JPH1055712A - Light guide plate for planar light source and its molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of parts and reduce a light scattering loss of an adhering part so as to brighten a screen by employing one flat face as a ragged light scattering face and the other face as a light emission face having numeral convergent lens units to be emitted to a specified direction. SOLUTION: A light scattering face and a light emission face are formed on a double-sided flat face of a translucent light guide plate by fine processing. Preferably, the light scattering face of a wedge-shaped extremely thin eccentric light guide plate is a grid-shaped pattern roughly faced in a ragged shape, as a substantially rectangular light scattering part is further from a light incident face a side parallel to the light incident face is lengthened, and a distance between the adjacent light scattering parts is reduced. It is preferable that a shape of the convergent lens unit to be formed on the light emission face is a multi-linear prism. This light guide plate is provided with a synthetic resin ejection-molded and formed for a die made of a nest top shaped dies 2 and 2' for forming a cavity having dies 1 and 1', a thickness part A and a thickness part B, a heat insulation layers 3 and 3', a face roughened gold layer 4 adhered thereto, and a fine convergent lens shaped gold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate for a planar light source suitable for a backlight of a liquid crystal display device and the like, and a method for forming the light guide plate.

[0002]

2. Description of the Related Art Since a planar light source device is thin and lightweight, it can be used as an OA for word processors, personal computers, and the like.
(Office Automation) It is used for backlights and light-emitting signs of liquid crystal display devices used for devices and various monitors of image signals, and thin evacuation guide lights with enhanced decorativeness. The surface light source device is a so-called direct type in which a plurality of straight or U-shaped fluorescent lamps are arranged in a space directly below a display surface and a diffusion plate is disposed thereon, or a side end portion (edge) of a resin transparent light guide plate. Almost all are so-called edge light types, in which one or two fluorescent lamps are arranged and a diffusion film and a prism sheet are arranged on the light emitting surface. In recent years, light guide plates for planar light sources used for backlights of liquid crystal display devices typified by notebook personal computers have been required to meet the demands for thinner, lighter, lower power, higher brightness, and higher definition liquid crystal display devices. A wedge-shaped uneven light guide plate having a tapered inclined surface has been proposed.

Further, the size of liquid crystal display devices has been increasing, and a light guide plate for a planar light source is required to have a thin, wedge-shaped, uneven thickness and a large-screen light guide plate. The injection molding method of the planar light source light guide plate used for the backlight of the liquid crystal display device is performed by injecting and filling the molten resin into the mold cavity and holding the pressure through the molten resin on the spool until the gate portion is cooled and solidified. A method of obtaining a molded product in a mold after applying pressure to the cavity and solidifying the gate is usually performed. A light guide plate for a planar light source is used as an injection molding method, for example, as disclosed in
96820, JP-A-6-324632, JP-A-7-324
159623 and JP-A-7-164496.

In general, filling in such injection molding,
In the pressure-holding step, pressure distribution is generated in the cavity due to the flow resistance and cooling of the molten resin, and uneven cooling is likely to occur. Particularly, it is remarkable in an ultra-thin light guide plate in which the thickness of the thin portion of the uneven thickness light guide plate is 1 mm or less. In addition, if the distance from the gate to the flow end is long, the filling may be poor. For the method of injection-molding an ultra-thin walled light-guiding plate in which the thickness of the thin-walled light-guiding plate is 1 mm or less, use of a highly fluid resin, high-speed injection molding, a method of increasing the mold temperature, a high injection pressure or a high Injection molding is performed using conditions such as the use of pressure-holding conditions, but this is not sufficient.

[0005] The use of a high-flowable resin tends to improve the filling property of a thin-walled molded product, but there is a problem that the molecular weight of the synthetic resin is reduced, the mechanical strength of the resin is reduced, and its use is restricted. When the injection pressure or the holding pressure is employed, the sink in the thick portion is reduced, but the residual stress in the thin portion having a high cooling rate is increased, and the molded product is likely to be deformed or warped. There is a problem that disadvantages occur. Among these factors, the mold temperature has the greatest effect on the effect, and increasing the mold temperature is very effective. However, when the mold temperature is increased, the cooling time required for cooling and solidifying the plasticized resin increases, and the molding efficiency decreases. For this reason, there is a demand for a method of improving the resin fluidity in the mold without increasing the mold temperature and a method of preventing the required cooling time from being prolonged even if the mold temperature is increased. There is also a method in which holes for heating and cooling are attached to the mold, and heating and cooling of the mold are repeated by alternately flowing a heat medium and a coolant.However, this method uses a large amount of heat and cools The time gets longer.

US Pat. No. 3,544,518 discloses a method of improving the mold surface reproducibility by coating the mold wall surface forming the mold cavity with a substance having low thermal conductivity. Further, JP-A-53-8
No. 6,754 discloses a mold in which a heat insulating layer is coated on a metal mold wall surface, and a thin metal layer is coated on a cross-sectional surface of the metal mold.

