JP2014199377A - Anisotropic diffusion sheet and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anisotropic diffusion sheet having good diffusion capability and to provide a manufacturing method for the same.SOLUTION: An anisotropic diffusion sheet 10 has a diffusion functional layer 11 having a continuous phase and dispersion phases which have a different refractive index from that of the continuous phase, an average aspect ratio greater than 1, and longitudinal directions thereof aligned to a single direction. When an angle αH is defined as an average of absolute values of two angles at which gain becomes half a peak gain in a direction which is parallel to a sheet surface and in which diffusion is most effective, and an angle αL is defined as an average of absolute values of two angles at which the gain becomes half the peak gain in a direction in which diffusion is least effective, a ratio αH/αL satisfies 3≤αH/αL≤5.

Description

  The present invention relates to an anisotropic diffusion sheet having anisotropic diffusion characteristics and a method for producing the anisotropic diffusion sheet.

  Diffusion sheets that are used in various screens and displays and have a function of diffusing light are known. In addition to the isotropic diffusion characteristics of this diffusion sheet, those having anisotropy are widely used for the purpose of obtaining an effect such as an improvement in viewing angle (for example, see Patent Document 1).

JP 2004-221916 A

  In such a diffusion sheet having anisotropy, it is manufactured by a method such as adding a diffusion material such as an oval shape, a needle shape, or a rod shape to a resin as a base material and orienting these diffusion materials in one direction. Things are widely used. However, there is a problem that it is difficult to select or adjust a diffusing material having such a shape as to obtain diffusion characteristics having desired anisotropy.

  The subject of this invention is providing the manufacturing method of the anisotropic diffusion sheet which has favorable spreading | diffusion performance, and an anisotropic diffusion sheet.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.
Invention of Claim 1 is an anisotropic diffusion sheet provided with the diffusion functional layer (11) in which the diffusing action which diffuses light has anisotropy, and the diffusion functional layer includes a continuous phase having a refractive index difference and A gain in a direction in which the average aspect ratio of the dispersed phase is greater than 1, the major axis is oriented in one direction, parallel to the sheet surface, and has a maximum diffusion effect Is the average of the absolute values of the two angles at which the gain is ½ of the peak gain and the angle αH, and the average value of the absolute values of the two angles at which the gain in the direction in which the diffusion action is minimum is ½ of the peak gain Is an anisotropic diffusion sheet (10) characterized in that the ratio αH / αL satisfies 3 ≦ αH / αL ≦ 5.
Invention of Claim 2 is the manufacturing method of the anisotropic diffusion sheet of Claim 1, Comprising: The extrusion process which melt-extrudes the mixture of the at least 2 sort (s) of resin which has incompatibility, and shape | molds a sheet | seat, After the extrusion step, the sheet is stretched in one direction, the dispersed phase is stretched in the one direction, and the stretching step is oriented in the one direction. is there.
The invention of claim 3 is the method for producing an anisotropic diffusion sheet according to claim 2, wherein the at least two types of incompatible resins have a refractive index difference between 0.001 and 0.2. It is a manufacturing method of the anisotropic diffusion sheet characterized by using what becomes the following.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the anisotropic diffusion sheet which has favorable diffusion performance, and an anisotropic diffusion sheet can be provided.

It is a figure explaining anisotropic diffusion sheet 10 of an embodiment. It is a figure explaining the diffusion functional layer 11 of embodiment. It is a figure explaining an example of the manufacturing method of anisotropic diffusion sheet 10 of an embodiment.

Embodiments of the present invention will be described below with reference to the drawings. In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
Moreover, although words, such as a sheet | seat, are used, these are used in order of a board | plate, a sheet | seat, and a film in order of the thickness as a general usage. However, such proper use has no technical meaning and can be replaced as appropriate.
Furthermore, numerical values such as dimensions and material names of each member described in the present specification are examples of the embodiment, and the present invention is not limited thereto, and may be appropriately selected and used.
In this specification, terms that specify shapes and geometric conditions, for example, terms such as parallel and orthogonal, and the like mean strictly, and also include a state having an error that can be regarded as parallel or orthogonal. .

