JP7086153B2 - Surface protection film - Google Patents

Description

The present invention relates to providing a surface protective film.
The present invention also relates to a surface protective film used in the manufacturing process of a liquid crystal display. More specifically, the surface of the optical member such as the polarizing plate, the retardation plate, and the antireflection film is protected by attaching to the surface of the optical member such as the polarizing plate, the retardation plate, and the antireflection film constituting the liquid crystal display. It relates to a surface protective film used to do so.
The surface protective film according to the present invention has particularly excellent antistatic performance. Therefore, a plastic film that easily generates static electricity is used for the purpose of protecting the surface of an optical film such as a polarizing plate, a retardation plate, and an antireflection film in which a plastic film is used as a constituent member.

Conventionally, in the manufacturing process of optical members such as polarizing plates, retardation plates, and antireflection films, which are members constituting liquid crystal displays, a surface protective film for temporarily protecting the surface of the optical members is attached. Ru. Such a surface protective film is used only in the process of manufacturing the optical member, and is peeled off from the optical member and removed when the optical member is incorporated into the liquid crystal display. Since such a surface protective film for protecting the surface of the optical member is used only in the manufacturing process, it is also generally called a process film.

As described above, the surface protective film used in the process of manufacturing the optical member has an adhesive layer formed on one side of the optically transparent polyethylene terephthalate (PET) resin film, and is attached to the optical member. A peel-treated release film for protecting the pressure-sensitive adhesive layer is bonded onto the pressure-sensitive adhesive layer until they are combined.
In addition, optical members such as polarizing plates, retardation plates, and antireflection films are inspected with optical evaluations such as display capability, hue, contrast, and foreign matter contamination of the liquid crystal display plate with the surface protective film bonded. Therefore, as the required performance for the surface protective film, it is required that bubbles and foreign matters do not adhere to the pressure-sensitive adhesive layer.
Further, in recent years, when the surface protective film is peeled off from an optical member such as a polarizing plate, a retardation plate, or an antireflection film, the peeling charge generated by the static electricity generated when the adherend peels off the adhesive layer is a liquid crystal display. There is a concern that it may affect the failure of the electric control circuit of the display, and excellent antistatic performance is required for the adhesive layer.
Further, when the surface protective film is attached to an optical member such as a polarizing plate, a retardation plate, or an antireflection film, the surface protective film may be once peeled off and then reattached for various reasons. At that time, it is required that it can be easily peeled off from the optical member of the adherend (reworkability). Further, at this time, it is required that the adherend is not contaminated, that is, so-called adhesive residue does not occur.
Further, when the surface protective film is finally peeled off from an optical member such as a polarizing plate, a phase difference, or an antireflection film plate, it is required to be able to peel off quickly. It is required that the adhesive strength does not change much depending on the peeling speed so that the peeling can be performed quickly even by the so-called peeling at a high speed.

As described above, in recent years, as the required performance for the pressure-sensitive adhesive layer constituting the surface protective film, (1) balancing the adhesive force in the peeling speed in the low speed region and the high speed region, and (2) glue. It is required from the viewpoint of ease of use when using the surface protective film that it is required to prevent the remaining generation, (3) to have excellent antistatic performance, and (4) to have rework performance.
However, although each of these (1) to (4), which is the required performance for the pressure-sensitive adhesive layer constituting the surface protective film, can be satisfied, the pressure-sensitive adhesive layer of the surface protective film is required. It was a very difficult task to satisfy all the required performances (1) to (4) at the same time.
In the present specification, the "low speed region" means that the peeling speed is around 0.3 m / min, and the "high speed region" means that the peeling speed is around 30 m / min.

For example, the following proposals are known for (1) balancing the adhesive force at the peeling speed in the low speed region and the high speed region, and (2) preventing the generation of adhesive residue. There is.

Acrylic adhesion made mainly of a copolymer of a (meth) acrylic acid alkyl ester having an alkyl group having 7 or less carbon atoms and a copolymerizable compound containing a carboxyl group, which is crosslinked with a crosslinking agent. In the agent layer, when the adhesive is adhered for a long period of time, there is a problem that the adhesive is transferred to the adherend side and the adhesive force to the adherend is greatly increased with time. To avoid this, a copolymer of a (meth) acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms and a copolymer compound having an alcoholic hydroxyl group is used, and the copolymer is crosslinked with a cross-linking agent. Those provided with a treated pressure-sensitive adhesive layer are known (Patent Document 1).
Further, a copolymer of a (meth) acrylic acid alkyl ester and a carboxyl group-containing copolymer compound was blended in a small amount with the same copolymer as described above, and a pressure-sensitive adhesive layer was provided by cross-linking the copolymer with a cross-linking agent. Things have been proposed. However, when they are used to protect the surface of plastic plates with low surface tension and a smooth surface, they have the problem of causing peeling phenomena such as floating due to heating during processing and storage, and high speed, which is a manual work area. There was also a problem that the re-peelability was inferior when the product was peeled off.

