JP7769028B2 - Antistatic surface protection film and optical film - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive composition and a surface protection film. More specifically, it relates to an antistatic surface protection film with antistatic properties. More specifically, it provides a method for producing an antistatic surface protection film that has low contamination of adherends, does not deteriorate over time, and has excellent antistatic properties upon peeling, and also provides an antistatic surface protection film.

When optical films such as polarizing plates, retardation plates, lens films for displays, antireflection films, hard coat films, and transparent conductive films for touch panels, and optical products such as displays using the same, are manufactured and transported by laminating a surface protective film to the surface of the optical film to prevent the surface from being soiled or scratched in later processes. In order to improve work efficiency by eliminating the need to peel off and re-laminate the surface protective film, visual inspection of the optical film product is sometimes performed with the surface protective film still attached to the optical film.
Conventionally, surface protection films having a pressure-sensitive adhesive layer provided on one side of a substrate film have been commonly used to prevent scratches and dirt from adhering during the manufacturing process of optical products. The surface protection film is attached to the optical film via a pressure-sensitive adhesive layer with weak adhesive strength. The pressure-sensitive adhesive layer has weak adhesive strength so that when a used surface protection film is peeled off and removed from the surface of the optical film, it can be easily peeled off and the pressure-sensitive adhesive does not adhere to and remain on the optical film of the adherend (preventing the occurrence of so-called adhesive residue).

In recent years, in the production process of liquid crystal display panels, there have been a few cases where the peeling electrification voltage that occurs when peeling off and removing a surface protection film that has been attached to an optical film has destroyed circuit components such as driver ICs that control the display screen of the liquid crystal display panel, or damaged the alignment of liquid crystal molecules.
Furthermore, in order to reduce the power consumption of liquid crystal display panels, the driving voltage of liquid crystal materials has been reduced, and as a result, the breakdown voltage of driver ICs has also been reduced. Recently, there has been a demand for the peeling electrification voltage to be within the range of +0.7 kV to -0.7 kV.
For this reason, in order to prevent problems caused by high peeling electrification voltage when peeling the surface protection film from the adherend, an adhesive layer containing an antistatic agent for keeping the peeling electrification voltage low has been proposed.

For example, Patent Document 1 discloses a surface protection film using an adhesive comprising an alkyltrimethylammonium salt, a hydroxyl group-containing acrylic polymer, and a polyisocyanate.
Furthermore, Patent Document 2 discloses a pressure-sensitive adhesive composition comprising an ionic liquid and an acrylic polymer having an acid value of 1.0 or less, and pressure-sensitive adhesive sheets using the same.
Furthermore, Patent Document 3 discloses an adhesive composition comprising an acrylic polymer, a polyether polyol compound, and an alkali metal salt treated with an anion-adsorbing compound, and a surface protection film using the same.
Furthermore, Patent Document 4 discloses a pressure-sensitive adhesive composition comprising an ionic liquid, an alkali metal salt, and a polymer having a glass transition temperature of 0° C. or less, and a surface protection film using the same.
Furthermore, Patent Documents 5 and 6 disclose mixing polyether-modified silicone into the pressure-sensitive adhesive layer of a surface protection film.

Japanese Patent Application Laid-Open No. 2005-131957 Japanese Patent Application Laid-Open No. 2005-330464 Japanese Patent Application Laid-Open No. 2005-314476 Japanese Patent Application Laid-Open No. 2006-152235 JP 2009-275128 A Patent No. 4537450

In the above-mentioned Patent Documents 1 to 4, an antistatic agent is added to the inside of the adhesive layer. However, as the thickness of the adhesive layer increases and as time passes, the amount of antistatic agent that migrates from the adhesive layer to the adherend to which the surface protection film is attached increases. Furthermore, in optical films such as LR (Low Reflective) polarizing plates and AG (Anti Glare)-LR polarizing plates, the surface of the optical film is treated with an anti-fouling agent such as a silicone compound or a fluorine compound, resulting in a high peeling electrification voltage when the surface protection film used for such optical films is peeled from the optical film as the adherend.

Furthermore, when polyether-modified silicone is mixed into the adhesive layer as described in Patent Documents 5 and 6, it is difficult to fine-tune the adhesive strength of the surface protection film. Furthermore, because polyether-modified silicone is mixed into the adhesive layer, changes in the conditions for applying and drying the adhesive composition onto the substrate film can subtly change the surface characteristics of the adhesive layer on which the surface protection film is formed. Furthermore, from the perspective of protecting the surface of the optical film, the thickness of the adhesive layer cannot be made extremely thin. Therefore, the amount of polyether-modified silicone mixed into the adhesive layer must be increased depending on the thickness of the adhesive layer, which results in increased susceptibility to contamination of the adherend surface and changes in adhesive strength and susceptibility to contamination of the adherend over time.

In recent years, with the spread of 3D displays (stereoscopic displays), there are products in which an FPR (Film Patterned Retarder) film is laminated to the surface of an optical film such as a polarizing plate. The FPR film is laminated after the surface protection film that was previously laminated to the surface of the optical film such as a polarizing plate is peeled off. However, if the surface of the optical film such as a polarizing plate is contaminated by the adhesive or antistatic agent used in the surface protection film, it becomes difficult for the FPR film to adhere. For this reason, surface protection films used in this application are required to be ones that cause minimal contamination to the adherend.

Meanwhile, some LCD panel manufacturers have adopted a method for evaluating the contamination potential of surface protection films on substrates by first peeling off the surface protection film that has been attached to an optical film such as a polarizing plate, reattaching it in a state where air bubbles have been mixed in, heat-treating the film under specified conditions, and then peeling off the surface protection film and observing the surface of the substrate. With this evaluation method, even if the amount of surface contamination on the substrate is minute, if there is a difference in the surface contamination between the area where the air bubbles have been mixed in and the area where the adhesive of the surface protection film was in contact, air bubble marks (sometimes called "bubble stains") will remain. Therefore, this is an extremely strict evaluation method for the contamination potential on the substrate surface. In recent years, there has been a demand for surface protection films that do not pose any problems with contamination on the substrate surface, even when judged by such a strict evaluation method. However, it has been difficult to solve this problem with previously proposed surface protection films that use an adhesive layer containing an antistatic agent.

Therefore, there is a need for a surface protection film for use with optical films that causes very little contamination to the adherend and whose contamination resistance to the adherend does not change over time. Furthermore, there is a demand for a surface protection film that exhibits low peeling electrification voltage when peeled from the adherend.

