JP3237887B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible liquid crystal display device using a plastic film as a substrate.

[0002]

2. Description of the Related Art Conventionally, this type of liquid crystal display device mainly uses a TN (twisted nematic) liquid crystal cell. This is between 9 substrates with transparent electrodes.
It comprises a liquid crystal cell provided with a liquid crystal layer having a 0 degree helical structure, and a pair of upper and lower polarizers disposed so as to sandwich the liquid crystal cell. Although the TN type liquid crystal display element occupies the mainstream of the liquid crystal display element, the number of time divisions increases with the recent increase in the size of the dot matrix type liquid crystal display element. It is becoming difficult to cope with the time-sharing characteristics described above, and in particular, the time-sharing drive with a duty ratio of 1/64 or more causes a phenomenon that the display characteristics such as the contrast and the viewing angle deteriorate.

[0003] Therefore, recently, such a TN type has been replaced with an SBE (Super-twisted B).
irrefringence Effect) or ST
A liquid crystal display element having a mode display method called N (Super-Twisted Nematic) has been proposed,
It has already been put to practical use. It is oriented substantially horizontally with respect to the substrate between two substrates with transparent electrodes,
A liquid crystal cell having a structure twisted at a twist angle of not less than 360 degrees and not more than 360 degrees, for example, 180 degrees and having a liquid crystal layer exhibiting a positive dielectric anisotropy, and a pair of upper and lower members disposed so as to sandwich the liquid crystal cell And a polarizer.

In such a mode of display called SBE or STN, since the birefringence effect of the liquid crystal is used, Δn · d (Δn = ne−no, ne:
The color changes due to a slight change in the refractive index in the major axis direction of the liquid crystal molecules, no: the refractive index in the minor axis direction of the liquid crystal molecules, and d: the cell gap = the thickness of the liquid crystal layer. If there is a specific change, color unevenness occurs. For this reason, in this type of liquid crystal cell, polished glass plates or the like in which the cell gap can be easily controlled are used as the upper and lower substrates.

However, recently, in view of thinning, weight reduction, easiness of processing, and cost reduction of a liquid crystal display element, polyethylene terephthalate or polyether sulfone having a thickness of about 100 to 200 μm is used as a liquid crystal cell substrate. There is a tendency to use plastic films such as polysulfone, polycarbonate, and polyarylate, and technical developments for this purpose have been made.

In a liquid crystal display device using such a plastic film as a substrate, the transparent electrode line pattern is liable to be broken, which is one of the causes of a defect in an effective display area. Even during mounting by thermocompression bonding or the like, there is a defect that the lead electrode terminal of the transparent electrode on the substrate as the connection portion is disconnected. Such a defect in the case where a plastic film is used as a substrate is a main cause of lowering the yield as compared with the case of a liquid crystal display element using a glass substrate.

[0007]

As described above, in a liquid crystal display device using a plastic film as a substrate, the transparent electrode made of ITO or the like on the plastic film is
Compared to glass substrates, films are formed by a low-temperature process,
Various characteristics such as adhesion strength, friction resistance, and hardness of the transparent electrode on the plastic film tend to be inferior to those of the transparent electrode on the glass.

In addition, the flexibility of the plastic film causes curling or distortion, and the thermal dimensional stability of the substrate is poor, so that a disconnection failure easily occurs in a cell forming step after patterning the transparent electrode. In state. When the liquid crystal display element and the drive circuit board are connected via an anisotropic conductive film, they are connected by thermocompression bonding.
Approximately 100-170 ° C for plastic film as substrate
This heating is considered to be one cause of the disconnection of the transparent electrode at the connection part.

According to the present invention, when a plastic film is used as a substrate of a liquid crystal display element, disconnection in a cell of the liquid crystal display element and disconnection at a connection portion with a drive circuit board are prevented in consideration of properties of the plastic film itself. It is intended to provide means capable of performing such operations.

