JP5171201B2 - Liquid crystal display device and manufacturing method thereof - Google Patents

Description

The present invention relates to a liquid crystal display device and a manufacturing method thereof, such as TN (Twisted Nematic), ECB (Electrically Controlled Birefringence), STN (Super Twisted Nematic), IPS (In-Plane Switching), FFS (Fringe Field Switching), and the like. It can be applied to the liquid crystal mode. In the present invention, the lower surface of the alignment film is formed into a groove shape to give the alignment film an alignment ability in a specific direction, so that the productivity is higher than before, the liquid crystal has a sufficient alignment regulating force for liquid crystal, and high image quality. To be able to secure.

  Conventionally, in liquid crystal display panels of various liquid crystal modes such as TN, ECB, STN, IPS, and FFS, liquid crystal molecules are aligned in a certain direction by an alignment process, and various techniques have been proposed for this alignment process.

  The rubbing method, which is one of the alignment treatments, is the most frequently used method. After forming an alignment film of a polymer film made of polyimide or the like on a transparent electrode, a roller having a cloth attached to the surface is used. By rubbing the alignment film in a certain direction, the alignment film is imparted with alignment ability. However, in the rubbing method, rubbing debris or the like may adhere to the surface of the alignment film, and the TFT (thin film transistor) on the panel may be destroyed due to generation of static electricity.

  A so-called grating method, which is an alignment treatment method that replaces the rubbing method, forms a grating (groove) by processing the substrate surface, and aligns liquid crystal molecules using elastic strain caused by the grating. In the grating method, liquid crystal molecules are aligned in a parallel direction along the grating where the elastic free energy is most stable.

  Concerning this grating method, M. Nakamura et al. J. Appl. Phys, 52, 210 (1981) has a method of irradiating light to a layer of a photosensitive polymer to form a grating linearly at regular intervals. Proposed. Japanese Patent Application Laid-Open No. 11-218763 proposes a method of forming a grating-like alignment film by irradiating a photopolymerizable monomer on a substrate with light. Japanese Patent Application Laid-Open No. 2000-105380 proposes a method of forming a grating-like alignment film by applying a transfer technique to form a grating uneven shape on a resin coating film formed on a substrate surface. Yes.

  In this grating method, it is known that the anchoring energy can be controlled by adjusting the pitch and height of the grating (Y. Ohta et al., J.J. Appl. Phys., 43, 4310 (2004)).

  In the grating method, a method for improving the anchoring strength by utilizing the alignment regulating force of the alignment film material itself such as polyimide has been proposed. That is, Japanese Patent Application Laid-Open No. 5-88177 proposes a method of patterning photosensitive polyimide by a photolithography method, and Japanese Patent Application Laid-Open No. 8-114804 has a stripe shape in a predetermined direction. In the direction orthogonal to the direction, an uneven shape having a sawtooth surface shape is formed on the surface of the first alignment film, and an organic substance having aligned molecular axes is aligned on the first alignment film. A method of forming a film has been proposed. Japanese Patent Laid-Open No. 3-209220 proposes a method of applying an alignment material after photo-etching photosensitive glass to form a concavo-convex shape on the surface.

According to the grating method, contamination of the alignment film surface and generation of static electricity due to the rubbing method can be prevented.
JP-A-11-218763 JP 2000-105380 A JP-A-5-88177 JP-A-8-114804 Japanese Patent Laid-Open No. 3-209220 M. Nakamura et al. J. Appl. Phys, 52, 210 (1981) Y. Ohta et al., JJAppl. Phys., 43, 4310 (2004)

However, when the liquid crystal molecules are aligned by using only the elastic strain effect by the grating method, the ratio T of the groove pitch P to the height H (=) in order to obtain the anchoring strength equivalent to that of the rubbing method. It is necessary to increase H / P) sufficiently. Specifically, according to the above-mentioned Y. Ohta et al., JJAppl. Phys., 43, 4310 (2004), the azimuth anchoring strength (about 1 × 10 ⁻⁴⁾ equivalent to the alignment film subjected to the rubbing treatment. In order to obtain [J / m ² ]), the ratio T between the pitch P and the height H of the grooves needs to be 1 or more.

Therefore, since the pitch of the grating assumed in practical use is 1 [μm] or more, in order to ensure a sufficient azimuth anchoring strength, when merely aligning liquid crystal molecules using only the elastic strain effect, It is necessary to set the depth of the grating to 1 [μm] or more. Here, in the liquid crystal display panel, since the cell gap is about 3 to 4 [μm], when the depth of the grating is 1 [μm] or more, the periodic unevenness with the depth of 1 [μm] or more is the panel. It will be formed in the plane, and the retardation of the liquid crystal will change in the panel plane, making it difficult to ensure a sufficient contrast ratio. In consideration of productivity, it is desirable to secure a sufficient anchoring strength by setting the depth of the grating to less than 1 [μm].
In addition, the method using the alignment regulating force of an alignment film such as polyimide has the following problems. For example, in the case of the methods disclosed in JP-A-5-88177 and JP-A-3-209220, the alignment control force due to the unevenness of the surface is compared with the alignment control force due to the alignment film. Is oriented in the alignment direction of the molecular long axis of the alignment film. However, since the direction of the molecular long axis of the alignment film is not controlled, it cannot be said that a sufficient alignment regulating force is obtained as a whole.
In the case of the method of JP-A-8-114804, the molecular axis of the alignment film is controlled by the unevenness of the surface, but the alignment film is a photopolymerized liquid crystal material, which is reliable, There is a problem that it is not possible to use polyimide which is used in normal mass production with excellent mechanical properties. Further, since the alignment direction of the liquid crystal is parallel to the groove, there is a problem that the groove needs to be controlled to have a very complicated shape in order to control the pretilt angle. That is, it is necessary to form serrated irregularities in a direction substantially perpendicular to the stripe-shaped irregularities, and there is no choice but to use a method with extremely low productivity by using a stamp or the like.

