JP2010211027A - Moire fringe suppression film and prism sheet with moire fringe suppression function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a moire fringe suppression film which has a thin film thickness and a high moire fringe suppression effect and is capable of emitting uniform diffused light and is capable of maintaining high front brightness of a backlight and a liquid crystal display surface, when being used as a moire fringe suppression film for the backlight unit used in a liquid crystal display device. <P>SOLUTION: The moire fringe suppression film has a light diffusing layer wherein light diffusing particles are dispersed in a resin binder, on a light-transmissive base, and the light diffusing particles are aspherical porous particles and have a volume average particle size of ≤4 μm and a pore volume of 1.0 to 2.0 ml/g, and a center line average roughness Ra of a surface of the light diffusing layer is ≤0.5 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a moire fringe suppression film used as a component of a backlight unit such as a liquid crystal display device (LCD).

  In a liquid crystal display device equipped in a computer, a mobile phone, a digital camera, or the like, a backlight unit is incorporated as a device for illuminating the liquid crystal display surface from the back side. An example of a general configuration of a liquid crystal display device is shown in FIG. In a conventional backlight unit 2, light emitted from a light source 3 such as a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is incident on a light guide plate 5 while being reflected by a reflection sheet 6 or the like, and the light guide plate The light emitted from the upper surface of 5 is condensed in the front direction through the light diffusion film (lower diffusion film) 7. The light emitted from the light diffusing film (lower diffusing film) 7 is incident from the surface (non-prism surface) of the prism sheet 8 on which the prism row is formed, and the surface on which the prism row is formed. By emitting from the (prism surface), the light is further concentrated in the front direction. Thus, the light emitted from the prism surface is incident from the lower surface of the liquid crystal module 1 having the liquid crystal display surface, and is used as illumination from the back side. In some cases, a light diffusion film (upper diffusion film) 9 is disposed between the prism sheet 8 and the liquid crystal unit 1.

Thus, the prism sheet 8 is refracted by the prism inclined surface formed on the transparent substrate surface and deflected in the front direction by refracting light emitted from the light diffusion film (lower diffusion film), thereby observing the liquid crystal display. It works to increase the brightness in the front direction seen by the person. At this time, the direction of arranging the prism sheet 8 in the optical path may be arranged with the non-prism surface facing the exit surface of the light guide plate, or conversely with the prism ridge facing the exit surface of the light guide plate. However, in the conventional backlight unit, since it is not necessary to adjust the incident angle to the prism sheet, the non-prism surface is often arranged with the exit surface of the light guide plate.
In general, a prism sheet is formed by a series of continuous prism rows with their ridges maintained at regular intervals and parallel to each other, and each prism unit is usually an isosceles triangle in cross section. Therefore, a visible pattern called moire fringes is formed when overlapping with the compartments of the liquid crystal cells arranged at equal intervals, and a shade pattern may be observed when the image is observed.
Moire fringes are striped patterns that are coarser than the pitch intervals and occur between the pitch of the prism rows and the pitch of the pixels of the liquid crystal panel.
When such moire fringes occur, a light and dark stripe pattern is formed on the background of the liquid crystal display surface, which causes a reduction in image quality of the display image. In particular, suppression of moire fringes is important in liquid crystal display devices that require high-resolution display.

As a means for making it difficult to generate moiré fringes, a light diffusing film (upper diffusing film) is inserted on the emission side of the prism sheet. The insertion of the upper diffusion film is not necessarily sufficient for reducing the moire fringes and causes a decrease in the luminance of the liquid crystal display surface, but has been conventionally employed as an effective measure for reducing moire fringes. Since moire fringes are also eliminated by performing good light diffusion, the suppression of moire fringes has conventionally been considered as a secondary effect of the light diffusing film and has hardly been designed independently. In addition, in order to make light diffusion advantageous, many of them were relatively thick.
Recently, however, there has been a strong demand for further thinning of liquid crystal display devices, and the backlight unit has been studied to reduce its components and reduce its components and overall configuration while maintaining the same performance as before. ing. For example, in a backlight unit in which the prism ridges of the prism sheet are arranged toward the light exit surface of the light guide plate, the light guide plate can be provided without arranging a light diffusion film between the light exit surface of the light guide plate and the prism sheet. Depending on the combination of the design and the design of the prism sheet, a sufficient light collecting effect can be obtained.

Depending on whether the prism sheet having the prism row on one side is inserted into the optical path, the non-prism surface is arranged toward the exit surface of the light guide plate, or the ridge of the prism is arranged toward the exit surface of the light guide plate, The difference in the light collection effect will be described below.
FIG. 2 and FIG. 3 show the arrangement of optical elements of a general backlight unit in which the non-prism surface of the prism sheet is arranged toward the light exit surface of the light guide plate. The light emitted from the upper surface of the light guide plate 15 is condensed in the front direction due to the diffusion effect of the light diffusion film (lower diffusion film) 17 and becomes emitted light having a spread in the emission angle distribution. Incident from a non-prism surface. Then, the light having a wide emission angle distribution is further deflected in the front direction and emitted before being emitted from the prism row through the prism sheet base. Since the deflection angle due to refraction of the prism array is limited, in order to make the luminance distribution in the front direction of the backlight high and uniform, the light once deflected in the front direction by the light diffusion film needs to be incident on the prism sheet. The light diffusion film (lower diffusion film) 17 was essential. Moreover, in order to efficiently collect the light diffused at a wide angle in the front direction in the front direction of the backlight, it is necessary to arrange two prism sheets 18 so that the prism rows are almost orthogonal to each other. At least three optical sheets in total including one diffusion film (lower diffusion film) and two prism sheets were required.

  On the other hand, FIG. 4 shows an arrangement of each optical element of the backlight unit in which the prism surface of the prism sheet is arranged with the light exiting surface of the light guide plate. The light emitted from the upper surface of the light guide plate 25 travels through the air layer to the prism row, enters the ridge from one slope of the prism unit in the prism row 32, and then enters the other slope at an incident angle larger than the critical angle. The light is totally reflected by this slope, and is greatly condensed and emitted in the front direction of the backlight. Therefore, by designing the prism row in accordance with the characteristics such as the direction of the emitted light of the light guide plate, the light diffusion film (lower diffusion film) is not used, and only one prism sheet is used in the front direction of the backlight. High luminance distribution can be realized.

  Thus, the arrangement of the prism sheet as described above has the advantage that the number of parts can be reduced, the backlight unit can be made thinner, and the productivity is improved. However, compared with the conventional backlight unit using the lower diffusion film, the moire fringes are more easily observed and there is a tendency to cause a deterioration in the image quality of the display surface of the liquid crystal display device. Conventionally, an attempt has been made to make the light emitted from the prism sheet more uniform by installing a film having a light diffusing function on the exit side which is the non-prism surface of the prism sheet. However, no consideration has been given to the suppression of moire fringes, and the suppression is insufficient or the front luminance is sacrificed, but the moire fringes are efficient and sufficient. This has not been achieved.

  Conventionally, various backlight units using a configuration in which the prism surface of the prism sheet is directed to the light exit surface of the light guide plate, which has the advantage of reducing the number of parts, have been studied, but there are insufficient measures to suppress moire fringes. Also have problems to be solved. For example, a backlight unit having the following configuration is considered to be slightly effective in suppressing moire fringes, but is still insufficient. For example, as a means for obtaining the brightness uniformity of a backlight, a non-prism surface of a prism sheet having a rough surface has been studied (see, for example, Patent Document 1). In addition, it was considered that the light emitted from the light guide plate is incident on the prism surface of the prism sheet, and the non-prism surface on the output side is processed to have a concavo-convex surface or a diffusion plate containing diffusing particles is disposed ( For example, see Patent Document 2). Further, a study has been made in which a prism-like lens is formed on the incident surface and a light diffusing layer containing a light diffusing material is provided on the exit surface (see, for example, Patent Document 3).