A backlight of a liquid crystal display device using a light guide plate for a planar light source generally has a configuration as shown in FIG. FIG. 2 is a schematic diagram showing a cross-sectional view of a conventional surface light source device.
In FIG. 2, 1 is a transparent light guide plate, 2 is a light scattering portion, 3 is a reflection film, 4 is a diffusion film, 5 is a prism sheet,
6 is a primary light source, and 7 is a light incident surface. A light scattering portion is formed on one side of the light guide plate by printing or the like, and the light scattering portion is formed so as to be small near the primary light source and to be larger as the distance from the primary light source increases so that the entire light emitting surface shines uniformly. I have.
The arrangement of the light scattering portions, for example, the manner of changing the shape and size, varies depending on the light emitting area and the thickness of the light guide plate.
Techniques relating to such a surface light source device include, for example, JP-A Nos. 2-17, 4-52286 and 4-16.
2002, JP-A-5-173130, JP-A-6-1
86562, JP-A-6-265888, and the like. Japanese Patent Laid-Open No. 2-17 discloses a first element provided with a reflective layer on the side opposite to the exit surface of a light guide plate, and a number of lenses for emitting light from a light exit surface of the first element in a predetermined direction. A surface light source element combining a second element having a unit has been proposed. Japanese Patent Application Laid-Open No. 7-117144 discloses a method for manufacturing a light guide plate for a surface light source that collects light in a direction in which a second element having a large number of lens units is provided. .

However, there is no known resin transparent light guide plate used in a surface light source device, which is formed by injection molding a light guide plate for a surface light source having a light scattering portion on one surface and a prism integrated on the other surface.

[0009]

SUMMARY OF THE INVENTION The present invention provides a light guide plate for a surface light source in which a light scattering portion and a prism of fine processing are integrally formed on the front and back surfaces of a transparent light guide plate. The number of parts can be reduced, and the light scattering loss at the bonding part of the constituent parts can be reduced, and the brightness of the screen can be improved. One surface of the transparent light guide plate is a light scattering surface having an uneven shape, and the other surface is a light emitting surface on which a plurality of converging lens units for emitting light in a predetermined direction are formed. The transparent light-guiding plate for the shape light source does not need to raise the temperature of the entire mold, and has the same effect as increasing the temperature of the mold, improving the transferability of the mold and resin filling during injection molding. The present invention meets the demand for a method of forming a large-screen ultra-thin light guide plate in a good and efficient manner by reducing the internal residual strain and extending the flow distance.

[0010]

SUMMARY OF THE INVENTION The present applicant has previously described a mold for a resin light guide plate and a method for molding a resin light guide plate using the mold. One surface forming the mold surface of the mold is roughened in the metal for injection-molding a light guide plate having a light-scattering portion having an uneven surface formed on one side perpendicular to the light-emitting surface of the opposite surface. A metal mold having a patterned surface and a back surface of the metal sheet having a layer structure comprising a heat insulating layer made of a heat-resistant resin polymer, and a resin light guide plate molding die, and injection molding using the metal mold Proposed the law. (Japanese Patent Application No. 7-337673) As a result of diligent studies on a method of more efficiently forming a large-screen ultra-thin walled light guide plate with good efficiency, the present inventors have found that the thickness of the heat-insulating layer made of a heat-resistant polymer has been reduced. It has been found that the above problem can be solved by controlling, and furthermore, a transparent light guide plate for a two-sided micro-machined planar light source in which a number of converging lens units for emitting light in a predetermined direction are formed on the light exit surface of the light guide plate. It has been clarified that the present invention can be obtained, thereby completing the present invention. That is, the present invention provides a light guide plate for a planar light source in which a primary light source is arranged on a side end surface of a resin transparent light guide plate, wherein one plane of the transparent light guide plate is formed as an uneven light scattering surface, and the other is formed. This is a light guide plate for a planar light source characterized by a double-sided fine processing in which a flat surface is formed as a light emitting surface and a plurality of converging lens units for emitting light in a predetermined direction are formed.

The light-scattering surface is arranged in a lattice pattern with a roughened pattern, and the light-scattering portion is formed in a substantially rectangular shape, and the side parallel to the rectangular light-incident surface becomes more distant from the light-incident surface. It is preferable to increase the length of the light scattering portion and to reduce the distance between the adjacent light scattering portions. Further, the shape of the converging lens unit is preferably a multi-linear prism, and more preferably, the shape of the planar light source light guide plate is an uneven thickness shape having a wedge-shaped thick portion and a thin portion.

