JP5281812B2 - Prism sheet - Google Patents

Description

  The present invention relates to a backlight prism sheet used in a liquid crystal display device.

  As a backlight for illuminating a transmissive liquid crystal display from the back, there are an edge light system and a direct system. The edge light system is a system in which light from a light source disposed on an end surface of a light guide plate is extracted in a front direction from a main surface orthogonal to the end surface by the light guide plate. In the direct method, as disclosed in Patent Document 1, a plurality of light sources are arranged on the back surface of the apparatus, light is incident on the diffusion sheet, light is uniformized by the diffusion sheet, and light is emitted to the emission surface facing the incident surface. It is a method to take out.

  There is an increasing demand for large-sized image display devices in monitors for televisions and personal computers. For backlights used in large-sized image display devices, the direct method, which is advantageous in terms of brightness improvement and uniformity, has become the mainstream. ing. The direct type backlight includes a reflector, a light source, a diffusion sheet, a prism sheet, and the like from the back side. The reflection plate has a function of reflecting light emitted from the light source to the back side in the front direction. The diffusion sheet has a function of diffusing light to reduce the appearance of the image of the light source and making the in-plane luminance uniform. As disclosed in Patent Document 2, the prism sheet has a function of converting diffused light into appropriate directivity.

  A plurality of sheets for controlling these viewing angles may be used as disclosed in Patent Document 3 for the purpose of further improving the luminance and separately controlling the left and right and upper and lower viewing angles.

  When a plurality of sheets are used in this way, there is a problem that handling when assembling the backlight becomes complicated. To solve this problem, as disclosed in Patent Document 4, a configuration in which a diffusion sheet and a viewing angle control sheet are bonded is proposed.

  As the light source, a fluorescent light that is a linear light source or a point light source such as a light emitting diode (LED) arranged in a plane is used.

FIG. 1 shows a typical prism sheet structure. In the figure, 11 is a transparent medium substrate, and 12 is a prism formed on the surface. Each prism consists of two sides, and the apex angle is 2θ _{p as} shown. Even when the apex of the prism 12 is rounded, when the intersection of the extensions of the two sides is 13, the angle appearing at the intersection 13 is called the apex angle. As the medium base material, polycarbonate resin or polystyrene resin is usually used.

A problem in such a configuration, in the case where the average prism frequency f ₀ and the frequency (pixel arrangement frequency) f _p and is close to the liquid crystal of the pixel array of prisms, and the ratio of the two is an integer, mutual interference There was a problem that a moire interference pattern due to the occurrence of.

  In Patent Document 5, as an arrangement pattern configuration example of a prism sheet, the prism sheet is configured by repeating a first prism zone having a first average prism frequency and a second prism zone having a second average prism frequency. Has been.

  Patent Document 6 describes that at least two groups of prisms having a certain height at which the peak portion or the valley bottom portion of the prism sheet is different are arranged adjacent to each other.

Patent Document 7 describes that moire interference is reduced by making a prism meander in a curved shape instead of a linear shape and randomly arranging the prisms.
Japanese Patent Laid-Open No. 2-17 JP 62-144102 A JP-A-9-197109 JP 2005-221619 A Japanese National Patent Publication No. 11-501149 Special table 2000-508786 JP-T-2002-504698

The prism sheet of Patent Document 5 and 6, when the average prism frequency f ₀ and is close to the pixel array frequency f _p, in the case where the pixel arrangement frequency f _p and the repetition period becomes consistent, or a simple integer ratio In some cases, mutual interference moire interference occurs.

  The prism sheet of Patent Document 7 is difficult to manufacture at low cost by extrusion roll molding. This is because, as is well known, it is assumed that the shape of the roll type of the extrusion roll is a parallel straight line. In addition, the fact that the basic period of the array pattern is limited to 40 times or less of the prism drop is also a limiting factor.