[0010]

In order to achieve the above object, the present invention provides a liquid crystal cell having a transparent electrode formed inside and a liquid crystal layer provided between a pair of oriented plastic film substrates. Wherein the plastic film is a non-stretched film formed by a melt extrusion method, wherein CL <PL / sin θ (C
L: maximum crack length, PL: pattern width of the transparent electrode,
θ: Machine direction of plastic film and transparent electrode
The line direction of the pattern of the transparent electrode formed on the plastic film is parallel to the machine direction of the plastic film or the largest crack generated in the machine direction is transparent. It is characterized in that it is formed to be inclined to an angle that does not cross the electrode pattern. In addition, the present invention
Is a plastic liquid crystal display device similar to the above.
The film is a non-stretched film formed by melt extrusion.
CL <PL / sinθ (CL: maximum turtle
Crack length, PL: pattern width of connection terminal of transparent electrode,
θ: The contact between the machine direction of the plastic film and the transparent electrode
Angle of the connection terminal pattern with the line direction)
The transparent electrode formed on the plastic film
The line direction of the pattern of the pole connection terminal is plastic
Parallel to machine direction of film or machine direction
The largest crack that has occurred in the transparent electrode pattern
It is characterized by being formed to be inclined to an angle that does not
It is.

Further, the present invention provides a similar liquid crystal display device, wherein the plastic film contains a filler,
Consists of a film formed by a uniaxial stretching method , and CL <
PL / sin θ (CL: length of the largest stretch mark, PL: transparent
Pattern width of bright electrode, θ: stretch of plastic film
Angle between the direction and the line direction of the transparent electrode pattern)
Satisfactorily, the line direction of the pattern of the transparent electrode formed on the plastic film is parallel to the stretching direction of the plastic film or the most in the stretching direction.
It is characterized in that a large stretch mark is formed to be inclined to an angle that does not cross the pattern of the transparent electrode.
The present invention also provides a liquid crystal display device having the same
Plastic films contain fillers and can be used for uniaxial stretching.
CL <PL / sin
θ (CL: length of maximum stretch mark, PL: connection of transparent electrode
Terminal pattern width, θ: stretch of plastic film
Direction and the line direction of the pattern of the connection terminal part of the transparent electrode
The plastic film so as to satisfy the angle
Pattern line of the connection terminal part of the transparent electrode formed on
The direction is parallel to the stretching direction of the plastic film
Alternatively, the largest stretching mark in the stretching direction is the pattern of the transparent electrode.
Be inclined to an angle that does not cross the
It is characterized by the following.

[0012]

According to the structure of the present invention, by optimizing the angle between the direction at the time of forming the plastic film substrate and the line direction of the transparent electrode pattern of the liquid crystal display element, the disconnection occurring inside the cell and the drive circuit can be prevented. It is possible to prevent disconnection occurring at a connection portion.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a liquid crystal display device to which the present invention is applied, and FIG. 2 is a plastic film used as a film substrate of the liquid crystal display device. The plastic film is wound as a roll film by extrusion molding. FIG.

In FIG. 1, a transparent electrode pattern (horizontal line) 3 for scanning is formed on an upper substrate 1, a transparent electrode pattern (vertical line) 4 for data is formed on a lower substrate 2, and alignment films 5 and 6 are further formed. It is formed and subjected to an alignment treatment. The pair of upper and lower substrates 1 and 2 are spaced apart and opposed to each other, sealed with a sealing agent 8 while maintaining a uniform interval by a gap agent 7, and a liquid crystal 9 is sealed therebetween to form a liquid crystal layer. A liquid crystal cell is configured. Upper and lower polarizers 10 and 11 are provided above and below the liquid crystal cell.

