Image display device

Abstract

The present invention addresses the problem of providing an image display device that outputs audio by vibrating a display panel using a vibrator, the audio being viewed at a sufficient sound pressure up to a high pitch region. The present invention solves the problem by having a display panel having a pixel pitch of 25-100 dpi and an oscillator attached to the display panel, and when the length of the diagonal line of the display panel is A, the maximum length Lmax of the oscillator in the lateral direction of the display panel satisfies' Lmax < = (A / 0.15) 1 / 2 '.

Description

Technical Field

[0001] The present invention relates to an image display device that uses a vibrator to output audio. Background Art

[0002] A vibrator, which is attached in contact with various objects serving as a vibration plate and generates sound by vibrating the objects, is used for various purposes.

[0003] For example, in an office, during a presentation or telephone conference, by installing a vibrator on a conference table, whiteboard, or screen, audio can be output instead of a speaker. In a vehicle such as a car, by installing a vibrator on a console, A-pillar, or ceiling, guidance sounds, warning sounds, and music can be emitted. In addition, in the case of a vehicle that does not emit engine sound, such as a hybrid car or an electric car, by installing a vibrator on a bumper, a vehicle approach notification sound can be emitted from the bumper.

[0004] Furthermore, in recent years, thin displays such as liquid crystal displays and organic electroluminescent displays (organic EL (Electro Luminescence) displays) have become mainstream image display devices.

[0005] There is also known an image display device in which a display panel used for such a thin display is used as a vibration plate, and a vibrator is attached to a non-display surface of the display panel to vibrate the display panel to output audio.

[0006] For example, Patent Document 1 discloses an image display device (display speaker) including a display panel, a vibrator, and a vibration clock, wherein the vibrator is bonded to the display panel surface, and the vibration clock is combined with the vibrator. In Patent Document 1, a piezoelectric element such as a piezoelectric element is exemplified as the vibrator.

[0007] In this image display device, audio is output by vibrating the display panel with a vibrator, and a vibrating bell is provided, thereby achieving audio output with a sufficient sound pressure up to a bass range.

[0008] Previous technical literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2021-090167 Summary of the invention

[0011] Technical issues to be solved by the invention

[0012] In recent years, thin displays such as liquid crystal displays and organic EL displays have tended to become larger.

[0013] Here, according to the research of the present inventors, as described in Patent Document 1, when audio is output by vibrating a display using a vibrator, in a large display, even when the image display device is viewed at an appropriate viewing distance, the sound pressure in the high-frequency region becomes low, and sometimes the image cannot be viewed with appropriate audio.

[0014] The object of the present invention is to solve the problems of the prior art and to provide an image display device that outputs audio by vibrating a display panel using a vibrator, wherein audio with sufficient sound pressure can be heard up to a high-pitched region according to the size of the display panel and the pixel pitch.

[0015] Means for solving technical problems

[0016] In order to achieve such an object, the present invention has the following structure.

[0017] [1] An image display device comprising:

[0018] A display panel having a pixel pitch of 25 to 100 dpi; and a vibrator mounted on a non-display surface of the display panel,

[0019] When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator in the lateral direction of the display panel satisfies:

[0020] Lmax≤(A / 0.15) 1 / 2 .

[0021] [2] An image display device comprising:

[0022] A display panel having a pixel pitch of 50 to 200 dpi; and a vibrator mounted on a non-display surface of the display panel,

[0023] When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator in the lateral direction of the display panel satisfies:

[0024] Lmax≤(A / 0.3) 1 / 2 .

[0025] [3] An image display device comprising:

[0026] A display panel having a pixel pitch of 100 to 400 dpi; and a vibrator mounted on a non-display surface of the display panel,

[0027] When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator in the lateral direction of the display panel satisfies:

[0028] Lmax≤(A / 0.6) 1 / 2 .

[0029] [4] The image display device according to any one of [1] to [3], wherein:

[0030] The display panel has an aspect ratio of 16:9.

[0031] [5] The image display device according to any one of [1] to [4], wherein:

[0032] The vibrator is a piezoelectric film having electrode layers on both surfaces of a piezoelectric layer.

[0033] [6] The image display device according to [5], wherein:

[0034] The vibrator is made of stacked layers of piezoelectric films.

[0035] [7] The image display device according to [5] or [6], wherein:

[0036] The piezoelectric film has a protective layer covering the electrode layer.

[0037] [8] The image display device according to any one of [5] to [7], wherein:

[0038] The piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material.

[0039] [9] The image display device according to [8], wherein:

[0040] The polymer material has a cyanoethyl group.

[0041]

[10] The image display device according to [9], wherein:

[0042] The polymer material is cyanoethylated polyvinyl alcohol.

[0043]

[11] The image display device according to any one of [6] to

[10] , wherein:

[0044] The vibrator is made by folding a single piezoelectric film and stacking multiple piezoelectric films.

[0045]

[12] The image display device according to any one of [6] to

[11] , wherein:

[0046] The adjacent piezoelectric films stacked are bonded together by an adhesive layer.

[0047] Effects of the Invention

[0048] According to the present invention, in an image display device that outputs audio by vibrating a display panel using a vibrator, audio with sufficient sound pressure can be heard even in a high-pitched region according to the size and pixel pitch of the display panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a diagram schematically showing an example of the image display device of the present invention.

[0050] Figure 2 Yes Figure 1 A conceptual diagram showing a partial enlargement of the image display device shown.

[0051] Figure 3 This is a diagram schematically showing another example of a vibrator used in the image display device of the present invention.

[0052] Figure 4 This is a diagram schematically showing an example of a piezoelectric film used for a vibrator.

[0053] Figure 5 This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0054] Figure 6 This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0055] Figure 7 This is a conceptual diagram for explaining an example of a method for producing a piezoelectric film.

[0056] Figure 8 This is a diagram schematically showing an example of wiring being drawn out from a vibrator.

[0057] Fig. 9 This is a conceptual diagram used to illustrate the effect of line array.

[0058] Fig.10 It is a graph showing the results of Examples of the present invention.

[0059] Fig.11 This is a graph showing the results of comparative examples of the present invention. DETAILED DESCRIPTION

[0060] Hereinafter, the image display device of the present invention will be described in detail based on preferred embodiments shown in the drawings.

[0061] In addition, the description of the constituent elements described below is made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0062] The following drawings are conceptual drawings for explaining the image display device of the present invention, and therefore, the size, thickness, shape, positional relationship, etc. of each component and each part are different from those of an actual object.

[0063] In the present invention, a numerical range expressed by "to" means a range including the numerical values ​​described before and after "to" as a lower limit and an upper limit.

[0064] Furthermore, in the present invention, the 1st and 2nd numbers added to the electrode layer and the protective layer are added for the convenience of distinguishing two basically identical components and for explaining the image display device of the present invention. Therefore, the 1st and 2nd numbers in these components have no technical meaning and are irrelevant to the actual use state and the positional relationship between them.

[0065] exist Figure 1 and Figure 2 , an example of the image display device of the present invention is schematically shown.

[0066] like Figure 1 and Figure 2 As shown, the image display device 10 of the present invention has a vibrator 14 mounted on the non-display surface (non-image display surface) of the display panel 12. The non-display surface refers to the surface on the back side of the display surface (image display surface) of the display panel 12. In the following description, the non-display surface of the display panel 12 is also referred to as the back side of the display panel 12.

[0067] exist Figure 1 In the image display device 10 shown, two columns of five transducers 14 are separated in the longitudinal direction of the display panel 12 and arranged in the width direction of the display panel 12 .

[0068] As an example, each row of five transducers 14 corresponds to the right channel and the left channel of the audio output of stereo reproduction.

[0069] In the image display device 10 of the present invention, the number and positions of the vibrators 14 mounted on the display panel 12 are not limited to the example shown in the figure, and various forms can be used.

[0070] For example, the number of transducers 14 in each column corresponding to the right channel and the left channel of the stereo audio output may be 4 or less, or 6 or more. In addition, there may be a plurality of columns of transducers in each of the right channel and the left channel.

[0071] Furthermore, the columns of the transducers 14 mounted on the display panel 12 may include one column or a plurality of columns corresponding to the audio output of monaural reproduction.

[0072] Furthermore, the image display device 10 of the present invention may be a device having only one transducer 14 or a device having a plurality of transducers 14 arranged regularly or irregularly in a two-dimensional manner.

[0073] That is, in the image display device 10 of the present invention, the position and number of the vibrators 14 mounted on the display panel 12 may be appropriately set according to the size and purpose of the image display device 10 .

[0074] In the image display device 10 of the present invention, the display panel 12 is not limited, and various known display panels can be used.

[0075] In particular, it is preferred to use display panels used in so-called thin televisions, such as liquid crystal display panels, organic EL display panels (OLED (Organic Light Emitting Diode: organic light emitting diode) display panels), micro LED (Light Emitting Diode: light emitting diode) display panels, inorganic EL display panels and plasma display panels.

[0076] Among them, a self-luminous display panel such as an OLED display panel is preferred because a backlight is not required and a vibrator 14 described later can be directly mounted on the panel to output audio well. Among them, an OLED display panel is preferably used.

[0077] In the first embodiment of the image display device 10 of the present invention, the pixel pitch (pixel density) of the display panel 12 is 25 to 100 dpi (dot per inch). This pixel pitch corresponds to a so-called full HD display panel. Regarding the full HD pixel pitch, 23 inches is 92 dpi, and 80 inches is 30 dpi.

[0078] In the second embodiment of the image display device 10 of the present invention, the pixel pitch of the display panel 12 is 50 to 200 dpi. This pixel pitch corresponds to the pixel pitch of the display panel of a so-called 4K TV. The pixel pitch of a 4K TV is 185 dpi for a 23-inch TV and 60 dpi for an 80-inch TV.

[0079] In the third embodiment of the image display device 10 of the invention, the pixel pitch of the display panel 12 is 100 to 400 dpi. This pixel pitch corresponds to the pixel pitch of the display panel of the so-called 8K TV. Regarding the pixel pitch of 8K TV, 23 inches is 370 dpi, and 80 inches is 120 dpi.

[0080] In the image display device 10 of the present invention, the aspect ratio of the display panel is not limited, but is preferably 16:9, similar to a common display panel used in a television (television receiver) or a computer monitor.

