KR102683664B1 - Multi-functional sheet capable of diffusion and retroreflection, preparation method thereof and back light unit comprising the same - Google Patents

Abstract

The present invention includes a transparent substrate and a reflective layer having a hollow diffusion pattern on one surface of the transparent substrate, wherein the hollow diffusion pattern of the reflective layer has a thickness of 50 to 200 ㎛ and a size of 30 to 200 ㎛, and in the reflective layer The portion excluding the hollow diffusion pattern is coated with a cured material containing a white pigment, a reactive compound, and a photoinitiator, and the white pigment is titanium oxide having an average particle diameter of 300 to 700 nm in an amount exceeding 15% by weight and 30% by weight based on the total weight of the cured product. Provided is a composite functional sheet contained in a range of less than % by weight, a manufacturing method thereof, and a backlight unit containing the same.
The composite functional sheet with integrated diffusion and retroreflection functions according to the present invention is used in a backlight unit to diffuse and condense incident light to uniform brightness, while some light that cannot be diffused reaches the lower light guide plate through retroreflection. By letting it spread and then diffusing it again, luminance and light efficiency can be maximized. In addition, the reflective layer with the hollow diffusion pattern of the composite functional sheet is formed as a single layer rather than a lamination using an inkjet printing process on a transparent film, so when a reflective polarizing film is laminated on a diffusion sheet coated with polymer beads, Compared to this, it is possible to reduce the thickness of the backlight unit and make it thinner, and the process cost can be lowered.

Description

Complex functional sheet capable of diffusion and retroreflection, manufacturing method thereof, and backlight unit comprising the same

The present invention relates to a multi-functional sheet capable of diffusion and retroreflection, a manufacturing method thereof, and a backlight unit including the same.

A liquid crystal display (LCD) is a display device that can control a desired image by individually supplying data signals according to image information to pixels arranged in a matrix and adjusting the light transmittance of the pixels. Since it does not emit light, it is designed to display images by installing a back light unit on the back.

Currently, the backlight unit widely applied to liquid crystal displays depends on the attachment type of the lamp (light source), either the edge type, which attaches the lamp around the edge and reflects the light forward to the center, or the edge type, which attaches the lamp evenly to the entire back of the panel to emit light. It is divided into a direct type that shoots light, and among these, the edge type is mainly used in small display devices because it has excellent light uniformity and can be made thinner.

Figure 1 shows the structure of an edge-type backlight unit 1, including a lamp 10, a reflection sheet 20, a light guide plate 30, a diffusion sheet 40, prism sheets 51 and 52, and a protective film 60. ) includes. Specifically, light from a point light source provided from the lamp 10, for example, LED light, is changed to the state of a surface light source through the light guide plate 30, and then passes through the diffusion sheet 40 to be diffused and primary condensed to achieve uniform luminance. In the prism sheets 51 and 52 above, side light is changed to front light and secondary light convergence occurs, thereby increasing luminance. In this way, light passing through the optical sheets with specific functions is provided to the LCD panel 70 through the protective film 60.

Meanwhile, as the diffusion sheet, a polymer bead laminated sheet manufactured by dispersing beads such as PS, PMMA, silicon, etc. as diffusion particles on a transparent substrate made of resin such as PET or PC and then roll casting is mainly used. In such a diffusion sheet, if the effect of concentrating light incident at a certain range of effective angles is not complete, there is a disadvantage in that some light is lost. To solve this problem, attempts are being made to maximize light collection through recycling of lost light by additionally laminating a reflective polarizing film on the backlight unit.

However, the use of an additional optical film increases the thickness of the backlight unit, making it difficult to make the product thinner, which also results in an increase in manufacturing costs.

Therefore, the present invention is to reduce the thickness of the backlight unit by reducing the number of optical sheets included in the backlight unit. The purpose of the present invention is to provide a composite functional sheet combining diffusion and retroreflection functions and a method of manufacturing the same. It is done.

Another object of the present invention is to provide a backlight unit including the diffuse and retroreflective composite functional sheet.