In a liquid crystal display device having such a structure, an example of a plastic film used for the upper and lower substrates 1 and 2 is to melt a material such as polyether sulfone, polysulfone, polyarylate, polycarbonate, polyolefin, or the like. It consists of an unstretched plastic film formed by an extrusion method, and the film is subjected to a surface treatment of a gas barrier film and a solvent-resistant film. Film produced by such a manufacturing method, not less than a little due to the flatness of the die, which is generally an extrusion slit,
As shown in FIG. 2, there is a fine uneven line-shaped defect called a die line L. The die line L is generated in the machine direction (MD), which is the winding direction of the film.

Referring to FIG. 4, the relationship between the occurrence of disconnection of the transparent electrode in the liquid crystal display portion of the liquid crystal display element and the die line L of the non-stretched plastic film will be described.
To explain one of the upper and lower substrates 1 and 2, the line direction of the pattern of the transparent electrode 3 formed on the substrate 1
When patterning is performed so as to be perpendicular to the MD direction of the roll film, a crack 12 called a crack is generated in a direction along the die line L, and the crack 12 traverses the pattern of the transparent electrode 3, As a result, the pattern of the transparent electrode 3 is broken, and the liquid crystal display element becomes defective in display.

FIG. 5 illustrates the occurrence of a connection failure with the drive circuit board at the connection terminal portion of the liquid crystal display element. In the connection terminal portion of the liquid crystal display element, the substrate 1 of the liquid crystal display element and the drive circuit board 13 are aligned with the extraction electrode terminal 3 a of the transparent electrode 3 on the substrate 1 and the connection terminal 14 on the drive circuit board 13. Then, the anisotropic conductive film 15 is interposed between the two substrates and connected by thermocompression bonding. 15a is a conductive particle.

In this case, if the pattern of the transparent electrode 3 is formed perpendicular to the MD direction of the roll film as the substrate 1, cracks 12 are generated in the connection portions along the die line L as in the case of FIG. . Since the crack 12 is in a direction crossing the lead electrode terminal 3 a of the transparent electrode 3, the connection of the transparent electrode 3
Is disconnected, and the liquid crystal display element causes display failure.

In the present invention, in order to prevent disconnection of the transparent electrode 3 of the substrate 1 caused by the crack 12,
As shown in FIG. 3, the pattern 3 of the transparent electrode 3 is formed on the substrate 1 so that the line direction of the transparent electrode pattern for the data signal and the scanning signal is parallel to the MD direction of the roll film. I do. With this configuration, even if a crack due to the die line L occurs in the MD direction of the roll film, the crack matches the direction of the pattern of the transparent electrode 3 and the probability of disconnection of the pattern of the transparent electrode 3 is extremely small. That is, the production yield of the liquid crystal display element is improved.

Here, the angle between the MD direction of the roll film and the line direction of the pattern of the transparent electrode formed on the film substrate is most preferably 0 degree, that is, parallel, but the angle due to the die line is not preferable. It is necessary that the angle of the crack generated does not cross the transparent electrode or the lead-out electrode terminal of the transparent electrode. In general, when the angle is 45 ° or less, it is possible to prevent the occurrence of disconnection. . Here, in order to reduce the probability of disconnection, let P _{L be} the pattern width of the transparent electrode, C _{L be the} maximum crack width to occur, and θ be the angle between the MD direction of the roll film and the line direction of the pattern. C _L <P _L / s
It is necessary to confirm in advance the maximum crack width to be generated so that in θ, and select θ that sufficiently satisfies the above equation.

The occurrence of cracks described in the above embodiment occurs at the connection portion with the drive circuit board 13 at the anisotropic conductive film 15.
This is remarkable in the portion of the lead electrode terminal 3a of the transparent electrode of the substrate 1 connected through the substrate. This is because the anisotropic conductive film 15 is connected by applying heat and pressure.
The line direction of the pattern of the lead electrode terminal 3a of the transparent electrode is preferably arranged in parallel with the MD direction, as in the above embodiment.
If it is less than or equal to °, it was confirmed that the occurrence of disconnection at the extraction electrode terminal 3a portion can be prevented.

