JP4851292B2 - Surface protection film - Google Patents

Description

  The present invention relates to a surface protective film that is attached to an optical sheet such as a polarizing plate or a retardation plate to protect the optical sheet. More specifically, the present invention relates to a surface protective film having antistatic properties, easily washed out contaminants and transparency.

  A general surface protective film has a structure of surface protective layer / water resistant layer / antistatic layer / base film / antistatic layer / adhesive layer / separate film, and one side (separate film side) of the base film is The adhesive layer consists of a separate film, an adhesive layer, and an antistatic layer. The adhesive layer uses an adhesive with little adhesive residue, and the antistatic layer has an antistatic function. Yes. The other surface of the surface protective film is composed of an antistatic layer, a water-resistant layer, and a surface protective layer. The antistatic layer is as described above, and the water-resistant layer affects the antistatic layer from the external environment (humidity). The surface protective layer has many functions.

  At present, in the process of processing the optical sheet and mounting the optical sheet on other members, the optical sheet is used as a measure for preventing damage or contamination of the optical sheet during this operation. A surface protective film is pasted on the sheet in advance. Conventionally, this surface protective film is coated with an adhesive on the back surface and dried, and after a release film is bonded to this surface, it is cut according to the target polarization angle and phase angle of the optical sheet. In general, it is stored in a laminated state.

  The reason for imparting an antistatic function to the surface protective film is that dust is caused by static electricity generated in the process of manufacturing the optical sheet, and defective products are generated by the static electricity generated when the surface protective film is peeled off from the optical sheet. This is to prevent this. Further, the surface protective layer is provided with transparency, easy cleaning of contaminants, and the like. About transparency, when performing each inspection process in the state where the surface protection film was stuck on the optical sheet, it corresponds to finding defective products such as foreign matters and scratches.

  Contaminant easy-cleaning property is because adhesive sticking out of the film adheres to the surface of other protective films when sticking the optical sheet and surface protective film or when it is cut. This is a hindrance when shipping the product, so it is necessary to wipe it off easily. Examples of the method for removing the pressure-sensitive adhesive attached to the surface protective film include dry wiping and wiping with a cloth soaked with an organic solvent such as alcohol or ethyl acetate. Contaminant easy-cleaning property is required at the time of such wiping.

  As a countermeasure against the above-described drawbacks, for example, Patent Documents 1 to 3 propose a surface protective film in which a dirt prevention layer is provided on one side of the protective film. In addition, the surface protective film is required to have printing suitability (printer ink suitability for use in process control), scratch resistance, and the adhesion between the surface protective layer of the surface protective film and the substrate film. It has been demanded.

JP 2001-305346 A JP 11-256115 A JP 11-256116 A

  However, the above prior art does not satisfy all the functions described above. In addition, there is a demand for a surface protective film and a coating material for forming the surface protective layer, which have higher performance than before. In addition, for the purpose of simplifying the production method, the current surface protection film construction system, the 3-coat system (surface protective layer / water resistant layer / antistatic layer / base film), to the 2-coat system (surface protective layer / antistatic layer) Further, there is a demand for a coating material for forming a surface protective layer that can be applied to a layer / base film) and (coat layer for antistatic surface / base film) and a surface protective film using the same.

Therefore, the object of the present invention is less generation of static electricity when peeling from an optical sheet such as a polarizing plate, easy cleaning of contaminants by the adhesive, printability, and adhesion between the base film and the surface protective layer. An object of the present invention is to provide a surface protective film that is excellent and also has transparency.
Furthermore, the objective of this invention is providing the coating material for surface protection layer formation in which 1 coat system called antistatic surface protection layer / base film is possible as a structure of a surface protection film.

The above object is achieved by the present invention having the following constitution.
1. A surface protective film comprising a base film, an adhesive layer provided on one surface of the base film, and a surface protective layer provided on the other surface of the base film, wherein the surface protective layer is a carbon nanotube (A) and a side chain containing a unit having a linear or branched alkyl group having 5 to 64 carbon atoms bonded directly or via another atomic group to a carbon atom of the main chain as a side chain A surface protective film comprising a polyurethane resin (B) having a long-chain alkyl group.

