−論文−● Development of Light-Diffusive UV-Curable Resins for a Novel Thin Backlight System
機能樹脂研究所

佐内康之

LCDバックライトは、反射板、導光板、拡散板、プリズムシート等多くの部材を必要とするために、LCD 全体に占める厚さ、重さ、コストの割合が大きい。また、バックライト構成部材界面での反射や部材による光の吸収などにより光の取り出し効率が低下するという問題がある。
筆者らは、次世代モバイル用表示材料技術研究組合（Technology Research Association for Advanced DisplayMaterials, 通称 TRADIM）にて株式会社クラレと共同で、1) 薄型化および軽量化、2) 光取り出し効率の向上、3)アセンブリの簡略化を達成するために、複数の光学フィルムの機能を一枚のフィルムに集約したバックライトの開発に取り組んだ。光学フィルムは、高輝度で白色の散乱光を出射する必要があるが、波長依存性があるため、白色光は得られにくい。筆者らは、Mie 散乱理論に着目し、マトリックスであるUV 硬化樹脂と光拡散材との屈折率差、光拡散材の粒径を最適化することにより、散乱光を白色光に近づけることができた。さらに、UV 硬化樹脂に求められる、速硬化性、低粘度、支持フィルム密着性、金型離型性といったプロセス特性を満足する設計手法を確立し、UVX-5113を開発した。
UVX-5113の連続塗工試験により光学フィルムを作製し、バックライトを試作した。得られたバックライトの厚さは従来品の1/3以下の0.26mmであり、光学特性も良好であった。

1緒

言In these backlight systems, the light guide plate withthe shape of a slab or a wedge has many dot patterns in

1. Introduction

the rear. Incident lights from the light source such as cold

LCD is widely utilized for the information terminals suchcathode fluorescent lamps and light emitting diode (LED)as cellular phones, personal digital assistants. As for thesepropagate through the light guide. The propagating lights

applications, LCD should be thin, light, flexible and hard tothat reach the dot patterns are diffused through the light

break for convenience.

guide, and then diffused lights are radiated toward thediffuser. Emanated lights are diffused by the diffusive

But conventional LCD backlight systems considerably

elements in the diffuser, and they behave as Lambertian.

occupy in terms of weight and thickness in LCD, andgenerally flexibility is not enough, because they areAdditionally, a diffuser has a function that it makes

essentially composed of a light guide plate, a reflector, athe dot patterns invisible. Orthogonal prism sheets on adiffuser, and prism sheets (Fig. 1).

diffuser collimate the diffused lights in order to increase
the brightness to the direction of viewers effectively.
Conventional backlight systems also have a reflector so
as to avoid backward emission of light.
These backlight systems have an advantage that highLCD Panel

uniformity of brightness can be easily achieved by arranging

Prism Sheetthe dot patterns appropriately. But they necessarily havePrism SheetDiﬀuserdisadvantage of lowering efficiency as long as they have toutilize diffusion of light.

1.0mm

Light Guidewith Dot Patterns
Reﬂector

Fig.1 Structure of a coventional backlight system.

東亞合成グループ研究年報

26

TREND 2008

第 11 号

3. UV-curable resins

Recently, several types of backlight systems withhigh performance have been proposed to achieve higher
brightness, higher quality and higher efficiency

1-5)

Most thermoplastic resins are highly viscous and very. In

tough materials to pour into a mold. Especially, a metal

addition to those performances, backlight systems have beenmold for producing optical films has very small precise

demanded to be thinner, lighter, and to simplify assembling.

shapes of lens patterns. This means that thermoplastic

Some research groups have proposed some novel systems

resins cannot be used for this application without organic6-10)

diluents. But if organic solvents are used as diluents, they

to satisfy these requirements.

must be dried up during manufacturing process. It takes

2. OPF Backlightmuch time to remove all solvents and makes productivity

In a previous paper, we have reported a novel ultra slim

lower.

backlight system using the optical-patterned film (OPF

Furthermore, the apparatus and energy cost also high.

backlight) that is composed of a single component (Fig. 2).

