KR101971949B1 - polarizer, liquid crystal display device including the same, and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device, comprising: a liquid crystal panel; A backlight unit including an LED package and supplying light to the liquid crystal panel; A first polarizer attached to a first surface of the liquid crystal panel; And a second polarizer attached to a second surface of the liquid crystal panel and positioned between the liquid crystal panel and the backlight unit, wherein the first and second polarizers have a color coordinate system of L * a * b * A liquid crystal display device having a b value in the range of 1.0 to 2.7.

Description

[0001] The present invention relates to a polarizing plate, a liquid crystal display including the polarizing plate, and a manufacturing method thereof,

The present invention relates to a liquid crystal display, and more particularly, to a polarizing plate having improved transmittance, a liquid crystal display including the same, and a method of manufacturing the same.

2. Description of the Related Art As an information society has developed, there has been an increasing demand for a display device for displaying images. Recently, a liquid crystal display (LCD), a plasma display panel (PDP) Various flat panel displays (FPDs) such as organic light emitting diodes (OLED) have been utilized.

Of these flat panel display devices, liquid crystal display devices are widely used because they have advantages of miniaturization, weight reduction, thinness, and low power driving.

Generally, in a liquid crystal display device, two substrates on which electric field generating electrodes are respectively formed are arranged so that the two electrodes are formed to face each other, a liquid crystal material is injected between the two substrates, and a voltage is applied to the two electrodes The liquid crystal molecules are moved by the electric field, and the image is expressed by the transmittance of the light depending on this. Such a liquid crystal display device is applied to a variety of applications ranging from portable devices such as mobile phones and multimedia devices to notebook computers or computer monitors and large-sized televisions.

The active matrix liquid crystal display (AM-LCD) in which the pixel electrodes connected to the thin-film transistors and the thin-film transistors are arranged in a matrix manner can be realized in various forms, Widely used.

Such a liquid crystal display device includes a liquid crystal panel as a display panel for displaying an image, and a polarizing plate is attached to both sides of the liquid crystal panel to selectively transmit light, thereby realizing a desired image.

1 is a view schematically showing a conventional polarizer structure.

As shown in Fig. 1, a conventional polarizing plate 10 includes a polarizing film 12 and first and second supporting films 14 and 16.

The polarizing film 12 is formed by stretching polyvinyl alcohol (PVA) in which iodine ions are dyed. Light that oscillates in a direction parallel to the absorption axis after the absorption axis is formed in the stretching direction And selectively transmits only light oscillating in a direction perpendicular to the absorption axis.

The polyvinyl alcohol as a material of the polarizing film 12 is strong in hydrophilicity and weak in moisture resistance, so that the intermolecular bonding of the polarizing film 12 is weakened by moisture, so that shrinkage occurs in the stretched direction. Therefore, in order to prevent this, the polarizing film 12 is shrunk by using the first and second supporting films 14 and 16 by adhering a protective substrate having little dimensional change due to moisture on both sides of the polarizing film 12 .

The first and second support films 14 and 16 are made of triacetyl cellulose (TAC) and attached to the polarizing film 12 by a thermal curing method using an aqueous adhesive.

However, since the polarizing plate 10 selectively transmits only the light vibrating in a direction perpendicular to the absorption axis, the transmittance is 50% or less, and the transmittance of the polarizing plate 10 varies depending on the degree of alignment of the iodide ion. It is not easy to control completely. Further, the transmittance of the polarizing plate 10, which can be maximized, due to the problem that the transmittance decreases due to the crystalline region of the polyvinyl alcohol as the material of the polarizing film 12 and the high stretching is difficult due to the possibility of breakage in the stretching process, About 43.0%.

Since the liquid crystal display device uses such a polarizing plate for the upper and lower portions of the liquid crystal panel, the transmittance of the liquid crystal display device is further lowered.

In order to solve the above problems, the present invention provides a polarizing plate having improved transmittance, a liquid crystal display including the polarizing plate, and a manufacturing method thereof.

It is another object of the present invention to provide a polarizing plate capable of increasing a contrast ratio, a liquid crystal display including the polarizing plate, and a manufacturing method thereof.