  However, in the prism sheet of Patent Document 1 in which the conventional roughening process is applied to the non-prism surface, the number of parts can be reduced, but it is insufficient for suppressing moire fringes. Further, in the configuration of Patent Document 2 in which a diffusion plate is inserted on the exit surface side which is a non-prism surface of the prism sheet, it is effective to remove the dot image formed on the light guide plate reflection plate. Removal of moire fringes has not been studied. Considering the removal with the diffusion plate, the thickness of the diffusion plate is increased, so that the brightness of the liquid crystal display surface is liable to be lowered, and there is a possibility that the thinning of the entire liquid crystal display device is hindered. Furthermore, in the prism sheet of Patent Document 3 in which the conventional light diffusion layer is applied to the non-prism surface, the effect of widening the viewing angle is obtained and the effect of suppressing moire fringes is limited, although the number of parts can be reduced. Even if it can be suppressed, the luminance of the liquid crystal display surface may be lowered.

As described above, in the prism sheets described in Patent Documents 1 to 3, various light diffusion layers are formed on the exit surface side of the prism sheets. However, the structure of these light diffusing layers is the same as the conventional structure for obtaining uniform light diffusion, such as roughening the surface or containing a conventionally used light diffusing material, and guiding the prism surface. Despite the use of a configuration in which moire fringes are more likely to occur toward the exit surface of the optical plate, new studies have not been made particularly on reducing moire fringes. That is, in the prism sheet described in Patent Documents 1 to 3, the light collected from the prism sheet exit surface is further incident on the light diffusion layer, which reduces the brightness of the liquid crystal display surface. However, on the other hand, a great effect is not always obtained in reducing moire fringes. Further, in response to the recent technological trend to reduce the thickness of the entire liquid crystal display device, no study has been made on reducing the thickness. In any case, the light diffusion layer of these prism sheets is not intended to prevent the occurrence of moire fringes, and its effect is limited.
On the other hand, a light diffusion film having a light diffusion layer containing porous particles as diffusion particles having high diffusion efficiency has been studied (see Patent Document 4 or Patent Document 5). Patent Document 4 describes a light diffusion film having a light diffusion layer formed from spherical porous silica having an average primary particle diameter of 2.5 μm or more and 10 μm or less and a resin binder. Patent Document 5 describes a light diffusion sheet in which porous transparent fine particles are dispersed in a transparent base material layer. However, these light diffusion films and light diffusion sheets are intended to improve the light diffusion function by using porous particles, but the basic functions and usage patterns are qualitatively different from conventional light diffusion films and sheets. is not. It is not a method of use that demonstrates the unique moire fringe suppression function that is unique to the light diffusion layer with porous particles, and that has been studied and optimized for moire fringe suppression. Not a thing. Like other patent documents, these light diffusing films and light diffusing sheets are primarily intended for uniform light diffusion, and the effect of preventing the occurrence of moire fringes is secondary and the magnitude of the effect is limited. there were.

Moire fringes are generated between light that has undergone periodic intensity changes by an optical material. For this reason, the generation | occurrence | production can be suppressed by the strong light-diffusion effect | action which generally lose | disappears a periodic intensity change. Therefore, it is possible to take measures by increasing the concentration of diffusing particles in the light diffusing layer or inserting a light diffusing film having a sufficiently thick film in the light path. However, if the moire fringes are suppressed only by improving the light diffusion function of the conventional light diffusion film as described above, the amount of light in the front direction is insufficient, and the front luminance of the backlight unit or the liquid crystal display device is likely to be lowered. . Further, if the light diffusing film itself is made thicker, it cannot meet the demand for thinning the backlight unit and the liquid crystal display device.
There are various methods that can be used to perform light diffusion, and the most suitable method for each situation requiring light diffusion has been studied and used. However, so far, these methods have not been studied from the viewpoint of suppressing moire fringes, and more efficient and lowering the front luminance while meeting the demand for thinning the entire backlight unit. Therefore, there has been a demand for a method of suppressing moire fringes that can minimize the adverse effects of the above.

JP-A-5-341132 JP 9-2111230 A JP-A-10-160914 JP 2004-061598 A JP 2004-348000 A

  The object of the present invention is to produce a uniform diffused light at the same time as a thin film having a high effect of suppressing moire fringes when used as a moire fringe suppressing film for a backlight unit used in a liquid crystal display device. An object of the present invention is to provide a moiré fringe suppression film that can maintain high front luminance of a backlight unit or a liquid crystal display surface. In particular, when applied to a backlight unit having a prism surface disposed on the light exit surface side of the light guide plate, it is possible to reduce the thickness of the entire backlight unit, generate uniform diffused light, and suppress moire fringes. It is in providing the moiré fringe suppression film which can do.

The present inventors use porous particles having a specific pore volume, and in a moire fringe suppression film having a light diffusion layer containing the porous particles as diffusion particles, the volume average particle size and light of the porous particles are reduced. By setting the center line average roughness on the surface of the diffusion layer to a specific range, even if the thickness of the light diffusion layer is thin, it effectively prevents moiré fringes without significantly reducing the front brightness and is uniform. It has been found that the uniform luminance distribution of the backlight unit and the liquid crystal display device can be realized by the diffused light, and the present invention has been completed.
That is, the present invention is a light diffusing sheet having a light diffusing layer in which a light diffusing particle is dispersed in a resin binder on a light transmissive substrate, wherein the light diffusing particle is a non-spherical porous particle having a volume average. Moire fringes having a particle size d of 4 μm or less, a pore volume of 1.0 to 2.0 ml / g, and a center line average roughness Ra of the surface of the light diffusion layer of 0.5 μm or less A suppression film is provided.
Furthermore, the present invention provides a prism sheet with a moire fringe suppressing function, characterized in that a prism shape having ridges parallel to each other is formed on the opposite side of the light transmissive substrate with respect to the light diffusing layer.
The present invention further includes a light guide plate and a light source disposed on at least one end face side of the light guide plate, a prism sheet having a prism surface disposed on the exit surface side of the light guide plate, and the prism. Provided is a backlight unit having the moire fringe suppression film on the exit surface side of the sheet.
Still further, the present invention provides the light source plate and the light source arranged on at least one end face side of the light guide plate, and the moire fringe arranged on the emission surface side of the light guide plate with the prism surface facing the emission surface side of the light guide plate. Provided is a backlight unit having a prism sheet with a suppression function.
Furthermore, this invention provides the liquid crystal display device which has the said backlight unit provided with the said moire fringe suppression film and the said prism sheet | seat with a moire fringe suppression function.

Moire fringes are an optical effect that occurs when light passes through the overlapping of two components having different periodic structures, and can be suppressed by effectively scattering the optical path. Therefore, the moire fringe suppression film does not necessarily have to satisfy a high haze value, and it is effective to generate diffused light having a structure finer than the periodic structure that generates moire fringes.
The porous particles contained in the light diffusion layer of the moiré fringe suppression film of the present invention contain many pores with a pore volume of 1.00 to 2.00 ml / g, and the pores are composed of a binder resin and Because it contains air, the light incident on the light diffusion layer is repeatedly reflected and refracted many times while passing through the binder holding the pores and porous particles, and the binder resin and air in the pores. . As a result, as compared with normal resin particles, light is scattered favorably even by a relatively small amount of porous particles and a relatively thin light diffusion layer. For this reason, it is possible to reduce the light loss at the time of transmitting through the prism sheet and to maintain the total light transmittance at a high value while suppressing the generation of the moire fringes by favorably scattering the incident light to the moire fringe suppression film. Further, it is possible to suppress the occurrence of moire fringes while keeping the front luminance of the liquid crystal display surface high. The reason for the above effect of the present invention is not necessarily clear, but basically, these porous particles have irregularities that are a few steps smaller than the order of the particle diameter on the surface of the porous particles. It is finer than the ridge line pitch of the prism and the pixel pitch of the liquid crystal element. For this reason, the optical path of light passing through a regular structure such as a prism or a liquid crystal pixel is more effectively scattered through reflection and refraction by the fine structure of the surface of the porous particle, and the addition amount of the porous particle is small Even so, it is considered that the generation of moire fringes can be effectively suppressed with a much smaller addition amount compared to light diffusing particles that do not have such fine irregularities on the surface.

