CN101737707B - Light diffusion sheet for back light module and manufacture method thereof - Google Patents

Abstract

The invention discloses a method for making a light diffusion film for a backlight module, which comprises the following steps: (1) preparing a sticky fixing layer on one side surface of a substrate; The fixed layer arrangement is fixed on the surface of the substrate; (3) the substrate with the surface microstructure obtained in step (2) is used as an electroforming template for precision electroforming, and the microstructure is transferred to the electroformed metal plate; ( 4) Using the metal electroformed sheet obtained in step (3) as an embossing template, heat or ultraviolet embossing is applied to the material of the light diffusion sheet to produce a light diffusion sheet. The present invention utilizes the micro-nano imprinting technology to imprint the microlens structure on the transparent base material, the method is simple and convenient, reduces the production cost of the diffusion film, and is especially suitable for producing an ultra-thin structure, which can effectively reduce the thickness of the backlight module. And has good optical performance.

Description

Light diffusion sheet for backlight module and manufacturing method thereof

technical field

The invention relates to a backlight module for uniform illumination, in particular to a manufacturing method of a light diffusion film in the backlight module, which is suitable for a backlight module of a liquid crystal display device and a projection screen based on a light diffusion sheet structure.

Background technique

Today's liquid crystal display devices mostly use backlight illumination from the back of the liquid crystal panel, and there are backlight devices such as side light type and vertical type. Taking the backlight module of the side-light lighting method for notebooks as an example, as shown in Figure 1, it has: a lamp tube 1, which is semiconductor lighting or cold light source lighting, and is in the form of a line as a light source; a reflector 2; a light guide plate 7, in the shape of a square plate; the lower light diffusion film 8 has a transparent substrate 4, an anti-adhesive material 3 at the bottom, and a diffusion layer 5 at the top; the prism grid film 6 is located on the lower side of the upper light diffusion film 9 .

The functions of the above-mentioned side-lit liquid crystal display module are as follows: first, the light tube 1 emits light to the light guide plate 7, and is guided by the microstructure on the top surface of the light guide plate 7 to emit light from its surface; secondly, the light guided by the light guide plate 2 Enter the lower light-diffusing film 8, be diffused by the light-diffusing film 8, and emit from its surface; then, the light emitted by the lower light-diffusing film 8 enters the prism grid film 6, and passes through the prism in the near normal direction Then the light emitted from the prism grid film 6 enters the upper light-diffusing film 9 , and enters the liquid crystal part 10 after being further diffused and homogenized.

The light-diffusing film in the liquid crystal backlight display module usually includes: a transparent substrate layer 4 and a light-diffusing layer 5 . The adhesive layer 3 is used to prevent interference fringes from being closely bonded between the back of the light diffusion film and the surface of the light guide plate 7 and causing troubles.

There are two main functions of the light diffuser: the first one is to effectively use the image light to ensure the high brightness of the screen, and the light can be limitedly diffused and emitted to the area where the estimated observer exists. The second function is that the brightness of the edge portion of the screen is increased to reduce the unevenness of brightness, wherein the unevenness of brightness between the edge portion of the screen and the center portion of the screen is unfavorable in terms of viewing angle.

Common manufacturing methods of light diffusion sheet, one is heat treatment casting method, the main materials such as methyl methacrylate (MMA), azobisisobutyronitrile (AIBN), poly(meth)acrylate methyl, poly(formaldehyde) base) (meth)acrylic monomer or polymer such as ethyl acrylate, polyester such as polyethylene terephthalate, polypropylene terephthalate, polycarbonate, polystyrene, polymethyl Thermoplastic resins such as pentene, or hardened resins, transparent glass, transparent ceramics, etc., are fully stirred and mixed or melted, and covered on the surface of the film; the second is the coating method (Chinese invention patent CN 101029940A), Mix a plurality of spherical scattering particles and a plurality of non-spherical scattering particles, and the material is composed of glass, acrylic or organic polymers, etc., and are bonded to the surface of the substrate by spraying, UV glue coating or printing; the third is the mechanical processing method (invented in China) Patent CN1734290A), continuously changing the cut-in amount of the cutting tool on the transfer roller, forming a plurality of microlens patterns on the surface of the transfer roller, and then applying a contact bonding step, applying energy-absorbing and energy-cured resin materials to the surface of the transfer roller, The base film and resin are then contact bonded and hardened.

These methods suffer from some major disadvantages:

1) It takes 4 to 8 hours for the process of heat treatment and casting, and the production efficiency is low.