Next, as a plastic film as a substrate used in the liquid crystal display element of the present invention, polyethylene terephthalate containing a fixed amount of a filler such as inorganic fine powder and formed by a uniaxial stretching method is used. An example of the case will be described. The configuration of the liquid crystal display device of the present invention is the same as that of FIG. A stretch-formed plastic film containing a filler generally has improved surface smoothness, slipperiness, solvent resistance, heat resistance, dimensional stability, and the like, and is easy to handle in the production of a liquid crystal display device. However, since it is optically anisotropic, an interference color is generated due to the birefringence effect, and the display quality is reduced.

Therefore, as shown in FIG. 8, the in-plane maximum refractive index direction of the plastic film, that is, the stretching direction (TD) is used.
Alternatively, the machine direction (MD) and the transmission axis (TR
The interference color is prevented by matching the direction of S) or the absorption axis (ABS). In this drawing, the twist (twist) angle of the liquid crystal is ω> 160 °, and it is actually 2 °.
40 °, and the angle between the upper and lower rubbing directions and the axial direction of the polarizing plate is β = 45 °.

In such a configuration, the angle α between the line direction of the pattern of the transparent electrode 3 and the extending direction of the substrate is shown in FIG.
15 ° as shown in FIG. 9A or 75 ° as shown in FIG.
° is selected. Here, as shown in FIG. 10, the filler portion 17 of the plastic film 1 used in the example has a fine needle-like stretch mark 16 in the stretch direction (TD) as shown in FIG.

The angle between the line direction of the pattern of the transparent electrode 3 and the extending direction of the substrate is 75 °.
In FIG. 9B, when a stress is applied by patterning, heat treatment for cell formation, mounting, etc., the stretch marks 1
The crack 16a generated along 6 crosses the pattern of the transparent electrode 3 (FIG. 11). As a result, the pattern of the transparent electrode 3 is broken, and the liquid crystal display element has a display defect.

At the connection (FIG. 12) between the lead electrode terminal 3a of the transparent electrode and the connection terminal 14 of the drive circuit board 13, an anisotropic conductive film 15 disposed between the two substrates is used.
When the connection was made by thermocompression bonding, a crack 16a was similarly formed in the connection portion along the stretch mark 16, resulting in disconnection and display failure.

In the present invention, the angle between the stretching direction (TD) of the plastic film and the line direction of the pattern of the transparent electrode 3 for the data signal and the scanning signal is 0 °, that is, parallel, so that the crack 16a is caused. Disconnection of the connecting portion can be eliminated. In this embodiment, as shown in FIG. 6, the angle is set to 15 °,
Usually, the line direction of the pattern of the transparent electrode 3 is set to 0 ° to 45 ° with respect to the stretching direction (TD) of the plastic film.
By patterning in such a way that the above-mentioned cracks occur, there is no occurrence of disconnection in the connection part.

When the pattern width of the transparent electrode is 0.3 mm, the stretching direction (T
D) When a crack 16a having a maximum width of about 0.4 mm is generated in the case of D), when the angle of the line direction of the pattern of the transparent electrode 3 with respect to the stretching direction (TD) of the plastic film is set to 45 °, disconnection occurs. Is very small, and the yield is improved. Here, in order to further reduce the probability of disconnection, the pattern width of the transparent electrode is set to P
_L , the maximum crack width is C _L , and the angle of the line direction of the pattern with respect to the stretching direction (TD) is θ, C _L <P _L
It is necessary to check in advance the maximum crack width to be generated so that / sin θ, and to select θ that sufficiently satisfies the above equation.

Another embodiment of the present invention will be described with reference to FIG. The configuration of the liquid crystal display device of the present invention is the same as that of FIG. 1. The plastic film used as the substrate of the liquid crystal display device contains a certain amount of a filler such as an inorganic fine powder, as in the above-described embodiment. It is a polyethylene terephthalate film formed by a stretching method.