  It is also conceivable to randomize the prism array with random numbers. However, simply randomizing may make it difficult to manufacture a portion where the pitch is too small. A similar pitch may happen by several consecutive pitches, and moire may occur at that portion.

  An object of this invention is to provide the prism sheet which is excellent in the moire interference reduction effect and can be manufactured cheaply.

The prism sheet according to the present invention is
A prism sheet for a backlight of a liquid crystal display,
A plurality of prisms are provided on the exit surface or the entrance surface, and the apex angles of the two hypotenuses constituting each row of the prisms are formed to be (2π / 360) × 70 rad or more (2π / 360) × 110 rad or less,
Average prism frequency of the prism substantially equal to the frequency f ₀ of the 0th,
The arrangement phase of the prisms is given by a pattern having at least a first fundamental frequency f ₁ and phase modulated with a phase modulation index φ,
the absolute value of the difference between any integral multiple of f ₀ and _{f 1} is greater than or equal to 0.15 times the _{f 1,}
And φ> 0.5,
In addition, φ × f ₁ is selected to be smaller than 0.5 × f ₀ . With this configuration, the moire interference reduction effect is excellent, and it can be manufactured at low cost.

の解として得られるX（n）の値とし、
θ_pをプリズム頂角の半角として、厚み方向座標成分Y（n）は、

を満たすように選定されることが好ましい。 The pattern having the first basic frequency f ₁ and phase-modulated by the phase modulation index φ is sinusoidal, and the two-dimensional position coordinates (X (n), Y The creeping direction coordinate component X (n) of (n)) is defined as n = 1, 2, 3,.

The value of X (n) obtained as a solution of
With θ _p as the half angle of the prism apex angle, the thickness direction coordinate component Y (n) is

It is preferable to select so as to satisfy.

At this time, the following approximate expression can be used as the solution of Equation 1 above.

の解として得られるX（n）の値とし、
θ_pをプリズム頂角の半角として、厚み方向座標成分Y（n）は、

を満たすように選定されることが好ましい。 Or, when a triangular wave function connecting crests and peaks of a cosine wave with a straight line is denoted as triang (X), the pattern having the _first fundamental frequency f ₁ and phase-modulated by the phase modulation index φ is triang (X). And the creeping direction coordinate component X (n) of the two-dimensional position coordinate (X (n), Y (n)) of the extended intersection of the two hypotenuses is n = 1, 2, 3 ... as consecutive integers

The value of X (n) obtained as a solution of
With θ _p as the half angle of the prism apex angle, the thickness direction coordinate component Y (n) is

It is preferable to select so as to satisfy.

At this time, the following approximate expression can be used as the solution of Equation 4 above.

Here, the ratio f ₀ / f ₁ should be selected as an irrational number, not a rational number. It can be avoided that the phase value of the average prism frequency and the phase value of the modulation frequency are exactly the same combination again.

Further, the first fundamental frequency _{f 1} and the pixel array frequency _{f p,} it is preferable that the relation of _{f p <f 1 <20 ×} f p holds.

  ADVANTAGE OF THE INVENTION According to this invention, the prism sheet which is excellent in a moire interference reduction effect and can be manufactured cheaply can be provided.

  An embodiment of a prism sheet according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. In addition, for clarity of explanation, the following description and drawings are simplified as appropriate.

<Embodiment 1>
A prism sheet 1 according to a first embodiment of the present invention will be described with reference to FIGS. In addition, the prism sheet 1 of this invention is not restricted to a sheet-like thing, A film-like thing is also contained.

  As shown in the conceptual diagram of FIG. 1, the prism sheet 1 is formed by arranging the prisms 12 in parallel on the surface of the transparent medium substrate 11, and the apex angle of each of the two oblique sides constituting each row of the prisms 12 is 70. It is formed in the range of ° ((2π / 360) × 70 rad) to 110 ° ((2π / 360) × 110) rad.