2. The polyurethane resin (B) having a long-chain alkyl group in the side chain has both a linear or branched long-chain alkyl group having 2 to 64 carbon atoms and two active hydrogen-containing groups in the same molecule. Obtained by reacting an active hydrogen-containing compound (b), a polyisocyanate compound (a), and two active hydrogen-containing compounds (c) other than the above (b) in the presence or absence of an organic solvent. 2. The surface protective film as described in 1 above.
3 . The polyurethane resin (B) having a long-chain alkyl group in the side chain is composed of the following unit A: 5 to 80% by mass and unit B: 20 to 95% by mass, and the weight average of the polyurethane resin (B) 2. The surface protective film according to 1 above, wherein the molecular weight is 5,000 to 500,000.

4 . 2. The surface protective film as described in 1 above, wherein the surface resistance value is 10 ¹² Ω / □ to 10 ⁵ Ω / □.
5 . 2. The surface protective film according to 1 above, wherein the contact angle of water with the surface protective layer is 80 ° to 100 °.
6 . 2. The surface protective film according to 1 above, wherein the haze value is 0.2 to 10%.
7 . 2. The surface protective film according to 1 above, wherein the content of the carbon nanotubes (A) in the surface protective layer is 0.1 to 25% by mass.
8 . A side containing a unit having a linear or branched alkyl group having 5 to 64 carbon atoms, which is bonded to the carbon nanotube (A) as a side chain, directly or via another atomic group to a carbon atom of the main chain A coating material for forming a surface protective layer, wherein the polyurethane resin (B) having a long-chain alkyl group in the chain is dissolved or dispersed in an organic solvent.

  According to the present invention, there is little generation of static electricity when peeling from an optical sheet such as a polarizing plate, easy cleaning of contaminants by an adhesive, printability, and excellent adhesion between a base film and a surface protective layer, Furthermore, it is possible to provide a surface protection film of a one-coat system having transparency.

Next, the present invention will be described in more detail with reference to preferred embodiments.
The surface protective film of the present invention comprises a base film, an adhesive layer provided on one side of the base film, and a surface protective layer having antistatic properties provided on the other side of the base film (hereinafter simply referred to as “surface protective layer”). It may be called “surface protective layer”). That is, the structure of the surface protective film on the surface protective layer side is characterized by comprising a structure of a one-coat system such as a surface protective layer / base film, and a conventional three-coat system structure or a method of manufacturing a two-coat system structure Is more simplified. For this reason, the surface protective film of this invention can reduce the frequency | count of a coating at the time of manufacture, and is excellent also in cost performance.

The surface protective film of the present invention is characterized in that the surface protective layer contains carbon nanotubes and polyurethane resin.
Conventionally, as a conductive material for imparting an antistatic function to a surface protective film, metal particles, metal short fibers, conductive polymers such as polyaniline, carbon powder such as carbon black, those using a surfactant, and A combination of these components and a conductive polymer material is known. Among these materials, metal particles and metal short fibers have high specific gravity, and tend to be separated from the conductive polymer material when used in a solution state in combination with the conductive polymer material.

  In general, a conductive polymer material is added with a strongly acidic dopant in order to increase its conductivity. When a surface protective film is produced using the dopant, there is a problem that rust is generated in a production facility. When a surface protective film is produced using a surfactant as a conductive material, the antistatic function is easily changed by the influence of the surrounding environment and moisture. In order to obtain sufficient chargeability using carbon black, an addition rate of 20% by mass or more is necessary with respect to the coating material for forming the surface protective layer. The physical properties of the are reduced.

On the other hand, since the carbon nanotube (A) used in the present invention has high shape anisotropy, it can impart high conductivity to the surface protective layer even when added in a small amount. The transparency of is also good. The carbon nanotube used in the present invention is not particularly limited, and examples thereof include those having a single-layer structure in which carbon hexagonal mesh surfaces are closed in a cylindrical shape or a multilayer structure in which cylindrical structures are arranged in a nested manner. Single-walled carbon nanotubes are generally thinner than multi-walled carbon nanotubes are expected to be more secure a number of conductive paths uniformly dispersed units bodies per volume if. In addition, multi-walled carbon nanotubes generally have more layers than single-walled carbon nanotubes, so the number of conductive paths per unit mass is reduced but stable conductivity is exhibited.

  Any conventionally known carbon nanotubes can be used in the present invention, but the carbon nanotubes are preferably hollow cylinders having a diameter of 1 to 100 nm and a length of 1 to 50 μm. The method for producing the carbon nanotube is not particularly limited, and a carbon nanotube obtained by chemical vapor deposition, catalytic vapor deposition, chemical vapor deposition, arc discharge, laser evaporation or the like can be used. By using the hollow cylindrical carbon nanotube as described above for the surface protective layer of the surface protective film, the transparency and film formability of the surface protective layer are improved. Carbon nanotubes are extremely thin and have high conductivity, so when used as an antistatic agent for surface protective films, they exhibit the same antistatic effect with less content than when using conventional carbon black. can do.