On the other hand, UV-curable resins are low viscous

Incident lights from the light source propagate by a totalliquid before cure even without organic solvents, because

reflection through the light guide. Propagated lights which

low molecular weight of acrylic monomers act as reactive

reach the contact points of the light guide and optical-diluents. When UV-curable resins are employed as thepatterns are picked up toward the optical-patterned film,

material for optical-patterned films, drying process is notfor those contact points play a role of“optical window”.

required.

Picked up lights are reflected at slope of the optical-

Moreover, they can cure rapidly when UV is radiated as

patterned film, and then, they are radiated toward the LCD

shown in Fig. 3. They have the advantages of low energy

panel from OPF backlight. High uniformity of brightnesscosts, space-saving, and high productivity due to theirca n be achieved by a r ra ng ing the optica l- patter n sfeatures. UV-curable resins are expected to be the best

appropriately11,12). The size of a single optical-pattern has

way to obtain OPF backlight with high productivity by abeen optimized about several tens micrometers.

roll-to-roll continuous process when a UV-radiation system

We are also trying to manufacture OPF backlight system
by a roll-to-roll continuous process13,14)

with conveyer is adapted. We will propose new materials, and when ourand principles for a novel backlight system.

attempt gets success, our new backlight system will be oneof the best tools to achieve a thin, light, and flexible LCDwith high productivity.
Multi-functional acrylic oligomer
Acrylic monomer

UV radiation
polymerization
LCD Panel
Optical-Patterned Film

Photo -initiator

Substrate Film

Thickness<<1.0mmFig.3 Schematic of UV-curing of acrylates.

Light Guide
Optical Window

4. Light-diffusive particles

Fig.2 Structure of OPF backlight.

The refractive indexes of UV-curable resins should behigher than that of a light guide film in order to obtainhigh brightness. And the difference of the refractive index
between UV-curable resins and light diffusive particles will
be required to achieve sufficient light diffusivity. Further,diffused light must be white as a light source of LCDs.

東亞合成グループ研究年報

27

TREND 2008

第 11 号

However, it is difficult to pick diffused light up as white

Table 1 Formulations of UV-curable
resins with polymer particles.

light, because scattering intensity and efficiency depend on
wavelengths. So the refractive indexes and the diameters ofthe light-diffusive particles have to be optimized, and light-RunNo.

diffusive particles should be easy to design and control
their refractive index and particle size. Viewed in these

UV -Curable Resins
n25Dn25D(b efore cure)(cured film )Polymer Particles

Haze

n25D

D
(µm)

(%)

lights, acrylic polymer particles are expected to be suitable

11.50301.5330

1.497

2.4

42

materials, because the refractive indexes can be easily

2

1.54611.5701

1.497

2.4

94

3

1.5552

1.5810

1.497

2.4

974

1.54611.5701

1.497

3.794

5

1.5552

1.5810

1.497

3.7

96

6

1.54611.5701

1.497

5.4

91

7

1.5552

1.5810

1.497

5.4

90

varied by copolymerization of various types of acrylic
monomers, methacrylic monomers, and styrene derivatives.
The diameter of the particles can be well-defined from 1to 10 micrometers by changing conditions of polymerization
process. While the dispersibility of light-diffusive particles* The ratio of UV-resin and polymer particles was 90 to 10 by weight.
*Film thickness of UV-resin was 50µm.

with UV-curable resins is important in order to produceuniform optical films, most commercially available acrylic
particles show a tendency to aggregate or get swollen in
UV-curable resins. We have solved this problem by using

The tint of backlight using these films with high haze

graft polymerization method of macromonomeric surfactant

value was shown in Fig. 5. They were found to be deviatedwith monomers. The light diffusive particles we employedfrom the center of chromaticity coordinates.

showed good dispersibility and tolerance toward various

This phenomenon meant that the transmitted light wasorganic solvents. Their trade name is“ ARON TM-series”.

not white, and other factors existed to control scattering
properties of light-diffusive UV-curable resins.

