JP7370714B2 - Optical components with protective film - Google Patents

Description

The present invention relates to a surface protection film with high adhesiveness and an optical member to which the surface protection film is attached.

Surface protection films are used in various fields to protect the surfaces of various adherends by being attached to them. In recent years, surface protection films have been used to protect the surfaces of various members in the optical and electronic fields. In the optical field, electronic field, etc., adherends provided with an anti-fingerprint coating layer, adherends provided with a curved surface, etc. are sometimes used.

For example, Patent Document 1 discloses that a pressure-sensitive adhesive film is provided with a pressure-sensitive adhesive layer crosslinked with a pressure-sensitive adhesive composition containing an acrylic polymer having a specific monomer composition, an antistatic agent, a crosslinking agent, etc. for antistatic surface protection. It has been proposed to use it as a film. Patent Document 1 also describes attaching an adhesive layer to a low refractive index layer (antifouling layer) containing a fluorine compound.

Patent Document 2 proposes a surface protection sheet having a pressure-sensitive adhesive layer of a pressure-sensitive adhesive composition containing an onium salt and a base polymer on one side of a support film. Patent Document 2 describes that it is possible to achieve both adhesion and repulsion resistance (adhesion to curved surfaces) by using a crosslinking agent in combination.

JP2017-222797A (Claims 1, 6 and 8, paragraph [0060]) JP2018-205421A (Claims 1 and 4, paragraph [0078])

When attaching a surface protection film to a curved surface, the effect of repulsion of the base material layer supporting the adhesive layer tends to appear, making it difficult to make the surface protection film follow the curved surface. Some surface protection films using conventional acrylic pressure-sensitive adhesives claim to have high adhesiveness, but even if the adhesiveness is high for flat surfaces, the adhesiveness for curved surfaces is insufficient. If the adhesiveness to the curved portion is insufficient, even if a surface protection film is applied, the film will lift from the edge. Starting from this floating portion, the film tends to peel off, making it impossible to effectively protect the surface of the adherend.

On the other hand, in the optical field or the electronic field, members whose surfaces are coated with anti-fingerprint coating are sometimes used. Intermolecular forces are difficult to act on the anti-fingerprint coating, and even if a surface protection film is applied, the adhesive force of the adhesive layer will be impaired. Therefore, even if a conventional surface protection film is used, it is difficult to attach it to the anti-fingerprint coating with high adhesive strength.

One aspect of the present invention includes a base layer and an adhesive layer disposed on at least one surface of the base layer,
The adhesive layer includes an acrylic polymer,
The present invention relates to a surface protection film having a peel strength of 0.2 N/25 mm or more under the conditions of a temperature of 23° C. and a peel rate of 300 mm/min in a 180° peel test on anti-fingerprint coated glass.

Another aspect of the present invention relates to an optical member to which the surface protection film is attached via the adhesive layer.

High adhesion of the surface protection film to curved surfaces can be ensured.

The surface protection film according to the above aspect of the present invention is provided with an adhesive layer containing an acrylic polymer, and has a peel strength of 0.2 N/25 mm or more in a peel test on anti-fingerprint coated glass under predetermined conditions. This configuration not only ensures high adhesion to adherends coated with anti-fingerprint coatings, but also prevents floating, etc. It becomes possible to paste with high adhesive strength without causing any problems. That is, even when attached to a curved surface, lifting and peeling of the surface protection film can be suppressed, and the surface protection film can be made to follow the curved surface. Even when the curved surface is coated with anti-fingerprint coating, the followability to the curved surface can be improved. Therefore, the surface of the adherend can be more effectively protected.

On the other hand, in a surface protection film using a conventional acrylic adhesive, the peel strength measured under the same conditions as above is, for example, 0.13 N/25 mm or less. Even a surface protection film exhibiting such peel strength exhibits sufficient adhesive strength without causing any lifting when attached to a flat surface. This is because when pasting on a flat surface, the stress applied to the base material layer and adhesive layer is small, so there is almost no effect of the repulsive force of the base material layer, and the stress distribution of the adhesive layer is relatively uniform. be. However, when attaching a surface protection film to a curved surface, stress is applied to the base material layer and adhesive layer by placing the film along the curved surface, so the influence of the repulsive force of the base material layer becomes large and the adhesive The stress distribution in the agent layer also becomes non-uniform. Therefore, the conventional adhesive force (peel strength) as described above is insufficient for curved surfaces, and the surface protection film floats from the edges, making it difficult to follow the curved surface. Furthermore, since the adhesiveness to the anti-fingerprint coating is low, the ability to follow the curved surface coated with the anti-fingerprint coating is low.

Note that the 180° peel test of the surface protection film is conducted at a temperature of 23° C. according to JIS K6854-2:1999. The anti-fingerprint coated glass used as the adherend for the peel test is a glass plate with a thickness of 1.5 mm and a width of 25 mm ± 0.5 mm, with a 10 nm thick anti-fingerprint coat layer formed on the entire surface of one side. . The adhesive layer of the surface protection film is pasted on the surface of the anti-fingerprint coating layer, and one end of the surface protection film is pulled 180 degrees in the opposite direction at a speed of 300 mm/min (peel speed) to peel it off from the anti-fingerprint coating layer. The strength at that time is determined as the peel strength. The anti-fingerprint coating layer is formed by applying an anti-fingerprint coating agent (manufactured by Daikin Industries, Ltd., Optool UD509) to one side of the glass plate and drying it. Note that if the same anti-fingerprint coating agent is not available, the anti-fingerprint coating layer can be formed using an anti-fingerprint coating agent containing a perfluoropolyether-containing alkylsilane. The contact angle (static contact angle) of water on the surface of the anti-fingerprint coating layer is adjusted to 110°±10°. As the glass plate, a soda glass plate is used. The soda glass plate used has a water contact angle of 50±5° on the surface on which the anti-fingerprint coating layer is formed.

The present invention also includes the use of the surface protection film for optical members.

Below, the surface protection film according to the above aspect of the present invention and the optical member to which the surface protection film is attached will be described in more detail.

[Surface protection film]
The peel strength of the surface protection film in the above peel test may be 0.2 N/25 mm or more, and may be 0.25 N/25 mm or more. Further, a high peel strength of 0.30 N/25 mm or more or 0.35 N/25 mm or more (or 0.40 N/25 mm or more) can also be ensured. The upper limit of the peel strength is not particularly limited, but from the viewpoint of suppressing the adhesive from remaining on the adherend during peeling, it is preferably 1 N/25 mm or less.

Note that when the surface protection film is exposed to high temperatures, the base layer may shrink and/or the viscoelasticity of the adhesive layer may change, resulting in a decrease in adhesiveness. The surface protection film according to the above aspect of the present invention can ensure high adhesiveness even when exposed to high temperatures, and can ensure high followability to curved surfaces. The tackiness after being exposed to high temperatures is evaluated using, for example, a surface protection film that is exposed to a temperature of 150° C. for 30 minutes and left to cool to room temperature (20° C. or higher and 35° C. or lower).

(Adhesive layer)
The adhesive layer of the surface protection film may be disposed on at least one surface (specifically, the main surface) of the base layer. Although the adhesive layer may be placed on both surfaces of the base layer, it is usually placed on one surface. The adhesive layer only needs to be placed on at least a partial area of one surface of the base layer, and may be placed on the entire surface. The adhesive layer may be disposed continuously on one surface of the base layer, or may be disposed at multiple locations at intervals. When the adhesive layer is arranged in a plurality of places, it may be arranged in a fixed pattern, it may be arranged at random, or a combination thereof may be used.

(acrylic polymer)
The acrylic polymer contained in the adhesive layer contains acrylic monomer units. The acrylic polymer may contain one type of acrylic monomer unit. From the viewpoint of easy control of the physical properties of the polymer, it is preferable that the acrylic polymer contains two or more types of acrylic monomer units.

Examples of the acrylic monomer include (meth)acrylic acid, (meth)acrylic acid ester, (meth)acrylamide compound, glycidyl (meth)acrylate, and the like. The acrylic monomer may have one (meth)acryloyl group, or may have two or more (meth)acryloyl groups. A monomer having two or more (meth)acryloyl groups also functions as a crosslinking agent. When using a monomer having two or more (meth)acryloyl groups, the peel strength can be adjusted by controlling the type and/or amount thereof.

