JP2021124707A - Light diffusion control film - Google Patents

Abstract

To provide a light diffusion control film with great versatility that can achieve excellent concealability while ensuring near-infrared radiation transmissivity.SOLUTION: A light diffusion control film has an optical functional layer. The optical functional layer has transmitted light diffusivity of 50% or more at a wavelength 600 nm, and the optical functional layer has transmitted light diffusivity of 75% or less at a wavelength 900 nm.SELECTED DRAWING: None

Description

The present invention relates to a light diffusion control film including an optical functional layer capable of diffusing and transmitting incident light in a straight line depending on the wavelength.

In biometric authentication technology, biometric information is identified by detecting near infrared rays emitted from the human body. In recent years, the development of small electronic devices equipped with such biometric authentication technology has been promoted.

In the above biometric authentication technology, a sensor for detecting near infrared rays is used, but in a small electronic device, it is desired that the sensor be concealed from the user from the viewpoint of design and functionality. ing. From this point of view, it has been studied to cover the above-mentioned sensor with an optical article capable of diffusing and transmitting visible light while ensuring transparency to near infrared rays.

Here, Patent Document 1 discloses an optical article for infrared communication having a function of scattering and reflecting light in the visible light region to develop a white color and a function of suppressing transmission of light in the visible light region. ..

Japanese Unexamined Patent Publication No. 2012-89593

By the way, in recent years, small electronic devices have been further miniaturized and realized in complicated shapes, and optical articles are required to be versatile enough to meet such demands in order to cover the above-mentioned sensors. Has been done.

However, Patent Document 1 discloses an optical article having a thickness of 2 mm as a specific example of the above-mentioned optical article for infrared communication, and an optical article having such a relatively thick thickness has been developed in recent years. It cannot be suitably used for small electronic devices.

The present invention has been made in view of such an actual situation, and provides a highly versatile light diffusion control film capable of achieving excellent concealment while ensuring transparency to near infrared rays. The purpose is.

In order to achieve the above object, first, the present invention is a light diffusion control film provided with an optical functional layer, wherein the transmitted light diffusion rate of the optical functional layer at a wavelength of 600 nm is 50% or more, and the optical. Provided is a light diffusion control film characterized in that the transmitted light diffusion rate of the functional layer at a wavelength of 900 nm is 75% or less (Invention 1).

In the light diffusion control film according to the above invention (Invention 1), excellent concealment property and excellent transparency to near infrared rays are achieved by satisfying the above-mentioned conditions for the transmitted light diffusion rate at wavelengths of 600 nm and 900 nm, respectively. can do. Further, since the light diffusion control film is in the form of a film, it can be adapted to various shapes of the product to be incorporated, and has excellent versatility.

In the above invention (Invention 1), the difference between the transmitted light diffusivity at a wavelength of 600 nm and the transmitted light diffusivity at a wavelength of 900 nm of the optical functional layer is preferably 30 points or more (Invention 2).

In the above inventions (Inventions 1 and 2), the total light transmittance of the optical functional layer at a wavelength of 600 nm is preferably 50% or more (Invention 3).

In the above inventions (Inventions 1 to 3), the total light transmittance of the optical functional layer at a wavelength of 900 nm is preferably 50% or more (Invention 4).

In the above inventions (Inventions 1 to 4), it is preferable that the optical functional layer is composed of a pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer and a pressure-sensitive adhesive (Invention 5). ..

In the above invention (Invention 5), the content of the tackifier in the tacky composition is 20% by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic acid ester polymer. It is preferable that there is (Invention 6).

In the above inventions (Inventions 5 and 6), one surface of the optical functional layer is laminated on a polyethylene terephthalate film having a thickness of 50 μm, and the other surface of the optical functional layer is laminated on a non-alkali glass plate. In the body, the adhesive strength measured when the polyethylene terephthalate film is peeled from the optical functional layer is preferably 0.005 N / 25 mm or more and 50 N / 25 mm or less (Invention 7).

In the above inventions (Inventions 1 to 7), the thickness of the optical functional layer is preferably 1 μm or more and 250 μm or less (Invention 8).

In the above inventions (Inventions 1 to 8), it is preferable to use the device having a biometric authentication function using light in the near infrared region (Invention 9).

The light diffusion control film according to the present invention can achieve excellent concealment while ensuring transparency to near infrared rays, and is more versatile.

Hereinafter, embodiments of the present invention will be described.
The light diffusion control film according to this embodiment includes an optical functional layer. The optical functional layer may be an adhesive layer capable of exhibiting a predetermined adhesiveness, as will be described later. Further, the light diffusion control film according to the present embodiment may include a base material and a release sheet together with the optical functional layer. Since the light diffusion control film according to the present embodiment is in the form of a film, it can be easily adapted to the shape of the product in which the light diffusion control film is incorporated, and can be suitably used for a product for which thinning is desired. That is, the light diffusion control film according to this embodiment has high versatility.

1. 1. Physical Properties of Light Diffusion Control Film (1) Optical Characteristics In the optical functional layer in this embodiment, the transmitted light diffusion rate at a wavelength of 600 nm is 50% or more, and the transmitted light diffusion rate at a wavelength of 900 nm is 75% or less. The wavelength of 600 nm is a wavelength included in the visible light region (wavelength region of about 400 to 700 nm), and the wavelength of 900 nm is a wavelength included in the near infrared light region (wavelength region of about 800 to 900 nm). be. Further, the transmitted light transmittance is a value obtained by dividing the diffused transmittance by the total light transmittance, as described in a test example described later, and briefly, all the light transmitted through the optical functional layer. It represents the ratio of diffused and transmitted light to (light that is a combination of diffused and transmitted light and straight-line transmitted light).

