JP6672624B2 - Quantum dot sheet, backlight and liquid crystal display - Google Patents

Description

  The present invention relates to a quantum dot sheet, a backlight, and a liquid crystal display.

  Developments for higher luminous efficiency and higher color rendering of liquid crystal display backlights, lighting devices, and the like are in progress. In recent years, in order to realize such a light emitting device, a light source that emits primary light (such as a blue LED that emits blue light) and a quantum dot phosphor (hereinafter, referred to as “quantum dot”) composed of semiconductor fine particles are combined. Light emitting devices have been developed.

The quantum dots are, for example, semiconductor fine particles composed of a core of CdSe and a shell of ZnS, and nano-sized compound semiconductor fine particles composed of a ligand covering the periphery of the shell. Since the quantum dot has a particle diameter smaller than the Bohr radius of the exciton of the compound semiconductor, a quantum confinement effect appears. Therefore, the luminous efficiency of the quantum dots is higher than that of a phosphor (rare-earth phosphor) using a rare-earth ion as an activator, and a high luminous efficiency of 90% or more can be realized.
In addition, since the emission wavelength of the quantum dot is determined by the band gap energy of the compound semiconductor fine particles quantized in this way, an arbitrary emission wavelength, that is, an arbitrary emission spectrum can be obtained by changing the particle size of the quantum dot. Can be. By combining these quantum dots with a blue LED or the like, it is possible to realize a backlight with high luminous efficiency and high color rendering (for example, see Patent Documents 1 to 3).

Quantum dots can be incorporated into a backlight device by the on-chip method of incorporating the quantum dots in the light source, the on-edge method of disposing a transparent tube containing the quantum dots between the light source and the light guide plate, and the light exit side of the light guide plate. And an on-surface method in which a sheet containing quantum dots (quantum dot sheet) is arranged on a light source.
However, in the on-chip method, since the quantum dots are incorporated in the light source, the quantum dots are exposed to a high temperature, and the conversion efficiency of the quantum dots is inferior. Further, in the on-edge method, since the transparent tube containing the quantum dots is arranged between the light source and the light guide plate, the size increases. In particular, since downsizing is required for mobile devices, it is difficult to cope with the on-edge method.
On the other hand, the on-surface method does not have the above-mentioned problem, and it is also possible to use a conventional backlight device. For this reason, it is currently being studied to incorporate the quantum dots into the backlight device by the on-surface method.

  However, in an on-surface type backlight using a quantum dot sheet, the edge region may not be white but may be tinted, or the tint may change depending on the viewing direction. Further, although there is a front luminance as a general requirement of the backlight, a quantum dot sheet capable of achieving a good balance between the front luminance, the tint of an edge region, and the angle dependence of the tint has not been proposed.

International Publication No. 2012/132239 JP-A-2015-18131 JP 2015-28139 A

  In view of the above problems, an object of the present invention is to provide a quantum dot sheet, a backlight, and a liquid crystal display device capable of favorably balancing front luminance, tint of an edge region, and angle dependency of tint.

The present inventors have intensively studied to solve the above problems. As a result, they have found that the cause of the above-mentioned problem is that the secondary light emitted from the quantum dot has no directivity, while the primary light has directivity, and has solved the problem.
That is, the present invention provides the following quantum dot sheets [1] to [8], a backlight, and a liquid crystal display device.

[1] A quantum dot sheet, wherein the quantum dot sheet has a quantum dot-containing layer containing a binder resin and quantum dots that absorb primary light and emit secondary light. When one surface was vertically irradiated with visible light using a halogen lamp (12 V, 48 W) as a light source, and the intensity of transmitted light was measured every degree in a range of -85 degrees to +85 degrees, A quantum dot sheet that satisfies at least one of the following conditions A-1 and B-1.
<Condition A-1>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -30 degrees to + 30 degrees when upon the _{P 30,} less than 50 _{P 30} is 15 or more.
<Condition B-1>
The absolute value of α is not less than 1 degree and less than 30 degrees, where α is a diffusion angle indicating an intensity half of the maximum value.
[2] The quantum dot sheet according to [1], further satisfying the following condition A-2.
<Condition A-2>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -45 degrees to + 45 degrees when upon the _{P 45,} less than 60 _{P 45} 20 or more.
[3] The quantum dot sheet according to [1] or [2], further satisfying the following condition A-3.
<Condition A-3>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -60 degrees to + 60 degrees when upon the _{P 60,} less than 75 _{P 60} 25 or more.
[4] The quantum dot sheet according to any one of [1] to [3], further satisfying the following condition B-2.
<Condition B-2>
The absolute value of β is 3 degrees or more and less than 45 degrees, where β is a diffusion angle indicating an intensity of １ ／ of the maximum value.

[5] The quantum dot sheet according to any one of [1] to [4], wherein both surfaces of the quantum dot-containing layer are sandwiched between light-transmitting substrates.
[6] The quantum dot sheet according to any one of [1] to [5], further including a light diffusion layer.
[7] At least one light source that emits primary light, an optical plate disposed adjacent to the light source for guiding or diffusing light, and a quantum dot sheet disposed on a light emission side of the optical plate. A backlight provided with the quantum dot sheet according to any one of [1] to [6] above.
[8] A liquid crystal display device including a backlight and a liquid crystal panel, wherein the backlight is the backlight according to [7].

  The quantum dot sheet, the backlight, and the liquid crystal display device of the present invention can improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color.

FIG. 2 is a cross-sectional view showing one embodiment of the quantum dot sheet of the present invention. It is sectional drawing which shows other embodiment of the quantum dot sheet of this invention. It is sectional drawing which shows other embodiment of the quantum dot sheet of this invention. FIG. 1 is a cross-sectional view illustrating an embodiment of a backlight according to the present invention. FIG. 9 is a cross-sectional view illustrating another embodiment of the backlight according to the present invention. FIG. 1 is a cross-sectional view illustrating one embodiment of a liquid crystal display device of the present invention. FIG. 3 is a diagram illustrating an intensity distribution of transmitted light of the quantum dot sheet of Example 1. FIG. 9 is a diagram showing an intensity distribution of transmitted light of the quantum dot sheet of Comparative Example 1. FIG. 13 is a diagram illustrating an intensity distribution of transmitted light of the quantum dot sheet of Comparative Example 3.

Hereinafter, embodiments of the present invention will be described.
[Quantum dot sheet]
The quantum dot sheet of the present invention is a quantum dot sheet, wherein the quantum dot sheet has a quantum dot-containing layer including a binder resin and a quantum dot that absorbs primary light and emits secondary light. A visible light with a halogen lamp (12 V, 48 W) as a light source is vertically irradiated on one of the surfaces of the dot sheet, and the intensity of the transmitted light is in a range of -85 degrees to +85 degrees every one degree. When measured, it satisfies at least one of the following conditions A-1 and B-1.
<Condition A-1>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -30 degrees to + 30 degrees when upon the _{P 30,} less than 50 _{P 30} is 15 or more.
<Condition B-1>
The absolute value of α is not less than 1 degree and less than 30 degrees, where α is a diffusion angle indicating an intensity half of the maximum value.

Condition A-1
Condition A-1 is requesting that P ₃₀ indicating the sum of intensities of up to -30 degrees to + 30 degrees at the time of 1 and the normalized maximum value of the intensity of the transmitted light is less than 15 or more 50.
Hereinafter, the reason why the front luminance, the tint of the edge area, and the angle dependency of the tint can be improved by satisfying the condition A-1 will be described.

First, a description will be given of the cause of the color in the edge region and the unevenness of the color in the surface.
The secondary light emitted from the quantum dots is evenly diffused at 360 degrees. On the other hand, primary light has directivity and the diffusion direction is not uniform. Also, among the primary lights, those that are transmitted without being absorbed by the quantum dots also have directivity and the diffusion direction is not uniform.
Therefore, when primary light is incident on a quantum dot sheet obtained by simply forming a quantum dot-containing layer, of the transmitted light, the secondary light is uniformly diffused, while the primary light has directivity. . Secondary light, which is uniform diffusion, diffuses a large percentage of light up to a high angle, and light easily leaks from the edge area of the quantum dot sheet, while primary light has a small percentage of high-angle diffused light, Light hardly leaks from the area. For this reason, the ratio of the primary light increases in the edge region, and the edge region takes on the tint of the primary light (blue tint when the primary light is blue).
When the primary light has directivity, the amount of primary light is sufficient in a low-angle region, while the amount of primary light is small in a high-angle region. For this reason, the color differs between the low-angle region and the high-angle region, and the color has an angle dependence.
As described above, it is considered that the tint of the edge region and the angle dependence of the tint are caused by the directivity of the primary light.