In this specification, acrylic acid and methacrylic acid may be collectively referred to as (meth)acrylic acid. Furthermore, acrylic esters and methacrylic esters may be collectively referred to as (meth)acrylic esters (or (meth)acrylates). Acrylamide (or compound) and methacrylamide (or compound) may be collectively referred to as (meth)acrylamide (or compound). An acryloyl group and a methacryloyl group may be collectively referred to as a (meth)acryloyl group.

The (meth)acryloyl group that the acrylic monomer has is a polymerizable functional group. Therefore, the acrylic polymer obtained by polymerizing monomers contains residues formed by polymerizing at least some (meth)acryloyl groups. This residue is represented by -C-C(-R ¹ )(-C(=O)-)-, where R ¹ is a hydrogen atom or a methyl group. The acrylic polymer may contain some (meth)acryloyl groups of the acrylic monomer in a polymerizable free state. In this specification, an acrylic monomer unit having a (meth)acryloyl group contained in an acrylic polymer means a monomer unit corresponding to an acrylic monomer. Therefore, the acrylic monomer unit having a (meth)acryloyl group includes the above-mentioned residue and/or an acrylic monomer unit having a free (meth)acryloyl group.

Examples of (meth)acrylic acid esters include esters of (meth)acrylic acid and hydroxy compounds. (Meth)acrylic acid esters include (meth)acrylic acid esters of aromatic hydroxy compounds (including phenols), (meth)acrylic acid esters of alicyclic hydroxy compounds, and (meth)acrylic acid esters of aliphatic hydroxy compounds. Examples include esters. From the viewpoint of easily ensuring appropriate viscoelasticity and high adhesiveness, the acrylic polymer preferably contains at least (meth)acrylic acid ester units of an aliphatic hydroxy compound.

Examples of (meth)acrylic acid esters of aromatic hydroxy compounds include aralkyl (meth)acrylates (benzyl (meth)acrylate, etc.), aryl (meth)acrylates (phenyl (meth)acrylate, etc.), and the like. In these (meth)acrylic esters, the aralkyl moiety and the aryl moiety may have a substituent (first substituent). The first substituent includes an alkyl group (for example, a C _1-6 alkyl group (methyl group, ethyl group, etc.)), a halogenated alkyl group (for example, a halogenated C _1-6 alkyl group), a hydroxyalkyl group (for example, , hydroxy C _1-6 alkyl group), alkoxy group (for example, C _1-6 alkoxy group (methoxy group, ethoxy group, etc.)), hydroxy group, epoxy group, glycidyl group, and/or halogen atom.

Examples of (meth)acrylic esters of alicyclic hydroxy compounds include cycloalkyl (meth)acrylates (cyclohexyl (meth)acrylate, etc.), (meth)acrylic esters of crosslinked cyclic hydroxy compounds (dicyclopentanyl (meth)acrylate, etc.). In these (meth)acrylic esters, the cycloalkyl moiety and the bridged ring may have a substituent (second substituent). Examples of the second substituent include aryl groups (phenyl group, tolyl group, etc.), halogenated aryl groups, and/or those exemplified for the first substituent.

Examples of the (meth)acrylic acid ester of an aliphatic hydroxy compound include alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate.

The alkyl moieties of alkyl (meth)acrylates and hydroxyalkyl (meth)acrylates include methyl, ethyl, propyl, butyl, t-butyl, hexyl, 2-ethylhexyl, octyl, decyl, lauryl, myristyl, cetyl, stearyl, isostearyl. , behenyl, etc. The alkyl moiety may be either linear or branched. Examples of alkyl (meth)acrylates include C _1-26 alkyl (meth)acrylates. Examples of the hydroxyalkyl (meth)acrylate include hydroxy C _1-26 alkyl (meth)acrylate. As the hydroxyalkyl (meth)acrylate, hydroxy C _1-10 alkyl (meth)acrylate is preferred, and hydroxy C _1-6 alkyl (meth)acrylate may also be used.

The alkyl moiety of the alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate may have a substituent (tertiary substituent). Examples of the third substituent include alicyclic hydrocarbon groups (cycloalkyl groups, bridged cyclic hydrocarbon groups, etc.), halogenated alicyclic hydrocarbon groups, aryl groups (phenyl groups, tolyl groups, etc.), and halogenated aryl groups. Examples of the group and/or the first substituent may be mentioned.

A (meth)acrylamide compound is an acid amide of (meth)acrylic acid. A (meth)acrylamide compound has a structure in which the carboxy group of (meth)acrylic acid is replaced with -C(=O)-N<. (Meth)acrylamide compounds include (meth)acrylamide, alkyl (meth)acrylamide (N,N-dimethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-t-butyl (meth)acrylamide, N-( (2-hydroxyethyl)(meth)acrylamide, etc.), aryl(meth)acrylamide (N-phenyl(meth)acrylamide, N-(4-hydroxyphenyl)(meth)acrylamide, etc.), (meth)acrylic acid and cyclic amines Examples include acid amides ((meth)acryloylmorpholine, etc.), (meth)acrylamidic acids (6-(meth)acrylamidohexanoic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, etc.), and the like.

When the acrylic polymer contains C _14-26 alkyl (meth)acrylate units (hereinafter sometimes referred to as first monomer units), even higher adhesiveness can be ensured. When the acrylic polymer contains the first monomer unit, the adhesive becomes less polar and easily interacts with the low-polar anti-fingerprint coating, and the long side chains allow it to slip through the anti-fingerprint coating and connect to the adherend. It becomes easier to interact. Therefore, high adhesive strength can be obtained even to adherends having anti-fingerprint coatings. Moreover, when the acrylic polymer contains the first monomer unit, high adhesiveness can be ensured even after the surface protection film is exposed to high temperatures, and high conformability to curved surfaces can be maintained. This is thought to be due to the increased interaction between the adhesive, anti-fingerprint coat, and adherend, which maintains sufficient adhesiveness even after exposure to high temperatures.

As the first monomer unit, a C _16-22 alkyl (meth)acrylate unit or a C _16-20 alkyl (meth)acrylate unit is more preferable. Moreover, from the viewpoint of easily ensuring high adhesiveness, it is preferable that the first monomer unit contains at least an isostearyl (meth)acrylate unit.

The first monomer unit may have a third substituent (excluding hydroxyalkyl groups, hydroxy groups, epoxy groups, and glycidyl groups).

The acrylic polymer may contain one type of first monomer unit, or may contain two or more types of first monomer units.

The proportion of the first monomer unit in the acrylic polymer is, for example, 1% by mass or more, and may be 5% by mass or more. From the viewpoint of more easily ensuring the effect of the first monomer unit as described above, the proportion of the first monomer unit is preferably 15% by mass or more, more preferably 20% by mass or more, and 35% by mass or more or 40% by mass. It may be more than that. The upper limit of the proportion of the first monomer unit is not particularly limited, but from the viewpoint of easy control of the physical properties of the adhesive, it may be 70% by mass or less or 60% by mass or less.

The proportion of the first monomer unit in the acrylic polymer is, for example, 1% by mass or more and 70% by mass (or 60% by mass), 5% by mass or more and 70% by mass (or 60% by mass), 15% by mass or more and 70% by mass or less. mass% (or 60 mass%) or less, 20 mass% or more and 70 mass% (or 60 mass%) or less, 35 mass% or more and 70 mass% or less (or 60 mass%), 40 mass% or more and 70 mass% (or 60 mass%) mass%) or less.

In addition, in this specification, the ratio of each monomer unit in an acrylic polymer is the mass ratio of each monomer to the total amount of constituent monomers. The proportion of each monomer unit can be determined from the composition of the constituent monomers determined by ¹ H-NMR or the like of the acrylic polymer. The ratio of each monomer unit corresponds to the mass ratio (charge ratio) of each monomer to the total amount of raw material monomers of the acrylic polymer.

The acrylic polymer may contain a C _1-13 alkyl (meth)acrylate unit (hereinafter sometimes referred to as a second monomer unit). The second monomer unit may be a C _1-10 alkyl (meth)acrylate unit. When the acrylic polymer contains the second monomer unit, it is easy to control the glass transition point (Tg) of the acrylic polymer.

