CN103649622A - Method for manufacturing optical sheet - Google Patents

Abstract

Provided are a method for manufacturing an optical sheet and an optical sheet manufacturing device, which can achieve quality improvement in an optical sheet by minimizing the occurrence of streaks on a printing surface when printing a dot pattern on the rear surface of the optical sheet. Ink (54) is sprayed from a nozzle (51) onto an original plate (60) for a light guide plate. At this point, warpage is removed by applying suction to and adsorbing the non print surface of the original plate (60) and a gap distance (D) that is a distance between the nozzle (51) and the original plate (60) is adjusted to be 2.8 mm or less, then the dot pattern is printed by spraying the ink.

Description

Manufacturing method of optical sheet

technical field

The present invention relates to an optical sheet, a manufacturing method thereof, a manufacturing device, a surface light source device and a transmissive image display device using the optical sheet.

Background technique

As a backlight used as a surface light source device of a liquid crystal display (transmissive image display device), a so-called bottom backlight type backlight and an edge light type backlight are known. Among them, the bottom backlight surface light source device is a surface light source device that arranges light sources such as cold cathode tubes and LEDs on the back side of the light guide plate, and emits light incident from the back side of the light guide plate to the front side.

On the other hand, an edge-lit surface light source device is a surface light source device that arranges light sources such as cold cathode tubes and LEDs on the side of a transparent plate, that is, a light guide plate, and emits light incident from the side of the light guide plate to the front side. As conventional backlights, bottom backlight type surface light source devices are often used from the viewpoint of improving luminance. However, in recent years, along with the increase in the use of thin and high-brightness LED light sources and the thinning of liquid crystal displays, the use ratio of edge-lit surface light source devices is increasing.

In the light guide plate in such an edge-light type surface light source device, dot printing is performed on the back side, so that light incident from the side is diffusely reflected on the back side and emitted from the front side. As a method of performing dot printing on the back surface of a light guide plate, a method using screen printing is known (for example, refer to Patent Document 1). However, when performing dot printing by screen printing, it is necessary to prepare different plates for each pattern. Therefore, there is a problem that the degree of freedom is low in screen printing.

On the other hand, dot pattern printing using inkjet printing is known as a method other than screen printing (for example, refer to Patent Document 2). There is no need to prepare multiple plates when inkjet printing is used, so it is possible to cope with various printing patterns, and the degree of freedom can be increased.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 7-49421

Patent Document 2: Japanese Patent Application Laid-Open No. 2006-136867

Contents of the invention

However, in recent years, surface light source devices using such light guide plates have come to require high precision, for example, high precision of 150 dpi or higher.

In addition, in recent years, since liquid crystal displays are used in televisions and the like, larger and thinner light guide plates have been required. When manufacturing a light guide plate, it is ideal that the original plate of the light guide plate is in the shape of a plate without warping, but actually, warping and bending may occur due to moisture absorption during storage, uneven heating, and the like. It is estimated that the effect of such warpage will become more pronounced as the light guide plate becomes larger and thinner.

However, in the light guide plate disclosed in the above-mentioned Patent Document 2, the requirements for high precision and the improvement of the warpage of the light guide plate original plate are not high. Therefore, when dot pattern printing is performed on a light guide plate using the dot pattern printing disclosed in Patent Document 2, streaks may be seen on the printed surface due to unevenness in distance between dots and disorder in dot shape. If streaks are seen on the printed surface in this way, there is a problem that the quality of a liquid crystal display using an optical sheet, etc. will fall.

Therefore, the object of the present invention is to provide a manufacturing method and manufacturing apparatus of an optical sheet, which can suppress occurrence of streaks on the printed surface when dot pattern printing is performed on the back of the optical sheet, thereby realizing a product using the optical sheet. quality improvement.

The present invention is a method of manufacturing an optical sheet that emits light incident from a light incident surface from a light exit surface intersecting the light incident surface, and passes the optical sheet through a nozzle. The back of the original plate of the sheet material is sprayed with ink to print a dot pattern, wherein the non-printed surface of the original plate is sucked and adsorbed to eliminate the warping of the original plate, and the distance between the nozzle and the original plate is adjusted to 2.8mm or less, and then the ink is sprayed. Print dot pattern.