Next, the meaning of the condition A-1 will be described.
Normally, the intensity of transmitted light is greatest in the normal transmission direction (0 degree), and decreases as the angle increases in the plus direction and the minus direction. As the angle increases in the plus direction and the minus direction, the degree of decrease in the intensity of the transmitted light increases as the diffusion becomes weaker. This tendency is the same when the maximum value of the transmitted light intensity is normalized to 1.
Therefore, the maximum value of the intensity of the transmitted light was 1 and the normalized, P ₃₀ is the sum of the intensities of up to -30 degrees to + 30 degrees when normalized would indicate the strength of the diffusion of the sample. Since the intensity in the normal transmission direction (0 degree) differs greatly depending on the type of the sample and the light source, even if the measured values of the intensity from -30 degrees to +30 degrees are summed as they are, the sum is used for comparison of the diffusion intensity. I can't connect.
In the high-angle region, the ratio of the primary light is small, while in the low-angle region, the ratio of the primary light is large. Therefore, it is considered that the sum of the intensities in the angle range excluding the high angle appropriately represents the intensity of diffusion of the primary light.
Therefore, it P ₃₀ is 15 or more, it means that stronger diffusion of quantum dots sheet, and diffusion to the primary light strong.
The directivity can be made closer to uniformity by strong diffusion. On the other hand, if the diffusion is too strong, the front luminance decreases. Therefore, by satisfying the condition A-1 (P ₃₀ is less than 15 or more 50), while improving the color and tint of the angular dependence of the edge region caused by the directivity of the primary light, the front brightness It is considered that the decrease can be suppressed, and the balance between the front luminance, the color of the edge region, and the angle dependence of the color can be improved.
On the other hand, when P ₃₀ is less than 15, can not be sufficiently uniform the directivity of the primary light, it appears not to be improved color and angle-dependent color the edge region. It is also contemplated that P ₃₀ is greater than or equal to 50, the diffusion is too strong the front luminance decreases.

P ₃₀ is a front luminance, the color of the edge area, from the viewpoint of better balance in color angle dependence, preferably 30 to 49 or less, more preferably 35 or more 48 or less, More preferably, it is 40 or more and 48 or less.

Condition B-1
Condition B-1 is that an absolute value of α is equal to or more than 1 degree and less than 30 degrees when α is a diffusion angle indicating half the maximum value of the transmitted light intensity of −85 degrees to +85 degrees. Is demanding.
Hereinafter, the reason why the front luminance, the tint of the edge region, and the angle dependence of the tint can be improved by satisfying the condition B-1 will be described.

As described above, the intensity of the transmitted light is usually highest in the normal transmission direction (0 degree), and decreases as the angle increases in the plus direction and the minus direction. As the angle increases in the plus direction and the minus direction, the degree of decrease in the intensity of the transmitted light increases as the diffusion becomes weaker. In other words, if the diffusion increases, the intensity of the transmitted light is less likely to decrease even if the angle increases in the plus and minus directions. Therefore, the angle α indicating the intensity of 最大 of the maximum value of the intensity of the transmitted light indicates the intensity of diffusion within the angle α.
As described above, the ratio of the primary light is large in the low-angle region. Therefore, the fact that the absolute value of α is 1 degree or more means that the quantum dot sheet has strong diffusion and that the primary light has strong diffusion.
As described above, the tint of the edge region and the angle dependence of the tint are considered to be caused by the directivity of the primary light, but the directivity can be made closer to uniformity by strong diffusion. On the other hand, if the diffusion is too strong, the front luminance decreases.
For this reason, by satisfying the condition B-1 (the absolute value of α is 1 degree or more and less than 30 degrees), while improving the tint of the edge region due to the directivity of the primary light and the angle dependence of the tint, It can be considered that a decrease in the front luminance can be suppressed, and the balance between the front luminance, the tint of the edge region, and the angle dependence of the tint can be improved.
On the other hand, when the absolute value of α is less than 1 degree, it is considered that the directivity of the primary light cannot be sufficiently uniform, and the tint of the edge region and the angle dependence of the tint cannot be improved. If the absolute value of α is 30 degrees or more, it is considered that the diffusion is too strong and the front luminance decreases.

  The absolute value of α is preferably 15 degrees or more and less than 30 degrees, and more preferably 20 degrees or more and 29 degrees or less from the viewpoint of further improving the tint of the edge region and the angle dependence of the tint. It is even more preferable that the angle is from 25 degrees to 29 degrees.

α can be calculated based on an intensity distribution diagram created by an approximate curve obtained by linear interpolation of the intensity value for each degree and the maximum value of the transmitted light intensity. The same applies to β described later.
Note that the angle indicating 1/2 of the maximum value of the transmitted light intensity exists in the plus direction and the minus direction, respectively. In the present invention, the absolute value of α means the average value of the absolute values in the plus direction and the minus direction. The same applies to β described later.

  From the above, by satisfying the condition A-1 or the condition B-1, it is possible to improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color. From the viewpoint of further improving the balance between the front luminance, the tint of the edge region, and the angle dependency of the tint, it is preferable to satisfy the conditions A-1 and B-1.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition A-2.
<Condition A-2>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -45 degrees to + 45 degrees when upon the _{P 45,} less than 60 _{P 45} 20 or more.

−45 degrees to +45 degrees indicates the entire range of the stable fixation field. The stable gazing field of view is a range in which information can be reasonably received by the effective visual field + head movement. The horizontal direction is ± 30 to 45 degrees, the upper direction is 20 to 30 degrees, and the lower direction is 25 to 40 degrees. (For example, the Internet <URL: http://dbnst.nii.ac.jp/view_image/2515/4526?height=785&width=421>).
By setting P ₄₅ to 20 or more and less than 60, it is possible to have an appropriate diffusion in the entire range of the stable gazing field, and to further improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color. P ₄₅ is more preferably 40 or more 59 or less capable, more preferably 45 or more 58 or less, and still further preferably 50 or more 58 or less.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition A-3.
<Condition A-3>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -60 degrees to + 60 degrees when upon the _{P 60,} less than 75 _{P 60} 25 or more.

The position where the viewer can easily see the screen of the display device is the position facing the screen. However, since the portable information terminal is held by hand, it often shifts from a position facing the portable information terminal. Also, when the screen is viewed by a plurality of persons, the persons located at the left and right ends see the screen obliquely. In such a case, the angle formed by the eyes of the viewer and the edge of the screen may be about 60 degrees.
Satisfying the condition A-3 means that the film has an appropriate diffusion even in the high-angle region as described above. Therefore, by satisfying the condition A-3, it is possible to further improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color.
P ₆₀ is more preferably 45 or more 70 or less, more preferably 50 or more 65 or less, and still further preferably 55 or more 65 or less.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition A-4.
<Condition A-4>
Less than P ₄₅ -P ₃₀ 5 or more 13.

When P ₄₅ −P ₃₀ is 5 or more, it means that the diffusion does not rapidly decrease between 30 degrees and 45 degrees. Further, that P ₄₅ −P ₃₀ is less than 13 means that the diffusion between 30 degrees and 45 degrees is not too strong. Therefore, by satisfying the condition A-4, it is possible to further improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color.
P ₄₅ -P ₃₀ is more preferably 7 or more and 12 or less, and even more preferably 9 or more and 11 or less.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition A-5.
<Condition A-5>
P ₆₀ -P ₄₅ of less than 4 or more 8.

The fact that P ₆₀ -P ₄₅ is 4 or more means that the diffusion does not suddenly weaken between 45 degrees and 60 degrees. Further, that P ₆₀ -P ₄₅ is less than 8, means that the diffusion between 45 degrees and 60 degrees is not too strong. Therefore, by satisfying the condition A-5, the tint of the edge region and the angle dependency of the tint can be further improved.
P ₆₀ -P ₄₅ is more preferably 5 or more and 7 or less.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition B-2.
<Condition B-2>
Absolute value of β is 3 degrees or more and less than 45 degrees when β is a diffusion angle indicating an intensity that is ３ of the maximum value of transmitted light intensity of −85 degrees to +85 degrees.

As described above, when the diffusion increases, the intensity of the transmitted light does not easily decrease even if the angle increases in the plus direction and the minus direction. Therefore, the angle β indicating the intensity of １ ／ of the maximum value of the intensity of the transmitted light indicates the intensity of diffusion within the angle β. As described above, since the ratio of the primary light is large in the low-angle region, the front luminance and the color of the edge region are satisfied by satisfying the condition B-2 (absolute value of β is equal to or more than 3 degrees and less than 45 degrees). It is considered that the angle dependence of taste and color can be better balanced.
Further, the maximum intensity of the transmitted light and the intensity of １ ／ of the maximum value are recognized as an intensity difference by human eyes, but the intensity difference is not too large, so that there is no pain due to the intensity difference. is there. And, as described above, the maximum angle of the stable fixation field is 45 degrees.
That is, satisfying the condition B-1 makes it possible to better balance the front luminance, the color of the edge area, and the angle dependence of the color without suffering from the difference in intensity within the range of the stable field of view. Means
The absolute value of β is more preferably not less than 20 degrees and not more than 43 degrees, more preferably not less than 25 degrees and not more than 42 degrees, and even more preferably not less than 30 degrees and not more than 40 degrees.

Further, the quantum dot sheet of the present invention preferably further satisfies the following condition B-3.
<Condition B-3>
The difference between the absolute value of β and the absolute value of α is 2 degrees or more and less than 11.5 degrees.

When the difference between the absolute value of β and the absolute value of α exceeds 2 degrees, the diffusion between the angle indicating the intensity of 最大 of the maximum and the angle indicating the intensity of ３ of the maximum is It means that it does not weaken rapidly. Further, the difference between the absolute value of β and the absolute value of α is less than 11.5 degrees, which means that the angle indicating the intensity of 最大 of the maximum value and the angle indicating the intensity of １ ／ of the maximum value Means that the spread between the two is not too strong. Therefore, by satisfying the condition B-3, it is possible to further improve the balance between the front luminance, the color of the edge region, and the angle dependence of the color.
The difference between the absolute value of β and the absolute value of α is more preferably 6 degrees or more and less than 11.5 degrees, and even more preferably 9 degrees or more and 11 degrees or less.

