KR20080008085A - Plasma display device - Google Patents

Abstract

A plasma display device is provided to protect an entire surface of panel from external shock by forming a shock-absorbing layer. A plasma display device includes an external light shielding sheet(100). The external light shielding sheet includes a base part(110) and a pattern part(120). The base part is formed to transmit light at a predetermined refractive angle. The pattern part is formed on the base part. A refractive index of the pattern part is smaller than a refractive index of base part. A shock-absorbing layer is formed on at least one side of the external light shielding sheet. The shock-absorbing layer is formed of a material having adhesive strength of 0.2N/25mm and more. The shock-absorbing layer is formed with a transparent color.

Description

Plasma Display Device

1 is a diagram illustrating an embodiment of a structure of a plasma display panel;

2 illustrates an embodiment of an electrode arrangement of a plasma display panel;

FIG. 3 illustrates an embodiment of a method in which a frame of an image is time-divided and driven into a plurality of subfields in the plasma display apparatus.

Figure 4 is a view showing an embodiment of the cross-sectional structure of the external light blocking sheet according to the present invention,

5 is a view showing the front surface of the external light blocking sheet according to the present invention;

6A to 7B illustrate various embodiments of a laminated structure of an external light shielding sheet according to the present invention;

8 illustrates an embodiment of a plasma display device according to the present invention;

9 is a view showing an embodiment of the structure of an impact absorbing layer according to the present invention;

10A-10B illustrate embodiments of a frontsheet in accordance with the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device. In particular, in order to block external light incident from the outside of a panel, an external light shielding sheet made of two materials having different refractive indices is provided on the front surface of the panel, whereby the brightness and contrast of the panel are increased The present invention relates to a plasma display apparatus which can protect an entire surface of a panel from external impact by forming an impact absorbing layer that is improved and absorbs external impact on one surface of an external light shielding sheet.

In general, a plasma display panel (hereinafter referred to as a PDP) generates a discharge by applying a predetermined voltage to electrodes installed in a discharge space, and the plasma generated during gas discharge excites a phosphor, thereby causing an image including a character or graphic. As a device for displaying a display device, it is easy to increase in size, weight, and planar thickness, provide a wide viewing angle from side to side, and realize full color and high brightness.

When a black image is realized by such a PDP, external light is reflected from the front of the panel of the PDP due to the white phosphor exposed on the lower panel of the panel, whereby the black image is perceived as a dark color of a bright series and contrast. There is a problem that is lowered. In addition, since the front surface of the panel is exposed from an external impact, there is a problem that can be easily damaged.

The present invention has been made to solve the above-mentioned problems of the prior art, and effectively block external light incident on the panel to prevent reflection of light, and improve the clear contrast of the PDP and at the same time the An object of the present invention is to provide a plasma display device including an external light shielding sheet capable of protecting a front surface thereof.

According to an aspect of the present invention, there is provided a plasma display apparatus including: a base unit for transmitting light by refracting at a predetermined angle; It is formed on the base portion, comprising an external light blocking sheet having a pattern portion having a refractive index smaller than the base portion, characterized in that the shock absorbing layer is formed on at least one surface of both sides of the external light blocking sheet.

At this time, the shock absorbing layer is formed of a material having an adhesive force of 0.2N / 25mm or more, characterized in that the substantially transparent index.

In addition, the thickness of the shock absorbing layer is 25um to 500um, more preferably 50um to 100um.

In addition, the base portion is characterized in that formed of a transparent plastic material.

In addition, the thickness of the external light shielding sheet is 20um to 250um, the refractive index of the pattern portion is characterized in that 0.3 times to 0.99 times the refractive index of the base portion.

In addition, the pattern portion is formed in a darker color than the base portion, it is characterized in that the substantially black.

In addition, the lower end of the pattern portion is disposed to the panel side, the upper end is disposed to the user side, the width of the lower end of the pattern portion is 5um to 150um, characterized in that the upper end width of the pattern portion is formed to 130um or less.

In addition, the external light shielding sheet may include an AR layer for preventing reflection of external light; A NIR shielding layer that shields near infrared rays emitted from the panel; And an EMI shielding layer for shielding electromagnetic waves, wherein the external light shielding sheet is installed on a front surface of the panel.

