JP3143271B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ST for performing color display.
The present invention relates to an N (super twisted nematic) liquid crystal display device.

[0002]

2. Description of the Related Art FIG. 12 is a sectional view showing the structure of a conventional liquid crystal display device 21. The liquid crystal display device 21 is an STN type liquid crystal display device that performs color display, and the liquid crystal display device 2
2, first and second polarizing plates 23 and 24, retardation plate 25,
It includes a transflective plate 26 and a light source 27. A liquid crystal display element 22 is disposed between the first and second polarizers 23 and 24, and a retardation plate 25 is disposed between the first polarizer 23 and the liquid crystal display element 22. A semi-transmissive reflection plate 26 and a light source 27 are provided on the side of the second polarizing plate 24 opposite to the liquid crystal display element 22.
Are arranged in this order. The retardation value of the retardation plate 25 is selected to be about 560 nm.

[0003] The liquid crystal display element 22 comprises a translucent substrate 2.
8, 29, color filter 30, transparent electrodes 31, 32,
It includes alignment films 33 and 34 and a liquid crystal layer 35. For example, one of the light-transmitting substrates 28 and 29 made of glass has a color filter 3 on one surface 28 a of the substrate 28.
0, a transparent electrode 31 and an alignment film 33 are formed in this order, and a transparent electrode 32 and an alignment film 34 are formed on one surface 29a of the substrate 29.
Are formed in this order. For example, ITO (Indium Tin O
The transparent electrodes 31 and 32 realized by xide) are formed in a plurality of strips parallel to each other. The substrates 28, 29 are arranged so that the surfaces 28a, 29a of the substrates 28, 29 face each other and the transparent electrodes 31, 32 are orthogonal to each other. An STN type liquid crystal layer 3 is provided between the substrates 28 and 29.
5 are interposed. The product d · Δn of the thickness d of the liquid crystal layer 35 and the refractive index anisotropy Δn of the liquid crystal molecules is 0.75 μm to 0.85
It is selected in the range of μm.

[0004]

In the STN-type liquid crystal display device 21 described above, a display by multiplex driving is performed by utilizing a steep rise of a voltage-transmittance curve. Further, coloring caused by the birefringence effect of the liquid crystal molecules is compensated by the retardation plate 25, and color display is performed using the color filter 30. The light from the light source 27 passes through the semi-transmissive reflection plate 26 and the second polarizing plate 24 and passes through the liquid crystal display element 22.
Incident on. The incident light is controlled by the liquid crystal molecules of the liquid crystal layer 35, passes through the liquid crystal display element 22, and is
The light exits through the first polarizing plate 23. Also, the first
Light incident from the polarizing plate 23 side is reflected by the semi-transmissive reflecting plate 26 and is emitted again from the first polarizing plate 23 side. Also at this time, the light incident on the liquid crystal layer 35 is emitted while being controlled by the liquid crystal molecules of the liquid crystal layer 35. In the liquid crystal display device 21,
Although such transmissive display and reflective display are performed as needed, there is a problem that the black purity is low and a good contrast ratio cannot be obtained.

[0005] It is an object of the present invention to provide a liquid crystal display device which is excellent in black purity, and which can provide high contrast and stable color display.

[0006]

SUMMARY OF THE INVENTION The present invention provides a first polarizing plate,
A liquid crystal display element, a second polarizing plate, a transflective plate and a light source are arranged in this order, and an optical compensating member is provided between any one of the first and second polarizing plates and the liquid crystal display element. Disposed, the liquid crystal display element is a super-twisted nematic liquid crystal layer interposed between at least a pair of light transmissive substrates, a transparent electrode formed on the liquid crystal layer side surface of the light transmissive substrate, and an alignment film And a color filter, the liquid crystal display device is a normally white type, and the optical compensation member includes a first retardation plate and a second retardation plate, and the retardation of each retardation plate Both the retardation values are selected in the range of 400 nm to 470 nm, and the crossing angles of the slow axes of the retarders are 35 ° to 5 °.
5 °, the product d · Δn of the thickness d of the liquid crystal layer of the liquid crystal display element and the refractive index anisotropy Δn of the liquid crystal molecules is selected in the range of 0.80 μm to 0.94 μm, The liquid crystal display device is characterized in that the twist angle of the liquid crystal molecules between the substrates is set in a range of 240 ° to 260 °.

