Patent Publication Number: US-2023139767-A1

Title: Display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2021-0145399 filed on Oct. 28, 2021 in the Korean Intellectual Property Office, the entirety of which is hereby incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a display apparatus, and more particularly, to a display apparatus capable of reducing defects that may occur due to stress applied to a polarizing member and a display panel of the display apparatus. 
     Description of the Related Art 
     Display apparatuses are implemented in a wide variety of types such as televisions, monitors, smart phones, tablet PCs, laptops, and wearable apparatuses. 
     Recently, various types of flexible display apparatuses such as a foldable display apparatus, a rollable display apparatus, and a stretchable display apparatus have been developed, thereby increasing portability thereof. However, the repeated folding and unfolding of flexible display apparatuses can lead to various issues, including cracking and separation or delamination of the components of the displays. 
     BRIEF SUMMARY 
     A flexible display apparatus refers to a display apparatus including a display panel having flexibility such that the display panel can be folded, rolled, or bent while maintaining display characteristics of a flat panel display apparatus. 
     For example, a foldable display apparatus may be folded to occupy a small area when carrying the apparatus, and may be unfolded in use thereof to use a wide display screen. 
     Therefore, a user of the foldable display apparatus repeats operations of folding and unfolding the foldable display apparatus many times. 
     The flexible display apparatus may be formed by stacking a plurality of layers having various functions and various properties, such as a cover window, a polarizing member, a display panel part, and a plate assembly, among others. 
     A flexible display apparatus may operate in a bendable or foldable scheme, such as an inner or inward folding scheme in which display surfaces face each other or a display panel part is disposed in an inner portion, or an outer or outward folding scheme in which non-display surfaces face each other or a display panel part is disposed in an outer portion. 
     When a conventional flexible display apparatus is folded, stress may be applied to the plurality of layers constituting the display apparatus. 
     Because the plurality of layers constituting the display apparatus have different physical properties and are disposed at different positions, magnitudes and types of stresses applied to the respective layers may be different from each other. 
     For example, when the flexible display apparatus is folded in an in-folding scheme, a strong tensile stress may be applied to a lower portion of the polarizing member of the apparatus, and a strong compressive stress may be applied to an upper portion of the display panel part of the apparatus. 
     The tensile stress and the compressive stress have forces of opposite directions. Thus, when a difference between the tensile stress and the compressive stress increases, the stress applied to the plurality of layers increases. 
     Accordingly, cracks may occur in the lower portion of the apparatus. In the upper portion of the apparatus, not only cracks but also a layer lift-off phenomenon or separation of the layers may occur. Thus, a likelihood of defects in the display apparatus may increase for flexible display devices compared to conventional display devices. 
     According to one or more embodiments of the disclosure, a display apparatus is provided that is capable of reducing the difference between the tensile stress and the compressive stress respectively applied to a polarizing member and a display panel part (which may also be referred to herein as a display panel), thereby reducing the stress applied to each of the polarizing member and the display panel part. 
     In one or more embodiments, a display apparatus is provided that is capable of reducing a difference between a stress applied to a polarizing member and a stress applied to a display panel part. 
     In one or more embodiments, a display apparatus is provided that is capable of reducing occurrence of a stain in a display panel due to a phase retardation. 
     In one or more embodiments, a display apparatus is provided that is capable of increasing a puncture strength. 
     In one or more embodiments, a flexible display apparatus is provided that is capable of operating in an in-folding scheme that may reduce occurrence of cracks in a polarizing member and occurrence of cracks in and a layer lift-off of the display panel. 
     A display apparatus according to an embodiment of the present disclosure includes a display panel part (or display panel), a polarizing member, and a neutral plane compensation member between the display panel part and the polarizing member. 
     The neutral plane compensation member includes a first layer and a second layer, wherein a thickness of the first layer is in a range from 20 μm to 60 μm, a modulus (or modulus of elasticity) of the first layer is in a range from 1.0×10 8  Pa to 1.0×10 10  Pa, and a thickness of the second layer is in a range from 20 μm to 60 μm, and a modulus of the second layer is in a range of 1.0×10 4  Pa to 1.0×10 6  Pa. 
     In one or more embodiments, a flexible display apparatus according to an embodiment of the present disclosure includes a display panel part, a polarizing member, and a neutral plane compensation member between the display panel part and the polarizing member, and may be bent or folded toward the display panel. 
     The neutral plane compensation member includes a first layer and a second layer, wherein a thickness of the first layer is in a range of 20 μm to 60 μm, a modulus of the first layer is in a range of 1.0×10 8  Pa to 1.0×10 10  Pa, a thickness of the second layer is in a range of 20 μm to 60 μm, and a modulus of the second layer is in a range of 1.0×10 4  Pa to 1.0×10 6  Pa. 
     According to an embodiment of the present disclosure, disposing the neutral plane compensation member including the first layer and the second layer between the polarizing member and the display panel part may allow a difference between the tensile stress and the compressive stress respectively applied to the polarizing member and the display panel part to be reduced, thereby reducing the stress applied to each of the polarizing member and the display panel part. 
     According to an embodiment of the present disclosure, the neutral plane compensation member disposed between the polarizing member and the display panel part has a phase retardation value smaller than or equal to a predefined value, thereby reduce the occurrence of the stain due to the phase retardation. 
     According to an embodiment of the present disclosure, the neutral plane compensation member having a predetermined thickness is disposed between the polarizing member and the display panel part, such that an overall thickness of the display apparatus may be increased, so that the puncture strength of the display apparatus may be increased. 
     According to an embodiment of the present disclosure, in the flexible display apparatus that may be bent or folded toward the display panel part, the tensile stress is applied to the lower portion of the polarizing member while the compressive stress is applied to the upper portion of the display panel part. In this regard, the difference between the compressive and tensile stresses may be reduced due to the neutral plane compensation member disposed between the polarizing member and the display panel part. Thus, the occurrence of cracks in the polarizing member and the occurrence of cracks in and a layer lift-off of the display panel part may be reduced. 
     Additional features and aspects will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the concepts provided herein. Other features and aspects of the concepts may be realized and attained by the structure particularly pointed out in the written description, or derivable therefrom, and the claims hereof as well as the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain various principles of the disclosure. Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals should be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience in some embodiments; however, the relative dimensions including the size and thickness of the components illustrated in the drawings are drawn to scale with respect to at least one actual working embodiment of the present disclosure. 
         FIG.  1    is a cross-sectional view of a display apparatus according to an embodiment of the present disclosure and an enlarged cross-sectional view of a partial area thereof. 
         FIG.  2    is an enlarged cross-sectional view of a display panel part according to an embodiment of the present disclosure. 
         FIG.  3    illustrates a difference between stresses applied to a polarizing member, an adhesive portion, and a display panel part of a display apparatus according to each of a first embodiment and a second embodiment of the present disclosure. 
         FIG.  4 A  is a photograph showing cracks in a liquid crystal layer of a polarizing member that may occur according to each of the first embodiment and the second embodiment of the present disclosure, and  FIG.  4 B  is a photograph showing a lift-off phenomenon of a cathode electrode of a display panel part that may occur according to each of the first embodiment and the second embodiment of the present disclosure. 
         FIG.  5 A  is a cross-sectional view of a display apparatus according to a third embodiment of the present disclosure and an enlarged cross-sectional view of a partial area thereof. 
         FIG.  5 B  illustrates a difference between stresses applied to a polarizing member, an adhesive portion, and a display panel part according to each of the first embodiment, and the second embodiment of the present disclosure, and a difference between stresses applied to a polarizing member, an adhesive portion, a neutral plane compensation member and a display panel part according to the third embodiment of the present disclosure. 
         FIG.  6    illustrates a thickness of each of a first layer and a second layer of a neutral plane compensation member according to an embodiment of the present disclosure, and an applicable range of an elastic modulus of the second layer thereof. 
         FIG.  7    illustrates a light path where light incident on a display apparatus emits by a polarizing member and a reflective plate of a display panel part. 
         FIG.  8 A  illustrates change in a polarized state of light of a reference example according to a circular polarizing plate of  FIG.  7    in a Poincare sphere for comparison of stains based on a phase retardation.  FIG.  8 B  illustrates a reflection visual perception. 
         FIG.  9 A  illustrates change in a polarized state of light in a Poincare sphere when a phase retardation decreases compared to that in  FIG.  8 A , and  FIG.  9 B  illustrates a reflection visual perception. 
         FIG.  10 A  illustrates change in a polarized state of light in a Poincare sphere when a phase retardation increases compared to that in  FIG.  8 A , and  FIG.  10 B  illustrates a reflection visual perception. 
         FIG.  11    illustrates change in a polarized state of light according to the circular polarizing plate of  FIG.  6    in a Poincare sphere. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which may be illustrated in the accompanying drawings. In the following description, when a detailed description of well-known functions or configurations related to this document is determined to unnecessarily cloud a gist of the inventive concept, the detailed description thereof will be omitted. The progression of processing steps and/or operations described is an example; however, the sequence of steps and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a particular order. Like reference numerals designate like elements throughout. Names of the respective elements used in the following explanations are selected only for convenience of writing the specification and may be thus different from those used in actual products. 