(Embodiment)
FIG. 1 is a diagram illustrating an anisotropic diffusion sheet 10 of the present embodiment.
FIG. 1A is a plan view of the anisotropic diffusion sheet 10, and FIG. 1B is parallel to the straight line A1-A2 shown in FIG. It is the figure which expanded a part of cross section parallel to thickness.
The anisotropic diffusion sheet 10 is an optical member used for display devices such as various screens and displays.
In FIG. 1, the normal direction (thickness direction) of the sheet surface of the anisotropic diffusion sheet 10 is the z direction, and two directions parallel to the sheet surface and orthogonal to each other are an x direction and a y direction. Here, it is assumed that the sheet surface indicates a surface in the planar direction of the sheet when viewed as the entire sheet. In the present embodiment, in order to facilitate understanding, the x direction and the y direction are assumed to be parallel to the lateral side and the longitudinal side of the anisotropic diffusion sheet 10 shown in FIG. .

The anisotropic diffusion sheet 10 has a diffusing action for diffusing light. The diffusion characteristics of the anisotropic diffusion sheet 10 have anisotropy, and the diffusion action for light incident from the normal direction to the sheet surface of the anisotropic diffusion sheet 10 is the diffusion action in the y direction. Rather, the diffusion effect in the x direction is greater.
The anisotropic diffusion sheet 10 has a laminated structure including a diffusion functional layer 11 having a diffusion action and support layers 12 and 13 integrally laminated on both surfaces thereof.

FIG. 2 is a diagram for explaining the diffusion functional layer 11 of the present embodiment. In FIG. 2, a part of the diffusion functional layer 11 as viewed from the z direction is schematically shown.
The diffusion functional layer 11 is a layer having a function of diffusing light. The diffusion functional layer 11 has a diffusion action having the anisotropy as described above.
The diffusion functional layer 11 is formed of two types of resins having a difference in refractive index and having incompatibility that do not melt together. These two types of incompatible resins have a structure in which the respective resins exist independently as a continuous phase (sea phase) and a dispersed phase (island phase) in the diffusion functional layer 11 (so-called sea / island structure). It has become. In order to facilitate understanding, in FIG. 2, the dispersed phase (island phase) is indicated by a broken line.
The diffusion function layer 11 is preferably about 40 to 100 μm in thickness from the viewpoint of realizing diffusion characteristics having sufficient anisotropy.

These two types of incompatible resins are transparent thermoplastic resins. Examples of the two types of incompatible resins include polyolefin resins, polyester resins, acrylic resins, polystyrene resins, polycarbonate resins, and copolymers thereof.
Examples of the polyolefin resin include polyethylene resin, polypropylene resin, polybutene resin, polypentene resin, polymethylpentene resin, cyclic polyolefin resin, and copolymers thereof.
Of these two types of incompatible resins, one type is preferably a polyolefin resin, and more preferably two types are polyolefin resins.

Of the two types of incompatible resins, the resin that forms the sea phase preferably has a higher composition ratio than the resin that forms the island phase.
Of the two types of incompatible resins, the resin that forms the island phase preferably has a lower melt viscosity and a higher melt flow rate than the resin that forms the sea phase.
Furthermore, the resin that forms the island phase preferably has lower rigidity than the resin that forms the sea phase.
By adopting the above-described configuration, a stable sea / island structure can be formed.
In addition, when the composition ratio of two types of incompatible resins is equal, a higher melt flow rate tends to form a sea phase.
Two types of incompatible resins may be appropriately selected according to the above-described tendency and desired optical performance.
Moreover, it is preferable that the blending ratio of these two types of incompatible resins is about 20:80 to 80:20 in mass ratio.