In order to solve these problems, a) 100 parts by weight of a (meth) acrylic acid alkyl ester containing a (meth) acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms as a main component, b) a carboxyl group is contained. 1 to 15 parts by weight of the copolymerizable compound of 1) and c) 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms are added to the copolymer of the above-mentioned copolymer. b) A pressure-sensitive adhesive composition containing an equivalent or more of a cross-linking agent with respect to the carboxyl group of the component has been proposed (Patent Document 2).
The pressure-sensitive adhesive composition described in Patent Document 2 does not cause a peeling phenomenon such as floating during processing or storage, and moreover, the adhesive strength does not increase significantly with time and is excellent in re-peelability. It is supposed to be. In addition, even if it is stored for a long period of time, especially in a high temperature atmosphere, it can be peeled off again with a small force. It is said that it can be peeled off.

Further, regarding (3) excellent antistatic performance, a method of kneading an antistatic agent into a base film is shown as a method for imparting antistatic properties to the surface protective film. Examples of the antistatic agent include (a) various cationic antistatic agents having a cationic group such as a quaternary ammonium salt, a pyridinium salt, and a primary to tertiary amino group, and (b) a sulfonic acid base and a sulfuric acid. Anionic antistatic agents having anionic groups such as ester bases, phosphate ester bases and phosphonic acid bases, (c) amphoteric antistatic agents such as amino acid-based and aminosulfate ester-based, (d) amino alcohol-based and glycerin-based , Nonionic antistatic agents such as polyethylene glycol-based agents, (e) high molecular weight antistatic agents obtained by increasing the molecular weight of the antistatic agents as described above, and the like are disclosed (Patent Document 3).
Further, in recent years, it has been proposed to contain such an antistatic agent in the base film, or to directly contain the antistatic agent in the pressure-sensitive adhesive layer instead of applying it to the surface of the base film.

Regarding (4) rework performance, for example, a pressure-sensitive adhesive in which an isocyanate-based compound curing agent and a specific silicate oligomer are blended in an acrylic resin in an amount of 0.0001 to 10 parts by weight based on 100 parts by weight of the acrylic resin. An agent composition has been proposed (Patent Document 4).
In Patent Document 4, an acrylic acid alkyl ester having an alkyl group having about 2 to 12 carbon atoms, a methacrylate alkyl ester having an alkyl group having about 4 to 12 carbon atoms, or the like is used as a main monomer component, and for example, a carboxyl group-containing monomer or the like. It is said that it can contain other functional group-containing monomer components. Generally, it is preferable to contain the above main monomer in an amount of 50% by weight or more, and the content of the functional group-containing monomer component is 0.001 to 50% by weight, preferably 0.001 to 25% by weight. , More preferably 0.01 to 25% by weight. Such a pressure-sensitive adhesive composition described in Patent Document 4 has a small change in cohesive force and adhesive force with time even under high temperature or high temperature and high humidity, and exhibits an excellent effect on the adhesive force on a curved surface. It is said to have reworkability.
In general, when the pressure-sensitive adhesive layer has a soft property, adhesive residue is likely to occur, and reworkability is likely to decrease. That is, it is difficult to peel off when they are erroneously pasted together, and it is easy to re-paste them. From this, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group with the main agent to make the pressure-sensitive adhesive layer have a certain hardness in order to have reworkability.

Japanese Unexamined Patent Publication No. 63-225677 Japanese Unexamined Patent Publication No. 11-256111 Japanese Unexamined Patent Publication No. 11-070629 Japanese Unexamined Patent Publication No. 8-199130

In the prior art, the required performance for the adhesive layer constituting the surface protective film is to balance the adhesive force in the peeling speed in the low speed region and the high speed region, to have excellent antistatic performance, and to have excellent antistatic performance. It has been required to have rework performance. However, although each of these (1) to (4) can satisfy the individual required performances, all the required performances (1) to (4) required for the pressure-sensitive adhesive layer of the surface protective film are satisfied. I couldn't do that.

The present invention has been made in view of the above circumstances, has excellent antistatic performance, has an excellent balance of adhesive force in peeling speed in a low speed region and a high speed region, and has excellent durability and durability. An object of the present invention is to provide a surface protective film having excellent rework performance.

In order to solve the above problems, the present invention forms a pressure-sensitive adhesive layer obtained by cross-linking a pressure-sensitive adhesive composition containing an acrylic polymer, an antioxidant, and a cross-linking agent on one side of a resin film. The acrylic polymer is one or more of (A) alkyl (meth) acrylates having an alkyl group having 4 to 10 carbon atoms with respect to 100 parts by weight of the acrylic polymer. A total of 85 to 98.5 parts by weight, (B) a total of 4 to 14.9 parts by weight of one or more copolymerizable monomers containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group. One or more of the above-mentioned (A) alkyl (meth) acrylates having an alkyl group having 4 to 10 carbon atoms, which comprises a copolymer obtained by copolymerizing one or more kinds with a total of 0.1 to 2 parts by weight. Of the total of 85 to 98.5 parts by weight, 2-ethylhexyl (meth) acrylate is contained in a proportion of 50 parts by weight or more, and the pressure-sensitive adhesive composition is based on 100 parts by weight of the acrylic polymer. It contains 0.1 to 5 parts by weight of the cross-linking agent, does not contain a polyether-modified siloxane compound, and the antioxidant is solid at a temperature of 30 ° C. and has a melting point of 30 to 50 ° C. Provided is a surface protective film characterized by being an ionic compound of.