Furthermore, the moire fringe suppressing film of the present invention preferably uses a porous particle having a volume average particle diameter as fine as possible, and the volume average particle diameter d of the porous particle is 4 μm or less. By uniformly dispersing porous particles with such a small particle size in the light diffusion layer, it is possible to suppress the occurrence of visible coating unevenness, non-uniform haze, and non-uniform light diffusion light. Can do. Furthermore, in the present invention, when the center line average roughness Ra of the surface of the light diffusing layer is 0.5 μm or less, and having the center line average roughness in such a numerical range, It is considered that there is no overlap or aggregation of the porous particles in the light diffusion layer.Therefore, a large difference in light diffusion function does not occur depending on the location of the light diffusion layer. Uniform light diffusion light can be obtained.
In the prism sheet with moire suppressing function of the present invention, the light diffusion layer described above is formed on the surface opposite to the surface having the ridgeline of the prism, so that the light source light deflection action by the prism and the deflected light source light As described above, the effect of suppressing the generation of moire fringes by effectively scattering the light can be achieved simultaneously with a single sheet, so that uniform diffused light with high front luminance can be obtained.
Furthermore, since the backlight unit of the present invention has the above moire fringe suppression film, generation of moire fringes can be effectively suppressed and high front luminance can be maintained. Further, this backlight unit does not generate a mottled pattern due to uneven distribution of porous particles in the luminance unevenness of the surface light source, and the uniformity of light emission is not impaired.

The moire fringe suppression film of the present invention has a light diffusion layer containing a resin binder and porous particles on one surface of a light-transmitting substrate, and the volume average particle size of the porous particles of the light diffusion layer is 4 μm. Hereinafter, the pore volume is 1.0 to 2.0 ml / g, and the center line average roughness Ra of the surface of the light diffusion layer is 0.5 μm or less. For this reason, the diffusion efficiency by the pores is very good, and even when the particle content is small and the film thickness is thin, moire fringes can be suppressed and high front luminance can be achieved. Furthermore, the porous particles having a small volume average particle diameter are uniformly dispersed in the light diffusion layer. As a result, the center line average roughness of the light diffusion layer can be reduced to 0.5 μm or less. As a result, the uneven distribution and overlap of the porous particles that cause the above-mentioned cause are not generated, and the mottled pattern due to the local fluctuation of the haze value is not visually recognized.
The moire fringe suppression film of the present invention is arranged such that the light source is disposed on at least one side end face side of the light guide plate and the light guide plate, and the prism ridge is directed to the light exit side of the light guide plate. In the configuration of a backlight unit that has a prism sheet and is very easy to generate moire fringes, when arranged on the exit surface side of the prism sheet as shown in FIG. 5, the moire fringes are maintained while maintaining high front luminance. Is extremely effectively suppressed. Further, since the film itself is thin, it does not hinder the thinness of the entire backlight unit, which is a feature of the backlight unit, and the moire fringe suppression film does not generate a mottled pattern.

The prism sheet with a light diffusing function of the present invention has a prism shape having ridges parallel to each other on the opposite side of the light diffusing layer with the light-transmitting substrate interposed therebetween. Moire fringes generated between the prism surface and the liquid crystal cell while effectively diffusing the light incident from the prism surface by the light diffusion layer on the opposite side and maintaining high front brightness Can be effectively prevented. In addition to the function of integrating the prism sheet and the moire fringe suppression film, there is no mottled pattern caused by the light diffusion layer, reducing the total number of parts in the backlight unit and making the backlight unit thinner. Also have.
Further, the backlight unit using the moire fringe suppression film or the prism sheet with the moire fringe suppression function provides a light source in which the moire fringes are effectively suppressed while maintaining a high front luminance and suppressing the reduction thereof. And non-uniform intensity distribution of light emission does not occur. By using them, the thickness of the entire unit can be reduced.
Furthermore, the liquid crystal display device having these backlight units on the back surface of the liquid crystal display surface can provide a liquid crystal display device that prevents the occurrence of moire fringes on the display surface while maintaining high front luminance of the display surface. Uniform display surface brightness can be achieved.
Further, as described above, since the thickness of the entire backlight unit can be suppressed, it is possible to contribute to thinning of the liquid crystal display device itself.

It is the exploded view which showed an example of the general structure of a liquid crystal display device. The perspective view which shows the structure of the backlight unit which has arrange | positioned the non-prism surface of a prism sheet to the output surface side of a light-guide plate. The conceptual diagram which showed a part of optical path from the light source in the backlight unit shown in FIG. The conceptual diagram which showed the structure of the backlight unit which has arrange | positioned the prism surface of a prism sheet to the output surface side of a light-guide plate, and a part of optical path from a light source. The perspective view which shows the structure of the backlight unit which has a moire fringe suppression film of this invention.

  Hereinafter, various parts of the moire fringe suppressing film including the best mode, the prism sheet with the moire fringe suppressing function, the backlight unit, and the liquid crystal display device for carrying out the present invention will be described.

  The light diffusion layer of the moire fringe suppression film of the present invention contains porous particles as a light diffusion material. The porous characteristics of the porous particles are represented by pore volume and average pore diameter, and the average pore diameter is preferably 10 nm to 30 nm. If the porous particle has a pore diameter in this range, scattering by a fine structure much finer than the periodic structure that generates moire fringes may disturb the optical path of incident light and effectively suppress the occurrence of moire fringes. it can. Furthermore, to maintain high diffusion efficiency for incident light, to suppress moire fringes well with a small addition amount to the light diffusion layer and a thin film thickness of the light diffusion layer, and to keep the front luminance of the backlight unit and the liquid crystal display device high. The pore volume is preferably in the range of 1.00 to 2.00 ml / g. By setting the pore volume of the moire fringe suppressing film of the present invention to 1.00 ml / g or more, the probability that incident light is irregularly diffused not only on the surface of the diffusing particle but also at the interface with the pore in the particle. Becomes extremely high. For this reason, even if the content of the porous particles in the light diffusion layer is kept low, an equivalent moire fringe suppressing effect can be obtained.

By setting the pore volume in this way, the content of the porous particles can be kept low, so that the pot life generated by a paint containing a large amount of porous particles is reduced, or the paint is formed with such a paint. It is possible to prevent a decrease in adhesive strength with the substrate due to a relative decrease in the resin component of the coated film.
On the other hand, if the pore volume of the porous particles increases so as to exceed 2.00 ml / g, the front luminance tends to decrease. This is because when the pore volume is increased, a large number of vacancies that are extremely complicated are formed in the particles. When this is added to the light diffusion layer as diffusing particles, there are many vacancies that are not filled with the binder resin. This is thought to be due to the fact that the angle of refraction at the hole interface is increased and the light rays traveling in the front direction are relatively reduced.
Further, when the pore volume increases, the amount of the binder resin filling the pore volume also increases, so that the total amount of the binder resin in the porous particles also increases. Therefore, it is considered that the porous particles have characteristics more similar to those of the binder resin, and the aggregation of the porous particles is likely to occur. For this reason, the coating material for forming the light diffusing layer tends to thicken and easily gel. For the above reasons, when a light diffusion layer is formed using a light diffusion layer coating material containing porous particles having a pore volume in the above range, the thin light diffusion layer does not significantly reduce the front luminance. Moire fringes can be suppressed efficiently. Furthermore, neither thickening nor gelation of the paint itself occurs.

  A moiré fringe suppression film having a large pore volume in the range of 1.00 to 2.00 ml / g has a high light diffusing ability, and thus the front luminance tends to decrease due to various causes. There is also an advantage that fringes can be effectively suppressed. The pore volume of the porous particles can be measured by a mercury intrusion method (porosimeter method), and can be obtained at the time of pore distribution measurement by a mercury porosimeter (eg, Shimadzu Autopore IV95 series). Porous particles are polygons with irregular cross-sections with irregular angles and side lengths, rather than spherical ones, so that the optical path of light passing through prism arrays and liquid crystal pixel arrays is more efficiently scattered. An irregular shape having a shape is preferred. Since the spherical shape has a lower light diffusion function than the amorphous shape, more particles are contained in order to suppress the moire fringes well, and the front luminance tends to decrease. As the structure, it is preferable that primary particles aggregate to form amorphous aggregated particles having a volume average particle diameter of 1 to 10 μm. The finer the particle size, the higher the moire fringe suppression function tends to be, and it is easy to reduce the thickness of the light diffusion layer and moire fringe suppression film, so that dispersion is not difficult when manufacturing a coating for forming the light diffusion layer. A small particle size is preferred.

