JP2016074899A - Adhesive composition for surface protective film and surface protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition for surface protective film capable of forming an adhesive layer excellent in antistatic property and transparency, low in stain property and corrosive nature to an adherend and exhibiting good high speed peeling property and a surface protective film having the adhesive layer by curing the same.SOLUTION: There is provided an adhesive composition for surface protective film containing (A) a (meth)acrylic resin having weight average molecular weight of 100,000 to 400,000 of 40 to 60 mass%, (B) polyoxyalkylene polyol of 30 to 50 mass%, (C) polyoxyalkylene monoalkyl ether of 0.5 to 2 mass%, (D) polyisocyanate of 4.0 to 15 mass%, (E) an ionic compound of 0.5 to 2.0 mass% and (F) a tin-based catalyst of 0.005 to 0.1 pts.mass based on 100 pts.mass of total amount of above (A) to (E) and having acid value of 0 to 5 mgKOH/g.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition for a surface protective film and a surface protective film.

In recent years, in the field of optical components / electronic components, surface protection films are often used for the purpose of protecting the surfaces of optical components / electronic components. The surface protective film is composed of a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer is formed on a transparent substrate such as polyethylene, polyester, and polypropylene, and a release film laminated on the surface of the pressure-sensitive adhesive sheet on the pressure-sensitive adhesive layer side.
In such a surface protective film, static electricity may be charged to the pressure-sensitive adhesive sheet when the release film is peeled from the pressure-sensitive adhesive sheet and / or when the pressure-sensitive adhesive sheet is peeled from the adherend. When static electricity is charged on the pressure-sensitive adhesive sheet, there are cases where surrounding dust adheres to the pressure-sensitive adhesive sheet and stains the optical parts and electronic parts that are adherends.

In order to solve this problem, it has been proposed to form the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet using a pressure-sensitive adhesive imparted with antistatic properties.
For example, Patent Document 1 and Patent Document 2 disclose a pressure-sensitive adhesive layer comprising an acrylic copolymer containing a polyether polyol compound as an antistatic agent. However, the pressure-sensitive adhesive layer containing a polyether polyol compound has a problem with transparency. For this reason, the pressure-sensitive adhesive layer containing the polyether polyol compound could not be used for the pressure-sensitive adhesive layer of the surface protective film requiring transparency from the viewpoint of quality assurance.

  In addition, as an adhesive capable of forming an adhesive layer having both antistatic properties and transparency, one obtained by grafting polyether polyol onto an acrylic polymer has been proposed (for example, see Patent Document 3).

JP-A-6-128539 JP 2005-325255 A JP 2010-6980 A

As the adhesive layer of the surface protective film, in addition to being excellent in antistatic properties, transparency, and high-speed peelability, it has low corrosiveness to the adherend, and even if the adhesive sheet is peeled off from the adherend, There is a demand for a low-contamination material that does not leave an adhesive (no adhesive residue).
However, the pressure-sensitive adhesive layer of the conventional surface protective film has not obtained sufficient performance for all the above items.
Specifically, the pressure-sensitive adhesive described in Patent Document 3 can form a pressure-sensitive adhesive layer having excellent antistatic properties and transparency, but has a high acid value and high corrosiveness to an adherend. For this reason, the pressure-sensitive adhesive described in Patent Document 3 is a pressure-sensitive adhesive for a surface protective film that protects a surface protective component using a material that easily corrodes the surface, such as a film having an ITO (Indium Tin Oxide) layer on the surface. It was difficult to use for the agent layer.
Furthermore, recently, in addition to being excellent in antistatic properties, transparency, and corrosiveness, as a pressure-sensitive adhesive layer for a surface protective film, it is excellent in that zipping does not occur or the peel strength does not increase significantly even if the peeling speed is increased. It is required to have high-speed peelability.

  The present invention has been made in view of the above circumstances, and forms an adhesive layer having excellent antistatic properties and transparency, low contamination and corrosiveness to the adherend, and good high-speed peelability. It is an object to provide a pressure-sensitive adhesive composition for a surface protective film, and a surface protective film having a pressure-sensitive adhesive layer obtained by curing the same.

The present invention employs the following configuration.
(1) (A) 40-60 mass% of (meth) acrylic resin having a weight average molecular weight of 100,000-400,000, (B) 30-50 mass% of polyoxyalkylene polyol, and (C) polyoxyalkylene mono Alkyl ether 0.5-2 mass%, (D) polyisocyanate 4.0-15 mass%, (E) ionic compound 0.5-2.0 mass%, (F) said (A)- A pressure-sensitive adhesive composition for a surface protective film, comprising 0.005 to 0.1 parts by mass of a tin-based catalyst with respect to 100 parts by mass of the total amount of (E), and having an acid value of 0 to 5 mgKOH / g .