Generally, when forming a low-definition dot pattern, even if the distance between the nozzle and the original plate is long, there will be almost no streaks on the printed pattern (the printed dots are formed in a straight line), so in order to avoid the nozzle and the original plate contact, set the Gap Distance to a large value. However, when forming a high-definition dot pattern, if the gap distance is large, streaks may be generated on the printed pattern, and the streaks cause a problem that the quality of the product deteriorates. Here, in the manufacturing method of the optical sheet according to the present invention, when performing dot pattern printing, the non-printing surface of the original plate is sucked and sucked to eliminate warping, and the distance between the nozzle and the original plate is adjusted to 2.8 mm or less. . By suctioning and absorbing the non-printing surface of the original plate to eliminate warping, and adjusting the distance between the nozzle and the original plate to 2.8mm or less, it is possible to suppress the occurrence of streaks on the printing surface of the dot pattern printing on the optical sheet. Therefore, the improvement of the quality of the product using an optical sheet can be aimed at. In addition, a more preferable distance between the nozzle and the original plate when performing dot pattern printing is 1.8 mm or less, and a more preferable range is 1.0 mm or less.

Therefore, it is possible to adjust the distance between the nozzle and the original plate to be 2.8 mm or less when printing the dot pattern.

Original plates used for optical sheets such as light guide plates are seldom completely flat, and often slightly warped. If the distance between the inkjet nozzle and the original plate becomes too long due to the influence of the warp, streaks may be generated on the printing surface. Here, when performing dot pattern printing, the non-printing surface of the original plate is sucked and sucked to eliminate warping, and the distance between the nozzle and the original plate is adjusted to 2.8mm or less, so that the occurrence of streaks on the printing surface can be more reliably suppressed. produce. As a result, the quality improvement of the product using an optical sheet can be aimed at further.

Furthermore, an aspect in which the thickness of the original plate is 4.5 mm or less may be employed.

It is preferable to adjust the thickness of the original plate to preferably 4.5 mm or less in this way. In addition, the thickness of the original plate is more preferably adjusted to 2.0 mm or less.

In addition, when printing the dot pattern, the original plate is placed on the table, and the distance between the nozzle and the table is not more than the distance obtained by adding the thickness of the original plate to 2.8 mm.

By taking into account the thickness of the original plate in this way, the distance between the nozzle and the original plate can be controlled by the distance between the table on which the original plate is placed and the nozzle.

Furthermore, an optical sheet manufactured by the manufacturing method of an optical sheet may be used, and a surface light source device including a light source arranged laterally to the light incident surface of the optical sheet may be used. Furthermore, a transmissive image display device including the above-mentioned surface light source device and a transmissive image display portion arranged to face the light exit surface of the optical sheet and display an image by being irradiated with light emitted from the light source can also be produced.

The present invention is an apparatus for manufacturing an optical sheet that emits light incident from a light incident surface from a light exit surface intersecting the light incident surface, and passes the light to the optical sheet through a nozzle. Ink is sprayed on the back of the original plate of the original material to print a dot pattern. Among them, the non-printed surface of the original plate is sucked and adsorbed to eliminate the warpage of the original plate, and the distance between the nozzle and the table on which the original plate is placed is adjusted to 2.8mm plus the original plate. The distance obtained from the thickness of the plate is below, thereby jetting the ink to print the dot pattern.

According to the manufacturing method and manufacturing apparatus of the optical sheet involved in the present invention, when the printing of the dot pattern is carried out on the back surface of the optical sheet, the generation of streaks on the printed surface can be suppressed, so that the quality of the product using the optical sheet can be improved. improve.

Description of drawings

FIG. 1 is an exploded side sectional view schematically showing a transmissive image display device using a light guide plate according to an embodiment.

2 is a plan view schematically showing a transmissive image display device using the light guide plate according to the embodiment.

FIG. 3 is a perspective view showing a light guide plate manufacturing apparatus according to the embodiment.

4 is a side view schematically showing the relationship between the inkjet nozzles and the original plate of the light guide plate when printing a dot pattern.

5 is a plan view showing a conveyor belt on which a light guide plate is placed when printing a dot pattern.

Both (a) and (b) of FIG. 6 are diagrams showing other arrangement patterns of printed dots.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, in each embodiment, the same code|symbol is attached|subjected to the same element, and overlapping description is abbreviate|omitted. In addition, for convenience of illustration, the dimensional ratios in the drawings do not necessarily match the dimensional ratios described.

