JP2003195007A - Lens array forming method and optical film or sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens array forming method for forming a lens array where a plurality of particulates having translucency are arrayed in a single layer on the surface of base material having translucency, and forming the accurate lens array where the particulates are arrayed in the single layer very densely for optical film or sheet having the lens array formed by the lens array forming method, and the optical film or sheet having the lens array formed by the lens array forming method. <P>SOLUTION: This method has a cushion layer forming stage 1, a coating stage 2, a heating and pressuring stage 4, and a solidifying stage 5, and the stage 2 is a stage to coat the surface of the cushion layer with coating liquid adjusted so that the amount of solidified binder after performing the stage 5 shows a volume ratio being 1 to 30% to the total amount of the particulates and set so that the contact angle of a droplet to the surface of the cushion layer is ≤30°. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention has a lens array forming method for forming a lens array in which a plurality of fine particles are arranged in a single layer on a surface of a substrate, and a lens array formed by such a lens array forming method. Optical film or sheet.

[0002]

2. Description of the Related Art Conventionally, the above lens array has been used as a light diffusion sheet or a brightness enhancement sheet in electronic display materials and screen materials.

As a lens array forming method for forming such a lens array, a method described with reference to FIG. 1 is known.

FIG. 1 is a diagram for explaining a conventional method for forming a lens array.

As shown in FIG. 1A, when the spherical fine particles P are arranged on the surface of the base material B in order to form a lens array, a gap S is formed between the arranged fine particles P, which is desired. The optical characteristics of may not be obtained. Therefore,
In order to fill the gap S, a method of filling the lower part of the fine particles P in the cushion layer C is known. In this method, as shown in FIG. 1 (b), a cushion layer C is formed on the surface of the base material B, and the fine particles P are directly scattered and arranged on the action layer C, and then pressure is applied. Then, the lower part of the fine particles P is embedded in the cushion layer C.

[0006]

However, as the particle size becomes smaller, the particles tend to fly up when the particles are sprayed, and it becomes difficult to uniformly arrange the particles on the surface of the substrate.

Therefore, a method has been proposed in which fine particles are dispersed in a solvent containing a binder, a solvent in which the fine particles are dispersed is applied, and then dried. In the method of applying the solvent containing the binder, as shown in FIG. 1C, the gap generated between the arranged fine particles P is filled with the binder J. However, if the amount of the binder J is too small with respect to the amount of the fine particles P, the gap is not completely filled and desired optical characteristics cannot be obtained. On the contrary, if the amount of the binder J is too large with respect to the amount of the fine particles P, the viscosity of the binder J becomes high before the fine particles P settle on the surface of the base material B to be arranged, and the fine particles P settle down slowly. As shown in FIG. 1 (d), the fine particles P may overlap with each other and may not be arranged in a single layer.

In view of the above circumstances, the present invention provides a lens array forming method capable of forming a highly accurate lens array in which fine particles are arranged in a single layer at high density, and a lens formed by such a lens array forming method. It is intended to provide an optical film or sheet having an array.

[0009]

The lens array forming method of the present invention for achieving the above object is a lens array forming method for forming a lens array in which a plurality of fine particles are arranged in a single layer on the surface of a substrate. First step of forming a cushion layer on the surface of the material, and second step of applying a coating liquid in which a plurality of fine particles are dispersed in a solvent containing a binder to the surface of the cushion layer formed on the surface of the base material and drying the same. And a third step of embedding the lower part of the fine particles in the coating liquid of the cushion layer coated with the coating liquid in the cushion layer, and fixing the fine particles on the cushion layer with the lower part of the fine particles embedded in the cushion layer. The second step comprises adjusting the volume of the binder in the liquid applied to the surface of the cushion layer to a volume ratio of 1 to 30% with respect to the total amount of the fine particles. Is, the lens array forming method, wherein the contact angle of the droplet with respect to the surface of the cushioning layer is a step of applying a 30 degrees or less of the coating liquid.

In the lens array forming method of the present invention, since the lower part of the fine particles is embedded in the cushion layer in the third step, it is arranged even if the amount of the binder contained in the solvent is smaller than that in the case without the cushion layer. It is possible to completely fill the gaps generated between the fine particles, and it is difficult for the fine particles to overlap with each other, which is likely to occur when the binder amount is increased. In addition, since the coating liquid has good wettability with respect to the surface of the cushion layer, the fine particles easily spread until they settle on the surface of the base material and are arranged, and from this point also, it is difficult for the fine particles to overlap each other. As a result, the lens array forming method of the present invention can form a highly accurate lens array in which fine particles are arranged in a single layer at high density.