In order to achieve the above object, the present invention includes a transparent substrate; and a reflective layer having a hollow diffusion pattern on one surface of the transparent substrate, wherein the hollow diffusion pattern of the reflective layer has a thickness of 50 to 200 ㎛ and a size of 30 to 200 ㎛, and a portion of the reflective layer excluding the hollow diffusion pattern. is coated with a cured product containing a white pigment, a reactive compound, and a photoinitiator, and the white pigment is titanium oxide having an average particle diameter of 300 to 700 nm in an amount of more than 15% by weight and less than 30% by weight based on the total weight of the cured product. A multi-function sheet included in the scope is provided.

In addition, the present invention is a method of manufacturing the composite functional sheet, which includes (i) inkjet printing a curable composition containing a white pigment, a reactive compound, and a photoinitiator on one side of a transparent substrate, excluding the circular or polygonal display portion, to create a hollow diffusion pattern; forming a reflective layer having a; and (ii) performing curing by irradiating ultraviolet rays to the reflective layer, wherein titanium oxide having an average particle diameter of 300 to 700 nm as the white pigment is greater than 15% by weight and 30% by weight based on the total weight of the curable composition. A manufacturing method included in the following range is provided.

Additionally, the present invention provides a backlight unit including a multi-function sheet.

The composite functional sheet with integrated diffusion and retroreflection functions according to the present invention is used in a backlight unit to diffuse and condense incident light to uniform brightness, while some light that cannot be diffused reaches the lower light guide plate through retroreflection. By letting it spread and then diffusing it again, luminance and light efficiency can be maximized.

In addition, the reflective layer with the hollow diffusion pattern of the composite functional sheet is formed as a single layer rather than a lamination using an inkjet printing process on a transparent film, so when a reflective polarizing film is laminated on a diffusion sheet coated with polymer beads, Compared to this, it is possible to reduce the thickness of the backlight unit and make it thinner, and the process cost can be lowered.

Figure 1 schematically shows the structure of a typical edge-type backlight unit.
Figure 2 schematically shows the structure of a multi-function sheet according to an embodiment of the present invention.
Figures 3a and 3b respectively illustrate the top and side surfaces of a multi-function sheet according to an embodiment of the present invention.
Figure 4 shows the diffusion and retroreflection paths of light when the composite sheet according to an embodiment of the present invention is used in a backlight unit having the structure of Figure 1.
Figure 5 shows the manufacturing process of a multi-function sheet according to an embodiment of the present invention.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

One embodiment of the present invention relates to a multi-function sheet incorporating diffusion and retroreflection functions. Hereinafter, the multi-function sheet will be described with reference to the drawings.

Figure 2 schematically shows the structure of a multi-function sheet according to an embodiment of the present invention, and Figures 3a and 3b illustrate the top and side surfaces of the multi-function sheet, respectively.

Referring to Figure 2, the composite functional sheet 100 according to an embodiment of the present invention includes a transparent substrate 110 and a reflective layer 120 formed on one surface of the transparent substrate, and the semi-upper layer is a hollow diffusion layer. It has a pattern (121).

The transparent substrate 110 may be a transparent film with a transmittance of 90% or more. Examples of the transparent film include polymethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), or two of them. Combinations of the above may be included. Additionally, the thickness of the transparent substrate may be 50 to 200 ㎛.

The reflective layer 120 is formed on one side of the transparent substrate and has a hollow diffusion pattern 121 with a certain thickness and size, and the portion excluding the pattern is a cured material containing a white pigment, a reactive compound, and a photoinitiator. It is coated.

Referring to FIGS. 3A and 3B, the hollow diffusion pattern 121 evenly distributed on the reflective layer 120 serves as a passage for a surface light source that passes through the transparent substrate and is dispersed therefrom, and the light diffused through this passes through. is directed toward the polarizing film of the upper LCD panel. The shape of this hollow diffusion pattern is not particularly limited as long as it can serve as a passage for light. For example, it may have a circular or polygonal (square, pentagon, hexagon, etc.) cross section and a certain thickness.

The size of the hollow diffusion pattern may be 30 to 200 ㎛, specifically 50 to 100 ㎛, and the size of the pattern is a diameter when the cross-section is circular, and a line segment passing through the center of gravity on the cross-section when the cross-section is polygonal. It can be the length of . When the size of the hollow pattern satisfies the above range, it is advantageous for sufficient diffusion and condensation of incident light.

