JPH0980208A - Light diffusing formed member and backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light diffusing formed member formed by kneading and forming at least 2 kinds of transparent thermoplastic resins (amorphous thermoplastic resin) specified by melt index and refractive index. SOLUTION: At least 2 kinds of the transparent and thermoplastic resins, between which the difference of melt index is 2-10 times and the difference of refractive index is 0.03-0.28, are selected, are used as the main component and kneaded and formed into a sheet to form the light diffusing formed member. And the light diffusing formed member formed into 50-500μm thickness is assembled as a light diffusing plate of a backlight device of a liquid crystal panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for a liquid crystal panel incorporating a light diffusive molding member made of a transparent thermoplastic resin and a sheet-shaped molding thereof.

[0002]

2. Description of the Related Art Generally, a point light source or a line light source is used as a light source.
A light diffusing sheet is used as one of means for uniformly emitting and illuminating the light in a plane. For this purpose, studies have been made on the improvement of the light diffusivity of the sheet, and various methods have been proposed. The content of the proposal is basically based on a sheet made of a thermoplastic resin, and is subjected to various processes to impart light diffusing properties. Specifically, it is divided as follows. First, one of them is an embossed sheet obtained by forming polycarbonate into a sheet and then passing it through an embossing roll to physically form irregularities on the surface. (JP-A-4-275501) In addition, in two of them, a surface of a PET (polyethylene terephthalate) film or the like is coated with particles of high refractive index such as zirconium oxide or silicon particles together with a transparent resin to form a light diffusing layer. There is a light diffusion sheet provided with. (JP-A-6-59107) And three of them are light diffusing plates made of a melt mixture of two or more polymers containing at least one crystalline polymer such as polypropylene, polyethylene, nylon and PET. To be (Japanese Patent Laid-Open No. 52-55651)

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The embossed sheet disclosed in Japanese Patent Publication No. 501 has the finer and deeper unevenness necessary for manifesting the light diffusion performance.
Depends on the thickness of the polycarbonate. That is, the thinner the thickness, the harder it is to form fine and deep irregularities. Further, there is a high risk that the sheet will be damaged (scratch or crack) when passing through the embossing roll. Therefore, it is necessary to carry out under sufficient molding control. These are the same and common problems with resins other than the polycarbonate described in this publication.

In the light diffusing sheet provided with the light diffusing layer described in JP-A-6-59107, dispersion of particles in the matrix resin of the coating and dispersion in the coating are likely to occur, and the coating is stable and uniform. Is difficult to obtain, and becomes thicker than the thickness of the base sheet itself, and because the matrix resin is different from the base resin, it reduces the overall brightness, that is, the total light transmittance. Works, but this is inevitable.

Further, both the embossed sheet and the light-diffusing layer / light-diffusing sheet require post-processing and require separate processing steps, so that they cannot be manufactured all at once. There are many disadvantages in terms of waste and productivity. And the third example is JP-A-52-556.
Unlike the other two publications described above, the publication No. 51 is intended to manufacture a desired light diffusing plate all at once. However, the crystalline polymer is used as a substrate to impart light diffusivity by utilizing its crystallinity, and the brightness of light after diffusion, that is, the total light transmittance, tends to decrease. Is inevitable. This is because a crystalline polymer lacks transparency unlike an amorphous polymer originally.

The present invention has been made by intensive studies to solve the above problems, and the first object of the present invention is to diffuse light with a uniform brightness together with excellent total light transmittance. The purpose of the present invention is to provide a molded member, and a second object thereof is to obtain the molded member at once by molding without post-processing. And the third purpose is to provide effective utilization means of the molded member.