Method for measuring transmitted light intensity The transmitted light intensity can be measured as follows.
First, visible light from a halogen lamp (12 V, 48 W) is applied as a parallel light beam to one of the surfaces of the quantum dot sheet. In measuring the intensity of transmitted light, the surface on which the quantum dot sheet is irradiated with light is the light incident surface (the surface facing the optical plate for guiding or diffusing light) when the quantum dot sheet is used as a backlight. It is preferable that
After irradiating the light, the transmitted light is scanned by the light receiver every one degree within a certain angle range, and the intensity (luminous intensity) at each angle is measured. The measurement range is ± 85 degrees with the vertical direction being 0 degrees (specular transmission direction). At the time of intensity measurement, the brightness of the light source is kept constant. Further, when measuring the intensity (luminous intensity), the aperture angle of the light receiver detected by the stop of the light receiver is set to 1 degree. Therefore, for example, in the measurement at 0 degree (specular transmission direction), the range of ± 0.5 degree is measured, and in the measurement of 1 degree, the range of 0.5 to 1.5 degrees is measured, and the measurement of -1 degree is performed. Then, the range of -0.5 to -1.5 degrees is measured. There is no particular limitation on the device for measuring the intensity, and a general-purpose goniophotometer (goniophotometer) can be used. In the present invention, a GC5000L (trade name: Nippon Denshoku Industries Co., Ltd .; light flux diameter: about 3 mm, inclination angle in light flux: within 0.8 degree, aperture angle of light receiver: 1 degree) used as a variable angle photometer in the present invention. did.
7 to 9 are diagrams showing the normalized intensity distribution of the transmitted light of the quantum dot sheets of Example 1 and Comparative Examples 1 and 3. Note that the intensity distribution diagrams in FIGS. 7 to 9 are approximate curves obtained by linear interpolation of the intensity values for each degree.
The above-mentioned P ₃₀ , P ₄₅ , P ₆₀ , α and β are average values obtained by measuring 20 times.

  As shown in FIGS. 7 to 9, in the quantum dot sheet of the present invention, the shape of the intensity distribution diagram of the transmitted light is convex upward, and it is directed from the front direction (0 degree) to the plus direction and the minus direction. It is preferable that the shape becomes substantially gradually decreasing.

Transmittance The total light transmittance of the quantum dot sheet of the invention according to JIS K7361-1: 1997 is not particularly limited, but is usually about 40% or more.
In the measurement of the intensity of the total light transmittance, the surface on which the quantum dot sheet is irradiated with light is a light incident surface when the quantum dot sheet is used as a backlight (opposing an optical plate for guiding or diffusing light). Side surface).

Surface Roughness The quantum dot sheet of the present invention preferably has an arithmetic average roughness Ra of at least one surface of 0.1 to 10 μm, more preferably 0.2 to 8 μm, and 0.5 to 5 μm. Is more preferable. Further, it is preferable that both surfaces of the quantum dot sheet satisfy the range of Ra.
By setting Ra to 0.1 μm or more, it is possible to prevent the quantum dot sheet from being in close contact with a member that comes into contact with the quantum dot sheet. Examples of the member that comes into contact with the quantum dot sheet include a prism sheet located on the light exit side of the quantum dot sheet, and an optical plate for guiding or diffusing light located on the light incident side of the quantum dot sheet. Further, by setting Ra to 10 μm or less, it is possible to suppress the light leakage of the polarizing plate and the decrease in the front luminance.
Further, by controlling the intensity of diffusion, from the viewpoint of balancing the suppression of the angle dependence of the tint, the suppression of the tint of the edge region, the light leakage of the polarizing plate, and the suppression of the decrease in the front luminance, Ra is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. Further, by setting Ra on the light incident surface side to 1 μm or more, retroreflectivity is provided, the light recycling rate is increased, and the content of quantum dots can be reduced.
In addition, Ra and Rz _JIS described later are based on JIS B0601: 2001, and are average values measured 20 times with a cutoff value of 0.8 mm.

The quantum dot sheet of the present invention preferably has a ten-point average roughness Rz _{JIS of} at least one surface of 0.1 to 20 μm, more preferably 0.2 to 10 μm, and more preferably 0.5 to 8 μm. It is more preferred that there be. Further, it is preferable that both surfaces of the quantum dot sheet satisfy the range of Rz _JIS .
The fact that Rz _JIS satisfies the above range indicates that the surface roughness of the quantum dot sheet has a certain randomness and that there is no extreme unevenness in the roughness. Therefore, when the Rz _JIS satisfies the above range, the bias of diffusion can be reduced and local adhesion can be prevented.
Further, by controlling the intensity of diffusion, from the viewpoint of balancing the suppression of the angle dependence of the tint, the suppression of the tint of the edge region, the light leakage of the polarizing plate, and the suppression of the decrease in the front luminance, Rz _JIS is preferably from 1 to 10 μm, more preferably from 2 to 8 μm.
In order to set Ra and Rz _JIS within the above range, a light diffusion layer described later may be located on the outermost surface of the quantum dot sheet.

Configuration of Quantum Dot Sheet The quantum dot sheet of the present invention has a quantum dot containing a binder resin and a quantum dot that absorbs primary light and emits secondary light.
As the quantum dot, the first quantum dot that absorbs the primary light of the wavelength corresponding to blue and emits the secondary light of the wavelength corresponding to red, and absorbs the primary light of the wavelength corresponding to blue and corresponds to green It is preferable to include at least one of the second quantum dots that emits secondary light of a predetermined wavelength, and it is more preferable to include both the first quantum dots and the second quantum dots.
Primary light having a wavelength corresponding to blue preferably has a peak wavelength in the range of 380 to 480 nm, and more preferably has a peak wavelength of 450 nm. The secondary light having a wavelength corresponding to green preferably has a peak wavelength in the range of 495 to 570 nm, and more preferably has a peak wavelength of 528 nm. The secondary light having a wavelength corresponding to red preferably has a peak wavelength in the range of 620 to 750 nm, and more preferably has a peak wavelength of 637 nm.

1 to 3 are sectional views showing an embodiment of the quantum dot sheet of the present invention. The quantum dot sheet 100 of FIG. 1 has light transmitting base materials 21a and 21b and light diffusion layers 42a and 42b on upper and lower surfaces of the quantum dot containing layer 10. The quantum dot sheet 100 in FIG. 2 has barrier layers 32a and 32b, light-transmissive substrates 21a and 21b, and light diffusion layers 42a and 42b on upper and lower surfaces of the quantum dot-containing layer 10. The quantum dot sheet 100 in FIG. 3 has substrates 21a and 21b on the upper and lower surfaces of the quantum dot-containing layer 10, and has barrier films 30a and 30b on a light-transmitting substrate via adhesive layers 51a and 51b. And light diffusion films 40a and 40b on the barrier film via adhesive layers 52a and 52b.
1 to 3 have configurations (light-transmitting substrate, barrier layer, light diffusion layer, etc.) other than the quantum dot-containing layer, the quantum dot sheet of the present invention has at least a quantum dot-containing layer. Any condition that satisfies at least one of the above-mentioned conditions A-1 and B-1 may be employed, and the structure (light-transmitting substrate, barrier layer, light-diffusing layer, etc.) other than the quantum dot-containing layer may be changed as necessary. It may be provided.
Although the quantum dot sheet in FIGS. 1 to 3 has only one quantum dot-containing layer, the quantum dot sheet may have two or more quantum dot-containing layers.

It is preferable that the quantum dot sheet has a vertically symmetric configuration with respect to the quantum dot-containing layer as shown in FIGS. With this configuration, the strain is evenly dispersed, the flatness of the quantum dot sheet can be improved, and the adhesiveness of the interface of the quantum dot sheet can be improved. When the flatness of the quantum dot sheet is good, it is preferable in that the uniformity of in-plane luminance can be improved.
The layer configuration vertically symmetrical in the thickness direction means that the number of layers and the type of layers in the upper and lower layers are the same, and the thickness of each layer is substantially the same. In order to be able to say that the thicknesses are substantially the same, the ratio of the thicknesses of the upper and lower layers in the target relationship is preferably in the range of 0.95 to 1.05, and more preferably in the range of 0.97 to 1.03. Is more preferred.
Further, it is preferable that the layers having a symmetric relationship have substantially the same composition. In order for the composition to be substantially the same, it is preferable that 90% by mass or more of the constituent components of the layer is the same, more preferably 95% by mass or more is the same, and 99% by mass or more is the same. More preferred.

Quantum dot containing layer Quantum dots (first quantum dots and second quantum dots) will be described below.
Quantum dots are semiconductor nanometer-sized fine particles that have specific optical and electrical properties due to the quantum confinement effect (quantum size effect) in which electrons and excitons are confined in small nanometer-sized crystals. It exhibits properties and is also called semiconductor nanoparticles or semiconductor nanocrystals.
The quantum dot is a semiconductor nanometer-sized fine particle, and is not particularly limited as long as it is a material that produces a quantum confinement effect (quantum size effect). For example, as described above, there are semiconductor fine particles whose emission color is regulated by their own particle size, and semiconductor fine particles having a dopant. As the quantum dots in the present invention, both semiconductor fine particles whose emission color is regulated by their own particle diameter and semiconductor fine particles having a dopant can be used, and both can obtain excellent color purity.