In the light diffusion layer of the moire suppressing film of the present invention, light diffusion mainly occurs due to pores in the porous particles. Therefore, a large difference is inherently caused in the light scattering characteristics between the portion where the porous particles where pores are concentrated in the light diffusion layer and the other portion. This characteristic difference is considered to increase as the porous particles having a larger particle diameter having a larger total pore volume in the particles are used. Therefore, when the porous particles are aggregated to generate coarse particles, a large difference in haze value is generated at the portion, and the particles are visually recognized as unevenness. For this reason, in order to obtain uniform diffused light, it is preferable to use porous particles having a particle size as small as possible, and to cope with insufficient diffusion function by increasing the number of particles. Specifically, the volume average particle size of the binary particles of the porous particles is more preferably 1.0 to 4.0 μm, and most preferably 1.5 to 3.5 μm, which needs to be 4.0 μm or less. Further, the primary particles are preferably those having a particle size of 10 to 100 nm.
Also, the width of the particle size distribution of the secondary particles should be large so that irregular reflection and refraction occur more efficiently. Both organic fine particles and inorganic fine particles can be used, but among them, inorganic materials such as porous silica, porous alumina, porous titanium oxide, and porous glass are easy to take a large refractive index difference from the binder resin, and the particle surface Since it is easy to raise the reflectance in, it is preferable at the point which can obtain diffuse reflected light efficiently. Furthermore, it is also preferable in that the surface hardness of the light diffusion layer can be easily improved. Among these, porous silica particles are more preferable.

In the present invention, since the porous particles in the light diffusion layer efficiently scatter incident light in the present invention, the light diffusion layer has extremely low loss, and the incident light is converted into diffuse transmitted light on the surface opposite to the incident light. Conversion can be performed, and generation of moire fringes can be effectively suppressed. The moiré fringe suppression film of the present invention is contained in a smaller amount than a conventional light diffusion film used in combination with a prism sheet arranged with the prism ridge facing the light exit surface side of the light guide plate. A light diffusing particle achieves the same or better moire fringe suppression effect as before. For this reason, compared with the achieved equivalent moire fringe suppression effect, the amount of light diffusing particles contained is always smaller than when a conventional light diffusing film is used, and as a result, high front luminance can be realized. In order to effectively suppress the moire fringes while maintaining the brightness of the liquid crystal display surface using the present moire fringe suppressing film, the content of the porous particles in the light diffusion layer is set to a solid content 100 of the resin binder. 2-40 mass% is preferable with respect to mass%, 5-30 mass% is more preferable, and 8-20 mass% is the most preferable. When the content of the porous particles is 2% by mass or more, the excellent light diffusion effect can be efficiently utilized. When the content is 40% by mass or less, since the resin binder resin is sufficiently contained in the light diffusing layer, a light diffusing layer having good adhesiveness can be formed on the light transmissive substrate. Furthermore, as a result of the amount of the porous particles not being too large, the unevenness of the surface of the light diffusing layer becomes conspicuous, the probability that outgoing light is largely deflected, and the front luminance is not lowered.
Since the light diffusion layer in the moire fringe suppression film of the present invention has good diffusion efficiency of porous particles, the light diffusion layer can be made thinner than before, and the moire fringe suppression film can be made thinner. is there. The thickness of the light diffusion layer of the present invention is preferably 8 μm or less. As a result, a light diffusing layer having an extremely thin film thickness can be realized, and the moiré fringe suppressing film can be greatly thinned. A film thickness of 6 μm or less is more preferable in terms of thinning. Furthermore, it is most preferable that it is 4 micrometers or less. However, if the film thickness is less than 2 μm, the efficiency of light diffusion tends to be lowered even if the particle size and content of the diffusing particles are adjusted. Therefore, even when considering thinning, the film thickness is in the range of 2 to 6 μm. preferable.

  It is preferable that the porous particles are uniformly distributed in the light diffusion layer. In places where film thickness fluctuations or surface irregularities occur, the distribution of the porous particles is biased according to the fluctuations, or the localization and overlap of the porous particles occur, making it uniform. Generation of light diffusion tends to be impaired, and mottled patterns and uneven light diffusion are likely to occur. Conversely, if the film thickness does not fluctuate and the surface roughness of the light diffusion layer is small, there is no localization of porous particles that causes at least unevenness, and the porous particles are uniformly dispersed. It is thought that mottled patterns do not occur. In order to achieve uniform dispersion of the porous particles in the light diffusion layer, the center line average roughness average roughness Ra of the porous particle light diffusion layer surface should be 0.5 μm or less. It is necessary and Ra is more preferably 0.4 μm or less, and most preferably 0.3 μm or less.

  Furthermore, in order to efficiently suppress the moire fringes without significantly reducing the front luminance, and to suppress the film thickness of the entire moire fringe suppression film, the thickness t of the light diffusion layer and the volume average particle diameter d The ratio, t / d, is preferably 0.8 to 1.7. When t / d is smaller than 0.8, the porous particles easily protrude from the resin binder surface of the light diffusion layer. For this reason, extremely rough irregularities are formed on the surface of the light diffusion layer, and the light emitted from the light diffusion layer is likely to be greatly deflected in a direction having a large angle from the front direction. Further, since the surface of the porous particles rich in fine irregularities appears on the outermost layer, irregular reflection at the time of emission tends to be remarkable, and the front luminance tends to decrease. Furthermore, compared to when there is a sufficient film thickness with respect to the particle size of the porous particles, it is difficult to uniformly distribute the porous particles, and uneven light diffusion due to coating film unevenness is likely to occur. For this reason, in order to more efficiently suppress the moire fringes and keep the front luminance high, it is preferable that the individual porous particles are buried in the binder resin of the light diffusion layer. When t / d is 0.8 or more, the light diffusing particles can be sufficiently embedded in the binder resin. When t / d is larger than 1.7, there are many opportunities for two particles to be partially overlapped in the light diffusion layer, and unevenness is likely to occur again on the surface of the light diffusion layer. Furthermore, since a large difference occurs in the light scattering characteristics between the portion where the porous particles overlap and other portions, the coating film unevenness occurs, and uneven light diffusion light tends to be visually recognized. In this case, since the porous particles are sufficiently embedded in the binder resin, the front luminance tends to recover, but the film thickness of the light diffusion layer is increased and the film thickness of the moire fringe suppression film is decreased. The object of the present invention cannot be achieved.

When the film thickness is small and only one porous particle is embedded in the light diffusion layer in the light diffusion layer, the light diffusion characteristics are greatly different from the part where the porous particle is not present. Therefore, it is preferable that the porous particles are uniformly distributed in the light diffusion layer. If the distribution is biased, the haze value corresponding to the light diffusion performance varies greatly depending on the location of the light diffusion layer, and a mottled pattern is likely to occur.
Here, the thickness of the light diffusing layer does not measure the height from the apex of the projecting light diffusing material, but measures the height from the sheet-like substrate on the surface of the resin binder holding the light diffusing material. And When the porous particles are protruding, the height of the top of the porous particles varies greatly and does not necessarily represent the actual thickness of the light diffusion layer, whereas the thickness of the binder resin layer is It becomes constant by leveling at the time of applying the coating material for the diffusion layer. When the thickness is measured using a point contact type film thickness meter, it is obtained by measuring at least 10 points and taking an average value of 3 points from the lowest. Or it is calculated | required also by taking the SEM photograph of the cross section of a light-diffusion layer, measuring the film thickness of 3 points | pieces, and taking the average value.
The porous particles generally have extremely high diffusion efficiency, and can form a light diffusion layer having a high haze value with a small addition amount and a thin film thickness. However, since the light diffusing function of each porous particle is extremely high, it may be applied uniformly. However, if the film thickness fluctuates due to the occurrence of uneven coating or the particles are localized, local diffusion of light Dynamic strength occurs. This becomes a local fluctuation of the haze value, and it inhibits the generation of uniform light diffusion light of the light diffusion film although it has a fine contrast. In particular, when such a light diffusion film is used on the exit surface side of the prism sheet in a backlight unit having a configuration in which the prism row side of the prism sheet is arranged facing the exit side of the light guide plate There is no further diffusing element between the light diffusing film and the liquid crystal display panel, and the local fluctuation of the light diffusing intensity generated in the light diffusing film is likely to directly affect the liquid crystal display device.