In the lens array forming method of the present invention, the cushion layer is a thermoplastic polymer, and in the third step, the cushion layer coated with the coating solution is heated to form the cushion layer. It may be a step of embedding the lower part of the fine particles in the applied coating liquid in the cushion layer.

In the lens array forming method of the present invention, a surfactant capable of improving wettability is added to the dispersion liquid containing fine particles, or the fine particles have a circularity of 90% or more and an average particle diameter. Is preferably in the range of 1 to 30 μm.

The optical film or sheet of the present invention which achieves the above object is characterized by having a lens array formed by the lens array forming method of the present invention.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

The present embodiment is a method for producing an optical sheet having a lens array in which a plurality of light-transmitting beads are arranged in a single layer, to which the lens array forming method of the present invention is applied.

FIG. 2 is a flowchart outlining the steps of the optical sheet manufacturing method of this embodiment.

As shown in FIG. 2, the optical sheet manufacturing method of this embodiment is roughly divided into a cushion layer forming step 1, a coating step 2, a drying step 3, and a heating and pressing step 4.
And solidifying step 5.

First, the cushion layer forming step 1 is a step of forming a cushion layer on the surface of the base material. Therefore, the cushion layer forming step 1 is the first step in the present invention.
Corresponds to the process. The coating step 2 is a step of coating the coating liquid on the surface of the cushion layer formed on the base material. The coating liquid applied in this step is a plurality of beads dispersed in a solvent containing a binder. Therefore, this coating step 2 corresponds to the second step in the present invention. The drying step 3 is a step of drying the coating liquid applied by performing the coating step 2.

FIG. 3 is a diagram schematically showing a state of the base material from immediately after the application of the coating solution to the surface of the cushion layer to the completion of drying.

FIG. 3 (a) schematically shows a state on the substrate immediately after the coating step is performed. As shown in FIG. 3A, a large number of beads P are dispersed in the solvent of the coating liquid A applied to the surface of the cushion layer C formed on the base material B. When the coating liquid A is applied to the cushion layer C, the wettability of the coating liquid A with respect to the cushion layer C causes the coating liquid A on the cushion layer C to start to spread in the horizontal direction on the surface of the cushion layer C. The beads P start to settle on the surface of the cushion layer C. FIG. 3B schematically shows a state on the base material immediately after the drying process is started. When the drying process is started, the solvent evaporates rapidly and the sedimentation of the beads P is also promoted. FIG. 3C schematically shows a state on the substrate some time after the drying process is started. As shown in FIG. 3C, the solvent has considerably evaporated, and a large number of beads P have begun to be arranged in a single layer without overlapping each other. FIG. 3D schematically shows a state on the base material after the drying process is completed, and a partially enlarged view enlarging a range surrounded by a dashed line in the figure is shown in the lower left. ing. On the surface of the cushion layer C, the solvent is completely evaporated, and a large number of beads P are arranged in a single layer without any space. Further, the binder J contained in the solvent is solidified on the surface of the cushion layer C, and the solidified binder J fixes the lower part of the beads P arranged in a single layer and arranges the arranged beads P.
The lower part of the gap S generated between them is filled.

The heating / pressurizing step 4 shown in FIG.
In the step performed after the step of heating, both the cushion layer and the binder solidified in the drying step are softened by heating, and further, the softened state is pressed to form a single-layer array. This is a step of embedding the lower portion of the beads in the cushion layer. Therefore, the heating / pressurizing step 4 corresponds to the third step in the present invention.

FIG. 4 shows that after the heating and pressurizing step is performed,
It is a figure which shows the mode on a base material typically.