[0007]

In order to achieve the above first and second objects, in the light diffusing molded member of the present invention, the melt index (hereinafter referred to as MI) is 2 to
10 times, refractive index (hereinafter referred to as n _D ) 0.03 to 0.2
At least two kinds of transparent and different thermoplastic resins having a difference of 8 are selected and kneaded with this as a main component and molded into a sheet or the like. The third object is to achieve the above by incorporating the light diffusing sheet member molded to a thickness of 50 to 500 μm as a light diffusing plate of a backlight device used in a liquid crystal panel. The details will be described below.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the resin of interest is first of all transparent and thermoplastic.
Here, the transparency is desirably about 80% or more in terms of total light transmittance (%), and the thermoplasticity is imparted with fluidity by heating and pressurizing at a predetermined temperature, and a molded article such as a sheet is obtained. It is not thermosettable. Resins satisfying these two properties are mainly characterized by being amorphous or having a low crystal density relative to the amorphous density. Further, the permeable / thermoplastic resin requires that the resin is not simply used for molding, but that at least two kinds of resins of different kinds are mixed and kneaded, and further, in the selection of the two kinds. , The difference in MI between the resins is 2 to 10 times, preferably 2 to 5 in terms of magnification.
(For example, if the MI of one resin is 5, the other MI is 25), and the difference in n _D is 0.03 to 0.2.
8, preferably 0.05 to 0.2 (e.g., with _{n D} of one resin is 1.61, if _{n D} of other resins 1.46, the difference 0.15) conditions At the same time, it is imperative to be satisfied, so that only with a very limited range of resin combinations can the said objectives be achieved.

The above conditions are required for the following reasons. When the light from a line light source or a point light source is directly or indirectly incident on the light diffusing plate and emitted for illumination, the brightness (luminance) as a sheet is first required, but this is a heat with excellent transparency. Selection of plastic resin is necessary. Such properties are found in crystalline polymers with lower crystal density or in amorphous polymers. However, even with such a resin, it is necessary to mix at least two kinds of resins having an MI difference of at least twice, which is to further promote light diffusion on the surface of the obtained molding member. Is. However, if the difference is too large and exceeds 10 times, the moldability is unfavorably deteriorated and the surface properties of the obtained molded member and the mechanical properties are deteriorated. Also, if MI
= Even if the molded sheet is made of at least two kinds of transparent thermoplastic resins having a difference of 2 to 10 times, the difference in n _D is 0.0.
If it is less than 3, the overall light diffusivity is not improved, which is not preferable. On the other hand, when it exceeds 0.28, even if the light diffusion property is improved, there is a drawback that the light reflection becomes large and the transparency is deteriorated, which is not preferable. More effectively, it is preferable to use two kinds of resins, but three kinds or more may be used. However, even if there are three or more kinds, it is necessary that the above-mentioned condition range of MI and n _D is satisfied. still,
For example, in the case of mixing three kinds, MI = 2 between each mixed resin.
There are cases where there is a difference of -10 times and n _D = 0.03 to 0.28, and there are cases where there is no such difference. In the case of the former, there is no problem because it is included in the above conditions as in the case of mixing two kinds,
In the latter case, a difference of MI = 2 to 10 times and n _D = 0.03 to 0.28 between at least two of the three resins is acceptable. .

Before being kneaded and molded, they are first mixed, but the mixing ratio is about 5 to about 5% of high MI transparent / thermoplastic resin.
60% by weight, preferably 20 to 50% by weight, low MI
Of about 95-40% by weight, preferably 80-50% by weight. From now on, rather than high MI
It can be said that it is desirable to mix a large amount of the resin having a low MI, but the higher the ratio of the resin having a high MI is, the rougher the surface of the molded body is, and the dimensional accuracy of the molded body is deteriorated. . Regarding the mixing method, there is no specific condition, and addition of a substance other than the resin referred to in the present invention during the mixing is allowed as long as it does not impair the achievement of the object of the present invention.

[0011] The in selecting the resin, as long as it allowed to satisfy the above condition, but are not certain, as a guide for selecting, 2-100 in MI, 1 at n _D.
It is preferable to select from among the transparent and thermoplastic resins within the range of 3 to 1.7. Then, the resins within the above range are specifically shown in Table 1, but it goes without saying that the table is merely an example. In Table 1,
MI values of the resin and the test load (kgf), based on the refractive index measurement method described in the test temperature (° C), and _{n D} value (JISK7105, measured with an Abbe refractometer whose light source the D line Value) and the value of total light transmittance.
In the table, poly (4-methylpentene-1) and tetrafluoroethylene / perfluoroalkoxyethylene copolymer are crystalline unlike other resins, but crystalline unlike ordinary crystalline polymers. And the specific gravity of the amorphous material are close to each other, so that they have high transparency. That is, even a resin which is generally called a crystalline polymer, a thermoplastic resin that exhibits high transparency derived from an amorphous portion can be said to be a kind of the transparent / thermoplastic resin according to the present invention.