The thickness of the hollow diffusion pattern may be determined by the thickness of the cured material coated on the portion excluding the pattern. For example, as the cured material is coated through a printing process, the hollow diffusion pattern may have a thickness range realized through the printing process, such as 50 to 200 μm, specifically 60 to 150 μm.

In addition, it is advantageous for the hollow diffusion pattern to be uniformly distributed over 20% to 80%, specifically 40% to 60%, of the total area of the reflective layer in order to induce sufficient diffusion of the surface light source and maximize light collection efficiency.

Meanwhile, the cured coating layer formed on the portion of the reflective layer 120 excluding the hollow pattern may include a white pigment with a high refractive index, particularly titanium oxide, and may exhibit a reflectance of 80% or more, that is, 80 to 100%. Here, the reflectance can be measured in a conventional manner, and can be measured through the method performed in the examples and comparative examples below. For example, light is transmitted through an optical sheet at an incident angle of about 5° and reflected. The reflectance in the visible light region with a wavelength of 380 to 780 nm can be measured using a UV/VIS/NIR spectrometer (solidspec-3700, Shimadzu).

The titanium oxide has excellent dispersibility in the composition forming the cured coating layer, and can be advantageously used as a reflective material compared to other white pigments such as calcium carbonate.

In one embodiment of the present invention, titanium oxide used as the white pigment may be included in a range of more than 15% by weight and less than 30% by weight, specifically 20 to 25% by weight, based on the total weight of the cured product. At this time, if the content of titanium oxide is less than 15% by weight, it is difficult to secure sufficient reflectance, and if it is more than 30% by weight, the dispersibility in the composition for forming a reflective layer decreases, resulting in poor stability of the composition, and the viscosity of the composition is 50cP. If it increases beyond this, ink jetting application may be difficult, and problems with surface wrinkle formation due to excessive curing may occur.

In addition, the titanium oxide preferably has an average particle diameter of 300 to 700 nm, for example, 500 to 600 nm in order to secure a desired level of reflectance at the above content. Here, the “average particle size” refers to a particle size whose volume accumulation based on particle weight is equivalent to 50% of the particle size distribution determined by particle size distribution measurement using a particle size measurement method common in the field, for example, laser diffraction.

If the average particle size of the titanium oxide used is less than 300 nm, agglomeration may occur due to physical adsorption between particles, which reduces dispersibility and makes inking difficult. On the other hand, if the average particle diameter exceeds 700 nm, the nozzle may be clogged when ink is ejected through the inkjet head, and the roughness may increase due to the large particles on the surface hardened after printing, resulting in a decrease in reflectivity. Additionally, if an excessive amount of titanium oxide is used to increase reflectivity, inkjetting may be difficult due to increased viscosity, as mentioned above.

Additionally, titanium oxide, zircon oxide, barium sulfate, or a combination of two or more thereof may be used as the white pigment.

The cured coating layer containing the white pigment can reflect light that is not diffused through the hollow pattern to the optical sheet located below. Through this recycling of light, the light that reaches the lower optical sheet diffuses back to the upper part, thereby maximizing light efficiency and brightness.

Figure 4 shows the diffusion and retroreflection paths of light when the multi-function sheet according to an embodiment of the present invention is used in a backlight unit having the same structure as that of Figure 1. Referring to FIG. 4, when light is emitted from the lower light guide plate 30 to the upper composite function sheet 100, most of the light passes through the hollow diffusion pattern on the transparent base film and is directed to the LCD panel 70, Some of the light that does not pass through the diffusion pattern is reflected back to the lower light guide plate 30 by the cured coating layer containing white pigment and then diffuses back to the upper composite functional sheet 100. As a result, light efficiency can be increased without loss of light and luminance can be maximized by increasing light collection.

In addition, since the composite functional sheet of the present invention integrates diffusion and retroreflection functions in one layer, the thickness of the backlight unit is reduced compared to the case where a reflective polarizing film is laminated on an existing diffusion sheet coated with polymer beads. You can do it.