In the present invention, dot pattern printing in a method of manufacturing a light guide plate which is an optical sheet used in a surface light source device of a transmissive image display device such as a liquid crystal display device is a main feature. In this embodiment, first, the structure of the liquid crystal display device including the light guide plate will be described, and then, the dot pattern printing in the manufacturing method of the light guide plate will be described.

FIG. 1 is an exploded side sectional view schematically showing a liquid crystal display using a light guide plate according to a first embodiment of the present invention, and FIG. 2 is a rear view thereof. As shown in FIG. 1 , a transmissive image display device, a liquid crystal display device 1 includes a transmissive image display unit 10 and a surface light source device 20 . The surface light source device 20 is arranged on the rear side of the transmissive image display unit 10 , and emits light from the rear side of the transmissive image display unit 10 . In the following description, as shown in FIG. 1 , the arrangement direction of the surface light source device 20 and the transmissive image display unit 10 is referred to as the Z direction (thickness direction), and the two directions perpendicular to the Z direction are mutually orthogonal. The two directions are called X direction and Y direction.

The transmissive image display unit 10 includes a liquid crystal cell 11 and a linear polarizer 12 , and the linear polarizer 12 is disposed on both surfaces of the liquid crystal cell 11 . For the liquid crystal cell 11 and the linear polarizing plate 12, elements used in known liquid crystal display devices can be used. As the liquid crystal cell 11, well-known liquid crystal cells, such as a TFT type and an STN type, can be illustrated.

The surface light source device 20 includes a light guide plate 30 and an LED light source 22 which are optical sheets. The light guide plate 30 is formed of light-transmitting translucent resin and has a plate shape. The translucent resin is a resin that transmits light. In addition, the light guide plate 30 may be in the form of a sheet, or may be in the form of a film. In addition, the thickness T of the light guide plate 30 is preferably 1.0 to 4.5 mm.

The light guide plate 30 includes a plate-shaped member made of a translucent resin. The refractive index of translucent resin exists in the range of 1.49-1.59, for example. As the translucent resin used for the light guide plate 30, methacrylic resin is mainly used. Other resins may be used as the resin used for the light guide plate 30, and a styrene-based resin may also be used. As the translucent resin, acrylic resin, styrene resin, polycarbonate resin, cyclic olefin resin, MS resin (copolymer of acrylic and styrene), etc. can be used. Furthermore, additives such as a light diffusing agent, an ultraviolet absorber, a heat stabilizer, and a photopolymerization stabilizer may be added to the light guide plate 30 .

In addition, the light guide plate 30 is a rectangular parallelepiped, and as shown in FIG. 2 , includes a front surface 31 and a back surface 32 , which are a pair of principal surfaces facing each other in the Z-axis direction (thickness direction). In addition, the light guide plate 30 includes a pair of side surfaces 33 facing each other in the X-axis direction and a pair of side surfaces 34 facing each other in the Y-axis direction. The front surface 31 and the back surface 32 are formed in a direction intersecting the side surfaces 33 , 34 , more specifically, in a direction perpendicular to the side surfaces 33 , 34 . Their surfaces 31, backs 32, and sides 33, 34 are all rectangular.

Among them, the surface 31 may be a flat surface or a surface provided with unevenness. When providing unevenness to the surface 31 , for example, a plurality of protrusions protruding in the Z-axis direction and whose longitudinal direction is along the X-axis direction can be arranged parallel to each other at intervals in the Y-axis direction. The shape of the protruding portion may be a shape whose surface is prism-shaped, or may have a semicircular or semi-elliptical cross-sectional shape when the protruding portion is cut in a direction perpendicular to the longitudinal direction. In addition, it is preferable that the cross-sectional shape of the protrusion section when cut in a direction perpendicular to the longitudinal direction is the same shape. In addition, it is preferable that the extending direction of the protrusion is parallel to the incident direction of the light emitted from the light source when it enters from the side surface of the light guide plate.

In addition, the surface 31 functions as a surface from which planar light can be emitted. The front surface 31 is arranged on the side of the transmissive image display unit 10 , and the back surface 32 is arranged on the side opposite to the transmissive image display unit 10 . Various films 41 are disposed between the light guide plate 30 and the transmissive image display unit 10 on the front side of the light guide plate 30 . Furthermore, a reflective sheet 42 for reflecting light in the light guide plate 30 to the front surface 31 side is arranged at a position opposite to the back surface 32 . Examples of the various films 41 include a diffusion film, a prism film, a brightness enhancement film, and the like.