     A shape, a size, a ratio, an angle, a number, etc., disclosed in the drawings for illustrating embodiments of the present disclosure are not necessarily to scale, and the present disclosure is not limited thereto. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and “including” when used in this specification, specify the presence of the stated features, integers, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, operations, elements, components, and/or portions thereof. 
     In interpreting a numerical value, the value is interpreted as including an error range unless there is a separate explicit description thereof to the contrary. 
     It will be understood that when an element or layer is referred to as being “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer, or one or more intervening elements or layers may be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layers, it may be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. In addition, it will also be understood that when a first element or layer is referred to as being present “on” or “beneath” a second element or layer, the first element may be disposed directly on or beneath the second element or may be disposed indirectly on or beneath the second element with a third element or layer being disposed between the first and second elements or layers. 
     In descriptions of temporal relationships, for example, temporal precedent relationships between two events such as “after,” “subsequent to,” “before,” etc., another event may occur therebetween unless “directly after”, “directly subsequent” or “directly before” is not indicated. 
     It will be understood that, although the terms “first,” “second,” “third,” and so on may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present disclosure. 
     Features of various embodiments of the present disclosure may be partially or overall coupled to or combined with each other, and may be variously inter-operated with each other and driven technically as those skilled in the art can sufficiently understand. Embodiments of the present disclosure may be carried out independently from each other, or may be carried out together in co-dependent relationship. 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. For convenience of description, a scale of each of elements illustrated in the accompanying drawings differs from a real scale, and thus, is not limited to a scale illustrated in the drawings. 
     Hereinafter, various configurations of the display apparatus that may reduce a difference between the tensile stress and the compressive stress respectively applied to the polarizing member and the display panel part to reduce a stress applied thereto will be described in detail. 
       FIG.  1    is a cross-sectional view of a display apparatus according to an embodiment of the present disclosure and an enlarged cross-sectional view of a partial area thereof.  FIG.  2    is an enlarged cross-sectional view of a display panel according to an embodiment of the present disclosure. 
     Referring to  FIG.  1   , a display apparatus  1  may include a plate assembly  100 , a display panel part  200  (which may also be referred to herein as a display panel  200  or a display panel assembly  200 ), an adhesive part  400  (which may also be referred to herein as an adhesive layer  400 ), a polarizing member  500 , and a cover window part  600  (which may also be referred to herein as a cover window  600 ). 
     The cover window part  600  may be disposed on the polarizing member  500  and the display panel part  200 . The cover window part  600  may protect the polarizing member  500  and the display panel part  200  from damage caused by external shocks and scratches. In an embodiment, the cover window part  600  protects an upper surface of the polarizing member  500  and an upper surface of the display panel part  200 . 
     The cover window part  600  may include a protective layer  610 , a pattern layer  620 , and a cover window  630  disposed on each other. In an embodiment, the protective layer  610  is closest to the polarizing member  500  and the cover window  630  is disposed furthest from the polarizing member  500  to form an external surface of the apparatus  1  with the pattern layer  620  between the protective layer  610  and the cover window  630 . 
     The protective layer  610  may be a layer in which a pattern is formed that may be visible to a user even when the display panel  220  does not display an image. The protective layer  610  may be a decorative layer. Embodiments of the present disclosure are not limited thereto. 
     The pattern layer  620  may be disposed along an edge or an outer periphery of the protective layer  610 . 
     For example, the pattern layer  620  may be disposed at an upper surface of the protective layer  610  and correspond to a bezel area or a non-display area of the display panel  220 . Embodiments of the present disclosure are not limited thereto. For example, the pattern layer  620  may be disposed at a rear or bottom surface of the protective layer  610  opposite to the upper surface. 
     The pattern layer  620  may be a layer in which a decoration is printed or formed, and may be a decorative layer. Embodiments of the present disclosure are not limited to terms. 
     The pattern layer  620  may include an organic material such as black ink or carbon black, or an inorganic material such as a silicon oxide film (SiO 2 ), a silicon nitride film (SiN x ), and a metal, etc. 
     Further, the pattern layer  620  may include a black matrix. 
     When the pattern layer  620  is present, and even when the display panel part  200  does not display an image, the bezel area of the display panel part  200  may be displayed in substantially the same color as that of the display area of the display panel part  200 . Thus, the user may see the screen of the display panel part  200  in a wider manner. 
     The cover window  630  may be disposed on the protective layer  610  and the pattern layer  620 . 
     The cover window  630  may protect the protective layer  610 , the pattern layer  620 , the polarizing member  500 , and the display panel part  200  under the cover window  630  from external impact, moisture, heat, and the like. 
     Accordingly, the cover window  630  may be composed of a glass or plastic film having impact resistance and light transmittance. 
     When the cover window  630  is formed of glass, a protective film including polyethylene terephthalate (PET) may be further disposed at one surface of the cover window  630 , such as a top or bottom surface in an embodiment, to prevent scattering of fragments that may occur when the cover window  630  is broken by external force or stress. 
     Further, when the cover window  630  is composed of the plastic film, the plastic film may be an acrylic film, a transparent polyimide (colorless polyimide film), or the like. 
     A hard coating layer is disposed on the cover window  630  and is configured to protect the cover window  630  from external impact. 
     The hard coating layer may include a transparent organic/inorganic composite material, thereby effectively protecting the cover window  630  and reducing deterioration of light transmittance. 
     The plate assembly  100  may be disposed under the display panel part  200 . The plate assembly  100  protects the display panel part  200  from external moisture, heat, and shock, and may dissipate heat generated from the display panel part  200  to an outside. In an embodiment, the plate assembly  100  protects a bottom surface or side surfaces, or both, of the display panel part  200 . 
     The plate assembly  100  may act as a frame having impact resistance to protect the display panel part  200 . 
     The plate assembly  100  may include a lower plate  110 , and an upper plate  120 . 
     The upper plate  120  may be disposed on the lower plate  110 . 
     Each of the lower plate  110  and the upper plate  120  may include a metal material with high thermal conductivity and excellent charge transfer. 
     A support layer  130  may be disposed on the upper plate  120 . 
     The support layer  130  may be disposed at a rear or bottom surface of the display panel part  200 , and may protect the display panel part  200  from external moisture, heat, and impact or the like. 
     The support layer  130  may act as a back plate that supports the rear or bottom surface of the display panel part  200 . The support layer  130  may be composed of a polyethylene terephthalate (PET) film or a metal thin-film. Embodiments of the present disclosure are not limited thereto. 
     The plate assembly  100  and the cover window part  600  as described above may include first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  that may fix or attach adjacent layers to each other, but the same is not necessarily required. In an embodiment, one or more of the layers of the plate assembly  100  and the cover window part  600  are coated directly on each other without an intervening adhesive layer. 
     For example, the first adhesive layer  101  may be disposed between the lower plate  110  and the upper plate  120  and configured to fix or attach the lower plate  110  and the upper late  120  to each other, the second adhesive layer  103  may be disposed between the upper plate  120  and the support layer  130  and configured to fix or attach the upper plate  120  and the support layer  130  to each other, and the third adhesive layer  105  may be disposed between the support layer  130  and the display panel part  200  and configured to fix or attach the support layer  130  and the display panel part  200  to each other. 
     Further, the fourth adhesive layer  601  may be disposed between the polarizing member  500  and the protective layer  610  and configured to fix or attach the polarizing member  500  and the protective layer  610  to each other, and the fifth adhesive layer  603  may be disposed between the protective layer  610  and the cover window  630  and configured to fix or attach the protective layer  610  and the cover window  630  to each other. 
     Each of the first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  may be formed of a material having high adhesive force and/or high transparency. 
     Each of the first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  in accordance with the present disclosure may include a layer having an adhesive function as well as adhesion (or stickiness) function. 
     Each of the first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  may be formed between adjacent layers and may have an adhesive force so that bubbles or peeling do not occur even when a bending or a curvature thereof occurs, and may have viscoelastic properties used for the display apparatus  1 . 
     Each of the first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  may include an acrylic-based composition or a silicone-based composition. For example, each of the first to fifth adhesive layer  101 ,  103 ,  105 ,  601 , and  603  may include an optical clear adhesive (OCA) composition or a pressure sensitive adhesive (PSA) composition. 
     The display panel part  200 , the adhesive part  400 , and the polarizing member  500  may be disposed between the plate assembly  100  and the cover window part  600 . 
     The display panel part  200  may be disposed on the plate assembly  100 . 
     The display panel part  200  is shown in more detail in the detailed view of  FIG.  1    and may include an array part  210  (which may also be referred to herein as an array  210 ), a pixel part  220  (which may be also be referred to herein as a pixel  220 ), a sealing layer  230 , and a touch electrode layer  240  stacked on each other in sequential order in an embodiment. 