According to an aspect of the present invention, there is provided a liquid crystal display comprising: a liquid crystal panel; A backlight unit including an LED package and supplying light to the liquid crystal panel; A first polarizer attached to a first surface of the liquid crystal panel; And a second polarizer attached to a second surface of the liquid crystal panel and positioned between the liquid crystal panel and the backlight unit, wherein the first and second polarizers have a color coordinate system of L * a * b * A liquid crystal display device having a b value in the range of 1.0 to 2.7.

The LED package emits white light of a red series.

The present invention also provides a method of manufacturing a polarizing film, comprising: supplying a polarizing film; Dyeing the polarizing film by dyeing iodine ions; Stretching the dyed polarizing film; Drying the stretched polarizing film; And attaching the first and second supporting films to both sides of the dried polarizing film, wherein the polarizing plate is a polarizing plate having a color coordinate system of L * a * b * Of the polarizing plate.

The polarizing film is stretched by an increase of 0.1% to 10% at a stretching ratio of 5 to 6 times.

The polarizing film is shortened by 1% to 20% in a drying time of 1 minute to 5 minutes.

The polarizing film and the first and second supporting films are adhered with an ultraviolet curable adhesive.

The present invention also provides a liquid crystal display comprising the steps of: preparing the aforementioned first and second polarizing plates; Attaching the first and second polarizing plates to both surfaces of a liquid crystal panel; Preparing a backlight unit for supplying light to the liquid crystal panel, the backlight unit including an LED package; And disposing the backlight unit on a lower portion of the second polarizer, wherein the LED package emits white light of a red-based color.

The step of preparing the backlight unit includes increasing the rank of the LED package.

In the present invention, the transmittance of the liquid crystal display device can be improved by increasing the transmittance by adjusting the hue of the polarizing plate. Accordingly, the contrast ratio can be increased and the cost can be reduced.

At this time, the white color coordinate according to the international standard can be adjusted by adjusting the LED package color of the backlight unit.

1 is a view schematically showing a conventional polarizer structure.
2 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.
3 is a schematic diagram of a polarizer manufacturing apparatus according to an embodiment of the present invention.
4 is a view showing color coordinates of a polarizing plate according to an embodiment of the present invention and a polarizing plate according to a comparative example.
FIG. 5A is a graph showing the transmittance of the polarizing plate according to the embodiment of the present invention and the polarizing plate according to the comparative example, and FIG. 5B is a graph showing the transmittance of the polarizing plate according to the comparative example arranged orthogonally with the polarizing plate according to the embodiment of the present invention And the transmittance of the polarizing plate with respect to the wavelength.
FIG. 6A is a view showing a white zone in CIE 1931 color coordinates, and FIG. 6B is a view showing a white binning chart of the LED package corresponding to the white region in FIG. 6A.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

2 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

2, the liquid crystal display device of the present invention includes a liquid crystal panel 110 for displaying an image, a first polarizer 120 attached to one surface of the liquid crystal panel 110, A second polarizer 130 attached to the second polarizer 130, and a backlight unit 150 below the second polarizer 130.

Although not shown, the liquid crystal panel 110 is composed of a liquid crystal layer formed between the first and second substrates and the first and second substrates, and is provided on either one of the first substrate and the second substrate, An electrode is formed. Accordingly, the liquid crystal molecules of the liquid crystal layer are arranged by the electric field generated between the two electrodes, thereby controlling the transmittance of the light supplied from the backlight unit 150.

On the other hand, the liquid crystal panel 110 includes a color filter layer composed of red, green, and blue color filter patterns.

A first adhesive layer 142 is disposed between the first polarizer 120 and the liquid crystal panel 110 and a second adhesive layer 144 is disposed between the second polarizer 130 and the liquid crystal panel 110 Located. The first adhesive layer 142 may be formed on the first polarizing plate 120 and the second adhesive layer 144 may be formed on the second polarizing plate 130. Here, the first and second adhesive layers 142 and 144 may be pressure sensitive adhesives (PSAs).