Meanwhile, the multi-functional sheet according to one embodiment of the present invention can be formed through a series of processes of inkjet printing and ultraviolet curing of a curable composition on a transparent base film, which will be described with reference to FIG. 5.

Figure 5 shows the manufacturing process of a composite functional sheet according to an embodiment of the present invention. The composite functional sheet of the present invention is (i) a curable composition containing a white pigment, a reactive compound and a photoinitiator on one side of a transparent substrate, and a circular shape. Alternatively, it can be manufactured by inkjet printing on the portion excluding the polygonal display portion to form a reflective layer with a hollow diffusion pattern, and then (ii) curing the reflective layer formed through inkjet printing by irradiating ultraviolet rays.

Inkjet printing applied in the present invention is a non-contact method that uses pressure to spray the ink composition in the form of drops to the desired area. It consumes less material and has excellent precision, and the print head does not touch the substrate, preventing damage to the substrate on which printing is performed. there is. In addition, since UV curing is performed immediately after printing to form a coating layer, a fast process speed can be secured.

The circular or polygonal display unit can be designed by displaying a design of the corresponding shape on a transparent substrate or temporarily installing a structure of the corresponding shape.

The cured coating layer formed through the inkjet printing generally has a printable thickness range, for example, 50 to 200 ㎛, specifically 60 to 150 ㎛. The thickness of this cured coating layer corresponds to the hollow diffusion pattern as described above.

As described above, the white pigment included in the curable composition may include titanium oxide in an amount of more than 15% by weight and less than 30% by weight, specifically 20 to 25% by weight, based on the total weight of the curable composition. At this time, if the content of titanium oxide is less than 15% by weight, it is difficult to secure sufficient reflectance, and if it is more than 30% by weight, the dispersibility in the composition for forming a reflective layer decreases, resulting in poor stability of the composition, and the viscosity of the composition is 50cP. If it increases beyond this, ink jetting application may be difficult, and problems with surface wrinkle formation due to excessive curing may occur.

Additionally, titanium oxide, zircon oxide, barium sulfate, or a combination of two or more thereof may be used as the white pigment.

The reactive compound included in the curable composition may include a monofunctional acrylate monomer, a multifunctional acrylate monomer, or a combination thereof.

The monofunctional acrylate-based monomer serves to improve the adhesion between the substrate and the printing layer while lowering the viscosity of the composition, and examples of its use include 2-hydroxyethyl acrylate (2-HEA) and hydrocarbons. These include hydroxypropyl acrylate (HPMA), 2-hydroxyethyl methacrylate (2-HEMA), and hydroxypropyl methacrylate (HPMA).

The multifunctional acrylic monomer serves to increase the crosslinking density and curing sensitivity of the cured film in the composition, and usable examples include 1,6-hexanediol diacrylate (HDDA) and neopentyl glycol diacrylate. Bifunctional monomers such as acrylate (neopentylglycol diacrylate, NPGDA), dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), or pentaerythritol triacrylate ( Monomers with three or more functional groups such as pentaerithritol triacrylate (PETA), dipentaerithritol pentaacrylate (DPPA), and dipentaerithritol hexaacrylate (DPHA) may be included. In particular, 1,6-hexanediol diacrylate (HDDA) has low viscosity and hydrophilic properties and can increase the dispersibility of white pigment. Additionally, a composition containing this may be used in a solvent-free form that does not contain a solvent.

The reactive compound may be included in an amount of 40 to 80% by weight, for example, 60 to 80% by weight, based on the total weight of the composition. When the above content range is satisfied, curing sensitivity can be increased without causing surface wrinkles of the cured product. , a viscosity that allows ink jetting can be achieved.

The photoinitiator included in the curable composition is a component that initiates the curing reaction of the reactive compound, examples of which include Irgacure 819 (bisacryl phosphine-based), Darocur TPO (monoacryl phosphine-based), Irgacure 369 (α-aminoketone-based), and Irgacure184 ( α-hydroxyketone type), Irgacure 907 (α-aminoketone type), Irgacure 2022 (bisacryl phosphine/α-hydroxyketone type), Irgacure 2100 (phosphine oxide type), Darocur ITX (isopropyl thioxanthone), Irgacure 500 (α-hydroxyketone type) , Irgacure 651 (benzyldimethyl-ketal type), Darocur MBF (phenylglyoxylate type), Darocur 1173 (α-hydroxyketone type), etc.