In the optical functional layer of the present embodiment, the transmitted light diffusivity at a wavelength of 600 nm is a relatively high value of 50% or more, so that a large amount of visible light components are diffused and transmitted, while the transmitted light diffusing at a wavelength of 900 nm is present. When the rate is a relatively low value of 75% or less, a large amount of near-infrared light components transmitted straight through is present. Therefore, according to the light diffusion control film according to the present embodiment, the light source of near-infrared light and the light receiving sensor arranged on the back surface of the light diffusion control film are suppressed from being visually recognized from the light source. It is possible to satisfactorily transmit the emitted near-infrared light and the near-infrared light directed to the light receiving sensor. As a result, by using the light diffusion control film according to the present embodiment, for example, a near-infrared light sensor for biometric authentication can be concealed without impairing its function.

In the optical functional layer of the present embodiment, the transmitted light diffusivity at a wavelength of 600 nm is 50% or more as described above. When the transmitted light diffusion rate is 50% or more, the light diffusion control film according to the present embodiment can appropriately suppress the straight-line transmission of visible light, and can achieve good concealment. From this viewpoint, the transmitted light diffusing rate at a wavelength of 600 nm is preferably 60% or more, particularly preferably 70% or more, and further preferably 75% or more. The upper limit of the transmitted light diffusivity at a wavelength of 600 nm is not particularly limited, and may be, for example, 100% or less, particularly 95% or less, or even 90% or less. However, from the viewpoint of facilitating compatibility with the value of the transmitted light diffusivity at a wavelength of 900 nm, it is preferably 88% or less, and particularly preferably 85% or less.

Further, in the optical functional layer of the present embodiment, the transmitted light diffusivity at a wavelength of 900 nm is 75% or less as described above. When the transmitted light diffusion rate is 75% or less, the light diffusion control film according to the present embodiment can transmit near-infrared light satisfactorily in a straight line, and can detect near-infrared rays satisfactorily. .. From this viewpoint, the transmitted light diffusivity at a wavelength of 900 nm is preferably 60% or less, more preferably 50% or less, particularly preferably 45% or less, and further preferably 40% or less. Is preferable. The lower limit of the transmitted light diffusivity at a wavelength of 900 nm is not particularly limited, and may be, for example, 1% or more, particularly 5% or more, or even 10% or more. However, from the viewpoint of facilitating compatibility with the value of the transmitted light diffusivity at a wavelength of 600 nm, it is preferably 15% or more, particularly preferably 25% or more, and further preferably 35% or more. preferable.

In the optical functional layer of the present embodiment, the difference between the transmitted light diffusivity at a wavelength of 600 nm and the transmitted light diffusivity at a wavelength of 900 nm is preferably 30 points or more, and particularly preferably 35 points or more. Furthermore, it is preferably 40 points or more. When the above difference is 30 points or more, it becomes easy to better balance the diffusion transmission of visible light and the straight transmission of near infrared light. The upper limit of the above difference is not particularly limited, and may be, for example, 100 points or less, 80 points or less, particularly 60 points or less, and further 50 points or less. Well, especially 45 points or less.

In the optical functional layer of the present embodiment, the total light transmittance at a wavelength of 600 nm is preferably 50% or more, more preferably 55% or more, particularly preferably 60% or more, and further 65%. % Or more, and most preferably 68% or more. When the total light transmittance at a wavelength of 600 nm is 50% or more, the light diffusion control film according to the present embodiment can easily satisfy the above-mentioned transmitted light transmittance at a wavelength of 600 nm. As a result, the versatility of the light diffusion control film according to the present embodiment becomes higher. That is, for example, when the light diffusion control film according to the present embodiment is laminated on the backlight of the touch panel, the function of the light diffusion control film according to the present embodiment is exhibited without impairing the function of the backlight. Can be done. The upper limit of the total light transmittance at a wavelength of 600 nm is not particularly limited, and may be, for example, 100% or less, particularly 95% or less, but the transmitted light transmittance at the wavelength of 600 nm described above. From the viewpoint of facilitating the filling, it is preferably 88% or less, more preferably 80% or less, particularly preferably 75% or less, and further preferably 72% or less.

In the optical functional layer of the present embodiment, the total light transmittance at a wavelength of 900 nm is preferably 50% or more, more preferably 60% or more, particularly preferably 70% or more, and further 74. It is preferably 0.7% or more. When the total light transmittance at a wavelength of 900 nm is 50% or more, the light diffusion control film according to the present embodiment can easily transmit near-infrared light without blocking it, and is arranged on the back surface of the film. Sensors and the like can easily exert their functions more effectively. The upper limit of the total light transmittance at a wavelength of 900 nm is not particularly limited, and may be, for example, 100% or less, 95% or less, particularly 90% or less, and further. May be 85% or less.

In the optical functional layer of the present embodiment, the linear transmittance at a wavelength of 600 nm is preferably 30% or less, more preferably 25% or less, particularly preferably 20% or less, and further preferably 15%. The following is preferable. When the straight-line transmittance at a wavelength of 600 nm is 30% or less, the light diffusion control film according to the present embodiment can easily satisfy the above-mentioned transmitted light transmittance at a wavelength of 600 nm, for example, an object arranged on the back surface thereof. Will be more effective and easier to conceal. The lower limit of the straight transmittance at a wavelength of 600 nm is not particularly limited, and may be, for example, 0% or more, 1% or more, particularly 4% or more, and further. It may be 8% or more.

In the optical functional layer of the present embodiment, the linear transmittance at a wavelength of 900 nm is preferably 15% or more, more preferably 30% or more, particularly preferably 40% or more, and further 45%. The above is preferable. When the straight-line transmittance at a wavelength of 900 nm is 15% or more, the light diffusion control film according to the present embodiment can easily satisfy the above-mentioned transmitted light transmittance at a wavelength of 900 nm. In particular, the near-infrared light transmitted through the light diffusion control film according to the present embodiment is more likely to be transmitted straight ahead, and the sensor or the like arranged on the back surface of the film is more likely to exert its function more effectively. It becomes a thing. The upper limit of the straight transmittance at a wavelength of 900 nm is not particularly limited, and may be, for example, 100% or less, particularly 90% or less, or even 80% or less.