[0007]

According to the present invention, the liquid crystal display device comprises a first polarizing plate, a liquid crystal display element, a second polarizing plate, a transflective plate and a light source arranged in this order. The first and second retardation plates, which are optical compensating members, are arranged between one of the polarizing plates and the liquid crystal display element, and are configured as a normally white type. The retardation values of the first and second retardation plates are both 400 nm to 47 nm.
The crossing angle of the slow axes of the retarders is set in the range of 35 ° to 55 °. The liquid crystal display element further includes a super-twisted nematic liquid crystal layer in which liquid crystal molecules are twisted by 240 ° to 260 ° between the pair of translucent substrates. A color filter, a transparent electrode, and an alignment film are formed on the liquid crystal layer side surface of one of the substrates, and a transparent electrode and an alignment film are formed on the liquid crystal layer side surface of the other substrate.
The product d · Δn of the thickness d of the liquid crystal layer of the liquid crystal display element and the refractive index anisotropy Δn of the liquid crystal molecules is 0.80 μm to 0.94 μm.
m.

[0008] The liquid crystal display device selectively performs, as necessary, a transmissive display in which display is performed by transmitting light from a light source and a reflective display in which display is performed by reflecting ambient light. Yes, in the liquid crystal display device, excellent black purity,
It was confirmed that a color display having a high contrast ratio was obtained.

[0009]

FIG. 1 is a sectional view showing the structure of a normally white liquid crystal display device 1 according to a first embodiment of the present invention. The liquid crystal display device 1 is an STN type liquid crystal display device that performs color display, and includes a liquid crystal display element 2, first and second polarizing plates 3, 4, first and second retardation plates 5a, 5b,
It includes a transflector 6 and a light source 7. For example, a neutral gray type having a single transmittance of 44.5% and a degree of polarization of 97.8% was selected and manufactured by Nitto Denko Corporation under the trade name "F".
The liquid crystal display element 2 is arranged between the first and second polarizing plates 3 and 4 realized by “1225 DUN”. Also, the first and second polarizers 3 and the liquid crystal display element 2 are provided between the first and second polarizers 3 and 2.
Phase difference plates 5a and 5b are arranged, and a semi-transmissive reflection plate 6 and a light source 7 are arranged in this order on a side of the second polarizing plate 4 opposite to the liquid crystal display element 2.

A first retardation plate 5a disposed on the first polarizing plate 3 side and a second retardation plate 5 disposed on the liquid crystal display element 2 side
Both b are realized by, for example, uniaxially stretching a polymer material such as polycarbonate into a film shape. For example, the thickness is selected to be about 50 μm, and the retardation value is selected to be in the range of 400 nm to 470 nm.
In the present embodiment, the retardation values of the first and second retardation plates 5a and 5b are both set to 430 nm. As the transflective plate 6, a non-directional material having a transmittance of, for example, 2.5% is selected. For example, a transflective plate obtained by depositing aluminum on a low-gloss polyester film is used. Further, the light source 7 is realized by, for example, a cold cathode tube.

The liquid crystal display element 2 includes a light transmitting substrate 8,
9, a color filter 10, transparent electrodes 11 and 12, alignment films 13 and 14, and a liquid crystal layer 15. For example, of the light transmitting substrates 8 and 9 realized by glass, for example, the substrate 8
The color filter 10 and the transparent electrode 1
1. An alignment film 13 is formed in this order, and a transparent electrode 12 and an alignment film 14 are formed in this order on one surface 9a of the substrate 9. The color filter 10 includes a plurality of filters having red (R), green (G), and blue (B) spectral characteristics. The plurality of filters are realized by, for example, a polyester-based anion-type resin, and are formed by, for example, an electrodeposition method. The transparent electrodes 11 and 12 are realized by, for example, ITO, and are formed in a plurality of strips parallel to each other. The alignment films 13 and 14 are realized by, for example, a polyimide resin.
The surface is subjected to an alignment treatment such as a rubbing treatment.
The substrates 8 and 9 are arranged so that the surfaces 8a and 9a face each other, and a liquid crystal material serving as a liquid crystal layer 15 is injected between the substrates 8 and 9 and sealed. The substrates 8 and 9 are arranged so that the longitudinal directions of the transparent electrodes 11 and 12 formed on the substrates 8 and 9 are orthogonal.