Further, the alkyl (meth) acrylate having an alkyl group having 4 to 10 carbon atoms (A) is butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, and heptyl (meth). Selected from a group of compounds consisting of meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, and decyl (meth) acrylate. It is preferable that there is only one type or more.

Further, the (C) carboxyl group-containing copolymerizable monomer is (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2- (Meta) acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl maleic acid, It is preferably one or more selected from the compound group consisting of carboxypolycaprolactone mono (meth) acrylate and 2- (meth) acryloyloxyethyl tetrahydrophthalic acid.

Further, it is preferable that the surface resistivity of the pressure-sensitive adhesive layer is 5.0 × 10 ^{+ 11} Ω / □ or less.

The present invention also provides a pressure-sensitive adhesive film in which the pressure-sensitive adhesive layer is formed on one side or both sides of a resin film.

The present invention also provides a surface protective film characterized in that the pressure-sensitive adhesive layer is formed on one side of a resin film.

According to the present invention, it is possible to satisfy all the performances required for the pressure-sensitive adhesive layer of the surface protective film, which cannot be solved by the prior art.

Hereinafter, the present invention will be described based on a preferred embodiment.
The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition containing an antioxidant, and comprises an acrylic polymer containing an alkyl (meth) acrylate having an alkyl group having 4 to 10 carbon atoms as a main component. With respect to 100 parts by weight of the acrylic polymer, 85 to 98.5 parts by weight of the alkyl (meth) acrylate as the main component, 0.1 to 15 parts by weight of the copolymerizable monomer containing a hydroxyl group, and carboxyl. The group-containing copolymerizable monomer contains 0.1 to 2 parts by weight and the cross-linking agent contains 0.1 to 5 parts by weight, and the antistatic agent is an ionic compound having a melting point of 30 to 50 ° C. be.

As the main component alkyl (meth) acrylate, an alkyl (meth) acrylate having an alkyl group having 4 to 10 carbon atoms is preferable, and a butyl (meth) acrylate, an isobutyl (meth) acrylate, a pentyl (meth) acrylate, and a hexyl (meth) acrylate are used. A compound consisting of a meta) acrylate, a heptyl (meth) acrylate, an octyl (meth) acrylate, an isooctyl (meth) acrylate, a 2-ethylhexyl (meth) acrylate, a nonyl (meth) acrylate, an isononyl (meth) acrylate, and a decyl (meth) acrylate. One or more selected from the group is preferable.
It is preferable that 85 to 98.5 parts by weight of the main component alkyl (meth) acrylate is contained with respect to 100 parts by weight of the acrylic polymer.

Examples of the hydroxyl group-containing copolymerizable monomer include hydroxyalkyls such as 8-hydroxyoctyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate. Examples thereof include (meth) acrylates and hydroxyl group-containing (meth) acrylamides such as N-hydroxy (meth) acrylamide, N-hydroxymethyl (meth) acrylamide and N-hydroxyethyl (meth) acrylamide.
8-Hydroxyoctyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, N-hydroxy (meth) acrylamide, N-hydroxymethyl (meth) ) At least one selected from the compound group consisting of acrylamide and N-hydroxyethyl (meth) acrylamide is preferable.
It is preferable that the copolymer containing a hydroxyl group is contained in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the acrylic polymer.

Examples of the carboxyl group-containing copolymerizable monomer include (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, and 2- (meth). Acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl maleic acid, carboxypolycaprolactone mono ( One or more selected from the group of compounds consisting of meta) acrylate and 2- (meth) acryloyloxyethyl tetrahydrophthalic acid is preferable.
It is preferable that the copolymer containing a carboxyl group is contained in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive composition of the present invention preferably crosslinks the pressure-sensitive adhesive polymer when forming the pressure-sensitive adhesive layer. As a method for causing the cross-linking reaction, cross-linking may be performed by optical cross-linking such as ultraviolet rays (UV), but it is preferable that the pressure-sensitive adhesive composition contains a cross-linking agent.
Examples of the cross-linking agent include a bifunctional or trifunctional or higher isocyanate compound, a bifunctional or trifunctional or higher epoxy compound, a bifunctional or trifunctional or higher acrylate compound, and a metal chelate compound. Among them, a polyisocyanate compound (bifunctional or trifunctional or higher functional isocyanate compound) is preferable, and a trifunctional or higher functional isocyanate compound is more preferable.
It is preferable that the cross-linking agent is contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the acrylic polymer.

The trifunctional or higher functional isocyanate compound may be a polyisocyanate compound having at least three or more isocyanate (NCO) groups in one molecule. The polyisocyanate compound is classified into an aliphatic isocyanate, an aromatic isocyanate, an acyclic isocyanate, an alicyclic isocyanate and the like, but any of them may be used. Specific examples of the polyisocyanate compound include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and trimethylhexamethylene diisocyanate (TMDI), diphenylmethane diisocyanate (MDI), and xylylene diisocyanate (XDI). , Aromatic isocyanate compounds such as hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylenedi isocyanate (TOID), and tolylene diisocyanate (TDI).
Examples of trifunctional or higher functional isocyanate compounds include bullet-modified and isocyanurate-modified compounds of diisocyanates (compounds having two NCO groups in one molecule), and trivalent or higher-valent polyols such as trimethylolpropane (TMP) and glycerin. Examples thereof include an adduct form (polyol modified form) with (a compound having at least 3 or more OH groups in one molecule).