The first polarizing plate 120 is attached to a front surface of the liquid crystal panel 110, that is, a surface on which light is output. The first polarizing plate 120 includes a first polarizing film 122 and a first inner supporting film 124 on the first surface of the first polarizing film 122 and a first inner supporting film 124 on the second surface of the first polarizing film 122. [ And the first inner supporting film 124 is attached to the liquid crystal panel 110. [

The second polarizing plate 130 is attached to the rear surface of the liquid crystal panel 110, that is, the surface from which the light is incident from the backlight unit 150. The second polarizing plate 130 includes a second polarizing film 132 and a second inner supporting film 134 on the first surface of the second polarizing film 132 and a second inner supporting film 134 on the second surface of the second polarizing film 132, And the second inner supporting film 134 is attached to the liquid crystal panel 110. [

The first polarizing film 122 and the second polarizing film 132 may be made of polyvinyl alcohol (PVA) that is formed by dying iodine ions. The first and second inner support films 124 and 134 and the first and second outer support films 126 and 136 may be made of triacetyl cellulose (TAC) It is preferable that the film 124 and the second external support film 134 have no phase delay. On the other hand, the first and second outer support films 126 and 136 may be formed of an acrylic film having a low moisture permeability.

Here, the absorption axis of the second polarizing film 132 of the second polarizing plate 130 is arranged to be perpendicular to the absorption axis of the first polarizing film 122 of the first polarizing plate 120.

A backlight unit 150 is disposed below the second polarizer 130. The backlight unit 150 includes a reflector 152, a light guide plate 154, optical sheets 156, and a light emitting diode (LED) assembly 158.

The LED assembly 158 includes an LED printed circuit board 158a and an LED package 158b on the LED printed circuit board 158a. The LED package 158 is disposed on one side of the light guide plate 154 to supply light.

The light guide plate 154 reflects and refracts light incident from the LED package 158b into the interior of the LED package 158b and transmits the light to the liquid crystal panel 110 to implement a surface light source.

The reflection plate 152 is positioned below the light guide plate 154 and reflects light passing through the back surface of the light guide plate 154 toward the liquid crystal panel 110 to improve the brightness of light. On the other hand, the reflector 152 may be in the form of a sheet and extend to the outside of the LED assemblies 158.

The optical sheets 156 are disposed on the light guide plate 154 and the optical sheets 156 spread or condense light from the light guide plate 154. The optical sheets 156 may include at least one sheet having a light diffusing function and at least one sheet having a light converging function.

The structure of the edge type backlight unit 150 in which the LED package 158b as the light source is disposed on one side of the liquid crystal panel 110 has been described. However, when the light source is directly under the liquid crystal panel 110 a direct type backlight unit may be used.

In the present invention, the first polarizing plate 120 and the second polarizing plate 130 have a bluish hue, and accordingly, in a colorimetric system having a color coordinate system such as L * a * b *, the first polarizing plate 120 ) And the second polarizing plate 130 have a b value in the range of 0 to 3, preferably 1.0 to 2.7, and more preferably 1.0 to 2.5. Here, the L value of the color difference meter represents brightness and is displayed in the range of 0 to 100, and a value and b value are plane coordinate system, the horizontal axis is a, the vertical axis is b, the + a side is red (red) Green (breen), + b stands for yellow (yellow), and -b stands for blue (blue).

In this case, the value of a may be adjusted according to the change of the b value of the first polarizer 120 and the second polarizer 130. The first polarizer 120 and the second polarizer 130 may have a value in the range of -1.0 to -2.0 Lt; RTI ID = 0.0 > a < / RTI >

The hue of the first polarizer 120 and the second polarizer 130 may vary depending on the concentration of iodine ions or the process conditions in the manufacturing process. Particularly, by adjusting the concentration of iodine ion (I3-) which is involved in absorption of light of a short wavelength, that is, a blue series, according to process conditions, the first polarizer plate 120 and the second polarizer plate 130 are bluish It is possible to have a color.

3 is a schematic diagram of a polarizer manufacturing apparatus according to an embodiment of the present invention.

3, the polarizing plate manufacturing equipment according to the embodiment of the present invention includes a first supply unit 212, a dyeing unit 213, a stretching unit 214, a drying unit 215, first and second A second supply portion 222, a third supply portion 232, an attachment unit 240, a hardening unit 250, and a recovery roll 260. The coating units 216a, 216b,

First, the polarizing film 210 is supplied from the first supply unit 212. The first supply unit 212 may be a supply roll in which the polarizing film 210 is wound, and may further include moving means (not shown) for moving the polarizing film 210. Here, the moving means may be a motor that provides a rotational force to the supply roll, which may be directly connected to the rotation axis of the supply roll, or connected to the rotation axis of the supply roll via a pulley and a belt or the like.