According to one aspect of the present invention for solving the above problem, a pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, and molecules of the liquid crystal formed on at least one substrate And an electrode for applying a voltage to the liquid crystal formed on at least one substrate, the alignment layer comprising a base layer having a main surface in which a plurality of grooves are formed in parallel, and The coating film covers the main surface where the grooves are formed, and the coating film has a horizontal alignment ability to align the molecular long axis indicating the longitudinal direction of the molecules of the liquid crystal in parallel with no voltage applied to the main surface. Each of the grooves is a groove having a U-shaped cross section extending along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction. Has a covering rate of 50 percent on the main surface where the grooves are formed. And a liquid crystal display device in which the molecular long axis of the liquid crystal is horizontally oriented in the orthogonal direction perpendicular to the predetermined direction of the groove. The
  In addition, according to another aspect of the present invention for solving the above-described problem, the substrate is formed on a pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, and at least one of the substrates. An alignment layer for aligning molecules of the liquid crystal and an electrode for applying a voltage to the liquid crystal formed on at least one substrate, the alignment layer having a main surface in which a plurality of grooves are formed in parallel It consists of a base layer and a film covering the main surface where the groove is formed, and the film is oriented in parallel with the major axis indicating the longitudinal direction of the molecules of the liquid crystal with no voltage applied to the main surface. Each of the grooves has a U-shaped cross section extending along a predetermined direction and is repeatedly arranged at a given pitch along an orthogonal direction perpendicular to the predetermined direction. The coating has a coverage on the main surface on which the groove is formed. 0% or more and less than 100%, and formed so that a part of the main surface including the apex of the convex portion formed between adjacent grooves is exposed. A liquid crystal display device is provided that is oriented horizontally in an orthogonal direction orthogonal to the predetermined direction.
  In addition, according to another aspect of the present invention for solving the above-described problem, the substrate is formed on a pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, and at least one of the substrates. In a method for manufacturing a liquid crystal display device comprising an alignment layer for aligning the molecules of the liquid crystal and an electrode formed on at least one substrate for applying a voltage to the liquid crystal, the alignment layer has a plurality of parallel grooves. A base layer having a main surface disposed on the surface and a film covering the main surface on which the groove is disposed, and the film extends in the longitudinal direction of the molecules of the liquid crystal with no voltage applied to the main surface. Each of the grooves is a groove having a U-shaped cross section extending along a predetermined direction and along an orthogonal direction orthogonal to the predetermined direction. The coating was repeatedly formed at a given pitch, and the coating formed the grooves The coverage of the surface is 50% or more, and the coating is performed so that the thickness increases as it approaches the bottom of each groove, so that the molecular long axis of the liquid crystal is oriented in the orthogonal direction perpendicular to the predetermined direction of the groove. A method for manufacturing a horizontally aligned liquid crystal display device is provided.
In addition, according to another aspect of the present invention for solving the above-described problem, the substrate is formed on a pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, and at least one of the substrates. In a method for manufacturing a liquid crystal display device comprising an alignment layer for aligning molecules of the liquid crystal and an electrode formed on at least one substrate for applying a voltage to the liquid crystal, the alignment layer has a plurality of grooves. A base layer having a main surface arranged in parallel and a film covering the main surface on which the groove is arranged, and the film is a longitudinal direction of the molecules of the liquid crystal in a state where no voltage is applied to the main surface. Each of the grooves has a U-shaped cross section extending along a predetermined direction, and has an orthogonal direction perpendicular to the predetermined direction. Arranged repeatedly at a given pitch along the coating The covering ratio of the formed main surface is 50% or more and less than 100%, and the main surface including the apex of the convex portion formed between the adjacent grooves is exposed so as to be exposed. Thus, there is provided a method of manufacturing a liquid crystal display device in which the molecular major axis of the liquid crystal is oriented horizontally in an orthogonal direction perpendicular to the predetermined direction of the groove.

  The present invention is characterized in that the alignment layer for aligning liquid crystal molecules has a two-layer structure. That is, the alignment layer is composed of a lower base layer and an upper film. The base layer has a plurality of grooves (gratings) formed on its surface (main surface). On the other hand, the film is made of a polymer alignment film such as polyimide, and has a horizontal alignment ability to align the molecular long axis of the liquid crystal parallel to the principal surface. A predetermined direction in which the groove of the grating extends by combining the base layer on which the striped grating is formed in this way and the coating film having the horizontal alignment ability (hereinafter, this predetermined direction may be referred to as a linear direction in the present specification). The molecular major axis of the liquid crystal can be oriented in an orthogonal direction orthogonal to the alignment. Hereinafter, this orientation state may be referred to as orthogonal orientation. On the other hand, the conventional simple grating method is one in which the molecular long axes of liquid crystals are aligned in parallel along the linear direction of the grooves. Hereinafter, this alignment state may be referred to as parallel alignment.

In the conventional grating method, the molecular long axis of the liquid crystal is aligned in parallel with the linear direction of the groove. Therefore, it is necessary to increase the aspect ratio of the groove, which has been a major obstacle to display quality and productivity. On the other hand, the present invention combines the grating and a film having a horizontal alignment ability so that the molecular major axis of the liquid crystal is aligned in the orthogonal direction, not in the linear direction of the groove. This orthogonal orientation is obtained by a combined effect or a synergistic effect combining the grating of the base layer and the horizontal orientation ability of the polymer film, and has never been known so far. Since parallel alignment along the conventional groove depends only on the grating, it is necessary to increase the aspect ratio of the groove. On the other hand, since the orthogonal orientation of the present invention is obtained by the combined effect of the grating and the polymer film, the groove aspect ratio itself does not need to be larger than that of the conventional simple grating method, and productivity and display quality are improved. Excellent on.
In the present invention, since the liquid crystal molecules are aligned in a direction orthogonal to the direction of the groove, there is an advantage that the tilt angle can be easily expressed only by making the cross-sectional shape of the groove asymmetric. In addition, the present invention has an advantage that it can be used as it is with the existing production equipment because it is not a special material for the alignment film but polyimide having a long track record can be used.

  In the present invention, orthogonal orientation of liquid crystal molecules is realized by coating the surface of the grating with a horizontal alignment film. In order to achieve orthogonal orientation, it is not always necessary to completely cover the grating surface with an orientation coating. The desired orthogonal orientation can be obtained if the surface of the grating is coated with at least 50% horizontal orientation coating. In the orthogonal orientation, the molecular major axis of the liquid crystal does not necessarily have to be precisely oriented at an angle of 90 ° with respect to the linear direction of the grating. In the practical range, the orthogonal orientation of the present invention can tolerate the case where the major axis of the liquid crystal molecules intersects the linear direction of the grating in the range of 80 ° to 100 °.

  Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic partial perspective view showing a main part of a liquid crystal display device according to the present invention. A liquid crystal display device according to the present invention basically includes a pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, and an alignment layer formed on at least one substrate and aligning liquid crystal molecules. And an electrode formed on at least one of the substrates for applying a voltage to the liquid crystal. FIG. 1 schematically shows one substrate on which an alignment layer is formed. The electrodes are not shown for easy viewing of the figure.

  The alignment layer includes a base layer having a main surface on which a plurality of grooves M are formed in parallel, and a coating covering the main surface on which the grooves M are formed. However, the plurality of grooves M need not be geometrically strictly parallel, and may be substantially or substantially parallel as long as the effects of the present invention are achieved. This coating is made of a polymer film such as polyimide. In the illustrated example, the polymer chains constituting the organic polymer film are aligned along the groove M. However, this is a schematic representation of the state of the polymer chain, and the present invention is not necessarily limited to such a polymer chain arrangement. This film has a horizontal alignment ability for aligning the molecular long axis indicating the longitudinal direction of the molecules of the liquid crystal in parallel with the main surface in the state where no voltage is applied. In this specification, the coating film having the alignment ability with respect to the liquid crystal molecules may be referred to as an alignment film hereinafter. The main surface represents the surface of the base layer on which the plurality of grooves M are formed, and is parallel to the substrate surface.

  Each groove M extends along a given linear direction and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the linear direction. The cross section of the base layer along the orthogonal direction has a concavo-convex structure in which a concave portion corresponding to the bottom of each groove M and a convex portion corresponding to the boundary of adjacent grooves M appear alternately.

  As a feature of the present invention, the liquid crystal molecules are horizontally aligned with the long axis of the liquid crystal molecules oriented in an orthogonal direction orthogonal to the linear direction of the groove. In the alignment using the conventional grating, the liquid crystal molecules are parallel alignment oriented in parallel with the linear direction of the groove M. In the present invention, the orthogonal orientation different from the conventional parallel orientation is realized by coating the grating with a horizontal orientation film. This orthogonal alignment is obtained by a synergistic effect of the grating base layer and the horizontal alignment film, and does not require a larger aspect ratio than in the prior art. The aspect ratio representing the ratio of the groove depth to the arrangement pitch of the grooves M can be kept below 1 according to the present invention. Further, the horizontal alignment film does not necessarily have to cover 100% of the main surface of the grating completely, and it is sufficient that the coverage is at least 50%.

  FIG. 2 is a schematic diagram showing another example of the cross-sectional shape of the grating base layer. In the embodiment shown in FIG. 1, the convex portion has an inverted V shape, while the concave portion has a U shape. On the other hand, in the embodiment shown in FIG. 2, both the convex portion and the concave portion are U-shaped. Thus, a wide variety of patterns can be considered for the cross-sectional shape of the grating base layer used in the present invention. In some cases, a tilt angle (tilt angle) can be given to the major axis of the liquid crystal molecules oriented in the orthogonal direction by making the slope from the convex part to the concave part of the concavo-convex pattern asymmetric between the right side and the left side. This tilt angle may reach 30 ° in a practical range, and this range is called horizontal alignment. In this specification, the horizontal alignment is not limited to the case where the tilt angle is 0 °, but the tilt angle region included in the horizontal alignment category within the practical range is also included in the concept of horizontal alignment.

  As is apparent from the above description, the present invention can be applied to grating base layers having a wide variety of uneven patterns. Basically, orthogonal orientation, which has never existed in the past, can be obtained by covering the grating base layer with a horizontal alignment film at a coverage of at least 50% in any irregular pattern.

  FIG. 3 is a schematic cross-sectional view showing parameters that define the concave / convex pattern of the grating. As shown in the figure, the alignment layer is composed of a base layer (PLN) on which a concavo-convex pattern is formed, an electrode (ITO) formed thereon, and a horizontal alignment film (PI) covered thereon. ing. PI is an abbreviation for polyimide film. ITO represents a material constituting the electrode.

  As shown in the drawing, the concave / convex pattern of the grating is defined by the arrangement pitch P and the height H of the convex portion. The arrangement pitch P is an interval between adjacent concave portions. The height H represents the height of the convex portion, which is also the depth of the grating groove. The grating is formed so that the aspect ratio H / P representing the ratio of the groove depth H to the groove arrangement pitch P is less than 1 according to the present invention. W represents the width of the convex portion. As the ratio of the width W to the pitch P is smaller, the concavo-convex pattern is closer to the cross-sectional shape shown in FIG. 1, and the convex portion is sharpened to a V shape. On the other hand, as the ratio of the width W to the arrangement pitch P increases, the cross-sectional shape becomes U-shaped in both the convex portion and the concave portion as shown in FIG.

  By covering the concavo-convex pattern defined by such parameters P, H, and W with the horizontal alignment film PI, a desired orthogonal alignment can be obtained. As a method for coating the horizontal alignment film, various methods such as spin coating, spraying, and dipping can be employed. The illustrated example shows a state in which the liquid alignment film applied to the main surface of the grating has moved to the recess during the heat treatment process. As is apparent from the figure, the coverage of the alignment film does not necessarily have to be 100%. Even when the convex part of the grating is partially exposed, the desired orthogonal orientation can be obtained even when the alignment film stays thick in the concave part. can get.

  FIG. 4 is a schematic view for defining the coverage of the alignment film with respect to the main surface where the grooves are formed. In this specification, two types of coverage (1) and (2) are adopted. In the case of (1), the coverage is defined by a region where the alignment film PI is present and a region where the alignment film PI is absent as shown in the figure. As described above, the alignment film PI tends to move from the convex portion toward the concave portion in the drying / thermosetting process. In this case, a range where there is no alignment film PI at the convex portion is represented by P1. Therefore, the region where the alignment film PI is provided is given by P-P1. Therefore, the coverage ratio R1 = (P−P1) / P. Note that an SEM is used to detect the region with and without the alignment film PI.