  As shown in FIG. 2, the prism sheet 1 is disposed on the light emission side of the light source side diffusion sheet 16, and the reflector 14, the light source 15, the light source side diffusion sheet 16, and the prism sheet 1 constitute a backlight.

  The light emitted from the light source 15 and the light reflected by the reflecting plate 14 enter the light source side diffusion sheet 16. This light is diffused by the light source side diffusion sheet 16, and the in-plane luminance is made uniform. The directivity of the light diffused by the light source side diffusion sheet 16 is almost Lambertian and enters the prism sheet 1. The prism sheet 1 converts the directional characteristics of incident light into a front-enhanced type and emits it to a liquid crystal panel (not shown).

ここで、Xは位置座標、ａ_ｎは第ｎ次波の振幅、ｆ_ｐは画素配列周波数である。 Next, the moire interference reducing action that is a feature of the present invention will be described.
In general, the pixel arrangement pattern g _p (X) of the liquid crystal can be expressed by a Fourier series as follows.

Here, X is the position coordinates, a _n is the amplitude of the n-th order wave, f _p is the pixel array frequency.

ここで、ｆ_０は平均プリズム周波数（第０の周波数）、ｆ_１は位相変調周波数（第１の基本周波数）、φは位相変調指数(ｒａｄ)、Ｒｅ（）は実部抽出記号、Ｊ_ｋは第1種k次のベッセル関数である。つまり、プリズム１２の配列位相は、少なくとも位相変調周波数ｆ_１を有し、位相変調指数φにて位相変調された模様によって与えられる。 On the other hand, the pattern g _z (X) of the average prism frequency component of the prism arrangement can be expressed by a Fourier series as follows.

Here, f ₀ is an average prism frequency (0th frequency), f ₁ is a phase modulation frequency (first fundamental frequency), φ is a phase modulation index (rad), Re () is a real part extraction symbol, J _k Is the kth-order Bessel function of the first kind. That is, the arrangement phase of the prisms 12 is given by a pattern having at least the phase modulation frequency f ₁ and phase-modulated by the phase modulation index φ.

For example, the phase modulation index φ is selected to be approximately 1.44. Then, as can be understood from FIG. 3, J ₀ (1.44) ≈J ₁ (1.44) ≈J ₋₁ (1.44) ≈0.55, and after J ₂ 0.26 Because of the following, it can be relatively ignored. Therefore, g _z (X) can be expressed by the following approximate expression.

In Equation 9, the amplitude of each wave can be attenuated by 0.55 times by distributing the prism spectrum to three waves having different frequencies. Therefore, even when the average prism frequency f ₀ is an integer multiple of the pixel arrangement frequency f _p , the moire spectrum amplitude caused by the interference between both can be attenuated to 0.55 times. Therefore, the occurrence of moire interference can be reduced.

In the prism sheet of the present embodiment, the value of the phase modulation index φ is limited to a range of φ> 0.5. In the case of φ = 0.5, J ₀ (0.5) ≈0.94, so that the degree of modulation of the prism pitch becomes small, and if it is 0.5 or less, the effect of the present invention cannot be expected.

Further, in the prism sheet of this embodiment, the product of φ and f ₁ is selected so as to be smaller than 0.5 × f ₀ . The reason is that the local frequency f (X) of the prism array is less than half of the average prism frequency f ₀ , that is, the local pitch of the prism array is more than twice that of the average prism, and the ratio to the pixel pitch becomes small and moire. This is to prevent the occurrence of interference. Further, the local frequency f (X) of the prism array is more than twice the average prism frequency f ₀ , that is, the local pitch of the prism array is less than half of the average prism, and the pitch is too fine, making the molding difficult. It is for preventing.

The local frequency f (X) of the prism array is obtained as follows by differentiating the exponent phase of Equation 8 by j2πX. Therefore, it is understood that φ × f ₁ represents the frequency shift.