The polarizing film 210 may be formed of polyvinyl alcohol (PVA).

The polarizing film 210 supplied from the first supply unit 212 is transferred to the dyeing unit 213 and the iodide ions are adhered to the polarizing film 210 in the dyeing unit 213. At this time, a potassium iodide solution may be used for the iodide ionization, and the iodide ion ratio may be in the range of about 0.005 wt% to 0.5 wt%.

On the other hand, the polarizing film 210 may be subjected to a washing process using de-ionized water before the dyeing unit 213, and the polarizing film 210 may be subjected to a washing process Can be swollen.

Then, the polarizing film 210 to which the iodine ions are dyed is transmitted to the elongating unit 214, and the polarizing film 210 is elongated in the elongating unit 214. At this time, the polarizing film 210 drawn by aligning the iodine ions in the stretching direction has an absorption axis in the stretching direction. Thus, the stretched polarizing film 210 absorbs light oscillating in a direction parallel to the absorption axis, and transmits light oscillating in a direction perpendicular to the absorption axis. In one example, the polarizing film 210 can be stretched in the longitudinal direction, that is, in the machine direction (MD). Here, the stretching ratio increases from 5 times to 6 times by about 0.1% to 10%.

On the other hand, the crosslinking step can be carried out together by stretching the polarized polarizing film 210 in an aqueous solution of boric acid. That is, the polarized film 210 is immersed in an aqueous solution of boric acid and stretched so that boric acid cross-links the polymer and the polymer of the polarizing film 210 in which iodine ions are dyed to prevent sublimation of iodide ions. The crosslinking step may be carried out separately from the stretching step.

Next, the stretched polarizing film 210 is transferred to the drying unit 215 and dried. At this time, the drying unit 215 may include an oven, and the drying temperature may be 50 to 65 degrees Celsius. On the other hand, the drying time is reduced by about 1% to 20% from about 1 minute to 5 minutes.

Next, the dried polarizing film 210 is transferred to the first and second coating units 216a and 216b. The first and second coating units 216a and 216b are located opposite to each other with respect to the polarizing film 210 and the first and second coating units 216a and 216b have polarizing films 210 passing therebetween, Are coated with an adhesive on both sides thereof. At this time, the adhesive may be an aqueous adhesive or an ultraviolet (UV) curable adhesive.

Then, the polarizing film 210 coated with the adhesive is transferred to the attaching unit 240.

The second supply part 222 is disposed apart from the first supply part 212 and the first support film 220 is supplied from the second supply part 222. The second supply unit 222 may be a supply roll in which the first support film 220 is wound and may further include a moving unit (not shown) for moving the first support film 220. Here, the moving means may be a motor that provides a rotational force to the supply roll, which may be directly connected to the rotation axis of the supply roll, or connected to the rotation axis of the supply roll via a pulley and a belt or the like.

The first support film 220 may be made of triacetyl cellulose (TAC).

Next, the first supporting film 220 is transferred to the attaching unit 240.

On the other hand, the third supply part 232 is disposed on the opposite side of the second supply part 222 with respect to the first supply part 212 from the first supply part 212, (230). The third supply part 232 may be a supply roll in which the second support film 230 is wound, and may further include a moving unit (not shown) for moving the second support film 230. Here, the moving means may be a motor that provides a rotational force to the supply roll, which may be directly connected to the rotation axis of the supply roll, or connected to the rotation axis of the supply roll via a pulley and a belt or the like.

The second support film 230 may be made of triacetyl cellulose or an acrylic film having a low moisture permeability.

Next, the second supporting film 230 is transferred to the attaching unit 240.

Meanwhile, the first support film 220 and the second support film 230 may be subjected to a cleaning step before the attachment unit 240.

The attachment unit 240 includes first and second attachment rolls 242, 244. The first and second attachment rolls 242, 244 may be spaced from each other and positioned opposite each other. Alternatively, the first and second attachment rolls 242 and 244 may be positioned offset from each other.