Plasma display device according to the present invention for solving the above technical problem includes a shock absorbing layer to protect the front surface of the panel from an external shock, the shock absorbing layer is characterized in that formed of a material having an adhesive force of 0.2N / 25mm or more do.

At this time, the shock absorbing layer is a substantially transparent material, characterized in that formed of a pressure-sensitive adhesive-based material.

In addition, the thickness of the impact absorbing layer is 25um to 500um, preferably 50um to 100um.

In addition, the shock absorbing layer is an AR layer to prevent reflection of external light; And at least one of an NIR shielding layer for shielding near infrared rays emitted from the panel, and an EMI shielding layer for shielding electromagnetic waves.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating an embodiment of a structure of a plasma display panel.

Referring to FIG. 1, the plasma display panel includes a scan electrode 11 and a sustain electrode 12, which are sustain electrode pairs formed on the upper substrate 10, and an address electrode 22 formed on the lower substrate 20. It includes.

Each of the sustain electrode pairs 11 and 12 is typically a transparent electrode 11a or 12a formed of indium tin oxide (ITO), a metal such as silver (Ag), chromium (Cr), or chromium / copper. And the bus electrodes 11b and 12b which may be formed in a stack of / chromium (Cr / Cu / Cr) or in a stack of chromium / aluminum / chromium (Cr / Al / Cr). At this time, the bus electrodes 11b and 12b are formed on the transparent electrodes 11a and 12a to reduce the voltage drop caused by the transparent electrodes 11a and 12a having high resistance.

In addition, the PDP has a function of light blocking to reduce the reflection and absorption of external light generated from the outside of the upper substrate 10, and to improve the purity of the upper substrate 10 and the contrast of the PDP. Black Matrix (BM) is formed.

The black matrix is interposed between the first black matrix 15 formed at a position overlapping the partition wall 21 formed on the lower substrate 20, the transparent electrodes 11a and 12a and the bus electrodes 11b and 12b. It is composed of the second black matrices 11c and 12c formed. As such, the black matrix formed by separating the first and second black matrices 15, 11c and 12c is called a separate type BM, and since the second black matrices 11c and 12c form a layer between the electrodes, the black matrix is black. It may also be called a layer or a black electrode layer.

An upper dielectric layer 13 and a protective layer 14 are stacked on the upper substrate 10 on which the scan electrode 11 and the sustain electrode 12 are formed, respectively, and charged particles, which generate plasma, are accumulated on the upper dielectric layer 13. . The protective layer 14 protects the upper dielectric layer 13 from sputtering of charged particles generated during gas discharge, and increases emission efficiency of secondary electrons.

In addition, the address electrode 22 is formed on the lower substrate 20 in a direction crossing the scan electrode 11 and the sustain electrode 12, and the lower dielectric layer 24 is formed on the lower substrate 20 on which the address electrode 22 is formed. ) And a partition wall 21 are formed, and phosphors 23 which emit light by ultraviolet rays generated during gas discharge and generate visible light are coated on the lower dielectric layer 24 and the partition wall 21.

The partition wall 21 includes a vertical partition wall 21a formed in a direction parallel to the address electrode 22 and a horizontal partition wall 21b formed in a direction crossing the address electrode 22 to physically distinguish discharge cells. Ultraviolet rays and visible light generated by the discharge are prevented from leaking to the adjacent discharge cells.

Since the structure of the panel shown in FIG. 1 is only an embodiment of the structure of the plasma display panel according to the present invention, the present invention is not limited to the structure of the plasma display panel shown in FIG. 1. For example, the PDP according to the present invention may have a structure in which each of the sustain electrode pairs 11 and 12 omits the transparent electrodes 11a and 12a made of ITO and includes only the bus electrodes 11b and 12b. Since the structure does not use the transparent electrodes 11a and 12a, there is an advantage of lowering the unit cost of panel manufacturing, and the bus electrodes 11b and 12b may be various materials such as photosensitive materials in addition to the materials listed above.

In addition, the partition structure of the PDP shown in FIG. 1 represents a close type in which the discharge cells are closed by the vertical partition 21a and the horizontal partition 21b, but the present invention is not limited thereto. The exhaust passage is provided in at least one of the stripe type, which is the omitted structure, the differential partition structure having a different height between the vertical partition 21a and the horizontal partition 21b, the vertical partition 21a or the horizontal partition 21b. A channel type barrier rib structure in which a usable channel is formed, a groove type barrier rib structure in which a groove is formed in at least one of the vertical barrier rib 21a or the horizontal barrier rib 21b, and the like may be used.