2) In the coating method, in order to improve the effect of uniform diffusion of the light diffusion film, the stacking density of the particles must be increased. Due to the uneven coating of the material, uniform light diffusion cannot be fully achieved. Another major disadvantage of the coating method is that since different materials (such as synthetic resins) are used for the diffusion film base material, adhesive, and diffusion particles, it is easy to cause deformation or discoloration (yellowing) due to heat or ultraviolet rays. When the adhesiveness between the tiny diffusion particles and the adhesive is insufficient, it will also lead to poor strength and a decrease in light transmittance.

3) Although the machining method is more flexible, it requires high-precision machining equipment, resulting in increased production costs and decreased efficiency.

Therefore, on the premise of ensuring the optical properties and service life of the light diffusion film, it is necessary to seek a method for manufacturing a light diffusion film that is easy to process and has high production efficiency.

Contents of the invention

The purpose of the present invention is to provide a light diffusion sheet and its production method. Through the improvement of the method, the production cost can be reduced, and the production of high-quality light diffusion sheet can be realized with a more convenient technology. The light diffusion sheet produced is suitable for liquid crystal backlight display modules, also suitable for projection screens based on light diffusers.

In order to achieve the above object, the general idea of the present invention is to realize the microlens array by using microparticle arrangement, and then transfer the surface morphology of microparticles to hard metal materials by electroforming, and roll-to-roll or plane-to-plane The method embosses transparent polymer polymer materials to realize the production of large-format light diffusion sheets.

The technical solution adopted in the present invention is: a light diffusion sheet for backlight module, comprising a transparent substrate layer, a diffusion layer integral with the substrate layer is provided on one surface of the substrate layer, the diffusion layer The layer has a distributed concave microlens structure.

Or, a light diffusion sheet for a backlight module, comprising a transparent substrate layer, a UV curable resin layer is compounded on one side surface of the substrate layer, and the UV curable resin layer has a distributed concave microlens structure .

In the above technical solution, the microlens structure is concave hemispherical or other irregular concave shape; the distribution state of the microlens structure is random distribution or orderly arrangement.

The base material layer can be in the form of a film or a plate.

In order to obtain the above-mentioned light diffusion plate, the present invention provides a method for manufacturing a light diffusion sheet for a backlight module, comprising the following steps:

(1) preparing an adhesive fixing layer on one side surface of a substrate;

(2) Arranging and fixing particles of micro-nano structure size on the surface of the substrate through the fixing layer:

(3) Using the substrate with the surface microstructure obtained in step (2) as an electroforming template for precision electroforming, and transferring the microstructure to the electroformed metal plate;

(4) Using the metal electroformed sheet obtained in step (3) as an embossing template, heat or ultraviolet embossing is applied to the material of the light diffusion sheet to produce a light diffusion sheet.

In the above technical solution, the fixed layer in the step (1) is obtained by uniformly coating the surface of the substrate with an adhesive material; the adhesive material can be an organic polymer; or, the fixed layer in the step (1) is obtained by applying It can be obtained by softening the surface (for example, softening by heating); or, the fixed layer itself can be viscous. The thickness of the fixed layer is determined according to the size and shape of the microparticles. The lower part of the particles settles in the fixed layer, and the upper part is still outside the fixed layer, forming an imprinted microstructure. In the above technical solution, the embossing method may be plane-to-plane or roll-to-roll embossing.

In the above technical solution, in the step (1), the substrate material is metal with flat surface, such as nickel, stainless steel, chromium, or glass, silicon wafer or organic polymer plate.

In the step [2], the microparticles can have different shapes such as spherical, ellipsoidal, cylindrical, etc., and the particle material can be silicon dioxide, polystyrene (Polystyrene, PS), polycarbonate ( polycarbonate), ceramic microbeads, etc.

In the step [3], the precision electroforming transfer material is nickel or copper metal.

In the above technical solution, in the step (4), a hot embossing method is adopted, and the material of the light diffusion sheet is a transparent organic polymer material.

Alternatively, in the step (4), the ultraviolet imprinting method is adopted, and the light diffusion sheet material is composed of a substrate layer of a transparent organic polymer material and a UV resin cured layer compounded on one side of the substrate layer.

The polymer material can be polycarbonate (PC: Polycarbonate), polyvinyl chloride (PVC: Polyrinyl Chloride), polyester (PET: Polyester), acrylic acid (PMMA: PolymethylMethacrylate), UV-sensitive adhesive or polyene (BOPP: Biaxial Oriented Plypropylene), etc., can be expressed as a rigid plate type or a film type.