     The display panel part  200  may generate an image to be displayed. A type of the display panel part  200  is not limited. However, the display panel part may include an organic light-emitting display panel, a micro light-emitting diode display panel, etc., which are advantageous for realizing a flexible display apparatus. 
     The array part  210  may include a plurality of signal lines configured to supply various signals to a plurality of pixels, a switching thin-film transistor, and a driving thin-film transistor. 
     The signal lines may include a gate line, a data line, a pixel driving power line, and the like. 
     The detail view of  FIG.  1    also provides additional detail of the polarizing member  500 . The polarizing member  500  may be disposed on the display panel part  200 . 
     The adhesive part  400  may be disposed between the display panel part  200  and the polarizing member  500  to fix the polarizing member  500  to the display panel part  200 . 
     The adhesive part  400  may be formed of the same material as that of each of the first to fifth adhesive layers  101 ,  103 ,  105 ,  601 , and  603  as described above. 
     The display panel part  200  may include various metal materials used for the thin-film transistors, the signal lines, the electrodes, and the light-emitting element layer. 
     External light incident on the display panel part  200  may be reflected from the above metal material. Visibility of the display apparatus  1  may be deteriorated due to reflection of external light. 
     Accordingly, the polarizing member  500  includes a retardation film (or phase retardation film) that selectively transmits light therethrough to reduce reflection of external light incident on the display panel part  200 , thereby improving outdoor visibility of the display apparatus  1 . 
     The polarizing member  500  may refer to an optical part that receives unpolarized light in which polarized states are mixed with each other in disorder and selectively transmits therethrough light linearly polarized in a specific direction. 
     As shown in the detail view of  FIG.  1   , the polarizing member  500  may include a compensation film layer  510 , a retardation film layer (or a phase retardation film layer)  520 , a polarizing film layer  530 , and a base layer  540 . 
     The polarizing film layer  530  may act as a polarizer capable of absorbing light linearly polarized in parallel to an absorption axis and transmitting therethrough light linearly polarized in perpendicular to the absorption axis, that is, light linearly polarized in parallel to a transmission axis. 
     The polarizing film layer  530  may be formed of polyvinyl alcohol (PVA) which is dyed with iodine ions or dichroic dyes and thus is elongated. 
     The base layer  540  may be disposed on the polarizing film layer  530 . 
     The base layer  540  may be a protective film that protects the polarizing film layer  530  from external moisture. 
     A surface treatment for anti-reflection, anti-glare, and/or surface reinforcement may be performed or applied on the base layer  540 . 
     The base layer  540  may be formed of triacetyl cellulose, a cyclic olefin polymer, a polycarbonate, an acryl, or a polyethylene terephthalate. Embodiments of the present disclosure are not limited thereto. 
     The retardation film layer  520  may be disposed under the polarizing film layer  530 . 
     In accordance with an embodiment of the present disclosure, “under the polarizing film layer  530 ” may mean that the display panel part  200  is disposed under the polarizing film layer  530 . In one or more embodiments, “under the polarizing film layer  530 ” may mean that the retardation film layer  520  is directly below, and disposed directly on, the polarizing film layer  530  in sequential order as shown in the detail view of  FIG.  1   . 
     According to an embodiment of the present disclosure, the polarizing film layer  530  may be a quarter-wavelength plate (QWP or λ/4 plate). 
     Since the quarter-wavelength plate has a phase retardation of a wavelength (λ) of light of λ/4, a polarizing direction of incident light thereon may be changed. 
     Accordingly, linearly polarized light passing through the quarter-wavelength plate may be converted into circularly polarized light. Circularly polarized light passing through the quarter-wavelength plate may be converted into linearly polarized light. 
     For example, the quarter-wavelength plate may have various wavelength dispersion characteristics such as reverse wavelength dispersion, flat wavelength dispersion, and forward wavelength dispersion. 
     According to an embodiment of the present disclosure, the polarizing film layer  530  may be a quarter-wavelength plate rQWP having reversed wavelength dispersion. 
     A retardation value required to achieve circular polarization of light may vary based on a wavelength of the light. 
     In this regard, the quarter-wavelength plate rQWP with the reverse wavelength dispersion may achieve a phase retardation so that light is closer to circularly polarized light, in comparison with a quarter-wavelength plate having forward wavelength dispersion or flat wavelength dispersion. 
     The retardation film layer  520  may include liquid crystals aligned in one direction. 
     For example, the liquid crystal may be a nematic liquid crystal or a smectic liquid crystal. 
     Further, the retardation film layer  520  may be formed to be aligned in one direction by coating a mixture of liquid crystals and dichroic dye and applying photo-alignment to the mixture. 
     For example, the retardation film layer  520  may be formed by forming an alignment film on a substrate, mixing the liquid crystals and the dichroic dye, coating the mixture on the alignment film, and aligning the mixture using polarizing ultraviolet (UV). 
     The compensation film layer  510  may be disposed under the retardation film layer  520 . 
     The compensation film layer  510  may block reflection of external light not only in a frontward direction but also in a lateral direction, thereby reducing reflectance of external light due to a viewing angle. 
     According to an embodiment of the present disclosure, the compensation film layer  510  may be a +C plate (positive C plate). 
     The +C plate may have a refractive index relationship in different directions characterized by the equation nx=ny&lt;nz where nx is a refractive index in an x direction, ny is a refractive index in a y direction, and nz is a refractive index in a z direction. 
     The compensation film layer  510  may include liquid crystals aligned in one direction. 
     For example, the liquid crystal may be a nematic liquid crystal or a smectic liquid crystal. 
     Further, the compensation film layer  510  may be formed to be aligned in one direction by coating a mixture of liquid crystals and dichroic dye and applying photo-alignment to the mixture. 
     For example, the compensation film layer  510  may be formed by forming an alignment film on a substrate, mixing the liquid crystals and the dichroic dye, coating the mixture on the alignment film, and aligning the mixture using polarizing ultraviolet (UV). 
     The display apparatus  1  according to an embodiment of the present disclosure includes the display panel part  200  and the polarizing member  500 . The adhesive portion  400  may be disposed between the display panel part  200  and the polarizing member  500  to fix or attach the polarizing member  500  to the display panel part  200 . 
     The polarizing member  500  may be laminated to the display panel  200  by the adhesive part  400 . 
     The base layer  540 , the polarizing film layer  530 , the retardation film layer  520 , and the compensation film layer  510  of the polarizing member  500  may be sequentially stacked in a direction toward the display panel part  200 . 
     Accordingly, the retardation film layer  520  and the compensation film layer  510  may constitute a lower portion of the polarizing member  500  with respect to an entire stack of the polarizing member  500 . 
     Each of the phase retardation film layer  520  and the compensation film layer  510  of the polarizing member  500  may include liquid crystals aligned in one direction. 
     Since the liquid crystal is vulnerable to stress, the layers relatively vulnerable to the stress may constitute the lower portion of the polarizing member  500 . 
     The display panel part  200  may include an array part  210 , a pixel part  220 , and a sealing layer (or an encapsulation layer)  230 . The array part  210 , the pixel part  220 , and the sealing layer  230  may be sequentially stacked in a direction toward the polarizing member  500 . 
     With reference to  FIG.  1    and  FIG.  2   , and as explained in more detail below, the pixel part  220  may include an anode electrode  222 , a light-emitting element layer  224 , and a cathode electrode  225 . The anode electrode  222 , the light-emitting element layer  224 , and the cathode electrode  225  may be sequentially stacked in a direction toward the polarizing member  500 . 
     Accordingly, the cathode electrode  225  and the sealing layer  230  may constitute an upper portion of the display panel part  200  with respect to an entire stack of the display panel part  200 . 
     A planarization layer  226  including an organic material and a second passivation layer  227  including an inorganic material may be disposed between the cathode electrode  225  ( FIG.  2   ) and the sealing layer  230 . 
     Further, the sealing layer  230  may include an inorganic, an organic, or an organic and an inorganic composite layer to prevent penetration of external moisture and oxygen. 
     An upper portion of the display panel part  200  composed of the cathode electrode  225  ( FIG.  2   ) and the sealing layer  230  may include a stack of the organic material layers and the inorganic material layers, and thus may be vulnerable to stress. 
     Accordingly, layers that are relatively vulnerable to stress constitute the upper portion of the display panel part  200  in an embodiment. 
     When the display apparatus  1  is a flexible display apparatus, greater stress may be applied to the lower portion of the polarizing member  500  and the upper portion of the display panel part  200  while the adhesive part  400  is interposed therebetween. 
       FIG.  2    is a cross-sectional view providing additional detail of the display panel part  200 . Referring to  FIG.  2   , with continuing reference to  FIG.  1   , a buffer layer  213  may be formed on a base substrate  211 , and a switching thin-film transistor including an active layer  214 , a gate electrode  216 , a first electrode  218   a , and a second electrode  218   b  may be disposed on the buffer layer  213 . 
     A light-blocking layer  212  configured to prevent light from being incident on the active layer  214  of the switching thin-film transistor may be disposed between the base substrate  211  and the buffer layer  213 . 
     A gate insulating layer  215  capable of insulating the active layer  214  and the gate electrode  216  from each other may be disposed between the active layer  214  and the gate electrode  216 . 
     An interlayer insulating layer  217  may be disposed on the active layer  214  and the gate electrode  216 . The first electrode  218   a  and the second electrode  218   b  may be electrically connected to the active layer  214  via contact holes formed in the interlayer insulating layer  217 , respectively. 
     The first electrode  218   a  may be a source electrode, and the second electrode  218   b  may be a drain electrode. 
     The pixel part  220  may include a plurality of pixel areas configured by the signal lines. 
     A plurality of pixels configured to display an image according to signals supplied to the signal lines may be disposed in the pixel areas, respectively. 
     Each of the plurality of pixels may include a switching thin-film transistor in a pixel area, an anode electrode  222  electrically connected to the switching thin-film transistor, a light-emitting element layer  224  formed on the anode electrode  222 , and a cathode electrode  225  electrically connected to the light-emitting element layer  224 . 