The LED light source 22 is disposed on the side of the light guide plate 30 , facing the side surface 33 along the Y-axis direction of the light guide plate 30 . The side surface 33 of the light guide plate 30 is an incident surface on which the light emitted from the LED light source 22 is incident. The plurality of LED light sources 22 are discretely arranged along the longitudinal direction (Y-axis direction) of the side surface 33 . Light incident from the side surface 33 of the light guide plate 30 is emitted from the surface 31 . The surface of the light guide plate 30 serves as an emission surface from which light incident from the side surface 33 is emitted.

The arrangement interval of the LED light sources 22 is usually 5 mm to 20 mm. The LED light source 22 is arranged along the side surface 33 facing across the Y axis. Instead of this form, they may be arranged along the four sides of the light guide plate 30 , or may be arranged along the opposite side surfaces 34 across the X-axis. Alternatively, they may be arranged along any one of the side surfaces 33 and 34 . In addition, the light source is not limited to an LED light source, and may also be other light sources. Furthermore, a linear light source such as a cold cathode tube may be arranged as the light source.

The LED light source 22 is composed of, for example, white LEDs, and a plurality of LEDs are arranged at one place to constitute one light source unit. In addition, LEDs of three different colors of red, green, and blue may be arranged in close proximity as one light source unit. Here, when light source units having a plurality of LEDs are discretely arranged along the arrangement direction, it is preferable to arrange LEDs of different colors as close as possible to each other.

As the LED light source, LED light sources with various light distributions can be used. It is preferable that the luminosity in the normal direction (X-axis direction) of the LED light source is the largest, and the half-value width of the luminosity distribution is 40-80 degrees. LED light source. In addition, specific examples of the type of LED light source include a Lambertian type, a cannonball type, and an edge emission type.

The size of the light guide plate 30 in plan view is set so as to be suitable for the screen size of the target transmissive image display unit 10 . Specifically, a light guide plate in which the length of two orthogonal sides is generally 250 mm×440 mm or more (the length L of the diagonal line is 506 mm or more) is used. In addition, a light guide plate having a large size of 500 mm×800 mm or more (diagonal length L of 943 mm or more) may be used. Alternatively, the plan view shape of the light guide plate 30 is a rectangle here, but other shapes such as a square may also be used. In addition, the thickness T of the original plate (translucent resin sheet) of the light guide plate 30 is 4.5 mm or less, for example, it may be 2.0 mm or 1.0 mm.

Here, a rectangle of 250 mm×440 mm or more means a rectangle having one side of 250 mm or more and the other side of 440 mm or more. In addition, the rectangle of 500 mm x 800 mm or more means the rectangle whose one side is 500 mm or more and the other side is 800 mm or more.

In addition, the original plate 60 of the light guide plate 30 may satisfy the following formula (1).

[mathematical formula 1]

L/T≤0.01...(1)

Wherein, L is the length (mm) of the diagonal line of the original plate, and T is the thickness (mm) of the original plate. The length L of the diagonal line is 500 mm or more.

Furthermore, a plurality of printing dots 35 are formed on the back surface 32 of the light guide plate 30 . The printed dots 35 are formed by dot pattern printing using inkjet printing. The printed dots 35 are formed such that their diameters become smaller as they get closer to the LED light source 22 on the rear surface 32 , and gradually increase in diameter as they move away from the LED light source 22 .

In addition, for the printed dots 35, in addition to the method shown in FIG. 2, for example, as shown in FIG. way of the back side of the light panel 30 . When the printing dots 35 are arranged in a grid, a square grid, a triangular grid, a cubic grid, a hexagonal grid, or a cage grid can be used. Alternatively, as shown in FIG. 6( b ), a plurality of printing dots 35 of approximately the same size may be randomly arranged. In addition, among these forms, the size of the printing dot 35 may be changed appropriately.

Next, the dot pattern printing in the manufacturing method of the light guide plate 30 is demonstrated. Dot pattern printing is performed using inkjet printing. When performing dot pattern printing using inkjet printing, ink is jetted from an inkjet nozzle to an original plate when manufacturing the light guide plate 30 to print a dot pattern.

