TWI431367B - A low cost and simple method for preparation of a diffusion sheet - Google Patents

Description

Method for manufacturing simple low-cost diffusion film

The invention relates to a method for manufacturing a diffusion film, in particular to a method for manufacturing a diffusion film which has both simple and low cost and scratch resistance.

A liquid crystal display (LCD) is a non-self-illuminating display device that requires a backlight to achieve the display function. The module formed by the entire group of backlights is called a backlight module, and the backlight module is composed of a light source and an optical sheet group. The optical sheet group includes a light guide plate, a diffusion film, a cymbal sheet, and the like.

The main function of the diffusion film is to homogenize the backlight source, generally the traditional diffusion film master In the diffusion film substrate (transparent polymer substrate), a chemical particle is added as a scattering particle, and the existing diffusion film has fine particles dispersed between the resin layers, so that the light passes through the diffusion layer continuously. The two media with different refractive indices pass through, so the light will undergo many refraction and scattering phenomena, thus causing the effect of optical diffusion.

In the following, the invention of the recent diffusion film, a few examples are considered to be compared:

(1) As described in Us. Pat. No.6888663, the clay is used as the diffusion particle, and after being swollen and modified by the interface, it is mixed with the polymer to form a diffusion film by means of a thermal process. . The advantage is that only a small amount of clay (<3wt%) has a good effect (haze ~ 80%, penetration ~ 80%), and the inorganic material also has the advantages of ultraviolet radiation resistance, heat resistance and weather resistance. The disadvantage is that the clay will be severely aggregated due to the activation of temperature during the thermal process, resulting in light scattering and a decrease in transmittance.

(2) As described in Us. Pat. No. 6871994, polymer beads (beads) are used as a diffusing agent, and an adhesive is added to form a coating, and then coated on a transparent polymer substrate. A diffusion film is formed. The polymer microbeads are used as a diffusing agent, and the light transmittance is good, but the main disadvantage is that the polymer is not resistant to ultraviolet light (UV) irradiation, and the heat resistance and weather resistance are inferior to the inorganic diffusion particles.

(3) As disclosed in the Republic of China invention patent 1237127, it is a diffuser structure that can improve penetration. The advantage is that an anti-reflective layer is added on the surface of the incident light of the diffuser plate to improve the transmittance. 5% higher. The disadvantage of this patent is that it requires a second anti-reflective coating process, which increases manufacturing costs.

(4) As disclosed in the invention patent specification of the Republic of China Invention No. 200523626, it is a diffusion plate process method with ultraviolet suppression function, which has the advantages of avoiding the yellowing and deformation of the material in the use of the diffusion plate. However, the ultraviolet absorbers used herein are all organic substances, and have the disadvantage that they are easily deteriorated after absorbing ultraviolet rays.

(5) As disclosed in the invention patent specification of the Republic of China Invention No. 200506035, it is a light diffusing plate which has high light diffusibility and maintains excellent color tone. The utility model has the advantages that an organic UV absorber, a stabilizer and the like are added in the process to maintain heat resistance and deformation resistance of the diffusion plate. The disadvantage is that in addition to the addition of a diffusing agent, other UV absorbers, stabilizers and other substances need to be added in the process, which will cause the whole system to be too complicated, affect the stability of the system, and increase the overall material cost; Another disadvantage of using an organic UV absorber is that it is prone to deterioration after absorbing ultraviolet rays.

Clay is an inorganic substance existing in nature. The cations between the clay layers are adsorbed to maintain electrical neutrality. The cations adsorbed in the clay are easily exchanged by other organic or inorganic cations, and the organic modifier is intercalated to its interlayer intercalation reaction. The interlayer spacing is expanded, and the oleophilic property of the organic compound can be blended with the high molecular polymer, and has good compatibility and tablets. Stripping, forming a nanocomposite, and further improving the optical, mechanical and thermal properties of the polymer.

The advantage of clay in the application of composite materials is that its physical properties, chemical properties and mechanical properties are quite special. It is an inorganic mineral mainly composed of aluminum oxide (Al ₂ O ₃ ) and cerium oxide (SiO ₂ ). The bismuth silicate layer structure has a particle size of about 1 micrometer, and each particle layer stack is stacked from hundreds to thousands of layers, and an average granule layer stack has about 850 Silicate Sheets. Each layer has an aspect ratio of about 100-1000, an average cubic ratio of 100 nm×100 nm×1 nm, and a d-spacing between each layer and another layer is about 6-17 Å. The main group is mostly distributed in the layer spacing of 11-13À.

The ions interposed between the layers and the layers can be divided into three types: cation exchange type clay, anion exchange type clay and neutral ion exchange type clay. The majority of the cation exchange type clays are mostly Li ⁺ Na ⁺ , Ca ²⁺ , Mg ²⁺ , Ba ²⁺ , La ²⁺ , Ce ^{2+ ,} etc., also contain partially crystal water. These cations provide a cation exchange capacity (CEC value) which replaces the cation contained in the clay, and the CEC value varies depending on the material. In the present invention, the cation exchange equivalent can be 90 to 150 meq/100g.

There are many types of clay, such as Smectite, Mica, Vermiculite, Brittle, etc., among which the montmorillonite of cation exchange clay in Smectite Clay is most often used.

Liquid crystal display (LCD) is non-self-luminous The display device needs a backlight to achieve the display function. The module formed by the entire group of backlights is called a backlight module, so the backlight module is composed of a light source and an optical sheet group. The optical sheet group includes a light guide plate, a diffusion film, a cymbal sheet, and the like.