  In the case of (2), the coverage is defined in a region where the thickness of the alignment film PI on the bottom surface is halved. As shown in the drawing, the alignment film PI accumulated at the bottom of the convex portion becomes thinner as the convex portion is inclined, and the thickness is halved in the range of P2. The coverage R2 is defined by (P−P2) / P. Theoretically, the coverage ratio R1 is considered to be closer to the true coverage ratio than the coverage ratio R2. However, it may be technically difficult to distinguish between the region with the alignment film and the region without the alignment film by SEM. In particular, it is difficult to measure a region without an alignment film. On the other hand, the definition of the coverage ratio R2 has an advantage of easy measurement because it uses a change in the thickness of the alignment film PI.

  FIG. 5 is a graph showing the results of actually measuring the coverage ratio for a plurality of samples in which the uneven pattern parameters P, H, and W were changed. The graph of (1) is a sample in which the alignment pitch P is 3 μm, the convex width W is 0.3 μm, and the grating height H is changed from 0.2 to 0.9 μm. It is the result of actually measuring the rate. The convex width W = 0.3 μm is one tenth of the arrangement pitch P = 3.0 μm, and the concave / convex shape has a convex portion close to a V shape and a concave portion having a U shape.

  As apparent from the graph (1), the coverage ratio R1 is almost 100%, and it can be seen that the main surface of the grating is almost completely covered with the alignment film PI. Further, the coverage ratio R2 is 80% or more, which indicates that the grating main surface is substantially covered. In the case of the coverage ratio R2, the coverage ratio decreases as the grating height H increases (the aspect ratio increases).

  The graph of (2) is the measurement result of the sample when the protrusion width W is increased to 0.8 μm with respect to the graph of (1). The protrusion width W is 0.8 μm with respect to the arrangement pitch P = 3.0 μm, and the V-shape is slightly changed from the V-shape due to the increased protrusion width. In this sample, the coverage ratio R1 is 80% or more, and the coverage ratio R2 is 60% or more. The coverage ratio R2 is not clearly dependent on the aspect, but in the case of the coverage ratio R1, the coverage ratio decreases as the aspect ratio clearly increases.

  The graph of (3) is a case where the convex portion width W is further expanded to 1.2 μm. In this case, the arrangement pitch P = 3. The convex width W = 1.2 μm with respect to μm is almost half, and both the convex and concave portions are U-shaped. The coverage R1 can be ensured to be approximately 60% or more. Also, the coverage ratio R2 can be secured to 50% or more regardless of the aspect ratio.

  Considering the results of the graphs (1) to (3) comprehensively, the coverage is improved as the convex width W is narrower. Further, although not remarkable when looking at the grating height, the coverage ratio tends to decrease as the aspect ratio increases (the difference between the irregularities increases). In any case, the coverage R2 is 50% or more, and the desired orthogonal orientation ability can be obtained by setting the grating parameters P, H, and W within an appropriate range. When the coverage is less than 50%, the orthogonal orientation ability is disturbed, and the uniformity of the screen may be impaired.

  FIG. 6 is a schematic diagram showing the alignment state of the liquid crystal held on the pair of substrates. As shown in the figure, the molecular long axes of the liquid crystals are aligned horizontally in a certain direction and are horizontally aligned. In this specification, this alignment state may be referred to as homogeneous alignment. In addition, the alignment direction of the molecular long axes of the liquid crystal may be referred to as an alignment direction in this specification. Therefore, the orthogonal orientation unique to the present invention is a homogeneous alignment in which the alignment direction coincides with the orthogonal direction of the grating.

  In the liquid crystal display device, the alignment of the liquid crystal is controlled using the alignment layer and the applied voltage is controlled to switch the alignment state, thereby performing a desired image display. The change in the alignment state can be converted into a change in luminance by a pair of upper and lower polarizing plates, for example. (A) represents the crossed Nicols arrangement of a pair of polarizing plates, and the transmission axes of the upper and lower polarizing plates are orthogonal to each other. The transmission axis of the lower polarizing plate on the incident side is parallel to the alignment direction of the liquid crystal. The transmission axis of the polarizing plate on the output side is orthogonal to the alignment direction of the liquid crystal. When the liquid crystal is in an ideal homogeneous orientation, incident light is completely blocked by a pair of polarizing plates, and leakage light becomes zero. Therefore, a black display can be obtained.

  (B) represents the paranicol arrangement of a pair of polarizing plates. Under this Paranicol condition, the transmission axes of the upper and lower polarizing plates are both parallel to the alignment direction of the liquid crystal. In this case, the incident light is emitted as it is without being absorbed. Therefore, white display can be obtained. When the paranicol arrangement is adopted in the state where no voltage is applied, the display is normally white. Conversely, when the crossed Nicols arrangement is adopted, normally black display is obtained when no voltage is applied.

  FIG. 7 is a graph showing the effect of the present invention. This graph shows the result of measuring the amount of transmitted light under the crossed Nicols condition shown in FIG. 6A by creating a liquid crystal display panel using a substrate sample on which a grating with a pitch of 3 μm is formed as described in FIG. Represents. While the grating is fixed at a pitch of 3 μm, samples with the grating height changed from 0.1 μm to 1 μm are prepared, and the transmittance is measured under crossed Nicols conditions. The height of the grating corresponds to the depth of the groove.

  In the graph of FIG. 7, the horizontal axis represents the grating height (μm), and the vertical axis represents black luminance (nit) as an index indicating the transmittance. Under crossed Nicols conditions, the closer the liquid crystal homogeneous alignment is to the ideal state, the lower the black luminance. The graph in FIG. 7 corresponds to the samples (1), (2), and (3) in FIG. 5 in which three types of protrusion widths are changed, and the black luminance is measured for each. In other words, three characteristic curves are represented using the convex width as a parameter. For a pitch of 3 μm, a sample with a convex width of 0.3 μm has the sharpest convex shape. A sample having a convex width of 0.8 μm and a sample having a width of 1.2 μm are also prepared and evaluated.

