JP5471047B2 - Light diffusion film - Google Patents

Description

  The present invention relates to a light scattering material, and more specifically, light having a light diffusion layer that can be suitably used for a member intended to diffuse light, such as a lighting cover, a lighting signboard, various displays, or a transmission screen. It relates to a diffusion film.

  Conventionally, a light diffusing film having a light diffusing layer has been used in a lighting cover, a lighting signboard, various displays, a transmissive screen, and the like to uniformly spread light from a light source and enhance visibility. For example, in a liquid crystal display device equipped in a personal computer, a mobile phone, a digital camera, etc., a light diffusion film is arranged between the backlight and the liquid crystal display element, so that the light of the backlight is uniformly distributed over the entire display. It is spreading.

  As an example, FIG. 1 shows a general configuration around a backlight of a liquid crystal display device. The light emitted from the light source 2 passes through the light guide plate 3 and the reflection plate 4 and is uniformly diffused and passed in the plane direction by the light diffusion film 1 and guided to the liquid crystal display element unit 5 disposed above the diffusion film.

  FIG. 2 shows a configuration of a general light diffusion film. A light diffusion layer composed of a light diffusing agent 7 and a transparent binder resin 8 is laminated on one side of a transparent substrate 6 (for example, Patent Document 1). As the substrate 6, a resin film made of a transparent resin such as polyethylene terephthalate, polycarbonate, polystyrene, acrylic resin, acetyl cellulose, or a transparent inorganic material such as glass is used. The light diffusing agent is fine particles made of glass, acrylic resin, styrene resin, MS resin (styrene / methyl methacrylate copolymer), silicone resin, etc. The binder is acrylic, polyester resin, silicone resin, epoxy resin, etc. Is used. Usually, a light diffusion film is arrange | positioned so that the surface where the light-diffusion layer is not laminated | stacked turns into the surface at the side of a light source.

  Moreover, the laminated body 9 is formed on the other surface of the light diffusion film for several purposes. Specifically, an antireflection layer (Patent Document 2) that prevents reflection of light from the light guide plate, an anti-blocking layer (Patent Documents 3, 4, and 5) that prevents adhesion with the light guide plate, and prevents damage to the light guide plate. There is a damage prevention layer (Patent Document 6).

  In recent years, a light diffusion film for a backlight of a liquid crystal display, a film used for a light extraction layer in organic EL illumination, and the like are required to have both high light transmittance and high diffusion rate. However, when trying to increase the light transmittance (total light transmittance), the amount of light diffusing agent has to be reduced, so the light diffusivity decreases. The addition amount of the diffusing agent must be increased, and as a result, the total light transmittance is lowered.

JP 2008-250129 A JP-A-10-239504 JP 2006-126822 A JP 2007-286166 A Utility Model No. 2529650 International Publication No. 03/032074 Pamphlet

  An object of the present invention is to provide a light diffusing film which is excellent in both light transmittance and light diffusivity, and can be suitably used for a light source device of various displays, illumination use, and the like.

（ただし、Ｔ_Ｆ→Ｂ、Ｈ_Ｆ→Ｂは光拡散層を積層した面から光を入射したときの全光線透過率ＴおよびヘイズＨをそれぞれ表し、Ｔ_Ｂ→Ｆ、Ｈ_Ｂ→Ｆは光拡散層を積層した面の裏側から光を入射したときの全光線透過率ＴおよびヘイズＨをそれぞれ表す。） The present invention is a light diffusing film in which a light diffusing layer containing a light diffusing agent comprising polyamide porous particles is laminated on a transparent substrate, and the content of the light diffusing agent in the light diffusing layer is 25 to 60% by weight. The light diffusion film is characterized in that the change rate ΔT% of the total light transmittance defined by the following formula is 1 or more and the change rate ΔH% of the haze is 0.5 or more.

(Where T _{F → B} and H _{F → B} represent the total light transmittance T and haze H when light is incident from the surface on which the light diffusion layers are laminated, respectively, and T _{B → F} and H _{B → F} represent light. The total light transmittance T and haze H when light is incident from the back side of the surface on which the diffusion layers are laminated are shown.)

  The polyamide porous particles used in the present invention are temporarily uniform by mixing a polyamide solution (A) in which polyamide is dissolved in a good solvent in which polyamide is dissolved and a non-solvent (B) in which polyamide cannot be dissolved. It is preferable to use polyamide porous particles having a crystallinity of 40% or more produced by a method in which a mixed solution is formed and then allowed to stand.