The pressure-sensitive adhesive composition of the present invention contains an ionic compound having a melting point of 30 to 50 ° C. as an antistatic agent. The antistatic agent may be a quaternary ammonium salt-type ionic compound containing an acryloyl group.
Since these antistatic agents have a low melting point and have a long-chain alkyl group, it is presumed that they have a high affinity with acrylic polymers.

The antistatic agent, which is an ionic compound having a melting point of 30 to 50 ° C., is an ionic compound having a cation and an anion, and the cation is a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, and the like. Nitrogen-containing onium cations such as pyrrolidinium cations and ammonium cations, phosphonium cations, sulfonium cations, etc., and the anions are hexafluorinated phosphate (PF _6- ⁾ , thiocyanate (SCN- ⁾ , alkylbenzene sulfonic acid. Examples thereof include compounds that are inorganic or organic anions such as salts (RC ₆ H ₄ SO _3- ⁾ , perchlorates (ClO _4- ⁾ , ^and borate tetrafluoride (BF _4- ). It is preferably solid at room temperature (for example, 30 ° C.), and a melting point of 30 to 50 ° C. can be obtained by selecting the chain length of the alkyl group, the position of the substituent, the number of substituents, and the like. The cation is preferably a quaternary nitrogen-containing onium cation, and is a quaternary pyridinium cation such as 1-alkylpyridinium (the carbon atom at the 2nd to 6th positions may have a substituent or may be unsubstituted), or 1, Examples thereof include a quaternary imidazolium cation such as 3-dialkyl imidazolium (the carbon atom at the 2, 4 and 5 positions may have a substituent or not substituted), a quaternary ammonium cation such as tetraalkylammonium and the like. ..
The antistatic agent, which is an ionic compound having a melting point of 30 to 50 ° C., is preferably contained in an amount of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the acrylic polymer.

The acryloyl group-containing quaternary ammonium salt-type ionic compound is an ionic compound having a cation and an anion, and the cation is (meth) acryloyloxyalkyltrialkylammonium [R _3N ⁺ -C _n H _2n . -OCOCQ = CH ₂ , but Q = H or CH ₃ , R = alkyl] and other (meth) acryloyl group-containing quaternary ammonium, and the anion is hexafluorinated phosphate (PF _6- ⁾ , thiocyan acid. Salt (SCN- ⁾ , organic sulfonate (RSO _3- ⁾ , perchlorate (ClO _4- ⁾ , tetrafluoride borate (BF _4- ), ^{F -} containing imide salt (RF ₂ ^- N-), etc. Examples thereof include compounds which are inorganic or organic anions of the above. ^Examples of the RF of the ^F _- containing imide salt (RF ^2N- ) include a perfluoroalkanesulfonyl group such as a trifluoromethanesulfonyl group and a pentafluoroethanesulfonyl group, and a fluorosulfonyl group. Examples of the F-containing imide salt include bis (fluorosulfonyl) imide salt [(FSO ₂ ) ₂ N- ^] , bis (trifluoromethanesulfonyl) imide salt [(CF ₃ SO ₂ ) ₂ N- ^] , and bis (pentafluoroethanesulfonyl). ) Bissulfonylimide salts such as imide salt [(C ₂ F ₅ SO ₂ ) ₂ N- ^] can be mentioned.
The acryloyl group-containing quaternary ammonium salt-type ionic compound is preferably copolymerized in an acrylic polymer in an amount of 0.1 to 5.0% by weight.

Specific examples of the antistatic agent are not particularly limited, but specific examples of the ionic compound having a melting point of 30 to 50 ° C. are 1-octylpyridinium dodecylbenzenesulfonate and 1-dodecylpyridinium thiosian. Examples thereof include acid salt, 3-methyl-1-dodecylpyridinium hexafluorophosphate, 1-dodecylpyridinium dodecylbenzenesulfonate, 4-methyl-1-octylpyridinium hexafluorophosphate and the like.
Specific examples of the acryloyl group-containing quaternary ammonium salt-type ionic compound include dimethylaminomethyl (meth) acrylate methyl hexafluorophosphate [(CH ₃ ) ₃ N ⁺ CH ₂ OCOCQ = CH ₂ ·. PF _6- ^, however, Q = H or CH ₃ ], dimethylaminoethyl (meth) acrylate bis (trifluoromethanesulfonyl) imidemethyl salt [(CH ₃ ) ₃ N ⁺ (CH ₂ ) ₂ OCOCQ = CH ₂ · (CF ₃ ) SO ₂ ) ₂ N- ^, but Q = H or CH ₃ ], dimethylaminomethyl (meth) acrylate bis (fluorosulfonyl) imidemethyl salt [(CH ₃ ) ₃ N ⁺ CH ₂ OCOCQ = CH ₂ · (FSO ₂ ) ₂ N- ^, however, Q = H or CH ₃ ] and the like.

