JP7657638B2 - Adhesive resin composition for surface protective film and surface protective film - Google Patents

Description

The present invention relates to an adhesive resin composition for a surface protective film and a surface protective film.

In recent years, plastic films, pressure sensitive adhesives, and adhesives have been used in a variety of fields due to their wide range of functions. Under these circumstances, they are increasingly being used in applications that were few in the past, such as not only flat plate-like objects but also curved surfaces and areas that require bending movements. Examples include flexible displays and foldable displays, and demand for these displays has been expanding rapidly in recent years. Accordingly, demand for surface protection films that can conform to curved surfaces is expected to increase.

For example, Patent Document 1 discloses a pressure-sensitive adhesive composition that includes a (meth)acrylic polymer having a hydroxy group and an acid value of 0 mgKOH/g or more and less than 16 mgKOH/g, an alkylene oxide chain-containing (meth)acrylic oligomer having an acid value of 0.1 mgKOH/g or more and 40 mgKOH/g or less, a polyether-modified silicone having a reactive group, a polyisocyanate compound as a crosslinking agent, and an ionic compound. It is disclosed that the pressure-sensitive adhesive composition can provide a surface protection film for optical components that can simultaneously achieve high levels of antistatic properties and low contamination of the adherend.

JP 2017-128636 A

However, there is a demand for a pressure-sensitive adhesive composition that can produce a surface protection film that is easier to peel off and reduces contamination by the pressure-sensitive adhesive when peeled off, compared to the technology described in Patent Document 1, etc.

The present invention has been made in consideration of the above circumstances, and provides an adhesive resin composition for surface protection films that, when used as a surface protection film, has good adhesion and peelability and is improved in terms of contamination caused by the adhesive when peeled off.

That is, the present invention includes the following aspects.
(1) A pressure-sensitive adhesive resin composition for a surface protective film, comprising a crosslinkable functional group-containing polymer (A) and a crosslinking agent component (B),
The glass transition temperature Tg of the crosslinkable functional group-containing polymer (A) is −75.0° C. or more and 0.0° C. or less,
The crosslinking agent component (B) contains an aliphatic or alicyclic polyisocyanate having a weight average molecular weight of 1,400 or more and 200,000 or less and an average number of isocyanate groups of 2.0 or more and 6.5 or less,
the content of the crosslinking agent component (B) is 0.5 parts by mass or more and 15.0 parts by mass or less relative to 100 parts by mass of the crosslinkable functional group-containing polymer (A);
The crosslinkable functional group-containing polymer (A)
An acrylic polymer (A1) obtained by copolymerizing a crosslinkable functional group-containing monomer and a (meth)acrylic acid ester monomer having an ester group terminal carbon number of 1 or more and 18 or less, and having a glass transition temperature Tg of −75.0° C. or more and 0.0° C. or less, or
A urethane-based polymer (A2) having a glass transition temperature Tg of −75.0° C. or more and 0.0° C. or less,
the crosslinkable functional group is at least one selected from the group consisting of a hydroxyl group, an epoxy group, and a carboxy group;
The adhesive resin composition for a surface protective film, wherein the aliphatic or alicyclic polyisocyanate is a polyisocyanate derived from at least one diisocyanate (b1) selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, a bifunctional polyol (b2) having a number average molecular weight of 1,500 or more, and a tri- or higher functional polyol (b3) having a number average molecular weight of 500 or more .
( 2 ) The adhesive resin composition for surface protective films according to ( 1 ), wherein the content of the structural unit derived from the crosslinkable functional group-containing monomer is 0.01 mass% or more and 25 mass% or less, based on the total mass of the crosslinkable functional group-containing polymer (A).
( 3 ) The adhesive resin composition for surface protective films according to (1) or (2) , wherein the weight average molecular weight of the crosslinkable functional group-containing polymer (A) is 2.0×10 ⁵ or more and 2.5×10 ⁶ or less.
( 4 ) The adhesive resin composition for surface protection films according to any one of (1) to (3), wherein the ratio NCO/OH of the molar amount of isocyanate groups of the diisocyanate (b1) to the total molar amount of hydroxyl groups of the polyol (b2) and the polyol ( b3 ) is 3 or more and 30 or less.
( 5 ) The mass ratio (b3)/(b2) of the polyol (b3) to the polyol (b2) is 0.1/99.9 or more and 99.9/0.1 or less, and
Relative to 100 parts by mass of the diisocyanate (b1),
The content of the polyol (b2) is 0.1 parts by mass or more and 250 parts by mass or less,
The adhesive resin composition for surface protective films according to ( 4 ), wherein the content of the polyol (b3) is 0.1 parts by mass or more and 190 parts by mass or less.
( 6 ) The adhesive resin composition for surface protective films according to ( 4 ) or (5), wherein the polyol (b2) and the polyol ( b3 ) are one or more polyols selected from the group consisting of polyester polyols, polyether polyols, epoxy polyols, polyolefin polyols, and polycarbonate polyols.
( 7 ) The adhesive resin composition for surface protective films according to any one of (1) to ( 6 ), wherein the crosslinking agent component (B) has an isocyanate group content of 1% by mass or more and 10% by mass or less.
( 8 ) The adhesive resin composition for surface protective films according to any one of (1) to (7), wherein the crosslinking agent component ( B ) is applied onto glass, and after storage for 168 hours under a 23°C and 65% humidity environment, a cured film having a thickness of 50 μm is formed, and the Konig hardness under a 23°C environment is 60 or less.
( 9 ) A plastic film;
An adhesive layer is provided on one or both sides of the plastic film,
A surface protection film, wherein the adhesive layer is made of a cured product of the adhesive resin composition for surface protection films according to any one of (1) to ( 8 ).
( 10 ) The surface protective film according to ( 9 ), wherein the adhesive layer has a thickness of 1 μm or more and 1000 μm or less.
( 11 ) The adhesive resin composition for surface protection films is applied onto a 38 μm-thick polyethylene terephthalate film that has been subjected to a release treatment, dried at 135° C. for 3 minutes to cure, and then stored in a 23° C., 50% RH environment for 7 days. The adhesive layer obtained by peeling the release-treated polyethylene terephthalate film from the surface protection film having an adhesive layer of 20 μm in thickness is then stored in a 23° C., 50% RH environment for 7 days, and then wrapped in a mesh sheet, immersed in ethyl acetate at 23° C. for 1 week, removed, and dried at 120° C. for 2 hours. The surface protection film according to ( 9 ) or ( 10 ), wherein the gel fraction calculated by the above calculation is 90% by mass or more and 100% by mass or less.
( 12 ) The surface protective film according to any one of (9) to (11), wherein the adhesive resin composition for surface protective films is applied onto a 38 μm-thick polyethylene terephthalate film that has been subjected to a release treatment, and then dried and cured at 135° C. for 3 minutes. The adhesive layer is then peeled off from the surface protective film having a 20 μm-thick adhesive layer, which has been stored for 7 days under a 23° C., 50% RH environment, and the adhesive layer is laminated to a thickness of 200 μm, and then cut into a width of 10 mm and a length of 40 mm. The laminated adhesive layer is set in a tensile tester so that the chuck distance is 10 mm, and a Young's modulus in a tensile test performed at a speed of 300 mm/min under ^{a 23} ° C. environment is 0.01 N/ ^mm2 or more and 0.22 N/ mm2 or less.
( 13 ) The surface protection film according to any one of (9) to (12), wherein the adhesive resin composition for surface protection films is applied onto a polyethylene terephthalate film having a thickness of 25 μm, dried at 135° C. for 3 minutes to be cured, and then stored in an environment of 23° C. and 50% RH for 7 days to form a surface protection film having an adhesive layer having a thickness of 20 μm, a width of 25 mm, and a length of 100 mm . The surface protection film is then attached to a glass substrate, pressed back and forth once with a 2 kg roller, and aged at 23° C. for 30 minutes, and the 180-degree peel adhesive strength measured at 23° C. and a speed of 300 mm/min is 0.02 N/25 mm or more and 2.50 N/ 25 mm or less.