  The light diffusing film of the present invention can be used as a light diffusing film excellent in both light transmittance and diffusivity by disposing the surface on which the light diffusing layer is laminated on the light source side. The light diffusion film of the present invention also has an effect of preventing adhesion with the light guide plate.

  The light diffusing film of the present invention is prepared by laminating a light diffusing layer comprising a light diffusing agent and a transparent binder resin on one side of a transparent substrate. FIG. 3 shows the configuration of the present invention. Unlike a normal light diffusion film, the light diffusion film of the present invention is a light diffusion film that is used by arranging a surface on which a light diffusion layer is laminated on the light source side (light guide plate side).

  The light diffusing agent used in the present invention is only required to be composed of porous particles, and specific examples include porous silica particles, porous acrylic particles, and polyamide porous particles. Of these, porous particles made of an inorganic material such as silica tend to damage the light guide plate, and therefore porous particles made of an organic material are preferred. In particular, porous polyamide particles that have a large refractive index difference with respect to an acrylic resin often used as a transparent binder resin and have high light scattering properties are preferred.

  As the polyamide constituting the porous particles, various known ones can be used. Examples include polyamides obtained by ring-opening polymerization of cyclic amides such as ε-caprolactam and ω-laurolactam, or polycondensation of amino acids such as ε-aminocaproic acid, ω-aminododecanoic acid, and ω-aminoundecanoic acid. it can. In addition, dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, 1,4-cyclohexyldicarboxylic acid or derivatives thereof, ethylenediamine, hexamethylenediamine, 1,4-cyclohexyldiamine, m-xylylenediamine And polyamides obtained by polycondensation of diamines such as pentamethylenediamine and decamethylenediamine.

  The melting point of the polyamide used is preferably 110 to 320 ° C. In particular, the temperature is preferably 140 to 280 ° C. If the melting point is lower than 110 ° C., there may be a problem in thermal stability during processing.

  Specific examples of the polyamide include polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 66 / 6T (T represents a terephthalic acid component), polyamide 46, and polyamide 9T. Or polyamide 66 is preferred. These polyamides can be used as a mixture of two or more kinds, and can also be used as a copolymer.

  There is no limitation on the shape of the porous particles used in the present invention, and any shape such as a spherical shape, a substantially spherical shape, a sloping ball (C-type) shape, or a dumbbell shape can be used, preferably 70% by weight or more. It is desirable that 80% by weight or more, more preferably 90% by weight or more is uniform particles composed of one kind of particle shape.

  The number average particle diameter of the porous particles is preferably 0.1 to 30 μm, more preferably 1 to 20 μm. If the number average particle diameter is smaller than 0.1 μm, it becomes a Rayleigh scattering region of visible light and the forward scattering effect is lowered, which is not preferable. Moreover, since the thickness of a light-diffusion layer will become thick when a number average particle diameter is larger than 30 micrometers, it is unpreferable.

  In the particle size distribution, the ratio of the volume average particle size (or volume reference average particle size) to the number average particle size (or number reference average particle size) is preferably 1 to 2.5. When the ratio of the volume average particle diameter to the number average particle diameter (particle size distribution index PDI) is larger than 2.5, the handling as a powder becomes worse.

The BET specific surface area of the porous particles is preferably 3 to 120 m ² / g. When the specific surface area is less than 3 m ² / g, the internal scattering effect is decreased, which is not preferable. On the other hand, if the specific surface area is larger than 120 m ² / g, the surface energy of the powder is high and the particles are likely to aggregate, which makes it difficult to form a uniform dispersion layer when forming the light diffusion layer.

  Moreover, it is preferable that an average pore diameter is 0.01-0.8 micrometer. If the average pore diameter is smaller than 0.01 μm, the resin binder or the like cannot sufficiently enter into the pores, so that scattering unevenness may occur in the light diffusion layer formed by remaining bubbles. Further, if the average pore diameter is larger than 0.8 μm, the scattering characteristics may be deteriorated due to having a size larger than the wavelength region of visible light.

The porosity index (RI) of the porous particles is preferably 5 to 100. Here, the porosity index (RI) is defined as the ratio (Sp / Sp ₀ ) of the specific surface area (Sp) of the porous spherical particles to the specific surface area (Sp ₀ ) of the smooth spherical particles having the same diameter. If the porosity index is less than 5, the pore volume is small and the multiple scattering characteristic of light is lost, and the scattering property may be lowered. When the porosity is greater than 100, it becomes difficult to handle.

