TWI386686B - Preparation of Optical Film and Its Product - Google Patents

Description

Preparation method of optical film and its product

The present invention relates to a method for preparing an optical film, and more particularly to a method for preparing an optical film applied to a display; the present invention further relates to an optical film.

The thinning of a liquid crystal display (LCD) is a current state of the art, and in order to achieve this, an optical film used as a concentrating sheet in a backlight module includes a substrate layer and a substrate disposed thereon. a brightness enhancing layer on the layer, and a back coating (or "light diffusion layer") disposed on the substrate layer away from the brightness enhancing layer, and the back coating layer generally includes a plurality of particles, and The back coating layer is formed into a concave-convex light-incident surface for injecting light from the light source.

However, when the backlight is activated, the general optical film is easily perceived by the observer at two viewing angles as follows: 1. The rainbow pattern appears on the surface; 2. The surface is extremely visible, and The surface of the optical film is divided into light and dark boundaries between bright and dark places. Both of these conditions will reduce the viewer's visual satisfaction with the LCD produced and thus need to be improved.

In addition, the ideal optical film should have high haze (highly homogenized light from the light source) and high brightness (meaning a large amount of light); the national I287115 patent uses the geometry of its light-incident surface. The configuration first diffuses and homogenizes the light from the light source, and then the light is more concentratedly emitted by the brightening layer, so that under the action of the back coating and the brightness enhancing layer, And improved the brightness and uniformity of the optical film, the case is also said And when the particle size of the particles of the back coat layer is large, the haze can be markedly higher. In the embodiment of the case, the thickness of the back coat was exemplified by 40 μm.

In practice, it has been found that when the operating conditions of the substrate layer and the brightness enhancing layer are fixed, and only the relevant operating conditions of the back coating are changed, as the haze of the optical film is increased, the gain ratio is The downward trend, especially when the haze is increased to more than 20%, the gain effect is likely to have dropped drastically, and this problem cannot be solved by the technique of the above patent.

Through a multi-party test by the applicant, it was found that when a back coating layer of the optical film is formed by a composition having a special formula, the rainbow on the surface of the corresponding optical film can be made only at a thin thickness. The lines and the light and dark lines have completely disappeared. Further, the gain ratio of the optical film can be effectively slowed down as the haze is greatly lowered; in other words, the optical film produced has a higher haze and a higher haze. Gain ratio.

Accordingly, it is an object of the present invention to provide a method of preparing an optical film comprising the steps of: preparing an optical film comprising a back coating layer, a substrate layer, and a brightness enhancing layer, and the back The coating is formed by coating a composition comprising a plurality of particles and a master glue, a master glue hardener, and a solvent master solution on the base material layer; the method is characterized in that: The material of the particles is selected from polymethyl methacrylate, polystyrene, cerium oxide, glass, or a combination thereof, and the particle diameter of the particles is between 0.5 μm and 10 μm; The main glue is UV a resin and/or a thermosetting resin; the solvent is butanone, methyl isobutyl ketone, isopropanol, ethyl acetate, toluene, or a miscible combination thereof; wherein the particles and the main gum solution are The weight ratio is between 0.001 and 0.03, and the solid content of the main glue solution (ie, the wt% of the main glue in the main glue solution) is between 20% and 60%.

Referring to FIG. 1 (for the sake of illustration, the dimensions of the elements are not drawn to the original scale), another object of the present invention is to provide an optical film 1 which is thin in thickness and whose surface does not show a rainbow line and a light-dark boundary, and its structure is included. A back coating layer 11, a substrate layer 12, and a brightness enhancing layer 13 are sequentially stacked; the optical film 1 of the present invention is characterized in that it is prepared by the method of the present invention as described above, and the back coating The layer 11 has a thickness of between 1 and 10 μm and includes a fixing area 111 formed by the main glue, and particles 112 fixed by the fixing area 11 and protruding from the fixing area 111. The formed convex region 113 is further converted by the amount of the material used in the method of the present invention, and it is inferred that the weight ratio of the particles 112 to the main rubber in the back coating layer 111 is between 0.0017 and 0.15.