The photoinitiator may be included in an amount of 1 to 10% by weight, for example, 2 to 7% by weight, based on the total weight of the composition. When the above range is satisfied, the curing reaction can be smoothly achieved and an increase in viscosity of the cured composition can be prevented.

Additionally, the curable composition may further include one or more additives among a dispersant, a reactive diluent, an adhesion enhancer, and a surfactant, if necessary.

The dispersant may be a polymeric, nonionic, anionic or cationic dispersant, examples of which include acrylic, polyalkylene glycol and its ester, polyoxyalkylene polyhydric alcohol, esteralkylene oxide adduct, and alcoholalkylene. There are oxide adducts, sulfonic acid esters, sulfonates, carboxylic acid esters, carboxylic acid salts, alkylamide alkylene oxide adducts, and alkylamines, and these can be used alone or in combination of two or more. Among these, it is advantageous to use an acrylic-based dispersant that has excellent ink storage properties.

The dispersant may be included in an amount of 1 to 7% by weight, for example, 1.5 to 5% by weight, based on the total weight of the composition. When the content of the dispersant satisfies the above range, the pigment can be sufficiently dispersed to avoid pigment aggregation or reduction in curing sensitivity. You can.

The adhesion enhancer is capable of improving the adhesion between the substrate and the printing layer, and can be used as one or more selected from the group consisting of phosphate-based acrylates such as alkoxy silane compounds and phosphate acrylate, and the alkoxy Examples of silane compounds include 3-Glycidoxypropyl trimethoxysilane (KBM-403 (Shin-Etsu, USA)), 3-Glycidoxypropyl methyldimethoxysilane (3-Glycidoxypropyl methyldimethoxysilane) , KBM-402), 2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane (2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane, KBM-303), 3-glycidoxypropyl methyldiethoxysilane (3- Glycidoxypropyl methyldiethoxysilane, KBE-402), 3-Glycidoxypropyl triethoxysilane (KBE-403), 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propyl Partially hydrolyzates of 3-Triethoxysilyl-N-(1,3 dimethyl-butylidene) propylamine, KBE-9103), and 3-Methacryloxypropyl trimethoxysilane (KBM-503) ), etc., and one or more types can be used.

The surfactant may be a commercially available product, for example, Megafack F-444, F-475, F-478, F-479, F-484, F-550, F-552 from DIC (DaiNippon Ink & Chemicals). F-553, F-555, F-570, RS-75 or Surflon S-111, S-112, S-113, S-121, S-131, S-132, S-141 and S from Asahi Glass -145 or Fluorad FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430 and FC-4430 from Sumitomo 3M or Zonyl FS-300, FSN, FSN from Dupont. -100 and BYK-306, BYK-307, BYK-310, BYK-320, BYK-330, BYK-331, BYK-333, BYK-342, BYK-350, BYK-354, BYK-355 from FSO and BYK. , BYK-3550, BYK-356, BYK-358N, BYK-359, BYK-361N, BYK-381, BYK-370, BYK-371, BYK-378, BYK-388, BYK-392, BYK-394, BYK In the group consisting of -399, BYK-3440, BYK-3441, BYK-UV 3530, BYK-UV 3570 or Tego's Rad 2100, Rad 2011, Glide 100, Glide 410, Glide 450, Flow 370, Flow 425, Wet500, etc. You can use whatever you choose.

The content of the adhesion promoter and surfactant may be appropriately selected within a range that does not impair the physical properties of the curable composition.

Meanwhile, ultraviolet irradiation in the curing step is irradiated with a dose of 0.5 to 5 J/cm ² , for example, 1 to 3 J/cm ² using radiation with a wavelength of 250 to 410 nm, specifically 360 to 410 nm. It can be done.

The composite functional sheet of the present invention manufactured as described above uses an inkjet printing process on a transparent film to form a single layer rather than a laminated reflective layer with a hollow diffusion pattern, so that it is reflected in the diffusion sheet coated with polymer beads. Compared to the case of using a laminated polarizing film, the thickness of the backlight unit can be lowered to make it thinner and the process cost can be lowered.