[0081] In the image display device 10 of the present invention, the shape of the display panel is not limited to the rectangular shape as shown in the example of the figure, and various shapes such as square, circle, ellipse, and trapezoid can be used.

[0082] In the image display device 10 of the illustrated example, the vibrator 14 is formed by stacking a plurality of piezoelectric films 16 by folding the piezoelectric film 16 having flexibility multiple times in a bellows shape.

[0083] In the piezoelectric film 16, a first electrode layer 28 is provided on one surface of a piezoelectric body layer 26, and a second electrode layer 30 is provided on the other surface, a first protective layer 32 is provided on the surface of the first electrode layer 28, and a second protective layer 34 is provided on the surface of the second electrode layer 30. That is, the vibrator 14 shown in the figure is a stacked piezoelectric element (stacked piezoelectric body).

[0084] Furthermore, in the vibrator 14 , the adjacent piezoelectric films 16 stacked by folding are bonded together by the adhesive layer 20 .

[0085] The vibrator 14 of the illustrated example is formed by folding a rectangular (long) piezoelectric film 16 four times at equal intervals to stack five layers of the piezoelectric film 16 .

[0086] In the image display device 10 of the present invention, when the rectangular piezoelectric film 16 is folded, the folding line formed by the folding of the piezoelectric film 16 may coincide with the length direction or the width direction in the planar shape of the vibrator 14. The planar shape of the vibrator 14 refers to the shape of the vibrator 14 when the piezoelectric film 16 is viewed in the stacking direction.

[0087] In the following description, for convenience, a folding line formed by folding the piezoelectric film 16 , that is, a line at the top outside the end of the folded portion is also referred to as a “ridge line”.

[0088] For example, if a 25×20 cm rectangular piezoelectric film is folded four times at 5 cm intervals in the 25 cm direction, a piezoelectric element is obtained which is a 5×20 cm rectangular (long strip) piezoelectric element with a ridge line that coincides with the 20 cm in the length direction and is made up of five layers of piezoelectric films (reference Figure 8 ). Furthermore, if a 100×5 cm rectangular piezoelectric film is folded four times at intervals of 20 cm in the direction of 100 cm, a piezoelectric element is obtained which is made of five layers of stacked piezoelectric films and has the same planar shape of a 5×20 cm rectangle (long strip) and whose ridges coincide with 5 cm in the width direction.

[0089] In addition, as a preferred embodiment, Figure 1 The vibrator 14 shown in FIG. 1 is a vibrator having a rectangular planar shape produced by folding a rectangular piezoelectric film 16. However, in the image display device of the present invention, the shape of the piezoelectric film 16 is not limited to a rectangle, and various shapes can be used.

[0090] As an example, a circle, a rounded rectangle (oval), an ellipse, a hexagon or other polygonal shape is illustrated.

[0091] As described above, the vibrator 14 is formed by folding the piezoelectric film 16 multiple times and stacking them. The vibrator 14 shown in the figure is formed by folding the piezoelectric film 16 four times to stack five layers of the piezoelectric film 16. The adjacent stacked piezoelectric films 16 are bonded together by the bonding layer 20.

[0092] The image display device 10 of the present invention can increase the expansion and contraction force of the piezoelectric element compared to the case of using a single piezoelectric film by stacking a plurality of piezoelectric films 16 and pasting adjacent piezoelectric films 16. As a result, the display panel 12 serving as a vibration plate can be bent with a large force and output audio with a high sound pressure.

[0093] The stacked piezoelectric element as a vibrator used in the image display device of the present invention is not limited to a structure in which one piezoelectric film 16 is stacked by folding and adjacent piezoelectric films 16 are bonded together by the bonding layer 20 .

[0094] That is, Figure 3 As schematically shown in FIG. 1 , the vibrator used in the image display device of the present invention may have a structure in which a plurality of slice-shaped (single-sheet-shaped) piezoelectric films 16 are stacked and adjacent piezoelectric films 16 are bonded together via an adhesive layer 20 .

[0095] Although the structure in which the piezoelectric films 16 are stacked by folding one piezoelectric film 16 as in the example of the vibrator 14 is a structure in which a plurality of piezoelectric films 16 are stacked, the lead-out of the electrode for driving the vibrator 14, i.e., the piezoelectric film 16, can be set at one location in each electrode layer described later. As a result, the vibrator 14 in which one piezoelectric film 16 is folded and stacked can simplify the structure and electrode wiring, and also has excellent productivity.

[0096] Furthermore, since the vibrator 14 is formed by folding and stacking one piezoelectric film 16, the electrode layers of adjacent piezoelectric films facing each other have the same polarity due to the stacking. As a result, the vibrator 14 is also advantageous in that a short circuit does not occur even when the electrode layers are in contact with each other.

[0097] In the image display device 10 of the present invention, the number of stacked layers of the piezoelectric film 16 in the vibrator 14 is not limited to 5 layers as shown in the example of the figure. That is, the image display device 10 of the present invention may be an image display device formed by stacking 4 or less layers of the piezoelectric film 16 by folding the piezoelectric film 16 3 or less, or may be an image display device formed by stacking 6 or more layers of the piezoelectric film 16 by folding the piezoelectric film 16 5 or more.

[0098] In the image display device 10 of the present invention, the number of stacked layers of the piezoelectric film 16 in the vibrator 14 is not limited, but is preferably 2 to 10 layers, more preferably 3 to 7 layers, and even more preferably 4 to 6 layers.

[0099] On this point, in the cascade Figure 3The same also applies to the structure of the slice-shaped piezoelectric film 16 shown.

[0100] In the image display device 10 of the present invention, when the number of stacked piezoelectric films 16 is large, the output of the piezoelectric element becomes large, and as a result, high sound pressure audio output can be performed. On the other hand, from the perspective of the thickness of the vibrator 14, that is, the thickness of the image display device 10, a small number of stacked layers is more disadvantageous.

[0101] Therefore, the number of stacked layers of the piezoelectric film 16 in the vibrator 14 of the image display device 10 of the present invention can be appropriately set according to the strength of the toughness of the display panel 12, the size of the display panel 12, the position of pasting to the display panel 12, the strength of the toughness of the piezoelectric film 16, the dimension of the piezoelectric film surface direction of the vibrator 14, the required sound pressure in the image display device 10 and the thickness of the image display device 10, etc.

[0102] In the vibrator 14 of the illustrated example, among the piezoelectric films 16 stacked by folding, the piezoelectric films 16 adjacent to each other in the stacking direction are bonded together by the adhesive layer 20 .

[0103] By bonding the piezoelectric films 16 adjacent to each other in the stacking direction with the adhesive layer 20 , the expansion and contraction of each piezoelectric film 16 can be directly transmitted, and the stacked body formed by stacking the piezoelectric films 16 can be driven without loss.

[0104] In the present invention, various known adhesives (adhesive materials) can be used as the adhesive layer 20 as long as the adjacent piezoelectric films 16 can be adhered to each other.

[0105] Therefore, the adhesive layer 20 can be a layer composed of a binder (adhesive material), a layer composed of an adhesive (adhesive material), or a layer composed of a material having the characteristics of both a binder and an adhesive. In addition, a binder refers to an adhesive that has fluidity when attached and then becomes solid. And, an adhesive refers to an adhesive that is a soft solid in a gel state (rubber state) when attached and the gel state does not change afterwards.

[0106] Furthermore, the adhesive layer 20 may be formed by applying an adhesive having fluidity such as a liquid, or may be formed using a sheet-like adhesive.

[0107] Although it will be described later, the vibrator 14 as a stacked piezoelectric element expands and contracts itself by expanding and contracting the stacked plurality of piezoelectric films 16, and as described later, the display panel 12 is bent and vibrated, thereby outputting sound. Therefore, in the vibrator 14, it is preferable to directly transmit the expansion and contraction of each stacked piezoelectric film 16. If a viscous substance such as a material that mitigates the transmission of vibration exists between the piezoelectric films 16, the transmission efficiency of the expansion and contraction energy of the piezoelectric film 16 becomes low, thereby reducing the driving efficiency of the vibrator 14.

[0108] Considering this point, the adhesive layer 20 is preferably an adhesive layer composed of an adhesive agent, which can obtain a solid and hard adhesive layer 20, rather than an adhesive layer composed of an adhesive agent. As a more preferred adhesive layer 20, specifically, an adhesive layer composed of a thermoplastic adhesive such as a polyester adhesive and a styrene-butadiene rubber (SBR) adhesive is preferably exemplified.

[0109] Bonding is different from adhesion and is useful when a high bonding temperature is required. In addition, thermoplastic adhesives are preferred because they have "relatively low temperature, short time and strong bonding".

[0110] In the vibrator 14 , the thickness of the adhesive layer 20 is not limited, and may be appropriately set to a thickness that can exhibit sufficient adhesive strength according to the material forming the adhesive layer 20 .

[0111] In the vibrator 14, when the adhesive layer 20 is thin, the transmission effect of the expansion and contraction energy (vibration energy) of the piezoelectric layer 26 is improved, and the energy conversion efficiency can be improved. On the other hand, when the adhesive layer 20 is thick and has high rigidity, the expansion and contraction of the piezoelectric film 16 may be restricted.

[0112] Considering this point, the adhesive layer 20 is preferably thinner than the piezoelectric layer 26. That is, in the vibrator 14, the adhesive layer 20 is preferably hard and thin. Specifically, the thickness of the adhesive layer 20 after adhesion is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0113] In the image display device 10 of the illustrated example, the vibrator 14 is attached to the display panel 12 via an adhesive layer 68 .

[0114] Thus, the expansion and contraction of the vibrator 14 is directly transmitted to the display panel 12 , so that the display panel 12 can be vibrated appropriately.

[0115] In the image display device 10 of the illustrated example, the adhesive layer 68 for bonding the display panel 12 and the vibrator 14 is not limited, and various adhesives can be used as long as they can bond the display panel 12 and the vibrator 14 (piezoelectric film 16 ).

[0116] In the image display device 10 of the present invention, the adhesive layer 68 for bonding the display panel 12 and the vibrator 14 can use various adhesive layers similar to the adhesive layer 20 for bonding the adjacent piezoelectric film 16. The adhesive layer 68 is also preferably the same.

[0117] In the image display device 10 of the present invention, the thickness of the adhesive layer 68 is not limited, and may be appropriately set to a thickness that can exhibit sufficient adhesive strength according to the material forming the adhesive layer 68 .