The details of the methods for measuring the total light transmittance (%), the diffuse transmittance (%), the transmitted light transmittance (%), and the straight-line transmittance (%) at each of the wavelengths of 600 nm and 900 nm described above are as described above. , As described in the test example described later.

(2) Adhesive Strength When the optical functional layer in the present embodiment is an adhesive layer capable of exhibiting a predetermined adhesiveness, one surface of the optical functional layer is laminated on a polyethylene terephthalate (PET) film having a thickness of 50 μm. , Adhesive strength measured when the polyethylene terephthalate (PET) film is peeled from the optical functional layer in a laminate formed by laminating the other surface of the optical functional layer on a non-alkali glass plate (adhesive strength against PET film). Is preferably 0.005 N / 25 mm or more, more preferably 0.05 N / 25 mm or more, particularly preferably 0.5 N / 25 mm or more, and further preferably 1.5 N / 25 mm or more. It is preferably 3N / 25 mm or more, and most preferably 3N / 25 mm or more.

When the adhesive strength is 0.005 N / 25 mm or more, the optical functional layer can be easily fixed to the object on which the optical functional layer is laminated, and the light diffusion control film according to the present embodiment can be used. The product manufactured by using the product easily exhibits the desired performance.

The upper limit of the adhesive strength can be appropriately set as needed, and may be, for example, 50 N / 25 mm or less, 25 N / 25 mm or less, and particularly 10 N / 25 mm or less. It may be 5N / 25mm or less. The details of the method for measuring the adhesive strength are as described in Test Examples described later.

2. Components of Light Diffusion Control Film (1) Optical Functional Layer The optical functional layer in this embodiment is not limited as long as the above-mentioned optical characteristics can be achieved. For example, the optical functional layer may be an adhesive layer capable of exhibiting a predetermined adhesiveness. Usually, a product in which an optical functional layer is incorporated is often a product in which predetermined members are bonded to each other by an adhesive layer, but by using the optical functional layer in the present embodiment as the adhesive layer. , It is possible to effectively reduce the number of members constituting the above product.

When the optical functional layer in the present embodiment is a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains a (meth) acrylic acid ester polymer and a pressure-sensitive adhesive from the viewpoint of easily achieving the above-mentioned optical properties. It preferably consists of a pressure-sensitive adhesive formed from the composition. In particular, the (meth) acrylic acid ester polymer and the tackifier are not completely mixed in the pressure-sensitive adhesive, but are mixed while being appropriately separated (hereinafter, may be referred to as "moderately mixed state"). As a result, the above-mentioned optical characteristics can be easily realized. In addition, in this specification, a (meth) acrylic acid ester means both an acrylic acid ester and a methacrylic acid ester. The same applies to other similar terms. In addition, the concept of "polymer" shall be included in "polymer".

(1-1) (Meta) Acrylic Acid Ester Polymer The (meth) acrylic acid ester polymer has the above-mentioned weight from the viewpoint of facilitating the realization of the above-mentioned appropriate mixed state and the viewpoint of easily exhibiting the desired adhesive strength. As the monomer unit constituting the coalescence, it is preferable to contain a (meth) acrylic acid alkyl ester, and in particular, it is preferable to contain a (meth) acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group.

Examples of (meth) acrylic acid alkyl esters having 1 to 20 carbon atoms in the alkyl group include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, propyl (meth) acrylic acid, and n- (meth) acrylic acid. Butyl, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, (meth) acrylate Examples thereof include n-dodecyl (lauryl (meth) acrylate), myristyl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate and the like. Above all, from the viewpoint of facilitating the realization of the above-mentioned appropriate mixed state and further improving the adhesiveness, it is preferable to contain a (meth) acrylic acid alkyl ester having 2 to 15 carbon atoms in the alkyl group, particularly ( It is preferable to use at least one of 2-ethylhexyl acrylate and n-dodecyl (meth) acrylate (lauryl (meth) acrylate), and further 2-ethylhexyl acrylate and n-dodecyl methacrylate (methacrylic acid). It is preferable to use at least one of lauryl). The above-mentioned (meth) acrylic acid alkyl ester may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer preferably contains 75% by mass or more of (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms as a monomer unit constituting the polymer. It is more preferably contained in an amount of 90% by mass or more, particularly preferably 90% by mass or more, and further preferably 95% by mass or more. When the lower limit of the content of the (meth) acrylic acid alkyl ester is as described above, the (meth) acrylic acid ester polymer tends to exhibit suitable adhesiveness, and the obtained optical functional layer (adhesive layer) becomes The above-mentioned appropriate mixed state can be easily realized, and the above-mentioned optical characteristics can be easily exhibited. Furthermore, the desired adhesive strength can be exhibited. Further, the (meth) acrylic acid ester polymer preferably contains a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms in an amount of 99.9% by mass or less, particularly 99% by mass or less. It is preferably contained, and more preferably 98% by mass or less. When the upper limit of the content of the (meth) acrylic acid alkyl ester is as described above, a suitable amount of other monomer components such as a reactive functional group-containing monomer can be introduced into the (meth) acrylic acid ester polymer. ..

The (meth) acrylic acid ester polymer may contain a reactive functional group-containing monomer having a reactive functional group in the molecule as a monomer unit constituting the polymer. In particular, when the adhesive composition contains a cross-linking agent, the reactive functional groups of the reactive functional group-containing monomer react with the cross-linking agent, and the cohesive force of the obtained pressure-sensitive adhesive can be easily controlled. Become. As a result, the obtained optical functional layer (adhesive layer) can easily exert a desired adhesive force.