Further, in a method of molding a light guide plate for a planar light source using a mold having a mold cavity having a thick portion and a thin portion, a heat insulating layer is coated on both surfaces of a mold wall surface constituting the mold cavity. And fine processing of irregularities on the flat part on the heat insulating layer,
Using a heat-insulating layer-coated mold in which a metal layer subjected to fine processing of a number of converging lens units is closely adhered to the other flat portion, the difference between the maximum thickness of the thick portion of the mold cavity and the minimum thickness of the thin portion is A,
When the difference between (the thickness of the mold cavity + the thickness of the heat-insulating layer) in the maximum thickness portion of the mold cavity and the (thickness of the mold cavity + the thickness of the heat-insulating layer) in the minimum thin portion of the mold cavity is B, A> 0.5 mm, A ≧ B, preferably A =
It is preferable to use a heat-insulating-layer-coated mold having a relationship of 0.5 to 10 mm and 0.7A ≧ B to form a light-guided light-guiding plate for a planar light source.

Further, it is preferable that the thickness of the finely processed metal layer is not more than 1/3 of the thickness of the heat insulating layer, and the thickness is from 0.01 to 1 mm. Hereinafter, the present invention will be described in detail. One of the materials for the transparent light guide plate used in the injection molding of the present invention is a transparent synthetic resin, such as a styrene-based polymer, polycarbonate, and methacrylic resin. Of these, methacrylic resins and polycarbonates are particularly preferred from the viewpoint of excellent transparency and light resistance. As the most preferable materials for the transparent light guide plate, for example, the present applicant discloses Japanese Patent Application Nos. 7-33766 and 7-5867.
No. 1 is shown.

The shape of the light guide plate for a planar light source is a flat or wedge-shaped uneven thickness having a so-called thick portion and a thin portion. In the wedge shape, a light beam incident from the thick portion on the side end face of the light guide plate is fixed. It is preferable that light is emitted from the end of the light guide plate since it approaches the terminal end (thin portion) of the light guide plate while repeating reflection while receiving a change in direction due to scattering. And when molding the terminal part of the light guide plate, as a method of improving the fluidity of the resin at the terminal part,
The mold for covering a heat insulating layer of the present invention is effective.

The metal used for the mold of the present invention is a metal generally used for a mold. For example, a metal mold generally used for molding a synthetic resin such as iron or a steel material containing iron as a main component, aluminum or an alloy containing aluminum as a main component, a zinc alloy, and a beryllium-copper alloy is included. Particularly, a mold made of a steel material can be used favorably. It is preferable to apply chrome plating or nickel plating to the mold wall surface forming the mold cavity of the main mold made of these metals. Chromium plating or nickel plating has excellent adhesion to the heat insulating layer and also has excellent corrosion resistance. In injection molding, since heating and cooling are repeatedly applied to the mold, it is very important that the adhesion is stable and large, and in order to withstand tens of thousands of moldings, the above plating effect is large and preferable. is there.

The heat insulating material forming the heat insulating layer of the present invention is a substance having a thermal conductivity of 1/10 or less, preferably 1/20 or less of the thermal conductivity of the metal forming the main mold. Preferred heat insulating layers are various heat-resistant resin polymers, various ceramics, and the like. Most preferably used are heat-resistant polymers. The heat-resistant polymer has a glass transition temperature of 150 ° C. or higher, preferably 200 ° C. or higher, more preferably 230 ° C.
And / or a melting point of 200 ° C. or higher, preferably 25 ° C.
It is a heat-resistant polymer having a temperature of 0 ° C or higher, more preferably 280 ° C or higher. The smaller the thermal conductivity of the heat-resistant polymer, the more preferable,
The thermal conductivity is 0.002 cal / cm · sec · ° C. or less, and a general polymer has this thermal conductivity or less. The toughness of the heat-resistant polymer is preferably 10% or more. The elongation at break is performed according to ASTM D638,
The tensile speed is 5 mm / min.

The polymer which can be used favorably as the heat-insulating layer in the present invention is a heat-resistant polymer having an aromatic ring in its main chain, and various amorphous heat-resistant polymers, various polyimides and epoxy resins soluble in organic solvents. And so on. Examples of the non-crystalline heat-resistant polymer include polysulfone, polyether sulfone, polyallylsulfone, polyarylate, polyphenylene ether, polybenzimidazole and the like. There are various kinds of polyimides, and they are classified into a linear type and a thermosetting type, and various types are known as respective polyimide precursors.

The heat-insulating layer used in the present invention has a low thermal conductivity, an excellent heat resistance, a high tensile strength, a large elongation and a high resistance to cooling and heating cycles, and a good application to a mold body. A linear high molecular weight polyimide is preferred because of its good adhesion to the mold. For example, the preferred product names are Kapton (manufactured by Toray), Novax (manufactured by Mitsubishi Chemical), Upilex S or Upilex R (manufactured by Ube Industries), LarcTPI (manufactured by Mitsui Toatsu Chemicals), and the like. In order to firmly adhere the polyimide layer to the mold, it is most preferable to apply a precursor solution of linear high molecular weight polyimide to the mold and then heat to form the polyimide. The precursor of the linear high molecular weight polyimide is synthesized by, for example, subjecting an aromatic diamine and an aromatic tetracarboxylic dianhydride to a ring-opening polyaddition reaction.
These polyimide precursors are heated to cause a dehydration cyclization reaction to form a polyimide. The polyimide precursor polymer has good adhesion to a mold because of a polar group such as a carboxyl group. The above polyimide precursor polymer is dissolved in a solvent such as N-methylpyrrolidone and applied to the mold wall. To adjust the viscosity during coating, adjust the surface tension of the solution, add an additive to adjust the thixotropic property, and / or increase the adhesion to the mold to the polyimide precursor solution Minor additives can be added. Among these polyimides, pyromellitic dianhydride-based polyimide is most preferable because of its excellent heat resistance and mechanical properties. Particularly, a varnish modified for coating can be excellent.