  As described above, the magnitude of the moire fringe suppression effect and the height of the front luminance are in a trade-off relationship, and various adjustments can be made to sufficiently suppress the moire fringes and not reduce the front luminance as much as possible. It is important for practical use. Among the parameters for adjusting these, as described above, the content of the porous particles, the ratio of the volume average particle diameter (d) of the porous particles to the film thickness (t) of the light diffusion layer (t / D), etc., and after selecting the porous particles, it is important to adjust these within the range defined in the present invention to achieve both good moire fringe suppression effect and high front luminance.

The light diffusion layer may contain inorganic particles, organic particles, or inorganic-organic hybrid material particles, if necessary, in addition to the porous particles. For example, white pigments such as titanium oxide and zinc oxide, and fillers such as calcium carbonate and talc can be contained within a range that does not inhibit various characteristics of the light diffusion layer. Organic particles such as acrylic particles and acrylic urethane particles may be contained. Moreover, the layer containing the said particle | grain can also be laminated | stacked on another light-diffusion layer.
If necessary, the light diffusion layer may contain a curing agent, a curing catalyst, a dispersant, a plasticizer, an antistatic agent, an ultraviolet absorber, an anti-degradation agent, etc., and these form a light diffusion layer. It is blended when making paints. However, it is preferable that transmitted light is not attenuated by the presence of a substance having absorption in the visible light region, and it is preferable that the light diffusion layer does not contain a substance having absorption in the visible light region.
The light diffusing layer can be formed by applying and drying a coating material for the light diffusing layer containing the porous particles and the like, the binder resin, and the solvent on the substrate, and integrating the substrate and the light diffusing layer. You can also For example, by using a binder resin in which porous particles are dispersed, a base sheet and the entire light diffusion layer are prepared by a normal sheet manufacturing method such as an extrusion method, and the film thickness of the entire moire fringe suppression film Can be made thinner. However, when the content of the porous particles is large, the mechanical properties of the sheet itself may be weak. To ensure the strength, the moire fringe suppression function and the support function of the moire fringe suppression film are separated. It is preferable to use a transparent substrate or a transparent film as a support for the light diffusion layer.

As the binder resin, the porous particles can be uniformly dispersed in the resin and can be formed into a sheet shape, or a paint can be prepared by further adding a solvent, applied onto a light-transmitting substrate, and a coating film laminated. If it can, it will not specifically limit, General resin for shaping | molding, resin for coating materials, etc. can be used. Examples thereof include acrylic resins, vinyl chloride resins, polyester resins, polyurethane resins, styrene resins, polycarbonate resins, and cycloolefin resins.
Solvents used in the light diffusing layer paint when forming the light diffusing layer by coating include solubility of the binder resin, dispersibility of porous particles, etc., film thickness of the diffusing layer to be formed, and coating film drying properties, etc. In consideration, it can be used by appropriately selecting from known solvents usually used for coatings.

The light-transmitting substrate used as the support for the moire fringe suppression film of the present invention is not particularly limited as long as it has sufficient physical strength and light transmittance as a support, but may be a transparent substrate. preferable. It is selected from transparent or translucent resin sheets or films such as polyethylene terephthalate (PET) film, polyethylene naphthalate (PEN) film, acrylic film, polypropylene film, polycarbonate, cycloolefin, and acrylic because of its smoothness and mechanical strength. . Among these, a PET film or a PEN film is particularly preferable from the viewpoint of its mechanical strength. The thickness of the substrate is preferably 5 to 250 μm, more preferably 10 to 100 μm. When the thickness is less than 5 μm, not only handling becomes difficult, but curling due to heat shrinkage occurs, and workability tends to be remarkably lowered. If it is thicker than 250 μm, the total thickness of the moire fringe suppression film will be too thick to be used for thin electronic devices, etc., and the visible light transmittance of the substrate itself will be easily reduced, and the front luminance of the backlight unit will be reduced. Tend to. In particular, when the total thickness of the moire fringe suppression film is thinned to reduce the thickness of the backlight unit, particularly the liquid crystal display device for mobile phones, the thickness is preferably 7 to 50 μm.
In order to improve adhesion to the light diffusion layer, at least one of the surfaces of the substrate is subjected to an easy adhesion treatment such as an easy adhesion treatment layer applied or a corona treatment. Preferably it is.

As a method for producing the moiré fringe suppressing film of the present invention, for example, a light diffusion layer coating is applied to one surface of a transparent sheet-like substrate to form a light diffusion layer. The coating material for the light diffusion layer is prepared by mixing porous particles, a resin binder, a solvent, an antistatic agent, and other additives blended as necessary. Conventionally, a light diffusion sheet and a light diffusion film are produced by extruding a mixture containing a resin binder and light diffusion particles. Further, a light diffusion film is produced by forming a coating film with a coating material for a light diffusion layer on a film substrate in the middle of the stretching process and stretching the entire substrate. However, when the porous particles are non-spherical amorphous particles, they are likely to be associated with each other by contact between the particles. For this reason, when a process involving molding and deformation of such a coating film is performed, the particles tend not to be rearranged uniformly and localize, and it becomes difficult to obtain uniform light diffusion.
The adjusted coating material for the light diffusion layer is applied on the light-transmitting substrate while maintaining a state in which the porous particles are well dispersed. A general coating method can be used as a coating method. For example, each coating method such as blade, knife, cast, dipping, impregnation machine, screen, spin, reverse roll, air doctor, gravure, spray, curtain, extrusion, fountain, kiss, rod, squeeze, forward rotation roll, kiss roll, etc. Is available.
It is preferable to fix the uniformly dispersed porous particles by drying the coating film formed by these coating methods as it is.
For drying the coating film, a general drying method can be used. For example, drying methods such as hot air, infrared rays, microwaves, induction heating, ultraviolet ray curing, and electron beam curing can be used. After drying, if necessary, heat curing is performed at a predetermined temperature and time.

The total thickness of the moiré fringe suppression film thus produced is 20 to 300 μm, but 20 to 100 μm is preferable in that the backlight unit can be thinned. In particular, in the case of a backlight unit used in a liquid crystal display device for a mobile phone, which is strongly demanded to be thin, the total thickness is less than 100 μm, more preferably 20 to 70 μm, which greatly contributes to the thinning of the display unit and the mobile phone. This is preferable.
The moire fringe suppression film produced as described above is used as a moire fringe suppression film for a backlight unit using a prism sheet, from the inclined surface of the light guide plate to the incident surface of the liquid crystal display surface in accordance with the configuration of each backlight unit. The following configuration can be used by inserting it at any position where the most effective effect is obtained, but the number of components is small, the thickness of the entire backlight unit can be reduced, and moire fringes are likely to occur. The backlight unit is preferably used.
That is, a back having a configuration including a light guide plate and a light source disposed on at least one side end surface side of the light guide plate, and a prism sheet disposed on one side emission surface side of the light guide plate with a prism ridge directed toward the emission side of the light guide plate The light unit is preferably used so that the moire fringe suppression film of the present invention is disposed and fixed on the light exit surface side of the prism sheet.
Furthermore, the liquid crystal display device of the present invention can be manufactured by arranging and fixing the emission surface of the backlight unit thus manufactured on the back side of the liquid crystal display surface by a conventionally known method.
There is no particular problem with the direction in which the moire fringe suppression film is inserted, but it is possible to give various functions to the incident side surface by setting the light-transmitting substrate to the incident side and the light diffusion layer to the emission side. This is preferable because there is a possibility.