[0118] Here, in the image display device 10 of the present invention, when the adhesive layer 68 is thin, the transmission effect of the expansion energy (vibration energy) of the piezoelectric film 16 is improved, thereby improving the energy conversion efficiency. In addition, if the adhesive layer is thick and has high rigidity, it is also possible to limit the expansion and contraction of the vibrator 14.

[0119] Taking this into consideration, the thickness of the adhesive layer 68 for bonding the display panel 12 and the vibrator 14 after bonding is preferably 10 to 1000 μm, more preferably 30 to 500 μm, and even more preferably 50 to 300 μm.

[0120] As described above, in the image display device 10 of the illustrated example, the vibrator 14 is formed by folding and stacking the piezoelectric film 16. As long as the piezoelectric film 16 has flexibility to bend and stretch, various known piezoelectric films 16 can be used.

[0121] In the present invention, the term "flexible" has the same meaning as the commonly interpreted "flexible", and means being able to bend and bend, and specifically, being able to bend and stretch without being broken or damaged.

[0122] In the image display device 10 of the present invention, as a preferred embodiment, the piezoelectric film 16 includes electrode layers provided on both surfaces of the piezoelectric body layer 26 and a protective layer provided to cover the electrode layers.

[0123] Figure 4 In FIG. 1 , an example of the piezoelectric film 16 is schematically shown in a cross-sectional view. Figure 4 In the figures, hatching is omitted to simplify the drawings and clearly illustrate the structure.

[0124] In the following description, unless otherwise specified, the term "cross section" refers to a cross section in the thickness direction of the piezoelectric film. The thickness direction of the piezoelectric film refers to the stacking direction of the piezoelectric film.

[0125] like Figure 4 As shown, the piezoelectric film 16 shown in the figure has a piezoelectric layer 26, a first electrode layer 28 stacked on one surface of the piezoelectric layer 26, a first protective layer 32 stacked on the first electrode layer 28, a second electrode layer 30 stacked on the other surface of the piezoelectric layer 26, and a second protective layer 34 stacked on the second electrode layer 30.

[0126] In the piezoelectric film 16 , the piezoelectric layer 26 can utilize various known piezoelectric layers.

[0127] In the piezoelectric film 16, as Figure 4 As schematically shown in FIG. 1 , the piezoelectric layer 26 is preferably a polymer composite piezoelectric body including piezoelectric particles 40 in a polymer matrix 38 composed of a polymer material.

[0128] Among them, the polymer composite piezoelectric body (piezoelectric layer 26) preferably meets the following requirements: In the present invention, the normal temperature is 0 to 50°C.

[0129] (i) Flexibility

[0130] For example, when it is held in a lightly bent state like a newspaper or magazine for carrying, it is constantly subjected to relatively slow and large bending deformation of less than several Hz from the outside. At this time, if the polymer composite piezoelectric body is hard, a correspondingly large bending stress will be generated, and cracks will be generated at the interface between the polymer matrix and the piezoelectric particles, which may result in damage. Therefore, the polymer composite piezoelectric body is required to have moderate softness. In addition, if the strain energy can be diffused to the outside as heat, the stress can be relieved. Therefore, the loss tangent of the polymer composite piezoelectric body is required to be moderately large.

[0131] (ii) Sound quality

[0132] The speaker vibrates the piezoelectric particles at a frequency in the audio frequency band of 20Hz to 20kHz. Through the vibration energy, the entire vibration plate (polymer composite piezoelectric) vibrates as a whole, thereby reproducing the sound. Therefore, in order to improve the transmission efficiency of vibration energy, the polymer composite piezoelectric is required to have a moderate hardness. In addition, if the frequency characteristics of the speaker are smooth, the change in sound quality when the lowest resonance frequency f0 changes with the change in curvature also becomes smaller. Therefore, the loss tangent of the polymer composite piezoelectric is required to be moderately large.

[0133] As is well known, the lowest resonance frequency f0 of a speaker diaphragm is given by the following equation: Here, s is the stiffness of the vibration system, and m is the mass.

[0134] [Formula 1]

[0135]

[0136] At this time, the greater the curvature radius of the curved portion of the piezoelectric film, the lower the mechanical stiffness s, so the lowest resonance frequency f0 becomes smaller. That is, the sound quality (volume, frequency characteristics) of the speaker changes according to the curvature radius of the piezoelectric film.

[0137] In summary, the polymer composite piezoelectric body is required to exhibit a hard action for vibrations of 20 Hz to 20 kHz, and a soft action for vibrations of several Hz or less. In addition, the polymer composite piezoelectric body is required to have a moderately large loss tangent for vibrations of all frequencies below 20 kHz.

[0138] Generally, polymer solids have a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximization (absorption) in the loss modulus. Among them, the relaxation caused by the micro-Brownian motion of the molecular chain in the amorphous region is called the main dispersion, and a very large relaxation phenomenon can be observed. The temperature that causes this main dispersion is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most prominently manifested.

[0139] In the polymer composite piezoelectric body (piezoelectric body layer 26), by using a polymer material having a glass transition point at room temperature, in other words, a polymer material having viscoelasticity at room temperature in the matrix, a polymer composite piezoelectric body that exhibits a hard action for a vibration of 20 Hz to 20 kHz and a soft action for a slow vibration of several Hz or less is realized. In particular, from the perspective of appropriately showing the performance, it is preferred to use a polymer material having a glass transition point Tg at a frequency of 1 Hz at room temperature in the matrix of the polymer composite piezoelectric body.

[0140] The polymer material constituting the polymer matrix 38 preferably has a maximum value of the loss tangent Tanδ of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature.

[0141] Thus, when the polymer composite piezoelectric body is slowly bent by an external force, stress concentration at the polymer matrix / piezoelectric particle interface in the maximum bending moment portion is alleviated, and high flexibility can be expected.

[0142] Furthermore, the polymer material constituting the polymer matrix 38 preferably has a storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement of 100 MPa or more at 0° C. and 10 MPa or less at 50° C.

[0143] This can reduce the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force, and can also exhibit a strong action against acoustic vibrations of 20 Hz to 20 kHz.

[0144] Furthermore, it is more preferable that the relative dielectric constant of the polymer material constituting the polymer matrix 38 is 10 or more at 25° C. Thus, when voltage is applied to the polymer composite piezoelectric body, a higher electric field is applied to the piezoelectric particles in the polymer matrix, and thus a larger deformation amount can be expected.

[0145] However, on the other hand, in consideration of ensuring good moisture resistance, etc., it is also preferable that the relative dielectric constant of the polymer material be 10 or less at 25°C.

[0146] Preferred examples of polymer materials satisfying such conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate.

[0147] Furthermore, as these polymer materials, commercially available products such as HYBRAR 5127 (manufactured by KURARAY CO., LTD.) can also be preferably used.

[0148] As the polymer material constituting the polymer matrix 38, a polymer material having a cyanoethyl group is preferably used, and cyanoethylated PVA is particularly preferably used. That is, in the piezoelectric film 16 and the piezoelectric layer 26, as the polymer matrix 38, a polymer material having a cyanoethyl group is preferably used, and cyanoethylated PVA is particularly preferably used.

[0149] In the following description, the above-mentioned polymer materials represented by cyanoethylated PVA are also collectively referred to as "polymer materials having viscoelasticity at room temperature".

[0150] These polymer materials having viscoelasticity at room temperature may be used alone or in combination (mixed) of two or more.

[0151] In the piezoelectric film 16 , a plurality of polymer materials may be used in combination in the polymer matrix 38 of the piezoelectric layer 26 as needed.

[0152] That is, in the polymer matrix 38 constituting the polymer composite piezoelectric body, in addition to the above-mentioned polymer material having viscoelasticity at room temperature, other dielectric polymer materials may be added as needed for the purpose of adjusting dielectric properties and mechanical properties.

[0153] As dielectric polymer materials that can be added, for example, fluorine-based polymers such as polyvinylidene fluoride (PVDF), vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, polyvinylidene fluoride-trifluoroethylene copolymers, and polyvinylidene fluoride-tetrafluoroethylene copolymers, vinylidene cyanide-vinyl acetate copolymers, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl pullulan, cyanoethyl sucrose, and cyanoethyl sorbitol, and synthetic rubbers such as nitrile rubber and chloroprene rubber are exemplified.

[0154] Among them, it is preferable to use a polymer material having a cyanoethyl group.

[0155] Furthermore, in the polymer matrix 38 of the piezoelectric layer 26 , these dielectric polymer materials are not limited to one kind, and multiple kinds may be added.

[0156] Furthermore, in addition to dielectric polymer materials, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene and isobutylene, and thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica may be added for the purpose of adjusting the glass transition point Tg of the polymer matrix 38.

[0157] Furthermore, for the purpose of improving adhesiveness, a tackifier such as rosin ester, rosin, terpenes, terpene phenols, and petroleum resin may be added.

[0158] The amount of polymer materials other than polymer materials having viscoelasticity at room temperature added to the polymer matrix 38 of the piezoelectric layer 26 is not particularly limited, but is preferably 30% by mass or less in terms of the proportion in the polymer matrix 38 .

[0159] Thus, the characteristics of the added polymer material can be manifested without damaging the viscoelastic relaxation mechanism in the polymer matrix 38, so that preferred results can be obtained from the perspectives of high dielectric constant, improved heat resistance, and improved adhesion with the piezoelectric particles 40 or electrode layers.

[0160] The polymer composite piezoelectric body that becomes the piezoelectric layer 26 contains piezoelectric particles 40 in such a polymer matrix. The piezoelectric particles 40 are dispersed in the polymer matrix, preferably uniformly (substantially uniformly).

[0161] The piezoelectric particles 40 are preferably composed of ceramic particles having a perovskite-type or wurtzite-type crystal structure.

[0162] Examples of ceramic particles constituting the piezoelectric particles 40 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO 3 ), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe 3 ) (BFBT).

[0163] The particle size of the piezoelectric particles 40 may be appropriately selected according to the size and purpose of the piezoelectric film 16. The particle size of the piezoelectric particles 40 is preferably 1 to 10 μm.

[0164] By setting the particle size of the piezoelectric particles 40 within the above range, a preferable result can be obtained from the viewpoint of being able to achieve both high piezoelectric characteristics and flexibility.