Di spersion Polymerization usin g “ Macromonomer”
Mac rom onom er” as a Reactive D ispersan
ispe rsan t

Seed --Particle
Particle

0 .4 5Polymerization
Aggregation

Polymerization
Precipitation

Stabilization

Mo nome r
M a c romo nome r
Initia tor
SSolveolve nt

Run 3
Run 5
Run 70 .4

Mac r om onome r

Polymerization(Growth in Diameter)

0 .3 5yFeatures of ARON TM -series

Diameter
1-10µmWide Range of Refractive Index

0 .3

Highly Crosslinking Density

Light -Diffusive Function

Excellent Solvent Resistance

0 .2 5

Fig.4 Manufacturing process and features ofARON TM-series.

0 .20 .20 .2 50 .30 .3 50 .40 .4 5x

5. Formulations and optical properties

Fig.5 Chromaticity coordinates for backlights
using 20µm thickness ofcured films.

We prepared UV-curable formulations with various
refractive indexes, and then added well-defined polymer
particles (Table 1). The haze values of UV-cured films werealso shown in the same table. These data indicated that

Koike et al . proposed the backlight system using a highly

the light strongly diffused when the differential refractive

scattering optical transmission (HSOT) polymer whichindexes between matrix and polymer particles were larger

consisted of the micro particles in the transparent matrix

or the diameter of particles was small.

by analyzing Mie scattering theory. In Mie scattering
theory, scattering efficiency Qsca depends on the diameter ofmicro particles D, the differential refractive index between

東亞合成グループ研究年報28

TREND 2008

第 11 号

matrix and micro particlesΔ n, and the wavelength ofincident light λ .

25R un7

Koike et al . reported that colorless HSOT backlightsystem could be achieved by optimizing ρ values that wereTransmittance (%)

obtained from D, Δn, and λ , as shown in Fig. 615).

2.5

Qsca

2R un9R un101155

R un111051.5435nm

10400545nm

500615nm

0.50R un8

2000.1

0.2

0.3

0.4

600700800

Wavele ng th ( nm )

0.5

0.6

Fig.7 Parallel transmittance of light-diffusive
UV-cured films.

0.7

ρFig.6 The relation between Qsca and ρ(=The tint of backlights using them was shown in Fig. 8,nD).

and colorless transmittance was found to be obtained whenρ value was around 0.35.
Then we calculated ρ values of model formulations (Table2) and the dependence of parallel transmittance was shown

0.45

R un 7in Fig. 7. They clearly showed the wavelength dependence

R un 8of parallel transmittance, and the optimized ρ value was0.4

R un 9determined both theoretically and experimentally.

R un 1 00.35

yR un 1 10.3

Table 2 Formulations of UV-curable resins
with polymer particles.
RunNo.

UV -Curable Resins

Polymer Particles

Haze

n25D

D(µm)

(%)

0.25
0.2
0.2

0.25

0.3

0.35

0.4

0.45

n25D

n25D

(before cure)(cured film )71.5552

1.5810

5.4

0.45

90

8

1.53731.5608

5.4

0.34

90

9

1.5382

1.5681

5.4

0.38

91

10

1.5614

1.5898

5.4

0.50

88

The scattering behavior of the cured films was evaluated11

1.5754

1.6122

5.4

0.62

79

by a goniophotometer. Fig. 9 shows the relation betweenxFig.8 Chromaticity coordinates for backlightsusing 20µm thickness of cured films.

scattering angles and relative light intensity at three* T he ratio of U V-c u r a b le re sin an d pol ym er pa rtic les w as 90 to
10 by w e igh t.

different wavelengths, which correspond to red, green,* F il m t hickn ess of U V-curabl
Ve re sin w as 50 µ m .
* R un7 w as th e sam e sam p le as in T able 1.

and blue. The uniformity of relative light intensity on eachwavelength was relatively good, when ρ value was 0.35. Onthe contrary, the scattering angle on 438nm and 558nm wasobviously narrower than that on 680nm, and the uniformity

東亞合成グループ研究年報

29TREND 2008

第 11 号

was not sufficient, when ρ value was 0.62.
In this case, the transmitted light will get reddish, whenU V L am pa viewer watches the display diagonally.