Here, in the case of the differential barrier rib structure, the height of the horizontal barrier rib 21b is more preferable, and in the case of the channel barrier rib structure or the groove barrier rib structure, it is preferable that the channel is formed in the horizontal barrier rib 21b or the groove is formed. something to do.

On the other hand, in one embodiment of the invention is shown and described that each of the R, G and B discharge cells are arranged on the same line, it may also be arranged in other formation. For example, a delta type arrangement in which R, G, and B discharge cells are arranged in a triangular shape may be possible, and the shape of the discharge cell may be not only square but also various polygonal shapes such as pentagon and hexagon.

2 is a diagram illustrating an embodiment of an electrode arrangement of a plasma display panel.

Referring to FIG. 2, the plurality of discharge cells constituting the plasma display panel may be arranged in a matrix form. The plurality of discharge cells are provided at the intersections of the scan electrodes Y1 to Ym, the sustain electrodes Z1 to Zm, and the address electrodes X1 to Xn, respectively. The scan electrodes Y1 to Ym may be driven sequentially or simultaneously, and the sustain electrodes Z1 to Zm may be driven simultaneously. The address electrodes X1 to Xn may be driven by being divided into odd-numbered and even-numbered electrodes or sequentially driven.

Since the electrode arrangement shown in FIG. 2 is only an embodiment of the electrode arrangement of the plasma display panel according to the present invention, the present invention is not limited to the electrode arrangement and driving method of the plasma display panel shown in FIG. 2. For example, a dual scan method in which two scan electrodes of the scan electrodes Y1 to Ym are simultaneously scanned is possible, and the address electrodes X1 to Xn are divided up and down at the center of the panel. It may be driven.

FIG. 3 is a diagram illustrating an embodiment of a method in which a frame of an image is time-divided and driven into a plurality of subfields in the plasma display apparatus.

Referring to FIG. 3, referring to FIG. 3, a unit frame may be time-division driven into a predetermined number, for example, eight subfields SF1,..., SF8 to express the gray level of an image. Each subfield SF1, ..., SF8 is divided into a reset section (not shown), an address section A1, ..., A8, and a sustain section S1, ..., S8. .

In each address section A1, ..., A8, a data signal is applied to the address electrode X, and corresponding scan pulses are sequentially applied to each scan electrode Y. FIG. Sustain pulses are alternately applied to the scan electrode Y and the sustain electrode Z in each of the sustain periods S1, ..., S8, so that the discharge cells selected in the address periods A1, ..., A8 are alternately applied. Cause sustain discharge.

The luminance of the plasma display panel is proportional to the number of sustain discharges in the sustain periods S1, ..., S8 occupied in the unit frame. When one frame forming one image is represented by eight subfields and 256 gray levels, each subfield in turn has different sustain pulses at a ratio of 1, 2, 4, 8, 16, 32, 64, and 128. The number of can be assigned. Alternatively, in order to obtain luminance of 133 gray levels, cells may be sustained by addressing cells during subfield 1, subfield 3, and subfield 8 sections.

Meanwhile, the number of sustain discharges allocated to each subfield may be variably determined according to the weights of the subfields. That is, in FIG. 3, a case in which one frame is divided into eight subfields has been described as an example. However, the present invention is not limited thereto, and the number of subfields forming one frame may be variously modified according to design specifications. . For example, the plasma display panel may be driven by dividing one frame into eight or more subfields or the like, such as 12 or 16 subfields.

4 is a view showing an embodiment of the structure of an external light shielding sheet according to the present invention.

Referring to FIG. 4, the external light blocking sheet 100 according to the present invention includes a base part 110, a pattern part 120, and an impact absorbing layer 130.

The base unit 110 is preferably made of a transparent plastic material, for example, a resin-based material formed by a UV curing method so as to transmit light smoothly, and protects the front surface of the panel. In order to increase the effect, a rigid glass material may be used.