According to the adhesive resin composition for surface protection films of the above aspect, it is possible to provide an adhesive resin composition for surface protection films that has good adhesion and peelability when made into a surface protection film, and has improved contamination caused by the adhesive when peeled off. The surface protection film of the above aspect has an adhesive layer formed by curing the adhesive resin composition for surface protection films, has good adhesion and peelability, and has improved contamination caused by the adhesive when peeled off.

In this specification, the term "polyol" refers to a compound having two or more hydroxyl groups (-OH) in one molecule.
In this specification, the term "polyisocyanate" refers to a reaction product in which a plurality of monomer compounds having two or more isocyanate groups (--NCO) are bonded together.
In this specification, unless otherwise specified, "(meth)acrylic" includes both methacrylic and acrylic, and "(meth)acrylate" includes both methacrylate and acrylate.

<Adhesive resin composition for surface protective film>
The adhesive resin composition for a surface protective film of this embodiment contains a crosslinkable functional group-containing polymer (A) and a crosslinker component (B).

The glass transition temperature Tg of the crosslinkable functional group-containing polymer (A) is −75.0° C. or more and 0.0° C. or less, preferably −72.0° C. or more and 0.0° C. or less, more preferably −72.0° C. or more and −25.0° C. or less, even more preferably −72.0° C. or more and −50.0° C. or less, and particularly preferably −72.0° C. or more and −55.0° C. or less. When the glass transition temperature Tg of the crosslinkable functional group-containing polymer (A) is within the above range, a surface protection film can be obtained that can be applied without air bubbles and is easy to peel off, and that has improved contamination by the pressure-sensitive adhesive during peeling.
The glass transition temperature of the crosslinkable functional group-containing polymer (A) can be, for example, a value measured by evaporating the organic solvent and water in a solution in which the crosslinkable functional group-containing polymer (A) is dissolved or dispersed under reduced pressure, vacuum drying the solution, and measuring the temperature at a heating rate of 5° C./min using a differential scanning calorimeter (DSC) measuring device.

The crosslinking agent component (B) contains an aliphatic or alicyclic polyisocyanate having a weight average molecular weight of 1,400 or more and 200,000 or less and an average number of isocyanate groups of 2.0 or more and 6.5 or less.

The content of the crosslinking agent component (B) is 0.01 parts by mass or more and 15.0 parts by mass or less, preferably 0.1 parts by mass or more and 13.0 parts by mass or less, more preferably 0.5 parts by mass or more and 12.0 parts by mass or less, even more preferably 0.6 parts by mass or more and 11.0 parts by mass or less, and particularly preferably 0.8 parts by mass or more and 10.0 parts by mass or less, relative to 100 parts by mass of the crosslinking functional group-containing polymer (A). When the content of the crosslinking agent component (B) is within the above numerical range, the curing property, attachment property, and peelability when made into a surface protective film tend to be excellent, and the contamination resistance tends to be further improved. The content of the crosslinking agent component (B) can be calculated, for example, from the blending amount of the crosslinking agent component (B) used when producing the adhesive resin composition for surface protective film.

The adhesive resin composition for surface protection films of this embodiment has the above-mentioned configuration, and thus a surface protection film is obtained that has good adhesion and peelability and is improved in terms of contamination caused by the adhesive when peeled off.

<Crosslinkable Functional Group-Containing Polymer (A)>
The crosslinkable functional group-containing polymer may be any polymer containing a crosslinkable functional group capable of reacting with the isocyanate group of the polyisocyanate. The crosslinkable functional group is a functional group capable of forming a crosslinked structure with the crosslinking agent component (B), and specifically includes, for example, a hydroxyl group, a thiol group, an amino group, an epoxy group, a carboxyl group, etc., among which, a hydroxyl group, an epoxy group, or a carboxyl group is preferred, and a hydroxyl group is more preferred.

The crosslinkable functional group-containing polymer is obtained by polymerizing a crosslinkable functional group-containing monomer.
The content of the constitutional unit derived from the crosslinkable functional group-containing monomer is preferably 0.01% by mass or more and 25% by mass or less, more preferably 0.1% by mass or more and 20% by mass or less, even more preferably 0.5% by mass or more and 18% by mass or less, and particularly preferably 1.0% by mass or more and 17% by mass or less, based on the total mass of the crosslinkable functional group-containing polymer (A). By the content of the constitutional unit derived from the crosslinkable functional group-containing monomer being within the above numerical range, a surface protective film having good adhesion and peelability and improved contamination by the adhesive during peeling can be obtained. The content of the constitutional unit derived from the crosslinkable functional group-containing monomer can be calculated, for example, from the blending amount of the crosslinkable functional group-containing monomer used in the production of the crosslinkable functional group-containing polymer.

The crosslinkable functional group-containing polymer (A) is preferably an acrylic polymer (A1) that is copolymerized with a crosslinkable functional group-containing monomer and a (meth)acrylic acid ester monomer having an ester group terminal with 1 to 18 carbon atoms, and has a glass transition temperature Tg of -75.0°C or more and 0.0°C or less, or a urethane polymer (A2) that has a glass transition temperature Tg of -75.0°C or more and 0.0°C or less.

The crosslinkable functional group-containing polymer (A) is more preferably an acrylic polymer (A1) that is obtained by copolymerizing a crosslinkable functional group-containing monomer with a (meth)acrylic acid ester monomer having an ester group terminal with 1 to 18 carbon atoms and has a glass transition temperature Tg of -75.0°C or more and 0.0°C or less.

[Acrylic polymer (A1)]
The acrylic polymer (A1) contains at least one polymerizable (meth)acrylic monomer unit having a crosslinkable functional group as a crosslinkable functional group-containing monomer unit. The crosslinkable functional group preferably contains a hydroxyl group, a carboxyl group, or an epoxy group, and more preferably contains a hydroxyl group.

The acrylic polymer (A1) may contain a single crosslinkable functional group, or may contain a combination of two or more different types of crosslinkable functional groups. In other words, the acrylic polymer may be obtained by polymerizing a single polymerizable (meth)acrylic monomer having a crosslinkable functional group, or may be obtained by copolymerizing a combination of two or more polymerizable (meth)acrylic monomers having different types of crosslinkable functional groups.

The acrylic polymer (A1) preferably contains, in addition to the polymerizable (meth)acrylic monomer unit having a crosslinkable functional group, one or more (meth)acrylic acid ester monomer units having an ester group terminal with 1 or more and 18 or less carbon atoms.
That is, the acrylic polymer (A1) may be obtained by copolymerizing one or more polymerizable (meth)acrylic monomers having a crosslinkable functional group and one or more (meth)acrylic acid ester monomers having an ester group terminal carbon number of 1 to 18. The (meth)acrylic acid ester monomer may or may not have a crosslinkable functional group, but it is preferable that it does not have a crosslinkable functional group.

The number of carbon atoms at the ester group terminal of the (meth)acrylic acid ester monomer is preferably 1 or more and 18 or less.

Examples of the polymerizable (meth)acrylic monomer having a crosslinkable functional group include the following (i) to (v). These may be used alone or in combination of two or more.
(i) Acrylic esters having a hydroxyl group, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, and 8-hydroxyoctyl acrylate.
(ii) Methacrylic acid esters having a hydroxyl group, such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, and 8-hydroxyoctyl methacrylate.
(iii) (meth)acrylic acid esters having a polyvalent hydroxy group, such as acrylic acid monoesters or methacrylic acid monoesters of glycerin, and acrylic acid monoesters or methacrylic acid monoesters of trimethylolpropane.
(iv) Unsaturated carboxylic acids such as acrylic acid and methacrylic acid.
(v) (meth)acrylic acid esters having an epoxy group, such as glycidyl methacrylate.

Examples of (meth)acrylic acid ester monomers having 1 or more and 18 or less carbon atoms at the ester group terminal include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and Examples of (meth)acrylic acid esters include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate. These may be used alone or in combination of two or more.