As the epoxy resin, an epoxy resin cured product combined with a curing agent or an epoxy resin mixed with various fillers in an appropriate amount can be used (hereinafter, the epoxy resin cured product is referred to as an epoxy resin). Epoxy resins generally have a large coefficient of thermal expansion and a large difference in the coefficient of thermal expansion from a metal mold.
However, glass, silica, clay,
Powder of talc, calcium carbonate, alumina, mica, etc.
A filler-containing epoxy resin in which an appropriate amount of whiskers, carbon fibers, or the like is mixed with an epoxy resin to reduce the difference in thermal expansion coefficient from a metal mold can be used favorably as the heat insulating layer of the present invention.

A compounded epoxy resin obtained by adding a tough thermoplastic resin such as nylon or various compounds such as rubber to an epoxy resin or a compounded epoxy resin with a filler to impart toughness can be improved. In particular, a polymer alloy cured by mixing polyethersulfone or polyetherimide with an epoxy resin is excellent in toughness and can be excellent. The injection molding method has economic value in that a wedge-shaped uneven light guide plate having a tapered slope can be obtained by a single molding. The methacrylic resin has a high viscosity at the time of melting and, in the case of an ultra-thin molded product having a thickness of 1 mm or less, the fluidity of the resin is extremely deteriorated and may not be sufficiently filled. The preferred uneven light guide plate for a planar light source in the present invention has a mold cavity thickness of the thinnest thin portion of 0.1.
It is a very thin light guide plate of の 1 mm.

The mold cavity is generally of a complicated shape, and it is extremely difficult to apply a mirror-like coating to the surface of the mold cavity and the wall surface of the mold having such a complicated shape. It is preferable that the surface is polished later, or the coating layer is shaved by a numerically controlled machine tool such as a numerically controlled milling machine and then polished to a mirror finish. The relationship between the thickness of the mold cavity and the thickness of the heat insulating layer of the present invention satisfies the following conditions. That is, A: the difference between the thickness of the mold cavity thick portion and the thickness of the mold cavity thin portion (difference in thickness of the mold thickness variation), B: (mold cavity thickness + insulation layer thickness) of the mold cavity thick portion and the mold A> 0.5 mm and A ≧ B as a difference between (mold cavity + heat insulation layer thickness) of the cavity thin portion. Preferably, A = 0.5-10 mm, and 0.7
A> B ≧ 0 mm, more preferably A = 1 to 5 mm,
And 0.5A> B ≧ 0 mm.

In the present invention, the thickness of the heat insulating layer covering the mold wall surface constituting the mold cavity is appropriately selected within a range of 5 mm or less, and the heat insulating layer is thin at the thick portion of the mold cavity.
It is thickly covered with the thin part of the mold cavity. In the present invention, the case where only the thin portion of the mold cavity is covered with the heat insulating layer and the thick portion of the mold cavity does not have the heat insulating layer is also included. In this case, the mold cavity thick part (mold cavity + heat insulation layer thickness)
Is equal to the mold cavity thickness. When the thick part of the mold cavity is sufficiently thick, it is preferable to cover only a part of the thin part of the mold cavity with the heat insulating layer without the need for the heat insulating layer. A preferable thickness of the heat insulating layer is 0.01 mm to 3 mm, more preferably 0.1 mm to 2 mm, and a mold in which the (mold cavity + heat insulating layer thickness) value of the heat insulating layer coating mold is uniform.

In the present invention, a thin metal layer is present on the heat insulating layer. The adhesive resin layer also becomes a heat insulating layer. If the thickness of the heat insulating layer exceeds 5 mm, the cooling effect of the mold decreases,
Molding efficiency decreases. The higher the temperature of the mold, the thinner the thickness of the heat-insulating layer made of the heat-resistant polymer, and the lower the temperature of the mold, the thicker the thickness of the heat-insulating layer. It is most preferable to use a prepared mold. Also, (mold cavity thickness + heat insulation layer thickness)
The maximum value is within the range of 1 to 3 times the minimum value, and 3
If it exceeds twice, the cooling efficiency of the mold decreases, and the molding efficiency deteriorates. In the present invention, the mold covered with the heat insulating layer is a mold in which both the mold wall surface constituting the mold cavity and the mold wall surface constituting the core mold are coated. The effect is great, and the transferability of the finely machined surface of the mold is excellent and particularly preferable.