By carrying out this heating and pressing step, the lower part of the beads P arranged in a single layer is embedded in the cushion layer C, and as a result, the softened binder J is generated between the arranged beads P. The upper part of the gap is completely filled. In the solidification step 5 shown in FIG. 2, the softened cushion layer C is solidified while the lower part of the beads P is embedded, and the softened binder J is formed in the upper part of the gap between the arranged beads P. Is a step of fixing the beads P to the cushion layer C by solidifying the beads P in a completely filled state. Therefore, this solidifying step 5 corresponds to the fourth step in the present invention. When this solidifying step 5 is completed,
The optical sheet having the lens array is completed. The completed optical sheet has a highly precise lens array because the beads are arranged in a single layer with high density and the gaps formed between the arranged beads are completely filled with the cushion layer and the binder. It has become a thing.

In this embodiment, the heating and pressing step is performed after the drying step. However, the heating and pressing step is performed first, the drying step is performed after the heating and pressing step, and the drying step is solidified. You may make it serve also as a process.

Next, each of the base material, the cushion layer, and the coating liquid used in the method of manufacturing the optical sheet of this embodiment will be described in detail.

First, the raw material of the base material is not particularly limited, and a raw material having a desired light transmittance is selected according to the application of the optical sheet to be manufactured. When the optical sheet to be produced is used as a retroreflective sheet or a light diffusing sheet, a transparent base material is generally used. The transparent base material is usually made of glass or plastic, but it is preferable to use flexible and lightweight plastic as a raw material. Examples of polymers used for plastics include cellulose polyester, cellulose polyether, polycarbonate, polystyrene, polyacrylate, polymethacrylate, polysulfone, polyester, polyethylene, polyvinyl alcohol and norpornene resin.
It is preferable to use any one polymer of cellulose ester (eg cellulose triacetate), polyester (eg polyethylene terephthalate), polycarbonate, polyvinyl alcohol, polysulfone and polyether sulfone. The thickness of the base material is not particularly limited, but is preferably 25 to 350 μm, more preferably 30 to 310 μm, and most preferably 45 to 200 μm. preferable. When a base material thinner than 25 μm is used, the base material may curl due to the influence of the binder in the coating liquid described later. In such a case, it is preferable to provide a curl prevention layer on the surface opposite to the surface on which the coating liquid is applied. The anti-curl layer is preferably formed of the same polymer as the polymer forming the binder described later. The base material is obtained by dissolving the polymer constituting the base material in a solvent and forming a film of the solution. Examples of the film forming method include a known solution film forming method and a melt casting method, but are not limited thereto. In the solution casting method, a polymer solution is cast on a casting belt to form a substrate as a polymer film. In the melt casting method, the polymer resin is heated, melted, and cast. When film-forming the base material,
Additives may be mixed with the polymer solution or melted polymer resin. Examples of additives include plasticizers, ultraviolet absorbers, lubricants, deterioration inhibitors, dispersants, dyes, pigments,
Examples include, but are not limited to, defoaming agents, lubricants, browning inhibitors, preservatives and the like. The additive may be added during the step of forming the base material into a film.

The cushion layer formed on the surface of the base material is made of a permeable thermoplastic resin that does not react with the base material. Specifically, urethane resins and the like are preferable. Note that the material is not limited to the thermoplastic resin, and may be a material that is softened by irradiation with light. Also, like the base material,
When the manufactured optical sheet is used for a retroreflective sheet or a light diffusing sheet, the cushion layer is also generally transparent. The refractive index of such a transparent cushion layer is
In order to make the light transmittance of the optical sheet to be manufactured uniform, it is most preferable that it is the same as the refractive index of the base material. However, it is preferable that the amount is less than 0.2, and it is more preferable that the amount is less than 0.1. Further, when the optical sheet to be produced is used as a light diffusion sheet, it is preferable that the difference between the refractive index of the cushion layer and the refractive index of the beads embedded in the cushion layer is a certain value or more. Specifically, the ratio of both refractive indices is preferably 0.95 or less or 1.05 or more, and 0.83 or less or 1.15.
More preferably, it is more than 0.71 and most preferably 0.71 or less or 1.25 or more. Furthermore,
Although the layer thickness of the cushion layer is not particularly limited, it is a parameter that controls the amount of embedding in the lower portion of the bead together with the pressing force. The layer thickness of such a cushion layer is, for example, about 6 μm.

Next, the coating liquid is obtained by dispersing a plurality of transparent beads in a solvent containing a binder. Moreover, a surfactant is added to the coating liquid. In addition to the surfactant, any additive may be added.