FIG. 3 is a perspective view showing a light guide plate manufacturing apparatus according to the embodiment. When performing dot pattern printing, a light guide plate manufacturing apparatus (optical sheet manufacturing apparatus) 200 as shown in FIG. 3 is used. The manufacturing apparatus 200 of the light guide plate shown in FIG. 3 is equipped with the conveyance unit 70 which conveys the translucent resin sheet 60 (original plate of the light guide plate 30 ), and the inkjet head 50 . Moreover, the manufacturing apparatus 200 is equipped with the UV lamp and the inspection apparatus which are not shown in figure on the downstream side of the inkjet head 50 in the moving direction A of the original plate 60. As shown in FIG.

The transport unit 70 includes: a transport belt 71 on which the translucent resin sheet 60 is placed and transported; a pair of transport rollers 72 that move the transport belt 71 (only one is shown in FIG. 3 ); and a suction box. 73 , for suctioning the translucent resin sheet 60 placed on the conveyor belt 71 .

The conveyor belt 71 is stretched over a pair of conveyor rollers 72 and extends in the horizontal direction (direction A in the drawing). The conveying roller 72 on the drive side is rotationally driven by a motor not shown, and moves the conveying belt 71 . The printing surface 60 a of the original plate 60 faces upward, and the non-printing surface 60 b (see FIG. 4 ), which is the surface opposite to the printing surface 60 a , is arranged in contact with the conveyor belt (table) 71 .

The suction box 73 has a box shape and is arranged between the conveyor belts 71 separated in the vertical direction. A plurality of suction boxes 73 are arranged along the movement direction A. As shown in FIG. The suction box 73 is connected to an exhaust unit such as a vacuum pump, for example, so that the inside of the box can be decompressed.

4 is a side view schematically showing the relationship between the inkjet nozzles and the original plate of the light guide plate when printing a dot pattern. A plurality of ink jet nozzles 51 are provided on the ink jet head 50 . Fig. 5 is a diagram showing a conveyor belt on which a light guide plate is placed when printing a dot pattern. The suction box 73 has a top plate 73a on which the conveyor belt 71 is placed. The outer surface of the top plate 73a is a flat surface, and constitutes a surface on which the conveyor belt 71 slides. Furthermore, the translucent resin sheet 60 is placed on the conveyor belt 71 . That is, the conveyor belt 71 functions as a table on which the original plate 60 is placed.

A plurality of openings 73 b and 71 a are provided on the top plate 73 a of the suction box 73 and the conveyor belt 71 . The distance between the openings 73b and 71a is, for example, about 5 cm. The shape of the openings 73b and 71a may be other than circular. When the conveyor belt 71 is arranged at a predetermined position, the opening 71a of the conveyor belt 71 and the opening 73b of the top plate 73a coincide. Then, the vacuum pump unit is operated to reduce the pressure in the suction box 73, and the non-printing surface 60b of the original plate 60 that is transported is adsorbed on the conveyor belt 71 to eliminate warpage. Then, the distance between the conveyer belt 71 (table) on which the original plate 60 is placed and the inkjet nozzles 51 is adjusted to be equal to or less than 2.8 mm plus the thickness T of the original plate 60 .

In addition, the original plate 60 may be conveyed continuously or intermittently in the light guide plate manufacturing apparatus 200 . In addition, the table on which the original board 60 is placed is not limited to the conveyance belt 71, and other conveyance trays etc. may be sufficient. In addition, the light guide plate manufacturing apparatus 200 may be configured without a transport unit. What is necessary is just to mount the original board 60 on the table, and to remove the warpage of the original board 60 by suctioning and sucking the non-printing surface 60b of the original board 60.

When manufacturing the light guide plate 30 , first, the surface of the original plate 60 to be the back surface ( 32 ) of the original plate 60 (translucent resin sheet included in the light guide plate 30 ) may be subjected to a liquid repellent treatment.

The degree of liquid-repellent treatment is such that the contact angle when a water drop drops on the surface of the liquid-repellent-treated original plate 60 is 80° to 130°, preferably 85° to 120°, more preferably 90° to 110°. By setting the contact angle to 80 degrees or more, it is possible to prevent the reflection dots (printed dots) 35 from being connected to each other, and to provide more dense reflection dots 35 . Furthermore, by making the contact angle 130 degrees or less, the high adhesiveness of the reflection point 35 and the original plate 60 can be maintained.