A metal layer coated with a heat insulating layer of polyimide or the like and having a thickness of 0.01 to 1 mm or less of the thickness of the heat insulating layer and having a thickness of 0.01 to 1 mm, which is in close contact with the heat insulating layer and has been subjected to fine processing. Is used. The uneven thickness light guide plate for a planar light source according to the present invention is a thickness uneven light guide plate for a planar light source in which a primary light source is disposed at a thick portion on a side end surface of a resin transparent light guide plate, and one plane of the transparent light guide plate is provided. Is a light scattering surface having concavo-convex shapes, and is formed by fine processing on both sides in which a plurality of converging lens units for emitting the other plane in a predetermined direction on the light emitting surface are formed. The light-scattering surface is arranged in a lattice pattern with a roughened pattern, and the light-scattering portion is formed in a substantially rectangular shape. As the distance from the light-incident surface increases, the length of a side parallel to the rectangular light-incident surface increases. An uneven thickness light guide plate for a planar light source, wherein the distance between adjacent light scattering portions is reduced.

The light-scattering portion is formed such that the thick portion of the light guide plate is 1
As the light source becomes the next light source, the distance from the light source increases, that is, the light source gradually expands or becomes denser toward the thin portion. The plane figure of the shape may be any shape such as a circle, an ellipse, a triangle, a square, a polygon, a semicircle, a crescent, or a combination of two or more of these plane figures. The light of the primary light source is scattered on the roughened surface by roughening one surface of the light guide plate with the fine irregularities in the shape of the plane figure, and the luminous efficiency and the uniform light emission on the surface of the light guide plate are uniform. The performance is improved. The height and depth of the unevenness exhibiting such an effect is 1 to 5
About 0 μm is good.

As a method of forming fine irregularities on the mold, a known method such as etching, cutting, electric discharge machining, laser machining, electroforming, and casting is suitably applied to the surface of the mold metal plate. Used. For example, a method in which an arrangement pattern of light scattering portions is formed in advance on a photographic film or the like, a mask corresponding to this arrangement pattern is formed on a surface of a mold metal layer by a photoresist method, and then the mold metal layer is chemically etched. Are known. As a desirable arrangement pattern of light scattering portions having fine unevenness, for example, the arrangement, shape, size, and the like of a grain pattern are described in Japanese Patent Application Laid-Open No. 7-104296 by the present applicant.

As an example of the electroforming method, first, steel,
A master having a desired shape and an array pattern is placed on the surface of a metal base material for transfer such as aluminum or brass, and the shape pattern is etched or cut to form fine irregularities to form an electroform for electroforming. Make it. Next, the resultant is put into an electrodeposition layer and subjected to an electrodeposition process of laminating a metal plating on the surface of the electroform, and the thickness of the plating layer is set to a desired thickness in a range of 0.1 to 1 mm. After the electrodeposition, the electroform is taken out of the electrodeposition bath, and the laminated plating portion is peeled off from the electroform of the base material, whereby the unevenness of the electroformed surface is transferred to the surface of the laminated plating material. The transferred laminated plating plate is used as a metal layer of a mold part for injection molding.

A metal mold surface is covered with a heat insulating layer,
When the injected synthetic resin comes into contact with the surface, the surface of the mold is heated by the heat of the synthetic resin. The lower the thermal conductivity of the heat insulating layer and the thicker the heat insulating layer, the higher the mold surface temperature. Therefore, the smaller the thickness of the metal layer adhered on the heat insulating layer, the better, and the effect of the present invention can be obtained. And
The thickness of this thin metal layer is preferably uniform. If the thickness variation of the metal layer is large, the mold surface reproducibility of the thick portion of the metal layer is deteriorated, and the fluidity of the synthetic resin material changes.

The metal layer of the present invention can be coated by various methods, but is preferably coated by plating. The plating described here is chemical plating (electroless plating) and electrolytic plating. Generally, plating is performed through some of the following steps. That is, first, chemical plating is performed in contact with the heat insulating layer. Pretreatment → chemical corrosion (chemical etching with acid and alkali:
→ Surface neutralization → Neutralization → Sensitivity treatment (Enhance activation effect by adsorbing a reducing metal salt on the synthetic resin surface) → Activation treatment (noble metal such as palladium which has catalytic action) To the heat insulating layer resin surface) → chemical plating (chemical nickel, copper plating, etc.) → electrolytic plating (electrolytic nickel, copper, chromium plating, etc.).