The raw material of the beads is not particularly limited, like the raw material of the base material, and a raw material having a desired light transmittance is selected according to the use of the optical sheet to be produced. When the optical sheet to be produced is used as a retroreflective sheet or a light diffusing sheet, transparent beads are generally used. Glass or plastic is usually used as a raw material for the transparent beads, but it is preferable to use glass as a raw material in terms of light transmittance and durability. As the shape of the beads is closer to a sphere, the beads are more uniformly arranged on the base material, which is preferable in terms of optical characteristics. Specifically, the roundness is preferably 90% or more. The particle diameter of the beads is determined according to the application of the optical sheet to be produced, but if the particle diameter of the beads is too small, it becomes difficult to arrange the beads at a high density, and if it is too large, the resolution as an optical sheet decreases. Therefore, the average particle diameter of the beads is preferably 1 to 30 μm, more preferably 2 to 20 μm.
When the manufactured optical sheet is used as a light diffusion sheet of a liquid crystal display device, beads smaller than liquid crystal pixels (matrix) must be used.

As the solvent, a solvent that dissolves the binder and uniformly disperses the beads and does not react with the beads is used. Specifically, water or an organic solvent can be used. Examples of the organic solvent include aliphatic hydrocarbons (eg, pentane, hexane, heptane, octane,
Isooctane, cyclohexane, etc.), aromatic hydrocarbons (eg, benzene, toluene, xylene, etc.), halogenated hydrocarbons (eg, methyl chloride, methylene chloride, carbon tetrachloride, trichloroethane, etc.), alcohols (eg, methanol, industrial tanol) , Isopropyl alcohol, n-butyl alcohol, etc.), ketones (eg, acetone, methyl ethyl ketone, etc.), esters (eg, methyl formate, ethyl formate, methyl acetate, ethyl acetate, etc.) and mixtures thereof. It is not limited to the solvent used.

As described above, the binder is mixed in the solvent in order to fix the beads to the cushion layer by solidifying them while completely filling the upper gaps formed between the arranged beads. As such a binder, a natural or synthetic polymer can be used. For example, cellulose ester, cellulose ether, polycarbonate, polystyrene, polyacrylate, polymethacrylate, polysulfone, polyester, polyethylene,
Examples include, but are not limited to, polyvinyl alcohol, gelatin, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyurethane, polypropylene and norbornene resins. A known polymer that is an adhesive may be used as the binder. Further, like the refractive index of the cushion layer, the refractive index of the binder is most preferably the same as the refractive index of the base material in order to make the optical transmittance of the optical sheet to be manufactured uniform, and even if it is different. , The difference in refractive index between the two is 0.5
It is sufficient to control the amount to less than 0.2, preferably less than 0.2, and more preferably less than 0.1. Furthermore, when the optical sheet to be produced is used as a light diffusion sheet, the relationship between the refractive index of the binder and the refractive index of the beads fixed by the binder is the relationship between the refractive index of the cushion layer and the refractive index of the beads. The same is preferable.

Further, it is necessary to adjust the amount of the binder so that the amount of the solidified binder after the solidification step shown in FIG. 2 becomes 1 to 30% with respect to the total volume of the beads dispersed in the coating liquid. There is. If it is less than 1%, that is, if the amount of the binder is too small with respect to the total volume of the beads, the upper part of the gap generated between the arranged beads cannot be completely filled, and the desired optical characteristics cannot be obtained. The beads cannot be fixed to the cushion layer, and the beads are detached from the cushion layer. On the other hand, if it is higher than 30%, that is, if the amount of the binder is too much with respect to the total volume of the beads, it takes time to settle the beads as described with reference to FIG. 3, and the beads settle on the cushion layer surface. Before arranging, the viscosity of the binder becomes high and the sedimentation of beads becomes dull,
Beads overlap each other. Furthermore, the amount of the binder after solidification is preferably 2 to 15%, and more preferably 3 to 10%, based on the total volume of the beads dispersed in the coating liquid.

The surfactant is added in order to improve the wettability of the coating liquid. As described with reference to FIG. 3, when the coating liquid is applied to the cushion layer, the coating liquid on the cushion layer starts to spread in the horizontal direction of the cushion layer due to the wettability of the coating liquid with respect to the cushion layer. The beads inside begin to settle on the surface of the cushion layer. Therefore, the better the wettability of the coating liquid, the less likely the beads will overlap. In this embodiment, the contact angle of the droplet of the coating liquid with respect to the cushion layer surface is 30 degrees or less,
A surfactant is added. If the contact angle of the liquid droplets of the coating liquid with respect to the cushion layer surface is 30 degrees or less without adding the surfactant, the addition of the surfactant is unnecessary.