     A first passivation layer  219  and an overcoat layer  221  may be disposed between the switching thin-film transistor and the anode electrode  222 . 
     The first passivation layer  219  may be formed of an inorganic material. The overcoat layer  221  may be formed of an organic material. 
     The anode electrode  222  may be electrically connected to the second electrode  218   b  of the switching thin-film transistor via a contact hole formed in the first passivation layer  219  and the overcoat layer  221 . 
     The light-emitting element layer  224  may include, for example, an organic light-emitting element formed on the anode electrode  222 . 
     The organic light-emitting element may be implemented to emit light of the same color for the pixels, such as white light, or to emit light of different colors for different pixels, such as red, green, or blue light. 
     In another embodiment of the present disclosure, the organic light-emitting element may be composed of a first element layer in which red, green, and blue light emit from pixels, and a second element layer which is disposed on the first element layer and in which red, green, and blue light emit from pixels. A charge generation layer may be disposed between the first element layer and the second element layer. The charge generation layer may include an N-type charge generation layer and a P-type charge generation layer. 
     In another example, the light-emitting element layer  224  may include a micro light-emitting diode element electrically connected to each of the anode electrode and the cathode electrode. 
     The micro light-emitting diode element refers to a light-emitting diode implemented in a form of an integrated circuit (IC) or a chip, and may include a first terminal electrically connected to the anode electrode and a second terminal electrically connected to the cathode electrode. 
     The bank layer  223  is disposed at a boundary between the respective light-emitting element layers  224  to reduce color mixing between the light-emitting element layers  224  displaying different colors. 
     A planarization layer  226  and a second passivation layer  227  may be disposed on the cathode electrode  225 . 
     The planarization layer  226  may be formed of an organic material, and the second passivation layer  227  may be formed of an inorganic material. 
     A sealing layer (or an encapsulation layer)  230  may be disposed on the second passivation layer  227  to prevent moisture or foreign substances from penetrating into the light-emitting element layer  224 . The sealing layer  230  may secured thereto via an adhesive layer  228 . 
     A touch electrode layer  240  ( FIG.  1   ) may be disposed on the sealing layer  230 . 
     The touch electrode layer  240  may have a ToE (Touch Sensor on Encapsulation) structure in which a touch electrode and a touch line are disposed on the sealing layer  230  of the display panel part  200 . Embodiments of the present disclosure are not limited thereto. 
     The touch electrode layer  240  may detect a user&#39;s touch input such as presence or absence of screen touch or touch coordinates, and may detect an input signal from a touch of a user or a tool through the cover window part  600 . 
     The touch electrode layer  240  may be implemented in various schemes, such as a resistive film scheme, a capacitive scheme, an optical scheme, or an electromagnetic scheme. However, embodiments of the present disclosure are not particularly limited. 
     The touch electrode layer  240  may include a touch sensor structure including a plurality of touch electrodes and a plurality of touch routing lines for connecting the touch electrodes to a touch sensing circuit. 
       FIG.  3    illustrates a difference between the stresses applied to the display panel part  200 , the polarizing member  500 , and the adhesive part  400  of the display apparatus according to each of a first embodiment and a second embodiment of the display apparatus  1  when the display apparatus  1  is folded in an inner folding scheme in which display surfaces of the display panel part  200  face each other or the display panel part  200  is disposed in an inner portion or configuration. 
     The first embodiment and the second embodiment of the display apparatus  1  have different thicknesses of the cover window  630 . Conditions of the other components thereof are substantially the same as each other. 
     A thickness w 1  of the cover window  630  according to a first embodiment of the display apparatus  1  is 60 μm, and a thickness w 2  of the cover window  630  according to a second embodiment of the display apparatus  1  is 90 μm. 
     Based on change in a thickness of the cover window  630 , a magnitude of a stress applied to each of the polarizing member  500  and the display panel part  200  may vary. 
     The polarizing member  500  has a relatively high modulus of elasticity and is disposed above the adhesive part  400 . Thus, when the thickness of the cover window  630  increases, greater tensile stress may be applied to the polarizing member  500 . 
     Further, the display panel part  200  has a relatively high modulus of elasticity and is disposed under the adhesive part  400 . Thus, greater compressive stress may be applied to the display panel part when the thickness of the cover window  630  increases. 
     The adhesive part  400  disposed between the polarizing member  500  and the display panel part  200  has a relatively low modulus of elasticity, and thus may serve to reduce the compressive stress applied to the display panel part  200  and the tensile stress applied to the polarizing member  500 . 
     It may be identified that in the first embodiment of the display apparatus  1 , a difference A between a magnitude of the tensile stress A′ applied to the polarizing member  500  and a magnitude of the compressive stress A″ applied to the display panel part  200  is quite large. 
     Referring to  FIG.  3   , it may be identified that in the first embodiment of the display apparatus  1 , the magnitude of the tensile stress A′ applied to the polarizing member  500  increases by a ratio of about 0.025 in a (+) tensile direction. It may be identified that in the first embodiment of the display apparatus  1 , the magnitude of the compressive stress A″ applied to the display panel part  200  increases by a ratio of about 0.012 in a (−) compressive direction. 
     Therefore, it may be identified that in the first embodiment of the display apparatus  1 , the difference A between the magnitude of the tensile stress A′ applied to the polarizing member  500  and the magnitude of the compressive stress A″ applied to the display panel part  200  has a ratio of about 0.037. 
     Further, it may be identified that in the second embodiment of the display apparatus  1 , a difference B between the magnitude of the tensile stress B′ applied to the polarizing member  500  and the magnitude of the compressive stress B″ applied to the display panel part  200  is quite large. 
     Referring to  FIG.  3   , it may be identified that in the second embodiment of the display apparatus  1 , the magnitude of the tensile stress B′ applied to the polarizing member  500  increases by a ratio of about 0.03 in the (+) tensile direction. It may be identified that in the second embodiment of the display apparatus  1 , the magnitude of the compressive stress B″ applied to the display panel part  200  increases by a ratio of about 0.01 in the (−) compressive direction. 
     Therefore, it may be identified that, in the second embodiment of the display apparatus  1 , the difference B between the magnitude of the tensile stress B′ applied to the polarizing member  500  and the magnitude of the compressive stress B″ applied to the display panel part  200  has a ratio of about 0.04. 
     When the tensile stress is applied to the lower portion of the polarizing member  500 , cracks may occur frequently in the lower portion of the polarizing member  500 . 
       FIG.  4 A  illustrates a crack phenomenon occurring in a layer including the liquid crystal of the polarizing member  500 . 
     Referring to  FIG.  4 A , it may be identified that a plurality of cracks are generated in an oblique direction in the polarizing member  500  in which a plurality of layers are stacked. 
     Further, when the compressive stress is applied to the upper portion of the display panel part  200 , cracks or layer lift-off (or lifting or separation) of the layers may occur frequently in the upper portion of the display panel part  200 . 
       FIG.  4 B  illustrates a lift-off phenomenon in which the cathode electrode  225  of the display panel part  200  is lifted off. 
     Referring to  FIG.  4 B , it may be identified that the cathode electrode  225  and the sealing layer  230  disposed on the light-emitting element layer  224  of the display panel part  200  are lifted off from the light-emitting element layer  224 . 
     The crack phenomenon in the lower portion of the polarizing member  500  or the lift-off phenomenon of the layer in the upper portion of the display panel part  200  may vary depending on a thickness distribution of each of the layers of the display apparatus. 
     For example, in the first embodiment of the display apparatus  1  with the relatively smaller thickness of the cover window  630 , the lift-off phenomenon of the cathode electrode  225  in the display panel part  200  may occur. In the second embodiment of the present disclosure having the relatively larger thickness of the cover window  630 , the cracks may occur in the retardation film layer  520  or the compensation film layer  510  of the polarizing member  500 . 
     Hereinafter, a display apparatus  2  according to one or more embodiments of the present disclosure is described that may reduce the difference between the tensile stress and the compressive stress respectively applied to the polarizing member  500  and the display panel part  200  to reduce the overall stress applied to the polarizing member  500  and the display panel part  200 . 
       FIG.  5 A  is a cross-sectional view of a display apparatus  2  according to one or more embodiments of the present disclosure and an enlarged cross-sectional view of a partial area of the display apparatus  2 . 
     The display apparatus  2  may have the same configuration as that of the display apparatus  1  described with reference to  FIG.  1    to  FIG.  4 B  except as otherwise described herein, and particularly with respect to a neutral plane compensation member  300  disposed between the display panel part  200  and the adhesive part  400  for the polarizing member  500  in the display apparatus  2 . 
     Therefore, embodiments of display apparatus  2  of the present disclosure will be described with a particular emphasis on the neutral plane compensation member  300 , and the descriptions duplicate with those of the display apparatus  1  will be omitted. 
     A neutral plane compensation member  300  may be disposed between the display panel part  200  and the polarizing member  500 . 
     Further, the adhesive part  400  may be disposed between the polarizing member  500  and the neutral plane compensation member  300 . Thus, the display apparatus  2  may include the plate assembly  100 , the display panel part  200 , the neutral plane compensation member  300 , the adhesive part  400 , the polarizing member  500 , and the cover window part  600  stacked in sequential order. 
     The neutral plane compensation member  300  may include a first layer  310  and a second layer  301 . For example, the first layer  310  may act as a neutral plane compensation layer. However, embodiments of the present disclosure are not limited thereto. For example, the second layer  301  may act as a fixing layer or an adhesive layer. Embodiments of the present disclosure are not limited thereto. 