According to the present invention, a thin metal plate of 1 mm or less can be attached to the surface of the heat insulating layer. Examples of the thin metal plate include SUS304H and a copper plate.
The 04H tension annealing material is preferably used because it hardly warps, and such a thin metal plate surface etching method is preferable. On the other mold plane of the uneven thickness light guide plate for a planar light source of the present invention, a number of converging lens units for emitting light in a predetermined direction on a light emitting surface are formed. The uneven thickness light guide plate for a planar light source of the present invention is such that an incident light beam is reflected in a light scattering portion in a direction of an emission surface, and the emission light can be concentrated and converged in a specific direction by a converging lens on the emission surface. is there. As such a convergent lens shape, a convex lenticular lens, a triangular prism lenticular lens, a polygonal pyramidal lenticular lens, or the like is appropriately used. Among these, a multi-line prism having a convex lens and a triangular prism-shaped lenticular lens is the most preferable shape of the uneven light guide plate for a planar light source.

A general prism shape has an apex angle of 60 to
120 °, height 10-50 μm, pitch 25-10
A range of 0 μm is desirable, a vertex angle of 90 °, a height of 25 μm,
A pitch of 50 μm is typically used. As a method for forming a lens having a fine convex shape on the mold, a known method such as an etching process, a cutting process, and an electroforming process is appropriately used on the surface of the mold metal plate.

Generally, the pressure loss of a fluid flowing between parallel plates is expressed by the following equation. ΔA = β × LηQ / H ² ΔP = pressure loss, H = distance between parallel plates (mold cavity thickness), η = viscosity, β = constant, Q = flow rate, L = flow distance, ie pressure loss is viscosity and flow distance And is proportional to the square of the distance between the parallel plates. In the injection molding, as is clear from the above formula, the pressure loss increases as the distance from the gate increases, and the resin pressure pressing the mold surface decreases. This is because the viscosity of the resin increases with time because the injected synthetic resin is cooled at a portion in contact with the mold surface. Then, the force with which the injected resin is pressed against the mold surface with time and the fluidity in the flowing direction decrease. Also, at the flow end, the transferability of the mold surface is reduced. In particular, when L and η in the above formulas are large, that is, in a large-sized thin-walled molded product having a high viscosity, a problem occurs in fluidity and transferability of a mold surface. The present invention has an effect of delaying the cooling rate in the thin portion by covering the thin portion of the mold cavity with the heat insulating layer, and can perform molding without significantly lowering the fluidity of the synthetic resin.

In synthetic resin injection molding, mold temperature and molding cycle time are closely related. Generally, the relationship between the mold temperature (Td) during molding and the required cooling time in the mold (θ) is expressed by the following equation. θ = − (D ² / 2πα) ln [π / 4 (Tx−Td) /
(Tc-Td)] θ: Cooling time (sec), D: Maximum thickness of molded product (c
m), Tc: heated resin temperature during molding (° C.), Tx: softening temperature of molded synthetic resin (° C.), α: thermal diffusivity of synthetic resin,
Td: mold temperature (° C.) Cooling time (θ) is proportional to the square of the maximum thickness (D) of the molded product, and is a function of (Tx−Td) / (Tc−Td).

The coating of the heat-insulating layer on the thin portion of the mold cavity in the mold has the same function as increasing the cooling time by increasing the thickness of the thin portion of the light guide plate. On the other hand, when the mold temperature is lowered, the cooling time is shortened. Therefore, it is very economically preferable from the viewpoint of the molding cycle that the thickness of the heat-insulating layer is thin so that the flowability can be improved and the transferability of the mold surface can be improved. In the case of injection-molding the uneven thickness light guide plate, the maximum thickness of the molded product is determined by the above-mentioned relational expression between the mold temperature (Td) and the required cooling time in the mold (θ). In the thin portion of the mold cavity, the heat insulation layer may be thickened, and (mold cavity thickness + heat insulation layer thickness) is important for the molding cycle time. Therefore, when the thickness of the mold cavity is sufficiently large, covering the heat insulating layer is not preferable because the molding efficiency is reduced. In the thin part of the mold cavity, the heat insulation layer is thickly covered, (mold cavity thickness + heat insulation layer thickness)
A mold having a uniform value is preferable, and a balance between the flowability of the synthetic resin, the transferability of the mold surface, and the molding efficiency is preferable.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the vicinity of a mold cavity in a mold for molding a light-thickness light guide plate for a planar light source according to the present invention. In FIG. 1, metal molds 1 and 1 ′ are nested piece molds 2,
2 ′, the mold cavity has a thick portion (a) and a thin portion (b), and the mold wall surfaces constituting the mold cavity are covered with heat insulating layers 3 and 3 ′. This is a heat-insulating-layer-coated mold in which the metal layers 4 and 4 'adhered to the metal were present. Then, the metal layer 4 is formed densely from the thick portion to the thin portion in a finely roughened pattern with an uneven shape, and the metal layer 4 ′ is formed in a number of fine converging lens shapes. I have.