The second monomer unit may have a third substituent (excluding hydroxyalkyl groups, hydroxy groups, epoxy groups, and glycidyl groups).

The acrylic polymer may contain one type of second monomer unit, or may contain two or more types of second monomer units.

The proportion of the second monomer unit in the acrylic polymer is, for example, 0.1% by mass or more and 99% by mass (or 96% by mass) or less, 1% by mass or more and 99% by mass (or 96% by mass) or less, 5% by mass 99 mass% or more (or 96 mass%) or less, 30 mass% or more and 99 mass% (or 96 mass%) or less, 40 mass% or more and 99 mass% or less (or 96 mass%), 0.1 mass% or more and 80 mass% % (or 65 mass%) or less, 1 mass% or more and 80 mass% (or 65 mass%) or less, 5 mass% or more and 80 mass% or less (or 65 mass%), 30 mass% or more and 80 mass% (or 65 mass%) %) or less, 40% by mass or more and 80% by mass (or 65% by mass) or less, 0.1% by mass or more and 60% by mass (or 50% by mass) or less, 1% by mass or more and 60% by mass or less (or 50% by mass) , 5% to 60% by mass (or 50% by mass), 35% to 60% by mass (or 50% by mass), or 40% to 60% by mass (or 50% by mass) good.

At least one type selected from the group consisting of (meth)acrylic acid units, hydroxyalkyl (meth)acrylate units, and (meth)acrylate units having an epoxy group (including glycidyl (meth)acrylate units) Also preferred are acrylic polymers containing (sometimes referred to as units). Since the third monomer unit can form a crosslinking point, in the acrylic polymer containing the third monomer unit, the cohesive force of the acrylic polymer is increased and higher adhesiveness is easily ensured. Moreover, the durability and heat resistance of the acrylic polymer can also be improved. The functional groups (carboxy group, hydroxyl group, and epoxy group) possessed by the third monomer unit easily interact with the surface of the adherend. It is thought that adhesiveness can be ensured.

The acrylic polymer may contain one type of third monomer unit, or may contain two or more types of third monomer units.

The proportion of the third monomer unit in the acrylic polymer is, for example, 0.1% by mass or more and 90% by mass (or 80% by mass) or less, 0.5% by mass or more and 90% by mass or less (or 80% by mass), 1 Mass% to 90% by mass (or 80% by mass), 3% by mass to 90% by mass (or 80% by mass), 0.1% by mass (or 0.5% by mass) to 70% by mass, 1% by mass % (or 3 mass%) or more and 70 mass% or less, 0.1 mass% or more and 60 mass% or less (or 50 mass%), 0.5 mass% or more and 60 mass% or less (or 50 mass%), 1 mass% 60% by mass or more (or 50% by mass), 3% by mass or more and 60% by mass (or 50% by mass), 5% by mass or more and 60% by mass (or 50% by mass), 10% by mass or more and 60% by mass ( 20% to 60% by mass (or 50% by mass), 0.1% to 30% by mass (or 20% by mass), 0.5% to 30% by mass (or 20% by mass) or less, 1% by mass or more and 20% by mass (or 15% by mass) or less, or 5% by mass or more and 20% by mass (or 15% by mass) or less.

The acrylic polymer preferably contains at least an acrylic monomer unit having one (meth)acryloyl group, and may further contain an acrylic monomer unit having two or more (meth)acryloyl groups. As the first to third monomers, those having one (meth)acryloyl group are used. When the acrylic polymer contains an acrylic monomer unit having two or more (meth)acryloyl groups, it becomes easier to increase the cohesive force of the acrylic polymer and ensure higher adhesiveness. Therefore, the adhesion to the anti-fingerprint coating can be further improved. Moreover, the durability and heat resistance of the acrylic polymer can also be improved. Examples of the acrylic monomer having two or more (meth)acryloyl groups (hereinafter sometimes referred to as a fourth monomer unit) include poly(meth)acrylates of polyols.

Examples of polyols include aliphatic polyols, polyols having a ring structure (aliphatic ring, aromatic ring, and/or oxygen-containing ring, etc.), or alkylene oxide adducts thereof (C _2-4 alkylene oxide adducts, etc.). Specific examples of alkylene oxide include ethylene oxide, propylene oxide, and trimethylene oxide.The total number of alkylene oxides in the alkylene oxide adduct is, for example, 1 to 20 per molecule of polyol, It may be 2 to 14.

Examples of the fourth monomer unit include alkylene glycol di(meth)acrylate (ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, etc.), polyalkylene glycol di(meth)acrylate (diethylene glycol di(meth)acrylate, etc.) ) acrylate, triethylene glycol di(meth)acrylate, etc.), trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc.

The acrylic polymer may contain one type of fourth monomer unit, or may contain two or more types of fourth monomer units.

The fourth monomer unit may have a substituent (fourth substituent). Examples of the fourth substituent include those exemplified for the first substituent, second substituent, and third substituent.

The proportion of the fourth monomer unit in the acrylic polymer is, for example, 0.1% by mass or more and 5% by mass or less, 0.1% by mass or more and 2% by mass or less, or 0.1% by mass or more and 1% by mass or less. It's okay.

The acrylic polymer preferably contains at least one selected from the group consisting of a first monomer unit, a second monomer unit, and a third monomer unit. In addition to the first monomer unit, the second monomer unit, and/or the third monomer unit, the acrylic polymer may further include a fourth monomer unit. From the viewpoint of easily ensuring higher adhesiveness, it is preferable that the acrylic polymer contains at least a first monomer unit. The acrylic polymer containing the first monomer unit may further contain at least one selected from the group consisting of the second monomer unit, the third monomer unit, and the fourth monomer unit. It is also preferable that the acrylic polymer includes at least a second monomer unit and a third monomer unit. In this case, it is preferable to combine it with a tackifier.

The acrylic polymer may further include a monomer unit other than the acrylic monomer (hereinafter sometimes referred to as a fifth monomer unit). Examples of the fifth monomer include radically polymerizable monomers and cationically polymerizable monomers. Examples of the fifth monomer include those having a polymerizable group other than the (meth)acryloyl group. The fifth monomer may be a monofunctional monomer having one polymerizable group, or a polyfunctional monomer having two or more polymerizable groups. The polyfunctional monomer also functions as a crosslinking agent. In the acrylic polymer containing the fifth monomer unit, at least a portion of the polymerizable group is converted into a residue obtained by polymerizing the polymerizable group. The acrylic polymer may have unpolymerized active (that is, free) polymerizable groups.

Examples of the polymerizable group include groups having a polymerizable carbon-carbon unsaturated bond (vinyl group, allyl group, and/or dienyl group, etc.).

Examples of the fifth monomer include vinyl monomers, allyl monomers, diene monomers, and acid anhydrides of unsaturated polycarboxylic acids.

The acrylic polymer may contain one type of fifth monomer unit, or may contain two or more types of fifth monomer units.

The fifth monomer unit may have a substituent (fifth substituent). Examples of the fifth substituent include those exemplified for the first substituent, second substituent, and third substituent.

Examples of vinyl monomers include aliphatic olefins (ethylene, propylene, etc.), olefins having an aliphatic hydrocarbon ring (vinylcyclohexane, cyclohexyl vinyl ether, etc.), aromatic olefins (styrene, α-methylstyrene, vinyltoluene, etc.) , olefins having an oxygen-containing ring, cyclic olefins, vinyl halides (such as vinyl chloride), vinylidene halides (such as vinylidene chloride), and vinyl esters (such as vinyl acetate). Examples of the cyclic olefin include cycloalkenes (cyclohexene, etc.), bridged cyclic olefins (norbornene, etc.), and the like.

Allyl monomers include aliphatic allyl compounds (allyl alcohol, allyl ethers (allyl methyl ether, allyl ethyl ether, allyl glycidyl ether, etc.), allyl esters (allyl methyl carbonate, etc.)), allyloxycarboxylic acids (allyloxypropion etc.), allyl compounds with aliphatic hydrocarbon rings (allyl cyclohexane, allyl cyclohexane propionate, etc.), allyl compounds with aromatic hydrocarbon rings (allyl phenyl acetate, allyl 4-hydroxybenzoate, allyl phenyl carbonate) etc.), allyl compounds having an oxygen-containing ring, etc.).

Examples of diene monomers include butadiene, isoprene, dimethylbutadiene, and the like.

Examples of the acid anhydride of unsaturated polycarboxylic acids include maleic anhydride, Hett's acid anhydride, 5-norbornene-2,3-dicarboxylic anhydride, and the like.

The proportion of the fifth monomer unit in the acrylic polymer is, for example, 0.1% by mass to 30% by mass (or 25% by mass), 1% by mass to 30% by mass (or 25% by mass), 5% by mass. more than 30% by mass (or 25% by mass), more than 10% by mass and less than 30% by mass (or 25% by mass), more than 0.1% by mass (or 1% by mass) and less than 20% by mass, or 5% by mass (or (10% by mass) or more and 20% by mass or less.

Note that the first to fifth monomer units are monomer units that do not contain a nitrogen atom.

Acrylic polymers containing nitrogen-containing monomer units (hereinafter also referred to as sixth monomer units) are also preferred. When the acrylic polymer contains the sixth monomer unit, it becomes easier to interact with the adherend and the cohesive force increases, making it easier to ensure higher adhesion to curved surfaces or anti-fingerprint coating layers. Become.

Examples of the sixth monomer include those containing a nitrogen atom among the above-mentioned acrylic monomers, and monomers containing a nitrogen atom other than the acrylic monomer. In addition, the sixth monomer includes an acrylic monomer having an amino group and/or cyano group as a substituent, and an amino group and/or cyano group as a substituent and a polymerizable group other than a (meth)acryloyl group. Also included are monomers having.

Examples of the acrylic monomer containing a nitrogen atom include (meth)acrylamide compounds and poly(meth)acrylates of polyols having a nitrogen-containing ring. These acrylic monomers may have an amino group and/or a cyano group as a substituent. In addition, acrylic monomers containing a nitrogen atom include (meth)acrylic acid esters having amino groups and/or cyano groups as substituents, and (meth)acrylic esters having amino groups and/or cyano groups as substituents, and two or more ( Acrylic monomers having a meth)acryloyl group are also included. Examples of the (meth)acrylamide compound and (meth)acrylic ester include those exemplified for the acrylic monomer. Examples of the acrylic monomer having two or more (meth)acryloyl groups include those exemplified for the fourth monomer.

The sixth monomer also includes olefins having a nitrogen-containing ring, vinyl cyanides (acrylonitrile, methacrylonitrile, etc.), allyl compounds having a nitrogen-containing ring (4-allylmorpholine, etc.), and unsaturated carboxylic acid imides. Ru. These sixth monomers may have an amino group and/or a cyano group as a substituent.

Examples of olefins having a nitrogen-containing ring include N-vinylcarboxylic acid imides (for example, N-vinylacetamide, N-vinylphthalimide, etc.), N-vinyl cyclic amides (N-vinyl-pyrrolidone, N-vinyl-ε-caprolactam, etc.) , and other nitrogen-containing cyclic compounds having a vinyl group (eg, vinylimidazole (1-vinylimidazole, 2-methyl-1-imidazole, etc.)).

Examples of the unsaturated polycarboxylic acid imide include maleimide (N-methylmaleimide, N-methoxycarbonylmaleimide, 5-norbornene-2,3-dicarboximide, N-phenylmaleimide, etc.).

In the sixth monomer, the amino group of the substituent includes a free amino group (-NH ₂ ), a monosubstituted amino group (-NH-), and a disubstituted amino group (-N<).

The sixth monomer may further have a substituent (sixth substituent) other than the amino group and the cyano group. Examples of the sixth substituent include those exemplified for the first to fifth substituents.

The acrylic polymer may contain one kind of sixth monomer unit, or may contain two or more kinds of sixth monomer units.

Among the sixth monomers, a (meth)acrylamide compound and/or a sixth monomer having a nitrogen-containing ring are preferred. From the viewpoint of easily ensuring higher adhesiveness, the sixth monomer having a nitrogen-containing ring is particularly preferred. Examples of such a sixth monomer include an acid amide of (meth)acrylic acid and a cyclic amine, an olefin having a nitrogen-containing ring, an allyl compound having a nitrogen-containing ring, and/or an unsaturated polycarboxylic acid imide. . When a (meth)acrylamide compound is used, it is possible to form a crosslinking point like the third monomer unit, thereby increasing the cohesive force of the acrylic polymer and making it easier to ensure higher adhesiveness. Moreover, the durability and heat resistance of the acrylic polymer can also be improved.

From the viewpoint of easily ensuring higher adhesiveness, the acrylic polymer may include the sixth monomer unit and other monomer units. The other monomer unit is at least one type selected from the group consisting of the first monomer unit, the second monomer unit, the third monomer unit, the fourth monomer unit, and the fifth monomer unit. From the same viewpoint, an acrylic polymer containing a sixth monomer unit, a first monomer unit, and at least one monomer unit selected from the group consisting of second to fifth monomer units is also preferred.

The proportion of the sixth monomer unit in the acrylic polymer is, for example, 0.1% by mass or more or 1% by mass or more. From the viewpoint of further increasing the adhesion to the anti-fingerprint coating, the proportion of the sixth monomer unit is preferably 5% by mass or more or 10% by mass or more. The proportion of the sixth monomer unit is, for example, 30% by mass or less, and may be 25% by mass or less, or 20% by mass or less.

The proportion of the sixth monomer unit in the acrylic polymer is, for example, 0.1% by mass to 30% by mass (or 25% by mass), 1% by mass to 30% by mass (or 25% by mass), 5% by mass. more than 30% by mass (or 25% by mass), more than 10% by mass and less than 30% by mass (or 25% by mass), more than 0.1% by mass (or 1% by mass) and less than 20% by mass, or 5% by mass (or (10% by mass) or more and 20% by mass or less.

In the acrylic polymer containing at least a first monomer unit and a sixth monomer unit, the ratio of the sixth monomer unit to 100 parts by mass of the first monomer unit may be, for example, 1 part by mass or more, 5 parts by mass or more, or The amount may be 10 parts by mass or more. From the viewpoint of ensuring even higher adhesion to anti-fingerprint coated glass, the proportion of the sixth monomer unit is preferably 15 parts by mass or more or 20 parts by mass or more, more preferably 25 parts by mass or more or 30 parts by mass or more, and 40 parts by mass or more. Parts by mass or more are more preferable. The proportion of the sixth monomer unit is, for example, 70 parts by mass or less, and may be 60 parts by mass or less.

In the acrylic polymer, the ratio of the sixth monomer unit to 100 parts by mass of the first monomer unit is, for example, 1 part by mass or more and 70 parts by mass (or 60 parts by mass), 5 parts by mass or more and 70 parts by mass (or 60 parts by mass). ) or less, 10 parts by mass or more and 70 parts by mass or less (or 60 parts by mass), 15 parts by mass or more and 70 parts by mass or less (or 60 parts by mass), 20 parts by mass or more and 70 parts by mass or less (or 60 parts by mass), 30 parts by mass It may be at least 40 parts by weight and at most 70 parts by mass (or 60 parts by mass), or at least 40 parts by mass and at most 70 parts by mass (or 60 parts by mass).

(Crosslinking agent)
When the monomer used for the acrylic polymer has a crosslinkable functional group, a crosslinking agent may be used. That is, the acrylic polymer may contain units of a crosslinking agent capable of crosslinking the above functional groups. When the acrylic polymer has a third monomer unit and/or a crosslinkable substituent (first to sixth substituents), the acrylic polymer can further include a crosslinking agent unit. When a crosslinking agent is used, it becomes easier to increase the cohesive force of the acrylic polymer, and it becomes easier to ensure higher adhesiveness. Therefore, the adhesion to the anti-fingerprint coating can be further improved. Moreover, the durability and heat resistance of the acrylic polymer can also be improved.

Examples of crosslinkable functional groups contained in the monomer include carboxy group, hydroxy group, epoxy group, glycidyl group, carbamoyl group (-C(=O)-NH ₂ ), and monosubstituted carbamoyl group (-C(=O)- Examples include NH--R ² ), amino groups (for example, amino groups having active hydrogen such as -NH ₂ and -NH-), and sulfonic acid groups. Note that R ² is, for example, alkyl (including an alkyl group having a carboxy group and/or a sulfonic acid group) or aryl, corresponding to the above-mentioned (meth)acrylamide compound.

As the crosslinking agent, a compound having a known functional group that crosslinks with the above functional group can be used depending on the type of the above functional group of the monomer. Examples of the functional group of the crosslinking agent include an isocyanate group, an epoxy group, a glycidyl group, an amino group (for example, an amino group having an active hydrogen such as -NH ₂ and -NH-), an aziridine group, a carboxy group, and an acid anhydride group. groups, and/or metal chelates. Note that the amino group also includes -NH ₂ and -NH- which the hydrazide group has. As the crosslinking agent, a polyfunctional compound having two or more functional groups is used, but in the case of an acid anhydride group, a compound having one acid anhydride group in the molecule may be used.

The functional group of the crosslinking agent is selected depending on the type of crosslinkable functional group of the monomer used in the acrylic polymer. For example, when the monomer has a hydroxy group and/or an amino group, a crosslinking agent having an isocyanate group, an epoxy group, a glycidyl group, or the like is used. When the monomer has a carboxy group, a crosslinking agent, an aziridine compound, and/or a metal chelate having an isocyanate group, an epoxy group, a glycidyl group, an amino group, or the like can be used. When the monomer has an epoxy group and/or a glycidyl group, a crosslinking agent having an amino group (-NH ₂ , -NH-, etc.), a carboxy group, an acid anhydride group, or the like is used.

Examples of the crosslinking agent include polyisocyanate compounds, polyepoxy compounds (including polyglycidyl compounds), amino group-containing compounds, polyaziridine compounds, metal chelates, polycarboxylic acids, acid anhydrides, and the like.

The polyisocyanate compound may be any of an aliphatic compound, an alicyclic compound, and an aromatic compound. Modified products and adducts of these compounds can also be used as polyisocyanate compounds.

Examples of the aliphatic polyisocyanate compound include trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), lysine diisocyanate, dimer acid diisocyanate, and the like. Examples of the alicyclic polyisocyanate compound include isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and 1,4-cyclohexane diisocyanate. Examples of the aromatic polyisocyanate compound include toluene diisocyanate (TDI), xylylene diisocyanate (XDI), diphenylmethane diisocyanate (MDI), and the like.

As a modified product, the above polyisocyanate compound can be modified with a modified group (for example, isocyanurate group, allophanate group, buret group, urethane group, urea group, uretdione group, iminooxadiazinedione group, oxadiazinetrione group, uretonimine group). and/or carbodiimide groups). The modified product may be a multimer of isocyanate compounds.

Examples of adducts include compounds in which a diisocyanate compound is added to a polyol. The polyol may be any of aliphatic polyols (trimethylolpropane, pentaerythritol, sorbitol, etc.), alicyclic polyols, and aromatic polyols. The adduct is preferably a compound obtained by adding a diisocyanate compound (preferably an aromatic polyisocyanate compound (particularly TDI, XDI, etc.)) to an aliphatic polyol.

Examples of polyepoxy compounds (including polyglycidyl compounds) include various polyepoxy compounds and polyglycidyl compounds used as epoxy resins. For example, polyglycidyl ethers of polyols, polyglycidyl esters of polycarboxylic acids, polyglycidyl amines (triglycidyl isocyanurate, tetraglycidyl xylylene diamine, 1,3-bis(diglycidylaminomethyl) of polyamines (including nitrogen-containing rings)) cyclohexane, etc.), alicyclic polyepoxy compounds (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, etc.), and the like.

Examples of the amino group-containing compound include compounds having multiple amino groups. Examples of amino group-containing compounds include amino resins (melamine resins (hexamethylolmelamine, hexamethoxymethylmelamine, etc.), guanamine resins, etc.), polyamines (polymethylene diamine, bishexamethylene triamine, polyether diamine, diaminodiphenylmethane, etc.) , hydrazide (adipic acid dihydrazide, sebacic acid dihydrazide, isophthalic acid dihydrazide, etc.).

Examples of the polyaziridine compound include trimethylolpropane-tris(β-aziridinyl)propionate, 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate, N,N'-hexamethylene-1, Examples include 6-bis(1-aziridinecarboxamide) and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane.

A metal chelate is a compound in which a ligand is bonded to a metal atom. Examples of metal atoms include Fe, Ni, Mn, Cr, V, Ti, Ru, Zn, Al, Zr, and/or Sn. The ligand may be a monodentate ligand, a polydentate ligand, or a combination of both. The metal chelate may contain one type of ligand, or may contain two or more types of ligands.

Examples of monodentate ligands include halogen atoms (Cl, Br, etc.), acyloxy groups (pentanoyl group, hexanoyl group, etc.), alkoxy groups (methoxy group, ethoxy group, propoxy group, etc.), and the like.

Examples of polydentate ligands include β-ketoesters and β-diketones. Examples of the β-ketoester include acetoacetate (methyl acetoacetate, ethyl acetoacetate, etc.). Examples of the β-diketone include acetylacetone, 2,4-hexanedione, and benzoylacetone. These keto bodies can take the form of enolates in metal chelates. β-ketoester and β-diketone as polydentate ligands also include their respective enolate forms.

The polycarboxylic acid used as a crosslinking agent may be aliphatic, alicyclic, aromatic, or heterocyclic. Specific examples of polycarboxylic acids include adipic acid, sebacic acid, dodecanedioic acid, cyclohexanedicarboxylic acid, phthalic acid, isophthalic acid, and benzophenonetetracarboxylic acid.

Examples of the acid anhydride of the crosslinking agent include hexahydrophthalic anhydride, phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bisanhydrotrimellitate, and the like.

Note that the above-mentioned crosslinking agents are merely examples, and are not limited to those listed above. One type of crosslinking agent may be used alone, or two or more types may be used in combination as necessary.

The amount of the crosslinking agent is, for example, 0.05 parts by mass or more and 10 parts by mass based on 100 parts by mass of the total amount of constituent monomer units of the acrylic polymer (specifically, the total amount of the first to sixth monomer units). The amount may be 0.1 parts by mass or more and 7 parts by mass or less, or 0.1 parts by mass or more and 5 parts by mass or less. From the composition of the constituent monomers of the acrylic polymer and the crosslinking agent determined by ¹ H-NMR or the like of the adhesive, the amount of the crosslinking agent relative to 100 parts by mass of the total amount of each monomer unit can be determined. The amount of the crosslinking agent mentioned above corresponds to the mass (feeding ratio) of the crosslinking agent to 100 parts by mass of the total amount of raw material monomers of the acrylic polymer.

(tackifier)
The adhesive layer can further contain a tackifier. By using a tackifier, the Tg and viscoelasticity of the adhesive can be easily controlled, and the adhesion to the anti-fingerprint coating layer and/or the curved surface can be further increased.

Examples of the tackifier include rosins, terpenes, hydrocarbons, phenol resins, coumaron-indene resins, xylene resins, and the like. Examples of rosins include rosin ester, gum rosin, maleated rosin, hydrogenated rosin (hydrogenated rosin, hydrogenated rosin ester, etc.), disproportionated rosin, and rosin resin (maleic acid-modified rosin resin, etc.). It will be done. Examples of terpenes include terpene resins (terpene resins, aromatic modified terpene resins, pinene polymers, etc.). Examples of hydrocarbons include hydrocarbon resins (aromatic hydrocarbon resins, petroleum resins, styrene resins, hydrogenated products thereof, etc.), polybutene, and the like. Examples of the phenol resin include alkylphenol-formaldehyde resin, rosin-modified phenol resin, terpene phenol resin, and hydrogenated terpene phenol resin.

As the tackifier, one having a functional group that reacts with the functional group of the acrylic polymer and/or the crosslinking agent may be used. For example, when the acrylic polymer and/or crosslinking agent has an isocyanate group, an epoxy group, and/or a glycidyl group, a tackifier having a hydroxy group, a carboxy group, and/or an amino group may be used. Good too. When the acrylic polymer and/or crosslinking agent has a carboxy group and/or an acid anhydride group, a tackifier having an amino group may be used. By using such a tackifier, higher adhesion to anti-fingerprint coatings and/or curved surfaces can be ensured.