As the liquid crystal material, for example, 30% of trans liquid crystal, 30% of cyanophenylcyclohexane liquid crystal, 10% of biphenylcyclohexane liquid crystal, 10% of dicyclohexane liquid crystal, and 20% of other liquid crystal
And the addition of a levorotatory chiral dopant. Here, the twist angle φ of the liquid crystal molecules between the substrates 8 and 9 is set in the range of 240 ° to 260 °, and further, the product d of the thickness d of the liquid crystal layer 15 and the refractive index anisotropy Δn of the liquid crystal molecules.・ Δn is 0.80 μm or more
It is selected in the range of 0.94 μm. In the present embodiment, the twist angle φ is 240 °, and the thickness d of the liquid crystal layer 15 is 6.
0 μm, and the refractive index anisotropy Δn of the liquid crystal molecules is 0.1
As 40, the d · Δn was set to 0.84 μm.

FIG. 2 is a diagram showing the positional relationship between the components of the liquid crystal display device 1. As shown in FIG. The solid line P1 indicates the alignment axis of the liquid crystal molecules closest to the light transmitting substrate 8, the solid line P2 indicates the alignment axis of the liquid crystal molecules closest to the light transmitting substrate 9, and the solid line P3
Indicates the absorption axis of the first polarizing plate 3, the solid line P4 indicates the absorption axis of the second polarizing plate 4, the solid line P5 indicates the slow axis of the first retardation plate 5a, and the solid line P6 indicates the second retardation plate. 5b shows the slow axis.

The angle α indicates the angle between the orientation axis P1 of the liquid crystal molecules closest to the light transmitting substrate 8 and the absorption axis P3 of the first polarizer 3, and the angle β indicates the liquid crystal molecules closest to the light transmitting substrate 9. And the angle γ is the orientation axis P1 of the liquid crystal molecules closest to the translucent substrate 8 and the slow axis P5 of the first retardation plate 5a. And the angle δ is the angle between the alignment axis P1 of the liquid crystal molecules closest to the translucent substrate 8 and the slow axis P6 of the second retardation plate 5b. The angle θ indicates the angle between the slow axis P5 of the first retardation plate 5a and the slow axis P6 of the second retardation plate 5b, that is, the intersection angle θ. An angle formed between the alignment axis P1 of the liquid crystal molecules in contact with the liquid crystal molecules and the alignment axis P2 of the liquid crystal molecules closest to the translucent substrate 9, that is, the twist angle φ is shown.
In this example, the angles were set as shown in Table 1 below. The intersection angle θ is arbitrarily set within a range of 35 ° to 55 °.

[0015]

[Table 1]

The liquid crystal display device 1 configured as described above
Is a method in which a transmissive display in which display is performed by transmitting light from the light source 7 and a reflective display in which display is performed by reflecting ambient light are selected as necessary. That is, the light source 7
Is incident on the liquid crystal display element 2 after passing through the transflective plate 6 and the second polarizer 4. The incident light is applied to the liquid crystal layer 1.
The light passes through the liquid crystal display element 2 under the control of the liquid crystal molecules 5 and passes through the first and second retardation plates 5 a and 5 b and the first polarizing plate 3 and is emitted. Light incident from the first polarizing plate 3 side is reflected by the semi-transmissive reflecting plate 6 and exits again from the first polarizing plate 3 side. Also at this time, the light incident on the liquid crystal layer 15 is controlled by the liquid crystal molecules of the liquid crystal layer 15 and emitted. Such a transmissive display and a reflective display are selected as necessary, for example, a transmissive display in a dark place and a reflective display in a bright place.

