Diffusion brightness enhancement film and preparation method thereof

Abstract

A diffusion brightness enhancement film structurally comprises an upper layer, a middle layer and a lower layer, the upper layer is of a diffusion prism layer structure, the middle layer is of a transparent base material layer structure, the lower layer is of a back coating layer structure, the diffusion prism layer is composed of a plurality of prism strips, cross section bodies of the prism strips are of isosceles trapezoid structures, and circular protruding structures are arranged on the waist portions of isosceles trapezoids. Meanwhile, the diffusion effect is achieved, and the brightness can be improved.

Description

Technical Field

[0001] The invention relates to an optical film, belongs to the field of liquid crystal optical display, and specifically relates to a diffusion brightness enhancement film and a preparation method thereof. Background Art

[0002] Liquid crystal display (TFT-LCD) is mainly composed of liquid crystal panel and backlight module. Generally speaking, the backlight module is composed of light source, reflective film, light guide plate and optical module. The traditional optical module mainly includes two diffusers and two prisms, which are arranged from top to bottom as upper diffuser, upper brightening film, lower brightening film and lower diffuser. The diffuser can convert point light source or line light source into a uniform surface light source, while the brightening film can concentrate the originally divergent light in the axial direction, thereby improving the front brightness of the liquid crystal display. The backlight module of this structure needs to use more optical films, which is more expensive and has poor light source utilization. Moreover, with the trend of thinner and lighter liquid crystal displays, the functions of brightening and diffusion need to be compounded.

[0003] CN101354455A provides a diffusion brightening film, comprising: a substrate having a first surface and a second surface, the first surface and the second surface are arranged opposite to each other, the substrate has a diffusion material; and a prism structure is arranged on the second surface. The prism structure is an isosceles triangle.

[0004] CN103224640A discloses a method for preparing a diffusion brightening film, which is composed of a base film, a brightening layer and a diffusion layer. The lower surface of a transparent film substrate triacetyl cellulose TAC film or polyethylene terephthalate PET film is processed into a diffusion coating with unevenness, and an isosceles trapezoidal structure is coated on the upper surface of the film to increase and enhance the light. The top of the isosceles trapezoidal structure is one tenth to one eighth of the width of the bottom, which is convenient for a certain bonding space and strength with films or plate-shaped objects in other processes, and has the function of secondary light diffusion.

[0005] The known diffusion brightening films of the prior art cannot meet the current market demand. Current products require not only high brightness but also a wide viewing angle range. However, when two films are used alone, the gain of the diffusion coating on the viewing angle cannot meet the demand. In the actual production process, it is necessary to use a diffusion film. This leads to complex assembly process and increased cost in the production process.

[0006] At the same time, the known composites are mostly composed of an upper diffuser and an upper brightness enhancement film. The lower diffuser needs a higher haze because of its optical structure surface with diffusion effect, that is, more diffusion particles are added. When it is composited with the lower brightness enhancement film, it will face two situations. First, if too much adhesive is used, the adhesive layer will be thick and the diffusion particles will be covered, affecting the diffusion effect. Second, if too little adhesive is used, the adhesive layer will be too thin, which will lead to insufficient bonding and delamination. At the same time, in the current market environment where backlight modules are becoming thinner and lighter, and assembly is required to be easier and easier, a film that can replace the lower diffuser and the lower brightness enhancement film is urgently needed. Summary of the invention

[0007] In view of the requirements for brightness and viewing angle range of existing diffusion brightening films, and the difficulty in compounding a lower diffusion film with an upper brightening film, which leads to problems of insufficient diffusion and adhesive delamination leading to damage to optical performance during compounding, the present invention proposes a brightening film that has both a diffusion effect and can improve brightness. The film can also be compounded with an upper brightening film and an upper diffusion film, further simplifying the assembly process and greatly reducing production costs.