The present inventors have conducted extensive research to solve this problem.
In order to minimize contamination of the adherend and to minimize changes in antistatic performance over time, it is necessary to reduce the amount of antistatic agent added, which is presumed to be the cause of contamination of the adherend. However, reducing the amount of antistatic agent added increases the peeling electrification voltage when the surface protective film is peeled from the adherend. The present inventors have investigated a method for reducing the peeling electrification voltage when the surface protective film is peeled from the adherend without increasing the absolute amount of antistatic agent added. As a result, they have found that, rather than adding and mixing an antistatic agent into a pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer, the peeling electrification voltage when the surface protective film is peeled from the optical film (adherend) can be reduced by applying an appropriate amount of an antistatic agent component to the surface of the pressure-sensitive adhesive layer, thereby completing the present invention.

The present invention was made in consideration of the above circumstances, and aims to provide an antistatic surface protection film that causes minimal contamination of the adherend, does not deteriorate over time, and has excellent peel-off antistatic properties.

To solve the above problems, the technical concept of the antistatic surface protection film of the present invention is to apply an appropriate amount of antistatic agent to the surface of the adhesive layer after coating and drying an adhesive composition to form an adhesive layer, thereby minimizing contamination of the adherend and minimizing peel electrification voltage when peeled off from the adherend, which is an optical film.

To solve the above problems, the present invention provides an antistatic surface protection film comprising: a substrate film made of a transparent resin; an acrylic polymer copolymerized with (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18 and (B) at least one copolymerizable monomer containing a hydroxyl group, but not including a copolymerizable monomer containing a carboxyl group, on one side of the substrate film; and a pressure-sensitive adhesive layer formed on one side of the substrate film; the pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing (C) a difunctional or higher isocyanate compound, (D) a crosslinking accelerator, and (E) a keto-enol tautomer compound; and a release film laminated on one side of the resin film with a release agent layer containing an antistatic agent attached to the surface of the pressure-sensitive adhesive layer via the release agent layer; the release agent layer is formed from a resin composition containing a release agent mainly composed of dimethylpolysiloxane and an antistatic agent, and the antistatic agent from the release agent layer is transferred to the surface of the pressure-sensitive adhesive layer.

It is also preferable that the copolymerizable monomer group further includes (F) a polyalkylene glycol mono(meth)acrylate monomer.

It is also preferred that the (D) crosslinking accelerator is at least one selected from the group consisting of aluminum chelate compounds, titanium chelate compounds, and iron chelate compounds, and that the crosslinking accelerator is contained in an amount of 0.001 to 0.5 parts by weight per 100 parts by weight of the acrylic polymer of the copolymer, that the (E) keto-enol tautomer compound is contained in an amount of 0.1 to 300 parts by weight, and that the weight ratio of (E)/(D) is 70 to 1000.

Furthermore, the (B) hydroxyl group-containing copolymerizable monomer is preferably at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide, and is preferably present in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the acrylic polymer in the copolymer.

Furthermore, the copolymerizable monomer group may or may not further include (F) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and the (F) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate, and is present in an amount of 0 to 50 parts by weight per 100 parts by weight of the acrylic polymer in the copolymer.

Furthermore, the (C) difunctional or higher isocyanate compound includes a difunctional isocyanate compound that is an acyclic aliphatic isocyanate compound produced by reacting a diisocyanate compound with a diol compound, an aliphatic diisocyanate compound selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate, and a diol compound selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, polypropylene glycol, and the like. The trifunctional isocyanate compound is preferably one selected from the group consisting of pyrene glycol, an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, a biuret of an isophorone diisocyanate compound, an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, or an adduct of a hydrogenated xylylene diisocyanate compound, and is preferably 0.1 to 10 parts by weight per 100 parts by weight of the acrylic polymer of the copolymer.

The pressure-sensitive adhesive composition preferably also contains (G) a polyether-modified siloxane compound having an HLB value of 7 to 15 in an amount of 1.0 part by weight or less (excluding the case where the amount is 0 part by weight) per 100 parts by weight of the acrylic polymer of the copolymer.

It is also preferable that the antistatic agent in the release agent layer is an alkali metal salt.

The antistatic agent in the release _agent layer is preferably a Li salt, and is at least one selected from the group consisting of Li( _CF3SO2 ) _2N , Li( _FSO2 ) _2N , _{and LiCF3SO3} .

In order to solve the above-mentioned problems, the present invention also provides an antistatic surface protection film comprising: a substrate film made of a transparent resin; an acrylic polymer copolymer comprising (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18 and, as a copolymerizable monomer group, at least one copolymerizable monomer containing a hydroxyl group but not a copolymerizable monomer containing a carboxyl group; and a pressure-sensitive adhesive layer formed on one side of the substrate film; the pressure-sensitive adhesive layer comprising a pressure-sensitive adhesive composition containing (C) a difunctional or higher isocyanate compound, (D) a crosslinking accelerator, and (E) a keto-enol tautomer compound; and a release film laminated to the surface of the pressure-sensitive adhesive layer via the release agent layer, the release agent layer being formed from a resin composition containing a release agent primarily composed of dimethylpolysiloxane and an antistatic agent.

It is also preferable that the copolymerizable monomer group further includes (F) a polyalkylene glycol mono(meth)acrylate monomer.

The pressure-sensitive adhesive composition preferably also contains (G) a polyether-modified siloxane compound having an HLB value of 7 to 15 in an amount of 1.0 part by weight or less (excluding the case where the amount is 0 part by weight) per 100 parts by weight of the acrylic polymer of the copolymer.

It is also preferable that the antistatic agent in the release agent layer is an alkali metal salt.

The antistatic agent in the release _agent layer is preferably a Li salt, and is at least one selected from the group consisting of Li( _CF3SO2 ) _2N , Li( _FSO2 ) _2N , _{and LiCF3SO3} .

The present invention also provides an optical film to which the above-mentioned antistatic surface protection film is attached.

The present invention also provides an optical component to which the above-mentioned antistatic surface protection film is attached.

The antistatic surface protective film of the present invention causes little contamination of an adherend, and its low contamination property does not change over time. Furthermore, according to the present invention, even if the adherend is an optical film such as an LR polarizing plate or an AG-LR polarizing plate whose surface has been treated with an anti-contamination agent such as a silicone compound or a fluorine compound, the peeling electrification voltage generated when the antistatic surface protective film is peeled off from the adherend can be kept low, and an antistatic surface protective film having excellent peel-off antistatic performance without deterioration over time can be provided.
The antistatic surface protective film of the present invention can reliably protect the surface of an optical film, thereby improving productivity and yield.

1 is a cross-sectional view illustrating the concept of an antistatic surface protective film of the present invention. FIG. 2 is a cross-sectional view showing a state in which the release film has been peeled off from the antistatic surface protective film of the present invention. 1 is a cross-sectional view showing one embodiment of an optical component of the present invention.

The present invention will be described in detail below based on embodiments.
1 is a cross-sectional view showing the concept of the antistatic surface protective film of the present invention. This antistatic surface protective film 10 has a pressure-sensitive adhesive layer 2 formed on one surface of a transparent substrate film 1. A release film 5, which has a release agent layer 4 formed on the surface of a resin film 3, is attached to the surface of this pressure-sensitive adhesive layer 2.