     The first layer  310  of the neutral plane compensation member  300  may be disposed at a lower portion the adhesive part  400  and may contact the adhesive part  400 . In other words, the first layer  310  of the neutral plane compensation member  300  may be disposed directly on the adhesive part  400 , such as being disposed on a lower portion or bottom surface of the adhesive part  400  in the orientation shown in  FIG.  5 A . 
     The second layer  301  of the neutral plane compensation member  300  may be disposed above the display panel part  200  and contact the display panel part  200 . In an embodiment, the second layer  301  is disposed directly on the display panel part  200 , such as being disposed on an upper portion or top surface of the display panel part  200  in the orientation shown in  FIG.  5 A . In one or more embodiments, the first and second layers  310 ,  301  have an inverse orientation, namely, the second layer  301  is disposed on the adhesive part  400  and the first layer  310  is disposed on the display panel part  200 . 
     The first layer  310  may be a tri-acetyl cellulose (TAC) film. 
     The second layer  301  may include an acrylic composition or a silicone-based composition. For example, the second layer  301  may include an optical clear adhesive (OCA) composition or a pressure sensitive adhesive (PSA) composition. 
     The neutral plane compensation member  300  may be disposed between the polarizing member  500  to which strong tensile stress is applied and the display panel part  200  to which strong compressive stress is applied, and thus may serve as a compensation layer to reduce the difference between the stresses applied thereto. 
       FIG.  5 B  illustrates a difference between stresses applied to the polarizing member  500 , the adhesive part  400 , and the display panel part  200  stacked according to the first embodiment and the second embodiment of the display apparatus  1  described with reference to  FIG.  3   , and a difference between stresses applied to the polarizing member  500 , the adhesive part  400 , the neutral plane compensation member  300 , and the display panel part  200  stacked according to embodiments of the display apparatus  2  of the present disclosure in  FIG.  5 A . 
     In the example of the display apparatus  2  represented in  FIG.  5 B , a thickness of the neutral plane compensation member  300  is selected to be 60 μm, and a thickness of the adhesive part  400  is selected to be 50 μm. However, embodiments of the disclosure are not limited thereto and the thicknesses may be selected to be more or less than these values. 
     As described with reference to  FIG.  3   , in the first embodiment and the second embodiment of the display apparatus  1 , the polarizing member  500  and the display panel part  200  may be disposed or bonded to each other by the adhesive part  400  interposed therebetween. 
     A lower portion of the polarizing member  500  composed of the retardation film layer  520  and the compensation film layer  510 , and an upper portion of the display panel part  200  composed of the cathode electrode  225  are in a trade-off relationship with each other in terms of crack generation due to a difference between the tensile stress and the compressive stress respectively applied thereto. 
     Referring to  FIG.  5 B , it may be identified that in the first embodiment of the display apparatus  1 , the magnitude of the tensile stress A′ applied to the polarizing member  500  increases by a ratio of about 0.025 in the (+) tensile direction. It may be identified that in the first embodiment of the display apparatus  1 , the magnitude of the compressive stress A″ applied to the display panel part  200  increases by a ratio of about 0.012 in the (−) compressive direction. 
     Therefore, it may be identified that in the first embodiment display apparatus  1 , the difference A between the magnitude of the tensile stress A′ applied to the polarizing member  500  and the magnitude of the compressive stress A″ applied to the display panel part  200  has a ratio of about 0.037, as described above with reference to  FIG.  3   . 
     Accordingly, it may be identified that in the first embodiment of display apparatus  1 , the difference A between the magnitude of the tensile stress A′ applied to the polarizing member  500  and the magnitude of the compressive stress A″ applied to the display panel part  200  is quite large. 
     Referring to  FIG.  5 B , it may be identified that in the second embodiment of the display apparatus  1 , the magnitude of the tensile stress B′ applied to the polarizing member  500  increases by a ratio of about 0.03 in the (+) tensile direction. It may be identified that in the second embodiment, the magnitude of the compressive stress B″ applied to the display panel part  200  increases by a ratio of about 0.01 in the (−) compressive direction. 
     Therefore, it may be identified that in the second embodiment of the display apparatus  1 , the difference B between the magnitude of the tensile stress B′ applied to the polarizing member  500  and the magnitude of the compressive stress B″ applied to the display panel part  200  has a ratio of about 0.04, as described above with reference to  FIG.  3   . 
     Accordingly, it may be identified that in the second embodiment of the display apparatus  1 , the difference B between the magnitude of tensile stress B″ applied to the polarizing member  500  and the magnitude of compressive stress B″ applied to the display panel part  200  is quite large. 
     Referring to  FIG.  5 B , it may be identified that in one or more embodiments of the display apparatus  2 , the magnitude of the tensile stress C′ applied to the polarizing member  500  increases by a ratio of about 0.023 in the (+) tensile direction. It may be identified that in embodiments of the display apparatus  2 , the magnitude of the compressive stress C″ applied to the display panel part  200  increases by a ratio of about 0.006 in the (−) compressive direction. 
     Therefore, it may be identified that in embodiments of the display apparatus  2 , the difference C between the magnitude of the tensile stress C′ applied to the polarizing member  500  and the magnitude of the compressive stress C″ applied to the display panel part  200  has a ratio of about 0.029. 
     Accordingly, it may be identified that the difference C between the magnitude of the tensile stress C′ applied to the polarizing member  500  and the magnitude of the compressive stress C″ applied to the display panel part  200  in embodiments of the display apparatus  2  decreases significantly, compared to each of the difference A according to the first embodiment of the display apparatus  1  and the difference B according to the second embodiment of the display apparatus  1 . 
     Thus, according to one or more embodiments of the present disclosure, the tensile stress applied to the lower portion of the polarizing member  500  may be reduced, and the compressive stress applied to the upper portion of the display panel part  200  may be reduced. 
     When the neutral plane compensation member  300  is additionally disposed between the polarizing member  500  and the display panel part  200  as in embodiments of the display apparatus  2 , the neutral plane compensation member  300  may function as a compensation layer to reduce the stress applied to the lower portion of the polarizing member  500  and the stress applied to the upper portion of the display panel part  200 . 
     Therefore, according to one or more embodiments of the present disclosure, the neutral plane compensation member  300  including the first layer  310  and the second layer  301  is disposed between the polarizing member  500  and the display panel part  200 , such that the difference between the tensile stress and the compressive stress respectively applied to the polarizing member  500  and the display panel part  200  may be reduced. 
     A thickness of the first layer  310  of the neutral plane compensation member  300  may be in a range of 20 μm to 60 μm, and a modulus (which may be a modulus of elasticity) thereof may be in a range of 1.0×10 8  Pa to 1.0×10 10  Pa, while a thickness of the second layer  301  thereof may be in a range of 20 μm to 60 μm, and a modulus thereof may be in a range of 1.0×10 4  Pa to 1.0×10 6  Pa. 
     In accordance with embodiments of the present disclosure, the modulus is measured based on −20° C. 
     When the thickness and the modulus of the first layer  310  and the thickness and the modulus of the second layer  301  are out of the above defined ranges, the stress applied to the polarizing member  500  and the stress applied to the display panel part  200  may vary. This may cause a defect. Thus, while dimensions and moduli outside the above ranges may be less preferred, they are contemplated in the present disclosure and the disclosure should not be limited strictly to the above ranges. 
     In one embodiment of the present disclosure, the thickness of the first layer  310  may be 25 μm, the thickness of the second layer  301  may be 25 μm, and the modulus of the second layer  301  may be in a range of 0.7×10 5  Pa to 2.3×10 5  Pa. 
     In another embodiment of the present disclosure, the thickness of the first layer  310  may be 50 μm, the thickness of the second layer  301  may be 25 μm, and the modulus of the second layer  301  may be in a range of 0.5×10 5  Pa to 2.5×10 5  Pa. 
     In another embodiment of the present disclosure, the thickness of the first layer  310  may be 25 μm, the thickness of the second layer  301  may be 50 μm, and the modulus of the second layer  301  may be in a range of 1.0×10 5  Pa to 2.2×10 5  Pa. 
     In another embodiment of the present disclosure, the thickness of the first layer  310  may be 50 μm, the thickness of the second layer  301  may be 50 μm, and the modulus of the second layer  301  may be in a range of 0.6×10 5  Pa to 2.4×10 5  Pa. 
       FIG.  6    illustrates a thickness of each of the first layer  310  and the second layer  301  of the neutral plane compensation member  300  according to an embodiment of the present disclosure, and a range of an elastic modulus of the second layer  301  based on the thickness. 
       FIG.  6    illustrates a graph of a measurement of minimum and maximum values of the elastic modulus of the second layer  301  when a thickness of the first layer  310  is in a range of 25 μm to 50 μm, and a thickness of the second layer  301  is in a range of 25 μm to 50 μm. 
     An applicable range of a modulus of the second layer  301  which does not cause the defect may vary depending on a thickness of the first layer  310  and a thickness of the second layer  301 . 
     Referring to  FIG.  6   , it may be identified that when a thickness of the first layer  310  is 50 μm and a thickness of the second layer  301  is 25 μm, a modulus of the second layer  301  is in a range of 0.5×10 5  Pa to 2.5×10 5  Pa, and, in this setting, an applicable range of the elastic modulus of the second layer  301  is widest. 
     Further, Table 1 to Table 4 below show the minimum and maximum values of the elastic modulus of the second layer  301  as measured in thickness change on 1 μm basis when a thickness of the first layer  310  is in a range of 25 μm to 50 μm, and a thickness of the second layer  301  is in a range of 25 μm to 50 μm. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Second layer 
                 First layer thickness 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 modulus (×10 5  Pa) 
                 25 
                 26 
                 27 
                 28 
                 29 
                 30 
                 31 
                 32 
                 33 
                 34 
                 35 
                 36 
                 37 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Second 
                 25 
                 min. 
                 0.70 
                 0.69 
                 0.68 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
                 0.64 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
               