  The polyurethane resin used in the present invention has, as a side chain, a unit having a linear or branched alkyl group having 5 to 64 carbon atoms bonded to a carbon atom of the main chain directly or via another atomic group. Polyurethane resin containing. A typical example of these polyurethane resins is a polyurethane resin composed of the units A and B. Here, “polyurethane resin” is a general term for polyurethane resin, polyurea resin, and polyurethane-polyurea resin.

  The polyurethane resin used in the present invention has a long-chain alkyl group in the side chain, and this long-chain alkyl group is a linear or branched alkyl group having 5 to 64 carbon atoms (hereinafter referred to as “long-chain alkyl”). In some cases, the alkyl group may contain an unsaturated group.). The polyurethane resin comprises an active hydrogen-containing compound (b) such as a polyol, polyamine or polycarboxylic acid having both the above long-chain alkyl group and two active hydrogen-containing groups in the same molecule, and a polyisocyanate compound (a ) And two active hydrogen-containing compounds (c) other than (b) can be obtained in the presence or absence of an organic solvent. Except for the use of a compound having both a long-chain alkyl group and an active hydrogen-containing group, the above reaction is the same as a known method for producing a polyurethane resin.

The raw material components used for the production of a polyurethane resin having the above long-chain alkyl group as a side chain will be described below. As the compound (b) for introducing the unit A having a long-chain alkyl group into the polyurethane resin molecule, there is 0 between two carbon atoms having a long-chain alkyl group as a side chain and an active hydrogen-containing group. Bifunctional organic compounds having ˜3 carbon atoms can be mentioned as representative compounds. Examples of such compounds include 1,2- or 1,3-alkanediols (HOCH ₂ CH (OH) R, HOCH ₂ CH ₂ CH (OH) R) and dehydrated dimers thereof (HOCH (R ) CH ₂ OCH ₂ (R) CHOH etc.) (R is the above long chain alkyl group); 1,2- or 1,3-alkanediamine having a long chain alkyl group; 1-or having a long chain alkyl group 2-Monoglyceride, monoglycerin ether and the like are preferable. Particularly preferred is 1,2-alkanediol having a long-chain alkyl group.

  Examples of 1,2- or 1,3-alkanediols having a long chain alkyl group include octane 1,2 (or 1,3) -diol, decane 1,2 (or 1,3) -diol, and dodecane. 1,2 (or 1,3) -diol, tetradecane 1,2 (or 1,3) -diol, octadecane 1,2 (or 1,3) -diol, tetracosane 1,2 (or 1,3) -diol Etc. Examples of the 1- or 2-monoglyceride include, for example, 1- (or 2-) monocaprin glyceride, 1- (or 2-) monolauring glyceride, 1- (or 2-) monomyristating glyceride, 1- (or 2-). Examples of 1- or 2-monoglycerol ether include monopalmitic glyceride and 1- (or 2-) monoaraking glyceride, and examples include 1- or 2-monoglycerol ether.

In addition to the above, hydroxy fatty acids, 1,2- or 1,3-alkanediamines, symmetric α-glycols (RCH (OH) CH (OH) R: R is the above alkyl group) and alkylene oxides thereof Low molar adducts (number average molecular weight less than 500), higher alcohols, and polyester diols of the above 1,2- or 1,3-alkanediols and dibasic acids (OHCH (R) CH ₂ OC (O) R ′ CO (O) CH ₂ CH (R) OH, etc.) (R is the above alkyl group, and R ′ is a divalent organic group that is a residue of a dibasic acid). These are examples of preferred compounds used in the present invention. The present invention is not limited to these exemplified compounds, and any other compounds that are readily available from the currently marketed market are Can be used for invention.