[0165] In the piezoelectric film 16 , the amount ratio of the polymer matrix 38 to the piezoelectric particles 40 in the piezoelectric layer 26 may be appropriately set depending on the size or thickness of the piezoelectric film 16 in the plane direction, the application of the piezoelectric film 16 , the characteristics required of the piezoelectric film 16 , and the like.

[0166] The volume fraction of the piezoelectric particles 40 in the piezoelectric layer 26 is preferably 30 to 80%, and more preferably 50 to 80%.

[0167] By setting the amount ratio of the polymer matrix 38 to the piezoelectric particles 40 within the above range, a preferable result can be obtained from the viewpoint of being able to achieve both high piezoelectric characteristics and flexibility.

[0168] Furthermore, in the piezoelectric film 16 , the thickness of the piezoelectric layer 26 is not limited and may be appropriately set according to the size of the piezoelectric film 16 , the application of the piezoelectric film 16 , the characteristics required of the piezoelectric film 16 , and the like.

[0169] The thickness of the piezoelectric layer 26 is preferably 8 to 300 μm, more preferably 8 to 200 μm, further preferably 10 to 150 μm, and particularly preferably 15 to 100 μm.

[0170] By setting the thickness of the piezoelectric layer 26 within the above range, a preferable result can be obtained from the viewpoints of ensuring both rigidity and appropriate flexibility.

[0171] Furthermore, the thickness of the piezoelectric layer 26 is preferably 45 μm or more. Within the above range, the thickness of the piezoelectric layer 26 is more preferably 45 μm or more.

[0172] By setting the thickness of the piezoelectric layer 26 to be greater than 45 μm, a high-output (strong expansion and contraction) vibrator 14 can be stably obtained, the number of stacked piezoelectric films 16 can be reduced to make the piezoelectric element thinner, and the power consumption when the piezoelectric element is driven can be suppressed, which is preferable from this perspective.

[0173] This is the same even when the piezoelectric layer 26 is not a polymer composite piezoelectric. However, when the piezoelectric layer 26 is a polymer composite piezoelectric, by setting the thickness of the piezoelectric layer 26 to be 45 μm or more, the above-mentioned advantages can be obtained while ensuring sufficient flexibility of the piezoelectric film 16, which is more preferred from this aspect.

[0174] The piezoelectric layer 26 is preferably subjected to polarization treatment (Poling) in the thickness direction. The polarization treatment will be described in detail later.

[0175] In the piezoelectric film 16 , the piezoelectric layer 26 is not limited to the polymer composite piezoelectric body in which the piezoelectric particles 40 are contained in the polymer matrix 38 made of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA as described above.

[0176] That is, in the piezoelectric film 16 , the piezoelectric layer can utilize various known piezoelectric layers.

[0177] As an example, it is also possible to utilize a polymer composite piezoelectric body that contains the same piezoelectric particles 40 in a matrix containing dielectric polymer materials such as the above-mentioned polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, a piezoelectric layer composed of polyvinylidene fluoride, a piezoelectric layer composed of a fluororesin other than polyvinylidene fluoride, and a piezoelectric layer formed by stacking a film composed of poly-L-lactic acid and a film composed of poly-D-lactic acid, etc.

[0178] However, as described above, from the perspectives of being able to exhibit hard action for vibrations of 20 Hz to 20 kHz and soft action for slow vibrations below several Hz, and being able to obtain excellent acoustic properties and excellent flexibility, it is preferred to utilize the above-mentioned polymer composite piezoelectric body containing piezoelectric particles 40 in a polymer matrix 38 composed of a polymer material having viscoelasticity at room temperature such as cyanoethylated PVA.

[0179] Figure 4 The piezoelectric film 16 shown has the following structure: a second electrode layer 30 is provided on one side of the piezoelectric body layer 26, a second protective layer 34 is provided on the surface of the second electrode layer 30, a first electrode layer 28 is provided on the other side of the piezoelectric body layer 26, and a first protective layer 32 is provided on the surface of the first electrode layer 28. In the piezoelectric film 16, the first electrode layer 28 and the second electrode layer 30 form an electrode pair.

[0180] In other words, the stacked film constituting the piezoelectric film 16 has a structure in which both surfaces of the piezoelectric layer 26 are sandwiched between the first electrode layer 28 and the second electrode layer 30 , which are an electrode pair, and further sandwiched between the first protective layer 32 and the second protective layer 34 .

[0181] In this way, the region sandwiched between the first electrode layer 28 and the second electrode layer 30 is driven according to the applied voltage.

[0182] The piezoelectric film 16 may include, in addition to these layers, for example, an adhesive layer for bonding the electrode layer and the piezoelectric body layer 26 together, and an adhesive layer for bonding the electrode layer and the protective layer together.

[0183] The adhesive may be a binder or an adhesive. Furthermore, the adhesive may preferably be made of the same material as the polymer matrix 38, which is a polymer material obtained by removing the piezoelectric particles 40 from the piezoelectric layer 26. In addition, the adhesive layer may be provided on both the first electrode layer 28 side and the second electrode layer 30 side, or may be provided on only one of the first electrode layer 28 side and the second electrode layer 30 side.

[0184] In the piezoelectric film 16, the first protective layer 32 and the second protective layer 34 cover the first electrode layer 28 and the second electrode layer 30, and play a role in giving appropriate rigidity and mechanical strength to the piezoelectric layer 26. That is, in the piezoelectric film 16, the piezoelectric layer 26 including the polymer matrix 38 and the piezoelectric particles 40 shows very excellent flexibility for slow bending deformation, but on the other hand, there is a case where the rigidity or mechanical strength is insufficient depending on the application. The piezoelectric film 16 is provided with the first protective layer 32 and the second protective layer 34 to compensate for the deficiency.

[0185] The first protective layer 32 and the second protective layer 34 have the same structure, but are arranged at different positions. Therefore, in the following description, when there is no need to distinguish between the first protective layer 32 and the second protective layer 34, both members are collectively referred to as protective layers.

[0186] The protective layer is not limited, and various sheets can be used. As an example, various resin films are preferably exemplified. Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably used because of their excellent mechanical properties and heat resistance.

[0187] The thickness of the protective layer is not limited. Furthermore, the thicknesses of the first protective layer 32 and the second protective layer 34 are basically the same, but may be different.

[0188] If the rigidity of the protective layer is too high, not only will the expansion and contraction of the piezoelectric layer 26 be restricted, but also the flexibility will be impaired. Therefore, except when mechanical strength or good handling properties as a sheet-like object are required, it is more advantageous to make the protective layer thinner.

[0189] When the thickness of each of the first protective layer 32 and the second protective layer 34 is not more than twice the thickness of the piezoelectric layer 26 , a preferable result can be obtained from the viewpoint of achieving both rigidity and appropriate flexibility.

[0190] For example, when the thickness of the piezoelectric layer 26 is 50 μm and the first protective layer 32 and the second protective layer 34 are made of PET, the thickness of the first protective layer 32 and the second protective layer 34 are preferably 100 μm or less, more preferably 50 μm or less, and further preferably 25 μm or less.

[0191] In the present invention, the first protective layer 32 and the second protective layer 34 are used as preferred embodiments and are not essential components. Therefore, the piezoelectric film 16 may include only the first protective layer 32, only the second protective layer 34, or no protective layer.

[0192] However, considering the mechanical strength of the piezoelectric film 16 and the protection of the electrode layers, the piezoelectric film preferably has at least one protective layer, and more preferably has two protective layers covering the two electrode layers as shown in the example of the figure.

[0193] In the piezoelectric film 16, a first electrode layer 28 is provided between the piezoelectric layer 26 and the first protective layer 32, and a second electrode layer 30 is provided between the piezoelectric layer 26 and the second protective layer 34. The first electrode layer 28 and the second electrode layer 30 are used to apply a voltage to the piezoelectric layer 26. When a voltage is applied from the electrode layer to the piezoelectric layer 26, the piezoelectric film 16 expands and contracts.

[0194] The first electrode layer 28 and the second electrode layer 30 are basically the same except for their positions. Therefore, in the following description, when there is no need to distinguish between the first electrode layer 28 and the second electrode layer 30, both are collectively referred to as electrode layers.

[0195] In the piezoelectric film, the material for forming the electrode layer is not limited, and various conductors can be used. Specifically, examples include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, molybdenum, alloys thereof, indium tin oxide, and conductive polymers such as PEDOT / PPS (polyethylene dioxythiophene-polystyrene sulfonate).

[0196] Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified. Among them, copper is more preferred from the viewpoints of conductivity, cost, flexibility, and the like.

[0197] Furthermore, the method for forming the electrode layer is not limited, and various known methods such as film formation based on vapor deposition methods (vacuum film forming methods) such as vacuum evaporation and sputtering, or plating, or a method of pasting a foil formed of the above materials, or a coating method can be used.

[0198] Among them, it is particularly preferable to use a thin film of copper or aluminum formed by vacuum deposition as the electrode layer because the flexibility of the piezoelectric film 16 can be ensured. Among them, it is particularly preferable to use a thin film of copper formed by vacuum deposition.

[0199] The thickness of the first electrode layer 28 and the second electrode layer 30 is not limited. Furthermore, the thickness of the first electrode layer 28 and the second electrode layer 30 is basically the same, but may be different.

[0200] However, similar to the above-mentioned protective layer, if the rigidity of the electrode layer is too high, not only will the expansion and contraction of the piezoelectric layer 26 be restricted, but also the flexibility will be impaired. Therefore, as long as the resistance does not become too high, the thinner the electrode layer is, the more advantageous it is.

[0201] In the piezoelectric film 16 , if the product of the thickness of the electrode layer and the Young's modulus is lower than the product of the thickness of the protective layer and the Young's modulus, flexibility is not seriously impaired, which is preferable.

[0202] As an example, a combination in which the protective layer is PET and the electrode layer is composed of copper is shown as a specific example. The Young's modulus of PET is about 6.2 GPa, and the Young's modulus of copper is about 130 GPa. Therefore, in the case of this combination, if the thickness of the protective layer is set to 25 μm, the thickness of the electrode layer is preferably 1.2 μm or less, more preferably 0.3 μm or less, and further preferably 0.1 μm or less.

[0203] The piezoelectric film 16 has a structure in which a piezoelectric body layer 26 is sandwiched between a first electrode layer 28 and a second electrode layer 30 , and the stacked body is further sandwiched between a first protective layer 32 and a second protective layer 34 .

[0204] Such a piezoelectric film 16 preferably has a local maximum value of 0.1 or more in the loss tangent (Tan δ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement at room temperature.