               
                 layer 
                   
                 Max. 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
               
               
                 thickness 
                 26 
                 min. 
                 0.71 
                 0.70 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
               
               
                   
                   
                 Max. 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
               
               
                   
                 27 
                 min. 
                 0.72 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
               
               
                   
                   
                 Max. 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
               
               
                   
                 28 
                 min. 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.66 
                 0.65 
                 0.64 
                 0.63 
               
               
                   
                   
                 Max. 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
               
               
                   
                 29 
                 min. 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.66 
                 0.65 
                 0.64 
               
               
                   
                   
                 Max. 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
               
               
                   
                 30 
                 min. 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
                 0.64 
               
               
                   
                   
                 Max. 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
               
               
                   
                 31 
                 min. 
                 0.77 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
               
               
                   
                   
                 Max. 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
               
               
                   
                 32 
                 min. 
                 0.78 
                 0.77 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
               
               
                   
                   
                 Max. 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
               
               
                   
                 33 
                 min. 
                 0.80 
                 0.79 
                 0.77 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.67 
               
               
                   
                   
                 Max. 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
               
               
                   
                 34 
                 min. 
                 0.81 
                 0.80 
                 0.79 
                 0.78 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
               
               
                   
                   
                 Max. 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
               
               
                   
                 35 
                 min. 
                 0.82 
                 0.81 
                 0.80 
                 0.79 
                 0.78 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.70 
                 0.69 
               
               
                   
                   
                 Max. 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
               
               
                   
                 36 
                 min. 
                 0.83 
                 0.82 
                 0.81 
                 0.80 
                 0.79 
                 0.77 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.72 
                 0.71 
                 0.69 
               
               
                   
                   
                 Max. 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
               
               
                   
                 37 
                 min. 
                 0.84 
                 0.83 
                 0.82 
                 0.81 
                 0.80 
                 0.78 
                 0.77 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
                 0.71 
                 0.70 
               
               
                   
                   
                 Max. 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Second layer 
                 First layer thickness 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 modulus (×10 5  Pa) 
                 38 
                 39 
                 40 
                 41 
                 42 
                 43 
                 44 
                 45 
                 46 
                 47 
                 48 
                 49 
                 50 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Second 
                 25 
                 min. 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.52 
                 0.52 
                 0.51 
                 0.50 
               
               
                 layer 
                   
                 Max. 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
                 2.47 
                 2.48 
                 2.48 
                 2.49 
                 2.50 
               
               
                 thickness 
                 26 
                 min. 
                 0.60 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.55 
                 0.54 
                 0.53 
                 0.52 
                 0.51 
                 0.50 
               
               
                   
                   
                 Max. 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
                 2.46 
                 2.47 
                 2.48 
                 2.49 
                 2.50 
               
               
                   
                 27 
                 min. 
                 0.61 
                 0.60 
                 0.59 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.53 
                 0.52 
                 0.51 
               
               
                   
                   
                 Max. 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
                 2.47 
                 2.48 
                 2.48 
                 2.49 
               
               
                   
                 28 
                 min. 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.52 
                 0.51 
               
               
                   
                   
                 Max. 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
                 2.46 
                 2.47 
                 2.48 
                 2.49 
               
               
                   
                 29 
                 min. 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.53 
                 0.52 
               
               
                   
                   
                 Max. 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
                 2.47 
                 2.48 
                 2.48 
               
               
                   
                 30 
                 min. 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.52 
               
               
                   
                   
                 Max. 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
                 2.46 
                 2.47 
                 2.48 
               
               
                   
                 31 
                 min. 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
                 0.52 
               
               
                   
                   
                 Max. 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
                 2.47 
                 2.48 
               
               
                   
                 32 
                 min. 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
               
               
                   
                   
                 Max. 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
                 2.46 
                 2.47 
               
               
                   
                 33 
                 min. 
                 0.66 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
                 0.53 
               
               
                   
                   
                 Max. 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
                 2.47 
               
               
                   
                 34 
                 min. 
                 0.67 
                 0.66 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
               
               
                   
                   
                 Max. 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
                 2.46 
               
               
                   
                 35 
                 min. 
                 0.67 
                 0.66 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
                 0.54 
               
               
                   
                   
                 Max. 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
                 2.46 
               
               
                   
                 36 
                 min. 
                 0.68 
                 0.67 
                 0.66 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
                 0.54 
               
               
                   
                   
                 Max. 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
                 2.46 
               
               
                   
                 37 
                 min. 
                 0.69 
                 0.68 
                 0.67 
                 0.65 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.60 
                 0.58 
                 0.57 
                 0.56 
                 0.55 
               
               
                   
                   
                 Max. 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
                 2.45 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Second layer 
                 First layer thickness 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 modulus (×10 5  Pa) 
                 25 
                 26 
                 27 
                 28 
                 29 
                 30 
                 31 
                 32 
                 33 
                 34 
                 35 
                 36 
                 37 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Second 
                 38 
                 min. 
                 0.86 
                 0.84 
                 0.83 
                 0.82 
                 0.81 
                 0.80 
                 0.78 
                 0.77 
                 0.76 
                 0.75 
                 0.73 
                 0.72 
                 0.71 
               
               
                 layer 
                   
                 Max. 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
               
               
                 thickness 
                 39 
                 min. 
                 0.87 
                 0.86 
                 0.84 
                 0.83 
                 0.82 
                 0.81 
                 0.79 
                 0.78 
                 0.77 
                 0.76 
                 0.74 
                 0.73 
                 0.72 
               
               
                   
                   
                 Max. 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
               
               
                   
                 40 
                 min. 
                 0.88 
                 0.87 
                 0.85 
                 0.84 
                 0.83 
                 0.82 
                 0.80 
                 0.79 
                 0.78 
                 0.76 
                 0.75 
                 0.74 
                 0.73 
               
               
                   
                   
                 Max. 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
               
               
                   
                 41 
                 min. 
                 0.89 
                 0.88 
                 0.87 
                 0.85 
                 0.84 
                 0.83 
                 0.81 
                 0.80 
                 0.79 
                 0.77 
                 0.76 
                 0.75 
                 0.73 
               
               
                   
                   
                 Max. 
                 2.24 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
               
               
                   
                 42 
                 min. 
                 0.90 
                 0.89 
                 0.88 
                 0.86 
                 0.85 
                 0.84 
                 0.82 
                 0.81 
                 0.80 
                 0.78 
                 0.77 
                 0.76 
                 0.74 
               
               
                   
                   
                 Max. 
                 2.23 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
               
               
                   
                 43 
                 min. 
                 0.92 
                 0.90 
                 0.89 
                 0.87 
                 0.86 
                 0.85 
                 0.83 
                 0.82 
                 0.81 
                 0.79 
                 0.78 
                 0.76 
                 0.75 
               
               
                   
                   
                 Max. 
                 2.23 
                 2.24 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
                 2.32 
               
               
                   
                 44 
                 min. 
                 0.93 
                 0.91 
                 0.90 
                 0.89 
                 0.87 
                 0.86 
                 0.84 
                 0.83 
                 0.82 
                 0.80 
                 0.79 
                 0.77 
                 0.76 
               
               
                   
                   
                 Max. 
                 2.22 
                 2.23 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
                 2.32 
               
               
                   
                 45 
                 min. 
                 0.94 
                 0.93 
                 0.91 
                 0.90 
                 0.88 
                 0.87 
                 0.85 
                 0.84 
                 0.82 
                 0.81 
                 0.80 
                 0.78 
                 0.77 
               
               
                   
                   
                 Max. 
                 2.22 
                 2.23 
                 2.24 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
                 2.32 
               
               
                   
                 46 
                 min. 
                 0.95 
                 0.94 
                 0.92 
                 0.91 
                 0.89 
                 0.88 
                 0.86 
                 0.85 
                 0.83 
                 0.82 
                 0.80 
                 0.79 
                 0.78 
               
               
                   
                   
                 Max. 
                 2.22 
                 2.22 
                 2.23 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
                 2.31 
               
               
                   
                 47 
                 min. 
                 0.96 
                 0.95 
                 0.93 
                 0.92 
                 0.90 
                 0.89 
                 0.87 
                 0.86 
                 0.84 
                 0.83 
                 0.81 
                 0.80 
                 0.78 
               
               
                   
                   
                 Max. 
                 2.21 
                 2.22 
                 2.23 
                 2.24 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
                 2.31 
               
               
                   