Next, with reference to FIG. 5, a line for carrying out each step after the coating step shown in FIG. 2 on the base material on which the cushion layer is formed will be described.

FIG. 5 is a diagram showing a simplified state of the line during the execution of each step after the coating step shown in FIG.

A delivery roll 100 and a take-up roll 200 are provided on the line 10 shown in FIG. Further, a coating device 300 for carrying out a coating process is provided on a transport path R connecting the delivery roll 100 and the winding roll 200.
A coating roll 400 that determines the coating position, a drying chamber 500 that performs the drying process, and a nip device 600 that performs the heating and pressing process are provided. The transport route R
In addition, drive rolls and pass rolls are also deployed.

A cushion layer is already formed on the surface of the base material treated in the line 10 having such a structure.
Hereinafter, the base material on which the cushion layer is formed is referred to as a cushion layer forming base material CS. The cushion layer forming base material CS is a long sheet-like material. This cushion layer forming base material CS
Is set on the delivery roll 100 in a state of being wound into a roll and is conveyed in the direction of the arrow in the figure. The conveyance speed of the cushion layer forming base material CS may be in a known conveyance speed range, and specifically, in the range of 1 to 100 m / min, an optical sheet of good quality can be obtained with good productivity. The cushion layer forming base material CS delivered from the delivery roll 100 is conveyed while being wound around the coating roll 400.

The coating device 300 is a device that coats the coating liquid on the cushion layer surface of the cushion layer forming base material CS. The coating device 300 is a device that employs a slide coating method and includes a tank 301, a pump 302, a coating head 303, and a hopper (not shown). Tank 3
In 01, a solvent in which a binder and a surfactant are dissolved is stored, and a stirring blade (not shown) is provided. The hopper (not shown) is for adding beads to the tank,
The beads added from the hopper are uniformly dispersed in the solvent by stirring with a stirring blade in the solvent in the tank, and the coating liquid is adjusted. The coating liquid thus adjusted is sent to the coating head 303 by the pump 302. The delivery amount of the coating liquid at this time may be in any range as long as it is a known delivery amount. However, the delivery amount of the coating liquid is determined by the wet coating thickness T (μm) of the coating liquid.
When converted into, it is possible to arrange the beads in a single layer and a high density on the cushion layer in the following range,
preferable. Assuming that the average volume concentration of the beads contained in the coating solution is C (%) and the average diameter of the beads is D (μm), when the beads are arranged in the closest single layer on the cushion layer, T = 100πD / 3√3C, and when the beads are arranged in a square lattice on the cushion layer, T = 100π
It becomes D / 6C. When the wet coating thickness T is adjusted to fall within this range, the beads can be arranged on the cushion layer in a single layer and at high density. Specifically, the wet coating thickness T of the coating liquid is preferably 20 to 80 μm.

The coating head 303 has a slide surface 3031 on which the sent coating liquid is extruded and flows down.
The coating head 303 applies the coating liquid flowing down the slide surface onto the cushion layer surface of the cushion layer forming base material CS wound around the coating roll 400.
Apply from a predetermined application position close to. The coating apparatus 300 shown in FIG. 5 is for coating one type of coating solution, but may be a coating apparatus for coating two or more types of coating solutions in multiple layers, and further, an extrusion coating method or a dip coating method. A device that employs a spin coating method or a spin coating method may be used.

The cushion layer forming base material CS on which the coating liquid is applied to the cushion layer is conveyed to the drying chamber 500. In the drying chamber 500, the coating liquid applied to the cushion layer is air-dried or heat-dried to evaporate the solvent and the beads are arranged in a single layer on the cushion layer as shown in FIG. Also, the binder contained in the solvent solidifies on the surface of the cushion layer, and the solidified binder fixes the lower part of the beads arranged in a single layer and the lower part of the gap formed between the arranged beads. Is buried.