The pressure-sensitive adhesive composition of the present invention may contain a cross-linking retarder. Examples of the cross-linking retarder include β-ketoesters such as methyl acetoacetic acid, ethyl acetoacetate, octyl acetoacetic acid, oleyl acetoacetic acid, lauryl acetoacetic acid and stearyl acetoacetic acid, and β such as acetylacetone, 2,4-hexanedione and benzoylacetone. -Diketone can be mentioned. These are ketoenol remutable compounds, and in a pressure-sensitive adhesive composition using a polyisocyanate compound as a cross-linking agent, by blocking the isocyanate group contained in the cross-linking agent, the excess viscosity of the pressure-sensitive adhesive composition after the compounding of the cross-linking agent is performed. It is possible to suppress the rise and gelation and extend the pot life of the pressure-sensitive adhesive composition.
The cross-linking retarder is preferably a keto-enol telecommunication compound, and more preferably at least one selected from the compound group consisting of acetylacetone and ethyl acetoacetate.
When added, the cross-linking retarder is preferably contained in an amount of 1.0 to 5.0 parts by weight based on 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive composition of the present invention may contain a cross-linking catalyst. When the polyisocyanate compound is used as a cross-linking agent, the cross-linking catalyst may be a substance that functions as a catalyst for the reaction (cross-linking reaction) between the acrylic polymer and the cross-linking agent, and is an amine-based material such as a tertiary amine. Examples thereof include organic metal compounds such as compounds, organic tin compounds, organic lead compounds and organic zinc compounds.
Examples of the tertiary amine include trialkylamine, N, N, N', N'-tetraalkyldiamine, N, N-dialkylaminoalcohol, triethylenediamine, morpholine derivative, piperazine derivative and the like.
Examples of the organic tin compound include dialkyl tin oxide, a fatty acid salt of dialkyl tin, and a fatty acid salt of first tin.
The cross-linking catalyst is preferably an organic tin compound, and more preferably at least one selected from the compound group consisting of dioctyl tin oxide and dioctyl tin dilaurate.
When added, the cross-linking catalyst is preferably contained in an amount of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive composition of the present invention may contain a polyether-modified siloxane compound. 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-], the siloxane unit having a polyether group [-SiR ¹ (R ² O (R 2 O)). It has R ³ O) _n R ⁴ ) -O-]. Here, R ¹ is one or more kinds of alkyl groups or aryl groups, R ² and R ³ are one or more kinds of alkylene groups, and R ⁴ is one or more kinds of alkyl groups or acyl groups. Etc. (terminal group). Examples of the polyether group include a polyoxyalkylene group 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 having an HLB value of 7 to 12. When added, it is preferable that the polyether-modified siloxane compound is contained in an amount of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of the acrylic polymer. More preferably, it is 0.1 to 0.5 parts by weight.
The HLB is, for example, a hydrophilic lipophilic balance (hydrophilic lipophilic ratio) defined in JIS K3211 (surfactant term) and the like.
The polyether-modified siloxane compound can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group on a polyorganosiloxane backbone having a silicon hydride group by a hydrosilylation reaction. Specifically, dimethylsiloxane / methyl (polyoxyethylene) siloxane copolymer, dimethylsiloxane / methyl (polyoxyethylene) siloxane / methyl (polyoxypropylene) siloxane copolymer, dimethylsiloxane / methyl (polyoxypropylene) Examples thereof include siloxane polymers.
By blending the polyether-modified siloxane compound into the pressure-sensitive adhesive composition, the pressure-sensitive adhesive strength and rework performance of the pressure-sensitive adhesive can be improved.

The pressure-sensitive adhesive composition of the present invention may contain a polyether compound. Examples of the polyether compound are compounds having a polyalkylene oxide group, and examples thereof include polyether polyols such as polyalkylene glycol and derivatives thereof. Examples of the alkylene group contained in the polyalkylene glycol and the polyalkylene oxide group include, but are not limited to, an ethylene group, a propylene group, and a butylene group. The polyalkylene glycol may be a copolymer of two or more kinds of polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of the polyalkylene glycol copolymer include polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, polyethylene glycol-polypropylene glycol-polybutylene glycol, and the like. It may be a block copolymer or a random copolymer.
Examples of the polyalkylene glycol derivative include polyoxyalkylene alkyl ethers such as polyoxyalkylene monoalkyl ether and polyoxyalkylene dialkyl ether, polyoxyalkylene alkenyl ethers such as polyoxyalkylene monoalkenyl ether and polyoxyalkylene dialkenyl ether, and poly. Polyoxyalkylene aryl ethers such as oxyalkylene monoaryl ethers and polyoxyalkylene diaryl ethers, polyoxyalkylene glycol fatty acid esters such as polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene glycol mono fatty acid esters and polyoxyalkylene glycol di fatty acid esters, Examples thereof include polyoxyalkylene sorbitan fatty acid ester, polyoxyalkylene alkylamine, and polyoxyalkylene diamine.
Here, examples of the alkyl ether in the polyalkylene glycol derivative include lower alkyl ethers such as methyl ether and ethyl ether, and higher alkyl ethers such as lauryl ether and stearyl ether. Examples of the alkenyl ether in the polyalkylene glycol derivative include vinyl ether, allyl ether, oleyl ether and the like. Examples of the fatty acid ester in the polyalkylene glycol derivative include saturated fatty acid esters such as acetic acid ester and stearic acid ester, and unsaturated fatty acid ester such as (meth) acrylic acid ester and oleic acid ester.
The polyether compound is preferably a compound containing an ethylene oxide group, and preferably a compound containing a polyethylene oxide group.