[0012]

[Table 1]

In the present invention, at least two kinds of the corresponding resins including the resins exemplified in Table 1 may be mixed under the above conditions, so that the combination is specified. Not a thing. This is because it can be easily known in advance by an appropriate experiment, but for reference, the combinations thereof are as follows. Polycarbonate and poly (4-methylpentene-1), polyarylate and poly (4-methylpentene-1), polycarbonate and polyarylate, polymethylmethacrylate and acrylonitrile-styrene copolymer, polymethylmethacrylate and polystyrene, polysulfone And a tetrafluoroethylene / perfluoroalkoxyethylene copolymer.

The MI in the present invention is JISK721.
0 (1976), but in general, MI is not only the measurement temperature but also the molecular weight of the resin, the structural skeleton, etc. (the resin manufacturer often distinguishes by giving the product number). ) Also depends on. Therefore, also in the present invention, even if there are different values of MI, as long as they are called by the same name, the MI value of each resin exemplified in Table 1 which is the transparent / thermoplastic resin according to the present invention has a range. The reason for this is exactly due to this molecular weight and structure.
Further, the total light transmittance (measurement of transparency), diffuse transmittance, and haze value in Table 1 and Examples and Comparative Examples described later are measured based on JISK7105 (1981),
It was calculated, and its measurement was carried out by a spectrophotometer (U3410 type self-recording spectrophotometer: Hitachi, Ltd.) equipped with an integrating sphere accessory (P / N150-0909), and parallel to the total light transmittance. The light transmittance was directly read, and the diffuse transmittance and haze value were calculated.

As mentioned above, at least two types of transparency
The blended resin obtained by combining and mixing the thermoplastic resin as the main component is kneaded and molded to obtain a desired molded member, but the kneading / molding conditions are not particularly limited. In general, kneading is carried out by extruding into a gut shape and cutting into pellets by a twin-screw extruder having a barrel temperature adjusted to an extrusion molding temperature having a higher heat distortion temperature among the resins to be mixed. Done. Then, the obtained pellets are fed to an extruder having 1 to 2 axes and molded into a predetermined shape in a non-stretched state or slightly stretched through a mold. The molding here is generally extruded from a T-die into a sheet having a thickness of about 50 to 500 μm, but depending on the intended use, it may be a cylindrical shape or a laminate with another. The thinner the sheet thickness, the weaker the diffusivity and the more inconvenient in handling. Conversely, the thicker the sheet, the lower the light transmittance, which leads to a decrease in brightness when used for a backlight and an increase in weight. It is not preferable because it brings about.

When light is directly or indirectly incident on the molded member thus obtained, it is extremely bright and transparent, that is, it has a high total light transmittance and a haze value and an extremely high light diffusion transmittance. Show. Therefore, about 50-50
When a sheet-shaped molding member having a thickness of 0 μm, preferably 80 to 200 μm is used by being arranged with a light guide plate of a backlight device of a liquid crystal panel or with a light source without the light guide plate, the display screen of the liquid crystal panel is obtained. The whole image is extremely bright and can be clearly displayed without uneven illumination. This also leads to lower power consumption of the light source itself. The liquid crystal panel backlight device includes a direct type and an edge light type depending on the arrangement position of the light source, but the types thereof are not limited, and the size and mounting method are not limited. Further, the molding member is not limited to use as a light diffusing plate of a backlight device of a liquid crystal panel, for example, for an electric signboard, a projector projection screen, a photolithographic film projector, or a cylindrical shape. It can also be used for desk lamps.

It is considered that the constituent member obtained by the above-described structure exhibits the excellent effect of the light diffusion property for the following two reasons. The expression of the light diffusivity of the present invention is due to two synergistic actions of internal diffusion and surface (surface) diffusion. That is, in the internal diffusion, light incident from the surface of the molded body is scattered by refraction at the interface due to the presence of the transparent / thermoplastic resin having a different refractive index. The light scattered (diffused) inside is further subjected to surface diffusion, and finally emitted as large diffused light. This surface diffusion means light diffusion due to an appropriate roughness generated on the surface of the molded body.