  The polyamide porous particles used in the present invention preferably have a crystallinity measured by DSC of 40% or more. There are a method for obtaining crystallinity by X-ray analysis, a method for obtaining by a DSC measurement method, and a method for obtaining from a density, and a method for obtaining it by a DSC measurement method is preferred. When the degree of crystallinity is lower than 40%, it is not preferable because the porous particles are easily melted when thermally processed.

  The polyamide porous particles can be produced by a known method such as a phase separation method. For example, the solubility of polyamide is reduced by mixing non-solvent (B) that cannot dissolve polyamide near room temperature into polyamide solution (A) in which polyamide is dissolved in a good solvent that dissolves polyamide near room temperature. It can manufacture using the method of making it precipitate. In particular, it is preferable to produce by a method in which the solution (A) and the non-solvent (B) are mixed to temporarily form a uniform mixed solution and then left to stand. By this method, porous polyamide particles having a large surface area, a narrow particle distribution and a high crystallinity can be obtained. The single particles themselves become porous particles having a spherulite structure and can be suitably used as the light diffusing agent of the present invention.

  “Single particles themselves have a spherulite structure” means that the polymer fibrils are three-dimensionally or radially grown from one or more cores near the center of a single particle. It means that the spherulite structure.

  Examples of the transparent binder resin used in the present invention include acrylic resins, polyester resins, silicone resins, epoxy resins, cyclic polyolefin resins, styrene resins, MS resins, oligomers and monomer mixtures thereof.

  Examples of the material of the transparent substrate used in the present invention include a transparent resin such as polyethylene terephthalate, polycarbonate, polystyrene, acrylic resin, a resin film made of acetyl cellulose, or a sheet of transparent inorganic material such as glass. .

  The light diffusing layer of the light diffusing film of the present invention includes a transparent binder resin and a solvent, and a solution composition containing a polymerization initiator, an antioxidant, a light stabilizer, an antistatic agent, etc. The light diffusing agent composed of the porous particles can be made into a uniformly dispersed slurry by a dispersing machine or stirring, and then the slurry can be applied on a transparent substrate and cured to be laminated. At this time, a commercially available transparent paint may be used instead of the solution composition.

  Specifically, the uniformly dispersed slurry is uniformly applied to the surface of the transparent substrate using means such as a spray method, a dipping method, a curtain flow method, a roll coater method, and a printing method, and is cured by ultraviolet irradiation or heating. The method is used. Further, a light diffusing agent made of porous particles may be directly bonded to the transparent substrate with an adhesive or the like.

（ただし、Ｔ_Ｆ→Ｂ、Ｈ_Ｆ→Ｂは光拡散層を積層した面から光を入射したときの全光線透過率ＴおよびヘイズＨをそれぞれ表し、Ｔ_Ｂ→Ｆ、Ｈ_Ｂ→Ｆは光拡散層を積層した面の裏側から光を入射したときの全光線透過率ＴおよびヘイズＨをそれぞれ表す。） The light diffusion film of the present invention preferably has a total light transmittance change rate ΔT% defined by the following formula of 1 or more and a haze change rate ΔH% of 0.5 or more. More preferably, ΔT% is 2 or more, haze change rate ΔH% is 0.7 or more, particularly ΔT% is 3 or more, and haze change rate ΔH% is 1 or more.

(Where T _{F → B} and H _{F → B} represent the total light transmittance T and haze H when light is incident from the surface on which the light diffusion layers are laminated, respectively, and T _{B → F} and H _{B → F} represent light. The total light transmittance T and haze H when light is incident from the back side of the surface on which the diffusion layers are laminated are shown.)

  In the above, if ΔT% and ΔH% are 0 or more, it indicates that both the light transmittance and the light diffusibility, which are the effects of the present invention, are improved. The larger the numerical value, the more light transmittance or It can be judged that the light diffusibility is excellent.

  The content of the porous particles in the light diffusion layer of the light diffusion film in the present invention is preferably 25 to 60% by weight, although it depends on the film thickness. More preferably, it is 30 to 50% by weight. If the content is less than 20% by weight, the effects of the present invention may not be exhibited. On the other hand, if it exceeds 60% by weight, it is difficult to make the thickness of the light diffusion layer uniform. The film thickness of the light scattering layer is usually 5 to 100 μm. Preferably, it is the range of 8-50 micrometers.

  The light diffusing film of the present invention that can be produced as described above is excellent in both light transmittance and diffusivity when the surface on which the light diffusing layer is laminated is disposed on the light source side, a lighting cover, a lighting signboard, It can be suitably used for light sources such as various displays and transmission screens. Moreover, it can be applied to various uses such as LED and organic EL lighting that require light diffusion light. In particular, it is suitable for use as a light diffusion film constituting a backlight unit for liquid crystal display devices.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. The crystallinity, particle diameter, average pore diameter, porosity, specific surface area, total light transmittance, haze, and the like were measured as follows.

χ ；結晶化度（％）
ΔＨ_obs；サンプルの融解熱 （ｃａｌ／ｇ）
ΔＨ_ｍ；ポリアミドの融解熱 （ｃａｌ／ｇ） (Crystallinity) The crystallinity was measured by DSC (differential scanning calorimeter). Specifically, in a nitrogen stream at a flow rate of 40 ml / min, the heat of crystal fusion determined from the area of the endothermic peak at a heating rate of 5 ° C./min and a temperature range of 120 to 230 ° C. and the heat of crystal fusion of a known polyamide It calculated | required from ratio (the following formula). The heat of fusion of polyamide 6 is It was set to 45 cal / g according to the description of Vieweg et al., Kunststoffe IV polyamide, page 218, Carl Hanger Verlag, 1966.

χ: Crystallinity (%)
ΔH _obs ; heat of fusion of sample (cal / g)
ΔH _m : heat of fusion of polyamide (cal / g)

体積平均粒子径:

粒子径分布指数：

ここで、Ｘｉ；個々の粒子径、ｎは測定数である。 (Average particle size) The average particle size and particle size distribution were measured as an average value of 100 fine particles using an electron microscope (scanning electron microscope SEM). The number average particle size, volume average particle size, and particle size distribution index (PDI) are expressed by the following equations.
Number average particle size:

Volume average particle size:

Particle size distribution index:

Here, Xi: individual particle diameter, n is the number of measurements.

(Specific surface area) The specific surface area was measured at three points by the BET method using nitrogen adsorption.

即ち、粒子内累積細孔容積（Ｐ_１）とすると

で表される。
細孔径に対する累積細孔容積の図から、粒子内累積細孔容積を算出し、下式に従って、粒子内空孔率を算出する。このときポリアミド微粒子の密度ρは、ＤＳＣで求めた結晶化度χと結晶密度ρｃ、非晶密度ρａから求めた。ここでポリアミド６の結晶密度（ρｃ）は１．２３ｃｍ^３／ｇ、非晶密度（ρａ）は１．０９ｃｍ^３／ｇとした。

(Average pore diameter / porosity) The average pore diameter was measured with a mercury porosimeter. The average pore diameter was determined in the measurement range of 0.0036 to 14 μm. The porosity of the polyamide porous fine particles represents the ratio of the volume of polyamide to the volume of space in one particle. Here, the density of polyamide can be represented by ρ, and the porosity can be expressed by the following equation. here,
Vp: pore volume in the particle,
Vs: Intraparticle polymer volume.

That is, when the cumulative pore volume (P ₁ ) in the particle

It is represented by
From the graph of the cumulative pore volume with respect to the pore diameter, the intra-particle cumulative pore volume is calculated, and the intra-particle porosity is calculated according to the following equation. At this time, the density ρ of the polyamide fine particles was obtained from the crystallinity χ, the crystal density ρc, and the amorphous density ρa obtained by DSC. Here, the crystal density (ρc) of the polyamide 6 was 1.23 cm ³ / g, and the amorphous density (ρa) was 1.09 cm ³ / g.

The degree of porosity (RI) of the polyamide porous fine particles can be represented by the ratio of the specific surface area value Sp ₀ when assuming true spherical fine particles with the same particle diameter and the BET specific surface area Sp in the case of porous fine particles. Also,

で求められる。ｄは粒子の直径、ρは密度である。

Is required. d is the diameter of the particle and ρ is the density.

  The total light transmittance (T) and haze (H) were measured according to JIS K7361-1 and JIS K7136 using a Nippon Denshoku Industries haze meter NDH5000.