The liquid crystal display device 1 is a normally white liquid crystal display device, and displays images by subtractive color mixture. That is, when all the pixels on which the red (R), green (G), and blue (B) filters are formed are turned off, light incident on all the pixels is transmitted, and white display is performed. In addition, when a voltage is applied to all the pixels to turn them on, the incident light is cut off and black display is performed.
Further, when a voltage is applied only to the pixel on which the red (R) filter is formed and the pixel is turned on, only light incident on the pixel on which the red (R) filter is formed is blocked,
Since the light that has entered the pixels on which the green (G) and blue (B) filters are formed passes, the display is cyan (C). Similarly, when only the pixel on which the green (G) filter is formed is turned on, the display becomes magenta (M), and when only the pixel on which the blue (B) filter is formed is turned on, yellow (YE) is displayed. Is displayed.

FIG. 3 shows the first and second retardation plates 5a, 5a.
9 is a graph showing a relationship between a retardation value of b and a contrast ratio. This is because the first and second retardation plates 5
The crossing angle θ between the slow axes of a and 5b is 45 °, the retardation values are the same, the twist angle θ of the liquid crystal molecules of the liquid crystal layer 15 is 240 °, and d · Δn is 0 °. 0.84 μm (d = 6.0 μm, Δn = 0.140). The light source 7 is obtained by performing a transmission type display by multiplex driving with a 1/240 duty and a 1/13 bias at a temperature of 25 ° C. using a CIE standard light source C (JIS Z8105). . The measurement of the contrast ratio was performed in a dark room where the influence of ambient light can be ignored. Since the higher the black purity, the higher the contrast, the area where the contrast ratio becomes 3 or more was defined as the area where good display was obtained. FIG. 3 shows that when the retardation values of the first and second retardation plates 5a and 5b are selected in the range of 400 nm to 470 nm, a display having a contrast ratio of 3 or more can be obtained.

FIG. 4 shows the first and second retardation plates 5a and 5a.
13B is a graph showing the relationship between the intersection angle θ between the slow axes of b and the contrast ratio. This means that the retardation value of each of the first and second retardation plates 5a and 5b is 430n.
m, the twist angle φ of the liquid crystal molecules is 240 °, and d
Δn is 0.84 μm (d = 6.0 μm, Δn = 0.1
40). Further, it is obtained by performing transmissive display by multiplex driving under the same conditions as described above. From FIG. 4, the intersection angle θ is 35 °.
It can be seen that when the angle is set in the range of 55 °, a display having a contrast ratio of 3 or more can be obtained.

FIG. 5 shows the twist angle φ of the liquid crystal molecules in the liquid crystal layer 15.
6 is a graph showing a relationship between the contrast ratio and the contrast ratio. This is because the retardation value of each of the first and second retardation plates 5a and 5b is 430 nm, the intersection angle θ between the slow axes is 45 °, and d · Δn is 0.84 μm.
(D = 6.0 μm, Δm = 0.140). Further, it is obtained by performing transmissive display by multiplex driving under the same conditions as described above. FIG. 5 shows that when the twist angle φ is set in the range of 240 ° to 260 °, a display having a contrast ratio of 3 or more can be obtained.

FIG. 6 is a graph showing the relationship between d · Δn and the contrast ratio. This means that the mutual retardation values of the first and second retardation plates 5a and 5b are 430 nm.
The intersection angle θ between the slow axes is set to 45 °, the twist angle φ of the liquid crystal molecules of the liquid crystal layer 15 is set to 240 °, and d =
It is constant at 6.0 μm, and Δn is 0.133 to 0.157.
It was obtained by changing Further, it is obtained by performing transmissive display by multiplex driving under the same conditions as described above. As shown in FIG.
It can be seen that when the thickness is selected in the range of 80 μm to 0.94 μm, a display having a contrast ratio of 3 or more can be obtained.

The first and second retardation plates 5 described above
a, 5b retardation value, intersection angle θ, twist angle φ,
Since d · Δn acts in relation to each other, if any one of the values is out of the set range, a display with excellent black purity cannot be obtained, and a stable high-contrast color display cannot be obtained. However, it suffices that each is set within the setting range. For example, the first and second retardation plates 5
Even if the retardation values a and 5b do not match, a display with excellent black purity can be obtained, and a high-contrast and stable color display can be obtained.