[0008] The present invention first provides a diffusion brightness enhancement film, which comprises three layers: an upper layer, a middle layer and a lower layer. The upper layer is a diffusion prism layer structure with a thickness of 30-50 μm, the middle layer is a transparent substrate layer structure with a thickness of 50-250 μm, and the lower layer is a back coating layer structure with a thickness of 2-15 μm. The total thickness of the diffusion brightness enhancement film ranges from 90 to 320 μm. The diffusion prism layer is composed of a plurality of prism strips, and the main body of the cross-section of the prism strip is an isosceles trapezoidal structure, and the waist of the isosceles trapezoid has a circular protrusion structure.

[0009] One of the technical innovations of the diffusion brightness enhancement film of the present invention is to redesign the conventional isosceles triangle brightness enhancement film prism layer. First, the triangular prism structure is changed to a trapezoidal structure; second, circular protrusion structures are added to the two sides of the isosceles trapezoid. These circular protrusion structures can have a certain diffusion effect on the light source and can replace the lower diffusion film.

[0010] Furthermore, the width of the upper base of the isosceles trapezoidal structure is one tenth to one fifteenth, or one eleventh, one twelfth, one thirteenth, or one fourteenth of the width of the lower base, thereby further improving the brightness and viewing angle, while increasing the bonding area during compounding and improving the bonding strength.

[0011] Furthermore, the width of the upper base of the isosceles trapezoid in the cross section of the prism strip is 4-10 μm, or 5 μm, 6 μm, 8 μm, or 9 μm.

[0012] Furthermore, the lower base width of the isosceles trapezoidal cross-section of the prism strip is 54-70 μm, or 58 μm, 60 μm, 62 μm, 64 μm, 66 μm, or 68 μm.

[0013] Furthermore, the height of the isosceles trapezoid in the cross section of the prism strip is 40-60 μm, or 45 μm, 48 μm, 50 μm, 55 μm, 56 μm, or 58 μm.

[0014] Furthermore, the circular protrusions on the two sides of the isosceles trapezoidal cross section of the prism strip are uniform or irregular, and the particle size distribution range of the circular protrusions is 1-5 μm, or 2-4 μm.

[0015] Furthermore, the thickness of the diffusion prism layer is 35-45 μm, or 38 μm, 40 μm, or 42 μm.

[0016] Furthermore, the thickness of the transparent substrate layer is 60-240 μm, or 70 μm, 75 μm, 90 μm, 100 μm, 125 μm, 188 μm, or 220 μm.

[0017] Furthermore, the transparent substrate is selected from one or two or more of polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene (PE), polystyrene (PS), and polyamide resin (PA).

[0018] Furthermore, the transparent substrate is selected from polyethylene terephthalate.

[0019] Furthermore, the back coating layer comprises diffusion particles, and the diffusion particles are selected from polymethyl methacrylate (PMMA), polybutyl methacrylate (PBMA), polystyrene (PS), silicone, polyamide (PA) and polyester (PU).

[0020] Furthermore, the diffusion particles of the back coating layer are selected from polymethyl methacrylate.

[0021] Furthermore, the haze range of the back coating layer is 3-10%, or 5%, 7%, or 9%.

[0022] Furthermore, the diffusion prism layer is a light-curable acrylic resin, and the prism layer structure is obtained by a micro-replication process of a coating machine and then cured by ultraviolet light.

[0023] Furthermore, the diffusion brightness enhancement film and other brightness enhancement films form a composite structure, and the prism angles between the layers can be combined and are not limited to parallel and vertical.

[0024] Furthermore, the brightness enhancement films in the composite structure are connected by a bonding layer, and the thickness of the bonding layer is 0.8-1.2 μm, or 0.9 μm, 1.0 μm, or 1.1 μm. Figure 2 , Figure 3 shown.

[0025] Furthermore, the bonding layer is UV-curable acrylic glue, UV-curable polyurethane glue, or UV-curable polyester glue.

[0026] Furthermore, the bonding layer is UV-curable acrylic glue.