Referring to FIG. 1, the particles 112 of the optical film of the present invention for forming the protruding regions 113 of the back coating layer 11 are only partially embedded and fixed by the fixing region 111, thereby forming an unevenness. And the light from the light source is homogenized into the light incident surface 114. The back coating layer 11 of the optical film of the invention has only a low thickness, which can not only take into consideration the cost, but also achieve the desired effect; preferably, the thickness of the back coating layer 11 is between 1 and 8 μm; more preferably The ground is between 1 and 6 μm. Comparison of the weight ratio of the particles to the main glue The preferred and preferred range is described later; in the following embodiments, the thickness of the back coat layer 11 is between 4 and 6 μm.

The preparation method of the optical film of the invention can not only obtain the rainbow line and the light-dark boundary on the surface of the produced optical film, but further, the "low-thickness back coat layer produced by the film is obtained correspondingly. The optical film can have high haze and high gain ratio retention ratio as an ideal target; wherein "gain ratio retention rate" means that after the back coat layer is set, for the substrate layer and brightness enhancement The retention ratio of the layer to the luminance gain ratio of a fixed source. For example, when the luminance value of a fixed light source is 100, and the luminance value is increased to 159.88 after the substrate layer and the brightness enhancing layer are applied, the gain ratio of the substrate layer combined with the brightness enhancing layer is 59.88%; After adding the back coat layer to obtain the corresponding optical film, if the measured luminance value is 150 (that is, the gain ratio is 50%), it means that the "gain ratio retention rate" of the optical film is 83.50% ( That is 50/59.88).

Therefore, in addition to the basic operations described above, in order to facilitate the coating, preferably, the weight ratio of the particles to the main gum solution is between 0.0025 and 0.025, and the solid content of the main gum solution is higher. The best is between 25% and 55%. In the following examples, the weight ratio of the particles to the main gum solution is between 0.005 and 0.02, and the solid content of the main gum solution is between 30% and 50%.

The main glue is used to fix the particles after the back coat layer is formed, so that a UV-curing resin, a thermosetting resin, or a mixture thereof can be used. There is no particular limitation; further, the thermosetting resin can be mainly distinguished into an epoxy resin. (epoxy resin) and alkyd resin (alkyd resin) two series. The main glue hardener is an agent for hardening the main glue. Therefore, if a UV resin is used, the main glue hardener used is a photoinitiator; each of the photoinitiators can be used. The type of use and the type of hardener which can be used for the rest of the resin, the range of use thereof, the illuminating parameters, and the like are well known in the art and will not be described.

Preferably, the master gum is an aliphatic urethane oligomer having at least a hexafunctional group belonging to a UV resin, based on hardness, ease of handling, cost, and many considerations by those skilled in the art. ), epoxy acrylate, bisphenol-A epoxy acrylate, novolac epoxy acrylate, polyester diacrylate, or One of the combinations. In the following examples, the main gum used is a hexafunctional aliphatic urethane oligomer, and the brand of the photoinitiator used is CIBA IRGACURE 184, and the amount is corresponding. The amount of the main glue is 5 wt%.

In order to improve the quality of the back coating of the present invention (for example, to promote a flat surface, increase the smoothness of the surface, anti-soil adhesion, etc.), the composition used in the method of the present invention may further comprise an additive such as a leveling agent. Agent), a lubricant, an antifoulant, or a combination thereof. It is also recommended that the amount of the additive be between 0.3% and 5% of the corresponding amount of the main glue.

In the back coating of the optical film of the present invention, when the weight ratio of the particles to the main rubber is between 0.0045 and 0.1, the optical film of the present invention will be The step has a higher haze value and a gain ratio; in the following examples, the weight ratio of the particles to the main gel is between 0.01 and 0.0667.

In terms of haze and gain ratio retention, preferably, the haze is between 6.5% and 66%, and the gain ratio is preferably between 60% and 90%. In addition, in order to have a high haze and a high gain ratio retention ratio, the product of the haze and the gain ratio retention ratio of the optical film of the present invention is preferably between 6% and 42.5%, and the haze and gain ratio are retained. The sum of the rates is preferably between 88.5% and 130.5%.