The cushion layer forming base material CS that has left the drying chamber 500 is conveyed to the nip device 600. The nip device 600 is a device in which a pair of nip rolls 601 and 602 are arranged to face each other. Nip rolls 601 and 602
Has a heating function. The cushion layer-forming base material CS that has been conveyed has the set of nip rolls 60.
It is sent between No. 1 and 602 and heated and pressurized by each nip roll. As a result, both the cushion layer and the binder solidified in the drying chamber are softened, and the lower portion of the beads arranged in a single layer is embedded in the cushion layer as shown in FIG.

The cushion layer forming base material CS that has passed through the nip device 600 is naturally cooled in the transport path R while being wound up by the winding roll 200. The natural cooling in the transport route R corresponds to the solidifying step shown in FIG. 2, the softened cushion layer solidifies while the lower part of the beads is embedded, and the softened binder is the arranged beads. The beads are fixed to the cushion layer by solidifying while the upper part of the gap generated between them is completely filled. The optical sheet having the lens array is completed by such natural cooling in the transport path R and is wound up by the winding roll 200.

[0043]

EXAMPLES Examples to which the lens array forming method of the present invention is applied and comparative examples for comparison with the examples will be described below.

(Example 1) As the substrate, a sheet-like material made of polyethylene terephthalate (PET) having a thickness of 150 μm was used. The cushion layer was formed in advance by applying a urethane resin to the surface of such a base material. The thickness of the cushion layer formed on the surface of the base material is 6 μm
Met. Using such a cushion layer forming base material,
An optical sheet having a lens array was manufactured by the line 10 shown in FIG. The conveyance speed of the cushion layer-forming substrate in this line 10 was set to 20 m / min. As the beads, acrylic monodisperse particles (MX-1000 manufactured by Soken Chemical Co., Ltd.) having an average particle diameter of 10 μm and a specific gravity of 1.19 were used. A polyvinyl alcohol (PVA) solution was used as a binder, and the PVA solution and the surfactant were dissolved in a solvent and beads were dispersed to prepare a coating solution. The contact angle of the droplets of the coating liquid with respect to the surface of the cushion layer was 24 degrees when measured with a contact angle meter. P
The VA solution was adjusted to be 15% with respect to the total volume of the dispersed beads. The heating temperature by each nip roll of the nip device was 100 ° C., and a load of 1000 kg was applied by the nip device 600 to embed the lower part of the beads in the cushion layer, thereby manufacturing an optical sheet. The amount of solidified binder in the completed optical sheet is
It was 10% with respect to the total volume of the beads dispersed in the coating liquid.

(Example 2) An optical sheet was manufactured under the same conditions as in Example 1 except that the amounts of both the PVA solution and the surfactant dissolved in the solvent were different from those in Example 1. In this Example 2, the dissolved amount of both the PVA solution and the surfactant was set to be higher than that in Example 1. As a result, the contact angle of the liquid droplets of the coating liquid on the surface of the cushion layer was 22 degrees. The amount of the solidified binder in the completed optical sheet was 28% with respect to the total volume of the beads dispersed in the coating liquid.

Example 3 An optical sheet was manufactured under the same conditions as in Example 1, except that the amount of surfactant dissolved was different from that in Example 1. That is, in the third embodiment,
Unlike Example 2, the dissolution amount of the PVA solution was the same as that of Example 1, and the dissolution amount of the surfactant was smaller than that of Example 1. As a result, the amount of the solidified binder in the completed optical sheet was 10% as in Example 1 with respect to the total volume of the beads dispersed in the coating liquid, but the droplets of the coating liquid on the surface of the cushion layer. The contact angle was 28 degrees.

(Comparative Example 1) An optical sheet was manufactured under the same conditions as in Example 1 except that the dissolution amounts of both the PVA solution and the surfactant were different from those in Example 1. In Comparative Example 1, the dissolved amount of the PVA solution was made larger than the dissolved amount of any of the PVA solutions in Examples 1 to 3. Also,
The amount of the surfactant dissolved was the same as in Example 2. As a result, the contact angle of the liquid droplets of the coating liquid on the surface of the cushion layer was 22 degrees. Also, in the completed optical sheet,
The amount of the solidified binder was 32% with respect to the total volume of the beads dispersed in the coating liquid.