  As the polyisocyanate compound (a), any of those conventionally used in the production of polyurethane resins can be used and is not particularly limited. Preferable examples include toluene-2,4 (and / or 2,6) -diisocyanate (TDI), 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4- Chlor-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate diphenyl ether, 4,4′-methylenebis (phenylene isocyanate) (MDI), durylene diisocyanate, tolidine diisocyanate, xylylene diene Aromatic diisocyanates such as isocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4,4'-diisocyanate dibenzyl

  Aliphatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 1,10-decamethylene diisocyanate; 1,4-cyclohexylene diisocyanate, 4,4′-methylenebis ( Cyclohexyl isocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate (IPDI), hydrogenated MDI (H-MDI), hydrogenated XDI and the like, or these diisocyanate compounds and low molecular weight polyols or polyamines Of course, a polyurethane resin prepolymer obtained by reacting with a terminal such that is an isocyanate can also be used. These can be used alone or in combination of two or more.

  As said compound (c), conventionally well-known things, such as the short chain diol, polyamine, polycarboxylic acid, and high molecular polyol conventionally used for manufacture of a polyurethane resin, can be used, and it is not specifically limited. Examples of the short-chain diol include aliphatic glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, neopentyl glycol, and the like. Alkylene oxide low-mole adducts (number average molecular weight less than 500); 1,4-bishydroxymethylcyclohexane, alicyclic glycols such as 2-methyl-1,1-cyclohexanedimethanol and alkylene oxide low-mole additions thereof (Number average molecular weight less than 500); aromatic glycols such as xylylene glycol and its alkylene oxide low molar adduct (number average molecular weight less than 500);

Bisphenol A, thiobisphenol, bisphenols such as sulfonic bisphenol and alkylene oxide low mol adduct (number average molecular weight of less than 500); compounds such as alkyl dialkanolamines, such as alkyl diethanolamine C ₁ -C ₁₈ and the like. These can be used alone or in combination of two or more. If necessary, as long as the object of the present invention is achieved, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, tris- (2-hydroxyethyl) isocyanurate, 1,1,1-trimethylolethane, 1 Polyhydric alcohol compounds such as 1,1-trimethylolpropane can be used in combination.

As the polymer polyol, for example,
(1) Polyether diols, for example, those obtained by polymerizing or copolymerizing alkylene oxides (eg, ethylene oxide, propylene oxide, butylene oxide, etc.) and / or heterocyclic ethers (eg, tetrahydrofuran, etc.), specifically Is polyethylene glycol, polypropylene glycol, polyethylene glycol-polytetramethylene glycol (block or random), polytetramethylene ether glycol, polyhexamethylene glycol,

(2) Polyester diols such as aliphatic dicarboxylic acids (eg succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid etc.) and / or aromatic dicarboxylic acids (eg isophthalic acid, terephthalic acid etc.) And lower alkyl esters such as methyl esters and ethyl esters) and low molecular weight glycols (for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, 1,6- Hexamethylene glycol, neopentyl glycol, 1,4-bishydroxymethylcyclohexane, etc.), specifically polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyneo Emissions chill adipate diol, polyethylene / butylene adipate diol, polyneopentyl / hexyl adipate diol, poly-3-methylpentane adipate diol, polybutylene isophthalate diol,

(3) Polylactone diol, such as polycaprolactone diol, poly-3-methylvalerolactone diol,
(4) Polycarbonate diol, such as polyhexamethylene carbonate,
(5) Polyolefin diol such as polybutadiene glycol, polyisoprene glycol or hydride thereof,
(6) Polymethacrylate diols such as α, ω-polymethylmethacrylate diol, α, ω-polybutylmethacrylate diol, etc. The molecular weight of these polyols is not particularly limited, but usually the number average molecular weight is about 500 to 2,000. These polymer polyols can be used alone or in combination of two or more.

  Examples of polyamines include short chain diamines, aliphatic, aromatic diamines, and hydrazines. Examples of the short-chain diamine include aliphatic diamines such as ethylene diamine, trimethylene diamine, tetramethylene diamine, hexamethylene diamine, and octamethylene diamine; 4,4-diaminodicyclohexylmethane, 1,4-diaminocyclohexane, isophorone diamine, and the like. Alicyclic diamines; phenylenediamine, 3,3′-dichloro-4,4′-diaminodiphenylmethane, 4,4′-methylenebis (phenylamine), 4,4′-diaminodiphenyl ether, 4,4′-diamino Aromatic diamines such as diphenylsulfone; hydrazines such as hydrazine, carbodihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide; diamines containing unsaturated groups such as diallylamine compounds It is below. These can be used alone or in combination of two or more.