  The anti-sticking function, anti-static function, and scratch-preventing function according to the position in the backlight unit where the moire fringe suppression film is placed on the surface opposite to the light diffusion layer across the light-transmitting substrate For example, various functional layers for performing various necessary functions may be provided. Further, another layer having a light diffusing function can be formed to further enhance the light diffusing effect and increase the overall haze value. For example, a reflective layer for confining light to the light guide plate is usually formed on the surface opposite to the light exit side of the light guide plate so that the light emitted from the light guide plate is uniform in the direction away from the light source. A continuous or discontinuous reflection pattern is formed that increases the overall reflectivity in the direction away from the light source, but such a pattern is discontinuous with the brightness of the backlight unit. When it becomes necessary to further increase the haze value so as not to give the property, adjustment can be performed in this portion of the light diffusion layer instead of using a new light diffusion film.

It is also possible to form a prism row on the opposite side of the light diffusing layer with respect to the light transmissive substrate to form a prism sheet with a moire fringe suppressing function.
In the prism sheet with a moire fringe suppression function of the present invention, prism shapes having ridges parallel to each other are formed on the opposite side of the light diffusing layer of the light diffusion layer of the moire fringe suppression film of the present invention.
The structure of the prism sheet with a moire fringe suppression function may be a three-layer structure in which a prism substrate and a light diffusion layer are separately formed on both surfaces of a transparent substrate or a transparent film as a base. It may have a configuration in which either the layer or the light diffusion layer is integrated with the light-transmitting substrate. That is, it may have a two-layer structure in which the layer having the prism row or the light diffusion layer itself serves as a light-transmitting substrate as a support, and the other layer is formed thereon. Alternatively, a layer having a prism row and a light diffusion layer may be directly laminated. However, those using an independent transparent substrate or a transparent substrate such as a transparent film can form a prism array and a light diffusion layer through the coating process, and the composition and shape of each layer can be easily controlled independently. preferable.
That is, as a more preferable aspect of the prism sheet with a moire fringe suppressing function of the present invention, a light-transmitting substrate, a light diffusion layer formed on one surface of the light-transmitting substrate, and the light of the light diffusion layer are provided. And a prism layer formed on the opposite side across the transparent substrate.

  The layer having the prism row of the prism sheet with the moire fringe suppressing function of the present invention is an arrangement of prisms having a triangular cross-sectional shape having apex angles, and the prism rows having ridges formed in parallel and at equal intervals. It is preferable to have. The surface of the prism array preferably has a shape in which linear unit prisms having an isosceles triangle with the same cross section are arranged in parallel without gaps, and the apex angle of the isosceles triangle cross section of the prism array is 50 ° to 80 °. Is preferable, and is more preferably 60 ° to 70 °. By making the cross section of the isosceles triangle of the same shape, it becomes easy to manufacture the prism row, and the prism function can be surely exhibited while making the prism sheet thin. By setting the apex angle of the prism in the range of 50 ° or more and 80 ° or less, the total reflection on the slope of the prism row when the ridge of the prism row of the prism sheet of the present invention is arranged toward the exit surface side of the light guide plate. Due to the phenomenon, a high light collecting property in the front direction of the LCD is obtained. The interval between adjacent prism rows can be determined as appropriate in consideration of the degree of thinning of the thickness of the prism row portion, the ease of manufacturing the prism rows, the ease of occurrence of moire fringes, etc. It is preferable that it is 100 micrometers, and it is more preferable that it is 10-50 micrometers. The height of the prism rows also affects the spacing between the prism rows, but it is 7 when the total thickness of the prism sheets is reduced to reduce the thickness of the backlight unit, particularly the liquid crystal display device for mobile phones. It is preferable to be set to ˜50 μm.

The prism row in the prism sheet with a moire fringe suppressing function of the present invention may be formed integrally with the support or may be separately laminated on the support. For these, a known forming method can be used. An example of a method for manufacturing these prism sheets will be described below.
For example, as disclosed in Japanese Patent Application Laid-Open No. 11-171941, a continuous base is pressed against a mold roll with a pressing roll, and a liquid ultraviolet curable resin is applied to a contact start portion between the pressed base and the mold roll. , Irradiating with ultraviolet rays, fixing the shape, and peeling from the mold roll can be used.
Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 2002-258410, a liquid ultraviolet curable resin is attached to a mold roll, and then brought into contact with a continuous substrate, and the shape is fixed by irradiation with ultraviolet rays. A peeling method can be used.
Alternatively, an ultraviolet curable resin is applied to a transparent substrate by a known coating method, and the ultraviolet curable resin surface is pressed against a mold roll in an uncured state, and the shape is fixed by irradiating ultraviolet rays. A peeling method can be used.

For example, according to the above formation method, as a material used for the prism row in the prism sheet with a moire fringe suppression function of the present invention, a material that is transparent and initially has fluidity and is cured and solidified by light such as ultraviolet rays, Alternatively, any material can be used without particular limitation as long as it is a material that softens and becomes fluid by heating and becomes solid again by cooling. For example, an ultraviolet curable resin composition, a thermoplastic resin, or the like can be used.
The UV curable resin composition is mainly composed of various UV curable oligomers and monomers such as unsaturated polyesters, acrylics, vinyl ethers, maleimides and epoxies, reactive diluents, polymerization initiators, polymerization accelerators. An agent, an organic solvent, and the like may be mixed and mixed as necessary.
As the thermoplastic resin, a general-purpose thermoplastic resin that becomes fluid by heating, such as polyethylene, polypropylene, polystyrene, acrylic, polyester, and polycarbonate, can be used.
Among these, it is preferable to use an ultraviolet curable resin composition. The reason for this is that when the thermoplastic resin is heated to a temperature higher than the glass transition temperature of the substrate, the substrate may be deformed by heat, resulting in malfunctions. Furthermore, if an ultraviolet curable resin composition is used, the thermoplasticity Compared to the case of using a resin, the heating / cooling time can be shortened to each stage, which is advantageous in terms of production efficiency.

  As a method for producing the prism sheet of the present invention, for example, after forming a light diffusion layer having a moire fringe suppressing function on one surface of a light-transmitting substrate, the prism surface can be formed on the other surface. . Further, for example, after a sheet having the prism row on one surface is formed by the above method, a light diffusion layer is formed on the opposite side of the sheet from the prism surface. The sheet having the prism row may be formed on the substrate or formed integrally with the substrate. For example, in the case of a sheet having the substrate, the prism row on the substrate is A light diffusing layer coating is applied to a surface different from the surface to be formed by the above-described application method and the above-described drying method and dried to form a light diffusing layer.

The thus manufactured prism sheet with a moire fringe suppressing function has a total thickness of 20 to 300 μm, but 20 to 100 μm is preferable in that the backlight unit can be thinned. In particular, in the case of a backlight unit used in a liquid crystal display device for a mobile phone, which is strongly demanded to be thin, the total thickness can be less than 100 μm, more preferably 20 to 70 μm. It will contribute greatly.
In order to produce a backlight unit for a liquid crystal display device using the prism sheet with moire fringe suppression function produced as described above, the moire fringe suppression function of the present invention is provided adjacent to the exit surface of the light guide plate having a light source. What is necessary is just to arrange | position and fix a prism sheet by a conventionally well-known method, with a prism surface facing the output surface side of a light-guide plate. In this case, the total thickness of the backlight unit can be greatly reduced as compared with the conventional four-sheet configuration using the lower diffusion film, the upper diffusion film, and the two prism sheets.
Further, the liquid crystal display device of the present invention is manufactured by arranging the light emitting surface of the backlight unit thus manufactured on the back side of the liquid crystal display surface by a conventionally known method. Can do.