  When the protrusion width is 0.3 μm, although it depends on the grating height, a black luminance of 2.5 nit is obtained under the best conditions. This shows that the liquid crystal is homogeneously aligned and the liquid crystal alignment characteristics are good. The next sample with a convex width of 0.8 μm has a grating height in the range of 0.4 μm to 0.7 μm, the black luminance is less than 4 nits, and the sample with a convex width of 1.2 μm has a grating height. In the range of 0.4 to 0.7 μm, the black luminance is slightly over 4 nits. Thus, it can be seen that the orientation characteristics are reduced in proportion to the increase in the convex width.

  When the convex width is 0.3 μm, the concave width is the remaining 2.7 μm. Thus, by making the convex portion width smaller than the concave portion width of the grating, liquid crystal molecules can be homogeneously aligned along the orthogonal direction of the grating, depending on the grating height. Similarly, when the convex portion width is 0.8 μm, the concave portion width is 2.2 μm. Even in this sample, the width of the convex portion is smaller than the width of the concave portion, and a desired homogeneous orientation can be obtained. Furthermore, even in a sample having a convex portion width of 1.2 μm, the concave portion width is 1.8 μm, and the convex portion width is smaller than the concave portion width, so that a desired homogeneous orientation is obtained.

  On the other hand, when the grating height increases beyond an appropriate value, the homogeneous orientation is disturbed, and the black luminance is rapidly increased. For example, when attention is paid to a sample having a convex portion width of 0.3 μm, it can be seen that when the grating height exceeds 0.7 μm, the transmittance rapidly increases, and homogeneous alignment along the orthogonal direction of the grating cannot be obtained. Thus, when the ratio of the grating height to the grating pitch (aspect ratio) is increased, the original effect of the grating is strong and the liquid crystal molecules tend to be oriented along the linear direction of the grating. If the value exceeds a certain value, the liquid crystal display device is aligned in parallel to the grating, so that the liquid crystal display device is not homogeneously aligned but twisted. Therefore, since the orientation state changes, the leakage light becomes large, and the black luminance is deteriorated. In other words, in order to obtain a homogeneous alignment along the orthogonal direction of the grating, it is necessary to suppress the aspect ratio of the grating to a certain extent, which is different from the conventional simple grating method. Similarly, for samples with a convex width of 0.8 μm or 1.2 μm, when the grating height exceeds 0.8 μm and the aspect ratio increases, the alignment direction of the liquid crystal molecules deviates from the orthogonal direction of the grating and changes to the linear direction. However, low black luminance cannot be obtained.

  FIG. 8 is a partially enlarged cross-sectional view of the liquid crystal display panel 1 applied to the liquid crystal display device according to the first embodiment of the present invention. The liquid crystal display device of this embodiment is a so-called transmission type or reflection type, and a polarizing plate or the like is provided on the front side surface or the like that is the upper side of the liquid crystal display panel 1 in FIG. In the transmissive type, a backlight device is provided on the back side which is the lower side of the liquid crystal display panel 1 in FIG. 8, and in the reflective type, a front light device is provided on the surface side which is the upper side of the liquid crystal display panel 1 in FIG. Provided.

  In the liquid crystal display panel 1, the liquid crystal is sandwiched between the TFT array substrate 2 and the CF substrate 3. Here, the CF substrate 3 is formed by sequentially forming a color filter 5, an insulating film 6, an electrode 7 made of a transparent electrode, and an alignment film 8 on a glass substrate 4 which is a transparent insulating substrate. The electrode 7 is usually formed by depositing ITO (Indium Tin Oxide) over the entire surface, but may be patterned for each pixel or for each sub-pixel. The alignment film 8 is formed by applying a mixture of soluble polyimide and polyamic acid as a liquid crystal alignment material for inducing horizontal alignment by a printing method and then baking it at a temperature of 200 ° C. for 75 minutes to form a polyimide thin film with a thickness of 50 nm. ], And then it is created by imparting alignment ability by rubbing treatment. The rubbing direction is the direction of the arrow in this figure, and is the direction orthogonal to the extension direction (linear direction) of the groove M described later.

  On the other hand, as shown in FIG. 9, the TFT array substrate 2 forms an insulating film 11 by forming a TFT or the like on a glass substrate 10 which is a transparent insulating substrate, and an electrode 12 is formed on the insulating film 11. The alignment film 13 is formed in order. As is clear from the above description, the alignment layer of the present invention is constituted by the insulating film 11, the electrode 12 and the alignment film 13 which are sequentially formed on the substrate 10. The inner insulating film 11 and the electrode 12 correspond to the base layer shown in FIG. 1, and the alignment film 13 also corresponds to the film shown in FIG.

  The TFT array substrate 2 is formed so that the shape of the main surface for forming the alignment film 13 is a groove shape in which a groove extending linearly in a predetermined direction is repeatedly formed in a direction perpendicular to the predetermined direction, The alignment film 13 is formed by covering the groove shape with a polymer film. In this embodiment, the surface shape of the insulating film 11 is formed in this groove shape, and the surface on which the alignment film 13 is formed is formed in the groove shape. Here, the grooves M extend along a given linear direction and are repeatedly arranged at a given pitch P along an orthogonal direction orthogonal to the linear direction. The cross section of the insulating film 11 along the orthogonal direction has a concavo-convex structure in which a concave portion corresponding to the bottom of each groove M and a convex portion corresponding to the boundary between adjacent grooves M appear repeatedly. As a characteristic matter, the coverage of the grating by the alignment film 13 is ensured to be 50% or more, so that the major axis of the liquid crystal molecules 15 is oriented horizontally in the orthogonal direction perpendicular to the linear direction of the groove M. . In this embodiment, the convex portion has a reverse V shape that completely loses the flatness of the top surface, while the concave portion has a U shape that retains the flatness on the bottom surface, and the alignment film is almost 100% covered. The grating is coated at a rate.

  Here, the cross-sectional shape of the groove M is formed in a substantially arc shape having a symmetrical shape with the vertex of the groove M as the center. The groove M is formed with a pitch P of 1 [μm] and a height (depth) H of 400 [nm], whereby the ratio T (= H / P) of the pitch P to the height H is less than 1. Of 0.4.