(2) The pressure-sensitive adhesive for surface protective film according to (1), wherein the monomer unit derived from a hydroxyl group-containing (meth) acrylate monomer is contained in the (A) (meth) acrylic resin in an amount of 0.5 to 5 mol%. Composition.
(3) The pressure-sensitive adhesive composition for a surface protective film according to (1) or (2), wherein the (E) ionic compound is an alkali metal salt.
(4) The pressure-sensitive adhesive composition for a surface protective film according to any one of (1) to (3), wherein the (F) tin-based catalyst is dioctyltin dilaurate.

(5) A surface protective film in which a pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition for a surface protective film according to any one of (1) to (4) is formed on one surface of a transparent substrate.
(6) The surface protective film according to (5), wherein the pressure-sensitive adhesive layer has a surface specific resistance value of 1.0 × 10 ¹⁰ Ω / □ or less and a haze value of 2.0% or less.

According to the pressure-sensitive adhesive composition for a surface protective film of the present invention, by curing this, it has excellent antistatic properties and transparency, low contamination and corrosiveness to the adherend, and good high-speed peelability. An adhesive layer can be realized.
Moreover, since the adhesive layer which hardened | cured the adhesive composition for surface protection films of this invention is formed in the single side | surface on a transparent base material, the surface protection film of this invention is suitable as a surface protection film.

Hereinafter, the present invention will be described in detail.
The pressure-sensitive adhesive composition for surface protective film of the present invention (hereinafter sometimes referred to as “pressure-sensitive adhesive composition”) comprises (A) (meth) acrylic resin, (B) polyoxyalkylene polyol, and (C ) Polyoxyalkylene monoalkyl ether, (D) polyisocyanate, (E) ionic compound, and (F) tin-based catalyst.
In the present invention, the (meth) acrylic resin means an acrylic resin or a methacrylic resin, and is a polymer mainly composed of (meth) acrylate. In addition, a main component means that the sum total of (meth) acrylate exceeds 50 mol%. (Meth) acrylate means acrylate or methacrylate.

"(A) (Meth) acrylic resin"
(A) There is no limitation in particular as a (meth) acrylate monomer used for superposition | polymerization of (meth) acrylic-type resin.
Examples of (meth) acrylate monomers include alkyl (meth) acrylate, cyclic alkyl (meth) acrylate, aromatic (meth) acrylate, alkoxyalkyl (meth) acrylate, alkoxy (poly) alkylene glycol (meth) acrylate, Fluorinated alkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylate, amide group-containing (meth) acrylate, epoxy group-containing (meth) acrylate, silicone-modified (meth) acrylate, multifunctional (meth) acrylate, etc. .

  Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, Isobutyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, isodecyl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) Examples thereof include acrylate and isostearyl (meth) acrylate.

  Cyclic alkyl (meth) acrylates include cyclohexyl (meth) acrylate, norbornyl (meth) acrylate, isobornyl (meth) acrylate, norbornanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate , Dicyclopentanyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, tricyclodecane dimethylol di (meth) acrylate, and the like.

  Examples of the aromatic (meth) acrylate include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, phenoxypropyl (meth) acrylate, and phenoxypolypropylene glycol (meth) acrylate. .

Examples of the alkoxyalkyl (meth) acrylate include methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, 2-methoxyethoxyethyl (meth) acrylate, 2-ethoxyethoxyethyl (meth) acrylate and the like. Is mentioned.
Examples of the alkoxy (poly) alkylene glycol (meth) acrylate include methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, and methoxydipropylene glycol (meth) acrylate.

Examples of the fluorinated alkyl (meth) acrylate include octafluoropentyl (meth) acrylate.
Examples of the dialkylaminoalkyl (meth) acrylate include N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate.
Examples of the amide group-containing (meth) acrylate include (meth) acrylamide and diacetone (meth) acrylamide.
Examples of the epoxy group-containing (meth) acrylate include glycidyl (meth) acrylate.

Polyfunctional (meth) acrylates include polyethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tripropylene glycol di (meth). An acrylate etc. are mentioned.
The (meth) acrylate monomer used for the polymerization of these (A) (meth) acrylic resins may be used alone or in combination of two or more. Among these, alkyl (meth) acrylate is preferably used from the viewpoint of obtaining a pressure-sensitive adhesive layer having good adhesiveness and transparency.

  The (A) (meth) acrylic resin is the above-mentioned (A) from the viewpoint of reacting and integrating with (B) polyoxyalkylene polyol and (C) polyoxyalkylene monoalkyl ether via (D) polyisocyanate. In addition to the (meth) acrylate monomer used for the polymerization of the (meth) acrylic resin, it is preferable to include a hydroxyl group-containing (meth) acrylate monomer as a copolymerization component.