The substrate film 1 used in the antistatic surface protective film 10 of the present invention is made of a transparent and flexible resin. This allows for visual inspection of the optical component, which is the adherend, with the antistatic surface protective film attached to the optical component. The transparent resin film used as the substrate film 1 is preferably a polyester film such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or polybutylene terephthalate. In addition to polyester films, films made of other resins can also be used as long as they have the required strength and optical suitability. The substrate film 1 may be a non-stretched film or a uniaxially or biaxially stretched film. The stretch ratio of the stretched film and the axial orientation angle formed by crystallization of the stretched film may be controlled to specific values.
The thickness of the substrate film 1 used in the antistatic surface protection film 10 according to the present invention is not particularly limited, but a thickness of, for example, about 12 to 100 μm is preferred, and a thickness of about 20 to 50 μm is more preferred because it is easy to handle.
If necessary, an antifouling layer for preventing surface contamination, an antistatic layer, a hard coat layer for preventing scratches, etc. may be provided on the surface of the base film 1 opposite to the surface on which the pressure-sensitive adhesive layer 2 is formed. The surface of the base film 1 may also be subjected to an adhesion-enhancing treatment such as surface modification by corona discharge or application of an anchor coating agent.

The adhesive layer 2 used in the antistatic surface protection film 10 of the present invention is not particularly limited as long as it adheres to the surface of the adherend, is easily peeled off after use, and is not likely to contaminate the adherend. However, when considering durability after application to an optical film, it is common to use an acrylic adhesive made by crosslinking a (meth)acrylate copolymer.

In particular, a pressure-sensitive adhesive layer is preferred in which the main component of the acrylic pressure-sensitive adhesive is made of an acrylic polymer copolymer containing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, and (B) at least one copolymerizable monomer containing a hydroxyl group, but not including a copolymerizable monomer containing a carboxyl group.
The copolymerizable monomer group may further include (F) a polyalkylene glycol mono(meth)acrylate monomer.
Furthermore, a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition containing, in addition to the acrylic polymer, (C) a difunctional or higher isocyanate compound, (D) a crosslinking accelerator, and (E) a keto-enol tautomer compound is preferred.

(A) Examples of (meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 18 include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and undecyl (meth)acrylate. Examples of the acrylates include methyl (meth)acrylate, ...
When the total amount of the acrylic polymers in the copolymer is 100 parts by weight, it is preferable that the copolymer contains 50 to 95 parts by weight of (A) (meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 18.

Examples of the copolymerizable monomer (B) containing a hydroxyl group include hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide.
It is preferable that the compound is at least one selected from the group consisting of 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide.
When the total amount of the acrylic polymers in the copolymer is taken as 100 parts by weight, the copolymer preferably contains 0.1 to 10 parts by weight of the copolymerizable monomer (B) containing a hydroxyl group.

The (C) bifunctional or higher isocyanate compound may be at least one or two or more selected from polyisocyanate compounds having at least two isocyanate (NCO) groups per molecule. Polyisocyanate compounds are classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, alicyclic isocyanates, etc., and any of these may be used. Specific examples of polyisocyanate compounds include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and trimethylhexamethylene diisocyanate (TMDI), and aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylene diisocyanate (TOID), and tolylene diisocyanate (TDI).
Examples of tri- or higher functional isocyanate compounds include biuret-modified and isocyanurate-modified difunctional isocyanate compounds (compounds having two NCO groups in one molecule), and adducts (polyol-modified compounds) with tri- or higher functional polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane (TMP) and glycerin.
As the difunctional or higher functional isocyanate compound (C), it is possible to use only the trifunctional isocyanate compound (C-1) or only the difunctional isocyanate compound (C-2).It is also possible to use the trifunctional isocyanate compound (C-1) and the difunctional isocyanate compound (C-2) in combination.

Furthermore, the (C-1) trifunctional isocyanate compound used in the present invention is selected from the (C-1-1) first aliphatic isocyanate compound group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, and a biuret of an isophorone diisocyanate compound. Furthermore, it is preferable to include at least one or more of the above and at least one or more selected from (C-1-2) a second group of aromatic isocyanate compounds consisting of an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound. It is preferable to use the (C-1-1) first group of aliphatic isocyanate compounds and the (C-1-2) second group of aromatic isocyanate compounds in combination. In the present invention, the balance of adhesive strength between the slow-release region and the fast-release region can be further improved by using, as the (C-1) trifunctional isocyanate compound, at least one compound selected from the (C-1-1) first group of aliphatic isocyanate compounds and at least one compound selected from the (C-1-2) second group of aromatic isocyanate compounds in combination.

The trifunctional isocyanate compound (C-1) preferably contains at least one selected from the first group of aliphatic isocyanate compounds (C-1-1) and at least one selected from the second group of aromatic isocyanate compounds (C-1-2), with a total content of 0.5 to 5.0 parts by weight per 100 parts by weight of the acrylic polymer of the copolymer. The mixing ratio of the at least one selected from the first group of aliphatic isocyanate compounds (C-1-1) and the at least one selected from the second group of aromatic isocyanate compounds (C-1-2) is preferably within a range of 10%:90% to 90%:10% by weight for (C-1-1):(C-1-2).

Furthermore, the (C-2) bifunctional isocyanate compound used in the present invention is preferably an acyclic aliphatic isocyanate compound, which is a compound produced by reacting a diisocyanate compound with a diol compound.
For example, when a diisocyanate compound is represented by the general formula "O=C=N-X-N=C=O" (where X is a divalent group) and a diol compound is represented by the general formula "HO-Y-OH" (where Y is a divalent group), examples of compounds produced by reacting a diisocyanate compound with a diol compound include compounds represented by the following general formula Z:

[General formula Z]
O=C=N-X-(NH-CO-O-Y-O-CO-NH-X) _n -N=C=O

Here, n is an integer of 0 or greater. When n is 0, the general formula Z represents "O=C=N-X-N=C=O." The bifunctional acyclic aliphatic isocyanate compound may include a compound in which n is 0 in the general formula Z (a diisocyanate compound that has not reacted with the diol compound), but it is preferable to include a compound in which n is an integer of 1 or greater as an essential component. The bifunctional acyclic aliphatic isocyanate compound may also be a mixture of multiple compounds in which n is different in the general formula Z.

Diisocyanate compounds represented by the general formula "O=C=N-X-N=C=O" are aliphatic diisocyanates. X is preferably an acyclic, aliphatic divalent group. The aliphatic diisocyanate is preferably one or more compounds selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

The diol compound represented by the general formula "HO-Y-OH" is an aliphatic diol. Y is preferably an acyclic, aliphatic divalent group. The diol compound is preferably one or more compounds selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, and polypropylene glycol.