Same as the overall concept, a method for manufacturing a light diffusion sheet for a backlight module includes the following steps:

(1) preparing an adhesive fixing layer on one side surface of a substrate;

(2) Arranging and fixing particles of micro-nano structure size on the surface of the substrate through the fixing layer;

(3) The substrate with the surface microstructure obtained in step (2) is subjected to UV embossing to transfer the pattern on the UV glue for curing, and then use the cured UV glue plate as an electroforming template for precision electroforming, Transfer of microstructures to electroformed metal plates;

(4) Use the metal electroformed sheet obtained in step (3) as an embossing template, and obtain a light diffusing sheet by hot embossing or ultraviolet embossing.

Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art as a manufacturing method of a diffusion film (plate) utilizing micro-nano imprinting technology:

1. The present invention makes the microstructure as the light diffusion layer directly on the surface of the transparent substrate or coated with a thin UV adhesive layer, without requiring a large amount of adhesives, diffusion particles and other materials like coating and printing methods, and avoiding possible occurrences. It is especially suitable for the production of ultra-thin diffusion films due to the decrease in astigmatism effect and physical deformation caused by weak adhesion, different thermal expansion coefficients, etc.

2. Low-cost microstructure processing technology: the production cost of microparticles on the microparticle motherboard is low. The size and shape of the microstructure are controlled by the size, shape and thickness of the fixed layer of the microparticles, and it is easy to realize a closely arranged microlens structure. In this way, glare can be isolated to achieve a soft and comfortable feeling of light, and the performance of the light diffuser can be improved.

3. The manufacturing process is convenient and reliable: the proposed method is easy to realize the micro-nano structure on the large-format substrate, and the ultraviolet lighting system can realize the ultraviolet imprinting process, which can not only process the light diffusion sheet directly on the transparent substrate, but also use the embossed Methods The mother board was made, and the master board was electroformed and transferred for roll-to-roll embossing, which could effectively reduce the production cost of the light diffusion sheet and improve its production efficiency.

4. The present invention is particularly suitable for making an ultra-thin structure, can effectively reduce the thickness of the backlight module, and has good optical performance.

Description of drawings

FIG. 1 is a schematic diagram of the use of a side-lit liquid crystal backlight module currently used in the background art.

2-6 are schematic flow charts of manufacturing a light diffusion sheet according to Embodiment 1 of the present invention.

7-8 are another method for making a light diffusing sheet embossing mold core according to Embodiment 2 of the present invention.

9-10 are schematic diagrams of the third embodiment of the present invention, arranging and fixing micro-particles as a diffusion sheet imprint master.

Fig. 11a is a schematic diagram of a device using an electroforming plate of a light diffusion sheet for thermal roll-to-roll embossing in Embodiment 4 of the present invention.

Fig. 11b is a schematic diagram of the microstructure of the light diffusion sheet obtained by roll-to-roll thermal embossing in Example 4 of the present invention.

Fig. 12a is a schematic diagram of a device using an electroforming plate of a light diffusion sheet for UV roll-to-roll embossing in Embodiment 5 of the present invention.

Fig. 12b is a schematic diagram of the microstructure of the light diffusion sheet obtained by roll-to-roll UV imprinting in Example 5 of the present invention.

Figure 13 is a schematic diagram of the surface of the diffuser in Embodiment 5 of the present invention as a circular microlens structure

Fig. 14 is a schematic diagram of the structure of the surface of the diffuser with elliptical microlenses in the sixth embodiment of the present invention.