  In addition to the above, active hydrogen-containing compounds having a thiol group or a carboxyl group (eg, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid; phthalic acid, isophthalic acid, terephthalic acid Aromatic dicarboxylic acids such as alicyclic dicarboxylic acids such as hexahydrophthalic acid, hexahydroisophthalic acid and hexahydroterephthalic acid). As the active hydrogen-containing compound, a diol compound and a diamine compound are preferable. As the two active hydrogen-containing compounds, short chain diol, short chain diamine and polymer diol are particularly preferable.

  A polyurethane resin having a long-chain alkyl group by reacting the above raw material components in an organic solvent or in the absence of a solvent so that the equivalent ratio of the isocyanate group to the active hydrogen-containing functional group is 1: 1. Is obtained. The polyurethane resin includes a unit in which a linear or branched long-chain alkyl group having 5 to 64 carbon atoms as a side chain is bonded to a main chain carbon atom directly or through another atomic group. And those composed of the following unit A and unit B are typical.

The structural unit A is a unit formed from the compound (b) and the compound (a), and the structural unit B is conventionally used in the production of polyurethane resins such as polyester diol and polyether diol. A unit formed from the compound (c) and the compound (a), and the divalent organic group of R ₂ is a residue of these active hydrogen-containing compounds (c) (an organic having two active hydrogen-containing groups). This is a portion obtained by removing an active hydrogen-containing group that reacts with an isocyanate group from a compound). X is a residue of the used diisocyanate compound (a portion obtained by removing the isocyanate group from the diisocyanate compound). For example, when the above diol is used as the organic compound having two active hydrogen-containing groups, Y ₁ and Y ₂ are —O—.

The case where the above side chain is formed using 1,2-alkanediol having a long chain alkyl group is referred to as the long chain alkyl group directly bonded to the main chain, and there is no Z in the structural unit A A case. In the case where the side chain is formed using a monoglyceride having a long chain alkyl group, Z is —CH ₂ O—, and the long chain alkyl group is bonded to the main chain via another atomic group. When combined with. The proportions of the structural unit A and the structural unit B in the polyurethane resin are 5 to 80% by mass (A) and 20 to 95% by mass (B), respectively, preferably 10 to 60% by mass (A) and 40 to 40% by mass, respectively. 90% by mass (B).

  The manufacturing method of the polyurethane resin which has a long chain alkyl group in the side chain using said raw material is not specifically limited, The manufacturing method of a conventionally well-known polyurethane resin can be used. For example, the polyisocyanate compound (a), the compound (b), and the compound (c) are reacted with an isocyanate group in the presence or absence of an organic solvent that does not contain active hydrogen in the molecule. In a blending ratio of about 1: 1 with the hydrogen-containing functional group, usually, it is usually 20 to 150 ° C., preferably 60 to 110 ° C., and almost no isocyanate groups are obtained by the one-shot method or multistage method. To obtain a polyurethane resin.

  The compound (b) is preferably used so that the content in the polyurethane resin is 5 to 80% by mass, more preferably 5 to 40% by mass. If the amount of the compound (b) used is too small, the effect of the present invention will be insufficient, and if it is too large, the film-forming property of the surface protective layer formed will be deteriorated or the coating strength will be insufficient. The weight average molecular weight (measured by gel permeation chromatography (hereinafter abbreviated as GPC), converted to standard polystyrene) of the polyurethane resin used in the present invention is preferably 5,000 to 500,000, and 10,000. More preferably, it is in the range of ~ 200,000. If the molecular weight is too small, the scratch resistance of the surface protective layer to be formed is inferior, and if the molecular weight is too large, the viscosity of the coating for forming the surface protective layer tends to be high and the formation of the surface protective layer tends to be difficult.

The surface resistance value of the surface protective layer of the surface protective film of the present invention is preferably 10 ¹² Ω / □ to 10 ⁵ Ω / □. If the surface resistance value of the surface protective layer is larger than 10 ¹² Ω / □, static electricity generated when the protective film is peeled off cannot be prevented, and adhesion of dust or the like is induced. In addition, when a protective film is applied to a liquid crystal display, there is a problem of destroying the elements of the liquid crystal display due to peeling charging that occurs when the surface protective film is peeled off. If the surface resistance value is less than 10 ⁵ Ω / □, it is over-specification, and the amount of carbon nanotubes used increases or the amount of paint applied increases, and the economic efficiency required for the surface protective film decreases.