These two types of incompatible resins preferably have a refractive index difference of about 0.001 to 0.2 in order to obtain a light diffusing action. The difference in refractive index between the two types of resins is more preferably about 0.005 to 0.06, and further preferably about 0.01 to 0.05.
When the refractive indexes of the two types of resins are less than 0.001, a sufficient diffusing action cannot be exhibited. Further, when the refractive index difference between the two types of resins is 0.2 or more, the diffusion effect is too large, and the total amount of light transmitted through the anisotropic diffusion sheet 10 is reduced. It is not suitable as an optical member used in a display device. Therefore, the above range is preferable.

  Further, these two types of incompatible resins form the sea / island structure as described above in the diffusion functional layer 11. At this time, the island phase is not spherical but has a size in the y direction larger than that in the x direction when viewed from the z direction, and is oriented in the y direction. Examples of such shapes include needles, rods, and spheroids. Thereby, the diffusion functional layer 11 realizes a diffusion action having anisotropy that the light diffusion action in the direction (x direction) orthogonal to the island phase orientation direction (y direction) is larger.

The average length L1 of this island phase in the y direction (major axis direction) is about 0.15 to 200 μm, and more preferably about 2 to 100 μm. The average length L2 of the island phase in the x direction (short axis direction) is about 0.1 to 10 μm, and more preferably about 0.7 to 2 μm.
The ratio (aspect ratio) L1 / L2 between the average dimension of the island phase in the y direction (major axis direction) and the average dimension in the x direction (minor axis direction) is preferably in the range of 1.5 to 1000, More preferably, it is about 1.5-50, More preferably, it is about 1.5-10. By setting such an aspect ratio, the degree of anisotropy can be increased.

The diffusion functional layer 11 exhibits diffusion characteristics having anisotropy with respect to light incident from the normal direction (z direction) of the sheet surface. In this embodiment, since it has the above-described sea / island structure, the light diffusing direction is the x direction, and the light diffusing direction is the y direction.
Here, with respect to the light incident from the normal direction (z direction) of the sheet surface, in the direction in which light is most diffused (x direction), the angle at which the gain becomes 1/2 of the peak gain is αH, and the light is most When the angle at which the gain is ½ of the peak gain in the non-diffusion direction (y direction) is αL, the ratio αH / αL of these angles indicates the anisotropy of the diffusion characteristics of the diffusion function layer 11. It becomes a diffusion anisotropy value.
The angles αH and αL are average values of absolute values since there are two angles at which the gain is ½ of the peak gain in each direction. Here, the angle at which the peak gain can be obtained is 0 ° (the normal direction of the sheet surface).

Generally, in various screens and displays, it is preferable that the viewing angle in the horizontal direction of the screen is about three times wider than the vertical direction of the screen. In addition to the anisotropic diffusion sheet 10, an optical sheet having diffusion performance (an optical sheet that diffuses isotropic light such as a surface mat layer) is used in combination with various screens and displays. There are many. Therefore, the anisotropic diffusion sheet 10 preferably has a diffusion anisotropy value αH / αL satisfying 3 ≦ αH / αL ≦ 5, and 3.5 ≦ αH from the viewpoint of realizing a good viewing angle. It is more preferable to satisfy /αL≦4.5.
Further, in this anisotropic diffusion sheet 10, the angles αH and αL satisfy αH> 10 ° and αL> 3 °, which is used for display devices such as various screens and displays, and realizes a good viewing angle. From the viewpoint of

The support layers 12 and 13 are layers that support the diffusion function layer 11 described above, facilitate film formation, and impart sufficient rigidity as an optical sheet.
The support layers 12 and 13 are transparent resin sheet-like members.
Examples of the material of the support layers 12 and 13 include polyolefin resins, polyester resins, acrylic resins, polystyrene resins, polycarbonate resins, and copolymers thereof. Examples of the polyolefin resin include polyethylene resins, polypropylene resins, polybutene resins, polypentene resins, polymethylpentene resins, cyclic polyolefin resins, and copolymers thereof.
The support layers 12 and 13 support the diffusion functional layer 11 to facilitate the formation of the diffusion functional layer 11 and give sufficient rigidity as the anisotropic diffusion sheet 10. It is preferable to have a thickness and rigidity that can be achieved.