If the polyether compound has a polymerizable functional group, it can also be copolymerized with a (meth) acrylic polymer. As the polymerizable functional group, a vinyl functional group such as a (meth) acrylic group, a vinyl group or an allyl group is preferable. Examples of the polyether compound having a polymerizable functional group include polyalkylene glycol mono (meth) acrylic acid ester, polyalkylene glycol di (meth) acrylic acid ester, alkoxypolyalkylene glycol (meth) acrylic acid ester, and polyalkylene glycol monoallyl. Examples thereof include ether, polyalkylene glycol diallyl ether, alkoxypolyalkylene glycol allyl ether, polyalkylene glycol monovinyl ether, polyalkylene glycol divinyl ether, alkoxypolyalkylene glycol vinyl ether and the like.

Further, as other components, copolymerizable (meth) acrylic monomer containing alkylene oxide, (meth) acrylamide monomer, dialkyl-substituted acrylamide monomer, surfactant, curing accelerator, thermoplastic, filler, curing retarder, etc. Known additives such as processing aids, antioxidants, and antioxidants can be appropriately added. These may be used alone or in combination of two or more.

The main acrylic polymer used in the pressure-sensitive adhesive composition of the present invention is an alkyl (meth) acrylate having an alkyl group having 4 to 10 carbon atoms, a copolymerizable monomer containing a hydroxyl group, and a copolymer containing a carboxyl group. It can be synthesized by copolymerizing with a polymerizable monomer. The polymerization method of the acrylic polymer is not particularly limited, and an appropriate polymerization method such as solution polymerization or emulsion polymerization can be used.
Acrylic polymers include polyalkylene glycol mono (meth) acrylic acid ester monomers, hydroxyl group-free nitrogen-containing vinyl monomers, alkoxy group-containing alkyl (meth) acrylate monomers, and acryloyl group-containing quaternary ammonium salt-type ionic compounds. Other monomers may be copolymerized.
The pressure-sensitive adhesive composition of the present invention can be prepared by adding a cross-linking agent, an antistatic agent, and an appropriate additive to the above acrylic polymer.

The adhesive force of the pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition at a peeling speed of 0.3 m / min in a low-speed region is 0.05 to 0.1 N / 25 mm, and the peeling speed in a high-speed region is 30 m. The adhesive strength at / min is preferably 1.0 N / 25 mm or less. As a result, it is possible to obtain a performance in which the adhesive strength does not change much depending on the peeling speed, and it is possible to quickly peel off even by peeling at a high speed. Further, since it is reattached, even when the surface protective film is once peeled off, it does not require an excessive force and can be easily peeled off from the adherend.

The surface resistivity of the pressure-sensitive adhesive layer obtained by cross-linking the pressure-sensitive adhesive composition is preferably 5.0 × 10 ^{+ 11} Ω / □ or less, and the peeling band voltage is preferably ± 0 to 0.5 kV. In the present invention, "± 0 to 0.5 kV" means 0 to −0.5 kV and 0 to +0.5 kV, that is, −0.5 to +0.5 kV. If the surface resistivity is large, the performance to release the static electricity generated by charging during peeling is inferior. Therefore, by making the surface resistivity sufficiently small, the peeling band generated by the static electricity generated when the adherend peels off the adhesive layer. The voltage is reduced, and it is possible to suppress the influence on the electric control circuit of the adherend and the like.

The gel fraction of the pressure-sensitive adhesive layer (the pressure-sensitive adhesive after cross-linking) obtained by cross-linking the pressure-sensitive adhesive composition of the present invention is preferably 95 to 100%. Due to such a high gel content, the adhesive force does not become excessive at the peeling speed in the low speed region, and the elution of unpolymerized monomers or oligomers from the acrylic polymer is reduced, resulting in reworkability and high temperature / high temperature. Durability in humidity is improved, and contamination of the adherend can be suppressed.

The pressure-sensitive adhesive film of the present invention is formed by forming a pressure-sensitive adhesive layer formed by cross-linking the pressure-sensitive adhesive composition of the present invention on one or both sides of a resin film. Further, the surface protective film of the present invention is a surface protective film formed by forming a pressure-sensitive adhesive layer formed by cross-linking the pressure-sensitive adhesive composition of the present invention on one side of a resin film. Since the pressure-sensitive adhesive composition of the present invention contains each component of the acrylic polymer in a well-balanced manner, it has excellent antistatic performance and balances the adhesive strength in the peeling speed in the low-speed region and the high-speed region. Further, it is also excellent in durability performance and rework performance (no contamination transfer to the adherend after tracing the surface protective film on the surface protective film through the adhesive layer with a ballpoint pen). Therefore, it can be suitably used as a surface protective film for a polarizing plate.