Examples of hydroxyl group-containing (meth) acrylate monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 1,3-butanediol (meth) acrylate, Examples include hydroxyl group-containing (meth) acrylates such as 1,4-butanediol (meth) acrylate, 1,6-hexanediol (meth) acrylate, and 3-methylpentanediol (meth) acrylate.
Among these, 2-hydroxyethyl (meth) acrylate is preferably used in terms of copolymerizability and reactivity.

The (A) (meth) acrylic resin contains 0.5 to 5 mol% of a monomer unit derived from a hydroxyl group-containing (meth) acrylate monomer as a copolymerization component of the (A) (meth) acrylic resin. It is preferable that it is contained in an amount of 0.6 to 3 mol%.
In the (A) (meth) acrylic resin, the total amount of (meth) acrylate monomers excluding the hydroxyl group-containing (meth) acrylate monomer is preferably more than 50 mol%, more preferably more than 70 mol%, and still more preferably 90. More than mol% is contained.

In the (A) (meth) acrylic resin, other polymerizable monomers other than a hydroxyl group-containing (meth) acrylate monomer may be used as a copolymerization component as long as the polymerizability is not impaired. However, in order to prevent the adhesive layer formed by curing the adhesive composition from directly touching the wiring made of ITO, silver, copper, etc., other polymerizable monomers may be carboxyl groups (chemical formula: —COOH ) Is preferably used.
Examples of such polymerizable monomers include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, N-vinyl. Examples thereof include pyridine, N-vinylpyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, and dimethylallyl vinylketone.

  The (A) (meth) acrylic resin has a weight average molecular weight of 100,000 to 400,000, preferably 150,000 to 350,000, and more preferably 200,000 to 300,000. By setting the weight average molecular weight within the above range, an adhesive composition is obtained in which an adhesive layer is obtained that hardly causes adhesive residue even when peeled from the adherend and has low contamination to the adherend. Moreover, the compatibility of (A) (meth) acrylic-type resin, (B) polyoxyalkylene polyol, and (C) polyoxyalkylene monoalkyl ether becomes favorable by making a weight average molecular weight into the said range. For this reason, it becomes an adhesive composition from which the adhesive layer excellent in transparency is obtained.

Here, the weight average molecular weight is measured at room temperature under the following conditions using gel permeation chromatography (manufactured by Showa Denko KK, Showex (registered trademark) GPC-101), and is calculated in terms of polystyrene. Is.
Column: Showa Denko KK, Shodex (registered trademark) LF-804
Column temperature: 40 ° C
Sample: 0.2% by mass tetrahydrofuran solution of copolymer Flow rate: 1 ml / min Eluent: Tetrahydrofuran Detector: RI detector (differential refractive index detector)

  (A) The glass transition temperature (Tg) of the (meth) acrylic resin is preferably −80 to −10 ° C., more preferably −70 to −20 ° C. When the Tg is in the range of −80 to −10 ° C., the wettability to the adherend is good and sufficient cohesive force is obtained. The Tg of the (A) (meth) acrylic resin can be adjusted by appropriately changing the type and / or composition ratio of the (meth) acrylate monomer used for the polymerization of the (A) (meth) acrylic resin.

Here, Tg refers to that obtained using the following method.
(A) A 10 mg sample was taken from the (meth) acrylic resin, and the temperature was changed from −80 ° C. to 200 ° C. at a rate of temperature increase of 10 ° C./min using a differential scanning calorimeter (DSC). Differential scanning calorimetry is performed, and the endothermic start temperature due to glass transition is defined as Tg. When two Tg are observed, a simple average value of the two Tgs is taken.

(A) The polymerization method of the (meth) acrylic resin is not particularly limited, and can be polymerized by a known method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization or the like. Moreover, either radical polymerization or ionic polymerization may be used. Among these, solution polymerization is particularly preferable.
The obtained copolymer may be any of random copolymer, block copolymer, alternating copolymer, and the like.

  (A) The polymerization initiator used in radical polymerization of the (meth) acrylic resin is not particularly limited, and can be appropriately selected from known ones. For example, 2,2′-azobis (isobutyronitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethylvaleronitrile) 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2,4,4-trimethylpentane), dimethyl- Azo polymerization initiators such as 2,2′-azobis (2-methylpropionate); benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl Peroxide, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) Oil-soluble polymerization initiator such as peroxide polymerization initiators cyclododecane like are preferably exemplified.

These polymerization initiators may be used alone or in combination of two or more.
The usage-amount of a polymerization initiator should just be a normal usage-amount, for example, can be 0.01-5 mass parts with respect to 100 mass parts of monomers, and is the range of 0.02-4 mass parts. It is preferably 0.03 to 3 parts by mass.
By controlling the amount of the polymerization initiator that decomposes per unit time, the molecular weight of the (A) (meth) acrylic resin can be controlled. For example, when it is desired to reduce the molecular weight of the (A) (meth) acrylic resin, the amount of the polymerization initiator used may be increased or / and a polymerization initiator having a low decomposition temperature may be used. (A) When it is desired to increase the molecular weight of the (meth) acrylic resin, the amount of the polymerization initiator used may be reduced or / and a polymerization initiator having a high decomposition temperature may be used.
The polymerization temperature of the (A) (meth) acrylic resin is not particularly limited, but is preferably 30 ° C. to 110 ° C., more preferably 50 to 100 ° C. in consideration of ease of control in production. is there. The polymerization time is preferably 2 to 12 hours in consideration of ease of control in production.