The diffusing film of the target object of the invention mainly functions to homogenize the backlight source. Generally, the conventional diffusion film is mainly used in the diffusion film substrate, and a chemical particle is added as a scattering particle, and the existing diffusion film has fine particle dispersion. Between the resin layers, when the light passes through the diffusion layer, it will continuously pass through the two media with different refractive indices, so that the light will undergo many refraction and scattering phenomena, thus causing the effect of optical diffusion.

According to the literature, nano-clay can be used not only on the diffusion particles of the diffusion film, but also anti-reflection and UV-blocking effects. The diffusion film has anti-reflection effect, which can increase the utilization of the light source and improve the brightness of the overall module. Isolation of UV light has the advantage of extending the life of the diaphragm. Therefore, nano-clay is applied to the diffusion film, which not only has a light-diffusing effect, but also has anti-reflection and ultraviolet-shielding effects.

The present invention mainly uses inorganic nano-montmorillonite as a diffusion particle, the advantages of which are as described in the prior art. In today's market, the trend of optical film is thinner and lighter. Therefore, the traditional diffusion plate has been gradually eliminated in the form of thermal process manufacturing. Instead, it is a coating process. The coating process is a method of energy saving and mass production, and a diffusion film can be formed by dispersing nano clay in a resin to form a coating, and then applying it on a transparent substrate by wet precision coating. Another advantage of the normal temperature wet coating process is that the dispersion stability of the nanoparticles is controlled and the dispersion effect is obtained. Fruit is farther than the hot process. Moreover, if a resin having a hardening effect is used, it is more resistant to scratching and abrasion.

The main application techniques of the present invention are wet dispersion grinding technology of nano clay and wet precision coating technology. Nano-wet clay is used for intercalation, interfacial modification and dispersion pulverization by nano-wet dispersion grinding technology, and then resin is added to form a coating; wet precision coating technology is to form a diffusion film. Cloth process techniques, such as wet roller coating.

The nano-clay used in this embodiment is montmorillonite (Southern Clay Co.), the cation exchange equivalent is 120 meq/100 g, the layer spacing is 12.41 Å, and the thermal stability is 500 °C. The experimental steps are divided into coating preparation, coating and optical measurement. The transparent substrate used in this embodiment is PET [as shown in FIG. 10].

(1) Coating preparation:

500g of montmorillonite, 2450g of toluene, 50g of dispersant, swell and disperse in ball mill: (a) premixing: nano-clay before the ball milling stage, before the pre-mixer The rotation speed of 1000 rpm was used for 2 hours of swelling treatment (swelling & wetting). (b) Ball mill dispersion treatment: using a zirconia grinding ball, 0.3 to 0.4 mm, the grinding ball volume accounts for 70% of the grinding chamber, the ball milling speed is 3000 rpm, and the dispersion grinding time is 2 hours. After 2 hours of dispersion grinding treatment, the interlayer spacing of montmorillonite was swollen from 12.41 6 to 60.4 À, and the particle size distribution was changed from d(50)=2.3 μm to d(50)=150 nm. The viscosity at this time is 20 cps (22 ° C, Measured at 20 rpm).

In order to prepare coatings with different solid contents, an appropriate amount of optical grade acrylic glue (UV hardening type) is added, and the solid content of the coating is adjusted to 3 wt%, 4 wt%, 5 wt%, and the viscosity is about 120 cps ( At 22 ° C, measured at 20 rpm), the coating was observed by a 30-day sedimentation test, and no precipitation occurred, indicating that the coating was quite stable.

(2) Coating experiment:

5 cm square of PET film [as shown in Figure 10], first with primer (acrylic resin) for the upper and lower sides of the treatment, and then UV light irradiation for drying to increase its binding with acrylic glue. Then, the coating is evenly coated on the upper and lower sides of the PET film by spin coating, and dried and cross-linked by UV lamp to form a diffusion layer with scratch resistance characteristics [as shown in the first figure 11 , 12].

(3) Optical measurement results

This experiment mainly measures haze, and its experimental values are shown in the following table:

It can be seen from the above table that by adding only 3 wt% of nano-clay, the reflectance can be reduced from the original 23% to 4.3%, the penetration is 94%, and the haze is 81%. The results show that the diffusion film produced by the method of the invention has the advantages of simplicity, energy saving and material cost, and has the advantages of scratch resistance and wear resistance.

(1) The representative representative of the case is: (1).

(2) A brief description of the symbol of the representative figure:

10‧‧‧Transparent polymer film

11‧‧‧Nano clay diffusion coating

12‧‧‧Nano clay diffusion coating

The first picture is a schematic diagram of the coating of "nano clay diffusion coating" on both sides of the polymer film.

10‧‧‧Transparent polymer film

11‧‧‧Nano clay diffusion coating

12‧‧‧Nano clay diffusion coating

Claims (2)

A method for producing a diffusion film, comprising the steps of: (a) preparing a diffusion particle: a mixture of nano clay, toluene, and a dispersant for swelling and dispersion treatment, wherein the nano-clay used has a cation exchange equivalent of 90 to 150meq/100g, the nano-clay is a layered structure, each layer has a length-to-thickness ratio of 100 to 1000; (b) the diffusion particles are added with an acrylic resin to form a coating; (c) a top and bottom surface is coated with an acrylic resin a substrate; (d) irradiating the upper surface of the substrate with UV light; (e) applying the coating to the surface of the substrate to form a diffusion layer by wet precision coating techniques; (f) using a UV lamp as the drying layer Cross-linking processing. As described in the first aspect of the patent application, the wet precision coating method may be a wet roller coating method, a spray coating method, a immersion plating method, or a spin coating method.