The acrylic polymer (A1) may further contain, in addition to the polymerizable (meth)acrylic monomer unit having a crosslinkable functional group, other monomer units other than the above-mentioned (meth)acrylic acid ester monomers.
That is, the acrylic polymer (A1) is obtained by polymerizing a polymerizable (meth)acrylic monomer having one or more crosslinkable functional groups, or by copolymerizing a polymerizable (meth)acrylic monomer having one or more crosslinkable functional groups with one or more other monomers. The other monomers may or may not have a crosslinkable functional group, but preferably do not have a crosslinkable functional group.

Examples of the other monomers include the following (i) to (ii). These may be used alone or in combination of two or more.
(i) Unsaturated amides such as (meth)acrylamide, N-methylol acrylamide, diacetone acrylamide, and dimethylaminopropyl acrylamide.
(ii) Styrene, vinyl toluene, vinyl acetate, (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.

Furthermore, as other monomers copolymerizable with the polymerizable (meth)acrylic monomer having a crosslinkable functional group, polymerizable ultraviolet-stable monomers disclosed in JP-A-1-261409 (Reference 1) and JP-A-3-006273 (Reference 2), etc., may be used.

Specific examples of the polymerizable ultraviolet-stable monomer include 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and 2-hydroxy-4-(3-methacryloxy-2-hydroxypropoxy)benzophenone.

For example, the above monomer components can be solution polymerized in the presence of a known radical polymerization initiator such as a peroxide or an azo compound, and the resulting solution can be diluted with an organic solvent, etc., as necessary, to obtain an acrylic polymer.

When obtaining a water-based acrylic polymer, it can be produced by a known method such as a method of solution polymerization of an olefinic unsaturated compound and converting it into a water phase, or emulsion polymerization. In this case, water solubility or water dispersibility can be imparted by neutralizing the acidic moiety of carboxylic acid-containing monomers such as acrylic acid and methacrylic acid, or sulfonic acid-containing monomers, with an amine or ammonia.

The weight average molecular weight Mw(A) of the crosslinkable functional group-containing polymer (A) is preferably 2.0×10 ⁵ or more and 2.5×10 ⁶ or less, more preferably 3.0×10 ⁵ or more and 2.0×10 ⁶ or less, even more preferably 3.5×10 ⁵ or more and 1.8×10 ⁶ or less, and particularly preferably 4.0×10 ⁵ or more and 1.5×10 ⁶ or less. When the weight average molecular weight of the crosslinkable functional group-containing polymer (A) is within the above range, a surface protection film that is easy to peel off and has improved contamination by the adhesive during peeling can be obtained. The weight average molecular weight Mw of the crosslinkable functional group-containing polymer (A) can be measured, for example, using the method described in the examples described below.

<Crosslinking Agent Component (B)>
The crosslinking agent component (B) contains an aliphatic or alicyclic polyisocyanate (b) having a weight average molecular weight of 1,400 or more and 200,000 or less and an average number of isocyanate groups of 2.0 or more and 6.5 or less.

The weight average molecular weight Mw(b) of the aliphatic or alicyclic polyisocyanate is from 1,400 to 200,000, preferably from 1,500 to 100,000, more preferably from 2,000 to 90,000, even more preferably from 3,000 to 80,000, and particularly preferably from 3,200 to 70,000. When the weight average molecular weight Mw(b) of the aliphatic or alicyclic polyisocyanate is within the above numerical range, a surface protective film having an adhesive layer with excellent adhesion, easier peeling, and improved contamination resistance can be obtained.
The Mw(b) of the aliphatic or alicyclic polyisocyanate is the weight average molecular weight based on polystyrene as determined by GPC measurement.

The average number of isocyanate groups in the aliphatic or alicyclic polyisocyanate is 2.0 or more and 6.5 or less, more preferably 2.2 or more and 6.3 or less, even more preferably 2.4 or more and 6.0 or less, and particularly preferably 2.5 or more and 5.9 or less. When the average number of isocyanate groups in the aliphatic or alicyclic polyisocyanate is within the above numerical range, a surface protection film having an adhesive layer with excellent adhesion, easier peeling, and improved contamination resistance can be obtained.

The average number of isocyanate groups (fn) of an aliphatic or alicyclic polyisocyanate can be calculated using the following formula. In the formula, "Mn" indicates the number average molecular weight of the aliphatic or alicyclic polyisocyanate, and "NCO%" indicates the isocyanate group content of the aliphatic or alicyclic polyisocyanate. The number average molecular weight Mn of an aliphatic or alicyclic polyisocyanate is the weight average molecular weight based on polystyrene measured by GPC. The method for measuring NCO% will be described later.

[fn] = [Mn]×[NCO%]/4200

The aliphatic or alicyclic polyisocyanate (b) is preferably a polyisocyanate derived from at least one diisocyanate (b1) selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, a bifunctional polyol (b2) having a number average molecular weight of 1500 or more, and a trifunctional or higher polyol (b3) having a number average molecular weight of 500 or more.

The ratio NCO/OH of the molar amount of isocyanate groups in the diisocyanate (b1) to the total molar amount of hydroxyl groups in the polyol (b2) and the polyol (b3) is preferably 3 to 30, more preferably 4 to 28, even more preferably 5 to 27, and particularly preferably 6 to 25. By having the NCO/OH ratio within the above numerical range, a surface protection film having an adhesive layer with excellent adhesion, easier peeling, and improved contamination resistance can be obtained.

The aliphatic or alicyclic polyisocyanate (b) may be a polyisocyanate having in one molecule all of the constituent units derived from diisocyanate, polyol (b2) and polyol (b3), or may be a mixture of polyisocyanates having in one molecule at least one constituent unit derived from a group consisting of diisocyanate, polyol (b2) and polyol (b3).

The aliphatic or alicyclic polyisocyanate (b) may have at least one structure selected from the group consisting of an allophanate structure, a uretdione structure, an iminooxadiazinedione structure, an isocyanurate structure, a urea structure, a urethane structure, and a biuret structure. Of these, it is preferable that it has at least one structure selected from the group consisting of a urethane structure, an allophanate structure, a biuret structure, a urea structure, and an isocyanurate group, and it is more preferable that it contains a urethane structure.

[Diisocyanate (b1)]
The diisocyanate (b1) is at least one selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates.

Examples of aliphatic diisocyanates include, but are not limited to, 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, ethyl (2,6-diisocyanato)hexanoate, 1,6-diisocyanatohexane (hereinafter sometimes abbreviated as "HDI"), 1,9-diisocyanatononane, 1,12-diisocyanatododecane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, etc. These aliphatic diisocyanates may be used alone or in combination of two or more.

Examples of alicyclic diisocyanates include, but are not limited to, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (hereinafter sometimes abbreviated as "hydrogenated XDI"), 1,3- or 1,4-diisocyanatocyclohexane, 3,5,5-trimethyl-1-isocyanato-3-(isocyanatomethyl)cyclohexane (hereinafter sometimes abbreviated as "IPDI"), 4-4'-diisocyanato-dicyclohexylmethane (hereinafter sometimes abbreviated as "hydrogenated MDI"), 2,5- or 2,6-diisocyanatomethylnorbornane, etc. These alicyclic diisocyanates may be used alone or in combination of two or more.

These aliphatic diisocyanates and alicyclic diisocyanates may be used alone, or two or more of them may be used in combination.
From the viewpoint of flexibility, the mass ratio of the alicyclic polyisocyanate to the aliphatic diisocyanate is preferably 0/100 or more and 30/70 or less.

Among them, the diisocyanate is preferably HDI, IPDI, hydrogenated XDI, or hydrogenated MDI, more preferably HDI or IPDI, and even more preferably HDI.

In the production of polyisocyanates, in addition to the diisocyanates described above, isocyanate monomers such as those shown below may be further used.
(1) Aromatic diisocyanates such as diphenylmethane-4,4'-diisocyanate (MDI), 1,5-naphthalene diisocyanate, tolylene diisocyanate (TDI), xylylene diisocyanate, and m-tetramethylxylylene diisocyanate (TMXDI).
(2) Triisocyanates such as 4-isocyanatomethyl-1,8-octamethylene diisocyanate (hereinafter sometimes referred to as "NTI"), 1,3,6-hexamethylene triisocyanate (hereinafter sometimes referred to as "HTI"), bis(2-isocyanatoethyl) 2-isocyanatoglutarate (hereinafter sometimes referred to as "GTI"), and lysine triisocyanate (hereinafter sometimes referred to as "LTI").

[Polyol (b2) and Polyol (b3)]
The polyol (b2) has a number average molecular weight of 1,500 or more and is a bifunctional polyol (diol).
The polyol (b3) has a number average molecular weight of 500 or more and is a tri- or higher functional polyol.

The number average molecular weight of the polyol (b2) is at least 1500, and preferably at least 1700. When the number average molecular weight of the polyol (b2) is at least the above lower limit, the hardness of the cured film obtained by curing the polyisocyanate alone is low and the flexibility is good.
On the other hand, the upper limit of the number average molecular weight of the polyol (b2) is not particularly limited, but may be, for example, 7,000, and is more preferably 6,500.
The number average molecular weight Mn of the polyol (b2) is, for example, a number average molecular weight based on polystyrene standards as measured by GPC. When two or more kinds of polyols (b2) are used in combination, the number average molecular weight of the mixture is calculated.

The number average molecular weight of the polyol (b3) is not less than 500, and preferably not less than 800. When the number average molecular weight of the polyol (b3) is not less than the above lower limit, the hardness of the cured film obtained by curing the polyisocyanate alone is low and the flexibility is good.
On the other hand, the upper limit of the number average molecular weight of the polyol (b3) is not particularly limited, but may be, for example, 4,000, preferably 3,000, and more preferably 2,500.
The number average molecular weight Mn of the polyol (b3) is, for example, a number average molecular weight based on polystyrene standards as measured by GPC. When two or more kinds of polyols (b3) are used in combination, the number average molecular weight of the mixture is calculated.

The polyol (b2) is preferably at least one bifunctional polyol (diol) selected from the group consisting of polyester polyols, polyether polyols, epoxy polyols, polyolefin polyols, and polycarbonate polyols, and is more preferably a bifunctional polyester polyol.

Examples of the bifunctional polyester polyol include the following polyester polyols (1) and (2).
(1) Polyester polyols obtained by a condensation reaction between a dibasic acid, or a mixture of two or more kinds thereof, and a dihydric alcohol, or a mixture of two or more kinds thereof.
(2) Polycaprolactone polyol obtained by ring-opening polymerization of ε-caprolactone with a dihydric alcohol.
Examples of the dibasic acid include carboxylic acids such as succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and 1,4-cyclohexanedicarboxylic acid.
Examples of the dihydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, trimethylpentanediol, and cyclohexanediol.

Among these, bifunctional polyester polyols are preferably bifunctional polycaprolactone polyols.

Commercially available bifunctional polycaprolactone polyols include, for example, "Placcel 210" (number average molecular weight 1000), "Placcel 220" (number average molecular weight 2000), "Placcel 230" (number average molecular weight 3000), and "Placcel 240" (number average molecular weight 4000), all of which are manufactured by Daicel Corporation.

The polyol (b3) may be a polyol having three or more functionalities, preferably a polyol having three to ten functionalities, more preferably a polyol having three to seven functionalities, still more preferably a polyol having three to five functionalities, particularly preferably a polyol having three to four functionalities, and most preferably a trifunctional polyol (triol).
The trifunctional polyol (triol) is preferably at least one trifunctional polyol (triol) selected from the group consisting of polyester polyols, polyether polyols, epoxy polyols, polyolefin polyols, and polycarbonate polyols, more preferably a trifunctional polyether polyol or polyester polyol, and even more preferably a trifunctional polyester polyol.

Examples of trifunctional polyester polyols include polyester polyols of either (1) or (2) below.
(1) Polyester polyols obtained by a condensation reaction between a dibasic acid, or a mixture of two or more kinds thereof, and a trihydric alcohol, or a mixture of two or more kinds thereof.
(2) Polycaprolactone polyol obtained by ring-opening polymerization of ε-caprolactone with a trihydric alcohol.
Examples of the dibasic acid include carboxylic acids such as succinic acid, adipic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and 1,4-cyclohexanedicarboxylic acid.
Examples of the trihydric alcohol include trimethylolpropane, glycerin, pentaerythritol, 2-methylolpropanediol, and ethoxylated trimethylolpropane.

Among these, trifunctional polyester polyols are preferably trifunctional polycaprolactone polyols.

Commercially available trifunctional polycaprolactone polyols include, for example, "Placcel 305" (number average molecular weight 550), "Placcel 308" (number average molecular weight 850), "Placcel 309" (number average molecular weight 900), "Placcel 312" (number average molecular weight 1250), and "Placcel 320" (number average molecular weight 2000), all manufactured by Daicel Corporation.

In the aliphatic or alicyclic polyisocyanate (b), the mass ratio of the polyol (b2) to the polyol (b3) (the mass ratio of (b2)/(b3)) is preferably from 0.1/99.9 to 99.9/0.1, more preferably from 1/99 to 99/1, even more preferably from 3/97 to 90/10, particularly preferably from 5/95 to 85/15, and most preferably from 7/93 to 80/20.
When the mass ratio of (b2)/(b3) is equal to or greater than the lower limit, the hardness of the cured film obtained by curing the polyisocyanate alone is low and the flexibility is better. Also, a surface protection film having better adhesion and flexibility is obtained. On the other hand, when the mass ratio of (b2)/(b3) is equal to or less than the upper limit, the surface protection film having better adhesion, flexibility and cohesion is obtained.
The mass ratio of (b2)/(b3) can be calculated, for example, from the blending amounts of each polyol during the production of the polyisocyanate.

In the aliphatic or alicyclic polyisocyanate (b), the content (charged amount) of the polyol (b2) relative to 100 parts by mass of the diisocyanate is preferably 0.1 parts by mass or more and 250 parts by mass or less, more preferably 0.5 parts by mass or more and 240 parts by mass or less, even more preferably 1.0 parts by mass or more and 230 parts by mass or less, and particularly preferably 3.0 parts by mass or more and 220 parts by mass or less.
When the content of polyol (b2) is equal to or more than the lower limit, the hardness of the cured film obtained by curing the polyisocyanate alone is low and the flexibility is better. Also, a surface protection film having better adhesion and curability can be obtained. On the other hand, when the content of polyol (b2) is equal to or less than the upper limit, the polyisocyanate can be maintained in a liquid state without gelling during production, and the flexibility of the surface protection film when made into the polyisocyanate is better.
The content of polyol (b2) can be calculated, for example, from the amounts of diisocyanate and polyol (b2) blended during the production of the polyisocyanate.

In the aliphatic or alicyclic polyisocyanate (b), the content (charged amount) of the polyol (b3) relative to 100 parts by mass of the diisocyanate is preferably 0.1 parts by mass or more and 190 parts by mass or less, more preferably 10 parts by mass or more and 180 parts by mass or less, even more preferably 20 parts by mass or more and 190 parts by mass or less, and particularly preferably 25 parts by mass or more and 180 parts by mass or less.
When the content of polyol (b3) is equal to or less than the upper limit, the polyisocyanate can be maintained in a liquid state without gelation during production, and the curability and flexibility of the surface protection film when made into the film are better. On the other hand, when the content of polyol (b3) is equal to or more than the lower limit, the hardness of the cured film obtained by curing the polyisocyanate alone is low and the flexibility is better. In addition, a surface protection film having excellent adhesion and curability can be obtained.
The content of polyol (b3) can be calculated, for example, from the amounts of diisocyanate and polyol (b3) blended when producing the polyisocyanate.

[Method for producing crosslinking agent component (B)]
When the crosslinking agent component (B) is an aliphatic or alicyclic polyisocyanate (b), it is obtained by reacting the above diisocyanate (b1), polyol (b2), and polyol (b3). Hereinafter, polyol (b2) and polyol (b3) may be collectively referred to simply as polyol.

The polyol (b2) and the polyol (b3) can be used alone or as a mixture. When used as a mixture, they may be mixed before reacting with a diisocyanate, or each polyol may be reacted with a diisocyanate alone to form a polyisocyanate and then mixed.
That is, examples of methods for producing polyisocyanates include a method of simultaneously reacting a diisocyanate with a polyol (b2) and a polyol (b3) to obtain a polyisocyanate; a method of mixing a reaction product of a diisocyanate with a polyol (b2) and a reaction product of a diisocyanate with a polyol (b3) to obtain a polyisocyanate; and a method of reacting a diisocyanate with a polyol (b2) or a polyol (b3) and then further reacting the remaining polyol to obtain a polyisocyanate.

The amounts of polyol (b2) and polyol (b3) are preferably such that the mass ratio of polyol (b2) to polyol (b3) is within the above range.

During the reaction, the molar ratio of the isocyanate groups of the diisocyanate to the hydroxyl groups of the polyol (b2) and polyol (b3) (the molar ratio of isocyanate groups/hydroxyl groups) is preferably 3 to 30, more preferably 4 to 25, even more preferably 5 to 23, and particularly preferably 6 to 22. By having the NCO/OH ratio within the above numerical range, a surface protection film having an adhesive layer with excellent adhesion, easier peeling, and improved contamination resistance can be obtained.

The reaction between polyol and diisocyanate is carried out as follows. The reaction temperature is usually from room temperature (about 23°C) to 200°C, and preferably from 60°C to 130°C. If the reaction temperature is above the lower limit, the reaction time is shorter. On the other hand, if the reaction temperature is below the upper limit, an increase in the viscosity of the polyisocyanate due to undesirable side reactions can be more effectively avoided, and discoloration of the resulting polyisocyanate can also be more effectively avoided.

The reaction may be carried out without a solvent or in any solvent that is inert to isocyanate groups. If necessary, a known catalyst may be used to promote the reaction between the isocyanate groups and the hydroxyl groups.

[Physical properties of crosslinking agent component (B)]
The isocyanate group content (NCO group content) of the crosslinking agent component (B), in a state substantially free of solvent or diisocyanate, is preferably 1 mass % or more and 10 mass % or less, more preferably 2 mass % or more and 9.5 mass % or less, even more preferably 2.2 mass % or more and 9.0 mass % or less, and particularly preferably 2.5 mass % or more and 8.5 mass % or less, based on the total mass of the crosslinking agent component (B).
The NCO group content can be determined, for example, by reacting the isocyanate groups in the crosslinking agent component (B) with an excess of an amine (such as dibutylamine) and then back-titrating the remaining amine with an acid such as hydrochloric acid.

Only the above-mentioned crosslinking agent component (B) is applied onto glass, and after storage for 168 hours in an environment of 23°C and 65% humidity, the Konig hardness of the 50 μm-thick cured film formed by the reaction between moisture in the air and the polyisocyanate composition in an environment of 23°C is 60 or less, preferably 57 or less, more preferably 55 or less, and even more preferably 54 or less. When the Konig hardness is equal to or less than the upper limit, the hardness is low and the flexibility is excellent.

[Isocyanate group/crosslinkable functional group]
The molar ratio of the isocyanate group of the crosslinking agent component (B) to the crosslinkable functional group (particularly, hydroxyl group) of the crosslinkable functional group-containing polymer (A) contained in the adhesive resin composition for surface protection film of this embodiment (the molar ratio of isocyanate group/crosslinkable functional group) is determined depending on the physical properties of the required surface protection film, and is usually 0.005 or more and 50 or less.

<Other ingredients>
The adhesive resin composition for a surface protective film of this embodiment may further contain other additives.
Examples of other additives include curing agents other than the crosslinking agent component (B) capable of reacting with the crosslinkable functional group-containing polymer (A), curing catalysts, solvents, pigments (extender pigments, coloring pigments, metallic pigments, etc.), tackifying resins, photopolymerization initiators, ultraviolet absorbers, light stabilizers, radical stabilizers, yellowing inhibitors that suppress coloring during the baking process, coating surface adjusters, flow adjusters, pigment dispersants, defoamers, thickeners, film-forming assistants, and the like.

Examples of the curing agent include melamine resins, urea resins, epoxy group-containing compounds or resins, carboxy group-containing compounds or resins, acid anhydrides, alkoxysilane group-containing compounds or resins, and hydrazide compounds.

The curing catalyst may be a basic compound or a Lewis acid compound.
Examples of the basic compound include metal hydroxides, metal alkoxides, metal carboxylates, metal acetylacetinates, hydroxides of onium salts, onium carboxylates, halides of onium salts, metal salts of active methylene compounds, onium salts of active methylene compounds, aminosilanes, amines, phosphines, etc. As the onium salts, ammonium salts, phosphonium salts, or sulfonium salts are preferable.
Examples of the Lewis acid compound include an organotin compound, an organozinc compound, an organotitanium compound, and an organozirconium compound.

Examples of the solvent include 1-methylpyrrolidone, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether (DPDM), propylene glycol dimethyl ether, methyl ethyl ketone, acetone, Examples of the solvent include methyl isobutyl ketone, propylene glycol monomethyl ether acetate, ethanol, methanol, iso-propanol, 1-propanol, iso-butanol, 1-butanol, tert-butanol, 2-ethylhexanol, cyclohexanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, ethyl acetate, isopropyl acetate, butyl acetate, toluene, xylene, pentane, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, and mineral spirits. These solvents may be used alone or in combination of two or more.

In addition, known pigments (extender pigments, color pigments, metallic pigments, etc.), ultraviolet absorbers, light stabilizers, radical stabilizers, yellowing inhibitors that suppress coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, defoamers, thickeners, and film-forming aids can be appropriately selected and used.

<Method for producing adhesive resin composition for surface protective film>
The adhesive resin composition for surface protection films can be produced by a conventional method, for example, a melt-kneading method using a general mixer such as a Banbury mixer, a single screw extruder, a twin screw extruder, a co-kneader, or a multi-screw extruder, or a method in which each component is dissolved or dispersed and mixed, then coated on a substrate film by a coater or the like, and the solvent is then removed by heating.

The adhesive resin composition for surface protection films of this embodiment may be foamed to achieve the effects of weight reduction, flexibility, and improved adhesion. Foaming methods include chemical methods, physical methods, and the use of thermally expandable microballoons. In each case, air bubbles can be distributed inside the material by adding a chemical foaming agent such as an inorganic foaming agent or an organic foaming agent, or a physical foaming agent, or by adding thermally expandable microballoons.

In addition, hollow fillers (pre-expanded balloons) can be added to reduce weight, increase flexibility, and improve adhesion.

The adhesive resin composition for surface protective films of this embodiment may contain a tackifier resin to adjust the adhesive strength and cohesive strength. Examples of tackifier resins include rosin-based tackifier resins, terpene-based tackifier resins, petroleum-based tackifier resins, and styrene-based tackifier resins. These tackifier resins may be used alone or in combination of two or more. The softening point of the tackifier resin is preferably 90°C or higher and 160°C or lower.

<Surface protection film>
The surface protection film of this embodiment includes a plastic film and an adhesive layer on one or both sides of the plastic film.
The adhesive layer is made of a cured product of the adhesive resin composition for surface protection films described above.

In the surface protection film of this embodiment, the adhesive layer is easy to peel off, and contamination caused by the adhesive when peeled off is improved.

In the surface protection film of this embodiment, the thickness of the adhesive layer can be appropriately determined depending on the application, but is preferably 1 μm or more and 1000 μm or less, more preferably 2 μm or more and 900 μm or less, even more preferably 3 μm or more and 800 μm or less, and particularly preferably 4 μm or more and 700 μm or less.

The surface protective film of this embodiment can be produced, for example, by applying the adhesive resin composition for surface protective films onto a substrate, drying it as necessary, and then curing it.
Examples of the method for applying the adhesive resin composition for surface protective films to a substrate include a method of applying the composition using an applicator, a roll coater, a knife coater, a gravure coater, etc. When drying is performed after the application, examples of the method include a heat drying method in which the obtained laminate is placed in a dryer or the like and dried for 1 minute to 30 minutes at a temperature of 50° C. to 150° C. Other drying methods include, for example, natural drying, hot air drying, infrared drying, etc.

The heating temperature during curing can be 70°C or higher and 160°C or lower, 75°C or higher and 155°C or lower, or 80°C or higher and 150°C or lower.

In the surface protection film of this embodiment, the adhesive resin composition for surface protection film is applied onto a 38 μm-thick polyethylene terephthalate film that has been subjected to a release treatment, dried at 135° C. for 3 minutes to cure, and then stored for 7 days under a 23° C., 50% RH environment to obtain an adhesive layer having a thickness of 20 μm. The adhesive layer is then wrapped in a mesh sheet after storage for 7 days under a 23° C., 50% RH environment, immersed in ethyl acetate at 23° C. for 1 week, removed, and dried at 120° C. for 2 hours. The gel fraction calculated by the above method is preferably 90.0% by mass or more and 100.0% by mass or less. When the gel fraction is equal to or more than the lower limit, the curability is superior.
The gel fraction referred to here is the percentage of the mass of the adhesive layer after immersion in ethyl acetate and drying relative to the mass of the adhesive layer before immersion in ethyl acetate.

In the surface protective film of this embodiment, the adhesive resin composition for surface protective film is applied onto a 38 μm thick polyethylene terephthalate film that has been subjected to a release treatment, dried at 135 ° C for 3 minutes to harden, and then stored in a 23 ° C, 50% RH environment for 7 days. The adhesive layer obtained by peeling the release-treated polyethylene terephthalate film from the surface protective film having an adhesive layer of 20 μm is laminated to a thickness of 200 μm, and then cut into a width of 10 mm and a length of 40 mm. The laminated adhesive layer is set in a tensile tester so that the chuck distance is 10 mm, and the Young's modulus in a tensile test performed at a speed of 300 mm / min in a 23 ° C environment is preferably 0.22 N / mm ² or less, more preferably 0.20 N / mm ² or less, and even more preferably 0.15 N / mm ² or less. By having the Young's modulus be equal to or less than the upper limit, the elastic modulus is lower, and the adhesion and followability to the adherend are more excellent.
Furthermore, the lower limit of the Young's modulus is preferably as small as possible, and can be set to, for example, 0.01 N/ ^mm2 .

In the surface protection film of this embodiment, the adhesive resin composition for surface protection film is applied onto a polyethylene terephthalate film having a thickness of 25 μm, dried at 135° C. for 3 minutes to harden, and then stored for 7 days in an environment of 23° C. and 50% RH. The surface protection film having an adhesive layer having a thickness of 20 μm, a width of 25 mm, and a length of 100 mm is attached to a glass substrate, pressed once back and forth with a 2 kg roller, and cured at 23° C. for 30 minutes. The 180-degree peel adhesive strength measured at 23° C. and a speed of 300 mm/min is preferably 0.02 N/25 mm or more and 2.50 N/25 mm or less, more preferably 0.03 N/25 mm or more and 2.40 N/25 mm or less, and even more preferably 0.04 N/25 mm or more and 2.30 N/25 mm or less. By having the 180-degree peel adhesive strength within the above numerical range, the peelability can be improved.

As described above, the surface protection film of this embodiment is easy to peel off and has improved resistance to contamination by the adhesive when peeled off, and is therefore suitable for use, for example, as a surface protection film for optical components.

The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[Physical Properties 1]
(Glass transition temperature Tg)
The glass transition temperature of the acrylic polymer (A) was determined by evaporating off the organic solvent and water in a solution of the acrylic polymer (A) under reduced pressure, vacuum drying the solution, and measuring the temperature at a temperature rise rate of 5° C./min using a differential scanning calorimeter (DSC) analyzer.

[Physical Properties 2]
(Number average molecular weight and weight average molecular weight)
The number average molecular weight and weight average molecular weight are those measured by gel permeation chromatography (GPC) using the following apparatus, using polystyrene as a standard.

(Measurement conditions)
Apparatus: Tosoh Corporation, HLC-802A
Column: Tosoh Corporation, G1000HXL x 1
G2000HXL x 1
G3000HXL x 1 Carrier: Tetrahydrofuran Detection method: Differential refractometer

[Physical Properties 3]
(Isocyanate Group Content)
First, 2 g or more and 3 g or less of the measurement sample was precisely weighed out (Wg) in a flask. Then, 20 mL of toluene was added to dissolve the measurement sample. Then, 20 mL of a 2N toluene solution of di-n-butylamine was added, mixed, and left at room temperature for 15 minutes. Then, 70 mL of isopropyl alcohol was added and mixed. Then, this liquid was titrated with a 1N hydrochloric acid solution (Factor F) as an indicator. The titration value obtained was V2 mL. Then, the titration value obtained without the sample was V1 ml. Then, the isocyanate group content (NCO%) (mass%) of the crosslinking agent component (B) was calculated from the following formula.

"Isocyanate group content (mass%)" = (V1-V2) x F x 42/(W x 1000) x 100

[Physical Properties 4]
(Average number of isocyanate functional groups)
The average number of isocyanate functional groups (average NCO number) of the crosslinking agent component (B) was calculated by the following formula. In the formula, "Mn" means number average molecular weight, and the value measured in the above "Physical Properties 2" was used. "NCO%" was the value calculated in the above "Physical Properties 3".

"Average number of isocyanate functional groups" = (Mn x NCO% x 0.01) / 42

[Preparation of cured film of crosslinking agent component (B)]
Each crosslinking agent component (B) was applied onto a glass plate using an applicator, and after storing the applied coating in an environment of 23° C. and 65% humidity for 168 hours, the coating was further heated at 50° C. for 24 hours to obtain a cured film having a thickness of 50 μm.

[Physical Properties 5]
(Konig hardness)
For each cured film, the Konig hardness (times) was measured in an environment of 23° C. using a Konig hardness tester (Pendulum hardness tester manufactured by BYK Gardner).

<Evaluation method>
[Preparation of Surface Protection Film 1]
Each adhesive resin composition for surface protection films was applied to a 38 μm-thick release-treated PET film using an applicator so that the thickness after drying would be 20 μm, and then dried for 3 minutes at 135° C. Thereafter, the film was stored for 7 days under an environment of 23° C. and 50% RH to obtain a surface protection film 1 for gel fraction measurement and tensile test. The release-treated PET film was peeled off and subjected to each evaluation.

[Preparation of Surface Protective Film 2]
Each adhesive resin composition for surface protection films was applied onto a 25 μm thick polyethylene terephthalate (PET) film using an applicator so that the thickness after drying would be 20 μm, and then dried for 3 minutes at 135° C. Thereafter, the film was stored in an environment of 23° C. and 50% RH for 7 days to obtain a surface protection film 2 for measuring 180° peel adhesive strength.

[Evaluation 1]
(Gel Fraction)
About 0.1 g to 0.2 g of the adhesive layer obtained by peeling off the peel-treated PET film from the surface protective film 1 obtained in the above "Preparation of Surface Protective Film 1" was collected, wrapped in a mesh sheet, immersed in ethyl acetate for one week, and then dried for two hours at 120° C. Next, the percentage of the mass of the adhesive layer dried after immersion in ethyl acetate relative to the mass of the adhesive layer before immersion in ethyl acetate was calculated as the gel fraction (mass%).
The curability was evaluated as good when the gel fraction was 90% by mass or more.