When (A) (meth) acrylic resin is polymerized by solution polymerization, various common solvents can be used. For example, as a solvent, esters such as ethyl acetate, n-propyl acetate and n-butyl acetate, aromatic hydrocarbons such as toluene and benzene, aliphatic hydrocarbons such as n-hexane and n-heptane, cyclohexane, Examples thereof include organic solvents such as alicyclic hydrocarbons such as methylcyclohexane, and ketones such as methyl ethyl ketone and methyl isobutyl ketone.
These solvents may be used alone or in combination of two or more.

  (A) The (meth) acrylic resin contributes to the adhesiveness of the adhesive layer formed by curing the adhesive composition to the adherend. The compounding quantity of (meth) acrylic-type resin is 40-60 mass% in an adhesive composition, Preferably it is 45-55 mass%. When the blending amount is less than 40% by mass, an adhesive layer formed by curing the adhesive composition containing (A) (meth) acrylic resin is not preferable because the adherend is contaminated. On the other hand, when the blending amount exceeds 60% by mass, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition may be inferior in high-speed peelability, which is not preferable.

"(B) Polyoxyalkylene polyol"
(B) If it is a polymer polyol which has an ether group as a polyoxyalkylene polyol, it will not specifically limit, A well-known polymer polyol can be used suitably.
Examples of (B) polyoxyalkylene polyols include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and derivatives or copolymers thereof. Among these, polypropylene glycol is preferable because it is easy to adjust the compatibility with the acrylic resin. These may be used alone or in combination of two or more.

  (B) The polyoxyalkylene polyol preferably has a number average molecular weight of 500 to 3,000, more preferably 800 to 2,000. If the number average molecular weight is in the range of 500 to 3,000, the cohesive force of the pressure-sensitive adhesive composition and the transparency of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition are improved. (B) The number average molecular weight of polyoxyalkylene polyol is obtained by measuring by GPC (gel permeation chromatography).

  (B) A polyoxyalkylene polyol contributes to the antistatic of the adhesive layer formed by hardening | curing an adhesive composition. The compounding quantity of polyoxyalkylene polyol is 30-50 mass% in an adhesive composition, Preferably it is 35-45 mass%. When the amount is less than 30% by mass, the antistatic property of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition may be inferior, which is not preferable. On the other hand, when the blending amount exceeds 50% by mass, an adhesive layer obtained by curing the adhesive composition contaminates the adherend, which is not preferable.

"(C) Polyoxyalkylene monoalkyl ether"
The (C) polyoxyalkylene monoalkyl ether is not particularly limited as long as it is a polymer monool having an ether group and a hydroxyl group at one end, and known polymer monools can be used as appropriate.
(C) Examples of polyoxyalkylene monoalkyl ethers include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether, polyethylene glycol monopropyl ether, polypropylene glycol monomethyl ether, polypropylene glycol monoethyl ether, polypropylene glycol monopropyl ether, polytetra Examples include methylene ether glycol monomethyl ether and derivatives or copolymers thereof. Among these, polyethylene glycol monoethyl ether is preferable in terms of high speed peelability.
These may be used alone or in combination of two or more.

(C) The polyoxyalkylene monoalkyl ether preferably has a number average molecular weight of 200 to 2,000, more preferably 300 to 1,000. When the number average molecular weight is in the range of 200 to 2000, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition has good transparency, no possibility of causing adhesive residue, and good high-speed peelability It becomes.
(C) The number average molecular weight of polyoxyalkylene monoalkyl ether is obtained by measurement by GPC (gel permeation chromatography).

  (C) The polyoxyalkylene monoalkyl ether contributes to the improvement of the high-speed peelability in the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition. (C) The compounding quantity of polyoxyalkylene monoalkyl ether is 0.5-2 mass% in an adhesive composition, Preferably it is 0.8-1.5 mass%. When said compounding quantity is less than 0.5 mass%, the high-speed peelability of the adhesive layer formed by hardening | curing an adhesive composition will worsen. On the other hand, when said compounding quantity exceeds 2 mass%, the adhesive layer formed by hardening | curing an adhesive composition contaminates a to-be-adhered body.