[0205] Thus, even if the piezoelectric film 16 is subjected to relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from being generated at the interface between the polymer matrix and the piezoelectric particles.

[0206] In the piezoelectric film 16 , the storage modulus (E′) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 10 to 30 GPa at 0° C. and 1 to 10 GPa at 50° C.

[0207] As a result, the piezoelectric film 16 can have a large frequency dispersion in the storage elastic modulus (E') at room temperature, that is, it can exhibit a hard action for vibrations of 20 Hz to 20 kHz and exhibit a soft action for vibrations of several Hz or less.

[0208] Furthermore, the piezoelectric film 16 preferably has a thickness and a storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement and a product of 1.0×10 6 ~2.0×10 6 N / m, 1.0×10 at 50°C5 ~1.0×10 6 N / m.

[0209] Thus, the piezoelectric film 16 can have appropriate rigidity and mechanical strength within a range that does not impair flexibility and acoustic characteristics.

[0210] Furthermore, the piezoelectric film 16 preferably has a loss tangent (Tan δ) of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained by dynamic viscoelasticity measurement.

[0211] Below, reference Figure 5 to Figure 7 , an example of a method for manufacturing the piezoelectric film 16 is described.

[0212] First, prepare Figure 5 The sheet 42b of the second electrode layer 30 is formed on the surface of the second protective layer 34 schematically shown in FIG. Figure 7 A sheet-like object 42 a of the first electrode layer 28 is formed on the surface of the first protective layer 32 schematically shown in FIG.

[0213] The sheet 42b can be made by forming a copper thin film or the like on the surface of the second protective layer 34 as the second electrode layer 30 by vacuum evaporation, sputtering, plating, etc. Similarly, the sheet 42a can be made by forming a copper thin film or the like on the surface of the first protective layer 32 as the first electrode layer 28 by vacuum evaporation, sputtering, plating, etc.

[0214] Alternatively, a commercially available sheet in which a copper thin film or the like is formed on a protective layer may be used as the sheet 42 b and / or the sheet 42 a .

[0215] The sheet-shaped object 42b and the sheet-shaped object 42a may be the same or different.

[0216] In addition, when the protective layer is very thin and has poor handling properties, a protective layer with a separator (pseudo-support) can be used as needed. In addition, as a separator, PET with a thickness of 25 to 100 μm can be used. The separator can be removed after the electrode layer and the protective layer are thermocompressed.

[0217] Then, if Figure 6 As schematically shown in FIG. 1 , a stacked body 46 is prepared in which the piezoelectric layer 26 is formed on the second electrode layer 30 of the sheet 42 b and the sheet 42 b and the piezoelectric layer 26 are stacked.

[0218] The piezoelectric layer 26 may be formed by a known method corresponding to the piezoelectric layer 26 .

[0219] For example, if Figure 4The piezoelectric layer (polymer composite piezoelectric layer) in which the piezoelectric particles 40 are dispersed in the polymer matrix 38 shown is produced as follows as an example.

[0220] First, the polymer material such as cyanoethylated PVA is dissolved in an organic solvent, and then piezoelectric particles 40 such as PZT particles are added and stirred to prepare a coating. The organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.

[0221] After the sheet 42b is prepared and the coating is prepared, the coating is cast (coated) on the sheet 42b, and the organic solvent is evaporated and dried. Figure 6 As shown in FIG. 1 , a stacked body 46 is produced in which the second electrode layer 30 is provided on the second protective layer 34 and the piezoelectric layer 26 is stacked on the second electrode layer 30 .

[0222] The coating material is not particularly limited in its casting method, and any known method (coating device) such as a bar coater, a slide coater, or a doctor knife can be used.

[0223] Alternatively, if the polymer material is a heat-meltable substance, the polymer material is heated and melted, and a molten product is prepared by adding the piezoelectric particles 40 thereto, and then extrusion molding is performed to form a molten product. Figure 5 The sheet 42b shown in FIG. 1 is extruded into a sheet and cooled, thereby making a sheet such as Figure 6 The stack 46 is shown.

[0224] As described above, in the piezoelectric layer 26 , a polymer piezoelectric material such as PVDF may be added to the polymer matrix 38 in addition to the polymer material having viscoelasticity at room temperature.

[0225] When adding these polymer piezoelectric materials to the polymer matrix 38, the polymer piezoelectric materials added to the coating material may be dissolved or added to a polymer material having viscoelasticity at room temperature that has been heated and melted and then heated and melted.

[0226] After forming the piezoelectric layer 26, a rolling process may be performed as necessary. The rolling process may be performed once or a plurality of times.

[0227] As is well known, the calendaring treatment refers to a treatment for flattening or the like by pressing a surface to be treated while heating it using a heat press, a heating roll, a heating roll pair, or the like.

[0228] Then, the piezoelectric layer 26 of the stacked body 46 including the second electrode layer 30 on the second protective layer 34 and the piezoelectric layer 26 formed on the second electrode layer 30 is subjected to a polarization process (Polling).

[0229] The method of polarization treatment of the piezoelectric layer 26 is not limited, and a known method can be used. For example, electric field polarization in which a DC electric field is directly applied to the object to be polarized is exemplified. In addition, when electric field polarization is performed, the first electrode layer 28 can be formed before the polarization treatment, and the electric field polarization treatment can be performed using the first electrode layer 28 and the second electrode layer 30.

[0230] Furthermore, when manufacturing the piezoelectric film 16 , it is preferable that the polarization treatment be performed in the thickness direction of the piezoelectric layer 26 rather than in the surface direction.

[0231] Then, if Figure 7 As schematically shown in FIG. 1 , a sheet 42 a prepared in advance is stacked on the piezoelectric layer 26 side of a stacked body 46 so that the first electrode layer 28 faces the piezoelectric layer 26 .

[0232] Furthermore, the laminated body 46 and the sheet 42 a are bonded together by thermocompression bonding using a heat press device and a heating roller so as to sandwich the first protective layer 32 and the second protective layer 34 .

[0233] Thus, the piezoelectric film 16 including the piezoelectric layer 26 , the first electrode layer 28 and the second electrode layer 30 provided on both surfaces of the piezoelectric layer 26 , and the first protective layer 32 and the second protective layer 34 formed on the surfaces of the electrode layers is produced.

[0234] The piezoelectric film 16 manufactured in this way is polarized in the thickness direction rather than in the plane direction, and even if no stretching treatment is performed after the polarization treatment, a large piezoelectric property can be obtained. Therefore, the piezoelectric film 16 has no in-plane anisotropy in the piezoelectric property, and when a driving voltage is applied, it expands and contracts isotropically in all directions in the plane direction.

[0235] As described above, the vibrator 14 is formed by folding the piezoelectric film 16 to stack a plurality of layers, and adhering the stacked adjacent piezoelectric films 16 to each other via the adhesive layer 20. Alternatively, Figure 2 As shown, a plurality of slice-shaped piezoelectric films 16 are stacked, and the stacked adjacent piezoelectric films 16 are bonded together via an adhesive layer 20 .

[0236] The image display device 10 of the present invention expands and contracts the piezoelectric layer 26 by applying a driving voltage to the first electrode layer 28 and the second electrode layer 30. To this end, the first electrode layer 28 and the second electrode layer 30 need to be electrically connected to an external device such as an external power source.

[0237] Various known methods can be used as a method of connecting the first electrode layer 28 and the second electrode layer 30 to an external device.

[0238] As an example, Figure 8 As schematically shown in FIG. 1 , the piezoelectric film 16 is extended at one end to provide a protrusion 12a protruding from the region where the piezoelectric film 16 is stacked. In the above, a method of providing a lead wiring for electrical connection to an external device on the protrusion 12a is exemplified.

[0239] In the present invention, the protruding portion specifically refers to a single-layer region that does not overlap with other piezoelectric films 16 in a planar shape, that is, when viewed in the stacking direction.

[0240] In addition, although Figure 8 The example shows that Figure 1 The vibrator 14 shown is formed by folding and stacking a single piezoelectric film 16. Figure 2 In the structure formed of the sliced ​​piezoelectric films 16 shown, it is only necessary to provide lead wiring for connecting to an external device in the same manner for each piezoelectric film 16 .

[0241] like Figure 8 As shown, a first lead wiring 72 and a second lead wiring 74 for electrical connection to an external device such as a power supply device are connected to the protruding portion 12 a of the vibrator 14 .

[0242] The first lead wire 72 is electrically drawn from the first electrode layer 28, and the second lead wire 74 is electrically drawn from the second electrode layer 30. In the following description, when there is no need to distinguish between the first lead wire 72 and the second lead wire 74, they are simply referred to as lead wires.

[0243] In the image display device 10 of the present invention, the connection method between the electrode layer and the lead wiring, that is, the lead-out method is not limited, and various methods can be used.

[0244] As an example, a method is described in which a through hole is formed in a protective layer, an electrode connecting member formed of a metal paste such as a silver paste is provided so as to fill the through hole, and a lead wiring is provided on the electrode connecting member.

[0245] As another method, a rod-shaped or sheet-shaped lead-out electrode is provided between the electrode layer and the piezoelectric layer or between the electrode layer and the protective layer, and a lead-out wiring is connected to the lead-out electrode. Alternatively, the lead-out wiring can be directly inserted between the electrode layer and the piezoelectric layer or between the electrode layer and the protective layer, thereby connecting the lead-out wiring to the electrode layer.

[0246] As another method, a method of making a portion of the protective layer and the electrode layer protrude from the piezoelectric layer in the surface direction and connecting the lead wiring to the protruding electrode layer is exemplified. In addition, the connection between the lead wiring and the electrode layer can be carried out by a known method such as a method using a metal paste such as silver paste, a method using solder, and a method using a conductive adhesive.

[0247] Preferred methods for extracting electrodes include the method described in Japanese Patent Application Laid-Open No. 2014-209724 and the method described in Japanese Patent Application Laid-Open No. 2016-015354.

[0248] Furthermore, in the vibrator 14, the end of the piezoelectric film 16 is not extended. As shown in Figure 18 of International Publication No. 2020 / 095812, a protrusion such as an island protruding from the piezoelectric film can be provided in the direction of the ridge line of the piezoelectric film 16, that is, in a direction orthogonal to the folding direction, and a lead-out wiring for connecting to an external device can be provided here.