Quantum dots have different emission colors depending on their particle diameters. For example, in the case of a quantum dot composed of only a core made of CdSe, the particle diameters are 2.3 nm, 3.0 nm, 3.8 nm, and 4 nm. The peak wavelengths of the fluorescence spectrum at 6.6 nm are 528 nm, 570 nm, 592 nm, and 637 nm. That is, the particle size of the quantum dot that emits secondary light having a peak wavelength of 637 nm is 4.6 nm, and the particle size of the quantum dot that emits secondary light having a peak wavelength of 528 nm is 2.3 nm.
The quantum dot-containing layer may contain a quantum dot other than a quantum dot that emits secondary light having a wavelength corresponding to red and a quantum dot that emits secondary light having a wavelength corresponding to green.
The content of the quantum dots is appropriately adjusted according to the thickness of the quantum dot-containing layer, the light recycling rate in the backlight, the desired tint, and the like. If the thickness of the quantum dot-containing layer is in the range described below, the content of the quantum dots is about 0.01 to 1.0 part by mass with respect to 100 parts by mass of the binder resin of the quantum dot-containing layer. When the content of the quantum dots is at this level, the transmitted light intensity is hardly affected.

Specific examples of the material serving as the core of the quantum dot include MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, and HgS. , HgSe and II-VI semiconductor compounds such as HgTe, AlN, AlP, AlAs, AlSb, GaAs, GaP, GaN, GaSb, InN, InAs, InP, InSb, TiN, TiP, TiOs such as TiAs and TiSb. A semiconductor crystal containing a semiconductor compound or a semiconductor, such as a group V semiconductor compound, a group IV semiconductor such as Si, Ge and Pb, or the like, can be exemplified. Alternatively, a semiconductor crystal including a semiconductor compound containing three or more elements, such as InGaP, can be used.
Further, as a quantum dot composed of semiconductor fine particles having a dopant, a semiconductor crystal obtained by doping a cation of a rare earth metal such as Eu ³⁺ , Tb ³⁺ , Ag ⁺ , or Cu ⁺ or a cation of a transition metal into the above-described semiconductor compound is used. It can also be used.
As a material serving as a core of the quantum dot, semiconductor crystals such as CdS, CdSe, CdTe, InP, and InGaP are used from the viewpoints of easiness of production, controllability of particle diameter capable of obtaining light emission in a visible region, and fluorescence quantum yield. Is preferred.

The quantum dot may be composed of one kind of semiconductor compound or two or more kinds of semiconductor compounds. For example, a quantum dot may be composed of a core composed of a semiconductor compound and a shell composed of a semiconductor compound different from the core. And a core-shell type structure having the following.
When a core-shell quantum dot is used, the semiconductor constituting the shell is made of a material with a higher band gap than the semiconductor compound that forms the core, so that excitons are confined in the core. Can be increased.
Examples of the core-shell structure (core / shell) having such a magnitude relation of band gap include CdSe / ZnS, CdSe / ZnSe, CdSe / CdS, CdTe / CdS, InP / ZnS, Gap / ZnS, Si / ZnS, InN / GaN, InP / CdSSe, InP / ZnSeTe, InGaP / ZnSe, InGaP / ZnS, Si / AlP, InP / ZnSTe, InGaP / ZnSTe, InGaP / ZnSSe, and the like.

The size of the quantum dot may be appropriately controlled depending on the material constituting the quantum dot so that light of a desired wavelength can be obtained. The energy band gap of a quantum dot increases as the particle size decreases. That is, as the crystal size decreases, the emission of the quantum dots shifts toward the blue side, that is, toward the high energy side. Therefore, by changing the size of the quantum dot, the emission wavelength can be adjusted over the entire wavelength range of the spectrum in the ultraviolet, visible, and infrared regions.
Generally, the particle diameter (diameter) of the quantum dot is preferably in the range of 0.5 to 20 nm, and particularly preferably in the range of 1 to 10 nm. Note that the narrower the size distribution of the quantum dots, the more vivid emission color can be obtained.
The shape of the quantum dot is not particularly limited, and may be, for example, a sphere, a rod, a disk, or another shape. When the particle size of the quantum dot is not spherical, the particle size can be a true spherical value having the same volume.
The quantum dots may be coated with a resin. Further, the refractive index of the binder resin of the quantum dot containing layer and n _A, the refractive index of the resin (coating resin) for covering the quantum dots upon the n _B, n _{B /} n _A is 1.02 or more, or 0 .98 or less is preferably satisfied. The quantum dots coated with the resin can improve the durability of the quantum dots. In addition, when the refractive index of the binder resin and the refractive index of the coating resin satisfy the above relationship, the quantum dots coated with the resin exhibit the function of internal diffusion particles described later.
In the present invention, the refractive index is based on light having a wavelength of 450 nm.

  Information such as the particle size, shape, and dispersion state of the quantum dots can be obtained by a transmission electron microscope (TEM). The crystal structure and particle size of the quantum dot can be obtained by X-ray crystal diffraction (XRD). Further, information on the particle diameter and surface of the quantum dot can be obtained from an ultraviolet-visible (UV-Vis) absorption spectrum.

  Examples of the binder resin for the quantum dot-containing layer include a thermoplastic resin, a cured product of a thermosetting resin composition, and a cured product of an ionizing radiation-curable resin composition. Among these, from the viewpoint of durability, a cured product of the thermosetting resin composition and a cured product of the ionizing radiation-curable resin composition are preferable, and a cured product of the ionizing radiation-curable resin composition is more preferable.

The thermosetting resin composition is a composition containing at least a thermosetting resin, and is a resin composition that is cured by heating.
Examples of the thermosetting resin include acrylic resin, urethane resin, phenol resin, urea melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin. In the thermosetting resin composition, a curing agent is added to these curable resins as necessary.

The ionizing radiation-curable resin composition is a composition containing a compound having an ionizing radiation-curable functional group (hereinafter, also referred to as “ionizing radiation-curable compound”). Examples of the ionizing radiation-curable functional group include an ethylenically unsaturated bond group such as a (meth) acryloyl group, a vinyl group and an allyl group, and an epoxy group and an oxetanyl group. Among them, an ethylenically unsaturated bond group is preferable. . Further, among the ethylenically unsaturated bonding groups, a (meth) acrylate group is preferable. Hereinafter, the ionizing radiation-curable compound having a (meth) acryloyl group is referred to as a (meth) acrylate compound.
In this specification, "(meth) acrylate" refers to methacrylate and acrylate. In the present specification, “ionizing radiation” means an electromagnetic wave or a charged particle beam having an energy quantum capable of polymerizing or cross-linking a molecule, and usually, an ultraviolet ray (UV) or an electron beam (EB) is used. In addition, charged particles such as electromagnetic waves such as X-rays and γ-rays, α-rays, and ion beams can be used.

The ionizing radiation-curable compound may be a monofunctional ionizing radiation-curable compound having only one functional group, or may be a polyfunctional ionizing radiation-curable compound having two or more functional groups. Or a mixture thereof.
The ionizing radiation-curable compound may be a monomer, an oligomer, a low molecular weight polymer, or a mixture thereof.
Among the ionizing radiation-curable compounds, monofunctional monomers are preferred in that they improve the adhesion between the quantum dot-containing layer and the light-transmitting substrate and suppress polymerization shrinkage. In particular, when the thickness of the quantum dot-containing layer is large, the above-described effect when a monofunctional monomer is used becomes remarkable.
In addition, when the adhesion of the quantum dot-containing layer is improved by using the monofunctional monomer, it becomes possible to adhere a member such as a light-transmitting substrate to the quantum dot-containing layer without using an adhesive layer. That is, by improving the adhesion of the quantum dot-containing layer using the monofunctional monomer, the configuration of the quantum dot sheet can be easily made to be vertically symmetrical in the thickness direction around the quantum dot-containing layer. In addition, by adhering the quantum dot-containing layer to a member such as a light-transmitting substrate without using an adhesive layer, the moisture resistance and oxygen resistance of the quantum dots can be improved.
The proportion of the monofunctional monomer in the total ionizing radiation-curable compound is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

  In addition, since the quantum dots are weak to humidity, it is preferable to use, as a main component, a compound having no hydroxyl group in the molecule as the ionizing radiation-curable compound. Specifically, the ratio of the ionizing radiation-curable compound having no hydroxyl group in the molecule to the total ionizing radiation-curable compound is preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass or more. More preferably, it is mass%.

  Examples of the ionizing radiation curable compound having no hydroxyl group in the molecule include ethyl (meth) acrylate, butyl (meth) acrylate, ethylhexyl (meth) acrylate, phenoxyethyl (meth) acrylate, octyl (meth) acrylate, and dicyclopentenyl ( Monofunctional (meth) acrylate compounds such as meth) acrylate, pentaerythritol tetra (meth) acrylate, 1,6-hexanediol di (meth) acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) Acrylate, tricyclodecane dimethanol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropaneethoxy tri (meth) acrylate, dipentaerythritol hex (Meth) acrylate, pentaerythritol ethoxy tetra (meth) acrylate, polyfunctional (meth) acrylate compounds such as ditrimethylolpropane tetra (meth) acrylate.