Among them: 1. Illumination light source; 2. Reflector; 3. Anti-bonding material; 4. Light diffusion film base material; 5. Diffusion particles; 6. Prism grid film; 7. Light guide plate; 8. Lower light diffusion film; 9. Optical diffusion film; 10. Liquid crystal part; 21. Microparticles; 22. Fixed layer; 23. Substrate; 31. Seed layer; 41. Concave mold core; 51. Convex mold core; 71. Polydimethylsilane; 111. Master plate of light diffusion sheet; 112. Base material of light diffusion sheet; 113. Rolling and pressing feeding wheel; 114. Rolling and pressing auxiliary wheel; 115. Heater; 116. Rolling and pressing main wheel feeding ; 117, rolling pressure feeding wheel; 118, feeding wheel; 121, light diffusion film master plate; 122, light diffusion film base material; 123, rolling pressure feeding wheel; 124, rolling pressure auxiliary wheel; 125, UV lamp; 126, 127, roll pressure feeding wheel; 128, feeding wheel; 129, UV glue container; 1210, UV curing glue; 1211, glue coating wheel.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Embodiment 1: Refer to Figures 2 to 6 for a schematic flowchart of a method for manufacturing a diffuser for a backlight module. The manufacturing process of embossing mold kernels is shown in accompanying drawings 2-5. Firstly, a fixed layer 22 is coated on the substrate 23, and the microparticles 21 are arranged and fixed on the fixed layer. The base material 23 can be metal with flat surface, such as nickel, stainless steel, chrome, or glass, silicon wafer or organic polymer plate. The fixing layer is a substance capable of binding or fixing the position of microparticles. The microparticles can have regular or irregular shapes such as spheres, ellipsoids, and columns, and the materials can be silicon dioxide, polystyrene (Polystyrene, PS), polycarbonate (polycarbonate), ceramic microbeads, and the like. Next, as shown in FIG. 3 , the surface of the microparticle 21 is metallized, and a seed layer 31 is planted. The material of the seed layer 31 includes nickel (Ni), copper (Cu) or silver (Ag). Carry out the electroforming of mold core again as shown in Figure 4, the mold core 41 of electroforming mode molding, electroforming material such as nickel (Ni), nickel cobalt (NiCo) alloy, nickel-iron (NiFe) alloy, nickel silicon carbide ( NiSiC) etc. The mold core 41 obtained in Fig. 4 is concave, and the mold core 41 is recast again to obtain a convex embossing mold core 51. The shape of the mold core 51 is opposite to that of the required microstructure of the diffuser, which can be used for embossing the light diffuser, that is, to complete the manufacturing process of the mold core.

The embossing mold core 51 is used to emboss the transparent material 61, and a concave shape is embossed on the surface of the transparent material 61 to form a light diffusion layer. The light diffusion sheet obtained through the above manufacturing process has the advantages of lightness, thinness, uniform diffusion, low production cost, and is convenient for manufacturing a wide-format light diffusion sheet for backlight modules.

Embodiment 2: Refer to Figures 7-8, another method for manufacturing a light-diffusing sheet embossing mold core. Using a cohesive material as a fixed layer to arrange the small balls will easily cause the small balls to fall off during electroforming, resulting in defects in the microstructure of the upper surface of the mold core. In order to avoid this situation, first use polydimethylsiloxane (Polydimethylsiloxane, PDMS) 71 to copy and transfer the surface microstructure of the master plate with microparticle arrangement, as shown in Figure 7, and then use it for electroforming. The following process can refer to Embodiment 1, obtaining a convex embossing core 51 .

Embodiment 3: see accompanying drawings 9-10. In order to further improve the stability of the micro-particle motherboard during electroforming, and ensure the product yield. In addition to using an adhesive film as the fixing layer, a method of softening the material of the fixing layer 22 can also be used to embed the microparticles in the fixing layer 22, as shown in FIGS. 9-10 . A thin film is coated on the surface of the substrate 23 . The film is polycarbonate dissolved in dichloromethane, and the coating thickness can be determined by the dissolved concentration and the speed and time of spin coating. After the surface has dried naturally, the microparticles are distributed and the substrate is heated. For the above-mentioned organic mixture, heat it to about 240°C for 5 minutes, the film layer of the organic mixture will soften, and the microparticles will sink into the fixed film by their own gravity (a little external force can also be applied), ensuring that the microparticles can be fixed by the fixed layer , and are not completely trapped in the fixed layer. After the mixture layer is cured, the microparticles are completely fixed, and the final embossed core of the diffusion sheet can be obtained according to the process of the first or second example of the present invention.

Embodiment 4: After the embossing mold core is obtained by electroforming, the roll-to-roll embossing method can be used to emboss the light diffusion film efficiently and quickly. Refer to the accompanying drawings 11a-11b for schematic diagrams of hot embossing. Specifically include the following steps:

[1] Wrap the electroformed metal sheet 111 on the embossing wheel 116, see Figure 11a. Light transmissive film substrate 112 enters impression wheels 114 and 116 via feed wheel 113 . The embossing wheels 114, 116, 117 are hydraulically driven to apply pressure, while the heater 115 heats the material to be pressed, and the temperature can reach 250°C. After the embossing of the base material 111 is completed, the feeding wheel 118 sends the base material 112 out of the embossing mechanism to obtain a diffusion film.

[2] The film substrate 112 can be film-type PC, PET polyester film, PET release film, the thickness can be 12um-125um and other specifications, and the common width is 20mm-2000mm. The structure of the diffusion film after embossing is shown in Figure 11b, and a light diffusion layer is realized on one side of the film substrate.