Examples of the reactive functional group-containing monomer include a monomer having a carboxy group in the molecule (carboxy group-containing monomer), a monomer having a hydroxy group in the molecule (hydroxy group-containing monomer), and a monomer having an amino group in the molecule (amino). Group-containing monomer) and the like are preferably mentioned. Of these, a carboxy group-containing monomer and a hydroxy group-containing monomer are preferable, and a carboxy group-containing monomer is particularly preferable. These reactive functional group-containing monomers may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid, and acrylic acid is particularly preferable. These may be used alone or in combination of two or more.

Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and (. Examples thereof include (meth) acrylic acid hydroxyalkyl esters such as 3-hydroxybutyl (meth) acrylic acid and 4-hydroxybutyl (meth) acrylic acid. These may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include aminoethyl (meth) acrylate and n-butylaminoethyl (meth) acrylate. These may be used alone or in combination of two or more.

The (meth) acrylic acid ester polymer preferably contains a reactive functional group-containing monomer in an amount of 0.1% by mass or more, and particularly preferably 1% by mass or more, as a monomer unit constituting the polymer. Further, it is preferably contained in an amount of 2% by mass or more. The (meth) acrylic acid ester polymer preferably contains a reactive functional group-containing monomer in an amount of 25% by mass or less, more preferably 15% by mass or less, and particularly 10% by mass or less. It is preferable that the content is 5% by mass or less. When the reactive functional group-containing monomer is contained in the above range, a good cross-linking reaction proceeds in the obtained optical functional layer (adhesive layer), and as a result, desired cohesive force and adhesiveness are easily exhibited. It becomes a thing. In addition, the above-mentioned appropriate mixed state can be easily realized, and the obtained optical functional layer (adhesive layer) can easily exhibit the above-mentioned optical characteristics.

The (meth) acrylic acid ester polymer may be a copolymer of the above-mentioned (meth) acrylic acid alkyl ester and the reactive functional group-containing monomer and other monomers. As the other monomer, a monomer containing no reactive functional group is preferable so as not to inhibit the above-mentioned action of the reactive functional group-containing monomer. Examples of such monomers include (meth) acrylic acid alkoxyalkyl esters such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more. Further, regarding the polymerization mode of the polymer, it may be a random copolymer or a block copolymer. Further, the polymer may be used alone or in combination of two or more.

The weight average molecular weight of the (meth) acrylic acid ester polymer is preferably 100,000 or more, more preferably 200,000 or more, particularly preferably 300,000 or more, and further preferably 500,000 or more. Is preferable. The weight average molecular weight is preferably 3 million or less, more preferably 2.4 million or less, particularly preferably 1.8 million or less, and further preferably 1.2 million or less, preferably 800,000. Most preferably: When the value of the weight average molecular weight of the (meth) acrylic acid ester polymer is the above, it becomes easy to realize the above-mentioned appropriate mixed state, and it becomes easy to exhibit the above-mentioned optical characteristics. Further, the obtained optical functional layer (adhesive layer) can easily exert a desired cohesive force and adhesive force. The weight average molecular weight in the present specification is a standard polystyrene-equivalent value measured by a gel permeation chromatography (GPC) method.

(1-2) Crosslinking Agent The adhesive composition described above preferably contains a crosslinking agent together with the (meth) acrylic acid ester polymer. The (meth) acrylic acid ester polymers can be crosslinked with each other by the above-mentioned reactive functional groups, and as a result, a crosslinked structure (three-dimensional network structure) is formed in the pressure-sensitive adhesive to achieve a desired cohesive force. It will be easy to do.

The cross-linking agent may be any one that reacts with the reactive functional group of the (meth) acrylic acid ester polymer. For example, an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an amine-based cross-linking agent, a melamine-based cross-linking agent, Examples thereof include an aziridine-based cross-linking agent, a hydrazine-based cross-linking agent, an aldehyde-based cross-linking agent, an oxazoline-based cross-linking agent, a metal alkoxide-based cross-linking agent, a metal chelate-based cross-linking agent, a metal salt-based cross-linking agent, and an ammonium salt-based cross-linking agent. As the cross-linking agent, one type may be used alone, or two or more types may be used in combination.

The isocyanate-based cross-linking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, isophorone diisocyanates, and alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate. , And their biurets, isocyanurates, and adducts, which are reactants with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Of these, it is preferable to use a trimethylolpropane-modified aromatic polyisocyanate, particularly a trimethylolpropane-modified tolylene diisocyanate.

The content of the cross-linking agent in the above-mentioned adhesive composition is preferably 0.01 part by mass or more, preferably 0.1 part by mass or more, with respect to 100 parts by mass of the (meth) acrylic acid ester polymer. It is more preferably 0.5 parts by mass or more, further preferably 1 part by mass or more, and most preferably 3 parts by mass or more. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly 10 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic acid ester polymer. It is preferably 6 parts by mass or less, and most preferably 4 parts by mass or less. When the content of the cross-linking agent is in the above range, the cross-linked structure is well formed while maintaining the above-mentioned appropriate mixed state, and the pressure-sensitive adhesive tends to have the desired cohesive force and stickiness. , It becomes easy to develop desired optical characteristics.

(1-3) Adhesive imparting agent The tackifier as described above is not particularly limited as long as it can obtain the above-mentioned optical properties. Examples of tackifiers include terpene resins such as terpene resin, aromatic-modified terpene resin, and terpenphenol resin; hydride terpene resin obtained by hydrogenating these terpene resins; and penten produced by thermal decomposition of petroleum naphtha. , Isoprene, piperin, 1.3-pentadiene and other C5 distillates obtained by copolymerizing C5 styrene resin and hydride petroleum resin of this C5 styrene resin; inden and vinyl toluene produced by thermal decomposition of petroleum naphtha. C9-based petroleum resin obtained by copolymerizing the C9 distillate of the above and hydride-based petroleum resin of this C9-based petroleum resin; Hydrogenated hydride-based resin; Styrene-based resin obtained by copolymerizing a styrene-based monomer such as α-methylstyrene or β-methylstyrene with an aliphatic monomer; Hydrogenation of these styrene-based resins by hydrogenation Examples include styrene resin. As these tackifiers, one type may be used alone, or two or more types may be used in combination.