  The ionizing radiation-curable compound preferably has a total carbon number of 8 or more from the viewpoint of increasing hydrophobicity and improving the moisture resistance of the quantum dot. Considering the adhesion of the quantum dot-containing layer in addition to the moisture resistance, the total carbon number of the ionizing radiation-curable compound is more preferably 8 to 20. For example, examples of the monofunctional (meth) acrylate monomer having a total carbon number of 8 or more include ethylhexyl (meth) acrylate, octyl (meth) acrylate, and the like.

The molecular weight of the ionizing radiation-curable compound is preferably from 100 to 2,000, more preferably from 120 to 1,000, and even more preferably from 150 to 500. When the molecular weight of the ionizing radiation-curable compound is 100 or more, it is easy to prevent liquid dripping at the time of production, and when the molecular weight is 2000 or less, the quantum is reduced by the pressure at the time of bonding in step (d) described later. The thickness of the dot-containing layer can be easily made uniform.
When a monofunctional monomer is used as the ionizing radiation-curable compound, the molecular weight of the monofunctional monomer is 100 from the viewpoint of prevention of liquid dripping during production, uniformization of the thickness of the quantum dot-containing layer, and adhesion of the quantum dot-containing layer. It is preferably from 500 to 500, more preferably from 120 to 400, and still more preferably from 150 to 250.

When the ionizing radiation-curable compound is an ultraviolet-curable compound, the ionizing radiation-curable composition preferably contains additives such as a photopolymerization initiator and a photopolymerization accelerator.
Examples of the photopolymerization initiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyl oxime ester, thioxanthone, and the like.
These photopolymerization initiators preferably have a melting point of 20 ° C. or less. When the melting point is 20 ° C. or less, it can be easily dissolved at room temperature when added to the ionizing radiation-curable compound at the time of production.
Further, the photopolymerization accelerator can reduce the polymerization inhibition by air at the time of curing and can increase the curing speed. For example, isoamyl p-dimethylaminobenzoate, ethyl p-dimethylaminobenzoate, etc. One or more selected ones are mentioned.

Internal Diffusion Particles When light diffusion is not sufficient, the quantum dot-containing layer may contain internal diffusion particles.
As the internal diffusion particles, both organic particles and inorganic particles can be used. Examples of the organic particles include particles made of polymethyl methacrylate, acrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone resin, fluorine-based resin, polyester, and the like. . Examples of the inorganic fine particles include fine particles made of silica, alumina, zirconia, titania, and the like.
Examples of the shape of the internal diffusion particles include a spherical shape, a disk shape, a rugby ball shape, and an irregular shape. Further, the internal diffusion particles may be any of hollow particles, porous particles, and solid particles.

The thickness of the quantum dot-containing layer is preferably from 10 to 200 μm, more preferably from 20 to 150 μm, even more preferably from 30 to 130 μm. When the thickness of the quantum dot-containing layer is within this range, it is suitable for reducing the weight and thickness of the display device, and can suppress color unevenness due to fluctuation in the thickness of the quantum dot-containing layer (manufacturing tolerance).
The thickness of the quantum dot-containing layer can be calculated, for example, by measuring the thickness at 20 locations from a cross-sectional image taken by using a scanning transmission electron microscope (STEM) and averaging the values at 20 locations. The acceleration voltage of the STEM is preferably 10 kv to 30 kV, and the magnification is preferably 1000 to 7000 times.
The thicknesses of other layers constituting the quantum dot sheet can be measured by the same method as described above. When the thickness is on the order of nanometers, the magnification of the STEM is preferably 50,000 to 300,000.

Light-Transmissive Substrate The quantum dot sheet of the present invention preferably has a light-transmissive substrate from the viewpoint of mechanical strength and stiffness. From this viewpoint, it is preferable that one or more light transmissive substrates are provided above and below the quantum dot-containing layer.
Further, it is preferable that the quantum dot sheet has a configuration in which both surfaces of the quantum dot-containing layer are sandwiched between light-transmitting substrates. According to this configuration, it is possible to protect the quantum dot-containing layer and to improve the oxygen resistance and moisture resistance of the quantum dots.

The light-transmitting substrate is not particularly limited, but preferably has a light-transmitting property, smoothness, heat resistance, and excellent mechanical strength. Examples of such a light-transmitting substrate include polyester, triacetyl cellulose (TAC), cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, Plastic films such as polyvinyl acetal, polyether ketone, acryl, polycarbonate, polyurethane, and amorphous olefin (Cyclo-Olefin-Polymer: COP) are included.
Among the above, from the viewpoints of mechanical strength, dimensional stability and heat resistance, polyesters stretched, especially biaxially stretched (polyethylene terephthalate, polyethylene naphthalate) are preferred.

The thickness of the light-transmitting substrate is preferably from 10 to 200 μm, more preferably from 20 to 150 μm, and still more preferably from 30 to 100 μm, from the viewpoint of the balance among weather resistance, mechanical strength, handleability and thinning.
The surface of the light-transmitting substrate may be subjected to a physical treatment such as a corona discharge treatment or an oxidation treatment, as well as a coating material called an anchor agent or a primer, in advance to improve the adhesiveness.

Barrier Layer The quantum dot sheet of the present invention preferably has a barrier layer in order to improve the moisture resistance and oxygen resistance of the quantum dots. The barrier layer may be provided on only one side of the quantum dot-containing layer, but is preferably provided on both sides of the quantum dot-containing layer.
The barrier layer may be provided on a light-transmitting substrate sandwiching the quantum dot-containing layer as shown in FIG. 2 or may be provided on another light-transmitting substrate as shown in FIG.
Further, the barrier layer is preferably provided on the side near the quantum dot-containing layer. For example, when a light diffusion layer described later is provided, it is preferable to provide a barrier layer on the quantum dot-containing layer side of the light diffusion layer.

The barrier layer is preferably made of an inorganic substance or an inorganic oxide, and examples thereof include a vapor-deposited film of an inorganic substance or an inorganic oxide, and a hydrolysis film of an inorganic alkoxide.
The barrier layer can be formed by a known method using a known inorganic substance, an inorganic oxide, an inorganic alkoxide, or the like, and the composition and the forming method are not particularly limited. The barrier layer may be a single layer or may have two or more layers. When two or more barrier layers are provided, each may have the same composition or different compositions.

Materials for the deposited film are silicon (Si), aluminum (Al), magnesium (Mg), calcium (Ca), potassium (K), tin (Sn), sodium (Na), boron (B), and titanium (Ti). , Lead (Pb), zirconium (Zr), yttrium (Y) and the like, or an oxide thereof, and a mixture of these with an organic material.
The inorganic alkoxide which is a material of the hydrolysis film is also called a metal alkoxide, and examples thereof include silicon alkoxide such as tetraalkoxysilane, titanium alkoxide, and aluminum alkoxide.

The thickness of the barrier layer is preferably from 5 to 1000 nm, more preferably from 7 to 700 nm, and more preferably from 10 to 500 nm, from the viewpoint of the balance between moisture resistance, oxygen resistance, crack suppression and light transmittance. More preferred. When the barrier layer is a vapor-deposited film, the thickness of the barrier layer is preferably 5 to 30 nm, more preferably 7 to 25 nm, and still more preferably 10 to 20 nm.
Examples of a method for forming a deposited film as a barrier layer include a physical vapor deposition method (PVD method) such as a vacuum deposition method, a sputtering method and an ion plating method, a plasma chemical vapor deposition method, and a thermal chemical vapor deposition method. A chemical vapor deposition method (CVD method) such as a growth method and a photochemical vapor deposition method may be used.

Light Diffusion Layer The quantum dot sheet of the present invention preferably has a light diffusion layer in order to easily satisfy at least one of the conditions A-1 and B-1 by appropriate diffusion.
The light diffusion layer may be provided only on one side of the quantum dot-containing layer, but is preferably provided on both sides of the quantum dot-containing layer. Further, the light diffusion layer is preferably arranged at the outermost layer of the quantum dot sheet or at a position that can be identified with the outermost layer. When the light diffusion layer is provided only on one side of the quantum dot-containing layer, it is preferable that the light diffusion layer be disposed on the light emitting surface side or at a position that can be identified with the outermost layer.
The position that can be identified with the outermost layer refers to the light diffusion when a thin film (layer having a thickness of 100 nm or less) that does not substantially affect the surface irregularities of the light diffusion layer is formed on the light diffusion layer. Refers to the position of the layer.
The light-diffusing layer may be provided on a light-transmitting substrate sandwiching the quantum dot-containing layer as shown in FIGS. 1 and 2, or may be provided on another light-transmitting substrate as shown in FIG. Good.

The light diffusion layer preferably has external diffusion due to surface irregularities. By arranging such a light diffusion layer at the outermost layer or at a position that can be identified with the outermost layer, it is possible to prevent the quantum dot sheet from adhering to a member (such as a brightness enhancement sheet) that comes into contact with the quantum dot sheet. Further, the condition A-1 and the condition B-1 can be easily satisfied by providing the external diffusion.
The light diffusion layer can be formed, for example, from a binder resin and diffusion particles.