Furthermore, in the prism sheet of the present embodiment, the absolute value of the difference between the average prism frequency f ₀ of the prism array and an arbitrary integer multiple of the phase modulation frequency f ₁ is selected to be 0.15 times or more of f ₁ . . Therefore, even if at the case where the pixel arrangement frequency _{f p} and the phase modulation frequency _{f 1} is met, the phase of one pixel period before and after the prism array, or 0.15Cycle, i.e. 54 ° ((2π / 360) × 54 rad), the occurrence of a zero beat moire pattern can be avoided.

の解として得られるX（n）の値とし、 Further, in the prism sheet of the present embodiment, in order to keep the thickness of the prism sheet substantially constant regardless of the prism local frequency, the prism sheet has the phase modulation frequency f ₁ and the phase at the phase modulation index φ. The modulated pattern is made into a sine wave, and the creeping direction coordinate component X (n) of the two-dimensional position coordinate (X (n), Y (n)) of the two oblique sides of each prism is n = 1, 2, 3 is a continuous integer,

The value of X (n) obtained as a solution of

を満たすように選定されている。本実施形態のプリズムシートは、この様に厚みが実質的に一定に保たれ、しかもプリズムが直線状配列であるため、押出ロール成形方式によって廉価に製造することができる。 With θ _p as a half angle of the prism apex angle, the thickness direction coordinate component Y (n) is substantially

It is selected to satisfy. The prism sheet of the present embodiment can be manufactured at a low cost by an extrusion roll forming method because the thickness is kept substantially constant as described above and the prisms are linearly arranged.

FIG. 4 shows a cross-sectional pattern of the prism array when f ₀ / f ₁ = 10.6 is selected as a representative example. In the figure, the unit of the horizontal axis is shown with the reciprocal of the average prism frequency, that is, the average period as a unit.

As more specific numerical examples, the phase modulation frequency f ₁ = ₁ cycle / mm and the average prism frequency f ₀ = 10.6 cycle / mm. Corresponding pixel arrangement frequency _{f p} is within 6cycle / mm.

この数１３は、数１１に代入して検算すれば判る通り、φ＜＜２πが成立する場合の数１１の第1次近次式である。 <Embodiment 2>
The following approximate expression can be used as the solution of Equation 11 in the first embodiment.

As can be understood from substituting into Equation 11 for verification, Equation 13 is the first-order approximation of Equation 11 when φ << 2π holds.

<Embodiment 3>
In the first embodiment, the formula 11 may be replaced with the formula 14, and the formula 12 may be replaced with the formula 15, that is, the cosine wave shape in the formulas 11 and 12 may be replaced with a triangular wave shape. However, the triangular wave function that connects the crests and valleys with straight lines is denoted as triang (X). The graph is shown in FIG.

<Embodiment 4>
The following approximate expression can be used as the solution of Equation 14 in the second embodiment.

The integration result Int (n) of the integral term of this equation can be expressed using the maximum integer that does not exceed the Gaussian integer symbol [Z] = Z as shown in Equation 17. Here, sign (U) is a selection function that becomes 1 only when U derived by Equation 18 is zero or positive, and becomes zero when U is negative. The graph is shown in FIG.

As a representative example, FIG. 7 shows a cross-sectional pattern of the prism arrangement when the phase modulation index φ by the triangular wave function is 1.44 and f ₀ / f ₁ = 10.6 is selected. In the figure, the unit of the horizontal axis is shown with the reciprocal of the average prism frequency, that is, the average period as a unit.

<Embodiment 5>
It is preferable to select the f ₀ / f ₁ ratio not as a rational number but as an irrational number.

As understood from the form of the exponent part of Equation 18, in this embodiment, by selecting the f ₀ / f ₁ ratio as an arbitrary irrational number rather than a rational number, the phase value of the average prism frequency and the modulation frequency It is possible to avoid the exact same combination again with the phase value. That is, it is possible to avoid the repetition of the same pattern in principle regardless of how many prism sheets have a high number of cycles.