As described above, the (meth) acrylic acid ester polymer and the pressure-sensitive adhesive are appropriately separated and mixed in the pressure-sensitive adhesive layer to realize the optical characteristics of the light diffusion control film according to the present embodiment. It will be easy. Therefore, when selecting the tackifier to be used, it is preferable to select it from the viewpoint of compatibility with the (meth) acrylic acid ester polymer. In this respect, it is preferable to use at least one of the above-mentioned terpene resin and hydrogenated petroleum resin as the tackifier. Further, the terpene resin does not have a functional group (for example, a hydroxy group) that enhances compatibility with the (meth) acrylic acid ester polymer, or even if it has, it is extremely small. From this point of view, it is preferable to use a terpene resin.

The softening point of the tackifier is preferably 50 ° C. or higher, more preferably 70 ° C. or higher, particularly preferably 90 ° C. or higher, and further preferably 110 ° C. or higher. Further, the softening point is preferably 180 ° C. or lower, particularly preferably 160 ° C. or lower, and further preferably 140 ° C. or lower. When the softening point of the tackifier is in the above range, it becomes easy to realize the above-mentioned appropriate mixed state, and the obtained optical functional layer (adhesive layer) easily realizes the above-mentioned optical characteristics satisfactorily. It becomes.

The content of the tackifier in the above-mentioned adhesive composition is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, based on 100 parts by mass of the (meth) acrylic acid ester polymer. It is preferable, particularly preferably 60 parts by mass or more, further preferably 80 parts by mass or more, and most preferably 95 parts by mass or more. When the content of the tackifier is 20 parts by mass or more, it becomes easy to realize the above-mentioned appropriate mixed state, and the obtained optical functional layer (adhesive layer) easily realizes the above-mentioned optical characteristics satisfactorily. It becomes a thing. The content is preferably 200 parts by mass or less, more preferably 175 parts by mass or less, and particularly 150 parts by mass or less, based on 100 parts by mass of the (meth) acrylic acid ester polymer. It is preferably 120 parts by mass or less. When the content of the tackifier is 200 parts by mass or less, the obtained optical functional layer (adhesive layer) can easily realize a desired adhesive force.

(1-4) Various Additives In the above-mentioned adhesive composition, if desired, various additives usually used for acrylic pressure-sensitive adhesives, such as active energy ray-curable components, photopolymerization initiators, and silane cups. Ring agents, antistatic agents, antioxidants, ultraviolet absorbers, light stabilizers, softeners, fillers, refractive index adjusters and the like can be added.

Moreover, the above-mentioned adhesive composition may contain diffusion fine particles. As a result, the obtained optical functional layer (adhesive layer) can easily achieve the above-mentioned optical characteristics. The shape, material, and the like of the diffused fine particles are not particularly limited as long as the above-mentioned optical characteristics can be achieved.

The average particle size of the diffused fine particles is preferably more than 0.1 μm, particularly preferably 0.3 μm or more, and further preferably 0.4 μm or more. The average particle size is preferably less than 0.8 μm, particularly preferably 0.6 μm or less, and further preferably 0.5 μm or less. When the average particle size of the diffused fine particles is in the above range, the obtained optical functional layer (adhesive layer) can easily achieve the above-mentioned optical characteristics. The average particle size of the diffused fine particles in the present specification is a value measured by a dynamic light scattering method.

The shape of the diffusing fine particles may be a fixed shape such as a spherical shape, or an irregular shape whose shape is not specified, but spherical fine particles that easily exhibit uniform light diffusivity are preferable.

Examples of diffused fine particles include organic diffused fine particles such as melamine resin, acrylic resin, polystyrene resin, polyethylene resin and epoxy resin; silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, titanium dioxide and the like. Inorganic diffused fine particles; examples thereof include diffused fine particles made of a silicon-containing compound having an intermediate structure between inorganic and organic. Among these, organic diffusing fine particles are preferable, and melamine resin is particularly preferable, from the viewpoint of easily achieving the above-mentioned optical characteristics. The above-mentioned diffusion fine particles may be used alone or in combination of two or more.

The content of the diffused fine particles in the above-mentioned adhesive composition is preferably 1 part by mass or more, particularly 6 parts by mass or more, with respect to 100 parts by mass of the above-mentioned (meth) acrylic acid ester polymer. Is preferable, and more preferably 12 parts by mass or more. The content is preferably 30 parts by mass or less, particularly preferably 25 parts by mass or less, and further 20 parts by mass with respect to 100 parts by mass of the above-mentioned (meth) acrylic acid ester polymer. The following is preferable. When the content of the diffused fine particles is in the above range, the obtained optical functional layer (adhesive layer) can easily achieve the above-mentioned optical characteristics.

(1-5) Preparation of Adhesive Composition The above-mentioned adhesive composition is prepared by mixing a (meth) acrylic acid ester polymer, a cross-linking agent and a tackifier, and optionally other additives. be able to.

The (meth) acrylic acid ester polymer can be produced by polymerizing a mixture of monomer units constituting the polymer by a usual radical polymerization method. The polymerization of the (meth) acrylic acid ester polymer can be carried out by a solution polymerization method or the like using a polymerization initiator, if desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone and the like, and two or more kinds may be used in combination.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used in combination. Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane1-carbonitrile), and 2 , 2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis (2-methylpropionate) , 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis (2-hydroxymethylpropionitrile), 2,2'-azobis [2- (2-imidazolin-2-yl)) Propane] and the like.