  The contact angle of water with the surface protective layer of the present invention is preferably 80 ° to 100 °. When the contact angle is lower than 80 °, the water repellency and dirt prevention ability are insufficient. The haze value of the surface protective film of the present invention is preferably 0.2 to 10%. More preferably, it is 0.2 to 5.0%. If the haze value is larger than 10%, the surface of the article to be protected becomes difficult to be seen in the manufacturing process, the inspection process, etc. for optical use.

  The proportion of carbon nanotubes in the surface protective layer of the surface protective film of the present invention is 0.1 to 25% by mass, preferably 1 to 15% by mass. When the proportion of the carbon nanotubes is less than 0.1% by mass, the antistatic property is not sufficiently exhibited, and when it exceeds 25% by mass, the transparency of the surface protective layer is lowered, which is insufficient for optical applications.

  In the coating material for forming a surface protective layer of the present invention, other binder resins can be used in combination with the polyurethane resin as necessary. The binder resin used in combination is not particularly limited. For example, conventionally known silicone resins, polyester resins, polyamide resins, polyimide resins, polystyrene resins, polyacrylic resins, epoxy resins, phenoxy resins, phenoxy ether resins. , Phenoxy ester resin, melamine resin, alkyd resin, polyurethane resin, polycarbonate resin, norbornene resin, cellulose resin, polyvinyl alcohol resin, polyvinyl formal resin, polyvinyl butyral resin, polyvinyl pyrrolidone resin, polyvinyl acetate Resin, polyvinyl acetal resin and the like. These binder resins are usually used at a ratio of 500 parts by mass or less per 100 parts by mass of the polyurethane resin having a long-chain alkyl group.

  In addition, the polyurethane resin can be cross-linked using polyisocyanate to strengthen the surface protective layer of the present invention and to provide scratch resistance and solvent resistance. As the polyisocyanate crosslinking agent used for this purpose, a conventionally known polyisocyanate crosslinking agent used as a crosslinking agent for polyurethane resins can be used, and is not particularly limited. For example, dimer of 2,4-toluylene diisocyanate, triphenylmethane triisocyanate, tris- (p-isocyanatephenyl) thiophosphite, polyfunctional aromatic isocyanate, aromatic polyisocyanate, polyfunctional aromatic aliphatic isocyanate , Polyfunctional aliphatic isocyanate, blocked polyfunctional aliphatic isocyanate, fatty acid-modified polyfunctional aliphatic isocyanate, block-type polyisocyanate, polyisocyanate prepolymer, and the like. These polyisocyanate crosslinking agents are particularly effective in improving heat resistance if they are in appropriate amounts, but if the amount used is too large, unreacted isocyanate remains, and the strength of the surface protective layer is reduced and the surface protective film is overlaid. Is used at a rate of 120 parts by mass or less, preferably 5 to 80 parts by mass per 100 parts by mass of the polyurethane resin having a long-chain alkyl group.

  Various additives may be added as necessary in the production of the coating material for forming the surface protective layer of the present invention. Examples of such additives include antioxidants (hindered phenols, phosphites, thioethers, etc.), light stabilizers (hindered amines, etc.), UV absorbers (benzophenones, benzotriazoles, etc.), gas Examples thereof include a discoloration stabilizer (such as hydrazine) and a metal deactivator, and two or more of these may be used in combination as required.

  In addition, the coating material for surface protective layer formation used by this invention can be prepared without a solvent according to a use, or can also be prepared using an organic solvent. Preferable organic solvents include, for example, methyl ethyl ketone, methyl-n-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, butyl acetate and the like. Acetone, cyclohexane, tetrahydrofuran, dioxane, methanol, ethanol, isopropyl alcohol, butanol, toluene, xylene, dimethylformamide, dimethyl sulfoxide, perchlorethylene, trichloroethylene, methyl cellosolve, butyl cellosolve, cellosolve acetate, etc. can also be used. . The coating material for forming the surface protective layer is usually used by adjusting the solid content to about 1 to 20% by mass.

  The base film used for the surface protective film of the present invention is not particularly limited, and films made of polyethylene, polypropylene, polyester, polyimide, polycarbonate, and the like and laminates thereof can be used. From the viewpoint of heat resistance at the time, a biaxially stretched polyethylene terephthalate film is preferable. The thickness of the base film is about 16 to 50 μm, and preferably 25 to 38 μm. This is because the thickness of the base film is less than 16 μm, and it is difficult to protect the protected member by dents or the like caused by protrusions from the outside. It is difficult to apply without attaching or to peel off the surface protective film. In addition, if the thickness of the film exceeds 50 μm, the rigidity of the base film is too large, and it is difficult to uniformly stick to the protected member without lifting, and the cost of the base film is too large. The economic efficiency required for the surface protective film is reduced.