The weight ratio (C-1/C-2) of the (C-1) trifunctional isocyanate compound to the (C-2) difunctional isocyanate compound is preferably 1 to 90. The amount of the (C) difunctional or higher isocyanate compound is preferably 0.1 to 10 parts by weight per 100 parts by weight of the acrylic polymer of the copolymer.

(D) The crosslinking accelerator may be any substance that functions as a catalyst for the reaction (crosslinking reaction) between the copolymer and the crosslinking agent when a polyisocyanate compound is used as the crosslinking agent. Examples of the crosslinking accelerator include amine compounds such as tertiary amines, metal chelate compounds, organotin compounds, organolead compounds, and organozinc compounds, among other organometallic compounds. In the present invention, metal chelate compounds and organotin compounds are preferred as crosslinking accelerators.

A metal chelate compound is a compound in which one or more multidentate ligands L are bonded to a central metal atom M. A metal chelate compound may or may not have one or more monodentate ligands X bonded to the metal atom M. For example, when the general formula of a metal chelate compound having one metal atom M is represented by M(L) _m (X) _n , m ≧ 1 and n ≧ 0. When m is 2 or more, the m Ls may be the same ligand or different ligands. When n is 2 or more, the n Xs may be the same ligand or different ligands.

Examples of the metal atom M include Fe, Ni, Mn, Cr, V, Ti, Ru, Zn, Al, Zr, and Sn.
Examples of the polydentate ligand L include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone (also known as 2,4-pentanedione), 2,4-hexanedione, and benzoylacetone. These are keto-enol tautomer compounds, and in the polydentate ligand L, the enol may be deprotonated to form an enolate (for example, acetylacetonate).
Examples of the monodentate ligand X include halogen atoms such as chlorine and bromine atoms, acyloxy groups such as pentanoyl, hexanoyl, 2-ethylhexanoyl, octanoyl, nonanoyl, decanoyl, dodecanoyl, and octadecanoyl groups, and alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, and butoxy groups.

Specific examples of metal chelate compounds include iron tris(2,4-pentanedionato)(III), iron trisacetylacetonate, titanium trisacetylacetonate, ruthenium trisacetylacetonate, zinc bisacetylacetonate, aluminum trisacetylacetonate, zirconium tetrakisacetylacetonate, iron tris(2,4-hexanedionato)(III), zinc bis(2,4-hexanedionato), titanium tris(2,4-hexanedionato), aluminum tris(2,4-hexanedionato), and zirconium tetrakis(2,4-hexanedionato).

Examples of organotin compounds include dialkyltin oxides, fatty acid salts of dialkyltins, and fatty acid salts of stannous tin. Traditionally, dibutyltin compounds have been widely used, but in recent years, the toxicity of organotin compounds has been highlighted, and tributyltin (TBT) contained in dibutyltin compounds in particular is of concern as an endocrine disruptor. From the perspective of safety, long-chain alkyltin compounds such as dioctyltin compounds are preferred. Specific examples of organotin compounds include dioctyltin oxide and dioctyltin dilaurate. While Sn compounds can be used provisionally, in light of the trend toward the use of safer substances, it is preferable to use metal chelate compounds of Al, Ti, Fe, etc., which are safer than Sn.
The crosslinking accelerator (D) in the pressure-sensitive adhesive composition according to the present invention is preferably at least one selected from the group consisting of aluminum chelate compounds, titanium chelate compounds, and iron chelate compounds.
The crosslinking accelerator (D) is preferably contained in an amount of 0.001 to 0.5 parts by weight per 100 parts by weight of the acrylic polymer in the copolymer.

Examples of the (E) keto-enol tautomer compound include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. In pressure-sensitive adhesive compositions using a polyisocyanate compound as a crosslinking agent, these compounds block the isocyanate groups of the crosslinking agent, thereby suppressing excessive viscosity increase and gelation of the pressure-sensitive adhesive composition after blending the crosslinking agent, and thereby extending the pot life of the pressure-sensitive adhesive composition.
The keto-enol tautomer compound (E) is preferably contained in an amount of 0.1 to 300 parts by weight per 100 parts by weight of the acrylic polymer in the copolymer.

In contrast to the crosslinking accelerator (D), the (E) keto-enol tautomer compound has the effect of inhibiting crosslinking. Therefore, it is preferable to appropriately set the ratio of the (E) keto-enol tautomer compound to the (D) crosslinking accelerator. To extend the pot life of the PSA composition and improve its storage stability, the weight ratio of (E)/(D) is preferably 70 to 1,000.

The acrylic polymer may further optionally contain (F) a polyalkylene glycol mono(meth)acrylate monomer as one of the copolymerizable monomers. The (F) polyalkylene glycol mono(meth)acrylate monomer may be a compound in which one of the hydroxyl groups of a polyalkylene glycol is esterified as a (meth)acrylate. Since the (meth)acrylate group serves as a polymerizable group, it can be copolymerized with the base polymer. The other hydroxyl groups may remain as OH or may be alkyl ethers such as methyl ether or ethyl ether, saturated carboxylic acid esters such as acetate ester, or the like.
Examples of alkylene groups in polyalkylene glycols include, but are not limited to, ethylene, propylene, and butylene groups. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols, such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of polyalkylene glycol copolymers include polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, and polyethylene glycol-polypropylene glycol-polybutylene glycol, and the copolymers may be block copolymers or random copolymers.
It is preferable that the average repeat number of alkylene oxides constituting the polyalkylene glycol chain of the (F) polyalkylene glycol mono(meth)acrylate ester monomer is 3 to 14. The "average repeat number of alkylene oxides" refers to the average number of repeating alkylene oxide units in the "polyalkylene glycol chain" portion contained in the molecular structure of the (F) polyalkylene glycol mono(meth)acrylate ester monomer.

The (F) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.
More specifically, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-mono(meth)acrylate, polyethylene glycol-polybutylene glycol-mono(meth)acrylate, polypropylene glycol-polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol-mono(meth)acrylate; methoxypolyethylene glycol-(meth)acrylate, methoxypolypropylene glycol-(meth)acrylate, methoxypolybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, methoxy-polyethylene glycol ethoxypolyethylene glycol-(meth)acrylate, ethoxypolypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-(meth)acrylate, ethoxypolypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-(polypropylene glycol)-(meth)acrylate, ethoxypolyethylene glycol-(polybutylene glycol)-(meth)acrylate, ethoxypolyethylene glycol-(polybutylene glycol)-(meth)acrylate, ethoxypolypropylene glycol-(polybutylene glycol)-(meth)acrylate, ethoxypolyethylene glycol-(polypropylene glycol)-(polybutylene glycol)-(meth)acrylate, and ethoxypolyethylene glycol-(polypropylene glycol)-(polybutylene glycol)-(meth)acrylate.
When the total amount of the acrylic polymers in the copolymer is taken as 100 parts by weight, the (F) polyalkylene glycol mono(meth)acrylate monomer is preferably contained in an amount of 0 to 50 parts by weight. In the pressure-sensitive adhesive layer according to the present invention, the pressure-sensitive adhesive composition does not necessarily contain the (F) polyalkylene glycol mono(meth)acrylate monomer.