                 48 
                 min. 
                 0.98 
                 0.96 
                 0.95 
                 0.93 
                 0.91 
                 0.90 
                 0.88 
                 0.87 
                 0.85 
                 0.84 
                 0.82 
                 0.81 
                 0.79 
               
               
                   
                   
                 Max. 
                 2.21 
                 2.22 
                 2.22 
                 2.23 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
                 2.30 
               
               
                   
                 49 
                 min. 
                 0.99 
                 0.97 
                 0.96 
                 0.94 
                 0.93 
                 0.91 
                 0.89 
                 0.88 
                 0.86 
                 0.85 
                 0.83 
                 0.82 
                 0.80 
               
               
                   
                   
                 Max. 
                 2.20 
                 2.21 
                 2.22 
                 2.23 
                 2.24 
                 2.24 
                 2.25 
                 2.26 
                 2.27 
                 2.28 
                 2.28 
                 2.29 
                 2.30 
               
               
                   
                 50 
                 min. 
                 1.00 
                 0.98 
                 0.97 
                 0.95 
                 0.94 
                 0.92 
                 0.90 
                 0.89 
                 0.87 
                 0.86 
                 0.84 
                 0.82 
                 0.81 
               
               
                   
                   
                 Max. 
                 2.20 
                 2.21 
                 2.22 
                 2.22 
                 2.23 
                 2.24 
                 2.25 
                 2.26 
                 2.26 
                 2.27 
                 2.28 
                 2.29 
                 2.30 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Second layer 
                 First layer thickness 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 modulus (×10 5  Pa) 
                 38 
                 39 
                 40 
                 41 
                 42 
                 43 
                 44 
                 45 
                 46 
                 47 
                 48 
                 49 
                 50 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Second 
                 38 
                 min. 
                 0.70 
                 0.69 
                 0.67 
                 0.66 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.58 
                 0.56 
                 0.55 
               
               
                 layer 
                   
                 Max. 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
                 2.45 
               
               
                 thickness 
                 39 
                 min. 
                 0.71 
                 0.69 
                 0.68 
                 0.67 
                 0.66 
                 0.64 
                 0.63 
                 0.62 
                 0.61 
                 0.59 
                 0.58 
                 0.57 
                 0.56 
               
               
                   
                   
                 Max. 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
                 2.44 
               
               
                   
                 40 
                 min. 
                 0.71 
                 0.70 
                 0.69 
                 0.68 
                 0.66 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.60 
                 0.59 
                 0.57 
                 0.56 
               
               
                   
                   
                 Max. 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
                 2.44 
               
               
                   
                 41 
                 min. 
                 0.72 
                 0.71 
                 0.70 
                 0.68 
                 0.67 
                 0.66 
                 0.64 
                 0.63 
                 0.62 
                 0.60 
                 0.59 
                 0.58 
                 0.56 
               
               
                   
                   
                 Max. 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
                 2.44 
               
               
                   
                 42 
                 min. 
                 0.73 
                 0.72 
                 0.70 
                 0.69 
                 0.68 
                 0.66 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.59 
                 0.58 
                 0.57 
               
               
                   
                   
                 Max. 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
                 2.43 
               
               
                   
                 43 
                 min. 
                 0.74 
                 0.72 
                 0.71 
                 0.70 
                 0.68 
                 0.67 
                 0.65 
                 0.64 
                 0.63 
                 0.61 
                 0.60 
                 0.59 
                 0.57 
               
               
                   
                   
                 Max. 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
                 2.43 
               
               
                   
                 44 
                 min. 
                 0.74 
                 0.73 
                 0.72 
                 0.70 
                 0.69 
                 0.67 
                 0.66 
                 0.65 
                 0.63 
                 0.62 
                 0.60 
                 0.59 
                 0.58 
               
               
                   
                   
                 Max. 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
                 2.42 
               
               
                   
                 45 
                 min. 
                 0.75 
                 0.74 
                 0.72 
                 0.71 
                 0.70 
                 0.68 
                 0.67 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.59 
                 0.58 
               
               
                   
                   
                 Max. 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
                 2.42 
               
               
                   
                 46 
                 min. 
                 0.76 
                 0.75 
                 0.73 
                 0.72 
                 0.70 
                 0.69 
                 0.67 
                 0.66 
                 0.64 
                 0.63 
                 0.61 
                 0.60 
                 0.58 
               
               
                   
                   
                 Max. 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
                 2.42 
               
               
                   
                 47 
                 min. 
                 0.77 
                 0.75 
                 0.74 
                 0.72 
                 0.71 
                 0.69 
                 0.68 
                 0.66 
                 0.65 
                 0.63 
                 0.62 
                 0.60 
                 0.59 
               
               
                   
                   
                 Max. 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
                 2.41 
               
               
                   
                 48 
                 min. 
                 0.78 
                 0.76 
                 0.75 
                 0.73 
                 0.71 
                 0.70 
                 0.68 
                 0.67 
                 0.65 
                 0.64 
                 0.62 
                 0.61 
                 0.59 
               
               
                   
                   
                 Max. 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
                 2.41 
               
               
                   
                 49 
                 min. 
                 0.78 
                 0.77 
                 0.75 
                 0.74 
                 0.72 
                 0.71 
                 0.69 
                 0.67 
                 0.66 
                 0.64 
                 0.63 
                 0.61 
                 0.60 
               
               
                   
                   
                 Max. 
                 2.31 
                 2.32 
                 2.32 
                 2.33 
                 2.34 
                 2.35 
                 2.36 
                 2.36 
                 2.37 
                 2.38 
                 2.39 
                 2.40 
                 2.40 
               
               
                   
                 50 
                 min. 
                 0.79 
                 0.78 
                 0.76 
                 0.74 
                 0.73 
                 0.71 
                 0.70 
                 0.68 
                 0.66 
                 0.65 
                 0.63 
                 0.62 
                 0.60 
               
               
                   
                   
                 Max. 
                 2.30 
                 2.31 
                 2.32 
                 2.33 
                 2.34 
                 2.34 
                 2.35 
                 2.36 
                 2.37 
                 2.38 
                 2.38 
                 2.39 
                 2.40 
               
               
                   
               
            
           
         
       
     