The thickness T1 of the external light shielding sheet is preferably 20 μm to 250 μm, in which case, the manufacturing process may be easy and may have an appropriate light transmittance. More preferably, the thickness T of the external light shielding sheet is 200 μm to 210 μm so that light emitted from the panel is more smoothly transmitted, and light incident from the outside is refracted to be effectively absorbed and blocked by the pattern unit 120. Is formed.

As shown in FIG. 4, the pattern part 120 formed on the base part 110 may have a triangular cross-sectional shape having a cross-sectional shape having a larger width of the lower end 120a than the upper end 120b, and more preferably. Is an isosceles triangle. In addition, the bottom width P1 of the pattern portion 120 may be formed to 5um to 150um, in which case it is possible to ensure the aperture ratio for light emitted from the panel can be smoothly emitted to the user side. In addition, in order to maximize the external light blocking effect of the external light blocking sheet 100, the upper end 120b of the pattern part 120 is disposed on the user side A from which light is incident from the outside, and the lower end 120a is the panel side B. It is preferable to arrange in).

In addition, the refractive index of the pattern portion 120 is preferably 0.3 times to 0.99 times the refractive index of the base portion 110. In general, external light that affects the brightness loss of the PDP is often present at the top of the user's head. Such external light is refracted by the inside of the pattern portion 120 to be absorbed and blocked, and light emitted from the inside of the panel to display an image causes total reflection on the inclined surface 120c of the pattern portion 120. The refractive index of the pattern portion 120 is formed to be smaller than the refractive index of the base portion 110 in the above range.

The pattern part 120 is formed of a material of darker color than the base part 110, and preferably, a material of black color. For example, the pattern unit 120 is formed of a carbon-based material or maximizes the effect of absorbing external light by applying a black dye and material.

The shock absorbing layer 130 formed on one surface of the external light blocking sheet 100 is formed of a material having a transparent color for smooth transmission of light, and preferably made of a material having an adhesive force of 0.2N / 25mm. For example, the shock absorbing layer 130 is made of a pressure sensitive adhesive (PSA) -based adhesive, and has an effect of transmitting detachment and light of the external light blocking sheet 100. In addition, in order for the external light absorbing sheet to be attached to the front surface of the panel at the same time as the external shock absorbing effect, the shock absorbing layer 130 is preferably formed at the lower end portion 120a of the pattern portion of the external light blocking sheet 100.

In addition, the thickness (T2) of the shock absorbing layer 130 is preferably 25um to 500um, in which case the light transmission efficiency is good, it may have an appropriate shock absorbing power. More preferably, in order to smoothly transmit the light emitted from the panel, and to sufficiently protect the panel from external pressure and impact, the thickness T2 of the shock absorbing layer 130 is formed to be 50um to 100um.

On the other hand, Figure 4 is only an embodiment of the structure of the external light blocking sheet according to the present invention, the present invention is not limited to the structure of the external light blocking sheet shown in FIG. For example, the pattern portion 120 may have an isosceles triangle having an asymmetric triangle in cross-sectional shape, or may have a trapezoidal shape of the pattern portion 120. At this time, it is preferable that the upper width P2 of the pattern portion 120 is 130 μm or less, thereby forming an inclination of the inclined surface 120c capable of effectively absorbing external light and reflecting the panel light in a relationship with the lower width P1. can do. Alternatively, at least one of the upper and left and right inclined surfaces of the pattern unit 120 may have a curved shape. In addition, as shown in FIG. 4, it is preferable that the adjacent pattern parts 120 are formed at regular intervals, but may be formed at different intervals.

5 is a view schematically showing the front surface of the external light blocking sheet according to the present invention.

Referring to FIG. 5, it is preferable that the external light shielding sheet 100 according to the present invention is formed at predetermined intervals in a row on the base portion 110. Not limited to this, another pattern portion may be further formed in an intersecting direction with the pattern portion 120 shown in FIG. 5 to increase external light blocking efficiency, and have a predetermined angle based on the pattern portion 120 shown in FIG. 5. The pattern portion 120 may be formed to have a slope of. In this case, it is possible to prevent the moire phenomenon that may occur due to the black matrix formed inside the panel and the interference between the black layer and the pattern unit 120.

6A to 7B are views illustrating various embodiments of a laminated structure of an external light shielding sheet according to the present invention.