When the difference between the thickness (a) of the thick part of the mold cavity and the thickness (b) of the thin part is A, A> 0.5 mm, preferably A = 0.5 to 10 mm. Furthermore, (mold cavity thickness + insulation layer thickness) of the mold cavity thick portion and (mold cavity thickness + insulation layer thickness) of the mold cavity thin portion
Is a mold having a coating thickness of the heat insulating layer that satisfies the relationship of A ≧ B, where B is the difference between the two. Preferably, 0.7> B ≧ 0. A preferable thickness of the metal layer is 1/3 or less of the thickness of the heat insulating layer and 0.001 to 1 mm, more preferably 0.05 to 1 mm.
The thickness is about 0.5 mm. The surface of the metal layer includes a textured surface, a metal surface patterned in an uneven pattern, a prism shape, and the like. The metal layer on one side of the mold has a thick portion of the mold cavity of 1
On the light source lamp side of the next light source, the unevenness of the light scattering portion is rough and densely formed toward the thin portion. On the other hand, the metal layer on the opposite mold side has a vertical angle of 90 degrees, a pitch of 50 μm, and a depth of 2 μm.
It is a metal layer formed in a 5 μm prism shape.

The optical characteristics were measured by the following apparatus and under the following conditions. (1) Measurement of Luminance and Luminance Distribution of Light Guide Plate Reflective film on light scattering part side of diffused light guide plate, diffusion film on light emitting surface side, cold cathode fluorescent tube (diameter 3 m)
m, length 220 mm) and connected to an inverter to produce a planar light source device. After turning on the power to make the cold cathode fluorescent tube emit light and leaving it for 30 minutes to stabilize the brightness,
The luminance distribution on the light guide plate surface was measured using a Minolta luminance meter (CA-1000). The luminance was measured at 25 divisions by dividing the vertical and horizontal into 5 parts each, and the average value was taken as the luminance value, and the luminance nonuniformity was compared with the value obtained by the percentage of the minimum value of the luminance ÷ the maximum value as the light uniformity. . (2) Measurement of transferability of fine shape of light guide plate The transferability of the fine shape was measured by measuring the height of fine protrusions at the center of the light guide plate using a surface roughness measuring instrument: Surfcom 570A manufactured by Tokyo Seimitsu Co., Ltd. The height of the prism shape was measured and measured.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following main mold, heat insulating layer, metal plate and synthetic resin were used. Main mold: A mold for injection molding made of steel (S55C). The mold obtained by the mold is a wedge-shaped (tapered) uneven thickness plate having a size of 160 mm × 220 m.
m, the thickness is 2.5 mm for the thick part and 0.8 mm for the thin part. The gate position is the side gate of the thick portion, and the size of the gate is 20 mm in width and 2 mm in thickness. The mold cavity is made of steel (S55C) and has a nested structure. The mold surface is mirror-like and the surface is hard chrome plated.
The thermal conductivity of the steel material is about 0.2 cal / cm · sec · ° C.

Heat insulation layer: covered with a polyimide resin. The nesting surfaces that make up the mold cavity are primed.
A straight-chain polyimide precursor, polyimide varnish “Trenice # 3000” (trade name, manufactured by Toray Industries, Inc.) is applied thereon, heated at 160 ° C. to partially imidize, and the coating and heating at 160 ° C. are repeated. To a predetermined thickness.
The thickness of the heat insulating layer in the thick part of the mold cavity was set to 0.2 mm, and the thickness of the heat insulating layer in the thin part was set to 0.7 mm, and then heated to 290 ° C. to form a polyimide layer. The polyimide layer has a softening temperature of 300 ° C. and a thermal conductivity of 0.0005 cal / cm · s.
ec · ° C., elongation at break was 60%. Finally, a curable epoxy resin-based elastic adhesive was applied to the outermost surface of the heat insulating layer of the polyimide layer, and a metal plate was placed thereon and heated at 80 ° C. to bond to form a heat insulating layer coating mold. For the metal plate, use a 0.3 mm thick nickel electroformed plate prism-shaped product (vertical angle = 90 °, pitch = 50 μm, height = 25 μm) for the fixed mold, and a thickness for the movable mold. Material SUS3 of 0.05mm
A pattern formed into a fine concave shape cut by etching with 04HT (thick part side is coarse, thin part side is densely concave, concave depth = 40 μm) was arranged.

Synthetic resin: methacrylic resin "Delpet 8"
0NH "(trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.).

[0041]

Example 1 A heat-insulating layer-coated mold produced by the above-described method was applied to a Dynamelter injection molding machine (M-150, manufactured by Meiki Co., Ltd.).
AII), molding temperature: 240 ° C, mold temperature set value: 70 ° C, molding cycle: 45 seconds, injection speed: 50m
Injection molding was performed under the molding conditions of m / sec and holding pressure: 50 kg / cm 2, and a good uneven thickness molded plate was obtained without changing the molding cycle time. The transferability and luminance value of the fine concave shape of the obtained light guide plate were measured. Table 1 shows the results.