The PSA composition may optionally contain (G) a polyether-modified siloxane compound having an HLB value of 7 to 15. The polyether-modified siloxane compound is a siloxane compound having a polyether group, and in addition to the usual siloxane unit [-SiR ¹ ₂ -O-], has a siloxane unit having a polyether group [-SiR ¹ (R ² O(R ³ O) _n R ⁴ )-O-]. Here, R ¹ represents one or more alkyl or aryl groups, R ² and R ³ represent one or more alkylene groups, and R ⁴ represents one or more alkyl groups, acyl groups, or the like (terminal groups). Examples of the polyether group include polyoxyalkylene groups such as a polyoxyethylene group [(C ₂ H ₄ O) _n ] and a polyoxypropylene group [(C ₃ H ₆ O) _n ].

The polyether-modified siloxane compound is preferably a polyether-modified siloxane compound (G) having an HLB value of 7 to 15. The content of the polyether-modified siloxane compound (G) having an HLB value of 7 to 15 is preferably 0.01 to 1.0 parts by weight, more preferably 0.1 to 0.5 parts by weight, per 100 parts by weight of the acrylic polymer of the copolymer.
HLB is the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) defined in, for example, JIS K3211 (surfactant terminology) or the like.

Polyether-modified siloxane compounds can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group onto a polyorganosiloxane main chain having a silicon hydride group by a hydrosilylation reaction.Specific examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymers, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymers, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymers.The HLB value of the polyether-modified siloxane compound can be adjusted by selecting the ratio of polyether groups to siloxane groups.
(G) The adhesive strength and reworkability of the adhesive can be improved by blending a polyether-modified siloxane compound having an HLB value of 7 to 15 into the adhesive composition. If the adhesive composition does not contain a polyether-modified siloxane compound, the cost will be lower.

Furthermore, other components such as copolymerizable (meth)acrylic monomers containing alkylene oxide, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, cure accelerators, plasticizers, fillers, cure retarders, processing aids, antioxidants, and antioxidants can be appropriately blended. These can be used alone or in combination of two or more types.

The copolymer used as the base component in the pressure-sensitive adhesive composition of the present invention can be synthesized by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 18 and (B) at least one copolymerizable monomer containing a hydroxyl group, but not including a copolymerizable monomer containing a carboxyl group. The copolymerizable monomer group may further include (F) a polyalkylene glycol mono(meth)acrylic acid ester monomer. The polymerization method for the copolymer is not particularly limited, and any appropriate polymerization method such as solution polymerization or emulsion polymerization can be used.
The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above-mentioned copolymer with (C) a difunctional or higher isocyanate compound, (D) a crosslinking accelerator, (E) a keto-enol tautomer compound, and further any additives as appropriate.

The copolymer is preferably an acrylic polymer, and preferably contains 50 to 100% by weight of an acrylic monomer such as a (meth)acrylic acid ester monomer, (meth)acrylic acid, or a (meth)acrylamide.
The acrylic polymer does not contain a copolymerizable monomer containing a carboxyl group as a copolymerizable monomer group, which is effective in improving the crosslinking rate and stabilizing the adhesive strength. It is preferable to use a copolymerizable monomer containing a hydroxyl group (B) as a monomer that reacts with the difunctional or higher isocyanate compound (C) used as a crosslinking agent. Preferred monomer compositions for the copolymer include one or more types each of (A) and (B), and one or more types each of (A), (B), and (F).

The adhesive layer obtained by crosslinking the adhesive composition preferably has an adhesive strength of 0.05 to 0.1 N/25 mm at a low peel speed of 0.3 m/min, and an adhesive strength of 1.0 N/25 mm or less at a high peel speed of 30 m/min. This results in performance in which the adhesive strength changes little depending on the peel speed, enabling rapid peeling even at high speeds. Furthermore, when the surface protection film needs to be peeled off once for re-application, excessive force is not required, and it can be easily peeled off from the adherend.

The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition preferably has a surface resistivity of 5.0 × 10 ⁺¹² Ω/□ or less and a peeling electrification voltage of "±0.6 kV or less." In the present invention, "±0.6 kV or less" means 0 to -0.6 kV and 0 to +0.6 kV, i.e., -0.6 to +0.6 kV. A high surface resistivity results in poor performance in dissipating static electricity generated by charging during peeling. Therefore, by sufficiently reducing the surface resistivity, the peeling electrification voltage that occurs with static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend can be reduced, thereby preventing the peeling electrification voltage from affecting the electrical control circuits, etc. of the adherend.

The gel fraction of the adhesive layer (crosslinked adhesive) obtained by crosslinking the adhesive composition of the present invention is preferably 95 to 100%. Such a high gel fraction prevents excessive adhesive strength at low peel speeds, reduces elution of unpolymerized monomers or oligomers from the copolymer, improves reworkability and durability at high temperatures and humidity, and suppresses contamination of the adherend.

The pressure-sensitive adhesive film of the present invention comprises a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one or both sides of a resin film. The surface protection film of the present invention comprises a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one side of a resin film. Because the pressure-sensitive adhesive composition of the present invention contains a well-balanced blend of the above-mentioned components (A) to (E), it has excellent antistatic properties, an excellent balance of adhesive strength at both low and high peel speeds, and also excellent durability and reworkability (no transfer of contamination to the adherend after tracing the surface protection film with a ballpoint pen through the pressure-sensitive adhesive layer). For these reasons, it is suitable for use as a surface protection film for polarizing plates.

The thickness of the adhesive layer 2 used in the antistatic surface protective film 10 of the present invention is not particularly limited, but is preferably, for example, approximately 5 to 40 μm, and more preferably approximately 10 to 30 μm. It is preferable that the adhesive layer 2 have a weak adhesive strength, i.e., a peel strength (adhesion) of the antistatic surface protective film to the surface of the adherend of approximately 0.03 to 0.3 N/25 mm, as this provides excellent operability when peeling the antistatic surface protective film from the adherend. Furthermore, to provide excellent operability when peeling the release film 5 from the antistatic surface protective film 10, it is preferable that the peel strength of the release film 5 from the adhesive layer 2 be 0.2 N/50 mm or less.

The release film 5 used in the antistatic surface protection film 10 of the present invention has a release agent layer 4 formed on one side of the resin film 3, the release agent being primarily composed of dimethylpolysiloxane, and a resin composition containing an antistatic agent.