The optical film of the present invention is exemplified in the following examples, having a haze between 7.2% and 64.41%, a gain ratio retention ratio between 62.79% and 87.64%, and ranging from 6.17% to 41.81. The product of the two, and the sum of the two between 92.9% and 129.34%. In a situation that is more in line with the specifications of current downstream manufacturers and considers the direction of technology development, these embodiments have a haze between 7.2% and 40%, and a gain ratio between 75.13% and 87.64%. The retention rate, the product of between 6.17% and 30.53%, is the sum of the two between 92.9% and 113.02%.

The hardness of the back coat layer of the optical film of the present invention is preferably between 2H and 4H in order to maintain its quality and avoid scratching; the hardness of each back coat layer in the following examples is Between 3H~4H. Further, the optical transmittance of the optical film of the present invention is preferably between 89% and 93%.

Moreover, a brightness enhancing layer having a suitable geometric configuration will help to provide a higher transmittance and gain ratio retention of the optical film of the present invention. Therefore, preferably, the brightness enhancing layer of the optical film of the present invention is The structure is taught by the patent of USP 2005/0237641, and includes a plurality of curved prisms arranged adjacent to each other. And each curved prism unit has at least one curved extended curved surface; the curved extended curved surface is adapted to guide light (from the substrate layer into the brightening layer) to tend to generate two-dimensional refraction, thereby improving the light collecting efficiency. Regarding various variations of the structure of the brightness enhancing layer, reference is made to the patent of USP 2005/0237641.

Further, the material of the brightness enhancing layer in the optical film of the present invention is not particularly limited, and any resin which is currently known to be used is also suitable for use; for example, acrylate, urethane acrylate, polyester Polyester acrylate, epoxy acrylate, phenol ethoxylated acrylate, bisphenol A ethoxylated acrylate, benzene epoxy acrylate (phenyl epoxy acrylate), o-phenylphenol ethyl acrylate, phenylthioethyl acrylate, benzyl acrylate, hexafunctional aromatic Hexafunctional aromatic urethane, bisphenol-A epoxy acrylate, phenolic epoxy acrylate, polyester diacrylate, or a combination of these.

The material of the substrate layer selected for the optical film of the present invention is not particularly limited except for the need to have light transmissivity, such as polyethylene terephthalate (PET), polyimide (PI). ), polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene (PE), polypropylene (PP), polyurethane resin, triacetate The cellulose (TAC) is user-friendly; the thickness of the substrate is 38 μm to 250 μm.

The brightness enhancing layer in the optical film of the present invention can be produced by hot-press molding on one surface of the substrate or by coating a solution of the above resin on the surface and then molding. Demonstrated in the examples is a resin containing 10% by weight of o-phenylphenol ethyl acrylate, 15% by weight of phenylthioethyl acrylate, and 75 % by weight of urethane acrylate. The solution is coated on a plane of a 188 μm thick PET substrate and reshaped to form a first embodiment of the patent of USP 2005/0237641 to form the brightness enhancing layer; wherein the brightness of the surface of the brightness enhancing layer The configuration is as shown in Fig. 4 of the patent.

Hereinafter, embodiments and effects of each object of the present invention will be described with reference to the respective embodiments and comparative examples. These examples will be prepared or tested using the following chemicals and equipment, and unless otherwise specified, are carried out under atmospheric pressure and atmospheric conditions. It should be noted that the embodiments are for illustrative purposes only and are not to be construed as limiting.

Use materials and equipment

1). PET substrate: prepared by Toyobo, model A4300.

2). Cerium oxide particles: Prepared by Dagussa Corporation, model number is OK-607, and the average particle diameter is 4.5 μm.

3). Master gum (having a hexafunctional aliphatic urethane oligomer): Prepared by Cognis, model 6625.

4). Isopropanol: prepared by Li Changrong Chemical Company with a purity of 99%.

5.) Photoinitiator: Prepared by CIBA Corporation, model number IRGACURE 184.

6.) o-Phenylphenol Ethacrylate: by Miwon Commercial Prepared by the company, model number is M1142.