It is considered that the generation of the appropriate surface roughness, which is a factor of the surface diffusion, is due to the low MI component. This is because when the molten resin is discharged from the mold and molded, a high MI component having a low melt viscosity is positively flowed, so that the low MI component remains inside and the high MI component remains in the surface layer. It exists in a simple state, and it is considered that it causes roughening. This is presumed from the fact that, after swelling the surface of the molded product with a solvent and observing it with an electron microscope, the high MI component is present in the surface in the form of streaks in the molding flow direction. It can be said that this is because the distribution state different from the sea-island distribution state generally referred to in the resin blend was obtained, which resulted in appropriate surface roughness and further light diffusion.

[0019]

EXAMPLES The present invention will be described in more detail below by way of examples along with comparative examples, but it goes without saying that the examples do not limit the present invention. Example 1 Polycarbonate pellets having MI = 5 and n _D = 1.58 were mixed with poly (4-methylpentene-1) pellets having MI = 10 and n _D = 1.46 at a ratio of 1: 1 (weight ratio). Then
After sufficiently drying, the barrel temperature was adjusted to 230 to 270 ° C. 2
It was supplied to a shaft extruder and extruded while being sufficiently kneaded to obtain a mixed pellet. Next, a single-screw extruder (barrel temperature 230-
(290 ° C.) was prepared, and the mixed pellets were supplied to the mixture and extruded into a sheet shape. The extruded sheet was substantially unstretched and wound into rolls. The obtained sheet had a thickness of 100 μm and was transparent, and when the surface was manually stroked, some unevenness was felt. Then, the total light transmittance, the diffuse transmittance and the haze value of this sheet were measured and summarized in Table 2. The high haze value together with the total light transmittance means that there is no light and there is no light, and that a large diffused light is emitted.

[0020]

[Table 2]

Example 2 Polycarbonate pellets having MI = 5 and n _D = 1.58 and poly (4-methylpentene-1) pellets having MI = 26 and n _D = 1.46 were mixed at a ratio of 1: 1 (weight ratio). ),
After sufficiently drying, the barrel temperature was adjusted to 230 to 270 ° C. 2
It was supplied to a shaft extruder and extruded while being sufficiently kneaded to obtain a mixed pellet. Next, as in Example 1, a single-screw extruder having a T-shaped die at the tip (barrel temperature of 230 to 290 ° C.)
The mixed pellets are supplied to, and extruded into a sheet,
A sheet having a thickness of 100 μm was obtained. The obtained sheet had larger surface irregularities than that of Example 1 and had a large haze value indicating light diffusivity. The results are summarized in Table 2.

Comparative Example 1 85% by weight of crystalline 6.6 nylon pellets and 15% by weight of amorphous polystyrene pellets were mixed and the mixture was placed in a twin-screw extruder (barrel temperature 250-290 ° C.). It was supplied and kneaded to obtain a kneaded chip. Then, using this blended chip, the sheet 1 was passed through a T-shaped die in the same manner as in Example 1 by a uniaxial extruder (barrel temperature of 250 to 290 ° C.).
To obtain a sheet having a thickness of 100 μm. The results are summarized in Table 2. In this comparative example, Example 2 of JP-A-52-55651 described above as a known example is additionally performed. The blend of crystalline polymers has low transmittance and poor light diffusibility (small haze value), so that it is at a level not practical for a light diffusing plate.

Comparative Example 2 Pellets of polymethylmethacrylate with MI = 2 (n _D = 1.49) and polystyrene with MI = 3 (n _D = 1.59) having an MI difference of 1.5 times are weighed. The mixture was mixed at a ratio of 1: 1 and was mixed with a twin screw extruder (barrel temperature 210 to 210
240 ° C.) and kneaded and extruded to obtain mixed pellets. Then, the mixed pellets were molded into a sheet through a T-shaped die by using the single-screw extruder of Example 1 (barrel temperature: 210 to 240 ° C.). The thickness of the obtained sheet is 1
It was 50 μm, and the surface was extremely smooth. The results are summarized in Table 2. It can be understood that although each is a resin which is amorphous and has excellent transparency, a molded sheet made of a blend has poor transparency and a weak light diffusion effect.