Examples of the binder resin of the light diffusion layer include a thermoplastic resin, a cured product of a thermosetting resin composition, and a cured product of an ionizing radiation-curable resin composition. Among these, from the viewpoint of abrasion resistance, a cured product of the thermosetting resin composition and a cured product of the ionizing radiation-curable resin composition are preferable, and a cured product of the ionizing radiation-curable resin composition is more preferable.
As the thermosetting resin composition and the ionizing radiation-curable resin composition, the same ones as those exemplified for the quantum dot-containing layer can be used.

The ratio of the average particle diameter of the diffusion particles to the thickness of the light diffusion layer (the average particle diameter of the diffusion particles / the thickness of the light diffusion layer) is preferably 0.10 to 2.00, and 0.15 to 1 .50, more preferably 0.20 to 1.00.
By setting the ratio of the average particle diameter of the diffusion particles of the light diffusion layer on the light emitting surface side to the thickness of the light diffusion layer to be 0.10 or more, strong external diffusion can be imparted. Further, by setting the ratio of the average particle diameter of the diffusion particles of the light diffusion layer on the light incident surface side to the thickness of the light diffusion layer to be 0.10 or more, retroreflectivity is provided and the light recycling rate is increased. In addition, the content of quantum dots can be reduced. Further, by setting the ratio of the average particle diameter of the diffusion particles to the thickness of the light diffusion layer to be 2.00 or less, the diffusion particles can be sufficiently retained in the light diffusion layer.
Further, from the viewpoint of easily obtaining the effect based on the above ratio, the average particle size of the diffusion particles of the light diffusion layer is preferably 1 to 20 μm, more preferably 1 to 10 μm.

The average particle diameter of the diffusion particles can be calculated by the following operations (1) to (3).
(1) A transmission observation image of the light diffusion layer is captured by an optical microscope. The magnification is preferably 500 to 2000 times.
(2) Ten arbitrary particles are extracted from the observation image, the major axis and minor axis of each particle are measured, and the average particle diameter of each individual particle is calculated from the average of major axis and minor axis. The long diameter is the longest diameter on the screen of each particle. Further, the minor axis refers to a distance between two points where a line segment orthogonal to the midpoint of the line segment constituting the major axis is drawn and the orthogonal line segment intersects particles.
(3) The same operation is performed five times on the observation image of another screen of the same sample, and the value obtained from the number average of the particle diameters of a total of 50 particles is defined as the average particle diameter of the internal diffusion particles.

  As the diffusion particles, both organic particles and inorganic particles can be used, and the same particles as those exemplified as the internal diffusion particles of the quantum dot-containing layer can be used.

The thickness of the light diffusion layer is preferably from 1 to 30 μm, more preferably from 3 to 20 μm, from the viewpoint of the holding power of the diffusion particles and the external diffusion property.
The diffusion particles of the light diffusion layer are preferably from 10 to 200 parts by mass, more preferably from 30 to 170 parts by mass, based on 100 parts by mass of the binder resin, from the viewpoint of the balance between the diffusivity and the coating film strength. More preferably, it is more preferably 50 to 150 parts by mass.

Adhesive Layer In order to stack the layers constituting the quantum dot sheet, an adhesive layer may be interposed between the layers. For example, in FIG. 3, an adhesive layer is provided between the light transmitting substrate and the barrier film, and between the barrier film and the diffusion film.
The adhesive layer can be formed from a general-purpose pressure-sensitive adhesive (adhesive), a thermosetting adhesive, or an ionizing radiation-curable adhesive.
The thickness of the adhesive layer is preferably from 0.5 to 20 μm, more preferably from 1 to 10 μm, from the viewpoint of adhesive strength and thinning.

  The quantum dot sheet may have other functional layers such as an antireflection layer and an antistatic layer.

The method for manufacturing the quantum dot sheet is not particularly limited, but for example, the quantum dot sheet can be manufactured in the following order (a) to (d).
(A) A step of laminating a light-transmitting substrate and a layer located on one surface of the quantum dot-containing layer based on the quantum dot-containing layer to obtain a laminate A.
(B) a step of laminating a light-transmitting substrate and a layer located on the other surface of the quantum dot-containing layer with reference to the quantum dot-containing layer to obtain a laminate B.
(C) A quantum dot-containing layer coating solution containing a binder resin component and a quantum dot that absorbs primary light and emits secondary light is applied to one surface of one of the laminates A and B. A step of coating to form a quantum dot-containing layer.
(D) a step of bonding the laminate on which the quantum dot-containing layer is not formed in step (c) to the surface of the laminate on which the quantum dot-containing layer is formed in step (c), on the side of the quantum dot-containing layer.

  In the step (d), an adhesive layer may be used, but by laminating without using the adhesive layer, a vertically symmetric configuration centering on the quantum dot-containing layer becomes possible as shown in FIGS. Therefore, it is preferable.

In the case where the binder resin of the quantum dot-containing layer is a cured product of the ionizing radiation-curable resin composition, in order to bond the laminate A and the laminate B without using the adhesive layer in the step (d), It is preferable to employ the method of (1).
First, the ionizing radiation-curable resin composition preferably contains a monofunctional monomer (in other words, the coating solution for the quantum dot-containing layer contains a monofunctional monomer).
Second, when forming the quantum dot-containing layer in the step (c), do not irradiate ionizing radiation or suppress the irradiation amount of ionizing radiation to leave uncured portions in the ionizing radiation-curable resin composition. Preferably, after the step (d), ionizing radiation is irradiated to advance the curing of the ionizing radiation-curable resin composition.
The combination of the first technique and the second technique is preferable in that in step (d), the workability of bonding the two laminates without interposing the adhesive layer is further improved.

[Backlight]
The backlight according to the present invention includes at least one light source that emits primary light, an optical plate that is disposed adjacent to the light source and guides or diffuses light, and a quantum light that is disposed on a light emission side of the optical plate. In a backlight including a dot sheet, the quantum dot sheet is the above-described quantum dot sheet of the present invention.
When the condition A-1 or the condition B-1 is satisfied even if light is incident from any of the upper and lower surfaces of the quantum dot sheet, the direction in which the quantum dot sheet is installed in the backlight is not particularly limited. On the other hand, when the condition A-1 or the condition B-1 is satisfied only when light is incident from one of the upper and lower surfaces of the quantum dot sheet, the light incident surface when the condition is satisfied is a light guiding or diffusing surface. The quantum dot sheet is installed in the backlight so as to face the optical plate for the purpose.

  As an example of the backlight of the present invention, an edge-light type backlight as shown in FIG. 4 or a direct-type backlight as shown in FIG. 5 can be employed.

  The optical plate 120 used for the edge light type backlight of FIG. 4 is an optical member for guiding the primary light emitted from the light source 110, and is a so-called light guide plate. The light guide plate has, for example, a substantially flat shape in which at least one surface is a light incident surface and one surface substantially orthogonal to the light incident surface is a light exit surface.

  The light guide plate is mainly made of a matrix resin selected from highly transparent resins such as polymethyl methacrylate. The light guide plate may be added with resin particles having a different refractive index from the matrix resin as needed. Each surface of the light guide plate may be not a uniform plane but a complicated surface shape, and may be provided with a dot pattern or the like.

  The optical plate 120 used for the direct-type backlight in FIG. 5 is an optical member (light diffusing material) having a light diffusing property for making the pattern of the light source 110 difficult to see. Examples of the light diffusing material include a milky white resin plate having a thickness of about 1 to 3 mm.

  Edge-light type and direct-type backlights include, in addition to the light source, the optical plate and the quantum dot sheet described above, a reflector, a light diffusion film, a prism sheet, a brightness enhancement film (BEF), and a reflection type, depending on the purpose. One or more members selected from a polarizing film (DBEF) and the like may be provided. The reflection plate is arranged on the side opposite to the light exit surface side of the optical plate. The light diffusion film, the prism sheet, the brightness enhancement film, and the reflection type polarizing film are arranged on the light exit surface side of the optical plate. By providing a structure including at least one member selected from a reflection plate, a light diffusion film, a prism sheet, a brightness enhancement film, a reflection type polarizing film, and the like, a backlight excellent in balance between front brightness, a viewing angle, and the like is provided. Can be.

In the edge light type backlight and the direct type backlight, the light source 110 is a light emitting body that emits primary light, and it is preferable to use a light emitting body that emits primary light having a wavelength corresponding to blue. Primary light having a wavelength corresponding to blue preferably has a peak wavelength in the range of 380 to 480 nm, and more preferably has a peak wavelength of 450 nm. The light source 110 is preferably an LED light source, and more preferably a monochromatic blue LED light source, from the viewpoint that a device for installing a backlight can be simplified and reduced in size. The number of the light sources 110 is at least one, and it is preferable that the number of the light sources be plural from the viewpoint of emitting sufficient primary light.
When only one of the first quantum dot and the second quantum dot is contained in the quantum dot-containing layer of the quantum dot sheet, in addition to the primary light source composed of a luminous body that emits primary light having a wavelength corresponding to blue, And an auxiliary light source. Specifically, when only the first quantum dots are contained in the quantum dot-containing layer, it is preferable to use a light emitter that emits light having a wavelength corresponding to green as the auxiliary light source. When only the second quantum dots are contained in the quantum dot-containing layer, it is preferable to use a light emitter that emits light having a wavelength corresponding to red as the auxiliary light source.