     An in-plane phase retardation value (R in ) of the neutral plane compensation member  300  may be 5 nm or less, or a phase retardation value (R th ) in a thickness direction of the neutral plane compensation member  300  may be 40 nm or less. 
     For example, when a film is not an optical film such as a phase retardation film or a polarizer included in a polarizing member, a phase retardation occurs naturally according to elongation thereof, and it may be very difficult to control the phase retardation value and distribution thereof. 
     Therefore, according to an embodiment of the present disclosure, the in-plane phase retardation value (R in ) of the neutral plane compensation member  300  is 5 nm or less, or the phase retardation value (R th ) in the thickness direction of the neutral plane compensation member  300  is 40 nm or less. In this case, even when the phase retardation distribution is included in the neutral plane compensation member  300 , the stain due to differences between antireflections at different positions of the display apparatus due to the phase retardation distribution may be reduced. 
     The increase in the phase retardation value due to the in-plane phase retardation (R in ) value of the neutral plane compensation member  300  may be compensated by the phase retardation film layer  520  of the polarizing member  500 . 
     The reason for the occurrence of the stain due to the phase retardation will be described with reference to  FIG.  7   , and  FIG.  8    through  FIG.  10   . 
       FIG.  7    illustrates a light path where light incident on a display apparatus emits through a polarizing member and a reflective plate of a display panel. 
     An adhesive layer  720  may be disposed on a reflective plate  710  of the display panel part. A phase retardation layer  730 , an inner protective base  740 , a polarizer  750 , and an outer protective base  760  may be disposed on the adhesive layer  720 . 
     The polarizer  750  may be a PVA (polyvinyl alcohol) film having a phase retardation of 0 degrees. The phase retardation layer  730  may be a quarter-wavelength phase retardation film. 
     As unpolarized light incident from an outside passes through the polarizer  750  at {circle around (1)}, only a first polarized orthogonal component of the light, which is one of two polarized orthogonal components, may transmit therethrough. 
     The polarized light is converted into circularly polarized light while passing through the phase retardation layer  730  at {circle around (2)}. Then, the circularly polarized light is reflected from the reflective plate  710  of the display panel part and thus the circular polarized direction may be changed. 
     As the circularly polarized light passes through the phase retardation layer  730  again at {circle around (3)}, only a second polarized orthogonal component, which is the other of the two polarized orthogonal components, may transmit therethrough. 
     The second polarized orthogonal component does not pass through the polarizer  750  at {circle around (4)}, such that light does not emit toward the outside, so that the polarizing member may obtain an antireflection effect. 
     With reference to the optical path of this circular polarizing plate, the change in the polarized state of the light is described using the Poincare sphere. 
       FIG.  8 A  illustrates change in a polarized state of light of a reference example according to a circular polarizing plate of  FIG.  7    in a Poincare sphere for comparison of stains based on a phase retardation.  FIG.  8 B  illustrates a reflection visual perception. 
       FIG.  8 A  illustrates change ({circle around (1)}, {circle around (2)}, {circle around (3)}, {circle around (4)}) in the polarized state of the light passing through the circular polarizing plate as described with reference to  FIG.  7    using the Poincare sphere. 
     The Poincare sphere expresses all polarized states of light on a sphere. An equator represents liner polarization, one pole S 3  represents left-handed circular polarization, and the opposite pole −S 3  represents right-handed circular polarization. An upper hemisphere may represent left-handed elliptical polarization, and a lower hemisphere may represent right-handed elliptical polarization. 
       FIG.  8 B  illustrates a color space using green-red color coordinates (a*) and blue-yellow color coordinates (b*). When a* increases in a positive direction, this may mean that an object become redder. When a* increases in a negative direction, this may mean that an object become greener. 
     Therefore, referring to  FIG.  8 A  and  FIG.  8 B , it may be identified that when light passes through the circularly polarizing plate as a reference, the display apparatus as the object illustrates a reflection visual perception of a red color. 
       FIG.  9 A  illustrates change in a polarized state of light in a Poincare sphere when a phase retardation decreases compared to that in  FIG.  8 A , and  FIG.  9 B  illustrates a reflection visual perception. 
     Referring to  FIG.  9   a    and  FIG.  9 B , it may be identified that when the phase retardation decreases compared to  FIG.  8 A  and  FIG.  8 B  as the reference, brighter red visual perception is achieved. 
     Referring to  FIG.  9 A , it may be identified that when the phase retardation decreases, the red light, the green light, and the blue light are relatively left elliptically polarized in comparison with  FIG.  8 A  as the reference. 
     Accordingly, referring to  FIG.  9 B , as the a* value increases in the positive direction, the object may become redder than in  FIG.  8 B  as the reference. 
       FIG.  10 A  illustrates change in a polarized state of light in a Poincare sphere when a phase retardation increases compared to that in  FIG.  8 A , and  FIG.  10 B  illustrates a reflection visual perception. 
     Referring to  FIG.  10 A  and  FIG.  10 B , it may be identified that when the phase retardation increases compared to  FIGS.  8 A and  8 B  as the reference, cyan visual perception is achieved. 
     Referring to  FIG.  10 A , it may be identified that when the phase retardation increases, the red light, the green light, and the blue light are relatively right elliptically polarized compared to  FIG.  8 A  as the reference. 
     Accordingly, referring to  FIG.  10 B , as the a* value increases in the negative direction, the object may become greener compared to  FIG.  8 B  as the reference. 
     Thus, referring to  FIG.  8    to  FIG.  10   , it may be identified that the color is changed relative to the reference example when the phase retardation increases or decreases. 
     Therefore, when a distribution of the first layer is large, different positions have different phase retardations and thus have different colors. Thus, there is a possibility that the stain may occur on the display apparatus. 
     Accordingly, according to an embodiment of the present disclosure, the in-plane phase retardation (R in ) value of the neutral plane compensation member  300  is 5 nm or less, or the phase retardation (R th ) value in a thickness direction of the neutral plane compensation member  300  is 40 nm or less. Thus, even when the phase retardation distribution is included in the neutral plane compensation member  300 , the stain due to differences between antireflections at different positions of the display apparatus due to the phase retardation distribution may be reduced. 
     Further, an in-plane phase retardation (R in ) axis of the neutral plane compensation member  300  may be horizontal or perpendicular to an in-plane phase retardation (R in ) axis of the phase retardation film layer  520  which is the quarter-wavelength plate QWP. 
       FIG.  11    illustrates change in a polarized state of light according to the circular polarizing plate of  FIG.  6    in a Poincare sphere. 
     Referring to  FIG.  11   , axes of the polarizer  750  as a PVA film with 0 degree phase retardation of the polarizing plate, and the phase retardation layer  730  as the quarter-wavelength phase retardation film are optimized. Thus, movement on the Poincare sphere due to the reflection may occur in an order of S 1  ({circle around (1)}), S 3  ({circle around (2)}), and S 1  ({circle around (3)}, {circle around (4)}). 
     When an axis of the neutral plane compensation member  300  according to an embodiment of the present disclosure is horizontal or perpendicular to an axis of the quarter-wavelength phase retardation film, the phase retardation value applied to the linearly polarized light transmitting through the polarizer may be equal to a phase retardation value (140 nm) of the quarter-wavelength phase retardation film±a phase retardation value (5 nm) of the neutral plane compensation member  300 . 
     However, when the axis of the neutral plane compensation member  300  according to an embodiment of the present disclosure is changed such that an angle defined between the axis thereof and the axis of the quarter-wavelength phase retardation film is 45 degrees or an arbitrary angle, the phase retardation value applied to the linearly polarized light transmitting through the polarizer may not be equal to a phase retardation value (140 nm) of the quarter-wavelength phase retardation film±a phase retardation value (5 nm) of the neutral plane compensation member  300 . Thus, it can be difficult to control the value. 
     Accordingly, certain display apparatuses may have problems such as local reflective staining, reflectance difference due to different process errors that may occur based on different production orders of the display apparatus, reflectance due to process adhesion distribution, and color difference. 
     Therefore, according to an embodiment of the present disclosure, the neutral plane compensation member  300  disposed between the polarizing member  500  and the display panel part  200  has a minimum phase retardation value below a predefined value, as described above, thereby reducing or preventing the occurrence of the stains due to the phase retardation. 
     Further, according to an embodiment of the present disclosure, the overall thickness of the display apparatus  1  increases due to the neutral plane compensation member  300  having the predetermined thickness disposed between the polarizing member  500  and the display panel part  200 , such that the puncture strength of the display apparatus  1  may increase. 
     When the puncture strength of the display apparatus  1  increases, a peeling (or lift-off) phenomenon between the layers, or cracks in the polarizing member may be greatly reduced even when the display apparatus  1  is folded. 
     A display apparatus according to an embodiment of the present disclosure may be described as follows. 
     A display apparatus according to an embodiment of the present disclosure may include a display panel, a polarizing member, and a neutral plane compensation member disposed between the display panel and the polarizing member. 
     According to some embodiments of the present disclosure, the neutral plane compensation member includes a first layer and a second layer, a thickness of the first layer may be in a range of 20 μm to 60 μm, and a modulus of the first layer may be in a range of 10 8  Pa to 10 10  Pa, and a thickness of the second layer may be in a range of 20 μm to 60 μm, and a modulus of the second layer may be in a range of 10 4  Pa to 10 6  Pa. 
     According to some embodiments of the present disclosure, the polarizing member may include a polarizing film layer, a retardation film layer, and a compensation film layer. 
     According to some embodiments of the present disclosure, an in-plane retardation value of the neutral plane compensation member may be 5 nm or less. 
     According to some embodiments of the present disclosure, a retardation value in a thickness direction of the neutral plane compensation member may be 40 nm or less. 
     According to some embodiments of the present disclosure, the retardation film layer may be a quarter-wavelength plate, wherein an in-plane retardation axis of the neutral plane compensation member may be horizontal or perpendicular to an in-plane retardation axis of the quarter-wavelength plate. 
     According to some embodiments of the present disclosure, a thickness of the first layer may be 25 μm, a thickness of the second layer may be 25 μm, and a modulus of the second layer may be in a range of 0.7×10 5  Pa to 2.3×10 5  Pa. 
     According to some embodiments of the present disclosure, a thickness of the first layer may be 50 μm, a thickness of the second layer may be 25 μm, and a modulus of the second layer may be in a range of 0.5×10 5  Pa to 2.5×10 5  Pa. 
     According to some embodiments of the present disclosure, a thickness of the first layer may be 25 μm, a thickness of the second layer may be 50 μm, and a modulus of the second layer may be in a range of 1.0×10 5  Pa to 2.2×10 5  Pa. 
     According to some embodiments of the present disclosure, a thickness of the first layer may be 50 μm, a thickness of the second layer may be 50 μm, and a modulus of the second layer may be in a range of 0.6×10 5  Pa to 2.4×10 5  Pa. 
     According to some embodiments of the present disclosure, the polarizing film layer, the phase retardation film layer, and the compensation film layer may be sequentially stacked in a direction toward the neutral plane compensation member. 
     According to some embodiments of the present disclosure, the retardation film layer may include a quarter-wavelength plate, the compensation film layer may include a +C plate layer, and the quarter-wavelength plate and the +C plate layer may include liquid crystals oriented in one direction. 
     According to some embodiments of the present disclosure, the display panel part may include an anode electrode, a light-emitting element layer, a cathode electrode, and a sealing layer stacked in a direction toward the neutral plane compensation member. 
     According to some embodiments of the present disclosure, the display panel part may include a touch electrode layer, the touch electrode layer may be disposed on the sealing layer. 
     A flexible display apparatus according to an embodiment of the present disclosure may include a display panel, a polarizing member, and a neutral plane compensation member disposed between the display panel part and the polarizing member. 
     According to some embodiments of the present disclosure, the neutral plane compensation member includes a first layer and a second layer, a thickness of the first layer may be in a range of 20 μm to 60 μm, and a modulus of the first layer may be in a range of 10 8  Pa to 10 10  Pa, a thickness of the second layer may be in a range of 20 μm to 60 μm, and a modulus of the second layer may be in a range of 10 4  Pa to 10 6  Pa, and the apparatus may be bent or folded toward the display panel. 
     It will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure without departing from the technical idea or scope of the disclosure. Thus, it may be intended that embodiments of the present disclosure cover the modifications and variations of the disclosure provided they come within the scope of the appended claims and their equivalents. 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.