Accordingly, the present invention additionally provides a backlight unit including the multi-function sheet.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention and the scope of the invention is not limited in any way.

Examples 1 to 2 and Comparative Examples 1 to 5

The composition (unit: weight %) shown in Table 1 below includes titanium oxide (TiO ₂ ) as a white pigment (the particle size of the titanium oxide used is shown in Table 1 below), an acrylic dispersant, and 1,6-hexanediol as a reactive compound. Pigment dispersion containing diacrylate (HDDA) (Tokushiki), pentaerythritol triacrylate (PETA) and 2-hydroxyethyl acrylate (2-HEA) as additional reactive compounds, adhesion promoter (KBE-9103, Shin) -Etsu) and a photoinitiator (Darocur TPO, BASF) were stirred and mixed for 2 hours to prepare a curable composition.

Each of the curable compositions prepared above was used to mark a circle or polygon on the surface of a PET film with a thickness of 125 ㎛, and then inkjet printed on the area excluding the display portion to form a reflective layer with a hollow diffusion pattern. Subsequently, the reflective layer is photocured by irradiating ultraviolet rays at a dose of 1 J/cm ² using a 395 nm short-wavelength UV LED lamp (12 W output) to produce a composite functional sheet in which a reflective layer with a hollow diffusion pattern is formed on the PET film. was manufactured.

Experiment example:

The physical properties of the composite functional sheets manufactured from the above examples and comparative examples were evaluated by the following method, and the results are shown in Table 1.

1) Thickness: Measured using a surface inspection device (Alphastep Stylus Profiler)

2) Reflectance: Light is transmitted through the sheet at an angle of incidence of approximately 5°, and the reflectance in the visible light region with a reflected wavelength of 380 to 780 nm is measured using a UV/VIS/NIR spectrometer (solidspec-3700, Shimadzu).

3) Adhesion: Evaluated as 0B to 5B by conducting a cross cut test (Standards: ASTM D3002, D3359)

4) Surface wrinkles: Check the surface wrinkles of the reflective layer with the naked eye after photocuring.

<Evaluation criteria>

○: No wrinkles occur on the surface of the reflective layer.

X: Wrinkles appear on the surface of the reflective layer

5) Viscosity: Measure the composition used for inkjet printing by adjusting the rotational torque to 90% at a temperature of 25°C using a Brookfield viscometer (Brookfield DV II+) according to ASTM D-2196.

6) Dispersion stability: Store the composition used in inkjet printing at room temperature and check whether the pigment settles within 2 weeks.

<Evaluation criteria>

○: No precipitation of pigment within 2 weeks

X: Pigment sedimentation confirmed within 2 weeks

division Example Comparative example One 2 One 2 3 4 5 Curable composition Furtherance titanium oxide
(entry size) 20
(550nm) 25
(550nm) 15
(550 nm) 30
(550 nm) 30
(550 nm) 20
(200nm) 20
(950nm) Acrylic dispersant 2.4 3.0 1.8 3.6 3.6 2.4 2.4 HDDA 28 35 21 42 42 28 28 PETA 10 10 10 10 5 10 10 2-HEA 35 23 48 10 15 35 35 KBE-9103 1.6 One 1.2 1.4 1.4 1.6 1.6 Darocur TPO 3 3 3 3 3 3 3 Viscosity (25℃, cP) 31.1 40.6 22.3 58.3 53.5 29.8 31.8 Dispersion Stability ○ ○ ○ X X X X reflective layer Thickness (㎛) 60 60 60 60 60 60 60 Hollow diffusion pattern size (㎛) 45 45 45 45 45 45 45 reflectivity(%) 85.3 88.5 79.5 88.7 88.4 79.8 78.9 cross cut 5B 5B 5B 3B 3B 3B 5B surface wrinkles ○ ○ ○ X X ○ ○

From Table 1, examples in which inkjet printing and curing were performed using a curable composition containing titanium oxide with an average particle diameter of 550 nm as a white pigment in a range of more than 15% by weight and less than 30% by weight based on the total weight of the curable composition. 1 to 2 ensured viscosity and dispersion stability suitable for inkjetting of the composition, thereby producing a composite functional sheet with excellent adhesion to the base film, no surface wrinkles, and a reflective layer with an excellent reflectance of 80% or more. In addition, since the reflective layer has a hollow diffusion pattern, when used as an optical member in a backlight unit, a complex function of diffusion and reflection (retroreflection) can be implemented with one layer.