"(D) Polyisocyanate"
Examples of (D) polyisocyanates include aromatic, aliphatic, and alicyclic polyisocyanates. (D) Examples of polyisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate. , Trimethylhexamethylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, tolylene diisocyanate (TDI), hydrogenated tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, polyphenylmethane polyisocyanate, xylene diisocyanate, hydrogenated xylene diisocyanate, tetramethylxylylene Diisocyanate, norbornene diisocyanate, naphthalene diisocyanate, Examples include methylol propane / tolylene diisocyanate trimer adduct, trimethylol propane / hexamethylene diisocyanate trimer adduct, isocyanate adducts such as hexamethylene diisocyanate isocyanurate, polyether polyisocyanate, polyester polyisocyanate and the like. .
These may be used alone or in combination of two or more.

(D) Polyisocyanate functions as a crosslinking agent in the pressure-sensitive adhesive composition of the present invention. (D) The compounding quantity of polyisocyanate is 4.0-15 mass% in an adhesive composition, Preferably it is 5.0-12 mass%. When the blending amount is less than 4.0% by mass, sufficient cohesive force cannot be obtained. On the other hand, when the above blending amount exceeds 15% by mass, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition becomes too hard and the wettability to the adherend is deteriorated.
The blending amount of (D) polyisocyanate is the sum (a1) of hydroxyl equivalents of (B) polyoxyalkylene polyol and (C) polyoxyalkylene monoalkyl ether, and (D) isocyanate equivalent (a2) of polyisocyanate. The ratio (a1 / a2) is preferably 0.95 <a1 / a2 ≦ 1.0. When the ratio (a1 / a2) is within this range, the cohesive strength of the pressure-sensitive adhesive composition and the stain resistance of the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition to the adherend are improved. .

"(E) Ionic compounds"
(E) As an ionic compound, the liquid or solid ionic compound which consists of an anion and a cation at 25 degreeC is mentioned. Specific examples include alkali metal salts, ionic liquids (liquid form at 25 ° C.), surfactants and the like. Among these, an alkali metal salt is preferable because the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition hardly contaminates the adherend.

Examples of the alkali metal salt include a compound comprising an alkali metal cation such as lithium, sodium or potassium and an anion. Specifically, sodium chloride, potassium chloride, lithium chloride, lithium perchlorate, potassium chlorate, potassium nitrate, sodium nitrate, sodium carbonate, sodium thiocyanate, LiBr, LiI, LiBF ₄ , LiPF ₆ , LiSCN, sodium acetate, Sodium alginate, sodium lignin sulfonate, sodium toluene sulfonate, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, etc. Is mentioned.
These alkali metal salts may be used alone or in combination of two or more.

  (E) An ionic compound contributes to the antistatic of the adhesive layer formed by hardening | curing an adhesive composition. (E) The compounding quantity of an ionic compound is 0.5-2.0 mass% in an adhesive composition, Preferably it is 0.8-1.5 mass%. When the blending amount is less than 0.5% by mass, the effect of improving charging characteristics due to the inclusion of the ionic compound cannot be sufficiently obtained. On the other hand, when the blending amount exceeds 2.0% by mass, the transparency of the pressure-sensitive adhesive layer formed by curing the pressure-sensitive adhesive composition is lowered. Moreover, when a compounding quantity exceeds 2.0 mass%, an ionic compound may bleed out from the surface of an adhesive layer, and there exists a possibility of contaminating a to-be-adhered body.

"(F) Tin catalyst"
(F) Examples of tin-based catalysts include dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate, and the like. Among these, dioctyltin dilaurate is preferable because (D) the curability of polyisocyanate can be effectively promoted and the safety is high.

  (F) The tin-based catalyst is a catalyst that accelerates the crosslinking reaction of the pressure-sensitive adhesive composition. (F) The compounding quantity of a tin-type catalyst is 0.005-0.1 mass part with respect to 100 mass parts of total amounts of said (A)-(E) in an adhesive composition, Preferably it is 0.01. It is -0.05 mass part. When the blending amount is less than 0.005 parts by mass, sufficient cohesive force cannot be obtained. On the other hand, when the compounding amount exceeds 0.1 parts by mass, the stability of the (A) (meth) acrylic resin is deteriorated and the pot life is shortened.

  The pressure-sensitive adhesive composition for a surface protective film of the present invention has an acid value of 0 to 5 mgKOH / g, preferably 0 to 1 mgKOH / g, and more preferably 0 to 0.1 mgKOH / g. When the acid value of the pressure-sensitive adhesive composition is in the range of 0 to 5 mgKOH / g, the pressure-sensitive adhesive composition can be used for a pressure-sensitive adhesive layer of a surface protective film that protects the surface of the film using a corrosive material.