As examples of the liquid repellent treatment, there are treatment using a surface modifier as a liquid repellent treatment agent, treatment using various energy rays, treatment using chemical adsorption, treatment using graft polymerization on the material surface, and the like.

The treatment using a surface modifier is a treatment for forming a liquid-repellent layer on the surface of the original plate 60 by adding a small amount of the surface modifier. Examples of the surface modifier of the liquid repellent treatment agent include vinyl polymers having perfluoroalkyl groups (Rf groups) in branched chains, Rf group-containing silicones, and the like. The liquid-repellent layer can be formed by impregnating a surface modifier into paper towels or the like and coating the surface, or spraying or inkjet printing the surface modifier onto the surface or the like.

The treatment using various energy rays is a treatment to impart liquid repellency to the surface by energy rays. Examples of energy lines are plasma, electron beam, ion beam, and the like. Examples of liquid-repellent treatment by plasma treatment include forming a liquid-repellent monomolecular film on the roughened surface after roughening the surface by plasma etching; fluorination of the surface by fluorine-based gas plasma , A film made of a liquid-repellent compound is formed on the surface by plasma CVD; a liquid-repellent thin film is formed on the surface by plasma polymerization.

Examples of surface-roughening treatment include providing unevenness on the surface of the original plate 60 by hot pressing, etching with chemicals, and sandblasting.

In the treatment by chemical adsorption, it is preferable to modify the ends of the adsorbed molecules with fluorine. In particular, from the viewpoint of liquid repellency, the terminal substituent is preferably a CF3 group

Among these treatment examples, surface fluorination using fluorine-based gas plasma is preferable in that surface treatment can be performed simply and uniformly.

The conveyor belt 71 is movable in a horizontal direction indicated by an arrow A by a motor not shown. The ink 54 ejected from the inkjet nozzle 51 is made of ultraviolet curable resin, lands on the original plate 60, and spreads gradually in a circular shape. Moreover, the light guide plate manufacturing apparatus 200 is equipped with the ultraviolet irradiation apparatus which is not shown in figure. Pigments may or may not be added to the ink.

The pigment is preferably at least any one of calcium carbonate particles, barium sulfate particles, and titanium oxide particles. The cumulative 50% particle diameter D50 of each of the calcium carbonate particles, barium sulfate particles and titanium oxide particles is 50 to 3000 nm, more preferably 100 to 1500 nm, and even more preferably 300 to 600 nm. Calcium carbonate particles, barium sulfate particles, and titanium oxide particles having a cumulative 50% particle diameter D50 in the range of 50 to 3000 nm can be appropriately selected from commercially available products based on the particle size distribution. The content ratio of the pigment in the ink is usually about 0.5 to 15.0% by mass based on the entire mass of the ink. An ink using a pigment of at least one of calcium carbonate particles, barium sulfate particles, and titanium oxide particles is an ink using an inorganic substance.

The photopolymerizable component is composed of photopolymerizable monomers and/or photopolymerizable oligomers which have photopolymerizable functional groups such as vinyl groups, and preferably have no hydroxyl groups. The content ratio of the photopolymerizable monomer having no hydroxyl group is preferably 65 to 75% by mass based on the entire mass of the ink. The content ratio of the photopolymerizable oligomer having no hydroxyl group is preferably 10 to 20% by mass based on the entire mass of the ink.

A photopolymerizable monomer without a hydroxyl group can be selected from, for example, 1,4-butanediol diacrylate (for example, manufactured by SARTOMER Japan Co., Ltd., SR213), 1,6-hexanediol diacrylate (for example, manufactured by SARTOMER Japan Co., Ltd. , SR238F), 1,3-butanediol diacrylate (for example, SARTOMER Japan Co., Ltd., SR212), 1,9-nonanediol diacrylate (for example, Shin-Nakamura Chemical Industry Co., Ltd., A-NOD -N) and propoxylated (2) neopentyl glycol diacrylate (for example, SARTOMER Japan Co., Ltd., SR9003).