The polarizing film 210 transferred to the attaching unit 240 and the first support film 220 on one side of the polarizing film 210 and the second support film 230 on the other side of the polarizing film 210 are disposed in the first and second The polarizing film 210 is adhered to the first and second supporting films 220 and 230 by an adhesive coated on both sides of the polarizing film 210 while being pressed between the adhering rolls 242 and 244.

In the embodiment of the present invention, the adhesive is coated on both sides of the polarizing film 210, but the adhesive may be coated on the first supporting film 220 and the second supporting film 230.

Next, the attached polarizing film 210 and the first and second supporting films 220 and 230 are transferred to the curing unit 250, and the curing unit 250 cures the adhesive. When the adhesive is an aqueous adhesive, it is cured by heat, and when it is a UV curable adhesive, it is cured by UV. Next, the polarizing film 210 and the first and second supporting films 220 and 230 are transferred to a drying unit (not shown) and can be subjected to a drying step.

The polarizing film 210 and the first and second supporting films 220 and 230 may then be transferred to the recovery roll 260 and wound on the recovery roll 260.

Although not shown, a step of forming an adhesive layer on one surface of one of the attached first and second supporting films 220 and 230 before transfer to the recovery roll 260, attaching the release film, and then drying It is possible.

As described above, in the present invention, the color of the polarizing plate can be controlled by increasing the stretching ratio and shortening the drying time.

On the other hand, when the UV curing type adhesive is used, the drying time can be further shortened in the drying step after the stretching of the polarizing film 210. Since the UV curing is performed in the curing step, there is no evaporation of moisture, The degree of freedom to be increased. Accordingly, it is possible to manufacture a polarizing plate having a bluish hue more easily.

FIG. 4 is a view showing color coordinates of a polarizing plate according to an embodiment of the present invention and a polarizing plate according to a comparative example, FIG. 5A is a view showing transmittance of a polarizing plate according to an embodiment of the present invention and a polarizing plate according to a comparative example And FIG. 5B is a graph showing the transmittance of the polarizing plate according to the comparative example arranged orthogonally to the polarizing plate according to the embodiment of the present invention arranged orthogonally with respect to the wavelength. Here, the comparative example corresponds to a conventional polarizing plate.

As shown in Fig. 4, the color coordinate of the polarizing plate P1 according to the comparative example is (-1.5, 4.0), and the color coordinate of the polarizing plate P2 according to the embodiment of the present invention is (-1.4, 2.5) The polarizing plate P2 according to the embodiment of the present invention has a bluish hue with a decrease in b value as compared with the polarizing plate P1 according to the comparative example.

As shown in FIG. 5A, the transmittance of the polarizing plate according to the embodiment of the present invention is shifted to a shorter wavelength than the transmittance of the polarizing plate according to the comparative example, that is, the transmittance of the blue wavelength band is improved Can be confirmed.

In addition, as shown in FIG. 5B, when two polarizing plates according to the embodiment of the present invention are arranged so that their absorption axes are vertical, blue light is transmitted in the black state, and the transmittance of the blue wavelength range is Which is higher than that of the comparative example.

On the other hand, as the colors of the first polarizing plate 120 (FIG. 2) and the second polarizing plate 130 (FIG. 2) are changed, the white color coordinates of the liquid crystal display device are changed. Therefore, the color of the LED package (158b in Fig. 2) as the light source of the backlight unit (150 in Fig. 2) is adjusted to match the white color coordinate of the liquid crystal display device. At this time, the LED package (158b in FIG. 2) has a reddish color in order to match x and y of white color coordinates based on BTS709.

The LED package may emit white light and may include a blue chip and a phosphor. Light emitted from the blue chip is absorbed by the phosphor and then emitted again as light of a long wavelength. Therefore, the white light of the LED package is composed of the emission spectrum of the blue chip and the spectrum of the long wavelength by the phosphor. At this time, the width and intensity of the spectrum are determined by the deviation of the manufacturing process of the blue chip and the thickness and concentration of the phosphor. Deviation of the white color coordinate of the LED package occurs according to the deviation, and the divided individual color coordinate areas are bin ).

FIG. 6A is a view showing a white zone in CIE 1931 color coordinates, and FIG. 6B is a view showing a white binning chart of the LED package corresponding to the white region in FIG. 6A.