Hereinafter, the present invention will be described using examples.
<< Preparation process of paint for diffusion layer (a) >>
Toluene 250 parts by mass Cyclohexanone 72 parts by mass Indeterminately shaped porous silica “Silysia 420” 27 parts by mass [average pore diameter: 17 nm, pore volume: 1.25 ml / g,
Volume average particle diameter (by laser method): 3.1 μm, manufactured by Fuji Silysia Chemical Ltd.]
Acrylic resin solution “Acridic WDU-938” 300 parts by mass [solid content 50%, solid content hydroxyl value 50, manufactured by DIC Corporation]
Antistatic agent “Nopcostat SN A-2” 2 parts by mass [imidazoline type cationic antistatic agent, manufactured by San Nopco]
40 parts by mass of polyisocyanate solution “Coronate HL” (solid content: 75%, HDI, effective NCO content in solid content: 17%, manufactured by Nippon Polyurethane Industry Co., Ltd.)
The above was stirred and mixed with a dispersion stirrer to obtain a coating material for diffusion layer (a). At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 15% (mass ratio).

<< Preparation Step of Diffusion Layer Paint (b) >>
Toluene 250 parts by mass Cyclohexanone 72 parts by mass Amorphous porous silica “Silysia 430” 27 parts by mass [average pore diameter: 17 nm, pore volume: 1.25 ml / g,
Volume average particle diameter (by laser method): 4.1 μm, manufactured by Fuji Silysia Chemical Ltd.]
Acrylic resin solution “Acridic WDU-938” 300 parts by mass Antistatic agent “Nopcostat SN A-2” 2 parts by mass Polyisocyanate solution “Coronate HL” b) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 15% (mass ratio).

<< Preparation Process of Diffusion Layer Paint (c) >>
Toluene 355 parts by mass Cyclohexanone 105 parts by mass Indeterminate shape porous silica “Silysia 250N” 27 parts by mass [average pore diameter: 24 nm, pore volume: 1.80 ml / g,
Volume average particle diameter (by laser method): 5.7 μm, manufactured by Fuji Silysia Chemical Ltd.]
Acrylic resin solution “Acridic WDU-938” 445 parts by mass Antistatic agent “Nopcostat SN A-2” 3 parts by mass Polyisocyanate solution “Coronate HL” c) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 10% (mass ratio).

<< Process for Preparing Diffusion Layer Paint (d) >>
Toluene 270 parts by mass Cyclohexanone 74 parts by mass Amorphous porous silica “Silysia 550” 35 parts by mass [average pore diameter: 7.0 nm, pore volume: 0.80 ml / g,
Volume average particle diameter (by laser method): 3.9 μm, manufactured by Fuji Silysia Chemical Ltd.]
Acrylic resin solution “Acridic WDU-938” 290 parts by mass Antistatic agent “Nopcostat SN A-2” 2 parts by mass Polyisocyanate solution “Coronate HL” d) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 20% (mass ratio).

<< Preparation Process of Diffusion Layer Paint (e) >>
Toluene 250 parts by mass Cyclohexanone 72 parts by mass Spherical porous silica “Pyrospher C-1504” 27 parts by mass [pore volume: 1.5 ml / g, volume average particle size (by laser method): 4.5 μm, Fuji Silysia Chemical (Manufactured by Kogyo)
Acrylic resin solution “Acridic WDU-938” 300 parts by mass Antistatic agent “Nopcostat SN A-2” 2 parts by mass Polyisocyanate solution “Coronate HL” e) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 15% (mass ratio).

<< Preparation Process of Diffusion Layer Paint (f) >>
Toluene 310 parts by mass Cyclohexanone 75 parts by mass True spherical acrylic urethane resin particles “BC-79” 80 parts by mass [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
Acrylic resin solution “Acridic WDU-938” 220 parts by mass Antistatic agent “Nopcostat SN A-2” 6 parts by mass Polyisocyanate solution “Coronate HL” 30 parts by mass or more were stirred and mixed with a dispersion stirrer, f) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 60% (mass ratio).

<< Preparation Step of Diffusion Layer Paint (g) >>
Toluene 310 parts by mass Cyclohexanone 75 parts by mass True spherical acrylic urethane resin particles “BG-06” 80 parts by mass [volume average particle diameter of about 6 μm, manufactured by Gifu Shellac Manufacturing Co., Ltd.]
Acrylic resin solution “Acridic WDU-938” 220 parts by mass Antistatic agent “Nopcostat SN A-2” 6 parts by mass Polyisocyanate solution “Coronate HL” 30 parts by mass or more were stirred and mixed with a dispersion stirrer, g) was obtained. At this time, the addition amount of the resin particles with respect to the solid content of the resin binder was 60% (mass ratio).

(Examples 1-4, Comparative Examples 1-8)
《Coating / drying / curing process to substrate》
As the substrate, a polyethylene terephthalate (PET) film having a thickness of 38 μm was used. On one surface of the substrate, the diffusion layer paint (a) was applied so as to have a dry film thickness of 3.0 μm and 8.0 μm and dried with hot air to obtain a dry coating film of the diffusion layer. Example 1 and Example 2 were designated. Similarly, the above-mentioned coating material for diffusion layer (b) was applied so as to have a dry film thickness of 8.0 μm and dried with hot air to obtain a dry coating film of the diffusion layer. 2. Similarly, each of the coatings (d) and (e) for the diffusion layer was applied to a dry film thickness of 7.0 μm and dried with hot air to obtain a dry coating film of the diffusion layer. 3 and Comparative Example 4. Further, the diffusion layer paint (f) was applied so as to have a dry film thickness of 9.0 μm and dried with hot air to obtain a dry coating film of the diffusion layer. ) Was applied so as to have a dry film thickness of 5.0 μm and dried in hot air to obtain a dry coating film of the diffusion layer. (Refer to Table 1 for the correspondence between the paint for the diffusion layer and the applied film thickness). After the above coating process, the film was stored in a constant temperature room at 40 ° C. for 48 hours in order to accelerate the curing reaction.
In these examples and comparative examples, as described later, each moire fringe suppression film produced using a light diffusion layer containing various diffusion particles has a moire suppression effect of a certain level or more and lowers the front luminance as much as possible. The content of the diffusing particles was adjusted so as not to cause it.

<< Prism sheet manufacturing process >>
As the substrate, a PET film having a thickness of 38 μm was used. On one surface of the substrate, the ultraviolet curable resin composition was heated to about 80 ° C. to lower the viscosity, and applied to a thickness of 30 μm by a die coating method. Unidic RC27-960 (a mixture of unsaturated polyester, acrylate monomer, photoinitiator, etc., manufactured by DIC) was used for the ultraviolet curable resin composition. Next, a flat plate mold on which a prism array plate having a prism pitch of 12.4 μm, a prism height of 10 μm, and an apex angle of 64 degrees is formed at 110 ° C. together with the substrate on which the uncured resin layer is formed. Heated for 2 minutes. Thereafter, the surface of the uncured resin layer on the substrate was superimposed on the mold surface, lightly pressed with a roller from the back surface of the substrate, and then irradiated with ultraviolet rays from the back surface side of the substrate to cure and fix the uncured resin. A high-pressure mercury lamp was used as the ultraviolet lamp, and the irradiation energy was an integrated value of 600 mJ / cm ² (measured with an ultraviolet illuminance meter “UVPF-36” manufactured by Eye Graphics Co., Ltd.). When the laminate of the mold, resin, and substrate was cooled to near room temperature and the substrate was peeled from the mold, a product in which a predetermined prism was formed on the substrate surface was obtained.