The acid value of the pressure-sensitive adhesive composition is a value measured according to JIS K0070, and is measured, for example, as follows.
About 2 g of a sample is precisely weighed into a 100 ml Erlenmeyer flask with a precision balance, and 10 ml of a mixed solvent of ethanol / diethyl ether = 1/1 (mass ratio) is added and dissolved therein. Further, 1 to 3 drops of phenolphthalein ethanol solution is added to this container as an indicator, and the mixture is sufficiently stirred until the sample becomes uniform. This is titrated with a 0.1N potassium hydroxide-ethanol solution, and the end point of neutralization is taken when the indicator is light red for 30 seconds. The value obtained from the result using the following general formula (1) is defined as the acid value of the composition.

Acid value (mgKOH / g) = [B × f × 5.611] / S (1)
In the above general formula (1), B is the amount (ml) of 0.1N potassium hydroxide-ethanol solution used, f is the factor of 0.1N potassium hydroxide-ethanol solution, and S is the sample. (G).

Moreover, you may add various well-known additives to the adhesive composition for surface protection films of this invention as needed in the range which does not impair transparency.
Additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, antioxidants, light stabilizers, UV absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, phosphate esters System and other flame retardants, and antistatic agents such as surfactants.

Moreover, you may dilute the adhesive composition for surface protection films of this invention using an organic solvent for the purpose of the viscosity adjustment at the time of coating.
Examples of the organic solvent include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol, and n-propyl acetate. These organic solvents may be used alone or in combination of two or more.

The method for producing the pressure-sensitive adhesive composition for a surface protective film of the present invention is not particularly limited. For example, the (A) (meth) acrylic resin, (B) polyoxyalkylene polyol, and (C A known method comprising :) a polyoxyalkylene monoalkyl ether; (D) a polyisocyanate; (E) an ionic compound; (F) a tin-based catalyst; and an additive and an organic solvent added as necessary. It can manufacture by mixing using.
Since the pressure-sensitive adhesive composition for a surface protective film of the present invention has the above composition, it is excellent in antistatic property and transparency by curing this, and has low contamination and corrosiveness to the adherend. A pressure-sensitive adhesive layer having good high-speed peelability can be formed.

In the surface protective film of the present invention, a pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition for a surface protective film is formed on one side of a transparent substrate. The thickness of the pressure-sensitive adhesive layer is usually 3 to 100 μm, preferably 5 to 50 μm.
Examples of the transparent substrate include polyethylene terephthalate, polyethylene, polypropylene, polystyrene, polyimide, polyvinyl alcohol, polyvinyl chloride, and cellulose. The thickness of the transparent substrate is usually 5 to 200 μm, preferably about 10 to 100 μm.

If necessary, the surface on which the pressure-sensitive adhesive layer is formed on the transparent substrate is subjected to easy adhesion treatment such as antifouling treatment, acid treatment, alkali treatment, primer treatment, corona treatment, plasma treatment, and ultraviolet treatment. May be.
In addition, as the transparent substrate, those subjected to antistatic treatment are preferably used. The antistatic treatment applied to the transparent substrate is not particularly limited, and a method of providing an antistatic layer on at least one surface of the transparent substrate, a method of kneading an antistatic agent in the transparent substrate, or the like can be used.

  As a method of forming the pressure-sensitive adhesive layer on the transparent substrate, a method of applying and curing the pressure-sensitive adhesive composition for a surface protective film on the transparent substrate is used. As a method of applying the pressure-sensitive adhesive composition for a surface protective film on the transparent substrate, a known coating method (coating method) can be used. For example, the coating can be performed using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, or a direct coater.

  In the surface protective film of the present invention, a separator can be bonded to the surface of the pressure-sensitive adhesive layer for the purpose of protecting the pressure-sensitive adhesive layer as necessary. As a base material constituting the separator, paper, plastic film, or the like can be used. As the separator, a plastic film is preferable from the viewpoint of excellent surface smoothness. The plastic film used as a separator will not be specifically limited if the above-mentioned adhesive layer can be protected, For example, the plastic film which consists of polyethylene, a polypropylene, a polyethylene terephthalate, polybutene etc. is mentioned.

The pressure-sensitive adhesive layer of the surface protective film preferably has a surface specific resistance value of 1.0 × 10 ¹⁰ Ω / □ (square) or less and a haze value of 2.0% or less.
Excellent antistatic performance is obtained when the surface resistivity of the pressure-sensitive adhesive layer is 1.0 × 10 ¹⁰ Ω / □ or less, more preferably 9.0 × 10 ⁹ Ω / □ or less. Therefore, a surface protective film can be used for the purpose of protecting the surface of the plastic film that is likely to generate static electricity.

  When the haze value of the pressure-sensitive adhesive layer is 2.0% or less, the pressure-sensitive adhesive layer is excellent in transparency. In order to make the pressure-sensitive adhesive layer more excellent in transparency, the haze value of the pressure-sensitive adhesive layer is more preferably 0.8% or less.