Examples of the resin film 3 include polyester film, polyamide film, polyethylene film, polypropylene film, and polyimide film, but polyester film is particularly preferred because of its excellent transparency and relatively low price. The resin film may be an unstretched film or a uniaxially or biaxially stretched film. The stretching ratio of the stretched film and the orientation angle in the axial direction formed by crystallization of the stretched film may be controlled to a specific value.
The thickness of the resin film 3 is not particularly limited, but is preferably about 12 to 100 μm, and more preferably about 20 to 50 μm, which is easy to handle.
If necessary, the surface of the resin film 3 may be subjected to an easy-adhesion treatment such as surface modification by corona discharge or application of an anchor coating agent.

The release agent that constitutes the release agent layer 4 and is primarily composed of dimethylpolysiloxane includes known silicone-based release agents, such as addition reaction, condensation reaction, cationic polymerization, and radical polymerization types. Examples of commercially available addition reaction silicone-based release agents include KS-776A, KS-847T, KS-779H, KS-837, KS-778, and KS-830 (manufactured by Shin-Etsu Chemical Co., Ltd.), and SRX-211, SRX-345, SRX-357, SD7333, SD7220, SD7223, LTC-300B, LTC-350G, and LTC-310 (manufactured by Dow Corning Toray Co., Ltd.). Examples of commercially available condensation reaction type release agents include SRX-290 and SYLOFF-23 (manufactured by Dow Corning Toray Co., Ltd.). Commercially available cationic polymerization products include, for example, TPR-6501, TPR-6500, UV9300, VU9315, and UV9430 (manufactured by Momentive Performance Materials), and X62-7622 (manufactured by Shin-Etsu Chemical Co., Ltd.). Commercially available radical polymerization products include, for example, X62-7205 (manufactured by Shin-Etsu Chemical Co., Ltd.).

The antistatic agent that makes up the release agent layer 4 is preferably one that has good dispersibility in the release agent solution whose main component is dimethylpolysiloxane, and that does not inhibit the curing of the release agent whose main component is dimethylpolysiloxane. Alkali metal salts are suitable as such antistatic agents.

Examples of alkali metal salts include metal salts of lithium, sodium, and potassium. Specifically, metal salts composed of cations such as Li ⁺ , Na ⁺ , and K ⁺ and anions such as Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SCN ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , (FSO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , and (CF ₃ SO ₂ ) ₃ C ⁻ are preferably used. Among these, lithium salts (Li salts ₎ such as LiBr, LiI, _LiBF4 , _LiPF6 , LiSCN, _LiClO4 , _LiCF3SO3 , _Li ( _FSO2 )2N, Li( _CF3SO2 ) _2N , Li( _{C2F5SO2 ) 2N} , and Li( _CF3SO2 ) _{3C are} particularly preferably used, and _{Li (CF3SO2 ) 2N} (abbreviated as LiTFSI), _Li ( _FSO2 ) _2N (abbreviated as LiFSI ₎ , and _LiCF3SO3 (abbreviated as LiTF or LiTf) are particularly preferably used. These alkali metal salts may be used alone or in combination of two or more. In order to stabilize the ionic substance, a compound containing a polyoxyalkylene structure may be added.
The amount of antistatic agent added to a release agent containing dimethylpolysiloxane as a main component varies depending on the type of antistatic agent and the degree of affinity with the release agent, but can be set taking into consideration the desired peel electrification voltage, staining properties on the adherend, adhesive properties, etc. when the antistatic surface protection film is peeled from the adherend.

There are no particular limitations on the method for mixing the dimethylpolysiloxane-based release agent with the antistatic agent. Any of these methods may be used: adding the antistatic agent to the dimethylpolysiloxane-based release agent, mixing, and then adding and mixing a catalyst for curing the release agent; diluting the dimethylpolysiloxane-based release agent with an organic solvent before adding and mixing the antistatic agent and catalyst for curing the release agent; or diluting the siloxane-based release agent with an organic solvent before adding and mixing the catalyst, and then adding and mixing the antistatic agent. If necessary, adhesion improvers such as silane coupling agents or materials that enhance the antistatic effect, such as compounds containing polyoxyalkylene groups, may also be added.

There are no particular limitations on the mixing ratio between the dimethylpolysiloxane-based release agent and the antistatic agent, but a ratio of approximately 5 to 100 parts antistatic agent (solids) per 100 parts dimethylpolysiloxane-based release agent is preferred. If the amount of antistatic agent added (solids) is less than 5 parts per 100 parts dimethylpolysiloxane-based release agent, the amount of antistatic agent transferred to the surface of the adhesive layer will be reduced, making it difficult for the adhesive to exhibit its antistatic properties. Furthermore, if the amount of antistatic agent added (solids) exceeds 100 parts per 100 parts dimethylpolysiloxane-based release agent, both the antistatic agent and the dimethylpolysiloxane-based release agent will be transferred to the surface of the adhesive layer, potentially reducing the adhesive properties of the adhesive.

The method for forming the adhesive layer 2 on the base film 1 of the antistatic surface protection film 10 of the present invention and the method for laminating the release film 5 may be any known method and are not particularly limited. Specific examples include (1) a method in which a resin composition for forming the adhesive layer 2 is applied to one side of the base film 1, dried to form an adhesive layer, and then laminating the release film 5; and (2) a method in which a resin composition for forming the adhesive layer 2 is applied to the surface of the release film 5, dried to form an adhesive layer, and then laminating the base film 1. Either method may be used.

The adhesive layer 2 can be formed on the surface of the base film 1 by a known method. Specifically, known coating methods such as reverse coating, comma coating, gravure coating, slot die coating, Mayer bar coating, and air knife coating can be used.

Similarly, the release agent layer 4 can be formed on the resin film 3 by a known method. Specifically, known coating methods such as gravure coating, Mayer bar coating, and air knife coating can be used.

FIG. 2 is a cross-sectional view showing the antistatic surface protective film of the present invention with the release film peeled off.
When the release film 5 is peeled off from the antistatic surface protective film 10 shown in Fig. 1, a portion of the antistatic agent (reference numeral 7) contained in the release agent layer 4 of the release film 5 is transferred (adhered) to the surface of the pressure-sensitive adhesive layer 2 of the antistatic surface protective film 10. Therefore, in Fig. 2, the antistatic agent transferred to the surface of the pressure-sensitive adhesive layer 2 of the antistatic surface protective film is schematically shown by spots reference numeral 7.
In the antistatic surface protective film of the present invention, when the antistatic surface protective film 11 shown in Fig. 2 with the release film peeled off is attached to an adherend, the antistatic agent transferred to the surface of the pressure-sensitive adhesive layer 2 comes into contact with the surface of the adherend, thereby making it possible to keep the peeling electrification voltage low when the antistatic surface protective film is peeled off again from the adherend.