Comparative Example 3 Pellets of polycarbonate with MI = 5 (n _D = 1.58) having a difference of 13 times and poly (4 with MI = 65)
- methylpentene _-1) (n D = 1.46) and 1 weight ratio: were mixed at a ratio of 1, and supplies it to the biaxial extruder (barrel temperature 230 to 270 ° C.), kneaded and The mixture was extruded to obtain a mixed pellet. Then, the mixed pellets were processed in the same manner as in Example 1 using a uniaxial extruder (barrel temperature of 230 to 290).
Attempting to form a sheet at a temperature of (° C.) Through a T-type die, the formability was poor and only a sheet containing bubbles could be obtained. Therefore, the total light transmittance and the like were not measured for this. The results are summarized in Table 2.

Comparative Example 4 Pellets of polystyrene (MI = 3) with n _D = 1.59 and a polycarbonate (MI = 5) with n _D = 1.58, in which the difference in refractive index was 0.01, Weight ratio 3:
Mix in a ratio of 2 and mix this in a twin-screw extruder (barrel temperature 2
10 to 260 ° C.) and kneaded and extruded to obtain mixed pellets. Then, the obtained mixed pellets were passed through a T-shaped die in the same manner as in Example 1, and a single-screw extruder (barrel temperature 2
50 to 280 ° C.) to form a sheet. The thickness of the obtained sheet was 100 μm. The results are summarized in Table 2. Excellent transparency, but poor light diffusion.

COMPARATIVE EXAMPLE 5 A tetrafluoroethylene-perfluoroalkoxyethylene copolymer (M of n _D = 1.35 having a refractive index difference of 0.3) (M
I = 15) and n _D = 1.65 polyether sulfone (MI = 5) were mixed in a weight ratio of 7: 3, and the mixture was extruded by a twin-screw extruder (barrel temperature: 280 to 380 ° C.) and mixed. Pellets were obtained. The obtained blended pellets were formed into a sheet through a T-die through a uniaxial extruder (barrel temperature of 280 to 380 ° C.) in the same manner as in Example 1. The thickness of the obtained sheet was 100 μm. The results are summarized in Table 2. Understand that transparency is not good.

[0027]

Since the present invention is configured as described above, it has the following effects. First, it is a resin molded member having both excellent light diffusivity and total light transmittance. This greatly improves the quality and performance of the conventional light diffusing plate, and contributes to the further improvement of the quality and performance of liquid crystal displays and the like. It is possible to rapidly manufacture a light-diffusing molded member that always has stable quality and performance.
In other words, this is because, unlike the conventional light-diffusing property imparting post-processing, it is manufactured all at once by molding.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Katsurakawa 163 Morikawara-cho, Moriyama-shi, Shiga Gunze Co., Ltd. Shiga Research Institute (72) Inventor Kensuke Taki 163 Morikawahara-cho, Moriyama-shi, Shiga Gunze Co., Ltd. Shiga Research In-house (72) Inventor Yoshihide Sakamoto 163 Morikawahara-cho, Moriyama-shi, Shiga Gunze Co., Ltd. Shiga Research Center

Claims (4)

[Claims] 1. A kneading / molding method comprising, as a main component, at least two kinds of transparent / thermoplastic resins having a melt index of 2 to 10 times and a refractive index of 0.03 to 0.28. A light diffusive molding member characterized by the above. 2. The light diffusion according to claim 1, wherein the transparent / thermoplastic resin is selected from the resins having a melt index of 2 to 100 and a refractive index of 1.3 to 1.7. Molded parts. 3. The light-diffusing molding member has a thickness of 50 to 500 μm.
The light-diffusing molded member according to claim 1 or 2, which is a sheet-shaped molded product of m. 4. A backlight device, characterized in that the light diffusing molded member according to claim 3 is provided as a light diffusing plate of a backlight device of a liquid crystal panel.