[0042]

COMPARATIVE EXAMPLE 1 A fixed-side mold was mirror-finished, and only one side was patterned into a fine concave shape, and a light guide plate conventionally used was injection-molded. A reflective film on the light-scattering portion side (concave surface) side of the obtained light guide plate, and a prism sheet (vertical angle = 90 °, pitch = 50 μm, height = 25 μm) on the light-emitting surface side;
The diffusion film was set, and a planar light source device was manufactured. The brightness and the light uniformity were compared. Table 1 shows the results.

[0043]

COMPARATIVE EXAMPLE 2 Injection molding was performed under the same molding conditions, using an uneven thickness mold that had been subjected to fine processing on the mold surface without a heat insulating layer. The molded product was not filled in the thin portion, and a good molded product was not obtained. 15% unfilled compared to fully filled. Increase the holding pressure to 80 kg / cm2 to complete filling,
The transferability and luminance value of the fine concave shape of the obtained light guide plate were measured. Table 1 shows the results.

As is apparent from the above results, the transparent light guide plate for a planar light source, in which the light scattering portion and the prism lens portion are integrally formed by using a mold having a heat-insulating layer and a fine-walled mold having a finely processed surface, is a metal mold. It has excellent resin filling properties and can be molded efficiently without increasing the mold temperature, and also has excellent light transferability of finely processed shapes and high light uniformity and high luminance value. Then, it is not necessary to separately incorporate a prism sheet, and a high-luminance planar light source device can be obtained.

[0045]

[Table 1]

[0046]

The light guide plate for a planar light source of the present invention is an integrally molded product obtained by patterning a fine prism shape and a fine concave shape by an injection molding method. There is no need to incorporate a prism sheet, and a high-luminance planar light source device can be obtained. In addition, by coating the lower part of the metal surface layer of the fine processing with a heat insulating layer, the transferability of the fine processing on the surface of the metal layer can be improved without increasing the mold temperature. The uneven thickness light guide plate for a planar light source having the above can be molded favorably.

[Brief description of the drawings]

FIG. 1 shows a sectional view of a mold according to the present invention.

FIG. 2 shows a cross-sectional view of a conventional surface light source device.

[Description of Signs] In FIG. 1, 1, 1 ′: metal mold 2, 2 ′: nested piece mold 3, 3 ′: heat insulating layer 4, roughened metal layer 4 ′: many fines In FIG. 2, 1: a transparent light guide plate 2: a light scattering section 3: a reflective film 4: a diffusion film 5: a prism sheet 6: a primary light source 7: a light incident surface

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location // B29C 45/37 B29C 45/37 B29K 101: 12 B29L 11:00

Claims (7)

[Claims] 1. A planar light source light guide plate in which a primary light source is disposed on a side end surface of a resin transparent light guide plate, wherein one plane of the transparent light guide plate is formed as an uneven light scattering surface and the other plane is formed. A light guide plate for a planar light source characterized by a double-sided microfabrication in which a plurality of converging lens units for forming a light exit surface and emitting in a predetermined direction are formed. 2. A light-scattering surface is arranged in a lattice pattern with a roughened pattern, and the light-scattering portion is formed in a substantially rectangular shape. As the distance from the light-incident surface increases, the light-scattering portion becomes more parallel to the rectangular light-incident surface. 2. The light guide plate for a planar light source according to claim 1, wherein the length of each side is increased, and the distance between adjacent light scattering portions is reduced. 3. The light guide plate for a planar light source according to claim 1, wherein the shape of the converging lens unit is a multi-linear prism. 4. The planar light source knitted meat according to claim 1, wherein the light guide plate for a planar light source has an uneven thickness having a wedge-shaped thick portion and a thin portion. Light guide plate. 5. A method for molding a light guide plate for a planar light source using a mold having a mold cavity having a thick portion and a thin portion, wherein a heat insulating layer is coated on both surfaces of a mold wall surface constituting the mold cavity. Then, using a heat-insulating-layer-coated mold in which a metal layer having been subjected to fine processing of irregularities on the flat part on the heat insulating layer and a fine processing of a number of converging lens units on the other flat part is closely attached, the thickness of the mold cavity is increased. The difference between the maximum thickness of the thick portion and the minimum thickness of the thin portion is A, (the thickness of the mold cavity + the thickness of the heat insulating layer) at the maximum thickness portion of the mold cavity, and the difference between the (thickness of the mold cavity) at the minimum thin portion of the mold cavity. 5. The bias for a planar light source according to claim 4, wherein when the difference between the thickness and the thickness of the heat insulating layer is B, a heat insulating layer coating mold having a relationship of A> 0.5 mm and A ≧ B is used. A method for forming a light guide plate. 6. The method according to claim 5, wherein A = 0.5 to 10 mm and 0.7A ≧ B. 7. The planar light source according to claim 5, wherein the thickness of the finely processed metal layer is equal to or less than 1/3 of the thickness of the heat insulating layer and is 0.01 to 1 mm. For forming a light guide plate with uneven thickness.