In this embodiment, when the twist angle of the liquid crystal in FIG. 8 is 180 °, the angle α between the line direction of the transparent electrode pattern and the extending direction of the substrate is 45 °. When the angle is set at an angle close to 45 °, cracks 16 a generated along the stretch marks 16 are generated particularly when the drive circuit board 13 is connected by thermocompression bonding via the anisotropic conductive film 15. Penetrates the lead electrode terminal 3a of the transparent electrode, and as a result, the probability of occurrence of disconnection and display failure increases.

In the embodiment of the present invention, as shown in FIG. 7, the display portion line of the pattern of the transparent electrode 3 for the data signal and the scanning signal is bent so that the line direction of the extraction electrode terminal 3a corresponds to the extension direction of the plastic film. It is patterned in parallel directions. As described above, even if the crack 16a due to the extension mark 16 occurs in the extraction electrode terminal 3a of the transparent electrode of the connection portion, the direction of the crack 16a matches the line direction of the extraction electrode terminal 3a.
The probability of occurrence of disconnection of the extraction electrode terminal 3a due to 6a became extremely small, and the production yield of the liquid crystal display element was further improved.

In this embodiment, the case where the angle between the direction of the crack 16a and the line direction of the extraction electrode terminal 3a is set to 0 ° which is the most desirable angle has been described. As described above, if the angle formed by the line direction is 45 ° or less in consideration of the width of a normal transparent electrode, the size of a stretch mark, and the like, disconnection of the transparent electrode can be prevented.

[0033]

In the structure of the present invention, attention is paid to the fact that cracks generated in the process of manufacturing a plastic film used as a substrate of a liquid crystal display element cause disconnection of a transparent electrode and a lead electrode terminal of the transparent electrode. By setting the line direction of the transparent electrode and the lead electrode terminal of the transparent electrode to a predetermined direction with respect to the machine direction or the stretching direction of the plastic film, the patterning of the liquid crystal display element, cell formation, mounting process, and the The transparent electrode and the lead electrode terminal of the transparent electrode in connection etc. can greatly reduce the occurrence of disconnection due to cracks, improve the yield, and greatly improve the productivity of the liquid crystal display device using a plastic film substrate. It has the effect of making it possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a configuration example of a liquid crystal display element of the present invention.

FIG. 2 is a perspective view showing the appearance of a plastic film wound up as a roll film by extrusion molding.

FIG. 3 is a plan view showing an arrangement of transparent electrodes formed on the plastic film of FIG. 2, which is one of the embodiments of the present invention.

FIG. 4 is a plan view showing an example of an arrangement of a substrate using the plastic film of FIG. 2 and a transparent electrode formed on the substrate.

FIG. 5 is a plan view showing an example of an arrangement of connection portions between a substrate using the plastic film of FIG. 2 and a drive circuit substrate.

FIG. 6 is an explanatory diagram in a case where an angle between a stretching direction of a plastic film and a line direction of a pattern of a transparent electrode is set to 15 ° as an example of the present invention.

FIG. 7 is a diagram illustrating another embodiment of the present invention in which the display unit line of the pattern of the transparent electrode is bent so that the line direction of the extraction electrode terminal is patterned in a direction parallel to the stretching direction of the plastic film. FIG.

FIG. 8 is a liquid crystal showing an angular relationship such as a rubbing direction and a polarizing plate direction in a super-twisted nematic type having a twist angle of 240 ° using a plastic film containing a filler and formed by a uniaxial stretching method. FIG. 3 is an explanatory diagram of an example of a display element.

9A is an angle α between the line direction of the pattern of the transparent electrode and the extending direction of the substrate in the liquid crystal display device of FIG.
(B) is an explanatory view showing a case where the angle is set to 75 °.

FIG. 10 is an explanatory view showing fine needle-like stretch marks formed in the stretch direction of a stretch-formed plastic film containing a filler.

FIG. 11 is an explanatory diagram showing a relationship between a transparent electrode and a generated crack in the case of FIG. 9B.