Among these, it is preferable to use a combination of a tackifier containing a hydroxy compound and a crosslinking agent containing a polyisocyanate compound. In this case, it is possible to obtain an adhesive that is flexible and has excellent stress relaxation properties. By using such an adhesive, the followability to curved surfaces can be further improved. It is thought that the reason why an adhesive with excellent stress relaxation properties is obtained is that a hydroxyl compound and a polyisocyanate compound react to form a polyurethane compound, which becomes entangled with the acrylic polymer.

Examples of the hydroxy compound include those having a hydroxy group among the above-mentioned tackifiers, and polyol compounds. Among the above-mentioned tackifying agents, those having a hydroxy group are preferably phenol resins (among them, terpene-modified phenol resins, etc.), xylene resins having a hydroxy group, and the like. Examples of the polyol compound include, in addition to the polyols described for the fourth monomer unit, polyether polyols, polyester polyols, oxyethylene-oxypropylene copolymers, poly(hydroxyalkyl) polyamines (tetrahydroxypropylethylenediamine, etc.), and the like. Among the polyol compounds, poly(hydroxyalkyl) polyamines, polyether polyols, and the like are preferred.

When at least one having a plurality of hydroxy groups is used as the tackifier, a polyurethane compound having a branched structure is likely to be formed. Such a polyurethane compound is considered to be more likely to entangle with the acrylic polymer, and is advantageous in further increasing the stress relaxation properties of the adhesive layer.

The adhesive layer may contain one type of tackifier, or may contain two or more types of tackifiers.

The ratio of the tackifier to 100 parts by mass of the acrylic polymer is, for example, 0.1 part by mass or more, and may be 1 part by mass or more. When the proportion of the tackifier is within this range, the anti-fingerprint coating and/or the adhesion to curved surfaces can be further enhanced. From the viewpoint of easily ensuring high tackiness even when the surface protection film is exposed to high temperatures, the proportion of the tackifier may be 10 parts by mass or more, 25 parts by mass or more, or 40 parts by mass or more. From the viewpoint of reducing adhesive residue when peeling the surface protection film from the adherend, the proportion of the tackifier is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and 60 parts by mass. The following may be used. From the viewpoint of further increasing the effect of suppressing the residual adhesive, the proportion of the tackifier may be 20 parts by mass or less, or 15 parts by mass or less.

The ratio of the tackifier to 100 parts by mass of the acrylic polymer is from 0.1 part by mass (or 1 part by mass) to 150 parts by mass, from 0.1 part by mass (or 1 part by mass) to 100 parts by mass, and from 0.1 part by mass (or 1 part by mass) to 100 parts by mass. 1 part by mass (or 1 part by mass) to 60 parts by mass, 0.1 part by mass (or 1 part by mass) to 20 parts by mass, or 0.1 part by mass (or 1 part by mass) to 15 parts by mass There may be.

From the viewpoint of further increasing the adhesiveness to curved surfaces, the ratio of the tackifier to 100 parts by mass of the acrylic polymer is preferably 10 parts by mass or more and 150 parts by mass (or 100 parts by mass), and 25 parts by mass or more and 150 parts by mass. (or 100 parts by mass) or less, more preferably 40 parts by mass or more and 150 parts by mass (or 100 parts by mass) or less. When the proportion of the tackifier is within such a range, even when the surface protection film is exposed to high temperatures, it becomes easy to maintain high cohesive force, so that high tackiness can be ensured.

From the viewpoint of increasing the stress relaxation properties of the adhesive layer, the proportion of the tackifier having a plurality of hydroxy groups is 0.001 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the acrylic polymer. is preferable, 0.005 part by weight or more and 0.1 part by weight or less is more preferable, and even more preferably 0.01 part by weight or more and 0.1 part by weight or less.

(others)
The content of the acrylic polymer in the adhesive layer is, for example, 10% by mass or more, and may be 30% by mass or more. From the viewpoint of easily exhibiting high adhesiveness due to the acrylic polymer, the content of the acrylic polymer in the adhesive layer is preferably 40% by mass or more, 50% by mass or more, or 80% by mass or more. It's okay.

The adhesive layer may contain additives as necessary. Known additives may be used as the additive. Examples of additives include softeners, anti-aging agents (or antioxidants), fillers, antistatic agents, colorants, pigments, metal powders, surfactants, plasticizers, surface lubricants, leveling agents, and corrosion agents. Examples include inhibitors, light stabilizers, ultraviolet absorbers, polymerization inhibitors, coupling agents, crosslinking retarders, and catalysts. However, it is not limited to these.

From the viewpoint of easily ensuring stable and high adhesiveness over time, the adhesive layer preferably does not contain a benzotriazole compound.

From the viewpoint of easily suppressing the adhesive from remaining on the adherend after the surface protection film is peeled off, the adhesive layer preferably does not contain an onium compound. Even when the adhesive layer does not contain an onium compound, high adhesion to the anti-fingerprint coating layer and/or curved surfaces can be ensured.

The thickness of the adhesive layer is, for example, 1 μm or more, and may be 10 μm or more. When the thickness of the adhesive layer is within such a range, it is easy to obtain a high cohesive force of the adhesive layer, and it is easy to ensure high adhesion to curved surfaces and/or anti-fingerprint coatings. When a surface protection film is attached to a curved surface, the thickness of the adhesive layer is 15 μm or more or 20 μm or more, from the viewpoint of reducing uneven stress distribution and easily exhibiting high cohesive force. It is preferable. When the thickness of the adhesive layer is within such a range, and even when the surface protection film is exposed to high temperatures, high shear adhesive strength can be ensured and high adhesiveness can be maintained. The thickness of the adhesive layer is, for example, 200 μm or less, and may be 150 μm or less. When the thickness of the adhesive layer is within such a range, the formation of coating marks and/or bubbles in the adhesive layer is suppressed while ensuring high adhesiveness. Therefore, a surface protection film suitable for being attached to an optical member can be obtained.

The thickness of the adhesive layer may be, for example, 1 μm or more and 200 μm (or 150 μm) or less, 10 μm or more and 200 μm (or 150 μm) or less, 15 μm or more and 200 μm (or 150 μm) or less, or 20 μm or more and 200 μm (or 150 μm) or less. .

(Base material layer)
For example, a resin film is used as the base material layer. Examples of the resin constituting the base layer include various resins (thermoplastic resins, thermosetting resins, photocurable resins, etc.) used for the base layer of surface protection films or adhesive films. The resin film may be formed of a cured product (including a semi-cured product) of a thermosetting resin or a photocurable resin. From the viewpoint of easily ensuring high conformability to curved surfaces, it is preferable to use a thermoplastic resin for the base material layer.

Examples of resins constituting the base layer include polyester resins, acrylic resins, olefin resins, vinyl resins (aromatic vinyl resins (styrene resins, etc.), polyvinyl acetate or its saponified products, halogenated vinyl resins, halogenated vinylidene resins, etc.). resin, polyvinyl acetal resin, polyvinyl butyral resin, etc.), polycarbonate resin, polyamide resin, polyimide resin, polysulfone resin, polyether sulfone resin, polyether ether ketone resin, polyphenylene sulfide resin, polyarylate resin, cellulose (cellulose ester, etc.) , epoxy resin, etc. The base material layer may contain one type of these resins, or may contain two or more types of these resins.

Among these resins, polyester resins (polyalkylene arylate, etc.) are preferred from the viewpoint of strength, flexibility, transparency, etc. of the base layer. Examples of polyalkylene arylates include poly(C _2-4 alkylene) arylates (eg, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, etc.). Moreover, when the base material layer contains a polyester resin, the repulsive force when the surface protection film is curved can be suppressed to a low level, so that higher adhesion to curved surfaces can be ensured. When the base material layer contains polyester resin, thermal shrinkage due to heating is small, so even if the surface protection film is exposed to high temperatures, the decrease in adhesive strength is suppressed and high conformability to curved surfaces can be ensured. .

The base material layer may contain known additives as necessary. Examples of additives include, but are not limited to, anti-aging agents (or antioxidants), ultraviolet absorbers, light stabilizers, plasticizers, colorants, fillers, and the like.

The base material layer may have a single layer structure or a multilayer structure of two or more layers. In the case of a multilayer structure, the composition (eg, resin type, additive type, and/or material composition) in at least two layers may be different.