[0027] The present invention also provides a method for preparing a diffusion brightness enhancement film, comprising the following steps:

[0028] Step (1), preparing a back coating liquid: adding adhesive and diffusion particles in sequence and stirring evenly, and adding solvent to adjust the viscosity of the coating liquid to be suitable for the coating process;

[0029] Step (2), preparing a back coating layer: coating the coating liquid prepared in step (1) on one side of the transparent substrate by a micro-concave coating process, drying the solvent in an oven, curing the substrate with ultraviolet light, and winding the substrate, with a coating line speed of 25-35 m / min;

[0030] Step (3), prism layer structure preparation: first, a trapezoidal prism structure is engraved on a copper roller, and then the desired final structure is obtained through a sandblasting process;

[0031] Step (4), preparation of prism film: coating prism glue on the other side of the substrate by micro-replication process, pre-curing and demolding by low-pressure ultraviolet light, and then completely curing and molding by high-pressure ultraviolet light irradiation to obtain a diffuse brightening film.

[0032] Furthermore, the viscosity of the coating liquid in step (1) is in the range of 12-30 cps.

[0033] Furthermore, the coating line speed in step (2) is 28 m / min, 30 m / min, and 32 m / min.

[0034] Furthermore, the prism glue in step (4) is a light-curing acrylic resin.

[0035] When the lower diffuser and the lower brightness enhancement film are difficult to be compounded, the lower diffuser requires a higher haze due to its optical structure surface with diffusion effect, that is, more diffusion particles are added. When compounded with the lower brightness enhancement film, there are two situations. First, if too much adhesive is used, the adhesive layer will be thicker and the diffusion particles will be covered, affecting the diffusion effect. Second, if too little adhesive is used and the adhesive layer is too thin, insufficient bonding will result in stratification. The diffusion brightness enhancement film of the present invention can be used as a substitute.

[0036] The diffusion brightness enhancement film of the present invention replaces the traditional lower diffusion film and lower brightness enhancement film, reduces the number of film sheets, simplifies the assembly process, and saves costs. If the diffusion film is added, the brightness and viewing angle will be further improved compared with a single diffusion prism film.

[0037] Furthermore, the diffusion brightness enhancement film of the present invention can be compounded with an upper brightness enhancement film and an upper diffusion film, so as to further simplify the assembly process and save costs.

[0038] When double-layer or multi-layer diffusion brightness enhancement films are combined, the diffusion effect is significantly enhanced and the viewing angle range is increased.

[0039] The cross section of the diffusion brightness enhancement film prism strip of the present invention is designed to be a trapezoidal structure, which improves the bonding effect during compounding and is not easy to delaminate. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the structure of the diffusion brightness enhancement film provided by the present invention.

[0041] Figure 2 It is a schematic diagram of the composite structure of the diffusion brightness enhancement film provided by the present invention and the traditional brightness enhancement film.

[0042] Figure 3 It is a schematic diagram of the composite structure of the diffusion brightness enhancement film provided by the present invention and the diffusion brightness enhancement film.

[0043] Among them, 101 is a back coating layer, 102 is a transparent substrate layer, 103 is a diffusion prism, 104 is a laminating layer B, 105 is a traditional brightness enhancement film, and 106 is a diffusion brightness enhancement film. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present invention are described below. The preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0045] Example 1

[0046] As attached Figure 1 As shown, the present invention provides a diffusion brightness enhancement film, wherein the film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; firstly, a back coating coating liquid is prepared, and a suitable viscosity is adjusted, and the coating liquid is coated on one surface of the substrate by a micro-concave coating process, and the solvent is removed by an oven and then cured by ultraviolet light, and then a prism structure is prepared on the other surface of the opposite substrate, and a structure copper roller is engraved in advance, and prism glue is added, and after low-pressure UV light pre-curing and demolding, it is completely cured and formed by high-pressure ultraviolet light irradiation to obtain the final diffusion brightness enhancement film. The prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on the two waists, the upper base width is 4μm, the lower base width is 60μm, and the height is 40μm. The circular protrusions on the two waists have different particle sizes, and the distribution range is 1-3μm; the transparent substrate layer is PET, and the thickness is 100μm; the back coating coating thickness is 7μm, and the haze is 5%.

[0047] Example 2

[0048] The present invention provides a diffusion brightness enhancement film, which is prepared according to the preparation method described in Example 1. The film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; the prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on both sides, the upper base width is 5 μm, the lower base width is 60 μm, the height is 40 μm, and the circular protrusions on both sides have different particle sizes, and the distribution range is 1-3 μm; the transparent substrate layer is PET, and the thickness is 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 5%.