Comparative Example 2 An optical sheet was manufactured under the same conditions as in Example 1 except that the amount of surfactant dissolved was different from that in Example 1. That is, in Comparative Example 2,
Unlike Comparative Example 1, the dissolution amount of the PVA solution was the same as that of Example 1, and the dissolution amount of the surfactant was smaller than the dissolution amount of any of the surfactants in Examples 1 to 3. As a result, the amount of the solidified binder in the completed optical sheet was 10% as in Example 1 with respect to the total volume of the beads dispersed in the coating liquid, but the droplets of the coating liquid on the surface of the cushion layer. Had a contact angle of 32 degrees.

(Comparative Example 3) An optical sheet was manufactured under the same conditions as in Example 1 except that the amounts of both the PVA solution and the surfactant dissolved were different. In Comparative Example 3,
The dissolved amount of the PVA solution was made smaller than the dissolved amount of any of the PVA solutions in Examples 1 to 3. The amount of the surfactant dissolved was smaller than the amount of the surfactant dissolved in Example 1, but was larger than the amount of the surfactant dissolved in Example 3. As a result, the contact angle of the coating liquid droplets with respect to the cushion layer surface was 26 degrees. The amount of the solidified binder in the completed optical sheet was only 0.8% with respect to the total volume of the beads dispersed in the coating liquid.

The surface of the optical sheets manufactured in each of the examples and comparative examples described above on which the beads are arranged was observed with a microscope, and the surface condition was visually evaluated. In addition, image data representing an image of the surface was acquired, and the image data was analyzed by binarization using a personal computer. In this analysis, assuming that the entire area of the image based on the image data is 100, the ratio of the voids of the beads in the entire area is determined as the arranged porosity (%), and the total number of beads arranged in the entire area is 10%.
The ratio of beads arranged so as to be 0 was determined as the overlapping ratio (%). The smaller the arrangement porosity, the higher the density of the beads arranged, and the smaller the overlap ratio, the smaller the beads and the single beads arranged in a single layer.

Table 1 shows the results of each of the examples and comparative examples.

[0052]

[Table 1]

Table 1 shows each of the examples and the comparative examples.
Binder amount after solidification, contact angle, relative to the total volume of the beads,
The arrangement porosity (%), the overlapping ratio (%), and the in-plane evaluation are shown in horizontal rows. The surface evaluation was made by visual inspection, but when the beads could be observed to be arranged in a single layer without gaps, it was marked with ◎, and it was observed that the beads were arranged in almost a single layer without gaps. The samples were marked with O, and the samples were marked with a large number of gaps or overlaps between beads, and the samples were marked with X when the gaps or overlaps were very noticeable.

In the optical sheet manufactured according to Comparative Example 3, the beads were not fixed on the cushion layer and detached from the cushion layer. Therefore, the overlapping ratio shows the smallest value, but the arrangement porosity becomes the worst value due to the detachment of the beads. The optical sheet manufactured according to Comparative Example 3 as described above is also marked with X in the surface evaluation by visual observation.

On the other hand, the optical sheet produced in Example 1 has the smallest arrangement porosity, and the overlapping rate is also the smallest except for the optical sheet produced in Comparative Example 3 in which desorption of beads occurs. In addition, the most favorable evaluation ⊚ is also attached to the visual evaluation of surface condition. The optical sheets manufactured in each of Example 2 and Example 3 are inferior to the optical sheets manufactured in Example 1 in terms of the arrangement porosity and the overlapping rate, but when viewed together with the results of the surface condition evaluation, they are acceptable. It is within the range. From these facts, it can be said that the optical sheets manufactured in each of Examples 1 to 3 are optical sheets having a highly accurate lens array in which fine particles are arranged in a single layer at high density.

Comparing the results shown in Comparative Example 1 and Example 2 in Table 1, respectively, the contact angle was the same, but the binder amount was higher than that of the optical sheet manufactured in Example 2. There are more optical sheets manufactured according to Comparative Example 1. The optical sheet manufactured according to Comparative Example 1 has a higher optical sheet density than the optical sheet manufactured according to Example 2.
Both the arrangement porosity and the overlapping ratio are significantly deteriorated, and the result of the surface condition evaluation is marked with x. From this, Comparative Example 1
Then, since the amount of the binder was too large, it took time for the beads to settle, the viscosity of the binder increased before the beads settle on the cushion layer surface, and the sedimentation of the beads became dull, and the beads overlap each other, It can be said that voids of beads were generated in the manufactured optical sheet. Further, when comparing the results shown in Comparative Example 3 and Example 1 and Example 3 in Table 1, respectively, the contact angles are almost the same among the three, and the binder amount is the optical sheet manufactured by Example 1. And the optical sheet manufactured according to Example 3 is the same, whereas only the optical sheet manufactured according to Comparative Example 3 has an extremely small amount of binder. From this, it can be said that in Comparative Example 3, since the amount of the binder was too small, the arranged beads could not be fixed to the cushion layer, and the beads were detached from the cushion layer. From these, it is understood that the amount of the binder needs to be adjusted so that the amount of the binder after solidification is 1 to 30% with respect to the total volume of the beads.