The photopolymerizable oligomer having no hydroxyl group preferably contains aliphatic urethane (meth)acrylate (for example, manufactured by SARTOMER Japan Co., Ltd., CN985B88, CN991). Aliphatic urethane (meth)acrylates are photopolymerizable oligomers having a polyurethane oligomer chain formed from aliphatic polyisocyanate and aliphatic polyol with acrylate or methacrylate groups bonded to it things. The glass transition temperature of the aliphatic urethane (meth)acrylate is preferably 40° C. or higher.

The photopolymerization initiator can be appropriately selected from photopolymerization initiators generally used in the field of ultraviolet curable resins. The content of the photopolymerization initiator in the ink is usually about 0.5 to 10.0% by mass.

The inkjet ink may contain components other than a pigment, a photopolymerizable component, and a photopolymerization initiator within a range not departing from the gist of the present invention.

When performing dot pattern printing, first, the non-printing surface 60b of the original plate 60 is sucked and adsorbed to eliminate warpage, and a predetermined amount of ink 54 is sprayed on the original plate 60 from the inkjet nozzle 51 to form the dot pattern printing portion 55 . Thereafter, until the dot pattern printing unit 55 arrives at the position where the ultraviolet irradiation device is installed, the table 52 is moved by a motor, and the original plate 53 is conveyed. Then, the dot pattern printing part 55 on the original plate 53 is irradiated with ultraviolet rays by an ultraviolet irradiation device, thereby curing the ink and producing printed dots 35 shown in FIG. 2 .

Here, in the present embodiment, when the ink 54 is ejected from the inkjet nozzle 51, the non-printing surface 60b of the original plate 60 is sucked and adsorbed to eliminate warpage, and the distance between the inkjet nozzle 51 and the original plate 53 is set as 2.8mm. When forming a low-definition dot pattern, even when the distance D between the inkjet nozzle 51 and the original plate 53 (hereinafter referred to as "gap distance") D is large, almost no streaks are generated on the printed pattern. Therefore, in order to avoid the inkjet nozzle 51 is in contact with the original plate 53 using a large gap distance D.

However, when forming a high-definition dot pattern, if the gap distance D is large, streaks may occur on the printed pattern, and the streaks may degrade the quality of the product. Therefore, here, the distance between the inkjet nozzle 51 and the original plate 60 when printing the dot pattern is adjusted to 2.8 mm. By adjusting the distance between the inkjet nozzles 51 and the original plate 60 to 2.8 mm, the occurrence of streaks on the printing surface of the dot pattern printing performed on the light guide plate 30 can be suppressed. Therefore, it is possible to improve the quality of the surface light source device 20 and the liquid crystal display device 1 using the light guide plate 30 .

The gap distance D for suppressing the occurrence of streaks on the printing surface of the dot pattern printing performed on the light guide plate 30 is 2.8 mm or less. Furthermore, by setting the gap distance D to be 1.8 mm or less, the occurrence of streaks can be further favorably suppressed. In addition, a small gap distance D is preferable, and the lower limit value of the gap distance D may be set to such a degree that contact between the inkjet nozzle 51 and the original plate 53 during dot pattern printing can be avoided. Specifically, the gap distance D can be set to 0.4 mm or more or 0.5 mm or more. From these viewpoints, the gap distance needs to be 0.4 to 2.8 mm, preferably 0.5 to 1.8 mm, more preferably 0.5 to 1.0 mm.

(example)

Hereinafter, an experiment was conducted about the occurrence of streaks on the printed surface of the optical sheet. In this experiment, the gap distance D was appropriately changed to manufacture a plurality of optical sheets, and the state of occurrence of streaks in each of these optical sheets was visually evaluated. The set gap distance D is 0.5mm, 1.3mm, 2.3mm, 4.0mm and 9.0mm.

In addition, as a common condition, the original board (optical sheet) uses the original board of a 40-inch panel. In addition, the ink viscosity of the ink used was 18.6 mPa·s, and the ink liquid volume was 30 pL. Also, the dot diameter of the dot pattern is set to be about 130 μm. Furthermore, the scanning (transportation) speed at the time of conveying the original plate was 400 mm/s, and the resolution was 150 dpi. In addition, ultraviolet irradiation was performed 1.5 seconds after the ink landed on the original plate. The integrated UV light quantity during ultraviolet irradiation was 0.25 J/cm ² .