When the surface protective film of the present invention has a pressure-sensitive adhesive layer having a surface resistivity of 1.0 × 10 ¹⁰ Ω / □ or less and a haze value of 2.0% or less, it is used as an optical component. It can be suitably used for the purpose of protecting the surface of the plastic film. In particular, it is suitable as a surface protective film used for the purpose of protecting the surface of an optical component such as a polarizing plate, a wavelength plate, a retardation plate, an optical compensation film, a reflective sheet, and a brightness enhancement film used in a liquid crystal display.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

<Synthesis of (meth) acrylic resin (A-1)>
In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirring device, 200 parts by mass of n-propyl acetate as an organic solvent, 103 parts by mass (0.80 mol) of n-butyl acrylate, methyl methacrylate 20 parts by mass (0.20 mol), 2-hydroxyethyl acrylate 1.2 parts by mass (0.01 mol), and 2,2′-azobis (isobutyronitrile) as a polymerization initiator 0.5 A polymer solution of (meth) acrylic resin (A-1) having a glass transition temperature of −36 ° C. and a weight average molecular weight of 230,000 was obtained by putting in parts by mass and polymerizing at 95 ° C. for 8 hours in a nitrogen stream.

<Synthesis of (meth) acrylic resin (A-2)>
In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirrer, 200 parts by mass of n-propyl acetate as an organic solvent, 92 parts by mass (0.50 mol) of 2-ethylhexyl acrylate, ethyl acrylate 30 parts by mass (0.30 mol), methyl methacrylate 20 parts by mass (0.20 mol), 2-hydroxyethyl acrylate 0.46 parts by mass (0.004 mol), 2,2 as a polymerization initiator '-Azobis (isobutyronitrile) 0.5 parts by mass, polymerized in a nitrogen stream at 95 ° C for 8 hours, (meth) acrylic resin having a glass transition temperature of -45 ° C and a weight average molecular weight of 240,000 A polymer solution of (A-2) was obtained.

<Synthesis of (meth) acrylic resin (A-3)>
Synthesized in the same manner as (meth) acrylic resin (A-1) except that the content of 2,2′-azobis (isobutyronitrile) used as a polymerization initiator was changed to 0.3 parts by mass. Thus, a polymer solution of (meth) acrylic resin (A-3) having a glass transition temperature of −36 ° C. and a weight average molecular weight of 620,000 was obtained.

The glass transition temperature and the weight average molecular weight of the (meth) acrylic resins (A-1) to (A-3) were measured by the method described above.
Table 1 shows the material (monomer) and content (mol) used for polymerization, the glass transition temperature, and the weight average molecular weight of (meth) acrylic resins (A-1) to (A-3).

<Examples 1-2 and Comparative Examples 1-7>
(A) (meth) acrylic resin, (B) polyoxyalkylene polyol, (C) polyoxyalkylene monoalkyl ether, (D) polyisocyanate, (E) ionic compound, and (F) shown in Table 2 A tin-based catalyst was blended, and the solid content concentration was adjusted to 50% by mass with ethyl acetate, which is an organic solvent, and mixed with a disper at room temperature to obtain a pressure-sensitive adhesive composition solution for a surface protective film. .

The resulting solution was cast on a transparent substrate so that the thickness after drying was 50 μm, and dried and cured at 50 ° C. for 5 minutes and at 110 ° C. for 5 minutes to form an adhesive layer. Formed. As the transparent substrate, a polyethylene terephthalate (PET) film having a thickness of 38 μm was used.
Subsequently, a PET film having a thickness of 50 μm was bonded to the surface of the pressure-sensitive adhesive layer as a separator to prepare a surface protective film.

<Acid value>
The acid value of each pressure-sensitive adhesive composition of Examples and Comparative Examples was measured by the method described above. The results are shown in Table 2.
<Surface specific resistance value>
The obtained surface protective film was cut into a size of 40 mm × 40 mm, and was allowed to stand for 3 hours in an environment of a temperature of 23 ° C. and a relative humidity of 65% to adjust the humidity. Then, the PET film of the separator was peeled off from the surface protective film, and the surface specific resistance value was measured by the method described in JIS K6911. The results are shown in Table 2. The surface specific resistance value means that the smaller the value, the higher the antistatic performance.

<Transparency>
The obtained surface protective film was cut into a size of 30 mm × 30 mm, the PET film of the separator was peeled off from the surface protective film, and the pressure-sensitive adhesive layer was bonded to a glass plate to obtain a measurement sample. About the sample for a measurement, the haze value was measured using haze meter "NM-150 (made by Murakami Color Research Laboratory Co., Ltd.)". The haze value (%) was calculated by dividing the diffuse transmittance by the total light transmittance and multiplying by 100. In addition, n number was made into 3 times and the average value was employ | adopted. The results are shown in Table 2. In addition, haze value means that transparency is so high that a value is small.