Further, comparing the results shown in Comparative Example 2 and Example 1 and Example 3 in Table 1, respectively, the binder amounts are almost the same, but the contact angle is The coating liquid used in 1 was the smallest, and the coating liquid used in Comparative Example 2 was the largest. The optical sheet manufactured according to Comparative Example 2 has poorer arrangement porosity and overlapping rate than the optical sheets manufactured according to Example 1 and Example 3, respectively, and the result of the surface condition evaluation is Δ. Has been.
As described above, the optical sheet manufactured according to Example 1 has a better result than the optical sheet manufactured according to Example 3. From these facts, it can be said that the beads are more likely to overlap with each other as the contact angle is larger, and voids of the beads are more likely to occur in the manufactured optical sheet, and the contact angle of the droplet of the coating liquid with respect to the cushion layer surface is 30 degrees or less. Therefore, it is necessary to add a surfactant so that Further, as a result of further study on the contact angle, the present inventors have concluded that the contact angle is preferably 20 degrees or less.

[0058]

As described above, according to the present invention, a lens array forming method capable of forming a highly accurate lens array in which fine particles are arranged in a single layer at a high density, and such a lens array. An optical film or sheet having a lens array formed by the forming method can be provided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional method for forming a lens array.

FIG. 2 is a flowchart schematically showing each step of the optical sheet manufacturing method of the present embodiment.

FIG. 3 is a diagram schematically showing a state of the substrate from immediately after the application of the coating liquid to the surface of the cushion layer to the completion of drying.

FIG. 4 is a diagram schematically showing a state on the base material after the heating and pressing step is performed.

FIG. 5 is a simplified view showing a state of a line in which each step after the coating step shown in FIG. 2 is being performed.

[Explanation of symbols]

1 Cushion layer forming process 2 coating process 3 drying process 4 Heat and pressure process 5 Solidification process 10 lines 100 delivery roll 200 winding roll 300 coating device 400 coating roll 500 drying room 600 nip device R transport route CS cushion layer forming base material B base material C cushion layer P beads J binder S gap

Claims (5)

[Claims] 1. A lens array forming method for forming a lens array in which a plurality of fine particles are arranged in a single layer on a surface of a base material, comprising: a first step of forming a cushion layer on the surface of the base material; The second step of applying a coating liquid in which a plurality of fine particles are dispersed in a solvent containing a binder to the surface of the formed cushion layer and drying the coating liquid, and the lower part of the fine particles in the coating liquid of the cushion layer coated with the coating liquid. Is embedded in the cushion layer, and a fourth step of fixing the fine particles on the cushion layer in a state where the lower portion of the fine particles is embedded in the cushion layer, wherein the second step is the surface of the cushion layer. In addition, the amount of binder in the applied liquid is 1 to 30 with respect to the total amount of the fine particles.
%, And a step of applying a coating liquid having a contact angle of the liquid droplets with respect to the surface of the cushion layer of 30 degrees or less, the method of forming a lens array. 2. The cushion layer is a thermoplastic polymer, and in the third step, the cushion layer coated with the coating liquid is heated to remove the lower part of the fine particles in the coating liquid coated on the cushion layer. The lens array forming method according to claim 1, wherein the lens array is embedded in the cushion layer. 3. The lens array forming method according to claim 1, wherein a surfactant capable of improving wettability is added to the dispersion liquid containing fine particles. 4. The lens array forming method according to claim 1, wherein the fine particles have a circularity of 90% or more and an average particle diameter of 1 to 30 μm. 5. An optical film or sheet having a lens array formed by the lens array forming method according to claim 1. Description: