JP2023001208A - optical sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet that is less prone to the problem of multi-sheet picking in which, upon picking an optical sheet one by one from a stack where optical sheets are stacked, a plurality of optical sheets are picked at one picking operation.

SOLUTION: An optical sheet has a surface protection film, a polarizing plate, and release film in this order. A coefficient of dynamic friction between the surface protection film and the release film is 0.4 or less. The polarizing plate has a thickness of 30 μm or more and 150 μm or less. The surface protection film-side surface of the polarizing plate has an arithmetic average roughness Ra of 0.001 μm or more and 0.3 μm or less in accordance with JIS B 0601: 2013.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to optical sheets.

Polarizing plates are widely used in image display devices such as liquid crystal display devices, particularly in recent years in various mobile devices such as smartphones. As a polarizing plate, there has been conventionally used a polarizer in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol-based resin film, and a protective film is laminated on one or both sides of the polarizer.

A polarizing plate is marketed as an optical sheet having a peelable surface protective film (also called a protect film) and a release film (also called a separate film) adhered to the surface to prevent the surface from being soiled or scratched. It is common to be

When the polarizing plate is attached to a display element such as a liquid crystal cell, the optical sheets are taken out one by one from the laminate in which the optical sheets are stacked. Then, the release film is peeled off from the optical sheet, and the optical sheet is bonded to the display element via the exposed pressure-sensitive adhesive layer.

Japanese Patent Application Laid-Open No. 2002-300002 proposes automating the optical sheet extraction process by a machine in order to efficiently perform the optical sheet extraction process (Patent Document 1). When the optical sheets are automatically taken out in this way, there is a problem that a plurality of optical sheets are taken out in one take-out (hereinafter sometimes referred to as multiple taking).

In addition, when the polarizing plate is thick, the optical sheet separates due to the weight of the optical sheet including the polarizing plate. Since the action is small, multiple pickings are likely to occur.

JP 2006-308912 A

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical sheet that is less likely to be taken multiple times when the optical sheets are taken out one by one from a laminate in which a plurality of optical sheets are stacked.

[1] having a surface protective film, a polarizing plate, and a release film in this order;
A coefficient of dynamic friction between the surface protective film and the release film is 0.4 or less,
The thickness of the polarizing plate is 30 μm or more and 150 μm or less,
An optical sheet in which the surface of the polarizing plate on the surface protection film side has an arithmetic mean roughness Ra of 0.001 μm or more and 0.3 μm or less in accordance with JIS B 0601:2013.
[2] The optical sheet according to [1], wherein the surface of the release film opposite to the polarizing plate has a silicon atom content of 3% or more.
[3] The release film has a marking on the surface opposite to the polarizing plate,
3. The optical sheet according to claim 1, wherein the ratio of the area of the marking to the area of the release film is 2% or less.

It is possible to provide an optical sheet that is less likely to be taken multiple times when the optical sheets are taken out one by one from a laminate in which a plurality of optical sheets are stacked.

1 is a schematic cross-sectional view showing an example of the layer structure of an optical sheet of the present invention; FIG. 1 is a schematic cross-sectional view showing an example of a laminate in which a plurality of optical sheets of the present invention are stacked; FIG. FIG. 2 is a schematic plan view of the optical sheet of the present invention viewed from the release film side; It is a schematic diagram showing an example of marking.

<Optical sheet>
FIG. 1 is a schematic cross-sectional view showing an example of the optical sheet of the present invention. The optical sheet 10 shown in FIG. 1 is a laminated film having a surface protection film 2, a polarizing plate 1, and a release film 3 in this order. In optical sheet 10, surface protective film 2, polarizing plate 1, and release film 3 are preferably laminated in this order. In the optical sheet 10, the surface protective film 2 and the release film 3 are preferably members constituting the outermost surface of the optical sheet.

The optical sheet 10 may be obtained by manufacturing a long optical sheet by roll-to-roll while conveying each member constituting the optical sheet 10 and cutting it, or by cutting each member into a predetermined shape. You may obtain by preparing each member and laminating|stacking one by one.

The shape of the optical sheet is not particularly limited, but may be rectangular, polygonal such as triangular, circular, elliptical, and combinations thereof.

Although the area of the optical sheet is not particularly limited, it is preferably 18600 to 2500 mm ² , more preferably 12600 to 6870 mm ² . When the area of the optical sheet is smaller than 18600 mm ² , the effect of the present invention is remarkable because it is difficult to separate the individual optical sheets due to their own weight as described above. When the area of the optical sheet is larger than 2500 mm ² , it is easy to adjust the frictional force as described below.

From a similar point of view, when the optical sheet has a rectangular shape with long sides and short sides, the length of the long side is preferably 17.3 to 6.6 cm, more preferably 15.5 to 11.0 cm. The length of the short side is preferably 10.8 to 3.7 cm, more preferably 8.7 to 6.2 cm.

In the present invention, the coefficient of dynamic friction between the surface protection film and the release film is 0.40 or less, preferably 0.30 or less. On the other hand, the coefficient of dynamic friction is preferably 0.10 or more, and preferably 0.10 or more, from the viewpoint of increasing the adhesion between the release tape and the surface protection film, etc. when the release tape is used to peel off the surface protection film, etc. It may be 20 or more. The method for measuring the coefficient of dynamic friction follows the method described in Examples below.

As will be described later, the coefficient of dynamic friction can be controlled by the ratio of silicon atoms present on the surface of the release film, the surface resistivity of the surface of the release film and the surface protective film, and the like. When controlling the dynamic friction coefficient by surface resistivity, at least one of the release film and the surface protection film preferably has an antistatic function, and both preferably have an antistatic function.

Each member of the optical sheet will be described below.
<Polarizing plate>
The polarizing plate 1 is a polarizing element containing at least a polarizer, and usually further contains a thermoplastic resin film laminated on one side or both sides thereof. The thermoplastic resin film can be a protective film that protects the polarizer, another optical film that has an optical function different from that of the polarizer, or the like. The thermoplastic resin film has a resin layer laminated on its surface (for example, a hard coat layer, an antistatic layer, an antiglare layer, a light diffusion layer, a retardation layer (a retardation layer having a retardation value of 1/4 wavelength, etc. ), at least one optical layer selected from an antireflection layer, a low refractive index layer, an antifouling layer, etc.). The thermoplastic resin film can be attached to the polarizer via an adhesive layer or a pressure-sensitive adhesive layer. The surface protective film 2 may be laminated on the surface of this resin layer.

Although the thickness of the polarizing plate 1 is not particularly limited, it is usually 200 μm or less. The thickness of the polarizing plate 1 is preferably 30 μm or more, more preferably 50 μm or more.

(1) Polarizer The polarizer that constitutes the polarizer 1 absorbs linearly polarized light having a vibration plane parallel to its absorption axis, and absorbs linearly polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). It is an absorptive polarizer having transmissive properties, and a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film can be preferably used. The polarizer is, for example, a process of uniaxially stretching a polyvinyl alcohol resin film; a process of dyeing a polyvinyl alcohol resin film with a dichroic dye to adsorb a dichroic dye; It can be produced by a method including a step of treating an alcohol-based resin film with a cross-linking liquid such as an aqueous boric acid solution; and a step of washing with water after the treatment with the cross-linking liquid.

As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers that can be copolymerized. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

As used herein, "(meth)acryl" means at least one selected from acryl and methacryl. The same applies to "(meth)acryloyl", "(meth)acrylate" and the like.

The saponification degree of the polyvinyl alcohol resin is usually 85 to 100 mol %, preferably 98 mol % or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The average degree of polymerization of the polyvinyl alcohol resin is usually 1,000 to 10,000, preferably 1,500 to 5,000. The average degree of polymerization of the polyvinyl alcohol-based resin can be determined according to JIS K6726.

A film obtained by forming such a polyvinyl alcohol-based resin is used as a raw film for a polarizer (polarizing film). A method for forming a polyvinyl alcohol-based resin into a film is not particularly limited, and a known method is adopted. Although the thickness of the polyvinyl alcohol base film is not particularly limited, it is preferable to use a film having a thickness of 5 to 35 μm in order to make the thickness of the polarizer 15 μm or less. More preferably, it is 20 μm or less.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before or during the cross-linking treatment. Moreover, you may uniaxially stretch in these several steps.

In the uniaxial stretching, the film may be uniaxially stretched between rolls having different circumferential speeds, or may be uniaxially stretched using hot rolls. The uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a swollen state using a solvent or water. The draw ratio is usually 3 to 8 times.

As a method of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing the film in an aqueous solution containing a dichroic dye is employed. Iodine and dichroic organic dyes are used as dichroic dyes. The polyvinyl alcohol resin film is preferably immersed in water before being dyed.

As a cross-linking treatment after dyeing with a dichroic dye, a method of immersing a dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid is usually adopted. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide.

The thickness of the polarizer is usually 30 μm or less, preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. In particular, setting the thickness of the polarizer to 15 μm or less is advantageous for thinning the optical sheet. The thickness of the polarizer is usually 2 μm or more.

(2) Protective film The protective film that can be laminated on one or both sides of the polarizer is a translucent (preferably optically transparent) thermoplastic resin, such as a chain polyolefin resin (polypropylene resin etc.), polyolefin-based resins such as cyclic polyolefin-based resins (norbornene-based resins, etc.); cellulose-based resins such as triacetyl cellulose and diacetyl cellulose; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate-based resins; (Meth) acrylic resins such as methyl methacrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile-butadiene-styrene resins; acrylonitrile-styrene resins; polyacetal resin; modified polyphenylene ether resin; polysulfone resin; polyethersulfone resin; polyarylate resin; polyamideimide resin;

Examples of linear polyolefin-based resins include polyethylene resins (polyethylene resins that are homopolymers of ethylene, copolymers mainly composed of ethylene), polypropylene resins (polypropylene resins that are homopolymers of propylene, and propylene resins that are mainly composed of propylene). In addition to homopolymers of chain olefins such as copolymers that form a chain olefin, copolymers composed of two or more types of chain olefins can be mentioned.

Cyclic polyolefin-based resin is a general term for resins polymerized using cyclic olefins as polymerized units, and is described, for example, in JP-A-1-240517, JP-A-3-14882, and JP-A-3-122137. resins. Specific examples of cyclic polyolefin-based resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (typically are random copolymers), graft polymers modified with unsaturated carboxylic acids or derivatives thereof, and hydrides thereof. Among them, norbornene-based resins using norbornene-based monomers such as norbornene and polycyclic norbornene-based monomers as cyclic olefins are preferably used.

Polyester-based resins are resins having an ester bond, except for the cellulose ester-based resins described below, and generally consist of polycondensates of polyhydric carboxylic acids or derivatives thereof and polyhydric alcohols. Divalent dicarboxylic acids or derivatives thereof can be used as polyvalent carboxylic acids or derivatives thereof, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. Dihydric diols can be used as polyhydric alcohols, such as ethylene glycol, propanediol, butanediol, neopentyl glycol, and cyclohexanedimethanol. A representative example of the polyester resin is polyethylene terephthalate, which is a polycondensate of terephthalic acid and ethylene glycol.

A (meth)acrylic resin is a resin containing a compound having a (meth)acryloyl group as a main constituent monomer. Specific examples of (meth)acrylic resins include, for example, poly(meth)acrylic acid esters such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymer; methyl methacrylate-(meth)acrylic acid Ester copolymer; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer; methyl (meth)acrylate-styrene copolymer (MS resin, etc.); (eg, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferably, a polymer containing poly (meth)acrylic acid C _1-6 alkyl ester as a main component such as polymethyl (meth)acrylate is used, and more preferably a polymer containing methyl methacrylate as a main component (50 to 100 % by weight, preferably 70 to 100% by weight) is used.

Cellulose ester resin is an ester of cellulose and fatty acid. Specific examples of cellulose ester resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Copolymers thereof and those in which a part of hydroxyl groups are modified with other substituents are also included. Among these, cellulose triacetate (triacetylcellulose) is particularly preferred.

Polycarbonate-based resins are engineering plastics composed of polymers in which monomer units are linked via carbonate groups.

It is also useful to control the retardation value of the protective film to a value suitable for an image display device such as a liquid crystal display device. For example, in an in-plane switching (IPS) mode liquid crystal display device, it is preferable to use a film having substantially zero retardation value as the protective film. A substantially zero retardation value means that the in-plane retardation value R ₀ at a wavelength of 590 nm is 10 nm or less, the absolute value of the thickness direction retardation value R _th at a wavelength of 590 nm is 10 nm or less, and the wavelength is 480 to 750 nm. The absolute value of the thickness direction retardation value R _th in is 15 nm or less.

For example, depending on the mode of the liquid crystal display device, the protective film may be stretched and/or shrunk to give a suitable retardation value. For example, for the purpose of viewing angle compensation, a single-layer or multi-layer retardation layer (or film) can be used as the protective film. In this case, the polarizing plate 1 may be an elliptically polarizing plate or circularly polarizing plate including a laminated structure of a polarizer and a retardation layer, or a polarizing plate including a retardation layer and having a viewing angle compensation function.

The thickness of the protective film is usually 1 to 100 μm, preferably 5 to 60 μm, more preferably 5 to 50 μm, from the viewpoint of strength, handleability, and the like. If the thickness is within this range, the polarizer can be mechanically protected, the polarizer will not shrink even when exposed to a wet and hot environment, and stable optical properties can be maintained.

When protective films are laminated on both sides of the polarizer, these protective films may be made of the same kind of thermoplastic resin, or may be made of different kinds of thermoplastic resins. Moreover, the thickness may be the same or may be different. Furthermore, they may have the same phase difference characteristics or different phase difference characteristics.

As described above, at least one of the protective films has a hard coat layer, an antiglare layer, a light diffusion layer, a retardation layer (at a quarter wavelength) on its outer surface (the surface opposite to the polarizer). A retardation layer having a retardation value, etc.), an antireflection layer, a low refractive index layer, an antistatic layer, and a surface treatment layer (coating layer) such as an antifouling layer may be provided.

From the viewpoint of suppressing air bubbles from entering between the surface protective film and the polarizing plate, the surface of the polarizing plate 1 on the side of the surface protective film 2 (the surface to which the surface protective film 2 is laminated) conforms to JIS B 0601:2013. is preferably small. Specifically, the surface Ra is preferably 0.3 μm or less, more preferably 0.2 μm or less, and still more preferably 0.15 μm or less. Ra of the surface is usually 0.001 μm or more, for example 0.005 μm or more.

The protective film can be attached to the polarizer via an adhesive layer, for example. As the adhesive for forming the adhesive layer, a water-based adhesive, an active energy ray-curable adhesive or a thermosetting adhesive can be used, preferably a water-based adhesive or an active energy ray-curable adhesive.

Examples of water-based adhesives include adhesives composed of a polyvinyl alcohol-based resin aqueous solution, water-based two-liquid type urethane-based emulsion adhesives, and the like. Among them, a water-based adhesive composed of an aqueous polyvinyl alcohol resin solution is preferably used. Polyvinyl alcohol-based resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. A polyvinyl alcohol-based copolymer obtained by saponifying a polymer, or a modified polyvinyl alcohol-based polymer obtained by partially modifying the hydroxyl groups thereof can be used. The water-based adhesive can contain cross-linking agents such as aldehyde compounds (glyoxal, etc.), epoxy compounds, melamine compounds, methylol compounds, isocyanate compounds, amine compounds, polyvalent metal salts, and the like.

When using a water-based adhesive, it is preferable to carry out a drying process for removing water contained in the water-based adhesive after bonding the polarizer and the protective film. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45°C may be provided.

The active energy ray-curable adhesive is an adhesive containing a curable compound that is cured by irradiation with an active energy ray such as ultraviolet rays, visible light, electron beams, and X-rays, and is preferably an ultraviolet curable adhesive. is.

The curable compound can be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of cationic polymerizable curable compounds include epoxy compounds (compounds having one or more epoxy groups in the molecule) and oxetane compounds (one or two or more oxetane rings in the molecule). compound), or a combination thereof. Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule) and radically polymerizable double bonds. Other vinyl-based compounds or combinations thereof can be included. A cationic polymerizable curable compound and a radically polymerizable curable compound may be used in combination. The active energy ray-curable adhesive usually further contains a cationic polymerization initiator and/or a radical polymerization initiator for initiating the curing reaction of the curable compound.

When bonding the polarizer and the protective film, surface activation treatment may be applied to the bonding surface of at least one of them in order to enhance the adhesiveness. Surface activation treatments include dry treatments such as corona treatment, plasma treatment, discharge treatment (glow discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, ionizing active ray treatment (ultraviolet treatment, electron beam treatment, etc.). ; ultrasonic treatment using a solvent such as water or acetone, saponification treatment, and wet treatment such as anchor coating treatment can be mentioned. These surface activation treatments may be performed singly or in combination of two or more.

When the protective films are laminated on both sides of the polarizer, the adhesive for laminating these protective films may be of the same type or different types.

(3) Other Optical Films The polarizing plate 1 can contain optical films other than the polarizer and the protective film, and typical examples thereof are a brightness enhancement film and a retardation film. When the polarizing plate 1 contains another optical film, the surface protection film 2 may be laminated on the surface of this optical film or the surface of the resin layer laminated on this optical film.

The brightness enhancement film is also called a reflective polarizing film, and uses a polarization conversion element having a function of separating light emitted from a light source (backlight) into transmitted polarized light and reflected polarized light or scattered polarized light. By arranging the brightness enhancement film on the polarizer, it is possible to improve the output efficiency of the linearly polarized light emitted from the polarizer by using retroreflected light that is reflected polarized light or scattered polarized light. A brightness enhancement film can be laminated on a polarizer via an adhesive layer. Another film such as a protective film may be interposed between the polarizer and the brightness enhancement film.

The brightness enhancement film can be, for example, an anisotropic reflective polarizer. An example of an anisotropic reflective polarizer is an anisotropic multilayer thin film that transmits linearly polarized light in one vibration direction and reflects linearly polarized light in the other vibration direction. (See JP-A-4-268505, etc.). Another example of the anisotropic reflective polarizer is a composite of a cholesteric liquid crystal layer and a λ/4 plate, a specific example of which is "PCF" manufactured by Nitto Denko Co., Ltd. etc.). Yet another example of an anisotropic reflective polarizer is a reflective grid polarizer, a specific example of which is a metal grid reflective polarizer (U.S. Patent No. 6288840, etc.), and a stretched film obtained by adding fine metal particles to a polymer matrix (see JP-A-8-184701, etc.).

As described above, the outer surface of the brightness enhancement film is coated with a hard coat layer, an antiglare layer, a light diffusion layer, a retardation layer (such as a retardation layer having a retardation value of 1/4 wavelength), an antireflection layer, and a low refractive index layer. A surface treatment layer (coating layer) such as an antistatic layer, an antistatic layer, and an antifouling layer may be provided. By forming such a layer, the adhesion to the backlight tape and the uniformity of the displayed image can be improved. The thickness of the brightness enhancement film 50 is usually 10 to 100 μm, preferably 10 to 50 μm, more preferably 10 to 30 μm, from the viewpoint of thinning the polarizing plate 1 .

(4) Adhesive layer The polarizing plate 1 preferably has an adhesive layer on its outermost surface. This pressure-sensitive adhesive layer can be used to bond the polarizing plate 1 to a display element (for example, a liquid crystal cell) or other optical members.
A release film 3 is preferably laminated on this pressure-sensitive adhesive layer. Moreover, the pressure-sensitive adhesive layer can also be used to laminate a polarizer and a protective film or a brightness enhancement film. The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition whose main component is a (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether resin. Among them, a pressure-sensitive adhesive composition using a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is preferable. The adhesive composition may be active energy ray-curable or heat-curable.

Examples of the (meth)acrylic resin (base polymer) used in the adhesive composition include butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-(meth)acrylate. Polymers or copolymers containing one or more of (meth)acrylic acid esters such as ethylhexyl as monomers are preferably used. Preferably, the base polymer is copolymerized with a polar monomer. Examples of polar monomers include (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, glycidyl ( Monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as meth)acrylates, can be mentioned.

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a metal ion having a valence of 2 or more, which forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound, which forms an amide bond with a carboxyl group; Examples include epoxy compounds and polyols that form ester bonds with carboxyl groups; and polyisocyanate compounds that form amide bonds with carboxyl groups. Among them, polyisocyanate compounds are preferred.

The active energy ray-curable pressure-sensitive adhesive composition has the property of being cured by being irradiated with an active energy ray such as an ultraviolet ray or an electron beam. It is a pressure-sensitive adhesive composition that can be adhered to an adherend such as the adhesive agent, and that can be cured by irradiation with an active energy ray to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably UV-curable. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Furthermore, if necessary, a photopolymerization initiator, a photosensitizer, and the like can be contained.

The adhesive composition contains fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, antistatic agents, tackifiers, fillers (metal powder, Other inorganic powders, etc.), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators, and other additives may be included.

The pressure-sensitive adhesive layer can be formed by applying an organic solvent-diluted solution of the above pressure-sensitive adhesive composition onto a substrate and drying it. The substrate can be a polarizer, a protective film, other optical films such as a brightness enhancement film, a release film (eg, release film 3), and the like. When an active energy ray-curable pressure-sensitive adhesive composition is used, a cured product having a desired degree of curing can be obtained by irradiating the formed pressure-sensitive adhesive layer with an active energy ray.

The thickness of the adhesive layer is usually 1 to 40 μm, but from the viewpoint of thinning the optical sheet and suppressing the dimensional change of the polarizing plate 1 while maintaining good workability, it is 3 to 25 μm (for example, 3 to 25 μm). 20 μm, more preferably 3 to 15 μm).

<Surface protection film>
The surface protective film 2 can include a base film and an adhesive layer laminated thereon. The surface protective film 2 is a film for protecting the surface of the polarizing plate 1, and is usually peeled off together with the pressure-sensitive adhesive layer after the optical sheet is laminated to, for example, a display element or other optical member. .

The base film is preferably a thermoplastic resin film. Thermoplastic resins constituting the thermoplastic resin film include, for example, polyethylene-based resins, polyolefin-based resins such as polypropylene-based resins; cyclic polyolefin-based resins; polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate; polycarbonate-based resins; (Meth)acrylic resins and the like can be mentioned. The base film may have a single layer structure or a multilayer structure.

The thickness of the base film can be 20-150 μm (eg, 30-80 μm, preferably 30-60 μm), and the thickness of the surface protective film 2 can be 40-200 μm (eg, 50-160 μm). As for the structure of the pressure-sensitive adhesive layer, the description of the pressure-sensitive adhesive layer of the polarizing plate described above is basically cited.

In particular, the pressure-sensitive adhesive layer preferably has a storage modulus of 0.15 MPa or less, more preferably 0.14 MPa or less, and even more preferably 0.10 MPa or less at 80°C. Usually, the storage elastic modulus of the pressure-sensitive adhesive layer at 80°C is 0.01 MPa or more. In this specification, the storage elastic modulus of the pressure-sensitive adhesive layer can be measured using a commercially available viscoelasticity measuring device, for example, a viscoelasticity measuring device "DYNAMIC ANALYZER RDA II" manufactured by REOMETRIC.

The surface of surface protective film 2 opposite to polarizing plate 1 preferably has a surface resistivity of 1×10 ⁷ to 1×10 ¹² Ω/□. It can be said that a surface protective film having such a surface resistivity has an antistatic function. A surface protection film having such a surface resistivity is less likely to be charged and has a coefficient of dynamic friction that is easily controlled to 0.40 or less. When the surface resistivity is more than 1×10 ¹² Ω/□, the surface protective film is easily electrified. The surface resistivity is measured by the method described in Examples below.

The surface protection film 2 can contain an antistatic agent. An antistatic agent can be contained, for example, in the pressure-sensitive adhesive layer. Instead of containing an antistatic agent in the adhesive layer, or together with this, an antistatic layer containing an antistatic agent may be provided on the surface of the base film opposite to the surface on which the adhesive layer is laminated. good.

Antistatic agents may include ionic compounds. An ionic compound is a compound having an inorganic or organic cation and an inorganic or organic anion.
Two or more ionic compounds may be used.

<Release film>
The release film 3 is a film that is temporarily adhered to protect the surface of the pressure-sensitive adhesive layer until it is bonded to a display element (for example, a liquid crystal cell) or another optical member. The release film 3 is usually composed of a thermoplastic resin film having one side treated with a release agent such as silicone or fluorine, and the release-treated side is attached to the pressure-sensitive adhesive layer. An antistatic layer is preferably formed on the surface of the release film 3 opposite to the polarizing plate 1 .

When the optical sheet 10 is obtained by cutting the optical sheet produced by roll-to-roll, in producing the long optical sheet, the release film is provided as a wound body in which the long release film is wound. There is something. In the roll of the release film, the surface (release-treated surface) to be bonded to the pressure-sensitive adhesive layer and the outermost surface of the optical sheet 10 are in contact with each other. It may be transferred to the surface of the sheet 10 that will be the outermost surface. As a result of investigation by the present inventors, it was found that using transfer makes it easier to prevent multiple picking.
On the other hand, the surface of the release film 3 is decorated in order to remove the protrusion of the pressure-sensitive adhesive layer and the like. Since the surface is cleaned by beautification, the transferred silicon atoms are removed, and the abundance of silicon atoms is often low. Therefore, it is effective to prevent multiple pickings by giving a proper appearance.

From the viewpoint of preventing multiple removal, the surface of the release film 3 opposite to the polarizing plate 1 preferably has a silicon atom abundance of 2% or more, more preferably 4% or more, and more preferably 6%. or more. On the other hand, since it is also necessary to carry out a proper appearance, the content of silicon atoms is usually 10% or less, preferably 8% or less. In the present invention, the abundance ratio of silicon atoms is a value determined by X-ray photoelectron spectroscopy, and the details are described in Examples below.

Of course, silicone may be applied to the surface of the release film 3 to adjust the abundance of silicon atoms.

Moreover, the ratio of silicon atoms present on one surface and the other surface of the release film 3 may be the same or may be different.

The surface of the release film 3 opposite to the polarizing plate 1 preferably has a surface resistivity of 1×10 ⁷ to 1×10 ¹² Ω/□. It can be said that a release film having such a surface resistivity has an antistatic function. A release film having such a surface resistivity is less likely to be charged, and the coefficient of dynamic friction is easily controlled to 0.40 or less. When the surface resistivity is more than 1×10 ¹² Ω/□, the release film tends to be electrified. The surface resistivity is measured by the method described in Examples below.

The surface resistivity of the release film can be controlled by forming an antistatic layer on the surface of the release film. The antistatic layer is formed, for example, by applying an antistatic spray to the release film or by applying and curing a resin composition containing an antistatic agent. As the static electricity removing spray, static electricity removing liquid "SB-8" manufactured by Showa Kako Co., Ltd. can be mentioned. As the antistatic agent, those exemplified above can be used.

The thermoplastic resin forming the release film 3 can be, for example, a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate, or the like. The thickness of the release film 3 is, for example, 10 to 50 μm.

<Marking>
The optical sheet 10 may have markings 4 on at least one of the surface protection film 2 and the release film 3 , and preferably the release film has the markings 4 . Surface protection film 2 or release film 3 preferably has marking 4 on the surface opposite to polarizing plate 1 . When the optical sheet 10 is obtained by cutting the optical sheet manufactured by roll-to-roll, the marking may be performed before cutting the long optical sheet or after the cutting.

By marking, for example, the absorption axis direction or the transmission axis direction of the polarizing plate 1 can be easily determined, and alignment becomes easy when the polarizing plate is attached to a liquid crystal cell, for example.
On the other hand, the present inventors' studies have revealed that the presence of markings on the optical sheet makes it easier for multiple pickings to occur. Although not intended to limit the present invention, the reason for this is thought to be that marking causes the coating film to swell on the surface of the optical sheet 10, increasing the coefficient of dynamic friction.

From the viewpoint of preventing multiple markings, the ratio of the marking area to the release film area is preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less.

From the same point of view, the height of the marking (coating film) from the film surface is preferably 0.1 to 0.2 μm, and may be 0.3 to 0.5 μm.

The marking 4 can be performed with an ink jet type or contact type pen using oily ink or water-based ink, and the marking can be a coating film thereof. The marking colors can be red, yellow, green, cyan, blue, magenta, white, black, and mixtures thereof, and may be marked in one color or in multiple colors. good.

FIG. 3 shows an example in which markings 4 are provided on the release film 3, and the linear markings 4 are formed between the two sides of the optical sheet 10 facing each other. The shape of the marking is not limited to this, and may be straight lines, dotted lines, broken lines, curved lines, and combinations thereof, as shown in FIGS. and a figure such as a combination thereof, or letters and numbers.

<Laminate of optical sheets>
By stacking a plurality of optical sheets, a laminate of optical sheets can be obtained, and this can be supplied to an optical sheet supply device. As shown in FIG. 2, the optical sheet laminate 100 preferably overlaps such that the release film 3 of one optical sheet 10 and the surface protection film 2 of another optical sheet 10 are in contact with each other.