(Reference Example 1)
100 g of polyamide 6 (manufactured by Ube Industries, “1010X1”, number average molecular weight 8000) was completely dissolved in 810 g of phenol at 70 ° C., then 90 g of isopropyl alcohol was added, and the mixture was slowly cooled with stirring to obtain a polyamide concentration of 10% by weight. A phenol / isopropyl alcohol solution was obtained and kept at room temperature. A mixture of 6.5 kg of isopropyl alcohol and 2.5 kg of water was prepared at 5 ° C. and mixed with the polyamide solution. When the solution became homogeneous, stirring was stopped and the mixture was allowed to stand, and polyamide 6 particles Was precipitated. After standing for 2 hours, the precipitated particles were filtered off using filter paper, and washed 5 times with 10000 ml of isopropyl alcohol at 25 ° C. on the filter paper. Next, it dried for 8 hours at the temperature of 60 degreeC using the hot air dryer. Furthermore, it dried for 8 hours at the temperature of 60 degreeC using the vacuum dryer. 10 g of dried particles are filled into a heat-insulated Soxhlet extractor, and isopropyl alcohol is refluxed for 10 hours in the extractor. Then, the particles are made into a 10 wt% water slurry and spray-dried at 180 ° C. to form polyamide 6. Polyamide porous particles were obtained. When the obtained particles were observed with a scanning electron microscope, they were porous spherulite particles having a number average particle size of 5.1 μm and a volume average particle size of 6.3 μm. The PDI was 1.23. The BET specific surface area was 28.2 m ² / g, the average pore diameter was 0.130 μm, and the crystallinity was 57%.

Example 1
A uniformly dispersed slurry was prepared by dispersing 15 parts by weight of MS resin and 80 parts by weight of toluene in 5 parts by weight of polyamide porous particles prepared in Reference Example 1. This slurry was coated on a commercially available triacetyl cellulose resin film (film thickness 80 μm) using a bar coater, and then heat-treated to laminate a light diffusion layer. At this time, the thickness of the light diffusion layer was 8 μm. The total light transmittance and the haze value were measured when light was applied from the surface of the film on which the light diffusion layers were laminated and when light was applied from the opposite surface. The results are shown in Table 1.

(Example 2)
A light diffusion film was prepared in the same manner as in Example 1 except that the weight of the polyamide porous particles was 15 parts by weight and the weight of the MS resin was 20 parts by weight. The results are shown in Table 1.

(Comparative Example 1)
A light diffusion film was prepared in the same manner as in Example 1 except that 5 parts by weight of Sekisui Chemical Co., Ltd. Techpolymer MBX-5 (5 μm) was blended in place of the polyamide porous particles. The results are shown in Table 1.

(Example 3)
30 parts by weight of polyamide porous particles prepared in Reference Example 1 and 50 parts by weight of urethane acrylate oligomer (UV-7600B manufactured by Nippon Gosei Kagaku), photopolymerization initiator 1-hydroxy-cyclohexyl phenyl ketone (manufactured by Wako Pure Chemical Industries) 8 parts by weight and 50 parts by weight of toluene were uniformly dispersed to prepare a slurry body. This slurry was coated on non-alkali glass (t = 1 mm) with a bar coater, cured by UV irradiation (850 mJ / cm ² ), and dried to prepare a film in which a light diffusion layer was laminated. The results are shown in Table 1.

Example 4
A light diffusion film was prepared in the same manner as in Example 3 except that the weight of the polyamide porous particles was 25 parts by weight. The results are shown in Table 1.

(Example 5)
A light diffusion film was prepared in the same manner as in Example 3 except that the weight of the polyamide porous particles was 20 parts by weight. The results are shown in Table 1.

(Comparative Example 2)
A light diffusion film was prepared in the same manner as in Example 3 except that the weight of the polyamide porous particles was 15 parts by weight. The results are shown in Table 1.

(Comparative Example 3)
A light diffusion film was prepared in the same manner as in Example 3 except that the weight of the polyamide porous particles was 10 parts by weight. The results are shown in Table 1.