7.) Phenylthioethyl acrylate: Prepared by Miwon Commercial, model number M1162.

8.) Amino acrylate acrylate: Prepared by Miwon Commercial, model HR3000.

9.) Wire rod: a total of five; prepared by RDS company, numbered #4, #5, #6, #8, #10, for the same solid content of the composition, the number of the pole When applied, the thicker the film formed.

Related test

1. Surface observation: Observe whether there is a rainbow line and a light-dark boundary on each optical film to be tested at a specific angle; if so, further observe the apparent degree of the rainbow line and the light-dark boundary.

2. Hardness test: A JIS K 5600 test was carried out using a pencil hardness tester model No. 3086 manufactured by Elcometer.

3. Penetration test: The test of JIS K 7106 was carried out by a haze meter of the type NDH-5000 produced by NIPPON.

4. Haze test: The test specification of JIS K 7105 was carried out using the above haze meter.

5. Gain ratio test: The TCO-03 test was carried out by a spectrophotometer manufactured by TOPCON Corporation and model SR-3A.

6. Gain ratio retention rate: the calculation method is as described above; the greater the brightness ratio retention ratio, the closer the gain ratio of the embodiment is to the comparison example, and the better the power efficiency.

<Example>

The composition to be used to form the back coat layer in each of the examples (optical film) is prepared using the above materials and using predetermined parameters (as listed in Table 1 below); wherein the photoinitiator used is used. The amount is 5% of the solid content (the amount of the main glue). Then, with a specific wire rod, each composition is coated on the surface of a PET substrate and formed into a wet film, and then dried in an oven at 80 ° C for 3 minutes before UV light (wavelength between 240 nm and 400 nm, The irradiation energy is 400 to 600 mJ/cm ² and is irradiated for 10 seconds. Then, the above-mentioned resin mixed solution is coated on the other surface of the substrate to shape the first embodiment of the USP 2005/0237641 patent. One of the optical films of the present invention is obtained by moving away from the brightening layer of the back coat layer, and its structure is as shown in FIG.

<Comparative example>

The comparative example differs from the respective examples only in that the comparative example has only one substrate layer and one brightness enhancing layer, and does not have a back coat layer. The comparative examples are only used to compare the apparent degree of rainbow lines and light and dark boundaries with the examples.

The hardness of each of the back coatings in the following examples is between 3H and 4H, and the thickness is between 4μm and 6μm; the optical transmittance of the optical films is between 89% and 93%. .

Further, the relevant operating parameters of the preparation methods of the embodiments of the present invention and the test results of the produced optical film are listed in the following tables; wherein, the transmittance, the haze, the gain ratio, and the gain ratio retention ratio are Units are %:

In terms of the rainbow pattern, the surface of the comparative example was clearly observed, but the surface of the optical film of each of the examples had no rainbow pattern; in addition, the light and dark surface of the optical film of each example was as shown in FIG. A gradual change, in contrast to the surface condition of the comparative example shown in Fig. 3, it is apparent that the surface of each of the examples does not observe the existence of the boundary line of the light and dark, so that the surface of each embodiment gives a better visual impression.

In addition, in the above Table 1, it can be found that the optical film haze values of the examples are all above 7.2%, and the gain ratio retention ratio is above 62.79%, which is in line with industry standards, and the haze values thereof are The product of the gain ratio retention ratio is above 6.17%, and the sum of them is above 92.9%.

In addition, the gain ratio retention ratios of the embodiments are observed in various haze ranges, and the haze value is found to be between 10% and 30%, and the gain retention ratio is between 80.34% and 85.20%. Between 30% and 50% of the haze value, the gain retention ratio is between 71.29% and 78.94%; if the haze value is above 50%, the gain retention ratio is equal to It is between 62.79% and 78.52%. It is obvious that in the other embodiments, the gain is better than the retention rate, which is consistent with the high-yield and high-gain ratio in the field. .

It can be seen from the above that, by the precise control between the proportions of the materials in the preparation method of the optical film of the invention, a back coating layer can be prepared, so that the corresponding optical film surface does not have rainbow lines and obvious light and dark boundaries. On the other hand, it is indeed possible to make the optical film have a high haze and a high gain ratio at the same time, thereby solving the long-standing trouble in the industry.