[Evaluation 2]
(Tensile test: Young's modulus)
The adhesive layer obtained by peeling off the peel-treated PET film from the surface protection film 1 obtained in the above "Preparation of Surface Protection Film 1" was laminated to a thickness of 200 μm and cut to a width of 10 mm and a length of 40 mm. The laminated adhesive layer was then set in a tensile tester so that the chuck distance was 10 mm, and the Young's modulus was measured at a speed of 300 mm/min using the tensile tester in a 23° C. environment.
Those having a Young's modulus of 0.22 N/mm2 or ^less were evaluated as having good adhesion and conformability to the adherend.

[Evaluation 3]
(180 degree peel adhesion and stain resistance)
The surface protection film 2 obtained in the above "Preparation of surface protection film 2" was cut to a width of 25 mm and a length of 100 mm to obtain a test piece. The test piece was then attached to a glass substrate, and pressed against the glass by rolling a 2 kg roller back and forth once. After curing for 30 minutes at 23°C, the 180° peel adhesion was measured using a tensile tester at a speed of 300 mm/min.
A value of 0.02 N/25 mm or more and 2.50 N/25 mm was evaluated as having good peelability.

Next, after measuring the 180-degree peel adhesion, the glass surface was visually observed and the stain resistance was evaluated according to the following evaluation criteria.

(Evaluation Criteria)
○: No contamination (no visible adhesive residue on the glass surface)
×: Contamination occurred (adhesive remains on the glass surface to the extent that can be visually confirmed)

<Synthesis of Crosslinkable Functional Group-Containing Polymer (A)>
[Synthesis Example 1-1]
(Synthesis of Acrylic Polymer A-1)
Into a four-neck flask equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, and a cooling tube, 96 parts by mass of 2-ethylhexyl acrylate (2EHA) and 4 parts by mass of 4-hydroxybutyl acrylate (4HBA) were added, and 240 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and the reaction was carried out at 65°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer A-1 having a solid content concentration of 30.0% by mass.

[Synthesis Examples 1-2 to 1-8]
(Synthesis of Acrylic Polymers A-1 to A-8)
Each acrylic polymer was synthesized in the same manner as in Synthesis Example 1-1, except that the blending ratio of each monomer was as shown in Table 1.

The compositions and physical properties of each synthesized acrylic polymer are shown in Table 1 below. In Table 1, the abbreviations for the monomers indicate the following compounds.

(Crosslinkable Functional Group-Containing Monomer (a1))
4HBA: 4-hydroxybutyl acrylate HEA: hydroxyethyl acrylate

((Meth)acrylic acid ester monomer (a2))
2EHA: 2-ethylhexyl acrylate iOA: isooctyl acrylate iNA: isononyl acrylate MA: methyl acrylate BA: butyl acrylate

<Synthesis of Crosslinking Agent Component (B)>
[Synthesis Example 2-1]
(Synthesis of Polyisocyanate Component B-1)
In a four-neck flask equipped with a thermometer, a stirring blade and a reflux condenser, 100 parts by mass of HDI was charged under a nitrogen gas flow, and 4.7 parts by mass of a bifunctional polycaprolactone polyol (manufactured by Daicel Corporation, trade name "Placcel 220", number average molecular weight 2000) (hereinafter, sometimes referred to as "polyol b2-1" or simply "b2-1"), and 33 parts by mass of a trifunctional polycaprolactone polyol (manufactured by Daicel Corporation, trade name "Placcel 308", number average molecular weight 850) (hereinafter, sometimes referred to as "polyol b3-1" or simply "b3-1") (amount such that the molar ratio of the isocyanate groups of HDI to the hydroxyl groups of polyol b2-1 and polyol b3-1 is 10.0) were stirred while maintaining the temperature in the reactor at 90 ° C. for 110 minutes. The reaction was stopped when the yield reached 40% by mass. The reaction liquid was filtered, and the unreacted HDI was removed using a thin-film distillation apparatus to obtain a polyisocyanate component B-1.

[Synthesis Examples 2-2 to 2-4, and Synthesis Example 2-8]
(Synthesis of Polyisocyanate Components B-2 to B-4, and B-8)
Each polyisocyanate component was synthesized in the same manner as in Synthesis Example 2-1, except that the types and blending ratios of the raw materials were as shown in Table 2.

[Synthesis Example 2-5]
(Synthesis of Polyisocyanate Component B-5)
A four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser was charged with 100 parts by mass of HDI and 8.9 parts by mass of trimethylolpropane (hereinafter, sometimes referred to as "polyol b3-3" or simply "b3-3") under a nitrogen stream, and the temperature inside the reactor was maintained at 75°C for 5 hours with stirring to carry out a urethane-forming reaction. The reaction liquid was filtered, and then unreacted HDI was removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate component B-5").

[Synthesis Example 2-6]
(Synthesis of Polyisocyanate Component B-6)
A four-neck flask equipped with a thermometer, a stirring blade, and a reflux condenser was charged with 100 parts by mass of HDI under a nitrogen stream, and the temperature inside the reactor was maintained at 62° C. with stirring. 0.095 parts by mass of trimethylbenzylammonium hydroxide was added and reacted for 4 hours. Thereafter, when the conversion rate reached 38% by mass, 0.02 parts by mass of phosphoric acid was added to stop the reaction. The reaction liquid was filtered, and unreacted HDI was removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter, sometimes referred to as "polyisocyanate component B-6").

[Synthesis Example 2-7]
(Synthesis of Polyisocyanate Component B-7)
A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 100 parts by mass of HDI under a nitrogen stream, and 30 parts by mass of polyol b3-1 (an amount such that the molar ratio of isocyanate groups of HDI to hydroxyl groups of polyol b3-1 becomes 11.4) was stirred while maintaining the temperature inside the reactor at 95° C. for 80 minutes. The reaction was stopped when the yield reached 39% by mass. After filtering the reaction liquid, unreacted HDI was removed using a thin-film distillation apparatus to obtain polyisocyanate component B-7.

The compositions and properties of each synthesized polyisocyanate component are shown in Table 2 below. In Table 2, the polyols are the following compounds.

(Polyol (b2))
b2-1: Difunctional polycaprolactone polyol, manufactured by Daicel Corporation, trade name "Placcel 220", number average molecular weight 2000
b2-2: Polytetramethylene ether glycol, manufactured by Asahi Glass Co., Ltd., trade name "Excenol 2020", number average molecular weight 2000

(Polyol (b3))
b3-1: Trifunctional polycaprolactone polyol, manufactured by Daicel Corporation, trade name "Placcel 308", number average molecular weight 850
b3-2: Trifunctional polycaprolactone polyol, manufactured by Daicel Corporation, trade name "Placcel 312", number average molecular weight 1250

(Polyol (b3′))
b3'-1: Trimethylolpropane (TMP)

<Production of adhesive resin composition for surface protective film>
[Example 1]
(Production of adhesive resin composition S-a1 for surface protective film)
To 100 parts by mass of the acrylic polymer A-1, 3.0 parts by mass of the polyisocyanate component B-3, 0.1 parts by mass of dioctyltin dilaurate (DOT, manufactured by Nitto Kasei Co., Ltd., product name "Neostan U-810") as a crosslinking accelerator, and ethyl acetate were added to obtain an adhesive resin composition S-a1 for surface protection films having a solid content of 30% by mass.

[Examples 2 to 8 and Comparative Examples 1 to 4]
(Production of adhesive resin compositions for surface protective films Sa2 to S8 and S-b1 to S-b4)
Each adhesive resin composition for surface protection film was produced using the same method as in Example 1, except that the types and blending ratios of the crosslinkable functional group-containing polymer (A) and the crosslinking agent component (B) were as shown in Tables 3 to 4.

The compositions and evaluation results of each adhesive resin composition for surface protection films are shown in Tables 3 and 4.