Further, in order to reduce the moire disorder, the first fundamental frequency _{f 1} and the pixel array frequency _{f p,} it is preferable that the relationship holds configuration of _{f p <f 1 <20 ×} f p.

  As will be understood from the above description, according to the present invention, at least one of the average prism frequency and the modulation frequency can always be kept in a non-integer ratio relationship with an arbitrary pixel frequency. Therefore, the same prism sheet can be shared by a wide range of screen size displays having various pixel arrangement periods.

  In the above description, the description has been made on the assumption that the entire width of one prism sheet is an array pattern that can be expressed by the equation having the set of parameters described above. However, it is obvious that the formula having different parameters for each section may be applied by dividing the entire width of one prism sheet into several partial widths. Accordingly, the scope of the present invention naturally includes such modifications.

It is the fragmentary perspective view which showed the prism sheet schematically. It is explanatory drawing which showed the structure of the backlight. It is the figure which showed the Bessel function. FIG. 3 is a diagram illustrating a cross-sectional pattern of the prism array according to the first embodiment. It is the graph which showed the triangular wave function which connected the mountain and valley of the cosine wave with the straight line. It is the graph which showed the integration result Int (n). FIG. 6 is a diagram illustrating a cross-sectional pattern of a prism array according to a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Prism sheet 11 Transparent medium base material 12 Prism 13 Intersection part 14 Reflecting plate 15 Light source f ₀ 0th frequency (average prism frequency)
f ₁ First fundamental frequency (phase modulation frequency)
pixel arrangement frequency f _p LCD φ phase modulation index

Claims (7)

A prism sheet for a backlight of a liquid crystal display,
A plurality of prisms are provided on the exit surface or the entrance surface, and the apex angles of the two hypotenuses constituting each row of the prisms are formed to be (2π / 360) × 70 rad or more (2π / 360) × 110 rad or less,
Average prism frequency of the prism substantially equal to the frequency f ₀ of the 0th,
Sequence phase of the prism, by repeating function to have at least a first fundamental frequency f _1, is given by the phase-modulated pattern in the amplitude of the phase modulation index phi,
the absolute value of the difference between any integral multiple of f ₀ and _{f 1} is greater than or equal to 0.15 times the _{f 1,}
And φ> 0.5,
And a prism sheet selected so that φ × f ₁ is smaller than 0.5 × f ₀ . The pattern having the first basic frequency f ₁ and phase-modulated by the phase modulation index φ is sinusoidal, and the two-dimensional position coordinates (X (n), Y ( The creeping direction coordinate component X (n) of n)) is defined as n = 1, 2, 3,.

The value of X (n) obtained as a solution of
With θ _p as the half angle of the prism apex angle, the thickness direction coordinate component Y (n) is

The prism sheet according to claim 1, wherein the prism sheet is selected so as to satisfy. The prism sheet according to claim 2, wherein the following approximate expression is used as the solution of Equation 1:

When a triangular wave function connecting crests and peaks of a cosine wave with a straight line is denoted as triang (X), the pattern having the _first fundamental frequency f ₁ and phase-modulated by the phase modulation index φ is integrated with triang (X). The creeping direction coordinate component X (n) of the two-dimensional position coordinate (X (n), Y (n)) of the extended intersection of the two oblique sides is n = 1, 2, 3,. As a continuous integer,

The value of X (n) obtained as a solution of
With θ _p as the half angle of the prism apex angle, the thickness direction coordinate component Y (n) is

The prism sheet according to claim 1, wherein the prism sheet is selected so as to satisfy. The prism sheet according to claim 4, wherein the following approximate expression is used as the solution of Equation 4:

The prism sheet according to any one of claims 1 to 5, wherein the ratio f ₀ / f ₁ is selected as an irrational number instead of a rational number. The first basic frequency f ₁ and the pixel array frequency f _p have a relationship of f _p <f ₁ <20 × f _p , according to any one of claims 1 to 6. Prism sheet.

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