[0249] Furthermore, in the image display device of the present invention, a plurality of these protrusions may be used in combination as necessary.

[0250] The image display device 10 of the present invention is an audio output device that outputs audio by vibrating a diaphragm with a vibrator (actuator), and outputs audio using the display panel 12 as the diaphragm.

[0251] As described above, in the image display device 10 of the present invention, the piezoelectric film 16 is formed by sandwiching the piezoelectric body layer 26 between the first electrode layer 28 and the second electrode layer 30 .

[0252] Preferably, the piezoelectric layer 26 is formed by dispersing piezoelectric particles 40 in a polymer matrix 38 .

[0253] When a voltage is applied to the second electrode layer 30 and the first electrode layer 28 of the piezoelectric film 16 having the piezoelectric layer 26, the piezoelectric particles 40 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric film 16 (piezoelectric layer 26) contracts in the thickness direction. At the same time, due to the relationship of the Poisson's ratio, the piezoelectric film 16 also expands and contracts in the surface direction.

[0254] The expansion and contraction is approximately 0.01 to 0.1%.

[0255] As described above, the thickness of the piezoelectric layer 26 is preferably about 8 to 300 μm. Therefore, the expansion and contraction in the thickness direction is very small, and is only about 0.3 μm at most.

[0256] In contrast, the piezoelectric film 16, that is, the piezoelectric layer 26, has a dimension in the plane direction that is significantly larger than its thickness. Therefore, for example, if the length of the piezoelectric film 16 is 20 cm, the piezoelectric film 16 expands and contracts by a maximum of about 0.2 mm when a voltage is applied.

[0257] As described above, the vibrator 14 is formed by laminating five layers of the piezoelectric film 16 by folding. The vibrator 14 is attached to the display panel 12 via the adhesive layer 68 .

[0258] The vibrator 14 also expands and contracts in the same direction due to the expansion and contraction of the piezoelectric film 16. The display panel 12 is bent due to the expansion and contraction of the vibrator 14, and as a result, vibrates in the thickness direction.

[0259] The display panel 12 outputs sound by the vibration in the thickness direction. That is, the display panel 12 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 16 and outputs sound corresponding to the driving voltage applied to the piezoelectric film 16.

[0260] Among them, it is known that a common piezoelectric film made of a polymer material such as PVDF is stretched in a uniaxial direction after a polarization treatment, so that the molecular chains are oriented relative to the stretching direction, and as a result, a larger piezoelectric property is obtained in the stretching direction. Therefore, a common piezoelectric film has in-plane anisotropy in piezoelectric properties, and has anisotropy in the amount of expansion and contraction in the plane direction when a voltage is applied.

[0261] In contrast, Figure 4 The piezoelectric film 16 shown in the figure, which is composed of a polymer composite piezoelectric body in which piezoelectric particles 40 are dispersed in a polymer matrix 38, can obtain a large piezoelectric property even without a stretching treatment after the polarization treatment. Therefore, the piezoelectric property has no in-plane anisotropy and expands and contracts isotropically in all directions in the plane direction. That is, the vibrator 14 is composed of Figure 4 The piezoelectric film 16 shown expands and contracts isotropically in two dimensions. The vibrator 14 formed by stacking the piezoelectric film 16 that expands and contracts isotropically in two dimensions can vibrate the display panel 12 with a larger force and output a louder and more beautiful sound, compared to the case where a conventional piezoelectric film such as PVDF that expands and contracts greatly in only one direction is stacked.

[0262] As described above, the vibrator 14 of the example shown in the figure is formed by laminating five layers of such piezoelectric films 16. The vibrator 14 of the example shown in the figure is also formed by bonding adjacent piezoelectric films 16 to each other via the bonding layer 20.

[0263] Therefore, even if the rigidity of each piezoelectric film 16 is low and the expansion force is small, the rigidity becomes higher by stacking the piezoelectric films 16, and the expansion force of the vibrator 14 also becomes larger. As a result, even if the display panel 12 has a certain degree of rigidity, the vibrator 14 can fully bend the display panel 12 with a large force, and the display panel 12 can fully vibrate in the thickness direction, so that the display panel 12 outputs sound.

[0264] Furthermore, when the piezoelectric layer 26 is thick, the expansion and contraction force of the piezoelectric film 16 increases, but the driving voltage required to expand and contract the same amount increases accordingly. As described above, in the vibrator 14, the thickness of the piezoelectric layer 26 is preferably only about 300 μm at most, so even if the voltage applied to each piezoelectric film 16 is small, the piezoelectric film 16 can be fully expanded and contracted.

[0265] In the image display device 10 of the present invention, the vibrator is not limited to the stacked piezoelectric element formed by stacking piezoelectric films 16 as shown in the example. That is, the image display device of the present invention can use various vibrators that vibrate a vibration plate to output audio, and known vibrators used as so-called exciters (audio exciters). In particular, it is preferable to use a capacitor-type vibrator in which electrode layers are provided on both sides of a piezoelectric body and a piezoelectric body layer.

[0266] Examples of such capacitor-type resonators include resonators using ceramic piezoelectric bodies such as PVDF, PZT, PLZT, barium titanate, zinc oxide, BFBT, and a piezoelectric element as disclosed in Patent Document 1.

[0267] Furthermore, as long as there is enough force to vibrate the display panel 12 by expansion and contraction, a single piezoelectric film that is not stacked may be used as a vibrator.

[0268] As described above, the image display device 10 of the present invention has the vibrator 14 mounted on the back surface of the display panel 12 , and the display panel 12 serving as a vibration plate is vibrated by the vibrator 14 , thereby outputting audio.

[0269] The image display device 10 of the illustrated example vibrates the display panel 12 serving as a vibration plate by the expansion and contraction of a capacitor-type vibrator 14 such as a stacked piezoelectric element formed by stacking piezoelectric films 16 , thereby outputting audio.

[0270] Here, in a first embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 25 to 100 dpi is used, and when the length of the diagonal line of the display panel 12 is set to A, the maximum length Lmax of the vibrator 14 in the lateral direction of the display panel 12 satisfies “Lmax≤(A / 0.15) 1 / 2 ”.

[0271] In the second embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 50 to 200 dpi2 is used, and when the length of the diagonal line of the display panel 12 is set to A, the maximum length Lmax of the vibrator 14 in the lateral direction of the display panel 12 satisfies "Lmax≤(A / 0.3) 1 / 2 ”.

[0272] In the third embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 100 to 400 dpi is used, and when the length of the diagonal line of the display panel 12 is set to A, the maximum length Lmax of the vibrator 14 in the lateral direction of the display panel 12 satisfies “Lmax≤(A / 0.6) 1 / 2 ”.

[0273] In addition, in the present invention, the horizontal direction of the display panel 12 means that, when the shape of the display panel is a rectangle, such as a common (general-purpose) display panel used in a full HD TV, a 4K TV, and an 8K TV, the direction of the long side is the horizontal direction. However, even if it is the same rectangle, in the case of a display panel in which the long side direction is aligned with the vertical direction and the long side direction is inclined relative to the horizontal direction under the normal use conditions of the image display device, the horizontal direction follows the following.

[0274] In the case of display panels of various shapes such as square, circular, and elliptical, an image display device using these display panels is appropriately set so that the horizontal direction in a normal use state is defined as the lateral direction of the display panel.

[0275] The image display device 10 of the present invention has such a structure, and can sufficiently output audio up to the high-pitched region according to the size and pixel pitch of the display panel 12 .

[0276] As described above, in recent years, thin displays such as liquid crystal displays and organic EL displays have tended to become larger.

[0277] However, according to the research of the inventors, in an image display device that outputs audio by vibrating a display panel using a vibrator, in a large image display device, even if the image display device is viewed at an appropriate viewing distance, the sound pressure of the audio, especially the sound pressure in the high-frequency region, becomes low, making it impossible to view with appropriate audio.

[0278] Specifically, if Figure 1 As shown, in the image display device in which the transducer 14 is arranged separately for the right channel and the left channel, when the image display device is viewed from the front of the transducer 14, audio from bass to treble can be appropriately listened to.

[0279] However, when the image display device is viewed at the center of the screen, the sound pressure of audio in the high-pitched region is particularly low, and appropriate audio cannot be heard.

[0280] The present inventors have conducted an in-depth study on this phenomenon and have found that the cause is a line array effect corresponding to the lateral length of the transducer 14 .

[0281] The line array effect is a phenomenon that occurs in a line sound source, such as a sound source in which point sound sources such as a normal dynamic speaker are arranged in a straight line (line shape).

[0282] Specifically, the line array effect in a line sound source refers to the phenomenon that the longer the line length L of the line sound source is, the longer the effective distance of the audio is, and the narrower the directivity is. The line length of the line sound source is, in other words, the length of the line array.

[0283] When the display panel 12 is bent and vibrated by the extension and contraction of the vibrator 14 installed in the display panel 12 as in the present invention, the display panel 12 is locally bent and deformed centered on the portion where the vibrator 14 is installed. Therefore, it is found that if the vibrator 14 is elongated, the area of ​​the bending deformation is also elongated, and as a result, a line array effect is exhibited. The details will be described later.

[0284] That is, Fig. 9 As schematically shown in the lower part of , when the line length L of the line sound source is short, the directivity is low and the effective distance of the audio is short. Fig. 9 As schematically shown in the upper part of , if the line length L of the line sound source becomes longer, the directivity becomes higher and the effective distance of the audio becomes longer.

[0285] And, if Fig. 9 As shown, the sound pressure of the audio output, especially the high-frequency area, gradually decreases from the center of the line sound source toward both sides in the line direction.

[0286] Therefore, especially when the display panel 12 is a large panel, Fig. 9 As shown, when viewed from the center, the sound pressure in the high-frequency region may be sufficient or insufficient depending on the line length L of the line sound source.

[0287] If the line length of the line sound source is L [m] and the frequency of the sound is f [Hz], the effective distance CD [m] of the line array effect can be expressed by the following formula.

[0288] CD=(L 2 ×f) / 700

[0289] therefore,

[0290] L = [(700 × CD) / f] 1 / 2

[0291] That is, in a line sound source, the longer the line length L is, and the higher the frequency f is, that is, the higher the frequency range is, the longer the effective distance CD based on the line array effect is, and as a result, the directivity becomes narrower.

[0292] Here, the vibrator 14 that vibrates the vibration plate causes the vibration plate to flexurally vibrate by linear expansion and contraction at each position, that is, each point, in one direction.