Embodiment 5: After the embossing core is obtained by electroforming, the roll-to-roll embossing method can be used to emboss the light diffusion film efficiently and quickly. See the schematic diagrams of hot embossing in Figures 12a-12b. Specifically include the following steps:

[1] Wrap the electroformed metal sheet 121 on the embossing wheel 126, see Figure 12a. The light-transmitting film base material 122 enters the UV glue coating container 129 through the feeding wheel. There are mesh holes on the glue coating wheel 1210, and the UV glue 1211 is evenly applied to the surface of the base material, and then the base material enters the embossing wheel 124 and the base material through the feeding wheel 13. 126. The embossing wheels 124, 126, 127 are hydraulically driven to apply pressure, while the heater 125 irradiates the UV glue, the UV glue is cured within a few seconds, and the microstructure on the electroformed metal sheet is transferred to the UV glue layer. After the embossing of the base material 121 is completed, the feeding wheel 128 sends the base material 122 out of the embossing mechanism to obtain a diffusion film.

[2] The film substrate 122 can be film-type PC, PET polyester film, PET release film, the thickness can be 12um-125um and other specifications, and the common width is 20mm-2000mm. The structure of the diffusion film after embossing is shown in Fig. 12b. A light diffusion layer is realized on one side of the thin UV adhesive layer 1211 of the film substrate, and the thickness of the UV adhesive layer is tens of microns.

Embodiment 6: The microstructure on the surface of the light diffusion sheet produced by the method proposed by the present invention is semi-spherical, as shown in Figure 13 . The hemispherical surface microstructure can realize uniform diffusion of incident light in all directions. The diameter of the hemisphere is between a few microns and hundreds of microns, and the maximum embossing depth can reach the radius of the sphere.

Embodiment 7: The surface microstructure of the light diffusion sheet produced by the method proposed in the present invention can be semi-elliptical, as shown in Figure 14 . The semi-elliptical microstructures arranged in the same direction can achieve different diffusion angles for the incident light in the direction of the major and minor axes of the ellipsoid, that is, realize the so-called directional diffusion. There is a larger divergence angle in the direction of the minor axis than in the direction of the major axis. A diffuser with such a microstructure can be used in display devices that require a compressed field of view. The length of the major and minor axes of the semi-ellipsoid is between a few microns and hundreds of microns, and the maximum imprint depth depends on the half length of the minor axis.

Claims (6)

1. a kind of manufacture method of light diffusion sheet for backlight module, is characterized in that, comprises the following steps: (1) preparing an adhesive fixing layer on one side surface of a substrate; (2) arranging and fixing particles of micro-nano structure size on the surface of the substrate through the fixing layer, and the particle size ranges from 10 to 200 microns; (3) Using the substrate with the surface microstructure obtained in step (2) as an electroforming template for precision electroforming, and transferring the microstructure to the electroformed metal plate; (4) Using the metal electroformed sheet obtained in step (3) as an embossing template, heat or ultraviolet embossing is applied to the material of the light diffusion sheet to produce a light diffusion sheet. 2. The manufacturing method of the light diffusion sheet according to claim 1, characterized in that: the fixing layer in the step (1) is obtained by uniformly coating an adhesive material on the surface of the substrate. 3. The manufacturing method of the light diffusion sheet according to claim 1, characterized in that: the fixing layer in the step (1) is obtained by softening the surface of the substrate. 4. The manufacturing method of the light diffusion sheet according to claim 1, characterized in that: in the step (4), a hot embossing method is adopted, and the material of the light diffusion sheet is a transparent organic polymer material. 5. The manufacturing method of the light diffusion sheet according to claim 1, characterized in that: in the step (4), the ultraviolet embossing method is adopted, and the light diffusion sheet material is made of a substrate layer of a transparent organic polymer material It is composed of a UV resin cured layer compounded on one side of the substrate layer. 6. A method for making a light diffusion sheet for a backlight module, comprising the following steps: (1) preparing an adhesive fixing layer on one side surface of a substrate; (2) arranging and fixing particles of micro-nano structure size on the surface of the substrate through the fixing layer, and the particle size ranges from 10 to 200 microns; (3) The substrate with the surface microstructure obtained in step (2) is subjected to UV embossing to transfer the pattern on the UV glue for curing, and then use the cured UV glue plate as an electroforming template for precision electroforming, Transfer of microstructures to electroformed metal plates; (4) Use the metal electroformed sheet obtained in step (3) as an embossing template, and obtain a light diffusing sheet by hot embossing or ultraviolet embossing.

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