<< Evaluation of optical characteristics >>
A haze meter NDH2000 (Nippon Denshoku Co., Ltd.) was used, and the haze and total light transmittance of the light diffusion film were measured. For brightness measurement, the backlight unit of a commercially available mobile phone is disassembled, and the four built-in films (lower light diffusion film, two prism sheets, upper light diffusion film) are removed, and the above is made. The prism sheet is arranged so that the prism surface is on the light guide plate exit surface side, and the moire fringe suppression film of the present invention is laminated on the exit surface side and incorporated in the backlight unit, so that the front luminance of the backlight unit is increased. It was measured. As a measuring apparatus, a multipoint luminance meter EyeWin390c (manufactured by Eye System) was used. The measurement area on the light emitting surface of the backlight unit excludes 15% of the total width from the left and right edges of the light emitting surface of each backlight unit, and 15% of the total vertical width of each light emitting unit. This is a rectangular area in the center portion excluded from the upper and lower ends of the. This measurement area was divided into 9 by 3 × 3, and the brightness of each area was measured and then averaged to obtain the front brightness value.
《Evaluation of moire fringe suppression effect》
For the evaluation of moire, a liquid crystal unit of a mobile phone was placed on the backlight unit where the luminance was measured, visually confirmed, and evaluated according to the following five-level evaluation criteria.

(Moire fringe evaluation value)
Evaluation value 1 ... Generation of moire fringes can be clearly confirmed, and luminance uniformity is low.
Evaluation value 2 ... The luminance uniformity is improved, but the occurrence of moire fringes can be clearly confirmed.
Evaluation value 3... Although faint, the presence of moire fringes can be easily confirmed.
Evaluation value 4... Moire fringes can be confirmed by gazing.
Evaluation value 5: Moire fringes cannot be confirmed at all.

<Method for measuring film thickness of light diffusion layer>
The film thickness of the light diffusion layer was measured at 10 points with an electronic micrometer K402B (manufactured by Anritsu Co., Ltd.), and an average value was obtained by taking 3 points from the smallest value.

In the moiré fringe suppression film of the present invention, the film thickness can be sufficiently achieved, and at the same time, the occurrence of moiré fringes can be prevented without reducing the front luminance of the display surface of the backlight unit or the liquid crystal display device. The improvement of the front luminance and the reduction of moire fringes in the backlight unit and the liquid crystal display device are still in a trade-off relationship. Since the moire fringe evaluation value in a state in which almost no moire fringes are generated is 4 or more, the practically no problem level is set to 4 or more. The evaluation results when the moire evaluation value is 4 are shown in Table 1.
《Observation of uneven application of mottled pattern》
The coating film after the light diffusing layer was applied was observed over room light, and the presence or absence of a fine mottled pattern due to the size of the partial haze value was confirmed.
Evaluation A mottled pattern is not visually recognized at all and is a uniform diffusion surface.
○ ... The mottled pattern can be recognized only after observing the diffusion surface.
Δ: The mottled pattern is visible but difficult to find.
X: The mottled pattern is clearly visible.

<< Surface roughness measurement method >>
For the measurement, a surface roughness shape measuring machine Handy Surf E-35B (manufactured by Tokyo Seimitsu Co., Ltd.) was used. A moire suppressing film was placed on a flat surface, and a stylus was placed on the light diffusion layer for measurement.

<< Evaluation of paint pot life >>
The pot life of the paint (the time until the paint becomes gelled and cannot be used) was compared by visual observation of the paint state. For the evaluation of pot life, the following criteria were used based on the paint of Example 1 having a pot life with no practical problems. The evaluation results are shown in Table 1.
○ The pot life is 24 hours or longer when left in a room at 23 ° C and 12 hours or longer when left in a constant temperature bath at 40 ° C.
Δ: It has a pot life of 12 hours or more and less than 24 hours in a room standing at 23 ° C. and 6 hours or more and less than 12 hours in a constant temperature bath at 40 ° C.
X ... It has a pot life of less than 12 hours when left indoors at 23 ° C and less than 6 hours when left in a constant temperature bath at 40 ° C.

  As can be seen from Table 1, the thickness of the light diffusion layer of the moire fringe suppression film can be sufficiently reduced, and high front luminance and suppression of moire fringes can be realized simultaneously. It is Examples 1-4 whose ratio t / d with the volume average particle diameter (d) micrometer of a porous particle exists in the range of 1.3-2.1. On the other hand, in Comparative Example 1, high front luminance and suppression of moire fringes can be realized at the same time, but the diffusion layer thickness exceeds 8 μm and thinning cannot be achieved. In Comparative Example 2, the diffusion layer can be made thinner and the moire fringes can be suppressed. However, the light diffusion layer is not sufficiently thick with respect to the volume average particle diameter of the porous particles, and the front brightness is high. I can't get it. In Comparative Example 3, as compared with the volume average particle diameter (d) of the porous particles, the film thickness (t) of the light diffusion layer is increased and t / d exceeds 2.1. In addition, it is difficult to realize a thin film. As in Comparative Examples 4 to 6, when porous silica having a relatively large volume average particle diameter was used as the diffusing material, when trying to make the light diffusion layer thin, the volume average particle diameter of the porous particles Since the light diffusion layer is not sufficiently thick, high front luminance cannot be obtained, and even if t / d is in the range of 1.3 to 2.1, the light diffusion layer thickness is increased. Therefore, the front luminance tends to decrease. On the other hand, as in Comparative Examples 7 and 8, when resin particles are used for the light diffusing material, a large amount of resin particles must be added if moire fringes are to be suppressed, resulting in a significant reduction in front luminance. You can see that

DESCRIPTION OF SYMBOLS 1 Liquid crystal module 2 Backlight unit 3 Light source 4 Reflective film 5 Light guide plate 6 Reflective sheet 7 Light diffusion film (lower diffusion film)
8 Prism sheet 9 Light diffusion film (upper diffusion film)
12 Conventional general backlight unit 13, 23 Light source 15, 25 Light guide plate 17 Light diffusion film (lower diffusion film)
18 Conventional general prism sheet 19 Light-transmitting substrate 20 Prism array 22 Backlight unit 30 having a prism sheet arranged with the prism array facing the exit surface side of the light guide plate The prism array faces the exit surface side of the light guide plate The prism sheet 31 arranged in a light transmitting manner 32 The prism array 33 The light diffusion layer 34 in the prism sheet The light transmitting substrate 35 The light diffusion layer 36 The moire fringe suppression film of the present invention

Claims (10)

A light diffusing sheet having a light diffusing layer in which a light diffusing particle is dispersed in a resin binder on a light-transmitting substrate, wherein the light diffusing particle is a porous particle, a volume average particle diameter d is 4 μm or less, and a pore A moire fringe suppressing film having a volume of 1.0 to 2.0 ml / g and a center line average roughness Ra of the surface of the light diffusion layer of 0.5 μm or less. 2. The moire fringe suppression film according to claim 1, wherein the ratio of the thickness t of the light diffusion layer to the volume average particle diameter d, t / d is 0.8 to 1.7. The moire fringe suppression film according to claim 1 or 2, wherein the porous particles are non-spherical indefinite. The total thickness of the moire fringe suppression film is 20 to 200 µm. The moire fringe suppression film according to any one of claims 1 to 3. 5. The light diffusing layer is obtained by coating a light diffusing layer coating containing a resin binder, light diffusing particles and a solvent on a transparent support, followed by drying and thermosetting as it is. Moire fringe suppression film of any one of these. A prism sheet with a moire fringe suppression function, wherein a prism shape having a twill parallel to each other is formed on the opposite side of the light transmissive layer of the light diffusion layer. A backlight unit comprising the moire fringe suppression film according to claim 1. A backlight unit comprising: the light guide plate, a light source disposed on at least one end face side of the light guide plate, and the prism sheet with a moire fringe suppression function according to claim 6 on the light exit surface side of the light guide plate. A liquid crystal display device comprising the backlight unit according to claim 7. A method for producing a moire fringe suppression film in which a light diffusing coating containing a resin binder, light diffusing particles, and a solvent is applied on a light transmissive substrate, and then dried and thermally cured to form a light diffusing layer. The light diffusing particles are porous particles, the light diffusing particles are non-spherical porous particles, the volume average particle diameter d is 4 μm or less, and the pore volume is 1.0 to 2.0 ml / g. And the center line average roughness Ra of the said light-diffusion layer surface is 0.5 micrometer or less, and ratio of the film thickness t of the said light-diffusion layer and the volume average particle diameter d, t / d is 0.8-1. A method for producing a moire fringe suppression film, which is .7.

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