The optical sheets 10 constituting the optical sheet laminate 100 may all be the same optical sheet, or may be partially different optical sheets. The number of optical sheets constituting the optical sheet laminate 100 is not particularly limited, but can be, for example, 100 to 500 sheets.

The optical sheet 10 taken out from the laminate 100 of optical sheets can be bonded to a display element (for example, a liquid crystal cell) after peeling off the release film 3 . Furthermore, the surface protective film 2 can be peeled off and incorporated into a display device (for example, a liquid crystal display device). In constructing a display device, the optical sheet 10 according to the present invention may be used for the polarizing plate arranged on the viewing side, may be used for the polarizing plate arranged on the backlight side, or may be used for the polarizing plate placed on the viewing side. and the polarizing plate on the backlight side.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

(1) Method for Measuring Dynamic Friction Coefficient A surface property measuring instrument TYPE: 14FW manufactured by Shinto Kagaku Co., Ltd. was used to measure the dynamic friction coefficient between the surface protective film and the release film. Specifically, first, an optical sheet was cut into a size of 11 cm×6.3 cm, and was attached to a fixture connected to a movable stage and a load cell of the measuring machine. Two optical sheets were arranged so that the release film and the surface protective film faced each other. Next, a load of 500 g is applied from above the overlapping films, and the moving distance of 15.0 mm is reciprocated 100 times at a speed of 5000 mm / min. An average was calculated. Although the dynamic friction coefficient did not change depending on the direction of the marking provided in the embodiment and the moving direction of the movable stage, if there is anisotropy, the dynamic friction coefficient in the direction in which the dynamic friction coefficient becomes maximum is adopted.

(2) Method for measuring silicon atom abundance The abundance of silicon atoms on the film surface was measured by X-ray photoelectron spectroscopy (XPS) using K-Alpha manufactured by Thermo Fisher Scientific.
The surface to be measured is the back surface of the release film (the surface opposite to the surface in contact with the pressure-sensitive adhesive layer). After measuring carbon atoms, oxygen atoms, and silicon atoms with a photoelectron extraction angle of 90°, the detected amount of silicon atoms was calculated.

(3) Method for measuring film thickness Measured using a digital micrometer “MH-15M” manufactured by Nikon Corporation.

(4) Evaluation method for multiple picking Two optical sheets were placed so that the surface protection film surface and the release film surface were overlapped, and they were rubbed together 10 times while being pressed by hand. After that, the stacked films were shifted by 1 cm, and only one sheet was held and lifted. If the two sheets were stuck together, it was shaken three times to see if one of the sheets fell off. If one of the sheets did not come off even after this operation, it was regarded as occurrence of multiple picking.

(5) Surface resistivity measurement method Surface resistivity (Ω /□) was measured using MCP-HT450 manufactured by Mitsubishi Chemical Analytic Tech. "over" in the table means that the surface resistivity is over 1×10 ¹² Ω/□.

<Production of optical sheet 1>
A polarizing plate having the following layer structure was prepared.
Protective film 1/polarizer/protective film 2
The protective film 1 was a cyclic olefin resin film and had a thickness of 23 μm.
The protective film 2 was a cyclic olefin resin film having a hard coat layer on its surface and had a thickness of 30 μm.
The polarizer was a film in which iodine was adsorbed and oriented on a PVA-based resin film, and had a thickness of 8 μm.

A release film having an adhesive layer was laminated on the surface of protective film 1 in the polarizing plate, and a surface protective film was laminated on the surface of protective film 2 in the polarizing plate to prepare optical sheet 1 .
A polyethylene terephthalate film (thickness: 38 μm) having an adhesive layer with a thickness of 20 μm was used as the surface protection film. The thickness of the surface protection film was 58 µm. An antistatic layer was formed on the side of the polyethylene terephthalate film opposite to the side in contact with the pressure-sensitive adhesive layer, and the surface resistivity of the surface protective film surface was 1×10 ⁹ Ω/□. A polyethylene terephthalate film was used as the release film. The thickness of the release film was 38 μm. A pressure-sensitive adhesive layer having a thickness of 20 μm was formed on the release film. In addition, the pressure-sensitive adhesive layer on the release film is a member that the polarizing plate is finally equipped with.
After that, the optical sheet 1 was cut into a rectangular shape with long sides of 110 mm and short sides of 63 mm.

<Optical sheet 2>
An optical sheet 2 was produced in the same manner as the optical sheet production 1, except that a surface protection film without an antistatic layer was used. The optical sheet 2 was cut into a rectangular shape with long sides of 110 mm and short sides of 63 mm.

<Example 1>
Silicone was applied to the release film surface (the surface of the release film opposite to the polarizing plate) of the obtained optical sheet 1 to prepare an optical sheet for evaluation. The abundance of silicon atoms was 7%. No marking was applied to the surface of the release film.

<Example 2>
A straight line as shown in FIG. An optical sheet for evaluation was produced in the same manner as in Example 1, except that the marking was formed by drawing.
The ratio of the marking area to the release film area was 1%. The marking height was 0.3 μm from the release film surface.