More specifically, in the TFT array substrate 2, the insulating film 11, novolak, formed organic resist material such as an acrylic, or Si0 _2, SiN, or Si0 _2, SiN with an inorganic material as a main component The

  Here, when the insulating film 11 is formed with a photosensitive organic resist material, the TFT array substrate 2 is pre-baked after coating the photosensitive organic resist material, and then a pattern corresponding to the groove M (stripe pattern) is formed. The resist material is exposed to ultraviolet rays or the like using a mask having it. Further, development and post-baking are performed, and the surface of the insulating film 11 is processed into a groove shape by applying a photolithography method. Instead of using a mask, exposure processing may be performed using interference of light beams irradiated from two different directions. Instead of the photolithography method, a technique such as a nanoimprint method may be applied.

  When the insulating film 11 is formed of an inorganic material, the TFT array substrate 2 is formed by depositing the inorganic material with a predetermined film thickness by vacuum evaporation, sputtering, CVD, or the like, and then using a photolithography method to form a photosensitive organic material. The resist material is patterned into a groove shape, and then wet etching or dry etching is performed to make the side surface of the alignment film 13 into a groove shape. The insulating film 11 can also be formed by using a photosensitive material which is a mixture of an inorganic material and an organic material, which are generally commercially available. In this case, the insulating film 11 is baked after being patterned by a photolithography method. Through the processes such as the above, organic components are scattered in the atmosphere, and the insulating film 11 is formed mainly from inorganic components.

  In the transmission type, the electrode 12 is usually formed by forming a transparent electrode material such as ITO on the entire surface and then patterning it. In the reflection type, a metal material such as aluminum or silver may be applied.

  The alignment film 13 is formed by applying a commonly used polyimide-based material by an offset printing method and then baking it at a temperature of 200 degrees for 75 minutes. The alignment film 13 is imparted with alignment ability by aligning the polymer chains in the alignment film in a predetermined direction with respect to the groove M by this baking treatment. Various methods such as spin coating, dipping in a bath of a solution diluted with a solvent such as gamma butyl lactone, and spraying by spraying can be applied to the coating method of the alignment film 13. it can.

  Here, in the process of applying the alignment material, drying, and baking the alignment film 13 with the surface shape of the lower layer in the groove shape, the direction of the polymer chain in the alignment film is in a predetermined direction with respect to the groove. Evenly, orientation ability is imparted.

  According to various examination results, in order to align the liquid crystal molecular axes in a certain direction by baking after coating, a groove M extending in a direction perpendicular to the certain direction is formed on the lower surface of the alignment film 13. It was found that the molecular axes of the alignment film are aligned in the direction from each apex to the skirt, and the alignment ability cannot be imparted in a specific direction.

  Further, for the groove M, even when the ratio T (= H / P) between the pitch P and the height H is less than 1, alignment ability can be sufficiently imparted, and the lower surface of the alignment film 13 can be provided. From the viewpoint of processing into a groove shape, the ratio T between the pitch P and the height H is set to less than 1, more preferably, the ratio T between the pitch P and the height H is set to less than 0.5 to improve productivity. be able to.

  In the liquid crystal display panel 1, after the TFT array substrate 2 and the CF substrate 3 are bonded together with a sealing material, nematic liquid crystal having a positive dielectric anisotropy is injected into the gap between the TFT array substrate 2 and the CF substrate 3. To be formed. In FIG. 8, liquid crystal molecules are denoted by reference numeral 15, and θ and θ / 2 are tilt angles of the liquid crystal molecules 15. In this case, when the alignment direction of the liquid crystal molecules 15 was confirmed by injecting liquid crystal, the liquid crystal molecules 15 were aligned in the direction perpendicular to the extending direction of the groove M on the side surface of the TFT array substrate 2 as shown in FIG. In addition, when the TFT array substrate 2 and the CF substrate 3 were bonded so that the extending direction of the groove M was orthogonal to the rubbing direction, it was confirmed that the liquid crystal molecules 15 were homogeneously aligned. In addition, when the TFT array substrate 2 and the CF substrate 3 were bonded so that the extending direction of the groove M was parallel to the rubbing direction, it was confirmed that the liquid crystal molecules 15 were twisted nematically aligned.

  FIG. 10 is a schematic diagram when a voltage is applied to the liquid crystal display panel 1. Even when a voltage is applied, the liquid crystal display panel 1 does not change the orientation of the liquid crystal molecules in the vicinity of the interface between the TFT array substrate 2 and the CF substrate 3, and the tilt angle of the liquid crystal molecules 15 gradually increases as the distance from the interface increases. Thus, at the central portion between the TFT array substrate 2 and the CF substrate 3, the tilt angle becomes about 90 degrees and becomes the maximum.

  The retardation at the time of voltage application was measured by a rotational analyzer method, and compared with the retardation of a liquid crystal cell in which both the TFT array substrate 2 and the CF substrate 3 were rubbed. Here, when the anchoring strength is weak, the tilt angle of the liquid crystal molecules at the interface on the TFT array substrate 2 side is changed by applying a voltage, so that the TFT array substrate 2 and the CF substrate 3 are both rubbed into a liquid crystal cell. The retardation is smaller than that. However, according to the measured results, when a voltage is applied, the liquid crystal display panel 1 of this embodiment has a retardation which is almost equal to that of a liquid crystal cell in which both the TFT array substrate 2 and the CF substrate 3 are rubbed, and this causes the TFT array to be measured. It was confirmed that sufficient anchoring strength was secured by the alignment film 13 on the substrate 2 side.

  In the first embodiment shown in FIG. 8, the case where the alignment ability is imparted to the alignment film 13 of the TFT array substrate 2 and the alignment film 8 of the CF substrate 3 by the groove shape and the rubbing treatment is described. On the contrary, the alignment film 13 of the TFT array substrate 2 and the alignment film 8 of the CF substrate 3 may be provided with alignment ability by rubbing treatment and groove shape, respectively. Both the alignment films 8 and 13 of the substrate 3 may be provided with alignment ability by a groove shape. In the example of FIG. 8, the case where nematic liquid crystal is applied has been described. However, various liquid crystals such as smectic and cholesteric can be widely applied.

  FIG. 11 is a perspective view showing a TFT array substrate of a liquid crystal display panel applied to Embodiment 2 of the present invention in comparison with FIG. In this TFT array substrate 22, the surface shape of the electrode 12 is formed in a groove shape instead of the surface shape of the insulating film 11, and the shape of the surface on which the alignment film 13 is formed is formed in a groove shape. The liquid crystal display panel of this embodiment is formed in the same manner as the liquid crystal display panel 1 of the embodiment 1 except that the groove shape processing is different.