As the pressure-sensitive adhesive for the surface protective film, generally known ones and those on the market can be used. Examples include trade name: SK Dyne (manufactured by Soken Chemical) and trade name: Nissetsu (manufactured by Nippon Carbide Industries). Preferably is 10 to 30 g / m ² coated at solids.

  The surface protective layer of the surface protective film of the present invention can be formed by applying the surface protective layer-forming coating composition of the present invention by any known coating method, for example, a gravure coating method, a reverse coating method, or a roll coating method. Examples of the means for dispersion / mixing when producing the coating material for forming the surface protective layer of the present invention include stirring, ultrasonic treatment, vibration dispersion, kneading, etc., and it is necessary to select the means depending on the concentration and viscosity of the paint. There is. For example, in mixing by stirring, a flask or a container with a lid can be rotated, or a device in which a screw type or brush type stirring blade rotates at high speed can be used, for example, a high-speed dissolver. In the case of using an ultrasonic processing apparatus, there is a method in which an ultrasonic transducer is placed in the container for processing. As a method using a kneading apparatus, a bead mill apparatus, a ball mill apparatus, a three-roller, or the like using ceramic fine particles can be used. The present invention is not limited to these methods.

  The surface protective film of the present invention is used in the same manner as a conventional surface protective film for protecting the surface of various plastic products that are easily charged, such as the optical sheet, as well as metal products and glass products. can do.

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. Moreover, in the following sentence, “part” indicates mass part, and “%” indicates mass%.
Synthesis Examples 1 to 3
After replacing the reactor equipped with a stirrer, reflux condenser, thermometer, nitrogen blowing tube and manhole with nitrogen gas, a long-chain alkyl group-containing diol component, a polymer diol component, a chain extender (short-chain diol component) and Solvents were added in the proportions shown in Table 1 and dissolved uniformly to prepare a solution having a total concentration of the above components of 30%. Subsequently, hexamethylene diisocyanate was added to this solution so that the equivalent ratio of the isocyanate group and the active hydrogen-containing functional group in the raw material composition was 1: 1, and the mixture was kept at 80 ° C. to synthesize a polyurethane resin. The synthesis reaction was performed until no absorption due to a free isocyanate group of 2,270 cm ⁻¹ was observed in the infrared absorption spectrum. Table 1 shows the raw material composition of the polyurethane resin and the properties of the obtained polyurethane resin (PU). The molecular weight of the polyurethane resin is a weight average molecular weight measured by GPC and converted to standard polystyrene.

A: Long chain alkyl group-containing one-end diol: manufactured by Daicel Chemical Industries, Ltd., trade name: Plaxel AD E1600, average molecular weight 355
B: Polycarbonate diol: manufactured by Daicel Chemical Industries, Ltd., trade name: Plaxel CD220, average molecular weight 2,000
C: 1,4-butanediol MEK: methyl ethyl ketone anone: cyclohexanone

Examples 1-5 and Comparative Examples 1-2
Using an ultrasonic oscillator (trade name: GT-170, manufactured by Ginsen Co., Ltd.), carbon nanotubes (CNT) were dispersed in a solution of a polyurethane resin and a solvent (MEK / anone), and the composition shown in Table 2 was obtained. A paint for forming a surface protective layer (solid content 5%) was prepared. These dispersions were applied to one side of a 50 μm thick biaxially stretched polyethylene terephthalate (PET) film so that the film thickness after drying was 0.5 μm. Coating was performed by a gravure coating method, and then the solvent was dried at 100 ° C. for 90 seconds in a dryer. Then, after drying SK Dyne 1491H (trade name) / curing agent L-45 (trade name) = 100 / 0.9 (mass ratio) manufactured by Soken Chemical Co., Ltd. as an adhesive composition on the other surface of the PET film. Apply to 20 μm, then dry at 100 ° C. for 3 minutes. Apply a silicone release agent to a 25 μm biaxially stretched polyester film, and apply the PET film adhesive to the release film. Laminating to the coated surface, surface protective films of Examples and Comparative Examples were obtained.

架橋剤：コロネートＬ（日本ポリウレタン工業社製 ポリイソシアネート）

Crosslinking agent: Coronate L (polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.)

Performance comparison <haze value>
Using a direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd., the haze value of the surface protective film was measured.
Haze value = measured value−base material haze value <surface resistance value>
In order to evaluate the antistatic property, the surface resistance value of the surface protective film was measured using a resistivity meter MCP-HT450 manufactured by Mitsubishi Chemical Corporation. The measurement conditions were a temperature of 23 ° C., a humidity of 65% RH, an applied voltage of 100 V, and 30 seconds.

<Contact angle>
Using a contact angle meter CA-DT-A manufactured by Kyowa Interface Science Co., Ltd., the droplet method was used at 20 ° C.
<Ethyl acetate resistance>
The surface protective film was rubbed with a load of 50 g / cm ² with a nonwoven fabric impregnated with ethyl acetate, and the appearance of the coating film was visually evaluated.
○: No change △: Somewhat changed ×: Changed

<Easy cleaning of contaminants>
1 g of the pressure-sensitive adhesive composition (SK Dyne 1491H / curing agent L-45 = 100 / 0.9) was rubbed against the surface protective layer, and easy-cleaning property at the time of wiping with Kimwipe (registered trademark) was confirmed.
○: Easily washable △: Remains slightly ×: Cannot be washed

<Scratch resistance>
The coating film of the surface protective layer of the surface protective film was rubbed with Scotch Bright (registered trademark, manufactured by Sumitomo 3M Co., Ltd.) with a load of about 10 g / cm ² , and the surface was visually checked for scratches.
○: 0 or more and less than 5 scratches that can be confirmed Δ: 5 or more and less than 10 scratches that can be confirmed ×: 10 or more scratches that can be confirmed

<Adhesion>
A cross-cut test (JIS K5400) was conducted for the adhesion between the surface protective layer of the surface protective film and the substrate PET film, and the adhesion was evaluated by the number of squares not peeled in 100 mm.
<Printability>
Magic Ink No. manufactured by Teranishi Chemical Industry Co., Ltd. 500 was described in the surface protective layer, and printability was evaluated from the writing situation of the ink.
○: The writing status of the magic ink is good. △: There is a slight ink repellency, but it is at a level where there is no problem. ×: The ink cannot be repelled.

  According to the present invention, there is little generation of static electricity when peeling from an optical sheet such as a polarizing plate, easy cleaning of contaminants by an adhesive, printability, and excellent adhesion between a base film and a surface protective layer, Furthermore, it is possible to provide a surface protection film of a one-coat system having transparency.

Claims (8)

A surface protective film comprising a base film, an adhesive layer provided on one surface of the base film, and a surface protective layer provided on the other surface of the base film, wherein the surface protective layer is a carbon nanotube (A) and a side chain containing a unit having a linear or branched alkyl group having 5 to 64 carbon atoms bonded directly or via another atomic group to a carbon atom of the main chain as a side chain A surface protective film comprising a polyurethane resin (B) having a long-chain alkyl group. The polyurethane resin (B) having a long-chain alkyl group in the side chain has both a linear or branched long-chain alkyl group having 2 to 64 carbon atoms and two active hydrogen-containing groups in the same molecule. Obtained by reacting an active hydrogen-containing compound (b), a polyisocyanate compound (a), and two active hydrogen-containing compounds (c) other than the above (b) in the presence or absence of an organic solvent. The surface protective film according to claim 1. The polyurethane resin (B) having a long-chain alkyl group in the side chain is composed of the following unit A: 5 to 80% by mass and unit B: 20 to 95% by mass, and the weight average of the polyurethane resin (B) The surface protective film according to claim 1 or 2 , which has a molecular weight of 5,000 to 500,000.

The surface protective film according to any one of claims 1 to 3, which has a surface resistance value of 10 ¹² Ω / □ to 10 ⁵ Ω / □. The surface protective film according to any one of claims 1 to 4 , wherein a contact angle of water with respect to the surface protective layer is 80 ° to 100 °. The surface protection film according to any one of claims 1 to 5 , wherein the haze value is 0.2 to 10%. The surface protective film according to any one of claims 1 to 6 , wherein the content of the carbon nanotube (A) in the surface protective layer is 0.1 to 25% by mass. A side containing a unit having a linear or branched alkyl group having 5 to 64 carbon atoms, which is bonded to the carbon nanotube (A) as a side chain, directly or via another atomic group to a carbon atom of the main chain A coating material for forming a surface protective layer, wherein the polyurethane resin (B) having a long-chain alkyl group in the chain is dissolved or dispersed in an organic solvent.