<Example 3>
An evaluation optical sheet was produced in the same manner as in Example 2, except that three lines were drawn.
The ratio of the marking area to the release film area was 3%.

<Examples 4 to 6>
Optical sheets for evaluation were produced in the same manner as in Examples 1 to 3, except that the coating amount of silicone was adjusted so that the proportion of silicon atoms was 3%.

<Examples 7 to 9>
Instead of applying silicone to the surface of the release film (the surface of the release film opposite to the polarizing plate) of the obtained optical sheet 1, static electricity removal liquid "SB-8" manufactured by Showa Kako Co., Ltd. was applied. , the surface resistivity was 1×10 ⁹ Ω/□. Optical sheets for evaluation were produced in the same manner as in Examples 1 to 3 except for the above.

<Examples 10 to 12>
Optical sheets for evaluation were prepared in the same manner as in Examples 7 to 9, except that the amount of the static electricity removing liquid applied was adjusted so that the surface resistivity was 1×10 ¹² Ω/□.

<Example 13>
The release film surface of the obtained optical sheet 2 (the surface of the release film opposite to the polarizing plate) was coated with static electricity removal liquid "SB-8" manufactured by Showa Kako Co., Ltd. to measure the surface resistance of the release film. The rate was set to 1×10 ¹² Ω/square. On the surface of the surface protection film (the surface of the surface protection film opposite to the polarizing plate), static electricity removal liquid "SB-8" also manufactured by Showa Kako Co., Ltd. is applied to reduce the surface resistivity of the surface protection film to 1. ×10 ¹² Ω/□. Thus, an optical sheet for evaluation was produced.

<Examples 14 to 16>
An optical sheet for evaluation was prepared in the same manner as in Example 13, except that the amount of static electricity removal liquid applied was adjusted to control the surface resistivity of the surface of the release film and the surface protective film to the values shown in Table 2. made respectively.

<Comparative Examples 1 to 3>
In Examples 1 to 3, the surface of the release film of the optical sheet was wiped several times with a cloth impregnated with IP solvent (an ethanol-based solvent obtained from Showa Kako Co., Ltd.). , and optical sheets for evaluation were prepared.

<Comparative Example 4>
In Example 1, silicone was not applied to the release film surface, and the release film surface of the optical sheet was wiped several times with a cloth impregnated with IP solvent (an ethanol-based solvent obtained from Showa Kako Co., Ltd.). An optical sheet for evaluation was produced in the same manner as above except for the above.

<Comparative Example 5>
An optical sheet for evaluation was prepared in the same manner as in Example 13, except that the amount of static electricity removal liquid applied was adjusted to control the surface resistivity of the surface of the release film and the surface protective film to the values shown in Table 2. made. The surface protection film was not coated with static electricity removal liquid.

The optical sheets for evaluation produced in Examples 1 to 16 and Comparative Examples 1 to 5 were evaluated for multi-layering. Tables 1 and 2 show the results.

Advantageous Effects of Invention According to the present invention, it is possible to provide an optical sheet that is less likely to be taken multiple times when the optical sheets are taken out one by one from a laminate in which a plurality of optical sheets are stacked.

REFERENCE SIGNS LIST 1 polarizing plate 2 surface protection film 3 release film 4 marking 10 optical sheet 100 laminate of optical sheets

Claims (5)

Having a surface protective film, a polarizing plate, and a release film in this order,
A coefficient of dynamic friction between the surface protective film and the release film is 0.4 or less,
The release film has a marking on the surface opposite to the polarizing plate,
The marking has a height of 0.5 μm or less from the film surface,
The dynamic friction coefficient was determined by cutting the optical sheet into a size of 11 cm × 6.3 cm, attaching it to a movable stage of a measuring machine and a fixing jig connected to a load cell, and measuring the release film and the surface protection. Two optical sheets were arranged so that the films faced each other, then a load of 500 g was applied from above the overlapping films, and a moving distance of 15.0 mm was reciprocated 100 times at a speed of 5000 mm/min. The optical sheet measured by calculating the average dynamic friction coefficient from the magnitude of the force detected by the load cell at the time. 2. The optical sheet according to claim 1, wherein the ratio of the area of the marking to the area of the release film is 5% or less. 3. The optical sheet according to claim 1, wherein the surface of the polarizing plate on the surface protection film side has an arithmetic mean roughness Ra of 0.001 μm or more and 0.3 μm or less according to JIS B 0601:2013. 4. The optical sheet according to any one of claims 1 to 3, wherein the surface of the release film opposite to the polarizing plate has a silicon atom content of 2% or more. The surface of the surface protective film opposite to the polarizing plate has a surface resistivity of 1×10 ⁷ to 1×10 ¹² Ω/□,
5. The optical sheet according to claim 1, wherein the surface of the release film opposite to the polarizing plate has a surface resistivity of 1×10 ⁷ to 1×10 ¹² Ω/□.

Images