T ransparent P lastic Substrate
Optical-Patterned Film

Relative Light Intensity（a.u.）100

ρ=0.35
ρ=0.62
10Coater1

M e tal M oldFig.10 A roll-to-roll continuous process for
manufacturing the optical-patterned film.

0 .1
6 8 0 nm0 .0 1

Photo- Curable Resin

5 5 8 nm
4 3 8 nm0 .0 0 1

In addition to optimization of optical properties, UV-2 0-1 5-10-50S c a t t e ri ng A n g l e5101520curable resins must show industrially sufficient curing rate,（ deg. ）good removability from a metal mold, and good adhesion toRelative Light IntensityĦa.u.ħ

100

a substrate film to establish a highly productive reliableρ=0.62

process. We have established the design principles to obtain10

the formulations which good removability from a mold and1adhesion to a film can be compatible by adjusting curing
rate and crosslinking reactions.

0 .1

Major properties of the optimized formulation wereshown in Table 3.

6 8 0 nm0 .0 15 5 8 nm
4 3 8 nm0 .0 0 1-20-1 5-10-50

S c a t t e ri ng A n g l e

51015

Table 3 Major properties of the optimized
formulation

20（ deg. ）Fig.9 The relation between scattering angles andrelative light intensity.

A roll-to-roll continuous process is expected to be one of
the best methods to manufacture optical-patterned films inhigh productivity.
And UV-curable resins are good solutions for thispurpose due to their excellent features, such as rapid
cure, space-saving, low viscosity, organic solvent-free, andT rade NameUVX -5113

Viscosity(mPa ･s at 25 o C)33

n D 25 (before cure)1.512

n D 25 (cured film)

1.550

Diameter of particles
(µm)

5.4

so on (Fig. 10).
The appearance of the obtained optical patterned film bya roll-to-roll process, the microscopic photograph of thelens patterns, and its cross section were shown in Photo.1.
UVX-5113 proved to show excellent adhesion to thesubstrate film and the remobalility from the metal mold.
Furthermore, the cross section showed that ARON TMseries possessed excellent tolerance toward UV-curable
resins, and they dispersed uniformly in the formulation16).

東亞合成グループ研究年報

30

TREND 2008

第 11 号

removability from a metal mold and good adhesion to a
substrate film. UV-curable resins have an advantage of highproductivity due to their features such as rapid cure, spacesaving, and organic solvent-free. We expect that our UVcurable formulations can provide optical-patterned films fora novel slim backlight system by a roll-to-roll continuous
process with high productivity.

7. References
1)

S.Zimmerman, K.Beeson, M. McFarland, J. Wilson, T.
Credelle, K. Bingaman, P. Ferm, J. Yardley,

Photo. 1 The obtained optical patterned film.

“Viewing-Angle-Enhancement System for LCDs”, SID
Symposium Digest, Vol.26. pp.793-796, 1995.
2)

Finally, we showed the assembled OPF backlight inK. kalantar, S. Matsumoto, T. Onishi, K. Takizawa,

photo. 2. We turned on LEDs to lighten the bent backlight,“Optical Micro Deflector Based Functional Light-and found out that it could radiate uniformly even with a

Guide Plate for Backlight Unit”, SID Symposium

bent shape unlike a conventional backlight system. The total

Digest, Vol.31. pp.1029-1031, 2000.
3)

thickness of the obtained OPF backlight was 0.26mm, andK. kalantar, S. Matsumoto, T. Katoh, T. Mizuno,

we have succeeded in achieving the thinnest backlight in the“Double-Side Emissive Backlight Unit for Transmissive

world17).

LCD using a Single Functional Light-Guide Plate”,
Proc. IDW ’03, pp.661-664, 2003.
4)

H. Jagt, H. Cornelissen, D. Broer, C. Bastiaansen,“Micro-structured Polymeric Linearly Polarized LightEmitting Lightguide for LCD Illumination”, SID
Symposium Digest, Vol.33. pp.1236-1239, 2002.

5)

F. Yamada, Y. Taira,“Optical Components DirectlyMolded on the LCD Glass Substrate”, SID Symposium
Digest, Vol.33. pp.1042-1045, 2002.

6)

A. Horibe, M. Izhuara, E. Nihei, Y. Koike,“Brighter Backlights Using Highly Scattered OpticalTransmission Polymer”, SID Symposium Digest,
Vol.26. pp.379-381, 1995.

Photo. 2 Appearance of the lightened

7)“ bendable” OPF backlight.

A. Tagaya, M. Nagai, Y. Koike, K. Yokoyama,“Thinliquid-crystal display backlight system with highlyscattering optical transmission polymers” Appl.
Opt.,Vol.40. PP.6274-6280, 2001.

6. Conclusions

8)

We have developed light-diffusive UV-curable resins

H. Suzuki, M. Horiguchi, T. Okumura, A. Tagaya, Y.
Koike,“Highly Efficient LCD Backlight Having No

with well-controlled scattering property by adjusting theOptical Film”, Proc. IDW ’03, pp.673-676, 2003.
9)

diameter of light-diffusive particles and the differential

M. Shinohara, J. Takagi, M. Oba, M. Takeuchi,

refractive index between UV-curable resin matrix and the“Curved Prism Array for Controlling Directivity ofparticles. Optical-patterns could be formed accurately

LED Backlight”, Proc. IDW ’03, pp.665-668, 2003.
10) A. Funamoto, Y. Kawabata, M. Ohira, S. Aoyama,

using the formulations due to their low viscosity, and thepolymer particles showed good dispersibility and tolerance“Prism-sheetless High Bright Backlight System for

toward UV-curable resins. Additionally, they showed good

Mobile Phone”, Proc. IDW ’04, pp.687-690, 2004.

東亞合成グループ研究年報

31TREND 2008

第 11 号11) A. Nagasawa, K. Fujisawa,“An Ultra Slim Backlight
Sy s t e m u s i n g O p t i c a l - Pa t t e r n e d F i l m”, S I D
Symposium Digest, Vol.36. PP. 570-573, 2005.
12) A. Nagasawa, T. Eguchi, Y. Sanai, K. Fujisawa,“ANovel Backlight System with the Unified Component”,
Proc. IDW/AD ’05, pp. 1285-1288, 2005.
13) T. Eguchi, A. Sonehara, A. Sugizaki, T. Ito, A.
Kumano, T. Takahashi,“New Color Filter Carried
Out by a Roll-to-Roll Process”, Proc. IDW ’04,
pp.579-582, 2004.
14) A. Sonehara, T. Eguchi, A. Sugizaki, T. Takahashi,
T. Ito, A. Kumano,“Properties of Column-Spacers ona flexible Color Filter using a Roll-to-Roll Process”,
Proc. IDW/AD ’05, pp. 347-350, 2005.
15) A. Tagaya, Y. Koike, Optical and Electro-OpticalEngineering Contact, Vol.38, No.1, pp.47-55, 2001.
16) Y.Sanai, C.Sakakibara, A.Nagasawa, K.Fujisawa,“Development of Light-Diffusive UV-Curable Resins
for a NovelSlim Backlight System”, SID’06 DIGEST,
pp458-461, 2006.
17) A.Nagasawa, T.Eguchi, Y.Sanai, K.Fujisawa,“A Slimand Bendable Backlight System Manufactured by a
Roll-to-Roll Continuous Process”, Proc.IDW’06,
pp945-948,2006.

東亞合成グループ研究年報

32

TREND 2008

第 11 号