially wavy uneven pattern is used as a raw sheet, and fine particles are formed on the crests or troughs of the raw sheet. In this state, the entire surface of the raw sheet is subjected to a conductive treatment such as metal vapor deposition, and electroplating is performed to produce a mold having a surface shape in which a corrugated pattern and fine irregularities are combined. By molding the resin sheet, a light diffusion sheet is obtained in which peaks are continuous in one direction, and peaks and valleys are repeated in a direction perpendicular to the direction, and fine irregularities are formed on at least a part of the surface. A method for producing a light diffusion sheet. The method of attaching fine particles to the crests or valleys of the original fabric sheet is to apply particles to the original fabric sheet by applying an aqueous dispersion in which fine particles are dispersed and drying. The manufacturing method of the light-diffusion sheet of Claim 1. The method for producing a light diffusing sheet according to claim 2, wherein a part of the surface of the original fabric sheet is made water-repellent before an aqueous dispersion in which fine particles are dispersed is applied to the original fabric sheet.

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