[0049] Example 3

[0050] The present invention provides a diffusion brightness enhancement film, which is prepared according to the preparation method described in Example 1. The film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; the prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on both sides, the upper base width is 5 μm, the lower base width is 54 μm, the height is 40 μm, and the circular protrusions on both sides have different particle sizes, and the distribution range is 1-3 μm; the transparent substrate layer is PET, and the thickness is 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 5%.

[0051] Example 4

[0052] The present invention provides a diffusion brightness enhancement film, which is prepared according to the preparation method described in Example 1. The film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; the prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on both sides, the upper base width is 5 μm, the lower base width is 60 μm, the height is 50 μm, and the circular protrusions on both sides have a particle size of 1-3 μm; the transparent substrate layer is PET with a thickness of 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 5%.

[0053] Example 5

[0054] The present invention provides a diffusion brightness enhancement film, which is prepared according to the preparation method described in Example 1. The film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; the prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on both sides, the upper base width is 5 μm, the lower base width is 60 μm, the height is 40 μm, and the circular protrusions on both sides have different particle sizes, and the distribution range is 3-5 μm; the transparent substrate layer is PET, and the thickness is 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 5%.

[0055] Example 6

[0056] The present invention provides a diffusion brightness enhancement film, which is prepared according to the preparation method described in Example 1. The film is sequentially provided with a prism layer, a substrate layer, and a back coating layer from top to bottom; the prism layer is composed of a plurality of prism strips; the cross-section of the prism strip is an isosceles trapezoid with circular protrusions on both sides, the upper base width is 6 μm, the lower base width is 60 μm, the height is 40 μm, and the circular protrusions on both sides have different particle sizes, and the distribution range is 1-3 μm; the transparent substrate layer is PET, and the thickness is 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 10%.

[0057] Example 7

[0058] When comparing the optical performance, a lower diffuser was added under the film prepared in Example 2 to test the brightness and viewing angle parameters.

[0059] Comparative Example 1

[0060] A brightness enhancement film, wherein the film is provided with a prism layer, a substrate layer, and a back coating layer in order from top to bottom; the prism layer is composed of a plurality of prism strips; the cross section of the prism strip is an isosceles triangle, the prism structure is 60 μm equal height, the height is 40 μm, the transparent substrate layer is PET, the thickness is 100 μm; the back coating layer is 7 μm thick, and the haze is 5%

[0061] Comparative Example 2

[0062] A brightness enhancement film, wherein the film is provided with a prism layer, a substrate layer, and a back coating layer in order from top to bottom; the prism layer is composed of a plurality of prism strips; the cross section of the prism strip is an isosceles trapezoid, the upper base width is 5 μm, the lower base width is 60 μm, the height is 40 μm, the transparent substrate layer is PET, and the thickness is 100 μm; the back coating layer has a coating thickness of 7 μm and a haze of 5%.

[0063] Table 1 provides the brightness and viewing angle of the embodiments and comparative examples.

[0064] serial number Brightness Viewing angle Example 1 103.5％ 105.4％ Example 2 104.2％ 104.9％ Example 3 105.6％ 103.5％ Example 4 105.3％ 103.6％ Example 5 103.3％ 104.8％ Example 6 103.6％ 105.2％ Example 7 105.9％ 106.4％ Comparative Example 1 100％ 100％ Comparative Example 2 101.8％ 101.3％

[0065] From the comparison of the test data of brightness and viewing angle provided in Table 1, it can be seen that the diffusion brightness enhancement film provided in Examples 1-6 significantly improves the brightness and viewing angle compared with the traditional brightness enhancement film, indicating that the diffusion brightness enhancement film can completely replace the lower diffusion and lower brightness enhancement films.

[0066] Table 2 (Prism layer composite PET) peeling force comparison test data

[0067]

[0068] It can be seen from Table 2 that the diffusion brightness enhancement film of the present invention has a good bonding effect and is not easy to separate. The vertical prism peeling force is higher than 210 gf, and the parallel prism peeling force is higher than 80 gf.