As shown in Figs. 6A and 6B, the color deviation due to the wavelength of the blue chip appears depending on the manufacturing process deviation of the blue chip, and color deviation occurs depending on the phosphor content, . Accordingly, the manufactured LED package is divided into several stages according to the x and y values, and the respective ranks are determined. At this time, the rank increases in the direction of increasing x and y values, and as the rank increases, the color of the LED package becomes a red series and the luminance increases.

Thus, by raising the rank of the LED package, the LED package can have a reddish color.

As a result of the experiment of the liquid crystal display device using the polarizing plate and the LED package according to the embodiment of the present invention, when the color coordinate of the polarizing plate is (-1.4, 2.5), the transmittance of the polarizing plate according to the embodiment of the present invention is about 43.2% The white color coordinates x and y of the liquid crystal display device are 0.2791 and 0.2922. On the other hand, in the case of the polarizing plate according to the comparative example in which the color coordinate of the polarizing plate is (-1.5, 4.0), the transmittance of the polarizing plate is about 43.1%, and the white color coordinates x and y of the liquid crystal display are 0.2790 and 0.2920. Therefore, the transmittance of the liquid crystal display device according to the embodiment of the present invention is increased by about 3.0% as compared with the comparative example. At this time, the polarization degree of the polarizing plate according to the example of the present invention and the comparative example are all 99.99 ".

As described above, in the present invention, the transmissivity of the liquid crystal display device can be improved, and accordingly, the contrast ratio can be increased.

Alternatively, instead of adjusting the color of the LED package, the color value of the color filter layer of the liquid crystal panel may be changed to reddish.

The present invention is not limited to the above-described embodiments, and various changes and modifications may be made without departing from the spirit of the present invention.

110: liquid crystal panel 120: first polarizer plate
122: first polarizing film 124: first inner supporting film
126: first external supporting film 130: second polarizing plate
132: second polarizing film 134: second inner supporting film
136: second external supporting film 142: first adhesive layer
144: second adhesive layer 150: backlight unit
152: reflector 154: light guide plate
156: Optical sheets 158: LED assembly
158a: LED printed circuit board 158b: LED package

Claims (8)

A liquid crystal panel;
A backlight unit including an LED package and supplying light to the liquid crystal panel;
A first polarizer attached to a first surface of the liquid crystal panel;
A second polarizing plate attached to a second surface of the liquid crystal panel and positioned between the liquid crystal panel and the backlight unit,
/ RTI >
Wherein the first and second polarizing plates have b values in the range of 1.0 to 2.7 in a colorimeter having a color coordinate system of L * a * b *, wherein the L value indicates brightness and is displayed from 0 to 100, And b are the abscissa and ordinate of the plane coordinate system respectively, the + a side is red, -a side is green, + b side is yellow, -b side is blue,
Wherein the LED package emits white light of a red-based color.
delete Supplying a polarizing film;
Dyeing the polarizing film by dyeing iodine ions;
Stretching the dyed polarizing film;
Drying the stretched polarizing film;
And attaching the first and second supporting films to both sides of the dried polarizing film
The polarizing plate manufacturing method according to claim 1,
Wherein the polarizer has a b value in the range of 1.0 to 2.7 in a colorimeter having a color coordinate of L * a * b *, wherein L value indicates brightness and 0 to 100, and a and b values are The horizontal axis and the vertical axis of the plane coordinate system, the + a side is red, -a side is green, + b side is yellow, -b side is blue,
Wherein the polarizing film is stretched by 0.1% to 10% at a stretching ratio of 5 to 6 times.
delete The method of claim 3,
Wherein the polarizing film is dried by a shortening of 1% to 20% at a drying time of 1 minute to 5 minutes.
The method of claim 3,
Wherein the polarizing film and the first and second supporting films are adhered with an ultraviolet curable adhesive.
Preparing first and second polarizing plates according to any one of claims 3, 5, and 6;
Attaching the first and second polarizing plates to both surfaces of a liquid crystal panel;
Preparing a backlight unit for supplying light to the liquid crystal panel, the backlight unit including an LED package;
Placing the backlight unit on a lower portion of the second polarizer;
Lt; / RTI >
Wherein the LED package emits red light of a white color.
8. The method of claim 7,
Wherein the step of preparing the backlight unit includes increasing a rank of the LED package.

Images