[0293] Therefore, the speaker unit using the vibrator 14 and the vibration plate can be regarded as a line sound source. Figure 1 and Figure 8 When the long strip-shaped vibrator 14 shown is arranged so that the longitudinal direction of the vibrator 14 coincides with the lateral direction of the display panel 12 , it is regarded as a lateral line sound source.

[0294] As a result, when the line length L of the vibrator 14 is long, Fig. 9 As shown in the upper part of , in the treble region (high frequency band), audio with sufficient sound pressure does not reach the center of the display unit.

[0295] Here, in the television, the appropriate viewing distance is determined according to the size of the display panel 12. Specifically, the smaller the size of the display panel 12, the shorter the appropriate viewing distance.

[0296] Furthermore, the more pixels a TV has, that is, the higher its resolution, the shorter its appropriate viewing distance. Therefore, among full HD TVs, 4K TVs, and 8K TVs, full HD TVs have the longest appropriate viewing distance, while 8K TVs have the shortest.

[0297] For example, if the screen size is 80 inches, the appropriate viewing distance is 3 meters for a full HD TV and 1.5 meters for a 4K TV.

[0298] For a 65-inch screen, the appropriate viewing distance is 2.5m for a full HD TV and 1.2m for a 4K TV.

[0299] If it is 55 inches, the appropriate viewing distance is 2m for Full HD TV and 1m for 4K TV.

[0300] Moreover, if it is 42 inches, the appropriate viewing distance is 1.5m for Full HD TV and 0.8m for 4K TV.

[0301] That is, in the image display device 10 , basically, sufficient sound pressure from the bass range to the treble range can be obtained at an appropriate viewing distance according to the resolution and size of the television (display panel).

[0302] Here, if the above-mentioned formula for calculating the effective distance of the line array effect is used, by replacing the appropriate viewing and listening distance corresponding to the size of the TV (display panel) with the effective distance CD of the line array effect, the frequency f that produces the line array effect at the appropriate viewing and listening distance can be calculated corresponding to the line length L of the vibrator 14.

[0303] For example, in the case of the transducer 14 having a line length L of 0.18 m, the frequencies at which the line array effect is manifested at an appropriate viewing distance in each size are as follows in a 4K TV and a full high definition TV (FHD).

[0304] [Table 1]

[0305] Cable length L = 0.18m

[0306]

[0307] Furthermore, in the case of a transducer having a line length L of 0.20 m, the frequencies at which the line array effect appears at viewing distances of various sizes are as follows in 4K TVs and full high-definition TVs (FHD).

[0308] [Table 2]

[0309] Cable length L = 0.20m

[0310]

[0311] Here, in most people's ears, especially for TV use, even if they cannot hear the high-frequency treble area above 16kHz, it will not have a big impact on the sound quality. In other words, even if the line array effect appears in the treble area above 16kHz and the directivity becomes narrow, there is no big problem with the sound quality.

[0312] Therefore, if the frequency at which the line array effect appears at an appropriate viewing distance is above 16kHz, the line array effect will not appear in audio with a frequency lower than 16kHz at an appropriate viewing distance, so a sufficiently wide directivity can be obtained in practical terms even in the high-frequency region.

[0313] That is, in the case of a transducer with a line length L of 0.18 m, in a 4K TV, if the display panel is 42 inches or larger, the line array effect is not apparent in audio with a frequency lower than 16 kHz at an appropriate viewing distance.

[0314] Therefore, in the case of a transducer with a line length L of 0.18 m along the horizontal direction of the display panel, in a 4K TV, if it is 42 inches or larger, sufficient sound pressure can be obtained from the bass region to the treble region at an appropriate viewing distance in the center of the display panel.

[0315] Furthermore, in the case of a transducer with a line length L of 0.18 m, in full HDTVs, in all sizes above 23 inches, at an appropriate viewing distance, the line array effect is not apparent in audio frequencies less than 16 kHz.

[0316] Therefore, in the case of a transducer with a horizontal line length L of 0.18 m along the display panel, in full HD TVs, in all display panels larger than 23 inches, sufficient sound pressure can be obtained from the bass region to the treble region at an appropriate viewing distance in the center of the display panel.

[0317] On the other hand, in the case of a transducer with a line length L of 0.20 m, in a 4K TV, if the display panel is 50 inches or larger, the line array effect is not apparent in audio with a frequency lower than 16 kHz at an appropriate viewing distance.

[0318] Therefore, in the case of a transducer with a line length L of 0.20 m along the horizontal direction of the display panel, in a 4K TV, if it is 50 inches or more, sufficient sound pressure can be obtained from the bass region to the treble region at an appropriate viewing distance in the center of the display panel.

[0319] Furthermore, even in the case of a transducer with a line length L of 0.20 m, in full HDTVs, in all sizes above 23 inches, at an appropriate viewing distance, the line array effect is not apparent in audio frequencies below 16 kHz.

[0320] Therefore, even in the case of a transducer with a horizontal line length L of 0.20 m along the display panel, in full HD TVs, in all display panels larger than 23 inches, sufficient sound pressure can be obtained from the bass area to the treble area at an appropriate viewing distance in the center of the display panel.

[0321] The inventors changed the line length L of the vibrator 14 from 0.1m to 0.33m in increments of 0.01m, and calculated the frequency at which the line array effect appears at an appropriate viewing distance for each size of 23 to 80 inches in full HD TV, 4K TV, and 8K TV.

[0322] Based on the results, the maximum line length L (maximum line length) of the transducer 14 at a frequency of 16 kHz or more at which the line array effect is exhibited at an appropriate viewing distance is detected in each size of the display panel at each resolution. In other words, the maximum line length L of the transducer 14 at which the line array effect is not exhibited at a frequency of less than 16 kHz at an appropriate viewing distance is detected in each size of the display panel at each resolution.

[0323] The results are shown in the following table.

[0324] [Table 3]

[0325]

[0326] As shown in the table, for example, when the size of the display panel 12 is 80 inches, if the line length L of the vibrator 14 is less than 36 cm in full HD, if the line length L of the vibrator 14 is less than 26 cm in a 4K TV, and if the line length L of the vibrator 14 is less than 18 cm in an 8K TV, then at an appropriate viewing distance, the line array effect will not be apparent when the frequency is less than 16 kHz.

[0327] Furthermore, for example, when the size of the display panel 12 is 50 inches, if the line length L of the vibrator 14 is less than 29 cm in full HD, if the line length L of the vibrator 14 is less than 20 cm in a 4K TV, and if the line length L of the vibrator 14 is less than 15 cm in an 8K TV, then at an appropriate viewing distance, the line array effect will not be apparent when the frequency is less than 16 kHz.

[0328] Here, the present inventors studied this table and obtained the following findings.

[0329] Specifically, it was found that the value obtained by dividing the length of the diagonal line (in cm) in each size by the square of the maximum line length (in cm) was approximately 0.15 in the case of a full HD display panel, approximately 0.3 in the case of a 4K TV display panel, and approximately 0.6 in the case of an 8K TV display panel.

[0330] That is, in the case of a full HD display panel, regardless of the size, when the length of the diagonal line (in cm) is divided by a coefficient of 0.15 and raised to the 1 / 2 power (root multiplication), the maximum line length (in cm) of the transducer 14 at which the line array effect does not appear when the frequency is less than 16 kHz at an appropriate viewing distance becomes.

[0331] Furthermore, in the case of a display panel of a 4K TV, regardless of the size, when the length of the diagonal line (in cm) is divided by a coefficient of 0.3 and raised to the power of 1 / 2, the maximum line length (in cm) of the vibrator 14 at which the line array effect does not appear when the frequency is less than 16 kHz at an appropriate viewing distance becomes.

[0332] Moreover, in the case of an 8K TV display panel, regardless of the size, when the length of the diagonal line (in cm) is divided by a coefficient of 0.6 and raised to the power of 1 / 2, the maximum line length (in cm) of the vibrator 14 at which the line array effect does not appear when the frequency is less than 16 kHz at an appropriate viewing distance becomes.

[0333] That is, by setting the maximum line length (in cm) of the transducer 14 to be less than the maximum line length (in cm) calculated by this formula, the line array effect is not manifested in audio with a frequency lower than 16 kHz at an appropriate viewing distance.

[0334] The present invention has been accomplished by obtaining this finding.

[0335] In a first embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 25 to 100 dpi is used, and when the length of the diagonal line of the display panel 12 is A (cm), the maximum length Lmax (cm) of the vibrator 14 in the lateral direction of the display panel 12 satisfies “Lmax ≤ (A / 0.15) 1 / 2 The display panel 12 with a pixel pitch of 25 to 100 dpi is a display panel corresponding to a full high-definition television.

[0336] In the second embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 50 to 200 dpi2 is used, and when the length of the diagonal line of the display panel 12 is set to A (cm), the maximum length Lmax (cm) of the vibrator 14 in the lateral direction of the display panel 12 satisfies “Lmax ≤ (A / 0.3) 1 / 2 ”. The display panel 12 with a pixel pitch of 50 to 200 dpi2 is a display panel corresponding to a 4K TV.

[0337] In the third embodiment of the image display device 10 of the present invention, a display panel 12 having a pixel pitch of 100 to 400 dpi is used, and when the length of the diagonal line of the display panel 12 is set to A (cm), the maximum length Lmax (cm) of the vibrator 14 in the lateral direction of the display panel 12 satisfies “Lmax ≤ (A / 0.6) 1 / 2 ". The display panel 12 with a pixel pitch of 100 to 400 dpi is the display panel corresponding to the 8K TV.

[0338] With such a structure, the image display device of the present invention can set the frequency at which the line array effect is exhibited to 16 kHz or more, which has little effect on the sound quality in the high-frequency region, at an appropriate viewing distance corresponding to the resolution and size of the display panel 12 .

[0339] As a result, in the image display device of the present invention, which outputs audio by vibrating the display panel 12 with the vibrator 14, sufficient sound pressure can be obtained from the bass region to the treble region in practical terms at an appropriate viewing distance at the center of the display panel.

[0340] In addition, Figure 1 ( Fig. 9) is shown in the example, the long strip-shaped vibrator 14 is arranged in a manner such that the length direction is consistent with the lateral direction of the display panel 12, but the present invention is not limited to this.