Next, the evaluation results of the display characteristics of the liquid crystal display device 1 of this embodiment will be described. First, at a temperature of 25 ° C., the liquid crystal display device 1 is set at a duty of 1/240,
The liquid crystal display device 1 is driven at a bias of 1/13, and the contrast ratio between the 12 o'clock and 6 o'clock directions and the 9 o'clock and 3 o'clock directions when the liquid crystal display device 1 is viewed from directly above, that is, the front-back direction and the left-right direction of the liquid crystal display device 1 are shown. The result of the measurement will be described. Here, the light source 7 is the CIE standard light source C (JIS
Z8105), and the measurement of the contrast ratio was performed in a dark room where the influence of ambient light can be ignored. FIG. 7 is a graph showing the contrast ratio in the direction of 12: 00-6 o'clock, and FIG. 8 is a graph showing the contrast ratio in the direction of 9-3: 00. Solid lines L1 and L3 show the results of the liquid crystal display device 1 of the first embodiment, and broken lines L2 and L4 show the results of the liquid crystal display device of the first comparative example. The liquid crystal display device of the first comparative example is a conventional liquid crystal display device using one retardation plate as shown in FIG. 12, wherein the retardation value of the retardation plate is 560 nm, and the twist angle of liquid crystal molecules is φ is 2
40 °, and d · Δn is 0.76 μm (d = 6.0 μm).
m, Δn = 0.126). 7 and 8, the liquid crystal display device 1 of the present example has a higher contrast ratio in both the 12: 00-6 o'clock direction and the 9 o'clock-3 o'clock direction than the liquid crystal display device of the first comparative example, and the viewing angle. It was confirmed that a display having excellent characteristics was obtained.

Next, under the same conditions, red (R),
The results of measuring the brightness (Y) of the display color when a voltage is applied to all the pixels on which the green (G) and blue (B) filters are formed and the pixel is turned on (black display) are shown below. It is shown in Table 2. Here, the display brightness (Y) is CIE1
931 XYZ color system (JIS Z8701- (198
It is a value (Y) representing lightness among the three stimulus values (X, Y, Z) of the light source color in 2)). Since the brightness (Y) of the liquid crystal display device 1 of the present example is smaller than that of the first comparative example, it can be seen that the black color of the display color is excellent.

[0025]

[Table 2]

FIG. 9 is a graph showing a chromaticity diagram of the XYZ color system. A solid line L5 shows the result of the color range of the liquid crystal display device 1 measured under the same conditions as described above. here,
x and y are values obtained based on the following equations (1) and (2) from the tristimulus values (X, Y, Z) in the above-described CIE1931 XYZ color system, and both are values indicating chromaticity. is there. The point W is a whiteness point (x = 0.31)
7, y = 0.329).

[0027]

(Equation 1)

In the liquid crystal display device 1 of this embodiment, as described above, cyan (C), magenta (M), and yellow (YE) are displayed by subtractive color mixture. Points C, M, and YE in FIG. 9 indicate cyan (C), magenta (M), and yellow (YE) in the liquid crystal display device 1.
Are respectively shown. This is similarly obtained in the liquid crystal display device described as the first comparative example, and it has been confirmed that the color range of the liquid crystal display device 1 of the present embodiment is substantially the same as the color range of the conventional liquid crystal display device. Was.

FIG. 10 is a graph showing the contrast ratio in the 12: 00-6 o'clock direction of the liquid crystal display device according to the second embodiment of the present invention, and FIG. 11 shows the contrast ratio in the 9--3 o'clock direction. It is a graph. The liquid crystal display device of the second embodiment is substantially the same as the liquid crystal display device 1 of the first embodiment, except that the twist angle φ of the liquid crystal molecules is set to 260 °. Solid lines L6 and L8 show the results of the liquid crystal display device of the second embodiment, and broken lines L7 and L9 show the results of the second comparative example. The second comparative example is configured in substantially the same manner as the first comparative example described above, except that the twist angle φ of the liquid crystal molecules is set to 260 °. From FIGS. 10 and 11, it can be seen that the liquid crystal display device of the second embodiment has a higher contrast ratio in any direction than the liquid crystal display device of the second comparative example, and a display with excellent viewing angle characteristics can be obtained. confirmed.