Examples of the organic peroxide include benzoyl peroxide, t-butylperbenzoate, cumenehydroperoxide, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate, and di (2-ethoxyethyl) peroxy. Examples thereof include dicarbonate, t-butylperoxyneodecanoate, t-butylperoxyvivarate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

In the above polymerization step, the weight average molecular weight of the obtained polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

Once the (meth) acrylic acid ester polymer is obtained, a cross-linking agent, a tackifier and, if desired, other additives are added to the solution of the (meth) acrylic acid ester polymer and mixed thoroughly. , To obtain a tacky composition (coating solution) diluted with a solvent.

Examples of the diluting solvent for diluting the adhesive composition into a coating solution include aliphatic hydrocarbons such as hexane, heptane and cyclohexane, aromatic hydrocarbons such as toluene and xylene, methylene chloride and ethylene chloride. Alcohols such as halogenated hydrocarbons, methanol, ethanol, propanol, butanol, 1-methoxy-2-propanol, ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, cyclohexanone, esters such as ethyl acetate and butyl acetate, ethyl cellosolves. Etc., a cellosolve solvent or the like is used.

The concentration and viscosity of the coating solution prepared in this manner may be any range as long as it can be coated, and is not particularly limited and can be appropriately selected depending on the situation. For example, the adhesive composition is diluted to a concentration of 10 to 40% by mass. It should be noted that the addition of a diluting solvent or the like is not a necessary condition when obtaining the coating solution, and the diluting solvent may not be added as long as the adhesive composition has a coatable viscosity or the like.

(1-6) Thickness The thickness of the optical functional layer in the present embodiment is preferably 1 μm or more, more preferably 10 μm or more, and the transmitted light diffusivity at a wavelength of 600 nm. From the viewpoint of easy filling, it is preferably 20 μm or more, more preferably 40 μm or more, particularly preferably 60 μm or more, further preferably 70 μm or more, and the transmitted light diffusivity at a wavelength of 900 nm. From the viewpoint of facilitating filling, it is particularly preferable that the length is 80 μm or more. Further, when the optical functional layer in the present embodiment is an adhesive layer, when the thickness is 1 μm or more, it becomes easy to develop a desired adhesive force. The thickness of the optical functional layer in the present embodiment is preferably 250 μm or less, preferably 180 μm or less, more preferably 120 μm or less, particularly preferably 100 μm or less, and further. Is preferably 95 μm or less, and most preferably 35 μm or less. When the thickness of the optical functional layer is 250 μm or less, it becomes easy to satisfy the transmitted light diffusivity at a wavelength of 900 nm. Further, the light diffusion control film according to the present embodiment can be easily adapted to the shape of the product into which the film is incorporated, and more excellent versatility can be achieved.

(2) Base material The light diffusion control film according to the present embodiment may include a base material together with an optical functional layer. In this case, for example, the base material can be laminated on one side of the optical functional layer. Although the composition and material of the base material are not particularly limited, the base material is made of a resin-based sheet containing a resin-based material as a main component from the viewpoint of excellent light transmission and not easily impairing the optical characteristics of the optical functional layer. It is preferably configured.

Examples of the resin-based sheet described above include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyolefin films such as polyethylene film and polypropylene film, cellophane, diacetyl cellulose film, triacetyl cellulose film, and acetyl cellulose butyrate. Film, Polyvinyl Chloride Film, Vinylidene Chloride Film, Polyvinyl Alcohol Film, Ethylene-Vinyl Acetate Copolymer Film, Polystyrene Film, Polycarbonate Film, Polymethylpentene Film, Polysulphon Film, Polyether Ether Ketone Film, Polyether Sulphon Film , Polyetherimide film, fluororesin film, polyamide film, acrylic resin film, polyurethane resin film, norbornene polymer film, cyclic olefin polymer film, cyclic conjugated diene polymer film, vinyl alicyclic hydrocarbon polymer Examples thereof include plastic films such as films and laminated films thereof.

Further, in the base material, for the purpose of improving the adhesion to the optical functional layer provided on the surface thereof, one side or both sides thereof can be surface-treated by a primer treatment, an oxidation method, an unevenness method or the like, if desired. .. Examples of the oxidation method include corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, ozone / ultraviolet treatment, and the like, and examples of the unevenness method include sandblasting method, solvent treatment method, and the like. These surface treatment methods are appropriately selected according to the type of the base material.

The thickness of the base material is preferably 1 μm or more, more preferably 10 μm or more, particularly preferably 25 μm or more, and further preferably 50 μm or more. The thickness of the base material is preferably 190 μm or less, particularly preferably 160 μm or less, and further preferably 120 μm or less.

(3) Release Sheet The light diffusion control film according to the present embodiment may include a release sheet together with an optical functional layer. In particular, when the optical functional layer is the adhesive layer described above, by laminating a release sheet on one side or both sides of the optical functional layer, the optical functional layer can be used until the optical functional layer is incorporated into the product. It is preferable to protect the surface with a release sheet.

Examples of the release sheet include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, and polybutylene terephthalate film. , Polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene / (meth) acrylic acid copolymer film, ethylene / (meth) acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film Etc. are used. In addition, these crosslinked films are also used. Further, these laminated films may be used.

Further, it is preferable that the peeling surface of the peeling sheet (particularly the surface in contact with the optical functional layer) is subjected to a peeling treatment. Examples of the release agent used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

The thickness of the release sheet is not particularly limited, but is usually about 20 to 150 μm.

3. 3. Method for Producing Light Diffusion Control Film The method for producing the light diffusion control film according to the present embodiment is not particularly limited, and can be produced by a conventional method. As a method for producing a light diffusion control film in which the optical functional layer is the adhesive layer described above, first, a coating solution of the adhesive composition described above is applied to the peeling surface of the release sheet to form a coating film. Subsequently, the coating film is heat-treated to cause a cross-linking reaction between the (meth) acrylic acid ester polymer and the cross-linking agent to form a pressure-sensitive adhesive layer. As a result, it is possible to obtain a light diffusion control film in which the release sheet and the optical functional layer (adhesive layer) are laminated.