FIG. 12 is an explanatory diagram showing a relationship between a connection portion of a lead electrode terminal of a transparent electrode and a crack in the case of FIG. 9B.

[Explanation of symbols]

 1, a substrate made of a plastic film 3, 4 a transparent electrode 3a an extraction electrode terminal 5, 6 an alignment film 7 a gap agent 8 a sealant 9 a liquid crystal 10, 11 a polarizing plate 12 a crack 13 a crack 13 a drive circuit board 14 a connection terminal 15 anisotropic Conductive conductive film 16 Stretch mark 16a Crack L Die line MD Machine direction

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Ota 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Masanori Itagaki 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-2-101429 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1343 G02F 1/1333 500

Claims (4)

(57) [Claims] 1. A liquid crystal layer is provided between a pair of plastic film substrates, each having a transparent electrode formed therein and subjected to an alignment treatment, to constitute a liquid crystal cell, and polarizing plates are disposed above and below the liquid crystal cell. In the liquid crystal display device, the plastic film is a non-stretched film formed by a melt extrusion method, and CL <PL / sin θ (C
L: maximum crack length, PL: pattern width of the transparent electrode,
θ: Machine direction of plastic film and transparent electrode
The line direction of the pattern of the transparent electrode formed on the plastic film is parallel to the machine direction of the plastic film or the largest crack generated in the machine direction is transparent. A liquid crystal display element formed to be inclined to an angle that does not cross an electrode pattern. 2. A liquid crystal layer is provided between a pair of plastic film substrates, each having a transparent electrode formed therein and subjected to an alignment treatment, to form a liquid crystal cell, and polarizing plates are disposed above and below the liquid crystal cell. In the liquid crystal display device, the plastic film is a non-stretched film formed by a melt extrusion method, and CL <PL / sin θ (C
L: Maximum crack length, PL: Connection terminal of transparent electrode
Pattern width, θ: machine direction of plastic film
Make a connection with the line direction of the pattern of the connection terminal of the transparent electrode.
Corner), the line direction of the pattern of the connection terminals of the transparent electrode formed on the plastic film is parallel to the machine direction of the plastic film or the largest crack generated in the machine direction is the pattern of the transparent electrode. the liquid crystal display element characterized by being formed to be inclined up to an angle without crossing the. 3. A liquid crystal cell is formed by providing a liquid crystal layer between a pair of plastic film substrates on which transparent electrodes are formed and subjected to alignment treatment, and polarizing plates are disposed above and below the liquid crystal cell. Wherein the plastic film contains a filler and is formed of a film formed by a uniaxial stretching method, and CL <PL / sinθ.
(CL: length of the largest stretch mark, PL: putter of transparent electrode
Width, θ: stretching direction of plastic film and transparent electrode
Angle of the pattern with the line direction)
, The line direction of the pattern of transparent electrodes formed on the plastic film is inclined until the angle without crossing the pattern of the transparent electrode maximum drawing marks parallel or the stretching direction to the extending direction of the plastic film A liquid crystal display element characterized by being formed by: 4. A liquid crystal layer is provided between a pair of plastic film substrates, each having a transparent electrode formed therein and subjected to an alignment treatment, to constitute a liquid crystal cell, and a polarizing plate is disposed above and below the liquid crystal cell. Wherein the plastic film contains a filler and is formed of a film formed by a uniaxial stretching method, and CL <PL / sinθ.
(CL: length of the largest stretch mark, PL: connection end of transparent electrode
Substrate pattern width, θ: How to stretch plastic film
Direction and the line direction of the pattern of the connection terminal of the transparent electrode.
So as to satisfy the angle), the line direction of the pattern of the connection terminal portions of the transparent electrode formed on the plastic film is parallel or the maximum drawing scars stretching direction transparent electrode with respect to the extending direction of the plastic film A liquid crystal display element formed to be inclined to an angle that does not cross the pattern.