  Since the backlight of the present invention uses the above-described quantum dot sheet of the present invention, it is possible to improve the color of the edge region of the backlight and the angle dependence of the color.

[Liquid crystal display]
A liquid crystal display device of the present invention is a liquid crystal display device including a backlight and a liquid crystal panel, wherein the backlight is the above-described backlight of the present invention.

  FIG. 6 is a sectional view showing an embodiment of the liquid crystal display device of the present invention. The liquid crystal display device 300 of FIG. 6 includes a backlight 200 and a liquid crystal panel 210. Further, the backlight 200 and the liquid crystal panel 210 are incorporated and fixed in the holder 220.

  The liquid crystal panel includes a polarizing plate (not shown), a color filter (not shown), and the like. The liquid crystal panel is not particularly limited, and a generally known liquid crystal panel of a liquid crystal display device can be used. For example, a liquid crystal panel having a general structure in which a liquid crystal layer is sandwiched between glass plates on the upper and lower sides, specifically, a display method such as TN, STN, VA, IPS, and OCB can be used.

  The polarizing plate is not particularly limited as long as it has desired polarization characteristics, and a generally known polarizing plate for a liquid crystal display device can be used. Specifically, for example, a polarizing plate obtained by stretching a polyvinyl alcohol film and containing iodine is preferably used.

The color filter is not particularly limited, and for example, a color filter generally known as a color filter of a liquid crystal display device can be used. The color filter is usually composed of a transparent coloring pattern of each color of red, green and blue, and each of these transparent coloring patterns is composed of a resin composition in which a colorant is dissolved or dispersed, preferably in which pigment fine particles are dispersed. .
The method of forming a color filter includes a method of forming an ink composition colored in a predetermined color and forming the ink composition by printing for each coloring pattern, and a method of forming a photosensitive resin composition of a paint type containing a colorant of a predetermined color. And a method of forming an object by a photolithography method.

  A display image of the liquid crystal display device is displayed in color by transmitting white light emitted from a backlight through a color filter. By using a color filter that matches the backlight spectrum of the quantum dots, the liquid crystal display device can realize a display that is excellent in brightness and efficiency and generates very clear colors.

  The liquid crystal panel may have a configuration in which an arbitrary layer is formed as a single layer or multiple layers on a color filter. The optional layer is not particularly limited and includes, for example, a sensor layer for a touch panel, a hard coat layer, an antistatic layer, a low refractive index layer, a high refractive index layer, an antiglare layer, an antifouling layer, an antireflection layer, and a high dielectric layer. A body layer, an electromagnetic wave shielding layer, an adhesive layer, and the like.

  Since the liquid crystal display device of the present invention uses the above-described backlight of the present invention, it is possible to improve the tint of the edge region of the display image and the angle dependence of the tint.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Note that “parts” and “%” are based on mass unless otherwise specified. The refractive index is a refractive index at a wavelength of 450 nm unless otherwise specified.

1. Measurement and Evaluation of Physical Properties of Quantum Dot Sheet The physical properties of the quantum dot sheets of Examples and Comparative Examples were measured and evaluated as follows. Table 1 shows the results.

1-1. Intensity of transmitted light According to the method described in the specification text, a light source angle of 0 was obtained by transmission measurement using a goniophotometer (GC-5000L, manufactured by Nippon Denshoku Industries Co., Ltd., light source: halogen lamp (12 V, 48 W)). The sensitivity and the sensitivity were set to 1000 times, the intensity of the transmitted light of the quantum dot sheet was measured every one degree, and the measured intensities were normalized to calculate P ₃₀ , P ₄₅ and P ₆₀ . In addition, an approximate curve was created by linear interpolation of the intensity value for each degree from the measurement results, and the absolute values of α and β were calculated from the approximate curve and the maximum value of the transmitted light intensity. Table 1 shows the average value measured 20 times. In addition, the intensity | strength measured the range of +/- 85 degree | times of the normal transmission direction (0 degree).

1-2. Surface roughness Ra and Rz of the surface of the quantum dot sheet were measured using a surface roughness measuring instrument (model number: SE-3400 / manufactured by Kosaka Laboratory Co., Ltd.) in accordance with JIS B0601: 2001 under the following measurement conditions. _JIS was measured. Table 1 shows the average value measured 20 times.
[Stylus of surface roughness detector]
SE2555N (trade name, radius of curvature: 2 μm, vertex angle: 90 degrees, material: diamond) manufactured by Kosaka Laboratory Co., Ltd.
[Measurement conditions of surface roughness measuring instrument]
・ Reference length (cutoff value λc of roughness curve): 0.8 mm
Evaluation length (reference length (cut-off value λc) × 5): 4.0 mm
・ Feeding speed of stylus: 0.5mm / s
・ Spare length: (cut-off value λc) × 2
-Vertical magnification: 2000 times-Horizontal magnification: 10 times

1-3. The color of the edge region was turned on, and the color of the edge region of the backlight was visually evaluated from the front. Evaluation was given as 1 point when the bluish color was not worrisome, 2 points when the bluish color was worrisome but no practical problem, and 3 points when the bluish color was strong and practically problematic. Based on the criteria, 20 subjects evaluated and calculated the average score. "AAA" if the average score is 1.25 or less, "AA" if the average score is more than 1.25 and 1.50 or less, and "AA" if the average score is more than 1.50 and 1.75 or less Is “A”, the average score is more than 1.75 points and 2.00 points or less, “B”, the average score is more than 2.00 points and 2.25 points or less is “B ⁻ ”, and the average score is 2 Those with more than .25 points were designated "C".

1-4. Angle Dependency of Color The backlights of the examples and comparative examples were turned on, and the color near the center of the backlight was visually evaluated from various directions. One point where the color change due to the angle is not bothersome, 2 points where the color change due to the angle is slightly worrisome but has no problem in practical use. Twenty test subjects evaluated based on an evaluation criterion in which the problematic level was set to 3 points, and the average score was calculated. "AAA" if the average score is 1.25 or less, "AA" if the average score is more than 1.25 and 1.50 or less, and "AA" if the average score is more than 1.50 and 1.75 or less Is “A”, the average score is more than 1.75 points and 2.00 points or less, “B”, the average score is more than 2.00 points and 2.25 points or less is “B ⁻ ”, and the average score is 2 Those with more than .25 points were designated "C".

1-5. Front Brightness The intensity (intensity before normalization) in the regular transmission direction (0 degree) measured in 1-1 above was used as an alternative parameter of the front brightness. "A" means that the transmission intensity at 0 degree before normalization is 20 or more, "B" means 10 or more and less than 20, "C" means 5 or more and less than 10, and "D" means less than 5. did.

1-6. Interference unevenness The presence or absence of interference unevenness of the quantum dot sheets of Examples and Comparative Examples was visually observed under fluorescent lamp illumination. "A" indicates that no interference unevenness was observed, "B" indicates that slight interference unevenness was observed, and "C" indicates that severe interference unevenness was observed.

2. Production of Quantum Dots Referring to the method described in the technical document “Journal of American Chemical Society. 2007, 129, 15432-15433”, an InP / ZnS core-shell quantum dot having a peak wavelength of a fluorescence spectrum of 637 nm (quantum dot A ) And an InP / ZnS core-shell quantum dot (quantum dot B) having a peak wavelength of the fluorescence spectrum of 528 nm.
Next, the quantum dot A was added to a mixture of aminopolystyrene (manufactured by SMA, trade name: SMA EF80) and an epoxy resin (manufactured by Loctite, trade name: E-30CL) dissolved in a solvent. A polystyrene mixture was prepared. After evaporating the solvent of the mixture and further curing the mixture to obtain a cured product, the cured product is pulverized with a ball mill to form a quantum dot C in which the quantum dot A is coated with aminopolystyrene and an epoxy resin. Obtained. The same operation was performed on the quantum dots B to obtain quantum dots D in which the quantum dots B were coated with aminopolystyrene and epoxy resin.

3. Production of quantum dot sheet [Example 1]
A 20 nm-thick barrier layer made of silicon oxide was formed on one surface of a biaxially stretched PET film having a thickness of 12 μm by a PVD method to obtain a barrier film. Next, on one surface of a biaxially stretched PET film having a thickness of 50 μm, a light diffusion layer coating solution a1 having the following formulation is applied so that the thickness after drying becomes 11 μm, dried, and then irradiated with ultraviolet light to form a light diffusion layer. Was formed to obtain a light diffusion film. Next, a light diffusion film, a barrier film, and a biaxially stretched PET film having a thickness of 50 μm were laminated in the above-described order via an adhesive layer having a thickness of 3 μm to obtain a laminate A (see FIG. 3). The barrier film and the light-diffusing film were bonded together such that the surfaces on the biaxially stretched PET film side faced each other. Next, a laminate B was obtained by the same operation as described above.
Next, on the biaxially stretched PET film side surface of the laminate A, a quantum dot-containing layer coating solution b1 having the following formulation is applied so as to have a thickness after drying of 100 μm, and then dried. A layer was formed.
Next, the quantum dot-containing layer not irradiated with ionizing radiation and the surface of the laminate B on the side of the biaxially stretched PET film are laminated to face each other, and ultraviolet light is irradiated from the light diffusion layer side of the laminate A to ionize radiation. The curing of the curable resin composition was advanced to obtain a quantum dot sheet of Example 1.

<Light diffusion layer coating liquid a1>
・ 30 parts of pentaerythritol triacrylate (manufactured by Nippon Kayaku Co., Ltd., KAYARAD-PET-30)
・ 70 parts of urethane acrylate (UV1700B, manufactured by Nippon Synthetic Chemical Company)
・ 5 parts of photopolymerization initiator (Irgacure 184, manufactured by BASF)
・ 0.1 part of silicone leveling agent (TSM4460, manufactured by Momentive Performance Materials)
・ 100 parts of urethane resin-based diffusion particles (average particle diameter 3 μm)
・ 500 parts of diluting solvent

<Quantum dot containing layer coating solution b1>
・ 100 parts of isononyl acrylate (monofunctional monomer, refractive index 1.45)
・ 5 parts of photopolymerization initiator (Irgacure 184, manufactured by BASF)
・ Quantum dot A 0.2 parts ・ Quantum dot B 0.2 parts ・ Diluent 5 parts

[Example 2]
A quantum dot sheet of Example 2 was obtained in the same manner as in Example 1 except that the addition amount of the urethane resin-based diffusion particles in the light diffusion layer coating liquid a1 was changed to 80 parts.

[Example 3]
The amount of the urethane resin-based diffusion particles in the light diffusion layer coating solution a1 was changed to 5 parts, the thickness of the light diffusion layer was changed to 3 μm, and the internal scattering particles (spherical alumina, spherical alumina, A quantum dot sheet of Example 3 was obtained in the same manner as in Example 1, except that 20 parts of an average particle diameter of 1.5 μm and a refractive index of 1.76) were added.

[Comparative Example 1]
Comparative Example 1 was prepared in the same manner as in Example 1, except that 20 parts of internal scattering particles (spherical alumina, average particle diameter 1.5 μm, refractive index 1.76) were added to the quantum dot-containing layer coating solution b1. A quantum dot sheet was obtained.

[Comparative Example 2]
Comparative Example 2 was prepared in the same manner as in Example 1 except that 20 parts of internal scattering particles (spherical zirconia, average particle diameter 0.1 μm, refractive index 2.2) were added to the quantum dot-containing layer coating solution b1. A quantum dot sheet was obtained.

[Comparative Example 3]
Laminates A and B were obtained in the same manner as in Example 1 except that the light diffusion layer coating solution a1 was changed to the following light diffusion layer coating solution a2, and the thickness of the light diffusion layer was changed to 2 μm. Next, on the light diffusion layers of the laminate A1 and the laminate B1, the following overcoat layer coating solution c1 is applied so that the thickness after drying becomes 120 nm, dried, and irradiated with ultraviolet rays to form an overcoat layer. The laminate A1 and the laminate B1 were obtained. Next, on the biaxially stretched PET film side surface of the laminate A1, a quantum dot-containing layer coating solution b2 having the following formulation is applied so that the thickness after drying becomes 100 μm, and dried, and the acrylic polyol and the isocyanate are completely removed. An unreacted quantum dot-containing layer was formed.
Next, the quantum dot-containing layer and the biaxially stretched PET film-side surface of the laminate B1 were laminated to face each other, and subjected to aging treatment at 50 ° C. for one week to allow the reaction between the acrylic polyol and the isocyanate to proceed. 3 quantum dot sheets were obtained.

<Light diffusion layer coating liquid a2>
・ 30 parts of pentaerythritol triacrylate (manufactured by Nippon Kayaku Co., Ltd., KAYARAD-PET-30)
・ 70 parts of urethane acrylate (UV1700B, manufactured by Nippon Synthetic Chemical Company)
・ 5 parts of photopolymerization initiator (Irgacure 184, manufactured by BASF)
・ 0.1 part of silicone leveling agent (TSM4460, manufactured by Momentive Performance Materials)
・ 5 parts of urethane resin-based diffusion particles (average particle diameter 3 μm)
・ 500 parts of diluting solvent

<Quantum dot-containing layer coating solution b2>
・ 162 parts of acrylic polyol (manufactured by DIC, Acridic A-807, solid content 50%)
-Isocyanate 32 parts (Mitsui Chemicals, Takenate D110N, solid content 60%)
0.4 parts of quantum dot C 0.4 parts of quantum dot D 400 parts of diluent solvent

<Overcoat layer coating solution c1>
・ 1 part of UV curable resin (KAYARAD-PET-30 manufactured by Nippon Kayaku Co., Ltd.)
-0.2 parts of photopolymerization initiator (Irgacure 127, manufactured by BASF)
・ 0.1 part of leveling agent (Seika Beam 10-28 (MB), manufactured by Dainichi Seika Kogyo Co., Ltd.)
・ 90 parts of diluent solvent

[Comparative Example 4]
Comparative Example 4 was performed in the same manner as in Example 1 except that 20 parts of internal scattering particles (spherical styrene beads, average particle diameter 3.0 μm, refractive index 1.59) were added to the quantum dot-containing layer coating solution b1. Was obtained.

[Comparative Example 5]
A quantum dot sheet of Comparative Example 5 was obtained in the same manner as in Example 1, except that the addition amount of the urethane resin-based diffusion particles in the light diffusion layer coating liquid a1 was changed to 0 part.

4. Production of backlight and liquid crystal display device A commercially available liquid crystal display device (diagonal 7 inches) using a blue LED as a light source was disassembled, and the backlight was taken out. The backlight was of an edge light type, and had a reflection plate below the light guide plate, a light diffusion film above the light guide plate, and two prism sheets. The two prism sheets had lower and upper stripe lines perpendicular to each other.
The light diffusion film was removed from the backlight, and the quantum dot-containing sheets of Examples 1 to 3 and Comparative Examples 1 to 5 were arranged between the light guide plate and the prism sheet. ~ 5 backlights were obtained.
Then, the backlights of Examples 1 to 3 and Comparative Examples 1 to 5 were returned to the places where the backlight of the disassembled liquid crystal display device was installed, and the liquid crystal display devices of Examples 1 to 3 and Comparative Examples 1 to 5 were returned. I got

  As is clear from the results in Table 1, the front-side luminance of the quantum dot sheets, the backlights, and the liquid crystal display devices of Examples 1 to 3 were higher than those of Comparative Examples 1 to 5. Thus, it is possible to improve the balance between the tint of the edge region and the angle dependence of the tint.

10: quantum dot-containing layers 21a, 21b, 31a, 31b, 41a, 41b: light-transmitting substrates 30a, 30b: barrier films 32a, 32b: barrier layers 40a, 40b: light diffusion films 42a, 42b: light diffusion layer 51a , 51b, 52a, 52b: adhesive layer 61: laminate A
62: laminate B
100: quantum dot sheet 110: light source 120: optical plate 130: reflector 140: prism sheet 200: backlight 210: liquid crystal panel 220: holder 300: liquid crystal display

Claims (7)

A quantum dot sheet, wherein the quantum dot sheet has a quantum dot-containing layer containing a binder resin and a quantum dot that absorbs primary light and emits secondary light, and the quantum dot sheet further comprises a light diffusion layer. The light diffusion layer contains diffusion particles, and irradiates a visible light with a halogen lamp (12 V, 48 W) as a light source vertically to any one surface of the quantum dot sheet; A quantum dot sheet that satisfies at least one of the following conditions A-1 and B-1 when the intensity of transmitted light is measured every degree within a range of -85 degrees to +85 degrees.
<Condition A-1>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -30 degrees to + 30 degrees when upon the _{P 30,} less than 50 _{P 30} is 15 or more.
<Condition B-1>
The absolute value of α is not less than 1 degree and less than 30 degrees, where α is a diffusion angle indicating an intensity half of the maximum value. The quantum dot sheet according to claim 1, further satisfying the following condition A-2.
<Condition A-2>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -45 degrees to + 45 degrees when upon the _{P 45,} less than 60 _{P 45} 20 or more. The quantum dot sheet according to claim 1, further satisfying the following condition A-3.
<Condition A-3>
The sum of the intensity of the maximum value of the intensity of the transmitted light of -85 degrees to + 85 degrees to 1 and normalized -60 degrees to + 60 degrees when upon the _{P 60,} less than 75 _{P 60} 25 or more. The quantum dot sheet according to any one of claims 1 to 3, further satisfying the following condition B-2.
<Condition B-2>
The absolute value of β is 3 degrees or more and less than 45 degrees, where β is a diffusion angle indicating an intensity of １ ／ of the maximum value.   The quantum dot sheet according to any one of claims 1 to 4, wherein both surfaces of the quantum dot-containing layer are sandwiched between light transmissive substrates. A back comprising: at least one light source that emits primary light; an optical plate disposed adjacent to the light source for guiding or diffusing light; and a quantum dot sheet disposed on a light exit side of the optical plate. A backlight according to claim 1, wherein the quantum dot sheet is the quantum dot sheet according to any one of claims 1 to 5 . A liquid crystal display device comprising a backlight and a liquid crystal panel, wherein the backlight is the backlight according to claim 6 .