First, referring to FIGS. 6A to 6B, the external light blocking sheet 200 according to the present invention includes an AR / NIR sheet 210, an EMI shielding sheet 220, an external light blocking layer 230, and an impact absorbing layer 240. It is made to include.

The AR / NIR sheet 210 is an anti-reflection (AR) layer 211 having a function of reducing glare by preventing light from being reflected from the outside on the front surface of the base sheet 213 made of a transparent plastic material. The rear surface is attached to the NIR (Near Infrared) shielding layer 212 to shield the near-infrared radiation emitted from the panel so that the signals transmitted using infrared rays, such as a remote control, can be normally transmitted.

EMI shielding sheet 220 is attached to the EMI shielding layer 221 on the front of the base sheet 222 made of a transparent plastic material to shield the electromagnetic interference (EMI) to prevent the EMI emitted from the panel to be emitted to the outside . At this time, the EMI shielding layer 221 is typically formed of a mesh structure using a conductive material, and ineffective for the EMI sheet 220 in which an image is not displayed in order to make the ground smooth. The display area is entirely coated with a conductive material.

Next, the external light source is most often present at the top of the user's head, indoors or outdoors. The external light blocking layer 230 is attached to effectively block the external light so that the black image of the PDP can be darker.

The shock absorbing layer 240 is a pressure-sensitive adhesive-based material having a predetermined thickness, and functions to protect the entire surface of the panel from external impact or pressure.

The adhesive 250 forms a layer between the AR / NIR sheet 210, the EMI shielding sheet 220, and the external light shielding layer 230 so that each sheet may be firmly attached. At this time, the adhesive 250 is preferably made of a material substantially the same as the impact absorbing layer 240, it is preferable to form a very thin than the thickness of the shock absorbing layer 240 only for the function of the adhesive. In addition, the material of the base sheet included in each sheet is preferably used the same material. In such a case, there is no manufacturing hassle, thereby increasing production efficiency and reducing manufacturing costs.

In FIG. 6A, the AR / NIR sheet 210, the EMI shielding sheet 220, the external light blocking layer 230, and the shock absorbing layer 240 are stacked in this order. As shown in FIG. 6B, the AR / NIR sheet 210 is stacked. ), As the external light blocking layer 230, the EMI shielding sheet 220, the shock absorbing layer 240 may be stacked in the order of the stacking order of each sheet may be differently stacked by those skilled in the art. In addition, at least one of the layers included in each sheet may be omitted.

As shown in FIGS. 7A to 7B, the optical sheet 320 may further include an optical sheet 320 to improve color temperature and luminance characteristics of light emitted from the panel. At this time, the optical characteristic sheet 320 is laminated to the optical characteristic layer 321 made of a predetermined dye and the adhesive on the front or rear of the base sheet 322 made of a transparent plastic material.

Meanwhile, at least one of the basesheets included in each sheet shown in FIGS. 6A to 7B may be omitted, or a rigid glass that is not made of plastic may be used.

8 is a view showing an embodiment of the structure of the shock absorbing layer according to the present invention.

Referring to FIG. 8, the shock absorbing layer 400 is attached to the front surface of the panel 300 formed by the upper plate 305 and the lower plate 310 bonded to each other.

The shock absorbing layer 400 is formed of a material having a transparent color in order to allow the light emitted from the panel 300 to be transmitted smoothly, preferably made of a material having an adhesive force of 0.2N / 25mm. For example, the shock absorbing layer 130 is made of a pressure-sensitive adhesive-based material to be easily attached to the front of the panel, so that the sheet having another function can be easily attached. In addition, a base sheet (not shown) made of a transparent plastic material may be attached to one surface of the shock absorbing layer 400.

In addition, the thickness T3 of the shock absorbing layer 400 is preferably 50um to 100um, in which case the light transmission efficiency is good, and may have an appropriate shock absorbing power.

9a to 9b are views showing various embodiments of the laminated structure of the front protective sheet according to the present invention. The lamination structure of the front protective sheet will be described with reference to FIGS. 9A to 9B, but overlapping descriptions described with reference to FIGS. 6A to 7B will be omitted.