From Tables 3 and 4, the surface protective films using the pressure-sensitive adhesive resin compositions S-a1 to S-a8 (Examples 1 to 8) for surface protective films containing a crosslinkable functional group-containing polymer (A) having a glass transition temperature Tg of -68.7°C or more and -57.3°C or less and an aliphatic polyisocyanate having a weight average molecular weight of 4180 to 21500 and an average number of isocyanate groups of 3.8 to 4.6 as the crosslinking agent component (B) were good in curability, attachment property, peelability, and contamination resistance.
In addition, in a comparison of surface protection films using pressure-sensitive adhesive resin compositions S-a2, S-a5, and S-a6 (Examples 2, 5, and 6) for surface protection films, which contain different types of crosslinkable functional group-containing polymer (A), the lower the glass transition temperature or the smaller the weight average molecular weight, the smaller the Young's modulus, the lower the elastic modulus, and the better the adhesion and conformability to the adherend tend to be.

On the other hand, in the surface protection films using the pressure-sensitive adhesive resin compositions S-b1 and S-b3 (Comparative Examples 1 and 3) containing 3.0 parts by mass of each of the polyisocyanate components B-5 to B-6 having a weight average molecular weight of less than 1,400 as the crosslinking agent component (B) per 100 parts by mass of the crosslinkable functional group-containing polymer (A), the curability, peelability and stain resistance were good, but the adhesion was poor.
In addition, a surface protection film using an adhesive resin composition S-b4 (Comparative Example 4) containing 3.5 parts by mass of a polyisocyanate component B-7 having a weight average molecular weight of less than 1,400 as a crosslinking agent component (B) per 100 parts by mass of the crosslinkable functional group-containing polymer (A) had good curability, peelability, and stain resistance, but poor adhesion and conformability to the adherend.
In addition, a surface protection film using an adhesive resin composition S-b2 (Comparative Example 2) for a surface protection film containing 0.05 parts by mass of a polyisocyanate component B-5 having a weight average molecular weight of less than 1,400 as a crosslinking agent component (B) per 100 parts by mass of the crosslinkable functional group-containing polymer (A) had good adhesion, but poor curability, peelability, and contamination resistance.

The adhesive resin composition for surface protection films of this embodiment can provide an adhesive resin composition for surface protection films that has good adhesion and peelability when used as a surface protection film and has improved contamination caused by the adhesive when peeled off.

Claims (13)

A pressure-sensitive adhesive resin composition for a surface protective film, comprising a crosslinkable functional group-containing polymer (A) and a crosslinking agent component (B),
The glass transition temperature Tg of the crosslinkable functional group-containing polymer (A) is −75.0° C. or more and 0.0° C. or less,
The crosslinking agent component (B) contains an aliphatic or alicyclic polyisocyanate having a weight average molecular weight of 1,400 or more and 200,000 or less and an average number of isocyanate groups of 2.0 or more and 6.5 or less,
the content of the crosslinking agent component (B) is 0.5 parts by mass or more and 15.0 parts by mass or less relative to 100 parts by mass of the crosslinkable functional group-containing polymer (A);
The crosslinkable functional group-containing polymer (A)
An acrylic polymer (A1) obtained by copolymerizing a crosslinkable functional group-containing monomer and a (meth)acrylic acid ester monomer having an ester group terminal carbon number of 1 or more and 18 or less, and having a glass transition temperature Tg of −75.0° C. or more and 0.0° C. or less, or
A urethane-based polymer (A2) having a glass transition temperature Tg of −75.0° C. or more and 0.0° C. or less,
the crosslinkable functional group is at least one selected from the group consisting of a hydroxyl group, an epoxy group, and a carboxy group;
The adhesive resin composition for a surface protective film, wherein the aliphatic or alicyclic polyisocyanate is a polyisocyanate derived from at least one diisocyanate (b1) selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates, a bifunctional polyol (b2) having a number average molecular weight of 1,500 or more, and a tri- or higher functional polyol (b3) having a number average molecular weight of 500 or more . The adhesive resin composition for surface protective films according to claim 1 , wherein the content of the structural unit derived from the crosslinkable functional group-containing monomer is 0.01 mass% or more and 25 mass% or less, based on the total mass of the crosslinkable functional group-containing polymer (A). The pressure-sensitive adhesive resin composition for surface protective films according to claim 1 or 2 , wherein the crosslinkable functional group-containing polymer (A) has a weight average molecular weight of 2.0 × 10 ⁵ or more and 2.5 × 10 ⁶ or less. The pressure-sensitive adhesive resin composition for surface protective films according to any one of claims 1 to 3 , wherein the molar ratio NCO/OH of the isocyanate groups of the diisocyanate (b1) to the total molar amount of hydroxyl groups of the polyol (b2) and the polyol (b3) is 3 or more and 30 or less. a mass ratio (b3)/(b2) of the polyol (b3) to the polyol (b2) is 0.1/99.9 or more and 99.9/0.1 or less; and
Relative to 100 parts by mass of the diisocyanate (b1),
The content of the polyol (b2) is 0.1 parts by mass or more and 250 parts by mass or less,
The adhesive resin composition for surface protective films according to claim 4 , wherein the content of the polyol (b3) is from 0.1 parts by mass to 190 parts by mass. The adhesive resin composition for surface protective films according to claim 4 or 5 , wherein the polyol (b2) and the polyol (b3) are one or more polyols selected from the group consisting of polyester polyols, polyether polyols, epoxy polyols, polyolefin polyols, and polycarbonate polyols. The adhesive resin composition for surface protective films according to any one of claims 1 to 6 , wherein the crosslinking agent component (B) has an isocyanate group content of 1% by mass or more and 10% by mass or less. The adhesive resin composition for surface protective films according to any one of claims 1 to 7, wherein the crosslinking agent component (B) is applied onto a glass sheet, and the resulting cured film has a thickness of 50 µm and a Konig hardness of 60 or less in a 23°C environment after storage for 168 hours in a 23°C and 65% humidity environment. A plastic film,
An adhesive layer is provided on one or both sides of the plastic film,
A surface protective film, wherein the adhesive layer is made of a cured product of the adhesive resin composition for surface protective films according to any one of claims 1 to 8 . The surface protective film according to claim 9 , wherein the adhesive layer has a thickness of 1 μm or more and 1000 μm or less. The adhesive resin composition for surface protection films is applied onto a 38 μm-thick release-treated polyethylene terephthalate film, dried at 135° C. for 3 minutes to harden, and then stored in a 23° C., 50% RH environment for 7 days. The adhesive layer obtained by peeling the release-treated polyethylene terephthalate film from a surface protection film having an adhesive layer of 20 μm in thickness is stored in a 23° C., 50% RH environment for 7 days, wrapped in a mesh sheet, immersed in ethyl acetate at 23° C. for 1 week, removed, and dried at 120° C. for 2 hours. The gel fraction calculated by the above is 90.0 mass % or more and 100.0 mass% or less . The adhesive resin composition for surface protection films is applied onto a 38 μm-thick release-treated polyethylene terephthalate film, dried at 135° C. for 3 minutes to cure, and then stored in a 23° C., 50% RH environment for 7 days. The adhesive layer is then peeled off from the surface protection film having a 20 μm-thick adhesive layer, and the peeled polyethylene terephthalate film is laminated to a thickness of 200 μm. The adhesive layer is then cut to a width of 10 mm and a length of 40 mm. The laminated adhesive layer is set in a tensile tester so that the chuck distance is 10 mm, and a Young's modulus in a tensile test performed at a speed of 300 mm/min in a 23 ° C. environment is 0.01 N/mm ² or more and 0.22 N/mm ² or less. The adhesive resin composition for surface protection films is applied onto a polyethylene terephthalate film having a thickness of 25 μm, dried at 135° C. for 3 minutes to be cured, and then stored in an environment of 23° C. and 50% RH for 7 days. The adhesive resin composition for surface protection films is applied onto a polyethylene terephthalate film having a thickness of 25 μm, dried at 135° C. for 3 minutes to be cured, and then the surface protection film having an adhesive layer having a thickness of 20 μm, a width of 25 mm and a length of 100 mm is attached to a glass substrate, pressed once back and forth with a 2 kg roller, and aged at 23° C. for 30 minutes. After that, the 180-degree peel adhesive strength measured at 23° C. and a speed of 300 mm/min is 0.02 N/25 mm or more and 2.50 N/25 mm or less.