<Adhesive strength>
The obtained surface protective film was cut into a size of 25 mm × 100 mm, and the PET film as a separator of the surface protective film was peeled off. Thereafter, the exposed pressure-sensitive adhesive layer (measurement surface) was attached to a glass test plate, and a 2 kg rubber roller (width: about 50 mm) was reciprocated once to prepare a measurement sample.
The obtained measurement sample was left in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 24 hours. Then, according to JIS Z0237, the 180 degree direction tensile test was done at 300 mm / min of peeling speed, and the adhesive force (g / 25mm) with respect to the glass plate of an adhesive layer was measured. The obtained measured value was defined as adhesive strength. The results are shown in Table 2.

<High speed peelability>
The adhesive strength (g / 25 mm) at the time of high-speed peeling (peeling speed 30 m / min) to the glass plate of the adhesive layer was the same as the measurement of the adhesive strength of the surface protective film except that the peeling speed was 30 m / min. Measured and evaluated as shown below. The measurement results are shown in Table 2.
○ Good: Less than 1.0 (g / 25 mm).
Δ Slightly good: 1.0 (g / 25 mm) or more and less than 2.0 (g / 25 mm).
X Defect: 2.0 (g / 25 mm) or more.

<Contamination to adherend>
The obtained surface protective film was cut into a size of 50 mm × 50 mm, the separator PET film was peeled off from the surface protective film, and the exposed pressure-sensitive adhesive layer was laminated on a glass plate to be a sample and left at 70 ° C. for 5 days. Then, the surface protective film was peeled off from the sample, the contamination property to the surface of a glass plate was confirmed visually, and the following reference | standard evaluated. The results are shown in Table 2.
○: The surface of the glass plate is not changed compared to before bonding.
X: Adhesive residue is confirmed on the surface of the glass plate.

  As shown in Table 2, the pressure-sensitive adhesive compositions of the examples had very low acid values and low corrosiveness to the adherend. Moreover, the pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition of the example had a small surface specific resistance value and high antistatic performance. Moreover, the adhesive layer obtained in the Example had a small haze value and high transparency. In addition, the pressure-sensitive adhesive layer obtained in the examples had low contamination to the adherend and good high-speed peelability.

On the other hand, in the comparative example 1, since the weight average molecular weight of (A) (meth) acrylic-type resin A-3 was large, it resulted in a haze value being large and transparency being inferior.
In Comparative Example 2, since the content of the (A) (meth) acrylic resin was large, the evaluation of high-speed peelability was Δ. Further, in Comparative Example 2, since the content of (B) polyoxyalkylene polyol was small, the surface specific resistance value was large, resulting in poor antistatic performance.
In Comparative Example 3, since the content of the (A) (meth) acrylic resin was small and the content of the (B) polyoxyalkylene polyol was large, the evaluation of the contamination on the adherend was x.

  In Comparative Example 4, since (C) polyoxyalkylene monoalkyl ether was not included, the evaluation of the fast peelability was x, the surface specific resistance value was large, and the antistatic performance was poor. Further, in Comparative Example 5, since the content of (C) polyoxyalkylene monoalkyl ether was large, evaluation of the contamination property to the adherend was x.

  In Comparative Example 6, since the content of the (E) ionic compound was small, the surface specific resistance value was large and the antistatic performance was inferior. Further, in Comparative Example 7, since the content of the (E) ionic compound is large, the evaluation of the contamination property to the adherend was x.

Claims (6)

(A) (Meth) acrylic resin having a weight average molecular weight of 100,000 to 400,000 and 40 to 60% by mass;
(B) 30-50 mass% polyoxyalkylene polyol,
(C) 0.5 to 2% by mass of polyoxyalkylene monoalkyl ether;
(D) 4.0 to 15% by mass of polyisocyanate;
(E) 0.5 to 2.0% by mass of an ionic compound;
(F) It contains 0.005 to 0.1 parts by mass of a tin-based catalyst with respect to 100 parts by mass of the total amount of (A) to (E), and has an acid value of 0 to 5 mgKOH / g. A pressure-sensitive adhesive composition for a surface protective film.   The pressure-sensitive adhesive composition for a surface protective film according to claim 1, wherein the (A) (meth) acrylic resin contains 0.5 to 5 mol% of a monomer unit derived from a hydroxyl group-containing (meth) acrylate monomer.   The pressure-sensitive adhesive composition for a surface protective film according to claim 1 or 2, wherein the (E) ionic compound is an alkali metal salt.   The pressure-sensitive adhesive composition for a surface protective film according to any one of claims 1 to 3, wherein the (F) tin-based catalyst is dioctyltin dilaurate.   The surface protection film in which the adhesive layer which hardened | cured the adhesive composition for surface protection films as described in any one of Claims 1-4 was formed in the single side | surface on a transparent base material. The surface protective film according to claim 5, wherein the pressure-sensitive adhesive layer has a surface specific resistance value of 1.0 × 10 ¹⁰ Ω / □ or less and a haze value of 2.0% or less.