On the other hand, Comparative Example 1 failed to secure sufficient reflectance of the reflective layer due to a somewhat insufficient content of titanium oxide used as a white pigment in the composition used for inkjet printing.

In Comparative Example 2, as the titanium oxide contained in the composition exceeded the above range, the viscosity increased to more than 50 cP, making ink jetting difficult and the dispersion stability of the composition decreased, resulting in overcuring and fine wrinkles on the cured surface. It has been done.

Comparative Example 3 is an attempt to suppress fine wrinkles by using the same amount of titanium oxide as Comparative Example 2 and reducing the increase in viscosity and crosslinking density (curing sensitivity) by reducing the amount of PETA (trifunctional monomer), a reactive compound. However, even in this case, fine wrinkles occurred due to the content of titanium oxide exceeding a certain range.

In addition, in Comparative Example 4, as titanium oxide with a small average diameter of 200 nm was used, physical adsorption and resulting agglomeration between pigment particles occurred, dispersibility was reduced, making inkjetting difficult, and as a result of excessive printing, the reflective layer Sufficient reflectance was not secured. In addition, in the case of Comparative Example 5 using titanium oxide with an average diameter of 950 nm, ink jetting was not smooth due to poor dispersion stability, and the roughness increased due to large particles on the surface cured after printing, resulting in low reflectance.

As the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (12)

transparent substrate; and a reflective layer having a hollow diffusion pattern on one surface of the transparent substrate,
The hollow diffusion pattern of the reflective layer has a thickness of 50 to 200 ㎛ and a size of 30 to 200 ㎛,
The portion of the reflective layer excluding the hollow diffusion pattern is coated with a cured material containing a white pigment, a reactive compound, and a photoinitiator,
As the white pigment, titanium oxide having an average particle diameter of 300 to 700 nm is contained in an amount of more than 15% by weight and less than 30% by weight based on the total weight of the cured product,
The hollow diffusion pattern has a polygonal cross-section,
A composite functional sheet in which some light that does not pass through the hollow diffusion pattern is retroreflected to the light guide plate by a cured coating layer containing the white pigment. The composite functional sheet according to claim 1, wherein the titanium oxide is contained in an amount of 20 to 25% by weight based on the total weight of the cured product. The composite functional sheet according to claim 1, wherein the reflective layer has a reflectance of 80% or more. The composite functional sheet according to claim 1, wherein the hollow diffusion pattern in the reflective layer is distributed over 20% to 80% of the total area of the reflective layer. delete The composite functional sheet according to claim 1, further comprising zirconium oxide, barium sulfate, or a combination of two or more thereof as the white pigment. The composite functional sheet according to claim 1, wherein the transparent substrate includes polymethacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), or a combination of two or more thereof. A method of manufacturing a multi-function sheet according to claim 1,
(i) inkjet printing a curable composition containing a white pigment, a reactive compound, and a photoinitiator on one side of a transparent substrate, excluding the circular or polygonal display portion, to form a reflective layer having a hollow diffusion pattern; and
(ii) performing curing by irradiating ultraviolet rays to the reflective layer,
A manufacturing method comprising titanium oxide having an average particle diameter of 300 to 700 nm as the white pigment in a range of more than 15% by weight and less than 30% by weight based on the total weight of the curable composition. The manufacturing method according to claim 8, wherein the reflective layer formed by inkjet printing has a thickness of 50 to 200 ㎛. The manufacturing method of claim 8, wherein the hollow diffusion pattern formed on the reflective layer has a thickness of 50 to 200 ㎛ and a size of 30 to 200 ㎛. The method of claim 8, wherein the reactive compound includes a monofunctional acrylate monomer, a multifunctional acrylate monomer, or a combination thereof. A backlight unit including the multi-function sheet according to claim 1.