By using the anisotropic diffusion sheet 10 having the support layers 12 and 13 as described above, the following effects can be expected in addition to the effects of providing rigidity as the sheet as described above.
When the diffusion functional layer 11 is formed as a single layer, the island phase may adhere to a roll used for transporting this layer because the adhesion between the island phase and the sea phase is small. Therefore, by laminating the support layers 12 and 13 on both sides of the diffusion functional layer 11, such adhesion can be prevented and stable production can be achieved.
In addition, by providing the support layers 12 and 13, when the anisotropic diffusion sheet 10 is wound or laminated and stored, the island phase is prevented from being transferred to the adjacent diffusion function layer 11, or diffused. Adhesion (blocking) between the functional layers 11 can be prevented.
Furthermore, compared with the case where the diffusion functional layer 11 is formed as a single layer and is uniaxially stretched, the uniaxial stretching with the support layers 12 and 13 laminated can increase the aspect ratio of the dispersed phase and is higher. Optical anisotropy can be imparted.

(Production method)
FIG. 3 is a diagram illustrating an example of a method for manufacturing the anisotropic diffusion sheet 10 of the present embodiment.
The anisotropic diffusion sheet 10 of the present embodiment is formed by extrusion molding in a state where the three layers of the support layers 12 and 13 and the diffusion functional layer 11 are integrally laminated by a melt extrusion molding method.
The manufacturing apparatus 70 shown in FIG. 3 includes melt extruders 71 and 72, a distribution block 73, a die (multimanifold die) 74, a cooling roll 75, a peeling roll 76, a take-up roll 77 (77a, 77b), and the like. This is an apparatus capable of producing a sheet of a two-kind three-layer structure.

The material B that forms the support layers 12 and 13 is charged into the melt extruder 71, melted, and sent to the distribution block 73.
The material A forming the diffusion functional layer 11 is charged into the melt extruder 72, melted, and sent to the distribution block 73. The material A forming the diffusion functional layer 11 is charged into the melt extruder 72 and melted in the state of a mixture of two types of incompatible resins.
The material A and the material B are distributed inside the distribution block 73 so that the layer of the material B is arranged on both sides of the layer of the material A and sent to the die 74. And with the die | dye 4, the layer of the material B is laminated | stacked integrally on both sides of the layer of the material A, is integrated as a 3 layer structure, and is discharged in sheet form.

At this time, the temperatures of the materials A and B in the melt extruders 71 and 72 and the die 74 are set to predetermined temperatures. This temperature is set higher than the melting points of the material A and the material B. The melting point temperature of the material B is lower than the melting point temperature of the material A. Therefore, when extruded from the die 74, the material B has a higher fluidity than the material A.
Since the material A can form a structure (so-called sea / island structure) in which two types of incompatible resins are present independently as a continuous phase and a dispersed phase (so-called sea / island structure), Compared with molten resin in molding, fluidity is low and film formation is difficult.
However, since the layer of the material B having a higher fluidity is laminated on both sides of the layer of the material A, the film is easily formed.

The sheet-like resin laminate C pushed out from the die 74 abuts on the cooling roll 75 and is cooled and solidified. At this time, the resin laminate C may be pressed against the cooling roll 75 by a not-shown pressing roll or the like.
The resin laminate C cooled by the cooling roll 75 is wound around the peeling roll 76 and peeled off from the cooling roll. A configuration in which a plurality of cooling rolls are further provided downstream of the cooling roll 75 may be employed.