As the above-mentioned heat treatment conditions, the heating temperature is preferably 50 ° C. or higher, and particularly preferably 70 ° C. or higher. The heating temperature is preferably 150 ° C. or lower, and particularly preferably 120 ° C. or lower. The heating time is preferably 10 seconds or longer, and particularly preferably 50 seconds or longer. The heating time is preferably 10 minutes or less, and particularly preferably 2 minutes or less. The above-mentioned heat treatment can also be used as a drying treatment for volatilizing the diluting solvent or the like from the coating film of the adhesive composition.

As a method for applying the coating liquid of the adhesive composition, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method and the like can be used.

4. Use of Light Diffusion Control Film The method of using the light diffusion control film according to the present embodiment is not particularly limited, but can be used, for example, for the production of a desired product. In that case, by laminating the optical functional layer in the light diffusion control film with other members, a product incorporating the optical functional layer can be obtained. Since the light diffusion control film according to the present embodiment is in the form of a film, it can be satisfactorily adapted to the shape of the product into which the light diffusion control film is incorporated. Therefore, it is possible to cope with a product having a special shape, and it is also possible to contribute to a thinning of the product.

Further, as described above, the light diffusion control film according to the present embodiment can diffuse and transmit visible light while transmitting near-infrared light in a straight line. As a result, the near-infrared light emitted from the article and the near-infrared light directed toward the article can be satisfactorily transmitted while hiding the article located on the back surface of the light diffusion control film. Therefore, it is preferable that the light diffusion control film according to the present embodiment is incorporated into a product that includes a light source for near-infrared light and a light receiving sensor, and that such a light source and the light receiving sensor are desired to be concealed. be. In particular, the light diffusion control film according to the present embodiment is suitable to be incorporated into a device having a biometric authentication function using light in the near infrared region.

The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the scope of the present invention is not limited to these Examples and the like.

[Example 1]
1. 1. Preparation of (meth) Acrylic Acid Ester Polymer A (meth) acrylic acid ester polymer was prepared by copolymerizing 80 parts by mass of 2-ethylhexyl acrylate, 15 parts by mass of lauryl methacrylate and 5 parts by mass of acrylic acid. The weight average molecular weight (Mw) of this (meth) acrylic acid ester polymer was measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement), and further calculated by polystyrene conversion. It was 700,000.
<Measurement conditions>
-Measuring device: HLC-8320 manufactured by Tosoh Corporation
-GPC column (passed in the following order): TSK gel superH-H manufactured by Tosoh Corporation
TSK gel superHM-H
TSK gel superH2000
-Measurement solvent: tetrahydrofuran-Measurement temperature: 40 ° C

2. Preparation of Adhesive Composition 100 parts by mass (solid content conversion value; the same applies hereinafter) of the (meth) acrylic acid ester polymer obtained in the above step 1 and trimethylolpropane-modified tolylene diisocyanate as a cross-linking agent (manufactured by Toyochem Co., Ltd.). , Product name "BHS8515") 3.72 parts by mass and terpen resin as a tackifier (manufactured by Yasuhara Chemical Co., Ltd., product name "YS Resin PX1150") 103.72 parts by mass in toluene as a solvent. To obtain a coating solution of the adhesive composition having a solid content concentration of about 40% by mass.

3. 3. Formation of optical functional layer A release sheet (manufactured by Lintec Corporation, product name "SP-PET752150") in which one side of a polyethylene terephthalate film is peeled off with a silicone-based release agent from the coating solution of the adhesive composition obtained in step 2 above. It was applied to the peeled surface of the above with a knife coater. The coating film thus obtained was heat-treated at 110 ° C. for 2 minutes, and the coating film was cured to obtain a pressure-sensitive adhesive layer having a thickness of 90 μm. As a result, a light diffusion control film in which the release sheet and the optical functional layer (adhesive layer) were laminated was obtained.

[Examples 2 to 4, Comparative Examples 1 to 2]
A light diffusion control film was produced in the same manner as in Example 1 except that the composition of the adhesive composition and the thickness of the optical functional layer were changed as shown in Table 1.

[Test Example 1] (Measurement of optical characteristics of optical functional layer)
For the optical functional layers formed in the examples and comparative examples, the total light transmittance at a wavelength of 600 nm (manufactured by Shimadzu Corporation, product name “ultraviolet visible near infrared spectrophotometer UV-3600”) (manufactured by Shimadzu Corporation, product name “UV-3600”). %) And diffusion transmittance (%) were measured.

Subsequently, the straight transmittance (%) for a wavelength of 600 nm was calculated by subtracting the diffusion transmittance (%) measured as described above from the total light transmittance (%) measured as described above. Further, the transmitted light transmittance (%) for a wavelength of 600 nm was also calculated by dividing the diffused transmittance (%) by the total light transmittance (%).

Table 2 shows the total light transmittance (%), transmitted light diffusing rate (%), and straight-line transmittance (%) obtained as described above at a wavelength of 600 nm.

Further, also in the case of a wavelength of 900 nm, the total light transmittance (%), the diffuse transmittance (%), the transmitted light transmittance (%) and the straight-line transmittance (%) were obtained in the same manner as described above. Table 2 shows the total light transmittance (%), transmitted light diffusing rate (%), and straight-line transmittance (%) at a wavelength of 900 nm.

Further, the difference (point) of the transmitted light diffusing rate was calculated by subtracting the transmitted light diffusing rate (%) at the wavelength of 900 nm from the transmitted light diffusing rate (%) at a wavelength of 600 nm. The results are also shown in Table 2.