The thickness of the base layer is preferably 300 μm or less from the viewpoint of suppressing excessive increase in repulsive force due to the base layer when a surface protection film is attached to a curved surface. From the viewpoint of suppressing the repulsive force of the base layer and easily ensuring high followability to a curved surface, the thickness of the base layer is preferably 250 μm or less. Even when the surface protection film is exposed to high temperatures, the thickness of the base material layer should be less than 250 μm (for example, 200 μm or less) from the viewpoint of being less affected by thermal contraction of the base material layer and easily ensuring high conformability to curved surfaces. ) is preferable, and may be 150 μm or less. From the viewpoint of easily ensuring appropriate strength, the thickness of the base material layer is preferably 5 μm or more or 10 μm or more. When the thickness of the base material layer is 30 μm or more or 35 μm or more, the influence of the repulsive force of the base material layer when pasting a surface protection film on a curved surface tends to be noticeable, but even within this range, the Adhesiveness can be ensured.

The thickness of the base material layer is, for example, 5 μm (or 10 μm) or more and 300 μm or less, 5 μm (or 10 μm) or more and 250 μm or less, 5 μm (or 10 μm) or more and less than 250 μm, 5 μm (or 10 μm) or more and 200 μm or less, and 5 μm (or 10 μm). 30 μm (or 35 μm) to 250 μm, 30 μm (or 35 μm) to less than 250 μm, 30 μm (or 35 μm) to 200 μm, or 30 μm (or 35 μm) to 150 μm There may be.

The ratio of the thickness Ta of the adhesive layer to the thickness Ts of the base material layer (=Ta/Ts) is preferably 0.1 or more and 2 or less, and more preferably 0.2 or more and 1.5 or less. When the thickness ratio Ta/Ts is in such a range, when a surface protection film is attached to a curved surface, it is easy to balance the repulsion force due to the base material layer and the cohesive force due to the adhesive layer, resulting in higher adhesiveness. is easily demonstrated.

The surface protection film may include a release film (or separator) that protects the adhesive layer, if necessary. Further, the surface protection film may include layers other than the base layer and the adhesive layer, if necessary. For example, the surface protection film may include another layer (for example, an antistatic layer) disposed on the surface of the base material layer on the opposite side to the adhesive layer. Further, another layer (for example, a precoat layer (anchor coat layer, etc.), etc.) may be provided between the base material layer and the adhesive layer. The thickness of another layer interposed between the base material layer and the adhesive layer is, for example, 50 μm or less, and may be 30 μm or less.

The surface protection film can prevent the adhesive from remaining on the adherend after being peeled off from the adherend, and has high adhesiveness even after being peeled off. In other words, the surface protection film has a high residual adhesion rate when it is peeled off from the adherend. For example, the residual adhesion rate to anti-fingerprint coated glass may be 60% or more, 70% or more, and a high value of 80% or more or 85% or more (even 90% or more) is ensured. You can also do that.

The residual adhesion rate for anti-fingerprint coated glass is the adhesive strength after attaching a surface protection film to anti-fingerprint coated glass, leaving it for one day at room temperature (temperature between 20°C and above and below 35°C), and then peeling off the surface protection film. This is the ratio (%) when the adhesive strength (initial adhesive strength) of an unused surface protection film is taken as 100%. The adhesion strength of each surface protective film is determined by peeling, which is measured using a surface protective film with a length of 70 mm and a width of 19 mm, at a temperature of 23°C and a peeling speed of 300 mm/min in the same manner as in the 180° peel test. It is required as strength. As the anti-fingerprint coated glass, the same anti-fingerprint coated glass as used in the 180° peel test is used.

The bending rigidity of the surface protection film is preferably 40 μN m ² or less from the viewpoint of suppressing the repulsive force of the film from increasing excessively when the surface protection film is attached to a curved surface while ensuring appropriate strength. , 35 μN·m ² or less is more preferable. When the bending rigidity of the surface protection film is within such a range, the adhesive layer tends to exhibit high adhesiveness, and it is easy to ensure higher conformability to curved surfaces. From the viewpoint of improving followability to curved surfaces, the bending rigidity of the surface protection film may be set to 20 μN·m ² or less, 15 μN·m ² or less, 10 μN·m ² or less, or 5 μN·m ² or less. . If the bending rigidity is within this range, the adhesive layer will not work properly even if the surface protection film is exposed to high temperatures and the adhesive layer loses its adhesion, and/or when it is attached to a curved surface coated with anti-fingerprint coating. Adhesiveness is more easily exhibited, and high conformability to curved surfaces can be ensured.

The bending rigidity of the surface protection film is calculated by the following formula.
Bending rigidity = E x bh ³ /12
(In the formula, E is the flexural modulus (Pa), b is the specimen width (m), and h represents the specimen layer thickness (m).)

The flexural modulus E (Pa) of the surface protection film is measured in accordance with JIS K 7171:2016. The bending modulus of elasticity was measured using a test piece (length 50 mm x width 6 mm) prepared from a surface protection film (if it has a separator, the surface protection film from which the separator was peeled off), at a test speed of 2 mm/min, between fulcrums. The distance is 25 mm, and the indenter radius is 5 mm.

A surface protection film can be produced by disposing an adhesive layer on at least one surface of a base layer. The adhesive layer can be formed, for example, by applying an adhesive containing the constituent components of the adhesive layer to at least one surface of the base layer. The adhesive can be applied to the base layer by a known coating method using a coater, dispenser, or the like. The adhesive may contain a solvent as necessary. The solvent may be removed at an appropriate stage of manufacturing the surface protection film. The adhesive coating may be dried and/or heated as necessary.

The adhesive can be prepared according to a known method for preparing acrylic adhesives. For example, an acrylic polymer is prepared by polymerizing the constituent monomers of the acrylic polymer in the presence of a polymerization initiator if necessary, diluted with a solvent as necessary, and adding components other than the monomers (crosslinking agent, tackifier, A pressure-sensitive adhesive can be obtained by mixing it with additives (additives, etc.). Polymerization of monomers may be performed under heating or under light irradiation. The polymerization initiator can be selected depending on the monomer and/or type of polymerization, and may be either a thermal polymerization initiator or a photopolymerization initiator. Polymerization of monomers may be carried out in the presence of a chain transfer agent, if necessary.

From the viewpoint of increasing the adhesion of the adhesive to the base layer, at least the area on the surface of the base layer to which the adhesive is applied may be surface-treated by a known method. Examples of the surface treatment include plasma treatment, corona discharge treatment, ultraviolet treatment, acid treatment, base treatment, and/or primer treatment (anchor coat treatment, etc.).

Surface protection films have high adhesion to curved surfaces and/or anti-fingerprint coatings, and are useful for attaching and protecting the surfaces of various adherends. Since it has high adhesion to anti-fingerprint coatings, it is also suitable for protecting the surfaces of such members (particularly optical members) in the optical and electronic fields where anti-fingerprint coated members are used. Moreover, although the surface protection film has high adhesiveness, it can suppress the adhesive from remaining on the surface of the adherend after being peeled off. Therefore, it is useful not only for protecting the surface of an adherend over a long period of time, but also for temporary surface protection on the assumption that it will be peeled off. The surface protection film can be used, for example, to protect the surface of an adherend during processing, assembly, transportation, and/or shipping.

[Optical member]
In the optical member according to one aspect of the present invention, a surface protection film is attached via an adhesive layer.

An optical member refers to a member that has optical properties (e.g., polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.) shall be.

Examples of the optical member include a substrate constituting an optical device (for example, a display device, an input device), a substrate attached to or attached to the optical device, and the like. The substrate may include a conductive layer and/or wiring. Examples of the display device include a liquid crystal display device, an organic electroluminescence display device, a display panel, and electronic paper. Examples of the input device include a touch panel.

Specific examples of optical members include polarizing plates, wavelength plates, retardation plates, optical security films, brightness enhancement films, light guide plates, reflective films, antireflection films, hard coat films, transparent conductive films (ITO films, etc.), and decorative films. Examples include films, decorative films, surface protection films, prisms, lenses, color filters, transparent substrates (glass sensors, glass display panels (LCDs, etc.), glass substrates, etc.), and substrates including these. Note that in these optical members, the film or plate includes forms such as a film, a sheet, a plate, and a panel. The optical member may have a sensor function.