  That is, in the TFT array substrate 22 according to this embodiment, the insulating film 11 is formed on the glass substrate 10 with a certain film thickness in the same manner as described above for the first embodiment. Subsequently, after depositing ITO, aluminum, silver or the like, a photosensitive resist is patterned into a groove shape by a photolithography method, and a groove shape is formed in the electrode 12 by wet etching treatment or dry etching treatment. As described above with respect to the first embodiment, the configuration shown in FIG. 11 may be applied to the CF substrate side.

  As in this embodiment, the same effect as in Embodiment 1 can be obtained by replacing the surface shape of the insulating film with the surface shape of the electrode 12 as the groove shape and the surface on which the alignment film is formed into the groove shape. be able to.

  FIG. 12 is a perspective view showing a TFT array substrate of a liquid crystal display panel applied to the liquid crystal display device according to the third embodiment of the present invention in comparison with FIG. In this TFT array substrate 32, instead of the surface shape of the insulating film 11, the surface shape of the glass substrate 10 which is an insulating substrate is directly formed into a groove shape, and the shape of the surface on which the alignment film 13 is formed is formed into a groove shape. Is done. The liquid crystal display panel of this embodiment is formed in the same manner as the liquid crystal display panel 1 of the embodiment 1 except that the groove shape processing is different. In the example of FIG. 12, although the insulating film is omitted, an insulating film may be provided as necessary.

  That is, the TFT array substrate 32 is formed by patterning a photosensitive resist into a groove shape by photolithography on the front side surface of the glass substrate 10, and then performing wet etching processing or dry etching processing to process the front side surface of the glass substrate 10 into a groove shape. Is done. Thereafter, the electrode 12 and the alignment film 13 are sequentially formed. Note that the configuration shown in FIG. 12 may be applied to the CF substrate side in the same manner as described above for the first embodiment. In Examples 1 to 3, the alignment film is formed on the base layer via the electrode, but the present invention is not limited to this. In some cases, an alignment film may be formed directly on the base layer.

  As in this embodiment, instead of the surface shape of the insulating film, the surface shape of the insulating substrate is changed to the groove shape, and the shape of the surface on which the alignment film is formed is changed to the groove shape. be able to.

  FIG. 13 is a perspective view showing a configuration of a TFT array substrate 42 applied to the liquid crystal display device according to the fourth embodiment of the present invention in comparison with FIG. The TFT array substrate 42 is formed with the grooves M so that the grooves M with a constant pitch P do not continue more than a predetermined number. More specifically, the TFT array substrate 42 is set so that the pitch P changes randomly in the continuous groove M. Thereby, the TFT array substrate 42 is set so that the continuous groove M does not function as a diffraction grating. The liquid crystal display panel of this embodiment is configured in the same way as the above-described embodiments except that the setting of the pitch P in the TFT array substrate 42 is different.

  That is, when the grooves M are formed with a constant pitch P, the periodic grooves M function as a diffraction grating, and rainbow-colored interference fringes are observed, so that the image quality is significantly deteriorated. In the case of a transmissive liquid crystal display panel, since the alignment film is in contact with the liquid crystal having a refractive index of approximately 1.5, the refraction of the transparent electrode such as ITO is not as great as when the groove M is exposed in the air. Since the rate is approximately 2, iridescent interference fringes are generated. In the reflective liquid crystal display panel, iridescent interference fringes become remarkable.

  However, as in this embodiment, if the pitch P is changed randomly and the grooves M with the constant pitch P are set so as not to be continuous more than a certain number, the generation of such rainbow interference fringes can be prevented. Degradation of image quality can be prevented.

  FIG. 14 is a plan view showing a liquid crystal display panel applied to the liquid crystal display device according to the fifth embodiment of the present invention, and FIG. 15 is a detailed cross-sectional view showing the liquid crystal display panel 51 taken along line AA. It is. FIG. 16 is a cross-sectional view showing a state in which a voltage is applied to the electrodes in comparison with FIG. In the liquid crystal display panel 51 of this embodiment, the same configuration as that of the above-described embodiment is denoted by the corresponding reference numeral, and a duplicate description is omitted as appropriate.

  In the liquid crystal display panel 51, the alignment film 8 of the CF substrate and the alignment film 13 of the TFT array substrate are provided with alignment ability by the groove shape. In creating the groove shape, any of the first to third embodiments may be applied.

  In the liquid crystal display panel 51, in these CF substrate and TFT array substrate, a groove M is formed so as to extend in the horizontal direction in the vertical direction from the center of one pixel, and vertical in the horizontal direction from the center of one pixel. A groove M is formed so as to extend in the direction, and thereby the groove M is formed in a quadrangular shape centered on the center of the pixel. As a result, the liquid crystal display panel 51 is formed with symmetrical grooves M in each direction with respect to the center of the pixel, and in the vertical direction from the center of one pixel so as to face the center of the pixel, the liquid crystal molecules 15 in the vertical direction. The liquid crystal molecules 15 are set so as to be aligned in the horizontal direction from the center of one pixel in the left-right direction.

  Further, in the liquid crystal display panel 51, in the TFT array substrate, a quadrangular pyramid-shaped protrusion is formed at the center of one pixel so as to protrude toward the CF substrate. Thus, the liquid crystal display panel 51 is set so that the tilt angle becomes smaller from the center of one pixel toward the periphery. As a result, in the liquid crystal display panel 51, the phase of light incident on the liquid crystal cell from the same polar angle is set to be substantially the same even if the azimuth is different, and the liquid crystal display panel 5 has a wide viewing angle. Configured to do.

  According to this embodiment, a desired viewing angle can be secured by changing the direction in which the groove extends within one pixel.

  That is, the viewing angle can be expanded by forming the grooves M symmetrically in each direction with respect to the center of one pixel. One pixel may be divided into a plurality of sub-pixels, and the grooves may be formed symmetrically with respect to each center.

  FIG. 17 is a plan view showing a liquid crystal display panel applied to the liquid crystal display device of Example 6 of the present invention in comparison with FIG. The liquid crystal display panel 61 is configured in the same manner as the liquid crystal display panel 51 of Example 5 except that the grooves M are formed concentrically. As a result, a conical projection is provided in the center of one pixel instead of the quadrangular pyramid projection.