FIG. 3 is a cross-sectional view showing an embodiment of an optical component according to the present invention.
The release film 5 is peeled off from the antistatic surface protective film 10 of the present invention, and in a state where the pressure-sensitive adhesive layer 2 is exposed, the film is then stuck to an optical component 8 as an adherend via the pressure-sensitive adhesive layer 2 .
That is, FIG. 3 shows an optical component 20 to which the antistatic surface protective film 10 of the present invention is attached. Examples of optical components include optical films such as polarizing plates, retardation plates, lens films, polarizing plates that also serve as retardation plates, and polarizing plates that also serve as lens films. Such optical components are used as components of liquid crystal display devices such as liquid crystal display panels, optical systems for various instruments, and the like. Examples of optical components also include optical films such as antireflection films, hard coat films, and transparent conductive films for touch panels. In particular, the antistatic surface protective film can be suitably used as an antifouling surface protective film attached to the antifouling surface of optical films such as low-reflection polarizing plates (LR polarizing plates) and anti-glare low-reflection polarizing plates (AG-LR polarizing plates), whose surfaces have been treated with a silicone compound, a fluorine compound, or the like to be antifouling-treated.
According to the optical component of the present invention, when the antistatic surface protective film 10 is peeled off from the adherend, that is, the optical component (optical film), the peeling electrification voltage can be suppressed to a sufficiently low level, so that there is no risk of damaging circuit components such as driver ICs, TFT elements, and gate line driving circuits, and the production efficiency in the process of manufacturing liquid crystal display panels and the like can be improved and the reliability of the production process can be maintained.

Next, the present invention will be further explained using examples.

<Production of Pressure-Sensitive Adhesive Composition>
[Example 1]
Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Subsequently, 100 parts by weight of 2-ethylhexyl acrylate, 4.5 parts by weight of 8-hydroxyoctyl acrylate, 10 parts by weight of polypropylene glycol monoacrylate (n = 12), and 60 parts by weight of a solvent (ethyl acetate) were added to the reactor. Subsequently, 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours, and the mixture was allowed to react at 65°C for 6 hours, yielding an acrylic copolymer solution of Example 1 having a weight-average molecular weight of 500,000. To this acrylic copolymer solution, 8.5 parts by weight of acetylacetone was added and stirred, followed by the addition of 2.5 parts by weight of Coronate HX (an isocyanurate of a hexamethylene diisocyanate compound) and 0.1 parts by weight of titanium trisacetylacetonate, followed by stirring and mixing, yielding the pressure-sensitive adhesive composition of Example 1.

[Examples 2 to 6 and Comparative Examples 1 to 3]
The pressure-sensitive adhesive compositions of Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the compositions of the pressure-sensitive adhesive composition of Example 1 were changed as shown in Tables 1 and 2. In Tables 1 and 2, the monomers contained (copolymerized) in the acrylic copolymer are (A), (B), (F), and a "carboxyl group-containing monomer."

Tables 1 and 2 are two separate tables showing the compounding ratios of each component, and in both cases, the numerical values in parts by weight, calculated with the total of group (A) being 100 parts by weight, are enclosed in parentheses. The compound names of the abbreviations for each component used in Tables 1 and 2 are shown in Tables 3 and 4. Coronate (registered trademark) HX, HL, and L are trade names of Nippon Polyurethane Industry Co., Ltd., and Takenate (registered trademark) D-140N, D-127N, and D-110N are trade names of Mitsui Chemicals, Inc. In the "Antistatic Agent" section of Table 2 and Table 7 described below, LiTFSI represents Li( _CF3SO2 ) _2N , LiFSI represents Li( _{FSO2 ) 2N} , LiTF _{represents LiCF3SO3} , and SH8400 represents polyether-modified silicone (manufactured by Dow Corning Toray Co., Ltd., product name: SH8400, main component: dimethyl, methyl (polyethylene oxide acetate) siloxane).

<Synthesis of Bifunctional Isocyanate Compound>
The bifunctional isocyanate compounds of Synthesis Examples 1 and 2 were synthesized by the following method: As shown in Tables 5 and 6, a diisocyanate and a diol compound were mixed in a molar ratio of NCO/OH=16, and reacted at 120° C. for 3 hours. Thereafter, unreacted diisocyanate was removed under reduced pressure using a thin-film evaporator, thereby obtaining the target bifunctional isocyanate compounds.

<Preparation of Antistatic Surface Protection Film>
[Example 1]
5 parts by weight of addition reaction type silicone (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-345), 0.5 parts by weight of Li(CF ₃ SO ₂ ) ₂ N, 95 parts by weight of a 1:1 mixed solvent of toluene and ethyl acetate, and 0.05 parts by weight of a platinum catalyst (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-212 Catalyst) were combined, stirred, and mixed to prepare a coating material for forming the release agent layer of Example 1. The coating material for forming the release agent layer of Example 1 was applied to the surface of a 38 μm thick polyethylene terephthalate film using a Mayer bar to a dry thickness of 0.2 μm, and the coating was dried in a hot air circulating oven at 120°C for 1 minute to obtain the release film of Example 1.
The pressure-sensitive adhesive composition of Example 1 was applied to the surface of a 38 μm-thick polyethylene terephthalate film so that the dried thickness was 20 μm, and then dried for 2 minutes in a hot air circulating oven at 100° C. to form a pressure-sensitive adhesive layer. The release agent layer (silicone-treated surface) of the release film of Example 1 prepared above was then laminated to the surface of this pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive film was kept warm in an environment of 40° C. for 5 days to cure the pressure-sensitive adhesive, thereby obtaining the antistatic surface protection film of Example 1.

[Example 2]
An antistatic surface protection film of Example 2 was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition of Example 1 was replaced with the pressure-sensitive adhesive composition of Example 2 and the antistatic agent used in the release agent layer was changed to LiCF ₃ SO ₃ .

[Examples 3 to 6]
The antistatic surface protection films of Examples 3 to 6 were obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition of Example 1 was replaced with the pressure-sensitive adhesive compositions of Examples 3 to 6, and the antistatic agent used in the release agent layer was changed to Li(FSO ₂ ) ₂ N.