9A to 9B, the front protective sheet 400 according to the present invention includes an AR / NIR sheet 410, an EMI shielding sheet 420, an impact absorbing layer 430, and an optical characteristic sheet 440. Is done. In FIG. 9A, the AR / NIR sheet 410, the EMI shield sheet 420, and the shock absorbing layer 430 are stacked in this order, and the optical characteristic sheet 440 is omitted. As the NIR sheet 410, the optical characteristic sheet 440, the EMI shielding sheet 220, and the shock absorbing layer 430 may be stacked in this order, the stacking order of each sheet may be differently stacked by those skilled in the art. In addition, at least one of the layers included in each sheet may be omitted as shown in FIG. 9A.

Meanwhile, at least one of the basesheets included in each sheet illustrated in FIGS. 9A to 9B may be omitted, or a rigid glass that is not made of plastic may be used.

10 is a view showing an embodiment of a plasma display device according to the present invention.

A plasma display device according to an exemplary embodiment of the present invention will be described with reference to FIG. 10, and overlapping contents described with reference to FIGS. 1 to 9B will be omitted.

The external light shielding sheet 100 according to the present invention is preferably attached to the front surface of the panel, the external light shielding sheet 100 is at least one of AR layer, NIR shielding layer, optical characteristic layer, EMI shielding layer, shock absorption. It may include.

As described above, the plasma display device according to the present invention has been described with reference to the illustrated drawings. However, the present invention is not limited by the embodiments and drawings disclosed herein, and the application is made by those skilled in the art within the technically protected scope of the present invention. It is possible.

Plasma display device of the present invention is configured as described above is attached to the front of the panel of the external light blocking sheet that absorbs and blocks the light incident from the outside as possible to realize a black image close to the primary color and at the same time clear contrast It can be improved. In addition, since the plasma display device of the present invention includes a shock absorbing layer, there is an advantage of protecting the front surface of the panel from external shock.

Claims (21)

A base portion for allowing light to be refracted and transmitted at a predetermined angle; An external light blocking sheet formed on the base part and having a pattern part having a refractive index smaller than that of the base part, And a shock absorbing layer formed on at least one surface of both surfaces of the external light blocking sheet. The method of claim 1, The shock absorbing layer is a plasma display device, characterized in that formed of a material having an adhesive force of 0.2N / 25mm or more. The method of claim 1, And the impact absorbing layer is a substantially transparent index. The method of claim 1, The thickness of the shock absorbing layer is a plasma display device, characterized in that 25um to 500um. The method of claim 1, The thickness of the shock absorbing layer is a plasma display device, characterized in that 50um to 100um. The method of claim 1, And the base portion is formed of a transparent plastic material. The method of claim 1, The thickness of the external light shielding sheet is a plasma display device, characterized in that 20um to 250um. The method of claim 1, And the refractive index of the pattern portion is 0.3 times to 0.99 times the refractive index of the base portion. The method of claim 1, And the pattern portion is formed in a darker color than the base portion. The method of claim 1, And the pattern portion is substantially black. The method of claim 1, A lower end of the pattern portion is disposed toward the panel side, and an upper end is disposed to the user side. The method of claim 1, The width of the bottom of the pattern portion is a plasma display device, characterized in that formed in 5um to 150um. The method of claim 1, And a top width of the pattern portion is 130 μm or less. The method of claim 1, The external light blocking sheet may include an AR layer to prevent reflection of external light; A NIR shielding layer that shields near infrared rays emitted from the panel; And Plasma display device comprising at least one of the EMI shielding layer for shielding electromagnetic waves. The method of claim 1, The external light blocking sheet is installed on the front of the panel plasma display device. panel; A shock absorbing layer that protects the front surface of the panel from an external impact, The shock absorbing layer is a plasma display device, characterized in that formed of a material having an adhesive force of 0.2N / 25mm or more. The method of claim 16, And the impact absorbing layer is formed of a substantially transparent material. The method of claim 16, The shock absorbing layer is a plasma display device, characterized in that formed of a pressure-sensitive adhesive-based material. The method of claim 16, The thickness of the shock absorbing layer is a plasma display device, characterized in that 25um to 500um. The method of claim 16, The thickness of the shock absorbing layer is a plasma display device, characterized in that 50um to 100um. The method of claim 16, The shock absorbing layer is an AR layer to prevent reflection of external light; A NIR shielding layer for shielding near infrared rays emitted from the panel; Plasma display device further comprises at least one of the EMI shielding layer for shielding electromagnetic waves.

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