  According to this embodiment, even if the grooves are formed concentrically, the same effect as that of Embodiment 5 can be obtained.

It is a schematic diagram which shows the principal part of the liquid crystal display device concerning this invention. It is a schematic diagram which similarly shows the other example of the principal part of the liquid crystal display device concerning this invention. It is sectional drawing which shows the uneven | corrugated pattern of a grating. It is a schematic diagram which defines a coverage. It is a graph which shows the measurement result of the coverage of the alignment film with respect to a grating. It is a schematic diagram which shows the orientation state of a liquid crystal molecule. It is a graph which shows the effect of the present invention. 1 is a schematic cross-sectional view showing a first embodiment of a liquid crystal display device according to the present invention. It is a typical principal part perspective view which similarly shows 1st Example. It is typical sectional drawing with which it uses for operation | movement description of the liquid crystal display device concerning 1st Example. It is a principal part perspective view which shows 2nd Example of the liquid crystal display device concerning this invention. It is a principal part perspective view which shows 3rd Example of the liquid crystal display device concerning this invention. It is a principal part perspective view which shows 4th Example of the liquid crystal display device concerning this invention. It is a top view which shows 5th Example of the liquid crystal display device concerning this invention. It is sectional drawing which similarly shows 5th Example. It is sectional drawing which similarly shows 5th Example. It is a typical top view which shows the 6th Example of the liquid crystal display device concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display panel, 2 ... TFT array substrate, 3 ... CF substrate, 10 ... Glass substrate, 11 ... Insulating film, 12 ... Electrode, 13 ... Alignment film, 15 ... Liquid crystal molecule, M ... Groove

Claims (8)

A pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, an alignment layer that is formed on at least one substrate and aligns molecules of the liquid crystal, and is formed on at least one substrate. And an electrode for applying a voltage to
The alignment layer comprises a base layer having a main surface in which a plurality of grooves are formed in parallel, and a coating covering the main surface in which the grooves are formed,
The coating has a horizontal alignment ability to align the molecular long axes indicating the longitudinal direction of the molecules of the liquid crystal in parallel with no voltage applied to the main surface,
Each groove is a groove having a U-shaped cross section extending along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction.
The coating has a covering ratio of 50% or more with respect to the main surface on which the grooves are formed, and is formed thicker toward the bottom of each groove.
Accordingly, the molecular long axis of the liquid crystal is oriented horizontally in the orthogonal direction perpendicular to the predetermined direction of the groove.
Liquid crystal display device.   A pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, an alignment layer that is formed on at least one substrate and aligns molecules of the liquid crystal, and is formed on at least one substrate. An electrode for applying a voltage to the
  With
  The alignment layer comprises a base layer having a main surface in which a plurality of grooves are formed in parallel, and a coating covering the main surface in which the grooves are formed,
  The coating has a horizontal alignment ability to align the molecular long axes indicating the longitudinal direction of the molecules of the liquid crystal in parallel with no voltage applied to the main surface,
  Each groove is a groove having a U-shaped cross section extending along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction.
  The coating has a coverage of 50% or more and less than 100% with respect to the main surface on which the groove is formed, and a part of the main surface including the apex of the convex portion formed between the adjacent grooves is exposed. Formed as
  Accordingly, the molecular long axis of the liquid crystal is oriented horizontally in the orthogonal direction perpendicular to the predetermined direction of the groove.
  Liquid crystal display device.   The coating has a coverage of less than 100% with respect to the main surface where the grooves are formed.
  The liquid crystal display device according to claim 1.   Each groove is formed so that the aspect ratio representing the ratio of the groove depth to the groove arrangement pitch is less than 1.
  The liquid crystal display device according to claim 1.   The main surface of the base layer is divided into a plurality of regions, and the predetermined directions of the grooves given to adjacent regions are different from each other.
  The liquid crystal display device according to claim 1.   The plurality of grooves are formed so that the number of grooves having a constant pitch does not continue more than a predetermined number.
  The liquid crystal display device according to claim 1.   A pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, an alignment layer that is formed on at least one substrate and aligns molecules of the liquid crystal, and is formed on at least one substrate. An electrode for applying a voltage to the
  In a method for manufacturing a liquid crystal display device comprising:
  The alignment layer is formed of a base layer having a main surface in which a plurality of grooves are arranged in parallel, and a coating covering the main surface in which the grooves are arranged,
  The coating has a horizontal alignment ability to align the molecular long axes indicating the longitudinal direction of the molecules of the liquid crystal in parallel with no voltage applied to the main surface,
  Each groove is a groove having a U-shaped cross section extending along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction,
  The coating covers the main surface on which the groove is formed so that the covering ratio is 50% or more and becomes thicker toward the bottom of each groove,
  Accordingly, the molecular long axis of the liquid crystal is oriented horizontally in the orthogonal direction perpendicular to the predetermined direction of the groove.
  A method for manufacturing a liquid crystal display device.   A pair of substrates bonded to each other through a predetermined gap, a liquid crystal held in the gap, an alignment layer that is formed on at least one substrate and aligns molecules of the liquid crystal, and is formed on at least one substrate. An electrode for applying a voltage to the
  In a method for manufacturing a liquid crystal display device comprising:
  The alignment layer is formed of a base layer having a main surface in which a plurality of grooves are arranged in parallel, and a coating covering the main surface in which the grooves are arranged,
  The coating has a horizontal alignment ability to align the molecular long axes indicating the longitudinal direction of the molecules of the liquid crystal in parallel with no voltage applied to the main surface,
  Each groove is a groove having a U-shaped cross section extending along a predetermined direction, and is repeatedly arranged at a given pitch along an orthogonal direction orthogonal to the predetermined direction,
  The coating has a coverage of 50% or more and less than 100% with respect to the main surface on which the groove is formed, and a part of the main surface including the apex of the convex portion formed between the adjacent grooves is exposed. Coated as
  Accordingly, the molecular long axis of the liquid crystal is oriented horizontally in the orthogonal direction perpendicular to the predetermined direction of the groove.
  A method for manufacturing a liquid crystal display device.

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