[0069] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. All equivalent changes and modifications made according to the content of the present invention are included in the patent scope of the present invention.

Claims

1. A diffusion brightness enhancement film, which comprises three layers: an upper layer, a middle layer and a lower layer. The upper layer is a diffusion prism layer structure with a thickness of 30-50 μm, the middle layer is a transparent substrate layer structure with a thickness of 50-250 μm, and the lower layer is a back coating layer structure with a thickness of 2-15 μm. The total thickness of the diffusion brightness enhancement film ranges from 90 to 320 μm. The diffusion prism layer is composed of a plurality of prism strips, and the cross-sectional main body of the prism strip is an isosceles trapezoidal structure, and the waist of the isosceles trapezoid has a circular protrusion structure.

2. The diffusion brightness enhancement film according to claim 1, characterized in that: The width of the upper base of the isosceles trapezoidal structure is one tenth to one fifteenth of the width of the lower base.

3. The diffusion brightness enhancement film according to claim 1, characterized in that: The upper base width of the isosceles trapezoidal cross section of the prism strip is 4-10 μm.

4. The diffusion brightness enhancement film according to claim 1, characterized in that: The lower base width of the isosceles trapezoidal cross section of the prism strip is 54-70 μm.

5. The diffusion brightness enhancement film according to claim 1, characterized in that: The height of the isosceles trapezoid in the cross section of the prism strip is 40-60 μm.

6. The diffusion brightness enhancement film according to claim 1, characterized in that: The circular protrusions on the two sides of the isosceles trapezoidal cross section of the prism strip are uniform or irregular, and the particle size distribution range of the circular protrusions is 1-5 μm, or 2-4 μm.

7. The diffusion brightness enhancement film according to claim 1, characterized in that: The transparent substrate is selected from one or two or more of polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene (PE), polystyrene (PS), and polyamide resin (PA).

8. The diffusion brightness enhancement film according to claim 1, characterized in that: The back coating layer comprises diffusion particles, and the diffusion particles are selected from polymethyl methacrylate (PMMA), polybutyl methacrylate (PBMA), polystyrene (PS), silicone, polyamide (PA) and polyester (PU).

9. The diffusion brightness enhancement film according to claim 1, characterized in that: The haze of the back coating layer ranges from 3 to 10%.

10. The diffusion brightness enhancement film according to claim 1, characterized in that: The diffusion brightness enhancement film and other brightness enhancement films form a composite structure, and the prism angles between the layers can be combined and are not limited to parallel and vertical.

11. The diffusion brightness enhancement film according to claim 10, characterized in that: The brightness enhancement films in the composite structure are connected by a bonding layer, and the thickness of the bonding layer is 0.8-1.2 μm.

12. The method for preparing the diffusion brightness enhancement film according to claims 1-11, comprising the following steps: Step (1), preparing a back coating liquid: adding adhesive and diffusion particles in sequence and stirring evenly, and adding solvent to adjust the viscosity of the coating liquid to be suitable for the coating process; Step (2), preparing a back coating layer: coating the coating liquid prepared in step (1) on one side of the transparent substrate by a micro-concave coating process, drying the solvent in an oven, curing the substrate with ultraviolet light, and winding the substrate, with a coating line speed of 25-35 m / min; Step (3), prism layer structure preparation: first, a trapezoidal prism structure is engraved on a copper roller, and then the desired final structure is obtained through a sandblasting process; Step (4), preparation of prism film: coating prism glue on the other side of the substrate by micro-replication process, pre-curing and demolding by low-pressure ultraviolet light, and then completely curing and molding by high-pressure ultraviolet light irradiation to obtain a diffuse brightening film.

13. The preparation method according to claim 12, characterized in that: The viscosity of the coating liquid in step (1) is in the range of 12-30 cps.

14. The preparation method according to claim 12, characterized in that: The coating line speed of step (2) is 28m / min, 30m / min, and 32m / min.

15. The preparation method according to claim 12, characterized in that: The prism glue in step (4) is a light-curing acrylic resin.

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