As the base film of the pressure-sensitive adhesive layer and the release film (separator) for protecting the pressure-sensitive adhesive surface, a resin film such as a polyester film can be used.
On the base film, on the side opposite to the side where the adhesive layer of the resin film is formed, antifouling treatment with silicone-based or fluorine-based mold release agent or coating agent, silica fine particles, etc., application of antistatic agent, etc. Antistatic treatment such as kneading can be applied.
The release film is subjected to a mold release treatment with a silicone-based or fluorine-based mold release agent or the like on the surface of the pressure-sensitive adhesive layer that is combined with the adhesive surface.

Hereinafter, the present invention will be specifically described with reference to Examples.

<Manufacturing of acrylic polymer>
[Example 1]
Nitrogen gas was introduced into a reactor equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen introduction tube, and the air in the reactor was replaced with nitrogen gas. Then, 60 parts by weight of the solvent (ethyl acetate) was added to the reaction apparatus together with 93 parts by weight of 2-ethylhexyl acrylate, 5.5 parts by weight of 8-hydroxyoctyl acrylate, and 1.5 parts by weight of acrylic acid. Then, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours and reacted at 65 ° C. for 6 hours to obtain an acrylic polymer solution 1 having a weight average molecular weight of 500,000 and used in Example 1. Got
[Examples 2 to 6 and Comparative Examples 1 to 3]
The composition of the monomers is the same as that of the acrylic polymer 1 used in Example 1 above, except that the compositions of the monomers are as described in (A) to (C) of Table 1, and the same as in Examples 2 to 6 and comparison. The acrylic polymer solution used in Examples 1 to 3 was obtained.
In Tables 1 and 2, (A) is an alkyl (meth) acrylate as a main component, (B) is a hydroxyl group-containing copolymerizable monomer, and (C) is a carboxyl group-containing copolymer. It is a sex monomer.

<Manufacturing of adhesive composition and surface protective film>
[Example 1]
To the acrylic polymer 1 of Example 1 produced as described above, 2.0 parts by weight of 1-octylpyridinium dodecylbenzenesulfonate was added and stirred, and then Coronate HX (isocyanurate form of hexamethylene diisocyanate compound) 1 .5 parts by weight was added and stirred and mixed to obtain the pressure-sensitive adhesive composition of Example 1. This pressure-sensitive adhesive composition is applied onto a release film made of a polyethylene terephthalate (PET) film coated with a silicone resin, and then dried at 90 ° C. to remove the solvent, and the pressure-sensitive adhesive layer has a thickness of 25 μm. I got a sheet.
After that, the adhesive sheet is transferred to the surface opposite to the antistatic and antifouling treated polyethylene terephthalate (PET) film on one surface, and "antistatic and antifouling treated". A surface protective film of Example 1 having a laminated structure of "PET film / adhesive layer / release film (PET film coated with silicone resin)" was obtained.
[Examples 2 to 6 and Comparative Examples 1 to 3]
Examples 2 to 6 and Comparative Examples 1 to 1 are the same as the surface protective film of Example 1 above, except that the compositions of the additives are as described in (D) to (E) of Table 1. 3 surface protection films were obtained.
In Tables 1 and 2, (D) is a cross-linking agent, and (E) is an antistatic agent.

In Table 1, the numerical values of the parts by weight obtained by assuming that the total of the groups (A) to (C) is 100 parts by weight are shown in parentheses. The compound names of the abbreviations of each component used in Table 1 are shown in Table 2. 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 Co., Ltd. Is.

<Test method and evaluation>
The surface protective films of Examples 1 to 6 and Comparative Examples 1 to 3 were aged at 23 ° C. and 50% RH for 7 days, and then the release film (silicone resin coated PET film) was peeled off to form an adhesive layer. Was used as a sample for measuring the surface resistance.
Further, the surface protective film on which the pressure-sensitive adhesive layer is exposed is attached to the surface of the polarizing plate attached to the liquid crystal cell via the pressure-sensitive adhesive layer, left for 1 day, and then left at 50 ° C., 5 atm for 20 minutes. A sample that had been autoclaved and left at room temperature for another 12 hours was used as a measurement sample for adhesive strength, peeling band voltage, reworkability, and durability.

<Adhesive strength>
The measurement sample obtained above (a 25 mm wide surface protective film bonded to the surface of the polarizing plate) was subjected to a peeling speed (0.3 m / min) in a low speed region using a tensile tester in the 180 ° direction. The peeling strength measured by peeling at the peeling speed (30 m / min) in the high speed region was defined as the adhesive strength.

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

<Peeling band voltage>
High-precision electrostatic sensors SK-035 and SK-200 (Keyence Co., Ltd.) measure the voltage (band voltage) generated by charging the polarizing plate when the measurement sample obtained above is peeled off by 180 ° at a tensile speed of 30 m / min. The maximum value of the measured value was taken as the peeling band voltage.