However, the above is only the preferred embodiment of the present invention, when not The scope of the invention is to be construed as being limited by the scope of the invention and the scope of the invention.

1‧‧‧Optical film

11‧‧‧Back coating

111‧‧‧fixed area

112‧‧‧ particles

113‧‧‧ protruding area

114‧‧‧Glossy

12‧‧‧Substrate layer

13‧‧‧Enhanced layer

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing the structure of an optical film of the present invention; and Fig. 2 is a photograph showing the surface condition of the embodiment 29 of the present invention, in which a clear boundary line between light and dark is not observed, but A gradual change; and Figure 3 is another photograph illustrating the surface condition of the comparative optical film with a distinct light-dark boundary observed between light and dark.

1‧‧‧Optical film

11‧‧‧Back coating

111‧‧‧fixed area

112‧‧‧ particles

113‧‧‧ protruding area

114‧‧‧Glossy

12‧‧‧Substrate layer

13‧‧‧Enhanced layer

Claims (16)

A method for preparing an optical film, comprising the steps of: preparing an optical film comprising a back coating layer, a substrate layer, and a brightness enhancing layer, wherein the back coating layer comprises a plurality of particles And a composition comprising a main glue, a master glue hardener, and a solvent main glue solution coated on the base material layer and cured; the method is characterized in that: the material of the particles is selected from Polymethyl methacrylate, polystyrene, cerium oxide, glass, or a combination of these, and the particle size of the particles is between 0.5 μm and 10 μm; the main glue is UV resin and / Or a thermosetting resin; the solvent is butanone, methyl isobutyl ketone, isopropanol, ethyl acetate, toluene, or a miscible combination thereof; wherein the weight ratio of the particles to the main gum solution is Between 0.001 and 0.03, the solid content of the main glue solution is between 30% and 50%. The method of claim 1, wherein the weight ratio of the particles to the main gum solution is between 0.0025 and 0.025. The method of claim 1, wherein the main gel is selected from an aliphatic urethane oligomer having at least a hexafunctional group, an epoxy acrylate, a bisphenol-A epoxy acrylate, Phenolic epoxy acrylate, polyester diacrylate, or a combination of these. The method of claim 1, wherein the composition further comprises an additive selected from the group consisting of a flat agent, a slip agent, an antifouling agent, or the like. According to the method of claim 4, wherein the additive is used in an amount of 0.3% to 5% by weight of the main rubber. An optical film prepared by the method of claim 1, wherein the back coat layer has a thickness of between 1 and 10 μm, and the back coat layer comprises a solid formed by the main glue. a region, and a convex region formed by the fixing region and protruding from the particles of the fixing region, and the weight ratio of the particles to the main rubber in the back coating layer is between 0.0045~ Between 0.1. The optical film of claim 6, wherein the back coating has a thickness of between 1 and 8 μm. The optical film of claim 7, wherein the thickness of the back coat layer is between 1 and 6 μm. The optical film according to claim 6, wherein the optical film has a haze of between 6.5% and 66%, a gain ratio retention ratio of between 60% and 90%, and a haze. The product of the gain-to-retention ratio is between 6% and 42.5%, and the sum of the haze and the gain ratio is between 88.5% and 130.5%. The optical film according to claim 9, wherein the optical film has a haze of between 7.2% and 64.41%. The optical film according to claim 9, wherein the optical film has a gain ratio retention ratio of between 62.79% and 87.64%. The optical film according to claim 9, wherein the product of the haze of the optical film and the gain ratio retention ratio is between 6.17% and 41.81%. The optical film according to claim 9, wherein the sum of the haze and the gain ratio of the optical film is between 92.9% and 129.34. %between. The optical film of claim 6, wherein the back coating has a hardness of between 2H and 4H. The optical film according to claim 6, wherein the optical film has a transmittance of between 89% and 93%. The optical film of claim 6, wherein the brightness enhancing layer comprises a plurality of curved prism units arranged adjacent to each other, each curved prism unit having at least one curved extended curved surface.