[Test Example 2] (Evaluation of concealment)
The surface of the light diffusion control film produced in Examples and Comparative Examples on the optical functional layer side was attached to a glass plate. Further, the release sheet was peeled off from the optical functional layer, and the obtained laminate of the optical functional layer and the glass plate was used as a measurement sample.

Subsequently, a television remote controller equipped with a near-infrared light source was visually confirmed to see if it could be visually confirmed through the measurement sample. Here, the surface on the near-infrared light source side of the TV remote controller and the surface on the optical functional layer side of the measurement sample are arranged so as to face each other. In addition, the distance between the near-infrared light source and the measurement sample and the distance between the measurement sample and the tester's eyes were arranged so as to be 5 cm each. From the confirmed results, the concealment property was evaluated based on the following criteria. The evaluation results are shown in Table 3.
⊚: Not only the details of the TV remote controller but also the outline were invisible.
〇: The outline of the TV remote controller could be visually recognized, but the details could not be visually recognized.
X: The outline and details of the TV remote controller were visible.

[Test Example 3] (Evaluation of near-infrared light detection performance)
Continuing from Test Example 2, the lens of the camera of the mobile phone equipped with a digital camera was placed at the position where the examiner's eyes were, without changing the arrangement of the remote controller for the television and the measurement sample. Then, with the camera function of the mobile phone equipped with a digital camera activated, the near-infrared light source was emitted by pressing an arbitrary button on the TV remote controller. Then, it is confirmed on the display screen of the digital camera-equipped mobile phone whether or not the near-infrared light emitted from the near-infrared light source can be received by the camera of the digital camera-equipped mobile phone, and the following criteria are used. The detection performance of near-infrared light was evaluated. The evaluation results are shown in Table 3.
⊚: A clear image of near-infrared light could be confirmed.
〇: The image of near-infrared light was confirmed, although it was a little unclear.
X: The image of near infrared light could not be confirmed.

[Test Example 4] (Measurement of adhesive strength)
The surface of the light diffusion control film produced in Examples and Comparative Examples on the optical functional layer side was attached to a polyethylene terephthalate (PET) film having a thickness of 50 μm, and then cut into a width of 25 mm and a length of 100 mm. The release sheet was peeled off from the cut pieces thus obtained, and the exposed surface of the exposed optical functional layer was attached to a non-alkali glass plate. Then, it was left for 24 hours under the conditions of normal pressure, 23 ° C., and 50% RH to prepare a measurement sample.

For the above measurement sample, PET from the optical functional layer using a tensile tester (manufactured by Orientec, product name "Tencilon") under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180 ° according to JIS Z0237: 2009. The adhesive strength (adhesive strength against PET film) (N / 25 mm) when the film was peeled off was measured. These results are shown in Table 3.

The details of the names and the like shown in Table 1 are as follows.
[Composition of (meth) acrylic acid ester polymer]
2EHA: 2-ethylhexyl acrylate LMA: lauryl methacrylate AA: acrylic acid [type of cross-linking agent]
TDI system: Trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem, product name "BHS8515")
[Type of adhesive]
Adhesive imparting agent 1: Terpene resin (manufactured by Yasuhara Chemical Co., Ltd., product name "YS resin PX1150", softening point 115 ° C.)
Adhesive imparting agent 2: Hydrogenated petroleum resin (manufactured by Arakawa Chemical Industry Co., Ltd., product name "Arcon M-100", softening point 100 ° C)
[Type of filler]
Filler 1: Melamine filler (manufactured by Nippon Shokubai Co., Ltd., product name "Eposter S12", average particle size: 1.2 μm)
Filler 2: Melamine filler (manufactured by Nippon Shokubai Co., Ltd., product name "Eposter S", average particle size: 0.2 μm)

As is clear from Table 3, in the light diffusion control film according to the embodiment, the near-infrared light source arranged on the back surface of the film can be well concealed, but the near-infrared light emitted from the light source is emitted. It was possible to transmit light well.

The light diffusion control film of the present invention can be suitably used for concealing the sensor in a small electronic device including a sensor for detecting light in the near infrared region.

Claims (9)

A light diffusion control film provided with an optical functional layer.
The transmitted light diffusing rate of the optical functional layer at a wavelength of 600 nm is 50% or more.
A light diffusion control film characterized in that the transmitted light diffusion rate of the optical functional layer at a wavelength of 900 nm is 75% or less. The light diffusion control film according to claim 1, wherein the difference between the transmitted light diffusion rate at a wavelength of 600 nm and the transmitted light diffusion rate at a wavelength of 900 nm of the optical functional layer is 30 points or more. The light diffusion control film according to claim 1 or 2, wherein the total light transmittance of the optical functional layer at a wavelength of 600 nm is 50% or more. The light diffusion control film according to any one of claims 1 to 3, wherein the total light transmittance of the optical functional layer at a wavelength of 900 nm is 50% or more. The invention according to any one of claims 1 to 4, wherein the optical functional layer is made of a pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer and a pressure-sensitive adhesive. Light diffusion control film. The claim is characterized in that the content of the tackifier in the tacky composition is 20% by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic acid ester polymer. The light diffusion control film according to 5. In a laminate in which one surface of the optical functional layer is laminated on a polyethylene terephthalate film having a thickness of 50 μm and the other surface of the optical functional layer is laminated on a non-alkali glass plate, the polyethylene terephthalate film is laminated on the optical. The light diffusion control film according to claim 5 or 6, wherein the adhesive strength measured when peeled from the functional layer is 0.005 N / 25 mm or more and 50 N / 25 mm or less. The light diffusion control film according to any one of claims 1 to 7, wherein the thickness of the optical functional layer is 1 μm or more and 250 μm or less. The light diffusion control film according to any one of claims 1 to 8, wherein the light diffusion control film is used in an apparatus having a biometric authentication function using light in the near infrared region.