<Reworkability>
After tracing the surface protective film of the measurement sample obtained above with a ball pen (load 500 g, 3 reciprocations), the surface protective film is peeled off from the polarizing plate, the surface of the polarizing plate is observed, and contamination is transferred to the polarizing plate. I confirmed that there was no such thing. The evaluation target criteria are "○" when there is no contamination transfer on the polarizing plate, "△" when contamination transfer is confirmed at least in part along the trajectory traced with the ballpoint pen, and along the trajectory traced with the ballpoint pen. When the transfer of contamination was confirmed and the detachment of the adhesive was confirmed from the surface of the adhesive, it was evaluated as "x".

<Durability>
The measurement sample obtained above was left in an atmosphere of 60 ° C. and 90% RH for 250 hours, then taken out to room temperature, left for another 12 hours, and then the adhesive strength was measured and compared with the initial adhesive strength. It was confirmed that there was no increase. The evaluation target criteria were evaluated as "◯" when the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, and "x" when the adhesive strength exceeded 1.5 times.

Table 3 shows the evaluation results. The surface resistivity is expressed by a method in which "m × 10 ^{+ n} " is set to "mE + n" (where m is an arbitrary real number and n is a positive integer).

The surface protective films of Examples 1 to 6 have an adhesive force of 0.05 to 0.1 N / 25 mm at a peeling speed of 0.3 m / min in a low speed region, and a peeling speed of 30 m / min in a high speed region. The adhesive strength is 1.0 N / 25 mm or less, the surface resistance is 5.0 × 10 ^{+ 11} Ω / □ or less, the peeling band voltage is ± 0 to 0.5 kV, and the surface is protected through the adhesive layer. After tracing the top of the film with a ball pen, there was no contamination transfer to the adherend, and the durability was excellent when left in an atmosphere of 60 ° C. and 90% RH for 250 hours.
That is, (1) to balance the adhesive force in the peeling speed in the low speed region and the high speed region, (2) to prevent the generation of adhesive residue, and (3) to have excellent antistatic performance. And (4) all the required performances of having rework performance are satisfied at the same time.

The surface protective film of Comparative Example 1 contains a small amount of alkyl (meth) acrylate as a main component, a large amount of a copolymerizable monomer containing a hydroxyl group, and does not contain a copolymerizable monomer containing a carboxyl group. The adhesive strength was small at a peeling speed of 0.3 m / min, the surface resistance and the peeling band voltage were high, and the durability was inferior.
The surface protective film of Comparative Example 2 has an excessive amount of a carboxyl group-containing copolymerizable monomer with respect to the main component alkyl (meth) acrylate, and has a large content of an isocyanate-based curing agent, so that the pot life is long. It became too short and the cross-linking proceeded before coating, so coating could not be performed.
The surface protective film of Comparative Example 3 does not contain a carboxyl group-containing copolymerizable monomer, a cross-linking agent, and an antistatic agent. The adhesive strength at a peeling speed of 30 m / min was too large, the surface resistance and the peeling band voltage were high, and the reworkability and durability were inferior.
As described above, in the surface protective films of Comparative Examples 1 to 3, (1) balancing the adhesive force at the peeling speed in the low speed region and the high speed region, and (2) preventing the generation of adhesive residue. , (3) It was not possible to satisfy all the required performances of having excellent antistatic performance and (4) having rework performance at the same time.

Claims (2)

A surface protective film formed by forming a pressure-sensitive adhesive layer obtained by cross-linking a pressure-sensitive adhesive composition containing an acrylic polymer, an antistatic agent, and a cross-linking agent on one side of a resin film.
The acrylic polymer is based on 100 parts by weight of the acrylic polymer.
(A) The total of one or more types of alkyl (meth) acrylates having an alkyl group having 4 to 10 carbon atoms is 85 to 98.5 parts by weight.
(B) The total amount of one or more copolymerizable monomers containing a hydroxyl group is 4 to 14.9 parts by weight.
(C) It is composed of a copolymer obtained by copolymerizing one or more kinds of copolymerizable monomers containing a carboxyl group with 0.1 to 2 parts by weight in total.
2-Ethylhexyl acrylate is contained in a proportion of 50 parts by weight or more in the total of 85 to 98.5 parts by weight of one or more of the above (A) alkyl (meth) acrylates having an alkyl group having 4 to 10 carbon atoms. And
The (C) carboxyl group-containing copolymerizable monomer is (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, 2- (meth) acryloyloxyethyl hexahydrophthalic acid, 2-. (Meta) acryloyloxypropyl hexahydrophthalic acid, 2- (meth) acryloyloxyethyl phthalic acid, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethyl maleic acid, carboxypoly One or more selected from the group of compounds consisting of caprolactone mono (meth) acrylate and 2- (meth) acryloyloxyethyl tetrahydrophthalic acid.
The pressure-sensitive adhesive composition contains 0.1 to 5 parts by weight of the cross-linking agent with respect to 100 parts by weight of the acrylic polymer, and does not contain a polyether-modified siloxane compound.
A surface protective film, wherein the antistatic agent is an ionic compound having a melting point of 30 to 50 ° C., which is a solid at a temperature of 30 ° C. The surface protective film according to claim 1, wherein the cross-linking agent is a trifunctional or higher functional isocyanate compound.