Next, the resin laminate C is uniaxially stretched in the transport direction by the take-up roll 77. At this time, the conveyance speed at the take-up roll 77 is faster than the conveyance speed at the cooling roll 75. The draw ratio is preferably 1.5 times or more, and may be appropriately set according to the desired optical performance and the aspect ratio of the island phase. By this stretching, the island phase in the layer of material A is stretched in the stretching direction and oriented in the stretching direction. Thereby, the diffusion functional layer 11 can exhibit an anisotropic diffusion action.
And the resin laminated body C is further cooled and solidified, and is cut | judged to a predetermined dimension, and the anisotropic diffusion sheet 10 is formed.

The cooled and solidified resin laminate C may be uniaxially stretched in the transport direction by passing between two nip rollers (not shown) having different speeds while heating to a predetermined temperature with a heater (not shown). At this time, the downstream nip roller has a higher conveying speed than the upstream nip roller. In addition, when extending | stretching with an extending | stretching apparatus, it is good also considering the extending | stretching direction of the resin laminated body C as a direction (width direction) orthogonal to a conveyance direction according to the structure of the apparatus.
In addition, the two types of incompatible resins used as the material A forming the diffusion functional layer may be mixed in advance and charged into the melt extruder 72, or may be mixed and melted when charged into the melt extruder 72. You may mix in the extruder 72 inside.

  According to this embodiment, it can be set as the anisotropic diffusion sheet which exhibits the favorable diffusion anisotropy which can be used suitably for display apparatuses, such as various screens and a display. Moreover, according to this embodiment, such an anisotropic diffusion sheet can be manufactured easily.

(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the scope of the present invention.
(1) The incompatible resin forming the diffusion functional layer 11 may be three or more types. You may increase the kind of resin to mix according to the optical performance to require.
Moreover, you may mix | blend various additives, such as a dispersion diameter regulator for improving the familiarity of resin to mix, antioxidant, and an antistatic agent, with the material which forms the diffusion functional layer 11. FIG.

(2) The two types of incompatible resins that form the diffusion functional layer 11 are not limited to the sea / island structure, and may have a structure that forms a co-continuous phase.

(3) The anisotropic diffusion sheet 10 may have a form including any one of the support layers 12 and 13, or a form not including the support layers 12 and 13 as long as it has sufficient rigidity. It is good.

DESCRIPTION OF SYMBOLS 10 Diffusion sheet 11 Diffusion functional layer 12,13 Support layer 70 Manufacturing apparatus 71,72 Melt extruder 73 Distribution block 74 Die 75 Cooling roll 76 Peeling roll 77 Take-off roll

Claims (3)

An anisotropic diffusion sheet comprising a diffusion functional layer having a diffusion function of diffusing light and having anisotropy,
The diffusion functional layer is
A continuous phase having a refractive index difference and a dispersed phase;
The average aspect ratio of the dispersed phase is greater than 1, the major axis direction is oriented in one direction,
Gain in the direction that minimizes the diffusion effect, with the average of the absolute values of the two angles that are parallel to the sheet surface and the gain in the direction that maximizes the diffusion effect is ½ of the peak gain, and the angle αH When the average value of the absolute values of the two angles at which is 1/2 of the peak gain is the angle αL, the ratio αH / αL is
3 ≦ αH / αL ≦ 5
Meeting,
An anisotropic diffusion sheet characterized by It is a manufacturing method of the anisotropic diffusion sheet according to claim 1,
An extrusion process in which a sheet is formed by melt-extruding a mixture of at least two types of incompatible resins;
After the extrusion step, the sheet is stretched in one direction, the dispersed phase is stretched in the one direction, and the stretching step is oriented in the one direction;
A method for producing an anisotropic diffusion sheet characterized by the above. In the manufacturing method of the anisotropic diffusion sheet according to claim 2,
The at least two kinds of resins having incompatibility use those having a refractive index difference of 0.001 or more and 0.2 or less,
A method for producing an anisotropic diffusion sheet characterized by the above.

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