As a result, no streaks were observed when the gap distance D was 0.5 mm, 1.3 mm, or 2.3 mm. In addition, when the gap distance D was 5.0 mm, inks on adjacent dots were in close contact with each other, and as a result, linear streaks were generated. Furthermore, when the gap distance D was 9.0 mm, the ink scattered to the non-printing area, and as a result, a large number of streaks were generated.

When the printed surface of the light guide plate was visually observed, almost no stripes were seen when the gap distance D was 2.3 mm, and stripes were clearly seen when the gap distance D was 4.0 mm, and almost no stripes were seen when the gap distance D was about 2.8 mm. In addition, when the gap distance D is 1.3 mm, almost no streaks can be seen. From this result, it is considered that if the gap distance D is used, almost no streaks can be seen. Therefore, the gap distance D in the present invention is defined as 2.8 mm, and it is more preferable to set the gap distance D to 1.8 mm.

Industrial availability

In the method for producing an optical sheet, the optical sheet, and the production apparatus for an optical sheet of the present invention, when dot pattern printing is performed on the back surface of the optical sheet, occurrence of streaks on the printed surface can be suppressed. According to the present invention, the quality of products (surface light source devices and transmissive image display devices) using optical sheets can be improved.

Explanation of symbols

1...liquid crystal display device, 10...transmissive image display unit, 11...liquid crystal cell, 12...linear polarizing plate, 20...surface light source device, 22...LED light source, 30...light guide plate, 31...front surface, 32...back surface, 33 , 34...side, 35...printing dots, 41...various films, 42...reflective sheet, 50...inkjet head, 51...inkjet nozzle, 52...table, 53...original plate, 54...ink, 55...dots Pattern printing section, 60...original plate (translucent resin sheet), 60a...printing surface, 60b...non-printing surface, 70...conveyor unit, 71...conveyor belt, 71a...opening, 72...conveyor roller, 73...pump Suction box, 73a...top plate, 73b...opening, 200...light guide plate manufacturing device (optical sheet manufacturing device), D...gap distance, L...diagonal length of the original plate, T...diagonal length of the original plate , A... the moving direction of the original plate.

Claims (9)

1. A method for producing an optical sheet, characterized in that, The optical sheet is an optical sheet that emits light incident from a light incident surface from a light exit surface intersecting the light incident surface, and is formed by jetting ink from an inkjet nozzle to the back of the original plate of the optical sheet. printing a little pattern, where, The non-printing surface of the original plate is sucked and adsorbed to eliminate the warping of the original plate, Adjust the distance between the nozzle and the original plate to be below 2.8mm, The ink is jetted to print the dot pattern. 2. The manufacturing method of the optical sheet according to claim 1, wherein the thickness of the original plate is 4.5 mm or less. 3. The method for producing an optical sheet according to claim 1 or 2, wherein a length L of a diagonal line of the original plate is 500 mm or more. 4. The manufacturing method of the optical sheet according to any one of claims 1 to 3, wherein the length L and thickness T of the diagonal of the original plate satisfy the following formula (1): [mathematical formula 1] L/T≤0.01...(1), Wherein, L is the length of the diagonal line of the original plate in mm, and T is the thickness of the original plate in mm. 5. The manufacturing method of the optical sheet according to any one of claims 1 to 4, wherein When printing the dot pattern, the original plate is placed on the workbench, The distance between the nozzle and the table is not more than the distance obtained by adding the thickness of the original plate to 2.8 mm. 6 . An optical sheet produced by the method for producing an optical sheet according to claim 1 . 7. A surface light source device, characterized in that it has: The optical sheet according to claim 6, and A light source arranged opposite to the light incident surface of the optical sheet. 8. A transmissive image display device, characterized in that: The surface light source device according to claim 7, and The transmissive image display unit is disposed opposite to the light emitting surface of the optical sheet, and is irradiated with light emitted from the light source to display an image. 9. An optical sheet manufacturing apparatus, characterized in that The optical sheet is an optical sheet that emits light incident from a light incident surface from a light exit surface intersecting the light incident surface, and prints dots by jetting ink from a nozzle to the back of the original plate of the optical sheet. pattern, where The non-printing surface of the original plate is sucked and adsorbed to eliminate the warping of the original plate, and the distance between the nozzle and the table on which the original plate is placed is adjusted to be 2.8mm plus the thickness of the original plate. less than the distance obtained, The ink is jetted to print the dot pattern.

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