As mentioned above, the surface protection film has high adhesion to curved surfaces and/or anti-fingerprint coatings. Therefore, it is suitable for attachment to an optical member having a curved surface and/or an anti-fingerprint coating layer. For example, it is preferable that the adhesive layer of the surface protection film be attached to an optical member having an anti-fingerprint coating layer on at least a portion of its surface so as to be in contact with at least a portion of the anti-fingerprint coating layer. Further, it is preferable that the adhesive layer of the surface protection film is attached to an optical member having a curved surface so as to be in contact with at least a portion of the curved surface.

Examples of the anti-fingerprint coating layer include those having a surface water contact angle (static contact angle) of, for example, 90° or more (preferably 100° or more). Examples of the material constituting the anti-fingerprint coating layer include fluororesin and silicone resin.

The curved surface may be any surface having a curvature other than 0, and may be either a concave surface or a convex surface. The curved surface includes a bent surface.

Since the surface protection film has high adhesiveness, even if it is attached to a curved surface provided with an anti-fingerprint coating layer, high followability to the curved surface can be obtained.

[Example]
EXAMPLES Hereinafter, the present invention will be specifically explained based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

《Synthesis examples 1 to 3》
In a reaction vessel, the monomers shown in Table 1 were placed in the mass ratio shown in Table 1 together with a predetermined amount of solvent (ethyl acetate), and a polymerization initiator was added. The resulting mixture was reacted at 55° C. for 8 hours while stirring under nitrogen gas flow to obtain polymer liquids containing acrylic polymers 1 to 3, respectively. As the polymerization initiator, azobisisobutyronitrile was used in an amount of 0.2 parts by mass based on 100 parts by mass of the total amount of monomers.

《Examples 1 to 5 and Reference Examples 1 to 2》
A crosslinking agent shown in Table 2 and, if necessary, a tackifier were added to the polymer liquid obtained in the synthesis example at a mass ratio shown in Table 2 to the acrylic polymer and mixed to prepare an adhesive solution. An adhesive solution was applied to one side of a base layer (polyethylene terephthalate film) having a thickness shown in Table 2, and dried to form an adhesive layer. The amount of the adhesive solution applied was adjusted so that the thickness of the adhesive layer after drying would be the value shown in Table 2. In this way, a surface protection film was produced.

《Comparative example 1》
A surface protection film was produced in the same manner as in Example 1, except that a silicone adhesive was used instead of the adhesive solution containing an acrylic polymer. The silicone adhesive is 1.2 parts by mass of peroxide (NIPER BMT-K-40, manufactured by NOF Corporation) per 100 parts by mass of silicone paint (KR-120, manufactured by Shin-Etsu Chemical Co., Ltd.). It was prepared by mixing.

"evaluation"
The following evaluations were performed using the surface protection films obtained in Examples, Reference Examples, and Comparative Examples.

(1) Peel strength (adhesion to anti-fingerprint coated glass)
A 180° peel test was performed on anti-fingerprint coated glass according to the procedure described above, and the peel strength (N/25 mm) was determined.

(2) Residual adhesion rate Measure the initial adhesion of the surface protection film and the adhesion of the surface protection film after it has been applied to anti-fingerprint coated glass using the procedure described above, and calculate the residual adhesion rate ( %) was calculated.

(3) Planar followability (before heating)
A surface protection film (120 mm long x 65 mm wide) was applied to the entire surface of one side of a flat soda glass (general purpose soda glass, 120 mm long x 65 mm wide x 0.55 mm thick) using a hand roller in an environment of 23°C and 50% RH. 65 mm) was attached. At this time, the state of the edge of the surface protection film was visually observed.

(4) Curved surface followability (before heating)
A surface protection film (length 120 mm x width 65 mm) was applied to the entire surface of one side of soda glass (general purpose soda glass) having a curved surface at one end in the length direction using a hand roller in an environment of 23°C and 50% RH. ) has been attached. At this time, the appearance of the edge of the surface protection film on the curved surface side was visually observed. The size of the glass used was 120 mm on the long side, 65 mm on the short side, and 0.55 mm in thickness. The radius of curvature R of the curved surface was 5 mm. The surface protection film was attached to the curved (convex) side. The height from the flat part of the glass to which the surface protection film was attached to the end of the curved surface was 2 mm.

(5) Curved surface followability (after heating)
The surface protection film was heated at 150°C for 30 minutes and allowed to cool to 23°C. The surface protection film was attached to soda glass having a curved surface in the same manner as in (4) above, except that the surface protection film was heated and allowed to cool, and the appearance of the edges was observed.

The followability of (3) to (5) was evaluated based on the following criteria.
A: No lifting of the edges was observed.
B: Lifting is observed at the edges.

(6) Bending rigidity The bending rigidity (μN·m ² ) of the surface protection film was determined by the procedure described above.

Table 2 shows the results of Examples, Reference Examples, and Comparative Examples. In Table 2, E1 to E5 are Examples 1 to 5, R1 and R2 are Reference Examples 1 and 2, and C1 is Comparative Example 1.

Even for R1 to R2 and C1, which have a peel strength of less than 0.2 N/25 mm against anti-fingerprint coated glass, the conformability to a flat surface is high, and no lifting of the edges is observed. The peel strength of R1 of 0.13 N/25 mm is the same as the peel strength of conventional high adhesive surface protection films. However, even with such a peel strength, the followability to curved surfaces was insufficient, and floating was observed at the edges. On the other hand, in E1 to E5, which had a peel strength of 0.2 N/25 mm or more against anti-fingerprint coated glass, high followability was obtained not only on flat surfaces but also on curved surfaces.

It has been shown that E1 to E4 have excellent followability to curved surfaces and high adhesiveness even after being exposed to a high temperature of 150°C. This is considered to be due to the fact that the influence of thermal shrinkage due to the base material layer is small.

Furthermore, in E1 to E4, a high residual adhesion rate was also ensured. From the viewpoint of ensuring a higher residual adhesion rate, the ratio of the tackifier to 100 parts by mass of the acrylic polymer may be 20 parts by mass or less (preferably 15 parts by mass or less).

The surface protection film according to the above aspect is suitable for use in protecting the surface of various adherends by being attached to them. The surface protection film exhibits high adhesiveness even when attached to an adherend having a curved surface and/or an anti-fingerprint coating layer. Surface protection films are also suitable for protecting the surfaces of various members in the optical and electronic fields.

Claims (7)

An optical member with a protective film, comprising an optical member and a surface protection film attached to the optical member via an adhesive layer,
The optical member includes an anti-fingerprint coating layer on at least a portion of the surface,
The adhesive layer is in contact with at least a portion of the anti-fingerprint coating layer,
The surface protection film includes a base layer and the adhesive layer disposed on at least one surface of the base layer,
The adhesive layer includes an acrylic polymer,
The ratio of the thickness Ta of the adhesive layer to the thickness Ts of the base layer (=Ta/Ts) is 0.4 or more and 2 or less,
The adhesive layer satisfies the following (i) or (ii),
(i) the acrylic polymer includes a first monomer unit: a C _14-26 alkyl (meth)acrylate unit, and the proportion of the first monomer unit in the acrylic polymer is 5% by mass or more;
(ii) the adhesive layer further includes a tackifier, and the ratio of the tackifier to 100 parts by mass of the acrylic polymer is 10 parts by mass or more;
The surface protection film is an optical film with a protective film, which has a peel strength of 0.30 N/25 mm or more at a temperature of 23° C. and a peel speed of 300 mm/min in a 180° peel test on anti-fingerprint coated glass. Element. The optical member with a protective film according to claim 1, wherein the surface protective film has a bending rigidity of 20 μN·m ² or less. The optical member with a protective film according to claim 1 or 2, wherein the base layer has a thickness of 200 μm or less. The optical member with a protective film according to claim 1, wherein the base layer has a thickness of 35 μm or more. The optical member with a protective film according to claim 1, wherein the adhesive layer has a thickness of 1 μm or more and 200 μm or less. The optical member with a protective film according to claim 1, wherein a static contact angle of water on the surface of the anti-fingerprint coated glass is 110°±10°. The optical member includes a curved surface,
The optical member with a protective film according to claim 1, wherein the adhesive layer is in contact with at least a portion of the curved surface.