(Reference Example 2)
100 g of polyamide 6 (manufactured by Ube Industries, Ltd., 1011FK, molecular weight: 11,000) was dissolved in 810 g of a phenol solution at 70 ° C., 90 g of isopropyl alcohol was added, and the mixture was slowly cooled with stirring. An isopropyl alcohol solution was obtained and kept at room temperature. While stirring, 8 kg of a mixed solution consisting of 5 kg of 2-propanol and 3 kg of water was added to this solution at room temperature over 15 seconds. When the solution became homogeneous, stirring was stopped and the mixture was allowed to stand to precipitate polyamide 6 particles. After standing for 30 minutes, the precipitated particles were filtered off using filter paper, washed 5 times with 1000 ml of 2-propanol at 25 ° C. on the filter paper, and dried at 60 ° C. for 8 hours using a vacuum dryer. Next, the dried particles are filled into a heat-insulated Soxhlet extractor, 2-propanol is refluxed in the extractor for 10 hours, and then a 10% by weight slurry of ion-exchanged water is spray-dried at 180 ° C. to obtain polyamide. Polyamide porous particles consisting of 6 were obtained. When the obtained particles were observed with a scanning electron microscope, they were porous spherulite particles having a number average particle size of 10.4 μm and a volume average particle size of 11.2 μm. The PDI was 1.08. The specific surface area was 9.8 m 2 / g, the average pore diameter was 0.124 μm, and the crystallinity was 50%.

(Example 6)
50 parts by weight of polyamide porous particles prepared in Reference Example 2, 100 parts by weight of urethane acrylate oligomer (UV-7600B manufactured by Nippon Synthetic Chemical), photopolymerization initiator 1-hydroxy-cyclohexyl phenyl ketone (manufactured by Wako Pure Chemical Industries) 8 parts by weight and 100 parts by weight of toluene were uniformly dispersed to prepare a slurry body. These were coated on a polyethylene terephthalate resin film (t = 100 μm) with a bar coater, cured by UV irradiation (850 mJ / cm ² ), and dried to produce a film in which a light diffusion layer was laminated. The results are shown in Table 1.

(Example 7)
The same procedure as in Example 6 was performed except that the polyamide porous particles were changed to 100 parts by weight. The results are shown in Table 1.

  From Table 1, the light diffusion film in which the light diffusion layer comprising the light diffusing agent comprising the polyamide porous particles of the present invention is laminated on the light source side surface has a total light transmittance change rate ΔT% and a haze change rate ΔH%. Both are excellent.

It is the exploded view which showed the general structure of the backlight vicinity part of a liquid crystal display device. It is sectional drawing which showed an example of the general structure of a light-diffusion film. It is sectional drawing which showed the structure of the light-diffusion film of this invention.

DESCRIPTION OF SYMBOLS 1 Light diffusing film 2 Light source 3 Reflecting plate 4 Light guide plate 5 Liquid crystal display element part 6 Transparent substrate 7 Light diffusing agent 8 Transparent binder resin 9 Laminate

Claims (2)

A light diffusing film in which a light diffusing layer containing a light diffusing agent composed of polyamide porous particles is laminated on a transparent substrate, wherein the content of the light diffusing agent in the light diffusing layer is 25 to 60% by weight, being defined rate of change [Delta] T% of the total light transmittance of 1 or more, and state, and are change rate [Delta] H% 0.5 or more haze, light diffusion, wherein a light diffusing layer is disposed on the light source side the film.

(Where T _{F → B} and H _{F → B} represent the total light transmittance T and haze H when light is incident from the surface on which the light diffusion layers are laminated, respectively, and T _{B → F} and H _{B → F} represent light. The total light transmittance T and haze H when light is incident from the back side of the surface on which the diffusion layers are laminated are shown.) A light diffusing film in which a light diffusing layer containing a light diffusing agent composed of polyamide porous particles is laminated on a transparent substrate, wherein the content of the light diffusing agent in the light diffusing layer is 25 to 60% by weight, The change rate ΔT% of the total light transmittance defined is 1 or more, and the change rate ΔH% of haze is 0.5 or more,
The polyamide porous particles are mixed temporarily with a polyamide solution (A) in which polyamide is dissolved in a good solvent in which polyamide is dissolved, and a non-solvent (B) in which polyamide cannot be dissolved, so that the mixture is temporarily uniform. forming a light diffusing film you characterized by subsequently produced by the method of standing, the degree of crystallinity is 40% or more of the polyamide porous particles.

(Where T _{F → B} and H _{F → B} represent the total light transmittance T and haze H when light is incident from the surface on which the light diffusion layers are laminated, respectively, and T _{B → F} and H _{B → F} represent light. The total light transmittance T and haze H when light is incident from the back side of the surface on which the diffusion layers are laminated are shown.)

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