JP2007003224A

JP2007003224A - Method and apparatus for measuring coefficient of viscosity of liquid crystal

Info

Publication number: JP2007003224A
Application number: JP2005180679A
Authority: JP
Inventors: Tetsuya Miyashita; 哲哉宮下; Tatsuo Uchida; 龍男内田; Yuhei Kuratomi; 雄平倉富
Original assignee: Tohoku University NUC; Tohoku Techno Brains Corp
Current assignee: Tohoku University NUC; Tohoku Techno Brains Corp
Priority date: 2005-06-21
Filing date: 2005-06-21
Publication date: 2007-01-11
Anticipated expiration: 2025-06-21
Also published as: JP4528992B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring a coefficient of the viscosity of a liquid crystal capable of measuring easily and highly accurately the rotational coefficient γ<SB>1</SB>of viscosity and coefficients η<SB>1</SB>, η<SB>2</SB>of shear viscosity of Miesowicz of an N-type liquid crystal cell. <P>SOLUTION: Observation of a response to an applied step-up voltage is performed once or in a plurality of times by changing a voltage range of the step-up voltage in the state where each optical axis of either of two orthogonal polarizers arranged on both sides of a liquid crystal cell sample having a homeotropic structure and of the sample is adjusted in parallel, to thereby determine a voltage range wherein a light leakage is removed. Then, the value of the rotational coefficient γ<SB>1</SB>of viscosity is determined from an ON-response characteristic measured by the step-up voltage in the determined voltage range in the state where each optical axis is crossed at about 45°, and then each value of the coefficients η<SB>1</SB>, η<SB>2</SB>of shear viscosity is determined from an OFF-response characteristic measured by a step-down voltage in a proper voltage range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、液晶の粘性係数測定方法及び装置に関し、特に、Ｎ型液晶セルの回転粘性係数γ₁及びミーソヴィッツ粘性係数のうちη₁、η₂を高精度に測定できる、液晶の粘性係数測定方法及び装置に関する。 The present invention relates to a method and an apparatus for measuring a viscosity coefficient of a liquid crystal, and more particularly, a method for measuring a viscosity coefficient of a liquid crystal capable of measuring η ₁ and η ₂ out of a rotational viscosity coefficient γ ₁ and a Misovitz viscosity coefficient of an N-type liquid crystal cell with high accuracy. And an apparatus.

近年、液晶テレビジョンの進歩に伴い、より高速でスイッチする液晶表示装置（Liquid Crystal Display：略号ＬＣＤ。以下、適宜この略号で記す。）の開発が強く望まれている。本発明者らはこれまでに、ＬＣＤの応答には液晶のフロー効果が重要な役割を演じていることを明らかにしてきた（非特許文献１）。このフロー効果の理論は、エリクセン-レスリー（Ericksen-Leslie）により立てられたものである（非特許文献２〜４）。この理論によれば、液晶を異方性粘性流体とみなして、連続弾性体理論を盛り込んだ流体力学系が、数１に示す運動方程式及び数２に示す角運動量保存式（非特許文献５）により記述される。 In recent years, with the progress of liquid crystal television, development of a liquid crystal display device (Liquid Crystal Display: abbreviation LCD, hereinafter abbreviated as appropriate) has been strongly desired. The present inventors have clarified that the flow effect of the liquid crystal plays an important role in the response of the LCD (Non-Patent Document 1). The theory of the flow effect was established by Ericksen-Leslie (Non-Patent Documents 2 to 4). According to this theory, the liquid dynamics system including the continuous elastic body theory with the liquid crystal regarded as an anisotropic viscous fluid has the equation of motion shown in Equation 1 and the angular momentum conservation equation shown in Equation 2 (Non-Patent Document 5). Is described by

上記数１、数２の式に含まれる係数α₁〜α₆は、レスリー粘性係数と呼ばれており、これらの間には、α₆＝α₂＋α₃＋α₅、なる関係があるので、全６つのうち独立なものは５つである。しかし、これらは測定系との対応が不確定であるため原理的に直接測定することができない。一方、測定系との対応が確定している（すなわち原理的には測定可能な）粘性係数として、ミーソヴィッツ（Miesowicz）粘性係数が知られている。これには、図８に示すような、分子の短軸方向、長軸方向に平行なせん断フローに対する粘性係数（ずれ粘性係数）η₁、η₂、分子の長軸回りのねじれ方向のフローに対する粘性係数（ねじれ粘性係数）η_3、及び分子の短径が圧縮される方向のフローに対する粘性係数（圧縮粘性係数）η₁₂の４つがある。これら４つに数２の式中の回転粘性係数γ₁（これも測定可能）を付加した５つのパラメータと、レスリー粘性係数α₁〜α₆との間には、数３に示す式で表される関係があることが知られている。そこで、これら５つのパラメータの値を精度よく測定できれば、数３の式をαについて解いた数４に示す式からレスリー粘性係数を算出し、その結果を用いて数１、数２の式をコンピュータによる数値解法で解くことにより液晶の応答性を正しく評価することができ、更には、液晶材料の改善にも寄与することができる。 The coefficients α _{1 to} α ₆ included in the above formulas 1 and 2 are called Lesley viscosity coefficients, and there is a relationship of α ₆ = α ₂ + α ₃ + α ₅ between them. Five of the six are independent. However, these cannot be directly measured in principle because their correspondence with the measurement system is uncertain. On the other hand, the Miesowicz viscosity coefficient is known as a viscosity coefficient whose correspondence with the measurement system is fixed (that is, measurable in principle). As shown in FIG. 8, the viscosity coefficient (displacement viscosity coefficient) η ₁ , η ₂ for the shear flow parallel to the minor axis direction and the major axis direction of the molecule, and the torsional flow around the major axis of the molecule. There are four viscosity coefficients (torsional viscosity coefficient) η ₃ and viscosity coefficient (compression viscosity coefficient) η ₁₂ for the flow in the direction in which the minor axis of the molecule is compressed. The five parameters obtained by adding the rotational viscosity coefficient γ ₁ (also measurable) in the equation (2) to these four and the Lesley viscosity coefficients α _{1 to} α ₆ are expressed by the equation shown in the equation (3). It is known that there is a relationship. Therefore, if the values of these five parameters can be measured with high accuracy, the Lesley viscosity coefficient is calculated from the equation shown in the equation 4 obtained by solving the equation of the equation 3 with respect to α. It is possible to correctly evaluate the responsiveness of the liquid crystal by solving by the numerical solution method, and further contribute to the improvement of the liquid crystal material.

液晶の粘性係数の測定方法としては、ＴＮ液晶セルの電気応答特性を使って、前記５つのパラメータを同時に動かして得た計算値と実測値とのフィッティングにより最適なパラメータ値を探す方法（非特許文献６）が知られている。なお、圧縮に係るパラメータη₁₂は、通常は無視してよいから、通常は同時に動かされるパラメータは４つである。又、回転粘性係数γ₁については、可動式の２つの表面に電圧を印加できる特殊な構造の回転粘性計を用いた測定方法（非特許文献７）が知られている。 As a method of measuring the viscosity coefficient of the liquid crystal, a method of searching for an optimum parameter value by fitting the calculated value obtained by moving the five parameters simultaneously with the actual measurement value using the electrical response characteristics of the TN liquid crystal cell (non-patented) Document 6) is known. Note that the parameter η ₁₂ related to compression is normally negligible, and therefore, normally four parameters are moved simultaneously. As for the rotational viscosity coefficient γ ₁ , a measuring method using a rotational viscometer with a special structure capable of applying a voltage to two movable surfaces (Non-Patent Document 7) is known.

然し、非特許文献６の測定方法では、同時に変化させるパラメータが４つと多く、計算に時間がかかる上、精度が低いという問題がある。又、非特許文献７の測定方法では、回転粘性係数γ₁しか測定できず、しかもその精度は不十分である。
一方、ホモジニアス配向の液晶セルを測定対象として、先ずオン応答特性を測定しその結果から回転粘性係数γ₁の値を決定し、次いでオフ応答特性を測定しその結果からミーソヴィッツのずれ粘性係数η₁、η₂の値を決定する測定方法（特許文献１）が提案されている。これによれば、他の粘性係数の影響が小さい電気光学的応答特性を用いて、先ず回転粘性係数を、次いでずれ粘性係数をフィッティングするから、測定精度が向上し、又、同時に変化させるパラメータが最大２個と少ないから計算時間を短縮できる。
S.Onda, T.Miyashita, T.Uchida: Asia Display 98 Proceedings(1998)p.1055 F.M.Leslie: Quart.J.Mech,Appl.Math.,19(1966)p.357 F.M.Leslie: Liquid Crystals(1968)p.365 J.L.Ericksen: Mol.Cryst.Liq.Cryst.(1969)p.153 C.Z.van Doorn: J.of Applied Physics,46,9(1975)p.3738 O.Cossalter, B.Carmer, D.A.Mlynsky: J.of Physics 2,At.Mol.Cluster Phys.Chem.Phys.Mech.Hydrodyn.Vol.6,No.12(1996)pp.1663-1669 K.Skarp, S.T.Lagerwall, B.Stebler: ”Measurement of hydrodynamic parameters for nematic 5CB”,Molecular Crystal Liquid Crystal,Vol.60(1980)pp.215-236 特開2005−114647号公報 However, the measurement method of Non-Patent Document 6 has a problem that there are as many as four parameters to be changed at the same time, and calculation takes time and accuracy is low. Further, the measuring method of Non-Patent Document 7 can measure only the rotational viscosity coefficient γ ₁ , and its accuracy is insufficient.
On the other hand, as a measurement object liquid crystal cell having a homogeneous alignment, first on response characteristics were measured to determine the value of rotating viscosity coefficient gamma ₁ from the result, then off response characteristic measured from the results of Misovittsu deviation viscosity eta ₁ , Η ₂ has been proposed as a measurement method (Patent Document 1). According to this, since the rotational viscosity coefficient is first fitted and then the deviation viscosity coefficient is fitted using the electro-optic response characteristic that is less influenced by other viscosity coefficients, the measurement accuracy is improved, and the parameters to be changed simultaneously are The calculation time can be shortened because there are few at most.
S. Onda, T. Miyashita, T. Uchida: Asia Display 98 Proceedings (1998) p.1055 FMLeslie: Quart. J. Mech, Appl. Math., 19 (1966) p. 357 FMLeslie: Liquid Crystals (1968) p.365 JLEricksen: Mol.Cryst.Liq.Cryst. (1969) p.153 CZvan Doorn: J. of Applied Physics, 46, 9 (1975) p. 3738 O. Cossalter, B. Carmer, DAMlynsky: J. of Physics 2, At. Mol. Cluster Phys. Chem. Phys. Mech. Hydrodyn. Vol. 6, No. 12 (1996) pp. 1663-1669 K. Skarp, STLagerwall, B. Stebler: “Measurement of hydrodynamic parameters for nematic 5CB”, Molecular Crystal Liquid Crystal, Vol. 60 (1980) pp.215-236 JP-A-2005-114647

前記特許文献１の測定方法では、初期配向構造がホモジニアス構造（平行配向構造）である液晶セルを測定対象としている。この場合、オン応答特性は低電圧から高電圧への切換えにより液晶分子が平行配向状態から垂直配向状態へ変化するときの透過率の応答特性であるから、駆動モードがＰ型である液晶セル（Ｐ型液晶セル）の粘性係数を測定していることになる。一方、駆動モードがＮ型である液晶セル（Ｎ型液晶セル）の場合は、電圧印加により液晶分子を垂直配向状態から平行配向状態へ変化させる。そこで、特許文献１記載の測定方法において、初期配向構造がホメオトロピック構造（垂直配向構造）である液晶セルを測定対象とすることで、Ｎ型液晶セルの粘性係数も測定できるであろうと予想した。 In the measurement method of Patent Document 1, a liquid crystal cell whose initial alignment structure is a homogeneous structure (parallel alignment structure) is a measurement object. In this case, since the ON response characteristic is a response characteristic of transmittance when the liquid crystal molecules change from the parallel alignment state to the vertical alignment state by switching from the low voltage to the high voltage, the liquid crystal cell having a P-type driving mode ( That is, the viscosity coefficient of the P-type liquid crystal cell is measured. On the other hand, in the case of a liquid crystal cell whose driving mode is N-type (N-type liquid crystal cell), liquid crystal molecules are changed from a vertical alignment state to a parallel alignment state by applying a voltage. Therefore, in the measurement method described in Patent Document 1, it was expected that the viscosity coefficient of an N-type liquid crystal cell could be measured by measuring a liquid crystal cell whose initial alignment structure is a homeotropic structure (vertical alignment structure). .

然しながら、ホメオトロピック構造の液晶セルのオン応答特性を測定する場合、次のような問題があることが判った。
ホメオトロピック構造の液晶セルのオン応答特性を正しく測定するためには、図２に示すような初期垂直配向状態の液晶セルにステップ状に電圧を印加し、平行配向状態へ遷移させる過渡期において、図３に示すような望ましい配向分布（液晶分子５の初期からの配向変化量がセル厚中心部位を極大として基板６に近い部位ほど小さくなるような配向分布）が維持されねばならない。 However, it has been found that there are the following problems when measuring the on-response characteristics of a liquid crystal cell having a homeotropic structure.
In order to correctly measure the on-response characteristics of a liquid crystal cell having a homeotropic structure, a voltage is applied stepwise to the liquid crystal cell in the initial vertical alignment state as shown in FIG. A desirable orientation distribution as shown in FIG. 3 (an orientation distribution in which the amount of change in orientation of the liquid crystal molecules 5 from the initial stage is maximized at the cell thickness center portion and closer to the substrate 6) must be maintained.

ところが、ホメオトロピック構造の液晶セルでは、ステップ状に急に電圧を印加されると、内部の液晶の乱れが生じ、平衡配向状態への過渡期に、図４に示すような望ましくない配向分布（液晶分子５の初期からの配向変化量がセル厚中心部位以外の部位にも極値をもつような配向分布）が現れてしまい、正しい測定結果が得られない場合が多々あるという問題があった。 However, in a liquid crystal cell having a homeotropic structure, when a voltage is suddenly applied in a stepped manner, the internal liquid crystal is disturbed, and an undesirable orientation distribution (as shown in FIG. There is a problem in that there are many cases in which a correct measurement result cannot be obtained because the orientation change amount from the initial stage of the liquid crystal molecules 5 has an extreme value in parts other than the cell thickness center part. .

本発明は、上記問題を解決し、Ｎ型液晶セルの回転粘性係数γ₁並びにミーソヴィッツのずれ粘性係数η₁及びη₂を容易に且つ高精度に測定し得る、液晶の粘性係数測定方法及び装置を提供することを目的とする。 The present invention solves the above-described problems and can easily and accurately measure the rotational viscosity coefficient γ ₁ of the N-type liquid crystal cell and the Missowitz shear viscosity coefficients η ₁ and η _2. The purpose is to provide.

本発明者らは、上記問題を解決するために鋭意検討した結果、次の知見を得た。
1)オン応答特性の測定に用いる昇段電圧（低側から高側へ階段状に変化する電圧）が適正電圧範囲を有するものであれば、図４のような望ましくない過渡配向状態を回避でき、常に図３のような望ましい過渡配向状態になる。
2)前記適正電圧範囲は、測定用試料を挟む２枚の直交偏光子の何れか１枚と試料との光軸同士を平行として電圧範囲を変えて応答を観測したときに該観測中の光漏れがなくなる電圧範囲に対応する。 As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
1) If the rising voltage used to measure the ON response characteristics (voltage that changes stepwise from the low side to the high side) has an appropriate voltage range, the undesirable transient orientation state shown in FIG. 4 can be avoided. The desired transient orientation state as shown in FIG. 3 is always obtained.
2) The appropriate voltage range is the light under observation when the response is observed by changing the voltage range with either one of the two orthogonal polarizers sandwiching the measurement sample and the sample parallel to each other. Corresponds to the voltage range where there is no leakage.

3)オフ応答特性の測定に用いる降段電圧（高側から低側へ階段状に変化する電圧）の電圧範囲は昇段電圧の適正電圧範囲に関わらず適宜に設定することができる。
本発明は、上記知見に基づいて成されたものであり、その要旨は以下の通りである。
[請求項１] 応答特性のエリクセン-レスリー理論値と実測値とのフィッティングにより粘性係数の値を決定する液晶の粘性係数の測定方法において、ホメオトロピック構造の液晶セルを試料とし、先ず該試料の両側に配置した２枚の直交偏光子の何れか１枚と前記試料との光軸同士を平行にした状態で、印加した昇段電圧に対する応答の観測を１回或いは前記昇段電圧の電圧範囲を変えて複数回行なって、前記観測中の光漏れが無くなる電圧範囲を決定し、次いで前記光軸同士を45°程度交叉させた状態で、前記決定した電圧範囲を有する昇段電圧を用いてオン応答特性を測定しその結果から回転粘性係数γ₁の値を決定し、次いで所定の電圧範囲を有する降段電圧を用いてオフ応答特性を測定しその結果からミーソヴィッツのずれ粘性係数η₁、η₂の値を決定することを特徴とする液晶の粘性係数測定方法。 3) The voltage range of the step-down voltage (voltage that changes stepwise from the high side to the low side) used for measuring the off-response characteristics can be set as appropriate regardless of the appropriate voltage range of the step-up voltage.
This invention is made | formed based on the said knowledge, The summary is as follows.
[Claim 1] In a method for measuring a viscosity coefficient of a liquid crystal in which the value of the viscosity coefficient is determined by fitting an Erichsen-Leslie theoretical value of response characteristics to an actual measurement value, a liquid crystal cell having a homeotropic structure is used as a sample. While observing the response to the applied step-up voltage once or changing the voltage range of the step-up voltage in a state where the optical axes of one of the two orthogonal polarizers arranged on both sides and the sample are parallel to each other. A plurality of times to determine a voltage range in which light leakage during the observation is eliminated, and then the on-response characteristics using the rising voltage having the determined voltage range in a state where the optical axes are crossed by about 45 ° measured results to determine the value of rotating viscosity coefficient gamma ₁ from then clear the response characteristic from then result measurements Misovittsu shift viscosity eta ₁ using a usual voltage having a predetermined voltage range liquid crystal viscosity coefficient measurement method characterized by determining the eta ₂ values.

[請求項２] 応答特性のエリクセン-レスリー理論値と実測値とのフィッティングにより粘性係数の値を決定する液晶の粘性係数の測定装置であって、液晶セルを照射する光源と、前記液晶セルへの印加電圧値を高低の双方向に切替え可能な電圧源と、前記高低双方の電圧値を設定可能な電圧設定手段と、前記液晶セルとこれを挟む直交偏光子との光軸同士の相対角度を設定可能な光軸角度設定手段と、前記光源から出て前記液晶セルを透過した光の透過率データを前記電圧源の切替え時点から100μs以下の時間間隔で採取可能な透過率測定器と、前記電圧源の切替え方向が高方向のときの前記透過率測定器の採取データに回転粘性係数γ₁を種々変えて計算した前記理論値をフィッティングさせてγ₁の値を決定し且つ前記電圧源の切替え方向が低方向のときの前記透過率の採取データにミーソヴィッツのずれ粘性係数η₁及びη₂を種々変えγ₁は前記決定した値に固定して計算した前記理論値をフィッティングさせてη₁、η₂の値を決定する演算を実行可能な演算器とを有することを特徴とする液晶の粘性係数測定装置。 [Claim 2] A device for measuring a viscosity coefficient of a liquid crystal that determines a value of a viscosity coefficient by fitting an Eriksen-Leslie theoretical value of response characteristics and an actual measurement value, the light source for irradiating the liquid crystal cell, and the liquid crystal cell The voltage source capable of switching the applied voltage value between high and low, voltage setting means capable of setting both the high and low voltage values, and the relative angle between the optical axes of the liquid crystal cell and the orthogonal polarizer sandwiching it An optical axis angle setting means capable of setting, a transmittance measuring device capable of collecting transmittance data of light that has exited from the light source and transmitted through the liquid crystal cell at a time interval of 100 μs or less from the time of switching of the voltage source, The value of γ ₁ is determined by fitting the theoretical value calculated by variously changing the rotational viscosity coefficient γ ₁ to the collected data of the transmittance measuring device when the switching direction of the voltage source is high, and the voltage source Low switching direction Said variously changed gamma ₁ deviations viscosity coefficient eta ₁ and eta ₂ of Misovittsu the collection data of the transmittance by fitting the theoretical values calculated by fixing the value of the determined eta ₁ when the direction, of eta ₂ An apparatus for measuring a viscosity coefficient of liquid crystal, comprising: an arithmetic unit capable of executing an operation for determining a value.

本発明によれば、Ｎ型液晶セルの回転粘性係数及びずれ粘性係数を高精度に且つ高能率に測定することができる。 According to the present invention, the rotational viscosity coefficient and shear viscosity coefficient of an N-type liquid crystal cell can be measured with high accuracy and high efficiency.

本発明では、測定用試料にホメオトロピック構造（垂直配向構造）の液晶セルを用いる。特に液晶分子長軸が基板面の法線と０°±30°以内の角度をなすように初期配向を調整した試料が望ましい。尚、液晶分子同士の方位角（液晶分子長軸の基板面への正射影像が基板面内の基準軸となす角度）の差は絶対値で10°以内（好ましくは２°以内）とするのがよい。又、試料のセル厚（セルギャップ）は、光学特性の変化を複屈折特性の変化や透過率の変化として検出するために、２〜10μｍとするのが好ましい。 In the present invention, a liquid crystal cell having a homeotropic structure (vertical alignment structure) is used as a measurement sample. In particular, a sample in which the initial alignment is adjusted so that the major axis of the liquid crystal molecule forms an angle within 0 ° ± 30 ° with the normal of the substrate surface is desirable. The difference between the azimuth angles of liquid crystal molecules (the angle formed by the orthogonal projection image of the liquid crystal molecule major axis to the substrate surface and the reference axis in the substrate surface) is within 10 ° (preferably within 2 °) in absolute value. It is good. The cell thickness (cell gap) of the sample is preferably 2 to 10 μm in order to detect a change in optical characteristics as a change in birefringence characteristics or a change in transmittance.

本発明では、試料のオン応答特性を測定する第１ステップに先立ち、第０ステップとして、第１ステップに用いる昇段電圧の適正電圧範囲を決定する。昇段電圧及び降段電圧における高側の電圧は周期10ms以下の方形波の交番電圧を用いるのがよい。低側の電圧についても同様であるが、降段電圧の場合には低側として０Vの一定電圧を用いることが可能である。 In the present invention, prior to the first step of measuring the on-response characteristics of the sample, the appropriate voltage range of the step-up voltage used for the first step is determined as the zeroth step. It is preferable to use a square-wave alternating voltage with a period of 10 ms or less as the higher voltage in the rising voltage and falling voltage. The same applies to the low-side voltage. However, in the case of the step-down voltage, a constant voltage of 0 V can be used as the low-side voltage.

前記適正電圧範囲は、次のようにして決定する。
(1)（始め：）試料とこれを挟む２枚の直交偏光子との光軸同士の配置を、２枚の直交偏光子のうち１枚の光軸と試料の光軸とが平行となるように設定する（⇒(2)へ）。尚、偏光子の光軸とは透過軸を指し、試料の光軸とは液晶分子長軸の最尤方位角方向に沿った軸を指す。 The appropriate voltage range is determined as follows.
(1) (Initial): The arrangement of the optical axes of the sample and two orthogonal polarizers sandwiching the sample is such that one of the two orthogonal polarizers is parallel to the optical axis of the sample. (⇒ Go to (2)). The optical axis of the polarizer indicates the transmission axis, and the optical axis of the sample indicates the axis along the maximum likelihood azimuth direction of the liquid crystal molecule long axis.

(2)低側と高側の電圧を適宜の値（例えば低側を０V、高側を10V）とした昇段電圧を印加する（⇒(3)へ）。
(3)昇段電圧の印加に対する応答を観測し、この観測中に光漏れが有るか否かを判定する（⇒判定結果が「有」ならば(4)へ、「無」ならば(5)へ）。
(4)低側及び／又は高側の電圧値を変えた昇段電圧（大抵の場合、低側の値を増加側に変更するだけでよい）を印加する（⇒(3)へ）。 (2) Apply a step-up voltage with appropriate values for the low-side and high-side voltages (for example, the low-side voltage is 0 V and the high-side voltage is 10 V) (see (3)).
(3) Observe the response to the application of ascending voltage and determine whether there is light leakage during this observation (⇒ If the judgment result is “Yes”, go to (4), if it is “No”, (5) What).
(4) Apply an ascending voltage with the low-side and / or high-side voltage values changed (in most cases, it is only necessary to change the low-side value to the increasing side) (⇒ to (3)).

(5)その時の昇段電圧の電圧範囲を適正電圧範囲として採用する（：終わり）。
次に、第１ステップとして、第０ステップで求めた適正電圧範囲を有する昇段電圧を用いて、オン応答特性を測定しその結果から回転粘性係数γ₁の値を決定する。オン応答特性は、オン切替え時点（低側から高側への切替え時点）からの液晶の透過率の経時変化で表される。オン応答特性の測定においては、試料とこれを挟む２枚の直交偏光子との光軸同士の配置を、２枚の直交偏光子のうち１枚の光軸（透過軸）と試料の光軸（液晶分子の最尤方位角方向に沿った軸）とが45°程度（好ましくは45°±20°以内）となるように設定した状態で測定を行う（この点はオフ応答特性の測定においても同じである）。 (5) The voltage range of the rising voltage at that time is adopted as the appropriate voltage range (: end).
Next, as a first step, the on-response characteristic is measured using the rising voltage having the appropriate voltage range obtained in the zeroth step, and the value of the rotational viscosity coefficient γ ₁ is determined from the result. The on-response characteristic is represented by a change with time in the transmittance of the liquid crystal from the on-switching point (the switching point from the low side to the high side). In the measurement of the on-response characteristics, the arrangement of the optical axes of the sample and two orthogonal polarizers sandwiching the sample is made by changing the optical axis (transmission axis) of one of the two orthogonal polarizers and the optical axis of the sample. Measurement is performed in a state in which the (axis along the maximum likelihood azimuth angle direction of the liquid crystal molecules) is set to about 45 ° (preferably within 45 ° ± 20 °). Is the same).

オン応答特性の実験値（実測値と同義）とフィッティングさせる理論値を計算する際には、回転粘性係数γ₁のみを種々変化させて計算する。他の粘性係数は初期値として他の液晶材料の値（文献所載の一般的な値）を入れておく。この計算方法は、前記数１及び数２に示した式を数値的に解き、その経時的に変化する配向の計算結果を用いて透過率の経時変化を計算するものである。尚、試料を直交偏光子で挟んだ場合、透過率Ｔの計算には式：Ｔ＝sin²（π×δ/λ₀）を用いる。ここで、λ₀は測定する光の波長、δは液晶セルのリタデーションである。 When calculating the experimental value of the on-response characteristic (synonymous with the actual measurement value) and the theoretical value to be fitted, only the rotational viscosity coefficient γ ₁ is changed in various ways. As other viscosity coefficients, values of other liquid crystal materials (general values described in literatures) are set as initial values. In this calculation method, the equations shown in Equations 1 and 2 are numerically solved, and the change in transmittance with time is calculated using the calculation result of the orientation that changes over time. When the sample is sandwiched between orthogonal polarizers, the equation: T = sin ² (π × δ / λ ₀ ) is used to calculate the transmittance T. Here, λ ₀ is the wavelength of light to be measured, and δ is the retardation of the liquid crystal cell.

ホメオトロピック構造の液晶セルでは、オン応答特性に対し、回転粘性係数γ₁の影響が大きく、他の粘性係数の影響は無視できる程度に小さいので、オン応答特性の実験値と計算値とをフィッティングさせることにより高精度に回転粘性係数γ₁を測定することができる。
次に、第２ステップとして、降段電圧を用いてオフ応答特性を測定しその結果からミーソヴィッツのずれ粘性係数η₁、η₂の値を決定する。オフ応答特性は、オフ切替え時点（高側から低側への切替え時点）からの液晶の透過率の経時変化で表される。ここで用いる降段電圧の所定の電圧範囲は、第１ステップでの適正電圧範囲と同じものであってもよく、又、それとは異なるものを適宜設定してもよい。というのは試料に降段電圧を印加して液晶分子を寝た状態から起き上がらせる時には、図４のような望ましくない過渡配向状態をとることはないからである。 In a homeotropic liquid crystal cell, the rotational viscosity coefficient γ ₁ has a large influence on the on-response characteristics, and the influence of other viscosity coefficients is so small that it can be ignored. By doing so, the rotational viscosity coefficient γ ₁ can be measured with high accuracy.
Next, as a second step, the off-response characteristics are measured using the step-down voltage, and the values of Misovitz's shear viscosity coefficients η ₁ and η ₂ are determined from the results. The off-response characteristic is represented by a change over time in the transmittance of the liquid crystal from the off-switching point (the switching point from the high side to the low side). The predetermined voltage range of the step-down voltage used here may be the same as the appropriate voltage range in the first step, or may be set appropriately differently. This is because when the step-down voltage is applied to the sample to raise the liquid crystal molecules from the sleeping state, the undesirable transient alignment state as shown in FIG. 4 is not taken.

オフ応答特性の実験値とフィッティングさせる理論値を計算する際には、ミーソヴィッツのずれ粘性係数η₁、η₂を種々変化させて、第１ステップと同様の方法で計算する。尚、回転粘性係数γ₁は第１ステップで決定した値に固定し、又、ねじれ粘性係数η₃、圧縮粘性係数η₁₂は第１ステップと同じ値を入れておけばよい。
オフ応答特性に対して、ねじれ粘性係数η₃、圧縮粘性係数η₁₂の影響は、無視し得る程度に小さいから、第２ステップでのフィッティングにより、ずれ粘性係数η₁、η₂を高精度に測定することができる。 When calculating the experimental value of the off-response characteristic and the theoretical value to be fitted, the calculation is performed in the same manner as in the first step while variously changing the Misovitz viscosity coefficients η ₁ and η ₂ . Incidentally, the rotational viscosity coefficient gamma ₁ is fixed to the value determined in the first step, also twist viscosity coefficient eta _3, compression viscosity coefficient eta ₁₂ may be by putting the same value as the first step.
Against off response characteristic, twist viscosity coefficient eta _3, the influence of the compression viscosity coefficient eta _12, because small negligibly, by fitting in the second step, the deviation coefficient of viscosity eta _1, eta ₂ with high precision Can be measured.

又、応答特性の計算において、同時に変化させるパラメータが、特許文献１によるP型液晶セルの測定の場合と同様、第１ステップでは１個、第２ステップでは２個と、特許文献１よりも前の技術におけるフィッティングでの４個に比べて少ないから、計算を２ステップに分けたことによる時間増分を考慮しても、計算時間は格段に短縮する。
尚、第１ステップで仮に用いたη₁、η₂が、第２ステップの結果と大きく異なる場合は、第２ステップで得られたη₁、η₂を用い、再度第１ステップの手続と第２ステップの手続を行うことにより、高精度化が可能である。 In the calculation of response characteristics, the parameters to be changed simultaneously are one in the first step and two in the second step, as in the case of the measurement of the P-type liquid crystal cell according to Patent Document 1. Therefore, even if the time increment due to the division of the calculation into two steps is taken into consideration, the calculation time is remarkably shortened.
If η ₁ and η ₂ temporarily used in the first step are significantly different from the result of the second step, η ₁ and η ₂ obtained in the second step are used, and the procedure of the first step is repeated. High accuracy can be achieved by performing a two-step procedure.

本発明の測定方法を効率的に実施するためには、例えば図５に示すような測定装置を用いるのが好適である。図５において、１は試料（液晶セル）10を照射する光源である。光源１は白色光源、単色光源等々のいかなる光源でもよい。試料10の入射側、出射側には偏光子11、12が互いの光軸を直交として（即ち直交偏光子として）配置される。８は光軸角度設定手段であり、これは、第０ステップから第１ステップに移る際に、試料10と偏光子11（又は12）との光軸同士の相対角度を０°（平行）から45°程度へと変更するためのものであり、図５では直交偏光子11、12をその面の中心を通る法線の回りに回転可能に保持するホルダで構成したが、ホルダの保持対象を直交偏光子11、12に代えて試料10としてもよい。 In order to efficiently carry out the measuring method of the present invention, it is preferable to use a measuring apparatus as shown in FIG. 5, for example. In FIG. 5, reference numeral 1 denotes a light source that irradiates a sample (liquid crystal cell) 10. The light source 1 may be any light source such as a white light source or a monochromatic light source. Polarizers 11 and 12 are arranged on the incident side and the emission side of the sample 10 with their optical axes orthogonal to each other (that is, as orthogonal polarizers). Reference numeral 8 denotes an optical axis angle setting means, which changes the relative angle between the optical axes of the sample 10 and the polarizer 11 (or 12) from 0 ° (parallel) when moving from the 0th step to the 1st step. In FIG. 5, the orthogonal polarizers 11 and 12 are constituted by holders that are rotatably held around a normal passing through the center of the surface. The sample 10 may be used in place of the orthogonal polarizers 11 and 12.

２は電圧源であり、これは、試料10への印加電圧値を高低の双方向に切替え可能なものであればよく、通常の２値電源及びスイッチング素子を用いて容易に構成できる。尚、第０ステップで昇段電圧の適正電圧範囲を探すのに便利なように、電圧源２の高低双方の電圧値を適当な範囲内で自在に設定（又は変更）し得る電圧設定手段７を備えている。
３は透過率測定器であり、これは、光源１から出て偏光子11、液晶セル10、偏光子12を順次透過した光の透過率データを、電圧源２の電圧値の高低双方向への切替え時点から100μs以下の時間間隔で採取可能なものが好ましい。透過率データの採取時間間隔が100μsよりも大きいと、透過率の時間分解能が粗くなってフィッティングの精度が低下する場合があるからである。透過率測定器３は、例えばフォトマルチプライアやフォトダイオード等の光検出器及び、ＡＤ変換器、デジタルオシロスコープ等を組合わせて構成できる。 Reference numeral 2 denotes a voltage source, and any voltage source can be used as long as the voltage applied to the sample 10 can be switched between high and low, and can be easily configured using a normal binary power source and a switching element. In order to conveniently find the appropriate voltage range of the step-up voltage in the 0th step, voltage setting means 7 that can freely set (or change) the voltage values of both the high and low voltages of the voltage source 2 within an appropriate range. I have.
Reference numeral 3 denotes a transmittance measuring device, which transmits the transmittance data of light emitted from the light source 1 and sequentially transmitted through the polarizer 11, the liquid crystal cell 10, and the polarizer 12 in both directions of the voltage value of the voltage source 2. A sample that can be collected at a time interval of 100 μs or less from the time of switching is selected. This is because if the transmission time interval of the transmittance data is larger than 100 μs, the time resolution of the transmittance becomes coarse and the fitting accuracy may be lowered. The transmittance measuring device 3 can be configured by combining, for example, a photodetector such as a photomultiplier or a photodiode, an AD converter, a digital oscilloscope, and the like.

４は演算器であり、これには、通常のコンピュータに、透過率測定器３の採取した透過率データに対して本発明に係る２ステップのフィッティング演算を行う機能を搭載したものが好ましく用いうる。この２ステップのフィッティング演算は、上述のように、電圧源２の切替え方向が高方向のとき（第１ステップ）の透過率データに、回転粘性係数γ₁を種々変えて計算した計算値をフィッティングさせてγ₁の値を決定し、更に、電圧源２の切替え方向が低方向のとき（第２ステップ）の透過率データに、ミーソヴィッツのずれ粘性係数η₁及びη₂を種々変えγ₁は第１ステップで決定した値に固定して計算した計算値をフィッティングさせてη₁、η₂の値を決定するというものである。 Reference numeral 4 denotes an arithmetic unit. For this, a computer equipped with a function for performing a two-step fitting operation according to the present invention on the transmittance data collected by the transmittance measuring device 3 can be preferably used. . As described above, this two-step fitting calculation is performed by fitting calculated values obtained by changing the rotational viscosity coefficient γ ₁ in various ways to the transmittance data when the switching direction of the voltage source 2 is high (first step). Then, the value of γ ₁ is determined. Further, the transmission coefficient data when the switching direction of the voltage source 2 is low (second step) is changed to various misovich viscosity coefficients η ₁ and η ₂ to obtain γ ₁ By fitting the calculated values fixed to the values determined in the first step, the values of η ₁ and η ₂ are determined.

尚、電圧源２の切替えタイミング、及び透過率測定器３のデータ採取開始タイミングは、同期制御することが好ましい。この同期制御は、演算器４としてコンピュータを用いる場合はそのコンピュータで行うようにしてもよく、或いは別途適宜に設けた同期制御手段により行ってもよい。 The switching timing of the voltage source 2 and the data collection start timing of the transmittance measuring device 3 are preferably controlled synchronously. In the case where a computer is used as the computing unit 4, this synchronization control may be performed by the computer, or may be performed by a separately provided synchronization control means.

［本発明例］
液晶材料にMLC2038（メルク社製）、配向膜にJALS-204（JSR社製）を用いて作製したホメオトロピック構造の液晶セル（セル厚＝2.5μm）を測定用試料とし、図５のように構成した測定装置を用いて、ステップ０として、試料と２枚の直交偏光子のうちの何れか１枚との光軸同士を平行とし、電圧範囲を表１の条件Ａとした昇段電圧を印加し、応答を観測すると、図６（ｂ）に示すように、大きな光漏れが現れた。次いで電圧範囲を表１の条件Ｂに変え、応答を観測すると、図７（ｂ）に示すように、僅かではあるがやはり光漏れが現れた。次いで電圧範囲を表１の条件Ｃに変え、応答を観測すると、図１（ｂ）に示すように、光漏れは現れなかった。 [Example of the present invention]
A liquid crystal cell with a homeotropic structure (cell thickness = 2.5 μm) manufactured using MLC2038 (manufactured by Merck) as the liquid crystal material and JALS-204 (manufactured by JSR) as the alignment film is used as a measurement sample, as shown in FIG. Using the configured measuring apparatus, as step 0, an ascending voltage is applied with the optical axis of the sample and any one of the two orthogonal polarizers parallel to each other and the voltage range set as condition A in Table 1 When the response was observed, a large light leak appeared as shown in FIG. Next, when the voltage range was changed to the condition B in Table 1 and the response was observed, light leakage still appeared as shown in FIG. 7B. Next, when the voltage range was changed to Condition C in Table 1 and the response was observed, no light leakage appeared as shown in FIG.

そこで、ステップ１として、試料と２枚の直交偏光子のうちの何れか１枚との光軸同士を45°に交叉させ、電圧範囲を表１の条件Ｃとした昇段電圧を印加し、図１（ａ）に示す透過率データ（オン応答特性曲線）を得、これと計算曲線とのフィッティングからγ₁＝134cP（１cP（センチポアズ）＝１mPa・s）を決定し、次いで、ステップ２として、電圧範囲を表１の条件Ａとした降段電圧を印加して得たオフ応答特性曲線（図示省略）と計算曲線とのフィッティングからη₁＝229cP、η₂＝27cPを決定した。 Therefore, as Step 1, the optical axis of the sample and one of the two orthogonal polarizers is crossed at 45 °, and a step-up voltage with a voltage range of condition C in Table 1 is applied. 1 (a) is obtained, and γ ₁ = 134 cP ( ₁ cP (centipoise) = 1 mPa · s) is determined from the fitting of the transmission data (on-response characteristic curve) and the calculated curve. Η ₁ = 229 cP and η ₂ = 27 cP were determined from fitting of an off-response characteristic curve (not shown) obtained by applying a step-down voltage with the voltage range as condition A in Table 1 and a calculated curve.

更に、同じ液晶材料を用いて、ホメオトロピック構造とはフローの影響が相異なるハイブリッド配向構造（HAN型）の液晶セルを作製し、その応答特性の実験値と、粘性係数に前記決定した値を用いた計算値とを比較し、良好な一致を得て、前記決定した値が正しいものであることが検証された。
［比較例(1)］
前記本発明例と同じ試料及び同じ測定装置を用い、試料と２枚の直交偏光子のうちの１枚との光軸同士を45°に交叉させ、電圧範囲を表１の条件Ａ（前記本発明例のステップ０において大きい光漏れが現れた条件）とした昇段電圧を印加し、得られた透過率データ（オン応答特性曲線）を図６（ａ）に示す。これと計算曲線とのフィッティングにおける最小二乗誤差は前記本発明例の場合に比べてかなり大きく、このフィッティングから求めたγ₁は、γ₁＝1000cPであり、前記本発明例で決定された正しい値とは全く異なる値であった。 Furthermore, using the same liquid crystal material, a liquid crystal cell with a hybrid alignment structure (HAN type), which has a flow effect different from that of the homeotropic structure, was prepared, and the experimental value of the response characteristic and the value determined above for the viscosity coefficient were used. The calculated values used were compared to obtain a good agreement, and it was verified that the determined values were correct.
[Comparative Example (1)]
Using the same sample and the same measuring apparatus as the present invention example, the optical axes of the sample and one of the two orthogonal polarizers are crossed at 45 °, and the voltage range is set to the condition A in Table 1 (the book FIG. 6 (a) shows the transmittance data (on response characteristic curve) obtained by applying a step-up voltage as a condition in which large light leakage appears in Step 0 of the inventive example. The least square error in the fitting of this and the calculated curve is considerably larger than that in the case of the present invention example, and γ ₁ obtained from this fitting is γ ₁ = 1000 cP, which is the correct value determined in the above example of the present invention. It was a completely different value.

［比較例(2)］
前記本発明例と同じ試料及び同じ測定装置を用い、試料と２枚の直交偏光子のうちの１枚との光軸同士を45°に交叉させ、電圧範囲を表１の条件Ｂ（前記本発明例のステップ０において僅かな光漏れが現れた条件）とした昇段電圧を印加し、得られた透過率データ（オン応答特性曲線）を図６（ａ）に示す。これと計算曲線とのフィッティングにおける最小二乗誤差は前記本発明例の場合と同程度に小さいにも拘らず、このフィッティングから求めたγ₁は、γ₁＝300cPであり、前記本発明例で決定された正しい値からは大きく外れた値であった。 [Comparative Example (2)]
Using the same sample and the same measuring apparatus as the present invention example, the optical axes of the sample and one of the two orthogonal polarizers are crossed at 45 °, and the voltage range is the condition B in Table 1 (the book FIG. 6A shows transmittance data (on-response characteristic curve) obtained by applying a step-up voltage, which is a condition in which slight light leakage appears in Step 0 of the inventive example. Although the least square error in the fitting of this and the calculated curve is as small as in the case of the present invention example, γ ₁ obtained from this fitting is γ ₁ = 300 cP and is determined in the above example of the present invention. The value was far from the correct value.

このように、ステップ０で光漏れが僅かにでも現れた時の電圧範囲を用いたステップ１でのオン応答特性曲線からでは、回転粘性係数を正しく求めることはできないのである。 Thus, the rotational viscosity coefficient cannot be obtained correctly from the on-response characteristic curve in step 1 using the voltage range when even a slight light leakage appears in step 0.

本発明例における透過率測定データを示すグラフである。It is a graph which shows the transmittance | permeability measurement data in the example of this invention. ホメオトロピック構造の液晶セルの１例を示す模式図である。It is a schematic diagram which shows an example of the liquid crystal cell of a homeotropic structure. 望ましい過渡配向状態の１例を示す模式図である。It is a schematic diagram which shows an example of a desirable transient orientation state. 望ましくない過渡配向状態の１例を示す模式図である。It is a schematic diagram which shows one example of the undesirable transient orientation state. 本発明に係る測定装置の１例を示す模式図である。It is a schematic diagram which shows an example of the measuring apparatus which concerns on this invention. 比較例(1)における透過率測定データを示すグラフである。It is a graph which shows the transmittance | permeability measurement data in a comparative example (1). 比較例(2)における透過率測定データを示すグラフである。It is a graph which shows the transmittance | permeability measurement data in a comparative example (2). ミーソヴィッツ粘性係数と流れ（フロー）状態との対応関係を示す説明図である。It is explanatory drawing which shows the correspondence of a Misovitz viscosity coefficient and a flow (flow) state.

符号の説明Explanation of symbols

１光源
２電圧源
３透過率測定器
４演算器
５液晶分子
６基板（相手基板との対面側に配向膜を有する）
７電圧設定手段
８光軸角度設定手段
10 試料（液晶セル）
11、12 偏光子（直交偏光子） DESCRIPTION OF SYMBOLS 1 Light source 2 Voltage source 3 Transmittance measuring device 4 Arithmetic unit 5 Liquid crystal molecule 6 Substrate (having an alignment film on the side facing the counterpart substrate)
7 Voltage setting means 8 Optical axis angle setting means
10 samples (liquid crystal cell)
11, 12 Polarizer (Orthogonal Polarizer)

Claims

応答特性のエリクセン-レスリー理論値と実測値とのフィッティングにより粘性係数の値を決定する液晶の粘性係数の測定方法において、ホメオトロピック構造の液晶セルを試料とし、先ず該試料の両側に配置した２枚の直交偏光子の何れか１枚と前記試料との光軸同士を平行にした状態で、印加した昇段電圧に対する応答の観測を１回或いは前記昇段電圧の電圧範囲を変えて複数回行なって、前記観測中の光漏れが無くなる電圧範囲を決定し、次いで前記光軸同士を45°程度交叉させた状態で、前記決定した電圧範囲を有する昇段電圧を用いてオン応答特性を測定しその結果から回転粘性係数γ₁の値を決定し、次いで所定の電圧範囲を有する降段電圧を用いてオフ応答特性を測定しその結果からミーソヴィッツのずれ粘性係数η₁、η₂の値を決定することを特徴とする液晶の粘性係数測定方法。 In a method for measuring the viscosity coefficient of liquid crystal, in which the value of the viscosity coefficient is determined by fitting the Eriksen-Leslie theoretical value of the response characteristic with the actual measurement value, a liquid crystal cell having a homeotropic structure is used as a sample, and firstly arranged on both sides of the sample 2 The response to the applied step-up voltage is observed once or a plurality of times while changing the voltage range of the step-up voltage in a state where the optical axes of any one of the orthogonal polarizers and the sample are parallel to each other. The voltage range in which light leakage during the observation is eliminated is determined, and then the on-response characteristics are measured using the rising voltage having the determined voltage range in a state where the optical axes are crossed by about 45 °. rotation value of viscosity coefficient gamma ₁ determines, then Misovittsu shift viscosity eta ₁ from the measured result of the off-response characteristics using a usual voltage having a predetermined voltage range, the value of eta ₂ from LCD viscosity measurement method, characterized by a constant.

応答特性のエリクセン-レスリー理論値と実測値とのフィッティングにより粘性係数の値を決定する液晶の粘性係数の測定装置であって、液晶セルを照射する光源と、前記液晶セルへの印加電圧値を高低の双方向に切替え可能な電圧源と、前記高低双方の電圧値を設定可能な電圧設定手段と、前記液晶セルとこれを挟む直交偏光子との光軸同士の相対角度を設定可能な光軸角度設定手段と、前記光源から出て前記液晶セルを透過した光の透過率データを前記電圧源の切替え時点から100μs以下の時間間隔で採取可能な透過率測定器と、前記電圧源の切替え方向が高方向のときの前記透過率測定器の採取データに回転粘性係数γ₁を種々変えて計算した前記理論値をフィッティングさせてγ₁の値を決定し且つ前記電圧源の切替え方向が低方向のときの前記透過率の採取データにミーソヴィッツのずれ粘性係数η₁及びη₂を種々変えγ₁は前記決定した値に固定して計算した前記理論値をフィッティングさせてη₁、η₂の値を決定する演算を実行可能な演算器とを有することを特徴とする液晶の粘性係数測定装置。 A device for measuring the viscosity coefficient of a liquid crystal that determines the value of the viscosity coefficient by fitting an Eriksen-Leslie theoretical value of a response characteristic and an actual measurement value, and a light source that irradiates the liquid crystal cell, and a voltage value applied to the liquid crystal cell. Light capable of setting a relative angle between optical axes of a voltage source that can be switched between high and low, voltage setting means capable of setting both the high and low voltage values, and the liquid crystal cell and an orthogonal polarizer sandwiching the liquid crystal cell. Axis angle setting means, a transmittance measuring device capable of collecting transmittance data of light emitted from the light source and transmitted through the liquid crystal cell at a time interval of 100 μs or less from the time of switching of the voltage source, and switching of the voltage source direction switching direction low high direction the rotational viscosity coefficient gamma ₁ to data collected transmittance meter variously changed by fitting the theoretical values calculated to determine the value of gamma ₁ and the voltage source when the When direction The transmittance of the collection variously changed gamma ₁ deviations viscosity coefficient eta ₁ and eta ₂ of Misovittsu the data the theoretical value eta ₁ by fitting calculated by fixing the value of the determined, to determine the value of eta ₂ An apparatus for measuring a viscosity coefficient of a liquid crystal, comprising: an arithmetic unit capable of executing a calculation.