[Comparative Example 1]
5 parts by weight of an addition reaction type silicone (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-345), 95 parts by weight of a 1:1 mixed solvent of toluene and ethyl acetate, and 0.05 parts by weight of a platinum catalyst (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-212 Catalyst) were combined, stirred, and mixed to prepare a coating material for forming the release agent layer of Comparative Example 1. The coating material for forming the release agent layer of Comparative Example 1 was applied to the surface of a polyethylene terephthalate film having a thickness of 38 μm using a Mayer bar so as to have a dry thickness of 0.2 μm, and the coating material was dried in a hot air circulating oven at 120° C. for 1 minute, to obtain the release film of Comparative Example 1.
The pressure-sensitive adhesive composition of Comparative Example 1 was applied to the surface of a 38 μm-thick polyethylene terephthalate film so that the dried thickness was 20 μm, and then dried for 2 minutes in a hot air circulating oven at 100° C. to form a pressure-sensitive adhesive layer. The release agent layer (silicone-treated surface) of the release film of Comparative Example 1 prepared above was then laminated to the surface of this pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive film was kept warm in an environment of 40° C. for 5 days to cure the pressure-sensitive adhesive, thereby obtaining an antistatic surface protection film of Comparative Example 1.

[Comparative Example 2]
An antistatic surface protection film of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the adhesive composition of Comparative Example 1 was replaced with the adhesive composition of Comparative Example 2.

[Comparative Example 3]
An antistatic surface protective film of Comparative Example 3 was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition of Example 1 was replaced with the pressure-sensitive adhesive composition of Comparative Example 3 and the antistatic agent used in the release agent layer was changed to Li(FSO ₂ ) ₂ N.

Table 7 shows the composition of the release agent layer in the antistatic surface protection films of Examples 1 to 6 and Comparative Examples 1 to 3.

<Test method and evaluation>
The surface protection films of Examples 1 to 6 and Comparative Examples 1 to 3 were aged for 7 days in an atmosphere of 23°C and 50% RH, and then the release film (a silicone resin-coated PET film) was peeled off to expose the pressure-sensitive adhesive layer, which was used as a sample for measuring surface resistivity.
Furthermore, this surface protection film with the exposed adhesive layer was attached to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, and after leaving it for one day, it was autoclaved at 50°C and 5 atmospheres for 20 minutes and then left at room temperature for a further 12 hours to prepare a sample for measuring adhesive strength, peeling electrification voltage, and reworkability.

<Adhesive strength>
The measurement sample obtained above (a 25 mm wide surface protection film attached to the surface of a polarizing plate) was peeled in a 180° direction using a tensile tester at a low peeling speed (0.3 m/min) and a high peeling speed (30 m/min), and the measured peel strength was taken as the adhesive strength.

<Surface resistivity>
After aging and before bonding to a polarizing plate, the release film (a silicone resin-coated PET film) was peeled off to expose the pressure-sensitive adhesive layer, and the surface resistivity of the pressure-sensitive adhesive layer was measured using a resistivity meter, Hiresta UP-HT450 (manufactured by Mitsubishi Chemical Analytech).

<Peeling electrification voltage>
The measurement sample obtained above was peeled off at an angle of 180° at a tensile speed of 30 m/min, and the voltage (charged voltage) generated when the polarizing plate was charged was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation), and the maximum measured value was taken as the peeling charged voltage.

<Reworkability>
The surface protection film of the measurement sample obtained above was traced with a ballpoint pen (load 500 g, 3 strokes back and forth), and then the surface protection film was peeled off from the polarizing plate and the surface of the polarizing plate was observed to confirm that no contamination transfer to the polarizing plate. The evaluation target criteria were as follows: "○" if no contamination transfer to the polarizing plate occurred, "△" if contamination transfer was confirmed in at least a part along the path traced with the ballpoint pen, and "×" if contamination transfer was confirmed along the path traced with the ballpoint pen and separation of the adhesive from the adhesive surface was confirmed.

The evaluation results are shown in Table 8. The surface resistivity was expressed as "m×10 ⁺ⁿ " as "mE+n" (where m is an arbitrary real number, and n is a positive integer).

The measurement results shown in Table 8 reveal the following.
The antistatic surface protection films of Examples 1 to 6 according to the present invention have an appropriate adhesive strength, do not contaminate the surface of the adherend, and exhibit a low peel electrification voltage when peeled from the adherend.
On the other hand, the antistatic surface protective film of Comparative Example 1, in which a silicone compound and an antistatic agent were added to the adhesive layer, had a low and good surface resistivity of the adhesive layer, but due to its high adhesive strength, the peeling electrification voltage was high and the reworkability was poor. Also, in Comparative Example 2, the adhesive gelled and became impossible to apply, probably due to the large amount of crosslinking accelerator added. Also, in Comparative Example 3, due to the inclusion of a monomer containing a carboxyl group, the adhesive strength was high and the reworkability was somewhat poor.
That is, in Comparative Examples 1 and 2, in which a silicone compound and an antistatic agent were mixed into the PSA, it was difficult to achieve both a reduction in peeling electrification voltage and resistance to staining of the adherend. On the other hand, in Examples 1 to 6, in which an antistatic agent was added to the release agent layer and then transferred to the surface of the PSA layer, a small amount of the antistatic agent was effective in reducing peeling electrification voltage, and there was no staining of the adherend, and a good antistatic surface protection film was obtained.

The antistatic surface protective film of the present invention can be used to protect the surfaces of optical films such as polarizing plates, retardation plates, and lens films for displays, as well as various other optical components, in the production processes of these optical components, etc. In particular, when used as an antistatic surface protective film for optical films such as LR polarizing plates and AG-LR polarizing plates, the surface of which has been treated with an anti-fouling agent such as a silicone compound or a fluorine compound, the amount of static electricity generated when the film is peeled off from the adherend can be reduced.
The antistatic surface protective film of the present invention causes little contamination to the adherend, and furthermore, has excellent antistatic properties against peeling without deterioration over time, and therefore can improve the yield of the production process, and is of great industrial value.

1...base film, 2...adhesive layer, 3...resin film, 4...release agent layer, 5...release film, 7...antistatic agent, 8...adherend (optical component), 10...antistatic surface protective film, 11...antistatic surface protective film with the release film removed, 20...optical component to which the antistatic surface protective film is attached.

Claims (2)

a pressure-sensitive adhesive layer formed on one side of a substrate film made of a transparent resin, the pressure-sensitive adhesive layer being made of an acrylic polymer of a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of 4 to 18 with (B) at least one copolymerizable monomer containing a hydroxyl group, but not including a copolymerizable monomer containing a carboxyl group, and the copolymerizable monomer group being further made of a pressure-sensitive adhesive composition containing (C) a difunctional or higher isocyanate compound, (D) a crosslinking accelerator, (E) a keto-enol tautomer compound, and (G) a polyether-modified siloxane compound having an HLB value of 7 to 15;
a release film, which has a release agent layer containing an antistatic agent laminated on one surface of a resin film, is bonded to the surface of the pressure-sensitive adhesive layer via the release agent layer;
the release agent layer is formed from a resin composition containing a release agent containing dimethylpolysiloxane as a main component and an antistatic agent,
An antistatic surface protection film, characterized in that the antistatic agent is applied to the surface of the pressure - sensitive adhesive layer. An optical film to which the antistatic surface protective film of claim 1 is adhered.