[0341] In the image display device of the present invention, for example, the length direction of the long strip vibrator 14 may be arranged to be inclined with respect to the lateral direction of the display panel 12. In this case, the maximum length Lmax of the vibrator 14 is not the length in the length direction of the long strip vibrator 14 nor the length from end to end of the vibrator 14 in the lateral direction of the display panel 12, but the maximum length of the vibrator 14 in the lateral direction of the display panel 12.

[0342] That is, in the image display device of the present invention, the maximum length Lmax of the vibrator 14 is the maximum length of the vibrator 14 in the lateral direction of the display panel 12 regardless of the shape of the vibrator and the arrangement state of the vibrator on the display panel 12 .

[0343] As mentioned above, the image display device of the present invention has been described in detail, but the present invention is not limited to the above-mentioned example, and various improvements and changes can be made without departing from the scope of the present invention.

[0344] Example

[0345] Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

[0346] [Fabrication of piezoelectric film]

[0347] pass Figure 5 to Figure 7 The method shown in Figure 4 The piezoelectric film shown.

[0348] First, cyanoethylated PVA (CR-V, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) at the following composition ratio. Then, PZT particles were added to the solution at the following composition ratio as piezoelectric particles, and the mixture was stirred by a propeller mixer (rotation speed 2000 rpm), thereby preparing a coating for forming a piezoelectric layer.

[0349] ·PZT particles···········300 parts by mass

[0350] ·Cyanoethylated PVA··········30 parts by mass

[0351] ·DMF··············70 parts by mass

[0352] The PZT particles used were obtained by wet-mixing powders of Pb oxide, Zr oxide and Ti oxide as main components in a ball mill so that Zr = 0.52 mol and Ti = 0.48 mol per Pb = 1 mol, calcining the mixed powder at 800°C for 5 hours and then pulverizing the mixed powder.

[0353] On the other hand, two sheets were prepared in which a copper thin film with a thickness of 0.1 μm was vacuum-deposited on a PET film with a thickness of 4 μm. That is, in this example, the first electrode layer and the second electrode layer were copper-deposited thin films with a thickness of 0.1 μm, and the first protective layer and the second protective layer were PET films with a thickness of 4 μm.

[0354] A coating material for forming a piezoelectric layer prepared in advance was applied onto a copper thin film (second electrode layer) of one sheet using a sloped sheet coater.

[0355] Next, the object coated with the coating on the sheet was heated and dried on a hot plate at 120° C. to evaporate DMF. Thus, a laminate having a second electrode layer made of copper on a second protective layer made of PET and a piezoelectric layer (polymer composite piezoelectric layer) having a thickness of 50 μm thereon was prepared.

[0356] The produced piezoelectric layer (laminated body) was subjected to a rolling process using a heating roller pair. The temperature of the heating roller pair was set to 100°C.

[0357] After the rolling process, the produced piezoelectric layer was polarized in the thickness direction.

[0358] Another sheet-like material was stacked on the stacked body so that the copper thin film (first electrode layer) faced the piezoelectric layer.

[0359] Next, the laminate and the sheet-like laminate were heat-pressed at 120° C. using a pair of heated rollers, thereby bonding the piezoelectric layer and the first electrode layer to produce a laminate such as Figure 4 The piezoelectric film shown.

[0360] [Example]

[0361] The fabricated piezoelectric film was cut into a rectangle of 22×18 cm.

[0362] The following steps were repeated 4 times at 4 cm intervals in the 22 cm direction: setting the adhesive layer, folding the piezoelectric film, and pressing the piezoelectric film with a roller to adhere the piezoelectric film. Thus, a rectangular sheet with a plane shape of 4×18 cm was prepared in which 5 layers of piezoelectric films were stacked and adjacent stacked piezoelectric films were adhered. Figure 8Therefore, in this vibrator, the side with a length of 18 cm becomes a ridge (folding line). In addition, in this stacked vibrator, a 2 cm excess (redundant portion) of the piezoelectric film is generated at the end, but the wiring is connected using this redundant portion (reference Figure 8 ) This point is also the same in the comparative example.

[0363] As the adhesive layer, a hot-melt sheet (Kuran Beter: thickness 30 μm) manufactured by Kurabo Industries Ltd. was used.

[0364] A PET panel having a thickness of 0.5 mm and a size of 121 cm x 69 cm was prepared. The size of the PET panel was the same as that of a 55-inch display panel.

[0365] The vibrator was pasted in the center of the panel in the vertical direction (width direction) and 30 cm from one end in the horizontal direction (length direction). Double-sided adhesive tape (TESA70420: thickness 200 um) made by TESA was used for pasting. In addition, the redundant part was not pasted for connecting wiring. The comparative example was the same in this regard.

[0366] The panel and the vibrator were attached so that their longitudinal and width directions were aligned with each other and the position 15 cm from one end in the vertical direction of the panel was aligned with the center of the vibrator (rectangle).

[0367] That is, in this example, if the panel made of PET is regarded as the display panel, the maximum length Lmax of the vibrator along the lateral direction of the display panel is 18 cm.

[0368] Furthermore, if the PET panel is regarded as a display panel of a 55-inch 4K TV, the diagonal length A is 140 cm, so

[0369] (140 / 0.3) 1 / 2 =21.6,

[0370] And meet the "Lmax≤(A / 0.3) 1 / 2 ”.

[0371] [Comparative Example]

[0372] The produced piezoelectric film was cut into a rectangle of 22×25 cm, and folded four times at 4 cm intervals in the 22 cm direction in the same manner as in the example, thereby producing a rectangular film of 4×25 cm in planar shape. Figure 8 Therefore, in this vibrator, the side with a length of 25 cm becomes the edge line (folding line).

[0373] This vibrator was bonded to the same PET panel as in the example in exactly the same manner as in the example.

[0374] That is, in this example, if the panel made of PET is regarded as the display panel, the maximum length Lmax of the vibrator along the lateral direction of the display panel is 25 cm.

[0375] Furthermore, if the PET panel is regarded as a display panel of a 55-inch 4K TV, the diagonal length A is 140 cm, so

[0376] (140 / 0.3) 1 / 2 =21.6,

[0377] And does not meet the "Lmax≤(A / 0.3) 1 / 2 ”.

[0378] [evaluate]

[0379] The PET panel to which the transducer was attached was regarded as a display panel of a 55-inch 4K TV, and the frequency characteristics of the sound pressure were measured.

[0380] The appropriate viewing distance for a 55-inch 4K TV is 1 meter. Accordingly, a microphone was set at a position 1 meter away from the center of the display panel in the normal direction (the direction perpendicular to the display panel = PET panel) and the frequency characteristics of the sound pressure output by the display panel were measured.

[0381] The input signal to the oscillator was set to a sine sweep signal (50 Vrms).

[0382] The sound pressure measurement results of the examples are shown in Fig.10 The sound pressure measurement results of the comparative example are shown in Fig.11 .

[0383] As in the embodiment, when the maximum line length (line length L) of the transducer is 18 cm and the viewing distance (effective distance CD) is 1 m, according to the above formula “CD=(L 2 ×f) / 700”, at a viewing distance of 1m, the line array effect is visible above 22kHz.

[0384] Therefore, when "Lmax≤(A / 0.3) 1 / 2 In the embodiment of ", Fig.10 As shown, when the frequency characteristics are measured at a distance of 1 m, no drop in sound pressure is observed in the high-frequency region up to 20 kHz.

[0385] On the other hand, when the maximum line length (line length L) of the transducer is 25 cm as in the comparative example, the line array effect is exhibited at 11 kHz or more at a viewing distance of 1 m.

[0386] Therefore, if "Lmax≤(A / 0.3) 1 / 2 In the comparative example of " Fig.11 As shown in FIG. 1 , when the frequency characteristics are measured at a distance of 1 m, the sound pressure decreases above 11 kHz, and there is a tendency for the sound pressure in the high-frequency region to be insufficient.

[0387] In addition, the sound pressure in the middle / bass region of the comparative example is higher because the area of ​​the oscillator of the comparative example is wider.

[0388] From the above results, the effects of the present invention are obvious.

[0389] Industrial Applicability

[0390] It can be preferably used for thin-screen televisions and the like.

[0391] Explanation of symbols

[0392] 10-image display device, 12-display panel, 14-oscillator, 16-piezoelectric film, 20, 68-adhesive layer, 26-piezoelectric layer, 28-first electrode layer, 30-second electrode layer, 32-first protective layer, 34-second protective layer, 38-polymer matrix, 40-piezoelectric particles, 42a, 42b-sheet, 46-laminated body, 72-first lead wiring, 74-second lead wiring.

Claims

1. An image display device, comprising: A display panel with a pixel pitch of 25 to 100 dpi and a vibrator mounted on a non-display surface of the display panel, When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator along the lateral direction of the display panel satisfies: Lmax≤(A / 0.15) 1 / 2 。 2. An image display device, comprising: A display panel with a pixel pitch of 50 to 200 dpi and a vibrator mounted on a non-display surface of the display panel, When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator along the lateral direction of the display panel satisfies: Lmax≤(A / 0.3) 1 / 2 。 3. An image display device, comprising: A display panel with a pixel pitch of 100 to 400 dpi and a vibrator mounted on a non-display surface of the display panel, When the length of the diagonal of the display panel is set to A, the maximum length Lmax of the vibrator along the lateral direction of the display panel satisfies: Lmax≤(A / 0.6) 1 / 2 。 4. The image display device according to any one of claims 1 to 3, wherein: The aspect ratio of the display panel is 16:

9.

5. The image display device according to any one of claims 1 to 3, wherein: The vibrator is a piezoelectric film having electrode layers on both surfaces of a piezoelectric layer.

6. The image display device according to claim 5, wherein: The vibrator is formed by stacking a plurality of piezoelectric films.

7. The image display device according to claim 5, wherein: The piezoelectric film has a protective layer covering the electrode layer.

8. The image display device according to claim 5, wherein: The piezoelectric layer is a polymer composite piezoelectric body having piezoelectric particles in a polymer material.

9. The image display device according to claim 8, wherein: The polymer material has a cyanoethyl group.

10. The image display device according to claim 9, wherein: The polymer material is cyanoethylated polyvinyl alcohol.

11. The image display device according to claim 6, wherein: The vibrator is formed by folding one piezoelectric film to stack a plurality of piezoelectric films.

12. The image display device according to claim 6, wherein: The stacked adjacent piezoelectric films are bonded together via an adhesive layer.

Images