Also, in the second embodiment, the same brightness (Y) as in the first embodiment can be obtained, and the black color of the display color is superior to that of the first and second comparative examples. confirmed. Further, it was confirmed that a display in a color range equivalent to that of the first embodiment was obtained. Note that the results of the second embodiment are also obtained by performing transmissive display by multiplex driving under the same conditions as in the first embodiment.

In the first and second embodiments, the first
Although the example in which the first and second retardation plates 5a and 5b are disposed between the polarizing plate 3 and the liquid crystal display element 2 has been described, the example in which the first and second retardation plates 5a and 5b are disposed between the second polarizing plate 4 and the liquid crystal display element 2 is also described. It belongs to the scope of the present invention.

[0032]

As described above, according to the present invention, in the normally white and transflective liquid crystal display device, the retardation values of the first and second retardation plates are both 400 nm or less.
The crossing angle between the slow axes of the retarders is set in the range of 35 ° to 55 °. The twist angle of the liquid crystal molecules is set in the range of 240 ° to 260 °, and the product d · Δn of the thickness d of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal molecules is 0.80 μm to 0.94 μm. Selected in the range. Accordingly, a high-contrast color display with excellent black purity and a display with excellent viewing angle characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device 1 according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between components of the liquid crystal display device 1;

FIG. 3 is a graph showing a relationship between retardation values of first and second retardation plates 5a and 5b and a contrast ratio.

FIG. 4 is a graph showing a relationship between a crossing angle θ of a slow axis of first and second retardation plates 5a and 5b and a contrast ratio.

FIG. 5 is a graph showing a relationship between a twist angle φ of liquid crystal molecules of a liquid crystal layer 15 and a contrast ratio.

FIG. 6 is a graph showing a relationship between d · Δn and a contrast ratio.

FIG. 7 is a graph showing a contrast ratio of the liquid crystal display device 1 in the direction of 12 o'clock to 6 o'clock.

FIG. 8 is a graph showing a contrast ratio in the 9 o'clock to 3 o'clock direction of the liquid crystal display device 1.

FIG. 9 is a graph showing chromaticity of the XYZ color system of the liquid crystal display device 1;

FIG. 10 is a graph showing a contrast ratio in the direction of 12 o'clock to 6 o'clock of the liquid crystal display device according to the second embodiment of the present invention.

FIG. 11 shows a 9 o'clock -3 of the liquid crystal display device of the second embodiment.
It is a graph which shows the contrast ratio of a time direction.

FIG. 12 is a cross-sectional view illustrating a configuration of a conventional liquid crystal display device 21.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal display element 3 1st polarizing plate 4 2nd polarizing plate 5a 1st retardation plate 5b 2nd retardation plate 6 Semi-transmissive reflective plate 7 Light source 8, 9 Translucent substrate 10 Color filter 11, 12 Transparent electrodes 13, 14 Alignment film 15 Liquid crystal layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-54216 (JP, A) JP-A-5-27229 (JP, A) JP-A-5-66399 (JP, A) JP-A-4- 282613 (JP, A) JP-A-2-19833 (JP, A) JP-A-5-27234 (JP, A) JP-A-3-269412 (JP, A) JP-A-5-27233 (JP, A) JP-A-5-27216 (JP, A) JP-A-5-27217 (JP, A) JP-A-5-66384 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1335 610

Claims (1)

(57) [Claims] 1. A first polarizing plate, a liquid crystal display element, a second polarizing plate, a semi-transmissive reflecting plate and a light source are arranged in this order, and either one of the first and second polarizing plates and the liquid crystal are arranged. An optical compensating member is disposed between the display device and the liquid crystal display device. In a liquid crystal display device including a formed transparent electrode, an alignment film, and a color filter, the liquid crystal display device is a normally white type, and the optical compensating member includes a first retardation plate and a second retardation. The retardation value of each retardation plate is 40
The intersection angle of the slow axes of the retarders is set in the range of 35 ° to 55 °. The thickness d of the liquid crystal layer of the liquid crystal display element and the refractive index of the liquid crystal molecules are selected. The product d · Δn with the anisotropy Δn is 0.80 μm to 0.94 μm
m, and a twist angle of the liquid crystal molecules between the substrates is set in a range of 240 ° to 260 °.